A series of bench-scale experiments were completed to evaluate acid gases of HCl, SO2, and SO3 on mercury oxidation across a commercial selective catalytic reduction (SCR) catalyst. The SCR catalyst was placed in a simulated flue gas stream containing O-2, CO2, H2O, NO, NO2, and NH3, and N-2. HCl, S-2, and SO3 were added to the gas stream either separately or in combination to investigate their interactions with mercury over the SCR catalyst. The compositions of the simulated flue gas represent a medium-sulfur and low- to medium-chlorine coal that could represent either bituminous or subbituminous. The experimental data indicated that 5-50 ppm HCI in flue gas enhanced mercury oxidation within the SCR catalyst, possibly because of the reactive chlorine species formed through catalytic reactions. An addition of 5 ppm HCl in the simulated flue gas resulted in mercury oxidation of 45% across the SCR compared to only 4% mercury oxidation when 1 ppm HCl is in the flue gas. As HCl concentration increased to 50 ppm, 63% of Hg oxidation was reached. SO2 and SO3 showed a mitigating effect on mercury chlorination to some degree, depending on the concentrations Of SO2 and SO3, by competing against HCl for SCR adsorption sites. High levels of acid gases of HC1 (50 ppm), SO2 (2000 ppm), and SO3 (50 ppm) in the flue gas deteriorate mercury adsorption on the SCR catalyst. (c) 2007 Elsevier B.V.. All rights reserved.