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Development of catalysts for natural gas-fired gas turbine combustors
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Due to continuously stricter regulations regarding emissions from power generation processes, further development of existing gas turbine combustors is essential. A promising alternative to conventional flame combustion in gas turbines is catalytic combustion, which can result in ultralow emission levels of NOx, CO and unburned hydrocarbons. The work presented in this thesis concerns the development of methane oxidation catalysts for gas turbine combustors. The application of catalytic combustion to different combustor concepts is addressed in particular.

The first part of the thesis (Paper I) reports on catalyst development for fuel-lean methane combustion. Supported Pd-based catalysts were investigated at atmospheric pressure. The effect on catalytic activity of diluting the reaction mixture with water and/or carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The catalytic activity was found to decrease significantly in the presence of water and CO2. However, modifying the catalyst by changing support material can have a considerable impact on the performance.

In the second part of this thesis (Papers II-IV), the development of rhodium catalysts for fuel-rich methane combustion is addressed. The effect of catalyst composition, oxygen-to-fuel ratio and catalyst pre-treatment on the methane conversion and the product gas composition was studied. An experimental investigation at elevated pressures of partial oxidation of methane/oxygen mixtures in exhaust gas-rich environments was also conducted. The most suitable catalyst identified for fuel-rich catalytic combustion of methane, i.e. Rh/Ce-ZrO2, showed benefits such as low light-off temperature, high activity and enhanced hydrogen selectivity.

In the final part of the thesis (Paper V), a numerical investigation of fuel-rich catalytic combustion is presented. Measurements and predictions were compared for partial oxidation of methane in exhaust gas diluted mixtures at elevated pressures. The numerical model was validated for several Rh-based catalysts. The key parameter controlling the catalytic performance was found to be the noble metal dispersion.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 67 p.
Series
Trita-KET, ISSN 1104-3466 ; R232
Keyword [en]
AZEP, catalytic combustion, CPO, methane oxidation, palladium, rhodium, support effect
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4239ISBN: 91-7178-543-4 (print)ISBN: 978-91-7178-543-5 (print)OAI: oai:DiVA.org:kth-4239DiVA: diva2:11407
Public defence
2006-12-19, D2, D, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20110125Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2011-01-25Bibliographically approved
List of papers
1. Catalytic combustion of methane in steam and carbon dioxide-diluted reaction mixtures
Open this publication in new window or tab >>Catalytic combustion of methane in steam and carbon dioxide-diluted reaction mixtures
2006 (English)In: Applied Catalysis, ISSN 0166-9834, E-ISSN 1873-3867, Vol. 312, 95-101 p.Article in journal (Refereed) Published
Abstract [en]

Supported palladium catalysts have been tested for methane combustion under lean conditions in the temperature range of 200-800 degrees C. The effect of diluting the reaction mixture with high amounts of water and carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The influence of support material, i.e. ZrO2 or doped CeO2, on the catalytic performance was also investigated.

The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order: Pd/ZrO2 < Pd/Zr-CeO2 < Pd/La-CeO2. The order of activity changed at higher temperatures resulting in Pd/La-CeO2 being the most active catalyst above 670 degrees C. This catalyst also shows a more stable performance with no distinct deactivation occurring at higher temperatures during cooling.

Both water and CO2 were found to have a negative influence on the catalytic activity. The inhibitory effect was, however, more pronounced for water. This inhibitory effect was present in the entire temperature range investigated. Adding CO2 in the presence of water resulted in conversions similar to the ones observed when feeding water alone for Pd/ZrO2 and Pd/La-CeO2, On the contrary, the activity of Pd/Zr-CeO2 was further decreased when co-feeding water and CO2.

Keyword
catalytic combustion, palladium, TPO, AZEP, water inhibition, CO2 inhibition
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6638 (URN)000240639000012 ()2-s2.0-33747828180 (Scopus ID)
Note
QC 20101126Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
2. Partial oxidation of methane over rhodium catalysts for power generation applications
Open this publication in new window or tab >>Partial oxidation of methane over rhodium catalysts for power generation applications
2005 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 100, 447-451 p.Article in journal (Refereed) Published
Abstract [en]

The partial oxidation of methane (POM) to syngas, i.e. H-2 and CO, over supported Rh catalysts was investigated at atmospheric pressure. The influence of support material, Rh loading and the presence of water vapor on the methane conversion efficiency and the product gas composition was studied. The catalysts containing ceria in the support material showed the highest activity and formation of H2 and CO. By increasing the Rh loading, a decrease of the ignition temperature was obtained. The addition of water vapor to the reactant gas mixture was found to increase the ignition temperature and the formation of hydrogen, which is favorable for combustion applications where the catalytic POM stage is followed by H-2-stabilized homogeneous combustion.

