Research Article PVP-Stabilized Palladium Nanoparticles …downloads.hindawi.com/journals/jnt/2013/906740.pdf · Research Article PVP-Stabilized Palladium Nanoparticles in Silica

Hindawi Publishing CorporationJournal of NanotechnologyVolume 2013 Article ID 906740 6 pageshttpdxdoiorg1011552013906740

Research ArticlePVP-Stabilized Palladium Nanoparticles in Silica asEffective Catalysts for Hydrogenation Reactions

Caroline Pires Ruas Daiane Kessler Fischer and Marcos Alexandre Gelesky

Laboratory Catalysis and Inorganic Synthesis School of Chemistry and Food Federal University of Rio Grande Avenue Italia Km 0896201-900 Rio Grande RS Brazil

Correspondence should be addressed to Marcos Alexandre Gelesky marcosgeleskyfurgbr

Received 9 August 2013 Accepted 11 November 2013

Academic Editor John A Capobianco

Copyright copy 2013 Caroline Pires Ruas et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Palladium nanoparticles stabilized by poly (N-vinyl-2-pyrrolidone) (PVP) can be synthesized by corresponding Pd(acac)2(acac =

acetylacetonate) as precursor in methanol at 80∘C for 2 h followed by reduction with NaBH4and immobilized onto SiO

2prepared

by sol-gel process under acidic conditions (HF or HCl) The PVPPd molar ratio is set to 6 The effect of the sol-gel catalyst on thesilica morphology and texture and on Pd(0) content was investigated The catalysts prepared (ca 2 Pd(0)SiO

2HF and ca 03

Pd(0)SiO2HCl) were characterized by TEM FAAS and SEM-EDS Palladium nanoparticles supported in silica with a size 66 plusmn

14 nm were obtained The catalytic activity was tested in hydrogenation of alkenes

1 Introduction

Poly (N-vinyl-2-pyrrolidone) stabilized metal nanoparticleshave attracted considerable interest when it comes to prevent-ing coagulation and precipitation of the metal nanoparticlesPolymer protecting agents allow preparation ofmetal colloidsthat can be stable for months with reasonable control oversize as well as shape [1] The nanoparticles are kineticallyunstable with respect to aggregation or the bulk metal andshould be stabilized by electrostatic or steric protection [2 3]Some of the protecting agents provide steric stabilization suchas surfactants [4] ionic liquids [5ndash8] and polyoxoanions[9] Their main disadvantage however is the problematicseparation of the catalytic particles from the product andunused reactants at the end of the reaction Immobilizationof the particles on a solid support can facilitate the separationprocess but may simultaneously lead to a decrease in activityThe nanoparticle synthesis involves addition of a polymerto the metal salt followed by chemical or thermal reductionto produce a stable black suspension of Pd(0) particles Thetypes of stabilizers and concentration the solvent polarity[10] and the aging time of colloidal suspensions [11] canhave an effect on the size shape and catalytic activity ofpalladium nanoparticles Platinum nanoparticles protectedby PVP have been synthesized by alcohol reduction methods

and incorporated into mesoporous SBA-15 silica duringhydrothermal synthesis [12] There have been several veryrecent reports in the literature of the catalytic propertiesof nanoparticles of Ag [13 14] Rh [15] Pt [16 17] andPd [18] in PVP Palladium colloid solutions stabilized bypoly(N-vinyl-2-pyrrolidone) can be used as catalysts withhigh reactivity in CndashC bond formation microwave-assistedreactions as shown by Heck [19] and Suzuki [20] Catalytichydrogenation reactions have been extensively evaluatedwithmetal nanoparticles [21 22] We were successful in applyingthe newmethod for the synthesis of PVP-stabilized palladium(0) nanoparticles and immobilized in SiO

2employing the sol-

gel process as catalysts for hydrogenation reactionsThemeandiameters of the palladium nanoparticles are determined byTEMThe aim of this study is to examine the catalytic activityin hydrogenation of alkenes

2 Experimental Section

21 General Palladium(II) acetylacetonate (Pd(acac)2) poly

(N-vinyl-2-pyrrolidone) (PVP-55 average molecular weight55000) and sodium borohydride (98) were purchasedfrom Sigma-Aldrich (Brazil) PdC (5) was provided byDegussa (Brazil) Methanol was purchased from Synth and

