Alain Kiennemann

Hydrogen production by ethanol reforming over Rh/CeO2-ZrO2 catalysts

Abstract Reforming of ethanol in excess of water (1–8 molar ratio) has been investigated on Rh/CeO 2 , Rh/ZrO 2 and Rh/CeO 2 –ZrO 2 (Ce/Zr=4, 2 and 1). Catalysts characterization was conducted by X-ray diffraction, BET surface area measurements, CO 2 adsorption, and temperature programmed reduction (TPR). At 400–500 °C all catalysts showed high activity and selectivity towards hydrogen production (between 5 and 5.7 mol of H 2 per mol of ethanol inlet) despite the considerable textural differences of the oxides (fluorite, monoclinic and tetragonal). The large variations of Rh dispersion (as monitored by TPR) between all catalysts had a small effect on H 2 production. Although it appears that the reaction is not sensitive to either the oxide or the metal structure Rh/CeO 2 (the most basic catalyst investigated) was the least reactive.

Stabilisation of active nickel catalysts in partial oxidation of methane to synthesis gas by iron addition

Abstract Mixed LaNixFe(1−x)O3 perovskite oxides (0≤x≤1) have been prepared by a sol–gel related method, characterised by X-ray diffraction (XRD), specific surface area measurements, transmission electron microscopy (TEM) coupled to an energy dispersive X-ray spectrometer (EDS). These systems are the precursors of highly efficient catalysts in partial oxidation of methane to synthesis gas. Studies on the state of these systems after test show the stabilisation of active nickel by increasing the amount of iron. These systems permit to control the reversible migration of nickel from the structure to the surface. The best mixed perovskite for the partial oxidation of methane is LaNi0.3Fe0.7O3.

Catalytic destruction of chlorinated C1 volatile organic compounds (CVOCs) reactivity, oxidation and hydrolysis mechanisms

Abstract LaCoO3 and LaMnO3+δ prove to be good catalysts for the total oxidation of chlorinated volatile organic compounds (CVOCs) to CO2 and HCl. Total destruction of CH2Cl2, CHCl3 and CCl4 is possible below 550°C. Different by-products are obtained in function of the nature of the catalysts and the chlorinated compounds. Conventional T50 and T90 values are replaced by T50(COx) and T90(COx) corresponding to the temperature at which CO+CO2 yields are equal to 50 and 90%, respectively. The proposed presentation of the catalytic results have the advantage to take into account the formation of by-products. The difference in behaviour depending upon the mixture of gases showed that the reaction mechanism is different for different chloromethanes. CCl4 reacts mainly by a hydrolysis mechanism. CHCl3 and CH2Cl2 react in two steps, hydrolysis and oxidation. These molecules result in a large number of intermediate chlorinated by-products. It is suggested, based on known chemistry of the reaction in liquid phase, that CCl4 reacts by a mechanism with formation of a + CCl 3 cation. A substitution by concerted mechanism is in line with the kinetic studies for CH2Cl2. The role of water partly that of a reaction partner in CCl4 — and partly that of a polar solvent — increases the mobility of the Cl− anion.

Study of the formation of LaMO3 (M=Co, Mn) perovskites by propionates precursors: application to the catalytic destruction of chlorinated VOCs

Abstract LaMO 3 (M=Co, Mn) have been obtained by a sol–gel-like method with propionic acid as solvent. The influence of the nature of the metallic source (metal, nitrate or chloride) on the gel formation has been studied by fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis ATD–ATG. After calcination, the obtained perovskites have been characterised by X-ray diffraction (XRD), FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) in order to investigate the influence of the preparation parameters on the final product. These mixed oxides have been used as catalyst for the destruction of chlorinated compounds. For each compound, the perovskite structure of LaCoO 3 decomposes in the same manner as LaOCl and Co 3 O 4 . Under the same test conditions, the perovskite with Mn is not altered. The stability of the structure has been explained by the formation of an oxygen overstoichiometric phase (LaMnO 3+ δ ) which is thermodynamically more resistant to chlorination than the stoichiometric LaMnO 3 . The catalytic behaviour of these oxides shows that two ways (hydrolysis and oxidation) are involved in the destruction of chlorinated hydrocarbons. The first one requires acidic sites and is less sensitive to the modification of the catalyst surface induced by chlorine than the second one requiring metallic oxidation sites.

