Mössbauer studies of high surface area pillared-clays containing mixed metal complexes

Lee, Woo Y.; Tatarchuk, Bruce J.

doi:10.1007/bf02400477

Cited by 15 publications

(3 citation statements)

References 8 publications

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“…The magnetic properties of these grains can be manipulated for tailored applications by altering the volume fraction of the magnetic component. Production of transition metal particles in clay minerals has been of considerable interest in the past. , Recently, Esmer and Yeniyol showed that sepiolite saturated with Fe 2+ cations by cation exchange can be oriented in a magnetic field.…”

Section: Methodsmentioning

confidence: 99%

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

et al. 2003

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This paper presents a small-angle X-ray scattering (SAXS) characterization of the structural organization of deposits of Fe-montmorillonite dispersions formed during frontal ultrafiltration in a magnetic field. The mineral colloidal dispersions are made up of platelike montmorillonite clay particles with average thickness and diameter of about 2 and 500 nm, respectively. A newly developed X-ray-compatible frontal ultrafiltration cell allowed simultaneously applying a transmembrane pressure (5 × 104 Pa) and a magnetic field. The Fe-montmorillonite dispersions obtained by cation exchange reaction displayed regular ordering of the particles with an anisotropic arrangement when subjected to a uniform magnetic field of strengths ranging up to 1.4 T. The degree of anisotropy and the particle concentration profiles as a function of the distance from the filter membrane were deduced from the measured SAXS intensity. For the same volume of filtered permeate (0.26 mL), the deposit formed in a magnetic field of 1 T exhibits an anisotropic arrangement of the platelike particles with their faces aligned parallel to the membrane. In the absence of a magnetic field, the deposits are composed of randomly oriented particles. The application of an external magnetic field produced uniaxially oriented deposits with a higher concentration of particles, and resulted in a higher permeation flow than in the absence of the field.

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Section: Methodsmentioning

confidence: 99%

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

et al. 2003

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“…Mixed pillared clays were first synthesized in 1979, but are still scarce. The few reported publications concern A1-Cr (Carrado et al, 1986a,b;Skoularikis et al, 1988), A1-Zr (Occelli & Finseth, 1986;Occelli & Rennard, 1984;Occelli, 1986Occelli, , 1987, A1-Si (Occelli & Rennard, 1984;Occelli, 1986Occelli, , 1987Vaughan et al, 1979Vaughan et al, , 1981Gaaf et al, 1983;Sterte & Shabtai, 1987), A1-Mg (Vaughan etal., 1979, 1981, A1-M (M = transition metal) (Vaughan, 1987), A1-UO2 ++ (Suib et al, 1986); A1-Ga (Bradley et al, 1991) and also AI-Fe (Carrado et al, 1986b;Skoularikis et al, 1988;Kostapapas et al, 1986;Lee & Tatarchuk, 1988;Lee et al, 1989). For most of the mixed pillared clays containing Fe, M6ssbauer spectroscopy was used but did not clarify the location of the Fe atoms and the existence of mixed (A1-Fe) pillars has not been proved.…”

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confidence: 99%

Pillaring of synthetic hectorite by mixed [Al_13-xFe_x] Pillars

Bergaya

Hassoun²,

Barrault³

et al. 1993

Clay miner.

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The pillaring of a Laponite by alumina pillars, iron pillars and mixed AI-Fe pillars was obtained by a simple in situ method starting from A1CI3 and/or FeCI 3 solutions with different molar ratio Fe/(Fe + AI), and from NaOH solution added simultaneously to the clay suspension. The All 3 pillars were evidenced by XRD and NMR spectra. The density and the charge of these pillars were calculated from the chemical analysis. The Fe pillars (in samples with Fe content >26%) are larger than A113 pillars and slowly reducible by hydrogen temperature programmed reduction (H2TPR), but we do not have any information on their structure. There is also an excess of non-pillar Fe retained by the pillared clays probably as oxyhydroxides. The isomorphic substitution in the mixed (A1-Fe)a3 pillars (in samples with an Fe content >26%) was evidenced by H2TPR results compared to the chemical analyses and by the interpretation of the 27A1 peaks in the NMR spectra.

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“…To prevent the clay layers from sintering, the thermal resistance of the pillars must be increased. One way of achieving this end, which has been tried by a number of authors − is to use mixed pillars. The existence of Al−Ga mixed polyoxycations, has been reported in the study of the hydrolisis of Ga 3+ and Al 3+ salts.…”

Section: Introductionmentioning

confidence: 99%

Differences in Structural, Textural, and Catalytic Properties of Montmorillonite Pillared with (GaAl₁₂) and (AlAl₁₂) Polyoxycations

et al. 1996

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This paper reports the preparation of a pillared montmorillonite using the mixed oligomer [GaO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ . Pillaring was performed with a starting solution having a molar ratio of Al 3+ /Ga 3+) 12, which is equivalent to the stoichiometric ratio of this polyoxycation. To determine the optimum conditions for obtaining the desired product, we varied the OH -/ (Al 3+ + Ga 3+ ) molar ratio in the range 1.5-2.5, which also produced variations in the pH of the oligomeric solution. The most favorable conditions were found to be OH -/(Al 3+ + Ga 3+ ) ) 2.0 and pH ) 3.7. The presence of mixed polyoxycations in the pillars of the synthesized materials was confirmed by NMR studies. The thermal stability and catalytic behavior of these materials in the hydrocracking and hydroisomerization of n-heptane have been compared with those of the material obtained from the same montmorillonite by pillaring with the [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ polyoxycation. The structure of the material pillared with the mixed polyoxycation shows higher thermal stability and retains 65% of its generated microporosity, up to 700 °C. This material also has greater stability in the number and strength of the Lewis acid sites of its pillars, resulting in higher selectivity for the isomerization of n-heptane.

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Mössbauer studies of high surface area pillared-clays containing mixed metal complexes

Cited by 15 publications

References 8 publications

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

Pillaring of synthetic hectorite by mixed [Al_13-xFe_x] Pillars

Differences in Structural, Textural, and Catalytic Properties of Montmorillonite Pillared with (GaAl₁₂) and (AlAl₁₂) Polyoxycations

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Mössbauer studies of high surface area pillared-clays containing mixed metal complexes

Cited by 15 publications

References 8 publications

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

Small-Angle X-ray Scattering Studies of Fe-Montmorillonite Deposits during Ultrafiltration in a Magnetic Field

Pillaring of synthetic hectorite by mixed [Al13-xFex] Pillars

Differences in Structural, Textural, and Catalytic Properties of Montmorillonite Pillared with (GaAl12) and (AlAl12) Polyoxycations

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Pillaring of synthetic hectorite by mixed [Al_13-xFe_x] Pillars

Differences in Structural, Textural, and Catalytic Properties of Montmorillonite Pillared with (GaAl₁₂) and (AlAl₁₂) Polyoxycations