PLATINUM METALS REVIEW · Platinum Metals Review: Journal Archive 2 An Editorial by Barry Copping Palladium-Polyaniline and Palladium-Polyaniline Derivative 3 Composite Materials

E-ISSN 1471–0676

PLATINUM METALS REVIEWA Quarterly Survey of Research on the Platinum Metals and

of Developments in their Application in Industrywww.platinummetalsreview.com

VOL. 51 JANUARY 2007 NO. 1

Contents

Platinum Metals Review: Journal Archive 2An Editorial by Barry Copping

Palladium-Polyaniline and Palladium-Polyaniline Derivative 3Composite Materials

By Kaushik Mallick, Michael Witcomb and Mike Scurrell

“Handbook of Homogeneous Hydrogenation” 16A book review by Ann K. Keep

The 20th Santa Fe Symposium on Jewelry 19Manufacturing Technology

A conference review by Christopher W. Corti

Welding of Platinum Jewellery Alloys 23By Duncan Miller, Katyusha Vuso, Penny Park-Ross and Candy Lang

Fuel Cells Science and Technology 2006 27A conference review by Donald S. Cameron

“Alcoholic Fuels” 34A book review by Gary Acres

37th International Conference on Coordination 36Chemistry

A conference review by David J. Robinson and Malcom Arendse

Scientific Bases for the Preparation of Heterogeneous 42Catalysts

A conference review by Mark R. Feaviour and Emma R. Schofield

“Platinum 2006 Interim Review” 45Abstracts 46

New Patents 50Final Analysis: Porous Platinum Morphologies: 52

Platinised, Sponge and BlackBy Allan Mills

Communications should be addressed to: The Editor, Barry W. Copping, Platinum Metals Review, [email protected]; Johnson Matthey Public Limited Company, Orchard Road, Royston, Hertfordshire SG8 5HE

2Platinum Metals Rev., 2007, 51, (1), 2

DOI: 10.1595/147106707X174311

The PGM Science Mine

The Platinum Metals Review website has extra features complementing the core of the original pub-lished Journal. The ‘PGM Science Mine’ includes a calendar of events, the opportunity to askquestions and have them answered, and some useful links. The fully searchable Directory of peopleand organisations with expertise in pgm science has now been enhanced by an A–Z listing format.Readers are welcome to submit their or their organisation’s details for inclusion in the Directory atany time. Finally, ‘Nuggets’ includes a list of recommended reading on aspects of catalysis.

Having completed fifty years of continuousservice to the platinum group metals (pgms)community, Platinum Metals Review celebratesanother significant enhancement for its manyreaders and contributors around the world. TheJournal Archive is now online at: www.platinummetalsreview.com/dynamic/volume/archive, giving full access, free ofcharge, to essential research articles dating backto 1957.

As the sole journal dedicated to the pgms,Platinum Metals Review has always been commit-ted to the dissemination of knowledge withinthe pgm community, promoting and supportingwork across all disciplines, in both academic andindustrial circles worldwide. The Contents pageof the first issue (1) provides a snapshot of thetechnologies of the day, from radio capacitors tothermocouples and the use of platinum inprocess catalysis.

Platinum Metals Review has always been at theforefront of developing technologies, and hastracked the progress of many important pgmapplications. Notable highlights include the useof platinum in anti-cancer drugs (2) and thedevelopment of platinum-based autocatalysts(3). There is a growing body of work on fuelcells, including some key reviews (see, for exam-ple, (4)). Other highly-cited articles includereviews of work on the palladium-hydrogen sys-tem (for example, (5)). Industrial processcatalysis continues to be an important area; for

example, the iridium-catalysed CativaTM processfor acetic acid manufacture (6).

From July 2004, Platinum Metals Review hasbeen published online as a quarterly E-journal.The key benefits of electronic publication arenow available for the entire back catalogue ofissues, including rapid location of articles usingthe Advanced Search function. For articles inissues from Volume 1, Issue 1, to Volume 47,Issue 3, article details and PDF files (includingentire issue PDF files) are presented. Articles inissues from Volume 47, Issue 4, onwards areavailable in both PDF and XHTML full text for-mats. Gaps in print archives can readily be filled.

The team at Platinum Metals Review has alreadyreceived favourable comments from users of theJournal Archive. Keith White, Sara Coles and Ihope that it will continue to provide an invalu-able tool for pgm science and technology formany decades to come.

BARRY COPPING, Editor

References1 Platinum Metals Rev., 1957, 1, (1), 12 B. Rosenberg, Platinum Metals Rev., 1971, 15, (2),

423 G. K. Acres and B. J. Cooper, Platinum Metals Rev.,

1972, 16, (3), 744 D. S. Cameron, Platinum Metals Rev., 1978, 22, (2),

385 F. A. Lewis, Platinum Metals Rev., 1982, 26, (1), 20

and references cited therein6 J. H. Jones, Platinum Metals Rev., 2000, 44, (3), 94

Platinum Metals Review: Journal Archive

One key property distinguishing classicalpolymers from metals is their low electrical con-ductivity. A new class of organic polymerscapable of conducting electricity has recentlybeen developed (1, 2). These polymers becomeconductive upon partial oxidation or reduction,a process commonly referred to as ‘doping’. Theelectrical properties of conductive polymers canbe changed reversibly over the full range of con-ductivity from insulators to metallic conductors.Their potential as novel materials in value-addedindustrial and consumer products is opening upwholly new avenues of application for polymer-ic materials.

Among conducting plastics, polyaniline hasbecome a particular focus of interest because ofits environmental stability (3), controllable elec-trical conductivity (4), and interesting redoxproperties associated with the chain nitrogen (5).The electrical properties of the aniline polymerscan be improved substantially by secondary dop-ing (6). Polyaniline compounds can be designedto achieve the particular conductivity requiredfor a given application. The resulting blends canbe as conductive as silicon and germanium or as

insulating as glass. Additional advantages arethat the compound can be mixed simply withconventional polymers, and it is easy to fabricatepolyaniline products into specific shapes. Theconductivity of polyaniline makes it an idealshield against static electric discharges, and as aconsequence polyaniline compounds have beenused in the packaging of electronics products.Polyaniline compounds are being tested for useas protective materials against electromagneticradiation. Further, scientists hope that one dayprinted circuit boards, electrochromic windowsin houses and cars, and conductive fabrics willcontain polyaniline compounds.

The presence of a number of intrinsic redoxstates (Figure 1) has substantially increased thenumber of potential applications of aniline poly-mers for use in practical devices. The anilinepolymers have a general formula of the type[(–B–NH–B–NH–)y (–B–N=Q=N–)1–y]x, inwhich B and Q denote respectively the C6H4

rings in the benzenoid and the quinoid forms. Inpolyaniline, the neutral intrinsic redox states(Figure 1) can vary from that of the fully oxi-dised pernigraniline (PNA; y = 0), to that of the

3

Palladium-Polyaniline and Palladium-Polyaniline Derivative Composite MaterialsA BRIEF OVERVIEW OF THEIR PREPARATION AND POTENTIAL APPLICATIONS

By Kaushik MallickMolecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa

Michael Witcomb*Electron Microscope Unit, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa; *E-mail:

[email protected]

and Mike ScurrellMolecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa

Palladium nanoparticles of different sizes and shapes combined with polyaniline and derivativesof polyaniline can give rise to a host polymer with interesting physical properties and importantpotential applications. The resulting composite can be produced in the form of nanofibres,nanorods, thin films, etc. Potential applications of this composite material for catalysis andsensor systems are discussed.

Platinum Metals Rev., 2007, 51, (1), 3–15

DOI: 10.1595/147106707X174203

fully reduced leucoemeraldine (LM; y = 1). The50% intrinsically oxidised polymer has beennamed emeraldine (EM; y = 0.5), and the 75%intrinsically oxidised polymer is named nigrani-line (NA; y = 0.75) (2). The synthesis andcharacterisation of polyaniline have beenreviewed previously by Geniès et al. (7), Lux (8)and Gospodinova et al. (9). Polyaniline is a mem-ber of the semi-flexible rod polymer family. Thesynthesis and characterisation of electroactivepolymers have become two of the most impor-tant areas of research into polymers, as well as inmaterials science over the past two decades.

Metal nanoparticles with different sizes andshapes can be combined with polyaniline toform hybrid materials. Hybrids represent a newclass of materials that may combine desirablephysical properties characteristic of both theirorganic and metallic components within a singlecomposite. The metallic portion offers thepotential for a wide range of electrical proper-ties, substantial mechanical hardness andthermal stability, whereas the polymer part canprovide high fluorescence efficiency, large polar-isability, plastic mechanical properties, ease ofprocessing and structural diversity.

The present article reviews both advances inmethods of synthesis and application-relatedperformance for various palladium-polyanilineand palladium-polyaniline derivative compositematerials systems.

Palladium-Polyaniline CompositeCoating for LD Polyethylene

Low-density polyethylene (LDPE) is a usefulsubstrate for a wide range of laboratory experi-ments as well as many industrial applications(10–13). Although LDPE is a relatively inertsubstrate, it can be graft-copolymerised withacrylic acid to enhance the growth and adhesionof polyaniline coatings so as to achieve a thinconductive surface layer. In an earlier work,Neoh and coworkers (14) reported the forma-tion of gold particles on the surface of apolyaniline film coated onto acrylic acid graft-copolymerised LDPE.

The thrust of this work was investigating howthe electroactive polymer substrate was affectedby the metal reduction process. The coating ofLDPE films with a polyaniline-palladium com-posite layer was studied by Wang et al. (15). Theyused two methods for the synthesis of thepolyaniline-palladium layer on the LDPE.Common to both was the initial step: the LDPEsurface was first graft-copolymerised withacrylic acid to enhance the adhesion of thepolyaniline-palladium layer. Subsequently, in thefirst method (Method 1 in Figures 2 and 3),polyaniline was deposited on the acrylic acidgraft-copolymerised LDPE. This was followedby a reaction with palladium nitrate which result-ed in a layer of palladium metal particles beingdeposited onto the polyaniline surface. In the

Platinum Metals Rev., 2007, 51, (1) 4

Leucoemeraldine (LM)

Emeraldine (EM)

Nigraniline (NA)

Pernigraniline (PNA)

Fig. 1 The various intrin-sic oxidation states ofpolyaniline. Reproducedfrom (2) with permissionfrom Elsevier

second method (Method 2 in Figures 2 and 3),polyaniline powder was first reacted with palla-dium nitrate. The powder was then treated withN-methylpyrrolidinone, after which it coatedthe acrylic acid graft-copolymerised LDPE. Thelatter method resulted in nanosized palladiummetal particles being distributed in the polyani-line coating, rather than being confined to thesurface of the polyaniline layer. In both meth-ods, the palladium metal particles conferredsurface conductivity on the LDPE substrate,even with the polyaniline in the undoped state.It was found that the polyaniline-palladiumcoating adhered excellently to the acrylic acidgraft-copolymerised LDPE substrate at low pal-ladium contents, but adhesion was weakenedsignificantly at high palladium contents due tothe palladium interfering with the interactionbetween the polyaniline and the acrylic acidgraft-copolymerised chains. The polyaniline wassynthesised in the reduced form, that is, leu-coemeraldine (LM). The advantage of using LM

is that it can very easily be oxidised, and palladi-um nitrate is reduced more rapidly.

X-ray photoelectron spectroscopy (XPS)analysis by Wang et al. (15) (Figure 2) of LM onacrylic acid graft-copolymerised LDPE afterreaction with Pd(NO3)2 revealed two Pd 3d5/2

peaks at 335 and 338 eV, which are the charac-teristic peaks for the Pd(0) and Pd(II) speciesrespectively. Initially, Pd(0) was the main oxida-tion state of palladium. For Method 1, theintensity of the Pd(II) peak increased with time,indicating that the Pd(II) species deposited onthe surface of polyaniline without further reduc-tion to Pd(0). By contrast, for the sample whichwas prepared using Method 2, XPS analysesconfirmed that the Pd 3d5/2 peak at 335 eV waspredominant throughout the reaction, while thepeak at 338 eV did not show any significantincremental change as the reaction progressed.It was concluded that Pd(0) remained the pre-dominant species on polyaniline for the samplewhich was prepared by Method 2. The disparity


Method 1 Method 2

Inte

nsity

332 335 338 341 344 332 335 338 341 344Binding energy, eV

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Fig. 2 XPS Pd 3d spectraof LM on acrylic acid-graftcopolymerised LDPE afterreaction by Method 1 for:(a) 10 min; (b) 60 min; (c)120 min; and (d) 180 min;and by Method 2 for: (e)10 min; (f) 60 min; and (g)180 min. Reproduced from(15) with permission fromElsevier

between the amounts of deposition of palladiumspecies for the two samples results from the dif-ference in the surface area and the availability ofthe reaction sites.

Figure 3 shows the scanning electronmicroscopy (SEM) images for the two methodscorresponding to the palladium(0)-polyanilinecomposite on the acrylic acid graft-copoly-merised LDPE film after different reactiontimes. In Figure 3 for Method 1, the average par-ticle size of 100 nm or less as estimated fromthese images does not increase substantially dur-ing the early stages, ~ 10 to 60 min (Figures 3(b)and 3(c)), of the reaction. After a reaction timeof 180 min or more, the surface of the LM filmwas covered with palladium (Figure 3(d)). Incontrast, for Method 2, during the initial stagesof the reaction (~ 10 min, Figure 3(f)), at aPd(II):N molar ratio of 1:5, the average particle

size was about 70 nm. After 180 min (Figure3(h)), the average particle size had increased bysome 300%. This increase in size was a directresult of the increase in size of the palladiumclusters accumulated on the surface of thepolyaniline powder as the reaction progressedand the subsequent dispersion of the particles inthe polyaniline-N-methylpyrrolidinone solution.

Chemical Deposition of Palladiumon Polyaniline

The reaction of polyaniline in its lowest oxi-dation state, LM, with palladium chloride andpalladium nitrate has been investigated by Wanget al. (16). Polyaniline was synthesised via theoxidative polymerisation of aniline by ammoni-um persulfate, and converted to emeraldine(EM) or 50% oxidised base by treatment withexcess 0.5 M sodium hydroxide. The fully


(c)

1 μμm

1 μμm

(b)(a)

1 μμm

(e)

1 μμm

(f)

0.2 μμm

(g) (h)

1 μμm

(d)

1 μμm

0.2 μμm

Fig. 3 SEM image ofLM on acrylic acid-graft copolymerisedLDPE after reaction byMethod 1 for: (a) 0min; (b) 10 min; (c) 60min; and (d) 180 min;and by Method 2 for:(e) 0 min; (f) 10 min;(g) 60 min; and (h)180 min. Reproducedfrom (15) with permis-sion from Elsevier

reduced form of the polyaniline, LM, wasobtained by the reduction of the EM base withanhydrous 98% hydrazine for 3 h, followed bythorough washing with deionised water. TheLM film obtained was then pumped dry underreduced pressure. Since the LM film is very eas-ily oxidised, the palladium uptake experimentswere conducted soon after the preparation ofthese films.

The LM film was used for the palladiumuptake experiments using palladium chlorideand palladium nitrate. The amounts of palladi-um deposited from the palladium precursors onthe LM film are indicated in Figure 4. This fig-ure shows that palladium nitrate reacts moreeffectively with LM than does palladium chlo-ride, a finding that Wang et al. confirmed wasreproducible. XPS measurements were per-formed to determine the state of the palladiumdeposited on the LM. Figure 5 shows the XPSPd 3d spectra of the LM films after reaction inpalladium chloride and palladium nitrate solu-tions for varying periods of time. For palladiumnitrate, it is quite clear that Pd(0) is the principalstate of the palladium deposited on the surface

of the LM film. For palladium chloride, whilePd(II) was the predominant state on the LMsurface at the beginning of the reaction, after300 min, the Pd(0) state became the predomi-nant species. Atomic force microscopy (AFM)images of the surface of the LM films after a 10min immersion in palladium chloride and palla-


Pd(NO3)2

PdCl2

0 50 100 150 200 250 300 350Reaction time, min

0.30

0.25

0.20

0.15

0.10

0.05Mol

ar ra

tio (P

d/N

) dep

osite

d

−•−

Fig. 4 Molar ratio of palladium deposited per mole ofLM at an initial molar ratio of Pd(II) in solution to LMof 1:4. Reproduced from (16) with permission from theRoyal Society of Chemistry

(a) (b)

(c) (d)

(e) (f)

332 335 338 341 344 332 335 338 341 344

Binding energy, eV

Inte

nsity

Fig. 5 XPS Pd 3d core-level spectra of LM basefilm after reaction withPdCl2 for: (a) 10 min; (b)30 min; and (c) 300 min;and after reaction withPd(NO3)2 for: (d) 10 min;(e) 30 min; and (f) 300min. Reproduced from (16)with permission from theRoyal Society of Chemistry

dium nitrate solutions are shown in Figures 6(a)and 6(b), respectively. A higher average rough-ness value, Ra, was achieved for the film when itwas treated in palladium nitrate, as a direct con-sequence of the larger amount of palladiumdeposited on this film.

Electrochemical Behaviour ofPolyaniline-Palladium CompositeFilms

The electrochemical behaviour of polyanilinefilms containing palladium nanoparticles wasinvestigated by Park et al. (17) when the filmswere immersed in a propylene carbonate solu-tion. To prepare the polyaniline-palladiumnanoparticle composite film, a preformedpoly(N-vinyl-2-pyrrolidone) stabilised palladiumnanoparticle colloid was dispersed in a N-methyl-2-pyrrolidone (NMP) solution. Then,polyaniline (36% oxidised state) was added slow-ly to the solution which was then stirred for 24 h.The resultant solution was cast on glassy carbonand dried under vacuum for 4 h at room temper-ature. This assembly was used as the workingelectrode. A platinum coil and Ag/Ag+ were usedas the counter and reference electrodes, respec-tively.

Figure 7 shows the electrochemical behaviourof polyaniline and polyaniline containing 20wt.% palladium nanoparticles. The cyclic voltam-mogram (CV) of the polyaniline film wascharacterised by the anodic peak near –0.5 V,which is associated with the transformation fromthe LM to the EM state. The second redox peakof polyaniline corresponds to the redox intercon-version of polyaniline from EM to PNA. Theanodic peak (~ –0.5 V) and cathodic peak (~–0.8 V) current of the polyaniline film containing

the palladium nanoparticles gradually decreasedwith successive cycles. In addition, the compos-ite film showed new anodic and cathodic peaks atabout –0.1 V and –0.3 V, respectively. The redoxpeak of the polyaniline-palladium nanoparticlecomposite film shifted to the positive potential


(a) Ra = 1.1 nm (b) Ra = 6.2 nm

100 nm 100 nm

0 0

5 μm 5 μm

Fig. 6 AFM images of LMfilms: (a) after reaction withPdCl2 and (b) after reactionwith Pd(NO3)2 for 10 min.Ra is the average roughnessvalue. Reproduced from(16) with permission fromthe Royal Society ofChemistry

(a)

50 μA

1

2

(b)

12

–1.2 –0.8 –0.4 0.0 0.4 0.8

E, V vs. Ag/Ag+

Fig. 7 Cyclic voltammograms of a polyaniline film: (a)without palladium nanoparticles, and (b) with palladiumnanoparticles (20 wt.%) on the glassy carbon electrodein 0.1 M LiClO4/propylene carbonate solution, measuredat a scan rate of 20 mV s–1. Reproduced from (17) withpermission from Elsevier

region in comparison with the polyaniline film.This result implies the presence of strong elec-trochemical interactions between polyaniline andpalladium nanoparticles. The complex formationprocess is readily evident in the CVs by the rapidgrowth of a pair of sharp redox waves at E1/2 =–0.2 V vs. Ag/Ag+ in the presence of palladiumnanoparticles.

The interaction between polyaniline and thepalladium nanoparticles was studied by UV-vis-ible spectroscopic measurements (Figure 8).Palladium nanoparticles, which were stabilisedand well dispersed in NMP solutions, showed acharacteristic plasmon absorption at 280 nm(Figure 8(a)). The absorption peaks observedfor polyaniline at 340 nm and 640 nm (Figure8(g)) indicate that the polyaniline was partiallyoxidised. Adding the polyaniline to a palladium-NMP solution caused a blue shift of the peaknear 640 nm resulting from the charge transferfrom the benzenoid to the quinoid (Figures8(b)–8(f)). The peak near 320 nm, which is dueto the π–π* transition of the phenyl ring, alsoblue shifted. These spectral changes indicatethat the coordination of the palladium particlesto the nitrogen atoms permitted the palladiumnanoparticles to interact with each otherthrough the π-conjugate chain. Such a blue shiftof the band at ~ 600 nm indicates the formationof a complex between the polyaniline and thepalladium nanoparticles.

Palladium and PolyanilineDerivative Composite Material

The derivatives of polyaniline have attractedgrowing scientific attention since their chemicalproperties are similar to those of polyaniline. Incomparison to the parent polymer, they exhibitbetter solubility in common organic solvents,which facilitates easier processing of these mate-rials.

Poly(3,5-dimethylaniline)-Palladium Nanofibre Composites

For the preparation of polymer-palladiumcomposite material an in situ synthesis approach ispreferable. Since the polymer and the nanosized

metal particles are produced simultaneously, thisis expected to yield a highly intimate contactbetween the two components.

An in situ chemical synthesis route was usedfor the synthesis of a poly(3,5-dimethylaniline)nanofibre and palladium nanoparticle (polymer-metal) composite material in which thenanoparticles were highly dispersed in the poly-mer fibre matrix (18). Transmission electronmicroscopy (TEM) images (Figure 9) illustratethe composite material at different magnifica-tions. Figure 9(a) shows an example of the largepopulation of polymer fibres with differentsizes, whereas Figure 9(b) images part of a sin-gle fibre, which is about 300 nm in diameter.The inset in Figure 9(b) shows the diffractionpattern from the fibre, revealing both diffusescattering from the amorphous polymer and dif-fraction rings. Dark field imaging confirms thatthe rings originate from the palladium nanopar-ticles. Figures 9(c) and 9(d) show TEM imagesof the surface morphology and internalmicrostructure of the polymer. It is clear thatthe surface is not smooth. On both the roughsurfaces and in the interior of the polymer, asshown by these and stereo pair images, there arehighly distributed dark regions of diameter


(g)

Abs

orba

nce

300 400 500 600 700 800Wavelength, nm

(f)

(e)

(d)

(c)

(b)

(a)

Fig. 8 UV-visible spectra obtained from palladiumnanoparticles (0.1 mM) dispersed in N-methyl-2-pyrroli-done solutions containing different concentrations ofpolyaniline: (a) 0 mM, (b) 0.02 mM, (c) 0.04 mM, (d)0.06 mM, (e) 0.08 mM and (f) 0.1 mM, (g) 0.12 mMpolyaniline in N-methyl-2-pyrrolidone solution.Reproduced from (17) with permission from Elsevier

about 2 nm. Electron energy loss spectroscopy(EELS) mapping for the palladium distributionhas confirmed that the dark spots are palladium.This is most clearly illustrated in Figure 10,which shows a fine strand of polymer compos-ite, in which the particles were not overlapping.Figure 10(a) is a zero-loss image of the strand.This is an energy-filtered image; that is, it isderived only from electrons which have retainedthe energy of the beam when passing throughthe thin sample. The image therefore containsno analytical information. In contrast, Figure10(b) is a palladium map from the same region.This palladium jump-ratio image was obtainedby dividing the Pd-N2,3 post-edge loss image bythe pre-edge loss image, thereby producing a sig-nal derived from electrons that have lost energyby generating Pd-N shell X-rays.

