Nanostructured Metallic Catalysts:Synthesis And Application In Partial Oxidation Of Methane To Syngas And Catalytic Reduction Of P-nitroophonel

The production and application of syngas is very important for the chemical industry. The catalytic partial oxidation of methane (POM) to syngas has been extensively investigated, due to the advantages of low cost, low energy consumption, and suitable H2/Co ratio which can be directly used as a feedstock for methanol or Fischer-Tropsch synthesis.The application of nanoparticles (NPs) in heterogeneous catalysis is highly desirable due to the unique properties. But NPs are unstable and aggregate easily especially at high temperatures. Core-shell structured metal materials have attracted great attentions in recent years because of the unique structures and properties. If a nano-material is enwrapped in a stable but porous shell, the stability of core material can be enhanced, and the core-shell interaction may also cause a change in electron charge, reactivity and functionality of the enwrapped material. On the other hand, if the metal NPs are introduced onto/into the spheres of silica, polystyrene and carbon, the metal dispersion will also be enhanced, and thus results in an improvement in catalytic efficiency.This dissertation focuses on the following two aspects of research activities:one is the synthesis of microporous silica encapsulated Ru or Ni-Ru nanoparticles (NPs) and their application in partial oxidation of methane to syngas; and the other is the synthesis of carbon spheres of different sizes with Ag or Ag-Au deposition and the obtained nano-composites are applied for the catalytic hydrogenation of p-nitrophonel. The following concluding remarks are obtained through the investigations:1. The core oxide nanoparticles (10-40nm) of RuO2and Ni-Ru-O (with Ni/Ru mole ratio being0.10.5,2,5,20) are prepared by reduction and precipitation methods. The core oxide NPs are encapsulated by a layer of porous SiO2(10-20nm in thickness), and the core-shell structured Ru@SiO2and Ni-Ru@SiO2can be obtained when the precursors are subject to an in site H2-reduction.2. The performance of core-shell catalyst is dependent upon the chemical composition of core particles. It is found that the Ni-based catalyst is active for the POM reaction but the coke deposition is also obvious, which makes catalyst deactivation and limits the practical application. The Ru-based catalyst is not only highly active, but also rather stable in POM, with less coke formation.3. Among the synthesized xNi-Ru@SiO2(x=0.1,0.5,2,5,20) binary metal core-shell catalysts, the5Ni-Ru@SiO2shows the best activity and stability, which can effectively reduce the amount of Ru metal in the catalyst (thus greatly reduce the catalyst cost) meanwhile maintain superior activity and stability of catalyst.4. The origin of the better catalyst performance of core-shell catalyst is likely due to the generation of the micro-capsular reactor via an in situ reduction of the core oxide precursor, the cavity between core surface and internal wall of shell may allow the reactant molecules having a longer contact time, favorable for surface adsorption and reaction, and consequently enhance catalytic efficiency.5. By tuning the preparation conditions such as temperature, time, and glucose concentration, the uniformly dispersed carbon spheres of different size (100-300nm) are obtained.6. By changing AgNO3concentration and kind of solvent, the optimal preparation conditions are obtained for Ag deposition on the carbon spheres of different size.7. The nano-composites of C140-Ag、C200-Ag、C300-Ag, and C200-Ag-Au are used for catalytic hydrogenation of p-nitrophonel, the results reveal that both C3oo-Ag and C2oo-Ag-Au are the superior candidates for the target. The possible reasons for the better performances are tentatively discussed.