| In order to cope with the increasing resource shortage,energy crisis and environmental degradation,many countries of the world have paid attention to the development and utilization of biomass resources.Catalytic conversion of biomass-derived carboxylic acid to high-value added chemicals is one of the hot topics in recent years.However,it is generally considered as a challenging process due to rigorous reaction conditions and uncontrollable selectivity.In this dissertation,levulinic acid,which was produced through the process of cellulose hydrolysis,was chosen as model substrate to systematically study the relationship between the type of catalyst,the preparation method and catalyst performance.Based on chemical reaction kinetics and theoretical calculation,the mode of absorption for the groups of substrate and intermediates on the different sites of catalyst surface were studied to reveal the reaction mechanism,which would provide the theoretical basis for the rational design of the catalytic system.1.Supported Ni-based catalysts were employed for conversion of levulinic acid(LA)to y-valerolactone(GVL).Various factors for catalyst preparation were systematically investigated,including the types of support,nickel precursors,precipitants,loading amounts of nickel,deposition-precipitation time and drying time.Under the optimal preparation conditions with MgO as support,[Ni(NO3)2]as precursor salt,[(NH4)2CO3]as precipitant,process of deposition-precipitation in 50 ℃ for 20 h and drying in 60 ℃ for 24 h,the productivity of GVL reached 0.32 molGVL·gNi-1·h-1,which was the highest compared to all reported Ni-based catalysts.The catalysts were characterized with different techniques(XRD,HR-TEM,XPS and H2-TPR).Under the optimal reaction conditions of LA transformation:150 ℃,2.0 MPa and 20 mL i-PrOH for 2 h,the highest selectivity of GVL was up to 93.3%.2.Several Ru-based catalysts and skeletal catalysts were employed for the hydrogenation of LA to 1,4-pentanediol(PDO)and monohydric alcohol.The skeletal Ru showed promising catalytic performance.Base on the difference of apparent activation energy between the transformation of GVL and PDO,the selectivity could be controlled by temperature.The results showed that the total yield of 2-butanol&2-pentanol was 79.1%and the yield of PDO was 74.6%,respectively at 140 ℃ and 100 ℃ using H2O as solvent.The Ru-based catalysts were characterized with diferent techniques(XRD,XPS,TEM and SEM).Combining results of characterization and theoretical calculation,high density of atomic steps and flat sites,which were provided by skeletal Ru were main active sites for the activation of PDO(C-O bonds and C-C bonds).3.The transformation of LA was employed to study the effects of preparation methods and process parameters on catalytic performance of skeletal Ru.The annealing treatment was used to improve the uniformity and activity of alloy made by arc melting method.Higher catalytic activity of catalyst was obtained and yield of PDO was also improved from 38.0%to 70.4%.The preparation parameters(including the milling time,heat treatment process and amounts of control agent)of mechanical alloying were researched.After the grinding of Ru and Al powder for 40 h with 0.2 mL ethanol as control agent and then treated at 500 ℃ for 2 h,the corresponding Ru-Al alloy phase was obtained and could be further transformed into highly active skeletal Ru.The induction melting method combines the process of melting and heat treatment.Alloy produced with the induction melting method had low crystallinity and good uniformity,which enhanced the activity of the corresponding skeletal Ru.The monohydric alcohol was obtained in high yield(68.5%)with skeletal Ru.Moreover,skeletal Ru catalyst also exhibited remarkable catalytic activity in hydrodeoxygenation of actic acid,succinic acid and cellulose using water as solvent. |
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