采用沉淀法和喷雾干燥技术制备了一个典型的费托合成铁基催化剂(100Fe/3K/6SiO_2,质量比)所得样品在不同温度下焙烧5 h.分别利用N_2吸附和穆斯保尔谱表征了催化剂的织构和物相性质,同时利用热重分析仪记录了催化剂在H2气氛中的还原过程,并利用气固反应模型对还原曲线进行了动力学模拟.结果表明,300~600℃焙烧后催化剂的还原过程可用相同的模型拟合,其中由α-Fe_2O_3还原为Fe_3O_4的过程可用一维晶相形成与生长模型或三维相界面反应模型描述,Fe_3O_4还原为α-Fe的过程受二维晶相形成与生长模型控制.而对于700℃焙烧后的催化剂,其还原过程可能受晶相形成与生长模型和收缩核模型共同影响.随着焙烧温度的提高,催化剂的还原能力减弱,还原过程活化能升高.这可能是由于焙烧温度的提高导致晶粒尺寸增大和晶格缺陷减少所致.
A typical iron-based Fischer-Tropsch catalyst was prepared by the combination of precipitation and spray drying. The catalyst was then calcined at different temperatures. The textural properties and the crystal structure of the calcined catalyst samples were characterized by N_2 adsorption and M(o)ssbauer effect spectroscopy, respectively. The thermogravimetric analysis was employed to follow the reduction process of the catalysts. The experimental data were then regressed using gas-solid reaction models. The results indicated that the reduction process of the catalysts calcined at 300-600℃ could be described by the same models. The reduction of u-Fe_2O_3 to Fe_3O_4 was regressed by the 1-dimentional formation and growth of nuclei model, and the reduction of Fe_3O_4 to α-Fe was controlled by the 2-dimentional formation and growth of nuclei model. The reduction of the catalyst calcined at 700 ℃ was influenced by both the formation and growth of nuclei model and the shrinking core model. With the increase of the calcination temperature, the reduction capability of the catalysts decreased and the apparent activation energy increased, being due to the increase of the crystal size and the decrease of the lattice defects in the catalysts.
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