Preparation of periodic mesoporous silica-included divacant Keggin units for the catalytic oxidation of styrene to synthesize styrene oxide

Periodic mesoporous composite catalysts, [(n-C4H9)4N]4[γ-SiW10O34(H2O)2]/SBA-15 (TBA-1*/SBA-15, where TBA-1* = [(n-C4H9)4N]4[γ-SiW10O34(H2O)2]), with TBA-1* loadings of 4.3-14.8% were prepared by simultaneous hydrolysis and co-condensation of the tetraethoxysilane (TEOS) in the presence of divacant Keggin-type polyoxometalate and triblock copolymer surfactant (P123) followed by hydrothermal treatment process. Structure integrity of the Keggin unit in as-prepared composites was studied by Fourier transform infrared spectroscopy (FT-IR), Raman scattering spectra, and 29Si magic-angle spinning (MAS) NMR. Periodic mesoporous structure of the composites was evaluated by low-angle X-ray powder diffraction (LXRD) patterns, nitrogen porosimetry, and transmission electron microscope (TEM) measurements. As-prepared TBA-1*/SBA-15 was used as an heterogeneous oxidation catalyst for the styrene epoxidation reaction to synthesize styrene oxide in the presence of dilute H2O2 (30%), and influences of solvent, molar ratio of styrene to H2O2, TBA-1* loading on the styrene conversion, styrene oxide yield and selectivity were considered.