Functionalization effect of multi-walled carbon nanotubes (MWCNTs) used as supports for Cu-based catalysts

Carbon nanotubes have been extensively used as catalytic supports of metals due to their high specific surface area, porous structure, excellent electronic properties and both thermal and chemical stability. Furthermore, their surface chemistry can be easily modified by means of different functionalization strategies, such as thermal and oxidative treatments, affecting the size, dispersion and catalytic properties of metal phase.
Moreover, defective sites, functional groups and metal-support boundaries present at the surface could also serve as active centers for reactants to start the catalytic cycle. Thus, the present work proposes to study the effect of functionalization on the properties of multi-walled carbon nanotubes (MWCNTs) used as supports and their interaction with copper particles in final catalysts.
Commercial MWCNTs were submitted to two treatments: oxidation in liquid phase by concentrated nitric acid and oxidation in gas phase by air flow. Cu-based catalysts were prepared through the ultrasound-assisted impregnation of each support with a given amount of copper precursor, in order to obtain a metal composition of 1 wt%, followed by drying and calcination under an inert atmosphere. Commercial MWCNTs without treatment were used as reference. The crystalline structure of the samples was characterized using X-ray
diffraction (XRD), while textural properties were analyzed using N2 physisorption (BET).
Infrared spectroscopy (FT-IR) and thermogravimetric analyses (TGA) were also used to identify the functional groups bonded to the surface. Distinctive physicochemical properties achieved in the MWCNTs supports could be related to the nature of the functionalization treatment used, with their consequent effects on the features of Cu catalysts.