The Experts below are selected from a list of 177 Experts worldwide ranked by ideXlab platform
Thomas Vogt - One of the best experts on this subject based on the ideXlab platform.
-
pressure induced hydration and order disorder transition in a synthetic potassium gallosilicate zeolite with gismondine topology
Journal of the American Chemical Society, 2008Co-Authors: Thomas VogtAbstract:Two high-pressure phases of a potassium gallosilicate with a gismondine framework (K−GaSi-GIS) were characterized using Rietveld refinements of in-situ high-pressure, high-resolution synchrotron X-...
-
pressure induced hydration and order disorder transition in a synthetic potassium gallosilicate zeolite with gismondine topology
Journal of the American Chemical Society, 2008Co-Authors: Yongjae Lee, Sun Jin Kim, Chi Chang Kao, Thomas VogtAbstract:Two high-pressure phases of a potassium gallosilicate with a gismondine framework (K-GaSi-GIS) were characterized using Rietveld refinements of in-situ high-pressure, high-resolution synchrotron X-ray powder diffraction data. The observed response of the K-GaSi-GIS framework under hydrostatic pressure is a gradual flattening of the so-called "double crankshaft" structural chain units. At pressures below 1.0(1) GPa, additional water molecules from the hydrostatic pressure-transmitting medium are inserted into the potassium-water guest network ("pressure-induced hydration") resulting in a "super-hydrated" high-pressure phase I. As the flattening of the double crankshaft structural units in the GIS framework continues above 1.6 GPa, the ellipticity of the cross-linking 8-ring windows is reduced below a certain threshold, and a disordering of the potassium-water guest structure along the 8-ring channel, characteristic of a disordered high-pressure phase II, is observed. The concerted framework distortion and guest network disordering accommodates the increased hydration level while maintaining the seven-fold coordination environment of the potassium cations to framework oxygen atoms and water molecules. We have thus established the atomistic details of a guest-host order-disorder transition under pressure-induced hydration conditions in a zeolite with GIS framework and compared it to other zeolites during pressure-induced hydration. We find that the structural changes mediated by the extra-framework cations and their coordination environment under PIH conditions are at the core of these different mechanisms and are driving the changes in the ellipticity of pore openings, order-disorder and disorder-order transitions, and framework distortions.
-
dehydration induced water disordering in a synthetic potassium gallosilicate natrolite
Journal of the American Chemical Society, 2007Co-Authors: Ivor Bull, John B. Parise, Aaron J Celestian, Thomas VogtAbstract:A new potassium gallosilicate zeolite with a natrolite topology (approximate formula K8.2Ga8.2Si11.8O40·11.5H2O) was synthesized under hydrothermal conditions and characterized as a function of temperature using monochromatic synchrotron X-ray powder diffraction and Rietveld analyses. Unlike the previously known tetragonal K8Ga8Si12O40·6H2O phase, the as-synthesized material contains twice the amount of water molecules in an ordered arrangement throughout the channels in an orthorhombic (I212121) symmetry. The ordered configuration of water molecules is stabilized below 300 K, whereas heating above 300 K results in a selective dehydration and subsequent disordering of water molecules in a tetragonal (I42d) symmetry. Above 400 K, the material transforms to a fully dehydrated tetragonal phase with a concomitant volume reduction of ca. 15%. The fully dehydrated material transforms back to its original state when rehydrated over a period of up to 2 weeks. The distribution of potassium cations within the chan...
-
pressure induced hydration at 0 6 gpa in a synthetic gallosilicate zeolite
Journal of the American Chemical Society, 2003Co-Authors: Joseph A Hriljac, Jonathan C Hanson, Thomas VogtAbstract:The onset of pressure-induced hydration and volume expansion is lowered to 0.6 GPa via the increased flexibility of the host lattice using isomorphous substitution of Al by larger Ga in a sodium aluminosilicate natrolite.
-
pressure induced volume expansion of zeolites in the natrolite family
Journal of the American Chemical Society, 2002Co-Authors: Thomas Vogt, Joseph A Hriljac, John B. Parise, Gilberto ArtioliAbstract:Powder diffraction patterns of the zeolites natrolite (Na16Al16Si24O80·16H2O), mesolite (Na5.33Ca5.33Al16Si24O80·21.33H2O), scolecite (Ca8Al16Si24O80·24H2O), and a gallosilicate analogue of natrolite (K16Ga16Si24O80·12H2O), all crystallizing with a natrolite framework topology, were measured as a function of pressure up to 5.0 GPa with use of a diamond-anvil cell and a 200 μm focused monochromatic synchrotron X-ray beam. Under the hydrostatic conditions mediated by an alcohol and water mixture, all these materials showed an abrupt volume expansion (ca. 2.5% in natrolite) between 0.8 and 1.5 GPa without altering the framework topology. Rietveld refinements using the data collected on natrolite show that the anomalous swelling is due to the selective sorption of water from the pressure-transmission fluid expanding the channels along the a- and b-unit cell axes. This gives rise to a “superhydrated” phase of natrolite with an approximate formula of Na16Al16Si24O80·32H2O, which contains hydrogen-bonded helical...
