Effect of oxygen vacancies on improving NO oxidation over CeO2 {111} and {100} facets for fast SCR reaction

Abstract Different exposed crystal surface CeO2 catalysts (nanopolyhedrons and nanocubes) are synthesized and treated by NH3 to investigate the effect of oxygen vacancies on improving NO oxidation for fast SCR reaction. The experiment results show that N-CeO2-NPs catalyst (treated by NH3) has the most oxygen vacancies of the four catalysts, thus leading to the best oxidation activity of NO, which further promotes the fast SCR reaction. From the XPS and Raman spectra results, it indicates that the more oxygen vacancies are due to the higher concentration of Ce3+ and surface adsorbed oxygen resulting from the NH3 treatment at high temperature. Meanwhile, the test of NO conversion to NO2 shows that the rich oxygen vacancies promote the conversion of NO to NO2, in which N-CeO2-NPs catalyst yields more remarkable promotion of NO oxidation to NO2, respectively. Also, the magnitude of the variety is in accordance with that of the oxygen vacancy content and concentration of Ce3+ ions. Thus, CeO2 with NH3 treatment is found to significantly enhance its NH3-SCR performance which leads to higher NOx removal efficiency of N-CeO2-NPs catalyst with {111} exposed crystal surface.