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Evaluating the effects of precious metal distribution along a monolith - supported catalyst for CO oxidation / Suad M. Al Adwani in Industrial & engineering chemistry research, Vol. 51 N° 19 (Mai 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 19 (Mai 2012) . - pp. 6672–6679 Titre : Evaluating the effects of precious metal distribution along a monolith - supported catalyst for CO oxidation Type de document : texte imprimé Auteurs : Suad M. Al Adwani, Auteur ; Joao Soares, Auteur ; William S. Epling, Auteur Année de publication : 2012 Article en page(s) : pp. 6672–6679 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Metal  Catalyst  Oxidation Résumé : Zone-coated diesel oxidation catalysts (DOCs) can be used to obtain overall improved performance in oxidation reaction extents. However, why this occurs and under what conditions an impact is expected are unknown. In order to demonstrate why these catalysts work better than their standard counterparts and how significant the improved performance is, the CO oxidation performance over a series of Pt–Pd/Al2O3 catalysts, each with a different distribution of precious metal down the length, while maintaining equivalent totals of precious metal, was modeled. Simulations with different flow rates, ramp rates, steady-state temperatures at the end of the ramp rate, different total precious metal loadings, and CO inlet values were compared. In terms of light off, at conversions less than 50%, the most significant differences were noted when the temperature was ramped to just at the CO oxidation light-off point, with catalysts containing more precious metal at the downstream portions leading to better light-off conversion performance. However, in terms of cumulative emissions over a long period of time, a “front-loaded” design proved best. These results are readily explained by decreased CO poisoning and the propagation of the exothermic heat from the front to the rear of the catalyst. Also, although the trends were the same, regardless of change in the parameter, the impact of different distributions was more apparent under conditions where a catalyst would be challenged, i.e., at low temperature ramp rates, higher CO inlet concentrations, and lower amounts of total catalyst used. At higher ramp rates, the input heat from the entering gas stream played an increasingly important role, relative to conduction associated with the exotherm, dampening the effects of the catalyst distribution. Therefore, although catalysts that are zone-coated with precious metals, or any active sites, could prove better in terms of performance than homogeneously distributed active site catalysts, this improvement is only significant under certain reaction conditions and thus application of these catalysts may not be appropriate for all drive cycles or applications. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202969u [article] Evaluating the effects of precious metal distribution along a monolith - supported catalyst for CO oxidation [texte imprimé] / Suad M. Al Adwani, Auteur ; Joao Soares, Auteur ; William S. Epling, Auteur . - 2012 . - pp. 6672–6679. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 19 (Mai 2012) . - pp. 6672–6679 Mots-clés : Metal  Catalyst  Oxidation Résumé : Zone-coated diesel oxidation catalysts (DOCs) can be used to obtain overall improved performance in oxidation reaction extents. However, why this occurs and under what conditions an impact is expected are unknown. In order to demonstrate why these catalysts work better than their standard counterparts and how significant the improved performance is, the CO oxidation performance over a series of Pt–Pd/Al2O3 catalysts, each with a different distribution of precious metal down the length, while maintaining equivalent totals of precious metal, was modeled. Simulations with different flow rates, ramp rates, steady-state temperatures at the end of the ramp rate, different total precious metal loadings, and CO inlet values were compared. In terms of light off, at conversions less than 50%, the most significant differences were noted when the temperature was ramped to just at the CO oxidation light-off point, with catalysts containing more precious metal at the downstream portions leading to better light-off conversion performance. However, in terms of cumulative emissions over a long period of time, a “front-loaded” design proved best. These results are readily explained by decreased CO poisoning and the propagation of the exothermic heat from the front to the rear of the catalyst. Also, although the trends were the same, regardless of change in the parameter, the impact of different distributions was more apparent under conditions where a catalyst would be challenged, i.e., at low temperature ramp rates, higher CO inlet concentrations, and lower amounts of total catalyst used. At higher ramp rates, the input heat from the entering gas stream played an increasingly important role, relative to conduction associated with the exotherm, dampening the effects of the catalyst distribution. Therefore, although catalysts that are zone-coated with precious metals, or any active sites, could prove better in terms of performance than homogeneously distributed active site catalysts, this improvement is only significant under certain reaction conditions and thus application of these catalysts may not be appropriate for all drive cycles or applications. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie202969u