2 Journal of Nanotechnology

used as received All other chemicals were purchased fromcommercial sources and used without further purificationAll solutions were prepared with double deionized waterGas chromatography analysis was performed with an Rtx-5 (30m times 025mm times 025 120583m) gas chromatograph with anFID detector and a 30m capillary column with 5 phenyland 95 dimethylpolysiloxane as the carrier gas and theN2(22mLmin) The nanoparticle formation and hydro-

genation reactions were carried out in a modified Fischer-Porter bottle immersed in a silicone oil bath and connectedto a hydrogen tank The temperature was maintained at75∘C by a hot-stirring plate connected to a digital controller(ETS-D4 IKA) with stirring at 1200 rpm The fall in thehydrogen pressure in the tank was monitored with a pressuretransducer interfaced through a Novus converter to a PC andthe data workup via Microcal Origin 50

22 Palladium Nanoparticles Solution The suspensions ofpalladium nanoparticles were prepared by the alcohol reduc-tion method [23] The Palladium nanoparticles solutionwas prepared from a solution containing Pd(acac)

2(30mg

01mmol) and it was dissolved in methanol (10mL) andpoly(N-vinyl-2-pyrrolidone (33mg 06mmol of monomericunits Mwsim55000) as a stabilizer Sodium borohydride(20mg 06mmol) was then added after reflux The solutionwas refluxed for 2 h resulting in a dark brown solution Thecolor change from yellow to dark indicates that the formationof palladium nanoparticles was completed

23 Synthesis of Palladium Nanoparticles Immobilized inSilica Silica immobilized Pd(0) nanoparticles were preparedby the sol-gel process under acidic conditions Typicalprocedure the Pd(0) nanoparticles solution (prepared inSection 22) was introduced in a Becker under vigorousstirring for 10 minutes and 2mL of tetraethoxy orthosilicate(2 g 9mmol) was then added The acid solution (HF orHCl) was introduced in a Becker under vigorous stirring at50∘C The temperature was kept at 50∘C and left to standfor a further 24 h The resulting material was isolated bycentrifugation (3000 rpm for 5min) andwashed several timeswith water and methanol and dried under vacuum

24 Adsorption and Desorption Isotherms The specific sur-face area analysis and pore size distribution of the sampleswas performed in a Gemini analyzer (Micromeritics Tristar3020)The adsorption datawas obtained at liquid-N2 temper-ature The 100mg of samples were preheated at 150∘C for 4 hunder vacuum Specific areawas assessed by the BETmethodAverage pore diameter and its distribution were obtained byBJH method

25 Hydrogenations Reactions The catalysts (50mg) wereplaced in a Fischer-Porter bottle and the alkene (1 g) wasadded The reactor was placed in an oil bath at 75∘C andhydrogen was admitted to the system at constant pressure(4 atm) under stirring until the consumption of hydrogenstoppedThe organic products were recovered by decantationand analyzed byGCThe reuse of the catalysts was performed

by simple extraction of the organic phase (upper phase)followed by the addition of the alkenes

26 Scanning Electron Microscopy (SEM) and Electron Dis-persive Spectroscopy (EDS) Elemental Analysis Themorphol-ogy of the materials was analyzed by SEM using a JEOLmodel JSM 6060 with 20 kV and 5000 magnification andthe electron dispersive spectroscopy (EDS) analysis wasperformed using a JEOL model JSM 5800 with 20 kV and5000 magnification The same instrument was used for theEDS with a Noran detector (20 kV with an acquisition timeof 100 s and 5000 magnification)

27 Sample Preparation and TEM Analysis The morpholo-gies of the obtained particles were determined on a JEOLJEM-2010 equipped with an EDS system and a JEOL JEM-120 EXII electron microscope operating at acceleratingvoltages of 120 kV The TEM samples were prepared bydeposition of the Pd(0) nanoparticles or Pd(0)SiO

2HF

isopropanol dispersions on a carbon-coated copper grid atroom temperature The histograms of the nanoparticles sizedistributions were obtained from themeasurement of around300 diameters (palladium nanoparticles) and 600 diameters(Pd(0)SiO

2HF) and reproduced in different regions of the

Cu grid assuming spherical shapes

28 FlameAtomic Absorption (FAAS) ThePalladiumpresentin the Pd(0)SiO

2HF was measured using an Analytik

Jena (Jena Germany) flame atomic absorption spectrometerequipped with a deuterium background correction systemand a transversely heated graphite atomizer using an air-acetylene (10 25 Lminminus1) flame under optimized condi-tions Pyrolytically coated graphite tubes hollow cathodelamp (operated at 3mA) and deuterium lamp were suppliedby Analytik Jena Hollow cathode lamps of Pd (120582) 2476 nm)from the same manufacturer were used as radiation sources

