The Influence of the Framework and Extraframework Content on the High Pressure Behavior of the GIS Type Zeolites: The Case of Amicite.

This paper reports a study, performed by in-situ synchrotron X-ray Powder Diffraction, of the high pressure behavior of the natural zeolite amicite [K4 Na4 (Al8 Si8 O32 )\ub710H2 O], the GIS-type phase with ordered (Si, Al) and (Na, K) distribution. The experiments were carried out up to 8.13(5) GPa in methanol:ethanol:water = 16:3:1 (m.e.w.) and 8.68(5) GPa in silicone oil (s.o.). The crystal structure refinements of the patterns collected in m.e.w. were performed up to 4.71(5) GPa, while for the patterns collected in s.o. only the unit cell parameters were determined as a function of pressure. The observed framework deformation mechanism\u2014similar to that reported for the other studied phases with GIS topology\u2014is essentially driven by the distortion of the \u201cdouble crankshaft\u201d chains and the consequent changed shape of the 8-ring channels. The pressure-induced over-hydration observed in the experiment performed in aqueous medium occurs without unit cell volume expansion, and is substantially reversible. A comparison is made with the high pressure behavior of the other GIS-type phases, and the strong influence on compressibility of the chemical composition of both framework and extraframework species is discussed

Compressibility behavior and pressure-induced over-hydration of zeolite K-AlSi-L

This paper reports a study, performed by in-situ synchrotron X-ray powder diffraction, of the high-pressure behavior of zeolite L. The experiments were performed using both penetrating (methanol: ethanol: water mixture, m.e.w.) and non-penetrating (silicon oil, s.o.) pressure transmitting media (PTM) to study the compressibility and the possible pressure-induced hydration (PIH) of this synthetic zeolite, technologically relevant as host-guest system exploited in numerous application fields. The experiments were performed from Pamb to 6.2 and 6.3 GPa in s.o. and m.e.w., respectively. The crystal structure refinements were performed up to 6.3 GPa and 3.1 GPa for the patterns collected in m.e.w. and s.o., respectively, while the unit cell parameters were determined in the whole pressure range for both media. A strong PIH effect is evident when zeolite L is compressed in m.e.w. and the over-hydration is essentially ascribable to the filling of most the H2O sites, to the appearance of a new H2O site and to the partially filling of the K sites. The over-hydration starts at a very low pressure (0.5 GPa) and the maximum H2O content can be estimated in 31.1 H2O molecules, against the original value of 18. The PIH is completely reversible upon P release. The main difference between the compression behavior of zeolite L in the two media is the higher compressibility in the non-penetrating one, evidenced by ΔV=− 6.3% and −9.9% in m.e.w. and s.o, respectively. Our data are consistent with the general behavior of zeolites compressed with penetrating media, when the intrusion of H2O molecules hinders the effects of the applied pressure. The results of this work are compared with those obtained on a K-gallosilicate with LTL topology, where PIH induces the formation of H2O nanotubes inside the zeolite channel

Supramolecular organization of water–ethanol solution in ferrierite under pressure

Turning disorder into organization is a key issue in science. In particular, supramolecular organization induced by external stimuli has opened new paths for the bottom-up fabrication of nanostructures. By using a combined strategy based on the synergy of X-ray powder diffraction experiments and modeling studies [1], we showed that high pressure - in combination with the shape and space constraints of a hydrophobic all-silica zeolite - separate an ethanol–water liquid mixture into ethanol dimer wires and water tetramer squares (Figure 1). Separation of ethanol from water was accomplished in an all-silica ferrierite (Si-FER), by using as pressure transmitting medium a mixture of (1:3) ethanol and water in the 0.20 to 1.34 GPa pressure range. The system was studied in situ by high-pressure synchrotron X-ray powder diffraction at BM01 beamline at ESRF and refined via first principles modeling. Upon separation, the confined supramolecular blocks alternate in a binary two-dimensional architecture that remains stable upon complete pressure release. This unique architecture might rationalize the high selectivity of Si-FER in the separation of alcohol–water mixtures, a key issue in biofuel production. Moreover, as ferrierite is an exceptionally selective catalyst for biofuel synthesis in its hydrophilic Brønsted acid form, while only its pore entrances are actually exploited, we suggest that pressure could also be beneficial for the catalytic performance by enforcing the intrusion of reactants. These results support the combined use of high pressures and porous networks as a viable strategy for driving the organization of molecules or nano-objects towards complex, pre-defined patterns relevant for the realization of novel functional nanocomposites. [1] Arletti, R., Fois, E., Gigli, L., Vezzalini, G., Quartieri, S., Tabacchi, G. (2017) Angewandte Chemie, DOI: 10.1002/anie.20170021

Differential penetration of ethanol and water in Si-chabazite: high pressure dehydration of azeotrope solution..

This study is aimed to shed light on the mechanisms at the basis of the differential penetration of alcohol and water in hydrophobic zeolites at ambient (Pamb) and non-ambient pressure. Here we report the effects of the penetration of water and alcohol in an all-silica chabazite (Si-CHA) compressed with an ethanol/water azeotrope solution (ethanol: water=95.63 : 4.37 by mass %). We collected in situ synchrotron X-ray Powder Diffraction (XRPD) data in order to monitor the structural modifications induced by the fluid penetration and to investigate the guest-guest and host-guest interactions. First principles molecular dynamics simulations allowed to complete the structural description at high pressure, providing an atomistic level description of the guest-guest hydrogen bond network. For a comprehensive understanding of the processes involving the Si-CHA + azeotrope interactions, both the zeolite and the alcohol/water solution were firstly investigated separately under pressure. The results obtained prove that both H2O and ethanol penetrate Si-CHA porosities even at Pamb. However, while in these conditions the H2O/ethanol ratio adsorbed inside Si-CHA is similar to that of the external azeotrope solution, under pressure the zeolite extra-framework content corresponds to a composition much richer in H2O than the azeotrope one. Hence, our results suggest that a dehydration effect occurred on the azeotrope solution, promoted by pressure. In addition, the experiment performed to test the elastic behavior of Si-CHA with a nonpenetrating pressure transmitting medium interestingly indicates that Si-pure chabazite is the most compressible zeolite among those up to now studied in silicone oil