INOR 302 |
| High surface area Mn and Fe oxides are desirable pigments, catalysts, carriers and electrode materials. Fe oxide is a major component in the high temperature water gas shift and ethylbenzene dehydrogenation catalysts. Mixed Fe-Mn oxides are components of Fischer-Tropsch catalysts. We have recently developed a modified Pechini or soft combustion method based on thermally easily decomposable organic acids as dispersants such as glyoxylic acid and ketoglutaric acid and demonstrated its applicability to the synthesis of high surface area Sn, In, Co, Ru, Ce, Y oxides and their mixtures. We have now applied and optimized the glyoxylic acid method for the preparation of porous Mn and Fe oxides. By dissolving Mn (II) acetate in aqueous glyoxylic acid and calcining in air in the temperature range 250-300C, BET surface areas >250 m2/g could be achieved. Similarly, solutions of Fe (II) acetate in aqueous glyoxylic acid with acid/metal ratios in the range 2 - 3 mol acid/mol metal and calcined in air at 320C resulted in surface areas >220 m2/g. High surface area Fe oxides can also be prepared by precipitation of Fe hydroxide followed by calcination but mixed Fe oxides with other metal oxides like Mn, Sn etc. can be easily prepared by the modified Pechini method from mixed metal solutions in aq. glyoxylic acid. The low decomposition temperature of the novel Pechini acids glyoxylic and ketoglutaric as compared to the traditional citric acid allows to burn off most of the carbon at a much lower calcination temperature of about 300C whereas citric acid would require about 500C leading to pronounced surface area loss by sintering. The residual carbon content of the order of a few % adds to the thermal stability and allows higher service temperatures than precipitated samples. |
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Synthesis and Characterization of Materials
7:00 PM-10:00 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Inorganic Chemistry |