Joseph A Hriljac - One of the best experts on this subject based on the ideXlab platform.
-
high pressure and temperature ion exchange of aluminosilicate and gallosilicate natrolite
ChemInform, 2012Co-Authors: Gemma L Hill, Edward Bailey, Neil C Hyatt, Ewan M Maddrell, Paul F. Mcmillan, Martin C Stennett, Joseph A HriljacAbstract:Application of pressure (1 GPa, 150 °C) enables the direct ion exchange of Cs+ for Na+ in both the alumino- and gallosilicate forms of natrolite, which does not occur at ambient pressure.
-
high pressure and temperature ion exchange of aluminosilicate and gallosilicate natrolite
Journal of the American Chemical Society, 2011Co-Authors: Gemma L Hill, Edward Bailey, Neil C Hyatt, Ewan M Maddrell, Paul F. Mcmillan, Martin C Stennett, Joseph A HriljacAbstract:The simultaneous application of high pressure and high temperature has been used to achieve direct ion exchange of large cesium cations for the small sodium cations found in the zeolite natrolite by putting it into a superhydrated state with increased pore size. The larger cations remain trapped upon pressure release, and thus, this method is a means of producing new cationic forms of zeolites.
-
pressure induced hydration at 0 6 gpa in a synthetic gallosilicate zeolite
Journal of the American Chemical Society, 2003Co-Authors: Joseph A Hriljac, Jonathan C Hanson, Thomas VogtAbstract:The onset of pressure-induced hydration and volume expansion is lowered to 0.6 GPa via the increased flexibility of the host lattice using isomorphous substitution of Al by larger Ga in a sodium aluminosilicate natrolite.
-
pressure induced volume expansion of zeolites in the natrolite family
Journal of the American Chemical Society, 2002Co-Authors: Thomas Vogt, Joseph A Hriljac, John B. Parise, Gilberto ArtioliAbstract:Powder diffraction patterns of the zeolites natrolite (Na16Al16Si24O80·16H2O), mesolite (Na5.33Ca5.33Al16Si24O80·21.33H2O), scolecite (Ca8Al16Si24O80·24H2O), and a gallosilicate analogue of natrolite (K16Ga16Si24O80·12H2O), all crystallizing with a natrolite framework topology, were measured as a function of pressure up to 5.0 GPa with use of a diamond-anvil cell and a 200 μm focused monochromatic synchrotron X-ray beam. Under the hydrostatic conditions mediated by an alcohol and water mixture, all these materials showed an abrupt volume expansion (ca. 2.5% in natrolite) between 0.8 and 1.5 GPa without altering the framework topology. Rietveld refinements using the data collected on natrolite show that the anomalous swelling is due to the selective sorption of water from the pressure-transmission fluid expanding the channels along the a- and b-unit cell axes. This gives rise to a “superhydrated” phase of natrolite with an approximate formula of Na16Al16Si24O80·32H2O, which contains hydrogen-bonded helical...
Z Gabelica - One of the best experts on this subject based on the ideXlab platform.
-
characterization of hexagonal and lamellar mesoporous silicas aluminosilicates and Gallosilicates by small angle x ray scattering
Journal of Applied Crystallography, 1997Co-Authors: G Van Den Bossche, R Sobry, F Fontaine, J M Clacens, Z GabelicaAbstract:Various mesoporous silicas and the corresponding aluminosilicates or Gallosilicates have been synthesized using a series of literature or `home made' recipes. The efficiency of Al or Ga incorporation in the siliceous walls of these materials depends markedly on the trivalent source and the evolution (ageing) of the so-formed Si-MIII gel-type phases at different starting pH values and temperatures, after adding the surfactant-structuring compounds. Crystallization at low temperature (e.g. < 373 K) yielded mesoporous compounds with hexagonal topology (MCM-41 type), involving double-layered Si walls possibly partly substituted by Al or Ga. Such structures remain stable after calcination in air at 873 K. When the same gels are crystallized at 423 K for 2 d, lamellar frameworks (MCM-50 type) are preferentially stabilized. They readily collapse on heating. The ultra-small-angle X-ray scattering (USAXS) data and the first part of the SAXS data show a power behaviour that indicates a fractal interface before calcination. After calcination, in the case of MCM-50 type materials, the fractal dimension significantly increases, the fractality region being larger than in the precursor. By contrast, in the case of MCM-41 type materials, the fractal region tends to disappear after calcination. The second part of the SAXS curve reflects the hexagonal or lamellar structure. Some precursors simultaneously exhibit both structures. The hexagonal parameter ranges from 4.6 to 5.8 nm, while the thickness of the wall is estimated to be of the order of 0.7 nm from observations of the satellite peaks in the vicinity of the successive peaks characterizing the hexagonal array. The successive peaks relative to the lamellar structure are consistent with the superposition of two or three layers, the thickness of which are of the order of 3.3, 2.85 and 2.5 nm. Predominant hexagonal structures are maintained after calcination while lamellar structures collapse during calcination. In the case of hexagonal structure, the hexagonal array is slightly contracted.
