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Preparation of SolidHeterogeneousCatalystsProf. Riikka PuurunenCHEM-E1130, Lecture 4, 23.1.2019
https://dx.doi.org/10.1021/cr500486u
https://pubs.acs.org/doi/pdfplus/10.1021/cr500486u
”Catalyst preparation
is the secret to
achieving the desired
activity, selectivity
and life time.”
James T. Richardson,
Principles of Catalyst
Development, 1989 (p. 134)
Learning outcomes (modified)After the course the students are able to:
1. give the definition of catalysis and describe concepts related to
heterogeneous and homogeneous catalysts
2. explain steps and methods in catalyst preparation
3. describe and apply selected catalyst characterization methods
4. explain why and how catalysts deactivate and how catalyst
deactivation can be postponed or prevented
5. give examples of where catalysts are applied
6. recognize challenges potentially solvable by catalytic reactions
Note, Prof. Puurunen, 7.1.2019: These learning outcomes have not yet been
accepted for the course. Students are welcome to comment on these proposed
learning outcomes. We will in practice follow these in the course in 2018-2019
Some feedback in MyCo Quiz 2(3):Quiz2
• “Interesting <quiz> questions, really made me rethink the lecture themes.”
• “It was an difficult topic but lecturer teached with ease and care without haste”
• “I like that we went very detailed with three different processes.”’
• “The second lecture was quite heavy, loaded with a lot of information. If all
the cases need to be presented, maybe it could be done in two lectures?”
• “The light grey font used in a few slides should in my opinion be changed to a
darker shade. At my own screen it looks fine, but in the lecture hall it was not
sufficiently visible (the projector always appears to change the colors a bit)”
• ” … So please explain the dispersion to me once again. ”
Quiz3
• 3 persons commented (lengthy) word-filling exercises has been heard
+ much more excellent feedback Thank You!
Feedback will help to develop the course (slides, quizzes…) further
Changed! 50%
To get started:let’s go to Presemo
Go to:
http://presemo.aalto.fi/cheme1130lect3(http://presemo.aalto.fi/cheme1130lect3/screen)
<note: lecture numbering is from 2018>
23.1.2019
5
Preparation of solidheterogeneouscatalysts - general
Three fundamental stages of catalystpreparation (IUPAC)1. Preparation of the primary solid (or first precursor solid)
associating all the useful components;
2. Processing of that primary solid to obtain the catalyst
precursor, for example by heat treatment;
3. Activation of the precursor to give the active catalyst
23.1.2019
8
Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
Primary
solid
Catalyst
precursor
Active
catalyst
Four main routes to prepare the ”primary solid”
23.1.2019
9
1 Deposition
2 Precipitation and co-precipitation
3 Gel formation
4 Selective removal
• Impregnation
• Ion exchange
• Gas phase depositions
• Solid-solid reactions
• Wash coat
• Synthesis of zeolites
and related materials
• Precipitation-deposition
Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
(OED: Deposition: the action of putting down)
IUPAC Manual of Methods and Procedures for Catalyst
Characterization, on catalyst preparation:
” All experimental parameters are critical for determining the
characteristics of the solid obtained after the first step:
* aggregate morphology of the carrier used, if any;
* quantities used (solutions, carrier);
* concentrations;
* stirring conditions (shape and volume of vessel are important);
* temperature and temperature changes;
* sequence and duration of all operations”
23.1.2019
10
Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
Is catalysis ”art”
or ”science”?
Targets usually: high dispersion & uniform distribution
23.1.2019
11
Munnik et al., Chem. Rev. 115 (2015) 6687.
https://dx.doi.org/10.1021/cr500486u
Julian Ross: Heterogeneous Catalysis -
Fundamentals and Applications, © Elsevier
2012., book link here. (Fig. 3.5)
Dispersion: atomic scale• Values between 1 and 0
• 1 (=100%): all (metal) atoms
are surface atoms
• Close to 0: large (metal)
particles
Distribution: macroscopic (often µm-mm)
Ross book:
Chapter 4
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12
Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here. Chapter 4: Catalyst preparation, link
Additional material
23.1.2019
13
Munnik et al.,
Chem. Rev. 115
(2015) 6687.
https://dx.doi.org/1
0.1021/cr500486u
Additional material
23.1.2019
14https://onlinelibrary.wiley.com/doi/book/10.1002/9783527626854
Additional
(detailed) material
(docroral students)
Topics to be covered today
1. Some properties of catalyst supports
2. Deposition Impregnation (there are many ways)
3. Other primary solid preparation methods
4. Processing of the primary solid to catalyst precursor
5. Activation
6. Current ”advanced” activities at Aalto University
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Some properties of solid catalystsupports
Support typically provides large surfacearea to disperse the active component
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19
Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here.
