The effect of annealing temperature on the structure of unsupported Co-promoted MoS2 nanosheets, prepared by mechanical activation of MoO3, S and Co(NO3)(2)center dot 6H(2)O followed by annealing in an Ar atmosphere, is reported. An increase in annealing temperature reduced the catalyst surface area but increased the MoS2 stack height. Annealing temperatures above 600 A degrees C also produced segregated CoxSy phases. The dibenzothiophene hydrodesulphurization activity and the direct desulfurization (DDS) to hydrogenation product ratio of the Co-MoS2 catalysts was significantly higher than for MoS2. Moreover, the DDS product selectivity of the Co-MoS2 catalysts was enhanced with increased annealing temperature up to 600 A degrees C. Above 600 A degrees C, the loss in activity and selectivity was due to segregation of CoxSy species and significant sintering of the MoS2 crystallites. Similar effects of high temperature sintering on the activity of MoS2 were also observed.