Effects of LiO Doping on the Surface and Catalytic Properties of CoO–FeO Solids Precalcined at Different Temperatures

The effects of Li 2 O treatment on the solid–solid interactions and the surface and catalytic properties of the Co 3 O 4 –Fe 2 O 3 system have been studied using TG, DTA and XRD methods, nitrogen adsorption studies at −196°C and the catalytic oxidation of CO by O 2 at 150–350°C. The results obtained showed that Li 2 O 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% Li 2 O). The solid–solid interaction leading to the formation of CoFe 2 O 4 took place at temperatures ≥700°C in the presence of the Li 2 O dopant. Lithia doping modified the surface characteristics of the Co 3 O 4 –Fe 2 O 3 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 (ΔE S ) 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 ΔE S due to Li 2 O doping occurred depending on the amount of lithia added. The doping of Co 3 O 4 –FeO solids, followed by precalcination at 500°C, effected a significant increase (144%) in their catalytic activity towards CO oxidation by O 2 . Precalcination at 700–1000°C of the mixed oxide solids doped with Li 2 O (0.52 and 0.75 mol%) resulted in an increase in their catalytic activity which decreased upon increasing the amount of Li 2 O added above this limit. The activation energy of the catalyzed reaction was determined for the pure and variously doped solids studied.