Combined in situ diffuse reflectance FTIR (DRIFT) and on-line mass spectroscopy, temperature-programmed and transient experiments were performed to evaluate the surface acidity and reactivity of a CuO/Al₂O₃ catalyst. The results show that only ammonia coordinated at Lewis acid sites was found on the CuO/Al₂O₃ catalyst. Sulfation of CuO/Al₂O₃ catalyst greatly increases the concentration and strength of the Lewis acid sites and the concentration of Brønsted acid sites. Ammonia adsorbed both on Lewis acid sites and Brønsted acid sites plays an important role in the selective catalytic reduction of NO over the CuO/Al₂O₃ catalyst-sorbents, which occurs between the adsorbed ammonia and gaseous NO, following an Eley-Rideal mechanism.

Key words: in situ diffuse reflectance FTIR (DRIFT), on-line mass spectroscopy, CuO/Al₂O₃, selective catalytic reduction (SCR), surface acidity