Investigation ofp-Difluorobenzene and Fluorobenzene Adsorbed on Completely Siliceous Zeolite ZSM-5

Abstract

The host−guest interactions of two related sorbates, p-difluorobenzene and fluorobenzene, in completely siliceous zeolite ZSM-5 have been examined by thermogravimetric analysis, powder X-ray diffraction (XRD), and FT-Raman spectroscopy. The powder XRD patterns reveal that the phase transition behavior of p-difluorobenzene/ZSM-5 is very different from that of closely related p-dichlorobenzene/ZSM-5 and p-xylene/ZSM-5 systems. FT-Raman spectra of p-difluorobenzene adsorbed in ZSM-5 indicate that the first 4 p-difluorobenzene molecules are located in the channel intersections. When the loading is greater than 4 molecules per unit cell (uc), additional molecules access the midsections of straight channels. The situation is different from that found in p-dichlorobenzene/ZSM-5 and p-xylene/ZSM-5 complexes where additional guest molecules reside in the zigzag channels. Adsorption of fluorobenzene into ZSM-5 induces only one transition in the framework at a loading of 4 molecules/uc. This behavior is distinctly different from that of similar chlorobenzene/ZSM-5 systems in which two successive transitions occur at 3 and 7 molecules/uc.