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Catalysts - KNCV

Catalysts

how to get them working

and keep them active

Hans Niemantsverdriet

Courtesy Süd-Chemie


Catalysts

how to get them working

and keep them active

Catalysis and Catalysts

Activating a catalyst

reduction

sulfidation

Keeping a catalyst active

the Cobalt GTL catalyst

The important role

of characterization

techniques:

TPR

XRD

XPS

XANES

TEM

Conclusions


What is a catalyst

Catalysts

• increase the rate of a reaction

• without being consumed in the process

ü offer alternative, energetically

favorable pathways for reactions

ü enable reactions to occur under

industrially achievable conditions

supported

catalyst

catalyst

pellets and

extrudates

Courtesy

Haldor Topsoe

ü allow selective production routes

without or with less undesirable

byproducts

ü are the work horses of the

chemical industry

ü are the key enablers for

sustainable (green)production


What is Catalysis

A

B

separation

P

catalyst

bonding

P

catalyst

A

B

reaction

catalyst

• Catalysis is a cycle of elementary steps (at least three)

• Catalytic sites are regenerated


CO Oxidation over a catalyst

The potential energy diagram


10 mm

1 nm

shaped catalyst

particles

catalytic

surface

1 m

catalyst bed

in a reactor

catalytically active

particles on a support

1 µ m

microscopic mesoscopic macroscopic


The Importance of Catalysis

• 85-90% of the products of the chemical industry is

made in catalytic processes

• these products and activities account for roughly

10-15% of the Dutch GDP

• fuels and energy

bulk and fine chemicals

environmental pollution control

Catalysts minimize byproducts and waste


Catalyst Preparation: Pore Volume Impregnation

Porous filled with particles precipitate

support solution during drying

Typical silica:

pore volume of 0.5 ml/g

specific area of 300 m 2 /g

metal loading 0.5 - 15 wt%


Shaped catalysts

pellets extrudates fused catalyst

Courtesy of

Haldor Topsoe A/S


Catalyst Characterization

What do we want to know about a supported catalyst

Composition

XPS, XANES, XRD

ICP, AAS

Surface Composition

LEIS, XPS, SIMS

Particle size

Electron Microscopy

H2 chemisorption

XRD line broadening

Surface Area

Total: BET

Metal: H2 or CO chemisorption

Pore size distribution:

Hg porosimetry

Morphology

Particles: TEM

Overall: SEM

Adsorbed Gases

FTIR, DRIFTS, TPD

Structure

XRD

XPS, EXAFS,TEM

Degree of Reduction

TPR, XPS , XANES

Concept, to be completed

© J.W. Niemantsverdriet,

TU/e, Eindhoven, The Netherlands


Catalyst Preparation:

Impregnation, Drying, Calcination, Reduction

Metal Catalyst (e.g. Co):

Impregnation:

Precipitation:

Calcination:

Reduction:

Co-nitrate in water

Co-(oxy)-hydroxide

Co-oxide

Co-metal

Follow reduction of calcined catalyst:

• TPR

• XRD

• XANES


XRD: X-ray Diffraction

X-rays

randomly oriented particles

Bragg’s Law

d

θ d sinθ

nλ = 2 d sinθ

2 θ


X-ray Diffraction of Co/SiO 2 Reduction

Co 3 O 4

CoO

Co

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Geus, J.W. Niemantsverdriet

J. Catal. 239 (2006) 326-339


X-ray absorption in a free atom

absorption

edge

binding energy

like in XPS


X-ray absorption by atoms in solids

XANES: X-ray absorption near-edge structure

EXAFS: Extended X-ray absorption fine structure


XANES of Cobalt Phases

XANES:

