Review of the Development of Heterogeneous Catalysts for Liquid and Vapor Phase Hydrogenolysis of Glycerol to Propylene Glycol (1,2-Propanediol): State-of-the-Art and Outlook

In the last two decades, various glycerol value addition techniques have been developed and discussed in the literature. Among all these processes, conversion of glycerol to 1,2-propanediol (1,2-PDO) has been recognized as one of the promising and commercially attractive glycerol value addition routes. This review is an attempt to scan out the progress in catalysts design and development for liquid and vapor phase glycerol hydrogenolysis for the production of 1,2-PDO. The development of supported and mixed metal oxide catalysts with their novel catalytic characteristics for glycerol conversion and 1,2-PDO selectivity has been scrutinized systematically. It was observed that among the non-noble metal catalysts, Cu-based catalysts have shown promising activity toward 1,2-PDO; however, their stability is an issue. Among noble metals, Pt- and Ru-based catalysts were reported active for glycerol conversion. Comparatively, catalysts composed of Pt, Ru, Pd as a noble metal, and Cu as a non-noble metal have resulted in higher catalytic activity and 1,2-PDO selectivity. This review also summarizes different reaction pathways for hydrogenolysis of glycerol to 1,2-PDO, the effect of additives (solid acid and base), and methods of catalyst preparation on the catalyst performances. Further, glycerol hydrogenolysis with in situ H2 production by glycerol reforming or by chemical transfer hydrogen using various hydrogen donors and the effect of different solvents on the glycerol hydrogenolysis process are also discussed. Reaction kinetic models are also included at the end.