Heterogeneous Catalysis by metalsThe basic conceptsJ. K. NrskovCenter for Atomic-scale Materials Physics Technical University of Denmark norskov@fysik.dtu.dk

http://www.fysik.dtu.dk/~norskov/EFCATS.pdf

Outline Catalysis challenges and opportunities The basic concepts Structure sensitivity The electronic factor in catalysis

Generality Changing the reactivity Lessons from biology

Challenges IDream reactions waiting for a catalyst:

Jens Rostrup-Nielsen: XVII Sympsio Iberoamericano de Catlisis, July 16-21, 2000

Challenges IIDreaming on . Fuel cells Photolytic water splitting (hydrogen economy) Heterogeneous catalysts for assymmetric synthesis Biomimetics, synthetic enzymes Non-thermal processes in general (e.g. electro- and photocatalysis) See: E. Derouane, CATTECH 5, 226 (2001)

Challenges IIIThe science of heterogeneous catalysis: A comprehensive scientific basis Much has been done Much more is needed (oxides, size effects, photocatalysis, electrocatalysis, relation to homogeneous and enzyme catalysis )

Making the insight useful! The ultimate test

Opportunities - design at the nano-scale Rational catalyst design- Discovery on the basis of insight Data-driven methods - Accelerated discovery by access to large amounts of data Bio-inspired catalysis

The basic conceptsIllustrated using the ammonia synthesisN2+3H2 2NH3

Ozaki and Aika, Catalysis 1 (Anderson and Boudart, Ed.)

Ammonia synthesisthe importance6 World population (billions) 5 4 3 40 2 1 0 1900 1925 1950 Year 1975 20 0 80 60 Consumption of nitrogen fertilizer (megaton) 100

Haber & Bosch

The catalystIn situ TEM Ru/BNSteps

Terraces1 nm

Hansen, Wagner, Hansen, Dahl, Topse, Jacobsen, Science 294, 1508 (2001)

The reaction mechanismRu(0001)

step

Logadottir, Nrskov

Density functional calculationsSelf-consistent GGA (RPBE)Perdew, Burke, Ernzerhof , PRL 80, 891 (1998) Hammer, Hansen, Nrskov, PRB 59, 7413 (1999)

Ultra-soft pseudopotentials, plane wave basisVanderbilt, PRB 41, 7892 (1996)

Slab geometry Complete structural relaxation Iterative method for finding transition statesMills, Jonsson, Schenter Surf. Sci. 324, 305 (1995)

http://www.fysik.dtu.dk/CAMPOS

Steps do everythingAu decorates steps:Hwang, Schroder, Gunther, Behm, Phys. Rev. Lett. 67, 3279 (1991)

Dahl, Logadottir, Egeberg, Larsen, Chorkendorff, Trnqvist, Nrskov, Phys.Rev.Lett. 83, 1814 (1999)

The rate-limiting stepRu(0001)

step

Logadottir, Nrskov

Rates of elementary stepsIndustrial conditions: T=350-500 C, p=100 atm, 3:1 gas Harmonic transition state Theory:

NH*+H*->NH2*+*

N2+2*->2N*

Rate-limiting stepEmmett, Brunauer, JACS 55 1738 (1933)

Two important parametersEa barrier for rate limiting step

DE stability of intermediates on surface

Logadottir, Nrskov

The Brnsted-Evans-Polanyi relation

Logatottir, Rod, Nrskov, Hammer, Dahl, Jacobsen, J. Catal. 197, 229 (2001)

The geometrical effect

The geometrical effect

Logatottir, Rod, Nrskov, Hammer, Dahl, Jacobsen, J. Catal. 197, 229 (2001)

The electronic effect

The electronic effect

Logatottir, Rod, Nrskov, Hammer, Dahl, Jacobsen, J. Catal. 197, 229 (2001)

What determines trends?- the role of the d-band centerN2/3d metals

Hammer and Nrskov, Adv. Catal. 45, 71 (2000)

The adsorbate-surface interaction

Hammer and Nrskov, Nature 376, 238 (1995) ; Adv. Catal. 45, 71 (2000)

Nitrogen adsorption on Cu and Ni

d

d

Hammer and Nrskov, Nature 376, 238 (1995).

