Rare earth containing catalysts for selective catalytic reduction of NOx with ammonia: A Review

Increasingly stringent regulations in many countries require effective reduction and control of NOx emissions. To meet these limits, various methods have been exploited, among which the selective catalytic reduction of NOx using ammonia as the reductant (NH3-SCR) is the most favored technology. High catalytic activity, N2 selectivity and resistance to deactivation by sulfur, alkaline metals and hydrothermal conditions are the optimal properties of a successful SCR catalyst. Rare earth oxides, particularly CeO2, have been increasingly used to improve the catalytic activity and resistance to deactivation of deNOx catalysts, both modifying traditional vanadium catalysts, and also developing novel catalysts, especially for low temperature applications. This review summarized the open literature concerning recent research and development progresses in the application of rare earths for NH3-SCR of NOx. Additionally, the roles of rare earths in enhancing the performance of NH3-SCR catalyst were reviewed.

Graphical AbstractThe low or high temperature activity of CeO2 catalysts can be adjusted by the addition of various compounds: 1) acidic component (such as WO3, TiO2, Nb2O5, sulfate and phosphate) improves the NOx conversions of catalyst at high temperatures; 2) transition metal (such as CuO, MnO2 and NiO) modification enhances the NOx conversions of catalyst at low temperatures but decreases the activity of catalyst at high temperatureFigure optionsDownload as PowerPoint slide