Catalytic destruction of chlorinated C2 compounds on a LaMnO3+δ perovskite catalyst

Abstract The LaMnO 3+ δ perovskite shows interesting performances in the total catalytic destruction of chlorinated C 2 hydrocarbons selectively to CO x (mainly CO 2 ) and HCl. It is shown that the unsaturated molecules are more difficult to destroy than the saturated ones. The saturated chlorinated C 2 hydrocarbons are readily converted to their unsaturated equivalent by an unimolecular elimination reaction probably catalysed by Lewis acid sites. The formation of higher chlorinated C 2 by-products can be explained by successive chlorination and dehydrochlorination reactions. Addition of water favours the destruction by decreasing the amount of chlorinated by-products and results in an enhanced carbon oxides formation. Oxygen must also be present to prevent the destruction of the active LaMnO 3+ δ oxygen overstoichiometric structure.

Characterization of dioxymethylene species over cu-zn catalysts

Abstract Dioxymethylenic species have been characterized upon adsorption of formaldehyde on zinc aluminate and copper supported on zinc aluminate, by both FTIR spectroscopy and chemical trapping. Dioxymethylene could be an intermediate in the synthesis of methanol on these catalysts in CO + H 2 and CO 2 + H 2 reactions, as shown by chemical trapping experiments.

Sur la preéparation de quelques tris(dialycoylamino)-stibines et sur quelques unes de leurs propriétés

Abstract Sb(NR2)3 compounds have been prepared by the reaction of SbCl3 with lithium salts of secondary amines. Reactions of Sb(NMe2)3 with secondary amines, alcohols, phenol and esters have been studied.

Promotion of active nickel catalysts in methane dry reforming reaction by aluminum addition

Abstract Mixed LaNixAl1−xO3 perovskite oxides have been prepared by a sol–gel related method and characterized by X-ray diffraction (XRD), specific surface area measurements and scanning electron microscopy (SEM) coupled to an energy dispersive X-ray spectrometer (EDS) shows the possibility to obtain a solid solution of LaNixAl1−xO3 (0.1⩽x⩽0.9) with propionic acid as solvent. These systems are highly efficient catalysts for syngas production in dry reforming of methane.

Homologation of carboxylic methyl esters via reductive carbonylation catalyzed by a cobalt-ruthenium mixed catalyst

Abstract Mixtures of cobalt acetate and ruthenium acetylacetonate promote the homologation of carboxylic methyl esters to the corresponding ethyl esters by CO-H 2 . The reaction of methyl formate is considered separately because of its tendency to decarboxylate. The behavior of five other methyl esters is considered as a function of the length and the size of the acyl group. In each case reductive carbonylation of the methyl ester gives methanol, ethanol, the carboxylic acid, and the ethyl ester. The formation of the last product is enhanced by the mixture of Co and Ru complexes. The mechanism is thought to be essentially the same as that previously proposed for homologation of methyl acetate.

Reactions CO/H2 en phase liquide. Synthese de precurseurs de l'ethanol par homologation du methanol.: I. Influences de la temperature et de la pression

The CO/H2 homologation of methanol to acetaldehyde and subsequently to its dimethyl acetal in the presence of cobalt acetate promoted by iodine was examined under various conditions. Temperature and pressure were found as critical parameters. High pressures (140 MPa) and low temperatures (160–170°C) give optimal yields and selectivity to acetaldehyde. According to pressure, temperature, contact time, gas ratio and ligand/catalyst ratio, the reaction is oriented towards acetaldehyde, its dimethyl acetal or methyl acetate.