Effects of Lewis acid strength of monovalent coinage metals and zeolite frameworks on catalytic CO2 cycloaddition with ethylene oxide: A DFT study

Abstract

CO₂ cycloaddition with epoxides is one of the potential routes to convert a waste product to more value-added products. In this work, the M06-L functional was employed to study the structure and electronic properties of complexes along the catalytic process in monovalent-exchanged zeolites. For the FAU zeolite, it was found that the greater Lewis acid character of Au(I) in FAU zeolite makes the Au(I)-FAU slightly more active than Cu(I)- and Ag(I)-FAU zeolites. Compared to the catalytic performance of Cu(II)-FAU zeolite (W. Sangthong and J. Sirijaraensre, J. Mol. Graph. Model., 2022, 117, 108321), these monovalent cations are still inappropriate catalysts for this reaction. In channel-type zeolites such as BEA and ZSM-5 zeolites, Au(I) is in the form of bidentate complex. The host–guest complementarity in the ZSM-5 framework makes Au(I) more catalytically active than the Au(I) in the FAU framework, due mainly to the greater stabilization of the transition state of CO₂ cycloaddition. The catalytic performance of Au(I) in zeolites is in the order of ZSM-5 (E_a = 25.8 kcal mol⁻¹) > BEA (E_a = 28.1 kcal mol⁻¹) > FAU (E_a = 34.1 kcal mol⁻¹). This study enhances the understanding of catalytic monovalent coinage cations and the effects of zeolite frameworks on the CO₂ cycloaddition reaction with ethylene oxide.