Experiments were conducted in a fixed-bed reactor containing a commercial V2O5/WO3/TiO2 catalyst to investigatemercury oxidation in the presence of HCl and O-2. Mercury oxidation was improved significantly in the presence of HCl and O-2, and the Hg-0 oxidation efficiencies decreased slowly as the temperature increased from 200 to 400 degrees C. Upon pretreatment with HCl and O-2 at 350 degrees C, the catalyst demonstrated higher catalytic activity for Hg-0 oxidation. Notably, the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O-2, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg-0 were first adsorbed onto the catalyst and then reacted with O-2 following its adsorption, which indicates that the oxidation of Hg0 over the commercial catalyst followed the Langmuir-Hinshelwood mechanism. Several characterization techniques, including Hg-0 temperature-programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS), were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O-2. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.