L. Lietti et al., REACTIVITY OF V2O5-WO3 TIO2 CATALYSTS IN THE SELECTIVE CATALYTIC REDUCTION OF NITRIC-OXIDE BY AMMONIA/, Catalysis today, 29(1-4), 1996, pp. 143-148
The physico-chemical characteristics and the reactivity of sub-monolay
er V2O5-WO3/TiO2 deNO(x) catalysts is investigated in this work by EPR
, FT-IR and reactivity tests under transient conditions. EPR indicates
that tetravalent vanadium ions both in magnetically isolated form and
in clustered, magnetically interacting form are present over the TiO2
surface. The presence of tungsten oxide stabilizes the surface V-IV a
nd modifies the redox properties of V2O5/TiO2 samples. Ammonia adsorbs
on the catalysts surface in the form of molecularly coordinated speci
es and of ammonium ions. Upon heating, activation of ammonia via an am
ide species is apparent. V2O5-WO3/TiO2 catalysts exhibits higher activ
ity than the binary V2O5/TIO2 and WO3/TiO2 reference sample. This is r
elated to both higher redox properties and higher surface acidity of t
he ternary catalysts, Results suggest that the catalyst redox properti
es control the reactivity of the samples at low temperatures whereas t
he surface acidity plays an important role in the adsorption and activ
ation of ammonia at high temperatures.