/Al 2 O 3

53% Co 0

• phase identification

• oxidation state

• in situ measurement

• at synchrotron

LURE, ORSAY

80% Co 0

85%

88%

89%

Abdool Saib, Armando Borgna

LURE, ORSAY

• quantitation

straightforward


XANES of Co/SiO 2 Reduction

Co 3 O 4

CoO

Co

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Geus, J.W. Niemantsverdriet

J. Catal. 239 (2006) 326-339


TPR of Co/SiO 2 Reduction

Co 3 O 4

CoO

Co

Co 3 O 4

CoO

Co

Co 3 O 4

CoO

Co

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Geus, J.W. Niemantsverdriet

J. Catal. 239 (2006) 326-339


TEM of Co/SiO 2 (after reduction – ex situ)

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Geus, J.W. Niemantsverdriet

J. Catal. 239 (2006) 326-339


Co/SiO 2 Reduction:

Reduction in two stages:

Co 3 O 4

CoO Co

Confirmed by in situ techniques

TPR, XRD, XANES

Small particles reduce slower

than large particles

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Geus, J.W. Niemantsverdriet

J. Catal. 239 (2006) 326-339


Oil Refinery

gas

LPG

atmospheric

distillation

hydrotreating

naphta

gasoline

crude

oil

kerosene

gas oil

reforming

kerosene

diesel

vacuum

gas oil

hydrocracking

atmospheric

residue

hydrotreating

fcc

vacuum

distillation

vacuum

residue

residue

conversion

low sulfur

fuel oil

Adapted from J.W. Gosselink, CaTTech 4 (1999)


Schuit Institute of Catalysis

Hydrodesulfurization

catalysis

thiophene

H

H

MoS 2


Schuit Institute of Catalysis

Hydrodesulfurization

catalysis

thiophene

MoS 2


Schuit Institute of Catalysis

Hydrodesulfurization

catalysis

H

H

MoS 2


Schuit Institute of Catalysis

Hydrodesulfurization

catalysis

butene

MoS 2


Hydrodesulfurization Catalysts:

Impregnation, Drying, Calcination, Sulfidation

Sulfide Catalyst (e.g. NiWS 2 ):

Impregnation: Tungsten and Nickel salts in water

Calcination: ±mixed oxide phase

Sulfidation: NiWS 2

Follow sulfidation process by XPS


X-ray Photoelectron Spectroscopy (XPS)

X-rays

photo electrons

photoelectron

sample

E b = hv – E

binding

k

energy

X-ray

energy;

known

kinetic

energy

measured

E k

Binding energies are

X-ray

photon;

energy


ϕ

E b

0

• element specific

• sensitive to

• oxidation state

• electronegativity

XPS is characteristic of the

Core level,

e.g. C 1s, Fe 2p or Pt 4f

The photo emission process

surface region

Vacuum technique!


X-ray Photoelectron Spectrometer

XPS (2008)

chemical mapping

depth profiling

in situ capabilities

Single-crystal surface science spectrometer

- TPD, RAIRS, LEED, XPS (2006)

- Kelvin Probe / work function measurement


Sulfidation of WO 3

41

39

37

WO 3

29

Sulfidation Temperature

650 0 C

W 4f

1. Reduction to W 5+

2. O-S Exchange

at Reduced Sites

3. WS 2 above 250°C

350 0 C

300 0 C

250 0 C

200 0 C

150 0 C

100 0 C

XPS Intensity (a.u)

Compare MoO 3 :

1. O-S Exchange

2. Internal redox:

2 Mo 6+ OS →Mo 5+ OS 2

2-

Mo 5+

Th. Weber et al, J. Phys. Chem. 100 (1996)

3. MoS 2 above 200°C

50 0 C

unsulfided

Sulfidation WO 3

is slow !

