Redox-Induced Engineering of Amorphous/Crystalline MnFeOx Catalyst Enables H2O/SO2-Tolerant NOx Abatement at Ultra-Low Temperatures

Abstract

Enhancing resistance to H₂O and SO₂ poisoning below 150 °C is essential for advancing Mn-based oxide catalysts in ultra-low temperature NH₃-SCR of NO. To address this challenge, an amorphous/crystalline MnFe_y catalyst with engineered Mn-O-Fe interfaces and abundant surface defects was developed using a redox-induced precipitation method. The optimized MnFe_0.2 catalyst demonstrates exceptional catalytic performance, achieving over 90% NO conversion and N₂ selectivity across a broad 120–260 °C range under highly humid conditions (15 vol% H₂O). Most significantly, MnFe_0.2 maintains remarkable stability under high humidity and SO₂ at 120 °C for 60 h, vastly outperforming conventionally coprecipitated MnFe_0.2(CP), which gradually deactivates. This superior performance is attributed to the uniform elemental distribution in MnFe_0.2, which enhances the Mn-O-Fe redox cycle through improved electron transfer. These features promote superior low-temperature reducibility and acidity, enabling effective reactant adsorption and activation. Mechanistic studies further reveal that SO₂ exposure deactivates MnFe_0.2(CP) by forming ammonium (bi)sulfates and MnSO₄, which hinder reactant adsorption and subsequent reactions. In contrast, the engineered Mn-O-Fe interfaces in MnFe_0.2 enable Fe species to preferentially interact with SO₂, shielding Mn from sulfation and significantly reducing deactivation. This work demonstrates a significant breakthrough in catalyst design for ultra-low temperature NH₃-SCR, paving the way for the broader application of Mn-based catalysts in industrial NO_x control technologies.