The Study Of Solid Solution And Evolution Of Surface Oxygen Vacancies On MnO_x-CeO₂ Catalyst Towards Model Soot Oxidation

A series of MnO_x-CeO₂ catalysts with various Mn/?Mn+Ce?molar ratios prepared by citric acid complex method which was optimized in before study had been studied for the catalytic combustion and repeated reaction of model soot.The activity of catalysts was evaluated by TPO while the structure properties,active sites,surface active species and their relationship with solid solution of the catalysts were characterized by XRD,BET,Raman,O₂-TPD,H2-TPR and XPS.The reaction process and especially the evolution of surface oxygen vacancies of CeO₂,MnOx and MnO_x-CeO₂ with the relatively highest activity in soot oxidation was investigated by in situ Raman.Also M0.1Ce0.9O₂?M=Mn,Fe,Cu?was prepared by hydrothermal method to study the properties of oxygen vacancies of CeO₂-based catalysts.The results found that the activity of all MnO_x-CeO₂ catalysts was higher than CeO₂ and MnOx,and the ignited temperature of MnO_x-CeO₂?Mn/?Mn+Ce?=0.4?,CeO₂,MnOx and in the case of catalyst absent was 256?,351?,358? and 458? respectively.MnO_x-CeO₂ with larger specific surface area,smaller average crystallite size and more surface oxygen vacancies exhibited better redox property relative to CeO₂ and MnOx.It is mainly attributed to the formation of Mn-Ce-O solid solution after manganese incorporated into the ceria lattice and more surface oxygen vacancies leading the enhancement of migration and transformation of active oxygen.And the irreversible phase separation,separation of Mn3O4,reduction of Mn⁴⁺ and consumption of Olatt occurred in the high-temperature reaction of MnO_x-CeO₂ and soot was responsible for the activity decline to some extent.On the basis of the evolution of surface oxygen vacancies,a plausible pathway of MnO_x-CeO₂ towards soot oxidation was proposed.Firstly frenkel-type oxygen vacancies transformed into intrinsic oxygen vacancies while Mn⁴⁺ changed to Mn³⁺,and then the oxygen supplement from CeO₂ recovered the Mn⁴⁺ while Ce⁴⁺ changed to Ce³⁺ with intrinsic oxygen vacancies which can adsorbed the gas oxygen to replenish the consumed oxygen.And the M0.1Ce0.9O₂?M=Mn,Fe,Cu?showed the similar and some different properties.