## 3 Results and Discussion
### FGD Through Zeolite 13X
#### 3.3.3 13X Characterization  
The XRPD patterns of pristine 13X, 13X [75 \({}^{\circ}\)C\(\_\)45 RH%], and 13X [75 \({}^{\circ}\)C\(\_\)30 RH%], presented in Figure S14, evidence the high crystallinity of these samples, which exhibit characteristic peaks of zeolite with an FAU topology and a minimal contribution of LTA-type zeolite. At low 2\(\Theta\) angles, both the position and intensity of the X-ray diffraction peaks exhibited differences between the unloaded and loaded 13X samples, suggesting that the zeolite structure is affected by exposure to SO\({}_{2}\). According to the literature, the zeolite \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Weight** & \(\mathbf{\lambda}\) & \(\mathbf{t}_{\mathfrak{b}}\) & \(\mathbf{\mu}_{max}\) & **Breakthrough Sulfur Capacity** \\ \hline
13X [75 \({}^{\circ}\)C\(\_\)30 RH%] & 0.14 g & 27 min & 30 min & 0.0076 & 51 mg/g \\
13X [75 \({}^{\circ}\)C\(\_\)45 RH%] & 0.14 g & 42 min & 45 min & 0.015 & 41 mg/g \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Breakthrough sulfur capacity (mg/g) of 13X in different conditions of RH%. Figure 5: Breakthrough curves for 13X adsorbents at 30 RH% and 45 RH% and C\({}_{0}\) = 600 ppm and 580 ppm SO\({}_{2}\), respectively; adsorbent quantity = 0.14 g uptake temperature = 75 \({}^{\circ}\)C.  
adsorptive desulfurization of SO\({}_{2}\) encompasses bothphysisorption and chemisorption processes [44]. In contrast to PC, 13X is characterized by the presence of primary porosities (referred to as supercages or \(\alpha\)-cages) accessible through a 12-ring window (12R) with a diameter \(\approx\)6 A interconnected by windows with a diameter of \(\approx\)7.4 A. The chemisorption of SO\({}_{2}\) in these large windows and supercages can occur by sulfur-sorbent \(\pi\)-complexation and sulfur-metal (S-M) direct coordinate bonding. On the other hand, the filling of the zeolite microporous adsorption space, as with slaked lime, can be considered a physisorption process. Moreover, the adsorbed molecule diffuses within a zeolite channel and becomes subjected to diverse energy fields, which are characterized by different potentials (i.e., polaritazion) [45]. This encompasses both monolayer and multilayer adsorption, as well as capillary condensation [13]. Our results indicate that the structure of the zeolite samples was affected by exposure to SO\({}_{2}\). After the FGD experiments, the decrease in the crystallite size (Table S12) in both 13X [75 \({}^{\circ}\)C_45 RH%] and 13X [75 \({}^{\circ}\)C_30 RH%] was concomitant with variations in the unit-cell volume (Table S13) as well as bond distances and angles in comparison to the pristine sample (Table S14). Tables S14 and S15 show the structural details and the atomic bond distances O1-O1 and O4-O4 limiting the 12-ring windows. All these features indicated the phenomenon known as \"adsorption-induced deformation\" due to the interactions between the adsorbate and the zeolite pore walls [46; 47]. The deformation pattern can be affected by several factors, such as limitations of the pore size and pore shape, the surface chemistry of the adsorbent, as well as interactions of the adsorbate molecules with the extra-framework cations and framework oxygens of the zeolite. The extra-framework content in zeolites is related to the zeolite framework type and the Si/Al ratio, and it affects the enthalpy of adsorption of gases in these materials [18]. According to [PERSON] et al. [46] and [PERSON] et al. [48], SO\({}_{2}\) and the 13X framework can interact by donor-acceptor interactions and hydrogen bonding. An alternative bridging mechanism proposes that both oxygens of the captured gas interact with distinct extra-framework cations of the zeolite. However, it is more accurate to refer to the entrance of the gas into the zeolite cavities rather than the surface contact when discussing the steady growth of parameters, such as the total unit-cell volume and the crystallographic free area (CFA) (Table S12 and Table S15, respectively).