Continuous hydrogen production by sequential catalytic cracking of acetic acid. Part II. Mechanistic features and characterisation of catalysts under redox cycling

Davidian, Thomas Guilhaume, Nolven Provendier, Helene Mirodatos, ClaudeIn this study, the mechanism of sequential cracking of acetic acid (AA) over Ni-based catalysts was investigated. During AA cracking, both thermal and catalytic reactions take place. Acetic acid is thermally decomposed into CH4, CO, CO2 and H-2, which further react on Ni through WGS and steam reforming reactions, whereas some coke accumulates on the catalyst. The statistical distribution of labelled C*O-2 species suggests fast isotopic exchange between CO2 and surface carbonates. During the regeneration, the coke deposited during cracking is fully burnt, and carbonates are thermally decomposed. O-18(2) isotopic labelling experiments coupled with physico-chemical characterisations of catalysts, after cracking and regeneration steps, reveal that the nickel is reduced by cracking products at the beginning of each cracking step, and oxidized during the regeneration. This redox cycling progressively extracts metallic Ni, initially present as Ni2+ species incorporated in spinel-type structures. (c) 2007 Elsevier B.V. All rights reserved

Analyse par DRX et MET de l'évolution de la solution solide LaNixFe1-xO3 et de la ségrégation de nickel dans les conditions d'obtention du gaz de synthèse par oxydation partielle du méthane

Des oxydes mixtes de formulation LaNixFe1-xO3 ont été préparés par la méthode des résines et ont été évalués comme catalyseurs pour l'oxydation partielle du méthane en gaz de synthèse sans traitement réducteur préalable. Les analyses DRX et MET montrent la formation d'une solution solide de LaNiO3 et de LaFeO3 et la grande homogénéité des systèmes. L'étude par DRX et MET des phases obtenues après tests a permis de contrôler la migration d'une partie du nickel hors de la structure perovskite et sa possible réintroduction par traitement oxydant pour les structures trimétalliques avec x≤0,4.Mixed perovskite oxides of LaNixFe1-xO3 (0≤x≤1) have been prepared by sol-gel like method and evaluated as catalysts for the partial oxidation of methane into synthesis gas without previous hydrogen treatment. The XRD and TEM analysis show the formation of a solid solution and the high homogeneity of the systems. The studies of the phases obtained after catalytic test permit to control the migration of a part of nickel and its possible redispersion under oxidative treatment for trimetallic structures with values of x lower than x=0.4

Hydrogen production from crude pyrolysis oil by a sequential catalytic process

International audienceA sequential process aiming at hydrogen production was studied over two Ni-based catalysts, using crude beech-wood oil as the feed. The process alternates cracking/reforming steps, during which a H2 + CO rich stream is produced and carbon is stored on the catalyst, with regeneration steps where the carbon is combusted under oxygen. The two catalysts exhibited good performances for H2 production from bio-oil, the gaseous products stream consisting in 45–50% H2. The regeneration step was found fast and efficient, the coke being readily combusted and the catalyst activity fully recovered. A positive heat balance between the endothermic cracking/reforming reactions and the exothermic coke combustion suggests that an autothermal process could be designed. Comparison of the thermal decomposition of bio-oil (empty reactor) with the catalytic cracking revealed that they are first decomposed into primary light gases (CO, CO2, CH4, C2+) and soots. These compounds are further reformed onto the catalyst by the steam contained in bio-oil, and equilibrated via the WGS reaction. The key roles of the catalyst are therefore (i) to improve the overall bio-oil gasification into syngas, (ii) to promote steam reactions and increase hydrogen production by steam reforming and WGS and (iii) to control and determine the nature of the coke formed during the cracking/reforming step. A Ni/Al2O3 catalyst with large Ni particles was found to promote the formation of carbon filaments, whereas on a Ni–K/La2O3–Al2O3 catalyst, with a lower Ni loading and highly dispersed Ni, the carbon was essentially deposited as an amorphous carbon layer

Hydrogen production from ethanol steam reforming over Ir/ceria catalysts: enhanced stability after Pr promotion

SSCI-VIDE+CARE:ING+HPR:CDS:YSC:CMIInternational audienceNon

From mechanistic to kinetic analyses of ethanol steam reforming over Ir/CeO2 catalyst

SSCI-VIDE+CARE:ING+HPR:CDS:YSC:CMIInternational audienceNon

From mechanistic to kinetic analyses of ethanol steam reforming over Ir/CeO2 catalyst

SSCI-VIDE+CARE:ING+FWA:WCA:CDS:HPR:CMI:YSCInternational audienceThis work presents a kinetic analysis of ethanol steam reforming (ESR) over a performing Ir/CeO2 catalyst based on a bi-functional mechanism. A first conventional power-law based kinetic study was carried out by varying the main operating parameters (temperature, steam/ethanol molar ratio and partial pressure of products). A limited fit was achieved between the experimental data and the data calculated from this model based on a single type of site, demonstrating the need of a kinetic analysis integrating more closely the demonstrated bi-functional mechanism of the reaction. A kinetic model considering two distinct adsorption sites, on ceria support and on iridium particles, was then considered and only reactions involving the two types of sites, i.e. occurring at the ceria/metal interface, were used to build that model. A good agreement between the experimental data and the model was obtained, without systematic deviations. The central role of the metal-support interface was also consistent with the deactivation of this catalyst upon sintering, related to both changes in metal and support dispersion with time on stream. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Spatially resolved operando infrared analysis of a microstructured catalytic surface for CO oxidation over Pt based catalysts

INGENIERIE+AVA:CDA:CMI:HPR:MOC:YSCA new experimental reactor concept was developed for operando and spatially resolved DRIFTS surface analysis over a microstructured catalytic reactor. Both gas and surface adspecies concentration profiles can be established along the channels coated with catalyst.The oxidation of carbon monoxide was studied from 25 to 300 °C over a Pt/CeO2–Al2O3 catalyst. For these operating conditions nearly isothermal conditions were observed for the microstructured reactor, with a continuous increase in conversion along the microchannels. In contrast, an important thermal effect with characteristic light-off was obtained in the fixed bed reactor, underlining the unique behaviour of the microstructured system.Modelling of the CO conversion and surface adspecies concentration as a function of temperature along the channels was performed on the basis of a simple reaction mechanism. Kinetic parameters depending on the catalyst composition were obtained, in good agreement with literature data