catal5010145 CHEM-E1130 Catalysis Deactivation of solid ... · 3. describe and apply selected catalyst characterization methods 4. explain why and how catalysts deactivate and how

CHEM-E1130 Catalysis

Deactivation of solid

heterogeneous catalysts

Prof. Riikka Puurunen

13.2.2019

https://doi.org/10.3390/catal5010145

https://doi.org/10.3390/catal5010145

Contents (+ 3 x Presemo)

• MyCo feedback quick view

• Introduction to deactivation of solid heterogeneous catalysts

• Deactivation mechanisms:

• poisoning,

• fouling/coking,

• sintering,

• others

• Prevention of catalyst decay & regeneration

• Conclusion / Take-home message

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 5:I like – I wish

(Many positive responses with similar message:)

• ” Thank you for organizing the guest lecture. I had no idea Wärtsilä had

anything to do with industrial chemistry, and I truly learned a lot. ”

• ” I really liked the last lecture (Wärtsilä). It was interesting to hear real life

examples of the processes that they use. Most interesting lecture so far!”

• “I wish that the proposed exam questions would be published so that

students could use them as a review material while studying for the exam.

Questions make you think more than just reading the slides making the

studying more efficient.”

• ” I wish also that there would be less true/false questions because they are

sometimes a little hard to interpret. For example, is the certain word used

there on purpose to make the sentence tricky or not.”

+ much more excellent feedback Thank You!

Feedback will help to develop the course (slides, quizzes…) further


• ” I'm still amazed how well the professor reads the feedback and actually takes

some actions to improve the course constantly. I highly appreciate that!”

• “I liked the fact that other characterization techniques were presented to us. …

Although, I think I have to go through the slides few times to understand the topic

properly, because I have never seen the equipment or used one..which would

probably help students to understand these techniques better.”

• ” I wish there would be a small summary of each technique with their main

differences. This lecture was pretty heavy and it is easy to mix up all the different

techniques.”

• ” I wish we could make our own catalysts or use those named techniques we have

gone through or do something related.”

• “Would it be possible to have a recap lecture before the exam or also in the middle

of the course? Just an idea that came to my mind.” I am thinking of this, for the

last lecture of the course




• ” I like the _Abbreviations_ slide, where all the abbreviations were easily

found.”

• ” I found this course <lecture> more difficult to understand than the

previous one because I have some difficulties to know what is really

important. It is better when there is the take-home message”

• “… Really hard to follow because there was so many technical words in

the slides. Although the emissions itself are quite interesting and there was

some good points in the lecture, but some of the more detailed stuff was

hard to follow. Maybe the slides could be improved to be more clearly?”

(several similar feedback items)




• ” I liked the clear comparison between Raman and Infrared.”

• ” I think that this course might be the best organized course I have taken at

Aalto.”

• ” The lecture material and quiz were really good.”

• “I wish next year the adsorption exercise can be returned as excel. Can't

see any point in terms of learning that I had to transfer my numbers to

word.”

• ” Maybe there could be more calculation exercises?”

• ” The link on the slide 27 did not work on my computer.”



response ”Link works if you upload Adobe Flash when the page is interactive”

Material

Lecture based on the review (+ 2017 lecture by Dr. Reetta Karinen):

Morris D. Argyle and Calvin H. Bartholomew: Heterogeneous Catalyst

Deactivation and Regeneration: A Review, Catalysts 5 (2015) 145-269;

DOI:10.3390/catal5010145 (open access).

