Hydrodesulfurization of dibenzothiophene, 4,6-dimethyldibenzothiophene, and their hydrogenated intermediates over Ni-MoS2/γ-Al2O3

The rate constants of all reaction steps in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT), and their tetra- and hexahydro intermediates TH(DM)DBT and HH(DM)DBT over Ni-MoS2/gamma-Al2O3 were determined. DBT, THDBT, DMDBT, and THDMDBT underwent desulfurization by hydrogenolysis of both C-S bonds, while HHDBT and HHDMDBT underwent desulfurization by cleavage of the aryl C-S bond by hydrogenolysis, followed by cleavage of the cycloalkyl C-S bond by elimination as well as by hydrogenolysis. Ni promoted the C-S bond breakage of DBT, THDBT, and HHDBT strongly, but promoted the (de)hydrogenation only weakly. The methyl groups suppressed the desulfurization in the order DMDBT > THDMDBT > HHDMDBT and promoted hydrogenation. These different degrees of steric hindrance are due to the hydrogenation of a phenyl ring, which makes the THDBT and HHDBT rings flexible. H2S strongly inhibited the desulfurization rates in the order (DM)DBT > TH(DM)DBT > HH(DM)DBT, but inhibited the (de)hydrogenation rates only slightly. 2-Methylpiperidine inhibited the hydrogenation of all molecules. (C) 2009 Elsevier Inc. All rights reserved.