FT-RAMAN STUDIES OF SINGLE-COMPONENT AND BINARY ADSORPTION IN SILICALITE-1

FT-Raman spectroscopy has been used to probe single-component and bina ry-component adsorption of benzene, p-xylene and cyclohexane in silica lite-1. It was shown that FT-Raman is not only able to probe the sorba te-framework interaction related to the phase transitions commonly obs erved when organic species are sorbed within silicalite-1, but also pr ovides a sensitive and direct probe of sorbate-sorbate interactions wi thin the zeolite framework. Single-component adsorption of benzene, p- xylene and cyclohexane in silicalite-1 has been considered at various loadings. In the case of benzene adsorption, FT-Raman spectroscopy was shown to detect the transformation in sorbate interactions associated with the transformation in crystal symmetry from monoclinic P2(1)/n.1 .1 to orthorhombic Pnma at a sorbate loading of 4 molecules per unit c ell. We also confirmed the results of Huang (J. Am. Chem. Sec., 1996, 118, 7233) in detecting the sorbate-induced crystal-phase transition f rom orthorhombic Pnma to orthorhombic P2(1)2(1)2(1) for the case of p- xylene adsorption at loadings in excess of 4 molecules per unit cell. No evidence of a crystal-phase transition as a function of sorbate loa ding was observed for the case of cyclohexane adsorption, consistent w ith earlier studies. It was shown that, in the case of benzene-p-xylen e co-adsorption, benzene and p-xylene access the sites most favoured d uring the respective single-component adsorption processes. In contras t, cyclohexane when co-adsorbed with either benzene or p-xylene was se en to compete for the same sites, forcing benzene and p-xylene into le ss favoured adsorption sites.