A molecular dynamics study of xenon sorbed in sodium Y zeolite. 1. Temperature and concentration dependence

Abstract

The sorption properties of xenon sorbed in sodium Y zeolite as a function of adsorbate concentration and temperature have been obtained from molecular dynamics simulations. The properties reported include the various site-site a center of self-diffusion coeffcients, the power spectra, and the distribution of site residence times. The location of the physical adsorption site for xenon is the same as for methane. The guest-host energy distribution function for xenon differs significantly from the bimodal function observed for methane. It is shown that the mean square displacement shows a crossover from ballistic to diffusive behaviour and the activation energy for diffusion is 4.1 kJ/mol. We suggest that the 15-cm-l frequency mode seen in the power spectra of the autocorrelation function corresponds to the XeXe dimers. The nonavailability of sorption sites at higher adsorbate concentrations is reflected in the guest-host distribution function, center of cage-center of mass radial distribution function, power spectra, and other properties.cage-center of mass radial distribution functions, distribution of guest-host energy, guest-guest pair and bon d ' g energy, IntroductionThe interest in the study of adsorption properties in restricted regions is growing. Several materials in nature permit the adsorption of small to medium sized guest molecules in voids of the order of several molecular diameters. These are known by the general name micropores. Some of these are simple adducts such as the urea-alkanes with purely physical interaction. The others

Xenon Diffusion in Zeolite NaY: Transition-State Theory with Dynamical Corrections

“…V ADD (t) ) V 0,ADD (r WIN (t) -r ADD ) 2 r WIN (t) > r ADD (22) the potential of mean force for the same points on the reaction coordinate. As a result, the first minimum is slightly lower than the second.…”

Investigation of the possibility of low pressure encapsulation of carbon dioxide in potassium chabazite (KCHA) and sodium chabazite (NaCHA) zeolites

“…However, more encapsulation studies have been carried out quantitatively in the following decades for different gases on a wide range of zeolites, including Ar in 3A [27,28], Ar in 4A [25,29,30], Kr in 3A [28,31,32], Kr in 4A [25,29], Kr in 5A [32], Xe in 4A [33], He and Ne in 3A and 5A [34], Ne in heulandite and stilbite [35], H 2 in CsA [36,37], H 2 in 4A [38], H 2 in 5A [39], CH 4 in 4A [25,[40][41][42], N 2 in 3A [27], N 2 in CsA [36]. A similar successful encapsulation was made on some other low-porosity zeolites by quantitative measurements of Ar in sodalite and cancrinite [43], Kr in sodalite and cancrinite [43], and He and Ne in tridymite and cristobalite [44].…”

Self-diffusivity and velocity autocorrelation functions for xenon in NaY using memory kernels

“…The moments reported here were computed from the forces using equations (31) and (32). In addition to the above expressions, frequency moments can equivalently be obtained directly from the atomic coordinates of the adsorbate and zeolite framework [19].…”

“…In all cases the derivatives in equation (32) were evaluated using a first-order finite difference scheme. Figure 2 illustrates both the second and fourth moment as a function of the time step used in the MD simulation and indicates that the accuracy of the computed moments is insensitive to the range of time step used.…”