Modeling reaction–diffusion processes within catalyst washcoats: II. Macroscale processes informed by microscale simulations

Blasi, Justin M.; Weddle, Peter J.; Karakaya, Canan; Diercks, David R.; Kee, Robert J.

doi:10.1016/j.ces.2016.02.005

Cited by 15 publications

(8 citation statements)

References 15 publications

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“…In addition, the fact that the M-type pore has the best performance for shorter length and the N-type and M-type pores have the same diffusion performance for longer length indicate that most gas molecules do not enter the pore from one end and diffuse out from the other end. That is to say, for a catalyst pellet with a given porosity, the effective distance the gas molecules can penetrate into the pore is limited, which is consistent with the conclusion obtained by considering the reaction and diffusion using Thiele modulus …”

Section: Resultssupporting

confidence: 88%

“…To study the reaction-diffusion processes within the complicated porous media, previous models have mostly based on dimensionless groups, such as Damköhler number, Thiele modulus, and the corresponding external/internal effectiveness factors, − which were defined based on Fick’s diffusion law using empirical effective diffusion coefficients and idealized pellet shapes. As gas diffusion in complicated pores does not follow Fick’s law, and actual pore microstructures are not considered directly, , these models and indexes, though helpful, are often used on a phenomenological and qualitative basis. , …”

Section: Introductionmentioning

confidence: 99%

“…To study the reaction-diffusion processes within the complicated porous media, previous models have mostly based on dimensionless groups, such as Damkoḧler number, Thiele modulus, and the corresponding external/internal effectiveness factors, 22−25 which were defined based on Fick's diffusion law using empirical effective diffusion coefficients and idealized pellet shapes. As gas diffusion in complicated pores does not follow Fick's law, 17 and actual pore microstructures are not considered directly, 23,24 these models and indexes, though helpful, are often used on a phenomenological and qualitative basis. 26,27 Since the pore structure in actual porous media is too complicated to be described integrally and elaborately, it is meaningful to first focus on some typical structures at microscale and try to characterize the coupling of reaction and diffusion in a more quantitative way.…”

Section: Introductionmentioning

confidence: 99%

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Simulation Study on the Reaction-Diffusion Coupling in Simple Pore Structures

Zhao

et al. 2017

Langmuir

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Most porous media (just like catalyst pellets) have complicated pore structures, and understanding the coupling of the diffusion and reaction processes in these pores is very important for improving their performance. In this work, a diffusion factor (D) and a reaction factor (R) are proposed to quantitatively describe the diffusion and reaction performance in these pores respectively at molecular level. The yield in unit time is used to quantify their productivity and is expressed as the product of D and R. Molecular dynamic simulations with the hard-sphere algorithm are carried out to study the reaction-diffusion coupling in several simple pore structures with the same volume, such as straight, T-shaped, and cross-shaped pores. The reaction formula based on activation energy is given for a simple irreversible reaction process from A to B. In terms of the proposed factors, D and R, analysis on the simulation results shows clearly that the overall productivity of these pore structures depends on the competition of D and R, which are both determined by the size and shape of the pore structures. The results demonstrate the effectiveness of the simulation approach used for evaluating the performance of the simple pore structures for simple reactions and the potential of its application in more complicated and practical cases. It also suggests the effectiveness of the proposed factors, D and R, for charactering the diffusion and reaction processes at molecular level.

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Section: Resultssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Simulation Study on the Reaction-Diffusion Coupling in Simple Pore Structures

Zhao

et al. 2017

Langmuir

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“…The diffusional limitations inside the catalyst washcoat can be estimated as follows [70,71]: (14) In the above equation, the term . s i,e f f indicates the effective rate of formation of species i on the surface of the catalyst, Φ indicates the Thiele modulus, δ indicates the thickness of the porous washcoat, and the term C i,interface indicates the concentration of species i at the gas-catalyst interface.…”

Section: Of 27mentioning

confidence: 99%

RETRACTED: Catalytic Combustion Characteristics of Methane-Air Mixtures in Small-Scale Systems at Elevated Temperatures

Chen

Gao

2018

Catalysts

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The catalytic combustion characteristics of methane-air mixtures in small-scale systems were investigated at elevated temperatures, with particular emphasis on identifying the main factors that affect formation and removal of combustion-generated pollutants. Computational fluid dynamics simulations were performed using detailed chemical kinetic mechanisms, and more insights were offered into the phenomena occurring in the temperature range where homogeneous and heterogeneous reaction pathways are both important. Reaction engineering analysis was performed to provide an in-depth understanding of how to achieve low emissions of pollutants. Spatial distributions of the major species involved were presented to gain insight into the interplay between the two competing pathways involved. The results indicated that the distribution of oxidized products depends critically on the feed composition, dimension, temperature, and pressure. Small-scale catalytic systems enable low emissions of pollutants even in a high temperature environment, along with high combustion efficiency. The interplay between the two competing pathways via radicals is strong, and the heterogeneous pathway can significantly inhibit the homogeneous pathway. The inhibiting effect also accounts for the low emissions of nitrogen oxides. Almost all of the nitrogen oxides emitted by small-scale catalytic systems are nitric oxide. Catalytic combustion technology can be used to reduce the formation of undesired products, especially pollutant nitrogen oxide gases far below what can be achieved without catalysts. Recommendations for the design of small-scale catalytic systems are provided.

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“…18 The work of Bertei et al [ 334] would be the closest to this goal. As an example of what is meant by "expressions to upscale pore-scale performance," see Blasi et al [ 420] who have modeled reaction-diffusion processes within catalyst washcoats. 19 Nishi et al [ 328] seems to be an exception.…”

Section: Notesmentioning

confidence: 99%

On governing equations and closure relations for the multiscale modeling of concentration polarization in solid-oxide fuel cells: mass transfer and concentration-induced voltage losses.

Júnior¹,

Janny²

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Modeling reaction–diffusion processes within catalyst washcoats: II. Macroscale processes informed by microscale simulations

Cited by 15 publications

References 15 publications

Simulation Study on the Reaction-Diffusion Coupling in Simple Pore Structures

Simulation Study on the Reaction-Diffusion Coupling in Simple Pore Structures

RETRACTED: Catalytic Combustion Characteristics of Methane-Air Mixtures in Small-Scale Systems at Elevated Temperatures

On governing equations and closure relations for the multiscale modeling of concentration polarization in solid-oxide fuel cells: mass transfer and concentration-induced voltage losses.

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