Experiment

Weill, Tillborg, Nilsson, Wassdahl, Mrtensson, Nordgren, Surf. Sci. 304, L451 (1994)

Micro-kinetic model10

Model output (% NH3)

N2 dissociation rate determining. N2 dissociation rate equal to rate at steps Realistic active site density

1

0.1

Ru/MgAl2O4

0.01

0.001

Ru Single Crystal0.0001 0.0001

Dahl, Sehested, Jacobsen, Trnqvist, Chorkendorff, J. Catal. 192, 391 (2000)

0.0010

0.0100

0.1000

1.0000

10.0000

Experimental output (% NH3)

The BEP relation for N2 dissociation6 5 4 3 2 1 0 -1 -2 -4 -3 -2 -1 0 1 2 3 4

Ea (eV)

Fe Ru Ru

E (eV)

We understand which metals are the best catalystsPredicted ammonia synthesis rates at 400 C, 50 bar, H2:N2=3:1, 5% NH310 1 10 0 Ru Os

FeCo

TOF(s -1 )

10 -1 10 -2 10 -3 10 -4 10 -5

Mo Ni

-0.8

-0.4

0.0

0.4

0.8

[E-E(Ru)](eV/N2 )Logatottir, Rod, Nrskov, Hammer, Dahl, Jacobsen, J. Catal. 197, 229 (2001)

What about other reactions?Ammonia synthesis is N2 activation: N2+3H2 2NH3 Fischer Tropsch synthesis is CO activation: nCO+(2n+1)H2 CnH2n+2+nH2O NO reduction is NO activation: 2NO+2H2 N2+2H2O Oxidation is O2 activation: O2+2X 2XO

..

N2 dissociation6 5 4 3 2 1 0 -1 -2 -4 -3 -2 -1 0 1 2 3 4

Ea (eV)

E (eV)

N2 and NO dissociation6 5 4 3 2 1 0 -1 -2 -4 -3 -2 -1 0 1 2 3 4

Ea (eV)

E (eV)

N2, NO and O2 dissociation6 5 4 3 2 1 0 -1 -2 -4 -3 -2 -1 0 1 2 3 4

Ea (eV)

E (eV)

N2, NO, O2 and CO dissociation6 5 4 3 2 1 0 -1 -2 -4 -3 -2 -1 0 1 2 3 4

Ea (eV)

E (eV)

Universality in heterogeneous catalysis-3 -2 -1 0 1 2 3

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

Ea (eV)

(b) Step sites

Ea (eV)

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

Nrskov, Logadottir, Bligaard, Bahn, Hansen, Bollinger, Bengaard, Hammer, Sljivancanin Mavrikakis, Xu, Dahl, Jacobsen J.Catal, soon, 2002

-3

-2

-1

0 1 E (eV)

2

3

Transition state structures

The Sabattier principle and the volcano curve-3 -2 -1 0 1 2 3

The general kineticsEa (eV)

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

(b) Step sites

Ea (eV)

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

P. Sabatier, La catalyse en chimie organique (Brange, Paris, 1920). A. A. Balandin, Adv. Catal. 19, 1 (1969).

-3

-2

-1

0 1 E (eV)

2

3

Universality in heterogeneous catalysis-3 -2 -1 0 1 2 3

Ea (eV)

Ammonia synthesis is N2 activation: N2+3H2 2NH3

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

(b) Step sites

Ea (eV)

Fe Ru

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

-3

-2

-1

0 1 E (eV)

2

3

Universality in heterogeneous catalysis-3 -2 -1 0 1 2 3

Ea (eV)

Fischer Tropsch synthesis is CO activation: nCO+(2n+1)H2 CnH2n+2+nH2O

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

(b) Step sites

Ea (eV)

Co,Ru Ni,Rh

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

-3

-2

-1

0 1 E (eV)

2

3

Universality in heterogeneous catalysis-3 -2 -1 0 1 2 3

Ea (eV)

NO reduction is NO activation: 2NO+2H2 N2+2H2O

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

(b) Step sites

Ea (eV)

Pt

Pd PtRh

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

-3

-2

-1

0 1 E (eV)

2

3

Universality in heterogeneous catalysis-3 -2 -1 0 1 2 3

Ea (eV)

Oxidation is O2 activation: O2+2X 2XO

5 4 3 2 1 0 -1 -2 5 4 3 2 1 0 -1 -2 1.0 0.8 0.6 0.4 0.2 0.0

(a) Flat surfaceN2 CO NO O2

(b) Step sites

Ea (eV)

Pt

Ag

Normalized TOF

(c) Step kinetics

0.2%, 2%, 20% NH3 100 bar 673 K H2:N2 = 3:1

-3

-2

-1

0 1 E (eV)

2

3

Changing the reactivityStructure Change of metal alloying Promotion Change of reaction conditions

Measured ammonia synthesis rates400 C, 50 bar, H2:N2=3:1

Co3Mo3N

Ru

Jacobsen, Dahl, Clausen, Bahn,Logadottir, Nrskov, JACS 123 (2001) 8404.

Interpolation in the periodic table

Jacobsen, Dahl, Clausen, Bahn, Logadottir, Nrskov, JACS 123 (2001) 8404.

Interpolation in the periodic table

Jacobsen, Dahl, Clausen, Bahn, Logadottir, Nrskov, JACS 123 (2001) 8404.

