Decomposition and reactivity of NH4HSO4 on V2O5/AC catalysts used for NO reduction with ammonia

The decomposition and reactivity of NH4HSO4 deposited or in situ formed on various V2O5/AC and V2O5/TiO2 catalysts are studied in detail using a temperature-programmed method. The results are correlated directly with the behavior of the catalysts in the NO reduction with NH3 in the presence of SO2. The decomposition and reaction of NH4HSO4 are easier on the V2O5/AC catalysts than on the V2O5/TiO2 catalysts. On the V2O5/AC catalysts, the decomposition and reactivity of NH4HSO4 are greatly dependent upon V2O5 loading, the temperatures for the decomposition, and reaction increase with increasing V2O5 loading. Most of the NH4SO4 deposited on the V2O5/AC can react with NO at 250 degreesC when V2O5 loading is below 5 wt%. The reactivity of NH4HSO4 with NO, other than its decomposition, is associated with the behavior of the catalysts for the SCR reaction in the presence of SO2. During the SCR reaction on the V2O5/AC catalysts of low V2O5 loading in the presence of SO2, the formed sulfate species stay on the catalyst surface and act as acid sites for NH3 adsorption. Simultaneously, the ammonium ions react continuously with NO to avoid the surface deposition of excess ammonium-sulfate salts. Such a process effectively ensures the catalyst being promoted but not poisoned by SO2. The interaction between the AC and vanadium species results in synergism in the activation and reaction of ammonium ions linked to sulfate species. A bridge-type activated ammonia species is proposed and discussed. (C) 2000 Academic Press.