The Use of Rare Earths in Catalysts for Selective Catalytic Reduction of NOx

Nitrogen oxides (NOx) can be reduced by technology of selective catalytic reduction (SCR) with NH3, while the spent commercial V2O5/TiO2 catalysts with biotoxicity for SCR technology is recognized as hazardous wastes in China. Rare earths (REEs) possess unique 4f electron orbit ensuring superior performance of oxygen storage and release, which plays a significant role in catalytic reaction. Thus, REEs are the important research subject in SCR catalysts recently and the proposed substitutes for V2O5/TiO2 catalysts. This review mainly summarizes the progress of 12 REEs including Ce, Sm and La in novel SCR catalysts in recent 5 years, and there is seldom study on Sc, Lu, etc. We primarily review the effect of REEs on improving the catalytic activity, N-2 selectivity and stability of Mn-, Fe-, V- and other based DeNOx catalysts. The REEs mainly improve the redox behavior via the formation of redox couples with other transition elements and providing more oxygen vacancies. In the aspect of resistance towards SO2, the REEs, such as Ce and Sm, could suppress the oxidation of SO2 to SO3 and attract the poison of SO2 from the main active components, thus improving the resistance towards SO2. We also review the molding and application of REEs-based catalysts. Additionally, the primitive design strategy of SCR catalysts is proposed, and the development prospect of REEs-based catalysts is forecast finally.

Automated summary

This review summarizes the recent progress in the application of rare earths (REEs) in novel selective catalytic reduction (SCR) catalysts. It discusses the effects of REEs on catalytic activity, selectivity, stability, and resistance to sulfur dioxide. The review also covers the preparation and application of REEs-based catalysts and proposes a design strategy for SCR catalysts. The development prospects of REEs-based catalysts are also predicted.