Thermally stable modified ZSM-5 zeolite materials with micro porosities and method of making same
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United States of America Patent
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Feb 6, 2001
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N/A
app pub date -
Feb 10, 1999
filing date -
Feb 11, 1998
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Expired
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Abstract
Disclosed herein are thermally stable ZSM-5 zeolite materials. The novel materials having substantially uniform micropores narrower (about 0.49 nm) or wider (about 0.55 nm and above) than those of conventional ZSM-5 zeolite (0.52-0.54 nm). Also disclosed is a preparation method (desilication/reinsertion/stabilization or DRS) for converting conventional ZSM-5 zeolite materials to the thermally stable zeolite materials of the present invention. The method of the present invention comprises the steps of sequentially treating ZSM-5 zeolite with aqueous solutions of sodium carbonate and sodium hydroxide to obtain a desilication of the zeolite, reinserting some of the silicon species (mainly sodium orthosilicate and sodium pyrosilicate) which have been selectively removed from the zeolite framework during the desilication operation, and activating the resulting materials in air or in the presence of steam at high temperatures. The amount of the reinserted silicon species depends on the pore size wanted.
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