A kinetic investigation of the effects of fluorine and nickel on the HDN of toluidine on fully sulfided tungsten sulfide catalysts

The effects of fluorine and nickel on the hydrodenitrogenation of o-toluidi ne on alumina-supported tungsten catalysts were studied in a continuous-flo w reactor at 320 to 370 degreesC and 3.0 MPa. The catalysts were prepared f rom ammonium tetrathio-tungstate and were fully sulfided. The kinetic data were obtained by varying the initial partial pressure of the reactant and t he reaction temperature; Langmuir-Hinshelwood models were used to fit the k inetic data. The simultaneous reactions of cyclohexene and o-toluidine enab led us to study the inhibition effect of o-toluidine on the hydrogenation o f cyclohexene and to determine the difference between the sites for these r eactions. The kinetic data suggest that the formation of toluene and 2-meth ylcyclohexylamine from o-toluidine occurs through a common partially hydrog enated intermediate, dihydrotoluidine, which leads to toluene by eliminatio n and 2-methylcyclohexylamine after further hydrogenation. Fluorination cha nges neither the activation energies for the hydrogenation reaction nor the heat of adsorption of o-toluidine. Fluorine thus does not change the intri nsic properties of the active sites but does affect the apparent activity b y influencing the number of active sites. Only a change in the morphology o f the metal sulfide surface, by stacking, can explain the fluorine effect. Addition of nickel changes the nature of the active site by creating a nick el-associated sulfur vacancy, which is highly active for hydrogenation. (C) 2001 Academic Press.