-
characterization of hexagonal and lamellar mesoporous silicas alumino and Gallosilicates by small angle x ray scattering saxs and multinuclear solid state nmr
Studies in Surface Science and Catalysis, 1995Co-Authors: Z Gabelica, J M Clacens, R Sobry, G Van Den BosscheAbstract:Summary Various mesoporous silicas and the corresponding alumino- or Gallosilicates have been synthesized using a series of literature or home made recipes. The efficiency of the Al or Ga incorporation markedly depends on the trivalent source and the evolution (aging) of the so formed Si-M(III) gel-type phases at different starting pH values, prior to the addition of the surfactant-structuring compounds. Low temperature (e.g. 29 Si-NMR data), eventually partly substituted for by Al or Ga, ( 27 Al- and 71 Ga-NMR). Such structures do remain stable after calcination in air at 600°C (TG-DSC and sorption data). The calcination either results in the expulsion of the (too voluminous) Ga(III) ions from the framework, or to a structural rearrangement of the remaining Al species. The resulting solids still exhibit quite strong Bronsted type acidic sites (NH 3 -TPD data). When the same gels are crystallized at 150°C fro 2 days, lamellar frameworks (MCM-50 type) are preferentially stabilized. They readily collapse upon heating but the final amorphous phase still involves both Al and/or Ga cationic (acidic) species randomly distributed in various structural environments. Small-angle X-ray scattering (SAXS) proved to be the choice method to unambiguously identify different topologies. The actual roughness (smoothness) of the various as-synthesized or calcined phases could be directly related to the fractal dimension derived from SAXS spectra. The presence of peaks at very small diffraction angles allowed us to estimate that the channel lengths of the thermally stable mesoporous materials essentially extend in the 150–200 nm range.
G Van Den Bossche - One of the best experts on this subject based on the ideXlab platform.
-
characterization of hexagonal and lamellar mesoporous silicas aluminosilicates and Gallosilicates by small angle x ray scattering
Journal of Applied Crystallography, 1997Co-Authors: G Van Den Bossche, R Sobry, F Fontaine, J M Clacens, Z GabelicaAbstract:Various mesoporous silicas and the corresponding aluminosilicates or Gallosilicates have been synthesized using a series of literature or `home made' recipes. The efficiency of Al or Ga incorporation in the siliceous walls of these materials depends markedly on the trivalent source and the evolution (ageing) of the so-formed Si-MIII gel-type phases at different starting pH values and temperatures, after adding the surfactant-structuring compounds. Crystallization at low temperature (e.g. < 373 K) yielded mesoporous compounds with hexagonal topology (MCM-41 type), involving double-layered Si walls possibly partly substituted by Al or Ga. Such structures remain stable after calcination in air at 873 K. When the same gels are crystallized at 423 K for 2 d, lamellar frameworks (MCM-50 type) are preferentially stabilized. They readily collapse on heating. The ultra-small-angle X-ray scattering (USAXS) data and the first part of the SAXS data show a power behaviour that indicates a fractal interface before calcination. After calcination, in the case of MCM-50 type materials, the fractal dimension significantly increases, the fractality region being larger than in the precursor. By contrast, in the case of MCM-41 type materials, the fractal region tends to disappear after calcination. The second part of the SAXS curve reflects the hexagonal or lamellar structure. Some precursors simultaneously exhibit both structures. The hexagonal parameter ranges from 4.6 to 5.8 nm, while the thickness of the wall is estimated to be of the order of 0.7 nm from observations of the satellite peaks in the vicinity of the successive peaks characterizing the hexagonal array. The successive peaks relative to the lamellar structure are consistent with the superposition of two or three layers, the thickness of which are of the order of 3.3, 2.85 and 2.5 nm. Predominant hexagonal structures are maintained after calcination while lamellar structures collapse during calcination. In the case of hexagonal structure, the hexagonal array is slightly contracted.
