| 1. |
- Gualtieri, Magdalena Lassinantti, et al.
(författare)
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Crack formation in α-alumina supported MFI zeolite membranes studied by in situ high temperature synchrotron powder diffraction
- 2007
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 290:1-2, s. 95-104
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Tidskriftsartikel (refereegranskat)abstract
- Cracks are frequently formed in α-alumina supported MFI membranes during calcination. To better understand crack formation, in situ powder diffraction data were collected during calcination of a type of MFI membrane (ca. 1800 nm thick) which is known to crack reproducibly. In addition, data for MFI powder and a blank support were also collected. Both a synchrotron radiation facility and an in-house instrument were used. The unit cell parameters were determined with the Rietveld method, and the strain in the direction perpendicular to the film surface was calculated for the film as well as for the support. The microstrain in the support was also estimated. Based on the results obtained here, a model for crack formation in this type of MFI membrane was proposed. The lack of cracks in other types of MFI membranes (ca. 500 nm) prepared in our laboratory is also explained by the model. In thicker MFI films, the crystals are well intergrown. During heating, the MFI crystals contract and the α-alumina support expands. Consequently, a thermal stress develops in the composite which eventually leads to formation of cracks in the film and structural defects in the support. In thinner films, the crystals are less well intergrown and the thermal expansion mismatch leads to opening of grain boundaries rather than cracks.
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| 2. |
- Lassinantti-Gualtieri, Magdalena, et al.
(författare)
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Accurate measurement of the thermal expansion of MFI zeolite membranes by in situ HTXRPD
- 2004
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Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 703-709
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Konferensbidrag (refereegranskat)abstract
- Template removal by calcination of MFI type membranes is often accompanied by crack formation. The thermal behavior of MFI type membranes, synthesized with and without masking, was studied to understand the mechanism. Masking prevents growth of zeolite in the interior of the Support during membrane synthesis. Rietveld refinements of powder diffraction data collected in situ at high temperature allowed to accurately determine the change in thermal expansion of the MFI film and the porous alpha-alumina support. During heating, a relatively large contraction of the cell volume during template removal occurred in the zeolite powder and in the film of the membrane prepared with masking. The much smaller decrease in the non-masked sample indicates that this membrane is under stress during heating and as a consequence, cracks are formed. The stress imposed in the membrane prepared without masking may be due to the opposite thermal behavior of the Substrate in combination with strong bonds between the membrane and the support.
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| 3. |
- Lassinantti Gualtieri, Magdalena, et al.
(författare)
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The influence of heating rate on template removal in silicalite-1: An in situ HT-XRPD study
- 2006
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 89:1-3, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The effect of heating rate on thermal behavior of TPA-silicalite-1 during calcination and the reaction kinetics for TPA decomposition were investigated. The cell parameters of the TPA-silicalite-1 during the heating cycles were determined with the aid of high temperature X-ray diffraction data and the Rietveld method. The template decomposition is accompanied by a large contraction of the unit cell. The unit cell dimensions during template removal are not affected significantly by the heating rate. Consequently, the rate of contraction is approximately proportional to the heating rate. The intensity of some diffraction peaks changes during heating, especially the 101/011 and the 200/020 peaks. The intensity change of those peaks shows the same dependence with temperature as the TPA occupancy, indicating that these parameters are related. An analysis of the kinetics for TPA decomposition based on the intensity change of the 101/011 and the 200/020 peaks was performed. The apparent activation energy (Ea) of the template decomposition in silicalite-1 determined with the Kissinger and the Flynn–Wall–Ozawa methods was 138 (±25) and 138 (±29) kJ mol−1, respectively. The reaction order, determined with the method of Kennedy and Clark, was close to 0.5 indicating that the rate-limiting step is mono-dimensional diffusion. Ea was 140 (±30) kJ mol−1, in good agreement with the results obtained with the other methods.With the results presented here, it is possible to discuss possible effects of the heating rate on the crack formation frequently observed in zeolite membranes during calcination.
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| 4. |
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| 5. |
- Lassinantti, Magdalena, et al.
