The promoting effect of S-doping on the NH_3-SCR performance of MnO_x/ TiO_2 catalyst

摘要

A series of S-doped MnOx/TiO2 catalysts were prepared by sol-gel method for the purpose of enhancing SCR performance. The obtained catalyst with mole ratio of S:Ti = 0.05:1 exhibited the best low temperature SCR performance and the widest active temperature window. According to the results of various analyses, the proper S was doped into TiO2 lattice via the replacement of Ti4+ by S4+ to generate Ti-O-S bond, along with increasing surface area, more surface Mn4+ species and more active oxygen species (O-2(-)). These enhanced properties improved the Bronsted acid sites and redox property of the properly S-doped MnOx/TiO2 catalyst. These advantages of S doping can essentially benefit the dc-NOx ability of MnOx/TiO2 catalysts. Meanwhile, the in situ DRIFT experiments revealed that the adsorbed NH4+ and gas-phase NO2 species were greatly increased after proper S-doping, along with the enhanced reactivity of the adsorbed NH3 and NOx species. Both E-R and L-H mechanisms occurred on the S-doped catalysts, while the promoting effect of S-doping was performed by facilitating the L-H route during SCR reaction.