Preparation Of Co - Coated Core - Shell Catalysts And Its Catalytic Performance

In this paper, with the help of cutting-edge preparation techniques of metal and nonmetal materials, new approaches to preparing catalysts were obtained through drawing on the experience of means of core-shell nano catalyst. All these approaches were employed to prepare metal nanopartical capsuled in Si O2 to form a serious of Metal@Si O2 core-shell structure catalysts, which had high thermostability, in the meantime, it was found that smaller-sized catalysts have better activity. Furthermore, the relationship between the properity and the size of the Ni nanopartical had been studied.According to this theme, some work had been carried out as follows:1. Uniform hollow Ni Pt alloy nanoparticals with controllable size were obtained by displacement reaction and adjusting the concentration of PVP solution, and after that, removed the Ni from the Ni Pt alloy by hydrochloric acid, the influence of pore size generated by dealloying of the Ni Pt alloy on hydrogenation of m-dinitrobenzene(DNB) was tested, and on this basis, an assumption was presented that the reaction activity is affected by the various adsorption capacity of reactant, intermediate and product on catalysts with different nanostructure.2. Dispersing the hollow Ni Pt alloy nanoparticals in the mixed solution of ethanol and ammonia, a layer of silica deposited on the surface of nanopartical with the addition of TEOS. Hollow Ni-Pt@Si O2 core-shell catalysts with tunable shell thickness were prepared by adjusting the amount of TEOS, and the Si O2 shell greatly improved the thermal stability of Hollow Ni Pt nanopartical.3. Different-sized Ni nanoparticals(3 nm, 5 nm, 10 nm, 60 nm) were prepared through thermal cracked and reduced by BTB of Ni(acac)2, then capsuled in Si O2 to form a serious of Ni@Si O2 core-shell structure catalysts by a reverse microemulsion method and classic stober method with excellent thermal stability.4.These serious of Ni@Si O2 core-shell catalysts were used for dry reforming of methane with CO2(DRM) reaction and remained stable for 1000 h. In addition the conversion of CH4 and CO2 were all above 90%, while the selectivity of H2 and CO were almost 99% with a H2/CO ratio around 1. The size of Ni nanoparticals is key factor to reaction activity, the conversion were higher on the smaller-size Ni catalysts. An conclusion was presented that the carbon deposition was even more and hardly to remove in larger-size Ni catalysts.By means of XRD and TEM, the feature of the as-prepared materials was analysed and characterized in detail, meanwhile, dry reforming of methane with CO2 reaction was used as probe to study the relationship between catalyst structure and catalytic property. The results indicated that these Ni@Si O2 core-shell catalysts exhibited higher activity and perfect thermal stability which due to the very tiny Ni core. Not only that, but also the crystalline Si O2 shell prevent the Ni core to sinter and grow up, that is the main reason for the stability. In addition, the resistance of carbon deposition was enhanced by the tiny Ni nanopartical. The results also showed such Ni@Si O2 core-shell catalysts were effective catalysts.