Promoting catalytic performance by balancing acid and redox sites on Mn3O4–Mn2P2O7/TiO2 for selective catalytic reduction of NO by NH3 at low temperature

The surface acidity and redox property of catalyst are extremely important in the selective catalytic reduction of NOx with NH3 (NH3-SCR) process. In this work, phosphoric acid was used to regulate the acidity and redox property of Mn3O4/TiO2 and Mn3O4–Mn2P2O7/TiO2 (MnPO/TiO2) catalyst was firstly prepared. And its effect on the catalytic activity was investigated in NH3-SCR. The experimental results showed that Mn2P2O7 modified Mn3O4/TiO2 catalyst exhibited excellent catalytic activity and strong resistance to SO2 and H2O than Mn3O4/TiO2. The Brunauer-Emmett-Teller (BET) results showed that the formation of Mn2P2O7 was beneficial to optimize pore structure and significantly increased the specific surface area of Mn3O4/TiO2 catalyst. At the same time, the generation of Mn2P2O7 led to partial obstruction of Mn3+/Mn4+ with Mn2+ redox cycles, which weakened the redox property of Mn3O4/TiO2 catalyst and then prevented excessive dehydrogenation of NH3. Furthermore, the introduction of Mn2P2O7 provided more acid sites for Mn3O4/TiO2 catalyst. The moderate redox property and enhanced acidity facilitated adsorption and activation of NO and NH3. In situ DRIFTs results showed that the SCR reaction over MnPO/TiO2 catalyst at 200 °C was predominantly controlled by L-H route.