低镍甲烷化催化剂中镍和氧化镧的分散研究

本文用X射线衍射法(XRD), 透射电镜(TEM), 配合电子衍射对Ni/Al2O3,Ni/γ-Al_2O_3-La_2O_3等催化剂中镍晶粒度和La_2O_3的分散状态进行了测量和讨论。用透射电镜测量了不同La_2O_3含量的催化剂中镍晶粒度分布, 其平均直径可与X射线宽化法测定值相比较。催化剂中随La_2O_3加入量的增加, Ni晶粒有细化趋势, 从而提高了甲烷化催化活性。对La_2O_3在γ-Al_2O_3表面作密置单层分散的模型提出了新的旁证, 并推断由于La_2O_3在γ-Al_2O_3表面高分散并产生较强相互作用, 使γ-Al_2O_3接近表层晶格发生畸变。

DISPERSION OF NICKEL AND La2O3 IN LOW-CONTAINING Ni-CATALYST OF METHANATION

Ni/γ-Al_2O_3, Ni/γ-Al_2O_3-La_2O_3 (La_2O_3 6.7%)and Ni/γ-Al_2O_3-La_2O_3 (La_2O_3 11.7%) catalysts were prepared by incipient wetness technique. The particle size distribution (Fig.9) and the average size of nickel in these catalysts were determined by Transmission Electron Microscopy (TEM). Average particle size could be compared with the data determined by X-Ray Diffraction (XRD)(see Table 3). It has been found that the particle size of nickel in catalysts is decreasing (Table 1) and activity of methanation is increasing (Fig.2) as adding La_2O_3 to Nicatalyst. Results of TEM and XRD in this paper support the model suggested by Xie Youchang et. al., of close-packed monolayer La_2O_3 dispersed on γ-Al_2O_3 surface, if the amount of La_2O_3 is less than the threshold value (0.28 La_2O_3/100 m~2 γ-Al_2O_3). X-Ray line broaden of γ-Al_2O_3 lattice, due to La_2O_3 highly dispersed on the surface of alumina.