2H NMR studies of binary adsorption in silicalite

Abstract

This paper reports the first ²H NMR studies of the binary adsorption of benzene–p–xylene and benzene–cyclohexane in the zeolite silicalite. The results demonstrate that the co-adsorption of a second component significantly influences the adsorption characteristics associated with pure benzene adsorbed within the same silicalite structure. Studies of equimolar, binary mixtures of benzene and p-xylene in silicalite indicate that benzene and p-xylene access the sites most favoured during the respective single-component adsorption process, with the two species forming chains of sorbed species along the straight channels of the zeolite structure. In contrast, mixtures of benzene and cyclohexane demonstrate the phenomenon of competitive adsorption. The larger cyclohexane molecules preferentially enter the straight channels within the silicalite framework, thereby forcing the benzene molecules, which would normally access the same adsorption sites, to take up positions in sites within the sinusoidal channels and channel intersections.