Abstract: Gold nanoparticles with different sizes were prepared by reducing HAuCl4 with nitromethane and were then supported on ZSM-5 zeolite by impregnation. The oxidation of β-ionone with molecular oxygen over Au/ZSM-5 was studied. The results indicated that β-ionone was catalytically oxidized to 5,6-epoxy-β-ionone, 4-oxo-β-ionone, 4-hydroxy-β-ionone, and a little dihydroactinidiolide. All the products were valuable flavors or their precursors. Compared with the traditional chromium catalyst, the Au/ZSM-5 catalyst could selectively catalyze the oxidation of β-ionone to epoxy compounds, and the catalyst could be easily separated after the reaction. The effects of the support, solvent, oxidant, reaction temperature, and time on the catalytic performance of Au/ZSM-5 were investigated. The catalytic activity of the Au/ZSM-5 catalyst decreased with increasing size of Au nanoparticles. In addition, the solvent played an important role in the performance of the catalyst. The catalytic activity of Au/ZSM-5 was maintained after repeated use five times.

Key words: gold, ZSM-5 zeolite, β-ionone, oxidation, molecular oxygen, \{5, 6\}-epoxy-β-ionone, 4-oxo-β-ionone, 4-hydroxy-β-ionone