An Ag-promoted Co/Al2O3 catalyst without reduction pretreatment for the selective hydrogenolysis of high-concentration glycerol to 1,2-propanediol

Abstract

The development of highly efficient catalysts for selective hydrogenolysis of biomass-derived glycerol to 1,2-propanediol (1,2-PDO) remains an important and challenging target. Herein, we present a strategy to enhance γ-Al₂O₃ supported Co catalysts via Ag promotion. The Co/Al₂O₃ catalyst exhibits no catalytic activity for selective hydrogenolysis of glycerol without reduction pretreatment and low selectivity for 1,2-PDO after reduction pretreatment. With Ag promotion, the CoAg/Al₂O₃ catalyst can be reduced and activated in situ in the reaction system, demonstrating high catalytic activity and good selectivity for 1,2-PDO (∼90 mol%) under high-concentration reaction conditions with 80 wt% glycerol aqueous solution. Catalyst characterization using TEM, XPS, XRD, and H₂-TPR reveals that Ag facilitates the in situ reduction of Co₃O₄ in the reaction system, which not only generates low-oxidizing-degree Co species (CoO_x), but also induces a significant number of oxygen vacancies (O_vac.). A reaction mechanism is proposed based on the heterolytic cleavage of H₂ to provide active H^δ− and H^δ+ species for the hydrogenolysis of the C–O bond in glycerol at the CoO_x–O_vac. sites of the catalyst. Notably, Ag plays a crucial role in guaranteeing the excellent catalytic behaviour of the CoAg/Al₂O₃ catalyst for the hydrogenolysis reaction and simplifying catalyst preparation and maintenance by eliminating the reduction pretreatment.