Reinvestigation into the synthesis of zeolites using diquaternary alkylammonium ions (CH3)(3)N+(CH2)(n)N+(CH3)(3) with n=3-10 as structure-directing agents

Abstract

Zeolite syntheses using a series of flexible, linear diquaternary ammonium ions (CH(3))(3)N(+)(CH(2))(n)N(+)(CH(3))(3) (Me(6)-diquat-n with n = 3-10) have been reinvestigated in order to explore the effects of inorganic synthesis variables, especially of the type and concentration of alkali cations, on the phase selectivity of the crystallization. Among the ammonium ions studied here, the Me(6)-diquat-3 ion was found to decompose to form tetramethylammonium ions under the highly basic conditions, leading to the crystallization of zeolite omega, which is a new example of in situ modification of structure-directing agents in zeolite synthesis. Unlike the other seven diquaternary cations, on the other hand, the Me(6)-diquat-5 ion exhibited a considerable diversity in the phase selectivity; this cation can crystallize five different zeolite structures (i.e., EU-1, ZSM-48, ZSM-12, MCM-22, and mordenite), depending on the oxide composition of synthesis mixtures. A combination of (1)H-(13)C CP MAS NMR and Raman measurements shows that the host-guest interactions in these five zeolites containing Me(6)-diquat-5 as a guest molecule are notably different from one another. (C) 2003 Elsevier Inc. All rights reserved.