CuO supported on Al2O3-coated cordierite-honeycomb CuO catalysts exhibit high activities for SO2 and NO removal from flue gas at 400 ° C. In a catalyst preparation process, it was found that acid treatment of the cordierite was crucial. This work presents a detailed study on the promoting effect of acid treatment on the catalysts' activities, with the aid of N-2 adsorption, inductively coupled plasma analysis, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis. Results show that acid treatment significantly increases the surface area and pore volume of the cordierite and consequently increases the Brunauer-Emmett-Teller areas and pore volumes of the catalysts and improves CuO dispersivity. These changes result in an improved SO2 removal activity. Na2O (an additive) content on the geometric surface of the catalyst is inversely responsible for NO removal activity. The pores created by acid treatment enable migration of Na2O into the pores and decrease its content on the catalyst's geometric surface, which accounts for the promoting effect of acid treatment on NO removal activity. The effect of the acid type on the catalyst's structure and activities is also evaluated.