The Microenvironment Change of Isolated Co Sites in Silicalite-1 Zeolite Induced by Balancing Cations for Boosting Propane Dehydrogenation

The metals that are embedded in zeolite frameworks exhibit a specific catalytic performance in combination with the corresponding microenvironment. The charge balancing cations that are produced by the valence mismatch between the doped metal and the Si atoms play a paramount role in modulating the microenvironment. Based on an ab initio molecular dynamics (AIMD) simulation and X-ray adsorption spectroscopy (XAS), we disclose for the first time that the local coordination of the Co active center in the Co@S-1 catalyst reduces from 4 to 3 after the charge balancing cations change from Na+ to H+. Such a dramatic change in the microenvironment greatly affects the catalytic performance. It was determined that the initial propane conversion surprisingly increases from 4.1% to 41.3% during propane dehydrogenation (PDH) due to this change. Further experiments and calculations verify that the H–Co@S-1 catalyst lowers both the first and second dehydrogenation energy barriers with its exoteric Co3c active site and polarized O atoms. These findings provide novel insight into modulating the microenvironment of the active center in heterogeneous catalysis.