Palladium Nanoparticles in Poly(o-methoxyaniline)

Metal-polymer composites with a nano- ormicro-structured morphology have potentialapplications in various fields such as sensors,organic light-emitting diodes (OLEDs), field-effect transistors and nonlinear optics. Amicrostructured 3D rod-like morphology of apalladium-poly(o-methoxyaniline) compositematerial has recently been reported by our group(19). An in situ reaction between palladiumacetate and o-methoxyaniline was employed.Figure 11(a) is a SEM image showing the prod-uct, which consists of regular straightnanofibres. An image at higher magnification,Figure 11(b), reveals the 3D structure of thenanofibres, which were up to about 15 μm inlength, 0.5 μm in width and 0.25 μm thick. Allthe fibres were uniform in morphology and verystraight, suggesting a high degree of rigidity.Raman spectroscopy was employed to determinethe structural orientation of the polymer. Asseen in Figure 12, the benzene C–H bendingdeformation mode lies at 1140 to 1190 cm–1 forthe reduced semiquinone and quinoid ring struc-ture. The band at 1260 cm–1 can be assigned tothe C–N stretching mode of the polaronic units.The band at 1337 cm–1 corresponds to theC–N•+ stretching modes of the delocalised pola-ronic charge carriers, while the C–C stretchingof the benzenoid ring was observed at 1600cm–1. A small peak positioned at 1460 cm–1 cor-


(a) (b)

(c) (d)

5 μm 100 nm

20 nm 6 nm

Fig. 9 (a) TEM image showing an example of the vari-ous sizes of poly(3,5-dimethylaniline)-Pd nanofibresproduced; (b) TEM image of a single polymer fibre hav-ing a diameter ca. 300 nm. The diffraction pattern (inset)reveals diffuse scattering from the amorphous polymerand diffraction rings from the palladium nanoparticles;(c) shows the surface morphology; and (d) the ca. 2 nmsized dark spots are the palladium nanoparticles, whichshow a high dispersion throughout the polymer.Reproduced from (18) with permission from theAmerican Chemical Society

(a) (b)

10 nm 10 nm

Fig. 10 (a) Zero-loss image of a poly(3,5-dimethylani-line)-Pd composite strand about 10 nm in diameter; (b)Pd-N2,3 edge jump-ratio image of the area shown in (a).All of the dark regions in (a) can clearly be identified aspalladium nanoparticles. Reproduced from (18) with per-mission from the American Chemical Society

responds to the C=N stretching mode of thequinoid units. A band of moderate intensity at1500 cm–1 corresponds to the bending deforma-tion of the N•+–H unit.

A wide variety of methods have been appliedto the preparation of polyaniline or substitutedpolyaniline type compounds by oxidative poly-merisation of the monomer (20). We havesuggested (19) that the mechanism for the poly-merisation process involves the formation of aradical cation accompanied by the release of anelectron, this being the initiation process for thepolymerisation reaction. During the addition ofpalladium acetate, the pH of the reaction mix-ture solution dropped to ~ 5. Spectroscopicanalysis confirmed that the –OCH3 substitutedaniline oxidation product had only a head-to-tail(–N–Ph–N–Ph–) like arrangement rather than ahead-to-head (–Ph–N=N–Ph–) type. The N–Ncharacteristics arise from the head-to-head cou-pling only under neutral or basic pH conditions.On the other hand, aniline or substituted anilineoxidation products obtained in acid media havea predominantly head-to-tail arrangement (2).

The presence of the electron-donating group(–OCH3) in the o-methoxyaniline facilitates therelay of electrons through N••–H2, which formsa covalent bond with Pd(II) and attains a specieslike [(OCH3)Ph–N•+–H2]. Under acidic condi-tions, the [(OCH3)Ph–N•+–H2] species undergopolymerisation (Figure 13), which is an oxida-tion process. Each step of polymerisation isassociated with a release of an electron (21),leading to the reduction of Pd(II) to Pd(0).Subsequent coalescence of the atoms forms pal-ladium clusters which are stabilised by thepolymer. Figure 14(a) is a TEM image of this

material revealing a uniform size distribution ofpalladium nanoparticles which are highly dis-persed in the polymer matrix. A typical energydispersive X-ray (EDX) spot analysis confirmedthat dark regions in the polymer are palladiumnanoparticles, Figure 14(b).

Palladium Nanoparticles in Poly(o-aminophenol) Needles

Another example of an in situ chemical syn-thesis approach has been given by us (21) forthe preparation of a palladium-poly(o-aminophenol) composite material. Figure 15(a)shows a SEM image of the needle-like morphol-ogy of the composite material. TEMmicrographs, Figures 15(b) and 15(c), indicatethat the palladium nanoparticles are of the orderof 2 nm in diameter and are highly dispersedwithin the polymer matrix. An IR spectroscopicstudy was used to determine the chemical struc-ture of the polymer. In the IR spectrum, Figure16, the characteristic band at 1588 cm–1 can beassigned to the C=C stretching of the quinoidrings, while the two peaks at 1499 cm–1 and 1470cm–1 are the characteristic bands of the C=Cstretching vibration mode for benzenoid rings.

Palladium-Polyaniline Compositeas a Sensor

Athawale et al. (22) have shown that palladi-


(a)

10 μm

(b)

1 μm

Fig. 11 SEM images of poly(o-methoxyaniline): (a)image at low magnification of fibre-like metal-polymercomposite material; and (b) image at higher magnifica-tion showing the 3D morphology of the composite fibres.Reproduced from (19) with permission from EDPSciences

1600

1500

1460

1337

12601140

11901165

1100 1200 1300 1400 1500 1600 1700Wavenumber, R, cm–1

Rel

ativ

e In

tens

ity (a

.u.)

Fig. 12 Raman spectra of poly(o-methoxyaniline).Reproduced from (19) with permission from EDPSciences

um-polyaniline can be used as a methanol sen-sor. The nanocomposite material wassynthesised by using a thermal reflux methodfollowed by the oxidative polymerisation of ani-line by ammonium persulfate, Figure 17. Thesynthesised nanocomposite was exposed to dif-ferent aliphatic alcohol vapours such as

methanol, ethanol and isopropanol. The resultsshowed that the nanocomposite was highlyselective and sensitive to methanol vapours. Thesensor responded rapidly and reversibly in thepresence of different concentrations ofmethanol vapour. The selectivity of thenanocomposite was further investigated byexposing it to mixtures of methanol–ethanol andmethanol–isopropanol. Except for the responsetime, the nanocomposite was found to exhibit


Pd

0 1 2 3keV

PdO

PdCu

(b)

(a)

6 nm

Fig. 14 (a) TEM image of the composite materialpalladium-poly(o-methoxyaniline) at high magnification.The dark spots are the 2–3 nm sized palladium nanoparti-cles dispersed within the polymer matrix; (b) EDXspectrum from the area shown in (a). The presence of pal-ladium is clearly indicated. The copper peak originatesfrom scattering from the TEM copper mesh support grid.Reproduced from (19) with permission from EDP Sciences

(a)

(b) (c)

1 μm

20 nm 6 nm

Fig. 15 (a) SEM image of the composite materialpalladium-poly(o-aminophenol) showing a cluster oflarger polymer needles; (b) TEM images of the compos-ite made up of polymer nanoneedles and palladiumnanoparticles (dark spots); and (c) TEM image at highmagnification of the palladium nanoparticles in the poly-mer matrix. Reproduced from (21) with permission fromSpringer Science and Business Media

Resonating structure

Fig. 13 Formation of theradical-cation species andthe polymerisation pathwayof o-methoxyaniline.Reproduced from (19) withpermission from EDPSciences

an exactly identical response to that for puremethanol. The palladium-polyaniline nanocom-posite was quite stable and showed no effects ofageing after exposure to different concentra-tions of methanol.

Catalytic Activity for theHydrogenation of Nitrobenzene

The catalytic activities of palladium-contain-ing electroactive polymer microparticles,typically 1.5 μm diameter, in the reduction ofnitrobenzene to aniline have been studied byHuang and coworkers (23). Polyaniline was syn-thesised by adding ammonium persulfate tohydrochloric acid with vigorous stirring for 16h. The resultant solid particles were then washedwith excess hydrochloric acid and dried underreduced pressure. Polyaniline-SiO2 microparti-cles were also synthesised at ambienttemperature by adding colloidal silica to a solu-tion of ammonium persulfate in hydrochloricacid with constant stirring. Aniline was thenadded and the solution stirred vigorously for 16h. The colloidal suspension was then cen-trifuged twice and stored in 1 M HCl until used.The oxidation state of the resultant polyanilineand polyaniline-SiO2 was that of the emeraldineform (EM and EM-SiO2, respectively). The fullyreduced forms of polyaniline, LM, and polyani-line-SiO2 (LM-SiO2) were obtained aftersuccessive treatments with sodium hydroxideand hydrazine.

Palladium chloride was used as the precursorfor incorporating palladium in EM, EM-SiO2,LM and LM-SiO2. Figure 18 shows the decreasein the concentration of palladium chloride as afunction of reaction time. From Figure 18, it isapparent that LM and LM-SiO2 are more effec-tive in uptaking palladium from the solutionthan either EM or EM-SiO2. It is also clear thatSiO2 plays no direct role in the reaction with pal-ladium.

The catalytic activity of the palladium-con-taining LM-SiO2 was tested for thehydrogenation of nitrobenzene and it was foundthat there was an almost complete conversion toaniline (Figure 19) after 2 h at 30ºC, whereas thecatalytic activity of the LM without palladium inthe hydrogenation of nitrobenzene was shownto be negligible.

Huang et al. concluded that the reactions arerapid when these electroactive polymers are


800 1000 1200 1400 1600Wavenumber, cm–1

Tran

smitt

ance

848

879

1081 11

41

1269

1397

1470 14

9915

88

1218

Fig. 16 IR spectrum of palladium-poly(o-aminophenol)composite material. Reproduced from (21) with permis-sion from Springer Science and Business Media

100 nm

Fig. 17 TEM image and electron diffraction pattern ofpalladium-polyaniline composite. Reproduced from (22)with permission from Elsevier

Fig. 18 Palladium uptake by the various oxidation statesof polyaniline. Reproduced from (23) with permissionfrom the Royal Society of Chemistry

reduced to their lowest oxidation states. Theelectroactive polymers synthesised with SiO2

offer a larger specific surface area and a fasterreaction rate for uptake reactions with palladiumchloride than does the electroactive polymerwithout SiO2. XPS analysis confirmed that thepalladium accumulation was in the form ofPd(II) rather than elemental metallic palladium.

ConclusionPalladium-polyaniline and the derivatives of

polyaniline composite materials are a veryimportant addition to the repertoire of novelmaterials. From the standpoint of synthesistechniques, the morphology of these compositematerials can be in various forms such as thinfilms, nanorods and nanofibres. The in situ

chemical synthesis route is one of the most ver-satile approaches for the preparation ofmetal-polymer composite materials. By exploit-ing this approach, our group first reported apalladium-based polymeric hybrid material inwhich palladium nanoparticles of size ~ 3 nmwere uniformly dispersed and encapsulated inthe matrices of various derivatives of polyani-line. The matrices had a range of morphologies.Considering the progress of research in thisfield, it can be concluded that, in the near future,palladium-polyaniline composites will producefurther significant advances in the field of mate-rials science.

AcknowledgementsKaushik Mallick expresses thanks to the

University of the Witwatersrand and to theNational Research Foundation, South Africa, forthe award of postdoctoral fellowships. Theauthors thank the referees and the PlatinumMetals Review editorial staff for their constructivecontributions.

References1 R. Gangopadhyay and A. De, Chem Mater., 2000,

12, (3), 6082 E. T. Kang, K. G. Neoh and K. L. Tan, Prog.

Polym. Sci., 1998, 23, (2), 2773 K. Amano, H. Ishikawa, A. Kobayashi, M. Satoh

and E. Hasegawa, Synth. Met., 1994, 62, (3), 2294 A. Ray, G. E. Asturias, D. L. Kershner, A. F.

Richter, A. G. MacDiarmid and A. J. Epstein,Synth. Met., 1989, 29, (1), 141

5 A. Hugot-Le Goff and M. C. Bernard, Synth. Met.,1993, 60, (2), 115

6 A. G. MacDiarmid and A. J. Epstein, Synth. Met.,1994, 65, (2–3), 103

7 E. M. Geniès, A. Boyle, M. Lapkowski and C.Tsintavis, Synth. Met., 1990, 36, (2), 139

8 F. Lux, Polymer, 1994, 35, (14), 29159 N. Gospodinova and L. Terlemezyan, Prog. Polym.

Sci., 1998, 23, (8), 144310 J. L. Shi, E. T. Kang, K. G. Neoh, K. L. Tan and

D. J. Liaw, Eur. Polym. J., 1998, 34, (10), 142911 H. S. Han, K. L. Tan, E. T. Kang and K. G. Neoh,

J. Appl. Polym. Sci., 1998, 70, (10), 197712 S. H. Park, J. S. Lee and K. D. Suh, J. Mater. Sci.,

1998, 33, (21), 514513 D. Bikiaris and C. Panayiotou, J. Appl. Polym. Sci.,

1998, 70, (8), 150314 K. G. Neoh, T. T. Young, N. T. Looi, E. T. Kang


(a) Calibration MixtureEthanol(20 cm3)

1 mmol 1 mmol

0.0 1.0 2.0 3.0 4.0Time, min

Res

pons

e, m

V

(b) Reaction Mixture

Fig. 19 Chromatograms showing: (a) a calibration mix-ture of 1 mmol of nitrobenzene and 1 mmol of aniline in20 cm3 ethanol, and (b) the composition of the reactionmixture containing 1 mmol of nitrobenzene and LM-SiO2

containing 4.3 wt.% Pd (Pd:nitrobenzene = 1:100 molebasis) in 20 cm3 ethanol after hydrogenation of nitroben-zene for 2 h. Reproduced from (23) with permission fromthe Royal Society of Chemistry

and K. L. Tan, Chem. Mater., 1997, 9, (12), 290615 J. G. Wang, K. G. Neoh and E. T. Kang, Appl.

Surf. Sci., 2003, 218, (1–4), 23116 J. G. Wang, K. G. Neoh, E. T. Kang and K. L.

Tan, J. Mater. Chem., 2000, 10, 193317 J.-E. Park , S.-G. Park , A. Koukitu , O. Hatozaki

and N. Oyama, Synth. Met., 2004, 141, (3), 26518 K. Mallick, M. J. Witcomb, A. Dinsmore and M.

S. Scurrell, Langmuir, 2005, 21, (17), 796419 K. Mallick, M. J. Witcomb and M. S. Scurrell, Eur.

Phys. J. E, 2006, 19, (2), 14920 K. Mallick, M. J. Witcomb, A. Dinsmore and M.

S. Scurrell, Macromol. Rapid Commun., 2005, 26, (4),232

21 K. Mallick, M. J. Witcomb, A. Dinsmore and M.S. Scurrell, J. Mater. Sci., 2006, 41, (6), 1733

22 A. A. Athawale, S. V. Bhagwat and P. P. Katre,Sens. Actuators B: Chem., 2006, 114, (1), 263

23 S. W. Huang, K. G. Neoh, E. T. Kang, H. S. Hanand K. L. Tan, J. Mater. Chem., 1998, 8, (8), 1743


Mike Scurrell hasPh.D. and D.Sc.degrees from theUniversity ofNottingham, U.K.,and is nowProfessor ofPhysical Chemistryat the University of

the Witwatersrand. He has beenfascinated by heterogeneous catalysis forthe past 35 years and continues to focuson structure-activity relationships in thisfield. Special current interests are incatalysis by gold and other preciousmetals, activation and conversion ofalkanes, and applications ofspectroscopic techniques to further ourunderstanding of surface chemistry andcatalysis.

Michael Witcombhas a Ph.D. degreefrom the Universityof Lancaster, U.K.,and now is Directorof the ElectronMicroscope Unit atthe University of theWitwatersrand,

where he holds a Personal Professorship.His current fields of research are thesynthesis and characterisation of metaland metal alloy nanoparticle-polymercomposites; precipitation processes inPt-C and Pd-C alloys; phase diagramstudies of intermetallic alloys; andmicrostructural characterisation ofhardmetals.

Kaushik Mallickobtained his Ph.D.degree from MagadhUniversity, India. Heis now apostdoctoralresearch fellow at theUniversity of theWitwatersrand in

Johannesburg, South Africa, working onmetal nanoparticle synthesis,characterisation and applications ofvarious homogeneous andheterogeneous catalytic systems. Hiscurrent research activities are centred onorganic electroactive materials with metalnanoparticles and inorganicsemiconductor composite materials forthe fabrication of various electronicdevices. He has published some 30research articles in various internationalpeer-reviewed journals.

The Authors

16

This book reviews the entire field of homoge-nous hydrogenation over the past forty years. Itcovers both the research literature and industrialprocesses, and aims for comprehensive coverage.The target readerships for this book are industrialchemists and chemistry graduates embarking onresearch in the field. The authors assume a degree-level knowledge of chemistry, but aim to describethe specialist area of homogeneous hydrogenationand provide guidance on the extensive literatureavailable.

The book is unique in covering all aspects ofhomogenous hydrogenation from unfunction-alised alkene hydrogenation to enantioselectivereduction of imines. The two editors are from anindustrial chemical company (DSM Pharmaceut-ical Products, The Netherlands) and a university(University of Amsterdam, The Netherlands). Thisdiversity is also reflected in the authors of theforty-five chapters, who represent a comprehen-sive cross-section of current industrial andacademic research in the field, as well as geograph-ic diversity including Europe, North America andthe Far East.

Precious Metal CatalystsThe many uses of precious metal hydrogenation

catalysts are reflected throughout the book. Thesecatalysts have been used extensively for enantiose-lective hydrogenation. The issues of metalrecycling and removal from products are coveredin topics such as catalyst immobilisation and deac-tivation.

The initial chapters cover individual preciousmetals. A chapter on rhodium covers both histori-cal development and reaction mechanisms. Iridium

was initially thought to be less catalytically activethan rhodium. However, it is in fact slow liganddissociation that gives rise to apparent lower reac-tion rates. In suitable non-coordinating solvents,iridium catalysts can produce faster reactions thantheir rhodium equivalents for some substrates,such as highly substituted alkenes. Further, ruthe-nium is a uniquely effective catalyst for somehydrogenations, such as the enantioselectivereduction of unfunctionalised ketones.

Platinum and palladium catalysts have beenused for alkene and alkyne reductions, includingpartial hydrogenation reactions such as the conver-sion of dienes to mono-enes. There are alsochapters on nickel, lanthanide and actinide cata-lysts.

Ionic hydrogenations were initially investigatedas a way to avoid the use of precious metal cata-lysts. However, the highest catalytic activities areseen with precious metals such as ruthenium.Precious metal clusters have been studied as aninteresting intermediate stage between homoge-nous and heterogenous catalysts. However, it isoften hard to tell whether observed activity is infact due to small amounts of mononuclear catalyst.

Colloids and nanoparticles are another exampleof the grey area between homogeneous and het-erogeneous catalysis. This chapter describes theuse of various stabilisers for these small particlesand their applications, such as the use of rutheni-um nanocatalysts for the reduction of benzene tocyclohexene.

Chapters on kinetics, spectroscopic methodsand the use of parahydrogen to investigate reactionmechanism cover the fundamental characterisationof homogeneous hydrogenation processes.

“Handbook of HomogeneousHydrogenation”EDITED BY JOHANNES G. DE VRIES (DSM Pharmaceutical Products, The Netherlands) AND CORNELIS J. ELSEVIER (University

of Amsterdam, The Netherlands), Wiley-VCH, Weinheim, Germany, 2007, in 3 volumes, 1632 pages, ISBN 978-3-527-31161-3,

£280.00, €420.00, U.S.$500.00

Reviewed by Ann K. KeepJohnson Matthey Catalysts, Orchard Road, Royston, Hertfordshire SG8 5HE, U.K.; E-mail: [email protected]


DOI: 10.1595/147106707X174564

Hydrogenation of FunctionalGroups

There is some overlap between the early chap-ters, which group catalytic processes by the metalcatalyst, and later chapters, which cover the hydro-genation of particular functional groups. This isuseful, as it ensures that an enquiring reader canfind relevant information by several differentapproaches. There are chapters on the reduction ofalkynes and dienes; and of aldehydes, ketones,imines and carboxylic acid derivatives. These reac-tions often use precious metal catalysts. Thechapter on arene and heteroaromatic reductioncovers the ruthenium and rhodium complexesused, although these are likely to be acting as het-erogeneous catalysts in the harsh conditionsnormally employed.

The reduction of carbon dioxide is not yet com-mercialised, but has been carried out withruthenium, rhodium and palladium catalysts in theresearch laboratory. A chapter on dehalogenationgives a table of the precious metal catalysts usedfor various substrates. A chapter on polymerhydrogenation describes how diene based poly-mers can also be hydrogenated with precious metalcatalysts, especially those based on rhodium.

The chapter on transfer hydrogenation coversrhodium, ruthenium and iridium catalysts. It dis-cusses the various donors used, the reactionmechanism and side reactions. Transfer hydro-genation can be used to racemise and therebyrecycle the unwanted isomer in dynamic kineticresolution.

The chapter on diastereoselective hydrogena-tion is lengthy and tabulates the precious metalcatalysts used according to substrate; functionalgroups in alkene substrates direct the stereochem-istry of the hydrogenation.

