Post on 21-Mar-2022
J. Sehested
Haldor Topsoe A/S
CINF Summer School 2016, Kysthusene, Tinkerup Strandvej 8a,Gilleleje
Fundamental andIndustrial aspects ofheterogeneous catalysis
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From nano to mega and back again
Reactor1m
Catalyst from0,001m = 1mm
Pore structure0,000000001m = 1nm
Active phase0,0000000001m = 1Å
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Our founder, Dr. Haldor Topsøe, had a strong passionfor science and determination to prove it could make a difference
Haldor Topsøe A/S in briefEstablished in 1940 by Dr. Haldor Topsøe.Private 100% family-owned company.2,600 employees in 10 countries.Headquarters in Copenhagen, Denmark.Production in Denmark, USA, China, and Brazil.Spends around 10% of revenue on R&D.Revenue 2015 ~850 M$
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Fundamental and industrial aspects of heterogeneous catalysis
• Industrial methanol production – equipment for producing synthesis gas
• Properties of nickel steam reforming catalysts• Sintering (stability of Ni particles)• Carbon formation over Ni catalysts
• Methanol synthesis catalysts:• How Zn helps Cu make methanol
• Conclusions
Industrial methanol production
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TODAY
FUTURE
Why methanol?!Essential bulk chemical – C1 building block
2015 demand: 71.6 MMT
2019 demand: >90 MMT
Source: IHS, 2015
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Typical methanol process ~ 2500 MTPDSteam
Pre-reformer
Secondaryreformer
Steam
Steam
Oxygen
Makeupcomp.
Light ends to fuel
Methanolreactor
Water
Rawmethanol
Raw methanol storage
Condensate
Steam reformer
Sulphur removal
Hydrogenator
Naturalgas
Productmethanol
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Pre-reformer; Primary reformer; Secondary reformer; ATR
Process Gas
O2 / Air
CH4 + H2O CO + 3H2 (-DH0298 = -206 kJ/mol)
CnHm + n H2O n CO + (n+m/2) H2 (-DH0298 < 0)
CO + H2O CO2 + H2 (-DH0298 = 41 kJ/mol)
CH4 + 1.5O2 CO + 2H2O (-DH0298 = 520 kJ/mol)
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Steam reforming and methane conversion
400 500 600 700 800 900 400 500 600 700 800 900
S/C = 5.0S/C = 2.5S/C = 1.0
S/C = 5.0S/C = 2.5S/C = 1.0
Reforming equilibrium temperature, °C
0
20
40
60
80
100Methane conversion, %
1 bar abs 20 bar abs
1000
CH4 + H2O CO + 3H2 (-DH0298 = -206 kJ/mol)
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Adiabatic pre-reforming
• Temperatures typically 400-600°C• Feed flexibility – conversion of HHC• Reducing size of down stream reformers• Removes traces of sulphur
Natural Gasand Steam
CH4, CO, CO2, H2
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Autothermal reforming/secondary reforming
Combustion zoneCH4 + 1½O2 CO + 2H2O
Thermal and catalytic zonesCH4 + H2O CO + 3H2CO + H2O CO2 + H2
Air or Oxygen
Natural gas,or reformed gas+ steam
burner
Synthesis gas
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The heart in steam reforming is the nickel catalysts
Ni(111),0.20nm
Ni(200),0.18nm
CnH2n+2 + nH2O nCO + (2n + 1) H2
CH4 + H2O CO + 3H2
CO + H2O CO2 + H2
Ni
Ni
Ni
ProcessGas
O2 /Air
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Fundamental and industrial aspects of heterogeneous catalysis
• Industrial methanol production – equipment for producing synthesis gas
• Properties of nickel steam reforming catalysts• Sintering (stability of Ni particles)• Carbon formation over Ni catalysts
• Methanol synthesis catalysts:• How Zn helps Cu make methanol
• Conclusions
Industrial methanol production
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Environmental TEM (ETEM)
Philips CM300-ST FEG
gas path:x = 5.4mm
x
FEG
Sample
Detectors- Tietz F114 CCD- GIF2000
Gas handling
QMS
FEG
Sample
Gas handling
Aberrationcorrector
Detectors-US1000 & Tridiem 863
§ 1-20mbar, 10-50Nml/min, 600-900oC
FEI Titan 80-300 Cs-corr
Adv. Catal. 50, 77 (2006)
4mm
S. Helveg
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Sintering of metal catalysts
Ni/MgAl2O4
H2O:H2 = 1:1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400 500 600 700 800
Time (hours)
Rel
ativ
eN
iare
a
800 °C
650 °C
Nickel steam reforming catalysts
H2O:H2 = 1:1, 30 bar g
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Sintering in steam reforming
Tubular reformingPrereforming Autothermal reforming
400-600°C 500-900°C 900-1200°CHigh steam partial pressures
2 mbar H2,750°C, 5h
2 mbar H2:H2O=1:1750°C, 5h
2 mbar H2,500°C, red.
