Influence of tungsten precursors on the structure and catalytic properties of WO3/SBA-15 in the selective oxidation of cyclopentene to glutaraldehyde

Mesoporous WO3/SBA-15 was synthesized by the conventional incipient wetness impregnation method from various tungsten precursors. The influence of different tungsten precursors on the structure Of WO3/SBA-15, as well as their catalytic performance for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA), was investigated. The dispersion and nature of the tungsten species were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectra (DRS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (NH3-TPD), and temperature-programmed reduction (H-2-TPR). Among the different tungsten sources, the tungstenic complex sources produced from the reaction of tungstic acid with oxalic acid showed the highest dispersion Of WO3 species, the strongest surface Bronsted and Lewis acid properties, and the strongest interaction with the SBA-15 support. As a consequence, this catalyst gave much higher CPE conversion and excellent GA selectivity. On the other hand, the catalyst prepared from the ammonium paratungstate showed the lowest activity owing to the presence of crystalline WO3 on the surface. Although the activity of the catalyst prepared from the reaction of tungstic acid with oxalic acid decreased slightly after the first recycle due to leaching of small amounts of active tungsten species, it remained nearly the same value after easy regeneration with heat treatment, demonstrating that the WO3/SBA-15 catalyst is a heterogeneous one in the target reaction.