Design of Bifunctional Catalyst and Kinetic Analysis for Glycerol Conversion to Propylene Glycol via Coupled Aqueous-Phase Reforming and Hydrogenolysis

This study reports the development of bifunctional catalysts for the selective conversion of glycerol into propylene glycol (PG) via catalytic transfer hydrogenolysis (CTH) coupled with in situ hydrogen provision via aqueous-phase reforming (APR). A structured four-stage experimental framework was adopted, comprising catalyst support screening, active metal composition optimization, reusability evaluation, and kinetic analysis. Screening of natural clay minerals (alumina, montmorillonite, kaolinite, Illite, and attapulgite) under APR–CTH conditions (250 °C, 6 h, and 20% v/v glycerol) identified alumina as the most effective support, owing to its amphoteric surface properties, strong metal–support interactions, and structural stability. Subsequent optimization using an augmented simplex centroid design revealed Cu–Mg/Al2O3 as the optimal formulation, achieving 86.16% glycerol conversion and 43.81% PG yield, while minimizing byproduct formation. Notably, Ni was excluded from the optimum composition due to its negative effect on PG selectivity and tendency to promote unselective hydrogenolysis. The optimized Cu–Mg/Al2O3 catalyst exhibited stable performance across ten consecutive cycles, maintaining a turnover frequency of 8.17 h–1 and a turnover number of 49.01 mol product per mol active site, underscoring its robustness and reusability. Kinetic modeling using a Langmuir–Hinshelwood framework revealed that glycerol reforming and hydrogenolysis to PG occurred primarily on basic sites with moderate activation energies (29.49–40.18 kJ·mol–1), while undesired PG hydrogenolysis to 2-propanol was confined to acidic sites with a significantly higher barrier (219.78 kJ·mol–1). This work establishes Cu–Mg/Al2O3 as a promising bifunctional catalyst and provides mechanistic and kinetic insights that advance the sustainable valorization of glycerol into PG, aligning with Sustainable Development Goals 12 and 13.