Effects of surface physicochemical properties on NH3-SCR activity of MnO2 catalysts with different crystal structures

Abstract

α-, β-, δ-, and γ-MnO2 nanocrystals are successfully prepared. We then evaluated the NH3 selective catalytic reduction (SCR) performance of the MnO2 catalysts with different phases. The NOx conversion efficiency decreased in the order: γ-MnO2 > α-MnO2 > δ-MnO2 > β-MnO2. The NOx conversion with the use of γ-MnO2 and α-MnO2 catalysts reached 90% in the temperature range of 140–200 °C, while that based on β-MnO2 reached only 40% at 200 °C. The γ-MnO2 and α-MnO2 nanowire crystal morphologies enabled good dispersion of the catalysts and resulted in a relatively high specific surface area. We found that γ-MnO2 and α-MnO2 possessed stronger reducing abilities and more and stronger acidic sites than the other catalysts. In addition, more chemisorbed oxygen existed on the surface of the γ-MnO2 and α-MnO2 catalysts. The γ-MnO2 and α-MnO2 catalysts showed excellent performance in the low-temperature SCR of NO to N2 with NH3.