Investigating the performance and deactivation behaviour of silica-supported copper catalysts in glycerol hydrogenolysis

Selective hydrogenolysis of glycerol to propylene glycol was performed over monometallic (5 and 20 wt%Cu) and a bimetallic (5 wt%Ru–Cu) catalyst. The catalytic materials used, were supported on commercial silica and synthesized hexagonal mesoporous silica (HMS). The catalysts (fresh and used) were characterized employing XRD, ICP, BET surface area, N2O chemisorption, TEM, TGA and TPR techniques. The performance of 5 wt%Cu monometallic catalysts is characterized by high propylene glycol selectivity (>90%) and relatively low activity. Increase of Cu loading to 20 wt% results in satisfactory activity. At 240 °C and 8 MPa hydrogen pressure, the 20 wt%Cu/HMS catalyst exhibits 43% glycerol conversion along with 91% propylene glycol selectivity and TOF 148 h−1. The bimetallic Ru–Cu catalyst supported on silica combines both good selectivity and activity providing evidence for synergetic effect between the two metals. Silica type (commercial or mesoporous) affects mainly the dispersion and hence the active copper metal area with the HMS supported monometallic catalysts exhibiting higher activity than those supported on commercial silica. Present results indicate that glycerol hydrogenolysis over Cu catalysts is a structure sensitive reaction. Partial loss of activity in consecutive glycerol hydrogenolysis tests was observed with the best performing 20 wt%Cu/HMS catalyst. Based on characterization results of the reused catalyst, the deactivation was attributed to a number a factors like partial collapse of the mesoporous network, agglomeration of the active metallic phase, presence adsorbed species on the catalytic surface and/or formation of coke during the reaction. No indication of Cu leaching to the liquid phase was provided.

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► Cu is associated with high selectivity to propylene glycol.
► Silica type used affects copper dispersion and hence the active copper metal area.
► Increased activity and selectivity are obtained over 20 wt%Cu/HMS catalyst.
► TOF increases as the dCu decreases providing evidence of structure sensitivity.
► Cu on mesoporous silica showed deactivation caused by various factors examined.