Supports: often refractory oxides
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Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here.
Chemical properties important
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Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here.
”Further on the Tammann –rule: http://onlinelibrary.wiley.com/doi/10.1002/zaac.200400540/pdf ”
• Supports can
be neutral,
acidic, basic,
amphoteric
• Thermal
history affects
Concept: point of zero charge, PZC
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PZC and Surface Groups of Aluminas Used as Carriers, Langmuir 2 (1986) 281, linkSource: Yingnan Zhao, Catalysis course lecture 2017
PZC: characterizes the
overall acidity/basicity of the
support
23.1.2019
23Munnik, de Jongh, de Jong, Recent developments in the synthesis of supported catalysts, Chem. Rev. 115 (2015) 6687.
Link: http://pubs.acs.org/doi/pdfplus/10.1021/cr500486u
Support’s surface groups influence themetal addition phase• Interaction with the active-
phase precursors
• Hydroxyl groups, -OH
• amount and acidity varies
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Puurunen, Doctoral thesis, Helsinki University of Technology, 2002
https://aaltodoc.aalto.fi/handle/123456789/2225
Two fundamental types of acidic sites
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OH vs temperature: Riikka Puurunen, Doctoral thesis, Helsinki University of Technology, 2002
http://lib.tkk.fi/Diss/2002/isbn9512261421/isbn9512261421.pdf
Lewis acid sites:• A molecular entity that is an electron-
pair acceptor and therefore able to
react with a Lewis base to form a Lewis
adduct… http://goldbook.iupac.org/html/L/L03508.html
• Also known as: Coordinatively
unsaturated sites (c.u.s.)
• (Often: surface aluminium sites)
Brønsted acid sites:• A molecular entity capable of donating a
hydron (proton) to a base, (i.e. a 'hydron
donor') https://goldbook.iupac.org/html/B/B00744.html
• (Often: hydroxyl i.e. ||-OH groups)
Hydroxyl group:
Brønsted acid
23.1.2019
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Catal. Sci.
Technol.,
2019,9, 509-
516
http://dx.doi.o
rg/10.1039/C
8CY02250J
Recent example
of literature
about Lewis
acid sites Additional material
Carbon supports show a large varietyof surface groups
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Emma Sairanen, Doctoral thesis, Aalto University 2015,
https://aaltodoc.aalto.fi/handle/123456789/15243
Carbon supports show a large varietyof surface groups
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Emma Sairanen, Doctoral thesis, Aalto University 2015,
https://aaltodoc.aalto.fi/handle/123456789/15243
phenol
Tamman temperature – limit for use at height temperatures
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Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here.
Tamman temperature: approximately half the temperature of
the melting point (in K).Examples
•
•
•
•
”On the Tammann –rule: http://onlinelibrary.wiley.com/doi/10.1002/zaac.200400540/pdf ”
Deposition Impregnation(There are many ways to introducethe active component on support)
Impregnation
“Impregnation consists in contacting a solid with a liquid
containing the components to be deposited on the surface.”
(IUPAC)
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Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied Chemistry 67
(1995) 1257-1306. https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here.
Fig. 4.8: Pore filling during wet
impregnation and the effect of
subsequent drying.
IUPAC / During impregnation many different processes take place with different rates
* selective adsorption of species (charged or not) by coulomb
force, van der Waals forces or H-bonds;
* ion exchange between the charged surface and the electrolyte;
* polymerisation/depolymerisation of the species (molecules, ions)
attached to the surface;
* partial dissolution of the surface of the solid.