35

33

31

Binding Energy (eV)

A.J. van der Vlies, G. Kishan, J.W. Niemantsverdriet, R. Prins, Th. Weber, J Phys Chem B106 (2002) 3449


Sulfidation of NiW/SiO 2 calcined catalysts

Sulfidation

Temperature

W 4f

Sulfidation

Temperature

Ni 2p

400 0 C

400 0 C

300 0 C

200 0 C

300 0 C

200 0 C

150 0 C

150 0C

100 0 C

50 0 C

100 0 C

50 0 C

25 0 C

unsulfided

25 0 C

unsulfided

48

46

44

42

40

38

Binding Energy (eV)

36

34

32

30

894

889

884

879

874

869

864

859

Binding Energy (eV)

Ni and W form sulfides in separate temperature regions

unfavorable for NiWS formation

G. Kishan, L. Coulier, V.H.J. de Beer, J.A.R. van Veen, J.W. Niemantsverdriet,

Journal of Catalysis 196, 180–189 (2000)

854

849

844

839


What is the best way to make

the active phase

S

Co/Ni, Mo/W

S

Ideal recipe:

1) form WS 2 particles & keep Ni oxidic

2) let Ni sulfide form directly on the edges

However, the natural order of sulfidation is: Ni first, W last


Use strong

chelating agent

for Ni:

CyDTA

1,2 - cyclohexane diamine

N,N,N’,N’ - tetra

acetic acid

Ni


Sulfidation of

NiW-CyDTA/SiO 2

NiW-CyDTA/SiO 2 /Si(100)

NiW-CyDTA/SiO 2 /Si(100)

NiW-CyDTA/SiO 2 /Si(100)

NiW-CyDTA/SiO 2 /Si(100)

Sulfidation

Sulfidation

W 4f

Ni 2p

Temperature Ni 2p N 1s Temperature

Sulfidation W 4f S 2p

400 0 C

Sulfidation

Temperature

Temperature

N 1s

400 0 C

350 0 C

350 0 C

300 0 C

400 0 C

350 0 C

400 0 C

S 2p

300 0 C

250 0 C

200 0 C

150 0 C

250 0 C

200 0 C

300 0 C

250 0 C

200 0 C

350 0 C

300 0 C

100 0 C

unsulfided

150 0 C

100 0 C

unsulfided

150 0 C

100 0 C

unsulfided

250 0 C

200 0 C

150 0 C

100 0 C

unsulfided

880

875

870

865 860 855

Binding Energy (eV)

850

845 406

404

402 400

Binding Energy (eV)

398

39644

40 38 36

Binding Energy (eV)

163 161

Binding Energy (eV)

Ni converts to sulfide when CyDTA decomposes,

at temperatures where WS 2 has been formed

G. Kishan, L. Coulier, V.H.J. de Beer, J.A.R. van Veen, J.W. Niemantsverdriet, Chem. Comm. (2000) 1103

42

34

32

30167

165

159

157


G. Kishan, L. Coulier, V.H.J. de Beer, J.A.R. van Veen, J.W. Niemantsverdriet, J. Catal. 2001

Activity of NiW/SiO 2 in Thiophene Desulfurization

1.6

Ni = 4 at/nm 2, W = 6 at/nm 2

1.4

1.2

1-butene

t-2-butene

c-2-butene

1.0

Yield (%)

0.8

0.6

0.4

0.2

0.0

W /SiO 2

calcined

NiW /SiO 2

uncalcined

NiW /SiO 2

calcined

NiW /SiO 2

NTA

NiW /SiO 2

EDTA

NiW /SiO 2

CyDTA

Key: Retard Ni Sulfidation!


Gas-To-Liquids process (GTL)

Sasol slurry phase distillate process

oxygen

80% Sasol SPD Diesel

" Most important product

" High performance fuel

" Low emissions

" Environmentally friendly

natural gas

steam

hydrocarbons

20% Sasol SPD Naphtha

" Low octane number

" Mostly alkanes

" Excellent feedstock for

chemicals

Synthesis gas

Fischer-Tropsch

process


Long term catalyst performance testing

under realistic Fischer-Tropsch synthesis

100 bbl/day slurry bubble column reactor, 230 °C, 20 bar, H 2 +CO conversion: 50-70 %,

feed gas: 50 vol. % H 2 , 25 vol. % CO, P H2O = 4-6 bar

1.0

relative activity

RIAF

0.8

0.6

0.4

0.2

0.0

0 10 20 30 40 50 60

Time on line (days)

