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Adsorption and desorption of SOx on diesel oxidation catalysts / Oliver Krocher in Industrial & engineering chemistry research, Vol. 48 N° 22 (Novembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 22 (Novembre 2009) . - pp. 9847–9857 Titre : Adsorption and desorption of SOx on diesel oxidation catalysts Type de document : texte imprimé Auteurs : Oliver Krocher, Auteur ; Markus Widmer, Auteur ; Martin Elsener, Auteur Année de publication : 2010 Article en page(s) : pp. 9847–9857 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : NO  oxidation  SO2Diesel  oxidation  catalysts Résumé : The deactivation of NO oxidation by SO2 was studied with the use of commercial diesel oxidation catalysts (DOC) and Pt/Al2O3 as reference material, coated on cordierite monolith. Despite their slightly different elemental compositions, the NO conversion rates of the fresh commercial catalysts were very similar. The maximum NO conversion was 38% at 350 °C, and above this temperature conversion started to be limited by the thermodynamics of the reaction. The rates of NO conversion strongly decreased with the start of SO2 dosing. For analysis of SO2 conversion and uptake, SO2 and SO3/H2SO4 were determined separately in the gas phase by absorption and titration. Under typical exhaust gas conditions (1 ppm SO2, 250 °C), the catalysts functioned as sulfur traps and stored a large part of the emitted SO2. The SOx storage was divided into two phases: a fast saturation of the catalyst surface with sulfuric acid, which hampered NO conversion, and a slow, long-lasting sulfation of the washcoat. The storage capacities of the oxidation catalysts reached their maxima at 250 °C due to the temperature dependency of sulfur adsorption and desorption. Adsorbed sulfuric acid desorbed between 350 and 400 °C, whereas more stable compounds, such as aluminum sulfate, were decomposed at higher temperatures. Deactivated catalysts could be completely regenerated within a few minutes at temperatures above 350 °C. However, repeated or lengthier thermal treatments resulted in a reduced sulfur storage capacity and irreversible activity losses for NO oxidation due to a reduction of the active surface by sintering. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900882p [article] Adsorption and desorption of SOx on diesel oxidation catalysts [texte imprimé] / Oliver Krocher, Auteur ; Markus Widmer, Auteur ; Martin Elsener, Auteur . - 2010 . - pp. 9847–9857. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 22 (Novembre 2009) . - pp. 9847–9857 Mots-clés : NO  oxidation  SO2Diesel  oxidation  catalysts Résumé : The deactivation of NO oxidation by SO2 was studied with the use of commercial diesel oxidation catalysts (DOC) and Pt/Al2O3 as reference material, coated on cordierite monolith. Despite their slightly different elemental compositions, the NO conversion rates of the fresh commercial catalysts were very similar. The maximum NO conversion was 38% at 350 °C, and above this temperature conversion started to be limited by the thermodynamics of the reaction. The rates of NO conversion strongly decreased with the start of SO2 dosing. For analysis of SO2 conversion and uptake, SO2 and SO3/H2SO4 were determined separately in the gas phase by absorption and titration. Under typical exhaust gas conditions (1 ppm SO2, 250 °C), the catalysts functioned as sulfur traps and stored a large part of the emitted SO2. The SOx storage was divided into two phases: a fast saturation of the catalyst surface with sulfuric acid, which hampered NO conversion, and a slow, long-lasting sulfation of the washcoat. The storage capacities of the oxidation catalysts reached their maxima at 250 °C due to the temperature dependency of sulfur adsorption and desorption. Adsorbed sulfuric acid desorbed between 350 and 400 °C, whereas more stable compounds, such as aluminum sulfate, were decomposed at higher temperatures. Deactivated catalysts could be completely regenerated within a few minutes at temperatures above 350 °C. However, repeated or lengthier thermal treatments resulted in a reduced sulfur storage capacity and irreversible activity losses for NO oxidation due to a reduction of the active surface by sintering. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900882p

