Catalytic Oxidehydration Of Glycerol Over SiO₂-MgO Supported Silicotungstic Acid Catalysts

Glycerol is a sustainable resource for its renewability and biological degradability.Recently,the catalytic conversion of glycerol to other chemicals has drawn much attention,especially the dehydration and oxydehydration of glycerol to acrolein and acrylic acid.Silicotungstic acid is known as a solid acid catalyst with tunable acidity and has been applied to conduct the dehydration of glycerol.Therefore,supported silicotungstic acid catalysts were synthesized and studied for dehydration of glycerol to obtain a high yield of acrolein and improve the stability.Further modification of the supported Silicotungstic acid catalysts was also conducted and studied for oxydehydration of glycerol to acrylic acid.A series of HSiW/(SiO2-MgO)y catalysts were prepared with the impregnation method and used to catalyze the dehydration reaction of glycerol to acrolein.Among the SiO2-MgO prepared with 3 different methods,the SiO2-MgO(?)prepared with co-precipitation method has the most medium-strength acid sites,largest surface area and also exhibited the best catalytic performance.(SiO2-MgO)y with different compositions were prepared and used to support the Silicotungstic acid.It was found that HSiW/(SiO2-MgO)1 has the best catalytic performance and the MgO content in the support has an effect on the surface area and pore structure of the catalysts.Catalytic activities of catalysts prepared with different calcination temperatures were also investigated.The catalyst calcined at 450? exhibited the maximum surface area of 256.18 m2/g and also showed the best catalytic performance.The optimal dehydration reaction conditions on HSiW/(SiO2-MgO)1 catalyst were as follows:the optimum reaction temperature was 300 ?,the optimum space velocity was 4.26h-1 and the best glycerol solution concentration was 5wt.%.Under the optimum reaction conditions,the glycerol conversion and the acrolein yield reached 100%,40.7%respectively.Oxydehydration of glycerol to value-added compounds was carried out over metal-doped SiW/SiO2-MgO catalyst.Effects of metal types(Cu,Ce,Ni and V)and loadings(2-8wt.%)on catalyst properties and catalytic activity were explored.Doping different types of metal and loading on the surface of SiW/SiO2-MgO catalyst affected surface chemistry and textural chemistry as well as the catalytic activity for glycerol conversion and product yield distribution.Among the doped catalysts,the V-doped catalyst got the highest glycerol conversion of 98.24%and the lowest hydroxyacetone yield of 6.97%.Besides,as the increase of the doping amount of V,the yield of acrolein decreased.However,the desired product acrylic acid was not observed.