α-Fe2O3/MnO2 heterojunction catalysts with enhanced low-temperature activity for selective N2 production in NH3-SCR

Abstract

Current commercial catalysts remain inadequate for industrial kiln operations under low-temperature exhaust conditions. Consequently, the development of catalysts with enhanced low-temperature NH₃-SCR activity and elevated NO_x reduction efficiency has become a strategic focus. In this study, a cryptomelane-type MnO₂ catalyst was synthesized through a one-step hydrothermal method, and an in-situ heterostructure was developed via α-Fe₂O₃ doping to enhance N₂ selectivity in NH₃-SCR. The results demonstrate that α-Fe₂O₃ incorporation elevates Mn⁴⁺ concentration, thereby promoting NH₃ adsorption and NH₄⁺ formation, which synergistically accelerates NO reduction. Additionally, surface-active oxygen species and Brønsted acid sites initially increased with α-Fe₂O₃ content but diminished when exceeding an optimal doping level. Under simulated flue gas conditions (500 ppm NO, 1000 ppm NH₃, 5 % O₂, 5 % H₂O, and a gas hourly space velocity of 36,000 h⁻¹), the 5 wt% α-Fe₂O₃-loaded catalyst exhibited enhanced low-temperature catalytic performance, achieving 82 % N₂ selectivity at 175 °C, compared to 74 % at 200 °C. The α-Fe₂O₃/MnO₂ catalyst demonstrated exceptional catalytic activity at low temperatures, suggesting a promising strategy for industrial flue gas denitrification.