Combination of V2O5/WO3 - TiO2, Fe - ZSM5, and Cu - ZSM5 Catalysts for the selective catalytic reduction of nitric oxide with ammonia / Oliver Krocher ; Martin Elsener in Industrial & engineering chemistry research, Vol. 47 n°22 (Novembre 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°22 (Novembre 2008) . - p. 8588–8593 Titre : Combination of V2O5/WO3 - TiO2, Fe - ZSM5, and Cu - ZSM5 Catalysts for the selective catalytic reduction of nitric oxide with ammonia Type de document : texte imprimé Auteurs : Oliver Krocher, Auteur ; Martin Elsener, Auteur Année de publication : 2008 Article en page(s) : p. 8588–8593 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : V2O5/WO3−TiO2,Fe−ZSM5,Cu−ZSM5 Résumé : Cordierite monoliths coated with V2O5/WO3−TiO2, Fe−ZSM5, and Cu−ZSM5 catalysts were combined to investigate the possibility of combining the advantages of the different single catalysts for the selective catalytic reduction of nitric oxide with ammonia (NO SCR) while minimizing their drawbacks. Selected combinations of two of the three above-mentioned catalysts were connected in series such that the volume of each catalyst was halved in order to maintain the total space velocity constant. The combinations V2O5/WO3−TiO2 followed by Fe−ZSM5 and the reversed catalyst order achieved markedly lower NOx reduction efficiencies (DeNOx) than the pure vanadia-based catalyst. Fe−ZSM5 applied downstream of V2O5/WO3−TiO2 did not reduce the N2O formed over the V-based catalyst at temperatures above 450 °C, as expected from the known N2O decomposition and N2O SCR activities of Fe−ZSM5. When V2O5/WO3−TiO2 was mounted downstream of Fe−ZSM5, ammonia slip was observed even at small NOx reduction efficiencies. The combination of Fe−ZSM5 and Cu−ZSM5 showed high activities at temperatures from 200 to 700 °C with small N2O formation, similar to pure Fe−ZSM5. V2O5/WO3−TiO2 combined with Cu−ZSM5 showed slightly higher activity at lower temperatures than V2O5/WO3−TiO2 only. At temperatures above 350 °C potential ammonia excess was selectively oxidized to nitrogen; in other words, Cu−ZSM5 functions as a selective catalyst for ammonia oxidation. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800951a [article] Combination of V2O5/WO3 - TiO2, Fe - ZSM5, and Cu - ZSM5 Catalysts for the selective catalytic reduction of nitric oxide with ammonia [texte imprimé] / Oliver Krocher, Auteur ; Martin Elsener, Auteur . - 2008 . - p. 8588–8593. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°22 (Novembre 2008) . - p. 8588–8593 Mots-clés : V2O5/WO3−TiO2,Fe−ZSM5,Cu−ZSM5 Résumé : Cordierite monoliths coated with V2O5/WO3−TiO2, Fe−ZSM5, and Cu−ZSM5 catalysts were combined to investigate the possibility of combining the advantages of the different single catalysts for the selective catalytic reduction of nitric oxide with ammonia (NO SCR) while minimizing their drawbacks. Selected combinations of two of the three above-mentioned catalysts were connected in series such that the volume of each catalyst was halved in order to maintain the total space velocity constant. The combinations V2O5/WO3−TiO2 followed by Fe−ZSM5 and the reversed catalyst order achieved markedly lower NOx reduction efficiencies (DeNOx) than the pure vanadia-based catalyst. Fe−ZSM5 applied downstream of V2O5/WO3−TiO2 did not reduce the N2O formed over the V-based catalyst at temperatures above 450 °C, as expected from the known N2O decomposition and N2O SCR activities of Fe−ZSM5. When V2O5/WO3−TiO2 was mounted downstream of Fe−ZSM5, ammonia slip was observed even at small NOx reduction efficiencies. The combination of Fe−ZSM5 and Cu−ZSM5 showed high activities at temperatures from 200 to 700 °C with small N2O formation, similar to pure Fe−ZSM5. V2O5/WO3−TiO2 combined with Cu−ZSM5 showed slightly higher activity at lower temperatures than V2O5/WO3−TiO2 only. At temperatures above 350 °C potential ammonia excess was selectively oxidized to nitrogen; in other words, Cu−ZSM5 functions as a selective catalyst for ammonia oxidation. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800951a

