Synthesis, characterization and catalytic application of mesoporous W-MCM-48 for the selective oxidation of cyclopentene to glutaraldehyde

Abstract

Tungsten-containing ordered MCM-48 has been synthesized under hydrothermal conditions via pH adjustment and characterized with various analytical and spectroscopic techniques including X-ray diffraction (XRD), N 2 adsorption, transmission electron micrographs (TEM), scanning electron micrographs (SEM), Laser-Raman spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier-transform infrared spectroscopy (FT-IR) and ammonia temperature-programmed desorption (NH 3-TPD). XRD and FT-IR results indicate that the substitution of tungsten occurs in the silicate framework structure of MCM-48. TEM and SEM investigations confirm the presence of ordered cubic structure in the novel W-MCM-48 material. NH 3-TPD and FT-IR-pyridine adsorption experiments indicate that the strong Brønsted and Lewis acid sites are formed upon incorporation of tungsten in the mesoporous MCM48 framework and the moderately strong acidity of the W-MCM-48 catalyst is beneficial to its good catalytic performance. The as-synthesized W-MCM-48 material is very active as a heterogeneous catalyst for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA) with environmentally benign aqueous hydrogen peroxide as the oxidant. Tungsten species could stably exist in the silica-based matrix of MCM-48 up to WO 3 content of 20 wt%. Both the proper content of tungsten species and its high dispersion account for its high activity. The 20 wt% W-MCM-48 catalyst shows CPE conversion of 85.2% and GA yield of 66.9%, respectively. Furthermore, almost no tungsten species are leached into the reaction solution, enabling the catalyst to be a promising candidate for its further application in industry.