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Modeling Proton Jumps in HY Zeolite: Effects of Acid Site Heterogeneity Usha Viswanathan, Justin T. Fermann, Leanna K. Toy, Scott M. Auerbach,*,,
 

Summary: Modeling Proton Jumps in HY Zeolite: Effects of Acid Site Heterogeneity
Usha Viswanathan, Justin T. Fermann, Leanna K. Toy, Scott M. Auerbach,*,,
Thom Vreven,§ and Michael J. Frisch§
Department of Chemistry and Department of Chemical Engineering, UniVersity of Massachusetts Amherst,
Amherst, Massachusetts 01003, and Gaussian, Inc., 340 Quinnipiac Street Building 40,
Wallingford, Connecticut 06492
ReceiVed: July 27, 2007; In Final Form: September 21, 2007
We have computed the total mean rate coefficient for proton transfer in bare H-Y zeolite, for comparison
with NMR experiments and previous calculations. We computed proton-transfer energies using two-layer
ONIOM calculations on an 8T-53T cluster, where xT indicates x tetrahedral atoms. Rate coefficients were
computed using truncated harmonic semiclassical transition state theory. The zero-point energy (ZPE) corrected
proton site energies in H-Y (FAU structure) were found to be O3 (0 kJ mol-1
), O1 O2 (16.1 kJ mol-1
), and
O4 (17.5 kJ mol-1
), in quantitative agreement with previous calculations and in qualitative agreement with
neutron diffraction occupancies. A new local minimum denoted O2* (31.4 kJ mol-1
relative to O3) was
located, with a proton bound to O2 but pointing into the sodalite cage. Transition states between each pair of
minima were fully characterized, yielding ZPE corrected activation energies ranging from 35.5 to 123.4 kJ

  

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

 

Collections: Chemistry