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Further investigations on Constraint Index testing of zeolites that contain cages

Carpenter, John R. and Yehb, Sheila and Zones, Stacey I. and Davis, Mark E. (2010) Further investigations on Constraint Index testing of zeolites that contain cages. Journal of Catalysis, 269 (1). pp. 64-70. ISSN 0021-9517. http://resolver.caltech.edu/CaltechAUTHORS:20100225-080357989

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Abstract

Zeolites such as SSZ-25 and SSZ-35 exhibit Constraint Indexes (CI) lower than expected. Two hypotheses for the origin of the lower CI values are that partial cages on the external surface of the zeolites significantly contribute to the overall conversions and that the large cages within the crystalline structures provide less steric hinderence at the active site than would be expected from the size of the pores. The effect of external surface activity is observed by comparing the as-synthesized materials to those passivated via dealumination with ammonium hexafluorosilicate. The external surface dealumination is verified by XPS and by the reduction in reactivity toward isopropanol dehydration observed from materials still containing their SDAs. The external surface of calcined zeolites is shown to have little influence on the CI value. Cage accessibility is investigated by comparisons of structures having larger cages to those that do not and by following the time dependent behavior of the CI values for these materials. The presence of large cages in the zeolites is shown to lower the CI values below those expected from the pore sizes, and the time dependence of the CI value can provide insight into the existence of these larger cage structures.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.jcat.2009.10.016DOIUNSPECIFIED
Additional Information:© 2009 Elsevier Inc. Received 6 August 2009; revised 8 October 2009; accepted 19 October 2009. Available online 22 November 2009. We would like to thank the Chevron Energy Technology Co. for financial support of this work and Kelly Harvey for assistance with the graphics and manuscript preparation.
Funders:
Funding AgencyGrant Number
Chevron Energy Technology Co. UNSPECIFIED
Subject Keywords:Constraint Index test; Zeolite shape selectivity; Cage effect; Hexane cracking; Structure-selectivity relationship; External surface dealumination
Record Number:CaltechAUTHORS:20100225-080357989
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100225-080357989
Official Citation:John R. Carpenter, Sheila Yeh, Stacey I. Zones, Mark E. Davis, Further investigations on Constraint Index testing of zeolites that contain cages, Journal of Catalysis, Volume 269, Issue 1, 1 January 2010, Pages 64-70, ISSN 0021-9517, DOI: 10.1016/j.jcat.2009.10.016. (http://www.sciencedirect.com/science/article/B6WHJ-4XS0D78-1/2/40e9ef69834808eabb792aa451e8d73a)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17585
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:02 Mar 2010 23:50
Last Modified:26 Dec 2012 11:48

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