Catalytic Transfer Hydrogenation Of Ethyl Levulinate To γ-valerolactone Over Zirconium(Ⅳ)Schiff Base Complexes On Mesoporous Silica Without Addition Of External Hydrogen

The gradual depletion of fossil fuels and rapid growth of world population have led researchers on a quest to develop efficient technology for the generation of sustainable liquid fuels and versatile chemicals from other natural resources.Biomass represents the fourth most abundant source which can be readily converted to useful compounds.Among those compounds,GVL has received considerable attention due to its utility in various research formats.Notably,it has been used as a monomer to make oligomers,fuel additives in gasoline and diesel,a green solvent for lacquers,and a coupling agent in dye baths.Therefore,the research how to improving the production of GVL from biomass efficiently is quiet significant.Base on this,we prepared a series of novel catalysts and investigated the catalytic activity of these catalysts for the conversion of EL.The main research work was done as follows:（1）We synthesized the novel Schiff base complex of zirconium and investigated the effect of the conversion of ethyl levulinate（EL）to GVL in isopropanol as a homogeneous catalyst.The effects of the different skeletons Schiff base complexes on the catalytic activity were investigated.Among them,Zr-（salphen）has the highest catalytic activity for the reaction.In addition,we investigated the effects of the type of solvent,reaction temperature,reaction time and amount of catalyst on the reactivity.Zr-（salphen）was used as a homogeneous catalyst in isopropanol at 160°C for 14 h to give a yield of 53.8%GVL.（2）Considering the shortcomings of the homogeneous catalyst,Zr-（salphen）was supported on the surface of MCM-41 and prepared a novel immobilized zircon Schiff base complex.The effect of the heterogeneous catalyst on the conversion of the EL into the GVL reaction was studied.We optimized the reaction conditions such as the type of solvent,reaction time,reaction temperature and the amount of catalysts.Under the optimum reaction conditions（isopropanol as solvent,70 mg catalyst,160°C,12 h）,a good catalytic effect,EL conversion of 95.5%and a GVL yield of 90%was obtained.The immobilized catalyst efficiently recycled at least five times without significant loss of activity.The recycled catalyst was characterized by IR,SEM,TEM and BET and the results show that the morphology and structure of the catalyst have not changed obviously.In addition,we proposed the reaction mechanism of Zr-（salphen）-MCM-41 catalyzed EL conversion.Based on the characterization and experimental results,we concluded that the key to heightened reaction performance was the large number of acid-base sites in the structure of Zr-（salphen）-MCM-41.（3）In order to improve the selectivity of GVL,we prepared a serise of catalysts containing the stronger acid sites（-SO₃H）,Zr-（salphen）-MCM-41-S₃₀,Zr-（salphen）-MCM-41-S₄₀,Zr-（salphen）-MCM-41-S₅₀,Zr-（salphen）-MCM-41-S₆₀.And the catalytic activity of these catalysts on the production of GVL was investigated.Under certain reaction conditions,Zr-（salphen）-MCM-41-S₅₀ exhibits the best catalytic activity.When Zr-（salphen）-MCM-41-S₅₀0 as catalysts,a results 93.5%yield of GVL with EL almost completely transformed at 150°C for 11 h was obtained.In addition,we did a further explanation for the reaction mechanism of EL conversion to GVL.