Effect of Li2O doping on the surface and catalytic properties of the Fe2O3-NiO/Al2O3 system

Ferrit-nickel/aluminium mixed oxide solids have the formula Fe2O3-0.42NiO/Al2O3 were treated with Li2O (0.75-3 mol%) and heated in air for 4 h at 500 degrees C and 800 degrees C, respectively. The effects of this treatment on the surface characteristics of these solids and their catalytic properties in relation to CO oxidation by O-2 have been investigated. The results reveal that Li2O doping at 0.75 mol% concentration resulted in an increase of 24% and 18%, respectively, in the value of the specific surface areas, S-BET, of the solids precalcined at 500 degrees C and 800 degrees C, while the addition of 3 mol% Li2O led to a slight decrease of ca. 10% in the S-BET value of the same solids. In contrast, irrespective of whether the doping process involved solids precalcined at 500 degrees C or 800 degrees C, a significant decrease of 37% and 78%, respectively, was observed in the catalytic activity of these materials. This decrease in catalytic activity was not accompanied by any appreciable change in the magnitude of the activation energy for the catalytic reaction, i.e. Li2O doping brings about a decrease in the concentration of catalytically active sites without changing their energetic nature.