Catalytic Soot Combustion Over Ag Or K Promoted Nanoflower-like Hydrotalcite-derived CoAlO Oxides

Diesel engines are utilized for heavy duty vehicles owing to the superior fuel efficiency and low-operating cost under lean combustion conditions.Soot particulates emitted by these engines cause serious health and environment problems.Trapping on a diesel particulate filter（DPF）combined with catalytic oxidation is considered as a promising technology to eliminate them.The nanoflower-like hydrotalcite-derived CoAlO-supported Ag catalyst（Ag/Co-LDO-H）is synthesized by a facile hydrothermal method for soot combustion.Compared with the Ag/Co-LDO-C reference catalyst synthesized by a co-precipitation method,the metallic Ag nanoparticles（NPs）are highly dispersed and stabilized on the CoAlO support because of their strengthened interactions through electron donation from Co to Ag species on Ag/Co-LDO-H.The ¹⁸O₂ isothermal experiment results demonstrate that the active oxygen species participating in soot oxidation are originated from adsorbed and dissociated oxygen on these electron-enriched Ag NPs,and 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 active oxygen species on the Ag NPs 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.Therefore,Ag/Co-LDO-H exhibits the higher activity in catalytic soot combustion due to the higher intrinsic activity,the higher dispersion of Ag NPs and the improved soot-catalyst contact efficiency.The nanoflower-like hydrotalcite-derived CoAlO-supported K catalyst（5K/Co-LDO-H）is synthesized by the hydrothermal method for soot combustion.The K loading promotes the transition of cobalt species from Co³⁺to Co²⁺.The interaction between K and Co increase the Co²⁺/Co³⁺ratio,which leads to the generation of oxygen vacancies.Thus,the adsorption of gaseous oxygen species is accelerated to enhance the soot combustion performance significantly.In addition,the K loading improves the intrinsic activities of K/Co-LDO-H,which is consistent with the large amount of active oxygen species.