Illustrating new understanding of adsorbed water on silica for inducing tetrahedral cobalt(II) for propane dehydrogenation

Highly dispersed metal sites on the surface of silica, achieved from immobilization of metal precursor within hydroxyl groups, has gained increasing attention in the field of heterogeneous catalyst. However, the special role of adsorbed water derived by hydroxyl groups on the silica is generally ignored. Herein, a new understanding of adsorbed water on the formation of highly dispersed tetrahedral Co(II) (Td-cobalt(II)) sites is illustrated. It is indicated that sufficient adsorbed water induces the transformation of precursor of Co(NO3)2 into intermediate of [Co(H2O)6]2+. Subsequently, [Co(H2O)6]2+ makes the highly dispersed Td-cobalt(II) sites to be available during direct H2-reduction process. A systematic characterization and DFT calculation prove the existence of the adsorbed water and the importance of the intermediate of [Co(H2O)6]2+, respectively. The as-synthesized catalyst is attempted to the propane dehydrogenation, which shows better reactivity when compared with other reported Co based catalysts.