• Earlier review: C. H. Bartholomew, Mechanisms of catalyst deactivation,

Appl. Catal. A 212 (2001) 17–60. DOI: 10.1016/S0926-860X(00)00843-7

Additional reading for the interested:

• F. S. Fogler, Elements of chemical reaction engineering, 4th ed. Pearson

2006, Chapter 10.7

http://dx.doi.org/10.3390/catal5010145

https://doi.org/10.1016/S0926-860X(00)00843-7

Let’s go to Presemo

Go to:

http://presemo.aalto.fi/cheme1130lect8

http://presemo.aalto.fi/cheme1130lect8/screen

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Deactivation of solidheterogeneouscatalysts: general

Catalyst deactivation

• Catalyst deactivation: the loss over time of catalytic

activity and/or selectivity

• Catalyst deactivation is a great problem in industrial

catalytic processes: costs $B’s per year

• All catalysts deactivate, in scale seconds to decades

• Poor operation conditions can lead to carbon

filaments and catastrophic failure in hours

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Morris D. Argyle and Calvin H. Bartholomew: Heterogeneous Catalyst Deactivation and

Regeneration: A Review, Catalysts 5 (2015) 145-269; DOI:10.3390/catal5010145 (open access).


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Ex

am

ple

s


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Ex

am

ple

s


Poisoning

• “Poisoning is the strong chemisorption of reactants,

products, or impurities on sites otherwise available

for catalysis.”

• Whether a species acts as a poison depends upon its

adsorption strength relative to the other species

competing for catalytic sites.

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• Example: oxygen can be a reactant in partial oxidation of

ethylene to ethylene oxide on a silver catalyst

and a poison in hydrogenation of ethylene on nickel.

• In addition to physically blocking of adsorption sites, adsorbed

poisons may induce changes in the electronic or geometric

structure of the surface.

• Poisoning may be reversible or irreversible (typically it is

irreversible).

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Conceptual two-dimensional model of poisoning by sulfur

atoms of a metal surface during ethylene hydrogenation




Five poisonous effects

Adsorbed poison:

1. Physically blocks several

adsorption/reaction sites on the metal surface.

2. Through its strong chemical bond, electronically modifies its nearest

neighbor metal atoms (and possibly further), modifying their abilities

to adsorb and/or dissociate reactant molecules.

3. Potential restructuring of the surface, possibly causing dramatic

changes in catalytic properties, for reactions sensitive to surface

structure.

4. Blocks access of adsorbed reactants to each other

5. Prevents or slows the surface diffusion of adsorbed reactants.

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Poisoning of Ni catalysts by S has beenwidely studied

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At saturation always about 8 S/nm2

1 nm-2 = 1014 cm-2


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• Selective poisoning: the most

active sites are blocked at low

poison concentrations

• Antiselective poisoning: sites

of lesser activity are blocked

first

• Non-selective poisoning: loss

of activity proportional to

poison concentration


Highly selective poisoning: methanation on Ni, Co, Fe and Ru catalysts

• Sulfure tolerance extremely low as H2S

concentration on ppb level

• Sulfur resistance depends on catalyst

metal and composition, reaction

conditions…

• It is possible to improve sulfur

resistance with additives or promoters

• e.g. Mo or B on Ni, Co or Fe

Fig. 8. Relative steady-state methanation activity profiles for Ni

(•), Co (▵), Fe (□), and Ru (○) as a function of gas phase H2S

concentration. Reaction conditions: 100 kPa; 400°C; 1%

CO/99% H2 for CO, Fe and Ru; 4% CO/96% H2 for Ni [26].

Figure: C. H. Bartholomew, Mechanisms of catalyst deactivation, Appl. Catal.

A 212 (2001) 17–60 and ref’s therein.

Poisoning

Poisoning is sometimes used to improve the system, e.g.

selectivity

Naphta catalytic reforming Pt catalyst in oil refining:

• Pre-sulfidation to prevent unwanted cracking reactions

Diesel emission catalysts

• V2O5 added to Pt to suppress SO2 oxidation to SO3

Fouling, coking

Argyle & Bartholomew:

• Fouling is the physical (mechanical) deposition of species

from the fluid phase onto the catalyst surface, which results

in activity loss due to blockage of sites and/or pores. In its

advanced stages, it may result in disintegration of catalyst

particles and plugging of the reactor voids.

