Reactivity of shape-controlled crystals and metadynamics simulations locate the weak spots of alumina in water

International audienceThe kinetic stability of any material in water relies on the presence of surface weak spots responsible for chemical weathering by hydrolysis. Being able to identify the atomistic nature of these sites and the first steps of transformation is therefore critical to master the decomposition processes. This is the challenge that we tackle here: combining experimental and modeling studies we investigate the stability of alumina in water. Exploring the reactivity of shape-controlled crystals, we identify experimentally a specific facet as the location of the weak spots. Using biased ab initio molecular dynamics, we recognize this weak spot as a surface exposed tetra-coordinated Al atom and further provide a detailed mechanism of the first steps of hydrolysis. This understanding is of great importance to heterogeneous catalysis where alumina is a major support. Furthermore, it paves the way to atomistic understanding of interfacial reactions, at the crossroad of a variety of fields of research

Innovative way to stabilize catalysts for biomass transformation methods

SSCI-VIDE+CDFA:ING+EGR:ATU:MBEInternational audienceNon

Innovative way to stabilize catalysts for biomass transformation methods

SSCI-VIDE+CDFA:ING+EGR:ATU:MBEInternational audienceNon

Unexpected selectivity of ferrierite for the conversion of isobutanol to linear butenes and water effects

International audienceFerrierite was shown to be highly efficient in the conversion of isobutanol to butenes with selectivity values higher than 98%. Furthermore, its isomerisation activity is remarkable since proportion of linear butenes higher than 80% was obtained in the present study confirming patents claims. This selectivity was shown to increase with temperature and contact time as well as with time on stream.Neither water added to the feed nor water generated by dehydration has an impact on the structure of ferrierite as shown by XRD and 27Al NMR. A slight enhancement of catalytic activity was observed below 250 °C and could be due to an increase in the number of BAS as suggested by in situ acidity measurements achieved at the reaction temperatures in presence of water vapor while competition of adsorption would inhibit the catalytic activity above 250 °C. Furthermore, water was shown to improve dramatically selectivity to linear butenes at low conversion. We propose that water inhibits the proton shift of isobutylcarbenium ions or deprotonation sites leading to isobutene but not acid sites able to isomerize isobutylcarbenium ions into linear carbocations leading to linear butenes. At high conversions, both coke formation and water generated by dehydration could improve selectivity to linear butenes by neutralization of unselective sites responsible for proton-shift reaction

Adsorption of H2 on a nickel catalyst by a frequency response method

SSCI-VIDE+ING+CUR:YSCInternational audienceKinetic experiments performed under stationary conditions mainly give information on the rate determining step. Numerous experiments must be done for a limited number of parameters obtained. On the opposite, unsteady state experiments give more details information about the kinetics of the different elementary steps, for a limited number of experiment

Cu/Carbon xerogel catalysts for the selective catalytic reduction of NO by NH3 : effect of the pore texture

peer reviewe

Adsorption of H2 on a nickel catalyst by a frequency response method

SSCI-VIDE+ING+CUR:YSCNational audienceThe presentation will be mainly focused on the study of transient experiments

Innovative way to stabilize alumina for biomass transformation reactions

SSCI-VIDE+CDFA:ING+EGR:ATU:MBENational audienceNon

Xylitol hydrogenolysis over Ru-based catalysts: neutral or alkaline conditions and basic oxide promoted catalysts

SSCI-VIDE+CDFA+MRI:MBE:CPI:NPRInternational audienceHydrogenolysis of biomass-derived sugar alcohols (e.g. xylitol) is a promising alternative way to fossil resources for responding to the increasing demand of ethylene and propylene glycols (EG and PG). The reaction in aqueous solution requires a heterogeneous catalyst (Ru or Ni) and a homogeneous alkaline promoter such as NaOH or Ca(OH)2 with polyol/OH- molar ratio around 0.2 to 0.4. High temperatures (180-220°C) and high H2 pressures (45-80 bar) are used. Ru based catalysts are particularly attractive since they exhibit the best activity. Numerous reactions occur such as (de)hydrogenation, retro-aldol condensation, decarbonylation, epimerization and dehydration, involving an interesting challenge to obtain selectively the desired products. The goal of our study was to investigate the effect of Ca(OH)2 amount for glycols production and to develop bifunctional catalysts associating a basic oxide and Ru on active carbon to operate in base-free conditions

Transformation of Sorbitol to Biofuels by Heterogeneous Catalysis: Chemical and Industrial Considerations Transformation du sorbitol en biocarburants par catalyse hétérogène : considérations chimiques et industrielles

Decreasing oil supplies and increasing energy demand provide incentives to find alternative fuels. First, the valorisation of edible crops for ethanol and biodiesel production led to first generation biofuels. Nowadays, research is focused on lignocellulosic biomass as a source of renewable carbon (second generation biofuels). Whereas the cellulosic ethanol production is in progress, a new way consisting of the transformation of ex-lignocellulose sugars and polyols towards light hydrocarbons by heterogeneous catalysis in aqueous phase has been recently described. This process is performed under mild conditions (T La raréfaction du pétrole et l’augmentation conjointe de la demande en carburants ont conduit à la recherche de carburants alternatifs. Dans un premier temps, la valorisation de ressources agricoles alimentaires pour la production d’éthanol et de biodiesel a permis de développer les biocarburants de première génération. Aujourd’hui les travaux de recherche s’orientent vers l’utilisation de biomasse lignocellulosique comme source de carbone renouvelable (biocarburants de deuxième génération). Alors que la filière de l’éthanol cellulosique est en plein développement, une nouvelle voie consistant à transformer des sucres et polyols d’origine lignocellulosique en alcanes légers par catalyse hétérogène bifonctionnelle en phase aqueuse a été récemment décrite. Ce procédé s’effectue à basse température et pression modérée (T < 300 °C et P < 50 bar). Il nécessite, d’une part, la formation d’hydrogène par reformage catalytique de carbohydrates en phase aqueuse et, d’autre part, la déshydratation/hydrogénation de polyols conduisant à un alcane par ruptures sélectives des liaisons C-O. Un défi lié à cette thématique réside dans le développement de systèmes catalytiques multifonctionnels stables, actifs et sélectifs dans les conditions de la réaction de transformation. L’objectif de l’article est de présenter les réactions mises en jeu, les systèmes catalytiques décrits dans la littérature pour ce type de transformation ainsi que des exemples d’applications industrielles