PHASE-TRANSFORMATION STUDY OF TITANIA IN V2O5 TIO2 AND MOO3/TIO2 CATALYSTS BY X-RAY-DIFFRACTION ANALYSIS/

The effect of the presence of vanadia or molybdena and the thermal tre atment on the phase transformation of titania in V2O5/TiO2 and MoO3/Ti O2 catalysts was investigated using X-ray powder diffraction (XRD) ana lysis. The titania support used was a commercial sample from Harshaw c ontaining anatase together with a small quantity of graphite. Tle XRD results suggest that when,the TiO2 SUPPort is calcined at 973 K, anata se is partially transformed into rutile, whereas at 1273 K it is total ly converted to rutile. In the presence of V2O5 the temperature of par tial conversion is reduced to 813 K, and a total transformation is not ed already at 973 K. MoO3 also induces this transformation, but is les s effective than V2O5. XRD results further show that when the V2O5/TiO 2 catalyst is subjected to calcination at 973 K, no crystalline V2O5 p hase is present. The same is not true for MoO3, which is present in a crystalline state at this calcination temperature. This study reveals clearly that vanadia and molybdena behave differently when impregnated on the same titanium dioxide support.