ABSTRACT
FERRIC/CHROMIC mixed oxides having the formula 0.85 Fe[2]O[3]: 0.15 Cr[2]O[3] were obtained by thermal decomposition of the mixed hydroxides prepared from mixed nitrate and sulphate solutions using NH[4]OH. Pure mixed hydroxides were heated at 500[degree sign] C. The doped solids were prepared by treating the precipitated hydroxides with different amounts of Li[2] and K[2]O [0.5, 0.75 and 1.5 mol%] followed by calcinations at 500 [degree sign] C. The techniques employed were XRD, N[2]-adsorption and oxidation of CO by O[2] at 200-300 [degree sign] C. The results revealed that pure and doped systems consisted of nanocrystalline phases having crystallite size varying between S-64 nm depending on the nature of ferric and chromic slats used and dopant concentration. Pure mixed solids consisted of a mixture of alpha and gamma-Fe[2]O[3] phase whose crystallite size decreases by increasing the dopant concentrations. K[2]O-doping of the investigated systems resulted in the formation of K[2]FeO[4] together with ferric oxide phases. Li[2]O-doping [0.5 and 0.75 mol%] led to the formation of LiFe[5]O[8] together with gamma-Fe[2]O[3] phase. However, the heavily Li[2]O-doped samples consisted entirely of LiFe[5]O[8]. The S[BET] of pure system prepared from ferric and chromic sulphates measured higher S[BET] values as compared to those prepared from mixed nitrates, whereas K[2]O-doping decreased the S[BET]. On the other hand, Li[2]O-doping exerted a measurable increase in the S[BET]. The increase was however, more pronounced in case of the system prepared by using mixed sulphate solutions. The catalytic activity was higher in case of the catalysts prepared by using mixed nitrates as compared to the catalysts prepared by using mixed nitrates as compared to the catalysts prepared by using mixed sulphate solutions. The doping process led to a progressive significant increase in the catalytic activity. The increase was, however, much more pronounced in case of the catalysts prepared from the mixed sulphates. The maximum increase in the K[200[degree sign] C] value due to doping with 1.5 mol% K[2]O attained 20.8% and 285% for the solids prepared from mixed nitrates and mixed sulphates, respectively. These values measured 27% and 241% in case of the catalysts prepared by using mixed nitrate and mixed sulphate solutions, respectively. The doping process did not affect the mechanism of the catalyzed reaction but increased the concentrations of active sites involved in catalytic reaction without changing their energetic nature