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Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
IUPAC / Impregnation can be made byat least 8 different methods• Impregnation by soaking, or with an excess of solution
• Dry or pore volume impregnation
• Incipient wetness impregnation
• Deposition by selective reaction with the surface of the support
• Impregnation by percolation
• Co-impregnation
• Successive impregnation
• Precipitation-deposition
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Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied Chemistry 67
(1995) 1257-1306. https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
And more:
+ vacuum impregnation
+ cyclic impregnation
+ …
”Wet impregnation”
(this example is called
”adsorption” in the Richardson
book)
23.1.2019
34Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 112.
Impregnation by soaking, or with an excess of solution (wet impregnation)
“Excess liquid is eliminated by evaporation or by draining.
Deposition of the active element is never quantitative.
The quantity deposited depends on the solid/liquid ratio.
Deposition is slow, requiring several hours or days.
Extensive restructuring of the surface (loss of surface
area, etc.) may occur. However, the method allows the
distribution of the species to be very well controlled
and high dispersions may be obtained. The method
works best if ion/solid interactions are involved.”
23.1.2019
35
Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
23.1.2019
36Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 114.
Dry or pore volume impregnation
Dry or pore volume impregnation
“The required amounts of components are introduced
in the volume corresponding to the pore volume of the
support. The method is best suited to deposition of
species which interact very weakly with the surface, and
for deposition of quantities exceeding the number of
adsorption sites on the surface. If the number of species
which can adsorb on the surface is smaller, a
chromatographic effect may occur, i.e. attachment to
the mouth of the pores. Redistribution inside the pores is
very slow.”
23.1.2019
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Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
Incipient wetness impregnation
“A procedure similar to
dry impregnation, but the
volume of the solution
is more empirically
determined to correspond
to that beyond which the
catalyst begins to look
wet.”
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Puurunen, Beheydt, Weckhuysen, ” Monitoring Chromia/Alumina Catalysts in
Situ during Propane Dehydrogenation by Optical Fiber UV–Visible Diffuse
Reflectance Spectroscopy,” Journal of Catalysis 204 (2001) 253–257.
https://doi.org/10.1006/jcat.2001.3372
Manual of Methods and Procedures for Catalyst Characterization, Pure and Applied
Chemistry 67 (1995) 1257-1306.
https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
Precursors in impregnation: soluble metal compounds
23.1.2019
39Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 262.
https://en.wikipedia.org/wiki/Nitrogen_dioxide
Toxic! MSDS
• Nitrates are often used in impregnation:
decompose to oxide & NO2 (&O2)
RECIPE
Metal-support interactions
From: Handbook of Heterogeneous Catalysis,
Ed. G. Ertl, H. Knözinger, J. Weitkamp, Wiley-VCH, 1997
Break + Presemo
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1. Amberlyst 35 ion exchange resin
2. Activated carbon
3. 3% Pd/C
4. monoclinic ZrO2
5. 3% Pt/ZrO2 (impregnation)
6. 17% CeO2/ZrO2
7. 3% Pt/17% CeO2/ZrO2 (impregnation)
8. 10% La2O3/ZrO2
9. 3% Pt/10% La2O3/ZrO2 (impregnation)
10. SiC
11. CoMo/Al2O3
12. NiMo/Al2O3
13. HSZ-690 zeolite
14. Uncoated microreactor plate
15. TiO2 coated microreactor plate
16. Monolith
23.1.2019
42
Catalyst demo samples to view
Break + Presemo
Go to: http://presemo.aalto.fi/cheme1130lect3
(http://presemo.aalto.fi/cheme1130lect3/screen)
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Other methods (2-4), basic description
Precipitation and co-precipitation(Julian Ross bookmore details)
Solubility product
a thermodymamic
quantity
* compound A+B-
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Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012.
Link to electronic book here. Chapter 4 is of catalyst preparation.
For Al(OH)3
pH of the (water) solution is crucial
Gel formation (and related processes)A series of widely different techniques is considered here which, starting from solutions, give gels or
solid-like substances, which retain all the active elements contained in the starting solutions, and
from which the solvent and reaction by-products are eliminated by evaporation or sublimation.
These gels are later decomposed or further transformed, usually to oxides.
The gel can be obtained by a range of different methods:
* chemical reaction, e.g. formation of a tridimensional polymer by alkoxide hydrolysis (sol-gel process)
and, more generally, by polymerisation (of an anion, such as molybdate);
* complexation, e.g. with an acid-alcohol such as citric acid [7];
* freeze drying;
* addition of a gum or a gelling agent (hydroxymethyl cellulose, etc.)