T. Hansen PhD thesis (2006)Ni/MgAl2O4
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Thermal stability of nickel catalysts
Sintering
Ni MgAl2O4 orAl2O3
Nickel steam reforming catalystsdeactivates over time due tothermal sintering
H2, 700°CNi/MgAl2O4
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Is it possible to reduce sintering?
After aging at 850°C, 30 bar g and H2O/H2 = 6 during 10 days
Huge Ni particles > 200 nm
Ni bimetallicparticles 5 – 50nm
Ni/Al2O3 Ni/Al2O3 + 11mol% precious metal
• Alloy with another metal:
F.Morales-Cano et al. (2012)
NiNi Ni
Promotor
carrier carrier
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Rings retrieved after 6months in an ATR
• Promoted catalysts tested in an ATR for 6 months• Ni volatilization and sintering are suppressed in
the presence of precious metal promotorNi/Al2O3
p-Ni/Al2O3
Catalyst after 6 months ATR operation
Ni/Al2O3 Ni/Al2O3 + preciousmetalF.Morales-Cano et al. (2012)
InventionExposure to Industrial Conditions
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Fundamental and industrial aspects of heterogeneous catalysis
• Industrial methanol production – equipment for producing synthesis gas
• Properties of nickel steam reforming catalysts• Sintering (stability of Ni particles)• Carbon formation over Ni catalysts
• Methanol synthesis catalysts:• How Zn helps Cu make methanol
• Conclusions
Industrial methanol production
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How does a carbon fiber grow?
Graphitewhisker
4 2
Ni
20nm
Ni
C fiber
Ni
C fiber 1
2
Baker et al, J. Catal. 26, 51 (1972), ibid.30, 86 (1973)
?
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Imaging of carbon formation
• CH4:H2=1:1, 2.1mbar, 536°C• Image size: 22x22nm2
• 10 frames/s (display rate x2.5)• Growth rate ~1nm/s
Nature 427 (2004) 426
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Graphene Formation at Ni Steps
5nm
0s 0.2s 0.4s 0.6s
0.8s 1.0s 1.2s 1.4s
§ Spontaneous formation of mono-atomic Ni step sites§ Transport of C and Ni atoms
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Surface dynamics
§ CH4:H2=1:1, 2.1 mbar, 525°C§ Image size: 21.3x21.3nm2, 10 frames/s
(display rate x2.5)
Nature 427 (2004) 426; Phys. Rev. B 73, 115419 (2006)
C H2
CH4
NiIIIIII
Ni
I: Surface transport ofC 1.42eV
II: Subsurfacetransport of C 1.55eV
III: Bulk C transport 2.33eV
Experimental GrowthBarriers 1.3-1.5eV
DFT - energy barriers for C transport
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Effect of Ni particle size on the limits for carbon formation
Bengaard et al. J. Catal. 209, 354 (2002)
Carbon formation in a mixture ofC4H10/H2/H2O/He
99
100
101
102
103
104
575 625 675 725 775 825 875Temperature (K)
Rel
ativ
ew
eigh
t(%
)15%Ni/MgAl2O4
0.92%Ni/MgAl2O4
dNi = 102 nm
dNi = 7 nm99
100
101
102
103
104
575 625 675 725 775 825 875Temperature (K)
Rel
ativ
ew
eigh
t(%
)15%Ni/MgAl2O4
0.92%Ni/MgAl2O4
dNi = 102 nm
dNi = 7 nm
Graphitewhisker
NiNi
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Effect of nanoparticle size
§ Energy gained by forming carbon layers
§ Stablizing interactions between the carbon layers
§ Bending the layers offsets the stabilization
Peng, Somodi, Helveg, Kisielowski,Specht, Bell, J. Catal. 2012, 286, 22.
