## 3 Results and Discussion  
### Characterization of Fresh Catalysts  
A preliminary TG analysis of 20% MgO/AC dried sample under N\({}_{2}\) up to 600 \({}^{\circ}\)C coupled to IR analysis of released gases indicated that nitrates decomposition was completed below 400 \({}^{\circ}\)C. Above this temperature, only a slow transformation of Mg(OH)\({}_{2}\) into MgO took place. Therefore, all catalysts treated at 600 \({}^{\circ}\)C consist of MgO dispersed on activated carbon without any residual presence of nitrate precursor salt.  
Table 1 reports a list of catalysts together with their corresponding values of BET surface area and total pore volume. Upon dispersion of 10 wt% of MgO on the AC support, the original surface area was correspondingly reduced by ca. 10%. Further addition of MgO up to 20 wt% did not further modify both the surface area and pore volume; however, dispersion of 30% MgO induced a marked drop of about 37% of the original values of the parent carbon suggesting that some MgO aggregation takes place at high loadings, partially clogging pores, as also observed by [PERSON] et al. [20].  
The pore size distribution (PSD) for raw AC and MgO/AC catalysts at different loadings are reported in Figure 1.  
The parent activated carbon shows a tri-modal PSD with a large fraction of very small micropores (diameter \(<\) 7 A), a fraction of micropores peaked at about 11 A, and mesopores in the range 25-70 A. The addition of 10 wt.% MgO results in a limited reduction of the large micropores, whereas the  
\begin{table}
\begin{tabular}{c c c c} \hline
**Catalyst** & **BET Area (m\({}^{2}\)/g)** & **Pore Volume (cm\({}^{3}\)/g)** & **Average Crystallite Size (nm)** \\ \hline MgO powder & 26 & 0.067 & - \\ AC & 641 & 0.81 & - \\
10\%MgO/AC & 576 & 0.63 & 11.5 \\
20\%MgO/AC & 578 & 0.61 & 22.3 \\
30\%MgO/AC & 403 & 0.44 & 32.6 \\ \hline \end{tabular}
\end{table}
Table 1: BET (Brunauer, Emmett, Teller) surface area, total pore volume, and average crystallite size for MgO/AC supported catalysts.  
addition of higher amounts of MgO (20 and 30 wt%) reduces both the fraction of very small micropores and that of mesopores. Furthermore, only for 20% MgO/AC, the amount of micropores with diameters around 11 A increases. On the contrary, the massive formation of MgO aggregates occurring for 30% MgO loading leads to a significant occlusion of ultramicro- and meso-pores.  
The good dispersion of MgO onto active carbon was confirmed by SEM/EDX analysis performed on cross sections of the impregnated carbon granules: The EDS maps for Mg, reported in Figure 2 for the case 20% MgO/AC sample, clearly indicate that the impregnation procedure with magnesium nitrate solution guaranteed a uniform penetration of the precursor throughout the entire volume of the carbon particles having original characteristic dimensions in the range from 0.42 to 0.84 mm.  
XRD patterns of AC and 10, 20, and 30 wt% MgO/AC are shown in Figure 3. Weak signals due to the characteristic reflections of MgO periclase (JCPDS 45-946) were found in the pattern of all MgO/AC samples, already for 10 wt% loading, in addition to the broad signals of the parent carbon support, which also contains some quartz impurities [25]. In contrast, [PERSON] et al. [21] did not detect MgO signals up to 20% MgO, most likely due to the much larger surface area of their activated carbon support. MgO signals become more intense by increasing the MgO content, indicating the formation of larger periclase crystallites. The average crystallite size, evaluated according to the Scherrer equation applied to the main MgO peak (42.8\({}^{\circ}\)) and reported in Table 1, progressively increases along with the MgO loading up to 32.3 nm for 30% MgO/AC. The significant occlusion of small micropores (<7 A) detected for this sample confirms that most of the MgO is located outside of the micropore structure of the AC support.  
Figure 1: Pore size distribution (PSD) of activated carbon (AC) and of 10, 20, and 30 wt% MgO/AC.  
Figure 2: SEM image (left) and Mg EDX mapping (right) of 20% MgO/AC.