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Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP / Ashok Kumar in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10334-10340 Titre : Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP Type de document : texte imprimé Auteurs : Ashok Kumar, Auteur ; Michael P. Harold, Auteur ; Vemuri Balakotaiah, Auteur Année de publication : 2011 Article en page(s) : pp. 10334-10340 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Catalyst  Diffusion  coefficient Résumé : A systematic study over Pt/BaO/Al2O3 powder catalyst is carried out using Temporal Analysis of Products (TAP) to estimate the effective diffusivity of stored NO, in the barium phase. The prenitration of PtBaO/ Al2O3 using sequential pulses of NO, followed by reduction with H2 results in the evolution of N2 and NH3. The reduction is carried out in the NOx transport limited regime in which diffusion of the stored NO, from BaO storage phase to Pt/BaO interface was determined to be the rate controlling process. The effluent profiles of N containing species (2N2 + NH3) were used to estimate stored NO, diffusivity in barium phase and the apparent activation energy. The activation energy (74-81 kJ/mol) is in good agreement with the estimated value of 75 kJ/mol from a recent NO, trap modeling study.1. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447924 [article] Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP [texte imprimé] / Ashok Kumar, Auteur ; Michael P. Harold, Auteur ; Vemuri Balakotaiah, Auteur . - 2011 . - pp. 10334-10340. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10334-10340 Mots-clés : Catalyst  Diffusion  coefficient Résumé : A systematic study over Pt/BaO/Al2O3 powder catalyst is carried out using Temporal Analysis of Products (TAP) to estimate the effective diffusivity of stored NO, in the barium phase. The prenitration of PtBaO/ Al2O3 using sequential pulses of NO, followed by reduction with H2 results in the evolution of N2 and NH3. The reduction is carried out in the NOx transport limited regime in which diffusion of the stored NO, from BaO storage phase to Pt/BaO interface was determined to be the rate controlling process. The effluent profiles of N containing species (2N2 + NH3) were used to estimate stored NO, diffusivity in barium phase and the apparent activation energy. The activation energy (74-81 kJ/mol) is in good agreement with the estimated value of 75 kJ/mol from a recent NO, trap modeling study.1. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447924

Experimental and theoretical investigation of controlling regimes during lean oxidation of methane and propylene on Pt /Al2O3 monolithic reactors / Saurabh Y. Joshi in Industrial & engineering chemistry research, Vol. 51 N° 22 (Juin 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 22 (Juin 2012) . - pp. 7482–7492 Titre : Experimental and theoretical investigation of controlling regimes during lean oxidation of methane and propylene on Pt /Al2O3 monolithic reactors Type de document : texte imprimé Auteurs : Saurabh Y. Joshi, Auteur ; Yongjie Ren, Auteur ; Michael P. Harold, Auteur Année de publication : 2012 Article en page(s) : pp. 7482–7492 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Controlling  regimes  Oxidation  methane Résumé : The performance of a catalytic reactor is bounded by the kinetic regime at low temperature (or before light-off) and the mass-transfer-controlled regime at high temperature. Pore diffusion may also be significant at intermediate temperature. We utilize the recently developed criteria (Joshi, S. Y.; Harold, M. P.; Balakotaiah, V. Chem. Eng. Sci.2010, 65, 1729–1747) to characterize the controlling regimes during lean oxidation of CH4 and C3H6 in Pt/Al2O3 monolithic reactors. First, we determine the global kinetics of lean oxidation of CH4 and C3H6 in a Pt/Al2O3 monolithic catalyst. We also present a method for estimation of the effective diffusivity of the limiting reactant and the external mass-transfer coefficient under reacting conditions. Further, we characterize the relative contributions of chemical kinetics, washcoat diffusion, and external mass transfer as a function of the various catalyst design and operating parameters. The analysis reveals that methane oxidation is kinetically controlled over a wide range of temperatures (350–600 °C) whereas propylene oxidation has a more classical transition between the kinetic and mass-transfer-controlled regimes. We use the bench-scale results to analyze the impact of various design and operating variables on transitions between the controlling regimes. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201653e [article] Experimental and theoretical investigation of controlling regimes during lean oxidation of methane and propylene on Pt /Al2O3 monolithic reactors [texte imprimé] / Saurabh Y. Joshi, Auteur ; Yongjie Ren, Auteur ; Michael P. Harold, Auteur . - 2012 . - pp. 7482–7492. