Characterization of the benzene molecule adsorbed in USY zeolite using double quantum filtered NMR spectral analysis

Abstract

The investigations of deuteron NMR relaxation including T 1, linewidths and double quantum filtered (DQF) spectral analyses are examined preliminary to probing the dynamics and exchange process of low-loading benzene molecules adsorbed into ultra-stable Y-type (USY) zeolite. DQF NMR is a sensitive method for the determination of the residual quadrupolar interaction resulting from the local order. The usual observed deuteron spectra of benzene- d 6 in USY retain the isotropic peak with no solid pattern over a broad temperature range. However, when observed in DQF spectra, an additional central line appears. It is evidence of the benzene in isotropic motion exchanging with the benzene situated at adsorption sites with non-vanishing quadrupolar interaction. We modified the cone model to describe the in-plane rotation around the hexad axis and the restricted wobbling motion of the benzene ring on the surface of the interaction site. The population profile of adsorbate thus determined provides useful knowledge of the site distribution in supercages of USY zeolite. Comparison with the result of NaY in terms of site distribution is also discussed briefly.