Al 2O 3-coated cordierite honeycomb supported CuO catalyst for selective catalytic reduction of NO by NH 3: Surface properties and reaction mechanism

Abstract

Al 2O 3-coated cordierite supported CuO catalyst shows high activities for selective catalytic reduction (SCR) of NO by NH 3 at 350–500 °C after being sulfated by SO 2. 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 CuAl 2O 4 may transfer to NH 2–NH 2, where aluminum species is responsible for NH 3 storage and copper species is responsible for activation of NH 3 to NH 2. The SCR reaction involves the adsorbed NH 2–NH 2 and gaseous NO, following Eley–Rideal mechanism. When NH 3 is insufficient, NO may convert to NO 2 through oxidation by O 2 or to N 2O and NO 2 through disproportionation.