The Microenvironment Change of Isolated Co Sites in Silicalite-1 Zeolite Induced by Balancing Cations for Boosting Propane Dehydrogenation
Xueqiu Wu, Shaojia Song, Min Yang, Peng Zhang, Chunming Xu, Yuechang Wei, Guoyong Huang, Jian Liu, Weiyu Song
Abstract
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 Co 3c active site and polarized O atoms. These findings provide novel insight into modulating the microenvironment of the active center in heterogeneous catalysis.