Activity measurements of an unpromoted molybdenum sulfide catalyst prepared by the decomposition of ammonium tetrathiomolybdate (ATTM) indicate that the catalyst exhibits a higher HYD activity than a catalyst prepared by the conventional method of reductive sulfiding of the oxide, as well as a commercial catalyst, The increased activity can be attributed to a valence state of molybdenum lower than 4 in the supported sulfide catalyst and a concomitant increase in the number of anion vacancies as determined by TPD studies, The results also indicate that the addition of a promoter Co to ATTM results in higher I-IDS, but not higher HYD activity of the catalyst.