Selective hydrogenolysis of biomass-derived sorbitol to propylene glycol and ethylene glycol on in-situ formed PdZn alloy catalysts

Article abstract of DOI:10.1016/j.apcata.2020.117770

Sorbitol hydrogenolysis to industrially important propylene glycol and ethylene glycol receives increasing attention, recently. Here, we developed an efficient and stable PdZn alloy catalyst, in-situ formed from a physical mixture of Pd/ZrO₂ and ZnO, for the sorbitol hydrogenolysis with Mg₃AlO_x as a solid base, and obtained a 54.6% yield of the two target glycols (493 K and 5.0 MPa H₂). The amounts of ZnO and Mg₃AlO_x strongly influenced the activity and selectivity, due to their effects on the formation of the PdZn alloys and the competitive metal-catalyzed dehydrogenation/hydrogenation and base-catalyzed retro-aldol condensation steps. The kinetic isotope effects, combined with the inhibiting effects of H₂ pressure on the activity in a broad range (3.0–8.0 MPa), confirm that the sorbitol dehydrogenation to hexose intermediates is the kinetically-relevant step in the sorbitol hydrogenolysis. This study provides insights into the catalytic functions and reaction parameters for the hydrogenolysis of polyols to the target glycols.