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Abstract

A novel in-situ IR technique is applied to study diffusion and counter-diffusion of benzene and ethylbenzene in H-ZSM-5 zeolite. The transport of the adsorbate molecules from a diluted feed stream into the catalyst or vice versa is studied in a precatalytic regime but under conditions close to a catalytic run. Diffusivities are evaluated for the single component as well as for the binary case at various temperatures and loadings. The diffusion coefficient determined for benzene at 415 K and a coverage of about 0.11 mmol benzene per gram zeolite (0.6 molecules benzene per unit cell) amounts to D = 9.7x 10-¹⁰ cm². s⁻¹ and is in excellent agreement with literature data obtained by different uptake techniques or NMR measurements. The activation energies for diffusion of benzene and ethylbenzene are 20 kJ.mol⁻¹ and 25 kJ.mol⁻¹, respectively. Counter-diffusion, under similar conditions, reduces the diffusivities, which were observed in the single-component case, by about 50%.