Characterization and HDS activity of mesoporous MoS2 catalysts prepared by in situ activation of tetraalkylammonium thiomolybdates

Unsupported molybdenum disulfide catalysts with unique morphological pore structure were synthesized from tetraalkylammonium thiometalates precursors by in situ activation during the hydrodesulfurization (HDS) of dibenzothiophene. The precursors used in this study are ammonium thiomolybdate (ATM), tetrapropylammonium thiomolybdate, tetrapentylammonium thiomolybdate, tetrahexylammonium thiomolybdate, tetraheptylammonium thiomolybdate (THepATM), and tetraoctylammonium thiomolybdate. The thermogravimetrical analysis carried out under nitrogen demonstrated that all precursors yield MoS2 bulk structure at 623 K, after one or two decomposition steps. The morphology of these catalysts observed by scanning electron microscopy presents large hemispherical or ovoid cavities with a cheese-like porous arrangement, high surface area (from 255 up to 329 m(2)/g), high content of carbon (C/Mo = 2.7-4.0), and type IV adsorption-desorption isotherms of nitrogen. The nature of the alkyl group affects the surface area, the pore size distribution, and the HDS selectivity. The highest selectivity for direct C-S bond cleavage is observed for the molybdenum disulfide catalyst formed from THepATM. X-ray diffraction studies showed that the catalysts are poorly crystallized, with a very weak intensity of the (002) line of 2H-MoS2 characteristic of exfoliated samples. (C) 2002 Elsevier Science (USA).