Hierarchical porous silica monoliths: A novel class of microreactors for process intensification in catalysis and adsorption

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True Microporosity and Surface Area of Mesoporous SBA-15 Silicas as a Function of Synthesis Temperature

International audienceA model based on hexagonal mesopores connected by micropores allows evaluation of the porosity of SBA-15 silicas and elucidation of the literature problems on the subject. The presence of micropores in the walls between the mesopores renders unreliable the surface area determination by the Brunauer-Emmett-Teller equation and the microporosity assessment by the t-plot method. A geometrical model allows calculation of the true surface area, as well as the real mesoporous and microporous pore volumes, the wall thickness and the wall density from the total pore volume, the pressure of pore-filling, and the cell parameter. The increase of synthesis temperature leads to a continuous increase of mesopore size and a continuous decrease of microporous volume until the disappearance of micropores for materials synthesized at nearly 130 C. The results are discussed on the basis of the collective properties of nonionic surfactants

Validity of the t-plot method to assess microporosity in hierarchical micro/mesoporous materials

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Size control of self-supported LTA zeolite nanoparticles monoliths

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Toluene Methylation by Methyl Mercaptan and Methanol over Zeolites—A Comparative Study

International audienceIn this study, we show that the Friedel-Crafts (FC) alkylation of aromatic hydrocarbons by thiols to form C-C bond is feasible. The gas phase reaction between toluene and CH3SH catalyzed by HZSM-5 zeolite was chosen as model reaction. In the temperature range of 350 - 550 °C, the alkylation of toluene to produce xylenes was the main reaction involved in the process. The reaction between toluene and CH3SH was compared with the well-known reaction between toluene and CH3OH. Significant similarities exist, notably the ability of both CH3SH and CH3OH to generate methoxonium species on the zeolite surface and to methylate the aromatic ring in a typical FC process. The maximum alkylation yield of 41% for CH3OH was reached at 350 °C, while that of 67.3% for CH3SH was reached at 450 °C. This difference in temperature can be correlated with the energy barriers required for the formation of methoxonium species, i.e. 24.6 kcal/mol (CH3OH) and 26.4 kcal/mol (CH3SH). The high performance in alkylation proved by CH3SH was attributed to its lower consumption in the side reactions, i.e. the formation of light hydrocarbons

Effet de la porosité des catalyseurs au Ni pour l'oligomérisation de l'éthylène

International audienceLes matériaux poreux échangés au nickel sont des catalyseurs performants pour l'oligomérisation de l'éthylène. La plupart d'entre eux, en particulier les zéolithes au Ni subissent une désactivation rapide à cause du blocage des pores par les (sous)produits volumineux. L'une des approches pour surmonter ce problème est de développer des catalyseurs avec des pores plus grands. À cet égard, nous avons préparé de nouveaux catalyseurs à base de matériaux mésostructurés de type MCM-41 et SBA-15.Les matériaux mésoporeux aluminés ont été obtenus par synthèse directe (Al-MCM-41) ou par traitement post synthèse (Al-SBA-15). Après échange ionique au Ni2+ suivi d'une activation thermique, nous avons obtenu des catalyseurs qui ont montré des performances bien supérieures à celles des matériaux zéolithiques. En effet, les activités (en gram d'oligomères per gram de catalyseur et heure) ont été entre 2 et 50 (pour les zéolithes) et entre 110 et 170 pour les matériaux mésoporeux. Notre présentation porte sur le rôle de la porosité, mais aussi de la nature des sites catalytiques dans l'oligomérisation

Process for dispersing functional molecules on the surface of a support and support made by this process

The present invention discloses a method for sepg. tethered functional organo-chains, through their dilution with tethered nonfunctional organo-chains, in the presence of soluble molecular derivs. that are able to self-assemble and to interact with the functional organo-silane

Selective Production of Propylene and 1-Butene from Ethylene by Catalytic Cascade Reactions

International audienceIn this study we report that ethylene can be simultaneously and selectively converted into propylene and 1-butene through one-pot catalytic cascade reactions. In a single continuous flow reactor, and under identical mild conditions (60 °C, 3 MPa), without the use of co-catalyst, ethylene was first dimerized/isomerized over Ni-AlKIT-6 catalysts to form butenes, which reacted then with the excess of ethylene over ReOx/Al2O3 to produce propylene and 1-butene with more than 86% total selectivity. The selectivity for 1-butene was 97.4% in the C4 fraction. The initial ethylene conversion was 73% and stabilized at 35% after 4 h on stream, with around 45% selectivity in propylene and 42% selectivity in 1-butene

Catalase-like activity of bovine met-hemoglobin: interaction with the pseudo-catalytic peroxidation of anthracene traces in aqueous medium

International audienceHemoglobin is a member of hemoprotein superfamily whose main role is to transport O2 in vertebrate organisms. It has also two known promiscuous enzymatic activities, namely peroxidase and oxygenase. Here we show for the first time that bovine hemoglobin also presents a catalase-like activity characterized by a Vmax of 344 µM/min, a KM of 24 mM and a kcat equal to 115 min-1. For high anthracene and hemoglobin concentrations and low hydrogen peroxide concentrations, this activity inhibits the expected oxidation of anthracene, which occurs through a peroxidase-like mechanism. Anthracene belongs to the polycyclic aromatic hydrocarbons family whose members are carcinogenic and persistent pollutants found in industrial waste waters. Our results show that anthracene oxidation by hemoglobine and hydrogen peroxide follows a typical bi-bi ping-pong mechanism with a Vmax equal to 0.250 µM/min, KM(H2O2) of 80 µM, KM(ANT) of 1.1 µM and kcat of 0.17 min-1. The oxidation of anthracene is shown to be pseudo-catalytic because an excess of hemoglobin and hydrogen peroxide is required to make PAH completely disappear. Thus bovine hemoglobin presents, in different degrees, all the catalytic activities of the hemoprotein group which makes it a very interesting protein for biotechnological processes and with which one can study structure-activity relationships