Construction of copper-modified indium oxide with asymmetric oxygen vacancies for carbon dioxide hydrogenation to...

The construction of defect sites and tandem catalytic systems is an important strategy for the high-value conversion of CO₂. In this study, Cu-In₂O₃ with asymmetric oxygen vacancies (Cu-In₂O₃-AO_v) was prepared through local structural regulation. It was then combined with UiO-66 to form a tandem catalytic system that enables the cascade process of CO₂ activation, conversion of oxygenated intermediates, and aromatization. Low-temperature controlled reduction and local Cu coordination modulation constructed non-equivalent InO coordination environments on the In₂O₃ surface, which generated oxygen vacancies with structural and electronic heterogeneity. Aberration-corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) results show that Cu substitutes for a portion of the In sites and forms a local asymmetric coordination environment. Synchrotron X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) further shows local structural distortion and the presence of multiple coordination environments in the catalyst. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicate that Cu-In₂O₃-AO_v promotes the conversion of CO₂, the formation of key oxygenated intermediates (i.e., HCOO* and CH₂O*), and accelerates the formation of aromatic precursors. Density functional theory (DFT) calculations demonstrate that asymmetric oxygen vacancies are capable of tuning the local electron distribution, enhancing CO₂ adsorption and activation, and reducing the energy barriers of key reaction steps. Under the reaction conditions of 320 °C, 3.0 MPa, a H₂/CO₂ molar ratio of 3:1, and a W(1%Cu-In₂O₃-AO_V)/W(UiO-66) ratio of 1:2, the tandem catalyst shows the best catalytic performance with the CO₂ conversion of 28.6% and the aromatics selectivity of 72.3%. This study reveals the structural effect and reaction mechanism of asymmetric oxygen vacancies in CO₂ hydrogenation. It also provides experimental and theoretical support for the rational design of defective metal oxide/MOFs tandem catalytic systems for high-value CO₂ conversion.