Pt/MgO exposed to C2H6:H2:He=12:15:33 mL/min 600 oC
Pt NPsca. 2nm
Pt NPsca. 4nm
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Fundamental and industrial aspects of heterogeneous catalysis
• Industrial methanol production – equipment for producing synthesis gas
• Properties of nickel steam reforming catalysts• Sintering (stability of Ni particles)• Carbon formation over Ni catalysts
• Methanol synthesis catalysts:• How Zn helps Cu make methanol
• Conclusions
Industrial methanol production
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7 m
~4 cm
Industrial methanol synthesis
Methanol synthesis from CO, CO2, H2
CO2 + 3 H2 → CH3OH + H2OCO + 2 H2 → CH3OHCO + H2O ↔ CO2 + H2
H2, CO, CO2
CH3OH
T range: 200-300oCP range: 50-100 barCatalyst pellets 4-6 mm
CH3OH
RecycleCompressor Purge
Make-upgas
Rawmethanol
Rawproductseparator
MethanolReactor
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The methanol catalystCu/ZnO/Al2O3
• Catalyst consists of Cu, ZnO, and Al2O3
ZnO
Cu
Al2O3
Zn: Increase dispersion,stabilizer, promotor
Al: Increase dispersion, stabilizer
Cu: Active metal
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How does Zn help Cu make methanol?Cu/ZnO/Al2O3
• The role of ZnO:
- ZnOx over-layers?
Lunkenbein et. al. Angew. Chem. Int. Ed. 54 (2015) 4544–4548
Schott et. al. Angew. Chem. Int. Ed. 52 (2013) 11925 –11929
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How does Zn help Cu make methanol?Cu/ZnO/Al2O3
• The role of ZnO:
- ZnOx over-layers?
- Morphology changes?
Grunwaldt et al. J. Catal. 194 (2000) 452–460 Hansen et al. Science 295 (2002) 2053-2055
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How does Zn help Cu make methanol?Cu/ZnO/Al2O3
• The role of ZnO:
- ZnOx over-layers?
- Morphology changes?
- Surface alloying?
Sano et al. J. Phys. Chem. B 106 (2002) 7627–7633Behrens et al. Science 336 (2012) 893 -897
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Combining UHV and plug-flow reactor
Fixed bed reactorHPC+UHV systemMeOH catalyst
Parallel approach
Characterization
HydrogenH
1HydrogenH
1
H2-treatment
:16h
• Characterization:X-ray Photoelectron Spectroscopy (XPS)Temperature Programmed Desorption of Hydrogen (H2-TPD)Reactive Frontal Chromatography by Nitrous Oxide (N2O-RFC)
Kuld et al. Angew. Chem. Int. 126 (2014) 5941–5945
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ResultsX-ray Photoelectron Spectroscopy (XPS)
• Analysis is focused on the Zn LMM Auger line• Quantify relative fractions of Zn and ZnO• Zn is increasing with H2 partial pressure
1200 1000 800 600 400 200 0
OK
LL
Cu
2p
Zn2p
Cu
LVV
ZnLM
M
O1s
C1s
Zn3p
Cu
3p
Cu
3s
Zn3s
Al Ka = 1486.6 eV
Inte
nsity
[cou
nts/
s]
Binding energy / [eV]
HPC+UHV system
Kuld et al. Angew. Chem. Int. 126 (2014) 5941–5945
510 505 500 495 490 485
Inte
nsity
Binding energy/ [eV]
ZnO
Zn LMM
ZnpH2 = 1 bar
pH2 = 0.3 barpH2 = 0.1 bar
pH2 = 0.06 bar
pH2 = 0.01 baroxidized
505 500 495 490 485
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
Inte
nsity
/a.u
.
