Oxygen vacancy defect engineering to promote catalytic activity toward the oxidation of VOCs: a critical review

Oxygen vacancy defect (OVD) engineering has been recognized as an effective strategy to prepare high-performance catalysts for the oxidation of volatile organic compounds (VOCs) because the generated oxygen-deficient sites can lead to an unbalanced electronic structure, resulting in rapid electron transfer, reducing the reaction temperature. Herein, the latest technologies used to increase the OVDs on the catalysts have been introduced and discussed based on the possible catalytic oxidation mechanism, especially the relationship between OVD and catalytic activity for gaseous VOC oxidation. Four approaches to generate OVDs have been summarized: (i) Control over the synthesis and/or calcination temperature, (ii) atom substitution (isovalent-substitution and aliovalent-substitution), (iii) surface modification (noble metal doping and transition metal doping), and (iv) in situ surface treatment (chemical etching and surface reduction). The novel and advanced characterization methods (HRTEM, STM, XPS, Raman, EPR, PALS, EELS, and XAFS) used to understand the existence of OVDs have been summarized. Furthermore, the potential future research on OVD engineering based on amorphous structure generation has been discussed. This review is expected to provide guidance for the design and fabrication of more effective catalysts used for VOC oxidation at lower temperatures.