Launch of MK-181 - fysik.dtu.dk

J. Sehested

Haldor Topsoe A/S

CINF Summer School 2016, Kysthusene, Tinkerup Strandvej 8a,Gilleleje

Fundamental andIndustrial aspects ofheterogeneous catalysis

2

From nano to mega and back again

Reactor1m

Catalyst from0,001m = 1mm

Pore structure0,000000001m = 1nm

Active phase0,0000000001m = 1Å

3

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$

4

Industrial methanol production

5

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


6

TODAY

FUTURE

Why methanol?!Essential bulk chemical – C1 building block

2015 demand: 71.6 MMT

2019 demand: >90 MMT

Source: IHS, 2015

7

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

8

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)

9

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)

10

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

11

Tubular steam reforming

Heat

Heat

Heat

Heat

Heat

Feed

Catalyst

~500°C

~900°C

12

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

14





• Conclusions


15

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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• Conclusions


22

Effect of whisker carbon formation

Decreasing H2O/CH4

23

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)

?

24

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

25

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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• Conclusions


30

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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Laboratory and pilot testing of methanol catalysts

Piteå, SwedenRavnholm, Denmark

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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

34



- 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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- 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


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


H2-TPD

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Zn

Cu

CharacterizationThe fixed bed reactor system

H2-TPD

Fixed bed reactor


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


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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


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MeOH activity vs. qZn

Fixed bed reactorMeOH catalyst


• 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


ln X =−

− ln(γ ) − ln +4γ

ρ−

4γρ

CO/CO2 = 0.5

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• 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

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