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 CO 2 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 In 2 O 3 /ZSM-5 catalyst in CO 2 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 (In 2 O 3 /ZSM-5-SiPr) retained nearly all of its strong acid sites and maintained a C 2+ hydrocarbon selectivity of >92.0%. However, the unmodified catalyst suffered a 60% loss of the number of strong acid sites and yielded 0% C 2+ selectivity. The derived 0.6Si/In 2 O 3 /ZSM-5-SiPr achieved a C 2+ selectivity of >92.0% with a space-time yield (STY) of 3.66 mmol g oxide –1 h –1, which is more than 2.6 times higher than that of the reported powder-mixed In 2 O 3 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 CO 2 hydrogenation.