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Title: Al next nearest neighbor, ring occupation, and proximity statistics in ZSM-5

Abstract

The distribution of framework Al in ZSM-5 was simulated for various Si/Al ratios and the results used to determine the fraction of Al atoms in next nearest neighbors (NNN) T sites. All the 4-, 5-, and 6-membered rings were identified in the unit cell and the fraction of these rings with 0, 1, 2, and 3 Al was calculated. Lastly, the radial distribution function of Al-Al pairs, the number of Al`s expected within a sphere of radius, r, centered around an Al(E), and the probability of finding at least one Al within a sphere of radius, r, centered around an Al(P) were calculated for different Si/Al ratios. Based on these results, the probability of locating NNN pairs of Al atoms situated at a distance suitable for the stabilization of M{sup 2+} and [M-O-M]{sup 2+} cations were carried out and then used to determine maximum values for M{sup 2+}/Al and [M-O-M]{sup 2+}/Al. The value of M{sup 2+}/Al is 0.12 for Si/Al = 12 and 0.07 for Si/Al = 24, and the value of [M-O-M]{sup 2+} is 0.30 for Si/Al = 12 and 0.19 for Si/Al = 24. The values of M{sup 2+}/Al obtained theoretically are in reasonable agreement with those observedmore » experimentally for Pd-ZSM-5. A significant finding of their simulation is that Loewenstein`s rule is the dominant factor governing short-range correlations of framework Al atoms, and hence the distribution of NNN pairs of Al atoms. As a consequence, analytical theories that include consideration of Loewenstein`s rule provide rather accurate estimates of the probability of finding Al NNN pairs.« less

Authors:
; ;  [1]
  1. Lawrence Berkeley National Lab., CA (United States)
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
687736
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 186; Journal Issue: 1; Other Information: PBD: 15 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 40 CHEMISTRY; ZEOLITES; ALUMINIUM; DISTRIBUTION; MOLECULAR STRUCTURE; MONTE CARLO METHOD

Citation Formats

Rice, M.J., Chakraborty, A.K., and Bell, A.T. Al next nearest neighbor, ring occupation, and proximity statistics in ZSM-5. United States: N. p., 1999. Web. doi:10.1006/jcat.1999.2544.
Rice, M.J., Chakraborty, A.K., & Bell, A.T. Al next nearest neighbor, ring occupation, and proximity statistics in ZSM-5. United States. doi:10.1006/jcat.1999.2544.
Rice, M.J., Chakraborty, A.K., and Bell, A.T. Sun . "Al next nearest neighbor, ring occupation, and proximity statistics in ZSM-5". United States. doi:10.1006/jcat.1999.2544.
@article{osti_687736,
title = {Al next nearest neighbor, ring occupation, and proximity statistics in ZSM-5},
author = {Rice, M.J. and Chakraborty, A.K. and Bell, A.T.},
abstractNote = {The distribution of framework Al in ZSM-5 was simulated for various Si/Al ratios and the results used to determine the fraction of Al atoms in next nearest neighbors (NNN) T sites. All the 4-, 5-, and 6-membered rings were identified in the unit cell and the fraction of these rings with 0, 1, 2, and 3 Al was calculated. Lastly, the radial distribution function of Al-Al pairs, the number of Al`s expected within a sphere of radius, r, centered around an Al(E), and the probability of finding at least one Al within a sphere of radius, r, centered around an Al(P) were calculated for different Si/Al ratios. Based on these results, the probability of locating NNN pairs of Al atoms situated at a distance suitable for the stabilization of M{sup 2+} and [M-O-M]{sup 2+} cations were carried out and then used to determine maximum values for M{sup 2+}/Al and [M-O-M]{sup 2+}/Al. The value of M{sup 2+}/Al is 0.12 for Si/Al = 12 and 0.07 for Si/Al = 24, and the value of [M-O-M]{sup 2+} is 0.30 for Si/Al = 12 and 0.19 for Si/Al = 24. The values of M{sup 2+}/Al obtained theoretically are in reasonable agreement with those observed experimentally for Pd-ZSM-5. A significant finding of their simulation is that Loewenstein`s rule is the dominant factor governing short-range correlations of framework Al atoms, and hence the distribution of NNN pairs of Al atoms. As a consequence, analytical theories that include consideration of Loewenstein`s rule provide rather accurate estimates of the probability of finding Al NNN pairs.},
doi = {10.1006/jcat.1999.2544},
journal = {Journal of Catalysis},
number = 1,
volume = 186,
place = {United States},
year = {1999},
month = {8}
}