The environment provided by the zeolite channels has been examined in high-silica zeolites having the MFI (ZSM-5), CHA (Chabazite), MOR (Mordenite), TON (ZSM-22), MTW (ZSM-12), FER (Ferrierite), and FAU (Faujasite) structures. Calorimetric measurements of CH 4 and O 2 at ∼210 K showed that structure affects the adsorption properties in a manner which depends on the pore dimensions. The differential heats for CH 4 at low coverage were 28 kJ/mol in FER, 27 kJ/mol in TON, 25 kJ/mol in MOR, 21 kJ/mol in MFI, 20.5 kJ/mol in MTW, 19.5 kJ/mol in CHA, and 14 kJ/mol in FAU. However, calorimetric data for acetonitrile in the acidic forms of these zeolites gave heats that were independent of structure within experimental error, with differential heats for the 1:1 adsorption complexes all being 100 ( 10 kJ/mol. A possible explanation lies in the additional orientation-dependent interaction resulting from the hydrogen bonding. These topology-sensitive, orientational interactions are observable in the temperature-sensitive, methyl-proton, NMR line shapes, where it is found that the barriers to reorientation of 1:1 adsorption complexes are much higher in small-pore zeolites. The implications of these measurements to "confinement" effects in catalysis are discussed.
Complexes of poly(ethylene oxide) and MgC12 having the general formula, MgCI~ 9 (CH~CH~O)n, with n = 4, 8, 12, 16, and 24 have been prepared. These materials are ionic conductors and electronic insulators. The conductivity of MgCI~ 9 (PEO)I~ is highest, and is comparable to that of LiCF3SO3 9 (PEO)9 above 80~ DSC analysis and a study of the temperature dependence of their conductivity indicate that these compositions consist of two crystalline phases, corresponding to pure PEO and the salt-rich complex, and coexisting elastomeric phases. Initial transport number measurements indicate that these materials principally conduct anions.The discovery (1) that poly(ethylene oxide) (PEO) and various alkali metal salts form complexes that have significant ionic conductivities stimulated interest in the science and applications of polymeric solid electrolytes (2). Examples of complexes of this type include LiC104 (PEO), and LiCF:~SO:~. (PEO),, in which n is typically 4 to 8 and PEO is (-CH2CH20-). Progress in this area has recently been reviewed by Armand (3).Electrochemical studies have shown that compositions of PEO with alkali metal salts have negligible electronic conductivity (4) and ionic conductivities as high as 10 -a (f~-cm)-' at 100~ (5). In general, such compositions are composed of both elastomeric and crystalline components, in addition to unreacted PEO. Differential scanning calorimetric (DSC) analysis has indicated that the relative fractions of these constituents as well as the compositions of the elastomeric phases depend on the concentration of salt in the polymer complex, the temperature, and the thermal history of the polymer electrolyte (6). It appears that ionic conductivity occurs principally in the e]astomeric phases (5).Because lithium can be used as a lightweight, high energy density battery electrode, many studies in the field of high conductivity solid electrolytes have been directed toward developing Li conductors. PEO complexes of lithium salts have been particularly interesting as potential solid electrolytes for lithium batteries: Initial reports suggested that some PEO complexes of lithium salts are nearly pure Li conductors (2, 3). However, recent studies agree that these compositions have appreciable anion conductivity (7-9) as well.Solid electrolytes for anions are rather rare. We felt it would be interesting to attempt to suppress the cation conductivity of PEO complex electrolytes in the hope of creating a family of solid state anion conductors. Our approach was to prepare PEO complexes of divalent cations and monovalent anions, in the expectation that doublycharged cations would be less mobile than singly-charged cations.Published precedent for this work is scarce. Most studies of PEO electrolytes have dealt with complexes of monovalent cations and anions, although Fontanella et al.(10) have recently prepared PEO complexes with calcium and barium thiocyanates and found them to have low conductivities. Since beginning this work, we have learned that Patrick et al. (11) and Abantes et ...
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Helium is an importantnatural resourceand it hasgreat importance for scientific research. It is currently extracted mainly from natural gas or inlarge air separation units. Heliumandneonareusually separatedfrom an separationcolumntogether. In order to obtain pure neon and helium they are further purified. This article discusses the main methods of extracting helium from the neon-helium mixture.Having compared rectification, freezing, membrane separation and sorption methods, the authors concluded that the adsorption method allows separation at relatively high temperature intervals and is more energy-efficient than the other methods considered. The paper presents existing examples of the application of the adsorption method for the purification of helium from neon, which have been implemented in Chinaand in the CIS. An overview of adsorption separation on new adsorbents, both on metal-organic bases and on single-walled carbon nanotubes, is also presented. In the future, the authors will conduct experiments to fill in the data gaps on adsorption and desorption of neon-heliummixture on different adsorbents.
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