Fourier transform infrared and quasi-elastic neutron scattering investigations on the binding states and the dynamics of benzene molecules in the pores of MCM-41 molecular sieves

The in-plane C−H/C−C, out-of-plane C−H, and the fundamental ν19 C−C stretch vibrations of benzene molecules were monitored by FTIR spectroscopy, for adsorption in MCM-41 at room temperature and at different loadings. The results were compared with the corresponding data on ZSM-5 zeolites. The frequency and the relative intensity of IR bands point to the development of a compressed state of benzene in the pores of MCM-41, the density of which depended upon loading and lay in general between that of bulk liquid and a solidlike phase formed in the pores of ZSM-5 zeolite on benzene adsorption. Quasi-elastic neutron scattering results reveal that the pore characteristics play a crucial role in deciding the dynamics of benzene molecules in a confined medium. Thus, in contrast to the molecular motions of benzene in ZSM-5 zeolite where only rotational motion was observed in the instrumental time window of 10-10−10-12 s, the benzene molecules adsorbed in MCM-41 exhibit only translational motion. Further, the value...