Progress and Reaction Mechanism of Co-Based Catalysts in the Selective Hydrogenation of α,β-Unsaturated Aldehydes

In recent years, Co-based catalysts have attracted considerable attention in research on selective hydrogenation reactions because of their mild activities and favorable selectivities for producing intermediate products, especially in the selective hydrogenation of α,β-unsaturated aldehydes (UAL). However, the low activity of Co-based catalysts for activating hydrogen limits their application in industry, and the diversity of forms and electronic states of Co-based catalysts also leads to the development of complex products and hydrogenation mechanisms at Co active sites. This review provides a comprehensive and systematic overview of recent progress in the selective hydrogenation of UAL over Co-based catalysts, where the preparation methods, hydrogenation properties, and UAL hydrogenation mechanisms of Co-based catalysts are carefully discussed. The influences of nanosize effects, electronic effects, and coordination effects on Co metal and Co oxides are investigated. In addition, the different reaction mechanisms at Co active sites are compared, and their strengths and weaknesses for C=O hydrogenation are further proposed. Finally, the outlook and challenges for the future development of Co-based hydrogenation catalysts are highlighted.