Abstract: The Ir/ZrO₂ catalyst was prepared by impregnation, and the effect of reduction temperature on its catalytic performance for hydrogenation of crotonaldehyde in gas phase was measured. With increasing reduction temperature, the crotonaldehyde conversion and selectivity for crotyl alcohol over the Ir/ZrO₂ catalyst first increase and then decrease. The catalyst reduced at 400 ^oC exhibits the highest crotonaldehyde conversion, reaching a value as high as 32.2%, and the selectivity for ctotyl alcohol is 74.3%. The results of X-ray photoelectron spectroscopy indicated that both Ir⁰ and Ir³⁺ species coexist on the catalyst surface after reduction at 400 ^oC. With increasing reduction temperature, the ratio of Ir⁰/Ir³⁺ increases, and the surface Ir species exists mainly as Ir⁰ when the reduction temperature is 600 ^oC. Additionally, NH₃ temperature-programmed desorption indicated that the amount and intensity of Lewis acid sites show a downward trend with increasing reduction temperature, which is attributed to the decline of Cl element in the catalyst. Therefore, it is concluded that the coexistence of Ir⁰ and Ir³⁺ and moderate-intensity of surface Lewis acid help improve the yield and selectivity of crotyl alcohol.

Key words: iridium, zirconium dioxide, supported catalyst, crotonaldehyde, selective hydrogenation, crotyl alcohol, Lewis acid