Unveiling the inductive strategy of different precipitants on MnFeOx catalyst for low-temperature NH3-SCR reaction

Abstract

Herein, the inductive strategy of three precipitants on dual transition metal MnFeOx catalysts for low-temperature NH3-SCR reaction was investigated in detail. The results showed that the anions of precipitants played the leading role in the formation of catalytic phase, in which carbonate induced the transfer of Mn precursor from MnCO3 to the ultimate Mn2O3 phase while that of hydroxyl from Mn3O4 to Mn5O8 phase. Iron coupling would alter the original transition behavior of manganese due to an internal synergistic effect. Furthermore, the cations decided the stability of hydroxyl groups on ammonium and sodium hydroxide precipitants, leading to the difference of morphology in catalysts. The activity results suggested that MnFe-ammonium carbonate (denoted as AC) catalyst possessed the higher catalytic efficiency than other catalysts, with over 90% NO conversion achieved from 75 to 225 °C. The abundant Mn4+ and Fe3+ and strong surface acidity of MnFe-AC catalyst were in favor of the redox circle and the adsorption of NH3. Both activation energy and TOF, relied on the amount of acid, confirmed that the precipitants had an effect on the intrinsic catalytic activity of the catalysts such as energy barrier and reaction rate. Transient reaction further revealed that both E-R and L-H mechanisms co-existed on all catalysts, while E-R mechanism contributed more during the SCR process. On this basis, the possible inductive mechanism model of three precipitants on MnFeOx catalyst was proposed.