Tracking Dynamics of Supported Indium Oxide Catalysts in CO₂ Hydrogenation to Methanol by In Situ TEM.

Abstract

Supported reducible oxides, such as indium oxide on monoclinic zirconia (In₂O₃/m-ZrO₂), are promising catalysts for green methanol synthesis via CO₂ hydrogenation. Growing evidence suggests that dynamic restructuring under reaction conditions plays a crucial but poorly understood role in catalytic performance. To address this, the direct visualization of the state-of-the-art In₂O₃/m-ZrO₂ catalyst under CO₂ hydrogenation conditions (T  =  553 K, P  =  1.9 bar, CO₂:H₂  =  1:4) is pioneered using in situ scanning transmission electron microscopy (STEM), comparing its behavior to In₂O₃ on supports with similar (tetragonal, t-ZrO₂ or anatase TiO₂) or lower (LSm-ZrO₂) surface areas. Complementary in situ infrared spectroscopy and catalytic tests confirm methanol formation under equivalent conditions. A machine-learning-based difference imaging approach differentiates and ranks restructuring patterns, revealing that partially reduced InO_x species on m-ZrO₂ undergo cyclic aggregation-redispersion via atomic surface migration, maintaining high active phase dispersion. High-resolution ex situ STEM analysis further shows the epitaxial formation of In₂O₃ mono- and bilayers on (100) m-ZrO₂ facets, highlighting strong oxide-support interactions. In contrast, sintering prevails on t-ZrO₂, a-TiO₂, and low-surface m-ZrO₂, correlating with lower methanol productivity. This work underscores the pivotal role of oxide-support interfacial interactions in the reaction-induced restructuring of InO_x species and establishes a framework for tracking nanoscale catalyst dynamics.