Structure analysis of a BEC-type germanosilicate zeolite including the location of the flexible organic cations in the channels

Abstract

A BEC-type zeolite (polymorph C of zeolite beta) with low germanium content (Si : Ge = 5.1) has been synthesised using the flexible linear diquaternary cationic form of pentamethyldiethylenetriamine (2,2′-(methylazanediyl)bis(N,N,N-trimethylethanammonium) as the organic structure-directing agent (SDA). The distribution of germanium within the framework and the location of the SDA within the pores have been determined by analysing synchrotron X-ray powder diffraction data collected on the as-synthesised form. The findings, which are corroborated by 13C and 19F NMR data, indicate that the structure of the SDA is retained during the synthesis and that the Ge atoms occupy only sites in the double 4-ring. Although the BEC framework structure has a three-dimensional 12-ring channel system, the SDA molecules are found to orient themselves in two dimensions along the channels running parallel to the a and b axes.