Effects of Li2O doping on the surface and catalytic properties of Co3O4-Fe2O3 solids precalcined at different temperatures

The effects of Li2O treatment on the solid-solid interactions and the surfa ce and catalytic properties of the Co3O4-Fe2O3 system have been studied usi ng TG, DTA and XRD methods, nitrogen adsorption studies at -196 degrees C a nd the catalytic oxidation of CO by O-2 at 150-350 degrees C The results obtained showed that Li2O doping followed by precalcination at 500-1000 degrees C enhanced the formation of cobalt ferrite to an extent pr oportional to the amount of dopant added (0.52-6.0 mol% Li2O). The solid-so lid interaction leading to the formation of CoFe2O4 took place at temperatu res greater than or equal to 700 degrees C in the presence of the Li2O dopa nt. Lithia doping modified the surface characteristics of the Co3O4-Fe2O3 s olids, 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 (Delta E-S) of cobal t/ferric mixed oxides was determined for the pure and doped solids from the variation in their specific surface areas as a function of the precalcinat ion temperature. Both an increase and a decrease in the value of Delta E-S due to Li2O doping occurred depending on the amount of lithia added. The do ping of Co3O4-Fe2O3 solids, followed by precalcination at 500 degrees C, ef fected a significant increase (144%) in their catalytic activity towards CO oxidation by O-2. Precalcination at 700-1000 degrees C of the mixed oxide solids doped with Li2O (0.52 and 0.75 mol%) resulted in an increase in thei r catalytic activity which decreased upon increasing the amount of Li2O add ed above this limit. The activation energy of the catalyzed reaction was de termined for the pure and variously doped solids studied.