Preparing Novel And High Performance Ni-based Catalytic Materials: Study On Their Application For CH₄ Reforming

Hydrogen is a green energy source with high energy density, which generates only water after combustion. It is not only environment benign, but could also replace the traditional fossil fuels to solve energy crisis. Therefore, it may play a key role on the the energy stage in the 21 th century. Presently, methane steam reforming(MSR) is still the most effective and feasible way for large-scale industrial hydrogen production. Due to the low cost, abundant storage and high activity of Ni, Ni-based catalysts have been widely used for CH4 reforming. However, it is well-known that Ni-based catalysts suffer from easy coking and sintering of the Ni active sites at high tmeperatures, which can deactivate the catalysts in the end. Therefore, to reduce the cost for hydrogen production and facilitate the application of hydrogen as a green energy, it is necessary to design and develop catalysts with more potent resistance to sintering and coking. With these goals, this thesis has performed a series of studies, with the main results summarized here.First, a series of supported Ni-Co/γ-Al2O3 bimetallic catalysts with a fixed 12% Ni loading but different Co contents were prepared by using the co-impregnation method and investigated for methane steam reforming. The addition of Co can significantly improve the coke resistance and the reaction stability of Ni/Al2O3 at a mild loss of the reforming activity. XPS and TEM results proved the existence of strong interaction between Ni and Co species. XRD and high-angle annular dark-field scanning transmission electron microscopy mapping(HAADF-STEM mapping) results of the reduced catalysts provided direct evidence for Ni-Co alloy formation upon Co addition onto Ni/Al2O3, which blocked part of the low coordinated active Ni sites, thus restricting their activation ability for C-H bonds, and suppressing the formation of C-C bonds. As a consequence, the coke formation of the catalysts can be effectively inhibited during the reaction.Second, mesoporous Al-SBA-EG and spherical dendritic Ni/KCC-EG supports were synthesized as supports for Ni. With impregnation method, 7% Ni/Al-SBA-1 and 7% Ni/KCC-1 catalysts were prepared with DDI water and ethylene glycol as the solvent. It was revealed that the catalysts prepared with both of the two supports in ethylene glycol solvent exhibited very high activity, stability and superior resistance to coking. XRD and TEM proved that the Ni sizes can be confined below 5 nm by the mesopores or channels of the supports, hence restricting the sintering of the Ni sites during the high temperature reaction, and effectively improving the activity and coke resistance of the catalysts.