Characterization of Tungsten-Based Catalyst Used for Selective Oxidation of Cyclopentene to Glutaraldehyde

Tungsten-containing hexagonal mesoporous silica (W-HMS) supported tungsten oxide catalysts (WOx/W-HMS) was prepared for the selective oxidation of cyclopentene with aqueous hydrogen peroxide to glutaraldehyde. X-ray diffraction (XRD) results indicated that the crystal form of the active phase (tungsten oxide) of the WOx/W-HMS catalysts was dependent on the W loading and calcination temperature. X-ray photoelectron spectroscopy (XPS) analysis revealed that the dispersed tungsten oxides on the surface of W-HMS support consisted of a mixture of W(V) and W(VI). It was found that a high content of amorphous W species in (5+) oxidation state resulted in the high catalytic activity. When the W loading was up to 12% (by mass) or the catalyst precursor was treated at temperature of 623 K, the catalytic activity decreased due to the presence of WO3 crystallites and the oxidation of W(V) to W(VI) on the catalyst surface. Furthermore, NH3-temperature-programmed-desorption (NH3-TPD) analysis showed that the effects of W loading and calcination temperature on the acidity of the catalysts were related to the catalytic activity. A high selectivity of 80.2% for glutaraldehyde with a complete conversion of cyclopentene was obtained over 8%WOx/W-HMS catalyst calcined at 573 K after 14 h of reaction.