Tungsten oxide catalysts supported on activated carbons: effect of tungsten precursor and pretreatment on dispersion, distribution, and surface acidity of catalysts

Abstract

Tungsten catalysts supported on activated carbon were prepared using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide. The catalysts were pretreated in He, dry air, or wet air at 623 K for 6 h before being characterized by N 2 adsorption at 77 K, temperature-programmed desorption, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, and by testing their behavior in the decomposition reaction of isopropanol. The dispersion of the supported tungsten oxide phase and their surface acidity depended on the metal precursor and atmosphere of pretreatments. Thus, the highest dispersion and surface acidity were found for the catalyst prepared from W(CO) 6 and the lowest dispersion for that prepared from (NH 4) 2WO 4. Dry air gave the highest dispersion, whereas wet air yielded the highest surface acidity. Air pretreatments of the catalyst prepared from W(CO) 6 seem to create metal oxide–support interactions, because of the very low particle size of the supported tungsten oxide phase and its homogeneous distribution.