The promoting effect of Zn on liquid phase hydrogenation of crotonaldehyde over amorphous Co-B catalysts has been investigated. It was found that when ZnCl₂ was introduced to the reactant, zinc ions could selectively block the active sites for C＝C bond hydrogenation. Moreover, zinc ions might polarize the carbonyl group as Lewis acid, making the nucleophilic attack of adjacent dissociatively adsorbed hydrogen atom much easier, thus leading to a higher yield of crotyl alcohol. On the other hand, in amorphous Co-Zn-B catalysts, zinc was in the form of Zn(OH)₂ and the amount of CoO and B₂O₃ increased with more zinc incorporated. These oxides were expected to nonselectively cover the active sites and depress the hydrogenation rates of the C＝C bond and the carbonyl group to a similar extent, thus marginally improving the selectivity towards crotyl alcohol.

Key words: amorphous alloy, Co-B, crotonaldehyde, crotyl alcohol, selective hydrogenation, Zn