ADSORPTION OF NO AND NH3 ON VANADIA TITANIA CATALYSTS - ESR AND XPS STUDIES OF ADSORPTION

The adsorption of NO and NH3 on V2O5/TiO2 catalysts has been studied by ESR and XPS at temperatures and pressures close to those used for industrial tail gas cleanup from power plants and HNO3 plants, using NO reduction with ammonia. The paper extends and confirms earlier studies on pure V2O5 and TiO2 samples. The reduction of the vanadia sites by adsorbed NH3 occurs over the whole range of temperatures studied while NO adsorption is observed on the titania support. Reduction of NO to N2 occurs on the reduced vanadia sites, which are reoxidized in the process. The reduced vanadia sites, however, are blocked by chemisorbed NH3, preventing the reduction of NO which causes a drop in the NO molar conversion. The presence of oxygen (or water) in the reaction mixture plays a major role in the selectivity of the vanadium oxide catalyst since it interacts with NH3 at the reduced vanadia sites, resulting in the elimination of the NH3 poisoning of the reduced surface sites at temperatures above 550 K.