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

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 H-2-TPR and O-2-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 degrees C) than CeO2 catalyst at 120 - 400 degrees 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.