# Exploring CeO\({}_{2}\)-Doped Co/SBA-15 Catalysts for Acetic Acid Oxidative Steam Reforming
## 3 Results and Discussion
### Catalyst Characterization
The reduction degree of Co species was assessed by quantifying the H\({}_{2}\) consumption throughout the TPR analysis by comparing the experimental and theoretical H\({}_{2}\) uptake (Table 2). The theoretical hydrogen uptake was calculated from the full reduction stoichiometry of the cobalt oxide loading (measured by ICP-OES). Meanwhile, the H\({}_{2}\) experimental uptake was obtained by the H\({}_{2}\)-TPR profiles' integration of the hydrogen uptake peaks, corresponding to the Co\({}_{3}\)O\({}_{4}\) reduction. All the catalysts exhibited a reduction degree above 95%, with slightly higher values observed for the Ce-doped samples, which is in agreement with the shift in the reduction profile toward lower temperatures for Co species. This slight increase in the reducibility can be attributed to the oxygen vacancy generation caused by the incorporation of ceria [26]. In this respect, the Co/10 CeO\({}_{2}\)-SBA-15 sample reached the highest reduction level, with its experimental uptake, in terms of \(\upmu\)mol H\({}_{2}\cdot\)gcat\({}^{-1}\), closely matching the theoretical value. After the catalysts' reduction step at 600 \({}^{\circ}\)C, samples were characterized by XRD analysis, and the resultant diffraction patterns are displayed in Figure 4. As can be discerned, no diffraction peaks corresponding to Co oxides can be distinguished, confirming that the reduction step proceeded successfully. In this sense, peaks arising at 20 = 44.1 and 76.4\({}^{\circ}\) are attributed to the cubic phase of Co\({}^{0}\) (JCPDS-15-0806). The Co\({}^{0}\) mean crystal sizes in the reduced catalysts were determined based on the principal Co\({}^{0}\) diffraction plane (111) using the Scherrer equation (Table 1). Notably, no diffraction features corresponding to Co\({}^{0}\) can be observed for Co/20 CeO\({}_{2}\)-SBA-15 and Co/30 CeO\({}_{2}\)-SBA-15 catalysts, which reached a mean crystallite size lower than the detectable limit of the technique. This suggests the metallic phase was widely dispersed on the SBA-15 support modified with 20-30 wt.% of ceria. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \begin{tabular}{c} **Theoretical Uptake** \\ **(\(\upmu\)mol H\({}_{2}\)/gcat)** \\ \end{tabular} & \
\begin{tabular}{c} **Experimental Uptake** \\ **(\(\upmu\)mol H\({}_{2}\)/gcat)** \\ \end{tabular} &
\begin{tabular}{c} **Degree of Co Reduction** \\ **(\%)** \\ \end{tabular} \\ \hline Co/SBA-15 & 1606 & 1530 & 95 \\ Co/5 CeO\({}_{2}\)-SBA-15 & 1674 & 1642 & 98 \\ Co/10 CeO\({}_{2}\)-SBA-15 & 1683 & 1679 & \textasci{}100 \\ Co/20 CeO\({}_{2}\)-SBA-15 & 1604 & 1554 & 97 \\ Co/30 CeO\({}_{2}\)-SBA-15 & 1572 & 1508 & 96 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental and theoretic H\({}_{2}\) consumption and Co reduction degree for Co/xCeO\({}_{2}\)-SBA-15 calcined catalysts. Figure 3: H\({}_{2}\)-TPR profiles of calcined catalysts. TEM micrographs for the reduced catalysts are presented in Figure 5, in which the well-ordered mesoporous structure typical for SBA-15 can be distinguished, indicating that the mesoporous structure is preserved. This observation aligns with the N\({}_{2}\) physisorption results obtained for the calcined samples. In all cases, dark zones can be distinguished on the SBA-15 channels corresponding to Co\({}^{0}\) and CeO\({}_{2}\) particles, as corroborated by EDX. Furthermore, in the micrograph of Co/SBA-15 (Figure 5A), particles on the external surface of the SBA-15 are clearly distinguishable, suggesting some Co\({}^{0}\) particle clustering, as reported before [52]. Moreover, not all of the SBA-15 surface or channels were filled with cobalt particles. On the other hand, in CeO\({}_{2}\)-doped catalysts (Figure 5B-E), smaller crystallites can be differentiated within SBA-15 channels, corroborating the higher active phase dispersion expected from the mean crystallite sizes shown in Table 1.  
From the TEM micrographs, particle size distribution histograms of the reduced catalysts were determined.