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ABSTRACTred by a variant of the homogeneous sulphide precipitation method. The seriem consimted of nOS2, eight powders with Co/(Co+No) ratios of 0.167 to 0.643, and COgS8. The catalystm were characterised by deuterium adsorption at 673 K, TPR and TPD.A double maximum was found for the dependence of activity with Co/(Co+PIo) fraction, in a range similar to that found by other workers. Hydrogen retained by the catalyst, and deuterium admorption at 673 K are not related to the hds activity. TPR and TPD measurements, however, show the same two-peak behaviour as the activity across the composition range. The TPR behaviour mhows two peaks of hydrogen uptake at 475 K and 650 K, the relative areas of which depend on the Co/(Co+nO) ratio in a complex way. The high temperature peak is strongly Correlated with hds activity, and thim activity is related both to the formation of defect sites at high temperature and the availability of adsorbed hydrogen. The adsorbed hydrogen measured by desorption between 300 K and 872 K is greatest in the Co/(Co+Mo) range 0.167 to 0.445, the range of highest activity for conventional catalymts, whereas combination of the T P R and TPD results yields the same pattern as is obtained for hds activity.The results show that the behaviour with rempect to hydrogen im strongly affected by the premence of both cobalt and molybdenum, the synergic effect is much greater than a c o m b i n a t K o f the components.A seriem of unsupported cobalt molybdenum sulphide powders ham been prepaThe activity of theme materials was tested using the hds of thiophen. INTRODUCTIONThe role of hydrogen in the activity of hydrodesulphurisation catalysts is imperfectly understood. able to absorb a substantial quantity of hydrogen, which is bound am sulfhydryl groups, and which elevates the hydrogenation activity of MoS2 but does not affect the hds activity ( 1 , Z ) . the cobalt-molybdenum sulphide system across the range of composition which corresponds with increased activity in commercial alumina-supported catalysts. The recent identification of a feature in the Mossbauer spectra of similar materialm (3) led us to extend the range to higher cobalt concentrations. At firmt, we hoped to obtain useful information from the adsorption of hydrogen measured volumetrically at the reaction temperature. It became clear that much more information could be obtained from studies involving temperature programmed method., and this paper prements results from such experiments.