La2NiO4/alpha-Al2O3 catalyst was prepared by a microwaves assisted self-combustion method using glycine or urea as fuel and metal nitrates as oxidizers. In order to understand the effect of the preparation method and the fuel type used on the catalytic properties, a sample was prepared by an incipient wetness nitrate impregnation method (without fuel). All obtained samples were used as catalysts precursors for the CO2 reforming of methane to syngas between 500 and 800 degrees C. The catalysts were characterized by X-ray diffraction (XRD), specific surface area measurements (BET), temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), before and after reactivity tests. XRD analyses indicate the formation of La3Ni2O6.92, La2NiO4 and LaAlxNix-1O3 crystalline structures independently of the preparation method. All samples prepared with fuel showed high CH4 and CO2 conversions with low carbon deposition. No change was observed in the crystalline structure of the perovskite-related oxides. On the other hand, the sample prepared by nitrate impregnation showed high activity but destruction of the perovskite-related structure with significant carbon formation, mainly multi-walled carbon nanotubes. (C) 2010 Elsevier B.V. All rights reserved.

Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(NixMgy)/Al, NixMgy and NixAly or prepared by impregnation: Ni/MgO (mol% Ni=5, 10). The catalysts, calcined at 600–900°C, were characterized by different techniques: BET, H2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182m2g−1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(NixMgy)/Al catalysts, the presence of NiAl2O4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(NixMgy)/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni0.05Mg0.95 (calcined at 750°C and tested at 800°C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CHx species, surface carbon, nickel carbide and carbon nanotubes.

A series of mixed oxides close to NiAl2O4 was obtained by a sol–gel like method (propionic acid). The characterization of the different structures was made by X-ray diffraction (XRD), scanning electron microscopy (SEM) or transmission electron microscopy (TEM). For the stoichiometric ratio of Ni to Al exactly equal to 0.5, homogeneous crystalline spinel phase was formed for a temperature of calcination equal or higher than 725°C. A solid solution was obtained for a Ni/Al ratio lower than 0.5. The spinel structure is non-tolerant concerning a change of nickel to aluminum ratio higher than 0.5: an excess of nickel gives large particles of NiO on spinel phase. Comparative reduction and dry reforming of these oxides was made to control the formation of Ni and its sintering for applications in methane dry reforming. Preliminary reactivity results in dry reforming of methane are given.

Bioethanol, obtained by biomass fermentation, could be an important hydrogen supplier as a renewable source. The development of active, selective and stable catalysts for bioethanol steam reforming is a key point.In this work, a fluorite type Ce-Zr-Co oxide, Ce2Zr1.5Co0.5O8-delta, is studied for hydrogen production by steam reforming of ethanol/water mixture and bioethanol solution. The catalyst is characterized before and after catalytic test by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM-EDX). The preparation method based on propionate polymerization in solution ensures the insertion of cobalt in the mixed oxide lattice and provides high micro-homogeneity at nanoscale level.The reduction procedure to activate the catalysts is controlled by thermo programmed reduction (TPR).The partially reduced Ce-Zr-Co oxide catalyst presents high ethanol conversion and high hydrogen selectivity. Superior alcohols (fusel oils) arising from the fermentation process do not influence the catalytic behavior compared to a model ethanol/water mixture.Decreasing activity is related to the formation of carbon filaments, evidenced by thermo programmed oxidation (TPO) measurements and transmission electron microscopy. (c) 2005 Elsevier B.V. All rights reserved.

