Probing the locations of benzene molecules inside completely siliceous ZSM-5 by FT-Raman spectroscopy

The locations of benzene molecules inside completely siliceous ZSM-5 at various loading levels were determined from FT-Raman spectra of benzene adsorbed in ZSM-5. In the low loading range (1-4 molecules/u.c.), all of the guest molecules reside at the channel intersections. In the intermediate loading range (5 and 6 molecules/u.c.), four benzene molecules are located at the intersections, while the remaining guest molecules access the zigzag channel segments. In the high loading range (7 and 8 molecules/u.c.), four guest molecules remain at the intersections and the rest of the benzene molecules move to the midsections of the straight channels. The changes in the Raman spectra of both sorbate and sorbent clearly indicate that the host framework undergoes two successive phase transitions at the loadings of 5 and 7 molecules/u.c., respectively. The zeolitic framework vibrations also indicate that there are very strong interactions between the guest molecules and the host framework in the high loaded phase.