Flexibility of the framework of zeolite Rho. Structural variation from 11 to 573 K. A study using neutron powder diffraction data

By means of the concept of universal optimum and general principles of inorganic gene, structures of paulingite-related zeolites and minerals have been constructed. The structures of zeolite Rho and paulingite are considered as members of zeolite family generated by the work of 4-colored cellular automaton (CA). The ideal symmetry of the members of the family is cubic, space group Im " 3m, a = 15 + 10n [Å ], where n is a number of the CA cycle (n = 0 for zeolite Rho and 2 for paulingite). A new hypothetical zeolite of the family with n = 1 is predicted and named ISC-1 (Institute of Silicate Chemistry-1); atomic coordinates and theoretical X-ray powder diffraction pattern have been calculated. It appears to be very probable that universal optimum contains all necessary information for its material realization (sharp configurations) and construction of materials with certain type of interaction potential (even with restrictions existing in theory for this potential).

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“…The zero-cycle of the CA shown in Fig. 3 corresponds to the structure of zeolite Rho [12][13][14] that is depicted in Fig. 4a.…”

Section: Paulingite: Cellular Automata Modelingmentioning

confidence: 99%

Where are genes in paulingite? Mathematical principles of formation of inorganic materials on the atomic level

Shevchenko

Krivovichev

2008

Struct Chem

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“…We have studied two different zeolite Rho materials having different unit cell compositions: one with a unit cell composition of Cs 1.35 (SiAl) 48 O 96 D, (hereafter denoted as Rho I) in which the Si/Al ratio is taken to be unity as these atoms were indistinguishable in diffraction experiments (Parise et al 1984), and second with a unit cell composition of D 5.3 Cs 0.7 Al 6 Si 42 O 96 (denoted as Rho II) with a Si/Al ratio of 7 (Fisher et al 1988). There are two important differences between these two structures: (i) the unit cell dimension changes from 1.4601 nm to 1.488 nm and (ii) the center-to-center window diameter changes from 0.543 nm to 0.596 nm.…”

Section: Structure Of Zeolite Rhomentioning

confidence: 99%

Quantum effect induced kinetic molecular sieving of hydrogen and deuterium in microporous materials

2007

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We report here our investigations using Monte Carlo and molecular dynamics (MD) simulations, as well as quasi-elastic neutron scattering experiments, to study the adsorption and diffusion of H 2 and D 2 in zeolite Rho. In the simulations, quantum effects are incorporated via the Feynman-Hibbs variational approach. At low temperatures, we observe a reversal of kinetic molecular sieving in which D 2 diffuses faster than H 2 . Based on fits of bulk data, we suggest new set of potential parameters for hydrogen, with the Feynman-Hibbs variational approach used for quantum corrections. The transport properties obtained from MD simulations are in excellent agreement with the experimental results, with both showing significant quantum effects on the transport at low temperature. The MD simulation results on two different structures of zeolite Rho clearly demonstrate that the quantum effect is very sensitive to pore size. High transport flux selectivity is noted at low temperatures, suggesting feasibility of kinetic isotope separation.

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“…There is no inaccessible pore space in the zeolite Rho structure and so it has a high pore volume. When in the Cs + -form, it shows structural flexibility upon dehydration, as the D8Rs distort to allow better coordination to the Cs + cations [15].…”

Section: Key Inorganic Cation-only Zeolites Pre-1990mentioning

confidence: 99%

Structural Chemistry of Zeolites

Wright

Pearce

2010

Zeolites and Catalysis

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IntroductionZeolites are tetrahedrally connected framework solids, based on silica, with intricate structures that possess channels and cages large enough to contain extra-framework cations and to permit the uptake and desorption of molecules varying from hydrogen to complex organics up to 1 nm in size. Their crystalline structure directly controls their properties and consequently their performance in applications such as ion exchange, separation, and catalysis, and is therefore of great interest to academics and technologists alike. A ''ball and stick'' representation of the most widely used zeolite A, with tetrahedral Al and Si atoms linked by O atoms and with chargebalancing Na + cations, is given in Figure 7.1.Originally discovered as aluminosilicate minerals, synthetic zeolites with a range of compositions are now widely prepared and subsequently modified for a wide range of applications. Many excellent articles, reviews, and books describe the structures of these solids, often in well-illustrated texts [1-3] and online resources [4]. Here we start by summarizing their structural chemistry, beginning with the key features of the best known and most widely used zeolites A and Y. Besides covering the periodic structures of these solids, other features such as secondary mesoporosity are also important to their performance and are discussed. This is followed by a summary of the structural chemistry of some of the important zeolite types prepared using inorganic and simple organic cations prior to the 1990s.Over the last 20 years there has been a major international effort to prepare new zeolitic materials, in the search for improved adsorbents and catalysts. Much of this has focused on the exploration of the use of complex organic alkylammonium ions, synthesized specifically as potential ''templates,'' giving high-silica-content zeolites or pure silica polytypes. The diversity of structures has also been increased by the inclusion of elements other than Al for Si in the framework, which may be either aliovalent (2+ or 3+) or isovalent (4+), and the search for new materials is encouraged by the tantalizing arrays of hypothetical structures that have been shown to be energetically feasible [5,6]. The remarkable products of this ongoing odyssey continue to show new structural features that are both intriguing and of practical importance or potential: increased crystallographic complexity leading to structures with novel

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Flexibility of the framework of zeolite Rho. Structural variation from 11 to 573 K. A study using neutron powder diffraction data

Cited by 67 publications

References 5 publications

Where are genes in paulingite? Mathematical principles of formation of inorganic materials on the atomic level

Where are genes in paulingite? Mathematical principles of formation of inorganic materials on the atomic level

Quantum effect induced kinetic molecular sieving of hydrogen and deuterium in microporous materials

Structural Chemistry of Zeolites

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