The transformation of different C-10 model molecules (n-decane, n-butyl cyclohexane, t-butyl cyclohexane, n-butyl benzene and tetralin) was studied on a sulfided NiMo/Y zeolite catalyst under industrial conditions : 380 degrees C, 5.7 MPa hydrogen pressure, presence of hydrogen sulfide and ammonia. Depending on the molecule, different reactions were observed, catalyzed either by the acid sites, or by the hydrogenating sites, or by both sites (bifunctional mechanism). Isomerization could concern the chain or the cycle, and occurred always through a bifunctional mechanism. The formation of the light products was mainly consecutive to isomerization, and consequently occurred also through the bifUnctional mechanism. However, some light products were formed through condensation-cracking reactions. Purely acid-catalyzed dealkylation of the alkyl aromatics was also observed, whereas the hydro-dehydrogenating function of the catalyst was responsible for the hydrogenation of the aromatics and the aromatization of the naphthenes.

The activity and the selectivity of a bifunctional NiMo sulfides-Y zeolite catalyst forn-heptane hydrocracking depend very much on the sulfidation agent, namely hydrogen sulfide, or dimethyldisulfide in solution inn-heptane orn-decane. The presence of a hydrocarbon during the sulfidation lowers the acid activity of the catalyst because of coking of the zeolite acid sites, and also decreases the hydrogenating activity, due to a poorer sulfidation of the catalyst.