Defect-Driven Redox Interplay on Anatase TiO₂: Surface-Structure Dependent Activation for CO₂ Hydrogenation Catalysis

Area of Science:

• Materials Science
• Surface Chemistry
• Catalysis

Background:

• Titanium dioxide (TiO2) is a key material in energy and environmental catalysis.
• Atomistic mechanisms of TiO2's dynamic response to reactive environments are poorly understood.
• Understanding these mechanisms is crucial for optimizing TiO2-based catalysts.

Purpose of the Study:

• To elucidate the atomistic mechanisms of anatase TiO2's dynamic response to H2 and CO2.
• To investigate the interplay between oxygen loss and replenishment on TiO2 surfaces.
• To correlate surface structure, defect dynamics, and reactivity for catalyst design.

Main Methods:

• 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
• Theoretical modeling

Main Results:

• H2 exposure causes TiO2 reduction via lattice oxygen loss, forming Ti3O5.
• CO2 exposure leads to oxygen replenishment, reversing TiO2 stoichiometry.
• The reverse water-gas shift (RWGS) reaction is selective to stepped/high-indexed TiO2 surfaces.
• H2 pretreatment creates oxygen vacancies, activating inert TiO2(101) facets for RWGS catalysis.

Conclusions:

• Defect engineering, specifically creating oxygen vacancies, can activate inert TiO2 facets.
• Understanding the atomic-scale competition between reduction and oxidation pathways is key.
• This work provides insights for designing adaptive catalysts for sustainable fuel synthesis.