Anne-Cécile Roger

Fe–Co based metal/spinel to produce light olefins from syngas

Abstract New metal/oxide (Co–Fe) catalysts (with no reduction or thermal pre-treatment) are efficient to produce light hydrocarbons with a low selectivity in CO 2 by the Fischer–Tropsch synthesis. The low selectivity in CO 2 is due to the occurrence of the CO 2 /H 2 reaction. These materials are stable under reaction conditions, and only few carbides are formed during the Fischer–Tropsch reaction. X-ray analyses indicate that the most degraded phase is the (Co–Fe) alloy phase in CO/H 2 reaction and the spinel phase in the CO 2 /H 2 reaction. It was demonstrated that these composites do not behave as the simple sum of a spinel phase and a (Co–Fe) alloy but have their own properties.

Hydrogen production by ethanol steam reforming. Study of cobalt-doped Ce-Zr catalysts.

Insertion of cobalt into Ce-Zr fluorite oxides is studied to provide active and selective catalysts for ethanol steam reforming. The controlled reduction of cobalt generates nanometric cobalt particles in strong interaction with the host oxide it comes from. High selectivity to hydrogen can be achieved compared to Ce-Zr fluorite oxides.

CO2 methanation over Ni-Ceria-Zirconia catalysts: effect of preparation and operating conditions

Ni-Ceria-Zirconia materials with various Ceria/Zirconia ratios were prepared by sol-gel and impregnation methods and were subsequently characterized by means of XRD, BET, TPR and TPO. Their catalytic activity and stability were evaluated in the CO2 methanation reaction. The main parameters which seem to monitor catalytic performance are the capacity of Ni2+ cations to incorporate into the mixed oxide structure and the obtained ratio between incorporated Ni2+ and surface Ni0 species. Catalysts prepared by sol-gel thus exhibited higher methane yield and an improved resistance to deactivation when compared to those obtained by impregnation. The process viability was then investigated in potential industrial conditions. Operating under moderate pressure was beneficial to catalytic activity, whereas working under sub-stoichiometric H2 resulted in a loss of both activity and stability. Even though metal sintering and carbon deposits are believed to cause deactivation, nickel partial reoxidation and site blocking have to be considered.

New class of acid catalysts for methanol dehydration

Abstract Herein, a new class of acid catalysts is proposed for the reaction of methanol dehydration. The coupling of Keggin anion with organic cation protection results in a crystalline molecularly defined hybrid structures with a strongly hydrophobic character. The thermal stability and catalytic behaviour of the new materials strongly depend on the nature of the Keggin structure.

Formation of cubic defined Sm-Sn pyrochlore structures: application to OCM

Abstract A series of Sm-Sn pyrochlores were synthesized from propionic acid solutions of Sm2O3, SnCl2 and BaCO3. The addition of increasing amounts of water during preparation is shown to influence the BaCl2 precipitation and the nature of the Sm, Sn containing species remaining in the solution. The mastership on this parameter permits the synthesis of doped Sm-Sn pyrochlores with well-known contents of barium and chlorine. The changes in conversion and C2 selectivity observed in the oxidative coupling reaction is interpreted in the light of a better knowledge of the preparation procedure ( species present on the surface and in the bulk).

Selective synthesis of C2-C4 olefins on Fe-Co based metal/oxide composite materials

Fe-Co based metal/oxide composite materials (Co γ Fe 1-γ ) α [Co β Fe 3-β O 4 ] were synthesized with various values of γ, a and β via oxido-reduction processes between cobalt and iron ions leading to the simultaneous crystallization of two phases: a Fe-Co alloy, and a Fe-Co spinel. The materials were characterized by XRD, TGA-TDA and SEM. These catalysts are efficient in Fischer-Tropsch reaction to produce C 2 -C 4 (50 wt %), CO 2 (<20 % molar selectivity), with high olefin/paraffin ratio (3.7).

Structure-controlled La-Co-Fe perovskite precursors for higher C2-C4 olefins selectivity in Fischer-Tropsch synthesis

Abstract Mixed La-Co-Fe perovskites are studied as precursors for FT catalysts. By changing the Co/Fe ratio and the La-content the precursor perovskite crystalline structure can be controlled (rhombohedral, orthorhombic or cubic), leading to different metal phases after reduction, to direct the selectivity toward C 2 -C 4 olefins. The catalysts present remarkable stability under test.

Beneficial effects of inorganic chlorine grafting on Sm2Sn2O7 pyrochlore during oxidative coupling of methane

Abstract The effect of Cl and Ba dopants in the Sm 2 Sn 2 O 7 pyrochlore in the reaction of oxidative coupling of methane is investigated. The preparation of the catalysts via propionate metallo-organic precursors is described. X.P.S. studies both with CO 2 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 σ follow the same order that the catalytic performances towards C 2 hydrocarbons.

Control of bulk and surface composition of doped Sm2Sn2O7 pyrochlore. Relation between formation of O-Ba-Cl graftings and C2-selectivity in the oxidative coupling of methane.

The use of propionate metallo-organic precursors,which were characterized by means of 119 Sn NMR, permits the reproducible obtention of various Sm-Sn pyrochlores (stoichiometric or tin deficient, pure or doped by Cl and Ba). X.P.S. studies together with temperature programmed CO 2 desorption showed that O-Ba-CI graftings are responsible for the good catalytic properties (75 % selectivity to C 2 at 16 % CH 4 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. BaCO 3 is not the active phase. The electrical conductivity (σ) of a set of pyrochlores was shown to follow the same sequence than the catalytic performances in C2-hydrocarbon formation. The effect of the O-Ba-Cl graftings on the electrical conductivity is discussed.

Preparation and characterization of ASnO3 (A=Ca, Sr or Ba) tin compounds for methane oxidative coupling

Abstract Tin containing perovskites ASnO 3 (A=Ca, Sr, Ba) are prepared by a solgelmethod starting from tin oxygenated precursor (SnO) or from chlorinated precursors (SnCl 4 ). The respective reactivity tests in oxidative coupling show that perovskites prepared from chlorinated precursors have a much higher C 2 hydrocarbons selectivity than that obtained from oxygenated ones (70% compared to 40% for BaSnO 3 ). This difference in reactivity is interpreted by the modification of the basicity of the system by bulk or surface chlorine (CO 2 thermodesorption).