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Synthesis of barium hexaaluminate by co-precipitation in microemulsion
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
(English)In: Materials Chemistry and Physics, ISSN 0254-0584Article in journal (Other academic) Submitted
Keyword [en]
barium hexaaluminate; reverse microemulsion; hydrothermal treatment; calcination
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8648OAI: oai:DiVA.org:kth-8648DiVA: diva2:14027
Note
QS 20120326Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2012-03-26Bibliographically approved
In thesis
1. Nanotemplated High-Temperature Materials for Catalytic Combustion
Open this publication in new window or tab >>Nanotemplated High-Temperature Materials for Catalytic Combustion
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Catalytic combustion is a promising technology for heat and power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high-temperature part of the catalytic combustor. The level of performance demanded on this part has proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed.

The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. Two template-based preparation methods were developed for this purpose. One method was based on soft templates (microemulsion) and the other on hard templates (carbon). Supports known for their stability, magnesia and hexaaluminate, were prepared using the developed methods. Catalytically active materials, perovskite (LaMnO3) and ceria (CeO2), were added to the supports in order to obtain catalysts with high activities and stabilities. The supports were impregnated with active materials by using a conventional technique as well as by using the microemulsion technique.

It was shown that the microemulsion method can be used to prepare catalysts with higher activity compared to the conventional methods. Furthermore, by using a microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using the conventional impregnation technique. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed on selected catalysts prepared by the microemulsion technique. The stability of the catalysts was assessed by measuring the activity before and after aging at 1000 C in humid air for 100 h. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparative purposes. The results showed that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method.

Carbon templating was shown be a very good technique for the preparation of high-surface-area hexaaluminates with excellent sintering resistance. It was found that the pore size distribution of the carbon used as template was a crucial parameter in the preparation of hexaaluminates. When a carbon with small pores was used as template, the formation of the hexaaluminate crystals was strongly inhibited. This resulted in a material with poor sintering resistance. On the other hand, if a carbon with larger pores was used as template, it was possible to prepare materials with hexaaluminate as the major phase. These materials were, after accelerated aging at 1400 C in humid air, shown to retain surface areas twice as high as reported for conventionally prepared materials.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xiii, 76 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:46
Keyword
Carbon templating, Catalytic combustion, Ceria, Gas turbine, Hexaaluminate, Magnesia, Methane, Microemulsion, Perovskite
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4800 (URN)978-91-7415-019-3 (ISBN)
Public defence
2008-06-13, D1, Huvudbyggnaden, Lindstedtsvägen 17, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100719Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2010-07-19Bibliographically approved

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