Hydrodemetallation (HDM) of nickel-5,10,15,20-tetraphenylporphyrin (Ni-TPP) over NiMo/gamma-Al2O3 catalyst prepared by one-pot method with controlled precipitation of the components
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In this work, a series of NiMo/gamma-Al2O3 catalysts is prepared by one-pot method with controlled precipitation of AlCl3 center dot 6H(2)O, (NH4)(6)Mo7O24 center dot 4H(2)O and NiCO3 center dot 2Ni(OH)(2)center dot 4H(2)O using urea and ammonium carbonate as additives. The molar ratio of urea to Al varied from 4.1 to 17.2 and the influence of this parameter on the surface and structural properties of the catalysts and HDM activity was studied. HDM of Ni-TPP was carried out in a batch reactor. The catalysts were characterized by BET, XRD, H-2-TPR, DRS, XPS, EDS, FT-IR, TG-DTA and NH3-TPD. The results show that urea employed as additive not only improves the solubility of Mo and Ni salt, but also adjusts the hydroxyl concentration and facilitates the formation of molybdate and polymolybdate. The existence of residual chlorine may improve the dispersion of the particles containing Ni and Mo on the surface of porous Al2O3, enhance hydrogen spillover and the acidity of the catalyst. HDM activity varied with the amount of urea to a maximum at urea/Al of 12.3 with activity of 98%. The highest activity occurred at this ratio is mainly due to better porosity, well dispersed active particles, increased octahedral molybdenum/nickel oxides and proper acidity. (C) 2012 Elsevier Ltd. All rights reserved.