The Nature of Hydrogen Production from Aqueous‐Phase Methanol Dehydrogenation with Ruthenium Pincer Complexes Under Mild Conditions

Abstract

Abstract A density functional theory (DFT) study was performed to unveil the nature of dihydrogen (H 2 ) production from aqueous‐phase methanol dehydrogenation catalyzed by a ruthenium pincer complex. Three catalytic cycles of methanol, formaldehyde, and formate dehydrogenations were investigated at the ωB97X‐D/BSI level. The calculated results indicate that the methanol‐assisted hydrogen‐release step is much more favorable than the direct hydrogen‐release one. The dehydrogenation step, the methanol‐assisted hydrogen‐release step, and the CO 2 ‐release step are the rate‐determining steps of methanol, formaldehyde, and formate dehydrogenations (stage I, stage II, and stage III), respectively. In addition, the formate dehydrogenation is proposed to be more difficult than the methanol and formaldehyde dehydrogenations according to calculated free‐energy profiles. Methanol and formaldehyde dehydrogenation likely follow an outer‐sphere mechanism, but formate dehydrogenation could involve both outer‐sphere and inner‐sphere mechanisms. These results add to our fundamental understanding of this efficient hydrogen‐generation reaction from methanol, which could be helpful in the implementation of the methanol/hydrogen economy.