Characteristics of MOR-Framework Zeolites Synthesized in Fluoride-Containing Media and Related Ordered Distribution of Al Atoms in the Framework

Abstract

MOR type zeolites with Si/Al ratios of 5.19−9.00 have been synthesized in the presence of fluoride ion (denoted by MS-F). Although MS-F has the same framework topology as conventionally synthesized mordenite (MS-C), the characteristics of MS-F, such as crystal morphology, adsorptivity for benzene and thermal stability, are quite different from MS-C. Solid-state 29Si MAS NMR measurements revealed that the number of Si atoms with a Si(2Al) environment in MS-F is less than that in MS-C of the same Si/Al ratio. Based upon the results of NMR measurements and those of benzene sorption and thermal stability, the ordered distribution of Al atoms in the framework of MS-F was determined by using the connectivity-configuration matrixes method under the restriction of Loewenstein's rule and the 2Al/5-ring avoidance rule. It is suggested that Al atoms are located at T1, T2, and T4 sites in MS-F, which is different from the case of MS-C occupying T1, T2, T3, and T4 sites. The differences in the characteristics between MS-F and MS-C can be explained by the different distribution of Al atoms in their framework.