3 Results and Discussion

The sol-gel process allows us to obtain solid products bycreating an oxide network via progressive polycondensationreactions of molecular precursors in a liquid medium Theprocess essentially consists of two steps hydrolysis andcondensation Both reactions are affected by the nature ofthe catalyst [24] Therefore in the present study two mainacids were evaluated HF orHClThe textural properties werefurther characterized by nitrogen adsorption Specific areapore diameter and pore volume were calculated by the BETmethod (Table 1) The pore volume was shown to be depen-dent of the acidic conditions (HF or HCl) Nevertheless thepore diameter was shown to be smaller for the materialsprepared in the presence of HCl as catalyst (entry 2) Theinvestigation of the palladium elemental concentrations inthe catalytic samples is shown in Table 1 The concentrationsof incorporated Pd(0) was determined using FAAS Theconcentrations are expressed as (mm) It is evident thatthe Pd(0) metal concentration increased for the materialsprepared in the presence of HF as catalysts (entry 1)

Journal of Nanotechnology 3

(a) (b)

Figure 1 Micrographs obtained by SEM of the resulting xerogels (a) Pd(0)SiO2HF and (b) Pd(0)SiO

2HCl

(a)

0 2 4 6 8 10 120

20

40

60

80

100

120

140

160

180

Cou

nts

Diameter (nm)

58 plusmn 11nm

(b)

Figure 2 (a) TEM micrographs showing the Pd(0) nanoparticles solution observed at 120 kV (b) Histogram illustrating the particle sizedistribution

(a)

4 6 8 10 12 140

102030405060708090

100110120130

Cou

nts

Diameter (nm)

66 plusmn 14nm

(b)

Figure 3 (a) TEMmicrographs showing the Pd(0) nanoparticles to Pd(0)SiO2HF observed at 120 kV (b) Histogram illustrating the particle

size distribution


Table 1 Textural properties of the xerogela

Entry Sample 119878BETm2gminus1 119881

119901cm3gminus1 119863

119901nm FAAS ()

1 Pd(0)SiO2HF (as prepared) 254 0005 12 202 Pd(0)SiO2HCl (as prepared) 634 003 2 033 Pd(0)SiO2HF (soxhlet) 328 0009 7 mdash4 Pd(0)SiO2HF (calcined) 225 0005 14 mdasha119878BET specific area determined by BET method 119881119901 pore volume and 119889119901 pore diameter

Table 2 Hydrogenation of alkenes at 4 atm of H2

a

Entry Cat Alkene 119905minb TOFc

1 Pd(0)SiO2HFd 1-hexene 12 1582 Pd(0)SiO2HFe 1-decene 10 743 Pd(0)SiO2HFf cyclohexene 49 604 Pd(0)SiO2HClg 1-hexene 31 4255 Pd(0)SiO2HClh 1-decene 35 1896 PdC (5) 1-decene 6 8aReaction conditions temperature 75∘C constant hydrogen pressure (4 atm) solvent less bTime for 100 conversion cTOF based on total metal (mmolhydrogenated product formed per mmol of Pd per minute) for 20 conversion dPd(0)SiO2HF (50mg 20 of Pd(0)) 12mmol of alkene ePd(0)SiO2HF(50mg 20 of Pd(0)) 7mmol of alkene fPd(0)SiO2HF (50mg 20 of Pd(0)) 12mmol of alkene gPd(0)SiO2HCl (50mg 03 of Pd(0)) 12mmol ofalkene hPd(0)SiO2HCl (50mg 03 of Pd(0)) 7mmol of alkene gPdC (50mg 50 of Pd(0)) 7mmol of alkene

0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

Con

vers

ion

()

Time (min)

Figure 4 Hydrogenation of 1-hexene (∙) 1-decene (998771) and cyclo-hexene (◼) by Pd(0)SiO

2HF under 4 atm of H

2(constant pressure)

at 75∘C and [alkene][Pd(0)] = 1279 to 1-hexene 752 to 1-decene and1290 to cyclohexene

