Catalytic activity of MnOx/TiO2 catalysts synthesized with different manganese precursors for the selective catalytic reduction of nitrogen oxides

Abstract

The effects of different manganese precursors on the low-temperature (100–300 °C) selective catalytic reduction of nitrogen oxide (NOx) were investigated. MnOx/TiO2 catalysts were prepared by a sol–gel method using three different precursors, manganese(II) nitrate (MN), manganese(II) acetate (MA2), and manganese(III) acetate (MA3). They had an overall high specific surface area, but the relatively small surface areas of MN–MnOx/TiO2 and MA3–MnOx/TiO2 were due to the existence of a Mn3O4 phase in these catalysts. There is no chemical reaction at the working temperature, which proves the high thermal stability of all the catalysts. The result of de-NOx (removal of NOx) efficiency in the low temperature region showed that the catalyst synthesized with manganese acetate had higher catalytic activity than the catalyst synthesized with manganese nitrate. Despite the relatively small surface area, the MA3–MnOx/TiO2 exhibited the highest de-NOx efficiency, which resulted from the most enriched Mn concentration and Mn4+ species (MnO2) as well as strong acid sites on catalyst surface.