Mössbauer spectroscopic studies of ferrous ion-exchanged Ca-A and Ca, Na-A zeolites

Gao, Zi; Rees, Lovat V.C.

doi:10.1016/s0144-2449(82)80006-7

Cited by 12 publications

(3 citation statements)

References 7 publications

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“…Thus, for the substituted Fe 3+ Td two components were separated by decomposing the spectra: (i) a component with a smaller asymmetry (Fe 3+ Td,1 , Scheme 1), and (ii) another one with larger asymmetry in the electric field around the iron ion (Fe 3+ Td,2 , Scheme 1), as suggested in refs 17 and 18. The extraframework Fe 3+ is probably closer to the octahedral coordination; i.e., it exhibits larger IS (> 0.3 mm/s) and smaller QS (0.8 < QS < 1.2 mm/s) values (analysis of Mo ¨ssbauer data for extraframework iron ions can be found, for example, in refs [29][30][31]. It should be noted (as mentioned previously) that the tetrahedral and octahedral terms are used only as approximations.…”

Section: Resultsmentioning

confidence: 99%

Interpreting the Oxidative Catalytic Activity in Iron-Substituted Ferrierites Using in Situ Mössbauer Spectroscopy

et al. 1998

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Iron- and iron + aluminum-substituted ferrierites (Fe−FER and Fe+Al−FER) have been characterized and their properties compared. Fe−FER exhibits excellent catalytic performance in mild oxidation processes, whereas Fe+Al−FER is hardly active. To specify the source of catalytic activity, in situ Mössbauer studies were performed to distinguish the various iron-containing species. Upon treatment in hydrogen performed on Fe−FER, the temporary presence of the Fe2+ state was evidenced in tetrahedral framework sites, and removal of iron did not occur in significant amounts from these lattice positions. In contrast, similar treatment on Al+Fe−FER results in permanent Fe3+ to Fe2+ reduction and in removal of iron in considerable amounts from the framework sites. From comparison of the behavior of samples and additional analysis of data, it is suggested that dinuclear Felattice−O−Feextralattice centers are present in Fe−FER and that they have a primary role in mild oxidations.

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Section: Resultsmentioning

confidence: 99%

Interpreting the Oxidative Catalytic Activity in Iron-Substituted Ferrierites Using in Situ Mössbauer Spectroscopy

et al. 1998

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“…67 Metal cation replacement will modify the pore opening from 0.4 nm in the normal Na form to 5 nm or 3 nm by ion exchange with aqueous solutions of calcium or potassium salts, respectively. 29,68,69 The typical morphology of zeolite LTA membrane is shown in Fig. 2.…”

Section: -65mentioning

confidence: 99%

LTA zeolite membranes: current progress and challenges in pervaporation

et al. 2017

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a Linde Type A (LTA) zeolite-based membranes have demonstrated excellent selectivity in pervaporation due to their unique structural framework and interaction with water. The development of LTA zeolite membranes for commercial application is limited by some parameters, particularly the complexity of the membrane preparation required to produce reproducible defect-free membranes and the high costs required for the membrane materials. In addition, the high content of Al in the zeolite framework makes the LTA zeolite membrane unsuitable for acidic conditions. A number of modification techniques have been proposed to produce a thin, defect-free, and high permselectivity LTA zeolite membrane with high reproducibility. Two major approaches are generally used to produce defect-free zeolite membranes, i.e. modifying either the seeding step or the synthesis process. Since the self-supported zeolite membrane has low mechanical stability, the LTA zeolite membrane is usually synthesized on an inorganic support to give better properties. Zeolite membrane costs can be reduced by several methods such as replacing the support, manufacturing a higher flux zeolite membrane, and fabricating a polymer-zeolite membrane.One should consider, however, that changing the support can dramatically influence and even reverse the obtained separation behavior. Despite various techniques used to prepare dense LTA zeolite membranes, a facile mass production technique with a highly reproducible result remains a significant challenge. To present a clear background for LTA zeolite and its performances in pervaporation, this paper includes a brief discussion on the recent trends related to LTA zeolite membranes. Some topics are discussed, including the features inherent to LTA zeolite, the transport phenomena in zeolite structures, preparation methods of LTA zeolite membranes, and the challenges associated with

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“…There have been numerous papers on zeolites (101,100,87,321), thin films (83,132,80,20), and slags used in steel making (40,259,108). Goodman and DeKock (113) examined specimens of duckweed, soybean, and peas which had been isotopically enriched in 57Fe by growing them in nutrient solutions which contain 67Fe.…”

Section: Miscellaneous Applicationsmentioning

confidence: 99%