Mechanisms of hydrodenitrogenation of alkylamines and hydrodesulfurization of alkanethiols on NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3

The simultaneous hydrodenitrogenation (HDN) of alkylamines and hydrodesulfurization (HDS) of alkanethiols, with the NH2 and SH groups attached to primary, secondary, and tertiary carbon atoms, were studied at 270-320 °C and 3 MPa over sulfided NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3 catalysts. Pentylamine and 2-hexylamine reacted by substitution with H2S to form alkanethiols and with another amine molecule to form dialkylamines. Alkenes and alkanes were not formed directly from pentylamine and 2-hexylamine, but indirectly by elimination and hydrogenolysis of the alkanethiol intermediates, as confirmed by their secondary behavior and the similar alkene/alkane ratios in the simultaneous reactions of amines and thiols. Only 2-methyl-2-butylamine, with the NH2 group attached to a tertiary carbon atom, produced alkenes as primary products by E1 elimination. NiMo/Al2O3 and CoMo/Al2O3 have a higher activity for the HDS of alkanethiols than does Mo/Al2O3; H2S has a negative influence. This shows that the thiols react on vacancies on the catalyst surface (Lewis acid sites). Mo/Al2O3 is the best HDN catalyst; H2S has a positive influence on the HDN of amines with the NH2 group attached to a secondary and a tertiary carbon atom. This indicates that the HDN of alkylamines occurs on Brønsted acid sites.