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.