Abstract
The effects of fluorine and nickel on the hydrodenitrogenation of o-toluidine on alumina-supported tungsten catalysts were studied in a continuous-flow reactor at 320 to 370°C and 3.0 MPa. The catalysts were prepared from ammonium tetrathiotungstate and were fully sulfided. The kinetic data were obtained by varying the initial partial pressure of the reactant and the reaction temperature; Langmuir–Hinshelwood models were used to fit the kinetic data. The simultaneous reactions of cyclohexene and o-toluidine enabled us to study the inhibition effect of o-toluidine on the hydrogenation of cyclohexene and to determine the difference between the sites for these reactions. The kinetic data suggest that the formation of toluene and 2-methylcyclohexylamine from o-toluidine occurs through a common partially hydrogenated intermediate, dihydrotoluidine, which leads to toluene by elimination and 2-methylcyclohexylamine after further hydrogenation. Fluorination changes neither the activation energies for the hydrogenation reaction nor the heat of adsorption of o-toluidine. Fluorine thus does not change the intrinsic properties of the active sites but does affect the apparent activity by influencing the number of active sites. Only a change in the morphology of the metal sulfide surface, by stacking, can explain the fluorine effect. Addition of nickel changes the nature of the active site by creating a nickel-associated sulfur vacancy, which is highly active for hydrogenation.
Published Version
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