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Visualizing Element Migration over Bifunctional Metal-Zeolite Catalysts and its Impact on Catalysis.

The catalytic performance of composite catalysts is not only affected by the physicochemical properties of each component, but also the proximity and interaction between them. Herein, we employ four representative oxides (In 2 O 3 , ZnO, Cr 2 O 3 , and ZrO 2 ) to combine with H-ZSM-5 for the hydrogenation of CO 2 to hydrocarbons directed by methanol intermediate and clarify the correlation between metal migration and the catalytic performance. The migration of metals to zeolite driven by the harsh reaction conditions can be visualized by electron microscopy, meanwhile, the change of zeolite acidity is also carefully characterized. The protonic sites of H-ZSM-5 are neutralized by mobile indium and zinc species via a solid ion-exchange mechanism, resulting in a drastic decrease of C 2+ hydrocarbon products over In 2 O 3 /H-ZSM-5 and ZnO/H-ZSM-5. While, the thermomigration ability of chromium and zirconium species is not significant, endowing Cr 2 O 3 /H-ZSM-5 and ZrO 2 /H-ZSM-5 catalysts with high selectivity of C 2+ hydrocarbons. This work preliminarily unveils the overlooked element migration and its profound impact on the catalytic behaviors of bifunctional catalysts for CO/CO 2 hydrogenation, providing insights into the rational design of emerging multifunctional catalysts.