• Important examples include mechanical deposits of carbon and

coke in porous catalysts, although carbon- and coke-forming

processes also involve chemisorption of different kinds of carbons

or condensed hydrocarbons that may act as catalyst poisons.

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Argyle & Bartholomew:

“The definitions of carbon and coke are somewhat arbitrary and by

convention related to their origin.”

• Carbon is typically a product of CO disproportionation, while

• coke is produced by decomposition or condensation of

hydrocarbons on catalyst surfaces and typically consists of

polymerized heavy hydrocarbons.

• A number of books and reviews treat the formation of carbons and

coke on catalysts and the attendant deactivation of the catalysts

[1,4,57–62].

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Analogously to structure-sensitive and structure-insensitive reactions…• In coke-sensitive reactions, unreactive coke is deposited on active

sites, leading to activity decline

• Examples: catalytic cracking and hydrogenolysis

• in coke-insensitive reactions, relatively reactive coke precursors

formed on active sites are readily removed by hydrogen (or other

gasifying agents).

• Examples: Fischer–Tropsch synthesis, catalytic reforming, and methanol synthesis

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Mechanism of formation?

• metal catalyst?

• metal oxide catalyst (or sulfide, sulfides being similar

to oxides)?

• Thermal, radical-based process?

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Figure 10. Conceptual model of fouling, crystallite encapsulation, and pore

plugging of a supported metal catalyst owing to carbon deposition.


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Figure 11. Formation, transformation, and gasification of carbon on nickel (a, g,

s refer to adsorbed, gaseous, and solid states respectively).



Polymeric

films/filamets

graphitic

vermicular

Atomically

adsorbed

carbide

(gasified)


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Figure 12. Formation and transformation of coke on metal surfaces (a, g, s refer to

adsorbed, gaseous, and solid states respectively); gas phase reactions are not

considered.


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Figure 13. Electron micrograph of 14% Ni/Al2O3 having undergone extensive carbon

deposition during CO disproportionation at 673 K, PCO = 4.55 kPa (magnification of

200,000). Courtesy of the BYU Catalysis Laboratory.



Vermicular

carbon

Cv


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On oxides and sulfides: cokeformation catalyzed by acid sites• Coke precursors: typically olefins or aromatics

• Dehydrogenation and cyclization reactions of carbocation

intermediates formed on acid sites lead to aromatics, which react

further to higher molecular weight polynuclear aromatics that

condense as coke

• Because of the high stability of the polynuclear carbocations, they

can continue to grow on the surface for a relatively long time

before a termination reaction occurs through the back donation of

a proton

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PAH, polyaromatic hydrocarbon


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Figure 16. Schematic of the four possible modes of deactivation by carbonaceous deposits in HZSM-5:

(1) reversible adsorption on acid sites, (2) irreversible adsorption on sites with partial blocking of pore

intersections, (3) partial steric blocking of pores, and (4) extensive steric blocking of pores by exterior

deposits.




• the order of reactivity for coke formation: polynuclear aromatics >

aromatics > olefins > branched alkanes > normal alkanes.

• In coking reactions involving heavy hydrocarbons (complex);

different kinds of coke may be formed and they may range in

composition from CH to C

• In bifunctional catalysts, different types of coke on metal &

support.

• ”Soft coke” on the metal sites (”high” H/C ratio)

• ”Hard coke” on the acid sites (”low” H/C ratio)

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Sintering

Sintering of the active component

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(Figure 17.) Two

conceptual models for

crystallite growth due to

sintering by

(A) atomic migration or

(B) crystallite migration.



(Also possible: C: vapor transport, at high temperatures, e.g. RuO4)


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Figure 18. Normalized nickel surface area (based on H2 adsorption) versus time

data during sintering of 13.5% Ni/SiO2 in H2 at 650, 700, and 750 °C. Reproduced

from [108]. Copyright 1983, Elsevier.


