Study On BaTiO₃Based Supports And Their Supported Nickel Catalysts

The methane catalytic reforming with carbon dioxide to synthesis gas has been suggested as an effective route to realize the resource utilization of methane and carbon dioxide, the two main greenhouse gas. The low cost Ni-based catalyst owns the well catalytic activity for the reaction of dry reforming of methane. However, the Ni-based catalyst is prone to deactivation, which is a key problem, due to the carbon deposition during the catalytic reforming reaction.The barium titanium oxide is a kind of composite oxide with the perovskite structure.The barium titanium material has been extensively used in the field of catalysis. The preparation of BaTiO3-based (composite) support can both increase the specific surface area of BaTiO3and make the (composite) support get a special macrostructure which is suitable for the gas-solid phase catalytic reaction, and is benefit for the improvement of catalyst performance.In this dissertation, the BaTiO-based supports were prepared by various methods and the macrostructure of the BaTiO3-based supports were investigated. Moreover, the activities, the anti-coking properties and the catalytic stabilities of BaTiO3-based supports supported BaTi1-xNixO3,Ni/BaTiO3-Al2O3Ni/BaTiO3-BaAl2O4-Al2O3catalysts were studied by the probe reaction of methane catalytic reforming with carbon dioxide to synthesis gas. Meanwhile, the effects of sol-gel method and La addition on the macro-properties, the surface properties and the catalytic performance of the catalysts were studied particularly in the sixth chapter.The BaTiO3-based supports and their supported nickel catalysts were characterized by means of XRD, FT-IR, BET, SEM, N2adsorption,EDS, XPS, TPR, TG, TPD,CO2pulse etc.1. A series of Ni-doped perovskite oxides BaTii-xNiO3were prepared by sol-gel method and characterized by XRD and TPR, and their catalytic performances for CO2reforming of CH4were evaluated. The results showed that the BaTi1-xNixO3samples possessed the characteristic perovskite structure after calcined in air at800℃for3h, and as they were reduced in situ by hydrogen some nickel crystallites of about10nm in size existed on the surface of the catalysts. The catalysts activities increased with the increase of nickel contents for the reaction of CH4reforming with CO2; however, the changes of the catalysts activities are not obvious as the x value of BaTi1-xNixO3reached0.175. The BaTi1-xNixO3catalyst with the x of0.175had the best performance.2. Wt.%BaTiO3-Al2O3(wt.%BaTiO3=0～100%) composite supports were synthesized through varying the BaTiO3content by the "sol-(xero)gel" method. Ni/wt.%BaTiO3-Al2O3nickel-based catalysts prepared by incipient wetness method were evaluated for dry reforming of methane carried out between690℃and800℃. The results demonstrate that BaTiO3particles are discontinuously dispersed on the surface of γ-Al2O3in the form of individual isolated particles for the wt.%BaTiO3-Al2O3composite supports. Meanwhile, the coexistence of BaAl2O4spinel phase with the BaTiO3phase on the surface of γ-Al2O3probably inhibits the Ni/wt.%BaTiO3-Al2O3catalysts from the formation of NiAl2O4spinel phase, improving the catalytic performance of the catalysts. The Ni/BaTiO3catalyst showed poor stability and severe coke formation in the dry reforming of methane tested at690℃, which was thought to be mainly originated from the excessive strong electronic donor intensity of Ni/BaTiO3catalyst as well as the resulted CO disproportionation reaction. Compared with the Ni/BaTiO3catalyst, the Ni/wt.%BaTiO3-Al2O3catalysts with the addition of BaTiO3had a higher dispersion of active nickel and a weakened electronic donor intensity of the NiOx species. As a result, the synthesized Ni/32.4%BaTiO3-Al2O3catalyst exhibited a high catalytic activity, excellent stability as well as coking resistance for lower temperature dry reforming of methane.3. A series of BaTiO3-BaAl2O4-Al2O3composite supports were prepared by the sol-gel method using hexadecyltrimethylammonium bromide as the structure template. The BaTiO3-BaAl2O4-Al2O3composite supports were characterized by X-ray diffraction, infrared spectroscopy, N2adsorption-desorption, transmission electron microscopy, and H2temperature-programmed reduction. The catalytic performance of the Ni/BaTiO3-BaAl2O4-Al2O3catalyst was investigated by CH4reforming with CO2. The results showed that the BaTiO3-BaAl2O4-Al2O3composite supports own a porous texture and high specific surface area, the BaTiO3and BaAl2O4phases, whose crystalline size is in the range of20～50nm, exist on the inside and outside surface of the composite support in the form of crystalline particles. The size of micropores of the composite support is10～20nm, The presence of both BaTiO3and BaAl2O4phases on the surface of the composite support weakens the strong interaction between the nickel species and γ-Al2O3of the Ni/BaTiO3-BaAl2O4-Al2O3catalyst, and the possibility of the formation of NiAl2O4spinel is decreased. The Ni/BaTiO3-BaAl2O4-Al2O3catalyst with17.33%Ba (Ti) content showed the excellent activity and stability for CH4reforming with CO2to synthesis gas.4. The various BaTiO3supported nickel-based catalysts were prepared by the sol-gel method/or modified by the addition of La, and the catalytic performance of the nickel-based catalysts were evaluated by the reaction of CH4reforming with CO2to synthesis gas. Compared with the catalysts prepared by impregnation method, the results indicated that the catalysts prepared by sol-gel method had a larger specific surface areas, exhibited higher catalytic activities and perfect performance of anti-coking. The decrease of CO2-TPD temperature and the increase of H2-TPD temperature of the catalysts indicated that the surface alkalinity of the catalyst is lowered and the reduction reaction between hydrogen and nickel crystalline particles of the catalyst is easy to take place. In addition, the modification effect of rare earth La addition was investigated, and it was found that the0.75NLBT catalyst with the composition of5wt%Ni-0.75wt%La owns the optimum catalytic performance.