Rhodium catalysts are unusual in performinghydrogen-mediated carbon–carbon bond forma-tion. The chapter on this reaction covers thecyclisation of enones or aldehydes with cationicrhodium complexes.

Enantioselective HydrogenationA substantial part of the book is occupied by

enantioselective hydrogenation reactions. This

reflects the enormous research interest in this area.These reactions generally use a precious metal cat-alyst in combination with a chiral ligand. Thesection on enantioselective alkene hydrogenationbegins with an introductory overview. There arethen chapters on the different types of chiral ligandused: phospholane, ferrocene-based, other bispho-sphines, bidentate phosphine ligands containingheteroatoms, monodentate ligands and bidentatephosphorus–nitrogen ligands. The enantioselectivehydrogenation of unfunctionalised alkenes is moredifficult and is described in a separate chapter.

The mechanism of enantioselective hydrogena-tion is not yet fully understood. Details arepresented in a chapter which describes mecha-nisms for rhodium, iridium and rutheniumcatalysts and the possible rate determining steps ofhydrogen addition and migratory insertion.

Whereas alkene hydrogenation tends to userhodium or iridium catalysts, ketone hydrogena-tions more commonly use ruthenium. These aredescribed in chapters on enantioselective ketoneand β-keto ester hydrogenations, and the hydro-genation of functionalised ketones.

The enantioselective hydrogenation of iminesand enamines is difficult, as amines can act as cat-alyst poisons and imines are prone to hydrolysis.However, this chapter includes examples of thesuccessful use of iridium, rhodium and rutheniumcatalysts for this type of reaction.

Enantioselective transfer hydrogenation hasalso been carried out with precious metal catalysts.A chapter on high-throughput experimentationand ligand libraries includes an interesting accountof how DSM’s phosphoramidite ligand library ledto a tonne-scale process. The following chapter, onindustrial applications, includes details of pilot-scale processes as well as fully commercialisedones. This is useful as many pharmaceutical prod-uct syntheses are abandoned at pilot scale despitepromising catalytic results.

Phase Separation and MiscellaneousTopics

The separation of product from metal catalysisis a perennial problem in homogeneous catalysis.The issue is addressed in chapters on two-phase



aqueous hydrogenation, supercritical and com-pressed carbon dioxide as reaction medium,fluorous catalysts and fluorous phase catalysis,ionic liquids and immobilisation techniques. Thelatter chapter addresses both research results andcommercial products such as Johnson Matthey’sFibreCat® supported catalysts.

The last part of the book is devoted to miscel-laneous topics, which include metal-catalysedregeneration of nicotinamide cofactors, catalystinhibition and deactivation, and chemical reactionengineering aspects.

ConclusionThe book covers many areas of current

research in homogeneous hydrogenation as well aslarge-scale industrial processes. The information islaid out well; many chapters include useful tablessummarising reaction conditions and catalystactivities. The complex structures of chiral ligands

are given in clear diagrams. The style inevitablyvaries between chapters, but most give a clear andcomprehensive overview of their subject.

The book comprises three hardback volumesand is accordingly priced quite highly. It is there-fore most likely to be bought as a reference workfor an academic or industrial library. In this con-text, I feel it is a useful starting point for futureexplorations of homogenous hydrogenation. Itoffers an up-to-date and wide-ranging review ofthe field.

The Reviewer

Ann Keep is a PrincipalScientist at Johnson MattheyCatalysts in Royston, U.K.Her main professional interestsare in transition metal catalysts,both homogeneous andheterogeneous.

19

The annual international Santa Fe Symposium®

is the foremost source of the latest research andtechnical information on jewellery materials andmanufacturing technology. Much of the industry’scurrent state of knowledge on platinum jewelleryalloys and manufacturing practice has been fea-tured at this Symposium over the years (1–3).Breaking with tradition, the 2006 Symposium – the20th Santa Fe Symposium – was held in Nashville,Tennessee, from 10th to 13th September 2006,rather than in Albuquerque, New Mexico, its spir-itual home.

Introduction of PalladiumThe 2006 Symposium was notable for featuring

the new jewellery metal – palladium. This had beena very hot topic in the U.S., Chinese and Europeanjewellery industries over the previous year, withmany U.S. alloy suppliers launching new 950 palla-dium alloys on the market and the retail industryshowing serious interest. However, a full technicalappraisal has been awaited, and the three presenta-tions on palladium ensured that a technicalunderstanding of the metal was placed on a soundfooting.

Palladium jewellery (Figure 1) is of interest as analternative white jewellery metal because its lowprice and low density (compared with those ofgold and platinum), coupled with its good whitecolour and tarnish resistance, make it a better low-cost alternative to 950 platinum than traditionalcheaper options such as 18 and 14 carat white gold.In addition, retailers may be able to obtain moreattractive margins.

The first presentation, ‘The Working Propertiesfor Jewelry Fabrication Using New Hard 950Palladium Alloys’, was by Professor Paolo Battaini(8853 SpA, Italy), who described progress to devel-

op two prototype 950 palladium alloys for wroughtapplication. The initial work was based on palladi-um-copper (Pd-Cu) and palladium-gallium (Pd-Ga)alloys, with indium and other alloying additions.

The annealed hardness of the Pd-Ga alloy, atHV 170, was much higher than that of the Pd-Cualloy at HV 70, and its melting range was substan-tially lower. As-cast ingots were subjected to coldrolling and annealing cycles down to thin sheet.This sheet was further subjected to a number ofmechanical processing operations, and the evolu-tion of the metallurgical structure and propertieswas followed. For the Pd-Ga alloy, this includedroll forming with continuous tungsten inert gas(TIG) welding to form seamed tube, that was fur-ther drawn down to tube of 8.5 mm diameter(easily accomplished, but dependent on goodlubrication). Other processes tested were theblanking of washers, drawing and ring rolling toform ring blanks as well as square bars being rolledand then drawn to wire of 0.7 mm diameter, usingdiamond nibs in the dies. Good lubrication wasalso important here. Tensile tests were performedon the wires. Typically, a cold-worked hardness of


DOI: 10.1595/147106707X166761

The 20th Santa Fe Symposium on JewelryManufacturing TechnologyPALLADIUM FEATURES AS A JEWELLERY METAL FOR THE FIRST TIME

Reviewed by Christopher W. CortiCOReGOLD Technology Consultancy, Reading, U.K.; E-mail: [email protected]

Fig. 1 Working a palladium alloy ring (courtesy of MannDesign Group)

HV 220 or greater was achieved before annealingto a hardness of HV 180. Good fine-grained,equiaxed microstructures were obtained.

For the Pd-Cu alloy, as-cast ingots were alsocold-rolled and annealed down to thin strip, androll-formed to square tube with continuous TIGwelding, and subsequently further drawn to small-er dimension. Typical hardness after heavy coldwork was HV 170, which reduced to around HV72 on annealing.

Laser welding and brazing studies were carriedout on the Pd-Ga alloy; it was found essential toestablish the correct process parameters for suc-cessful laser welding, and the use of an 18 caratnickel white gold filler allowed effective brazingwith an oxy-propane torch.

This work showed that the Pd-Ga alloy was themore promising of the two examined. Themechanical strength of the drawn and annealedwires was better than that of some platinum alloys,and indicated the suitability of the Pd-Ga alloy forchain manufacture.

An initial study, ‘Palladium Casting: AnOverview of Essential Considerations’, of theinvestment/lost wax casting of 950 palladiumalloys, was reported by Teresa Frye (TechformAdvanced Casting Technology, U.S.A.). This com-pany specialises in shell-mould casting of platinumjewellery and other high-tech metals for the aero-space and dental/medical industries. The purposeof the study was to obtain a better understandingof the casting characteristics of the new 950 palla-dium alloys appearing on the market, incomparison with those of the casting of platinumjewellery alloys. Frye covered several aspects: inwax sprueing, she noted that use of more auxiliaryfeed sprues was required for palladium thin sec-tions to facilitate filling of the mould cavity. As inthe case of platinum, investing the mould requiredthe use of phosphate-bonded investments due totheir high melting ranges (1400 to 1500ºC).Techform use ceramic face coats prior to investingthe wax tree, but considered that this was not nec-essary. Any investment suitable for platinumshould work well for palladium.

Frye found that the actual casting of palladiumposed the biggest technical challenge. This was due

mainly to the risk of oxidation, unlike for platinum,and so the use of protective atmospheres wasessential; Frye used argon, but nitrogen is also pos-sible. She also noted that overheating of themolten metal increased the chance of oxygenabsorption with consequent defect formation (gasporosity) during solidification. Devesting of thecast metal from the mould was found to be rela-tively straightforward, by using boiling dilutesodium hydroxide solution followed by waterblasting.

The study reported by Frye was conducted onpalladium alloys selected on the basis of certain cri-teria, including a minimum hardness of HV 110,ductility, recyclability, melt cleanliness and fluidity.This resulted in six commercial alloys being evalu-ated, with casting temperature of 1600ºC, flasktemperature of 950ºC, and vacuum followed byargon backfill atmosphere. Three of the test alloysresulted in brittle, defective castings, whereas theother three were ductile and crack-free. When thealloys were cast without vacuum, i.e. only argoncover, five of the alloys cast well, suggesting thatvacuum was detrimental to some alloys. Scanningelectron microscopy (SEM) analysis of a ductilefracture face showed the presence of low-meltinggallium-rich particles on the grain boundaries.

Based on this initial evaluation, Frye selectedtwo alloys which were subjected to form-fillingcasting tests using standard grid patterns and metalpour temperatures of 1590ºC, 1620ºC and 1760ºC.The latter temperature gave the best form-fill forHoover & Strong’s ‘TruPd’ and similar good fillswere obtained in comparative trials on a 950 Pt-Rualloy, cast at 1980ºC. Examination of cast rings in‘TruPd’ under the same conditions showed a lackof porosity.

Frye concluded that there is still much work tobe done on casting of palladium alloys, which pre-sent unique challenges compared with otherprecious metals. Recyclability of palladium alloyscraps is of particular concern.

Barrie-John Williams (Johnson Matthey, NewYork) gave the third presentation on palladiumjewellery alloys, ‘Palladium – Light, Bright andPrecious – a World View’, in which he reviewedpalladium as a jewellery metal. The presentation


21Platinum Metals Rev., 2007, 51, (1)

included a potted history of palladium, discoveredby Wollaston (4) in 1803, and some basic statisticson supply and demand, with particular referenceto the U.S. source of supply – the Stillwater mine.Williams noted that recent interest in palladium asa jewellery metal in its own right (as opposed to itsuse in white gold) started in China in 2003, andthat the Swiss began to use it for watches in 2005as an alternative to white gold.

Williams noted that pure palladium is too softfor jewellery use, so alloys of 95% palladium havebeen developed (i.e. 950 fineness) that are harderand better wearing. The qualities of palladium as ajewellery metal include its preciousness as a mem-ber of the platinum group metals, its natural brightwhite colour, good lustre and lack of tarnishing aswell as its lower density than that of gold and plat-inum. Like platinum it is rare, and its high purity at950 fineness is attractive in the market.

Current ISO standards of purity (ISO9202:1991 Jewellery – Fineness of precious metalalloys) are 950 and 500 finenesses. China hasadopted 950 and 990, and in the U.S.A., 950 isfavoured, as it is also in Germany and Switzerland.The U.K. assay offices have applied to have palla-dium recognised as a hallmarkable jewellery metal.

Williams noted that many 950 alloys are beingdeveloped and introduced to the market by alloymanufacturers, including Johnson Matthey, forboth wrought and casting applications. Most arebased on the Pd-Ru system with other alloyingadditions. He remarked that one of the disadvan-tages is the high cost of refining palladium alloyscrap.

Platinum AlloysPlatinum was also discussed at the Symposium.

John McCloskey (Stuller Inc, U.S.A.) presentedresults of a study of two common 950 platinumalloys, ‘Microsegregation in Platinum-Cobalt andPlatinum-Ruthenium Alloys’. Based on the respec-tive phase diagrams and using the Gulliver-Scheilequation to calculate the partition coefficient,McCloskey and his coworkers calculated thedegree of microsegregation to be expected in castalloys. Measurements on cropped sections of castingots by microprobe analysis showed that

localised concentrations of ruthenium from centreto edge of the primary dendrites varied between 2and 6% in an alloy containing 4.8% ruthenium.For the 4.8% cobalt alloy, the cobalt values variedbetween 4.3% minimum and 5.8% maximum.McCloskey used these data to calculate the parti-tion coefficients, and found broad agreement withthose calculated from the phase diagrams. Henoted that in the Pt-Ru alloy, the last liquid tofreeze is depleted in ruthenium and is almost pureplatinum (98% measured), whereas in the Pt-Coalloy, the cobalt concentration of the liquidincreases during solidification.

He concluded that the non-equilibrium freez-ing characteristics of the two alloys were distinctlydifferent and that this, together with the widerfreezing range, may explain the better casting char-acteristics of Pt-Co alloys.

The investment casting of platinum was inves-tigated by Appolonius Nooten-Boom II (HeanStudios, U.K.), and reported in a presentation (byJohn Wright (Consultant, U.K.)), ‘Dynamics of theRestricted Feed Tree’. Nooten-Boom showed howmetal flowed into the mould during casting, andhow improved fill can be obtained by use of arestricted feed system, which slows the feed ofmolten metal into the mould. This is contrary toconventional wisdom in the jewellery industry,although not in the engineering industry.

Technical InformationAndrea Basso’s (Legor Srl, Italy) ‘Jewelry and

Health: Recent Updates’ was a study on contactdermatitis in which 920 individuals were tested forallergies to metals commonly found in jewellery byskin patch tests using metal salts and metal discs(made of gold alloys of various carats). The patchtests using metal salts showed positive reactions toseveral metals in the order (maximum numberfirst): nickel, cobalt, palladium, potassium, gold,copper, mercury and silver, with platinum and zincshowing no positive reactions. Of the 266 patientspositive to nickel, some 53% were not positive toother metals. The other 47% were also sensitive tocobalt chloride, palladium chloride and gold thio-sulfate in that order. In the patch tests with metaldiscs, no type of allergic reaction was found in

subjects not sensitised to nickel. However, it wasnoted that where nickel release values were belowthose limits of the EU Directive (5), some sensi-tised patients still showed allergic reaction.

In his presentation ‘“Where Can I Find What IWant to Know?” Sources of Technical Infor-mation for Jewellers’, Chris Corti (COReGOLD,U.K.) discussed various sources and referencebooks giving technical information. This includedThe PGM Database (6), various handbooks andmanuals by Platinum Guild International, JohnsonMatthey, the World Gold Council and others, aswell as jewellery journals and websites. Corti’s sur-vey revealed a lack of up-to-date reference bookson the metallurgy and properties of jewellery met-als and their manufacturing technology. TheProceedings of the Santa Fe Symposium® wereconsidered important sources.

Jewellery ManufacturingTechniques

Stewart Grice (Hoover & Strong, U.S.A.) dis-cussed the diffusion bonding of difficult alloycombinations related to mokumé gane jewellery, andfocused on carat Au-Pt and Au-Pd combinations.A goldsmith’s experience in TIG welding of jew-ellery was presented by Kevin Lindsey (LindseyJewelers, U.S.A.) and showed its effective use inboth small workshops and factories.

Martin Moser (OTEC Präzisionsfinish GmbH,Germany) discussed the effect of machine finish-ing parameters on polishing of jewellery, and howthese can be used to optimise the finishing process.The investment casting of titanium jewellery wasreviewed by Hubert Schuster (JewelleryTechnology Institute, Italy) and the fundamentalsof shotting and graining were reviewed by JosephStrauss (HJE Company Inc, U.S.A.). KlausWeisner (EVE GmbH, Germany) discussed thespecifications of semi-finished jewellery materialsand the problems that can arise if orders are placedwith non-realistic expectations, drawing on hisexperience as an alloy supplier. The design aspectof jewellery was discussed by the designer BarbaraBerk (Barbara Berk Designs, U.S.A.) who spokeabout textile techniques such as weaving of wires,basketry and braiding in precious metals.

20th Anniversary of the Santa FeSymposium®

Valerio Faccenda (Consultant, Italy) summedup the achievements of the last 20 years of theSanta Fe Symposium® in terms of its contributionsto the jewellery industry: a fitting review of aunique resource that has made a major impact.

To mark the 20th anniversary of the Santa FeSymposium®, a special tribute was paid to EddieBell, the co-founder, by many delegates past andpresent, by way of recognition of his vision andcommitment to the industry. The highlight was thepresentation of a ‘concho’ belt to Eddie. The 11concho discs were crafted by skilled delegates, andincluded both platinum and palladium (donated byJohnson Matthey) as well as gold, silver and titani-um. This belt was a feast of goldsmiths’ skills. Afitting tribute!

ConclusionThe many questions to speakers at this

Symposium confirmed the wide technical interestin palladium as a jewellery metal. The Santa FeSymposium® proceedings are published as a bookand PowerPoint® presentations on CD-ROM.They can be obtained from the organisers viawww.santafesymposium.org. The 21st Symposiumwill be held in Albuquerque, New Mexico, U.S.A.,from 20th to 23rd May 2007.

References1 C. W. Corti, Platinum Metals Rev., 2000, 44, (4), 1562 M. Grimwade, Gold Bull., 2005, 38, (2), 783 M. Grimwade, Gold Bull., 2005, 38, (4), 1884 W. P. Griffith, Platinum Metals Rev., 2003, 47, (4), 1755 European Directive, 76/769/EEC – 12th

Amendment (94/27/EC)6 The PGM Database, http://www.platinummetalsre-

view.com/jmpgm/index.jsp

The Reviewer

Christopher Corti holds a Ph.D. in Metallurgyfrom the University of Surrey (U.K.) and iscurrently a consultant for the World GoldCouncil and the Worshipful Company ofGoldsmiths in London. He served as Editor ofGold Technology magazine and currently editsGold Bulletin journal and the Goldsmiths’Company Technical Bulletin. A recipient of theSanta Fe Symposium® Research Award,

Technology Award and Ambassador Award, he is a frequentpresenter at the Symposium.

22Platinum Metals Rev., 2006, 50, (4)

Welding TechniquesVarious joining techniques are theoretically

available to the platinum jeweller, including tradi-tional brazing with ‘solder alloys’, fusion welding,friction welding, arc welding and electron beamwelding (1). Until recently, only brazing and fusionwelding were accessible to the small- or medium-sized jeweller. In the past decade, laser weldingunits have become small enough and inexpensiveenough for application in the jewellery workshop(1–3). Even more recently, miniature electric resis-tance spot welding machines have been developedspecifically for the jewellery studio (4).

Traditional welding of platinum is carried out byinserting a thin over-sized sheet of identical metalbetween the pieces to be joined. Heat is applied tothe projecting sheet, fusing and sealing the joint (5).This contrasts with traditional brazing, using analloy of lower melting point, as is commonly thepractice in gold- or silver-smithing (1). Laser weld-ing uses high-intensity, focused laser light beams toapply energy to very small areas, resulting in veryrapid and efficient local melting (2). The positionof the weld spot is located using a stereomicro-scope with cross-hairs. Very little heat is generated,

and laser welds can be made on complicated parts,between dissimilar metals, and close to set stoneswithout damaging them (3). The new spot weldingunits use an electrode to create a high-intensityelectric spark, either to melt the parent metal or athin wire, to effect the weld (4). Both laser and spotwelding take advantage of the fact that platinumhas a low thermal diffusivity when compared withsilver or gold jewellery alloys (3). This means thatthe focused application of a small spot of intenseenergy can cause localised melting, without signifi-cant heating of the surrounding metal. This resultsin a comparatively small heat affected zone aroundthe weld, and the mechanical properties of the bulkof the workpiece remain unchanged.

Fusion welding, laser welding and spot weldingare now the three most commonly used joiningtechniques in platinum jewellery manufacture(1–3). We set out to compare these three tech-niques on three different platinum alloys, usingequipment actually in use in jewellery workshops.

Alloys and Sample PreparationThree different platinum alloys were tested: the

commonly-used platinum-5 wt.% ruthenium (Pt-

23

Welding of Platinum Jewellery AlloysCOMPARISON OF FUSION, LASER AND SPOT WELDING

By Duncan Miller, Katyusha Vuso, Penny Park-Ross and Candy Lang*Centre for Materials Engineering, University of Cape Town, Rondebosch 7701, South Africa; *E-mail: [email protected]

The relatively recent application of laser welding and spot welding to platinum has supplementedthe traditional joining techniques of conventional welding and brazing with a gas torch. Severalrecent publications (1–3) have promoted the use of laser welding, because of the superiorstrength of the joins compared with that of joins by conventional welding and brazing. Inthis paper we compare welds in three different platinum alloys, produced with three differentwelding techniques: conventional welding, laser welding and spot welding. The welds joiningcold-rolled bars were performed by jewellers operating in their own workshops. The extentsof the heat affected zones and consequent decrease in hardness were assessed in our laboratory.Laser and spot welding produced very narrow heat affected zones, with correspondinglynarrow regions of diminished hardness, while the conventional welding resulted in samplesbeing annealed and softened for their full lengths. Complete joining was difficult to achieveby laser and particularly spot welding, which could be problematic in joining thicker sections.With this knowledge, jewellers can design appropriately to take advantage of the novel joiningtechniques.


DOI: 10.1595/147106707X171954

5% Ru) and platinum-5 wt.% copper (Pt-5% Cu),and a novel heat-treatable platinum-3 wt.% vanadi-um (Pt-3% V) alloy (currently the subject of apatent application). Rectangular strips 1.2 mmthick were prepared by cold rolling. The Pt-5% Ruand Pt-5% Cu were hardened by cold work, andthe Pt-3% V specimens by heat treatment. Theresulting initial microhardness values were 256 HVfor Pt-5% Ru, 270 HV for Pt-5% Cu, and 457 HVfor Pt-3% V.

Joining was performed in all cases by abuttingflat surfaces which had been prepared by sawingthrough the bars transversely. Most of the sampleswere prepared without bevels or notches at the sur-faces to be joined. This was to test the penetrationof the laser and spot welding.

The fusion welding on all three sample materi-als was carried out by the conventional method ofinserting a thin sheet of the identical alloy betweenthe two parts to be joined, and heating the sheetlocally with an oxygen/propane flame until itfused. Laser welding was performed using a Rofin‘StarWeld’ YAG model SWL-Y 65 laser weldingmachine, in air. Owing to limited availability of thePt-3% V material, spot welding was carried outonly on the Pt-5% Ru and Pt-5% Cu samples,using a Lampert PUK2 microwelder, with an argonstream to exclude oxygen.

