Hydrothermal Stability Of SiO₂/Al₂O₃Support And Ni/SiO₂-Al₂O₃Catalyst

AI2O3has extensive pore structure, excellent thermal stability, high mechanical strength, favorable adsorption properties and surface acidity. Al2O3supported catalysts have been widely used in hydrogenation, dehydrogenation, reforming, desulfurization and other important chemical reactions, many of which are in aqueous system. AI2O3will rehydrate in the presence of water, resulting in the significant changes of structure, texture and surface acidity of catalyst. Moreover, the migration of the metal also causes the decay of the catalyst activity. Therefore, it is of great importance to research and develop high hydrothermal stability of support and catalyst.In the previous work, we had found that, the introduction of SiO2significantly inhibited the hydration of Al2O3, and improved the hydrothermal stability of Al2O3. This paper focuses on the structure changes of SiO2/Al2O3support under hydrothermal conditions. Moreover, the effect of Ni crystallite size and the metal-support interaction on the hydrothermal stability of Ni/SiO2-Al2O3catalyst were investigated. The main results are as follows:1>. The introduction of SiO2significantly decreased the hydration rate of Al2O3, reduced the formation rate of boehmite. With silicon content increasing, the decreased extent of hydration rate of Al2O3slowed down, and the hydrothermal stability of Al2O3improved. The addition of SiO2also reduced the structure changes of Al2O3under hydrothermal conditions. The structure changes were smaller with the higher silicon content. The7Si-Al2O3support almost maintained original structure after the hydrothermal treatment of200h.2、The Ni/SiO2-Al2O3catalysts with different Ni crystallite size were prepared through changing the Ni loading. The effect of Ni crystallite size on the hydrothermal stability of catalyst was investigated. It was found that SiO2/Al2O3support did not hydrate after the hydrothermal treatment of8h, but the Ni crystallite aggregated. The Ni crystallite size of catalyst was smaller, the metal Ni existence was more unstable, and the levels of Ni aggregation was greater. The Ni crystallite size of catalyst maintained at11~12nm after hydrothermal treatment.3、The Ni/SiO2-Al2O3catalysts with different metal-support interaction were prepared by changing the preparation method. The effect of metal-support interaction on hydrothermal stability of catalyst was investigated. The catalyst had weak interaction between metal Ni and support and large metal Ni crystallite size, which was prepared by using Nickel nitrate as nickel precursor. While the catalyst had strong interaction between metal Ni and support and small Ni crystallite size, which was obtained by using impregnated-deposition method. The catalyst had specifically strong interaction between metal Ni and support, and extremely small Ni crystallite size, which was prepared by using Nickel carbonate as nickel precursor. The results showed that the interaction between the metal Ni and support affected the hydrothermal stability of catalyst. The stronger interaction between metal Ni and support was, the less the levels of Ni aggregation would be.