Liquid-like Indium Mobility Governs the Activity, Selectivity, and Stability of In2O3–ZrO2/SAPO-34 Catalysts for Syngas-to-Olefin Conversion

Abstract

Indium-based oxide–zeolite catalysts have recently attracted attention for selective hydrocarbon synthesis from C1 feedstocks, yet their performance in syngas-to-light-olefin conversion remains poorly understood. In particular, the stability of indium species under hydrogen-rich conditions and their interaction with acidic zeotype components remain key challenges. Here, we investigate the structure–function relationships of In2O3–ZrO2/SAPO-34 catalysts for syngas conversion to light olefins, focusing on the roles of indium loading, oxide–zeolite ratio, and catalyst pretreatment. Catalytic testing combined with operando X-ray absorption spectroscopy, quasi in situ X-ray photoelectron spectroscopy, transmission electron microscopy, and NH3 temperature programmed-desorption reveals that catalyst performance is governed by the mobility and redistribution of indium species under reaction conditions. A catalyst containing 5 wt % In2O3 on ZrO2 exhibits the most favorable performance, achieving CO conversion up to ∼50% and stable C2–C4 olefin selectivity exceeding 70%, whereas higher indium loading leads to rapid deactivation associated with indium migration and partial blocking of access to zeolite acid sites by small indium nanoparticles. Importantly, H2 + H2O pretreatment stabilizes the high-loading catalyst by promoting the formation of larger indium particles and enhancing indium retention on ZrO2, thereby limiting migration toward SAPO-34 and preserving acid site accessibility. These findings demonstrate that indium mobility and oxide–zeolite interactions critically control activity and selectivity in In-based OX–ZEO catalysts and provide a strategy to stabilize highly active catalysts for syngas-to-olefin conversion.