Selective hydrogenation of paracetamol to acetamidocyclohexanone with silylated SiO2 supported Pd-based catalysts

Abstract

A series of catalysts comprising well-distributed Pd nanoparticles incorporated on silylated SiO₂ were fabricated by the wet impregnation method and investigated in the selective hydrogenation of paracetamol to 4-acetamidocyclohexanone. The catalysts calcined at different temperatures were characterized by TG, FT-IR, N₂ physisorption, TPR and XPS. The results showed that organic modification led to a catalyst surface composed of stable Si–(CH₃)₃ species even after calcination at 300 °C. Also, changes occurred in the size and electronic properties of the Pd particles through the different amounts of grafted groups on the SiO₂ support. The mode of adsorption of the paracetamol molecule was influenced by the quite bulky organic groups on the support, resulting in a significant improvement in selectivity towards 4-acetamidocyclohexanone and preventing full hydrogenation to some extent. The best result was obtained on the silylated Pd catalyst calcined at 500 °C, with 64.9% selectivity to keto at the paracetamol conversion of 60.5%, while the non-silylated SiO₂ supported Pd catalyst gave 4-acetamidocyclohexanone selectivity of 29.1% at 53.8% conversion.