| 1. |
- Hedlund, Jonas, et al.
(författare)
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The synthesis and testing of thin film ZSM-5 catalysts
- 2004
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 59:13, s. 2647-2657
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and catalytic testing of thin ZSM-5 films on glass and alumina beads is described. The thickness of the ZSM-5 films was controlled to 150, 350, 800 and 2300 nm. The samples were characterised by SEM, gas adsorption and p-xylene isomerisation and 1,3,5-tri-isopropyl benzene cracking test reactions. A reaction–diffusion model adequately described the p-xylene isomerisation data. Estimates of model parameters were obtained by fitting the model to the experimental data. In both cases, the reaction rate constant increased with increasing film thickness. The xylene reaction data showed that secondary reaction products increased as expected with increasing diffusion limitations, but the increase was less than that predicted by the variation of thickness only. The trends in the reaction data could be explained by more defects in the thicker films and/or partial poisoning of the zeolite by mobile support cations in thinner films and/or orientation effects.
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| 2. |
- Möller, K.P., et al.
(författare)
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The catalytic evaluation of structured zeolite catalysts
- 2004
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Ingår i: International Journal of Chemical Reactor Engineering. - : Walter de Gruyter GmbH. - 1542-6580. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- ZSM-5 films, with thicknesses between 150 and 2300 nm, supported on 3 mm diameter alumina beads are characterised in terms of their catalytic activity and selectivity for tri-isopropylbenzene cracking and para-xylene isomerisation at 450°C. A reaction-diffusion model adequately represents the experimental data and is used to estimate intrinsic reactivity and diffusion properties of the zeolite films. Results show that the external activity, overall activity and the diffusivity increase with increasing film thickness. The variation in reactivity and diffusivity, when compared to physio-chemical data, are a result of structural defects and non-homogeneities of the zeolite film. The measured diffusivities are within an order of magnitude of those extrapolated from literature. Thick zeolite films have the largest Thiele modulus as the increase in zeolite film thickness dominates over the structural defects. The largest selectivity improvements are observed for thick zeolite films
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| 3. |
- 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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| 4. |
- Öhrman, Olov
(författare)
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Molecular sieve film catalysts
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study, well defined ZSM-5 films were prepared on monoliths, ceramic foams, alumina beads, glass beads and crushed quartz glass by further refinement of a method originally developed at the division of Chemical Technology, Luleå University of Technology. The supports were seeded with silicalite-1 seeds and hydrothermally treated, either at 75 °C or at 150 °C in a single or several steps. By adding sodium to the solution the aluminum concentration increased in the zeolite, which is beneficial for catalytic activity. Consequently, films with different Si/Al ratios could be prepared. The film thickness could be controlled from 110 nm to 9000 nm. Short hydrothermal treatments and use of multi-step synthesis was utilized to prevent excessive bulk crystallization and ultrasound treatment was beneficial in order to remove sedimented crystals on top of the zeolite films. The choice of support material and its influence on the performance of thin ZSM-5 film catalysts was examined by testing the reactivity of the zeolite- coated materials in two reactions; para-xylene isomerization and triisopropylbenzene cracking. ZSM-5 films with a thickness of 150, 350, 800 and 2300 nm, respectively, were prepared on alumina beads and quartz glass. Based upon the zeolite content, the films on quartz glass were much more active for para-xylene isomerization and for cracking of triisopropylbenzene, which is attributed to poisoning of the films on alumina due to impurities in the support. Model parameters were fitted to experimental results. The simulations indicated that thicker films contained a higher fraction of defects, which may be caused by open grain boundaries and cracks. These defects explain higher xylene diffusivities and higher triisopropylbenzene cracking activity for thicker films. As expected, thicker films possessed higher diffusion resistance than thin films despite the higher fraction of defects. The present work has given substantial and valuable fundamental understanding of the performance of thin molecular sieve film catalysts. These findings will be beneficial for development of materials that may be used in novel industrial applications.
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| 5. |
- Öhrman, Olov, et al.
(författare)
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Synthesis and evaluation of ZSM-5 films on cordierite monoliths
- 2004
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 270:1-2, s. 193-199
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Tidskriftsartikel (refereegranskat)abstract
- Well-defined ZSM-5 films were prepared on cordierite monoliths using the seed film method. The monoliths were seeded with silicalite-1 seeds and hydrothermally treated either at 75 or at 150 °C in a single or several steps. By adding sodium hydroxide to the solution, the aluminum concentration in the zeolite increased. Consequently, films with different Si/Al ratios were prepared. The film thickness could be controlled from 110 nm to 9 μm. Multi-step synthesis was used to prevent bulk crystallization and ultrasound treatment was found to be beneficial (in order) to remove sedimented crystals on the top of the coatings. The zeolite-coated monoliths were active for p-xylene isomerization, and the test results indicated that the films became less deactivated than the films prepared on alumina beads.
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| 6. |
- Öhrman, Olov, et al.
(författare)
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Zeolite ZSM-5 coatings on inert packing materials
- 2001
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Ingår i: Zeolites and mesoporous materials at the dawn of the 21st century. - Amsterdam : Elsevier. - 0444502386 ; , s. 292-
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Konferensbidrag (refereegranskat)
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| 7. |
- Öhrman, Olov, et al.
(författare)
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ZSM-5 structured catalysts coated with silicalite-1
- 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. 677-684
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Konferensbidrag (refereegranskat)abstract
- Alumina beads were coated with ZSM-5 films ranging from 150 nm to 2300 nm ill thickness. The ZSM-5 boated alumina beads were Subsequently hydrothermally treated in a silicalite-1 synthesis solution ill two steps Whereupon a dense silicalite-1 film was formed oil top of the ZSM-5 film. The materials were tested with two probe reactions and the reactivity was compared before and after coating with silicalite-1. As expected, the para-xylene (pX) isomerization reactivity showed no change for samples with and without the top layer of silicalite-1 for equal amounts Of zeolite. Surprisingly, the triisopropylbenzene (TIPB) conversion did not decrease after the silicalite-1 film was introduced. As measured by XPS, the aluminum concentration at the Surface of the uncalcined silicalite-1 film surface was lower compared to that at the Surface of the calcined ZSM-5 film. However, after calcination the concentration of aluminum was higher at the silicalite-1 film surface than at the ZSM-5 film Surface. These results Suggest that aluminum migrates from the ZSM-5 film into the silicalite-1 film during calcination and testing which results in all active top layer.
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