Hydrophobic Sn–Ti submicrospheres for cyclohexanone Baeyer–Villiger efficient oxidation

In this paper, hydrophobic treatment by hexadecetyltrimethoxysilane (HDTMS) on the surface of Sn–Ti submicrospheres with regular morphology and uniform size prepared via a simple PVP-assisted sol-gel method was firstly reported. Their physical and chemical properties were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), N₂ adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FI-IR), Uvioletvisible diffuse reflection spectroscopy (UV-vis DRS), Water contact angle (WCA), Thermogravimetric analysis (TG), Inductively coupled plasma-Atomic emission spectrometry (ICP-AES), C elemental analysis and Transmission electron microscope (TEM) techniques, and the catalytic performance in the Baeyer-Villiger (B-V) oxidation of cyclohexanone in the oxygen-benzaldehyde system was also investigated. The regular submicrospheres with anatase crystal phase can be kept well by the successful grafted hydrophobic layer. When the weight ratio of HDTMS to 12%-ST submicrospheres was 1, the maximum hydrophobic angle of 126.0º for 12%-1-C₁₆-ST catalyst can be obtained. The cyclohexanone conversion and caprolactone yield over the 12%-1-C₁₆-ST catalyst was highest, whose value was 2.32 and 3.44 times, respectively, than that of 12%-ST without hydrophobic treatment. The 12%-1-C₁₆-ST catalyst also showed good stability with only a 3.74% drop of caprolactone yield after repeated use for 5 times. This method can provide a valuable reference and potential catalyst for the industrial application in the production of caprolactone.