Effect of oxygen vacancies on ceria catalyst for selective catalytic reduction of NO with NH3

Abstract

The effect of oxygen vacancies on ceria catalyst for selective catalytic reduction with NH3 (NH3-SCR) of NO was investigated. The characterizations indicated that CeO2-Ar catalyst calcined in Ar atmosphere possessed more oxygen vacancies than CeO2 catalyst calcined in ambient air. XPS results showed that the surface oxygen contents of CeO2 and CeO2-Ar catalysts were 70.2 and 67.9% respectively, indicative of the loss of surface oxygen and existence of oxygen vacancies on CeO2-Ar catalyst. The H2-TPR and O2-TPO experiments suggested that the presence of abundant oxygen vacancies improved the redox behavior, providing CeO2-Ar catalyst a superior ability to oxygen uptake and release. Furthermore, the adsorption capacity for NH3 and NO of CeO2-Ar catalyst was enhanced by oxygen vacancies. As a result, CeO2-Ar catalyst showed a quite higher NO conversion (>90% above 260 °C) than CeO2 catalyst at 120 – 400 °C. The proposed mechanism suggested that the oxygen vacancies accelerated the acidity cycle and redox cycle during NH3-SCR reaction. Under the action of surface adsorbed oxygen on oxygen vacancies, the adsorption and activation of NH3 and NO were promoted and the restore of Ce4+ from Ce3+ was facilitated, which were responsible for the enhancement of catalytic performance of CeO2-Ar catalyst.