The effects of particle size and gas velocity on sulfation of alumina support of CuO/ γ-A1₂0₃sorbent have been determined in a thermogravimetric analyzer (TGA). Sulfation rate of alumina support of CuO/ γ?-A1₂0₃ increases with increasing gas velocity up to 0.2 m/s and then decreases with a further increase in gas velocity. The bulk sulfation rate of alumina support decreases with decreasing particle size and sample weight. The slight increase of gas velocity enhances the sulfation rate via reduction of gas film resistance but the outward diffusion rate of SO3 also increases. As a result maximum rate of bulk sulfation appears at about 0.2 m/s. The concentration of SO3 in pores of CuO/γ?-A1₂0₃ pellet and bulk sulfation rate of alumina support decrease with decreasing particle size.