Soot oxidation over CeO2 and Ag/CeO2: Factors determining the catalyst activity and stability during reaction

Three model ceria catalysts, which are monocrystalline CeO2 nanocubes, polycrystalline CeO2 nanoparticles, and polycrystalline CeO2 spindles, were synthesized and analyzed with isothermal soot oxidation, H-2-TPR, and Raman spectroscopy. The results suggest that the initial activity of the catalyst is determined by the number of catalyst-soot contact points rather than the catalyst surface area, while the catalyst stability is closely related to the concentration of surface oxygen vacancies. Excessive surface oxygen vacancies may inhibit the regeneration of highly active O-2(-) and lead to catalyst deactivation during reaction. After impregnation with Ag, O- can be readily regenerated and transformed to O-2(-), resulting in a 10-fold increase in soot oxidation activity over Ag/CeO2. Among these catalysts, Ag supported on nanocubic CeO2 exhibits good availability of O-2(-) and therefore high catalytic activity and stability, and is thus considered a promising catalyst for application in gasoline particulate filters. (C) 2016 Elsevier Inc. All rights reserved.