Analysis of nanometre-sized pyrogenic particles in the scanning transmission electron microscope

The chemical reactions that take place at surfaces as well as internally in nanoscale particles are of great scientific interest, Such reactions control the catalytic properties of small metal particles and thus are technologically very important, In order to allow enhancement of the performance of such catalytic systems, an understanding of the processes taking place at the atomic scale is necessary; Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the dedicated scanning transmission electron microscope can give atomic-scale information and thus provide a unique opportunity to study such nanoscale systems. Here, iron particles from known positions in a ferrocene-seeded flame and their effects on soot formation are studied. Using EELS, spatial variations in oxidation state of the metal atoms are detected across individual nanometre-sized particles collected from the post-name region, The surfaces of these particles are found to be less oxidized than their centres, Additionally, the particles are imaged with atomic resolution allowing their structure to be identified. Using these results and those for particles collected from in-name regions, direct evidence is provided for the catalytic role of Fe-containing particles in the removal of carbonaceous soot produced during combustion of hydrocarbon-based fuels.