To investigate the mercury oxidation ability of V2O5-MoO3/TiO2 in actual flue gas, a test was performed in a coal-fired power plant The mercury oxidation ability of the operating selective catalytic reduction (SCR) deNO(x) system was also detected. The mercury conversion of V2O5-MoO3/TiO2 exceeded 90% in the actual flue gas, and the commercial SCR system almost lost the ability. This is mainly because the actual SCR catalyst has been running for 35,000 h and the test of V2O5-MoO3/TiO2 was in absence of NH3. To clarify the assumption, a laboratory experiment was carried out. V2O5-MoO3/TiO2 and the fresh commercial SCR catalyst were tested in the simulated flue gases in presence and absence of NH3. The results indicate that the mercury conversion of V2O5-MoO3/TiO2 is higher than that of the fresh commercial SCR catalyst even in the presence of NH3. The mercury oxidation ability of the fresh commercial SCR catalyst is stronger than that of the actual service ones. However, it is found that NH3 would inhibit mercury oxidation over V2O5-MoO3/TiO2 in the experiments. The main reason is that NH3 could compete with HCl for the same active sites on the catalyst surface. (C) 2015 Elsevier B.V. All rights reserved.