(författare)
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Faujasite-type films synthesized by seeding
- 2000
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 25-34
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Tidskriftsartikel (refereegranskat)abstract
- Thin and continuous Faujasite-type films were synthesized on α-alumina wafers using a seeding technique. Surface modified wafers were seeded with colloidal zeolite Y crystals prior to film growth in a synthesis mixture. The effects of hydrothermal treatment on film thickness, morphology and preferred orientation of the crystals constituting the film were investigated using scanning electron microscopy and X-ray diffraction. During hydrothermal treatment a precipitate formed rapidly, leaving an almost clear solution in the upper part of the reactor. Experiments at 60–100°C were performed with the sample placed in the upper part of the synthesis solution. An increase in the film growth rate with increasing temperature was observed. Adsorbed seeds were shown to be oriented with the {1 1 1} pyramid, parallel to the substrate surface. A change in the orientation with film growth was noted, probably due to the attachment of secondary crystals to the growing film surface. In one experimental series, film growth was effected at the bottom of the tube at 100°C. Faster film growth and multilayered films were obtained. A decrease in the film thickness after prolonged hydrothermal treatment was observed in all experimental series. This is probably due to the dissolution of the film and formation of zeolite P in the synthesis solution. The thicknesses of the films synthesized in this work are in the range of 150–2700 nm. The films are promising candidates for use in membrane applications.
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| 6. |
- Lassinantti, Magdalena, et al.
(författare)
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Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules
- 2001
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Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 67:1-3, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.
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| 7. |
- Lassinantti, Magdalena
(författare)
-
Synthesis, characterization and properties of zeolite films and membranes
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis was aimed to synthesize zeolite films in the absence of organic additives to avoid the potentially detrimental calcination procedure. Furthermore, the support surface was seeded with colloidal seed crystals prior to film growth. This technique has previously been used to prepare thin zeolite films. The films were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and gas permeation experiments. Films of three different types of zeolites were synthesized in this work; FAU-type zeolite, ZSM-5 and zeolite NaA. The thickness of the FAU-type zeolite films could be controlled by varying the synthesis temperature and duration. However, a maximum film thickness was found. Prolonged hydrothermal treatment caused the film thickness to decrease due to the transformation of FAU into zeolite P. The adsorbed seeds were oriented with the <111> pyramid parallel to the surface of the support. During growth, the crystals constituting the films became randomly oriented. The ZSM-5 films were tested as membranes for the separation of butane isomers. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Furthermore, the ZSM-5 membranes were found to be catalytically active, converting ethanol into diethylether and ethylene. The growth of silicious species into the porous support during zeolite NaA membrane synthesis was examined. Higher temperatures of synthesis resulted in relatively more growth into the porous support compared to the film growth on top of the support. By using a multi-step synthesis procedure at low temperature, thicker films with less growth into the support could be prepared.
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| 8. |
- Lassinantti, Magdalena, et al.
(författare)
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Synthesis of thin zeolite Y films on polished α-alumina wafers using a seeding technique
- 1999
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Ingår i: Porous materials in environmentally friendly processes. - Amsterdam : Elsevier. - 0444502440 - 9780444502445 ; , s. 181-187
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Konferensbidrag (refereegranskat)abstract
- Zeolite Y films were synthesized on polished α-alumina wafers by using a seeding technique which includes surface modification, seed adsorption and growth of the seed crystals into a dense film. The film thickness was found to be a linear function of synthesis duration up to a certain point. Further treatment reduced the film thickness. Continuous and crack free films with thicknesses in the range 210 to 2670 nm were synthesized in this work.
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| 9. |
- Sterte, Johan, et al.
(författare)
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Application of the seed-film method for the preparation of structured molecular sieve catalysts
- 2001
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Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 69:1-4, s. 323-329
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Tidskriftsartikel (refereegranskat)abstract
- The seed-film method has been applied for the preparation of various materials of potential interest as structured molecular sieve catalysts. The method has proven to be very flexible and allows for the reproducible preparation of a number of molecular sieve–substrate combinations as well as the control of the materials’ properties of importance in catalytic applications such as zeolite loading, film thickness, film density and crystal orientation. The preparation of thin molecular sieve films on ceramic foams, α-alumina pellets and porous alumina supports as well as various metal surfaces is described. The preparation of zoned coatings with a compositional gradient is also discussed.
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| 10. |
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