Catalysis Letters 7 (1990) 377-382 377 X-RAY DIFFRACTION STUDY OF A CoMo SULFIDE OBTAINED BY THE IMPREGNATED THIOSALT DECOMPOSITION METHOD Gabriela DIAZ, Rosario LUNA Instituto de Fisica, UNAM, Apdo. Postal 20-364, Mexico 01000 David RIOS-JARA and Leticia BAI~OS Instituto de Investigaciones en Materiales, UNAM, Apdo. Postal 70-360, 04510 Mexico, D.F., Mexico Received 27 April 1990; accepted 24 September 1990 Bulk sulfide catalysts, CoMo sulfides X-ray powder diffractometry was used to characterize the phases produced during the preparation of MoS 2 catalysts promoted with Co, by the impregnated thiosalt method. After a crystallization process at 673 K and 1043 K the X-ray analysis seems to indicate the presence of a mixed CoMo sulfide, in addition to the MoS 2 and Co9Ss. Unsupported molybdenum or tungsten sulfides, promoted by cobalt or nickel can be prepared by several procedures. Different methods have been proposed: the comaceration method described by Hagenbach et al. [1], the homogeneous sulfide precipitation (HSP) developed by Candia et al. [2], the decomposition of thiobismetalato complex salts [3], and some others. All of these methods look for the formation of mixed phases in the sulfided samples. Recently, a preparation procedure was reported called Impregnated Thiosalt Decomposition method (ITD) that selectively deposes the promoter on the surface of the MoS 2 precursor [4]. The CoMo and NiMo catalysts obtained by this technique showed an improved intrinsic catalytic activity, as compared with other catalysts prepared by conventional methods. In this letter, we report an X-ray diffraction characterization of the different phases obtained when preparing CoMo sulfides by the impregnated thiosalt method. We focussed our attention on one CoMo catalyst, with an atomic composition Co/Co + Mo = 0.3, which showed the highest activity in HDS and hydrogenation reactions, among other CoMo sulfided catalysts with a large range of compositions [5]. Pure ammonium thiomolybdate crystals [(NH4)2MoS4, ATM] were prepared by a conventional method [6]. The ATM crystals were impregnated with cobalt using an acetone solution of Co(NO3)2.6H20, as reported elsewhere [4]. 9 J.C. Baltzer A.G. Scientific Publishing Company