Preparation of WS 2 catalysts by in situ decomposition of tetraalkylammonium thiotungstates

Abstract

Tungsten tetraalkylammonium thiosalts are used as precursors for the in situ formation of WS 2 catalysts in dibenzothiophene (DBT) hydrodesulfurization. The thermal decomposition of alkyl-ammonium thiosalts proceeds directly to WS 2 without WS 3 formation, as in the case of ammonium thiotungstate (ATT), allowing good control of the catalyst’s stoichiometry. The alkyl-ammonium thiosalts give WS 2 particles with different characteristic morphologies. The hydrodesulfurization (HDS) activities of WS 2 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 WS 2.25C 1.7, WS 1.7 C 0.9 and WS 1.3 C 0.7 for the in situ catalysts derived from ammonium, methylammonium, and butylammonium precursors, respectively. The improved catalytic properties of WS 2 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.