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Catalytic and biological hydrogen production
J. K. NørskovCenter for Atomic-scale Materials Physics
Technical University of Denmarknorskov@fysik.dtu.dk
Why make hydrogen?Sulfur emissions DK
Year
• Ammonia synthesis(N2+3H2 2NH3)
• Methanol synthesis (CO+2H2 CH3OH)
polymers …
• Hydrogenation
• …..
• Energy carrier???
Catalytic and biological hydrogen production
• Heterogeneous gas phase processes - Steam reforming
• Electrolysis- An atomistic view- Problems – overpotentials and Pt
• Biological hydrogen evolution- Hydrogenases- Nitrogenases
• Biomimetic hydrogen evolution?
Steam reformingCH4+H2O 3H2+CO
Supported Ni catalyst
Rostrup-Nielsen, Sehested, NørskovAdv. Catal. 47, 65 (2002)
The atomic-scale picture
Ni(111)
Ni(211)
Bengaard, Nørskov, Sehested, Clausen, Nielsen, Molenbroek, Rostrup-Nielsen: J. Catal. 209, 365 (2002)
What determines the reactivity?
Bengaard, Nørskov
bBarrier for CH4 dissociation:
Ni(111)
Ni(211)
Ni Adatom(111)
Ni(100)
Nano-scale effects in catalysis
Lopez, Janssens, Clausen, Xu, Mavrikakis, Bligaard, Nørskov, J. Catal. 223, 232 (2004)
Au as catalyst for CO oxidation:Experimental data:
Schubert et al. J. Catal. 197, 113 (2001).
Okamura et al.Catal. Lett. 51, 53 (1998).
Lin et al. Catal. Lett. 17, 245 (1993).
Haruta et al. J. Catal. 115, 301 (1989).
Lee et al. J. Catal. 206, 305 (2002).
Schimpf et al. Catal. Today 72, 63 (2002).
Yuan et al.Catal. Lett. 42, 15 (1996).
Haruta Stud. Surf. Sci. Catal. 110, 123 (1997)
Haruta Catal. Today 36, 153 (1997).
Makinggold reactive:
Lopez, Janssens, Clausen, Xu, Mavrikakis, Bligaard, NørskovJ. Catal. 223, 232 (2004)
The main nano-effect: many low coordinates sites
# lowest coordinated atoms:~ 1 per particle
# atoms total:~ d3
=>
Activity~ 1/d3
Steam reforming – the main problem:Formation of Carbon Nano-fibers
In situ (high temperatureand pressure) TransmissionElectron Microscopy (TEM)
Helveg, Cartes, Sehested, Hansen, Clausen, Rostrup-Nielsen, Abild-Pedersen, NørskovNature 327, 426 (2004)
Carbon nucleation at steps
Ni(211)
Bengaard, Nørskov, Sehested, Clausen, Nielsen, Molenbroek, Rostrup-Nielsen: J. Catal. 209, 365 (2002)
Extra bonding at step
Ni(111)
Direct observation
Helveg, Cartes, Sehested, Hansen, Clausen, Rostrup-Nielsen, Abild-Pedersen, NørskovNature 327, 426 (2004)
C2H4 dissociation Ni(111)DFT: STM:
Ni(211)
Ni(111)
Vang, Vestergaard, Besenbacher, Dahl, Clausen, Honkala, Nørskov Nature Mat. (2004)
Step blocking ISTM – Ag/Ni(111)
Vang, Vestergaard, Besenbacher, Dahl, Clausen, Honkala, Nørskov Nature Mat. (2004)
Step blocking II
1
10
100
1000
1.5 1.6 1.7 1.8 1.9
1000/T (K-1)
k (m
mol
/(g·s
·bar
0.5 ) Ni 1wt%
Ag/Ni 0.1wt%/0.9wt% Cu/Ni 0.1wt%/1wt%
Step blocking changes rate constant for ethane hydrogenolysis:
Vang, Vestergaard, Besenbacher, Dahl, Clausen, Honkala, Nørskov Nature Mat. (2004)
Sinfelt
Step blocking III
Besenbacher, Chorkendorff, Clausen, Hammer, Molenbroek, Nørskov, Stensgaard, Science 279, 1913 (1998)
Electrolysis
Cathode: 2(H++e-) H2
Anode: H2O ½ O2 +2 H+____________________________________
Total: H2O ½ O2 +H2
∆G0 =2.46 eV (1.23 eV/electron)
Electrolysis
Cathode: 2(H++e-) H2
Anode: H2O ½ O2 +2 H+____________________________________
Total: H2O ½ O2 +H2
∆G0 =2.46 eV (1.23 eV/electron)
The hydrogen evolution process
Nørskov, Bligaard, Logadottir, Kitchin, Chen, Pandelov, Stimming, JES (2004)
Biological Hydrogen Production
– Purple bacteria – “photofermentation” using sunlight and oxidizing organic compounds
– Microalgae and cyanobacteria – “directbiophotolysis” resulting in water splitting
Purple BacteriaC2H4O2 + 2H2O → 2CO2 + 4H2
hν
Antenna
ReactionCenter
CytochromeComplexbc 1
ProtonChannel
ATPSynthase
hν
Energy
Q
QH2
H+H+
H+nH+
nH+
e-
C2
e- e-
ADP + Pi
ATP
H+
H2
e-
Fd
Nitrogenase
e-ATP
ATP
Organic acids CO + H + e2+ -
Biological analog of steam reformingD. Gust, Arizona State U.
