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

Abstract

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)Å, 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.