Identifying Oxygen Activation/Oxidation Sites for Efficient Soot Combustion over Silver Catalysts Interacted with Nanoflower-Like Hydrotalcite-Derived CoAlO Metal Oxides

Catalytic oxidation is an effective way to eliminate soot pollution emitted from diesel engines. However, the origination and specific location of active oxygen species are still unclear over noble metal catalysts because of the complex gas (oxygen)-solid (catalyst)-solid (reactant) reaction systems. Herein, we report the high catalytic performance of the nanoflower-like hydrotalcite-derived CoAlO-supported Ag catalyst synthesized by a facile hydrothermal method for soot combustion. Our characterization results demonstrate that metallic Ag nanoparticles (NPs) are highly dispersed on the CoAlO support because of their interactions through electron donation from Co to Ag species. The isotopic O-18(2) adsorption/desorption results reveal that gaseous oxygen is readily adsorbed and dissociated on these electron-enriched Ag NPs rather than oxygen vacancies of the CoAlO support. From the O-18(2) isothermal soot oxidation results, we newly discover that surface oxygen species adsorbed on Ag sites directly participate in soot oxidation, while those on the CoAlO support only play a negligible role. The kinetic results show that the strengthened Ag-CoAlO interactions can promote not only the quantity but also the intrinsic activity of oxygen species on Ag sites for soot combustion. In addition, the nanoflower-like morphology of the catalyst can greatly improve the soot-catalyst contact efficiency to further enhance the catalytic performance. Our work brings an insight into the identification of oxygen activation/oxidation sites involved in soot oxidation over Ag catalysts supported on hydrotalcite-derived CoAlO metal oxides by systematic isotopic and kinetic investigations, which is beneficial to the rational design of other related catalytic systems.