Abstract: The chemical adsorption behavior of three adsorbates(methanol, n-butylamine and hydrogen gas)on Ni-W/F-Al₂O₃-SiO₂ catalyst and supported Ni catalyst have been investigated. The roughness fractal dimension(D_r)and the chemisorption fractal dimension(D_c)of two catalysts were estimated based on the fractal geometry consideration. The difference between D_c and D_r was used to characterize the chemical heteorgeneity of the active sites on the catalyst surface. The results showed that the chemical heterogeneity of the acid sites of Ni-W/F-Al₂O₃ SiO₂ was very great and that of the supported Ni catalyst was decreased with increase of the impregnation time during catalyst preparation. For the supported Ni catalyst it is found that the chemical heterogeneity of its active surface was eliminated after four times impregnation.

Key words: solid catalyst, active surface, chemical heterogeneity, fratal dimension