Isomerization of light alkanes and alkenes was investigated on pure MoO3 powder which was gradually reduced under a rapid flow of hydrogen (1 atm) at 350degreesC. Incompletely reduced MoO3 samples readily isomerize alkanes in the order nC(4) much less than nC(5) < nC(6) = nC(7) = nC(8). The rates are at least as high as those measured on platinum metal. Isomerization of oletins is always faster than those of the corresponding alkanes. As a consequence of the inhibiting effect of water vapor on the reduction of the molybdenum oxides, very small MoO3 samples exhibit short-lived isomerization properties whereas larger samples whose reduction gives rise to higher water vapor level are more longer active. With all hydrocarbons marked poisoning effects by hydrocarbonaceous deposits take place. Physical adsorption of nitrogen and argon at - 195 degreesC shows that the samples become microporous on reduction. X-ray analysis of reactive samples always reveal the presence of two molybdenum oxides, i.e. MoO2 and an up-to-now undetermined oxide MoOx which is known to form only at low temperatures; in addition large amounts of amorphous materials are always present. XPS analysis and the catalytic results suggest that the suboxides containing only Mo6+ and Mo5+ ions are not responsible for the isomerization; then the formation of the isomerizing sites results from a deeper reduction state of the MoO3 sample. Many features of the reaction are in favor of a mechanism of the bifunctional acid type. (C) 2002 Elsevier Science B.V. All rights reserved.

The LaMnO3+δ perovskite shows interesting performances in the total catalytic destruction of chlorinated C2 hydrocarbons selectively to COx (mainly CO2) and HCl. It is shown that the unsaturated molecules are more difficult to destroy than the saturated ones. The saturated chlorinated C2 hydrocarbons are readily converted to their unsaturated equivalent by an unimolecular elimination reaction probably catalysed by Lewis acid sites. The formation of higher chlorinated C2 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 LaMnO3+δ oxygen overstoichiometric structure.

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 +CCl3 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.

Mixed LaNixFe(1-x)O-3 perovskite oxides (0 less than or equal to x less than or equal to 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. (C) 1999 Elsevier Science B.V. All rights reserved.

Silica supported cobalt catalysts have been prepared by a new method combining the precipitation of the metal precursor (cobalt nitrate) by oxalic acid with the hydrolysis and condensation of the silicium precursor (tetraethoxysilane). Depending on the pH during preparation, the textural properties (BET specific surface area, porosity) of the Co/SiO2 catalysts can be modified. In an acid medium (pathway A), the resulting silica is constituted by a polymeric net with few branchings, the catalysts are microporous. In basic medium (pathway B) silica is composed of more branched polymers leading to mesoporous catalytic systems. After calcination, the only crystallized phase detected by XRD is the Co3O4 spinel. At 773K, the surface degrees of reduction of the catalysts at cobalt isocontent (25wt.% Co) as determined by XPS is of 81% and 69% for systems prepared by pathways A and B, respectively. The presence of small unreduced CoII suggests the existence of non-crystallized cobalt silicate formed during the reduction by reaction of CoO with silica. The activity for the CO+H2 reaction for the 25wt.% catalysts prepared by pathway A increased with the specific surface area which can be controlled by the preparation parameters. The reduction degree has a direct influence on the selectivity for the Co/SiO2 catalysts. The presence of a part of unreduced cobalt (in interaction with the support) results in a better selectivity to the C5–C13 fraction (gasoline), whereas a higher reduction degree of cobalt favors the production of higher molecular weight hydrocarbons (waxes) (C22+ selectivity>40%).

The effect of Cl and Ba dopants in the Sm2Sn2O7 pyrochlore in the reaction of oxidative coupling of methane is investigated. The preparation of the catalysts via propionate metalloorganic precursors is described. X.P.S. studies both with CO2 thermodesorption experiments tend to show that O-Ba-Cl graftings are responsible for the good catalytic properties, the only role of barium being the stabilization of chlorine. The electrical conductivity of the catalysts is discussed. The values of sigma follow the same order that the catalytic performances towards C-2 hydrocarbons.

The use of propionate metallo-organic precursors,which were characterized by means of Sn-119 NMR, permits the reproducible obtention of various Sm-Sn pyrochlores (stoichiometric or tin deficient, pure or doped by Cl and Pa). X.P.S. studies together with temperature programmed CO2 desorption showed that O-Ba-Cl graftings are responsible for the good catalytic properties (75 % selectivity to C-2 at 16 % CH4 conversion) of the doped pyrochlores in the oxidative coupling of methane. The only role of barium is thought to be the stabilization of chlorine both in the bulk and on the surface of the pyrochlore. BaCO3 is not the active phase. The electrical conductivity (a) of a set of pyrochlores was shown to follow the same sequence than the catalytic performances in C-2-hydrocarbon formation. The effect of the O-Ba-Cl graftings on the electrical conductivity is discussed.

