Role of Hydrogenolysis and Nucleophilic Substitution in Hydrodenitrogenation over Sulfided NiMo/γ-Al2O3

The hydrodesulfurization of cyclohexanethiol and 2-methylcyclohexanethiol was studied over a sulfided NiMo/γ-Al2O3 catalyst. About two-thirds of the thiols reacted by elimination to (methyl)cyclohexene and one-third by hydrogenolysis of the C–S bond to (methyl)cyclohexane. These values are slightly lower than those for the selectivity to methylcyclohexene and slightly higher than those for the selectivity to methylcyclohexane in the hydrodenitrogenation of 2-methylcyclohexylamine. In aliphatic molecules that contain H atoms in the β position relative to the nitrogen atom, hydrodenitrogenation occurs predominantly (70–80%) by elimination of ammonia. Part of the remaining (20–30%) hydrodenitrogenation takes place by nucleophilic substitution of the amine by H2S, followed by elimination of H2S from the resulting thiol and, to a lesser extent, by C–S bond hydrogenolysis; the rest of the remaining hydrodenitrogenation takes place by direct hydrogenolysis of the C–N bond.