Arenesulfonic acid functionalized mesoporous silica as a novel acid catalyst for the liquid phase Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam

Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam was performed in liquid phase for the first time on arenesulfonic acid-functionalized SBA-15 (SBA-ar-SO3H) mesoporous silica with different loadings of the acid. The catalysts were prepared via co-condensation of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS) and tetraethyl orthosilicate (TEOS) in the presence of Pluronic 123 (EO20PO70EO20) and characterized by XRD, N2 adsorption-desorption, TGA, EA and acid-base titration method. The oxime conversion and selectivity to ɛ-caprolactam were found to increase with the loading of arene-SO3H groups. The influences of solvent and reaction temperature on the rearrangement of oxime in the liquid phase were examined. The oxime rearrangement and hydrolysis were proposed to be catalyzed on different active sites of SO3H and SiOH, respectively. The catalytic activity of SBA-ar-SO3H was also compared with the activities of other solid acid catalysts such as propylenesulfonic acid-functionalized SBA-15, H-ZSM-5, H-mordernite, Al-MCM-41 and Al-SBA-15. The results revealed that SBA-ar-SO3H has higher catalytic activity and lactam selectivity.