Glucose hydrogenolysis over Cu-La2O3/Al2O3: Mechanistic insights

Abstract

Glucose hydrogenolysis is an attractive route to produce propylene glycol, a commodity chemical with a wide variety of applications. In this report, the reaction mechanism was studied using 1-13C-d-Glucose and 13C NMR analysis. It was shown that propylene glycol is 13C labelled at either C1 or C3 positions, as indicated by mapping the 13C atom from the first carbon of glucose to fructose and then to propylene glycol obtained through isomerisation and retro-aldol condensation reactions. The direct retro-aldol condensation of glucose produced 13C labelled ethylene glycol. However, 1,2-butanediol and erythritol were not 13C labelled, indicating the cleavage of the C2-C3 bond during direct glucose hydrogenolysis. In addition, the effect of the reaction temperature on product distribution was studied by injecting the glucose solution at the reaction temperature. It was found that carbon loss was minimised by performing glucose hydrogenolysis at 140 °C. Finally, the dissociation of water at high temperature was found to catalyse pyruvaldehyde conversion to lactic acid and Humins, lowering down the propylene glycol yield.