Well-defined structures like ABO3 (A = Ba, Sr, Ca; and B = Ti, Zr) perovskites were prepared by a sol-gel method which permits the formation of a crystalline structure at low-calcination temperatures (∼700 °C). The perovskite structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) methods and the carbonate present at the surface was determined by Fourier transform infra-red spectroscopy. Reactivity studies showed that the perovskite structures are stable under oxidative coupling of methane (OCM) conditions. The yield increases followed the sequence Ca < Sr < Ba and Zr < Ti, and a stable BaTiO3 gives a C2 yield of 15% at 800 °C.

Compounds of general formula A2B2O7 have been characterized by X-ray diffraction and tested for catalytic activity in oxidative coupling of methane. Calculations of the rare earth-oxygen (AO) and cocation-oxygen (BO) bond energies provide a new way to estimate the influence of bulk parameters on the formation of C2 hydrocarbons. The observed values of C2 yields on A2B2O7 catalysts (A = Sm, Gd or Eu) (B = Ti, Zr, or Sn) indicate that they increase with decreasing cocation-oxygen bond energy. The best of these systems (Sm2Sn2O7) gives a C2 yield amounting to 20% at 973 K.

The study of the reactivity of A2B2O7 pyrochlore type structures (A = rare earth, B = Ti, Zr, Sn) has shown the strong influence of the B cocation on the C2 selectivity and yield in the oxidative coupling of methane. This has been related to the B-0 bond energy of the structure constituting elements and it has been found that a high C2 yield corresponds to low bonding energy (e.g. for Sn-0). The ability to create oxygen vacancies which can be involved in the reaction mechanism has been illustrated by these studies (reactivity, bonding energy calculation).

n-Propanol and isopropanol can be homologated into their next homologs by hydrocarbonylation mediated by cobalt-ruthenium catalytic mixtures. For given catalyst compositions, there is a depression in conversion due essentially to a dramatic inhibition of the hydrocarbon formation, whereas the yield and the selectivity to C4 products are highest. The effect of two important parameters (iodine promotion and total pressure) are investigated. Both alcohols lead to n- and isobutanol, suggesting a possible olefinic intermediate.

Journal Article Use of the Headspace Technique to Detect Chemisorbed Species on Catalytic Surfaces Get access R. Breault, R. Breault Laboratoire Chimie Organique Appliquée, E.R.A. 826, Départément de Chimie, Université Louis Pasteur, 1, rue Blaise Pascal, 67000 Strasbourg, France Search for other works by this author on: Oxford Academic PubMed Google Scholar S. Libs, S. Libs Laboratoire Chimie Organique Appliquée, E.R.A. 826, Départément de Chimie, Université Louis Pasteur, 1, rue Blaise Pascal, 67000 Strasbourg, France Search for other works by this author on: Oxford Academic PubMed Google Scholar J.P. Hindermann, J.P. Hindermann Laboratoire Chimie Organique Appliquée, E.R.A. 826, Départément de Chimie, Université Louis Pasteur, 1, rue Blaise Pascal, 67000 Strasbourg, France Search for other works by this author on: Oxford Academic PubMed Google Scholar A. Kiennemann A. Kiennemann Laboratoire Chimie Organique Appliquée, E.R.A. 826, Départément de Chimie, Université Louis Pasteur, 1, rue Blaise Pascal, 67000 Strasbourg, France Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Chromatographic Science, Volume 22, Issue 10, October 1984, Pages 449–451, https://doi.org/10.1093/chromsci/22.10.449 Published: 01 October 1984 Article history Received: 09 January 1984 Received: 23 May 1984 Published: 01 October 1984

AbstractBei der thermischen Dimerisierung von Acrolein (Ia) und Methylvinylketon (Ib) wird jeweils selektiv nur ein Dihydropyran (II) gebildet.