Predicting surface diffusivities of molecules from equilibrium adsorption isotherms

For SO2 adsorbed upon a variety of different surfaces, both the characteristic heat of adsorption and the activation energy for surface diffusion are predominantly detd. by the surface geometry of the substrate. A previously proposed [S.P. Rigby, 2002] fractal theory for the surface diffusion of mols. on heterogeneous surfaces was expanded and applied to past literature data on the surface diffusion of SO2 upon silica, porous glass, and carbon. The theor. predictions were found to be in line with the exptl. results. The Arrhenius parameters for the surface diffusivity, at a monolayer coverage, are functions of the surface fractal dimension, as obtained by gas adsorption. The compensation effect predicted by the theory was also obsd. These findings suggest that once the relevant model parameters were detd. for the particular chem. species, the surface diffusivity at a monolayer coverage on a given surface may be detd. from an equil. gas adsorption isotherm. The theory also allows the appropriate tortuosity factor to be calcd. [on SciFinder (R)]