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

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.