Highly selective catalysts for the hydrogenation of alkynols: A review

The semi-hydrogenation of alkynols to enols is a crucial process in the production of pharmaceuticals, agrochemicals, fragrances, and flavors that involves a complex set of parallel and consecutive isomerization and hydrogenation reactions and proceeds via several key intermediates. In view of the industrial importance of large-scale enol production through alkynol hydrogenation, various noble and non-noble metal (e.g., Ni and Pd)-based catalysts promoting this transformation have been developed. This paper reviews the design of highly selective catalysts for the semi-hydrogenation of alkynols, focusing on the role of additives, second metals, catalyst supports, and reaction conditions and combining catalytic reaction kinetics with theoretical calculations to establish the reaction mechanism and the decisive factors for boosting selectivity. Finally, a strategy for designing highly efficient and selective catalysts based on the characteristics of aqueous-phase alkynol hydrogenation is proposed.