Studies On The Catalytic Conversion Of Biomass With Electrochemical Methods

The accelerating and frequently fluctuating price of conventional fuel, together with growing environmental concerns has sparked renewed attention on the search for an alternative fuel. The development of green sustainable energy system becomes an important issue in the future. Biomass, nature products has showed its potential of being renewable resources. Preparation of fuels and chemicals from biomass has become an important way to solve the energy crisis worldwide. With traditional catalysts in the biomass conversion, many reactions occurred at high temperature and pressure. Furthermore, most of the catalysts and solvents are toxic and bring serious pollution problems. With the continuous development of economic society, green chemistry get more and more attention in the field of biomass conversion. Organic electro-synthesis is considered to be a kind of environmental friendly synthesis method and meet the requirements of the green chemistry. Thus, the electrochemical method was introduced to the catalytic conversion of biomass and achieved efficient conversion of monomer molecule and platform molecule under mild condition. The main work involeves:In the first chapter, we introduced the current development of biofuels and chemicals from biomass. Then, we introduced the fundamentals of electrochemistry and reviewed application of electrochemical method in the biomass conversion.In the second chapter, electrocatalytic hydrogenation (ECH) of phenol to cyclohexane and cyclohexanol was described. Experiments were run in a H-type cell with a Pt sheet as anode. The cathode material and structure were found to have a large effect on the ECH of phenol. Among the cathodes studied, the1.5%Pt supported on graphite gave the highest product yield and current efficiency. Temperature was another important variable, the yield of cyclohexane increased from44.1%at20℃to63.7%at60℃, but then dropped back to50.3%at80℃. Effects of electrolyte composition on ECH of phenol were also investigated. The yield of cyclohexane was highest when0.2mol/L HClOas electrolyte. Variable current studies in the range of10-90mA showed an increase in product yields with increasing current from10-30mA, but yields decreased when current above70mA. The suitable starting concentration of phenol was50mmol/L.In the third chapter, electrocatalytic hydrogenation (ECH) of furfural to furfuryl alcohol was demonstrated. Platinum (Pt), nickel (Ni),copper (Cu) and lead (Pb) were used as cathode materials. As expected, the cathode material, which serves as the hydrogenation catalyst, was found to have a large effect on the ECH of furfural. Among the cathode materials studied, the Pt gave the best product selectivity. So cathodic reduction was catalyzed by platinum supported on activated carbon fibers(Pt/ACF), a novel electrocatalyst. Incipient wetness impregnation and electrodeposition methods were employed to prepare the electrocatalyst Catalysts prepared by impregnation method were more active than prepared using electrodeposition method, presumably because of more active surface area. When using impregnation method,3%Pt/ACF showed the best activity and current efficiency, followed by5%Pt/ACF. Effects of electrolyte on product yield and current efficiency were also investigated. The yield of furfuryl alcohol was highest in the0.1mol/L HCL The initial furfural concentration and the electrolytic potential also strongly affected the product yield and current efficiency.In the fourth chapter, it was shown that the electrocatalytic oxidation of5-hydroxymethylfurfural (HMF) carried out in alkaline media over graphite supported Pt、Au and Pd. We demonstrated the synergistic effects of bimetallic Pd-Au catalysts for the selective formation of2,5-furandicarboxylic acid (FDCA). Results from electrolysis product analysis at various electrode potentials, along with cyclic voltammetry of HMF and its oxidation intermediates, revealed the unique catalytic properties of Pd and Au for competitive oxidation of alcohol and aldehyde side-groups present in HMF. Aldehyde oxidation was greatly favored over alcohol oxidation on the Au/G catalyst, which was very active for HMF oxidation to HFCA, however high electrode potentials were required for further oxidation of the alcohol group to FDCA. HMF oxidation on Pd/G followed two competitive routes to FDCA and the pathway was dependent on the electrode potential. Oxidation of aldehyde groups occurred much slower on Pd/G than Au/G at low potentials, but was greatly enhanced at increased potentials or by alloying with Au. It was found that Pd-Au bimetallic catalysts achieved deeply oxidized products (FFCA and FDCA) at lower potentials than monometallic catalysts and the product distribution was dependent on the electrode potential and surface alloy compositionIn conclusion, this thesis mainly focused on the green conversion of biomass derived derivative and platform molecules into chemicals and fuels through electrochemical methods. This develop a new way for the use of biomass resource.