Effect Of ZnO Morphorlogy On The Performance Of Co/ZnO Catalyst In Fischer-Tropsch Synthesis

Fischer-Tropsch Synthesis is a technology to convert syngas, which derived from coal, natural gas and biomass, into environment friendly liquid fuel and high-valued industrial chemicals. It has been acknowledged as one of the most efficient ways to solve the deficient supply of the liquid fuel. With high activity, high selectivity to linear paraffin and low water-gas shift activity, cobalt-based catalyst, a supported catalyst, is a promising catalyst for FT synthesis.The main work of this dissertation is to synthesize ZnO with different morphologies, which are characterized by X-ray diffraction, low temperature N2physical adsorption and scanning electron microscope. Then Co/ZnO catalysts, which prepared by incipient wetness impregnation, were evaluated in a fixed-bed. Several results have been abtained.(1)Referring to rod-like ZnO, the relationship between performance of catalyst and specific surface area is not so obvious. In fact, the crystal defect and the size of cobalt particles supported are keys to catalysts’ performance. When it comes to micro-nano structure ZnO microsphere, which is formed by plate-like ZnO after calcination, the Co/ZnO catalyst showed the best performance includes not only the activity but also the selectivity of C5+. So the unique microsphere with plate-like ZnO is more appropriate as catalyst support.(2)Without bringing any other inorganic ion and surfactant into the synthesis system, porous plate-like and plate-like ZnO are prepared by tuning the reaction temperature. And a conclusion that the polar facet of ZnO crystalline exposed is far more important than it’s specific area in Co/ZnO catalyst was made.(3) Hydroxide ion derived from hexamethylenetetramine (HMT) is the reason why ZnO and zinc hydroxide carbonate (ZHC) crystalline grains are formed. And there is an equilibrium between ZnO and ZHC, because of the consumption of HMT lows the pH of reaction aqueous, thus precursor is synthesized with different morphology by stacking of tiny crystalline grains, due to high surface energy of tiny ZnO and ZHC crystalline grains. Tuning the synthesis temperature changes the way of ZnO and ZHC crystalline grains stacking, the composite of precursor thereby affect performance of the Co/ZnO catalyst. When the temperature is raised to110℃the catalysts own the best activity and fastest deactivation.