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Metal oxides have always been considered as promising non-noble metal catalysts for VOC elimination and generally show distinct performance based on their reactive oxygen species (ROS). This work originally investigated the roles of adsorbed oxygen (O ads ) and lattice oxygen (O lat ) species in the catalytic oxidation of o -xylene. A series of metal oxide catalysts were synthesized through the pyrolysis of MOF precursors. The CeO 2 catalyst showed performance superior to that of other metal oxides at lower temperature, while the Co 3 O 4 catalyst had advantages over other metal oxides in the complete oxidation of o -xylene and CO 2 generation but also exhibited a larger decrease of o -xylene conversion with the drop of O 2 concentration. The o -xylene-TPD and o -xylene-TPSR ( 18 O 2 /He) profiles of CeO 2, Co 3 O 4, and CuO indicated that the O ads served as the primary ROS of CeO 2 and that the O lat played decisive roles in the cases of Co 3 O 4 and CuO. Notably, the surface O lat of Co 3 O 4 could be rapidly and completely replenished by gaseous oxygen, relying more on gaseous oxygen compared to CuO. Furthermore, in situ DRIFTS studies and DFT calculations disclosed the interactions of different ROS with o -xylene. The O ads on the CeO 2 surface favored the adsorption and cleavage oxidation of the aromatic ring at lower temperature, while the O lat on the Co 3 O 4 and CuO surface preferentially oxidized methyl groups and favored the oxidation of intermediates. Therefore, the different interactions with o -xylene and replenishment of ROS are responsible for the performance differences of CeO 2, Co 3 O 4, and CuO in the catalytic oxidation of o -xylene. This work might provide insights into the catalytic mechanism of metal oxides and benefit the design and application of efficient metal oxide catalysts for VOC elimination.
Ma et al. (Sat,) studied this question.