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 immobi-lization 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) (T-d-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 H-2-reduction process. A systematic characterization and DFT calculation prove the exis-tence 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.

Automated summary

Highly dispersed metal sites on silica surface achieved by immobilizing metal precursor within hydroxyl groups have gained attention. However, the role of adsorbed water derived from hydroxyl groups is often overlooked. This study illustrates the importance of sufficient adsorbed water in forming highly dispersed tetrahedral Co(II) sites. The adsorbed water induces the transformation of Co(NO3)(2) precursor into [Co(H2O)(6)](2+) intermediate, facilitating the formation of highly dispersed Td-cobalt(II) sites during H-2-reduction. The synthesized catalyst shows improved reactivity in propane dehydrogenation compared to other reported Co-based catalysts.