Mechanistic considerations on the involvement of dihydrointermediates in the hydrodesulfurization of dibenzothiophene-type compounds over molybdenum sulfide catalysts

The mechanism of the hydrodesulfurization of dibenzothiophene-type compounds involving their dihydroderivatives as intermediates was examined in the light of previous experimental results dealing with the effect of cobalt and nickel promoters on the selectivity of the reaction. It is suggested that the orientation of the hydrodesulfurization reaction regarding the so-called "direct desulfurization" or "hydrogenation" pathways depends on various factors: the distribution of the dihydrointermediates (two of them only among nine possible isomers can lead directly from dibenzothiophene to biphenyl): the availability of dissociated hydrogen on the catalytic centers on which they adsorb and the basicity of the sulfur anions associated to the catalytic centers.