AN EPR STUDY OF THE SURFACE-CHEMISTRY OF THE V2O5-WO3 TIO2 CATALYST -REDOX BEHAVIOR AND STATE OF V(IV)/

A series of catalysts built up by V2O5 and WO3 overlayers on TiO2 anat ase which have shown remarkable activity and selectivity in the select ive catalytic reduction (SCR) of nitric oxide have been investigated b y electron paramagnetic resonance spectroscopy. All the systems exhibi t spectra due to the presence of both isolated and magnetically intera cting V(IV) ions whose amount has been monitored as a function of the temperature of progressively reducing vacuum treatments. By comparison with binary systems (V2O5/TiO2 and WO3/TiO2) evidence has been provid ed for the structural features of V(IV) ions isolated at the surface o f the ternary systems. Although the two supported phases mainly intera ct with the TiO2 matrix, the present investigation reveals the existen ce of a mutual (structural and electronic) interaction between the two supported bidimensional phases which determines the special redox pro perties of the ternary systems. These properties are remarkably differ ent from that of V2O5/TiO2 systems and can contribute to an understand ing of the catalytic behaviour of the V2O5-WO3/TiO2 systems in the SCR reaction. (C) 1997 Academic Press.