Structure of natural and NH4-exchanged Sasbach faujasite: a single-crystal study

Riccardo Fantini,Linda Pastero,Giovanna Vezzalini,Rossella Arletti,Simona Quartieri,Francesco Di Renzo,Fernando Cámara

doi:10.1127/ejm/2018/0030-2745

Abstract

The interest for the environmental, industrial and technological applications of Si-rich zeolites is very high. Among the large-pore zeolites, faujasite is one of the most exploited. The aim of this paper is to obtain detailed structural information on natural and NH4 -exchanged faujasite before using this zeolite for dealumination tests, targeting the realization of large single crystals of allsilica faujasite. As one of the most Si-rich natural samples, faujasite from Sasbach (Na13.64 K0.87 Mg10.46 Ca8.89 Sr0.34 (Al51.95 Si139.57 ) O384 ·272.29 H2 O; space group Fd-3 m; a = 24.6906(2) A) was chosen for study. Single-crystal X-ray diffraction structural refinements of both natural and NH4 -exchanged samples are reported and discussed. In the natural faujasite sample, almost all the extraframework species could be located for the first time. In the NH4 -exchanged sample the ammonium and water molecule sites were located. Ammonium cations occupy two of the sites occupied by the extraframework species in the original mineral.

Highlights

IntroductionZeolites are natural and synthetic microporous materials that, thanks to unique physicochemical properties derived from their structural peculiarities, can be exploited for several purposes, spanning from low-added value agricultural and ion exchange applications to high-added value specialty industrial applications
This paper reports the results of a study aimed at testing the feasibility of the dealumination of large crystals of a natural faujasite sample, needed for single crystal X-ray diffraction experiments
Since the substitution of Si for Al involves the formation of Al salts - usually called extraframework aluminium species (EFAL) - it is necessary that these salts be water-soluble to facilitate their removal from the product

Summary

Introduction

Zeolites are natural and synthetic microporous materials that, thanks to unique physicochemical properties derived from their structural peculiarities, can be exploited for several purposes, spanning from low-added value agricultural and ion exchange applications to high-added value specialty industrial applications. Beyond their traditional applications as shape-selective catalysts and selective sorbents (Bish & Carey, 2001; Corma, 1977), zeolites can be exploited in several new fields, e.g. gas sensors (Baehtz et al, 2000) and biomedical devices (Lulf et al, 2013). It has been found that, depending on external moderate pressure, non-wetting fluids

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