Understanding the\nDifferent Roles of Adsorbed Oxygen\nand Lattice Oxygen Species in the Distinct Catalytic Performance of\nMetal Oxides for <i>o</i>‑Xylene Oxidation

Metal oxides have always been considered as promising\nnon-noble\nmetal catalysts for VOC elimination\nand generally show distinct performance based on their reactive oxygen\nspecies (ROS). This work originally investigated the roles of adsorbed\noxygen (O<sub>ads</sub>) and lattice oxygen (O<sub>lat</sub>) species\nin the catalytic oxidation of <i>o</i>-xylene. A series\nof metal oxide catalysts were synthesized through the pyrolysis of\nMOF precursors. The CeO<sub>2</sub> catalyst showed performance superior\nto that of other metal oxides at lower temperature, while the Co<sub>3</sub>O<sub>4</sub> catalyst had advantages over other metal oxides\nin the complete oxidation of <i>o</i>-xylene and CO<sub>2</sub> generation but also exhibited a larger decrease of <i>o</i>-xylene conversion with the drop of O<sub>2</sub> concentration.\nThe <i>o</i>-xylene-TPD and <i>o</i>-xylene-TPSR\n(<sup>18</sup>O<sub>2</sub>/He) profiles of CeO<sub>2</sub>, Co<sub>3</sub>O<sub>4</sub>, and CuO indicated that the O<sub>ads</sub> served\nas the primary ROS of CeO<sub>2</sub> and that the O<sub>lat</sub> played decisive roles in the cases of Co<sub>3</sub>O<sub>4</sub> and CuO. Notably, the surface O<sub>lat</sub> of Co<sub>3</sub>O<sub>4</sub> could be rapidly and completely replenished by gaseous oxygen,\nrelying more on gaseous oxygen compared to CuO. Furthermore, <i>in situ</i> DRIFTS studies and DFT calculations disclosed the\ninteractions of different ROS with <i>o</i>-xylene. The\nO<sub>ads</sub> on the CeO<sub>2</sub> surface favored the adsorption\nand cleavage oxidation of the aromatic ring at lower temperature,\nwhile the O<sub>lat</sub> on the Co<sub>3</sub>O<sub>4</sub> and CuO\nsurface preferentially oxidized methyl groups and favored the oxidation\nof intermediates. Therefore, the different interactions with <i>o</i>-xylene and replenishment of ROS are responsible for the\nperformance differences of CeO<sub>2</sub>, Co<sub>3</sub>O<sub>4</sub>, and CuO in the catalytic oxidation of <i>o</i>-xylene.\nThis work might provide insights into the catalytic mechanism of metal\noxides and benefit the design and application of efficient metal oxide\ncatalysts for VOC elimination.