PREPARATION OF MOS2 AND WS2 CATALYSTS BY IN-SITU DECOMPOSITION OF AMMONIUM THIOSALTS

The in situ decomposition of ammonium thiometallates during the hydrod esulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum d isulfide and tungsten disulfide catalysts, was investigated. It was fo und 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 propert ies of the catalysts. Surface areas of molybdenum and tungsten disulfi des increased as a function of uniaxial pressing, while catalytic acti vities 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 con dition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxia l pressing, while the CIM ratio remained almost constant at 1.6. The b est catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of ill situ decomposition a nd mechanical deformation of thiometallate precursors is discussed.