Highly Active and Water-Resistant Mn-Loaded MgAlOx Catalysts for NH3-SCR at Low Temperature

Advancing catalysts for low-temperature NH3-SCR enhances their viability as a terminal flue gas denitration solution across diverse operating regimes. A high-performance, hydrothermally stable catalyst for low-temperature SCR was synthesized by depositing MnOx onto MgAlOx composite oxide supports. These supports, featuring varied Mg/Al ratios, originated from layered double hydroxide (LDH) precursors. The obtained catalyst with the Mg/Al ratio of 2 (Mn/Mg2AlOx) possesses relatively high concentrations of active oxygen species (Oα) and Mn4+ and exhibits remarkable catalytic performance. The Mn/Mg2AlOx catalyst exhibits a wide operating temperature range (100–300 °C) for denitration, achieving over 80% NOx conversion, along with robust water resistance. The temperature-programed surface reactions and NO oxidation reactions are performed to elucidate the promoting effect of water on N2 selectivity, which is not only due to inhibition of catalyst oxidation capacity at high temperature but also is related to the competing adsorption of water and NH3. In situ DRIFTS analysis confirmed that the NH3-SCR mechanism over Mn/Mg2AlOx adheres to the Eley–Rideal (E–R) pathway. These findings highlight the significant promise of Mn/MgAlOx catalysts for deployment as downstream denitration units within exhaust treatment systems.