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

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-AOv) 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-AOv 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-AOV)/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.