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CePr and CeMn mixed oxide catalysts were synthesized by inserting Pr and Mn atoms into CeO2. Catalytic performance on soot combustion was investigated, and several characterizations were carried out using X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area analysis, H2 temperature-programmed reduction, and X-ray diffraction. Results show that a cubic fluorite structure solid solution can be formed with Pr and Mn doped into CeO2 lattice. Three oxygen species, namely, lattice oxygen OI (O2−), defect oxygen species OII (O2−, O22−, and O−), and hydroxyl-like groups and adsorbed molecular water OIII, exist in the solid solution structure. In general, the defect oxygen species OII is responsible for soot combustion. CePr exhibits fast oxidation rate because of the presence of open oxygen migration channel (OI↔OII↔OIII), and reactive oxygen species OII can continue to be replenished. CeMn possesses a large amount of surface active oxygen, which results in excellent low-temperature catalytic activity.

Four CePr mixed oxides with different structures were designed and synthesized using a solid-phase grinding method: a uniform solid solution of Ce and Pr (CePr-NN), Pr6O11-coated CeO2 (CePr-NO), CeO2-coated Pr6O11 (CePr-ON), and particle packing of CeO2 and Pr6O11 (CePr-OO) were obtained, and characterized by XRD, H2-TPR, TEM and TG. The results show that CePr-NN exhibits the best low temperature catalytic activity among the CePr catalysts. CeO2 is the major active phase on the surface of the CePr catalysts, and the use of Pr6O11 as the framework maintains the thermal stability of the CePr composite oxide. Moreover, both the oxygen storage capacity and mobility of the active oxygen of the catalyst were improved with the incorporation of Pr into CeO2, resulting in a higher combustion rate. The “molten state” which appeared during the preparation when nitrate was used as the precursor, plays a significant role in the migration of Ce and Pr, and is the premise of forming different structures of solid solution or coating structure.