A First-Principles Approach to Catalytic H2 Production and Chemistry:

Reaction Mechanismsand

Identification of Promising Catalysts

Manos Mavrikakis

Department of Chemical and Biological EngineeringUniversity of Wisconsin – Madison

Madison, Wisconsin 53706

Acknowledgements

A. Gokhale, S. Kandoi, L. Grabow, M. Han, D. Ford, A. Unrean

J. Greeley, Y. Xu, A. Nilekar, R. Nabar, P. Ferrin

J. A. Dumesic (UW Madison)

Jens Nørskov and colleagues @ CAMP - Denmark

DoE Catalysis Science Grant (BES-Chemical Sciences)

NSF - CTS

NPACI, DOE-NERSC, PNNL (supercomputing resources)

Outline

• H2 production:– An alternative mechanism for the Low Temperature

Water Gas Shift Reaction

• H2 catalytic chemistry:– Identifying Promising Catalysts from 1st Principles:

H2 and H on Bimetallic Near Surface Alloys (NSAs)

Water Gas Shift Reaction (WGSR)Ovesen, Stoltze, Nørskov, Campbell – J. Cat. 134, 445 (1992)

Ovesen, et.al. – J. Cat. 158, 170 (1996)C.T. Campbell – Studies in SS and Catalysis 38, 783 (1988)

NH3Synthesis

H2 Production

MeOH

Synthesis

CO + H2O CO2+H2 H = - 41 kJ/mol∆

Reaction Mechanisms

Red-ox Mechanism

OH* + * O* + H*OH* + OH* H2O* + O*CO* + O* CO2* + *

Formate Reactions CO2* + H* HCOO**

CO2* + H2O* + * HCOO** +OH*

CO2* + OH* + * HCOO** +O*

Carboxyl MechanismCO* + OH* COOH* + *COOH* + * CO2* + H*COOH* + OH* CO2* + H2O*COOH* + O* CO2* + OH*

CO(g) + * CO*H2O(g) + * H2O*

H* + H* H2(g) + 2*CO2* CO2(g) + *

H2O* + * OH* + H*

MethodsDensity Functional Theory – DACAPO total energy code 1,2

Periodic self-consistent PW91-GGA 3

Ultra-soft Vanderbilt pseudo-potentials 4

Plane wave basis sets with 25-Ry kinetic energy cut-off

Spin polarization as needed

Four-metal-layer slabs; (2x2) unit cell; top two layers relaxed

First Brillouin zone sampled at 18 k-points

Nudged Elastic Band method for reaction paths 5

1. B. Hammer, L. B. Hansen, J. K. Nørskov, Phys. Rev. B 59, 1999, 7413.2. J. Greeley, J. K. Nørskov, M. Mavrikakis, Annu. Rev. Phys. Chem. 53, 2002, 319.3. J. P. Perdew et al., Phys. Rev. B 46, 1992, 6671.4. D. H. Vanderbilt, Phys. Rev. B 41, 1990, 7892.5. G. Henkelman, H. Jónsson, J. Chem. Phys. 113, 2000, 9978.

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

Ene

rgy

(eV

)

CO(a)+2H2O(a)

CO(a)+2H(a)+2OH(a)

CO(a)+ 2H(a) +O(a) +H2O(a)

CO2(a)+2H(a)+ H2O(g)

Thermochemistry of WGS on TM(111)Redox Mechanism

Complete Dissociation : OH* +* O* + H*

CO(g)+2H2O(g)

CO(a)+2H2O(g)

Ru

Ni

RhIr

PdPtCu

Ag

AuDisproportionation : OH* + OH* H2O* + O*

Co

CO2(g)+H2(g)+H2O(a)CO2(a)+H2(g)

+H2O(a)

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

-1.00

CO2(a)+2H(a) +H2O(a)

CO(g)+2H2O(g)

CO(a)+2H2O(g)

CO(a)+2H2O(a)

H--OH(TS)1.36

CO(a) + H(a)+ OH(a)+H2O(a)

CO2(g)+ H2(g)+H2O(g)

