Effective diffusivities and counter-diffusivities of coronene and porphines dissolved in organic solvents were measured in alumina and silica alumina catalyst supports. The measured effective diffusivity was in the range of 10^-11-10^-10 m²/s and the counter-diffusivity, 10^-15-10^-14 m²/s.
Very small values of counter-diffusivities indicated that the flux of adsorbate desorbed was greatly decreased by the flow of desorbate formed in the opposite direction. Experimental results showed that diffusivities of porphines in aluminas increased with strength of adsorption. One of the possible explanation for this result was that the strongly adsorved molecules have the shielding effect on diffusing molecules through pore fluid.