Gel formation under the influence of heat and evaporation in the 'oil-drop' process is related to this group
of preparation methods.
The basic principle underlying these processes is to maintain together, without segregation, all the
active components present in a homogeneous solution. Once a gel or a solid-like substance is formed
segregation becomes difficult, because diffusion is strongly restricted. The success of the fabrication rests
on rapid transformation of the starting solution to a very viscous medium and the solid-like substance.
23.1.2019
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https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
1995 IUPAC, Pure and Applied Chemistry, 67,1257-1306
Selective removal, case: Raney nickel
• Ni–Al alloy is prepared by dissolving nickel in
molten aluminium followed by cooling
("quenching"). (Promotors may be added)
• Aluminium is leached with NaOH
• 2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2
• Surface area ~100 m2/g, developed in 1926 for
the hydrogenation of vegetable oils
• Raney Nickel tradename; other names:
“skeletal catalyst" or "sponge-metal catalyst”
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https://en.wikipedia.org/wiki/Raney_nickel
Processing of theprimary solid
Processing of the “primary solid” to obtain the “catalyst precursor”
• typically a heat treament
• often called ”calcination”
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Calcination, Wikipedia:
• ”Authorities differ on the meaning
of calcination (also referred to as
calcining)” • https://en.wikipedia.org/wiki/Calcination
Calcination, IUPAC:
• ”Heating to high
temperatures in air or
oxygen”• http://goldbook.iupac.org/html/C/C00773.html
“The catalysts were aged and dried at
60 and 120°C for 4 h, after which
they were calcined at 600◦C for 16 h” J. Catal. 204 (2001) 253–257.
https://doi.org/10.1006/jcat.2001.3372
Activation
Activation of the ”catalyst precursor” to give the active catalyst
• reduction of metal (hydrogenation catalysts)
• Can be with H2 or other reducing agent
• formation of sulfides (hydrodesulfurisation)
• With H2S or with sulfur-containing feed.
• Oxide sulfide (may not go through metallic state)
• deammoniation (acidic zeolites)
• Spontaneous activation at the beginning of the catalytic
reaction (selective oxidation catalysts)
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https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
1995 IUPAC, Pure and Applied Chemistry, 67,1257-1306
Examples: Ammonia
& steam reforming
catalysts
Example: FCC
Care with activated catalysts!
A pre-reduced catalyst is a potentially dangerous chemical
• Can burn ”pyrophorically” in contact with air
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More: https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
1995 IUPAC, Pure and Applied Chemistry, 67,1257-1306
http://www.hse.gov.uk/chemical-classification/labelling-packaging/hazard-symbols-hazard-pictograms.htm
Care with activated catalysts!
Methods to protect activated catalysts
• Passivation by controlled exposure to air at ambient
temperature / other passivating agents (e.g., Ni, Pt)
• Handling in inert atmosphere (N2) (e.g., HDS catalysts)
• Activated metal catalysts (essentially Ni) can be effectively
protected by a wax (stearic acid, etc.)
• “Part of the catalysts used in the fat and oil industry undergoes this treatment. ”
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More: https://old.iupac.org/publications/pac/1995/pdf/6708x1257.pdf
1995 IUPAC, Pure and Applied Chemistry, 67,1257-1306
http://www.hse.gov.uk/chemical-classification/labelling-packaging/hazard-symbols-hazard-pictograms.htm
Examples of ”advanced” catalyst preparation at Aalto University
Vacuum impregnation (Zhao)
• Similar to pore volume (dry)
impregnation. Precursor
solution is added to catalyst
powder in vacuum
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Photo: Riikka Puurunen 2017
23.1.2019
56
HAuCl4
Stirring
800 rpm
Stirring, 5 min
800 rpm
to reduceAu(III) to Au(0)
NaBH4H2O
Stirring, 30 min
800 rpm
H2SO4
Stirring, 2 min
800 rpm
Settling, 20 min
Au NPs immobilized to
TiO2
pH ~1
Stirring, 2 h
800 rpm
to protect Au NPs from coalescence
FiltrationDrying
110 oC, overnightCatalyst powder
Sol-immobilization: Au on titania
TiO2
PVA*
WashingTo obtain the catalyst
To adjust the pH, support acidified to promote metal deposition
To remove impurities and residues
Calcination (
(
For stability and PVA removal
Modified from: Khan & Marin et al., Applied Catalysis A: General, 562 (2018) 173-183. http://dx.doi.org/10.1016/j.apcata.2018.06.010
*PVA = polyvinyl
alcohol
23.1.2019
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(Wash)coating of microreactor plates
Stirring, 500 rpm
90 ˚C, 2 h
Stirring, 500 rpm
65 ˚C, 2 h
Stirring, 500 rpm
Room temp., 72 h
Catalyst powder (AuTiO2)H2O PVA
Stainless steel microreactor plate coated with Au/TiO2
+ CoatingCalcinationReady
to use!
