Study of Type-A Zeolites. Part 1:  Mechanism of He and Ne Encapsulation

Abstract

The mechanism of ambient pressure encapsulation of He and Ne in the R and β crystalline cages of type-A zeolites is demonstrated. Reversible and highly selective gas admission and entrapment are readily achieved at characteristic temperatures occurring between 77 and 570 K. The permeability of the zeolitic windows is governed by an interplay between the critical diameter of the encapsulate and the effective apertures dimension, which is shown to be strongly dependent on temperature. The blocking state of the zeolitic apertures is determined by a simultaneous thermal activation of both cation mobility and structural dilation/constriction of crystalline windows. Encapsulation in NaA (4A) principally occurs in the β cages of the Sodalite units, whereas the K-exchange form (3A) offers both R and β encapsulations. The effective free aperture dimension of the Ca exchange form (5A) is found to be too large to allow a practical gas enfoldment in either class of cavities, even at 77 K, where only poor encapsulation is observed. The counterion location vs size dependence, known only from crystallographic data, is sensed here for the first time by an encapsulation process, via the manifestation of different aperture occupancy states. While the blocking extent of the wider O 8 windows of the R cages is consistent with the size of exchangeable cations, a reverse correlation is evident for the narrower O 6 windows of the β cages.

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

“…Other methods for obtaining neon‐bearing compounds are by 1) formation of a network solid around the neon atoms, and 2) insertion of neon atoms into porous network solids, both of which do not rely on neon interactions with the solid, but rather the space requirements for neon encapsulation. Still, there are only a handful of experimental studies at specific temperature and pressure conditions that report neon encapsulation and insertions, such as in fullerene cages, ice structures, and van der Waals nitrogen networks, and as observed in porous zeolitic and silica networks, respectively …”

“…The formation of neon‐bearing network solids can give several insights into the properties of the empty and filled network states. For example, pore dimensions can be rigorously evaluated as a function of temperature from the decapsulation peak profiles of He and Ne, the thermodynamic stability may be increased as found in neon clathrate hydrates, and the mechanical properties of the filled and empty network states can be drastically different, as known with other inclusion species . A combination of structural and computational investigations on the neon‐bearing network solids can provide fundamental information on neon‐neon and neon‐network interactions, which may be used towards synthesis strategies that aim to stabilise exotic chemically‐bound neon compounds as known with the heavier noble gases …”

“…Still, there areo nly ah andful of experimental studies at specific temperature and pressure conditions that report neon encapsulationa nd insertions, such as in fullerenec ages, [4][5][6][7][8] ice structures, [9] and van der Waals nitrogen networks, [10] and as observed in porous zeolitic and silica networks, respectively. [11][12][13][14] The formation of neon-bearing network solids can give several insights into the properties of the empty and filled network states.F or example, pore dimensionsc an be rigorously evaluated as af unction of temperature from the decapsulation peak profiles of He and Ne, [14] the thermodynamic stabilitym ay be increased asf ound in neon clathrate hydrates, [9] and the mechanical properties of the filled and empty network states can be drastically different, ask nown with other inclusion species. [15][16][17][18][19][20][21][22][23][24][25] Ac ombination of structural and computational investigationso nt he neon-bearing network solids can provide fundamental information on neon-neon and neon-network interactions, [9] which may be used towardss ynthesis strategies that aim to stabilisee xotic chemically-bound neon compoundsa s knownw iththe heavier noble gases.…”

Mesoporous Silicon in Drug Delivery Applications

“…In the case of partially blocked pores, pycnometry might give more realistic results than the sorption method. However, there are some possible sources of error, for example trapping of He has been reported, especially if the sample contains micropores 147–149…”

Investigation of the possibility of low pressure encapsulation of carbon dioxide in potassium chabazite (KCHA) and sodium chabazite (NaCHA) zeolites

“…However, more encapsulation studies have been carried out quantitatively in the following decades for different gases on a wide range of zeolites, including Ar in 3A [27,28], Ar in 4A [25,29,30], Kr in 3A [28,31,32], Kr in 4A [25,29], Kr in 5A [32], Xe in 4A [33], He and Ne in 3A and 5A [34], Ne in heulandite and stilbite [35], H 2 in CsA [36,37], H 2 in 4A [38], H 2 in 5A [39], CH 4 in 4A [25,[40][41][42], N 2 in 3A [27], N 2 in CsA [36]. A similar successful encapsulation was made on some other low-porosity zeolites by quantitative measurements of Ar in sodalite and cancrinite [43], Kr in sodalite and cancrinite [43], and He and Ne in tridymite and cristobalite [44].…”