Oxygen vacancy-mediated MnO catalyst with high efficiency and stability for toluene oxidation.

Oxygen vacancy engineering in transition metal oxides is an effective strategy for improving catalytic performance. Herein, defect-enriched MnO catalysts were constructed by controlling the calcination temperature. The high content of oxygen vacancies and accompanying Mn ions were generated in MnO catalysts calcined at low temperature, which could greatly improve the low-temperature reducibility and migration of surface oxygen species. DFT theoretical calculations further confirmed that molecular oxygen and toluene were easily adsorbed over defective α-MnO (222) facets with an energy of -0.29 and -0.48 eV, respectively, and corresponding OO bond length is stretched to 1.43 Å, resulting in the highly reactive oxygen species. MnO-300 catalyst with abundant oxygen vacancies exhibited the highest specific reaction rate and lowest activation energy. Furthermore, the optimized catalyst possessed the outstanding stability, water tolerance and CO yield. In comparison with the fresh MnO-300 catalyst, the physical structure and surface property of the used catalyst remained almost unchanged regardless of whether undergoing the stability test at consecutive catalytic runs as well as high temperature, and water resistance test. In situ DRIFTS spectra further elucidated that introducing the water vapor had little effect on the reaction intermediates, indicating the excellent durability of the defect-enriched catalyst.