The metal distribution was determined by SEM-EDSanalysesMapping showed a homogeneous Pd(0) distributionin the silica grains for the materials prepared in the presenceof HF as catalysts Figure 1 illustrates the micrography ofsamples prepared by acids

According to Figure 1 particlemorphologies are in accor-dance to that usually observed for pure silica synthesized bythese acid-catalyzed conditions In this case a less organizedplate-like structure was observed for both cases

Figure 2(a) shows the micrograph of the isolated Pd(0)particles the mean size was shown to be ca 58plusmn11 nmwithirregularly shaped

In the case of Pd(0)SiO2HF prepared by acid catalysis

(HF) both the morphology and size (ca 66 plusmn 14 nm) weremaintained within the silica framework (Figure 3) It is clearthat the morphological structure of the nanoparticles did notchange with the presence of silica

The supported catalysts were evaluated in hydrogenationreactions 1-hexene 1-decene and cyclohexene hydrogenationreactions (Figure 4) For comparative purposes the dataconcerning the catalytic activity of commercial PdC (5)(Table 2) was also included

As shown in Table 2 all the supported systems weremore active exhibiting higher TOF in comparison tothose of commercial PdC (5) The structure generatedin Pd(0)SiO

2HCl might have afforded more active sys-

tems because the immobilized Pd content is less thanPd(0)SiO

2HF Besides according to porosimetric mea-

surements the pore diameter was much smaller for thePd(0)SiO

2HCl system

Finally the catalytic material Pd(0)SiO2HF can be

recovered by simple decantation and reused for at leastnine times without any significant loss in catalytic activity(Figure 5)

4 Conclusion

The palladium nanoparticles protected with PVP were suc-cessfully supported in silica prepared by sol gel process (acidcatalysis) The Pd(0) content in the resulting xerogels wasshown to be dependent of the preparative route In particularthe silica-based systems prepared under acidic conditions(HF) were shown to be the most active and stable The useof Pd(0)SiO

2HF as catalysts in hydrogenation of alkenes

gives better yields andTOFvalues undermoderate conditionsand shorter reaction times Recycling experiments show that


0 2 4 6 8 10 12 140

102030405060708090

100C

onve

rsio

n (

)

Time (min)

1a run2a run3a run4a run5a run

6a run7a run8a run9a run

(a)

1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

Recharges

TOF=

[Sub

st][C

at]minus

1middot[min]minus

1

middot

(b)

Figure 5 Recycling experiments for the hydrogenation of 1-hexene Conditions 100mg of Pd(0)SiO2HF (ca 2) 1-hexene (1 g 12mmol)

4 atm of H2(constant pressure) temperature 75∘C

Pd(0)SiO2HF could be used nine times with essentially no

loss in activity for the hydrogenation of 1-hexene The palla-dium nanoparticlessilica combination exhibits an excellentsynergistic effect that enhances the activity and durability ofthe catalyst for the hydrogenation of alkenes

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank CAPES for partial financialsupport and PPGQTA for scholarships They would alsolike to thank Prof Dr Jairton Dupont (UFRGS) and CME-UFRGS for the TEM and SEM microscopy analyses Theywould also like to thank Dr Fabio Andrei Duarte (UFSM)for performing the FAAS analysis

References

[1] T Teranishi andMMiyake ldquoSize control of palladiumnanopar-ticles and their crystal structuresrdquo Chemistry of Materials vol10 no 2 pp 594ndash600 1998

[2] J D Aiken III and R G Finke ldquoA review of modern transition-metal nanoclusters their synthesis characterization and appli-cations in catalysisrdquo Journal of Molecular Catalysis A vol 145no 1-2 pp 1ndash44 1999

[3] A Roucoux J Schulz and H Patin ldquoReduced transition metalcolloids a novel family of reusable catalystsrdquoChemical Reviewsvol 102 no 10 pp 3757ndash3778 2002

[4] V Mevellec A Roucoux E Ramirez K Philippot and BChaudret ldquoSurfactant-stabilized aqueous iridium(0) colloidal

suspension an efficient reusable catalyst for hydrogenation ofarenes in biphasic mediardquo Advanced Synthesis amp Catalysis vol346 no 1 pp 72ndash76 2004

[5] J Dupont and J D Scholten ldquoOn the structural and surfaceproperties of transition-metal nanoparticles in ionic liquidsrdquoChemical Society Reviews vol 39 no 5 pp 1780ndash1804 2010

