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Issue 24, 2015

High-silica, heulandite-type zeolites prepared by direct synthesis and topotactic condensation

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Abstract

There are both natural minerals and synthetic zeolites that possess the HEU framework topology. These materials have a limited compositional range (Si/Al < 6), and the natural zeolites often contain a large amount of impurities such as Fe3+. The preparation of impurity-free HEU-type zeolites with higher Si/Al ratio could open many areas of application, particularly in catalysis. Here, we report the first high-silica HEU-type zeolite that can be prepared via two different procedures. In the first method high-silica HEU (denoted CIT-8) is prepared using a topotactic condensation mechanism (layered precursor denoted CIT-8P); CIT-8P is obtained from a low-water synthesis in fluoride media. CIT-8 prepared in this manner has a product Si/Al ratio of 9.8 ± 0.7 and a micropore volume of 0.10 cm3 g−1 (measured by nitrogen adsorption). The variable temperature powder X-ray diffraction shows that CIT-8 forms via topotactic condensation from CIT-8P along the b axis. Additionally, high-silica heulandite can be synthesized directly from a hydroxide-mediated reaction mixture (denoted CIT-8H), and has a Si/Al ratio of 6.4 ± 0.3 and a micropore volume of 0.10 cm3 g−1. Both synthesis methods produce zeolites that expand the compositional range of HEU-type zeolites. These synthetic methods allow for the addition of other heteroatoms, and titanium-containing CIT-8 is prepared as an illustrative example.

Graphical abstract: High-silica, heulandite-type zeolites prepared by direct synthesis and topotactic condensation

Supplementary files

Article information


Submitted
31 Mar 2015
Accepted
19 May 2015
First published
27 May 2015

This article is Open Access

J. Mater. Chem. A, 2015,3, 12890-12897
Article type
Paper

High-silica, heulandite-type zeolites prepared by direct synthesis and topotactic condensation

J. E. Schmidt, D. Xie and M. E. Davis, J. Mater. Chem. A, 2015, 3, 12890 DOI: 10.1039/C5TA02354H

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