## 3 Results and Discussion
### Thermogravimetric Analysis  
Table 2 summarizes the kinetic results, which are discussed in the following paragraphs, and presents the required time for the investigated samples to reach a conversion rate of \(\alpha_{red}\) and \(\alpha_{ox}=0.8\) during reduction and oxidation. During the reduction, sample P9, with the highest water content (wc = 33 wt.-%), achieved the highest kinetic performance, as the conversion rate of \(\alpha_{red}=0.8\) was reached after 14 min, while samples P4 (wc = 25 wt.-%) and P7 (wc = 27 wt.-%) needed almost two more minutes to reach the same conversion rate. The samples with the lowest water \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **wc** & **Red2** & **Ox2** & **red5** & **ox5** & **red6** & **ox6** & **red9** & **ox9** \\  & **/wt.-\%** & **/min** & & **/min** & & **/min** & & **/min** \\ \hline P1 & 18 (wc\({}_{1}\)) & 18 & 10 & 21 & 15 & 26 & 19 & & \\ P2 & 20 (wc\({}_{1}\)) & 17 & 9 & 20 & 14 & 24 & 18 & & \\ P3 & 21 & 18 & 10 & 19 & 12 & 20 & 13 & 27 & 17 \\ P4 & 25 & 16 & 9 & 18 & 12 & 19 & 21 & & \\ P5 & 26 (wc\({}_{2}\)) & 15 & 8 & 16 & 10 & & & 22 & 14 \\ P6 & 27 (wc\({}_{2}\)) & 16 & 9 & 16 & 10 & & & 23 & 16 \\ P7 & 27 (wc\({}_{2}\)) & 16 & 9 & 17 & 10 & & & 24 & 15 \\ P8 & 33 (wc\({}_{3}\)) & 15 & 8 & 17 & 10 & & & 20 & 14 \\ P9 & 33 (wc\({}_{3}\)) & 14 & 8 & 16 & 10 & & & 18 & 14 \\ P10 & 33 (wc\({}_{3}\)) & 15 & 8 & 16 & 10 & & & 22 & 12 \\ \hline  & \multicolumn{2}{c}{wc\({}_{1}\)} & 18 & 10 & 21 & 14 & 25 & 18 & & \\  & \multicolumn{2}{c}{wc\({}_{2}\)} & 16 & 8 & 16 & 10 & & & 23 & 15 \\  & \multicolumn{2}{c}{wc\({}_{3}\)} & 15 & 8 & 16 & 10 & & & 20 & 13 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Time needed for each investigated sample (P1-P10) to reach a conversion rate of \(\alpha_{red}\) and \(\alpha_{ox}=0.8\) in the second (red2, ox2), fifth (red5, ox5), sixth (red6, ox6) and ninth (red9, ox9) cycles, respectively. For comparison, the average reaction times of the three sample groups with a similar water content (wc\({}_{1}\leq 20\) wt.-%, wc\({}_{2}=26\)–27 wt.-%, wc\({}_{3}=33\) wt.-%) are included. Figure 3: (**a**) Reduction at 800 \({}^{\circ}\)C during the 2 nd cycle. (**b**) Oxidation at 800 \({}^{\circ}\)C during the 2 nd cycle. Measured conversion rate of samples with a different water content over time. Sample P9 with the highest water content (wc = 33 wt.-%) shows the highest kinetic performance, followed by samples P4 and P7 with wc = 25 wt.-% and wc = 27 wt.-%, respectively. The samples P1 and P3 with the lowest water contents (P1: wc = 18 wt.-%, P3: wc = 21 wt.-%) reached the marked conversion rate of \(\alpha=0.8\) (horizontal dashed line) last. contents, P1 (wc = 18 wt.-%) and P3 (wc = 21 wt.-%), required as much as 18 min to achieve a conversion level of 80%. A similar trend was observed during the oxidation. It can be first concluded that the oxidation reactions are notably faster compared to the reduction reactions. Indeed, sample P9 reached the 80% level after about 8 min, while samples P4 and P7 achieved the same conversion rate about 1 min later. Finally, the samples with the lowest water content (P1, P3) needed two minutes more to make it to \(\alpha\) = 0.8. The results of the second redox cycle indicate that a higher water content during the pelletizing process leads to faster reaction kinetics. To determine the influence of the water content on the cycle stability, the conversion rate over several cycles was investigated. In the following discussions, the investigated samples were split into three categories depending on their water content, namely wc\({}_{1}\) \(\leq\) 20 wt.-% (Figure 4a,b), wc\({}_{2}\) = 26-27 wt.-% (Figure 4c,d), and wc\({}_{3}\) = 33 wt.-% (Figure 4e,f). Figure 4a,b illustrates the time-dependent conversion rates of samples P1 and P2, which had the lowest water content of equal to or less than 20 wt.-% (wc\({}_{1}\)). It is clear that the reduction reaction kinetics strongly decreases with the number of cycles (cf.