Effect of Li 2 O Doping on the Surface and Catalytic Properties of the Fe 2 O 3 –NiO/Al 2 O 3 System

Abstract

Ferric–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°C and 800°C, respectively. The effects of this treatment on the surface characteristics of these solids and their catalytic properties in relation to CO oxidation by O₂ 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, SBET, of the solids precalcined at 500°C and 800°C, while the addition of 3 mol% Li₂O led to a slight decrease of ca. 10% in the SBET value of the same solids. In contrast, irrespective of whether the doping process involved solids precalcined at 500°C or 800°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.