Keyword
catalytic combustion, partial oxidation of methane, rhodium catalysts, ceria
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6639 (URN)10.1016/j.cattod.2004.09.077 (DOI)000229275100041 ()2-s2.0-17344365926 (Scopus ID)
Note
QC 20101126. 11th Nordic Symposium on Catalysis. Oulu, FINLAND. MAY 23-25, 2004 Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
3. Effect of Ce-doping on Rh/ZrO2 catalysts for partial oxidation of methane
Open this publication in new window or tab >>Effect of Ce-doping on Rh/ZrO2 catalysts for partial oxidation of methane
2007 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 326, no 1, 8-16- p.Article in journal (Refereed) Published
Abstract [en]

The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pre-treatment was studied. Ceria doping of the support material resulted in significant improvements concerning the methane conversion and syngas selectivity, which could be related to a higher noble metal dispersion on the Rh/CeO2-ZrO2 catalyst. In addition, the light-off temperature was decreased by 128 degrees C when using CeO2-ZrO2, as support. X-ray photoelectron spectroscopy revealed the presence of different Rh oxidation states depending on catalyst composition and pre-treatment. A stabilization of partially oxidized (Rh delta+) species by ceria could be detected. An active and stable catalyst behavior could be observed for Rh/CeO2-ZrO2, irrespectively of catalyst pre-treatment, whereas an activation period was required for stabilizing the activity of the Rh/ZrO2 catalyst. The activity tests indicate that the indirect reaction mechanism, consisting of methane combustion followed by steam and dry reforming, prevails under the experimental conditions studied.

Keyword
partial oxidation of methane, Rh catalysts, catalytic combustion, ceria, XPS
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6640 (URN)10.1016/j.apcata.2007.03.019 (DOI)000247812600002 ()2-s2.0-34249299771 (Scopus ID)
Note
QC 20110125.Uppdaterad från submitted till published(20110125) Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
4. Fuel-rich catalytic combustion of methane in zero emissions power generation processes
Open this publication in new window or tab >>Fuel-rich catalytic combustion of methane in zero emissions power generation processes
Show others...
2006 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 117, no 4, 447-453 p.Article in journal (Refereed) Published
Abstract [en]

A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO2, Ce-ZrO2 or alpha-Al2O3 were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO2 < Rh/ZrO2 < Rh/alpha-Al2O3. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO2 is probably related to the high dispersion of Rh on Ce-ZrO2 and the high oxygen mobility of this support compared to pure ZrO2. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.

Keyword
catalytic combustion, catalytic partial oxidation (CPO) of methane, AZEP, rhodium catalysts, ceria
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6641 (URN)10.1016/j.cattod.2006.06.010 (DOI)000241085000009 ()2-s2.0-33748617867 (Scopus ID)
Note
QC 20110125Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
5. Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures
Open this publication in new window or tab >>Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures
Show others...
2007 (English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 62, no 15, 3991-4011 p.Article in journal (Refereed) Published
Abstract [en]

The partial oxidation of methane/oxygen mixtures with large exhaust gas dilution (46.3 vol% H2O and 23.1 vol% CO2) has been investigated experimentally and numerically over Rh/CeO2-ZrO2, Rh/ZrO2 and Rh/alpha-Al2O3 catalysts. Experiments were carried out in a short-contact-time (similar to 8 ms) reactor at 5 bar and included exhaust gas analysis, temperature measurements along the reactor, and catalyst characterization. Additional experiments were performed in an optically accessible channel-flow reactor and involved in situ Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and laser-induced fluorescence (LIF) of formaldehyde. A full elliptic two-dimensional numerical code that included elementary hetero-/homogeneous chemical reaction schemes and relevant heat transfer mechanisms in the solid was used in the simulations. The employed heterogeneous reaction mechanism, including only active Rh sites, reproduced the experiments with good accuracy. The ratio of active to geometrical surface area, deduced from hydrogen chemisorption measurements, was the single model parameter needed to account for the effect of different supports. This indicated that water activation occurring on support sites, resulting in inverse OH spillover from the support to the noble metal sites, could be neglected under the present conditions with high water dilution. An evident relationship between noble metal dispersion and catalytic behavior, in terms of methane conversion and synthesis gas yields, could be established. Both measurements and predictions indicated that an increasing Rh dispersion (in the order Rh/alpha-Al2O3, Rh/ZrO2, and Rh/CeO2-ZrO2) resulted in higher methane conversions, lower surface temperatures, and higher synthesis gas yields.

Keyword
partial oxidation of methane on rhodium, in situ Raman and LIF, catalyst support, catalyst selectivity, simulation, reaction engineering
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6642 (URN)10.1016/j.ces.2007.04.041 (DOI)000248779100012 ()2-s2.0-34347347126 (Scopus ID)
Note
QC 20110125Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved

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