Solvent-free glycerol hydrogenolysis through skeletal copper catalyst

Glycerol hydrogenolysis represents a promising route for the valorization of biodiesel-derived glycerol into propylene glycol; however, efficient operation under solvent-free conditions remains challenging due to mass-transfer limitations and competing reaction pathways. In this study, skeletal copper catalysts were prepared via Cu-Zn alloy precipitation followed by controlled, selective leaching, in which Zn served as a sacrificial component to generate a porous Cu framework with enhanced surface accessibility. The influence of leaching time on catalyst composition, porosity, reducibility, and catalytic performance was systematically investigated. Under solvent-free glycerol hydrogenolysis conditions, the optimally leached skeletal Cu catalyst exhibited glycerol conversion of up to 85.4% and propylene glycol selectivity of up to 83.5%, placing its performance among the highest reported for Cu-based catalysts operating without external solvent. Recycling experiments demonstrated stable catalytic performance over multiple reaction cycles. Gas chromatography–mass spectrometry analysis confirmed acetol as a key reaction intermediate, supporting a reaction pathway dominated by glycerol dehydration followed by hydrogenation to propylene glycol. Although direct acidity characterization was not conducted, the observed catalytic behavior is interpreted as consistent with the presence of residual Zn-derived species that may introduce Lewis-acidic functionality, in conjunction with metallic Cu sites responsible for hydrogenation. The mechanistic interpretations presented are based on catalyst composition, reaction behavior, and literature precedent. This work demonstrates that skeletal Cu catalysts derived from Cu-Zn dealloying provide an effective and sustainable platform for solvent-free glycerol hydrogenolysis and offers new insights into structure–performance relationships relevant to Cu-based biomass conversion catalysts.