Photocatalytic Perfomance Of Pd/SiC For Hydrogenation Of Furan Derivatives

Solar energy is a green, environmentally friendly and sustainable energy. Itwould be a significant to solve the energy crisis and environmental problemsbringing by social development of human being if sunlight can be utilized in thechemical processing and synthesis. Tetrahydrofuran and its derivatives asimportant organic solvents and synthetic raw materials of industrial processesare traditionally synthesized through hydrogenation reactions of furan and itsderivatives. However, these reactions are usually conducted under hightemperature and high pressure for long time with low conversions and poorstabilities. Therefore, it would be an importantly theoretical and practicalsignificance to exploit new chemicals synthetic routes from biomass, if we coulduse sunlight to enhance the catalytic activity at ambient temperatures, convertsolar energy to chemical energy, avoid environmental pollution and reduceenergy consumption.Cubic silicon carbide (β-SiC) has an excellent chemical stability and thermal conductivity, so it can be employed in many harsh reaction conditionssuch as strong acid or alkali. Moreover, SiC possesses suitable band gap (~2.4eV), and can absorb visible light. In this work, SiC support Pd nanoparticles wasemployed as catalyst to study the photocatalytic hydrogenation of furanderivatives, and various methods, such as XRD, XPS, TEM and PL, were usedto discuss the reaction mechanism. The main contents of the thesis are describedas follows.(1) Pd/SiC catalysts were prepared by liquid reduction method. The effects ofvarious reaction parameters, including the H2pressure, solvent, catalyst’s dosageand time were investigated for photocatalytic hydrogenation of furan. Afteroptimization of the reaction conditions, the furan conversion and turnoverfrequency (TOF) could reach99%and70h-1, respectively, using80mg3wt%Pd/SiC under1.0MPa of H2pressure at25°C for2.5h with10mL1-pentanol asthe solvent.(2) The dependences of the catalytic activity of Pd/SiC for furanhydrogenation on the intensity and wavelength range of light irradiation werestudied on the optimized reaction conditions, respectively. Increasing of the lightintensity resulted in a nearly linear increase for the conversion of furan. Thelight in the400-450nm wavelength range contributions the highestlight-induced conversion. The influences of different functional groups in furanderivatives on the hydrogenation performances were clarified. The presence ofelectron-donating groups such as methyl in furan rings usually has high conversion and selectivity; while the electron-withdrawing groups such ashalogen (-X) in furan rings can lower the conversion and selectivity. However,the location of C=C in furan rings does not have significantly influence for theactivity. The cyclic result suggests that Pd/SiC catalyst has excellent stability.(3) Combining with various characterizations, the mechanism for thephotocatalytic hydrogenation of furan derivatives on the Pd/SiC catalyst wasproposed. The work function (WF) of SiC is about4.0eV, which is lower thanthat of Pd (5.12eV). When Pd nanoparticles are supported on the SiC surface,there can form a Mott-Schottky contact. Then, the photo-generated electrons caneasily transfer from SiC to the surface active sites of Pd nanoparticles, whichcan activate C=C bonds in the furan rings by donating electrons back to the C=Canti-bonds. The holes left on the SiC support are filled by oxidizing H2, whichgenerates active hydrogen. The active hydrogen then migrates to Pdnanoparticles by reverse spillover, and reacts with C=C bonds in furan toproduce THF.