Facile Synthesis of Cyclohexanone Oxime <italic>via</italic> Solvent-Free Catalytic Oxidation of Cyclohexylamine Using Phosphorus-Modified TiO₂/SBA-15

A highly efficient P-TiO2/SBA-15 catalyst using titanium butoxide and phosphoric as raw materials was synthesized by liquid phase hydrolysis method， and the physio-chemical properties of the catalysts were characterized by X-ray photoelectron spectroscopy （XPS）， fourier transform infrared spectroscopy （FT-IR）， transmission electron microscope （TEM）， X-ray powder diffraction （XRD）， and N2 adsorption-desorption specific surface analyzer （BET） characterization techniques. The catalytic performance of P-TiO2/SBA-15 in the solvent-free oxidation of cyclohexylamine to cyclohexanone oxime was further studied. And the reaction conditions such as temperature and pressure were systematically optimized. Furthermore， a probable dual pathway mechanism of cyclohexylamine catalytic oxidation was also suggested. The results indicated that surface modified P-TiO2 nanoparticles could achieve high dispersion loading on SBA-15， which was beneficial for improving its catalytic efficiency. The best catalytic effect was achieved when the P-TiO2 loading was 10%. Under the premise of equal loading of active components， the 10% P-TiO2/SBA-15 composite exhibited significant catalytic performance advantages. Compared to the unloaded P-TiO2， the catalytic conversion efficiency of cyclohexylamine increased by 3.2 times to 68.3%， and the selectivity of the target product cyclohexanone oxime increased by 15.3% simultaneously. Under standardized reaction conditions （90 ℃， 1.0 MPa， 4 h）， the efficient conversion could be achieved using 0.3 g of composite catalyst， confirming the dispersion strengthening effect of ordered mesoporous carriers on active components. In addition， the titanium hydroxyl groups on the surface of P-TiO2/SBA-15 were the active centers for catalytic oxidation of cyclohexylamine. The method provides a novel and green route for the highly efficient preparation of cyclohexanone oxime， and has certain prospects for industrial applications.