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10600 J. Phys. Chem. 1995,99, 10600-10608 Transport Theory for Cationic Zeolites: Diffusion of Benzene in Na-Y
 

Summary: 10600 J. Phys. Chem. 1995,99, 10600-10608
Transport Theory for Cationic Zeolites: Diffusion of Benzene in Na-Y
Scott M. Auerbach,**tJl&Neil J. HensontJIAnthony K. CheethamJf*,lland Horia I. MetiuT3S
Departments of Chemistry, Materials, Physics, and the Materials Research Laboratory,
University of Califomia, Santa Barbara, Califomia 93106
Received: January 5, 1995; In Final Form: April 28, 1995@
We have modeled benzene diffusion in Na-Y zeolite (%:A1 = 2.0) over the temperature range 100-500 K.
We apply the kinetic Monte Carlo random walk model, with activation energies derived from a new zeolite-
hydrocarbon potential energy surface (PES). An Arrhenius fit yields the apparent activation energy E, = 41
kJ mol-', as compared with the previously determined experimental values 14-27 kJ mol-'. Minimum
energy paths from the new PES demonstrate "cartwheel" and "skateboard" hopping mechanisms for benzene
in Na-Y. Analysis of the results suggests that activation energies from long length scale diffusion
measurements, e.g. pulsed field gradient NMR, should be interpreted as site-to-window activation energies,
whereas those from short length scale experiments, e.g. spin-lattice relaxation NMR, correspond to intracage
site-to-site activation energies.
I. Introduction
The structural, thermochemical, and dynamical properties of
adsorbedhydrocarbonsplay a central role in catalyticprocesses
that take place within the cavities of zeolites and other shape-
selective,microporouscatalysts. Selectivity,for example, may

  

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

 

Collections: Chemistry