1,721,106 research outputs found
Amphiphilic Janus particles for aerobic alcohol oxidation in oil foams
Full text linkAmphiphilic Janus silica particles, tunable with oleophobic–oleophilic properties and low fluorine content (8 wt % F), exhibited prominent foamability for a variety of aromatic alcohols at low particle concentrations (<1 wt %) compared to randomly functionalized silica particles. When selectively loaded with Pd nanoparticles on the oleophilic hemisphere, the particles displayed more than a 2-fold increase in catalytic activity for the aerobic oxidation of benzyl alcohol compared to nonfoam bulk catalysis under ambient O2 pressure. The particles were conveniently recycled with high foamability and catalytic activity maintained for at least five consecutive runs
Synthesis of amine derivatives from furoin and furil over a Ru/Al<sub>2</sub>O<sub>3</sub> catalyst
Full text linkThe direct/reductive amination of carbohydrate-based furoin and furil with NH3/H2 was investigated to access amine derivatives. In the sole presence of NH3, cyclic amines, i.e. 2,3,5,6-tetra(furan-2-yl)pyrazine and 2,2′-bipyridine-3,3′-diol, were generated as the main products from furoin and furil, respectively. Over Ru/Al2O3 under NH3/H2, 2-amino-1,2-di(furan-2-yl)ethan-1-ol (i.e. alcohol–amine) was generated as the main product with 47% yield at 140 °C for 2 h starting from furoin. The catalyst could be recycled for at least three consecutive runs. An alcohol–imine was the main intermediate that underwent tautomerization to alcohol–enamine/keto–amine leading to cyclic by-products by self-condensation. DFT calculations, complementing the experimental observations, provided detailed molecular-level insight into the reactivity of the alcohol–imine intermediate. Its preferential adsorption on Ru centers via the NH group, with the OH group pointing away from the surface, was found to direct its hydrogenation towards the alcohol–amine as main product. By combining Ru/Al2O3 and a silica-anchored N-heterocyclic carbene (NHC) catalyst, the alcohol-amine could be accessed with 42% overall yield in a single reactor
On a rapid method to characterize intercrystalline defects in zeolite membranes using pervaporation data
No full textPera-Titus, Marc Llorens, Joan Cunill, FidelThis work presents a mass-balance-based model devoted to the characterization of intercrystalline defects active to permeation in film-like zeolite membranes using pervaporation data. Relevant structural information concerning such domains can be obtained from the slope and intercept of the line that describes the increase of the flux pervaporated through a membrane with the absolute pressure in the liquid feed. Capillary forces appear to govern mass transfer within intercrystalline pores. The suitability of the model is assessed by using a collection of zeolite NaA membranes prepared on our premises for the separation of ethanol/water mixtures. The results show that, although a membrane displays high selectivity, a reduced number of defects in the zeolite layers cannot be ruled out. The model offers the advantage of enabling the characterization of large defects in pervaporation membranes at experimental conditions similar to those in which they are likely to be used. (c) 2008 Elsevier Ltd. All rights reserved
Influence of pore size in benzoin condensation of furfural using heterogenized benzimidazole organocatalysts
No full textA designed N-heterocyclic carbene (NHC) catalyst was covalently anchored on a range of mesoporous and hierarchical supports, to study the influence of pore size in the benzoin condensation of furfural. The structural and spectroscopic characteristics of the anchored catalysts were investigated, also with the help of molecular dynamics simulations, in order to rationalize the degree of stability and recyclability of the heterogenized organocatalysts. Quantitative yields (99 %) and complete recyclability were maintained after several cycles, vindicating the design rationale.</p
Technical and economical feasibility of zeolite NaA membrane-based reactors in liquid-phase etherification reactions
No full textPera-Titus, Marc Llorens, Joan Cunill, FidelThis paper describes the pervaporation performance of film-like zeolite NaA membranes synthesized in our laboratory by template-free seeded hydrothermal towards the dehydration of n-pentanol/water and n-pentanol/water/DNPE mixtures (DNPE=di-n-pentyl ether, C10H22O). DNPE is a linear symmetric ether that can be used as blending additive in reformulated diesel fuels and that can be produced from C-4 feedstocks via n-pentanol, obtained in its turn by selective hydroformylation of linear butenes. The membranes showed selectivities up to 3000 in the dehydration of n-pentanol/water binary mixtures, and water/DNPE and n-pentanol/DNPE selectivities approaching infinity (i.e. DNPE does not pervaporate) in the dehydration of n-pentanol/water/DNPE ternary mixtures. On the basis of the separation results presented in this work, and using experimental reaction kinetics data, we discuss the feasibility of zeolite NaA membrane reactors to carry out the liquid-phase etherification reaction of n-pentanol to di-n-pentyl ether(DNPE) catalyzed by ion-exchange sulfonated resins. These catalysts suffer from strong deactivation in the progress of the reaction due to the generation of water. (C) 2009 Elsevier B.V. All rights reserved
Evaluation of Energy Heterogeneity in Metal−Organic Frameworks: Absence of Henry’s Region in MIL-53 and MIL-68 Materials?