ResultsThe welded specimens were sawn longitudinal-

ly with a jeweller’s saw, cold mounted in resin, andground and polished for microscopic examinationin reflected light. The fusion welds exhibited thebest penetration, whereas all the laser and spotwelds had median gaps, of various sizes up to halfthe specimen width, which were evident in thesawn sections (Figure 1).

Microhardness was measured with a Zwickmicrohardness tester and Vickers indenter. Figures2 and 3 show the effects of welding on the micro-hardness of Pt-5% Ru and Pt-5% Cu, respectively.These alloys showed similar patterns, with signifi-cant but narrow drops in microhardness in theweld zones for both laser and spot welding, andextensive softening due to recrystallisation alongthe length of the samples for fusion welding. All

three samples started out with very similar micro-hardnesses, so the overall softening due to fusionwelding was very obvious (Figures 2 and 3).

Etching showed that for Pt-5% Ru and Pt-5%Cu, both the laser and spot welds had local recrys-


Fig. 1 Polished section through the spot weld in Pt-5%Ru, showing incomplete joining

Fig. 2 Plot of microhardness (HV) against distancealong the length of welded bars of Pt-5% Ru, showingloss of hardness restricted to the weld zone of laser andspot welding, but an overall drop in microhardness alongthe entire length of the fusion weld specimen

Fig. 3 Plot of microhardness (HV) against distancealong the length of welded bars of Pt-5% Cu, showinglocalised loss of hardness in the weld zone in both laserand spot welding samples. The fusion weld sample hadthe same initial hardness as the other samples, andshowed reduced post-weld microhardness along its entirelength

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tallisation only in the immediate vicinity of thewelds. The cold worked microstructure, with flat-tened and elongated grains, was preserved withoutheat-affected alteration to within 2 to 3 mm of theweld line, whereas the heat affected zone of thefusion weld samples extended the full length of thespecimens. They were completely recrystallised.

Figure 4 shows the effect of laser and fusionwelding on the microhardness of Pt-3% V. Thelaser welded sample showed a steep but narrowdrop in microhardness across the weld zone. Afteretching, it was clear that local recrystallisation hadtaken place only in the immediate vicinity of theweld. The fusion welded Pt-3% V sample, whichstarted out with a microhardness of about 457 HV,showed a significantly decreased microhardness ofabout 200 HV across the specimen after welding,due to recrystallisation along the entire length ofthe sample, as evident from light microscopy(Figure 5).

Scanning electron microscopy with a Kevexenergy-dispersive X-ray analysis system on a LeicaS440 microscope was carried out principally toassess the effect of welding on alloy composition,which was determined at closely spaced pointsalong the lengths of the polished sections of select-ed welded specimens. Detectable loss of thealloying element was observed only in the case offusion welding of the Pt-3% V specimens. No lossof vanadium was detected in the weld zones of thelaser welded specimens, nor was alloying elementlost in the Pt-5% Ru and Pt-5% Cu specimensjoined by all three techniques.

DiscussionIt is clear from the results that traditional fusion

welding is capable of producing a good join in plat-inum jewellery alloys, but that the degree ofheating required causes extensive recrystallisation,which in turn reduces the overall hardness. Anyfusion welding towards the end of the manufactur-ing process will compromise the aim of theplatinum smith to increase the final hardness ofjewellery through work hardening or controlledheat treatment.

In our tests neither laser welding nor spot weld-ing produced good joins. All the welds wereincomplete, with internal voids of varying extent,and with welding only effective on the outer mar-gins. This is consistent with the results for buttwelding obtained by Volpe and Lanam in an exper-imental study comparing fusion welding withconventional brazing using solder (1). Their studyhad more success with laser welding bevelledjoints, and undoubtedly our welds would havebeen better if all the pieces to be joined had beenbevelled. The jeweller conducting the spot weldtests reported great difficulty in fusing and joiningthe flat ends of the platinum workpieces. The rec-ommended practice for microwelding is to melt athin wire of the same metal into the groove creat-ed by a bevelled joint (5).

We did not carry out any strength tests on ourexperimental joints. Laser welding has been report-ed to produce consistently stronger joints in bendtests than does brazing, especially when using awide 60º bevel joint in the laser welds (1). This is


Fig. 4 Plot of microhardness (HV) against distancealong the length of welded bars of Pt-3% V, showinglocalised softening associated with the weld zone in laserwelding. The fusion weld sample had the same initialhardness as the laser weld sample, and showed reducedpost-weld microhardness along its entire length

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easily done when joining simple components suchas bars or two sides of a ring shank, but requiressome ingenuity in making the bevel when joiningthicker sections to surfaces, for instance attaching aring shank to a bezel setting.

The results of the microhardness tests showedthat both laser welding and spot welding causedminimal recrystallisation, and that was restricted toa narrow zone in the immediate vicinity of theweld. This left the overall hardness of the work-piece unchanged. The implications formanufacture include retaining prior hardnessachieved through cold work or controlled heattreatment when welding in late-stage assembly orin repairing jewellery.

Fusion welding in air of the novel heat-treatablePt-3% V alloy resulted in an appreciable loss ofvanadium. Laser or spot welding would be the onlyeffective ways of joining such an alloy.

ConclusionsThis study has shown that laser and spot weld-

ing can be used to weld a variety of platinum alloys,producing a very narrow heat affected zone, andthus significantly limiting the extent of annealingand softening associated with the weld. This is instrong contrast to conventional fusion welding,where the heat generated tends to anneal large vol-umes of metal, if not the entire workpiece.

It is important to prepare the sections to bejoined by laser or spot welding appropriately. Ifpossible there should be a 60º notch or bevelbetween them, in order to get good penetration of

energy and to fill the gap with molten metal. Thismay require some ingenuity in design.

The primary advantage of using laser or spotwelding is the retention of desirable hardeningcaused by prior cold work or low temperature heattreatment.

AcknowledgementsWe thank Oro Africa and Sitali Jewellers in

Cape Town for performing the welds, and MirandaWaldron of the Electron Microscope Unit at theUniversity of Cape Town for assistance with thescanning electron microscopy. Chumani Mshumipolished the sectioned samples in the Centre forMaterials Engineering at the University of CapeTown, which provided laboratory and office facili-ties. This research was funded by a grant from theInnovation Fund, administered by the SouthAfrican National Research Foundation.


References1 C. Volpe and R. D. Lanam, ‘Laser Welding or

Conventional Soldering’, 1999 Platinum DaySymposium, Vol. 5, Platinum Guild InternationalUSA, Los Angeles, U.S.A., 1999; http://www.pgi-platinum-tech.com/pdf/V5N6.pdf

2 J. E. Gervais, ‘Making Soldering a Technique of thePast’, 1999 Platinum Day Symposium, Vol. 5,Platinum Guild International USA, Los Angeles,U.S.A., 1999; http://www.pgi-platinum-tech.com/pdf/V5N8.pdf

3 J. C. Wright, Platinum Metals Rev., 2002, 46, (2), 664 C. Patrich, ‘Changing Ring Widths and Saving

Time’, GZ Art + Design, 2005, 4, 345 “Practical Platinumsmith”, 4th Edn., Rühle-

Diebener-Verlag, Stuttgart, Germany, 2000, p. 21

The Authors

Duncan Miller is an HonoraryResearch Associate at theUniversity of Cape Town(UCT) and a member of theteam in the Centre forMaterials Engineeringstudying novel platinumjewellery alloys.

Katyusha Vuso is a recentgraduate from the Universityof Cape Town, who carriedout a research project onwelding of platinum jewelleryalloys.

Penny Park-Ross is aResearch Assistant in theCentre for MaterialsEngineering (UCT), and isresponsible for thelaboratory analysis of alloys.

Candy Lang is Professor inthe Department ofMechanical Engineering(UCT). She is leader of theteam developing novelplatinum alloys for thejewellery industry.

Following meetings in Amsterdam in 2002 (1)and Munich in 2004 (2), another in this series ofconferences was held on the 13th and 14thSeptember 2006 at the Turin Incontra ConferenceCentre, Turin, Italy, with the theme ‘ScientificAdvances in Fuel Cell Systems’. The conferenceseries (3) alternates with the Grove Symposium (4, 5), with a more technology-oriented content.

Authors from around the world submitted oralpapers and posters from which the programmewas compiled. Organised by the GroveSymposium Steering Committee and ElsevierScience, the meeting attracted almost 300 delegatesfrom universities, research organisations, and fuelcell component manufacturers. The 34 countriesrepresented included Japan (44 delegates), Italy (42delegates), Germany (39 delegates), the U.K. (31delegates) and the U.S.A. (12 delegates). As well as56 oral papers, there were six poster categorieswith 205 high-quality poster presentations. Theconference consisted of six sessions, covering thefollowing subject areas:– membranes– systems analysis and applications– component modelling and characterisation– electrocatalysis– fuels– fuel cell and stack technology.

The latter two categories attracted sufficientpapers to occupy two sessions each. Since thetopic of fuel cells covers such a wide area, for thisreview only papers involving use of the platinumgroup metals (pgms) have been selected.

Grove MedalFor the first time, the Grove Medal was pre-

sented at a Fuel Cells Science and Technologyconference, rather than at the Grove Fuel CellSymposium. The 2006 recipient was ShimshonGottesfeld for his sustained high-quality scientific

and technical contribution to the field of fuel cells,combined with his drive and vision to commer-cialise new fuel cell technology, building on hisresearch. Gottesfeld was Vice President and ChiefTechnology Officer of MTI Micro Fuel Cells Incfrom December 2000 until May 2006, and prior tothis he led the Fuel Cell Research Program at theLos Alamos National Laboratory (LANL) formore than 15 years. He is now a consultant withFuel Cell Consulting.

In a Plenary talk, Gottesfeld focused on someof the important milestones along the paths ofpolymer electrolyte fuel cell (PEFC) and directmethanol fuel cell (DMFC) science and technolo-gy, culminating in a new polymer electrolyteDMFC concept developed at MTI Micro FuelCells Inc. These milestones include reducing theplatinum loadings of solid PEFCs by an order ofmagnitude, by impregnating the catalyst withNafion® perfluorosulfonic acid polymer (in 1986),fabricating electrodes by the application of cata-lyst/Nafion® ‘inks’ in 1992, and developingPEFCs capable of tolerating a concentration of100 ppm of carbon monoxide in the hydrogen fuelby incorporating a small oxygen bleed into the fuelto oxidise the impurities on the anode (in 1998).The latest development is the Mobion® DMFCsystem, providing a high power density and highefficiency, up to 1100 Wh l–1, as compared with200 Wh l–1 for lithium prismatic batteries and 400 Wh l–1 for cylindrical lithium batteries.

Fuel ProcessingMost fuel cells require a supply of reasonably

pure hydrogen, and many projects exist to buildsmall, portable reformers for fossil or renewablefuels. In his talk ‘Fuel flexibility of bimetallic Pt-Nisystem: Hydrogen production from LPG havingdifferent C3:C4 ratios’, Ahmet Aksoylu (BogaziciUniversity, Turkey) explained that liquid petrole-

27

Fuel Cells Science and Technology 2006SCIENTIFIC ADVANCES IN FUEL CELL SYSTEMS

Reviewed by Donald S. CameronThe Interact Consultancy, 11 Tredegar Road, Reading RG4 8QE, U.K.; E-mail: [email protected]


DOI: 10.1595/147106707X170117

um gas (LPG) is one of the most promising hydro-carbon fuels for hydrogen production. However,the composition of LPG varies from country tocountry depending on local crude oil supplies andrefinery processes. In this study of indirect partialoxidation of LPG over platinum-nickel on δ-Al2O3

catalysts, the effects of temperature, steam:carbonratio, carbon:oxygen ratio and residence time onthe activity and the selectivity of the catalyst werevaried. The results indicated that the Pt-Nibimetallic system has high H2 production activityand selectivity in the temperature range 350 to450ºC, owing to the utilisation of the catalyst par-ticles as micro heat exchangers, in which heatproduced at platinum sites by oxidation catalysesthe endothermic steam reforming reaction.

A more efficient use of coal was proposed byGerardine Botte (Ohio University, U.S.A.), in hertalk ‘Hydrogen production from coal electrolysis’.In 1979 (6) a new means of coal gasification wasdiscovered at the University of Connecticut, usingplatinum electrodes to electrolyse coal slurries at25ºC to generate pure streams of CO2 and hydro-gen at the anode and cathode respectively, free oftar and sulfur compounds. The authors report thatthe reversible thermodynamic potential for thereaction is only –0.21 V. This compares with thepotential for conventional water electrolysis, whichis theoretically 1.23 V, but in practice is ratherhigher than this. Effectively, the free energychange resulting from the oxidation of carbon low-ers the voltage required for electrolysis. The CO2

product can be disposed of in a number of ways,while intermediate hydrocarbons which are alsoformed can be used to make byproduct oils.

One of the problems associated with the elec-trolysis is the low reaction rate. However, recentlyOhio University has developed improved catalystsand improved operating conditions for theprocess. These include using higher operating tem-peratures (80ºC), carbon fibre and titaniumelectrode support materials, and optimised plat-inum-iridium catalysts. The ratio of Pt:Ir is animportant parameter, and these catalysts are moreeffective than platinum, while rhodium does notfavour the carbon oxidation reaction.

In his talk entitled ‘Fuel processing in integrat-

ed microstructured heat-exchanger reactors – cur-rent status and future perspectives’, Gunter Kolb(Institut für Mikrotechnik Mainz GmbH (IMM),Germany) reported work on fuel processor com-ponents for systems rated from 100 W up to 100 kW, for a variety of fuels. The reactions takeplace inside heat exchangers, with exothermic cat-alytic combustion on one side and theendothermic reforming reaction on the other.Anode off-gas from the fuel cell is burned to pro-vide the heat required. In their 5 kW-ratedautothermal reactor for octane, which uses a rhodi-um catalyst, it is possible to obtain carbonmonoxide impurity levels in the product hydrogenlower than 20 ppm. The reactors are also arrangedfor water injection to remove CO by the water gasshift reaction – the latter is facilitated by introduc-ing a temperature gradient inside the heatexchanger, thus eliminating a second shift reactor.The estimated market for various applications isfor 1000 to 10,000 y–1 reformers for yachts and car-avans, and 10,000 to 100,000 y–1 for auxiliarypower units for vehicles.

Systems and ApplicationsThe topic of pgm use was an important feature

of a talk by Florian Finsterwalder (DaimlerChryslerAG, Germany) on ‘Achievements and challenges inautomotive PEM fuel cell stack development’. Forvehicle use, fuel cells must operate at temperaturesvarying from sub-zero to preferably around 120ºCto reject waste heat, in conditions with a wide rangeof humidity values. Between 1992 and 2006 therehas been a linear reduction in the amount of pgmsused on the electrodes for DaimlerChrysler vehi-cles, to a current value of 1.43 mg cm–2 Pt, and amaximum power density of 0.72 W cm–2. QuotingU.S. Department of Energy milestones for 2010,there are targets for cost of U.S.$30 kW–1 for vehi-cle fuel cells, maximum power density of 0.8 Wcm–2, and platinum metal loading of 0.3 g kW–1

(implying a platinum loading of 0.24 mg cm–2).Improved separators and membranes shouldenable the attainment of a power density of 2000 Wl–1 with durability of 4000 hours, and Finsterwalderis optimistic as to the industry meeting these targetsfor vehicle fleets numbering thousands.


The concept of a microchip with an integratedPEFC is being investigated at the University ofFreiburg, Germany, and also Micronas GmbH,Germany, by Gerhard Erdler and coworkers. Witha silicon chip as a basis, a palladium hydride anodeis used in conjunction with an air depolarised pla-tinised cathode and a polymer electrolyte. The 4mm square, 200 μm thick palladium anode ischarged with hydrogen, a 10 to 20 μm polymerlayer is applied by spin coating, and a platinumcatalysed carbon cloth cathode is applied on top.Current collection is carried out using gold tracks.The generator is intended to power devices suchas complementary metal oxide semiconductor(CMOS) chips used as body temperature monitorsand intelligent ‘BAND-AID®’ adhesive bandages,which require less than 100 μW for periods of upto one week.

MembranesMembranes play a vital role in the performance

and durability of PEFCs. Improvements in thisfield were addressed by Eiji Endoh (Asahi GlassCo Ltd, Japan). Nafion® type membranes undergoa glass transition at around 80ºC, whereas for ade-quate heat rejection, automotive use demandsoperation at 110 to 120ºC, possibly under condi-tions of low humidity. A “new perfluorinatedion-exchange polymer composite” (NPC) devel-oped by Asahi reduces the degradation rate by twoto three orders of magnitude as compared withconventional membrane materials. This has beenoperated continuously for more than 4000 hoursat 120ºC and 50% relative humidity. Whereas thecell voltage fell from around 750 mV to 450 mV at200 mA cm–2 during this time, under similar con-ditions, a conventional membrane electrodeassembly (MEA), also with 0.6 mg cm–2 platinumloading on the cathode and 0.2 mg cm–2 on theanode, failed after the first 100 hours. The voltagedecay was attributed to attack on the carbon sup-port of the cathode catalyst by peroxide releasedduring cell operation, the catalyst layer thicknesshaving been reduced by 44% during this periodfrom 18 μm to 8 μm. More oxidation-resistantcathode catalyst substrates are being sought toimprove the durability of the system. Asahi are

seeking improved performance stability beyond120ºC using low surface area forms of their cur-rent Ketjen black carbon support, and hope thatthese, in combination with thinner membranes,will enable maximum cell current density to beincreased from 1.6 to 2.0 A cm–2.

ElectrocatalysisThe link between carbon stability and catalyst

durability was highlighted by Sarah Hudson(Johnson Matthey Technology Centre, U.K.) inher talk ‘An investigation into the effect of tem-perature on the stability of carbons and carbonsupported Pt and Pt/Co alloy catalysts during1.2 V potentiostatic hold regimes’. For automotiveapplications, catalysts must survive repeatedpotential cycling and exposure to high potentialsduring idling or open-circuit conditions.Excursions to high potentials during startup andshutdown can be expected 30,000 times during a5000 hour fuel cell life. This equates to holding at1.2 V for 100 hours in an accelerated durabilitytest, and an interim target is sustaining this poten-tial for 24 hours. Catalyst degradation can occurdue to carbon loss by oxidation, while platinumsurface area loss may result from particle agglom-eration and also by dissolution and re-depositionas nanoscale Ostwald ripening.

Two carbons of surface area 850 m2 g–1 (C01)and 130 m2 g–1 (C03) were used to prepare threecatalysts: 40% Pt on C01 with an electrochemicalsurface area (ECA) of 118 m2 g–1 Pt; 40% plat-inum-cobalt (Pt-Co) on C01 (ECA 24 m2 g–1 Pt);and 30% Pt-Co on C03 (ECA 26 m2 g–1 Pt).Electrodes were prepared and corrosion ratesdetermined at 20, 40, 60 and 80ºC. These indicatethat at 80ºC less carbon corrosion is seen for heat-treated carbons of low surface area than forcommercial carbons of high surface area, forwhich carbon corrosion increases with rising tem-perature. The commercial platinum catalysts sinterduring 1.2 V potentiostatic holds at 80ºC, whereasthe electrochemical area loss increases with risingtemperature. However, Pt-Co alloy catalysts arestable to metal area loss at 80ºC. Extrapolatingthese results to higher temperatures, for the com-mercial catalysts it is predicted that at 120ºC there


will be significant carbon corrosion and loss ofmetal area, leading to low cell performance.However, for the carbon C03 of lower surfacearea, the corrosion rate appears to be independentof temperature. This is therefore the preferred car-bon support for operation at higher temperature,in combination with the Pt-Co alloy.

An interesting means of screening catalystsrapidly was presented by Christopher Lee (IlikaTechnologies Ltd/University of Southampton,U.K.) in his talk ‘High throughput preparation andelectrochemical screening of thin films for electro-catalysis in low temperature fuel cells’. Continuousthin-film binary and ternary alloys of varying com-positions are prepared using controlled andsimultaneous physical vapour deposition in a mod-ified molecular beam epitaxy system. The alloys aredeposited onto silicon wafers or 100-element elec-trochemical array electrode substrates, consistingof 10 × 10 arrays of 1 mm2 gold electrodes, inwhich each electrode is connected to a gold con-tact pad on the periphery of the substrate. Thecompositions of individual electrodes can quicklybe characterised using energy dispersive spec-troscopy (EDS) and high-throughput X-raydiffraction (XRD) experiments. Rapid electro-chemical characterisation can also be carried outon all 100 samples using specially developed cellhardware and software. For this purpose, the oxy-gen reduction reaction in pure oxygen-saturated0.5 M perchloric acid at 20ºC is used as the testreaction. Used to study the palladium-cobalt-goldternary alloy system, it was found that the 50% Pd-25% Co-25% Au alloy system exhibits stablesurface area. Adding gold to Pd-Co results inreduced activity, but this activity is still enhanced ascompared with that of pure palladium catalyst.

As well as being susceptible to poisoning bycarbon monoxide, low-temperature PEFCs areaffected by carbon dioxide. In her talk ‘Unravellingthe complexities of CO2 tolerance at PtRu/C andPtMo/C’, Andrea Russell (SouthamptonUniversity, U.K.) explained that the performancesof platinum-molybdenum/carbon catalysts werepreviously compared with those of platinum-ruthenium/carbon catalysts at 80ºC in 40 ppm COand 25% CO2. In contrast to the trend in CO tol-

erance, the PtRu/C was found to have better CO2

tolerance than PtMo/C. Deactivation of the anodein the presence of CO2 is caused by the build-up ofa CO-like poison. Two mechanisms have beenproposed to explain the conversion of CO2 to COunder PEFC anode conditions: either a reversedwater gas shift reaction or electrochemical reduc-tion of CO2 can result in formation of stronglyadsorbed CO species at the anode. Voltammetryindicates that at the PtRu/C catalysed anode, thereverse water gas shift reaction is dominant, whileat the PtMo/C anode, CO is oxidised at a potentialcorresponding to the Mo+4/+6 redox couple, andthe mechanism of CO2 poisoning proceeds via theelectrochemical mechanism, leaving CO-likespecies adsorbed on the catalyst.

