Design, Synthesis And Catalytic Properties Of C(Ni)-Based Nanocatalysts For Hydrogenation Reactions

With global energy shortages and environmental degradation getting worse year by year, catalytic chemistry plays a more and more important role in the industry. Carbon nanomaterials are widely used in heterogeneous catalysis due to their unique and controllable structure and surface properties, and they can be simply modified by other functional species as well, leading to highly efficient catalysts with homogeneous dispersion of metal nanoparticles. As a result, the synthesizing and optimizing of "green" carbon-based catalyst with high efficiency have attracted more and more attentions. In order to prepare novel carbon-based catalysts with high metal loading and dispersion, and outstanding structures, in this thesis, we did a series of researches on the design and synthesis of C(Ni)-based catalysts for selective hydrogenation reactions.Firstly, we synthesized C(Ni) nanocomposites with interlaced nanoflakes via a developed hydrothermal/solvothermal process followed by a heat treatment, and then novel Pd/C(Ni) nanocatalysts with high Pd dispersion have been synthesized through polyol reduction process under mild conditions. The catalytic properties of Pd/C(Ni) for the selective hydrogenation of4-octyne to cis-4-octene have been investigated under low temperature and atmospheric pressure, showing much better performance than Pd nanocatalysts supported on the conventional activated carbon (Pd/AC). It has been also found that the presence of Ni in C(Ni) is not only beneficial for the magnetic recycle of the catalysts, but also improve the isomerization reaction of cis-4-octene to trans-4-octene over Pd/C(Ni) catalysts for3.23times. And the kinetic calculation of catalytic reactions over different catalysts have been simulated to get the k values of different elementary reactions, which are helpful to calculate and further explain the better performance of Pd/C(Ni) than Pd/AC.As Ni species in C(Ni) nanocompostites are found to be able to influence the isomerization reaction of cis-4-octene, so Pt/C(Ni) nanocatalysts were subsequently synthesized for the selective hydrogenation of o-chloronitrobenzene to o-chloroaniline at room temperature and atmospheric pressure, showing promising catalytic properties. Meanwhile, it has been found that there is synergistic effect between Ni and Pt nanoparticles leading to a significant enhancement of the selectivity towards o-chloroaniline over Pt/C(Ni) catalysts, which is about15%higher than that of Pt/C catalyst. Taking the unique structure and excellent performances of C(Ni)-based catalysts into account, in order to optimize C(Ni)-based catalysts, low-cost cobalt are introduced as active metals instead of expensive Pd and Pt to in situ synthesize flower-like Co-Ni/C bimetallic catalysts with different Co/Ni molar ratios via a hydro therm al/solvothermal process. The morphologies of obtained Co-Ni/C bimetallic catalysts remain the same as those of Co/C or Ni/C monometallic catalysts. More importantly, their catalytic activities show a volcano-type curve as the increasing of Co/Ni molar ratios for the selective hydrogenation of o-chloronitrobenzene to o-chloroaniline at140℃and2MPa H2pressure. When the Co/Ni molar ratio is50:50, the conversion of o-chloronitrobenzene over Co50Ni50/C is the highest one, which is1.6and2times, respectively, as high as those over Ni/C and Co/C monometallic catalysts. The geometric effect of Co/Ni alloy are investigated to be the main reason for the enhanced catalytic activity of Co-Ni/C bimetallic catalysts.In order to controllably synthesize metal/carbon nanocomposites with ultrahigh metal loading and dispersion, and to expand their application fields, nickel/graphene-like carbon nanocomposite (Ni/G) with ultrahigh Ni loading and dispersion has been synthesized using a novel solvothermal process followed by a heat treatment. The SEM and TEM results show that this novel Ni/G nanocomposite is consisted of hollow quasi-micro spheres, which are assembled by a great number of Ni@G nanoparticles and the thin carbon shell has been investigated to be few-layer graphene. The Ni loading is high up to81wt.%. The growth mechanism of Ni/G precursor has been proposed to be a two-step process, i. e. the preferential formation of nickel alkoxide and their slow decomposition to Ni2+followed by the complexation of Ni2+and furfural oligomers leading to the formation of Ni/G-P, which are key factors for the high dispersion of Ni nanoparticles in Ni/G. The Ni/G shows excellent catalytic properties for the selective hydrogenation of o-CNB to o-CAN.