No full textPera-Titus, Marc Savonnet, Marie Farrusseng, DavidWe present in dos study a detailed thermodynamic analysis of N-2 adsorption at 77.4 K and low pressures in a series of metal-organic framework materials displaying different structures, pore textures, and framework flexibility. The energy heterogeneity of these materials has been quantified using a thermodynamic isotherm model developed in previous studies through two characteristic parameters. This formulation also allows the generation of an equation differing from the Dubinin-Astakhov isotherm that allows a proper description or gas adsorption at low pressures. Unlike zeolites or rigid coordination polymers, highly flexible MIL-53(AI) and MIL-68(In) materials are characterized by N-2 adsorption isotherms lacking of a characteristic Henry's region (linear trend) at low relative pressures. We argue about an unexpected promotion of energy heterogeneity on these materials due to sorbate-induced elastic deformation ascribed to compression tensions to explain this observation
Hexafluoroisopropanol : un solvant de choix permettant l’amination catalytique et sélective d’alcènes
No full textLe développement de méthodologies permettant la synthèse d'amines à partir de matières premières abondantes et peu onéreuses représente un enjeu majeur dans différents domaines de la chimie. Au cours de ce travail de thèse, nous avons développé différentes approches catalytiques permettant d’accéder à diverses amines à partir d'alcènes simples, via des voies d'hydroamination, hydroarylation, hydroaminoalkylation et hydroaminométhylation. Dans un premier temps, nous avons montré que la combinaison de triflate de bismuth et d'hexafluoroisopropanol (HFIP) conduisait à la formation d'espèces catalytiques hautement actives capables de promouvoir l'hydroarylation d'alcènes non activés tels que le 1-octène, le 1-heptène et le 1-undécène avec l'aniline, et ce avec des sélectivités élevées (71-92%). En combinant chimie expérimentale et chimie théorique, nous avons proposé un mécanisme réactionnel où l’HFIP stabilise les états de transition via des liaisons H avec l'anion triflate, assistant ainsi le catalyseur acide dans l'hydroarylation des alcènes.Par la suite, nous avons étudié cette réaction en présence d’un catalyseur hétérogène, et plus particulièrement l'Aquivion® PFSA, en utilisant l'hydroarylation du norbornène avec l'aniline en tant réaction modèle. Nous avons montré que l'Aquivion® PFSA était non seulement actif et stable mais pouvait également être recyclé au moins six fois sans diminution des performances catalytiques. Afin de permettre l’accès à des amines aliphatiques (secondaires et tertaires), nous avons ensuite développé une réaction, catalysée par la diméthylamine, de couplage entre le formaldéhyde et un alcène, conduisant à la formation d’aldéhydes β-insaturés (dérivés de l'acroléine). Par rapport à la littérature, cette voie de synthèse implique une séquence condensation domino imino-ène / transfert d'hydrure / aldol et a lieu sans assistance d’aucun métal de transition. Dans les conditions optimisées, un rendement allant jusqu'à 80 % a été obtenu. Lorsque de l’acide formique est ajouté au milieu, nous avons ensuite montré qu’il était possible de modifier le chemin réactionnel et d’accéder ainsi à des amines tertiaires via la réduction in situ d’un intermédiaire de type iminium.The development of synthesis methods allowing the preparation of amines from abundant and inexpensive raw materials represents a major challenge in various fields of chemistry. During this thesis work, we have developed different catalytic approaches allowing access to various amines from simple alkenes, via hydroamination, hydroarylation, hydroaminoalkylation and hydroaminomethylation pathways. First, we showed that the combination of bismuth triflate and hexafluoroisopropanol (HFIP) led to the formation of highly active catalytic species capable of promoting the hydroarylation of non-activated alkenes such as 1-octene, 1-heptene and 1-undecene with aniline, and this with high selectivities (71-92%). By combining experimental chemistry and theoretical chemistry, we have proposed a reaction mechanism where HFIP stabilizes the transition states via H bonds with the triflate anion, thus assisting the acid catalyst in hydroarylation of alkenes. Subsequently, we studied this reaction in the presence of a heterogeneous catalyst, and more specifically