Fine-tuningCorrelation between adsorption energies and activation barriers and the d-band center

Mavrikakis , Hammer, Nrskov Phys. Rev. Lett. 81, 2819 (1998)

CO tolerance of Pt alloy anodes for PEM fuel cells1,0 0,8M. Watanabe et al., Phys. Chem. Chem. Phys. 3 (2001) 306

Measured overages of CO on the alloy electrodes with 100 ppm CO/H2

1-coPt M

0,6 0,4 0,2 0,0

Calculated changes in CO adsorption energy2,0 1,0

-d, eV

1,5 1,0 0,5 0,0

0,6 0,4 0,2 0,0

S. Gottesfeld et al., J. Electrochem. Soc. 148 (2001) A11.

-0,5

-0,2

Pt Fe Co Ni Cu Ru Rh Pd Ag Ir Substrate M

Au

Christoffersen, Liu, Ruban, Skriver, Nrskov, J.Catal. 199, 123 (2001)

ECO , eV

0,8

How can the d-band center be changed?Calculated d band shifts:

Overlayer

Host

Ruban, Hammer, Stoltze, Skriver, Nrskov, J.Mol.Catal. A 115, 421 (1997)

Methane activationTransition state for CH4 dissociation on Ni(211)

Bengaard, Rostrup-Nielsen, Nrskov

Methane activation on Ni/Ru5e-7

Initial sticking probability

Thermal dissociation of CH4 at T = 530 K4e-7

3e-7

2e-7

1e-7

0 0 1 2

Ni Coverage [ML]Egeberg, Chorkendorff, Catal. Lett. 77, 207 (2001)

Promotion of ammonia synthesisRu/AC:

Promotion effect:

TOF(Cs - Ru/MgO) 10 2 TOF(Ru/SiO2 )McClaine, Davis, J. Catal. 210 (2002)

Aika, Hori, Ozaki, J. Catal. 27, 424 (1973)

Surface science studies

Bare, Strongin, Somorjai, J. Chem. Phys. {\bf 90}, 4726 (1986)

Ertl, Lee, Weiss, Surf. Sci. 114, 527 (1982).

The effect of adsorbatesN2 dissociation Ru(0001):

Mortensen, Hammer, Nrskov Phys.Rev.Lett. 80, 4333 (1998); Surf.Sci. 414, 315 (1998)

The electrostatic interactionDE=m E+1/2a E2+

Nrskov, Holloway, Lang:Surf. Sci. 137, 65 (1984) Mortensen, Hammer, Nrskov, Phys.Rev.Lett. 80, 4333 (1998)

E ~ 1 V/

Dipole momentsTerrace [e] N2,TS N NH NH2 NH3 -0.13 -0.03 0.18 0.25 0.35 Step [e] -0.15 0.01 0.24 0.27 0.56

Dahl, Logadottir, Jacobsen, Nrskov, Appl.Cat.A 222, 19 (2001)

Promotion by potassium101 100 -1 TOF (s ) 10-1 10-2 10-3 10-4 10-5 -100.0 -50.0 0.0 50.0 100.0

Fe

Ru Os

Co Mo Ni

[EN*-EN*(Ru)] (kJ/mol N2) Dahl, Logadottir, Jacobsen, Nrskov, Appl.Cat.A 222, 19 (2001)

Lessons from biology Catalysis at ambient temperature and pressure Extreme selectivity Direct coupling of energy into the important reaction coordinate (non-thermal catalysis)

NitrogenaseN 2 + 8H + 8e+

nitrogenase ATP

2NH 3 + H 2ADP AlF4-

complex formation

Fe protein MoFe protein 4Fe-4S cluster P-cluster

FeP (MgATP) 2+ MoFePnucleotide replacement reduction

k1

k -1

FeP (MgATP) 2 MoFePATP cleavage electron transfer

k4k3 k -3

k2

FeMo cofactor Fe protein

FePox(MgADP) 2 + MoFeP

FePox (MgADP, Pi ) 2 MoFeP

complex dissociation

Burgess, Lowe, Chem. Rev. 96, 2983 (1996) Schindelin, Kisker, Schlessman, Howard, Rees, Nature 387, 370 (1997)

N2 hydrogenation on FeMoco

Rod, Nrskov JACS 122, 12751 (2000)

The Fe Protein cycleMoFe protein Fe protein ATP

E

1)FeMoco P-cluster 4Fe-4S cluster

2)

E

3)ADPHPO 2 4

E

4)See also: Spee, Arendsen, Wassnik, Marrit, Hagen, Haaker, FEBS Lett. 432, 55 (1998)

Comparing the FeMoco and Ru(0001)

Rod, Logadottir, Nrskov J.Chem.Phys. 112, 5343 (2000)