Al2O3-coated cordierite honeycomb supported CuO catalyst for selective catalytic reduction of NO by NH3: Surface properties and reaction mechanism

Al2O3-coated cordierite supported CuO catalyst shows high activities for selective catalytic reduction (SCR) of NO by NH3 at 350–500 °C after being sulfated by SO2. Its surface properties and reaction mechanism are elucidated in this paper by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) coupled with mass spectroscopy. Results show that the catalyst has both Lewis and Brønsted acid sites, the Brønsted acidity is far weaker than the Lewis acidity and the protonated ammonia on Brønsted sites is less stable than the coordinated ammonia on Lewis sites. Ammonia coordinated on sulfated CuAl2O4 may transfer to NH2–NH2, where aluminum species is responsible for NH3 storage and copper species is responsible for activation of NH3 to NH2. The SCR reaction involves the adsorbed NH2–NH2 and gaseous NO, following Eley–Rideal mechanism. When NH3 is insufficient, NO may convert to NO2 through oxidation by O2 or to N2O and NO2 through disproportionation.