Synthesis, Characterization And Catalytic Performance Of Graphene-Based Composites

Graphene is made up of sp2carbon atoms. It is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice. To date, considerable attention has been paid to graphene due to its outstanding properties, such as unique electronic conductivity, thermal stability, optical properties, and mechanical strength arising from its strictly2D structure. Thus, in parallel with developments form the basic science perspective, graphene-based materials, for their superb properties, have emerged as quite intriguing materials form both perspectives of science and technology, especially using as support to fabricate supported catalyst and graphene-based hybrid materials.Layered double hydroxides (LDHs) belong to a family of highly ordered two-dimensional layered materials, where different M2+and M3+metal cations uniformly distribute and orderly prearrange in the brucite-like sheets, and various charge-compensating anions (A n-) are present in the interlayer space. According to the fact that LDHs can accommodate a large number of tunable M2+and M3+ions within the layers or in the interlayer space in the form of metal complexes, highly dispersed supported metal catalysts can be obtained by reducing calcined LDHs with desired active metal species. This kind of structural transformation endows LDH materials with extraordinary capability as catalyst precursors in various metal-catalyzed reactions. In comparison with other metal-supported catalysts, LDH-derived supported metal catalysts have two advantages:(i) Active components with adjustable content can be uniformly integrated into the LDH structure;(ii) metal nanoparticles with tunable particle size can be formed in a controllable manner. Hence, the combination of LDH and graphene can be used as an excellent precursor to fabricate novel graphene-based metal catalyst. Up to now, there are few reports focused on the fabrication of LDH/graphene hybrids.Based on the above background, in this thesis, we mainly focused on the fabrication of LDH/graphene hybrid precursors and gaphenen based metal catalyst drived form the prepared LDH/graphene precousors:(1) Established a novel approach to synthesize NiAl-LDH/graphene hybrid precursors. NiAl-LDH/graphene hybrid precursors were prepared by the coprecipitation method. In this method sodium hudroxide plays a dual roles, precipitator and reduction. Various experimental conditions such as crystal temperature, mass ratio of LDH to graphene, MⅡ/MⅢ ratio were investigated. XRD、FI-IR、UV-vis、XPS、SEM、TEM、TG-DTA、HRTEM、 RAMAN techniques were used to characterize the crystal structure、chemical composition、shapes、sizes and thermal stability of the LDH/graphene hybrid precursors.(2) Established a novel approach to synthesize graphene based Ni catalyst with uniform size and highly dispersion via a in-situ reduction of the LDH/graphene hybrid precursors. Here, the graphen in the hybrid precursor woked both as support and the carbon source in the reduction of the catalytic precursor. The catalytic behavior of the as-prepared graphene based Ni catalysts was investigated in liquid phase hydrogenation of trans-cinnamaldehyde. The influence of reaction condition such as pressure, temperature, time and solvent on the selective hydrogenation of CALD over Ni/graphene catalysts has been studied. The results indicate that the conversion of the CALD increased with the increasing of reaction temperature and H2pressure, high H2pressure is benefit for the hydrogenation of C=O bang, high reaction temperature (<100℃) is benefit for the hydrogenation of C=C band. The conversion of CALD increases with time, but upward trend is gradually reduced. The high catalytic performance of the prepared graphene based Ni catalyst can be attributed to its unique physical and chemical properties, such as high surface areas, highly Ni dispersion and more exposed reactive sites, unique synergistic effects between graphene and Ni nanoparticles and so on.