Synthesis of a merlinoite-type zeolite with an enhanced Si/Al ratio via pore filling with tetraethylammonium cations

A merlinoite type zeolite with an enhanced Si/Al ratio (around 3.8) compared to known isostructural materials has been synthesised hydrothermally from a gel with Si/Al=5 in the presence of tetraethylammonium and K+ cations. The zeolite has been characterised by a number of techniques and in its calcined form the structure was refined from synchrotron powder X-ray diffraction data [a = 14.1291 (10), b = 14.1308(10), c = 9.9274(5)Angstrom, Immm]. The different techniques reveal the enhanced Si/Al ratio of the zeolite. Tetraethylammonium is occluded within the tridimensional small pore channels, forcing the K+ and hence the Al content to diminish by 30-50% compared to conventional merlinoite-type zeolites. The thermal stability of the material is greatly improved, although if K+ cations in the zeolite are exchanged by NH4+ the stability decreases as a function of the degree of exchange, suggesting a low stability for the acidic form of merlinoite.