STUDY OF THE MORPHOLOGY OF VANADIA-TITANIA AND TIN-OXIDE-PROMOTED VANADIA-TITANIA CATALYSTS BY ELECTRON-MICROSCOPIC METHODS

An 8 wt% vanadia/titania catalyst, prepared by impregnation, was promoted with tin(IV)-oxide, resulting in a catalyst with a Sn:V:Ti atomic ratio of 1:20:262. The catalyst morphology was characterised by high resolution transmission electron microscopy, scanning transmission electron microscopy combined with energy dispersive X-ray analysis, and electron spectroscopic imaging/electron energy loss spectroscopy. The vanadia distribution was found to be inhomogeneous. A fraction of the titania was partly covered by vanadia, though there was a considerable amount of separate vanadia and titania crystallites as well. The presence of an amorphous layer on titania and its restructuring during electron beam irradiation is disputed as evidence for a vanadia monolayer. Tin-oxide promotion did not influence significantly the vanadia distribution; the low content of the promoter prevented the mapping of its distribution.