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On entropic barriers for diffusion in zeolites: A molecular dynamics study Andreas Schuring
 

Summary: On entropic barriers for diffusion in zeolites: A molecular dynamics study
Andreas Schušring
Universitašt Leipzig, Institut fušr Theoretische Physik, Augustusplatz 10-11, D­04109 Leipzig, Germany
Scott M. Auerbach
Department of Chemistry and Department of Chemical Engineering, University of Massachusettes, Amherst,
Massachusetts 01003
Siegfried Fritzsche and Reinhold Haberlandt
Universitašt Leipzig, Institut fušr Theoretische Physik, Augustusplatz 10-11, D­04109 Leipzig, Germany
Received 7 November 2001; accepted 28 March 2002
The self-diffusion of ethane in cation-free Linde type A zeolite has been studied by molecular
dynamics simulations for various temperatures. These simulations predict that the diffusivity
decreases with increasing temperature between 150 K and 300 K for a low loading of one molecule
per cage. The rate of cage-to-cage crossings shows the same temperature dependence. We explain
this phenomenon based on an analysis of the activation entropy that controls motion through
eight-ring windows separating adjacent cages. The diffusivity and the cage-to-cage rate constant
both decrease with temperature because heating the system moves ethane away from eight-ring
windows, on average, which increases the entropic barrier for cage-to-cage motion. © 2002
American Institute of Physics. DOI: 10.1063/1.1480011
I. INTRODUCTION
Zeolites1

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry