Proton-exchange membrane (PEM) fuel cells utilizing hydrogen as a fuel are a promising source for energy generation.  However, hydrogen gas is not readily available from sustainable resources and the source of hydrogen must be considered for development of sustainable energy production.  Dehydrogenation and partial oxidation of bioethanol to hydrogen gas can provide a renewable hydrogen source for PEM fuel cells.  Experimental studies have shown the success of Rh and Ni as catalysts for the partial oxidation of ethanol¹ (CH₃CH₂OH + H₂O → 4H₂ + CO), but the elementary steps of the reaction mechanism have not been determined.  Ab initio methods such as density functional theory (DFT) have been widely utilized for probing energies and reaction pathways for a variety of heterogeneous catalytic systems and are proving to be a good complement to experimental efforts.  Here, periodic DFT calculations are used to investigate the elementary steps of ethanol dehydrogenation and partial oxidation over single-crystal Rh(111), Ni(111), and Pd(111) surfaces as a model of the experimental catalysts.  The full dehydrogenation and C-C bond cleavage mechanism of ethanol to form C_ads , CO_ads and H₂ over a Rh(111) catalyst surface (and new results for dehydrogenation over Ni(111) and Pd(111) surfaces) will be presented, utilizing the Bell-Evans-Polanyi^2,3 approximation that the kinetic pathway can be determined from the thermodynamic reaction energies.

1)  Deluga, G.A., et al., Science 303 (2004) 993.

2)  Liu, Z., Hu, P., J. Chem. Phys. 115 (2001) 4977.

3)  Michaelides, A, et al., J. Am. Chem. Soc. 125 (2003) 3704.