Platinum supported WOx-ZrO2:: Effect of calcination temperature and tungsten loading

The influence of calcination temperature (500-880 degrees C) and of tungsten loading (2, 5 and 18 wt.%) on platinum supported on tungsten-oxide-promoted zirconia, where the platinum was added after high-temperature calcination of the support, has been studied. Catalysts were characterized by X-ray diffraction, temperature-programmed reduction, ammonia temperature-programmed desorption, X-ray photoelectron spectroscopy, laser Raman spectroscopy and catalytic activity for n-hexane isomerization 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.