Inhibitory effect of NO2 on the selective catalytic reduction of NOx with NH3 over one-pot-synthesized Cu-SSZ-13 catalyst

The selective catalytic reduction of NOx with NH3 (NH3-SCR) on a Cu-SSZ-13 catalyst prepared by a one-pot-synthesis method was inhibited by NO2 in the low temperature range. NH4NO3 that accumulated on the catalyst surface was the reason for this phenomenon. The key step of the NH3-SCR reaction over the catalyst at low temperatures was the formation of nitrate on the Cu sites. However, NO2, with its larger kinetic diameter, could not form nitrate species on the Cu sites efficiently, and part of these molecules formed NH4NO3 in combination with NH4+ on the Bronsted acid sites. The consumption rate of NH4NO3 by NO was lower than its accumulation under fast SCR conditions at low temperatures, making the active sites become blocked by NH4NO3 and inactive. The results of kinetic studies indicate that N-2 formation mainly results from the reaction between NO and NH3, even under fast SCR reaction conditions.