# The Effect of Carbon Nanofibers Surface Properties in Hydrogenation and Dehydrogen Reactions
## 3 Results
### Catalysts Characterisation
The assignment of the O 1 s components is not always elementary, and particular attention must be given. The peak at 530-531.5 eV is generally assigned to C=O species, while the one at 534.5-535 eV is relative to carboxylic groups. C-O-H and C-O-C bonds are the most critical species, and opposed opinions have been found in the literature regarding their assignment. However, since hydrogen is slightly less electronegative than carbon, carbon-oxygen bonds in the ether-like group should appear at slightly higher energy than carbon-oxygen bonds in hydroxyl groups, 533.0-533.2 eV and 531.5-531.8 eV respectively. It is interesting to notice that, as expected, the content of C-O single bonds decreases with an increase of the CNFs annealing temperature. Finally, the peak at 536.7-537.1 is generally assigned to adsorbed water. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Catalyst** & \begin{tabular}{c} **Pd Content** \\ **(at. \%)** \\ \end{tabular} & \begin{tabular}{c} **Relative Pd\({}^{0}\)** \\ **Content (\%)** \\ \end{tabular} & \
\begin{tabular}{c} **O Content** \\ **(at. \%)** \\ \end{tabular} &
\begin{tabular}{c} **Cl Content** \\ **(at. \%)** \\ \end{tabular} \\ \hline Pd/CNFs-PS-OX & 0.75 & 15.6 & 12.05 & 0.04 \\ Pd/CNFs-PS & 0.40 & 58.4 & 2.94 & 0.06 \\ Pd/CNFs-LHT & 0.57 & 59.1 & 2.60 & 0.04 \\ Pd/CNFs-HHT & 0.71 & 25.9 & 0.94 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Palladium, oxygen and chlorine atomic contents and relative abundance of Pd\({}^{0}\) of the four catalysts used. Figure 1: Pd 3d XPS analysis of (**a**) Pd/CNFs-PS-OX, (**b**) Pd/CNFs-PS, (**c**) Pd/CNFs-LHT and (**d**) Pd/CNFs-HHT. Lastly, the presence of chlorine impurities coming from the Pd precursor was detected by monitoring the Cl 2p3/2 emission in the binding energy region of 198-199 eV. Cl relative atomic content is reported in Table 2. Very low amount of inorganic chlorine was detected (<0.06%) either as chloride anions or chlorine covalently bonded to carbon atoms. Raman spectroscopy analysis was performed on the bare supports in a wavenumber range of 900-1900 cm\({}^{-1}\). This analysis allows for evaluating the structural disorder of the graphitic domains by monitoring the intensity of the peaks at 1348 and 1572 cm\({}^{-1}\) (Figure 3) and their relative ratio (Table 1). The two peaks are attributed to the D and G bands for sp\({}^{2}\) clusters respectively, and they are caused by a disorder in the sp\({}^{2}\)-hybridised carbon (D band) and by the stretching of the C-C bonds in the sp\({}^{2}\) graphitic domains (G band). The ratio I\({}_{\textrm{D}}\)/I\({}_{\textrm{G}}\) is then an index of the structural disorder and thus related to the size of graphitic domains. For the bare supports, as expected, the increase of the annealing temperature causes a decrease of the I\({}_{\textrm{D}}\)/I\({}_{\textrm{G}}\) ratio, with the CNFs-HHT being the most graphitic sample and the CNFs-PS the least graphitic one. This confirms XPS analysis, showing that a higher degree of graphitisation is reached at high pre-treatment temperatures. Nanoparticles dimension and size distribution of the four catalysts were measured from bright field transmission electron microscopy (TEM) micrographs (Table 3 and Figure 4). The particle size distribution ranges from 2.5 to 10 nm, with mean values around 5-7 nm in all the cases. It is worth  
Figure 3: Raman analysis of the CNFs-PS, CNFs-LHT and CNFs-HHT supports. Figure 2: O 1 s XPS analysis of (**a**) Pd/CNFs-PS-OX, (**b**) Pd/CNFs-PS, (**c**) Pd/CNFs-LHT and (**d**) Pd/CNFs-HHT. notice that nanoparticles tend to be slightly smaller when supported on CNFs with a high degree of graphitisation. The total metal loading was finally measured by SEM-EDX. In all the cases, the Pd loading was very close to the theoretical value of 1 wt% (Table 4). Unlike XPS, EDX is, in fact, a bulk sensitive analysis and thus more accurate in the calculation of the total metal loading.