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RANDOM WALK TREATMENT OF DUMB-BELL MOLECULES IN AN LTA ZEOLITE AND IN CHABAZITE
 

Summary: RANDOM WALK TREATMENT OF DUMB-BELL MOLECULES
IN AN LTA ZEOLITE AND IN CHABAZITE
Sch¨uringa,b,A., Auerbachb, S.M., Fritzschea, S., Haberlandta.,R.,
a Inst. f¨ur Theoretische Physik, Universit¨at Leipzig, Augustusplatz 10-11, D-04109 Leipzig, Germany
b Dept. of Chemistry and Dept. of Chemical Engineering, University of Massachusettes, Amherst,
MA 01003 USA
ABSTRACT
We analyse the mechanisms of self diffusion in zeolite-guest systems which show a non-monotonic
temperature dependence of the self diffusion coefficient D: ethane in a cation-free LTA zeolite [1] and
chlorine in silicious chabazite. In these systems D is influenced by jump rates for crossing energetic
barriers as well as for crossing entropic barriers [1]. The entropy-controlled jump rates were found to
decrease with increasing temperature. Employing random walk descriptions, simple analytical formu-
las are derived which relate the self diffusion coefficient of the guest molecules with the jump rates
for crossing the different barriers. The simple ansatz we use can be transfered to other zeolite-guest
systems.
INTRODUCTION
The diffusion of guest molecules in zeolites plays an important role in many industrial applications
of various species of these porous materials as the time scale of practically all such applications is
determined by diffusive processes. Zeolites are used as ion exchangers, molecular sieves and adsorbents.
The applications include a wide variety of technical processes e.g. in the petrochemical industry,

  

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

 

Collections: Chemistry