Catalysts and mechanisms for the selective heterogeneous hydrogenation of carbon-carbon triple bonds

The selective hydrogenation of carbon-carbon triple bonds to the corresponding double bonds, the semi-hydrogenation process, plays a very important role in polymer and fine chemical industry. Various heterogeneous catalysts have been exploited for the selective hydrogenation of alkynes and alkynols in the gas and liquid phase. Herein, the recent progress in developing semi-hydrogenation catalysts, from traditional Pd-based monometallic catalysts to intermetallic compounds and single-atom catalysts, is summarized. The activation of dihydrogen during hydrogenation and the full hydrogenation mechanism, along with relevant research methodologies, are discussed. This review provides a comprehensive overview on the catalysts and mechanisms of industrially relevant semi-hydrogenation processes, addresses some existing debates, and sheds light on future catalyst design for hydrogenation.