First principles study of heavy oil organonitrogen adsorption on NiMoS hydrotreating catalysts

The adsorption of quinoline, acridine, indole, and carbazole on the well-defined NiMoS hydrotreating catalyst edge surface has been studied by means of density-functional theory (DFT) using a periodic supercell model. Quinoline and acridine, the basic nitrogen-containing molecules present in heavy oils, are preferably adsorbed on the Ni-edge surface through the lone pair electrons of the nitrogen atom, which produces relatively high adsorption energies (-(delta)Ea = 16-26 kcal mol-1). Indole and carbazole, the non-basic nitrogen-containing molecules, primarily interact with the NiMoS catalyst edge surface through the p-electrons of the carbon atoms. While indole preferentially adsorbs on the NiMoS surface through the (beta)-carbon of the pyrrolic ring (-(delta)Ea = 19 kcal mol^-1), carbazole primarily interacts with the NiMoS surface through the phenyl rings (-(delta)Ea = 13 kcal mol-1). The relative adsorptivities and energetically preferred adsorption modes of the nitrogen-containing molecules in heavy oils can provide insights into experimenta observations about hydrodenitrogenation (HDN) kinetics and reaction pathways.