Advancements in SO₂ tolerance for low-temperature NH₃-SCR through tailoring oxidation ability and pore size in...

The detrimental effects of SO₂ poisoning pose a critical challenge for the practical implementation of Mn-based catalysts in low-temperature NH₃-SCR systems for NO_X abatement. The causes of NH₃-SCR catalyst deactivation are the deposition of ammonium sulfates on the active sites and the formation of metal sulfates due to reactions between SO₂ and the active metal oxide. Herein, a H₂O₂-assisted redox precipitation method has been employed to tailor MnCe-based catalysts by enlarging their pore size and enhancing their oxidation ability, thereby respectively increasing sulfate decomposition rates and reducing metal sulfate formation. As a result, MnCe-M-3H with an optimal H₂O₂/Mn molar ratio of 3 demonstrated a higher proportion of Mn⁴⁺, Ce³⁺, and O_Lat, and a larger pore size than MnCe-M (without H₂O₂). Crucially, MnCe-M-3H exhibits excellent low-temperature NH₃-SCR activity, achieving 85 % at 100 °C and 95 % at 150 °C, and the highest SO₂ tolerance. Characterization of the spent catalysts revealed that increasing the catalyst pore size reduced sulfate deposition. Moreover, catalysts with enhanced oxidation abilities mitigate SO₂ chemical poisoning, thereby reducing the formation of metal sulfates. Specifically, MnCe-M-3H-4S, with the strongest oxidation ability and large pore size, showed the lowest MnSO₄ proportions (8.3 %) and a low sulfate deposition rate (0.07 % h^-1 for ammonia sulfates, 0.20 % h^-1 for metal sulfates), demonstrating its highest SO₂ tolerance. This study confirms that increasing the pore size and enhancing the oxidation ability of MnCe-based catalysts effectively reduce both the sulfate deposition rate and metal sulfate formation, thereby improving their SO₂ tolerance and practical applicability in low-temperature NH₃-SCR systems.