External Surface Engineering of Zeolites to Mitigate Indium Poisoning in Tandem Catalytic CO ₂ Hydrogenation

As environmental and energy issues become increasingly apparent, the tandem catalytic hydrogenation of CO2 for direct hydrocarbon production has attracted significant attention. However, zeolite deactivation caused by metal migration severely hampers its development. This work reveals that for the In2O3/ZSM-5 catalyst in CO2 hydrogenation, indium species preferentially migrate to the external surface of ZSM-5 and interact with hydroxyl groups (e.g., Brønsted acid sites (BAS) and SiOH) via solid-state ion exchange, which is related to the subsequent poisoning of BAS within micropores. Based on this insight, a surface engineering strategy was developed by grafting silane onto the external surface, which significantly enhanced the resistance to indium poisoning. After a 22-h reaction, the silane-modified catalyst (In2O3/ZSM-5-SiPr) retained nearly all of its strong acid sites and maintained a C2+ hydrocarbon selectivity of >92.0%. However, the unmodified catalyst suffered a 60% loss of the number of strong acid sites and yielded 0% C2+ selectivity. The derived 0.6Si/In2O3/ZSM-5-SiPr achieved a C2+ selectivity of >92.0% with a space-time yield (STY) of 3.66 mmol goxide–1 h–1, which is more than 2.6 times higher than that of the reported powder-mixed In2O3 tandem catalysts, and demonstrated stability for over 260 h under harsh conditions. This strategy is generally applicable to multiple zeolites with varying Si/Al ratios and topologies. This work provides a universal approach for designing stable and highly active tandem catalysts resistant to metal migration during CO2 hydrogenation.