Electron energy loss spectroscopy of Pd and Pd–Au catalysts supported on multiwall carbon nanotubes

Abstract

The X-ray PhotoElectron Energy Loss Spectroscopy (XP-EELS) and Reflection Electron Energy Loss Spectroscopy (REELS) were used for analysing surface layers of “as-received” and functionalised multiwall carbon nanotubes (MWCNT), and MWCNT decorated with Pd and Pd–Au particles after calcination/reduction. The decorated MWCNT were previously applied as catalysts in a reaction of formic acid electrooxidation. These spectroscopies, used as complementary methods of structural surface analysis, provide information on the energy position, intensity and full width at half maximum of the quasi-elastic peak and inelastic π and π+σ energy loss peaks. Analysing the π+σ energy loss peak, the bulk and surface C sp2/sp3 components can be separated. Functionalisation of MWCNT, catalyst reduction and Ar+ ion sputtering increase the C sp3 content in comparison to the “as-received” MWCNT and calcined catalysts. The intensity ratios of surface and bulk C sp3 and sp2 components evaluated from the REELS π+σ energy loss peak indicate: (i) functionalisation leads to attachment of functional groups to the MWCNT surface, (ii) calcined catalysts show an amorphous carbon overlayer at the surface and (iii) reduction of calcined catalysts leads to increasing C sp3 hybridisations.