Noble Gas Immobilization in Zeolites

Abstract

It was discovered that the noble gases Ar, Kr and Xe can be trapped firmly in type A zeolites as well as in mordenites and chabazites when the molecular sieves are hydrothermally vitrified at temperatures between 340 and 650°C in the presence of pressurized gas. The occurrence of trapping in an amorphous nonzeolitic species was demonstrated by X‐ray diffraction, neutron scattering and electron scattering. The change in structure of loaded zeolites is also manifested by a substantial loss in sorption capacity for water as well as an almost complete disappearance of the specific surface area. – The gas release rates at temperatures below 550°C were found to be extremely low. The activation energies for the diffusion of Kr through amorphous Ca and Mg exchanged 5 A zeolite were determined to be 209 ± 15 and 187 ± 16 kJ/mol respectively. The estimated diffusion coefficients are exceedingly small. The trapped gas is neither liberated by hot water nor by liq. Rb at 150°C.

Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems

“…Trapping noble gases on surfaces and especially within nano-sized cages similar to those of zeolites can provide an unprecedented level of detail on the adsorption processes when surface science tools are used, which may further stimulate the manipulation of these trapped gases with atomic precision. Note that trapping of noble gases has been previously achieved using three-dimensional porous materials 13 14 15 . Surface immobilization of noble gases can be typically achieved by condensation at cryogenic temperatures 16 .…”

“…Previous reports show that the 2D silica film is permeable to small molecules, such as H 2 , CO and O 2 (refs 19 , 20 , 21 , 22 ), with a diffusion energy barrier of 0.5 eV for CO to go through the hexagonal prisms recently calculated from density functional theory (DFT) 21 . Note here the analogy with 3D zeolites, readily used as adsorbents and molecular sieves 13 23 . Another noble gas, xenon, has been shown to adsorb on zeolite chabazite, which is composed of the same secondary building block (the hexagonal prism) that makes up the 2D (alumino)silicate framework used here 24 .…”

Milestone Report - M4FT-15OR03120218 - A Literature Search on the Effects of the Decay of ⁸⁵Kr to ⁸⁵Rb on Long-term Storage Options

“…Given their affinity for Kr, zeolites might also be used to remove both Xe and Kr from off-gas streams. Other authors have also investigated zeolites as a matrix to encapsulate Xe or Kr (Bazan et al 2011;Heo et al 1999;Jameson et al 1997;Sears et al 2005;Seoung et al 2014;Simon et al 2015;Vansant et al 1984;Penzhorn et al 1982a). Therefore, we discuss the possible effects of the transmutation of Kr to Rb in a brief review of the relevant literature associated with Rb-bearing zeolites.…”

“…Historically, concerns have been expressed that the decay product of 85 Kr, 85 Rb, could cause corrosion and weakening in the canisters, ultimately leading to premature failure and release of 85 Kr. Vapor deposition in metal, immobilization in zeolites and immobilization in MOF materials have all been investigated as alternative storage media for Kr (Whitmell 1982;Whitmell 1985;Christensen et al 1982;Christensen et al 1983;Knecht 1977;Miyake et al 1984;Penzhorn et al 1982a;Maeck and Pence 1970;Soelberg et al 2008;Mueller et al 2006b). Even these storage methods may still be susceptible to the chemical effects caused by decay of 85 Kr to 85 Rb.…”

“…However, other solid sorbent-based methods are being investigated for the removal of Kr. These processes can involve zeolites (Christensen et al 1982;Christensen et al 1983;Knecht 1977;Miyake et al 1984;Penzhorn et al 1982a), Ag-loaded zeolites (Maeck and Pence 1970), or metal organic framework (MOF) materials (Soelberg et al 2013;Banerjee et al 2015;Liu et al 2014;Liu et al 2012;Thallapally et al 2013a).…”