The poisoning effect of Na+ and Ca2+ ions doped on the V2O5/TiO2 catalysts for selective catalytic reduction of NO by NH3

Deactivation of the supported V2O5/TiO2 catalysts due to deposition of alkali and alkaline earth metal salts in fly ashes is one of the most important problems in the selective catalytic reduction (SCR) of NOx by NH3. In this work, the poisoning effect of Na+ and Ca2+ ions doped on the V2O5/TiO2 catalysts for selective catalytic reduction of NO by NH3 has been studied. It has been shown that the Na+ and Ca2+ ions doped can poison the V2O5/TiO2 catalyst and the Na+ ions exhibit greater poisoning effect than Ca2+ ions. The NO rate constant k on the Na+-V2O5/TiO2 catalyst decreased very sharply from 97.1 to 35.0 cm3 g−1 s−1 with increasing Na/V molar ratio from 0.00 to 0.20. In comparison, k on the Ca2+-V2O5/TiO2 catalyst remained almost unchanged when Ca/V molar ratio was below 0.05. Further increasing Ca/V molar ratio to 0.20 resulted in an obvious decrease of k from 101.8 to 46.3 cm3 g−1 s−1. It was suggested that Na+ ions combined strongly with dispersed vanadia species, neutralized the Brønsted acid sites and reduced their reducibility. In comparison, Ca2+ ions slightly affected the Brønsted acid sites of catalyst. Besides, the dispersed vanadia species on the Ca2+-V2O5/TiO2 catalyst had higher reducibility than Na+-V2O5/TiO2 catalyst. The different poisoning effects of Na+ and Ca2+ ions doped on the V2O5/TiO2 catalyst were correlated not only to the surface acidity but also to the reducibility of catalyst.