Density-functional calculation of the adsorption and reaction of CO and H2O molecules over a 4Rh/CeO2(1Â 1Â 1) surface

We apply periodic density-functional theory (DFT) to investigate the water-gas-shift reaction, CO + H2O → CO2 + H2, on a 4Rh/CeO2(1 1 1) surface. Our calculated result shows that the 4Rh atoms gather together to form a cluster shape on the CeO2(1 1 1) surface (designated as 4Rh/CeO2(Rh-cluster)) would possess the largest mean adsorption energy, while that locating separately on top of Ce's (designated as 4Rh/CeO2(Rh-Ce)) the least. The CO molecule with its C-terminus facing toward the Rh atom at “a” position (Rha) of the 4Rh/CeO2(Rh-cluster) surface (designated as OC-Rha(a)) is calculated to have the greatest adsorption energy, 67.44 kcal/mol. A similar adsorption conformation of greatest adsorption energy is found for the H2O molecule, 24.2 kcal/mol. Among the possible reaction paths the one via carboxyl intermediate is more favorable. The calculated maximum barrier in this path is 25.87 kcal/mol, which involves the detachment of an H atom and the release of an CO2(g) from the adsorbed carboxyl intermediate HOOC-Rha(a).