Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: effect of precipitation agent

Abstract A series of Sm-Mn mixed oxide catalysts were prepared via precipitation using various precipitants, namely Na2CO3, (NH4)2CO3, and NH3·H2O, and evaluated for the selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. Various characterisation techniques were used to determine the physicochemical properties of the catalysts, and it is found that their catalytic performance is greatly influenced by the nature of the precipitation agent used. It is found that Sm0.1Mn-Na2CO3 and Sm0.1Mn-(NH4)2CO3 exhibit superior catalytic performance in the SCR reaction to that of Sm0.1Mn-NH3·H2O due to an abundance of surface acid sites, high surface concentration of Mn4+, and high NO oxidation capacity. From in situ DRIFT analysis, we conclude that the Sm-Mn catalysts follow both Eley-Rideal and Langmuir-Hinshelwood mechanisms, and that the Eley-Rideal mechanism is dominant at elevated temperatures.