Pressure-induced penetration of guest molecules in high-silica zeolites: the case of mordenite

Abstract

A synthetic high-silica mordenite (HS-MOR) has been compressed in both non-penetrating (silicone oil, s.o.) and penetrating [methanol : ethanol : water (16 : 3 : 1) (m.e.w.), water : ethanol (3 : 1) (w.e.), and ethylene glycol (e.gl.)] pressure transmitting media (PTM). In situ high-pressure (HP) synchrotron X-ray powder diffraction (XRPD) experiments allowed the unit cell parameters to be followed up to 1.6, 1.8, 8.4, and 6.7 GPa in s.o., w.e., m.e.w., and e.gl., respectively. Moreover, e.gl. was also used as a PTM in in situ HP Raman and ex situ IR experiments. The structural refinement of HS-MOR compressed in e.gl.at 0.1 GPa -the lowest investigated pressure -revealed the presence of 3.5 ethylene glycol molecules per unit cell. The infrared spectrum of the recovered sample, after compression to 1 GPa, is consistent with the insertion of ethylene glycol molecules in the pores. XRPD and Raman spectroscopy experiments performed under pressure indicated the insertion of a small number of guest molecules. Ethylene glycol is partially retained inside mordenite upon pressure release. A symmetry lowering was observed in s.o. above 0.8 GPa, while above 1.6 GPa the patterns indicated a rapid loss of long range order. From ambient pressure (P amb ) to 1.6 GPa, a high cell volume contraction (DV = À9.5%) was determined. The patterns collected with penetrating PTM suggested the penetration of guest molecules into the porous host matrix, starting from a very low P regime. The entrapment of PTM molecules inside micropores contributes to the stiffening of the structure and, as a consequence, to the decrease of the compressibility with respect to that measured in s.o. From the structural point of view, HS-MOR reacts to compression and to the penetration of different guest species with appropriate framework deformations. Interestingly, ethylene glycol is partially retained inside mordenite upon pressure release, which is of importance for potential application of this composite material.

Neon‐Bearing Ammonium Metal Formates: Formation and Behaviour under Pressure

“…In summary, our results have shown that neon, one of the most inert atoms, is able to form an inclusion compound with ammonium metal formates at high pressures. While other examples of either noble gas (He or Ar) or small‐molecule inclusions are known within porous network solids at high pressure, here we observe that the closed porosity of AMF at ambient conditions becomes accessible for inclusion of neon under pressure. This highlights the facile movement of the ammonium cations for allowing neon insertion throughout the metal formate structure upon compression and neon release upon decompression.…”

Supramolecular Organization in Confined Nanospaces

“…They observed that the intrusion of the glycol molecules greatly enhanced the stability of the zeolite framework against pressure‐induced amorphization. Importantly, the insertion of ethylene glycol occurred already at moderate pressures – namely at 0.1 GPa, and showed features of irreversibility upon decompression . The experiment indicated that it is not necessary to use extreme pressures to introduce organic molecules in zeolites.…”

“…The framework composition profoundly affects the uptake of the pressure medium in the zeolite channels, as demonstrated by several experiments ,,,. Whereas it was not possible to incorporate ethanol and methanol inside Na‐mordenite – which already contained six Na + and 19 H 2 O in the unit cell,, Arletti et al . reported the intrusion of these molecules into the empty pores of all silica mordenite ,…”

Steering polymer growth by molding nanochannels: 1,5-hexadiene polymerization in high silica mordenite

“…The sample used in this work is a commercial synthetic highsilica mordenite (HS-MOR; Si/Al=200). The pristine material has been fully characterized and previously used in many studies, namely on the adsorption of pollutants from wastewaters, [78][79][80] on the intrusion of ethylene glycol and water/alcohol mixtures at high pressure (HP) [81] and in the oligomerization of phenylacetylene at HP. [55] Structural data and relevant details of the Rietveld refinements on the pristine HS-MOR here used are reported in Table 1, as well as those of the synthesized host-guest compound HS-MOR hexa, later discussed (the final observed and calculated powder patterns for HS-MOR hexa are provided in the Supporting Information, Figure 1S; atomic coordinates, occupancy factors, thermal parameters and selected bond distances (Å) are reported in Tables 1S and 2S, respectively).…”

“…An additional peak of the difference Fourier map was ascribed to a H2O molecule site in the window between the 12MR and the side pocket, corresponding to the W1 site found in the pristine sample. [81] The refinement of the occupancy factor leads to a total H2O amount of 3.5 molecules per unit cell. This is in agreement with the results of the thermal analysis, indicating a water content of about 2.6 molecules per unit cell (corresponding to 1.5 wt%).…”