Showing papers on "Ammonium tetrathiomolybdate published in 1994"

Microemulsion-mediated synthesis of nanosize molybdenum sulfide particles

Abstract: A microemulsion-based method for the synthesis of molybdenum sulfide nanoparticles is reported. Molybdenum sulfide particles in the size range 10-80 nm have been precipitated in water-in-oil microemulsions (water-containing inverse micelles) formulated with polyoxyethylene(5) nonylphenylether (NP-5). The particles were synthesized in the NP-5/cyclohexane/water microemulsion system by acidifying ammonium tetrathiomolybdate solubilized in the water cores of the inverse micelles. Particle characterization was accomplished by chemical analysis, transmission electron microscopy, and ultraviolet/visible spectroscopy. The small size and the cage-like nature of the micro-emulsion water cores limit particle growth and aggregation. The particle size was found to be a function of the water-to-surfactant molar ratio and the average number of ammonium tetrathiomolybdate ions solubilized per water core. These trends are rationalized in terms of classical nucleation theory and aggregative growth concepts.

Characterization of supported molybdenum sulfide catalyst ex ammonium tetrathiomolybdate

Abstract: Active sulfide catalysts are conventionally prepared by converting the respective oxides to sulfides. Reductive sulfiding of the oxides is usually difficult and does not proceed in a regular manner. A supported molybdenum sulfide catalyst prepared by the decomposition of ammonium tetrathiomolybdate (ATTM) in hydrogen is unique in two respects, namely, the lower valence state of the supported molybdenum sulfide catalyst, and the presence of few oxygen atoms in the catalyst. The activity of a catalyst prepared by this technique (and subjected to different pretreatments) is compared with the activities of both a conventional and a commercial catalyst. The pretreatment consists of flash or temperature-programmed decomposition of the supported ATTM in helium followed by removal of excess sulfur by temperature-programmed reduction, or the decomposition of supported ATTM in hydrogen. The results clearly indicate that the activity of the catalyst prepared by the decomposition of ATTM is higher than the activities of both the conventionally prepared catalyst and the commercial catalyst.

The Role of Co in Unsupported Co-Mo Sulfides in the Hydrodesulfurization of Thiophene.

Abstract: Unsupported Co-Mo catalysts were prepared by impregnation of MoS2, obtained by thermal decomposition of ammonium tetrathiomolybdate, with a solution of cobalt nitrate in acetone. XRD and HREM showed that the MoS2 structure of the resulting catalysts remained intact upon addition of Co. The thiophene hydrodesulfurization and the consecutive butene hydrogenation properties indicated that the Co ions are preferentially situated at the edges of the MoS2 crystallites below Co/(Co + Mo) = 0.08 and promote the hydrodesulfurization (HDS) reaction. Further addition of Co leads to the segregation of Co9S8, which acts as a support for highly dispersed Co-promoted MoS2 crystallites. As a result of this structural effect, the Co-MoS2 crystallites become better accessible and the catalytic activity increases again above Co/(Co + Mo) = 0.2. The observed increase in activity upon physical mixing of Co-promoted MoS2 and Co9S8 might also be explained by such a structural effect, rather.than by a remote-control effect.