Chemisorbed Superoxide Species Enhanced the High Catalytic Performance of Ag/Co₃O₄ Nanocubes for Soot Oxidation

The respective action mode between surface-adsorbed oxygen and bulk lattice oxygen during catalytic soot oxidation is still not fully recognized. Herein, a series of Ag-loaded Co3O4 catalysts with different Ag loading amounts were prepared by the impregnation method, and 5% Ag/Co3O4 presented competitive catalytic activity toward soot combustion with a T50 below 290 °C in 10% O2/N2. This remarkable improvement in catalytic performance could be primarily attributed to the enhanced Ag–Co3O4 metal–support interaction induced by the formation of uniform, dispersive, and suitable size metallic Ag nanoparticles. The activation, activity, consumption–regeneration, identification, and reaction of surface-adsorbed oxygen along with the activity of bulk lattice oxygen were characterized by various designed and in situ techniques. The results demonstrated that the chemisorbed superoxide species (O2–) play the potentially responsible role for boosting soot combustion, while the bulk lattice oxygen is much less active within the tested temperatures, inducing a negligible activity contribution. Moreover, soot-temperature programmed reduction, isothermal kinetic study, and density functional theory calculation provided supplementary support for the enhancement effect of Ag–Co3O4 combination in the activation and utilization of surface-adsorbed oxygen. The overall objective of this work is to identify the role of surface-adsorbed oxygen and bulk lattice oxygen for soot oxidation over Ag/Co3O4 catalysts.