Calculation of the optimal macropore size in nanoporous catalysts and its application to DeNOx catalysis / Gang Wang in Industrial & engineering chemistry research, Vol. 47 n°11 (Juin 2008)  

Public ISBD [article]  inIndustrial & engineering chemistry research > Vol. 47 n°11 (Juin 2008) . - p. 3847–3855 Titre : Calculation of the optimal macropore size in nanoporous catalysts and its application to DeNOx catalysis Type de document : texte imprimé Auteurs : Gang Wang, Auteur ; Marc-Olivier Coppens, Auteur Année de publication : 2008 Article en page(s) : p. 3847–3855 Note générale : Bibliogr. p. 3855 Langues : Anglais (eng) Mots-clés : Macropores  Nanoporous catalyst  Molecular diffusion  DeNOx catalysis Résumé : Macropores act as broad highways for molecules to move in and out of a nanoporous catalyst. The macropore “distributor” network in such a hierarchically structured porous catalyst, containing both nanopores and macropores, is optimized with the aim to find the optimal effectiveness factor, ηopt, of a single reaction with general kinetics in the catalyst. Molecular diffusion is assumed to dominate transport in macropores. It is found that the ηopt−Φ0 relation qualitatively recovers the universal η−Φ relation when the generalized distributor Thiele modulus, Φ0, is defined in a way analogous to the generalized Thiele modulus, Φ, but using the molecular diffusivity in the macropores rather than the effective diffusivity in the nanopores. This is because the concentration gradient inside the optimal hierarchically structured, porous catalyst exists only in one principle direction (e.g., the radial direction in a spherical catalyst particle), and molecular diffusion in the macropores dominates the transport process in this principle direction. The universal ηopt−Φ0 relation is used to design a catalyst for power plant NOx emission control. Overall catalytic activity in a mesoporous catalyst with a median pore size of 32.5 nm could be increased by a factor of 1.8−2.8 simply by introducing macropores (occupying 20−40% of the total volume of the catalyst) with a width of 2−22 µm into the mesoporous catalytic material, so that the remaining mesoporous macropore walls are 5−33 µm thick. In practice, this would correspond to a deNOx catalyst consisting of mesoporous particles with a diameter of 5−33 µm and macropores in between them with a size of around 2−22 µm. Information like this is readily applicable to practical catalyst synthesis. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie071550%2B [article] Calculation of the optimal macropore size in nanoporous catalysts and its application to DeNOx catalysis [texte imprimé] / Gang Wang, Auteur ; Marc-Olivier Coppens, Auteur . - 2008 . - p. 3847–3855. Bibliogr. p. 3855 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°11 (Juin 2008) . - p. 3847–3855 Mots-clés : Macropores  Nanoporous catalyst  Molecular diffusion  DeNOx catalysis Résumé : Macropores act as broad highways for molecules to move in and out of a nanoporous catalyst. The macropore “distributor” network in such a hierarchically structured porous catalyst, containing both nanopores and macropores, is optimized with the aim to find the optimal effectiveness factor, ηopt, of a single reaction with general kinetics in the catalyst. Molecular diffusion is assumed to dominate transport in macropores. It is found that the ηopt−Φ0 relation qualitatively recovers the universal η−Φ relation when the generalized distributor Thiele modulus, Φ0, is defined in a way analogous to the generalized Thiele modulus, Φ, but using the molecular diffusivity in the macropores rather than the effective diffusivity in the nanopores. This is because the concentration gradient inside the optimal hierarchically structured, porous catalyst exists only in one principle direction (e.g., the radial direction in a spherical catalyst particle), and molecular diffusion in the macropores dominates the transport process in this principle direction. The universal ηopt−Φ0 relation is used to design a catalyst for power plant NOx emission control. Overall catalytic activity in a mesoporous catalyst with a median pore size of 32.5 nm could be increased by a factor of 1.8−2.8 simply by introducing macropores (occupying 20−40% of the total volume of the catalyst) with a width of 2−22 µm into the mesoporous catalytic material, so that the remaining mesoporous macropore walls are 5−33 µm thick. In practice, this would correspond to a deNOx catalyst consisting of mesoporous particles with a diameter of 5−33 µm and macropores in between them with a size of around 2−22 µm. Information like this is readily applicable to practical catalyst synthesis. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie071550%2B

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Mitigating deactivation effects through rational design of hierarchically structured catalysts / Sanjeev M. Rao in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010)  

Public ISBD [article]  inIndustrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 11087-11097 Titre : Mitigating deactivation effects through rational design of hierarchically structured catalysts : Application to hydrodemetalation Type de document : texte imprimé Auteurs : Sanjeev M. Rao, Auteur ; Marc-Olivier Coppens, Auteur Année de publication : 2011 Article en page(s) : pp. 11087-11097 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Catalyst Design Deactivation Résumé : The broad pore network of a hierarchically structured hydrodemetalation catalyst, containing both nano- and macropores, is mathematically optimized to maximize the conversion of nickel metalloporphyrins in crude oil residue. A random spheres model (RSM) describing the nanoporous catalyst at the mesoscale is combined with a two-dimensional continuum approach to model the entire catalyst at the macroscale. Catalysts with a spatially uniform as well as a nonuniform macroporosity distribution are optimized. The macroporosity profiles of the optimal nonuniform catalysts fluctuate about the optimal uniform value, while the spatially and temporally integrated reaction rates from both types of optimized catalysts are almost the same. Moreover, the integrated reaction rate of the optimal hierarchically structured catalysts are almost 8 times higher than the yield obtained from a purely nanoporous catalyst. For a time on stream of 1 year, approximately 21% less catalytic material is required in the optimal hierarchically structured catalyst, compared to the purely nanoporous one. The mathematical optimization tools employed here can be extended to other industrially important reactions affected by deactivation. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23448006 [article] Mitigating deactivation effects through rational design of hierarchically structured catalysts : Application to hydrodemetalation [texte imprimé] / Sanjeev M. Rao, Auteur ; Marc-Olivier Coppens, Auteur . - 2011 . - pp. 11087-11097. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 11087-11097 Mots-clés : Catalyst Design Deactivation Résumé : The broad pore network of a hierarchically structured hydrodemetalation catalyst, containing both nano- and macropores, is mathematically optimized to maximize the conversion of nickel metalloporphyrins in crude oil residue. A random spheres model (RSM) describing the nanoporous catalyst at the mesoscale is combined with a two-dimensional continuum approach to model the entire catalyst at the macroscale. Catalysts with a spatially uniform as well as a nonuniform macroporosity distribution are optimized. The macroporosity profiles of the optimal nonuniform catalysts fluctuate about the optimal uniform value, while the spatially and temporally integrated reaction rates from both types of optimized catalysts are almost the same. Moreover, the integrated reaction rate of the optimal hierarchically structured catalysts are almost 8 times higher than the yield obtained from a purely nanoporous catalyst. For a time on stream of 1 year, approximately 21% less catalytic material is required in the optimal hierarchically structured catalyst, compared to the purely nanoporous one. The mathematical optimization tools employed here can be extended to other industrially important reactions affected by deactivation. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23448006

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