Synthesis and characterization of gold nanoparticles supported on thiol functionalized chitosan for solvent-free oxidation of cyclohexene with molecular oxygen

• Gold nanoparticles supported on thiol functionalized chitosan.
• Liquid phase oxidation of cyclohexene to 2-cyclohexene-1-one and 1,2-cyclohexanediol.
• The highest conversion and highest selectivity to 2-cyclohexene-1-one reported.
• TEM images show that the immobilized gold nanoparticles have diameter around 3–6 nm.

The selective liquid phase oxidation of cyclohexene to 2-cyclohexe-1-one and 1,2-cyclohexanediol has been investigated over gold nanoparticles (GNPs) with molecular oxygen in a solvent-free condition. The gold nanoparticles were immobilized on thiolated chitosan derivative (TChD), by grafting thiol groups on the support. The catalyst was characterized by XPS, N2 adsorption/desorption, TEM, FT-IR and UV–vis spectroscopy. TEM results show that the majority of Au particles have diameters in the range of 3–6 nm. X-ray photoelectron spectroscopy (XPS) revealed the coexistence of both oxidized and metallic gold species on the surface of TChD. The results show that the catalytic performance of GNPs/TChD is quite remarkable and the catalytic activity over recycled catalyst remains at a high level after at least 4 cycles. Activity tests were carried out in an autoclave at 80 °C without any solvent. In order to obtain maximum conversion, the reaction parameters such as reaction temperature and time were optimized. Under optimized conditions, a maximum of 87% conversion and 70% selectivity was achieved with the GNPs/TChD catalyst.

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