Carbon versus alumina as a support for Co-Mo catalysts reactivity towards HDS of dibenzothiophenes and diesel fuel

A series of cobalt-molybdenum catalysts supported on two different carbons has been prepared by conventional successive impregnation and/or successive impregnation with sulfiding between impregnation. Commercial Co-Mo/Al2O3 catalyst and the synthesized Go-Mo supported carbon catalysts have been compared for activity in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and hydrotreated diesel fuel. HDS experiments were carried out in a batch magnetically stirred micro autoclave reactor at 2.9 MPa hydrogen pressure acid temperature range from 300 degrees C to 380 degrees C. The Co-Mo/carbon catalysts exhibited higher HDS activity for DBT and diesel fuel than the commercial Co-Mo/Al2O3 catalyst. However, large differences in catalytic behavior were observed for Co-Mo/carbon catalysts dependent on the preparation method and the nature of carbon support. The highest activity was observed for catalysts prepared by successive impregnation with sulfiding between impregnations. The HDS selectivity of DBT was found to be almost independent of the temperature. In contrast, a dramatic change in HDS selectivity for 4,6-DMDBT with temperature was observed. The kinetic behavior of HDS for both DBT and 4,6-DMDBT was verified to be pseudo-first order. Activation energies of each reaction step in the mechanism of HDS of DBT and 4,6-DMDBT were determined. (C) 1999 Elsevier Science B.V. All rights reserved.