Characterization of the pore structure and morphology of some ion-exchanged 12-heteropoly oxometalates

McGarvey, G.B.; Moffat, J.B.

doi:10.1016/0021-9517(91)90130-v

Cited by 42 publications

(15 citation statements)

References 13 publications

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“…The materials did not decompose or become amorphous under the applied conditions. In contrast to literature [29,351 which correlates the high specific surface areas of heteropoly compounds to micropores, the nitrogen adsorptiondesorption isotherms of Cs3A (measured after treatment at 473 K or at 623 K and lo4 mbar for 1 h) reveal the absence of micropores in this compound. The corresponding pore size distributions show that only pores are present of sizes similar to the crystallite size as determined by X-ray analysis.…”

Section: Fig 10 Xrd Coherence Lengths and Internal Stress Incontrasting

confidence: 97%

A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides

Berndt

Herein

Zemlin

et al. 1998

Ber Bunsenges Phys Chem

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Powder X-ray diffraction and cry0 electron diffraction techniques supported by computer simulations were used to determine the secondary structures of the series of heteropoly acid W A ) compounds Cs,%, P V M o 1~0 a . n H~0 (05x14). The structures of the caesium salts (25x14) are simple cubic with space group Pn3m. The free acid exhibits a tricliic lattice (P-1) for the majority of all crystals. A small fraction of thin crystals was detected with simple cubic structure (Pn3m). Computer simulations of the X-ray diffraction patterns suggested that the structure of Cs2H2PVh4011040~5H20 contains defects in the cation lattice. The caesium ion occupancy is U3. [H5O2lf-groups occupy 1/3 of the cation positions. The diffraction pattern of Cs4PVM01~0~5H20 could be simulated when only 3/4 of the anion positions are occupied. C~~H P V M O ,~O~.~H~O crystallises in a simple cubic lattice without any defects.The secondary structures of the investigated heteropoly salts can, therefore, be described by a single structure with variable site occupations, with the exception of Cs$€PVMolIOa~7H2O (caesium ion occupancy of 1 and polyanion occupancy of I). All salts belong to one phase with large stoichiometric variations. A mixture of acid and caesium salt, with the acid epitactly grown on the salts, an intergrowth-structure with varying caesium ion content, mixed crystals as well as the coexistence of a nanocrystalline X-ray-invisible form of free acid besides caesiurn salt could be excluded for the partly neuaalised materials. Selected physico-chemical properties of the HPA compounds, which depend on the caesium ion content, will be rationalised with the knowledge of the secondary structures.

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Section: Fig 10 Xrd Coherence Lengths and Internal Stress Incontrasting

confidence: 97%

A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides

Berndt

Herein

Zemlin

et al. 1998

Ber Bunsenges Phys Chem

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“…The lattice parameter did not appear to be affected by the nature of the anion. Both these parameters are smaller than those reported for the pure heteropoly acids, 4a,b, although the degree of hydration has been noted to have an effect on these values. It was assumed that less water is associated with the salts, when compared to the parent acid, due to the replacement of the protons by nonhydrated cations.…”

Section: Resultscontrasting

confidence: 58%

“…It has been previously noted that the ratio of the intensity of two indexed peaks in the XRD spectrum ( I [110]/ I [222]), decreases with the presence of micropores. , As summarized in Table , the values of the ratio of peak intensities have decreased significantly with the incorporation of the cations into the salts. The smaller ratio observed for the thallium salts indicates that, as has been noted previously, the size of the cation may be an important factor in establishing the microporous structure. In contrast, the elemental composition of the anion appears to play a less significant role.…”

Section: Resultsmentioning

confidence: 98%

“…

2 Surface areas and cation diameters for the silver and thallium salts of the three heteropoly acids. Values obtained previously are included for comparison. , …”

Section: Resultsmentioning

confidence: 99%

“…The crystallographic structure contains interstitial voids which are apparently separated from each other by the terminal oxygen atoms and the hydrated protons, and consequently the solid acids have low BET (N 2 ) surface areas. Substitution of the protons by certain of the monovalent cations from group 1A of the periodic table has been shown, from analyses of the nitrogen adsorption−desorption isotherms, to produce salts which have microporous structures and relatively high surface areas, apparently resulting from the translation and rotation of the Keggin anions so as to remove, at least partially, the barriers separating the interstitial voids from each other . Recent 129 Xe NMR studies have confirmed the existence of the microporous structures …”

Section: Introductionmentioning

confidence: 98%

See 2 more Smart Citations

Metal−Oxygen Cluster Compounds (Heteropoly Oxometalates) of 1B and 3B Monovalent Cations and Their Micropore Structure

Parent

Moffat

1996

Langmuir

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Silver and thallium, representatives from the periodic table's groups 1B and 3B, respectively, were employed as cations to synthesize stoichiometric and nonstoichiometric salts of 12-tungstophosphoric, 12-molybdophosphoric, and 12-tungstosilicic acids. All the solids, except silver 12-molybdophosphate, have high surface areas and microporous structures, as shown from the analysis of nitrogen adsorptiondesorption isotherms obtained at 77 °K. Powder X-ray diffraction, temperature-programmed desorption, infrared spectroscopy, and 1 H MAS NMR spectroscopy are employed to characterize the synthesized materials.

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Effect of Antimony on the Chemical–Physical Features and Reactivity in Isobutyric Acid Oxidehydrogenation of Keggin-Type Heteropolycompounds

Cavani¹,

Tanguy²,

Trifirò³

et al. 1998

Journal of Catalysis

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Characterization of the pore structure and morphology of some ion-exchanged 12-heteropoly oxometalates

Cited by 42 publications

References 13 publications

A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides

A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides

Metal−Oxygen Cluster Compounds (Heteropoly Oxometalates) of 1B and 3B Monovalent Cations and Their Micropore Structure

Effect of Antimony on the Chemical–Physical Features and Reactivity in Isobutyric Acid Oxidehydrogenation of Keggin-Type Heteropolycompounds

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