Pyrolytic transformation of the complex Cp2Mo2(CO)4(dmad) (Cp=cyclopentadienyl, dmad=dimethylacetylenedicarboxylate) under hydrogen at 550 °C gives, after a passivation step, Mo2C with an excess of carbon and oxygen. These impurities can be withdrawn with an appropriate reductive post-treatment. Based on thermogravimetric analyses and pyrolysis mass spectroscopy performed on the precursor, a preliminary decomposition scheme has been proposed.

Four catalysts were prepared by impregnation of γ-alumina :1wt% Pt/Al2O3, 1wt% Pt - 0.2 wt% Rh/Al2O3, 1wt% Pt - 12wt% CeO2/Al2O3 and 1wt% Pt - 0.2wt% Rh - 12wt% CeO2/Al2O3 and characterized by their activities and selectivities in CO + NO and CO + NO + O2 reactions in temperature programmed experiments from 100 to 550°C at a space velocity of 25000 h-1. In the reaction between CO and NO, at low temperature, NO gives mainly N2O the percentage of which in the products decreases when the temperature and the conversion increase. On the contrary for reactions CO + NO + O2, at low temperature and low conversion, the selectivity of NO transformation into N2O is low when oxygen is present in the gas phase because of a better adsorption of O2 than that of NO. Rhodium and ceria have a promoting effect on both CO + NO and CO + NO + O2 reactions, but the promoting effect of ceria manifests itself mainly in the presence of oxygen. During the reaction between CO + NO, besides its oxidation by NO, CO is oxidized in another process which is likely to involve the supports (alumina or ceria).

Les activités et les sélectivités ont été déterminées dans les réactions de composés oxygénés (benzofuranne, phénétole) avec l’hydrogène en phase gaz, entre 300 et 400°C, sous 30 bars sur des catalyseurs au fer. On a utilisé un oxyde de fer Fe sulfuré ou non, une boue rouge déchet industriel, et un catalyseur classique NiMo/Al2O3. Sur ces catalyseurs les produits de réaction sont généralement des hydrocarbures (C1, C2, C3, C4, C5 et C6), des aromatiques et leurs produits d’hydrogénation. Ces produits sont issus respectivement de l’hydrogénolyse de la liaison C-C, C-O ; et de l’hydrogénation des noyaux aromatiques. La caractérisation des catalyseurs indique que le fer présent dans Fe2O3 et dans la Boue rouge se réduit totalement en fer métallique (Fe2O3), et partiellement (Boue rouge) entre 300 et 400°C et que la sulfuration des mêmes catalyseurs aboutit à un mélange Fe1-xS et FeS.

The dehydrogenation of cyclohexane and the hydrogenolysis of butane were studied on bulk tungsten-molybdenum mixed carbides as a function of their composition. Some analogies with noble metals have been confirmed for selectivity in hydrogenolysis. Tungsten carbide gives only single hydrogenolysis like platinum, while molybdenum carbide leads to multiple hydrogenolysis like ruthenium. When the activities in cyclohexane dehydrogenation and butane hydrogenolysis are plotted versus the relative surface composition Mo(Mo + W), curves with a minimum are obtained. This change of the activities of the mixed carbide catalysts correlates with the molybdenum surface enrichment deduced from XPS results.

AbstractDie Thermodesorption von mit H2 bei 298, 573 und 773°Kbeladenem Pt‐Schwamm auf Al2O3, Si02 und MgO wird im Bereich 300‐800°Kuntersucht.