Effects of Li2O Doping on the Surface and Catalytic Properties of Co3O4–Fe2O3 Solids Precalcined at Different Temperatures

Abstract

The effects of Li2O treatment on the solid–solid interactions and the surface and catalytic properties of the Co3O4–Fe2O3 system have been studied using TG, DTA and XRD methods, nitrogen adsorption studies at −196°C and the catalytic oxidation of CO by O2 at 150–350°C. The results obtained showed that Li2O doping followed by precalcination at 500–1000°C enhanced the formation of cobalt ferrite to an extent proportional to the amount of dopant added (0.52–6.0 mol% Li2O). The solid–solid interaction leading to the formation of CoFe2O4 took place at temperatures ≥700°C in the presence of the Li2O dopant. Lithia doping modified the surface characteristics of the Co3O4–Fe2O3 solids, both increasing and decreasing their BET surface areas depending on the amount of dopant added and the precalcination temperature employed for the treated solids. The activation energy of sintering (ΔES) of cobalt/ferric mixed oxides was determined for the pure and doped solids from the variation in their specific surface areas as a function of the precalcination temperature. Both an increase and a decrease in the value of ΔES due to Li2O doping occurred depending on the amount of lithia added. The doping of Co3O4–FeO solids, followed by precalcination at 500°C, effected a significant increase (144%) in their catalytic activity towards CO oxidation by O2. Precalcination at 700–1000°C of the mixed oxide solids doped with Li2O (0.52 and 0.75 mol%) resulted in an increase in their catalytic activity which decreased upon increasing the amount of Li2O added above this limit. The activation energy of the catalyzed reaction was determined for the pure and variously doped solids studied.