The effect of the composition of the intercalating solutions in the catalytic performance of the derived pillared clays has been studied. A Colombian bentonite was treated with Al/Fe-, Al/Cu- and Al/(Fe-Cu)-solutions, and the resulting pillared solids were used in the catalytic wet peroxide oxidation (CWPO) of the azo dye methyl orange (MO) in aqueous solutions.The active metal ratio (AMR), here defined as the atomic percent ratio between the active metals (Fe and Cu) and the total content of metals (Al, Fe and/or Cu) in the intercalating solutions, was found to be a key factor for the properties of the pillared solids. Low AMR values, between 0 and 10%, were considered, and the efficiency for the incorporation of the active metals into the layered structure was followed by chemical analyses and cationic-exchange capacity measurements. Further characterization studies were carried out by X-ray diffraction, H-2 temperature-programmed reduction, scanning electron microscopy/energy dispersive X-ray analysis, nitrogen adsorption at -196 degrees C and thermal analysis. Considering the physicochemical properties together with the catalytic performance, it is proposed that isomorphic incorporation of the active metals into the Al-13-like polycations may take place. The obtained pillared solids exhibited better catalytic performance as the AMR values were lowered in the corresponding intercalating solutions, displaying also high stability to chemical leaching into the strongly oxidizing environment of the catalytic reaction, especially in the binary Al/Fe- and Al/Cu-systems. The Al/Fe-pillared clays attained most of their maximal removal of the azo dye in solution after only 1h of reaction at very mild experimental conditions (room temperature and atmospheric pressure of 18 degrees C and 0.7 atm). (C) 2010 Elsevier B.V. All rights reserved.