Study On Carbon Nanofibers Supported Pd-Pt Catalyst For Naphthalene Hydrogenation

The graphite structure of carbon nanofibers (CNFs) grown from catalyticdecomposition of carbonaceous gas depends on the catalyst, preparation method, anddepends also on the reaction conditions. In this thesis, the CNFs of different graphitestructures were prepared by methane decomposition on Ni-Cu/Al₂O₃ and Co/Al₂O₃catalysts prepared with coprecipitation, and a Co/Al₂O₃ (SG) catalyst prepared withsol-gel and a supercritical drying method. The CNFs grown on Ni-Cu/Al₂O₃ andCo/Al₂O₃ (SG) catalysts have a fishbone structure, while the CNFs grown onCo/Al₂O₃ catalyst have a parallel structure.The CNFs were investigated by a high resolution TEM and infrared spectroscopy(IR). The result indicates that the surfaces of CNFs appears a degree of disorder ofgraphite structure. At the surface of CNFs grown on the Ni-Cu/Al₂O₃ catalyst, itappears graphite layered edges, but the same layered like edges cannot be seen on thesurfaces of the CNFs grown on the other two catalysts. It was recomfirmed by FTIRthat a large amount of defects on the surfaces of these three kinds of CNFs. Not onlyCH groups, but also some oxygen-containing groups are detected.A controllable oxidation treatment was realized using a mixture of concentratedsulfuric and nitric acid in an autoclave with teflon liner. TEM, XRD, N₂ physisorption,IR spectroscopy and ion exchange methods were adopted to investigate the influenceof oxidation treatment on the texture and surface properties of CNFs. The resultsindicate that a treating at high temperature induces a uniform cutting, which lead tothe change of texture properties of CNFs. As to the CNFs grown on Ni-Cu/Al₂O₃, thesurface area, pore volume and average pore diameter changed severely if treated at150 Co. For the CNFs grown on the other two cobalt catalysts, with the surface areaand pore volume increased obviously for sample treated at 180 Co, the average porediameter was almost not changed. Many kinds of oxygen-containing groups e. g.carboxyl, carboxylic anhydride, phenol, quinine or ketone etc. were induced on thesurface through oxidation treatment. The amount of oxygen containing groupsinduced increased with the treating temperature increased. The fresh CNFs arehydrophobic, whereas good wettability can be realized after oxidation treatment. Thecontrollable hydrophilicity is beneficial to the preparation of supported catalyst. It wasfound that the surface sensitivity of fishbone CNFs is higher than that of parallel type.The supported Pd, Pt and Pd-Pt catalysts were prepared by incipient wetnessimpregnation method and used for the naphthalene hydrogenation with the presenceof thiophene. The catalysts were characterized with high-resolution TEM, H₂chemisorption and temperature programed reduction etc. The results indicate that theamount and properties of oxygen-containing groups influence strongly the dispersionof metal particles. With the treating temperature increased, the concentration ofoxygen-containing groups increased, and the dispersion of metals on the surface ofCNFs was improved. The activity of supported Pd/CNFs and Pt /CNFs catalysts wasvery low, whereas the activity of Pd-Pt/CNFs catalysts were high. The activity of thePd-Pt/CNFs catalyst increased with the treating temperature increased. Furthermore,the supported Pd-Pt/CNFs catalyst showed an excellent sulfur resistance. The paralleltype of CNFs is better than that of fishbone type of CNFs for sulfur resistancecatalyst.