Unsupported Ni/Mo(W)S2 Catalysts from Hexamethylenediammonium Thiometallates Precursors: In Situ Activation During the HDS of DBT

Abstract

Unsupported Ni/MoS2 and Ni/WS2 HDS cata- lysts were prepared by in situ activation of hexamethyl- enediammonium thiometallates promoted with Ni. The method involved an aqueous solution reaction of ammo- nium thiomolybdate (ATM) or ammonium thiotungstate (ATT) with Ni(NO3)2� 6H2O 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 N2 adsorption-desorption isotherms were obtained. The use of the hexamethylene- diammonium precursor led to a significant nickel promo- tion 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 hexamethylenediammo- nium precursor coupled with a lower crystallization rate of WS2 favors a correct nickel accommodation on the WS2 edges.