[6] P Migowski and J Dupont ldquoCatalytic applications of metalnanoparticles in imidazolium ionic liquidsrdquo Chemistry vol 13no 1 pp 32ndash39 2007

[7] J D Scholten B C Leal and J Dupont ldquoTransition metalnanoparticle catalysis in ionic liquidsrdquoACS Catalysis vol 2 no1 pp 184ndash200 2012

[8] X-D Mu D G Evans and Y Kou ldquoA general method forpreparation of PVP-stabilized noble metal nanoparticles inroom temperature ionic liquidsrdquo Catalysis Letters vol 97 no3-4 pp 151ndash154 2004

[9] J D Aiken III and R G Finke ldquoPolyoxoanion- and tetra-butylammonium-stabilized Rh(0)(n) nanoclusters unprece-dented nanocluster catalytic lifetime in solutionrdquo Journal of theAmerican Chemical Society vol 121 no 38 pp 8803ndash8810 1999

[10] N Gacemand and P Diao ldquoEffect of solvent polarity on theassembly behavior of PVP coated rhodium nanoparticlesrdquoColloids and Surfaces A vol 417 pp 32ndash38 2013

[11] I Miguel-Garcıa A Berenguer-Murcia T Garcıa and DCazorla-Amoros ldquoEffect of the aging time of PVP coatedpalladium nanoparticles colloidal suspensions on their catalyticactivity in the preferential oxidation ofCOrdquoCatalysis Today vol187 no 1 pp 2ndash9 2012

[12] H Song R M Rioux J D Hoefelmeyer et al ldquoHydrothermalgrowth of mesoporous SBA-15 silica in the presence of PVP-stabilized Pt nanoparticles synthesis characterization andcatalytic propertiesrdquo Journal of the American Chemical Societyvol 128 no 9 pp 3027ndash3037 2006

[13] P S Mdluli N M Sosibo P N Mashazi et al ldquoSelectiveadsorption of PVP on the surface of silver nanoparticles a


molecular dynamics studyrdquo Journal of Molecular Structure vol1004 no 1ndash3 pp 131ndash137 2011

[14] S W Kang and Y S Kang ldquoSilver nanoparticles stabilizedby crosslinked poly(vinyl pyrrolidone) and its application forfacilitated olefin transportrdquo Journal of Colloid and InterfaceScience vol 353 no 1 pp 83ndash86 2011

[15] N Yan Y Yuan and P J Dyson ldquoRhodium nanoparticle cata-lysts stabilized with a polymer that enhances stability withoutcompromising activityrdquo Chemical Communications vol 47 no9 pp 2529ndash2531 2011

[16] M Liu J Zhang J Liu and W W Yu ldquoSynthesis of PVP-stabilized PtRu colloidal nanoparticles by ethanol reductionand their catalytic properties for selective hydrogenation ofortho-chloronitrobenzenerdquo Journal of Catalysis vol 278 no 1pp 1ndash7 2011

[17] V L Nguyen M Ohtaki V N Ngo M T Cao and MNogami ldquoStructure andmorphology of platinum nanoparticleswith critical new issues of low high-index-facetsrdquo Advances inNatural Science vol 3 no 2 pp 1ndash4 2012

[18] V L Nguyen D C Nguyen H HirataM Ohtaki T Hayakawaand M Nogami ldquoChemical synthesis and characterization ofpalladiumnanoparticlesrdquoAdvances inNatural Science vol 1 pp1ndash5 2010

[19] D D L Martins H M Alvarez L C S Aguiar and O AC Antunes ldquoHeck reactions catalyzed by Pd(0)-PVP nanopar-ticles under conventional and microwave heatingrdquo AppliedCatalysis A vol 408 no 1-2 pp 47ndash53 2011

[20] D de Luna Martins H M Alvarez and L C S AguiarldquoMicrowave-assisted Suzuki reaction catalyzed by Pd(0)-PVPnanoparticlesrdquoTetrahedron Letters vol 51 no 52 pp 6814ndash68172010

[21] M A Gelesky S S X Chiaro F A Pavan J H Z DosSantos and J Dupont ldquoSupported ionic liquid phase rhodiumnanoparticle hydrogenation catalystsrdquo Dalton Transactions no47 pp 5549ndash5553 2007

[22] M A Gelesky C W Scheeren L Foppa F A Pavan S L PDias and J Dupont ldquoMetal nanoparticleionic liquidcellulosenew catalytically active membrane materials for hydrogenationreactionsrdquo Biomacromolecules vol 10 no 7 pp 1888ndash18932009

