Flame-made Catalysts

Traditionally, catalysts are prepared by wet-phase chemistry. Here, we have developed new processes for the synthesis of highly pure catalysts [1]. Resulting functional nanoparticles are used for environmental catalysis (pollution control, VOx/TiO2 for DeNOx), in automotive exhaust treatment (ceria/zirconia for three way catalysts) [2], fine chemical synthesis (TiO2/SiO2 for epoxidation for polymer manufacture) [3], in quantum dots and enantioselective hydrogenation for pharmaceuticals [4,5]. Continuous pilot-scale production makes these novel materials now accessible to industrial scale testing. Much enhanced activity (DeNOx, hydrogenation) and improved selectivity (epoxidation) unravel the advantageous role of dry, high temperature synthesis in the production of well-defined functional nanoparticles.

This dry technology has resulted in an application-oriented research with 2.5 times faster hydrogenation catalysts at comparable selectivity [4,6], 2 times higher DeNOx activity for vanadia/titania and improved product yield in epoxidation [1-3]. In-situ X-ray absorption near edge spectroscopy (XANES), UV- and IR-spectra revealed the preferred formation of the thermodynamically most favorable species within mixed oxides.

High thermal stability and good activity for the catalytic combustion of methane was observed for flame-made Pd/La2O3/Al2O3 and Pd-Pt/Al2O3 catalysts. The addition of La stabilizes Al2O3 against sintering whereas small amounts of Pt stabilize the Pd particles [7,8].

The use of two spray nozzles allows the synthesis of Pt/Ba/Al2O3 catalyst as used for NOx-storage-reduction in lean-fuel engines. The use of two nozzles results in the formation of individual Al2O3, BaCO3 and Pt particles, well mixed on the nanolevel, exhibiting good NOx storage behavior [9].

By correlating high temperature residence time and concentration of the metal oxide, production can be transferred from laboratory burners to pilot scale synthesis (500 g/h) [3].

 Recent, relevant references:

1. W. J. Stark, S. E. Pratsinis, Aerosol flame reactors for manufacture of nanoparticles, Powder Technol., 126, 103-108 (2002).
2. W. J. Stark, L. Mädler, M. Maciejewski, S. E. Pratsinis, A. Baiker, Flame-Synthesis of Nanocrystalline Ceria/Zirconia: Effect of Carrier Liquid, Chem. Comm., 588-589 (2003).
3. W. J. Stark, H. K. Kammler, R. Strobel, A. Baiker, S. E. Pratsinis, Flame-made titania/silica epoxidation catalysts: Toward large-scale production, Ind. Eng. Chem. Res., 41, 4921-4927 (2002).
4. R. Strobel, W. J. Stark, L. Mädler, S. E. Pratsinis and A. Baiker, Flame-made platinum/alumina: structural properties and catalytic behaviour in enantioselective hydrogenation, J. Catal., 213 (2), 296-304, (2003).
5. Schulz, H., W. J. Stark, M. Maciejewski, S. E. Pratsinis, and A. Baiker, "Flame-made nanocrystalline ceria/zirconia doped with alumina or silica: structural properties and enhanced oxygen exchange capacity", J. Mater. Chem., 13, 2979-84 (2003).
6. R. Strobel, F. Krumeich, W.J. Stark, S.E. Pratsinis, A. Baiker, "Flame spray synthesis of Pd/Al2O3 catalysts and their behaviour in enantioselective hydrogenation", J. Catal., 222 (2), 307-314 (2004).
7. R. Strobel, J. D. Grunwaldt, A. Camenzind, S. E. Pratsinis, A. Baiker, "Flame-made alumina supported Pd–Pt nanoparticles: Structural properties and catalytic behavior in methane combustion", Catal. Lett., 104 (1-2) 9-16 (2005).
8. R. Strobel , S. E. Pratsinis, A. Baiker, "Flame-made Pd/La2O3/Al2O3 nanoparticles: thermal stability and catalytic behavior in methane combustion", J. Mater. Chem., 15 (5), 605-610 (2005).
9. R. Strobel , L. Mädler, M. Piacentini, M. Maciejewski, A. Baiker, S. E. Pratsinis, "Beneficial use of two-nozzle flame synthesis for the preparation of Pt/Ba/Al2O3", Chem. Mater., submitted (2005).
10. B. Schimmoeller, H. Schulz, S. E. Pratsinis, A. Bareiss, A. Reitzmann, B. Kraushaar-Czarnetzki, Ceramic foams directly-coated with flame-made V2O5/TiO2 for synthesis of phthalic anhydride, J. Catal., 243, 82-92 (2006).
11. B. Schimmoeller, H. Schulz, A. Ritter, A. Reitzmann, B. Kraushaar-Czarnetzki, A. Baiker and S.E. Pratsinis; "Structure of flame-made vanadia/titania and catalytic behavior in the partial oxidation of o-xylene", Journal of Catalysis, 256 74-83 (2008).