Mechanism of the hydrodenitrogenation of o-toluidine and methylcyclohexylamine over NiMo/gamma-Al2O3

The hydrodenitrogenation (HDN) of o-toluidine and its reaction intermediate s was studied over a NiMo/gamma-Al2O3 catalyst. The kinetics of the HDN of methylcyclohexylamine and of the hydrogenation of cyclohexene were also stu died. Hydrogenation of o-toluidine alone produces methylcyclohexene and met hylcyclohexane. When a sufficient quantity of cyclohexene is added during t he HDN of toluidine, methylcyclohexylamine, the first intermediate in the h ydrogenation of toluidine, becomes detectable. Because of its strong adsorp tion constant and high rate constant for reacting further to methylcyclohex ene and methylcyclohexane, methylcyclohexylamine is not observed in the HDN of toluidine. Adding cyclohexene decreases the adsorption of methylcyclohe xylamine, thus enabling its detection. The rate and adsorption constants of methylcyclohexylamine and cyclohexene in the HDN of methylcyclohexylamine were calculated by fitting the kinetic data to a Langmuir-Hinshelwood equat ion. A two-site model was used to describe the surface reactions, with one site for the methylcyclohexylamine reactions and the other for the cyclohex ene reaction.