KINETICS OF THE HYDRODENITROGENATION OF ORTHO-PROPYLANILINE OVER NIMO(P) AL2O3 CATALYSTS/

The kinetics of the hydrodenitrogenation (HDN) of ortho-propylaniline (OPA) was studied over sulfided NiMo(P)/Al2O3 catalysts. A small amoun t of propylcyclohexylamine was observed in the reaction product, demon strating that hydrogenation of the phenyl group of OPA was one of the first and rate-limiting steps in the HDN reaction. A Langmuir-Hinshelw ood kinetic model with different sites for the HDN and hydrogenation c ould successfully fit the reaction network. Some kinetic parameters we re obtained by varying the initial reactant partial pressure at consta nt space time and by simultaneous reaction, while others were determin ed by varying the space time at constant reactant partial pressure. Th e HDN rate constants and the adsorption constants of OPA and NH3 were higher over the phosphate-containing catalyst than over the phosphate- free catalyst, while the activation energies as well as the heats of a dsorption of OPA did not show any difference between the two catalysts . This demonstrates that the nature of the catalyst sites did not chan ge by the introduction of phosphate. The promotive effect of phosphoru s in the HDN of OPA arises from an increased number of active sites fo r the hydrogenation of the phenyl ring of OPA as well as from a strong er adsorption of OPA due to increased MoS2 stacking and therefore less hindered adsorption. Phosphorus shows a promotive effect on the hydro genation of pure olefins, but a negative effect when nitrogen-containi ng compounds are present. This is due to a stronger adsorption of the nitrogen-containing compounds on the P-containing catalyst, and hence to a stronger inhibition. (C) 1997 Academic Press.