## 2 Materials and Methods
### Desulfurization Experiments
#### 2.3.3 Analysis of Reaction Products  
The concentration of SO2 in the gas phase exiting the bed reactor was monitored at \(\approx\)4 min intervals using a Micro GC Agilent 490 with a thermal conductivity detector (TCD). The uGC was equipped with a Porous Layer Open Tubular (PoraPLOT U) column. According to the product details, this column is suitable for switching systems that analyze polar (e.g., SO2) and apolar volatile compounds. Moreover, water elutes as a sharp and quantifiable peak, making the retention times of target compounds repeatable, as they are not influenced by water in the sample. This last feature is crucial for the proposed FGD system since it enables the monitoring of SO\({}_{2}\) concentrations independently of stream humidity adjustment. The uGC measurement parameters are listed in Table S3. The carrier gas, column configuration (temperature and pressure), injector temperature and time, and sample time were chosen according to the 490 Micro Gas Chromatograph User Manual for the PoraPlot 10 m instrument. The backflush-time and run-time values were established following preliminary tests to provide a suitable chromatogram for evaluating SO\({}_{2}\) peak areas. Indeed, the representative chromatogram in Figure S5 shows very good peak separation between SO\({}_{2}\) and other gaseous components (H\({}_{2}\)O and O\({}_{2}\)). Figure S6 displays the linear calibration of SO\({}_{2}\) up to 1200 ppm with an R\({}^{2}\) of 0.99935. The data trends of the SO\({}_{2}\) concentration versus time were transmitted to an online computer and stored in a data file. The actual SO\({}_{2}\) content in the stream flowing inside the reactor may be contingent upon the configuration of the reactor and the relative humidity content. Consequently, the concentration of SO\({}_{2}\) (in ppm) was evaluated over time for the two relative humidity conditions used in this study (30 and 45 RH%). The same configuration used for FDG measurements was maintained, i.e., a reactor loaded with two microfiber glass filters and a Teflon ring, devoid of adsorbent material. Figure S7 shows that, at equilibrium, the concentrations of SO\({}_{2}\) in the streams with 30 RH% and 45 RH% were 600 ppm and 580 ppm, respectively. Moreover, the experiments demonstrated a dead time of \(\approx\)5 min, during which minimal concentrations of SO\({}_{2}\) were detected from the uGC. To assess the effect of humidity on the SO\({}_{2}\) concentration and its reactor filling rate, Figure S7 also depicts the SO\({}_{2}\) concentration vs. time for dry conditions (4 RH%). This evidence demonstrates the absence of a dead time and the faster attainment of the equilibrium SO\({}_{2}\) concentration, namely, 610 ppm. The interaction of SO\({}_{2}\) with water vapor along the tubes or at the interface with the reactor walls and the sample holder may result in a slight delay in the attainment of equilibrium during FDG measurements. These experimental findings were integrated into the FDG data analysis, which included the determination of breakthrough curves, breakthrough times, and breakthrough sulfur capacities. In each experiment, the breakthrough curve was measured until the dimensionless concentration (C/C\({}_{0}\)) reached 0.90, where C\({}_{0}\) was the SO\({}_{2}\) air intake concentration obtained from Figure S7 and C was the outlet SO\({}_{2}\) concentration. Once this value is reached, the material removal efficiency becomes insufficient for effective utilization within the FGD process. Figure S8 shows a schematic diagram of a breakthrough curve, which illustrates the parameters considered in this work for the comparison of different experimental conditions. The breakthrough times (t\({}_{\text{b}}\)) were determined with the objective of investigating the impact of temperature and relative humidity on the loss rate of adsorbent efficiency in the removal of the adsorbate. A longer breakthrough time indicates a reduced frequency of regeneration of the adsorbent, which is economically more viable [21].