Mercury Oxidation over the V2O5(WO3)/TiO2 Commercial SCR Catalyst

Mercury oxidation by hydrochloric acid over the V2O5(WO3)/TiO2 commercial SCR catalyst was investigated. Both fresh and aged catalysts with honeycomb structure, which were exposed to a coal combustion flue gas in a coal-fired boiler for over 71 000 h. were examined. The aged catalysts were characterized by X-ray and SEM-EDX analysis to examine the presence of ash deposition oil the surface. The mercury oxidation rate was enhanced by increasing HCl concentrations and inhibited strongly by the presence of NH3. This behavior could be explained by 1 kinetic model assuming that HCl competes for the catalyst active sites against NH3. As the catalyst operation time increased, the mercury oxidation rate was observed to decrease considerably in the presence of NH3 while NO reduction rate was apparently nearly unchanged. By examining aged catalysts, deposits stemming from fly ash and SO2/SO3 were observed to accumulate continuously on the catalyst surface. The ash deposited on the surface may partially block the active catalyst sites and decrease their number. The decrease of the number of active sites on the catalyst surface caused NH3 to remain unreacted in the honeycomb catalyst. The decrease of the Hg-0 oxidation rate was caused by the inhibition effect of NH3 remaining in the catalyst.