Hydrodenitrogenation of Carbazole on Nitrided Molybdena-alumina Catalyst.

Abstract

The hydrodenitrogenation (HDN) of carbazole on the nitrided 12.5% MoO3/Al2O3 catalysts over a temperature range of 280-360°C and at a total pressure range of 5-15MPa was studied. The 12.5% MoO3/Al2O3 was nitrided at various nitriding temperatures (500, 700 and 900°C), NH3 pressures (0.1 and 0.5MPa), and NH3 flow rates (4 and 15l h-1), following after the temperature-programmed reaction with NH3. After nitriding, the nitrided catalysts were cooled to room temperature in flowing NH3 and passivated with 1% O2/He for 12h. It was difficult to remove nitrogen from the catalysts nitrided at 700 and 900°C, even though the catalysts were evacuated at 700°C. The catalyst nitrided at 900°C showed the highest activity among all catalysts in the HDN of carbazole, and that nitrided at 700°C displayed the second highest activity. The activities of the catalysts nitrided and reduced at 500°C showed similar values. Nitriding the MoO3/Al2O3 catalyst enhanced the C-N hydrogenolysis selectivity more than reducing the catalyst. The external mass transfer was negligible in the reaction. The formation of the denitrogenated compounds was on the order of 0.9 and 0.7 with respect to hydrogen in the range of 3-9MPa pressure and initial carbazole concentration of 0.023 to 0.35%, respectively. The sulfur compound inhibited the HDN of carbazole depending on its proton affinity. The XPS study showed that the molybdenum species between Mo4+ to Mo6+ ion were widely distributed and many nitrogen species, such as nitride-nitrogen, adsorbed NH3, and NHx, were present on the surface.