[23] F Durap O Metin M Aydemir and S Ozkar ldquoNew route tosynthesis of PVP-stabilized palladium(0) nanoclusters and theirenhanced catalytic activity in Heck and Suzuki cross-couplingreactionsrdquoApplied Organometallic Chemistry vol 23 no 12 pp498ndash503 2009

[24] C J Brinker and G W Scherer The Physics and Chemistry ofSol-Gel Processing Academic Press London UK 1990

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Advances in

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Smart Materials Research



MetallurgyJournal of


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MaterialsJournal of


Nano

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Journal ofNanomaterials


used as received All other chemicals were purchased fromcommercial sources and used without further purificationAll solutions were prepared with double deionized waterGas chromatography analysis was performed with an Rtx-5 (30m times 025mm times 025 120583m) gas chromatograph with anFID detector and a 30m capillary column with 5 phenyland 95 dimethylpolysiloxane as the carrier gas and theN2(22mLmin) The nanoparticle formation and hydro-

genation reactions were carried out in a modified Fischer-Porter bottle immersed in a silicone oil bath and connectedto a hydrogen tank The temperature was maintained at75∘C by a hot-stirring plate connected to a digital controller(ETS-D4 IKA) with stirring at 1200 rpm The fall in thehydrogen pressure in the tank was monitored with a pressuretransducer interfaced through a Novus converter to a PC andthe data workup via Microcal Origin 50

22 Palladium Nanoparticles Solution The suspensions ofpalladium nanoparticles were prepared by the alcohol reduc-tion method [23] The Palladium nanoparticles solutionwas prepared from a solution containing Pd(acac)

2(30mg

01mmol) and it was dissolved in methanol (10mL) andpoly(N-vinyl-2-pyrrolidone (33mg 06mmol of monomericunits Mwsim55000) as a stabilizer Sodium borohydride(20mg 06mmol) was then added after reflux The solutionwas refluxed for 2 h resulting in a dark brown solution Thecolor change from yellow to dark indicates that the formationof palladium nanoparticles was completed

23 Synthesis of Palladium Nanoparticles Immobilized inSilica Silica immobilized Pd(0) nanoparticles were preparedby the sol-gel process under acidic conditions Typicalprocedure the Pd(0) nanoparticles solution (prepared inSection 22) was introduced in a Becker under vigorousstirring for 10 minutes and 2mL of tetraethoxy orthosilicate(2 g 9mmol) was then added The acid solution (HF orHCl) was introduced in a Becker under vigorous stirring at50∘C The temperature was kept at 50∘C and left to standfor a further 24 h The resulting material was isolated bycentrifugation (3000 rpm for 5min) andwashed several timeswith water and methanol and dried under vacuum

24 Adsorption and Desorption Isotherms The specific sur-face area analysis and pore size distribution of the sampleswas performed in a Gemini analyzer (Micromeritics Tristar3020)The adsorption datawas obtained at liquid-N2 temper-ature The 100mg of samples were preheated at 150∘C for 4 hunder vacuum Specific areawas assessed by the BETmethodAverage pore diameter and its distribution were obtained byBJH method

25 Hydrogenations Reactions The catalysts (50mg) wereplaced in a Fischer-Porter bottle and the alkene (1 g) wasadded The reactor was placed in an oil bath at 75∘C andhydrogen was admitted to the system at constant pressure(4 atm) under stirring until the consumption of hydrogenstoppedThe organic products were recovered by decantationand analyzed byGCThe reuse of the catalysts was performed

by simple extraction of the organic phase (upper phase)followed by the addition of the alkenes

26 Scanning Electron Microscopy (SEM) and Electron Dis-persive Spectroscopy (EDS) Elemental Analysis Themorphol-ogy of the materials was analyzed by SEM using a JEOLmodel JSM 6060 with 20 kV and 5000 magnification andthe electron dispersive spectroscopy (EDS) analysis wasperformed using a JEOL model JSM 5800 with 20 kV and5000 magnification The same instrument was used for theEDS with a Noran detector (20 kV with an acquisition timeof 100 s and 5000 magnification)

27 Sample Preparation and TEM Analysis The morpholo-gies of the obtained particles were determined on a JEOLJEM-2010 equipped with an EDS system and a JEOL JEM-120 EXII electron microscope operating at acceleratingvoltages of 120 kV The TEM samples were prepared bydeposition of the Pd(0) nanoparticles or Pd(0)SiO

