## 3 Results and Discussion
### Breakthrough Experiments under Dry Conditions  
The following variables were taken as key performance indicators for the dynamic adsorption experiments: (i) the total (i.e., at saturation) specific CO2 uptake (\(q_{CO2}\); in mmol g-1), (ii) the percentage of total CO2 uptake at breakthrough time (which represents the percentage of used bed and provides a measure of the efficiency of the adsorbent in terms of mass transfer), (iii) the regeneration efficiency (which is defined as the ratio between the total CO2 uptake after the _nth_ cycle and that obtained for the fresh adsorbent), and (iv) the selectivity towards CO2 over N2. Detailed information on how indicators were calculated is given in the Supplementary Materials. Table 5 summarizes the results obtained from the dynamic adsorption experiments under dry conditions at 25 \({}^{\circ}\)C. The corresponding CO2 breakthrough curves are displayed in Figure S1 (Supplementary Materials). From the results listed in Table 5, it should be highlighted that the best \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Activated** **Biochars**} & \multicolumn{2}{c}{**CO2 Uptake at 14 kPa**} & \multicolumn{2}{c}{**CO2 Uptake at 101.3 kPa**} & \multicolumn{2}{c}{**Apparent Selectivity**} \\ \cline{2-7}  & **(mmol g-1)** & & **(mmol g-1)** & & **CO2/N2** \({}^{\circ}\) \\ \cline{2-7}  & **25 \({}^{\circ}\)C** & **50 \({}^{\circ}\)C** & **25 \({}^{\circ}\)C** & **50 \({}^{\circ}\)C** & **25 \({}^{\circ}\)C** & **50 \({}^{\circ}\)C** \\ \hline _AC\_VS\_600_ & 1.02 & 0.598 & 2.35 & 1.65 & 28.2 & 25.7 \\ _AC\_VS\_600\_P_ & 1.16 & 0.695 & 2.67 & 1.90 & 50.0 & 46.5 \\ _AC\_WS\_500_ & 1.30 & 0.738 & 2.63 & 1.91 & 43.4 & 28.9 \\ _AC\_WS\_500\_P_ & 1.00 & 0.627 & 2.44 & 1.78 & 45.6 & 28.6 \\ \hline \hline \end{tabular} \({}^{\circ}\)Calculated from Equation (1).  
\end{table} 
Table 4: CO2 adsorption capacities and apparent selectivities (deduced from single-component adsorption isotherms) for the activated biochars at 25 and 50 \({}^{\circ}\)C.  
performance was obtained for the AC_VS_600 adsorbent, which exhibited a CO\({}_{2}\) uptake in the first cycle of 0.99 mmol g\({}^{-1}\) (almost the same than that reported in Table 4 for static measurements at 25 \({}^{\circ}\)C and 14 kPa). This interesting finding could be explained by the relatively high volume of mesopores (0.027 cm\({}^{3}\) g\({}^{-1}\), as reported in Table 3), which can facilitate the diffusion of CO\({}_{2}\) molecules into ultra-micropores. Moreover, the AC_WS_500 adsorbent, for which we found the highest CO\({}_{2}\) uptake at equilibrium (1.3 mmol g\({}^{-1}\) at 14 kPa), appears to be the worst material under dynamic conditions (just 0.90 mmol g\({}^{-1}\) in cycle 1). This fact can also be related to the low volume of mesopores (0.011 cm\({}^{3}\) g\({}^{-1}\)) measured for this material. Therefore, the results reported here seem to confirm the key role of mesopores to enhance adsorption kinetics. Results shown in Table 5 (as well as breakthrough curves displayed in Figure S1) also indicate that the stability over the five adsorption/desorption cycles was dependent on the material tested. In this sense, the AC_VS_600 sample was the most stable with nearly constant percentages of used bed (76.2%-77.3%) and decent regeneration efficiencies (84.1%-89.8%). However, this fact could partly be attributed to the relatively low absolute pressure applied during regeneration for this adsorbent (21.5 kPa). In other words, the relatively poor results obtained in terms of regeneration efficiency for the rest of materials could be explained by an insufficient vacuum level during the regeneration step (absolute pressures of 31.3-31.5 kPa). Regarding the experimental CO\({}_{2}\)-over-N\({}_{2}\) selectivity at 25 \({}^{\circ}\)C, all the samples showed a very good behavior with values in the range of 44.5 to 58.6.