STUDY OF RESTRICTED DIFFUSION IN POROUS CATALYSTS BY NMR

The diffusion of 1,3,5 tri‐tert‐butylbenzene (TTB) into cylindrical γ‐alumina extrudates of varying micropore diameter and macropore volume has been studied by NMR spectroscopy. The proton NMR signal of the methyl proton of TTB in the micropores of the alumina extrudate was found to be well resolved and shifted upfield relative to that in the bulk liquid by 0.55 ppm. The area under the shifted peak is proportional to the liquid concentration of TTB in the micropores. The change in the intensity of this peak as a function of time and measurements of the amount of TTB absorbed on the surface alumina at equilibrium were used to calculate the effective diffusivity of TTB in each extrudate. Measured values of the effective diffusivity are in reasonable agreement with predictions using correlations in the literature. These observations suggest a new method for measuring the liquid‐phase effective diffusivity in porous materials. Copyright © 1990 American Institute of Chemical Engineers