Robert Reeve (Defence Science andTechnology Laboratory, U.K.) described their pro-ject to develop high-efficiency direct borohydridefuel cells for unmanned underwater vehicles(UUVs). These fuel cells combine high energy den-sity with a CO2-free exhaust for stealth. Sodiumborohydride can provide up to 5660 A h kg–1 ener-gy density, and can supply hydrogen whenplatinum or ruthenium is used as a decompositioncatalyst, yielding 948 kJ mol–1. Alternatively, directelectrochemical oxidation of borohydride can yieldup to 1273 kJ mol–1, and with oxygen- or hydrogenperoxide-depolarised cathodes, can provide up to1.64 V cell–1 at open circuit. For the anodes, thehighest energy density is provided by gold cata-lysts, since these do not catalyse the spontaneousdecomposition of borohydrides, and for the cath-odes, Pt/C catalysts are preferred. The 2 M sodiumborohydride fuel solution is stabilised by the addi-tion of 6 M sodium hydroxide, the alkalineconditions providing a tenfold reduction in thespontaneous decomposition of borohydride.Despite this, some decomposition still occurs dur-ing operation at high current density. This isattributed to pH changes within the pore structureof the electrode.

Cell and Stack TechnologyFor fuel cell MEAs it is important to maximise

the utilisation of pgms and thus reduce the plat-inum loading. In his talk entitled ‘Application of


ink jet technology to fuel cell membrane electrodeassembly production’, A. D. Taylor (University ofMichigan, U.S.A.) described a simple and elegantmeans of fabricating electrodes with very lowloadings of pgms. By substituting catalyst ink solu-tions in ordinary office ink-jet printers, it ispossible to deposit solutions with picolitre preci-sion. Catalysts are mixed with solvents andNafion® 5% solution to provide inks for the ordi-nary cartridges. By using colour cartridges loadedwith different concentrations of pgms in solution(or even different catalysts), it is possible to buildup multiple thin layers on membranes or electrodesupport materials. The technique producesextremely low loadings of catalysts, and for manyapplications it is necessary to use several passes ofthe printer to produce viable catalyst layers (fourpasses produced 21 μg cm–2 Pt). However, themethod offers a highly controllable means todeposit multiple layers, for example, with pureplatinum on the membrane with gradations ofPt/C catalysts on the gas face.

A huge effort is in progress by leading electron-ics companies, as well as fuel cell developers, tocommercialise DMFCs for mobile and remote off-grid applications. Peter Gray (Johnson MattheyFuel Cells, U.K.) in his talk ‘Leading performanceDMFC catalysts and MEAs for portable and con-sumer electronics’ reviewed the significantprogress made in improving their performanceand scaling-up manufacturing. As with other fuelcell systems, the stack incurs one of the largestcomponent costs. To achieve cost savings, Grayoutlined the options of reducing platinum metalloading, or improving cell performance at thesame loadings. Compared with a saving of 30%from lower metal loadings, by tripling the powerdensity to 150 mW cm–2, stack cost savings of 60%can be made, since the size and number of cellscan be reduced.

To produce a given performance at the end ofthe life of the device, costs can be pared by 20%by halving the degradation rate, or by 30% byreducing the decay rate to one third. Already,advanced MEAs have been demonstrated withhalf the degradation rate of baseline MEAs inaccelerated stack durability testing. These

advanced MEAs are being developed using car-bon-supported catalysts such as PtRu/C for theanode and Pt/C for the cathode, which togetherwith improvements in MEA design and construc-tion have doubled power densities to over 100 mW cm–2. Product lifetimes acceptable forconsumer electronics applications have alreadybeen demonstrated, and MEAs are in production.

An interesting example of the catalytic proper-ties of the pgms was illustrated by SadaeYamaguchi (Chiba Institute of Technology, Japan)in his talk entitled ‘Performance of one chambertype methane-oxygen fuel cell’. Natural gas orpropane fuel are mixed with air, and fed to a solidoxide fuel cell (SOFC) with only one chamber heldat 700ºC. The anodes are coated with a selectivecatalyst (platinum, palladium or nickel) whichenables them to carry out a partial oxidation reac-tion, generating CO, protons and electrons(Equation (i)):

2CH4 (g) + O2 (g) → 2CO (g) + 8H+(s) + 8e– (i)

The platinum, palladium or nickel coated elec-trodes are active for the anode reaction, but notfor the cathode reaction, while gold or silver coat-ed cathodes are active for oxygen reduction, butnot for the anode reaction. Protons in solid solu-tion are transported through the electrolyte to thecathode and are combined with oxygen to formwater (Equation (ii)):

2H+(s) + 2e– + ½O2 (g) → H2O (g) (ii)

It was found that the power density of the cellwas not affected by electrode cracking. This is animportant consideration, given that differentialthermal expansion is one of the fundamentalproblems of SOFCs. Due to the instability of ceriain low partial pressures of oxygen, yttria-dopedbarium zirconate was used as the electrolyte.However, current/voltage plots for palladium filmanodes and silver film cathodes show poor resultscompared with those for conventional SOFCs.One reason for this was the 0.7 mm thickness ofthe electrolyte tile, which could be substantiallyreduced. A tendency to form carbon on the anodecatalysts can be minimised by the use of 1%Ru/Al2O3 oxidation catalyst adjacent to the


anodes. At 700ºC with this catalyst 94% conver-sion of methane was obtained, of which 97% wasconverted to carbon monoxide. The system,although at an early stage of development, repre-sents a simple engineering concept withconsiderable potential for improvement.

Poster ExhibitionThe poster section attracted 205 high-quality

exhibits, a substantial proportion of which fea-tured preparation or use of pgm catalysts for fuelprocessing, or fuel cell stacks. The geographicaldistribution of the authors provides an indicationof the worldwide interest in fuel cells which is nowapparent.

Conclusions Angelo Moreno (ENEA, Italy) summed up the

conclusions from the conference in a final Plenarytalk. For gas processing, there are still clear winners

among the several competing reactor types forproducing hydrogen and the future appears verydiverse. There is considerable interest in process-ing diesel and biodiesel for military and civilianapplications.

The use of ink-jet printing for highly controlledapplication of catalysts to electrodes could presenta means to reduce pgm metal loadings while retain-ing MEA performance. However, it is evident thatthere may be trade-offs to be made against perfor-mance if ultra low metal loadings are to beachieved. Low EU capital cost targets for fuel cells(€1000 to €1500 kW–1 for stationary applicationsand €30 kW–1 for automotive applications) arechallenging, but ways are being found to meetthese objectives.

The European Union Framework Programmeis oriented mainly towards product research anddevelopment, while the fuel cell industry is movingtowards demonstration programmes and commer-


Membranes‘Inorganic/polymer composite membranes

for DMFC’, by G. Vaivars, R. Fakir, S. Ji, I.Sprinceana, Z. Wang and V. Linkov (Universityof the Western Cape, South African Institute forAdvanced Material Sciences, South Africa)

Fuel CCell aand SStack TTechnology‘Effects of shut down process on the PEFC

performance at sub-freezing condition’, by N.-Y.Lim, G.-G. Park, J.-S. Park, Y.-G. Yoon, W.-Y.Lee, T.-W. Lim and C.-S. Kim (Korea Institute ofEnergy Research, Republic of Korea)

Component MModelling aand CCharacterisation‘Dynamic modeling and identification of a

PEM fuel cell stack’, by S. Philipps and C. Ziegler(Fraunhofer Institute for Solar Energy Systems,Germany); J. Niemeyer (Universitat Karlsruhe,Control System Laboratory, Germany); and J. O.Schumacher (Center for Computational Physics,Zurcher Hochschule, Winterthur, Switzerland)

Electrocatalysis‘La0.6Sr0.4Co1–yFeyO3–δ as a potential anode for

IT-SOFCs: influence of the Co/Fe ratio onproperties and reactivity’, by F. Poletto, M. M.Natile, A. Galenda and A. Glisenti (University ofPadova, Italy); and T. Montini, L. Derogatis andP. Fornasiero (University of Trieste, Italy)

System AAnalyses aand AApplications‘An application for PEM fuel cell industrial

plant’, by G. Sibilia, A. Maggiore and D. Citelli(Nuvera Fuel Cells, Italy)

Fuels‘An unconventional Au/TiO2 PROX system

for complete removal of CO from non-refor-mate hydrogen’, by J. Steyn (AngloGold AshantiLtd, South Africa); G. Patrick and E. van derLingen (Mintek, Advanced Materials Division,South Africa); and M. S. Scurrell and D.Hildbrandt (University of the Witwatersrand,Johannesburg, South Africa)

Poster Prize AwardsThe posters were exhibited in six categories, and panels of judges shortlisted two from eachcategory. The authors of shortlisted papers were then invited to defend their poster for the finalselection panel. The prize winners were as follows:

cial development. The stack constitutes roughlyone third of the purchase cost of a fuel cell system,while part of the overall efficiency, and a majorproportion of reliability aspects are governed bythe balance of plant, for example compressors,inverters, valves and sensors. These attract com-paratively little attention in Europe, althoughlengthy trials in the U.S.A. and Japan have result-ed in more effort being devoted to their efficiencyand durability.

Small fuel cells, integrated into the electricitydistribution grid at local or residential level, willneed to be operated together for maximum avail-ability and efficiency. This will need carefulplanning to protect the grid against individual fuelcells, and the cells against the grid. It will be nec-essary to operate the cells in unison to balancesupply with demand so as to avoid shortages.Networked operation of linked residential fuelcells is already being demonstrated in Japan.

Many of the oral papers will be published in aspecial issue of the Journal of Power Sources in May2007.

References1 D. S. Cameron, Platinum Metals Rev., 2003, 47, (1), 282 D. S. Cameron, Platinum Metals Rev., 2005, 49, (1), 163 Fuel Cells Science and Technology 2006,

www.fuelcelladvances.com4 D. S. Cameron, Platinum Metals Rev., 2004, 48, (1), 325 D. S. Cameron, Platinum Metals Rev., 2006, 50, (1), 38

and Ref. 2 therein6 R. W. Coughlin and M. Farooque, Nature, 1979, 279,

(5711), 301

The Reviewer

Don Cameron is an independentconsultant on the technology of fuelcells and electrolysers. As well asscientific aspects, his interests includethe standardisation andcommercialisation of these systems. Heis Secretary of the Grove SymposiumSteering Committee.


Fig. 1 The historic Italian city of Turin, also a major industrial centrefamous for its motor manufacturing, provided the backdrop for Fuel CellsScience and Technology 2006

34

This book is Volume 112 of the ChemicalIndustries Series, a set of references and text-books. The majority of previous publications inthe series have been concerned with topicalchemical processes, and the catalyst technologyrelevant to them at the time of publication. Thisvolume is no exception. The chemical industry,together with oil and automotive interests, havemade a major contribution in the last thirty yearsto the reduction of emissions from motor vehi-cles using conventional fossil fuels (1, 2). Thisbook describes technology that takes this work animportant step further, namely the productionand use of alcoholic fuels, notably but not exclu-sively for use by the transport sector.

Alcohols as FuelsThe idea of using alcohol as a fuel in motor

vehicles is not new. Henry Ford, when helaunched the Model T, envisaged that it wouldrun on alcohol produced from renewable sources(3). Brazil has been using alcohol derived fromsugar cane for many years. It is from this experi-ence that alcohol is considered to be a viableproposition as an alternative to fossil fuels.

The book is a compilation of some 15 chapterscovering the production of methanol and ethanol,the use of alcohol blended fuels in automotiveapplications, and the use of alcohols in fuel cells.The chapters have been produced individually bysome 26 authors from the U.S.A. and Europe,reflecting the wide scope of the book and theinternational dimensions of the subject. Thefuture availability of oil, its security of supply and,increasingly, the impact of its use on climatechange, have all motivated the search for alterna-tive sources of energy, notably those that aresustainable, with minimal or zero impact on theenvironment. Alcohol produced from renewable

sources is one of the major contenders to meetthese challenges. To encourage these changes,government initiatives and fiscal incentives in theU.S.A., Brazil, Europe and the Far East not onlyencourage the development and production ofalcohol fuels, but also stipulate the phased intro-duction of alcohol-blended fossil fuels.

This book is therefore timely in providing forthe first time a comprehensive review of the pro-duction of alcohols, their use as fuels in internalcombustion engines, and also of more advancedconcepts such as fuel cells and fuel cell poweredportable energy applications. The book willappeal to a wide range of readers. People new tothe subject but interested in the development ofrenewable fuels will find much of value in thebook, even if they fail to follow the more techni-cal chapters on biochemistry and catalystdevelopments for fuel cell applications. Equally,people knowledgeable in the subject or interestedin specific areas such as the challenge of develop-ing catalysts for direct alcohol fuel cells, will findthe book and its extensive references of particularvalue.

Role of CatalystsFor readers of Platinum Metals Review, the ques-

tion arises as to what role platinum group metals(pgms) might play in the production and use ofalcoholic fuels. The book, like others in the series,emphasises the important role that catalysts playin both the production and use of alcoholic fuels.Concerning the benefits of using alcoholic fuelsfor carbon dioxide reduction, there is as yet noconsensus on these. The work of the U.S.Department of Agriculture contradicts that ofCornell University, who have both studied the‘well to wheels’ energy use and content of alco-holic fuels. It is suggested that the discrepancy

“Alcoholic Fuels”EDITED BY SHELLEY MINTEER (Saint Louis University, U.S.A.), CRC Press, Boca Raton, 2006, 296 pages,

ISBN 978-0-8493-3944-8, £56.99, U.S.$99.95

Reviewed by Gary AcresJohnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]


DOI: 10.1595/147106707X170009

arises in part from the dramatic increase in ener-gy efficiency due to lower energy use in thefertiliser industry and advances in fuel conversiontechnology in the last decade. The type of fertilis-er is not mentioned. However, assuming that it isnitrogen-based, improvements to the pgm cata-lyst gauze (4) and the process technology used toproduce nitrogen-based fertilisers may have had asignificant impact on the energy balance of alco-holic fuels.

Ethanol fuel also has a beneficial effect onautomotive emissions via its addition to gasolineand diesel fuels. While emission control usingplatinum, palladium and rhodium catalysts isimportant for conventionally fuelled engines, it isessential where alcoholic additives are used. Theadditives reduce (but do not eliminate) someemissions, but they increase the output of oxy-genated species such as aldehydes, which must becatalytically controlled.

Fuel Cell CatalystsOf particular interest is the role of pgm cata-

lysts in the development of fuel cells usingalcoholic fuels (5). The challenging developmentof high current density, durable anode catalystsfor the direct use of methanol in polymer elec-trolyte membrane fuel cells is described in detail.Progress has been made with platinum and plat-inum-ruthenium systems for use in portable andconsumer electronic applications such as mobiletelephones and laptop computers. Work contin-ues on making direct methanol fuel cells a viableoption for transport applications. Similarly, itwould be beneficial if catalysts were developedfor direct ethanol fuel cells, but so far this hasproved to be more challenging than the directmethanol system.

All fuel cell systems work most effectively onhydrogen-rich gas, which is produced frommethane or liquid fuels by steam reforming.Hydrogen from a renewable CO2-neutral sourcesuch as ethanol is attractive. Unfortunately, thecatalytic reforming of ethanol is not without itschallenges, as nickel and cobalt catalysts produceundesirable side products such as acetic acid. Thecatalyst systems currently preferred use rhodium

or palladium on a range of oxide supports. Thesedevelopments are described in detail, supportedby extensive literature references.

ConclusionsOverall, the book is timely, as interest in sus-

tainable sources of energy that are CO2-neutralgathers pace. However, while the book covers allaspects of the subject from production of alcoholfuels to their use, there is one omission. This isthe production of ethanol from sugar cane andsugar beet. Sugar cane is an established source ofethanol, notably in Brazil, while sugar beet,potentially a preferred starting material inEurope, has recently been selected by BP, BritishSugar and DuPont for their butanol plant in theU.K.

I would like to have seen a comparison of theattributes of various starting materials for ethanoland butanol production, but obviously that mustawait further study.

References1 G. J. K. Acres and B. J. Cooper, Platinum Metals

Rev., 1972, 16, (3), 742 M. V. Twigg, Platinum Metals Rev., 1999, 43, (4), 1683 The New York Times, 20 Sept. 1925, p. 244 Johnson Matthey Noble Metals, Gauze,

www.noble.matthey.com5 Platinum Metals Review fuel cell articles on Fuel

Cell Today, www.fuelcelltoday.com/FuelCellToday/PMRLinks


The Reviewer

Gary Acres is a graduate ofNottingham University. Following fiveyears with the United KingdomAtomic Energy Authority at Harwell,he joined the newly formed catalystresearch group of Johnson Mattheyin 1963, becoming Directorresponsible for research anddevelopment operations from 1974to 1985, and then Director, CorporateDevelopment until 1994 when heretired from full time employment.Since then he has held a number ofadvisory roles and is currently a

Consultant to Johnson Matthey on fuel cell and related activities.He is Chairman of the Grove Fuel Cell Symposium and the firstChairman of the European Fuel Cell Group. Since 2000, he hasbeen a Royal Academy of Engineering Visiting Professor onSustainable Development at the University of Birmingham. Hisawards include the Queen’s Award for Technology and theMacRobert Award for the development of automobile emissioncontrol catalyst systems.

36

The 2006 International Conference onCoordination Chemistry (ICCC) took place, forthe first time, on African soil, between the 13thand 18th August 2006 in the beautiful city ofCape Town, South Africa (1). Following on fromthe successful conferences in Merida (2004),Heidelberg (2002) and Edinburgh (2000), thisevent attracted over 600 delegates from approxi-mately 60 countries around the world andinvolved 287 scheduled oral presentations andover 330 poster presentations. Abstracts of allthe oral and poster presentations were edited byD. J. Robinson (one of the present reviewers)and I. M. Robinson, and published in hard copyand electronic versions (2). The page numbersgiven in brackets in this article refer to the rele-vant page number in these publications. Leadinginternational researchers were invited to give atotal of 8 Plenary and 49 Keynote lectures. Theconference was structured in terms of sixthemes, presented in parallel sessions. Thethemes were as follows:– Metals in Biology and Medicine– Metals in Materials, Nano-Structures and Devices– Metals in Catalysis and Industry– Metals in Self Assembly and Supramolecular

Systems– Metal Complexes in Solution: Structure,

Mechanism and Ligand Design– Precious Metals, Photochemistry and

Computational Chemistry.There were many contributions involving the

chemistry of the platinum group metals (pgms)throughout all of the themes. It would thereforebe impossible here to provide anything morethan a flavour of the diverse chemistry presentedin each area.

Plenary PresentationsThe excellent plenary presentations given, by

world leaders in their fields, straddled the themesof the conference. Of particular note was thefinal plenary lecture presented by Robert H.Grubbs, the Atkins Professor of Chemistry at theCalifornia Institute of Technology, U.S.A., andco-winner of the 2005 Nobel Prize in Chemistry.The 2005 Nobel Prize in Chemistry was sharedby Yves Chauvin, Robert H. Grubbs and RichardR. Schrock, for the development of the metathe-sis method in organic synthesis (3). In this lectureProfessor Grubbs described the early develop-ment of the now famous first and secondgeneration Grubbs’ catalysts, and the morerecent applications of these ruthenium catalystsin the synthesis of a wide variety of valuablechemicals and polymers. The other plenary lec-tures, by Professors Amilra Prasanna de Silva(Queen’s University Belfast, U.K.), Peter J.Sadler (University of Edinburgh, U.K.), HelderM. Marques (University of the Witwatersrand,South Africa), Tobin J. Marks (NorthwesternUniversity, U.S.A.), Rudi van Eldik (Universityof Erlangen-Nürnberg, Germany) and OmarYaghi (University of California, U.S.A.), similarlycovered extensive and equally important areas; itwas apparent that in these, coordination chem-istry is alive and thriving.

Metals in Biology and MedicineA significant number of contributions con-

cerned alternative pgm-containing complexes(particularly of platinum and palladium) withpotential anticancer activity. Ligands included L-ascorbic acid (p. 39), bidentate oxalate groups (p.42), 1,1′-bis(diphenylphosphine)ferrocene and


DOI: 10.1595/147106707X173817

37th International Conference onCoordination ChemistryPGMS PROMINENT IN A WIDE RANGE OF RESEARCH AND APPLICATIONS

Reviewed by David J. Robinson* and Malcolm ArendseAnglo Research, A Division of Anglo Operations Limited, 8 Schonland Street, Theta, Johannesburg, 2025, South Africa;

*E-mail: [email protected]

derivatives (p. 304), cyanoxime ligands (p. 314),branch-chained esters (p. 331), amine and dicar-boxylate ligands (p. 333) and hydantoinderivatives (p. 369). New insights into possible invivo reactions (p. 39) and the mechanism bywhich these platinum complexes may act werereported (p. 40), including kinetic studies (p.527), consideration of both DNA and RNA aspossible targets (p. 41), thermogravimetricbehaviour (p. 338), chemically triggering thecis/trans isomerisation of anticancer platinumdrugs (p. 372) and the synthesis of modelcalyx[n]arene complexes (p. 258). Novel pho-toactivation of several octahedral cis and transdiamino diazo platinum(IV) complexes wasreported to lead to novel reactions includingthose which may prove applicable to killing can-cer cells (pp. 2, 62).

Studies of the synthesis, characterisation andbiochemical activity of several new half-sandwicharene complexes of ruthenium and osmium weredescribed (pp. 2, 35, 371). Complexes of rutheni-um-containing polyaminocarboxylate (p. 38),thiosemicarbazone and isoniazide (p. 48), oxineand azole ligands (p. 325), photoactivatedpolypyridine ligands (p. 33) and substitutedchelating quinolinquinones (p. 368) were alsoreported. DNA binding studies of rutheniumcomplexes of polypyridines (pp. 326, 346), crownethers and bridging polypyridilic ligands (p. 349)were discussed, including the formation of ruthe-nium ‘molecular dots’ to capture DNA strands(p. 89). Ruthenium nitrides were prepared andstudied as models of biologically relevant inter-mediates (p. 215).

Several new polytopic metal complexes(including rhodium, palladium and platinum)possessing 2,6-di-tert-butylphenol pendantgroups were found to be active for electrontransfer and possible use in the prevention ofxenobiotic-induced oxidative stress in organisms(p. 65). Similarly, fundamental studies (p. 534)and interesting activity including greater cytotox-icity of a number of new derivatives oftitanocene or titanium organometallics includingthose coordinated to ruthenocene ligands (pp.30, 31) were reported.

