Effects of anaerobic SO2 treatment on nano-CeO2 of different morphologies for selective catalytic reduction of NOx with NH3

Abstract

Tuning surface acidity is a common strategy to improve the reactivity of Ce-based materials for selective catalytic reduction (SCR) of NOx with NH3. Traditionally, it is achieved by wet impregnation of sulfate species or treatment under an atmosphere of sulfur dioxide and oxygen. However, the two methods do not bring any change to the electronic state of CeO2, and Ce4+ ions which cause undesired side reactions are largely retained on the surface. Herein, we report a sulfation strategy that can tune the surface acid sites and regulate the electronic state of nano-CeO2. Using SO2 as reducible gas for surface sulfation, we prepared sulfated CeO2 (S-CeO2) catalysts of different morphologies and tested them for the NH3-SCR reaction. The characterization results revealed that the interaction between SO2 and nano-CeO2 is obviously affected by ceria morphology. Among the sulfated catalysts, that with rod morphology (S-CeO2-Rod) shows the highest NOx conversion, and exhibits superior sulfur and water tolerance. The excellent SCR activity of S-CeO2-Rod is attributed to the enrichment of oxygen vacancies and surface Ce3+ ions as a result of the abundant presence of sulfate species.