Defect-Driven Redox Interplay on Anatase TiO₂: Surface-Structure Dependent Activation for CO₂Hydrogenation Catalysis

Titanium dioxide (TiO₂) is one of the most extensively studied oxides as an active catalyst or catalyst support, particularly in energy and environmental applications, but the atomistic mechanisms governing its dynamic response to reactive environments and their correlation to reactivity remain largely elusive. Using in situ environmental transmission electron microscopy (ETEM), synchrotron X-ray diffraction (XRD), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), temperature-programmed reduction (TPR), reactivity measurements, and theoretical modeling, we reveal the dynamic interplay between oxygen loss and replenishment of anatase TiO₂under varying reactive conditions. Under H₂exposure, anatase TiO₂undergoes surface reduction via lattice oxygen loss, forming Ti₃O₅. In contrast, CO₂exposure induces oxygen replenishment, reversing stoichiometry. In mixed H₂/CO₂environments, the reverse water–gas shift (RWGS) reaction proceeds selectively on stepped and high-indexed TiO₂surfaces, whereas the thermodynamically stable TiO₂(101) surface remains inactive and intact. Critically, H₂pretreatment generates oxygen vacancies on TiO₂(101), transforming it into an active Ti₃O₅or defect-rich surface that catalyzes RWGS. By correlating surface structure, defect dynamics, and gas-phase interactions, this work deciphers the competition between H₂-driven reduction and CO₂-driven oxidation pathways at the atomic scale. These insights establish defect engineering as a strategic lever to activate inert TiO₂facets, advancing the design of adaptive catalysts for sustainable fuel synthesis technologies.