Synthesis and structure of a CDO zeolite precursor with a high Al content

Abstract

A new CDO zeolite precursor (PreCDO) with a Si/Al ratio of 8.7, the lowest among the layered precursors of this channel-based small-pore zeolite reported so far, has been synthesized using tetraethylammonium (TEA⁺) and tetramethylammonium (TMA⁺) ions in fluoride media. However, both the elemental analysis and ¹³C MAS NMR results reveal the presence of TEA⁺ only in PreCDO, although this layered phase did not crystallize without TMA⁺ or F⁻ present. The structure of PreCDO solved by a combination of synchrotron X-ray diffraction Rietveld analysis and computational modeling shows that the ferrierite (fer) layers of PreCDO are stacked with an interlayer distance of 2.7 Å. Its calcination led to a condensation along the a-axis, yielding a highly crystalline CDO zeolite.