Location of Zn2+ ions in Zn-Y zeolites and the SO2-induced activities in the isomerization of cis-but-2-ene
- 1 January 1981
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 77 (10) , 2429-2438
- https://doi.org/10.1039/f19817702429
Abstract
The SO2-induced isomerizations of cis-but-2-ene, the cis-trans conversion and the double-bond shift, have been studied over Zn-Y zeolites as functions of the degree of zinc-exchange of Na-Y zeolite. The location of Zn2+ in the zeolites has been examined by volumetric measurements of CO and CO2 adsorptions and by infrared absorption measurement of CO adsorption. The Zn2+ introduced may locate preferentially in the small cages (the prisms and the sodalite cages) for zeolites with degree of exchange less than ca. 60%. Above this level of exchange the divalent cations can locate in the supercages. These characteristic locations of Zn2+ have also been reported for the X-type zeolites. The Zn2+ in the supercages are the most effective for causing the SO2-induced cis–trans isomerization for both the X- and Y-type zeolites. The Zn2+ located in the small cages of Y zeolites can both initiate the SO2-induced cis–trans isomerization and generate the Brönsted acid sites necessary for the carbenium ion type isomerization. However, the Zn2+ in the small cages of X zeolites did not show such ability. The different results observed between the X-and Y-type zeolites have been ascribed to the difference in the distributions of SiO4– 4 and AlO5– 4 in the six-membered rings for the two types of zeolite.Keywords
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