Mechanistic insights and the role of spatial confinement in catalytic dimethyl ether carbonylation over SSZ-13 zeolite

Abstract

The SSZ-13 zeolite, which exhibits typical CHA topology characterized by 8-membered ring (8-MR) channels, has shown potential for catalyzing dimethyl ether (DME) carbonylation. However, current studies have yet to provide a comprehensive analysis of its catalytic mechanisms. In this study, we investigated the mechanism of SSZ-13-catalyzed DME carbonylation and the role of spatial confinement in this reaction. By exploiting the differences in the radii of the metal ions, we selectively replaced Brønsted acid sites (BAS) within specific channels, as confirmed by quantitative acidity analysis. Combining the activity data and the dissociation energies of the reactants on the BAS within different rings, we found that both the main and side reactions of DME carbonylation occurred on the 8-MR BAS of SSZ-13. Furthermore, the exchange of ions of different radii highlighted the confinement effect of the pore space in the SSZ-13 zeolite. Characterization of the deposits in spent catalysts, along with theoretical insights, revealed that the reduced cage space adversely affects the stabilization of side reaction intermediates, which in turn mitigates side reactions and improves the selectivity toward methyl acetate. This study presents an effective approach to modulate the acid site distribution and spatial confinement and provides critical insights into the determinants of the catalytic performance of SSZ-13. These findings offer valuable guidance for the future design and optimization of zeolites, aiming to enhance their efficacy in catalytic applications.