G. Alonso

Preparation of MoS2 and WS2 catalysts by in situ decomposition of ammonium thiosalts

The in situ decomposition of ammonium thiometallates during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum disulfide and tungsten disulfide catalysts, was investigated. It was found that very efficient catalysts for the HDS of DBT were obtained by in situ decomposition. Mechanical uniaxial pressing of the precursors (ammonium thiometallates) affected both textural and catalytic properties of the catalysts. Surface areas of molybdenum and tungsten disulfides increased as a function of uniaxial pressing, while catalytic activities went through a maximum. For MoS2, the hydrogenation selectivity was much higher for in situ catalysts than for ex situ ones. For WS2 catalysts, the hydrogenation selectivity was less sensitive to the condition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxial pressing, while the C/M ratio remained almost constant at 1.6. The best catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of in situ decomposition and mechanical deformation of thiometallate precursors is discussed.

Preparation of WS2 catalysts by in situ decomposition of tetraalkylammonium thiotungstates

Tungsten tetraalkylammonium thiosalts are used as precursors for the in situ formation of WS2 catalysts in dibenzothiophene (DBT) hydrodesulfurization. The thermal decomposition of alkyl-ammonium thiosalts proceeds directly to WS2 without WS3 formation, as in the case of ammonium thiotungstate (ATT), allowing good control of the catalyst’s stoichiometry. The alkyl-ammonium thiosalts give WS2 particles with different characteristic morphologies. The hydrodesulfurization (HDS) activities of WS2 catalysts derived from alkylthiosalts are higher than those of catalysts derived from the ammonium thiosalt. The reaction rate increases with the size of the cation in the precursor. No correlation of catalytic activities with surface areas is found. The S/W and C/W surface ratios determined by Auger electron spectroscopy decrease with increasing cation size. Surface composition is WS2:25C1:7 ,W S 1:7 C0:9 and WS1:3 C0:7 for the in situ catalysts derived from ammonium, methylammonium, and butylammonium precursors, respectively. The improved catalytic properties of WS2 catalysts derived from alkylammonium thiosalts in the HDS of DBT are attributed to the formation of carbon-containing tungsten sulfide phases on the catalyst’s surface.

Study of a MoS2 catalyst prepared in situ for hydrodesulfurization reaction

The present work is a study of the effect of compression on in situ formed molybdenum disulfide catalysts and their catalytic activity. High pressure compactation followed by in situ activation of catalyst precursors is found to double the activity for the hydrodesulfutization of dibenzothiophene (DBT), compared to a conventional catalyst. Compacted MoS2 catalysts show a similar improvement.