Metals in Materials, Nano-Structures and Devices

A number of interesting mixed metal andmixed-valence, halide-bridged complexes wereprepared with nickel and palladium, and studiedphotochemically as model complexes (p. 72); andruthenium-containing novel chromophorequenchers of rhenium(I) were also reported (p.377). In related work, the absorption of rutheni-um(II) photosensitisers was subject to atheoretical analysis (p. 414). The self-assembledmonolayer of peptide-linked rutheniumpolypyridyl complexes was probed by surface-enhanced resonance Raman spectroscopy(SERRS) (p. 383). The photoinduced energytransfer within ruthenium polypyridyl dyads wasdiscussed (p. 614). The synthesis and characteri-sation of several new ruthenium(II) complexeswith bidentate diimine and imine-phosphino lig-ands was addressed (pp. 401, 618); also the‘ship-in-a-bottle’ synthesis of related polypyridylcomplexes within the zeolite matrix (p. 410). Apotential novel application of substituted pyridylorganoiridium complexes in light emitting diodes(LEDs) was presented (p. 388).

The use of coordination complexes as precur-sors to the preparation of pgm-containingnanoparticles was the theme of several papers.Palladium ‘quantum dots’ were prepared frompalladium aroyl(seleno)urea precursors (p. 93),and ruthenium olefin complexes were used toproduce ruthenium nanoparticles (p. 105).

A series of half-sandwich ruthenium, iridiumand palladium complexes (p. 109) and novel η2-bound fullerene palladium and platinumcomplexes of ruthenocene were also described(p. 90). A new series of highly conducting thinfilms of gold nanoparticles have been prepared,with ruthenium complexes acting as the linksbetween particles (p. 92).

The interesting liquid crystal properties of ortho-metalated imine complexes of platinum(II) andpalladium(II) (p. 380) and ferrocene-containing β-diketone complexes of rhodium were reported (p.129). Ruthenium and osmium bipyridine complex-es have been used to prepare mesoporous silicatesusing sol-gel synthesis (p. 68).



Metals in Catalysis and IndustryA significant number of presentations

described the use of Grubbs’ (ruthenium) cata-lysts, and metathesis and unsymmetricalvariation of the ligand structures (p. 597).Interesting uses of the metathesis reactioninclude coupling within the coordination sphereto synthesise caged palladium and rhodiumdiphosphine complexes (p. 114), and alkenylbridged iron complexes (p. 564). Related ring-closing reactions were used to prepare pallada-(p. 436), platina- (p. 146) and rhoda-cycloalkanes(p. 426), and thermal decomposition of thesecomplexes was reported (p. 450).

Further insights into the mechanism of thepalladium-catalysed Stille and Heck reactionswere described (pp. 116, 148). Interesting poly-mers were prepared using palladium-catalysedcyclopolymerisation and copolymerisation reac-tions (p. 133). Extensive use of NMRspectroscopy and a computational density func-tional theory (DFT) study have shed light on themechanism of the palladium-catalysed alkynehydrogenation rection (p. 159). A new cationicpalladium dimer was reported to be a catalyst forthe Suzuki coupling reaction under mild condi-tions (p. 427). Novel ‘daisy-chain’ polymers weresuccessfully prepared using palladium(0)-catal-ysed couplings as the key carbon–carbon bondforming reactions (p. 202).

The synthesis, characterisation and intermole-cular interactions of potential new rhodiumhydroformylation catalysts were presented (pp.125, 430). Rhodium-catalysed asymmetric hydro-genation of itaconic acid derivatives wasdescribed as a route to pharmaceutically interest-ing products (p. 155).

Other non-ruthenium carbene and carbene-like fractions continue to attract researchattention from a number of research groups (pp.149, 443). For example, novel palladium car-benes have been prepared using novel silver andmercury reagents (p. 419) and using carbenetransmetalation (p. 425), sometimes employingN-heterocyclic carbenes (p. 271).

A number of new bimetallic complexes havebeen designed and synthesised to mimic

enzymes, and tested for both catalytic and bio-logical activity (p. 122). A number ofunsubstituted and phosphite substituted rutheni-um and osmium carbonyl clusters weredescribed (pp. 154, 439, 449), as were some tri-nuclear rhodium (p. 156) and tetranuclearruthenium (p. 437) catalyst precursors for asym-metric hydrogenation. The novel use of aplatinum-catalysed cycloisomerisation of cam-phor-derived bisalkynes was reported to producetetracyclic cyclopentenone derivatives (p. 124).Derivatives with a {Pt2S2} core have been devel-oped for organosulfur synthesis and dehal-ogenation of persistent organic pollutants (p.130), with the same core (and the selenium ana-logue) being useful in the synthesis of largermultimetallic complexes (p. 558). Several papersdescribed further development of the use ofdendrimer supports for ‘heterogenising’ homo-geneous catalysts, including cyclopentadienylruthenium fractions (p. 138).

Osmium complexes continue to be preparedas potential models of catalytic intermediates formore reactive catalysts, including osmabenzofu-ran and osmabenzene complexes (p. 140) asmodels of active metal sulfide sites (p. 611). Newtools are emerging for the improved elucidationof catalytic reaction mechanisms, includingmatrix-assisted laser desorption/ionisation massspectrometry (MALDI-MS) (p. 118) and in situNMR spectroscopy including high-pressuremethods (pp. 123, 143, 151, 444). Similarly, sys-tematic spectroscopic studies improvedcharacterisation techniques towards furtherunderstanding of the nature of bonding andbackbonding in a number of pgm complexes(pp. 120, 429) and the role of varying solventproperties (p. 448).

The effect of varying tertiary phosphine sub-stituents upon the solution and solid-statebehaviour of rhodium(I) complexes was report-ed (p. 420). While many catalysts depend on acis-bidentate ligand to arrange the complexgeometry, a specific ligand (SPANphos) hasbeen designed, modelled and synthesised to bindtrans to square planar, in an attempt to modifythe action of conventional palladium, platinum


and rhodium catalysts (p. 111). Indeed, anincreasing number of presentations featured the-oretical and fundamental studies of catalysts andcatalytic reactions. Examples includedplatinum(II) and palladium(II) catalysts (p. 432),rhodium hydroformylation reactions (p. 113),hydroxide assisted palladium catalyst activation(p. 134) and photocatalysed ruthenium degrada-tion of pesticides attached to titanium oxideparticles (p. 612).

Metals in Self Assembly andSupramolecular Systems

A number of new substituted terpyridine lig-ands and their square planar platinum(II)complexes have been used as metallotectons forthe assembly of heterometallic macrocyclic com-plexes (p. 193), and their interaction witharomatic molecules was reported (p. 489). Novelmixed-valence platinum(II)-platinum(IV) one-dimensional systems were reportedly assembledin a host-guest configuration (p. 472), and mole-cular magnets and molecular conductorscontaining platinum(II) centres were reported (p.490). Magnetic properties of one-dimensionalPt6Rh2 systems were reported (p. 508).

The photochemical properties of rutheniumpyridyl (p. 609), bipyridyl, polypyridyl (p. 623)and phenanthroline complexes continue toattract attention, including in the areas ofsupramolecular assemblies (p. 168), porphyrincomplexes (p. 467) and kinetically locked molec-ular architectures (p. 174). Similar bipyridylcomplexes have been found to aggregate withruthenium cyano complexes with significanthydrogen bonding (p. 198). The electronic prop-erties of cyano bridged polymetallic complexeswere reported, including those of several with aFe2Ru nucleus (pp. 452, 471), and others withmore complex Ru5 networks of ethynylpyridinebridges (p. 470). The interaction of rutheniumand osmium luminophores with cyclodextrins,and consequent electronic communication prop-erties were reported (p. 176).

A range of rhodium and rutheniumorganometallics have been used as buildingblocks in co-deposition reactions, yielding

extended hybrid networks using metal–π–areneand π–π–arene interactions (p. 115). Polymericrhodium pyrazine complexes were used to formnovel single-crystal hosts for reversible CO2 andO2 adsorption, both of which have been studiedby X-ray diffraction methods (p. 451, 506).

Platinum(II) complexes have been incorporat-ed to improve the sensitivity of cobalt(II)-basedquartz crystal microbalance gas sensors (p. 175),while other fluorophore containing moleculeshave been designed as sensors for palladium(II)(p. 584). Some new fluorosulfur (p. 462) and SNSand SCS (p. 620) pincer ligands were reported tobe useful in preparing mononuclear and binu-clear palladium complexes.

Metal Complexes in Solution:Structure, Mechanism and LigandDesign

The development and testing on behalf ofPolyMet Mining Corp of the PLATSOL™process for treatment of precious metal concen-trates were described (p. 210). Alternativepotential extractants for pgm recovery were pre-sented; these involve polyamine containing ionexchangers (p. 613) or functionalised guanadini-um groups (p. 619). Other early steps in thecomputational (p. 283) and experimental (p. 274)design of potential new extractants for pgmchloro anions were reported.

A range of new palladium(II) pyrazolyl (p.250) and pyrazolate (p. 280) complexes, and reac-tion kinetics of several platinum(II) andpalladium(II) amine (p. 550) and polyamine (p.579) complexes in aqueous systems were report-ed. Novel bimetallic complexes containingplatinum were prepared by the coordination ofisothiazolin-3-one (p. 554). A range of dialkylureas and thiocarbamic acid esters (p. 530),unsymmetrical thioureas (p. 568) and silsesquiox-anes (p. 566) have been coordinated topalladium(II) and platinum(II) fragments to pro-duce coordination compounds with interestingproperties (p. 594, 607). Similarly novel seleniumfunctionalised dodecaborane complexes of plat-inum(II) were reported (p. 546). The insertionreactions of selected platinum complexes were


described (p. 551).The kinetics of selected oxidative addition

reactions of platinum(II) complexes were report-ed (p. 587) and the cycloaddition of nitrones withpalladium or platinum nitriles was studied exper-imentally and theoretically (p. 598). Interestingproperties of heterometallic complexes contain-ing platinum or rhodium and a zirconocenefraction were presented (p. 219). 195Pt NMRspectroscopy (p. 281, 602) continues to be anincreasingly useful and user-friendly probe intothe speciation (p. 608) and coordination chem-istry of platinum, and the study of its chloroanion extraction (p. 276).

Improved elucidation of the speciation of therhodium chloro (p. 538, 539) and basic osmium(p. 565) systems was reported, using capillaryzone electrophoresis, potentiometry and compu-tational methods. Kinetic and computationalstudies of rhodium thiophene (p. 532) or phos-phine (p. 536) β-diketonato complexes and theanomalous behaviour of cobalt(III) and rhodi-um(III) multidentate amine complexes weredescribed (p. 240).

The coordination modes of amino function-alised dithiocarboxylate ligands to rhodium(I)centres have been studied computationally (p.235), while similar ruthenium(II) complexes werestudied electronically and described by DFTmethods as molecular multielectron reservoirs(p. 236). ‘Ruthenium trichloride’ continues to bea convenient starting material for the synthesis,via assisted ligation, of a range of rutheniumcomplexes (p. 553) including di-S,S-2-propionateligands which are potential antitumour reagents(p. 592).

Possible intermediates in pgm-catalysed alco-hol oxidation reactions include oxyl radicals. Onesuch ruthenium complex was prepared and stud-ied for its relevance in such a reaction (p. 254).

Precious Metals, Photochemistryand Computational Chemistry

The increasing use of high-level thermody-namic and quantum chemistry methods, inparticular DFT, even for molecules with heavymetal centres, was well illustrated (p. 260). The

fundamental role of water in the speciation andstabilisation of ion pairs involving pgm chloroanions was reported (p. 595). The active role ofwater in possible reaction mechanisms has beenstudied in the pH selective C=C versus C=Oreduction reaction of α,β-unsaturated aldehydes(p. 150).

Novel di- and trinuclear platinum-thaliumcompounds with unsupported metal–metalbond(s) were described (p. 279). The spectro-scopic and electrochemical properties of severalbenzimidazole platinum(IV) compounds weredescribed (p. 278). A number of novel tetrapalla-dium complexes with bridging silylene andgermylene ligands were reported (p. 272), and theenergy transfer properties of coordination poly-mers containing platinum and lanthanide unitswere described (p. 621).

In addition to those mentioned above, manyother presentations considered the coordinationof pgms (particularly ruthenium) to photoactiveligand components and the properties of the sub-sequently formed mononuclear (pp. 257, 263,264), dinuclear (p. 265) and polynuclear (p. 265,267) complexes. Ligand variations in noveldiruthenium paddlewheel complexes and theeffect of variations on the Ru–Ru bond were dis-cussed (p. 277).

Concluding RemarksDue to the size of the conference, the running

of parallel themes and the extent to which pgmsfeatured through many of the sessions, thereviewers were unable to attend all the relevantpresentations. However, it was clear that thecoordination chemistry of the pgms is in ahealthy state, in terms of both worldwide devel-opment and application. Worthy of note was thatthe 37th ICCC was timed and located close to anumber of related conferences, including theCape Organometallic Symposium, the Inter-national Symposium on Homogeneous Catalysisand the Structural Chemistry Indaba. Many visi-tors could therefore justify the long distancestravelled by attendance at two or more events.

Feedback received from delegates both duringand after this conference showed general agree-

ment that this 37th ICCC upheld the tradition ofthe series for well organised events. The review-ers look forward to the 38th ICCC, scheduledfor Jerusalem, Israel, from the 20th to 25th July2008 (4).

References1 ICCC37, 37th International Conference of

Coordination Chemistry, Cape Town, SouthAfrica, http://webhost.sun.ac.za/pgm_group/

2 “XXXVII International Conference onCoordination Chemistry”, eds. D. J. Robinson andI. M. Robinson, Document TransformationTechnologies, Stellenbosch, South Africa, 2006,ISBN 1-920-01705-4

3 V. Dragutan, I. Dragutan and A. T. Balaban,Platinum Metals Rev., 2005, 50, (1), 35

4 ICCC38, 38th International Conference ofCoordination Chemistry,http://www.kenes.com/iccc38/


The Reviewers

David John Robinson is currently the managerresponsible for sustainable developmentwithin Anglo Research and is based inJohannesburg, South Africa. He has beenactive in both fundamental and applied pgmchemistry research, and in particular, thedevelopment of improved separationtechnologies over a 15 year career with Anglo

Platinum. He has been involved directly in their production at themodern precious metals refinery near Rustenburg, South Africa.His interests include developing improved industry–academiaresearch collaborations and the application of improvedfundamental knowledge to the solution of real refining problems.

Malcolm Arendse is currently a lead researchscientist in the refining research group atAnglo Research in Johannesburg. He startedhis career as a lecturer at the University of theWestern Cape, South Africa, in 1986. Aftercompleting a Ph.D. in Inorganic Chemistry atthe University of Missouri-St. Louis, U.S.A.,he joined Anglo Platinum in 2003. His

research interests and activities have been in the areas of pgmrefining, separation, speciation and catalysis.

Musical entertainment for the Banquet at the 37th International Conference onCoordination Chemistry. A wide selection of photographs of the Conference isavailable at the website (1)

42

The 9th International Symposium on theScientific Bases for the Preparation ofHeterogeneous Catalysts took place on the cam-pus of the Université Catholique de Louvain inLouvain-la-Neuve, Belgium, from 10th to 14thSeptember 2006. This series of symposia was ini-tiated in 1975 on a four-yearly cycle; Reference (1)is a review of the 1978 Symposium. In 2006 the9th Symposium was attended by over 250 dele-gates, of whom 30% were from industry; about80% of the delegates originated from Europe. TheSymposium programme covered the followingtopics:– Key Aspects in Catalyst Preparation– Structured Catalysts– Supported Metal Catalysts– Micro- and Mesoporous Supports– Tailored Zeolites– Catalysis by Bases– Catalysts for Fuel Production.

Precious metal catalysts (including platinum,palladium, ruthenium and gold) were well repre-sented in the first four of these categories. Overthe course of four days, forty-one oral contribu-tions were heard, including seven keynotecommunications. In addition, more than one hun-dred posters were presented in two sessions.

Catalyst Preparation IssuesDuring the Symposium, many of the multitude

of issues associated with catalyst preparation werereferred to, including: the interaction of aqueousprecious metal ions with metal oxide supports,controlled preparation of metal nanoparticles, andthe single-step preparation of monolithic platinumgroup metal (pgm)-containing catalysts. Two ofthe major points that must be addressed in the

development of a new catalyst from bench to pro-duction are scale-up and reproducibility, topicsthat are conspicuous by their absence from thecatalysis literature. It was therefore encouragingfrom an industrial perspective to see groups tack-ling these issues, including T. Cukic andcoworkers (Leibniz Institute for Catalysis, Berlin,Germany) who assessed the preparation ofPd/Al2O3 hydrogenation catalysts. Several para-meters affecting catalyst activity were identifiedand, by the use of a regression model, genericrules to reproducibly obtain an active catalyst weredefined. The key preparation parameter was iden-tified as the ratio between the amount ofimpregnation solution and the volume of support.

In addition to this work, R. Prada Silvy andcoworkers (Université Catholique de Louvain,Belgium) presented a systematic investigation ofthe scale-up of a propane ammoxidation catalystprepared by coprecipitation of vanadium on alu-mina. They successfully showed the need togenerate a thorough understanding of the chem-istry involved and to employ flexible catalystpreparation strategies in order to produce largeramounts.

Structured CatalystsIndustrial heterogeneous catalysts tend to be

formed as extrudates or from slurries coated ontomonoliths or foams. M. Yates and coworkers(Instituto de Catálisis y Petroleoquímica, Spain)presented a simple single-step process for the pro-duction of dispersed pgm nanoparticles onformed ceramic supports with customised textur-al properties. This was achieved by incorporatingactivated carbon into a pgm-doped mixture; forexample, one of alumina/α-sepiolite (SiO2, MgO,


DOI: 10.1595/147106707X169786

Scientific Bases for the Preparation ofHeterogeneous CatalystsPGMs FEATURE IN GREATER UNDERSTANDING OF PRECURSORS AND ACTIVE SPECIES

Reviewed by Mark R. Feaviour* and Emma R. Schofield**Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; *E-mail: [email protected];

**E-mail: [email protected]

Al2O3, CaO). The porosity of the product wassuch that the pgm was still accessible to the reac-tants, in this case toluene for combustion. Thisobviated the washcoating step associated withconventional monolith-supported catalysts.

The issue of supports was also raised by M. V.Twigg (Johnson Matthey, U.K.) and J. T.Richardson (University of Houston, U.S.A.), whochallenged the delegates with the question of whystructured ceramic foams were not more com-monly used as catalyst supports. The BET surfaceareas of ceramic foams can be increased by wash-coating, and they have additional usefulproperties, including a ten-fold decrease in pres-sure drop compared to pellets, and coefficients of1D and 2D heat transfer five times higher. Theexamples selected to highlight the usefulness ofcatalytic metals loaded or washcoated onto ceram-ic foams were: silver for ethylene epoxidation,ruthenium for CO2 methanation and cobalt forFischer-Tropsch catalysis.

Supported Metal CatalystsThe significance of support morphology was

illustrated by a talk on Au/TiO2 catalysts by V.Caps and coworkers (Institut de Recherches sur laCatalyse, France) who compared the capability oflow surface area, poorly functionalised titania tostabilise the formation of small gold particles pre-pared by the deposition-precipitation method,with the tendency of more highly functionalisedtitania or titania-doped surfaces to cause agglom-eration. An alternative method of controllingparticle sizes in platinum, palladium, rutheniumand bimetallic palladium-platinum catalysts wasproposed by E. Sulman and coworkers (TverTechnical University, Russia). By this method thepgm precursor was impregnated into hyper-crosslinked polystyrene granules where controllednanoparticle growth can occur in the cavities andpores of the polymer matrix. Reduction with anaqueous reducing agent gave 1–2 nm metal parti-cles which were active in selective oxidation ofmonosaccharides.

On a more fundamental level, several authorspresented work highlighting the importance ofcomprehending the interaction between precious

metal complexes and metal oxide supports inaqueous solution, i.e. the types of systems associ-ated with catalyst preparation by impregnationand deposition-precipitation. In particular, J. R.Regalbuto and coworkers (University of Illinois,U.S.A.) illustrated in their presentation entitled‘Simple, scientific syntheses with common catalystprecursors’ that carrying out impregnation at thepH which maximises the electrostatic interactionbetween the substrate and adsorbing metal com-plex (of platinum, ruthenium, copper or cobalt)can yield catalysts with a high loading of ultra-small metal particles. This method claims tominimise the contamination of the catalyst byunwanted precursor counterions such as chloride,which may remain if impregnation is carried outunder non-optimal conditions. This presentationgenerated much interest and in the discussion ses-sion it was revealed that this approach isapplicable to surfaces of relatively low surfacefunctionality, e.g. α-Al2O3 shaped catalyst carriersdeveloped for high crush resistance.

The support interactions of pgm precursorsalso featured in the talk on catalyst preparation byK. Bourikas and coworkers (University of Patras,Greece) who outlined the possible modes of inter-facial deposition – electrostatic adsorption andadsorption through coordinative or hydrogenbonding – and illustrated experimental method-ologies by which it was possible to establish thepredominant mode. It was shown that [PtCl6]2–

and [Pt(NH3)4]2+ adsorb electrostatically, in con-trast to oxo-ions such as [Co(H2O)6]2+ in whichthere is inner-sphere coordination. The principlesof pH-optimised adsorption were also applied byA. Deffernez (Université Catholique de Louvain,Belgium) to depositing palladium and gold-palla-dium on carbon by determining the point of zerocharge of the carbon support, and determining theprecious metal species present across the pHrange.

The coordination chemistry theme was contin-ued by S. L. Soled and colleagues (ExxonMobilResearch and Engineering Co, U.S.A.) whoreported on the use of triethanolamine (TEA) asan impregnation aid in preparing Ru/SiO2 cata-lysts from ruthenium nitrosyl nitrate. The multiple


44

functionality of TEA caused it to bind both to thelabile ruthenium precursor and to the hydroxylgroups of the silica support. Partial decomposi-tion then gave a catalyst in which the rutheniumcrystals were distributed homogenously on the sil-ica, since migration of RuO2 was hindered.Organometallic metal carbonyl Ru5Pt clusterswere used as precursors with mesoporous silicasupports by O. Muraza and and coworkers(Eindhoven University of Technology, TheNetherlands). On decarbonylation by heating, 1.4nm bimetallic nanoparticles were obtained, adecomposition process which left the meso-porous silica intact.

