Existence of different catalytic sites in HDN catalysts

Abstract

The hydrodenitrogenation (HDN) of ortho-propylaniline (OPA) has been studied over NiMoP/Al 2O 3 catalysts with 0–4 wt% phosphorus, 0–3 wt% nickel and 0–12 wt% molybdenum. The HDN reaction was found to proceed via two reaction paths: hydrogenation of the phenyl ring followed by NH 3 elimination to propylcyclohexene, which further (de)hydrogenated to propylcyclohexane and propylbenzene, and direct C(sp 2)N bond hydrogenolysis to propylbenzene. The first denitrogenation path was promoted by Ni and inhibited by the presence of H 2S, where hydrogenation of the phenyl ring was suggested to be the rate-limiting step. The second denitrogenation path was promoted by phosphorus and inhibited by the presence of H 2S and Ni. It is suggested that at least two different kinds of catalytic sites are acting in the HDN of OPA over a sulphided Mo-based catalyst. The first site bears the characteristics of the NiMoS phase, is strongly promoted by Ni and is responsible for the hydrogenation reaction. The second site is a site associated with Mo, its activity is enhanced by phosphorus, but diminished by Ni and H 2S, and it is specially active for the C(sp 2)N bond cleavage reaction. Both sites are different from the catalytic site which is responsible for the aliphatic C(sp 3)N bond cleavage.