Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths

Noleen Maguire, A Sasegbon, A Abdelkader, Alexandre Goguet, Christopher Hardacre, Klaus Hellgardt, Kevin Morgan, Sergiy Shekhtman

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Abstract

The importance of accurately measuring gas diffusivity in porous materials has led to a number of methods being developed. In this study the Temporal Analysis of Products (TAP) reactor and Flux Response Technology (FRT) have been used to examine the diffusivity in the washcoat supported on cordierite monoliths. Herein, the molecular diffusion of propane within four monoliths with differently prepared alumina/CeZrOx washcoats was investigated as a function of temperature. Moment-based analysis of the observed TAP responses led to the calculation of the apparent intermediate gas constant, Kp, that characterises adsorption into the mesoporous network and apparent time delay, tapp, that characterises residence time in the mesoporous network. Additionally, FRT has been successfully adapted as an extensive in situ perturbation technique in measuring intraphase diffusion coefficients in the washcoats of the same four monolith samples. The diffusion coefficients obtained by moment-based analysis of TAP responses are larger than the coefficients determined by zero length column (ZLC) analysis of flux response profiles with measured values of the same monolith samples between 20 and 100 °C ranging from 2–5×10-9 m2 s-1 to 4–8×10-10 m2 s-1, respectively. The TAP and FRT data, therefore, provide a range of the lower and upper limits of diffusivity, respectively. The reported activation energies and diffusivities clearly correlate with the difference in the washcoat structure of different monolith samples.

Original languageEnglish
Pages (from-to)224-233
Number of pages10
JournalChemical Engineering Science
Volume87
Early online date24 Oct 2012
DOIs
Publication statusPublished - 14 Jan 2013

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Diffusion Coefficient
Fluxes
Diffusivity
Gases
Moment
Propane
Perturbation techniques
Residence Time
Porous Materials
Alumina
Aluminum Oxide
Perturbation Technique
Activation Energy
Adsorption
Correlate
Reactor
Porous materials
Time Delay
Time delay
Activation energy

Cite this

Maguire, Noleen ; Sasegbon, A ; Abdelkader, A ; Goguet, Alexandre ; Hardacre, Christopher ; Hellgardt, Klaus ; Morgan, Kevin ; Shekhtman, Sergiy. / Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths. In: Chemical Engineering Science. 2013 ; Vol. 87. pp. 224-233.
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Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths. / Maguire, Noleen; Sasegbon, A; Abdelkader, A; Goguet, Alexandre; Hardacre, Christopher; Hellgardt, Klaus; Morgan, Kevin; Shekhtman, Sergiy.

In: Chemical Engineering Science, Vol. 87, 14.01.2013, p. 224-233.

Research output: Contribution to journalArticle

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AU - Maguire, Noleen

AU - Sasegbon, A

AU - Abdelkader, A

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AB - The importance of accurately measuring gas diffusivity in porous materials has led to a number of methods being developed. In this study the Temporal Analysis of Products (TAP) reactor and Flux Response Technology (FRT) have been used to examine the diffusivity in the washcoat supported on cordierite monoliths. Herein, the molecular diffusion of propane within four monoliths with differently prepared alumina/CeZrOx washcoats was investigated as a function of temperature. Moment-based analysis of the observed TAP responses led to the calculation of the apparent intermediate gas constant, Kp, that characterises adsorption into the mesoporous network and apparent time delay, tapp, that characterises residence time in the mesoporous network. Additionally, FRT has been successfully adapted as an extensive in situ perturbation technique in measuring intraphase diffusion coefficients in the washcoats of the same four monolith samples. The diffusion coefficients obtained by moment-based analysis of TAP responses are larger than the coefficients determined by zero length column (ZLC) analysis of flux response profiles with measured values of the same monolith samples between 20 and 100 °C ranging from 2–5×10-9 m2 s-1 to 4–8×10-10 m2 s-1, respectively. The TAP and FRT data, therefore, provide a range of the lower and upper limits of diffusivity, respectively. The reported activation energies and diffusivities clearly correlate with the difference in the washcoat structure of different monolith samples.

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