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Defects in Zeolite Catalysts and Membranes
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

ZSM-5 is one of the most well-known zeolites. It has been synthesized for many different applications, including as catalyst for catalytic reactions and as a membrane in separation processes.  The main goal of this thesis is to investigate and characterize the defects in crystal and film growth of ZSM-5 for modification purposes.

Primarily, ZSM-5 crystals with carefully controlled thickness were synthesized in fluoride and hydroxide media. These synthesized catalysts were then characterized and the two synthesis routes were compared with each other in terms of stability. Then, in the synthesized catalysts, the role of defects during reaction was investigated. Furthermore, the growth of ZSM-5 nanocrystals and subsequent film formation was investigated to better understand how particles formed in synthesis solution (a hydrolyzed mixture of H2O-TEOS-TPAOH), followed by how these crystals interact to form a zeolite film. Finally, pre- and post-production modification of ZSM-5 and PHI membranes was investigated. Since, the roughness surface of the support could play a crucial role in having an even film, it was done as a pre-treatment technique for membrane synthesis. Additionally, a technique was developed in an attempt to plug the defects of grain boundaries to increase the membrane performance.

 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2020.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-76870ISBN: 978-91-7790-506-6 (print)ISBN: 978-91-7790-507-3 (electronic)OAI: oai:DiVA.org:ltu-76870DiVA, id: diva2:1373269
Public defence
2020-02-19, F1031, Luleå, 14:20 (English)
Opponent
Supervisors
Available from: 2019-11-26 Created: 2019-11-26 Last updated: 2020-01-21Bibliographically approved
List of papers
1. Stability of colloidal ZSM-5 catalysts synthesized in fluoride and hydroxide media
Open this publication in new window or tab >>Stability of colloidal ZSM-5 catalysts synthesized in fluoride and hydroxide media
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2019 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 278, p. 167-174Article in journal (Refereed) Published
Abstract [en]

ZSM-5 zeolite crystals with carefully controlled thicknesses in the range 20–110 nm, i.e. in the colloidal domain, were synthesized in fluoride and hydroxide media. The crystals were treated in steam at high temperature to evaluate the stability and evaluated by SEM, XRD, NMR and NH3-TPD. The results showed that the framework of crystals synthesized in fluoride media was more stable than the framework of crystals synthesized in hydroxide media. This should be an effect of lower concentration of structural defects and silanol groups in the former zeolites as reported by other groups. However, independently of the synthesis conditions, all crystals dealuminated rapidly when treated with steam at the conditions investigated in the present work.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
ZSM-5, Catalyst, Stability, Framework, Steam, Dealumination
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-71897 (URN)10.1016/j.micromeso.2018.11.007 (DOI)000459841900020 ()2-s2.0-85057248871 (Scopus ID)
Note

Validerad;2019;Nivå 2;2018-12-05 (svasva)

Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-11-26Bibliographically approved
2. Selective blocking of grain boundary defects in high-flux zeolite membranes by cokin
Open this publication in new window or tab >>Selective blocking of grain boundary defects in high-flux zeolite membranes by cokin
2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 16, p. 7295-7299Article in journal (Refereed) Published
Abstract [en]

Commercial application of zeolite membranes has been hindered by the challenge of preparing defect-free membranes. Herein, we report a facile method able to selectively plug grain boundary defects in high-flux MFI zeolite membranes by coking of iso-propanol at 350 °C. After modification, the permeance via defects was reduced by 70%, whereas that via zeolite pores was reduced by only 10%.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-62738 (URN)10.1039/C7TA01268C (DOI)000399390300006 ()2-s2.0-85017599078 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-04-25 (andbra)

Available from: 2017-03-28 Created: 2017-03-28 Last updated: 2019-11-26Bibliographically approved
3. Small ZSM-5 crystals with low defect density as an effective catalyst for conversion of methanol to hydrocarbons
Open this publication in new window or tab >>Small ZSM-5 crystals with low defect density as an effective catalyst for conversion of methanol to hydrocarbons
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2019 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308Article in journal (Refereed) Epub ahead of print
Abstract [en]

This work presents the synthesis of nearly defect-free ZSM-5 nanosized crystals, prepared in fluoride medium by seeding with silicalite-1. This material was carefully characterized and its catalytic performances in the methanol to hydrocarbons (MTH) reaction were assessed. Such fluoride-based material was compared to a reference ZSM-5, produced through a conventional alkaline synthesis but from the same seeding. Despite both the materials show closely identical morphology and they have a comparable acid site population, the catalyst prepared using the fluoride route showed significantly longer lifetime in MTH compared to the catalyst prepared using conventional synthesis at high pH. The slower deactivation for the samples prepared using the fluoride route was ascribed, thanks to a thorough in situ IR spectroscopy study, to its lower density of internal defects. According to the UV-Raman characterization of coke on the spent catalyst, the fluoride-based ZSM-5 catalyst produces less molecular coke species, most probably because of the absence of enlarged cavities/channels as due to the presence of internal defects. On the basis of these observations, the deactivation mechanism in the ZSM-5 synthesized by fluoride medium could be mostly related to the deposition of an external layer of bulk coke, whereas in the alkali-synthesized catalyst an additional effect from molecular coke accumulating within the porous network accelerates the deactivation process.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
ZSM-5, defects, hydrocarbons, deactivation, MTH, IR spectroscopy, OH groups
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-76102 (URN)10.1016/j.cattod.2019.09.023 (DOI)2-s2.0-85073006485 (Scopus ID)
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-11-26
4. An experimental study for finding the best condition for PHI zeolite synthesis using Taguchi method for gas separation
Open this publication in new window or tab >>An experimental study for finding the best condition for PHI zeolite synthesis using Taguchi method for gas separation
2018 (English)In: Chemical papers, ISSN 2585-7290, Vol. 72, no 5, p. 1139-1149Article in journal (Refereed) Published
Abstract [en]

Phillipsite zeolite particles and membranes were successfully synthesized at different operational and environmental conditions. Using an L9 orthogonal array of the Taguchi method, effects of experimental condition—synthesis temperature (130–150 °C), synthesis time (2–3 days), number of synthesized layers (1–3), and seeding suspension percentage—for membrane preparation with respect to CO2/CH4 ideal selectivity were investigated. The results showed that the ideal selectivity was improved up to 4.20 from 1.15 by increasing the number of synthesized layers, synthesis temperature, and seed solution concentration and by decreasing synthesis time. Moreover, the best synthesis conditions were defined based on the Taguchi method results and the membrane was synthesized with the highest ideal selectivity which was around 4.40. In addition, it was shown that T zeolite is formed beside PHI zeolite at low temperature even with long synthesis time.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-67048 (URN)10.1007/s11696-017-0366-6 (DOI)000430502800008 ()
Note

Validerad;2018;Nivå 2;2018-04-26 (andbra)

Available from: 2017-12-18 Created: 2017-12-18 Last updated: 2019-11-26Bibliographically approved

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Nabavi, Mohammad Sadegh

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