TEM and EELS investigations on carbon nanotubes for catalytic applications

Abstract

TEM and EELS investigations on carbon nanotubes for catalytic applications Carbon nanotubes have gained enormous scientific and technological interest in recent years not only because a new structure of carbon has raised chemical, physical and electronic research but also because traditional carbon chemistry with its established conventions has got new impact, specially in the area of catalysis.<br />But there are many differences between the various carbon nanotubes known now and little basic knowledge on the details how and why nanotubes are effective catalysts.<br />The aim of this work is the comparison of carbon nanotubes by means of transmission electron microscopy (TEM) and the quantification of their electron energy loss spectra (EELS).<br />Four types of nanotubes, which have been tested at the Fritz-Haber-Institut for their catalytic activity, were investigated.<br />These tubes fill the whole range from single wall carbon nanotubes (SWCNT) with a diameter of 2-5 nm up to the multi wall carbon nanotubes (MWCNT) with a diameter of up to 200 nm. These carbon nanotubes were used for catalytic reactions, namely oxidative dehydrogenation (ODH). As the surface of the nanotubes is the active site for the reaction EELS should be a suitable tool for these investigations. Low-Loss EELS spectra give information on the bulk and surface plasmons and therefore about the electron density. A change in the plasmon peak position during the reaction could be expected, because of the fact that the surface of the tube interacts with the gas flow.<br /> High Resolution Transmission Electron Microscopy (HRTEM) micrographs complement EELS spectra from the same specimens to get additional information on the surface structure.