• sintering rates are

significant above the

Hüttig temperature

(0.3Tmp) and

• very high near the

Tamman temperature

(0.5Tmp)

• New surface compounds

may accelerate sintering

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• sintering rates are

significant above the

Hüttig temperature

(0.3Tmp) and

• very high near the

Tamman temperature

(0.5Tmp)

• New surface compounds

may accelerate sintering

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Sintering of the porous support

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Figures: J. T. Richardson Principles of catalyst

development, Plenum press, 1989, p. 194, 196.

• Sintering is irreversible

• ”Sintering is more easily

prevented than cured”

Sintering of single-phase oxide carriers, five processes:(1) surface diffusion,

(2) solid-state diffusion,

(3) evaporation/condensation of volatile atoms or molecules,

(4) grain boundary diffusion, and

(5) phase transformations.

• “In oxidizing atmospheres, γ-alumina and silica are the most

thermally stable carriers;

• in reducing atmospheres, carbons are the most thermally stable

carriers.”

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• Additives and impurities affect the thermal properties of carriers by

occupying defect sites or forming new phases.

• Alkali metals accelerate sintering; while

• calcium, barium, nickel, and lanthanum oxides form thermally stable spinel phases with alumina.

• Steam (H2O) accelerates support sintering by forming mobile

surface hydroxyl (-OH) groups.

• Dispersed metals in supported metal catalysts can also accelerate

support sintering; for example, dispersed nickel accelerates the

loss of Al2O3 surface area in Ni/Al2O3 catalysts.

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Approximate surface areas of aluminaphases

Phase specific surface area, m2/g

Boehmite 400

Gamma-alumina 200

Sigma-alumina 120

Theta-alumina 50

Alpha-alumina 1

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Effects of sintering on catalytic activitySpecific activity (based on catalytic surface area) can

• Increase or decrease with increasing metal crystallite size

• Structure-sensitive reactions

• Examples: ethane hydrogenolysis, ethane steam reforming

• Be independent of metal crystallite size

• Structure-insensitive reactions

• Decrease in mass-based activity proportional to the decrease in metal surface area

• Example: CO hydrogenation on supported Co, Ni, Fe, Ru

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Prevention of catalyst decay & regeneration

Prevention of catalyst decayIt is often easier to prevent than cure catalyst deactivation

• Many poisons and foulants can be removed from feeds using

guard beds, scrubbers, and/or filters.

• Fouling, thermal degradation, and chemical degradation can be

minimized through careful control of process conditions,

- e.g., lowering temperature to lower sintering rate or

- adding steam, oxygen, or hydrogen to the feed to gasify carbon or coke-forming precursors.

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Multilayer strategy

in three-way

catalysts

(Bartholomew view)


Figure 34. Conceptual design (by C. H. Bartholomew) of an

advanced three-way catalyst for auto emissions control. Catalyst

layer 1 is wash-coated first onto the monolithic substrate and

consists of (a) well-dispersed Pd, which serves to oxidize

CO/hydrocarbons and to reduce NO and (b) CeO2/ZrO2 crystallites

(in intimate contact with Pd), which store/release oxygen

respectively, thereby improving the performance of the Pd. Catalyst

layer 2 (added as a second wash coat) is a particle composite of

Rh/ZrO2 (for NO reduction) and Pt/La2O3–BaO/Al2O3 (with high to

moderately-high activity for oxidation of CO and hydrocarbons). A

thin (50–80 μm) coat of Al2O3, deposited over catalyst layer 2, acts

as a diffusion barrier to foulants and/or poisons. Both the Al2O3

layer and catalyst layer 2 protect the sulfur-sensitive components of

catalyst layer 1 from poisoning by SO2.

