Synthesis and performance of highly dispersed Cu/SiO2 catalysts for the hydrogenolysis of glycerol

Abstract

The performance of Cu/SiO2 (commercial silica gel, SBA-15 and SBA-15 treated at 900°C) catalysts for the hydrogenolysis of glycerol to propylene glycol is investigated with emphasis on the stability characteristics. Cu catalysts with large crystals, small monodisperse crystallites or a highly dispersed XRD amorphous copper phase were obtained after calcination in stagnant air, in a flow of NO/N2 or a flow of air, respectively. Analysis by XRD, N2O surface oxidation and TEM confirmed the variation of the Cu specific surface area by the calcination conditions and the type of silica support used. The different dispersion characteristics resulted in different activities (20–50% glycerol conversion), while all the catalysts proved to be highly selective towards propylene glycol (92–97%). Present results indicate that glycerol hydrogenolysis over Cu-based catalysts is a structure sensitive reaction as significant variations in initial TOF were observed as a function of varying Cu crystallites. It is shown here that the presence of a solvent greatly influences the intrinsic reaction rate and the nature of structure sensitivity. The deactivation behaviour of all catalysts was studied, and based on detailed characterization of the spent samples it was attributed to Cu sintering and the presence of strongly adsorbed species on the catalytic surface. The 18wt%Cu/silica gel (air) catalyst presented only moderate deactivation (∼20%) while the catalyst supported on SBA-15 calcined at 900°C (SBA900C) proved to be the most stable with negligible deactivation after three consecutive runs.