Determination of effective diffusion coefficients through the walls of coated diesel particulate filters / Oliver Krocher in Industrial & engineering chemistry research, Vol. 48 N° 23 (Décembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 23 (Décembre 2009) . - pp. 10746–10750 Titre : Determination of effective diffusion coefficients through the walls of coated diesel particulate filters Type de document : texte imprimé Auteurs : Oliver Krocher, Auteur ; Martin Elsener, Auteur ; Martin Votsmeier, Auteur Année de publication : 2010 Article en page(s) : pp. 10746–10750 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Determination--Effective--Diffusion--Coefficients--through--Walls--Coated  Diesel--Particulate  Filters Résumé : We demonstrate in this paper that the effective diffusion coefficient in the wall of a particulate filter can be determined by measuring the diffusion of NO between two adjacent channels of a filter segment in a simple apparatus based on a modified experimental method of Beeckman. The effective diffusion coefficient in the walls of an uncoated SiC particulate filter is determined as 2.8 × 10−6 m2/s at room temperature. Coating the filter with 30 or 65 g/L of wall-integrated washcoat leads to an insignificant increase in the diffusion coefficient, whereas coating the same filter with a high washcoat loading of 140 g/L leads to a decrease of the diffusion coefficient to 2.0 × 10−6 m2/s. All of the determined diffusion coefficients increase with temperature proportional to T1.5. This indicates that the diffusion in the wall is mainly molecular diffusion and that Knudsen diffusion plays a minor role. Fitting the parallel pore model to the experimental diffusion coefficient of the uncoated filter results in a tortuosity factor of 3.5. The random pore model overpredicts the effective diffusion coefficient by almost 50%. Neither of the two models reproduces the threshold-type dependency of the effective diffusion coefficient on washcoat loading. However, all experimental results are predicted by both pore models with an accuracy of better than 50%, so that an estimation of the effective diffusion coefficient might be a feasible solution for many practical simulation tasks. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901269v [article] Determination of effective diffusion coefficients through the walls of coated diesel particulate filters [texte imprimé] / Oliver Krocher, Auteur ; Martin Elsener, Auteur ; Martin Votsmeier, Auteur . - 2010 . - pp. 10746–10750. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 23 (Décembre 2009) . - pp. 10746–10750 Mots-clés : Determination--Effective--Diffusion--Coefficients--through--Walls--Coated  Diesel--Particulate  Filters Résumé : We demonstrate in this paper that the effective diffusion coefficient in the wall of a particulate filter can be determined by measuring the diffusion of NO between two adjacent channels of a filter segment in a simple apparatus based on a modified experimental method of Beeckman. The effective diffusion coefficient in the walls of an uncoated SiC particulate filter is determined as 2.8 × 10−6 m2/s at room temperature. Coating the filter with 30 or 65 g/L of wall-integrated washcoat leads to an insignificant increase in the diffusion coefficient, whereas coating the same filter with a high washcoat loading of 140 g/L leads to a decrease of the diffusion coefficient to 2.0 × 10−6 m2/s. All of the determined diffusion coefficients increase with temperature proportional to T1.5. This indicates that the diffusion in the wall is mainly molecular diffusion and that Knudsen diffusion plays a minor role. Fitting the parallel pore model to the experimental diffusion coefficient of the uncoated filter results in a tortuosity factor of 3.5. The random pore model overpredicts the effective diffusion coefficient by almost 50%. Neither of the two models reproduces the threshold-type dependency of the effective diffusion coefficient on washcoat loading. However, all experimental results are predicted by both pore models with an accuracy of better than 50%, so that an estimation of the effective diffusion coefficient might be a feasible solution for many practical simulation tasks. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901269v