Effects of SO2 on standard and fast SCR over CeWO : A quantitative study of the reaction pathway and active sites

The influence of SO2 on the amounts of NO2, NH3 and NO adsorbed on CeWOx and the reaction pathway of fast and standard SCR were investigated using transient reaction experiments and in situ DRIFTS. The negative effect of SO2 was less severe during fast SCR. The SO2 adsorption inhibited NO adsorption and the “nitrite path”, which is detrimental for standard SCR at low temperatures. For fast SCR, although “nitrite path” and “NH4NO3 path” were inhibited, the greater amount of nitrates from NO2 adsorption, acceleration of NH4HSO4 decomposition, and promoted reaction between the NO gas, surface nitrates and adsorbed NH3 made the inhibitory effect of SO2 less severe. Brønsted acid sites are more active and make the main contribution to SCR with SO2. NH4HSO4 may not be the main cause of deactivation. When H2O and SO2 were present, “nitrite path” was seriously inhibited and “NH4NO3 path” was absent, causing decreased activity.