Experimental and theoretical description of the equilibrium adsorption of metal ion solutions on the surface of gamma-Al2O3 and MoO3/gamma-Al2O3 systems

The equilibrium adsorption isotherms of Mo, Co and Pt species on gamma-Al2O3 and Co and Pt on MoO3/-Al2O3 oxides were studied. The Molybdena-alumina catalysts for adsorption tests were prepared by impregnation of gamma-Al2O3 supports with aqueous solutions of ammonium heptamolybdate. The equilibrium adsorption data were obtained from liquid-solid adsorption process. L-type shaped adsorption curves were found for Mo and Co on gamma-Al2O3 and Co(Pt) on MoO3/gamma-Al2O3 whereas S-shaped were found in the Pt(Co) on MoO3/gamma-Al2O3 systems. In the Mo system, it was found that the molybdenum species in solution (tetrahedral and octahedral) affected the Mo adsorption. The adsorption of Co(II) ions over alumina or modified alumina did not depend on the alumina source. The shape of the Co adsorption isotherm on MoO3/gamma-Al2O3 appeared to be modified when Pt(IV) ions were present simultaneously. The adsorption process for Pt species depended on the presence of Mo(VI) and Co(II) ions on the supports surface. It was observed that the amount of Pt adsorbed on the surface of the MoO3/gamma-Al2O3 sample decreased in the presence of Co(II) ions in solution. Finally, the equilibrium parameters for the adsorption of Mo(VI) and Co(II) on gamma-Al2O3 and Co( II) and/or Pt(IV) on MoO3/-Al2O3 were determined.