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 (In₂ O₃ , ZnO, Cr₂ O₃ , and ZrO₂ ) to combine with H-ZSM-5 for the hydrogenation of CO₂ 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 C₂₊ hydrocarbon products over In₂ O₃ /H-ZSM-5 and ZnO/H-ZSM-5. While, the thermomigration ability of chromium and zirconium species is not significant, endowing Cr₂ O₃ /H-ZSM-5 and ZrO₂ /H-ZSM-5 catalysts with high selectivity of C₂₊ hydrocarbons.