Binding energy / eV
Al Ka 1486.6 eV Zn L3M4,5M4,5
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Cu
CharacterizationThe fixed bed reactor system
Fixed bed reactor
Kuld et al. Angew. Chem. Int. 126 (2014) 5941–5945
H2-TPD
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Zn
Cu
CharacterizationThe fixed bed reactor system
H2-TPD
Fixed bed reactor
Kuld et al. Angew. Chem. Int. 126 (2014) 5941–5945
N2O -RFC
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ResultsComparison of data
• Comparing the data from two systems showquantitatively same results
• Tool to measure the Zn coverage
lr
HPC+UHV systemFixed bed reactor
Kuld et al. Angew. Chem. Int. 126 (2014) 5941–5945
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Status
• Incorporation of Zn atoms in the surface of Cu nanoparticles• Relatively fast process (few hours)• Occurs under very mild conditions (PH2 ≥ 0.01bar/220°C)
• What is in the Zn coverage during synthesis?!• What is the influence on activity?
Nakamura et al. J. Catal. 160 (1996) 65-75
Model catalyst
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Modeling of Zn in CO, CO2, H2 atmospheresCuZn alloy formation
• ZnO reduces and alloys with Cu in synthesis via:
ZnO(s) + CO = ZnCu + CO2 (1)ZnO(s) + H2 = ZnCu + H2O (2)
• The amount of Zn in a Cu NP:
• Zn coverage is established by segregation energies:
Cu
ZnOCO, CO2 Zn
Cu
ZnCu
Zn
ZnO + CO + Cu = ZnCu + CO2
ln X =−
− ln(γ ) − ln +4γ
ρ−
4γρ
=(1 − )(1 − )
ZnCu,bulk + CuCu,surf = ZnCu,surf + CuCu,bulk
Kuld et al. Science 352 (2016) 969-974
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Modeling qZn for Cu nanoparticlesEffect of CO/CO2 ratio
• Segregation energies of Zn from bulk Cu toterraces, steps, and kinks are calculated by DFT
• Energies are corrected for Zn-Zn interaction
• qZn for a Cu nanoparticle is determined from thefraction of different surface sites in a cubo-octahedron1
Cu cubo-octrahedron size of dCu = 88Å (closest to the crystalsize of dCu = 85Å and dZnO = 87Å determined by XRD)
Kuld et al. Science 352 (2016) 969-9741Hardeveld and Hartog Surf. Sci. 15 (1969) 189-230
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Measurement of the Zn coverageMeOH catalyst exposed to different well-defined gas mixtures
• Direct Steady state measurements of Zn coveragein model gas atmospheres.
• Catalyst samples exposed to different CO/CO2,H2O/H2, and synthesis gasmixtures
=/0.96 −
/0.96
Kuld et al. Science 352 (2016) 969-974
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MeOH activity vs. qZn
Fixed bed reactorMeOH catalyst
Kuld et al. Science 352 (2016) 969-974
• Zn coverage established by H2-treatment• MeOH activity at 1 bar, CO/CO2/H2 = 18/18/64
and T: [90–140°C]• Relative MeOH activity was established at 130°C
(ramp down)• Strong dependency of qZn on activity
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Model predictionsEffect of particle size
• Thermodynamic model of Cu/Zn alloying:
• Combined with a second-order polynomial fit ofqZn and ActMeOH
• A huge increase in activity is seen when the ZnOparticle size is decreased
Kuld et al. Science 352 (2016) 969-974
ln X =−
− ln(γ ) − ln +4γ
ρ−
4γρ
CO/CO2 = 0.5
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Fundamental and industrial aspects of heterogeneous catalysis
• The mechanisms for sintering of nickel particles can be used to develop new catalysts
• Whisker carbon formation involves surface diffusion of carbon.
• Whisker carbon limits depends on particle size
• ZnO forms a surface alloy in Cu particles
• The Zn coverage in Cu is controlled by the gas environment during synthesis
• Zn in Cu boosts the activity
• Possibility to engineer better methanol catalysts
Industrial methanol production - conclusions
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AcknowledgementsAuthors, contributorsHaldor Topsoe A/S• Sebastian Kuld
• Max Thorhauge
• Stig Helveg
• Christian F. Elkjær
• Hanne Falsig
• Bodil Voss
• Poul Georg Moses
Technical University of Denmark, DTU• Ib Chorkendorff
• Christian Conradsen
• Thomas W. Hansen
Stanford University• J.K. Nørskov
• F. Abild-Pedersen
University of New Mexico• A.K. Datye
• A.T Delariva
• S.R Challa