Time on line (days)

Cobalt is expensive;

need to maximize catalyst life


XANES of wax coated/protected catalysts

from FT demonstration reactor

A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Niemantsverdriet

Appl. Catal. A: General 312 (2006) 12

/Al 2 O 3

53% Co 0

80% Co 0

85%

88%

89%

LURE, ORSAY

LURE, ORSAY

progressive reduction of unreduced cobalt during FTS


hydrogen resistant carbon (wt%)

‘polymeric carbon’ versus time on

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

stream

Polymeric carbon

amount

How much

If dispersion Co is 16% :

2.0 wt% C = 4 C atoms/Co surface atom

however, carbon is also on the support

0 20 40 60 80 100 120 140 160 180

Time on stream (days)

D.J. Moodley, J. van de Loosdrecht , A.M. Saib, M.J. Overett, A.K. Datye, J.W. Niemantsverdriet

Appl. Catal. 354 (2009) 102-110


What causes the deactivation

Long term catalyst performance testing

of Co FTS catalysts

100 bbl/day slurry bubble column reactor, 230°C, 20 bar, H 2 +CO conversion: 50-70 %,

feed gas: 50 vol. % H 2 , 25 vol. % CO, P H2O = 4-6 bar

RIAF

1.0

Normalized activity

0.8

0.6

0.4

0.2

Co/Al 2 O 3

0.0

0 10 20 30 40 50 60

Time on Time stream on line (days)

Deactivation mechanisms:

• Oxidation by water

• Cobalt-aluminate formation

• Poisoning (S, HCN,NH3)

• Sintering

• Carbon deposition

D.J. Moodley, J. van de Loosdrecht , A.M. Saib, M.J. Overett, A.K. Datye, J.W. Niemantsverdriet

Appl. Catal. 354 (2009) 102-110

J. van de Loosdrecht et al., Catal Today 123 (2007) 293


Regeneration: FT activity recovery

1.0

20 wt% Co/Al 2 O 3

0.8

RIAF

0.6

0.4

0.2

0.0

Recovery of activity possible

0 10 20 30 40 50 60

Time on line (days)

A.M. Saib, D.J. Moodley, I.M. Ciobîcă, M.M. Hauman,

B.H. Sigwebela, C.J. Weststrate, J.W. Niemantsverdriet,

J. van de Loosdrecht, Catal. Today (2010),


Mechanism redispersion of cobalt

HRTEM of Co/SiO 2 /Si(100) flat model catalyst

41

Reduced Oxidized Re-reduced

" Hollow spheres formed by Kirkendall effect

" Outward diffusion of cobalt is faster than inward diffusion of oxygen

" Vacancies created during metal to oxide transition coalesce in center of particle

A.M. Saib, D.J. Moodley, I.M. Ciobîcă, M.M. Hauman, B.H. Sigwebela, C.J. Weststrate,

J.W. Niemantsverdriet, J. van de Loosdrecht, Catal. Today (2010)


Requirements of a successful catalyst

• High activity per unit volume in the reactor

• High selectivity at high conversion; no byproducts

• Long life time

• Regenerable

• Reproducible preparation & activation

• Thermal stability (no sintering)

• High mechanical strength

• High attrition resistance


Acknowledgements

Hydrodesulfurisation

Leon Coulier

Armando Borgna

Gurram Kishan

Thomas Weber

Hannie Muysers

San de Beer

J A Rob van Veen

TU/e

Shell, TU/e

Fischer-Tropsch

Cobalt and Iron

Abdool Saib

Denzil Moodley

Deshen Kistamurthy

Jan van de Loosdrecht

Kees-Jan Weststrate

Prabashini Moodley

Emad Dad

Peter C Thüne

and many visitors

Bimetallics and Noble Metals:

Lizette Erasmus, Jannie Swarts

Financial Support: Sasol Technology, Foundation Technical Sciences STW ;

Netherlands Research Organisation NWO, TU/e


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