Methane dehydrogenation on monomeric Rh center located on (100) γ-alumina — A theoretical study

The reaction mechanism of methane dehydrogenation on monomeric Rh center located on (100) γ-alumina has been theoretically investigated at the PBE0/cc-pVTZ, SDD level. The (100) face of γ-alumina support is represented by an Al8O26H28 cluster, which is cut out from the ideal crystal structure. Then, two model Rh/γ-Al2O3 catalysts, in which Rh center interacts with one oxygen or two oxygen atoms of the (100) surface of γ-Al2O3, have been compared and denoted as Rh/Al8O26H27 and Rh/Al8O26H26, respectively. Toward methane activation, the model catalyst Rh/Al8O26H27 exhibits better performance than Rh/Al8O26H26. For the first CH bond cleavage of methane, the lowering of activation barriers on Rh/Al8O26H27 is mainly caused by lower substrate activation strain ΔE≠strain[substr], which is from substrate equilibrium geometry to the geometry it adopts in the TS, in comparison with that on Rh/Al8O26H26. These results are in qualitative agreement with the experimental results, where the partially reduced Rh+ is one of the active sites for methane dissociation.