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Regeneration of Poisoned Catalysts

• Supported Ni-based steam reforming catalysts (low surface

area): up to 80% of sulfur can be removed, 700C in steam

• (High-surface-area catalysts cannot tolerate the same

treatment without sintering)

• Regeneration of sulfur-poisoned noble metals in air rather

than steam, although this is frequently attended by sintering

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Regeneration of Catalyst Deactivated by Coke or Carbon• Carbonaceous deposits can be removed by gasification

• order of decreasing reaction rate of O2 > H2O > H2

• Rates of gasification of coke or carbon are greatly

accelerated by the same metal or metal oxide catalysts upon

which carbon or coke deposits.

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Regeneration of Catalyst Deactivated by Coke or CarbonExamples:

• metal-catalyzed coke removal with H2 or H2O can occur at a

temperature as low as 400 °C;

• β-carbon can be removed with H2 in a few h at 400–450 °C

and with oxygen in 15–30 min at 300 °C.

• Potential hot spots in the catalyst bed with oxygen

• Gasification of more graphitic or less reactive carbons or

coke species in H2 or H2O may require temperatures as high

as 700–900 °C,

• catalyst sintering.

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Redispersion of Sintered Catalysts

• Extensive patent literature;

mechanistic research called for

Example: supported Pt/alumina

• In catalytic reforming of

hydrocarbons: 1-nm clusters to

5–20-nm crystallites

• Redispersion by

“oxychlorination:” HCl or CCl4at 450–550 °C in 2–10%

oxygen for 1–4 h

• Dispersion from 0.25 to 0.81

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Summary

(not for exam)

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Figure: J. T. Richardson Principles of catalyst

development, Plenum press, 1989, p. 187.

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Extra material – some terminology


…to conclude…

Take-home message

Deactivation in nutshell

• Three main types: Poisoning, coking/fouling, sintering

• Catalyst deactivation is more easily prevented than cured

• Preventing/mitigating poisoning: purification of feed, guard beds

• The chemical structures of cokes or carbons formed in catalytic

processes vary widely with reaction type, catalyst type, and

reaction conditions.

Presemo, feedback questions

Go to:



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https://www.chronicle.com/interactives/is-email-making-professors-stupid

If you need to contact for the course through the assistents, please

https://www.chronicle.com/interactives/is-email-making-professors-stupid

Additional info

Once upon a time…… the professor studied deactivation CrOx/Al2O3 dehydrogenation catalysts, operando methods, Leuven

• (Coking) Monitoring chromia/alumina catalysts in situ during propane

dehydrogenation by optical fiber UV-visible diffuse reflectance spectroscopy

Puurunen, R. L., Beheydt, B. G. & Weckhuysen, B. M. 2001 In : JOURNAL

OF CATALYSIS. 204, p. 253-257; https://doi.org/10.1006/jcat.2001.3372.

• (Sintering) Spectroscopic Study on the Irreversible Deactivation of

Chromia/Alumina Dehydrogenation Catalysts Puurunen, R. & Weckhuysen,

B. 2002 In : JOURNAL OF CATALYSIS. 210, p. 418-430;

https://doi.org/10.1006/jcat.2002.3686.

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https://research.aalto.fi/portal/riikka.puurunen.html

https://research.aalto.fi/en/journals/journal-of-catalysis(96ae7541-26c4-4efb-aee4-7f5b0b613bc9)/publications.html

https://doi.org/10.1006/jcat.2001.3372




J. Catal. 2002, in situUV-vis fiberoptics

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Spectroscopic Study on the Irreversible Deactivation of Chromia/Alumina Dehydrogenation

Catalysts Puurunen, R. & Weckhuysen, B. 2002 In : JOURNAL OF CATALYSIS. 210, p. 418-

430; https://doi.org/10.1006/jcat.2002.3686.




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Tables 18-20, Argyle & Bartholomew: recommended reading for doctoral students


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catal5010145 CHEM-E1130 Catalysis Deactivation of solid ... · 3. describe and apply selected catalyst characterization methods 4. explain why and how catalysts deactivate and how