A Fourier transform-Raman investigation of the host-guest interactions of p-chlorotoluene, toluene, and chlorobenzene sorbed on completely siliceous ZSM-5

The host-guest interactions of three related sorbates including p-chlorotoluene, toluene, and chlorobenzene adsorbed on completely siliceous ZSM-5 have been examined by Fourier-transform (FT)-Raman spectroscopy. For p-chlorotoluene/ZSM-5 systems, a phase transition was detected at a loading of 4 molecules per unit cell (u.c.). Our work confirms the results of previous studies that p-chlorotoluene/ZSM-5 and p-xylene/ZSM-5 complexes exhibit similar phase-transition behavior. However, our data also show uniquely that the sorbate-sorbent interactions are significantly stronger in the p-chlorotoluene/ZSM-5 system. For the toluene/ZSM-5 system, a sorbate-induced phase transition in the ZSM-5 framework was also observed. Based on the information obtained from the C-H stretching region, we suggest that in the low-loaded phase, toluene molecules are located at the channel intersections, whereas in the high-loaded phase, the sorbate molecules occupy both intersections and midsections of the straight channels. In the chlorobenzene, two successive phase transitions were detected at 3 and 7 molecules/u.c. Below the coverage of 5 molecules/u.c., the guest species reside in the channel intersections. At higher loading levels, a string of sorbates is formed along the straight channels. Strong one-dimensional sorbate-sorbate interactions also occur.