| Biodiesel is a kind of clean,safe and renewable energy sources which could be an alternative of fossil fuels.However,the growing production of biodiesel through the transesterification of triglycerides generates a large surplus of glycerol as a major byproduct.Thus catalytic conversion of glycerol to valuable products has become a hot topic.A number of potential products can be obtained by the dehydration,oxidation,hydrogenolysis,esterification and etherification of glycerol.Glycerol carbonate(GC)can be a fine solvent in industrial coating,organic synthesis,concrete,cosmetic and medicine agent,etc.Transesterification of glycerol with dimethyl carbonate(DMC)is an environmentally-friendly,low-consumptive way to produce GC.In this work,a series of solid base-catalysts were prepared via a controlled calcination of Mg-Al layer double hydroxides(LDHs)and applied in synthesizing GC.It was found that the catalyst with Mg/Al = 2 exhibited the best performance with a conversion of 66.9%to glycerol and a selectivity of 97.1%to GC.What's more,it was confirmed that the structure of this catalyst can be "reproduced"after recycled application and had good activity even after 6-cycled reuse.Characterizations also disclosed that the performance of these catalysts depended heavily on their morphology,specific surface area and base-density.On the basis of previous results,a series of Ca-Al-Ox base-catalysts were prepared from Ca-Al hydrocalumite and applied in the transesterification of glycerol with DMC.It was found that the highest conversion of glycerol reached 93%with a selectivity of 97%to GC over Ca2Al-800 at 70 ? after reacting for 2 h.Bifunctional Cu solid-base catalysts(Cux/CayAlOy+1.5)were synthesized via controlled calcination and reduction,and applied in hydrogenolysis of glycerol.The conversion of glycerol reached 75.3%with a selectivity of 98.1%towards 1,2-PDO at 180 ?,2.0 MPa and 21 h.Characterizations disclosed that the TOF of Cu depended mainly on the basicity of catalyst.And the selectivity of 1,2-PDO increased with the improving dispersion of active Cu.These results indicated that both basicity and active Cu atom were indispensable for the hydrogenolysis of glycerol.A series of Cu/ZnO with similar composition but various morphology and interface were designed and applied in the continuous hydrogenolysis of glycerol in a fixed-bed reactor.Among them,Cu1.1/ZnO(nano sized ZnO particles dotted on Cu hybrid)derived from Cu1.1Zn1.9(BTC)2'9.4(H2O)was extremely active and stable under this experimental condition.The specific activity of surface Cu atom in Cu1.1/ZnO reached 100.4 mol-glycerol/mol-Cu/h(at 250 ?).Apart from Cu particle size and dispersion,characterizations confirmed that the interface between Cu and ZnO affected more in activating H-H bond.Although Cu1.1/ZnO and Cu/ZnO-CP showed much difference in their outline and microstructure,their large Cu-ZnO interface caused a similar conversion in their initial activity.But the structure of Cu/ZnO-CP(Cu supported on ZnO plate)also indicated a sintering of Cu in H2 atmosphere and causing deactivation,while this problem could be solved in Cu1.1/ZnO since the partial covered ZnO functioned as a physical space between Cu particles and prevented their sintering.Author also had an exploration on converting glycerol to public chemical(ethanol).It was found that this reaction was extemely temperature-sensitive and Nix/MgyCrzOy+1.5z performed a special potential in producing ethanol.The best yield reached 0.50 g-ethanol/g-cat/h at 250 ? over Ni2.4/Mg3.7Cr2.0O6.7.Characterizations confirmed that the formation of MgCrO4 in calcined precursor can improve the dispersion of Ni and specific surface area of catalyst.The strong synergestic effect between Ni and MgCr2O4 also accelerated the activation and spillover of H2.According to the experimental data,the mechanism can be summarized as a "two-step hydrogenation" process:1,2-PDO formed firstly from hydrogenolysis of glycerol,then 1,2-PDO further converted to ethanol throgh C-C cleavage and hydrogenolysis. |
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