Synthesis of tetraalkylammonium thiometallate precursors and their concurrent in situ activation during hydrodesulfurization of dibenzothiophene

The synthesis of tetraalkylammonium thiomolybdates and thiotungstates, (NR(4))(2)MS(4) {R: heptyl or cetyltrimethyl, M: Mo or W} using an aqueous solution method is reported. This method significantly improves the yield of tetraalkylammonium compounds compared to previous studies. The one-step rapid substitution of [NH(4)](+) ions from ammonium thiomolybdate (ATM) and/or ammonium thiotungstate (ATT) with [(Heptyl)(4)N](+) and/or [(CTriM)N](+) ions, respectively, is described. Tetraheptylammonium thiomolybdate, tetraheptylammonium thiotungstate, cetyltrimethylammonium thiomolybdate and cetyltrimethylammonium thiotungstate were synthesized and characterized using Fourier transform infrared (FTIR) and UV-Vis spectroscopies. Thermal analyses (TGA-DTA) were done to study the fragmentation and decomposition behavior of their molecular structures. These tetraalkylammonium thiometallate precursors were in situ-activated concurrently during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), producing MoS(2) and WS(2) catalysts, respectively. These catalysts analyzed by scanning electron microscopy showed large voids and S/M around 2 (M: Mo, W). High surface area (200-400 m(2)/g) and type IV adsorption-desorption nitrogen isotherms were obtained. The nature of the alkyl group affects both the surface area and HDS selectivity. In this respect, a high selectivity for direct C-S bond cleavage is observed for MoS(2) and WS(2) formed from THepATM and THepATT precursors, respectively. The X-ray diffraction study showed that the catalysts are poorly crystalline with a very weak (0 0 2) intensity except for the WS(2) catalyst formed from THepATT. (C) 2003 Elsevier B.V. All rights reserved.