Kinetic analyses and inhibition by naphthalene and H2S in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over CoMo-based carbon catalyst

Hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) in decane has been investigated over a Co-Mo/C catalyst, using a magnetically stirred autoclave reactor. The hydrodesulfurization reaction was found to be pseud o-first order with respect to 4,6- DMDBT. Direct desulfurization was detect ed to be Arrhenius-dependent with an activation energy of 35.7 kcal/mol, wh ile hydrogenation pathway showed a maxima at 340 degrees C. The activation energy of hydrogenation in the Arrhenius-dependent region was calculated to be 17.9 kcal/mol, as hydrogenation is thermodynamically limited at high te mperature. The reaction of hydrodesulfurization appears to proceed via two different partially dependent routes, hydrogenation and desulfurization, ov er the present catalyst. Hydrogenation of 3,3'-dimethylbiphenyl at differen t temperatures was also measured to identify the rates of the step involved in the hydrodesulfurization network of 4,6-DMDBT. Attention was particular ly paid to the effects of naphthalene and H2S on the two different reaction pathways to propose the mechanism of their inhibition. Two different catal ytic active sites, one for hydrogenation and the other for both hydrogenati on and direct desulfurization, are discussed to be present.