REACTIVITY OF V2O5-WO3 TIO2 DE-NOX CATALYSTS BY TRANSIENT METHODS/

The reactivity of ternary V2O5-WO3/TiO2 de-NO(x)ing catalysts with com positions similar to those of commercial catalysts (WO3 ca. 9% w/w, V2 O5 < 2% w/w) is investigated by transient techniques (temperature prog rammed desorption, TPD; temperature programmed surface reaction, TPSR; and temperature programmed reaction, TPR). The results indicate that the reactivity of the ternary catalysts in the SCR reaction increases on increasing the vanadia loading, and that the ternary catalysts are more active than the corresponding binary vanadia-titania samples with the same V2O5 loading. Indeed the SCR reaction is monitored at lower temperatures and high NO conversions are also preserved at high temper atures. TPSR and TPR data show that at low temperatures the SCR reacti on occurs via a redox mechanism that involves at first the participati on of the catalyst lattice oxygen and then the reoxidation of the redu ced sites by gas-phase oxygen. Based on TPSR and TPR data, the higher reactivity of the ternary catalysts has been related to their superior redox properties, in line with previous chemico-physical characterisa tion studies. The catalyst redox properties thus appear as a key-facto r in controlling the reactivity of V2O5-WO3/TiO2 de-NO(x)ing catalysts at low temperatures. The results also show that at high temperatures the surface acidity plays an important role in the adsorption and acti vation of ammonia.