Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over a synthesized nanosize-MoS2 catalyst were investigated in a batch reactor. The catalytic activity in hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene increased remarkably with H2S being remained in the reaction zone. The HDS reactions of the two substrates over the present catalyst were found to proceed via a network where direct desulfurization and hydrogenation routes are essentially involved. The product contribution from the hydrogenation route is much more pronounced. Isomerized components were also identified. Dibenzothiophene and 4,6-dimethyldibenzothiophene exhibited almost identical results in terms of the reactivity and selectivity. The increase in the catalytic activity with H2S is probably due to the increase in the number of the potentially active sites modified by H2S. The kinetic investigation of the hydrodesulfurization reactions revealed the amocatalysis-like phenomena attributed to the potentially modified active sites by self-produced H2S. TEM image reveals that the synthesized MoS2 may consist of a bent and/or a closed round layers which might play an important role in such autocatalysis behaviors of H2S in the hydrodesulfurization of polyaromatic thiophenes. (c) 2006 Elsevier B.V. All rights reserved.