Glucose hydrogenolysis over Cu-La2O3/Al2O3: Mechanistic insights

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-C-13-D-Glucose and C-13 NMR analysis. It was shown that propylene glycol is C-13 labelled at either C-1 or C-3 positions, as indicated by mapping the C-13 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 C-13 labelled ethylene glycol. However, 1,2-butanediol and erythritol were not C-13 labelled, indicating the cleavage of the C-2-C-3 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 degrees 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.