Indole Hydrodenitrogenation over Alumina and Silica Alumina-Supported Sulfide Catalysts Comparison with Quinoline

A detailed kinetic model was proposed to analyze experimental data obtained from indole hydrodenitrogenation (HDN) over gamma-Al2O3 and amorphous silica alumina (ASA)-supported NiMo catalysts. The goal was to investigate the support acidity effects on indole HDN and compare with a recent study on quinoline HDN. Similarly to quinoline HDN, indole HDN occurred via hydrogenation of the aromatic ring, followed by N-ring opening and exocyclic C-N bond breaking. The high support acidity of NiMo(P)/ASA exhibited a promoting effect for N-removal steps and adsorption of nitrogen compounds. However, in contrast to quinoline HDN, it did not clearly induce a positive effect for the hydrogenation step. The acidic function of ASA also favored the formation of byproducts such as toluene, cyclohexane, dimer, and trimer of indole. Catalytic conversion of a quinoline and indole mixture revealed a strong inhibiting effect of quinoline on indole HDN, whereas the inhibiting effect of indole on quinoline HDN was weak The inhibition was weaker over NiMo(P)/Al2O3 than over NiMo(P)/ASA. This result is in agreement with a relative ranking of apparent adsorption constants of quinoline, indole, and their products on NiMo(P)/Al2O3 and ASA.