Abstract
The surface and catalytic properties of Co3O4/Al2O3 solids treated with different proportions of MoO3 were investigated, the extent of MoO3 added varying between 0.50 mol% and 5.00 mol% (0.63–5.9 wt%). The pure sample was prepared by thermal decomposition at 600°C of aluminium hydroxide impregnated with a calculated amount of Co(NO3)2 dissolved in the least amount of distilled water. The MoO3-treated samples were prepared by thermal decomposition at 600°C of aluminium hydroxide treated with different proportions of ammonium molybdate followed by treatment with Co(NO3)2 solution.
The crystalline phases produced by thermal treatment of the pure and treated samples precalcined at 600°C were characterized using an XRD technique. The surface and catalytic properties of the various catalysts were studied using nitrogen adsorption at −196°C and CO oxidation by O2 at 100–150°C.
The results obtained revealed that molybdena treatment of the Co3O4/Al2O3 solids followed by precalcination at 600°C resulted in a decrease in the degree of crystallinity of the Co3O4 phase produced. This treatment effected a progressive small increase in the specific surface area of the treated solids (ca. 10%). However, the catalytic activity was found to be increased considerably by increasing the amount of MoO3 added (184%), reaching a maximum limit at 1.00 mol% MoO3.
The activation energies of the catalytic reaction calculated for both the pure and MoO3-treated solids suggested that MoO3 treatment did not modify the energetic nature of the active sites (surface cobalt species) but increased their concentration.