Low-Coordination Mn Single Atoms on CeO₂ Nano-Islands for Boosting Ultra-Low Temperature NH₃–SCR Activity and SO₂ Resistance

Mn-based catalysts are among the most promising candidates for the ultralow-temperature (≤150 °C) selective catalytic reduction of NO_x with NH₃ (NH₃–SCR). However, their narrow operating temperature window and insufficient resistance to SO₂/H₂O limit their broader practical application. In this work, Mn single atoms featuring a unique low-coordination configuration are uniformly anchored onto CeO₂ nanoislands that were predeposited on H₂Ti₃O₇ nanotubes (TNTs) via a newly developed in situ redox self-assembly strategy. The resulting catalyst, denoted as LC-Mn/CeO₂, exhibits exceptional ultralow-temperature NH₃–SCR activity and SO₂ resistance. It achieves over 90% NO_x conversion at 100 °C and maintains nearly 90% conversion for over 20 h at 140 °C in the presence of 50 ppm of SO₂ and 10 vol % H₂O. Experimental and DFT results reveal that the unique electronic modulation of the low-coordination Mn centers facilitates the formation of asymmetric oxygen vacancies. By promoting the oxidation of NO to NO₂, these vacancies significantly enhance the low-temperature reaction rate of the NH₃–SCR reaction. Simultaneously, the electron-rich environment of Mn sites suppresses the oxidation of SO₂ by weakening the Mn–SO₂ charge transfer, thereby improving SO₂ resistance. Our work provides a novel strategy of modulating the coordination environment of single atoms to enhance ultralow-temperature activity and SO₂/H₂O resistance.