Note! The role of PVA is different from the
catalyst preparation: Here the PVA acts as a
binder. Also the molar mass used here is
different.
For stability and PVA removal
For example as prepared on the previous slide, without calcination
Modified from: Khan & Marin et al., Applied Catalysis A: General, 562 (2018) 173-183. http://dx.doi.org/10.1016/j.apcata.2018.06.010
Atomic layer deposition (ALD)Irreversible saturating gas-solid reactions
Doctoral theses, e.g. :
• Lars-Peter Lindfors 1994
• Arja Hakuli 1999
• Riikka Puurunen 2002, link
• Leif Backman 2009, link
• Emma Sairanen 2015, link
• (… who’s next ?)
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ALD cycleReactant A
Reactant B
By-product
Substratebefore ALD
Step 2 /4purge
Step 4 /4purge
Step 1 /4 Reactant A
Step 3 /4Reactant BALD cycle
Reactant A
Reactant B
By-product
Substratebefore ALD
Step 2 /4purge
Step 4 /4purge
Step 1 /4 Reactant A
Step 3 /4Reactant B
Puurunen’s review articles:
• 2005, Journal of Applied Physics, general introduction + process review + Me3Al/H2O process, https://doi.org/10.1063/1.1940727
• 2013, Journal of Applied Physics, process review update + crystallinity review, https://doi.org/10.1063/1.4757907
• 2017, Journal of Vacuum Science and Technology A, on the history (two indepenent discoveries), https://doi.org/10.1116/1.4971389
First ALD article from Catalysis group
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• https://dx.doi.org/10.1007/s11244-019-01133-w (statistics for 23.1.2019)
• Preprint published in ChemRxiv: https://doi.org/10.26434/chemrxiv.7204847.v2
Conclusion & take-home message
Take-home message
• A lot of ”art” involved in catalyst preparation, in addition to
scientific knowledge on (typically) inorganic chemistry
• Careful documentation is key to reproducibility
• After this lecture (+ thinking + Quiz), you should at least be
able to:
• decribe the three fundamental stages of catalyst preparation and give some examples of these steps
• Be able to describe the principles the most common method of catalyst preparation: (pore volume) impregnation
23.1.2019
61
… thanks & congratulations for viewing this far ,
see you next week!
https://www.chem.
uci.edu/~potma/ca
rtoons.htm
+ whiteboard drawing
23.1.2019
63
+ presemo feedbackL3C Your (anonymous) greetings to the organizers
7 messages, 7 participants
15:41 » Presemo is nice!
15:41 » I would have like to learn something more about ALD
15:42 » Presemo was nice, kept the lecture more interactive.
Really liked it.
15:42 » Good lecture. I liked presemo because its a quick way
of recaping some of the taught subjects already in lecture!
15:42 » I think presemo worked really well :) also, it was nice
to see the catalysts
15:42 » A well balanced lecture. Just the right amount of new
information.
15:43 » The lecturer is very involved in the course that is why
it is interesting. The quiz helps to understand the lecture.
L3C Final questions: Your overall grade to today's lecture
8 participants
(1) 5 - superb, loved it!
(7) 4 - very good, enjoyed it
(0) 3 - good - average at Aalto University
(0) 2 - not so great, could have been more interesting
(0) 1 - poor, truly a waste of my time
L3C Final questions: I learned something new today
8 participants
(8) Yes
(0) No
(0) Maybe
23.1.2019
64
