Effects of K sub(2)O-Li sub(2)O doping on surface and catalytic properties of Fe sub(2)O sub(3)/Cr sub(2)O sub(3) system

The effects of K sub(2)O and Li sub(2)O-doping (0.5, 0.75 and 1.5 mol%) of Fe sub(2)O sub(3)/Cr sub(2)O sub(3) system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 degree C. The formula of the un-doped calcined solid was 0.85Fe sub(2)O sub(3):0.15Cr sub(2)O sub(3). The techniques employed were TGA, DTA, XRD, N sub(2) adsorption at -196 degree C and catalytic oxidation of CO oxidation by O sub(2) at 200-300 degree C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 degree C are amorphous in nature and turned to alpha -Fe sub(2)O sub(3) upon heating at 500 and 600 degree C. K sub(2)O and Li sub(2)O doping conducted at 500 or 600 degree C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline alpha - and gamma -Fe sub(2)O sub(3) together with K sub(2)FeO sub(4) and LiFe sub(5)O sub(8) phases. However, the heavily Li sub(2)O-doped sample consisted only of LiFe sub(5)O sub(8) phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K sub(2)O and Li sub(2)O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K sub(2)O and Li sub(2)O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 degree C, attained 30.8% and 26.5% for K sub(2)O and Li sub(2)O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.