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 22 (Juin 2012) . - pp. 7482–7492 Mots-clés : Controlling  regimes  Oxidation  methane Résumé : The performance of a catalytic reactor is bounded by the kinetic regime at low temperature (or before light-off) and the mass-transfer-controlled regime at high temperature. Pore diffusion may also be significant at intermediate temperature. We utilize the recently developed criteria (Joshi, S. Y.; Harold, M. P.; Balakotaiah, V. Chem. Eng. Sci.2010, 65, 1729–1747) to characterize the controlling regimes during lean oxidation of CH4 and C3H6 in Pt/Al2O3 monolithic reactors. First, we determine the global kinetics of lean oxidation of CH4 and C3H6 in a Pt/Al2O3 monolithic catalyst. We also present a method for estimation of the effective diffusivity of the limiting reactant and the external mass-transfer coefficient under reacting conditions. Further, we characterize the relative contributions of chemical kinetics, washcoat diffusion, and external mass transfer as a function of the various catalyst design and operating parameters. The analysis reveals that methane oxidation is kinetically controlled over a wide range of temperatures (350–600 °C) whereas propylene oxidation has a more classical transition between the kinetic and mass-transfer-controlled regimes. We use the bench-scale results to analyze the impact of various design and operating variables on transitions between the controlling regimes. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201653e

Methanol steam reforming in Pd − Ag membrane reactors / Sameer H. Israni in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) Titre : Methanol steam reforming in Pd − Ag membrane reactors : Effects of reaction system species on transmembrane hydrogen flux Type de document : texte imprimé Auteurs : Sameer H. Israni, Auteur ; Michael P. Harold, Auteur Année de publication : 2011 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Membrane  reactor  Steam  reforming Résumé : The objective of this study is to understand and quantify the effects of the reactant and product species of the methanol steam reforming reaction (CH3OH, H2O, CO2, CO) on the H2 flux through a Pd77Ag23 membrane. Various concentrations of said gases along with H2 were fed to a membrane separator apparatus containing a 3.9 μm thick Pd—Ag (23 wt % Ag) "nanopore" membrane. The decrease in H2 flux through the membrane due to the presence of these gases was quantified at different temperatures (225-300 °C) and pressures (3―5 bar). The data show that CO causes the largest drop in H2 flux while H2O has the least effect. A mechanistically based adsorption and reaction model was developed to quantify the fractional surface coverages of the non-H2 species. Estimates of surface parameters such as adsorption equilibrium constants and binding energies are consistent with literature values. The adsorption model was incorporated into a two-dimensional separator model that accounted for concentration polarization (radial transport) effects. The model simulations successfully captured most of the trends in the flux data. The developed flux model is suitable for incorporation into a Pd-Ag membrane reactor model in order to evaluate the potential of a methanol membrane reformer for coupled hydrogen generation and purification. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447913 [article] Methanol steam reforming in Pd − Ag membrane reactors : Effects of reaction system species on transmembrane hydrogen flux [texte imprimé] / Sameer H. Israni, Auteur ; Michael P. Harold, Auteur . - 2011. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) Mots-clés : Membrane  reactor  Steam  reforming Résumé : The objective of this study is to understand and quantify the effects of the reactant and product species of the methanol steam reforming reaction (CH3OH, H2O, CO2, CO) on the H2 flux through a Pd77Ag23 membrane. Various concentrations of said gases along with H2 were fed to a membrane separator apparatus containing a 3.9 μm thick Pd—Ag (23 wt % Ag) "nanopore" membrane. The decrease in H2 flux through the membrane due to the presence of these gases was quantified at different temperatures (225-300 °C) and pressures (3―5 bar). The data show that CO causes the largest drop in H2 flux while H2O has the least effect. A mechanistically based adsorption and reaction model was developed to quantify the fractional surface coverages of the non-H2 species. Estimates of surface parameters such as adsorption equilibrium constants and binding energies are consistent with literature values. The adsorption model was incorporated into a two-dimensional separator model that accounted for concentration polarization (radial transport) effects. The model simulations successfully captured most of the trends in the flux data. The developed flux model is suitable for incorporation into a Pd-Ag membrane reactor model in order to evaluate the potential of a methanol membrane reformer for coupled hydrogen generation and purification. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447913