Unsupported Ni/Mo(W)S-2 Catalysts from Hexamethylenediammonium Thiometallates Precursors: In Situ Activation During the HDS of DBT
Résumé
Unsupported Ni/MoS2 and Ni/WS2 HDS catalysts were prepared by in situ activation of hexamethylenediammonium thiometallates promoted with Ni. The method involved an aqueous solution reaction of ammonium thiomolybdate (ATM) or ammonium thiotungstate (ATT) with Ni(NO3)(2)center dot 6H(2)O and hexamethylenediamine. Ni-promoted precursors were then in situ activated during the hydrodesulfurization (HDS) of dibenzothiophene (DBT) producing Ni/MoS2 and Ni/WS2 catalysts. Solids were analyzed after the in situ activation by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and for textural properties by using the BET and BJH methods. Catalysts with relatively high surface area and type IV N-2 adsorption-desorption isotherms were obtained. The use of the hexamethylenediammonium precursor led to a significant nickel promotion of MoS2 and WS2 catalysts. For Ni/MoS2, the use of this carbon-containing precursor was found to be more beneficial for the final HDS catalytic activity than using the classical ammonium tetrathiomolybdate (ATM) without carbon. For Ni/WS2, compared to tetraalkylammonium thiosalts, the lower amount of carbon in excess formed during the decomposition of the hexamethylenediammonium precursor coupled with a lower crystallization rate of WS2 favors a correct nickel accommodation on the WS2 edges.