Alterations in the local structure of the Co/SiO2 dispersed carbon nanotubes induced by CO molecules during microwave irradiation

This study presents a detailed structural investigation of Co/SiO2 catalysts dispersed carbon nanotubes (CNTs) treated by microwave in Ar and CO ambient, using X-ray absorption spectroscopy and Raman scattering. For the local structure of the cobalt site in the Co/SiO2 catalysts dispersed CNTs treated by microwave in Ar, the coordination number (NCo–Co) of the first shell is 10.8 with a Co–Co bond length of 2.496 Å, corresponding to the Co–Co bonding in cubic cobalt metal. After the microware treatment in CO, partial amounts of the cobalt species in the Co/SiO2 catalysts are translated to Co2+. In terms of the local structure of carbon site, the π orbital in CNTs are more delocalized than those in graphite and the defects are significant in the case of treating by microwave in Ar. For the microwave treatment in CO, the C–C π* transition energy shifts to that of graphite and the C–C σ* increases, indicating that the defect density is reduced by the microwave treatment in CO ambient. This detailed knowledge of the local structural translation is useful to the modification of the structure of CNTs.