Synergistic removal of NO and N2O in low-temperature SCR process with MnOx/Ti based catalyst doped with Ce and V

Abstract

Aiming at understanding N2O formation in a low-temperature SCR process, mechanistic studies regarding the synergistic removal of NO and inhibition of N2O formation by the addition of Ce and V into MnOx/Ti based catalysts prepared by the sol-gel method were conducted and analyzed by various techniques, including BET, XRD, XPS, NH3-TPD, and FTIR. The results show that the addition of Ce raises the NO conversion efficiency and shifts the high performance region toward the low temperature range, while the addition of V generates less N2O. As an optimal formula, Mn(0.4)Ce(0.1)V(0.01)/Ti ensures a high NO conversion efficiency and low N2O formation. N2O mainly originates from (1) the direct oxidation of NH3 with O2 and (2) the reaction of NO and adsorbed NH3 in the low-temperature SCR process. The latter plays a dominant role at temperatures below 240°C. The strong redox properties on the MnOx/Ti catalyst surface result in a high NO conversion efficiency and generates numerous NH(ads) species that cause N2O formation. The slight addition of V promotes the formation of acid by bringing Lewis acid sites to the catalyst surface and effectively restricts N2O formation. Lewis acid sites have a positive function in maintaining a high NO conversion and inhibiting N2O formation compared to Brønsted acid sites. In addition, the well-dispersed V on the surface of Mn(0.4)Ce(0.1)V(0.01)/Ti results in improved textural properties, more lattice oxygen and less labile oxygen, as well as comparable Mn4+/Mn3+, which also improves the catalyst performance at low temperature.