Activity, selectivity and stability of Ni and bimetallic Ni-Pt supported on zeolite Y catalysts for hydrogenation of acetophenone and its substituted derivatives

The hydrogenation of acetophenone, p-hydroxy acetophenone (p-HAP) and p-isobutyl acetophenone was studied using Ni and bimetallic Ni-Pt supported on zeolite Y catalysts. A 10% Ni-supported-on-zeolite Y catalyst showed the optimum activity when compared to other Ni-supported catalysts. The activity of this catalyst decreased very rapidly on recycle; however, the bimetallic Ni-Pt-supported-on-zeolite Y catalyst was highly stable and showed constant activity on recycle. The addition of Pt catalyses the reduction of Ni2+ to Ni-0 characterised by X-ray photoelectron spectroscopy (XPS) and other techniques. For the Ni-Pt bimetallic catalyst, the hydrogen adsorption was found to be higher than that for monometallic catalysts; the adsorbed hydrogen reacts with the activated acetophenone complex to facilitate the catalytic process. The FTIR analysis of adsorbed acetophenone on the catalyst samples indicated that, in both monometallic and bimetallic catalysts supported on zeolite Y, the C=O bond of acetophenone is highly activated due to the strong interactions with the acidic sites present on the zeolite. Zeolite interactions with intermediate products and solvent moieties also influenced the selectivity behaviour. A trace amount of a base like NaOH acts as a promoter in improving the selectivity towards alcohol. A plausible reaction mechanism has been proposed for the hydrogenation of acetophenone and its derivatives using monometallic as well as bimetallic catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.