Copper sulfate (CuSO4) is a ubiquitous component in natural minerals and industrial dusts. However, CuSO4 has been believed usually that it has adverse effect on elemental mercury (Hg-0) removal from flue gas. Here, we offered a new insight into the effect of crystal water in copper sulfate on Hg-0 catalytic oxidation. The structure evolution of copper sulfate by density functional theory (DFT) calculation revealed anhydrous CuSO4 crystal contributing to a better HCl adsorption which provided a precondition for Hg-0 oxidation. Experimental results about the catalytic activity sequence of CuSO4 > CuSO4 center dot H2O > CuSO4 center dot 5H(2)O with HCl confirmed the negative effect of crystal water on Hg-0 catalytic oxidation. To realize industrial application, supported catalysts CuSO4/alpha-Al2O3 synthesized by wet impregnation method was employed for elemental mercury (Hg-0) oxidation and the results exhibited excellent performance in Hg-0 oxidation under 250 degrees C-400 degrees C. The Hg-0 conversion efficiency was above 97% in the presence of 2 ppm HCl + 6% O-2 at 300 degrees C. Combining computational and X-ray photoelectron spectroscopy (XPS) analyses together, Cu atoms exposure on the surface of anhydrous CuSO4 were the critical active sites for Hg-0 oxidation and the reaction obeyed the Eley-Rideal mechanism.