The hydrodesulfurization (HDS) of benzothiophene (BT) and dihydrobenzothiophene (DHBT) was studied over a sulfided Mo/gamma-Al2O3 catalyst at 5 MPa and 280 and 300 degrees C. In the absence of H2S, benzothiophene reacted by hydrogenation to dihydrobeilzothiopliene and by hydrogenolysis to ethylbenzene (EB) and. dihydrobenzothiophene reacted by hydrogenolysis to ethylbenzene. H2S inhibited both hydrogenation and hydrogenolysis, but the latter much more strongly. The reverse inhibition was observed for 2-methylpiperidine (MPi). In the presence of H2S and/or 2-methylpiperidine, dihydrobenzothiophene reacted to ethylbenzene as well as by total hydrogenation to octahydrobenzothiophene, and on to ethylcyclohexenes and ethylcyclohexane. Dihydrobenzothiophene did not react back to benzothiophene at and below 300, C, while the equivalent tetrahydrodibenzothiophene reacted fast to an equilibrium with tetrahydrodibenzothiophene, due to stabilization of the vinylic bond by the alkyl groups. The observed products and kinetic results were explained by a model in which the C-S bonds were mainly broken by hydrogenolysis. (C) 2008 Elsevier B.V. All rights reserved.