Selective Catalytic Reduction of Nitric Oxide by Ammonia over V₂O₅/TiO₂, V₂O₅/TiO₂/SiO₂, and V₂O₅−WO₃/TiO₂ Catalysts:  Effect of Vanadia Content on the Activation Energy

A systematic variation of the V 2 O 5 content of the title catalysts reveals a dependence of the activation energy of the selective catalytic reduction of nitric oxide by ammonia on the surface concentration of vanadia. A significant decrease in activation energy (from approximately 80 to 40 kJ/mol) is observed, as the vanadia surface concentration is increased (from 0.3 to 8 μmol/m 2 ). The same results were obtained from tests conducted both in the presence and absence of H 2 O and SO 2 . A possible mechanistic explanation is discussed.