This chapter presents frequency response study of mixture diffusion of benzene and xylene isomers in silicalite-1. One of the major applications of zeolites in catalysis was aromatic alkylation, in which molecular diffusion properties were found to play a significant role in the overall reactions, especially in the selectivity of products. Many studies on the single component diffusion of aromatic molecules were made using various methods. The diffusion of the single components and mixtures of benzene, and two xylene isomers in silicalite-1 was studied by a frequency response method. The responses of benzene, p-xylene and o-xylene single component in the same silicalite-1 show that the diffusivities of these three molecules increase in the sequence of o-xylene, benzene and p-xylene. The FR spectra of benzene/p-xylene and benzene/o-xylene binary mixtures in silicalite-1 have shown two distinct response peaks. The diffusion coefficients of benzene obtained from the mixture diffusion were from 5.6 x 10-3 to 3.3 x 10-12m2/s at 355 to 435K, which were consistent with those obtained previously from the single component study. The diffusivities of o-xylene in silicalite-1 obtained from the mixture diffusion were found to be two orders of magnitude smaller than those of benzene. A film resistance was observed in diffusion of the mixtures.

Frequency Response Study of Mixture Diffusion of Benzene and Xylene Isomers in Silicalite-1. D.Shen, L.V.C.Rees: Studies in Surface Science and Catalysis, 1995, 97, 235–42