Localization and mobility of benzene in sodium-Y zeolite by molecular dynamics calculations

Abstract

The nature of the adsorption sites and the mobility of benzene in sodium-Y zeolite around room temperature is investigated by using molecular dynamics calculations carried out at a loading of two molecules per cage. The motion of benzene is shown to be highly anisotropic, being confined largely to the cage walls. The simulation results correlate well with recent neutron diffraction and infrared absorption data.

Multiple-quantum NMR studies of spin clusters in liquid crystals and zeolites

“…Initially, the introduction of a small amount of benzene into dehydrated NaY zeolite allows the molecules to move randomly throughout the sample, translating along the interior supercage surfaces from site to site. The cationic SII sites appear to be preferred over the W sites, as predicted by Monte Carlo simulation [68]. As the bulk concentration .…”

“…Benzene occupation of W sites in NaY zeolite has also been predicted by Monte Carlo simulation [68] and obser'**,d by neutron diffraction [61], but in both cases the occupancy the W sites was found to be less favorable than occupancy of the Sll sites.…”

“…The physisorption of an aromatic molecule here is favorable due to the tendency of Na + ions to occupy the sodalite cage an aromatic molecule will bind both the ion and the molecule to the site, for the Na + ions are also attracted to the oxygen atoms that ring the sodalite cage aperture. Benzene i occupation of Sli sites in NaY zeolite has been predicted by Monte Carlo simulations [68] and directly observed in neutron diffraction experiments [61].…”

“…molecules are relatively small, allowing them to pass easily from supercage to supercage-at-room temperature. The molecules are expected to adhere to the cationic w (SII) and window (W) sites at lower temperatures [63][64][65][66]68], possibly creating strongly coupled spin networks between adjoining supercages. The smaller molecular size when compared to hexamethylbenzene allows it to adhere more closely to the wall of the supercage, shortening the distance between molecules in adjoining supercages and weakening the spin cluster isolation.…”

“…The dispersion and distribution of aromatic hydrocarbons, especially benzene, in faujacitic zeolites have been studied by several techniques, among them neutron diffraction [61][62], several single-quantum NMR techniques [63][64][65][66][67], and Monte Carlo simulations [68]. Two different molecular distribution modes for benzene in faujacitic zeolites are suggested by the results of the above studies; a uniform distribution [63] as depicted in Figure 5.1 (a), and an aggregated distribution [62] as depicted in Figure 5.1(b).…”