Reaction mechanisms for the heterogeneous hydrogenolysis of biomass-derived glycerol to propanediols

Biomass-derived glycerol is emerging as a renewable, cheap and versatile feedstock for the production of a variety of chemicals and fuels. In particular, hydrogenolysis of glycerol to other value-added chemicals over heterogeneous catalysts has been extensively studied in the past few years. The most desired products arising from this process are propanediols, i.e. 1,2-propanediol and 1,3-propanediol. Both diols are important industrial chemicals, being especially well-known as monomers for the production of many useful polymers. Although hydrogenolysis of glycerol is a promising new route for the production of propanediols, the design of applicable catalysts for its industrialisation is still a great challenge. In order to guide the rational development of efficient catalysts, several possible reaction mechanisms have been proposed based on experimental and theoretical investigations. A brief review is now presented on the reaction mechanisms for the hydrogenolysis of glycerol to propanediols over heterogeneous catalysts. The possible reaction mechanisms are summarised and classified. The main characteristics and general reaction conditions for each reaction mechanism are highlighted. Furthermore, the developing prospects and future direction of research are suggested.