Effects of K2O–Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K2O and Li2O-doping (0.5, 0.75 and 1.5 mol%) of Fe2O3/Cr2O3 system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400–600 °C. The formula of the un-doped calcined solid was 0.85Fe2O3:0.15Cr2O3. The techniques employed were TGA, DTA, XRD, N2 adsorption at −196 °C and catalytic oxidation of CO oxidation by O2 at 200–300 °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 °C are amorphous in nature and turned to α-Fe2O3 upon heating at 500 and 600 °C. K2O and Li2O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe2O3 together with K2FeO4 and LiFe5O8 phases. However, the heavily Li2O-doped sample consisted only of LiFe5O8 phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K2O and Li2O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K2O and Li2O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K2O and Li2O 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.

Research highlights▶ The effects of K2O and Li2O-doping (0.5, 0.75 and 1.5 mol%) of Fe2O3/Cr2O3 system on its surface and catalytic properties were investigated. ▶ Pure and differently doped solids were calcined in air at 400–600 °C. The formula of the un-doped calcined solid was 0.85 Fe2O3: 0.15 Cr2O3. ▶ The techniques employed were TGA, DTA, XRD, N2 adsorption at −196 °C and catalysis of CO oxidation by O2 at 200–300 °C. ▶ 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.