Innovations in Catalyst PreparationThe Symposium featured several talks demon-

strating novel catalyst preparation techniques. G.M. Veith and coworkers (Oak Ridge NationalLaboratory, U.S.A.) introduced the uses of mag-netron sputtering for preparing precious metalcatalysts, illustrated by Au/WO3, Au/C and Pt/Csystems. This technique relies on physical vapourdeposition of an atomic metal flux onto a con-stantly tumbling support material, with the metalloading increasing linearly with time. High-puritycatalysts with narrow particle size distributionswere accessible by this route, and good adhesionwas observed, even with supports such as SiO2

and WO3 which are less accessible using chemicaldeposition methods. Gold catalysts were also thefocus of the talk by J. K. Bartley and colleagues(Cardiff University, U.K.) who discussed a super-critical carbon dioxide precipitant technique beingused to prepare titania supports for gold catalysts.Using this technique, supercritical CO2 is added tothe support precursor, TiO(acac)2, in methanol,causing it to precipitate as small, amorphous par-ticles with a high surface area (160 m2 g–1). Theseare then calcined to give a TiO2 support. In COoxidation, Au/TiO2 prepared by the supercriticalroute gave 100% conversion, as compared withonly 10% for the untreated analogue.

F. Cambier and coworkers (Centre of Researchfor Industries, Belgium) presented a method ofcatalyst production using an inductive atmospher-ic plasma torch, which is currently being used to

prepare nanopowders, but which they intendusing to generate Al2O3, ZrO2 or SiO2 supportedpgm catalysts. A supported ionic liquid catalyst(SILCA) featured in a talk by P. Mäki-Arvela (ÅboAkademi University, Finland), who demonstratedthat partial hydrogenation of citral to citronellalcan be achieved using [N-butyl-4-methylpyridini-um][tetrafluoroborate] and Pd(II) acetylacetonateon active charcoal in a three-phase reaction.

ConclusionThis is a uniquely relevant series of Symposia

for anyone in the field of heterogeneous catalysis,and continues to highlight the pivotal role playedby pgms in this area. Despite the diversity of theresearch presented, one of the underlying themesto emerge from the discussions was the impor-tance of gaining a more fundamentalunderstanding of the base metal and preciousmetal species used as catalyst precursors and ofthe active metallic species involved in catalysis.For further information readers are directed tothe published proceedings (2).

References1 P. A. Sermon, Platinum Metals Rev., 1979, 23, (1), 142 “Scientific Bases for the Preparation of

Heterogeneous Catalysts”, Proceedings of the 9thInternational Symposium, Louvain-la-Neuve,Belgium, 10th–14th September, 2006, eds. E. M.Gaigneaux, M. Devillers, D. E. De Vos, S.Hermans, P. A. Jacobs, J. A. Martens and P. Ruiz,Studies in Surface Science and Catalysis, No. 162,Elsevier, Amsterdam, The Netherlands, 2006

The Reviewers

After gaining a Ph.D. at the Universityof Reading, Mark Feaviour joinedJohnson Matthey in 1999, and workedfor six years carrying out research onthe preparation of steam reforming,water gas shift, and other fuelprocessing catalysts. He now works inthe Core Science Coatings Group.

After three years as a lecturer at TrinityCollege in Dublin, Emma Schofieldmoved to Johnson Matthey in the U.K.,where she specialises in developingnew synthetic routes to heterogeneouscatalysts.

Platinum Metals Rev., 2007, 51, (1)

45Platinum Metals Rev., 2007, 51, (1), 45

DOI: 10.1595/147106707X174645

Johnson Matthey’s latest market survey ofplatinum group metals supply and demand waspublished in November 2006, providing detailedforecasts of pgm supply and demand for the fullcalendar year, plus short-term market outlookand six-month platinum and palladium priceprojections. The Interim Review updates infor-mation provided in the full annual survey“Platinum 2006” (1).

The platinum market has moved closer tobalance, with a predicted deficit of only 20,000oz in 2006. According to Johnson Matthey,global demand for platinum in 2006 was expect-ed to grow by 5 per cent to a record 7.02 millionoz, driven by increasing use in automotive cata-lysts. Supplies of the metal have increased byalmost the same rate, to a new high of 7 millionoz, due to expansion in South Africa.

Emissions legislation and growing produc-tion of diesel vehicles continue to drive platinumconsumption higher. Autocatalyst platinumdemand was expected to have grown from 3.82million oz to 4.38 million oz in 2006, duringwhich diesel cars accounted for over 50 per centof European light-duty vehicle sales. Many arenow fitted with platinum-catalysed particulatefilters in addition to diesel oxidation catalysts.Increasing use of catalysts on light- and heavy-duty diesel trucks in North America is furtheradding to demand.

Rising and volatile platinum prices havedepressed global jewellery demand, for whichplatinum purchases were anticipated to fall byover 10 per cent to 1.74 million oz. With plat-inum prices high and volatile, manufacturers andretailers in all major regions have cut back inven-tories. In China and Japan, recycling of old stockhas also continued to affect the amount of newmetal purchased.

The platinum market is expected to be closeto balance again in 2007, with expansions in pri-mary output continuing. Another rise in demandfor autocatalysts is expected to absorb much ofthis increase, and there are good prospects forfurther growth in the relatively price-inelasticindustrial sector. The performance of the

jewellery sector will however continue to dependheavily on the price of platinum.

Palladium supplies were forecast to haveexceeded demand by 1.63 million oz in 2006,with an increase in the use of the metal in auto-catalysts having been outweighed by lowerpurchases by the jewellery industry. This wouldhave left demand at 6.85 million oz, a fall of 6per cent. With growing output of palladiumfrom South Africa and significant sales expectedfrom Russian state stocks, supplies were expect-ed to grow by 1 per cent to 8.48 million oz. Thismarket surplus is being absorbed by investmentfunds.

Autocatalyst demand for palladium was fore-cast to rise from 3.87 million oz to 4.14 millionoz in 2006. With the palladium price significant-ly below that of platinum, there has beencontinuing substitution of platinum by palladi-um in three-way catalysts fitted to gasolinevehicles. 2006 also saw the first significant use ofpalladium in diesel exhaust aftertreatment. Bothtrends are likely to continue in 2007.

Global palladium jewellery demand was fore-cast to fall by 310,000 oz to 1.12 million oz.After rapid growth in 2004 and 2005 to fill thedistribution pipeline, purchases of palladium byChinese jewellers in 2006 were affected nega-tively by the recycling of old jewellery stock.However, retail sales to consumers appeared tobe healthy, suggesting that palladium demandmay recover as the rate of recycling diminishes.In the U.S.A., palladium jewellery has started toattract interest from both retailers and manufac-turers.

“Platinum 2006 Interim Review” is availablefree of charge in printed form from JohnsonMatthey PLC, Precious Metals Marketing,Orchard Road, Royston, Hertfordshire SG85HE, U.K.; E-mail: [email protected].

The report may also be freely down-loaded in PDF format from the website:http://www.platinum.matthey.com/.

Reference1 Platinum Metals Rev., 2006, 50, (3), 143

Platinum 2006 Interim Review

PROPERTIESFree-Standing Nanofibrous Platinum Sheets andTheir ConductivityX. PENG, Y.-H. LUO, J. JIN, J. HUANG, I. ICHINOSE, K. KURASHIMAand F. PAPADIMITRAKOPOULOS, Chem. Commun., 2006, (45),4688–4690

Nanofibrous Pt sheets (1) with a thickness of one toa few tens of nm were prepared over the sub-μmpores of a polycarbonate membrane filter by usinglong and rigid Cd(OH)2 nanostrands as templates.The sheet resistance of (1) at 10 nm reached 5797 Ωper square. The conductivity of (1) decreased with thethickness by more than two orders of magnitude.

SiO2 Nanotubes with Nanodispersed Pt in theWallsC. H. RÜSCHER, I. BANNAT, A. FELDHOFF, L. REN and M. WARK,Microporous Mesoporous Mater., 2007, 99, (1–2), 30–36

SiO2 nanotubes (NTs) of different wall thicknesswere prepared using fibres of [Pt(NH3)4](HCO3)2 saltcrystals (1) as templates. During growth of the SiO2

NT walls, by sol-gel condensation from tetraethylorthosilicate on the surface of (1), parts of (1) wereincorporated into the walls. Calcination in air at450ºC led to the formation of Pt nanoparticles andmicropores within the SiO2 NT walls.

Influence of Thermal Annealing on the Resistivityof Titanium/Platinum Thin FilmsU. SCHMID and H. SEIDEL, J. Vac. Sci. Technol. A, 2006, 24,(6), 2139–2146

The effect of thermal annealing at ≤ 700ºC on theroom-temperature resistivity of electron-beam-evapo-rated Ti/Pt thin films (on oxidised Si wafers) wasstudied. The Ti adhesion layer had a fixed thickness of5 nm. The thickness of the Pt top was 21–97 nm. Atannealing temperatures ≤ 450ºC, the film resistivity ofthe bilayer system showed a linear correlation with thereciprocal Pt film thickness. At ≥ 600ºC, the diffusionof Ti into the top layer led to an enhanced increase infilm resistivity, especially at low Pt thicknesses.

Isothermal Section of the Fe–Pt–Nd PhaseDiagram at 900ºCX. CHENGFU, G. ZHENGFEI, C. GANG, M. LEI and Z. BO, J. AlloysCompd., 2006, 424, (1–2), 128–130

Equilibrium phase diagrams for the ternary systemFe–Pt–Nd (1) at 900ºC (Nd ≤ 70%) were established.13 single-phase regions were determined. 23 two-phase regions and 11 three-phase regions wereidentified to exist at this isothermal section. TheNd3Pt4 phase decomposes gradually into the twoneighbouring compounds βNdPt and NdPt2 withintroduction of Fe. For Fe contents > 5 at.%, theexistence of Nd3Pt4 phase was not observed in (1).

Martensitic Transformation in FePd AlloyRevealed by Synchrotron RadiationM. MITSUKA, T. OHBA, T. FUKUDA, T. KAKESHITA and M.TANAKA, Mater. Sci. Eng.: A, 2006, 438–440, 332–335

Synchrotron radiation experiments were carried outin a precursor study of the martensitic transformationin Fe68.6Pd31.2. Six wavelengths, which give variouspenetration depths, were used for observing thetransformation behaviour. Oscillation photographswith various wavelengths were taken at temperaturesabove the martensitic transformation temperature.

Oxidation of Ruthenium Aluminide-Based Alloys:The Role of Microstructure and Platinum AdditionsF. CAO, T. K. NANDY, D. STOBBE and T. M. POLLOCK,Intermetallics, 2007, 15, (1), 34–43

The cyclic oxidation behaviour of six RuAl-basedalloys (1) was studied in air over 1000–1300ºC. Single-phase (1) formed a layered oxide structure duringoxidation. The presence of the δ-Ru-rich eutecticalong grain boundaries strongly accelerated the oxida-tion process. A single-phase Pt-containing (1)exhibited the highest oxidation resistance; this isderived from its rejection to the Ru-rich layer subse-quently formed during oxidation.

CHEMICAL COMPOUNDSPyrazole-Based Allylpalladium Complexes:Supramolecular Architecture and Liquid CrystalBehaviourM. C. TORRALBA, M. CANO, J. A. CAMPO, J. V. HERAS, E. PINILLAand M. R. TORRES, Inorg. Chem. Commun., 2006, 9, (12),1271–1275

The coordination of non-mesomorphic 3-substi-tuted pyrazoles HpzR to the [Pd(η3-C3H5)]+ fragmentgave [Pd(η3-C3H5)(HpzR)2]+ (1) (R = C6H4OCnH2n+1;n = 12, 14, 16, 18), which were isolated with BF4

–.(1) have liquid crystal properties, exhibitingmonotropic or enantiotropic smectic A mesophasesbetween ~ 40–80ºC. (1) with n = 12 has an interdig-itated layer-like supramolecular arrangement.

Dinitrogen Complexes of Pincer-Ligated IridiumR. GHOSH, M. KANZELBERGER, T. J. EMGE, G. S. HALL and A.S. GOLDMAN, Organometallics, 2006, 25, (23), 5668–5671

Precursors of the (PCP)Ir fragment (PCP = κ3-C6H3-2,6-(CH2PtBu2)2), including (PCP)IrPhH and(PCP)Ir(NBE), reacted with dinitrogen to give[(PCP)Ir]2(N2) (1). With excess dinitrogen, mononu-clear (PCP)Ir(N2) (2) was formed predominantly (~ 99% under typical conditions at 1 atm of N2), inequilibrium with small concentrations of (1). (1) selec-tively crystallised out at ambient temperature. (1) and(2) are pseudo-square planar.

Platinum Metals Rev., 2007, 51, (1), 46–49 46

ABSTRACTSof current literature on the platinum metals and their alloys

DOI: 10.1595/147106707X177282


ELECTROCHEMISTRYKinetics of Electron-Transfer Reactions atNanoelectrodesP. SUN and M. V. MIRKIN, Anal. Chem., 2006, 78, (18),6526–6534

Disk-type, polished Pt nanoelectrodes were charac-terised using voltammetry, SEM and scanningelectrochemical microscopy. A number of experimen-tal curves were obtained at the same nanoelectrode toattain accuracy and reproducibility similar to thosereported previously for μm-sized probes. A new ana-lytical approximation was developed and used foranalysis of steady-state tip voltammograms.

PHOTOCONVERSIONPhotooxidation of Olefins under Oxygen inPlatinum(II) Complex-Loaded MesoporousMolecular SievesK. FENG, R.-Y. ZHANG, L.-Z. WU, B. TU, M.-L. PENG, L.-P. ZHANG,D. ZHAO and C.-H. TUNG, J. Am. Chem. Soc., 2006, 128, (45),14685–14690

A cyclometallated Pt(II) complex (1) was incorpo-rated into (3-aminopropyl) triethoxysilane-modifiedchannels of ordered mesoporous silica SBA-15.Studies on the 1O2 generation demonstrated that theolefins in the nanochannels of SBA-15 could beenriched 8 times higher than those in a homogeneoussolution. The loaded (1) is stable. The photosensitisedoxidation occurs efficiently. Simple filtration can beused to recover and then recycle the Pt catalyst.

Effect of Substituents on the Photoluminescentand Electroluminescent Properties of SubstitutedCyclometalated Iridium(III) ComplexesH.-W. HONG and T.-M. CHEN, Mater. Chem. Phys., 2007, 101,(1), 170–176

Cyclometallated iridium complex dopants (1) usingsubstituted (4-CF3, 4-Me, 4-OMe, 4-F, 3-F) 2-phenyl-benzoxazole ligands have been synthesised. (1) arethermally stable (280–320ºC), depending upon thesubstituents, and sublimable. (1) emit bright yellow togreen light. The peak emission wavelengths of (1) canbe tuned depending upon the electronic properties ofthe substituents as well as their positions in the ring.

Visible Light Decomposition of Ammonia to N2

with Ru(bpy)32+ Sensitizer

J. NEMOTO, C. HARADA, Y. TAKEI, N. KATAKURA and M.KANEKO, Photochem. Photobiol. Sci., 2007, 6, (1), 77–82

Visible light decomposition of aqueous NH3 to N2

was investigated using either Ru(bpy)32+/K2S2O8 (1)

or Ru(bpy)32+/methylviologen dichloride (MV2+)/O2

(2) sensitiser systems. In the case of (1), GC analysisof the gaseous phase in the presence of 8.1 M NH3

showed that the photochemical oxidation of NH3

yielded N2. For (2), in an O2 atmosphere, the oxida-tion of MV+· to MV2+ takes place to accumulate aRu(III) complex, so that an oxidised product ofammonia ((NH3)ox) was then further oxidised to N2.

Ru Dye Uptake under Pressurized CO2

Improvement of Photovoltaic Performances forDye-Sensitized Solar CellsY. OGOMI, S. SAKAGUCHI, T. KADO, M. KONO, Y. YAMAGUCHIand S. HAYASE, J. Electrochem. Soc., 2006, 153, (12),A2294–A2297

Black dye [(C4H9)4N]3[Ru(Htcterpy)(NCS)3] (tcterpy= 4,4',4''-tricarboxy-2,2':6',2''-terpyridine) and N3dye [cis-di(thiocyanato)-N,N'-bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II)] (1) are adsorbed onnanoporous TiO2 layers, under a pressurised CO2

atmosphere, to bond the Ru dyes on inner surfaces ofTiO2 in nanoporous layers. The time needed foradsorption of (1) is shortened to 30 min; from 300min required for a dipping process. The amount of(1) adsorbed increased from 15 to 20 nmol cm–2 μm–1.

ELECTRODEPOSITION AND SURFACECOATINGSElectrochemical Characterization of PlatinumBlack Electrodeposited from Electrolyte IncludingLead Acetate TrihydrateM. SAITOU, Surf. Coat. Technol., 2006, 201, (6), 3611–3614

The effect of Pb acetate trihydrate (1) on Pt blackcoating for a H2PtCl6 electrolyte has been investigat-ed. (1) enhances the electrode reactions in Pt blackcoating. This is by mainly lowering the energy barrierfor the reduction of Pt(IV) to Pt(0) and by suppress-ing the reduction of Pt(IV) to Pt(II).

Deposition of Ni and Pd Sulfide Thin Films viaAerosol-Assisted CVDP. O’BRIEN and J. WATERS, Chem. Vap. Deposition, 2006, 12,(10), 620–626

Thin films (1) of Ni sulfide (NiS1.03, NiS2, α-Ni7S6,or mixtures thereof) and Pd sulfide (PdS, Pd16S7,Pd4S, or mixtures thereof) were prepared by aerosol-assisted (AA)CVD. Dithiocarbamate precursorsM(S2CNRR')2 (M = Ni, Pd; RR' = Et2, MeEt, MenBu,or MenHex) were used. (1) were grown on glass sub-strates at 400–525ºC. XRD, EDAX, and SEM wereused to characterise (1).

APPARATUS AND TECHNIQUECatalytic (Pt-Y) Membranes for the Purification ofH2-Rich StreamsP. BERNARDO, C. ALGIERI, G. BARBIERI and E. DRIOLI, Catal.Today, 2006, 118, (1–2), 90–97

Pt-loaded catalytic membranes (1), prepared fromFAU (Na-Y) zeolite membranes by ion-exchange,were used for the purification of H2-rich streams bymeans of CO selective oxidation. (1) present the zeo-lite layer on the inner surface of α-Al2O3 tubularsupports. A CO conversion of 98% and a selectivityof 62% were obtained on feeding (1) a H2-rich mix-ture containing ~ 10% CO at 200ºC (with λ = 1.66).CO removal to < 50 ppm was achieved at 200ºC and2 bar starting from 1% CO (with λ = 3.6).

47


HETEROGENEOUS CATALYSISCatalytic Performance of Pt-Sn/γ-Al2O3 for DieselSoot OxidationG. CORRO, J. L. G. FIERRO and F. BAÑUELOS ROMERO, Catal.Commun., 2006, 7, (11), 867–874

Presulfating γ-Al2O3, 1% Pt/γ-Al2O3 and 1% Pt-2%Sn/γ-Al2O3 resulted in the generation of surface sitesactive at low temperature in the oxidation of a fractionof soot particles produced during diesel combustion.Addition of Sn to 1% Pt/γ-Al2O3 caused an increaseof Pt resistance to deactivation. Surface Sn speciesmay prevent polymerised hydrocarbon residues reach-ing the interface between Pt and the support.

Effect of Hydrothermal Treatment on CatalyticProperties of PtSnNa/ZSM-5 Catalyst for PropaneDehydrogenation Y. ZHANG, Y. ZHOU, K. YANG, Y. LI, Y. WANG, Y. XU and P.WU, Microporous Mesoporous Mater., 2006, 96, (1–3), 245–254

The dehydrogenation of propane in the presence ofH2 using PtSnNa/ZSM-5 (1) was studied. Under mildhydrothermal treatment, the pore volume and theaverage pore diameter of (1) increased. However, theopposite occurred with an increase of hydrothermaltemperature and time. The intensity of Lewis acidsites on (1) decreased slightly from 400ºC to 550ºC,and an important loss of acidity took place at 650ºC.(1) hydrotreated at 650ºC exhibited Sn species lossand Pt sintering, which caused an activity decreaseand selectivity modifications during the reaction.

Selective Hydrogenation of Ethyne in Ethene-RichStreams on Palladium Catalysts. Part 1. Effect ofChanges to the Catalyst During ReactionA. BORODZINSKI and G. C. BOND, Catal. Rev., 2006, 48, (2),91–144

The effect of various changes to the Pd catalyst dur-ing its stabilisation in the selective hydrogenation ofethyne-ethene mixtures (formation of β-PdH andPdCx phases and of carbonaceous deposits) wasreviewed. A carbonaceous overlayer on the Pd sur-face creates sites at which selective ethynehydrogenation to ethene can occur. The carbona-ceous deposit on the support increases the selectivityto ethane formation by increasing the rate of ethenehydrogenation on support sites and by decreasing theeffective diffusivity of ethyne in the pores. (235 Refs.)

Supported Pd Catalyst Preparation Using LiquidCarbon DioxideJ. KIM, G. W. ROBERTS and D. J. KISEROW, Chem. Mater., 2006,18, (20), 4710–4712

Liquid CO2 (L-CO2) has an extremely low surfacetension which makes it an excellent wetting agent.Pd/α-Al2O3 and Pd/γ-Al2O3 pellet catalysts (1) wereprepared using L-CO2 to deposit Pd(hfac)2 onto thesupports, followed by reduction/activation using H2

at 45–150ºC. (1) have shown activity for the selectivehydrogenation of the aromatic rings in polystyrene.

Controlling Factors in the Direct Formation of H2O2

from H2 and O2 over a Pd/SiO2 Catalyst in EthanolQ. LIU and J. H. LUNSFORD, Appl. Catal. A: Gen., 2006, 314,(1), 94–100

The direct formation of H2O2 in EtOH overPd/SiO2 was studied under conditions that yield goodselectivities for the peroxide, moderate rates of for-mation, and concentrations of H2O2 that approach 2wt.%. Cl– or Br– and protons (from H2SO4) are essen-tial for limiting the combustion reaction. A selectivityfor H2O2 approaching 80% was achieved using 2 ×10–5 M Br– and 0.12 M H2SO4 with an O2:H2 ratio of15. Br– inhibits the loss of Pd from the support.

