ANALYSIS OF NANOMETER-SIZED PYROGENIC PARTICLES IN THE SCANNING-TRANSMISSION ELECTRON-MICROSCOPE

The chemical reactions that take place at surfaces as well as internal ly in nanoscale particles are of great scientific interest, Such react ions control the catalytic properties of small metal particles and thu s are technologically very important, In order to allow enhancement of the performance of such catalytic systems, an understanding of the pr ocesses taking place at the atomic scale is necessary; Z-contrast imag ing and electron energy-loss spectroscopy (EELS) in the dedicated scan ning transmission electron microscope can give atomic-scale informatio n and thus provide a unique opportunity to study such nanoscale system s. Here, iron particles from known positions in a ferrocene-seeded fla me and their effects on soot formation are studied. Using EELS, spatia l variations in oxidation state of the metal atoms are detected across individual nanometre-sized particles collected from the post-name reg ion, The surfaces of these particles are found to be less oxidized tha n their centres, Additionally, the particles are imaged with atomic re solution allowing their structure to be identified. Using these result s and those for particles collected from in-name regions, direct evide nce is provided for the catalytic role of Fe-containing particles in t he removal of carbonaceous soot produced during combustion of hydrocar bon-based fuels.