Aquivion® PFSA, using the hydroarylation of norbornene with aniline as a model reaction. We have shown that Aquivion® PFSA is not only active and stable but can also be recycled at least six times without decreasing catalytic performance.In order to allow access to aliphatic amines (secondary and tertiary), we then developed a reaction, catalyzed by dimethylamine, of coupling between formaldehyde and an alkene, leading to the formation of α,β-unsaturated aldehydes (derivatives of acrolein). Compared to the literature, this synthetic route involves a domino imino-ene condensation / hydride transfer / aldol condensation sequence and takes place without the assistance of any transition metal. Under the optimized conditions, a yield of up to 80% was obtained. When formic acid is added to the medium, we then showed that it was possible to modify the reaction path and thereby access tertiary amines via the in situ reduction of an iminium-type intermediate
Influence of pore size in benzoin condensation of furfural using heterogenized benzimidazole organocatalysts
Full text linkA designed N‐heterocyclic carbene (NHC) catalyst was covalently anchored on a range of mesoporous and hierarchical supports, to study the influence of pore size in the benzoin condensation of furfural. The structural and spectroscopic characteristics of the anchored catalysts were investigated, also with the help of molecular dynamics simulations, in order to rationalize the degree of stability and recyclability of the heterogenized organocatalysts. Quantitative yields (99 %) and complete recyclability were maintained after several cycles, vindicating the design rationale
Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry's Law
No full textPera-Titus, Marc El-Chahal, Rayan Rakotovao, Volainiana Daniel, Cecile Miachon, Sylvain Dalmon, Jean-AlainThe properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H-2 in a series of solvents (CHCl3, CCl4, n-hexane, ethanol, and water) when confined in the cavities of mesoporous solids (gamma-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H2 Still increases linearly with increasing pressure in the range 1-5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility
Development of novel heterogeneous selective catalysts for the direct amination of alcohols
No full textLes amines sont des composés largement utilisés dans l’industrie et dont, au vu des études récentes, la demande devrait augmenter dans les années à venir. À cet égard, le développement de technologies efficaces et écologiquement responsables pour leur production est nécessaire pour notre société. La transformation des alcools en amines via le mécanisme de borrowing hydrogen apparait comme une voie performante et durable. Ce travail se concentre sur le développement de nouvelles formulations hétérogènes pour synthétiser de manière sélective des amines primaires à partir d'alcools et d'ammoniac. Deux formulations bimétalliques ont été développées à partir d’une stratégie séquentielle de criblage intensif et d’optimisation des catalyseurs métalliques supportés. Ces formulations montrent une excellente activité et sélectivité vers l’amine primaire ciblée : la n-octylamine.Finalement, un modèle cinétique a été développé sur la base des données expérimentales collectées. Il permet de bien rendre compte des taux de conversion de l’ensemble complexe de réactions en cascade.Amines are important building blocks for many fields of the chemical industry and, according to recent studies, its demand is foreseen to increase over the following years. In this regard, the development of efficient and ecologically responsible technologies for its production is necessary for our society. The transformation of alcohols into amines via the so-called borrowing hydrogen mechanism stands out as an efficient and ecological route. This work centers its efforts in the development of novel heterogeneous formulations for the selective synthesis of amines from alcohols and ammonia via a sequential screening and optimization of monometallic and bimetallic supported catalysts. Two bimetallic formulations have been developed showing excellent activity and selectivity towards the targeted primary amine n-octylamine. Finally, a kinetic model has been developed on the basis of the experimental data collected. It correctly predicts the reaction rates of this complex ensemble of cascade reactions
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