Contribution à l'étude des mécanismes d'échange hétérogène. Echange de Cl36 entre H Cl et C H3 Cl gazeux sur films de tungstène

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Corrélation entre l’activité catalytique d’un film métallique et la nature des radicaux chimisorbés. I. — Étude du système hétérogène méthane, hydrogène et molybdène

On étudie dans un large domaine de température l’adsorption du méthane sur films de molybdène obtenu par évaporation sous vide ainsi que l’échange entre les radicaux adsorbés, marqués au 14 C, et la phase gazeuse. Les résultats font apparaître que la nature et le nombre des espèces radicalaires adsorbées évoluent lentement. On propose un schéma exprimant les différentes étapes des réactions d’adsorption

Characterization of rhodium catalysts supported on Al2O3. Fast and slow adsorption of H2

Hydrogen adsorption is studied on two Rh/Al2O3 catalyst: 1.04% Rh(∼100% dispersion) and 4.8% Rh (<10% dispersion). Hydrogen adsorption is decomposed into a fast process and a slow activated process, of almost equal importance. A systematic study of the influence of the reduction temperature, outgassing temperature and temperature at which hydrogen is put in presence of the catalyst is conducted. Adsorption isotherms in a large range of pressure (10-3-50 torr) and temperature (193K-500K) are measured allowing to calculate the isosteric heat of adsorption Q as a function of coverage. For both catalysts, very high initial values of Q are found(∼50 kcal/mole), much higher than on model unsupported catalysts, that seems characteristic of the adsorbed H during the slow process. It is proposed that Cl atoms bound to the metal and introduced during the preparation of the catalyst, are responsible of the slow adsorption. © 1989.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mechanism of WO3 Reduction and Carburization in CH4/H2 Mixtures Leading to Bulk Tungsten Carbide Powder Catalysts

International audienc

Fast, slow and strong adsorption of H2 on Rh/Al2O3 catalysts: effect of chlorine

Supported catalysts containing chlorine originating from the precursor salt used in preparation have been shown previously to exhibit two features towards hydrogen adsorption not found in model catalysts: (1) a very important slow adsorption (2) a very high heat of adsorption at low coverage (strong adsorption). In the present paper, the adsorption of hydrogen is studied on two Rh/Al2O3 chlorine-free catalysts: one prepared using Rh(NO3)3 as precursor; the second one, a previously studied catalyst that has been dechlorinated. It is shown here that both slow and strong adsorption is due mainly to the presence of chlorine. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe