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Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
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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.

Place, publisher, year, edition, pages
2007. Vol. 62, no 15, 3991-4011 p.
Keyword [en]
partial oxidation of methane on rhodium, in situ Raman and LIF, catalyst support, catalyst selectivity, simulation, reaction engineering
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6642DOI: 10.1016/j.ces.2007.04.041ISI: 000248779100012Scopus ID: 2-s2.0-34347347126OAI: oai:DiVA.org:kth-6642DiVA: diva2:11406
Note
QC 20110125Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Development of catalysts for natural gas-fired gas turbine combustors
Open this publication in new window or tab >>Development of catalysts for natural gas-fired gas turbine combustors
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
AZEP, catalytic combustion, CPO, methane oxidation, palladium, rhodium, support effect
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4239 (URN)91-7178-543-4 (ISBN)978-91-7178-543-5 (ISBN)
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

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