Mechanism of water vapor and SO2 poisoning resistance in iron-fortified micron spherical Ce1Mn7Ox for ultra-low temperature NH3-SCR of NOx

Abstract

Achieving ultra-low temperature resistance to water vapor and SO₂ poisoning in deNO_x catalysts remains a critical challenge for enabling ultra-low NO_x emissions from high-humidity, SO₂-containing flue gases in non-electric industries. Herein, we demonstrate enhanced anti-poisoning performance and N₂ selectivity in ultra-low temperature NH₃-SCR of NO_x via Fe doping into micron-spherical Ce₁Mn₇O_x-350 catalysts. The solvothermally synthesized Fe₁Ce₁Mn₇O_x-350 catalyst exhibited exceptional NH₃-SCR efficiency (>91% at 54–275 °C) and N₂ selectivity (>86% below 140 °C). Notably, under harsh conditions (5 vol% H₂O and 50 ppm SO₂), it maintained >90% NO_x conversion at 107–255 °C and achieved 100% efficiency at 127 °C for 30 hours without degradation. Mechanistic studies revealed that Fe doping suppressed solid-phase crystallization, forming a Mn₃O₄-dominated microsphere structure composed of loosely stacked nanoparticles with high surface area, which impeded dense ammonium sulfate deposition. Furthermore, Fe doping facilitated dynamic valence cycles (Ce³⁺ + Mn⁴⁺ → Ce⁴⁺ + Mn³⁺ and Fe²⁺ + Mn⁴⁺ → Fe³⁺ + Mn³⁺), enhancing chemisorbed oxygen concentration, low-temperature redox properties, and surface acidity, thereby boosting resistance to H₂O/SO₂ poisoning. In situ DRIFTS identified that trace thermally decomposable ammonium sulfite effectively inhibited bisulfate formation. DFT calculations further elucidated that the increased exposure of Mn₃O₄(103) planes hindered H₂O/SO₂ adsorption, while Fe-induced MnFe₂O₄(311) planes suppressed SO₂ oxidation to sulfates. This work provides a strategic design paradigm for robust ultra-low temperature deNO_x catalysts via valence cycle and crystallographic modulation, offering significant potential for practical applications in complex industrial flue gas remediation.