Density functional study of ethanol decomposition on Rh(111)

Ethanol decomposition on Rh(111) is systematically investigated using periodic density functional theory (DFT) calculations. The various adsorption modes of the intermediates involved are located. It is determined that ethanol adsorbs weakly on the Rh(111) surface. CH₃CH₂O, CH, and H prefer 3-fold sites with adsorption energies of 49.9, 146.6, and 64.3 kcal/mol, respectively. CO binds stably at the top site with a binding energy of 42.5 kcal/mol. CH₂CH₂O (3-fold-n¹(C ⁿ)-n¹(O)) and CHCO (3-fold-n²(C ⁿ)-n¹(C^α)) are inclined to adsorb on the surface to make the C and O atoms saturated. For the other intermediates, adsorption configurations are bridge-n¹(Cⁿ)-n ¹(O) for CH₂CHO, 3-fold-n¹(C ⁿ)-n¹(C^α)-n¹(O) for CH ₂CO, and 3-fold-n²(Cⁿ)-n¹(O) for CHCHO. For intermediates going along the decomposition pathway, energy barriers for the Cⁿ-H and C-C bond scission are gradually decreased; however, for the C^α-H or C-O bond cleavage, the energy barrier decreases first and then rises, presenting a V-shaped curve. The most favorable decomposition route for ethanol on Rh(111) is CH₃CH₂OH → CH₃CH₂O → CH₂CH₂O → CH₂CHO → CH₂CO → CHCO → CH + CO → C + CO, in which the dehydrogenation of CH₃CH₂O is the rate-determining step. © 2010 American Chemical Society.