## 3 Results and Discussions  
### Characterization of the Plastic Pyrolysis Char after Activation  
The changes in the textural and porous properties were analyzed by N\({}_{2}\) adsorption-desorption isotherms; see results in Table 1. The char obtained from the pyrolysis of the mixture of plastics displayed a poor surface area, 15 m\({}^{2}\cdot\)g\({}^{-1}\). The stabilized char slightly raised the area to 19 m\({}^{2}\cdot\)g\({}^{-1}\), probably due to the removal of the ash content and leachable content. The activation of the SC led to a considerable increment in the surface area of the resulting materials. For example, the activation under a CO\({}_{2}\) atmosphere led to a material with 68 m\({}^{2}\cdot\)g\({}^{-1}\), poorly higher than the 49 m\({}^{2}\cdot\)g\({}^{-1}\) value obtained under an inert N\({}_{2}\) atmosphere. A further area increment was produced by chemical activation under alkali presence. Thus, in the presence of NaOH, the resulting material developed a specific area of 247 m\({}^{2}\cdot\)g\({}^{-1}\). Highly enhanced results were obtained if KOH was used, leading to an almost doubled surface area, i.e., 487 m\({}^{2}\cdot\)g\({}^{-1}\). The N\({}_{2}\) isotherms depicted in Figure 1 performed a Type I according to IUPAC classification, characteristic of microporous materials. Furthermore, the H3 type hysteresis loops described during the desorption step, within relative pressures p/p\({}_{0}\) = 0.45-0.99, which features parallel branches that finally go up almost vertically, provide evidence of the presence of grove mesopores of non-rigid generation by flaky particles as described for other materials in the literature [39; 40]. The microporosity percentage analysis of the samples followed a similar trend to the total BET surface area, in which the relative importance of microporosity assessed either in terms of surface or volume percentage followed the order SC-KOH > SC-NaOH > SC-CO\({}_{2}\) > SC-N\({}_{2}\). Microporosity is expected to be produced as a consequence of the reaction of the alkali, e.g., NaOH or KOH, with the carbon and oxygen in the char, which enhances the gasification reaction and release of CO and CO\({}_{2}\). Moreover, the corresponding alkali carbonates (Na\({}_{2}\)CO\({}_{3}\) or K\({}_{2}\)CO\({}_{3}\)) and oxides (Na\({}_{2}\)O or K\({}_{2}\)O) promote the reaction at dynamic sites in the carbonaceous material, leading to the generation of plenty of porous channels [41]. If the efficiency of the two alkalis is compared, KOH has been reported to be more efficient than NaOH in producing a larger amount of micropores [16; 42; 43], which explains the larger porosity obtained for SC-KOH. This boosted porosity has been linked to the thermodynamics of the reaction between the alkali and carbon. The temperature required to trigger the reaction is lower in the case of KOH [44]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Sample**} & **S\({}_{\text{BET}}\)** & **S\({}_{\text{MP}}\)** & **S\({}_{\text{MP}}\)/S\({}_{\text{BET}}\)** & **V\({}_{\text{T}}\)** & **V\({}_{\text{MP}}\)** & **V\({}_{\text{MP}}\)/V\({}_{\text{T}}\)** \\  & **(m\({}^{2}\cdot\)g\({}^{-1}\))** & **(m\({}^{2}\cdot\)g\({}^{-1}\))** & **(\%)** & **(cm\({}^{3}\cdot\)g\({}^{-1}\))** & **(cm\({}^{3}\cdot\)g\({}^{-1}\))** & **(\%)** \\ \hline C & 15 & 1 & 5.4 & 0.025 & - & - \\ \hline SC & 19 & 18 & 92.2 & 0.040 & 0.036 & 90.0 \\ \hline SC-N\({}_{2}\) & 45 & 6 & 12.6 & 0.082 & 0.003 & 3.0 \\ \hline SC-CO\({}_{2}\) & 68 & 18 & 26.9 & 0.094 & 0.008 & 9.2 \\ \hline SC-NaOH & 247 & 185 & 74.9 & 0.217 & 0.084 & 38.9 \\ \hline SC-KOH & 487 & 414 & 85.0 & 0.300 & 0.180 & 60.0 \\ \hline \end{tabular}  
* SBT: specific surface area; S\({}_{\text{MP}}\), specific surface area of micropore; S\({}_{\text{EXT}}\): specific external surface area; V\({}_{\text{T}}\): total pore volume; V\({}_{\text{MP}}\): volume of micropore.  
\end{table} 
Table 1: Textural properties of the char from plastic pyrolysis before and after activation. The morphology of the particles was assessed by SEM.