Step enhanced dehydrogenation of ethanol on Rh

We have investigated the adsorption and decomposition of ethanol on the Rh(1 1 1) and Rh(5 5 3) surfaces at room temperature with special emphasis on the dehydrogenation. We use high resolution core level photoemission and density functional theory (DFT) based simulations. A detailed analysis of the C1s core level spectra, including analysis of the vibrational fine-structure and comparison to calculated C1s binding energy shifts, shows that the ethanol decomposes into CO, ethylidyne (C2H3), methylidyne (CH), atomic C, and hydrogen. At low ethanol exposures, CH is the dominating hydrocarbon fragment on Rh(1 1 1), whereas on Rh(5 5 3) atomic C dominates over CH, indicating an enhanced dehydrogenation due to the steps present on the latter surface. At higher ethanol exposures we find a similar behavior of atomic C dominating over hydrocarbons on Rh(5 5 3), while on Rh(1 1 1) atomic carbon remains a minority species. Our DFT based simulations show that the enhanced dehydrogenation results from a significant lowering of the CH dissociation barrier from Rh(1 1 1) to Rh(5 5 3), as well as from the dissociation changing from endothermic on Rh(1 1 1) to exothermic on Rh(5 5 3).