Steady-State and Transient Reactivity Study of TiO2-Supported V2O5−WO3 De-NOx Catalysts:  Relevance of the Vanadium−Tungsten Interaction on the Catalytic Activity

The reactivity of ternary V 2 O 5 −WO 3 /TiO 2 de-NO x catalysts (V 2 O 5 = 0−1.47% w/w, WO 3 = 0−9% w/w) in the selective catalytic reduction (SCR) reaction is investigated under steady-state and transient conditions. The results indicate that over the investigated catalysts the SCR reaction occurs via a redox mechanism and that the rate-determining step of the reaction is the catalyst reoxidation process. The reactivity of the V 2 O 5 −WO 3 /TiO 2 catalysts increases on increasing either the V 2 O 5 or the WO 3 loading; the reactivity of V and/or W in the ternary catalysts is higher than that of the corresponding binary samples. A synergism between the TiO 2 -supported V and W surface oxide species in the SCR reaction is suggested, that is exploited in the enhancement of the catalyst redox properties of the samples. Accordingly, tungsta increases the rate of the SCR reaction of V 2 O 5 /TiO 2 catalysts by favoring the catalyst reoxidation by gas-phase oxygen.