Hydrogenolysis Of Glycerol To Propanediols Over Ag-Cu Catalysts

With the rapid development of modern society,one of the main problems the whole world facing now is the energy crisis.As a result,renewable biomass materials are receiving more and more attention.Glycerol,which is a major by-product of biodiesel production,has been identified as a promising alternative to petroleum and natural gas for the production of commodity chemicals.Hydrogenolysis of glycerol to 1,2-propanediol and 1,3-propanediol has significant scientific importance and commercial interest due to the huge surplus of glycerol and the various application of propanediols.According to former researches,copper based catalyst shows a high conversion and selectivity to propanediols because of its lower activity for C-C bond cleavage.But the catalytic activity of Cu based catalyst is not high enough for industrial application.Therefore,modification of Cu based catalysts by a promoter to enhance the catalytic activity for glycerol hydrogenolysis is of great interest.In this paper,a series of supported Ag-Cu catalysts synthesized by impregnation method were studied for hydrogenolysis of glycerol to propanediols.The catalysts were characterized by H2-TPR,NH3-TPD,XRD,BET,N20 chemisorption,TG,ICP and SEM.It was observed that the loading of 5wt.%Ag to Cu-based catalysts facilitated the reduction,surface acidity and dispersion of the Cu particles,which improved the conversion of glycerol and promoted the generation of propanediols.It was also found that when loading 5wt.%Ag and 15wt.%Cu simultaneously on Al₂O₃,the catalyst had a better performance for the reaction because of the higher acidity,dispersion and surface area of the Cu species on the catalyst surface.In addition,effects of metal concentrations,metal impregnation sequence,reaction temperature,reaction pressure,reaction time,solvent and pH value of the solution on glycerol hydrogenolysis together with the recyclability of catalyst were investigated in detail.The optimal 5Ag-15Cu/Al₂O₃ achieved 66.4%glycerol conversion with 68.2%1,2-propanediol and 3.1%1,3-propanediol selectivity at 200? under 3.5 MPa in ethanol for 8 h.In order to improve the generation of 1,3-propanediol over Ag-Cu catalyst,various amounts and different types of heteropolyacids promoted 5Agl5Cu/Al₂O₃ catalysts were synthesized by impregnation method and analyzed by Py-FTIR,Raman spectroscopy and other techincals.The results showed that that heteropolyacids loading can facilitate the reduction,promote the dispersion,enhance the acidity and increase Bronsted acid sites of the Ag-Cu catalysts,which benefited the generation of 1,3-propanediol.Compared with phosphotungstic acid and phosphomolybdic,silicotungstic acid promoted AgCu catalyst had a better performance for 1,3-propanediol due to the better Cu dispersion and higher Bronsted acidity.In addition,when the reaction was performed at 220? under 3.5 MPa for 8 h in a 200 mL autoclave,the chosen 5Ag15Cu-10HSiW/Al₂O₃ achieved a 69.6%glycerol conversion with 35.6%1,2-propanediol selectivity and 21.5%1,3-propanediol selectivity.