Effect of C3H6 on selective catalytic reduction of NOx by NH3 over a Cu/zeolite catalyst: A mechanistic study

[Display omitted] ▸ C3H6 oxidation intermediates and coke formation induced poisoning, depending on temperature. ▸ Poisoning caused non-monotonic NO changes due to NH3 coverage changes along the catalyst. ▸ Changes in reaction pathways during fast and NO2 SCR in the presence of C3H6 were observed. The effects of C3H6 on key SCR reactions over a model Cu/beta zeolite catalyst were characterized using step-response method reactor testing. Under standard SCR conditions, C3H6 clearly inhibited the reduction reaction at 200°C and above. The inhibition was not caused by competitive adsorption between C3H6 and NH3, but by surface intermediate species formed during C3H6 oxidation, including acrolein-like and coke species as indicated by in situ DRIFTS. Similar to the standard SCR reaction, C3H6 also had a negative effect on the fast SCR reaction. Spaci-FTIR (spatially resolved capillary-inlet Fourier transform infrared spectroscopy) results indicated that NO2 was quickly reduced to NO by C3H6, leading to the occurrence of some standard SCR instead of purely fast SCR. However, C3H6 had a positive effect on NO2 SCR. The reduction of NO2 to NO by C3H6 resulted in the occurrence of the fast SCR reaction combined with NO2 SCR instead of pure NO2 SCR. The reaction pathway change also decreased N2O formation significantly.