STRUCTURAL CHEMICAL ZONING IN THE BOUNDARY PHASE ZEOLITE TNU-7 (EON)

Abstract

The synthetic details of the novel large-pore gallosilicate zeolite TNU-7 (EON) under wholly inorganic conditions, together with those of gallosilicate mazzite (MAZ) and mordenite (MOR) which themselves consist of the two structural components of TNU-7, are described. When the Na+ ion is used as an inorganic structure-directing agent, crystallization of the pure form of each material was found to be highly sensitive both to the presence of Ga in the synthesis mixture and to its concentration. Rietveld refinements based on the synchrotron X-ray diffraction data for the as-made Na+ form of these three gallosilicate zeolites, as well as for the Cs+- and Sr2+- exchanged forms of TNU-7, allow us to determine the favored extraframework cation positions in each material. Comparison of their calculated extraframework cation charge values per tetrahedral site suggests the existence of "structural chemical zoning" within the TNU-7 structure: it appears that this metastable zeolite is composed of maz and mor layers which are rich and poor in Ga, respectively.