Active sulfide catalysts are conventionally prepared by converting the respective oxides to sulfides. Reductive sulfiding of the oxides is usually difficult and does not proceed in a regular manner. A supported molybdenum sulfide catalyst prepared by the decomposition of ammonium tetrathiomolybdate (ATTM) in hydrogen is unique in two respects, namely, the lower valence state of the supported molybdenum sulfide catalyst, and the presence of few oxygen atoms in the catalyst. The activity of a catalyst prepared by this technique (and subjected to different pretreatments) is compared with the activities of both a conventional and a commercial catalyst. The pretreatment consists of flash or temperature-programmed decomposition of the supported ATTM in helium followed by removal of excess sulfur by temperature-programmed reduction, or the decomposition of supported ATTM in hydrogen. The results clearly indicate that the activity of the catalyst prepared by the decomposition of ATTM is higher than the activities of both the conventionally prepared catalyst and the commercial catalyst.