Influence of the nature of molybdenum compounds on the activity of Mo/γ-Al2O3 and NiMo/γ-Al2O3 hydrotreating catalysts

The influence of the nature of molybdenum compounds on the catalytic activity of sulfided NiMo/γ-Al2O3 catalysts was studied. The samples were prepared by impregnating the support with mixed aqueous solutions of nickel nitrate and molybdenum-containing compounds: ammonium paramolybdate and the 6-series heteropoly compounds (HPCs) ammonium 6-molybdonickelate (NiMo6-HPC) and ammonium 6-molybdoaluminate (AlMo6-HPC). Complexing agents (tartaric acid or a solution of NH3) were used for stabilizing mixed aqueous ammonium paramolybdate and nickel nitrate solutions and for simultaneously producing an acidic or alkaline medium. The starting molybdenum compounds and catalysts in the oxide form were characterized using IR spectroscopy and x-ray diffraction analysis. The activity of catalysts based on NiMo6-HPC in the hydrogenolysis of thiophene and in the hydrotreating of the diesel fraction was higher than that of catalysts based on ammonium paramolybdate: at 320°C, the degree of sulfur removal from the diesel fraction was higher by 13–16% and the average degree of hydrogenation of polycyclic aromatic hydrocarbons was higher by 14–15%. It was also found that the use of AlMo6-HPC does not cause such an effect.