2HF

isopropanol dispersions on a carbon-coated copper grid atroom temperature The histograms of the nanoparticles sizedistributions were obtained from themeasurement of around300 diameters (palladium nanoparticles) and 600 diameters(Pd(0)SiO

2HF) and reproduced in different regions of the

Cu grid assuming spherical shapes

28 FlameAtomic Absorption (FAAS) ThePalladiumpresentin the Pd(0)SiO

2HF was measured using an Analytik

Jena (Jena Germany) flame atomic absorption spectrometerequipped with a deuterium background correction systemand a transversely heated graphite atomizer using an air-acetylene (10 25 Lminminus1) flame under optimized condi-tions Pyrolytically coated graphite tubes hollow cathodelamp (operated at 3mA) and deuterium lamp were suppliedby Analytik Jena Hollow cathode lamps of Pd (120582) 2476 nm)from the same manufacturer were used as radiation sources

3 Results and Discussion

The sol-gel process allows us to obtain solid products bycreating an oxide network via progressive polycondensationreactions of molecular precursors in a liquid medium Theprocess essentially consists of two steps hydrolysis andcondensation Both reactions are affected by the nature ofthe catalyst [24] Therefore in the present study two mainacids were evaluated HF orHClThe textural properties werefurther characterized by nitrogen adsorption Specific areapore diameter and pore volume were calculated by the BETmethod (Table 1) The pore volume was shown to be depen-dent of the acidic conditions (HF or HCl) Nevertheless thepore diameter was shown to be smaller for the materialsprepared in the presence of HCl as catalyst (entry 2) Theinvestigation of the palladium elemental concentrations inthe catalytic samples is shown in Table 1 The concentrationsof incorporated Pd(0) was determined using FAAS Theconcentrations are expressed as (mm) It is evident thatthe Pd(0) metal concentration increased for the materialsprepared in the presence of HF as catalysts (entry 1)


(a) (b)


2HCl

(a)

0 2 4 6 8 10 120

20

40

60

80

100

120

140

160

180

Cou

nts

Diameter (nm)

58 plusmn 11nm

(b)


(a)

4 6 8 10 12 140

102030405060708090

100110120130

Cou

nts

Diameter (nm)

66 plusmn 14nm

(b)


size distribution




119901cm3gminus1 119863

119901nm FAAS ()



a



0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

Con

vers

ion

()

Time (min)
















2HCl system



4 Conclusion





0 2 4 6 8 10 12 140

102030405060708090

100C

onve

rsio

n (

)

Time (min)



(a)

1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

Recharges

TOF=

[Sub

st][C

at]minus

1middot[min]minus

1

middot

(b)







Acknowledgments


References



































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


2HCl

(a)

0 2 4 6 8 10 120

20

40

60

80

100

120

140

160

180

Cou

nts

Diameter (nm)

58 plusmn 11nm

(b)


(a)

4 6 8 10 12 140

102030405060708090

100110120130

Cou

nts

Diameter (nm)

66 plusmn 14nm

(b)


size distribution




119901cm3gminus1 119863

119901nm FAAS ()



a



0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

Con

vers

ion

()

Time (min)
















2HCl system



4 Conclusion





0 2 4 6 8 10 12 140

102030405060708090

100C

onve

rsio

n (

)

Time (min)



(a)

1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

Recharges

TOF=

[Sub

st][C

at]minus

1middot[min]minus

1

middot

(b)







Acknowledgments


References



































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119901cm3gminus1 119863

119901nm FAAS ()



a



0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

Con

vers

ion

()

Time (min)
















2HCl system



4 Conclusion





0 2 4 6 8 10 12 140

102030405060708090

100C

onve

rsio

n (

)

Time (min)



(a)

1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

Recharges

TOF=

[Sub

st][C

at]minus

1middot[min]minus

1

middot

(b)







Acknowledgments


References



































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 2 4 6 8 10 12 140

102030405060708090

100C

onve

rsio

n (

)

Time (min)



(a)

1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

Recharges

TOF=

[Sub

st][C

at]minus

1middot[min]minus

1

middot

(b)







Acknowledgments


References



































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article PVP-Stabilized Palladium Nanoparticles …downloads.hindawi.com/journals/jnt/2013/906740.pdf · Research Article PVP-Stabilized Palladium Nanoparticles in Silica