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.