Heterogeneous Catalysis by metalsThe basic conceptsJ. K. NrskovCenter for Atomic-scale Materials Physics Technical University of Denmark [email protected]
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)