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Laser-Laboratorium Göttingen e.V.

Laser-Laboratorium Göttingen e.V.

Vortrag am 17.09.15

Dr. Igor Rahinov

Head, Department of Natural and Life Sciences

The Open University of Israel

 
Gas-phase high-temperature/flame synthesis is an important tool for production of a plethora of metal/metal oxide materials, which play important role in heterogeneous catalysis. It is becoming increasingly clear that the 21st century with its growing demands to achieve 100% selectivity of the desired product molecule in multipath reactions (“green chemistry”) and to develop processes based on renewable energy, calls for intelligent design of smart catalytic materials resulting from a detailed understanding of the mechanism governing the formation of condensable matter from the gas phase.
Therefore, input gained from well-controlled experiments, is a necessary prerequisite for production of functional materials with tailored functionalities.
However, the high-temperature particle–laden environment imposes considerable challenges on in-situ diagnostics and methods addressing both solid and gas phase products and intermediates are required. In this work we have applied combination of molecular beam sampling and laser-based techniques to study iron oxide nanoparticle formation in flame (doped with Fe(CO)5) synthesis reactor.
These experiments deliver data able to make contact with outputs of detailed kinetic modeling. Recent studies indicate [1] that in contrast to the commonly accepted mechanism, postulating the decomposition of the precursor followed by oxidation of the nascent Fe atoms and late formation of iron oxide nanoparticles, the actual synthesis mechanism is more considerably more rich and complex.
Based on measurements and detailed computational fluid dynamics and kinetic simulations we conclude that the Fe(CO)5 precursor initially decomposes when leaving the burner surface, directly forming Fe atoms. For sufficiently high precursor concentrations homogeneous nucleation of iron atoms leads to formation of metallic iron nanoparticles and (in parallel) formation of FeO molecules. When passing the flame front, both start to decompose resulting in only gaseous species. Further downstream with decreasing temperature, a second nucleation process develops, leading to iron oxide nanoparticles via FeOOH and Fe(OH)2 –like species.
 
[1] M. Poliak, A. Fomin, V. Tsionsky, S. Cheskis, I. Wlokas and I. Rahinov Phys. Chem. Chem. Phys.,
17, 680-685 (2015) and S. Kluge, L. Deng, O. Feroughi, Schneider, M. Poliak, et. al. CrystEngComm,
(2015) (in press) DOI: 10.1039/C5CE00456J
 
„Gas-phase high-temperature synthesis of catalytic materials: unraveling the detailed mechanism“
 
Termin: 17. September 2015 um 09:00 Uhr
im Seminarraum des Laser-Laboratoriums in Göttingen
Hans-Adolf-Krebs-Weg 1, 37077 Göttingen

 





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