Microalgae and cyanobacteriaH2O → H2 + ½O2
Antenna
PS IIReactionCenter Cytochrome
Complexb f 6
hν hν
Energy
Q
QH 2
H+
H+
H2
e -
e-
PCe-
ProtonChannel
ATPSynthase
nH+
nH+
ADP + Pi
ATP
PS IReactionCenter
H O2H + + O2
H+ H+Fd
Hydrogenase
Biological analog of electrolysisD. Gust, Arizona State U.
The active sites of the enzymes
Einsle, Teczan, Andrade, Schmid, Yoshida, Howard, Rees, Science 2002, 297, 1696.
Hinnemann, Nørskov, JACS 126, 3920 (2004)
Vollbeda, Fontecilla-Camps, Dalton Trans.4030-3048 (2003).
Siegbahn, Blomberg, Wirstam, Crabtree Biol. Inorg. Chem. 6, 460 (2001)
Biological hydrogen evolution
Hinnemann, Moses, Bonde, Chorkendorff , Nørskov
pH=7
U=430 mV
([4S-4Fe]1+/2+ )
MoS2 nanoparticles are metallicNanoparticles:1-layer slab:
Bollinger, Lauritsen, Jacobsen, Nørskov, Helveg, Besenbacher, Phys. Rev. Lett. 87, 196803 (2001).
Electrolysis
Cathode: 2(H++e-) H2
Anode: H2O ½ O2 +2 H+____________________________________
Total: H2O ½ O2 +H2
∆G0 =2.46 eV (1.23 eV/electron)
Electro-thermo chemistry I
Example: H2O + * OH* +H++e-
1. Get ∆E for H2O + * OH* + 1/2H2 from DFT
2. Include the effect of water surroundings: ∆Ew
3. Calculate ∆G0 = ∆E +∆Ew+∆Ezpe-T∆S0
The effect of water I
Water layer
Ogasawara, Brena, Nordlund, Nyberg, Pelmenschikov, Petterson and Nilsson.PRL, 89, 2002, 276102
The effect of water IIIMixed OH+H2O∆Gw = -.33eV
Similar to Clay, Haq and Hodgon.PRL, 92, 2004, 46102
Electro-thermo chemistry II
4. Use definition of U=0 (SHE): 1/2H2 ↔ H++e- ,∆G(U=0,cH+=1M ) = 0
5. Calculate effects of potential and pH:∆G(U,cH+) = eU - kT ln(cH+)
6. Include effects of local fields (small here)
Two conventions:
• Use H2O(g) at 0.035 bar as referenceH2O(l)↔ H2O(g)(peq=0.035 bar at 300 K)
• Fix ∆Gtot(U=0, pH=0) = -2.46 eV for ½O2+2H++2e- H2O(avoids calculation for gas phase O2)
Water splitting
Direct route: Peroxy route:
H2O+* *OH+H++e- H2O+* *OH+H++e-
* OH *O+H++e- * OH *O+H++e-
2 *O *OO H2O+ *O *OOH+H++e-
*OOH *OO +H++e-
*OO O2+* *OO O2+*
• Steam reforming– detailed picture
• Electrolysis – emerging understanding
• Enzymatic processes– new inspiration
Hydrogen production
Thanks toB. Hinnemann, K. Honkala, T. Bligaard, J. Rossmeisl, H. Bengaard,
A. Logadottir, I. Remediakis, A. Hellman, P. G. Moses
I. Chorkendorff, O. Lytken, J. BondeCenter for Atomic scale Materials Physics, Technical University of Denmark
F. Besenbacher, E. Vestergaard, R. VangCenter for Atomic scale Materials Physics, University of Aarhus
S. Dahl, S. Helveg, B. S. Clausen, J. Rostrup-Nielsen, J. Sehested, J. HyldtroftHaldor Topsøe A/S
J. R. Kitchin, J. G. ChenUniversity of Delaware
U. Stimming, PandelovTechnical University Munich
The old volcanos
Trasatti, J. Electroanal. Chem., 39, 163 (1972) O’M Bockris, Reddy, Gamboa-Aldeco, Modern Electrochemistry 2A (2000).
Nudging the reactivity by alloyingCalculated d band shifts:
Overlayer
Host
Ruban, Hammer, Stoltze, Skriver, Nørskov, J.Mol.Catal. A 115, 421 (1997)
Methane activation on Ni/Ru
Ni Coverage [ML]0 1 2
Initi
alst
icki
ngpr
obab
ility
0
1e-7
2e-7
3e-7
4e-7
5e-7Thermal dissociation of CH4 at T = 530 K
Egeberg, Chorkendorff, Catal. Lett. 77, 207 (2001)
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