Interaction of different molecules with the hydrogenation and desulfurization sites of NiMoS supported particles with different morphology

In the search of insight concerning the interaction of molecules of different complexity with the desulfurization and hydrogenation sites, a series of NiMo sulfided catalysts with active particles of different morphology were tested in the hydrodesulfurization of dibenzothiophene, 4,6-dimethyldibenzothiophene, and in the hydrogenation of naphthalene and cyclohexene. The size and stacking of the NiMoS nanoparticles were modified both by increasing the Mo loading and by decreasing the metal-support interaction. The results show that not all the hydrogenation reactions take place at the same type of site, and that the hydrogenating sites at the top basal plane have greater hydrogenating power than those at the edge. The direct desulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene takes place at coordinatively unsaturated sites (CUS), whereas for the hydrogenation-desulfurization reaction route, the site where the rate controlling step takes place is influenced by the structure and reactivity of the reacting molecule. For dibenzothiophene, the rate controlling step takes place at hydrogenating sites at the top basal plane while for 4,6-dimethyldibenzothiophene it takes place at CUS. Therefore, to efficiently eliminate sulfur from molecules like 4,6-dimethyldibenzothiophene, as required in ultra-low sulfur fuels, the catalyst must have good hydrogenating capacity but more importantly, a high number of CUS.