We applied periodic density-functional theory to investigate the dehydrogenation of ethanol with and without H2O molecules on a 2Rh/γ-Al2O3(110) surface. In the absence of H 2O, the adsorption energy of ethanol on the surface was calculated to be -31.34 kcal/mol; ethanol might form a four- or five-membered-ring (oxametallacyclic) structure on the surface. Both rings are stable but can be dehydrogenated to form aldehyde and ethene, or the C-C bond can break to form CH3(a) + CO(a) with a dissociation barrier of 24.92 kcal/mol, eventually. When water molecules (3H2O) are present on the surface, the adsorption energy of ethanol is decreased to -21.25 kcal/mol; ethanol can neither form a ring structure on the surface nor create a path to produce aldehyde or ethene, but instead undertakes uniquely the scission of the C-C bond, forming CH3(a) + CO(a) with a barrier of 21.55 kcal/mol.
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