Advances in understanding the active sites of Cu catalysts in glycerol hydrogenolysis to 1,2-propanediol

Compared with fossil-dependent process, glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) is a green sustainable route with much advantage. The commercial scale of this reaction has been achieved, and catalysts with high efficiency are continuously developed. Cu-based catalysts are considered as the most selective catalysts for 1,2-PDO production, which are widely investigated up to now. Understanding the structure-activity relationship can help the design of new catalytic materials with improved activity, selectivity and stability. In this review, the roles of various active structures on Cu catalysts are summarized. We introduce firstly the pioneering works, showing that Cu species are the primary active sites which can catalyze both the glycerol dehydration and C = O bond hydrogenation steps. Then, we summarize various viewpoints about the structure-sensitive effect of Cu in the reaction. The functions of support and promoter are subsequently discussed in detail, and the roles of the secondary metal site are further overviewed. After that, we propose critical factors that should be considered when investigating the Cu structure sensitive effect, and summarize three general roles of support, promoter and secondary metal. Further important research directions for Cu catalysts in glycerol hydrogenolysis are also outlined.