-
characterization of hexagonal and lamellar mesoporous silicas alumino and Gallosilicates by small angle x ray scattering saxs and multinuclear solid state nmr
Studies in Surface Science and Catalysis, 1995Co-Authors: Z Gabelica, J M Clacens, R Sobry, G Van Den BosscheAbstract:Summary Various mesoporous silicas and the corresponding alumino- or Gallosilicates have been synthesized using a series of literature or home made recipes. The efficiency of the Al or Ga incorporation markedly depends on the trivalent source and the evolution (aging) of the so formed Si-M(III) gel-type phases at different starting pH values, prior to the addition of the surfactant-structuring compounds. Low temperature (e.g. 29 Si-NMR data), eventually partly substituted for by Al or Ga, ( 27 Al- and 71 Ga-NMR). Such structures do remain stable after calcination in air at 600°C (TG-DSC and sorption data). The calcination either results in the expulsion of the (too voluminous) Ga(III) ions from the framework, or to a structural rearrangement of the remaining Al species. The resulting solids still exhibit quite strong Bronsted type acidic sites (NH 3 -TPD data). When the same gels are crystallized at 150°C fro 2 days, lamellar frameworks (MCM-50 type) are preferentially stabilized. They readily collapse upon heating but the final amorphous phase still involves both Al and/or Ga cationic (acidic) species randomly distributed in various structural environments. Small-angle X-ray scattering (SAXS) proved to be the choice method to unambiguously identify different topologies. The actual roughness (smoothness) of the various as-synthesized or calcined phases could be directly related to the fractal dimension derived from SAXS spectra. The presence of peaks at very small diffraction angles allowed us to estimate that the channel lengths of the thermally stable mesoporous materials essentially extend in the 150–200 nm range.
Suman K Jana - One of the best experts on this subject based on the ideXlab platform.
-
benzylation of benzene by benzyl chloride over fe zn ga and in modified zsm 5 type zeolite catalysts
Applied Catalysis A-general, 2002Co-Authors: Vasant R. Choudhary, Suman K JanaAbstract:Liquid phase benzylation of benzene by benzyl chloride to diphenylmethane over H-ZSM-5, H-gallosilicate (MFI), H-galloaluminosilicate (MFI), H-ferrosilicate (MFI), H-ferroaluminosilicate (MFI), Fe 2 O 3 /H-ZSM-5, ZnO/H-ZSM-5, Ga 2 O 3 /H-ZSM-5 and In 2 O 3 /H-ZSM-5 zeolites (at 60 and 80°C) has been investigated. A complete or partial substitution of Al in H-ZSM-5 zeolite by Fe or Ga or an impregnation of the zeolite by Fe 2 O 3 , ZnO, Ga 2 O 3 or In 2 O 3 makes the zeolite highly active in the benzylation process. The redox function created due to the modification of the H-ZSM-5 zeolite by Fe, Zn, Ga or In seems to play very important role in the benzylation process. However, all these catalysts show a significant induction period for the reaction. The Ga 2 O 3 /H-ZSM-5 catalyst showed high benzene benzylation activity even in the presence of moisture in the catalyst and/or in the substrate. However, the reaction induction period is increased markedly with increasing the moisture and it is reduced by removing the moisture from the catalyst by refluxing with moisture-free benzene. It is also reduced by the HCl gas pretreatment to the catalyst before the benzylation reaction. The Ga 2 O 3 /H-ZSM-5 and In 2 O 3 /H-ZSM-5 catalysts showed excellent reusability in the benzene benzylation. Kinetics of the benzene benzylation (using an excess of benzene) over the H-GaMFI, H-GaAlMFI, H-FeMFI, Ga 2 O 3 /H-ZSM-5 and In 2 O 3 /H-ZSM-5 catalysts have also been thoroughly investigated. A plausible reaction mechanism for the reaction over the modified ZSM-5 zeolite catalysts is proposed.
-
alkylation of benzene by benzyl chloride over h zsm 5 zeolite with its framework al completely or partially substituted by fe or ga
Catalysis Letters, 1999Co-Authors: Vasant R. Choudhary, Suman K Jana, B P KiranAbstract:Liquid-phase benzylation of benzene by benzyl chloride to diphenylmethane over H-ZSM-5, H-gallosilicate(MFI), H-galloaluminosilicate(MFI), H-ferrosilicate(MFI) and H-ferroaluminosilicate(MFI) zeolites at 80°C has been investigated. A complete or partial substitution of Al in H-ZSM-5 zeolite by Fe or Ga results in a drastic increase in the catalytic activity of the zeolite in the benzylation process. The redox function of the zeolite is relatively more important than its acid function in the benzylation process.
