Ring opening of 1,2,3,4-tetrahydroquinoline and decahydroquinoline on MoS2/γ-Al2O3 and Ni–MoS2/γ-Al2O3

The hydrodenitrogenation of decahydroquinoline (DHQ) and quinoline on MoS2/γ-Al2O3 and Ni–MoS2/γ-Al2O3 proceeds via two routes. The first one proceeds via DHQ → propylcyclohexylamine → propylcyclohexene → propylcyclohexane, and the ring opening in DHQ is the rate-limiting step. The second route proceeds via 1,2,3,4-tetrahydroquinoline (14THQ) → o-propylaniline → propylcyclohexylamine and propylbenzene with the ring opening of 14THQ and the hydrogenation of o-propylaniline being the rate determining steps (the intrinsic rate of C(sp3)–N bond cleavage being slower in 14THQ than in DHQ). The active sites for the ring opening via Hofmann elimination are acidic –SH groups and basic S2− ions. The parallel conversion of dibenzothiophene (DBT) via direct desulfurization provides increasing concentrations of S2− ions and –SH groups. Nickel facilitates the adsorption of H2S and H2 and the mobility of hydrogen. Thus, the presence of DBT and Ni accelerates the rate of the C(sp3)–N bond cleavage. H2S as sulfur source enhances the ring-opening steps in a minor extent than DBT. The presence of –SH groups and the effect of Ni on them were probed by TPR, TPD and IR-spectroscopy of adsorbed 2,6-dimethylpyridine.