Effects of Ferric and Chromic Salts in Physicochemical, Surface and Catalytic Properties of Pure and Doped Fe2O3-Cr2O3 System | ||||
| Egyptian Journal of Chemistry | ||||
| Article 3, Volume 53, Issue 1, February 2010, Page 37-59 PDF (605.78 K) | ||||
| DOI: 10.21608/ejchem.2010.1203 | ||||
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| Abstract | ||||
| FERRIC/CHROMIC mixed oxides having the formula 0.85 Fe 2O3: 0.15 0.15CCr2O3 were obtained by thermal decomposition of the mixed hydroxides prepared from mixed nitrate and sulphate solutions using NH4OH. Pure mixed hydroxides were heated at 500°C .The doped solids were prepared by treating the precipitated hydroxides with different amounts of Li2O and K2O (0.5, 0.75 and 1.5 mol %) followed by calcination at 500°C. The techniques employed were XRD, N2-adsorption and oxidation of CO by O2 at 200-300°C. The results revealed that pure and doped systems consisted of nanocrystalline phases having crystallite size varying between 8-64 nm depending on the nature of ferric and chromic salts used and dopant concentration. Pure mixed solids consisted of a mixture of α and γ-Fe2O3 phase whose crystallite size decreases by increasing the dopant concentrations. K2O-doping of the investigated systems resulted in the formation of K2FeO4 together with ferric oxide phases. Li2O-doping (0.5 and 0.75 mol %) led to the formation of LiFe5O8 together with γ-Fe2O3 phase. However, the heavily Li2O-doped samples consisted entirely of LiFe5O8. The SBET of pure system prepared from ferric and chromic sulphates measured higher SBET values as compared to those prepared from mixed nitrates, whereas K2O-doping decreased the SBET. On the other hand, Li2O-doping exerted a measurable increase in the SBET. 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 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 k200°C value due to doping with 1.5 mol % K2O attained 30.8% 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. | ||||
| Keywords | ||||
| nanocrystalline; Fe2O3-Cr2O3; Doping and Catalytic behavior | ||||
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