Active Sites for HDS and Hydrogenation

Other metals, including iron or noble metals, are worthwhile for examination to compare the selectivity between hydrodesulfiirization and hydrogenation, although a series of metals are compared in the relationship between strength of metal-S and -H bonds and catalytic activity to confirm the Sabatier principle 

ROLES OF STERIC HINDRANCE IN ADSORPTION AND KINETIC PROCESSES OF HDS 

The hydrogenative bond fission step can be also postulated to suffer steric hindrance. Alkyl groups at other locations may be involved in this stage. In this sense, reactivities of 1,9-dialkyl DBTs are interesting to discuss at these stages. The same questions have been posed in the HDN of aromatic nitrogen species. So far, in depth discussion has not been attempted. 

Perot et al. proposed the formation of dihydro intermediates during the HDS of DBT and dialkyl-DBT, regardless of whether the route involves hydrogenolysis or direct desulfurization as seen in Fig. 19. They ascribed die inertness of 4,6-DMDBT to hindered P-elimination by substituted methyl groups. 

In conclusion, we believe that steric hindrance plays its role dominantly at the a-coordination stage. Details of Tt-coordination must be involved in competition for the catalyst surface even if the step may not be ratedetermining. Even so, participation of Tt-coordination may be influential in some petroleum refining reactions. 

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