HOMOGENEOUS CATALYSISPd(OAc)2/DABCO-Catalyzed Suzuki–MiyauraCross-Coupling Reaction in DMFJ.-H. LI, Q.-M. ZHU and Y.-X. XIE, Tetrahedron, 2006, 62, (47),10888–10895

For Suzuki-Miyaura cross-couplings usingPd(OAc)2/DABCO (1,4-diaza-bicyclo[2.2.2]octane),both aryl bromides and aryl chlorides reacted witharylboronic acids to form biaryls, heteroaryl-aryls, andbiheteroaryls in moderate to excellent yields usingDMF as the solvent. Additionally, the reactions ofaryl bromides were carried out under relatively mildconditions. DMF is a highly polar solvent and may actas a ligand to promote the reaction.

New Modular P-Chiral Ligands for Rh-CatalyzedAsymmetric HydrogenationO. G. BONDAREV and R. GODDARD, Tetrahedron Lett., 2006,47, (51), 9013–9015

Modular P-chiral ligands (1) derived from commer-cially available (S)-α,α-diphenylprolinol have beenprepared for the first time. (1) exhibited a high enan-tioselectivity in the Rh (prepared in situ from[Rh(COD)2]BF4)-catalysed hydrogenation of function-alised olefins such as methyl α-acetamidoacrylate (≤91% ee), methyl α-acetylaminocinnamate (≤ 95% ee),and dimethyl itaconate (≤ 95% ee). Catalyst optimisa-tion can be carried out easily by variation of thesubstituent attached to the P atom in (1).

Rhodium(I) Complex with Hexylamine andChloride Ligands, Catalytically Active in theSelective Hydrogenation of 1-HeptyneD. A. LIPRANDI, E. A. CAGNOLA, M. E. QUIROGA and P. C.L’ARGENTIÈRE, Ind. Eng. Chem. Res., 2006, 45, (17),5836–5840

A Rh(I)-chloride-hexylamine complex (1) wasobtained by reaction of RhCl3 with hexylamine intoluene under Ar, at 353 K. (1) shows catalytic activi-ty for 1-heptyne semihydrogenation at 303 K and 150kPa in homogeneous as well as heterogeneous systemsusing γ-Al2O3 as support. (1) is tetracoordinated withan empirical formula [RhCl(NH2(CH2)5CH3)3]. Whensupported, (1) shows higher activity and selectivitythan it does when it is unsupported.

48

Osmium Catalyzed Dihydroxylation of 1,2-Dioxines: A New Entry for StereoselectiveSugar SynthesisT. V. ROBINSON, D. K. TAYLOR and E. R. T. TIEKINK, J. Org.Chem., 2006, 71, (19), 7236–7244

3,6-Substituted 3,6-dihydro-1,2-dioxines were dihy-droxylated with OsO4 to give 1,2-dioxane-4,5-diols(peroxy diols), in yields from 33% to 98%, and withde values ≥ 90%. These peroxy diols were thenreduced to a stereospecific tetraol core with R,R,S,Sor “allitol” stereochemistry. The peroxy diols andtheir acetonide derivatives were also ring-opened withCo(II) salens to give hydroxy ketones such as psicose.

FUEL CELLSSynthesis and Characterization of Pt/CNanocatalysts Using Room Temperature IonicLiquids for Fuel Cell ApplicationsX. XUE, C. LIU, T. LU and W. XING, Fuel Cells, 2006, 6, (5),347–355

Pt/C nanocatalysts were prepared using room tem-perature ionic liquids as the solvent (Method (1)) andconventional preparation techniques (Method (2)),based on wet impregnation methods. (1) were homo-geneously dispersed with a narrow size distribution.(1) were more active for electrooxidation of MeOHthan (2). Surface area measurements of the Pt metal,conducted by electrooxidation of preadsorbed CO,indicated that (1) have higher surface area.

Aerogel-Based PEMFC Catalysts Operating atRoom TemperatureA. SMIRNOVA, X. DONG, H. HARA and N. SAMMES, J. Fuel CellSci. Technol., 2006, 3, (4), 477–481

Pt/C-aerogel (1) with 22 nm pore size distributionand low Pt loading (0.1 mg cm–2) was tested in aPEMFC. Power densities up to 0.5 mW cm–2 wereachieved at 0.6 V in air/H2 and 2 atm backpressure onboth cathode and anode. Continuous cycling withupper potential sweep limits of 1.0 and 1.2 V led todegradation effects that resulted in decreasing of theelectrochemical surface area of (1).

Insights into the Distribution of Water in a Self-Humidifying H2/O2 Proton-Exchange MembraneFuel Cell Using 1H NMR MicroscopyK. W. FEINDEL, S. H. BERGENS and R. E. WASYLISHEN, J. Am.Chem. Soc., 2006, 128, (43), 14192–14199

The distribution of H2O throughout a self-humidi-fying PEMFC (1), operating at ambient temperatureand pressure on dry H2 and O2, was investigated in situusing 1H NMR microscopy. The MEA consisted ofunsupported HiSpec 1000 Pt black and HiSpec 6000Pt-Ru black for the cathode and anode catalyst,respectively. The maximum power output from (1),while operating under conditions of constant externalload, occurs when H2O(l) is first visible in the 1HNMR image of the cathode flow field, and subse-quently declines as this H2O(l) continues to build up.

Monodisperse PtRu Nanoalloy on Carbon as aHigh-Performance DMFC CatalystY. H. LEE, G. LEE, J. H. SHIM, S. HWANG, J. KWAK, K. LEE, H.SONG and J. T. PARK, Chem. Mater., 2006, 18, (18), 4209–4211

Colloidal PtRu was prepared from the coreductionof Pt(acac)2 and Ru(acac)3 by 1,2-hexadecanediol inoctyl ether in the presence of oleylamine and oleicacid as surfactants. PtRu/Vulcan C (1) was obtainedby impregnation on the Vulcan C support; and thesurfactant was removed by acetic acid treatment. Inelectrochemical experiments (1) is reported to havehigher catalytic activity toward MeOH oxidation,compared with that of commercially available PtRucatalysts and earlier literature examples.

ELECTRICAL AND ELECTRONICENGINEERINGIn Situ Growth of CoPt Nanoparticles in PorousGermania NanospheresM. R. REGAN and I. A. BANERJEE, Mater. Lett., 2007, 61, (1),71–75

Mesoporous nanospheres of GeO2 (1) were used asa matrix to grow magnetic CoPt nanoparticles (2). (1)were prepared by biomineralisation via the recognitionof the peptide sequence T-G-H-Q-S-P-G-A-Y-A-A-H.The size of (2) embedded in (1) is in the 8–9 nmrange. The porosity of the nanocomposites was con-firmed by nitrogen isotherm analysis. This preparativeroute has potential for obtaining new optomagneticmaterials.

Microstructure Development and ElectricalProperties of RuO2-Based Lead-Free Thick FilmResistorsM. G. BUSANA, M. PRUDENZIATI and J. HORMADALY, J. Mater.Sci.: Mater. Electron., 2006, 17, (11), 951–962

Pb-free thick film resistive compositions, based onRuO2 as the conducting phase and bismuthate glass-es, were prepared. The sheet resistance spans twodecades by changing the RuO2 fraction from ~ 14–52wt.%. Resistors can be fabricated with good repro-ducibility; and their temperature coefficient ofresistance is ± 300 ppm/ºC.

Investigation of RuO2/4H–SiC Schottky DiodeContacts by Deep Level Transient SpectroscopyD. BUC, L. STUCHLIKOVA, U. HELMERSSON, W. H. CHANG andI. BELLO, Chem. Phys. Lett., 2006, 429, (4–6), 617–621

Schottky diodes (1) were prepared on n-type siliconcarbide (4H-SiC) by deposition of RuO2 contacts.The electrical and electronic properties of (1) wereinvestigated by current–voltage and capacitance–volt-age methods, and deep level transient spectroscopy.Deep energy levels with thermal activation energies of~ 0.27, 0.45, 0.56, 0.58 and 0.85 eV referenced to theconduction band minimum were revealed. The twoenergy levels at 0.56 and 0.85 eV are induced by diva-cancies and the incorporation of Ru impurities intothe SiC interfacial region.


50

METALS AND ALLOYSOxide-Dispersion Strengthened Platinum MaterialTANAKA KIKINZOKU KOGYO KK

European Appl. 1,712,646An oxide-dispersion strengthened material (1)

formed from Pt or alloys of Pt-Rh, Pt-Au, Pt-Rh-Auor Pt-Ir is claimed, which is stable in use at high tem-peratures and has excellent weldability. Dispersedadditive metal particles (2) are selected from Zr, Ca, Yor Sm and have average diameter of 0.2 μm or less,average interparticle distance 0.01–2.7 μm and con-centration 0.01–0.5 wt.%. The oxidation rate of (2) is50–100%, and the concentration of unbound O with-in (1) is ≤ 100 ppm.

ELECTRODEPOSITION AND SURFACECOATINGSPlatinum Aluminide Coatings for Turbine ComponentsHONEYWELL INT. INC U.S. Appl. 2006/0,222,776

Turbine components such as vanes or blades arecoated with an environment-resistant Pt aluminidecoating (1) by cold gas-dynamic spraying a powdermaterial containing Al, Pt and at least one other mate-rial chosen from Ni, Cr, Hf, Si, Y, Re, Zr, Co and Ta.After coating, at least one thermal diffusion treatmentsuch as a hot isostatic pressing process, vacuum heattreatment, or heat treatment in inert atmosphere, isapplied to metallurgically homogenise the coating. (1)contains (in wt.%): ≤ 50 Pt, ~ 12–30 Al, ~ 2–25 Cr,~ 0.1–5 Hf, ~ 1–5 Si, ~ 0.1–3 Y, ~ 0.1–3 Zr, and thebalance consists of Ni.

APPARATUS AND TECHNIQUERuthenium Complex Dye for Oxygen SensingROSEMOUNT ANAL. INC U.S. Appl. 2006/0,228,804

A Ru complex luminescence dye (1) for O sensingconsists of Ru(II)-tris(4,7-diphenyl-1,10-phenanthro-line) modified by covalently bonding long-chainhydrophobic organic groups containing C12H25 to theligands. (1) have increased solubility in non-polarorganic solvents such as toluene. Optical O sensorsinclude a source of excitation illumination, a sensinglayer containing (1) which receives excitation illumi-nation and generates luminescence based on theconcentration of O, and a luminescence sensor.

Platinum Apparatus for Manufacturing GlassFURUYA KINZOKU KK Japanese Appl. 2006-169,085

Glass manufacturing apparatus is made of Pt or Ptalloy with a surface roughness of Rmax < 4 μm and Ra ≤ 0.1 μm. This gives reduced contact resistancebetween the Pt surface and the molten glass, leadingto reduced friction and improved wettability.Wrinkles and surface deformation caused by expan-sion and shrinkage at high temperature aresuppressed, and contamination of glass by Pt particlesduring manufacture is inhibited.

JOININGBrazing Diamond Using a Metal InterlayerSMITH INT. British Appl. 2,426,223

A cutting element consists of a substrate, a thermal-ly stable polycrystalline diamond layer, a metalinterlayer of Mo or Ni and a braze joint (1) securingdiamond to substrate. (1) is a NiPdCr braze alloy, andmay be coated with carbide, Ru, W or Ta. (1) hasshear strength > 60,000 psi and thickness < 0.003".

HETEROGENEOUS CATALYSISReforming Catalyst Containing RhodiumJOHNSON MATTHEY PLC British Appl. 2,424,196

A reforming catalyst (1) containing Rh or Rh-Ptparticles, and including a promoter metal such as Ba,on a support material such as ceria or ceria and zirco-nia dispersed on an Al ion containing oxide isclaimed. (1) can be used in a fuel processing systemfor reforming diesel or a diesel-type fuel. The atomicratio of Rh or Rh-Pt to Ba is between 50:1–1:5.

Alkane Aromatisation Using Platinum-Zeolite CatalystSAUDI BASIC IND. CORP INC European Appl. 1,699,746

A Pt/ZSM-5 crystalline zeolite catalyst containing0.05–5% Pt is used in aromatisation of 1–4 C alkanesto aromatics such as benzene, toluene and xylenes bya process such as a Cyclar-type process. Temperaturesare between 350–650ºC and pressures are 10–2000kPa. A byproduct of the process is a light gas fractioncontaining ethane and methane, with a mole fractionratio of ethane relative to methane between 2–10,which can be used as a feedstream for a cracker.

Membrane Apparatus and Production of HydrogenROBERT GORDON UNIV. U.S. Appl. 2006/0,239,874

An apparatus and method for producing H2 gas, inparticular synthesis gas, includes an α-alumina mem-brane treated with a TiO2 washcoat on one side andan active γ-alumina layer on the other. A metal cata-lyst, preferably Rh, is deposited within the pores ofthe alumina. Advantages include 100% conversionrates for O2, and separate feed streams enabling safeuse of optimal ratios of O2 and methane. The synthe-sis gas can be produced from normally gaseoushydrocarbons obtained from remote oil wells, andconverted to liquid hydrocarbons for transport.

Exhaust Gas Purifying CatalystCATALER CORP U.S. Appl. 2006/0,270,550

An exhaust gas purifying catalyst prevents alloyingof precious metal particles even at high operatingtemperatures, to inhibit catalyst degradation. There isa substrate with a catalyst coating containing Rh (1),Pt and/or Pd (2), plus a refractory inorganic oxide.Weight ratio of (1):(2) is 1:0–1:1 in the upstream partrelative to exhaust gas flow, and in the downstreampart the weight of (2) is greater than that of (1). Theupstream part is 60–94% of the total system volume.

NEW PATENTS


DOI: 10.1595/147106707X172025

Black Photocatalyst for Forming HydrogenTOKYO UNIV. SCI. Japanese Appl. 2006-167,652

A photocatalyst (1) for hydrolysis is capable of usingvisible light efficiently. (1) includes a solid solution ofCuInS2 substituted with Ag or Ga to giveCu1–xAgxInS2 (0.4 ≤ x ≤ 0.6) or CuGa1–yInyS2 (0.7 ≤ y≤ 0.9). Ru, Pt or Rh is present as a photocatalyst pro-moter. On irradiation with visible and near-IR light,(1) generates H2 by photocatalytic hydrolysis of anaqueous solution containing S compounds whichinclude SO3

2– and S2–.

HOMOGENEOUS CATALYSISRhodium Crosslinking Silicone ElastomersWACKER-CHEMIE GmbH U.S. Patent 7,129,309

An addition-crosslinked silicone elastomer (1) isformed in the presence of at least one Rh or Irhydrosilylation catalyst, such as Rh2(C8H15O2)4 or[IrCl(olefin)2]2, or a mixture. (1) can be made trans-parent and colourless, is flexible and is suitable for useas food and baking moulds in the food industry. Thecatalysed addition crosslinkable components displayexcellent pot life and good high-temperature cure.

Hydrogenation of an Unsaturated CompoundBASF AG U.S. Appl. 2006/0,247,459

A monoolefinically unsaturated compound bearingat least two functional groups selected from nitrile,carboxylic acid, carboxylic ester or carboxamidegroups, is hydrogenated to a saturated compound inthe presence of a homogeneous catalyst containingRh, Ru, Pd, or Ni, preferably Rh, such asCp*Rh(C2H4)2. The Rh-containing catalyst is used inthe addition step to add terminal olefins bearing therequired functional groups to a precursor compound,and the same catalyst is retained in the reaction mix-ture and used for the hydrogenation step.Hydrogenation is carried out at a partial H2 pressureof 0.1–200 bar, average mean residence time of0.1–100 hours, and temperature of 30–160ºC.

FUEL CELLSCatalyst for Fuel ElectrodeTANAKA KIKINZOKU KOGYO KK

European Appl. 1,710,856A catalyst for a SPFC electrode is composed of fine

precious metal particles (1), on an electrically conduc-tive support such as C, in the weight ratio (1):Cbetween 60:40–95:5. (1) may include Pt and Ru in themolar ratio 1:1–1:3, and have average particle diame-ter 3–10 nm. (1) also contain O, in the weight ratio(1):O between 86:14–96:4.

Fuel Cell Electrode CatalystGENERAL MOTORS World Appl. 2006/124,248

A PEMFC with improved durability is claimed, byreplacing a C support in the cathode with Ti oxidemixed with electrically conductive particles of C. Ptparticles are deposited on the Ti oxide support to givegood O reduction capability and corrosion resistancein acid environment.

Electrode Catalyst LayerNISSAN MOTOR CO LTD Japanese Appl. 2006-147,345

An electrode catalyst layer for a PEMFC includes aconductive catalyst support, a catalyst containing Ptand a proton conductive polymer. A Pt-capture agent(1) capable of scavenging Pt ions is included to pre-vent loss of Pt over time. (1) generates an organic Ptcomplex of coordination number 2–4.

ELECTRICAL AND ELECTRONICENGINEERINGBlack Electrodes with RutheniumDU PONT European Appl. 1,701,372

A black electrode (1) is formed by sintering at atemperature of 500–600ºC after applying a Pb-freeblack conductive composition (2) to a substrate. (1)includes a crystallised glass component as a binder. (2)includes (in wt.%): 4–30 conductive particles of blackRuO2, Pb-free black Ru-based polyoxides selectedfrom Bi2Ru2O7, CuxBi2–xRuO7, GdBiRu2O7, or a mix-ture; 0–30 Pb-free non-conductive black oxide; and10–50 Pb-free Bi-based glass binder.

Material for Probe PinsTANAKA KIKINZOKU KOGYO KK

U.S. Appl. 2006/0,197,542Probe pins (1) are made of one or more elements

selected from Pt, Ir, Ru, Os, Pd and Rh and have aVickers hardness of ≥ 300. In particular, (1) may beformed from (in wt.%): 5–30 Rh and the balance Ir,or 5–40 Ir and the balance Pt. Optionally W, Niand/or Co may be added, to give for example (inwt.%): 5–10 W, 5–30 Ni or 10–30 Co and the balancePt. (1) are incorporated into probe cards.

Printed Circuit Board Using Ag-Pd NanoparticlesH.-J. CHO et al. U.S. Appl. 2006/0,208,230

A conductive ink (1) is dispersed with Ag-Pd alloynanoparticles containing 5–40 wt.% Pd, of diameter1–50 nm. (1) is formed by dissolving Pd acetate andAg acetate in sodium dodecyl sulfate aqueous solu-tion and then heating. A PCB is manufactured byspraying (1) onto a substrate, for example by usingink-jet printing to form a pattern, and curing to formwiring. Migration of Ag ions is reduced, and compet-itive price and excellent conductivity are claimed.

MEDICAL USESBiocompatible Bonding MethodSECOND SIGHT MED. PROD. INC U.S. Patent 7,142,909

An implantable device includes a hermetically sealedelectronics control unit such as an electrically insulat-ed integrated circuit, bonded directly to a flexiblecircuit or electrode. Bonding is achieved using adeposited rivet (1) of a biocompatible material such asPt or Au, preferably Pt. (1) is formed by electochem-ical deposition at a current density of 50–2000 mAcm–2. The device is suitable for long-term implanta-tion into living tissue, such as for a retinal or corticalelectrode array, and may enable the restoration ofsight to certain non-sighted people.


Platinum (as well as many other metals) maybe prepared in finely divided forms that areporous at all levels of magnification. Cracks andcrevices in the sponge-like opaque matrix thenallow visible light (of wavelength around 0.5 μm)to enter, whereupon it undergoes multiple reflec-tions and is unlikely to be reflected back out. Thiseffectively produces a high value for opticalabsorption, resulting in a velvety black appear-ance to the eye, even though the platinum is inthe metallic state. Other porous structures (suchas snow and plaster) consist of inherently trans-parent or translucent crystals, so light can berefracted as well as reflected out and they appearmatt white.

Three varieties of platinum in the porous stateare generally recognised: ‘platinised platinum’,‘platinum sponge’, and ‘platinum black’. Thefirst-named customarily signifies smooth metallicplatinum bearing a black adherent coating thatgives it a large surface area, enhancing repro-ducible contact between the metal and aqueouselectrolytes. Platinised platinum may also exert acatalytic action, promoting recombination ofhydrogen and oxygen, for example. The blackcoating is obtained by electroplating smooth,clean, metal foils in chloroplatinic acid solution.A deliberate trace of lead promotes adhesion tothe substrate. A current density of about 5 mAcm–2 is typical, with polarity of the electrodesreversed every 30 seconds for 15 minutes.

‘Platinum sponge’ is a particulate form of themetal obtained by strongly heating ammoniumchloroplatinate. This compound decomposes toleave platinum metal as the only involatile com-ponent. The particle size and degree of sinteringappear to depend on temperature and other fac-tors. Some preparations exhibit a grey rather thanblack appearance, and their catalytic activityvaries. Platinum sponge was the form in which

malleable iron-free platinum was first obtained byWollaston (1–3).

‘Platinum black’ is an especially finely dividedform of platinum, optimised for catalysing theaddition of hydrogen to unsaturated organiccompounds. Adams found that heating ammoni-um chloroplatinate in molten sodium nitrate at500ºC for 30 minutes was more effective thanignition in air (4). Pouring the molten mass intowater, followed by boiling and washing, gave amuddy brown precipitate (said to be platinumdioxide) that could be concentrated by centrifu-gation. Reduction of the suspension in water withgaseous hydrogen then gave a black suspensiongoing down to colloidal in particle size, i.e. 1 nmto 1 μm. Commercial preparations of platinumblack (5) are available with guaranteed specificsurface areas of 24.4 to 29.2 m2 g–1.

More details on these forms of platinum,together with scanning electron micrographsillustrating their structures, are available inReference (6).

ALLAN MILLS

References1 M. C. Usselman, Platinum Metals Rev., 1978, 22, (3),

1002 D. McDonald and L. B. Hunt, “A History of

Platinum and its Allied Metals”, Johnson Matthey,London, 1982, 450 pp

3 Th. Rehren, Platinum Metals Rev., 2006, 50, (3), 1204 L. B. Hunt, Platinum Metals Rev., 1962, 6, (4), 1505 Johnson Matthey Catalysts, Platinum Black – High

Surface Area, Datasheet,www.jmcatalysts.com/pct/search-msds-view.asp?productid=507

6 A. A. Mills, ‘Platinized Platinum, Platinum Spongeand Platinum Black’, Bull. Sci. Instrum. Soc., 2006,(89), 35 and references therein

The Author

Dr Mills is an Associate Senior Lecturer in the Department ofPhysics and Astronomy at the University of Leicester, U.K. Hecontinues a long-standing interest in the history of science andscientific instruments.

Platinum Metals Rev., 2007, 51, (1), 52 52

FINAL ANALYSIS

Porous Platinum Morphologies:Platinised, Sponge and Black

DOI: 10.1595/147106707X176210

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