ENVR 137 |
| High surface area niobia is a desirable absorbent, carrier and catalyst. We have prepared porous Nb2O5 by precipitation and combustion syntheses. BET surface areas above 200 m2/g could be achieved by both methods. For precipitation, aqueous ammonium Nb oxalate solutions were precipitated with various bases in Symyx' fully automated parallel 6x8 co-precipitation station followed by robotic parallel washing, drying and calcination. For wet combustion synthesis, we have been screening a variety of organic acids as dispersants and developed proprietary recipes for individual metals. By resorting to easily decomposable organic acids (as opposed to citric acid in the original Pechini combustion method), such as glyoxylic acid, glycolic acid and ketoglutaric acid, it was possible to obtain high surface area materials for many metals after careful optimization of the acid/metal ratio and calcination conditions, for instance Sn, In, Co, Ru, Fe, Mn and Y, as well as rare earth oxides and their mixtures. We have now applied and optimized combustion methods for the synthesis of high surface area niobia. Aqueous Nb glycolate and glyoxylate solutions were prepared and calcined in the temperature range 300-400°C. Glycolic acid was found to result in higher surface areas than glyoxylic acid (or traditional acids like oxalic and tartaric). Combustion synthesis is well suited for the preparation of mixed oxides from mixed metal solutions in aqueous organic acids.
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General Papers
6:00 PM-8:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Environmental Chemistry |