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

Abstract

The selective catalytic reduction of NO_x 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 Brønsted 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 N₂ formation mainly results from the reaction between NO and NH₃, even under “fast SCR” reaction conditions.