PLATINUM SUPPORTED WOX-ZRO2 - EFFECT OF CALCINATION TEMPERATURE AND TUNGSTEN LOADING

The influence of calcination temperature (500-880 degrees C) and of tu ngsten loading (2, 5 and 18 wt.%) on platinum supported on tungsten-ox ide-promoted zirconia, where the platinum was added after high-tempera ture calcination of the support, has been studied. Catalysts were char acterized by X-ray diffraction, temperature-programmed reduction, ammo nia temperature-programmed desorption, X-ray photoelectron spectroscop y, laser Raman spectroscopy and catalytic activity for n-hexane isomer ization in the presence of hydrogen. A maximum in catalytic activity, defined as ''moles of n-hexane convertedx(surface density of tungsten atoms)(-1) h(-1)'', is observed for the sample calcined at 700 degrees C. Regarding tungsten loading, samples calcined at 830 degrees C and containing 2 and 5 wt.% tungsten show a lower catalytic activity than a sample containing 18 wt.%. The catalytic activity is associated with the presence of crystalline WO3. (C) 1998 Elsevier Science B.V.