Abstract: Catalysts Ir/γ-Al₂O₃ were prepared by impregnating γ-Al₂O₃ with an aqueous solution or microemulsion solution ofH₂IrCl₆. The catalystswere characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscope (TEM). The catalytic performance of the supportediridiumcatalysts for the selective hydrogenation of avermectin to ivermectin was investigated. Compared with active carbon (AC), α-Al₂O₃, and TiO₂, γ-Al₂O₃ is a better support in this system. Among Ir, Ru, Pd, and Pt supported on γ-Al2O3, the catalyst Ir/γ-Al₂O₃ showed the best catalytic activity and selectivity to ivermectin. Ir/γ-Al₂O₃ prepared by means of microemulsion solution showed the best catalytic activity, but the catalytic selectivity to ivermectin was lower that over Ir/γ-Al₂O₃ modified with PVP (polyvinylpyrrolidone), which exhibited excellent activity as well as good selectivity.

Key words: Supported catalyst, Iridium, Avermectin, Ivermectin, Selective hydrogenation