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The most recent advances in magnetometric methods of investigation of supported Co-, Ni- and Fe-containing catalysts are outlined. Magnetic characteristics provide comprehensive information on (i) catalytic reactions, (ii) the size and distribution of ferromagnetic nanoparticles in topochemical reactions during the catalyst preparation and in the catalytic process and (iii) chemisorption on ferromagnets. The characteristic features and advantages of different magnetometric methods and their combinations with traditional methods of investigation of catalysts are considered.

International audience; Low-temperature oxidation of carbon-supported cobalt nanoparticles leads to the size-dependent effects probably related to the selective nucleation of oxide at the edges and the corners of cobalt crystallites. The initial oxidation rate depends on the oxygen partial pressure. Magnetic measurements of particle size are in good agreement with the results of transmission electron microscopy.

International audience; The genesis of cobalt metal particles in silica-supported Fischer-Tropsch catalysts was studied using in situ Foner vibrating-sample magnetic method. The cobalt promoted and unpromoted catalysts were prepared by aqueous (co)-impregnation using cobalt nitrate or acetate, ruthenium nitrosyl nitrate or perrhenic acid followed by oxidative pre-treatment in air and reduction in hydrogen. In several catalyst preparations, sucrose was added to the impregnating solutions. The genesis of cobalt metal phases in these catalysts was monitored in situ by the magnetic method during the temperature-programmed reduction in pure hydrogen. A considerably higher extent of cobalt reduction was found in the catalysts prepared from cobalt nitrate than in those prepared from cobalt acetate. Promotion with ruthenium and rhenium results in a considerable decrease in the temperature of the emergence of cobalt metal phases. Small superparamagnetic, single-domain and multi-domain ferromagnetic cobalt metal particles were observed in the reduced catalysts by the magnetic method. It was found that lower temperature calcination of the cobalt catalysts prepared from cobalt nitrate and addition of sucrose to the impregnating solution lead to a decrease in the concentration of multi-domain cobalt ferromagnetic metal particles and to an increase in the fraction of superparamagnetic cobalt particles. Superparamagnetic cobalt particles smaller than 6-7 nm were detected in the reduced catalysts prepared from cobalt nitrate with sucrose addition and in the catalysts prepared from cobalt acetate. Catalyst characterization using X-ray diffraction and X-ray photoelectron spectroscopy has confirmed the results about cobalt dispersion and reducibility in the cobalt silica-supported catalysts obtained by the Foner magnetic method.

International audience; The promotion of Co/SiO2 catalysts with noble metals such as Ru and Re substantially decreased the mean size of Co particles and increased the fraction of superparamagnetic particles. The Langevin function was used to approximate the magnetic field dependence of magnetization. This allowed the size of Co nanoparticles to be estimated. A decrease in the temperature of the reduction of Co/SiO2 in the presence of Ru and Re decreased the probability of the encapsulation of Co particles in carrier pores.