CO(a)+ O(a) +2H(a)+ H2O(a)

CO2(a)+ H2(g)+H2O(a)

H--O (TS)1.76

H--H(TS)1.07

CO--O(TS)

0.82

Ener

gy (e

V)

PES for Water Gas Shift Reaction on Cu(111)

OH DissociationOH+OH MechanismCOOH MechanismCOOH+OH Mechanism

CO2(a)+2H(a) +H2O(a)

CO(g)+2H2O(g)

CO(a)+2H2O(g)

CO(a)+2H2O(a)

H--OH(TS)1.36

CO(a) + 2H(a)+ 2OH(a)

CO2(g)+ H2(g)+H2O(g)

CO(a)+ O(a) +2H(a)+ H2O(a)

CO2(a)+ H2(g)+H2O(a)

OH--OH (TS)0.23

H--H(TS)1.07

CO--O(TS)

0.82

COOH(a) +H2O(a)+H(a)

CO2(g)+2H(a) +H2O(a)

CO(g)+2H2O(g)

CO(a)+2H2O(g)

CO(a)+2H2O(a)

H--OH(TS)1.36

CO(a) + OH(a) + H(a) + H2O(a)

CO2(g)+ H2(g)+H2O(g)

CO2(g)+ H2(g)+H2O(a)

CO--OH (TS)0.61

H--H(TS)1.07

COO--H (TS) 1.41

COOH(a)+ OH(a) +2H(a)

CO2(a)+2H(a) +H2O(a)

CO(g)+2H2O(g)

CO(a)+2H2O(g)

CO(a)+2H2O(a)

H--OH(TS)1.36

CO(a) + 2H(a)+ 2OH(a)

CO2(g)+ H2(g)+H2O(g)

CO2(a)+ H2(g)+H2O(a)

CO--OH (TS)0.61

H--H(TS)1.07

COOH--OH(TS)

0.42

//

H2O Dissociation on Cu(111)

//

Carboxyl Formation on Cu(111)

COOH + OH reaction on Cu(111)

////

WGSR/Cu Mechanism:Key points

• WGSR mainly proceeds via COOH intermediate, which decomposes via the COOH+OH reaction.

• H2O Activation is the RCS.

• Formate, a stable spectator species, is formed from CO2* and H*. Formate formation is equilibrated with CO2and H*.

• The combination of DFT and Microkinetics shows that we can fairly accurately predict experimental WGSR rates directly from First Principles.

Ideal Bimetallic Near Surface Alloys • Segregation properties of two metals are

critical• Consider two special classes:

– Overlayers– Subsurface Alloys

Overlayers* Subsurface Alloys

1. J. Kitchen, N. Khan, M. Barteau, J. Chen, B.

Yashhinskiy, and T. Madey, Surf. Sci. 544 (2003) 295

1Ni/Pt(111)

H2/Rh(111)

2. R. Schennach, G. Krenn, B. Klötzer, K. Rendulic, Surf. Sci. 540 (2003) 237

Hydrogen on NSA’s

2V/Rh(111 )

-

-

Eseg

Pt subsurface alloys

Pd subsurface alloys

Ir subsurface alloys

Ru subsurface alloys

Rh subsurface alloys

Re based overlayers

Ru based overlayers

H-induced segregation

-1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

1.25

|B.E

. Hhost

|Hso

l-|

B.E

.

|

Stability of NSA’s with respect to Hydrogen-induced Segregation

-

-

CoFe Ru Pd CuW IrNi

PtMoReTa Rh AuV

B.E.H (eV)-3.2 -3.1 -3.0 -2.9 -2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2-3.3

H Binding Energy Spectrum

Rh subsurfacealloys

Ru based overlayers

Re based overlayers

ThermoneutralH2 Dissociation

Pt subsurface alloys*

*Cu,Ir,Rh,Ni,Ru,Re,Co,Fe,W,Mo,V,Ta

Pd subsurfacealloys†

†Ir,Ru,Re,Fe,Mo,W,V,Ta

Overlayers Subsurface Alloys

Correlation of B.E.H with Clean Surface Properties

d ε (eV)

-3.4 -3.2 -3.0 -2.8 -2.6 -2.4 -2.2 -2.0

B.E

. H(e

V)

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

-2.0

-1.8

Pt subsurface alloysPd subsurface alloys

Rh subsurface alloys

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0

EbFS (eV, PW91)

Eb

TS (e

V, P

W91

)

O2 dissociation: Does EbTS follow Eb

FS?

Pt

Cu

Ir

Ag

Au +10%

Pt3Co

Pt3Co skin

Pt -2%

Pt3Fe

Pt3Fe skin

Y. Xu, A. V. Ruban, M. Mavrikakis, JACS 126, 4717 (2004).

Hydrogen B.E. (eV)

- 0.3 - 0.2 - 0.1 0.0 0.1 0.2

ETS

(eV

)

- 0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Au

Cu

Noble metals

V/Pd

Pd*/Re

Re/Pd

Ta/PdPd-terminated alloys

Ta/Pt

Mo/Pt

Re/Pt

Ru/PtPt-terminated alloys

BEP Plot for H2 Dissociation on NSA’sJ. Greeley, M. Mavrikakis, Nature Materials 3, 810 (2004)

---------------

Metal or Alloy

Sur

face

-Sub

surfa

ce

Ther

moc

hem

ical

Bar

rier (

eV)

0.0

0.2

0.4

0.6

0.8

1.0

Pt

Ir/P

t

Ru/

Pt

Rh/

Pt

Fe/P

t

Mo/

Pt

Co/

Pt

Cu/

Pt

Ni/P

t

Pd

Ta/P

d

V/P

d

-----

-----

Surface to Subsurface Diffusion of HThermochemical Barrier

J. Greeley, M. Mavrikakis, J. Phys. Chem. B 109, 3460 (2005)

Pt2+

Pd Pd

CuUPD/Pd + Pt 2+ Pt/Pd + Cu2+

Cu2+

Cu Pt

Pt

Ru

Pt

Ru

Metal monolayer deposition by galvanic displacement of a less noble

metal monolayer deposited at underpotentials

Electroless (spontaneous) deposition of one metal on

another metal

Brankovic, S. R.; Wang, J. X.; Adzic, R. R. Surf. Sci. 2001, 474, L173

Brankovic, S. R.; McBreen, J.; Adzic, R. R. J. Electroanal. Chem. 2001, 503, 99

Sasaki, K.; Wang, J. X.; Balasubramanian, M.; McBreen, J.; Uribe, F.; Adzic, R. R. Electrochim. Acta 2004, 49, 3873

Zhang, J.; Vukmirovic, M.; Xu, Y.; Mavrikakis, M.; Adzic, R. R. Angew. Chem. Int. Ed. (in press).

NSA’s - Summary• First-Principles Methods can help with identifying promising

bimetallic NSAs with interesting catalytic properties

• Example: 1. H and H2 on NSA’s: Fine-tuning BEH is possible2. Some NSA’s:

2.1. Activate H2 easily AND bind atomic H weakly useful for highly selective low TH-transfer reactions2.2. Allow easy H diffusion into the bulk (catalysis of H-storage)

• Developing Catalyst Preparation Techniques with Layer-by-Layer control of metal deposition (ALD-like) is critical for making the desired NSAs

Lars GrabowShampa Kandoi

University of Wisconsin-Madison

Department of Chemical and Biological Engineering

Amit Gokhale

Dr. Ye XuDr. Jeff Greeley

Acknowledgements

A. Gokhale, S. Kandoi, L. Grabow, M. Han, D. Ford, A. Unrean

J. Greeley, Y. Xu, A. Nilekar, R. Nabar, P. Ferrin

J. A. Dumesic (UW Madison)

Jens Nørskov and colleagues @ CAMP - Denmark

DoE Catalysis Science Grant (BES-Chemical Sciences)

NSF - CTS

NPACI, DOE-NERSC, PNNL (supercomputing resources)