THERMAL-STABILITY OF VANADIA-TITANIA CATALYSTS

The thermal behaviour of seven different 'pure' TiO2 (anatase) prepara tions, as well as of materials obtained by doping them with potassium sulfate and carbonate, silica, and the oxides of tungsten, molybdenum and vanadium has been investigated by TG-DTA, XRD, FTIR and surface-ar ea measurements. Vanadia-titania catalysts prepared by impregnation of these supports have also been investigated by the same techniques. Th e temperature at which anatase sintering and phase transformation to r utile occur strongly depends on the morphology of the TiO2 preparation . The anatase phase is much less stable in high-area, highly porous ma terials than in low-area powders. Vanadium oxide speeds up the anatase -to-rutile transition. However, common catalyst additives like silica, tungsten oxide and alkali-metal carbonates and sulfates strongly slow down both anatase sintering and its transformation to rutile. These p henomena influence the formulation of additives for vanadia-titania (a natase) catalysts for both selective oxidation and reduction of NO(x).