Rational design of rare earth-modified Mn-based catalysts for low-temperature NH3-SCR: Mechanisms, strategies, and prospects

Nitrogen oxides (NO x ) emitted from industrial processes pose severe environmental threats, necessitating efficient abatement technologies. Selective catalytic reduction with NH 3 (NH 3 -SCR) at low temperatures represents a promising route, with Mn-based oxides being among the most active candidates. However, their practical application is hindered by insufficient N 2 selectivity, susceptibility to SO 2 and H 2 O poisoning, and a narrow operational window. Rare earth (RE) modification has emerged as a highly effective strategy for optimizing Mn-based catalysts in low-temperature NH 3 -SCR of NO x , yet a systematic understanding of the structure-activity relationships and reaction mechanisms remains lacking. This review provides a systematic and mechanistic overview of recent advances in RE-modified Mn-based catalysts for low-temperature NH 3 -SCR. We first establish the structural-performance relationships of pure MnO x , focusing on valence states, crystal phases, morphologies, and synthesis methods. Subsequently, we classify and discuss three major catalyst families: RE-modified MnO x , RE-Mn composite oxides, and supported RE-Mn systems. Special emphasis is placed on the roles of RE elements in enhancing low-temperature activity, broadening the temperature window, improving N 2 selectivity, and constructing multi-level anti-poisoning mechanisms against H 2 O and SO 2 . We further elucidate the underlying reaction pathways and how RE doping modulates the electronic structure, active site distribution, and intermediate transformation. Finally, we identify key challenges for industrial deployment, such as long-term stability under complex flue gas, scalability, and cost-effectiveness, and propose future research directions toward the rational design of robust, high-performance SCR catalysts. This work provides a mechanistic framework and design principles for developing high-performance RE-Mn catalysts under practical flue-gas conditions.