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

Abstract

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 <i>T</i>₅₀ 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 <i>in situ</i> 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.