# Exploring CeO\({}_{2}\)-Doped Co/SBA-15 Catalysts for Acetic Acid Oxidative Steam Reforming
## 3 Results and Discussion
### Catalyst Characterization
In addition to Co\({}_{3}\)O\({}_{4}\) diffraction lines, Co/xCeO\({}_{2}\)-SBA-15 samples also show reflections at 20 = 28.5, 32.9, 47.5, 56.4, 66.5, and 79.1\({}^{\circ}\) according to the planes (111), (200), (220), (311), (400), and (420) of the cubic CeO\({}_{2}\) structure (JCPDS 01-089-8436), respectively. Comparing these XRD patterns, it is possible to observe that, as the CeO\({}_{2}\) content increases, Co\({}_{3}\)O\({}_{4}\) peaks become broader and less intense, suggesting more dispersed Co-species over the xCeO\({}_{2}\)-SBA-15-modified supports [46]. This effect was evidenced by the mean crystallite sizes on the Co\({}_{3}\)O\({}_{4}\) main diffraction line. Over \(x\)CeO\({}_{2}\)-SBA-15, smaller crystallite sizes were achieved (see Table 1) than over Co/SBA-15, thus indicating higher metal dispersion in the modified CeO\({}_{2}\) samples. Similarly, [PERSON] et al. developed a variety of Ni/SBA-15 catalysts for the hydrogenolysis of glycerol, while studying the impact of Ce incorporation, and concluded that high active phase dispersion was achieved as a consequence of the interactions between metallic oxide particles and the cerium oxide ones [47]. The reducibility was assessed for catalysts produced using H\({}_{2}\)-TPR analysis, the reducing profiles of which are depicted in Figure 3. In all cases, several reduction features can be distinguished. The Co/SBA-15 catalyst displayed three reduction stages at 344 \({}^{\circ}\)C, 393 \({}^{\circ}\)C, and 472 \({}^{\circ}\)C. The first two are associated with the reduction of Co\({}^{3+}\) to Co\({}^{2+}\) and afterwards to Co\({}^{0}\), while the third one, centered at 472 \({}^{\circ}\)C, is related to the existence of Co oxide species with a strong engagement with the SBA-15 support [34]. Cerium-modified catalysts showed a low-temperature reduction peak between 347 \({}^{\circ}\)C and 361 \({}^{\circ}\)C, which could be described as a simultaneous Co\({}^{3+}\) reduction to Co\({}^{2+}\) and Co\({}^{2+}\) reduction to Co\({}^{0}\)[48]. This reduction performance could be correlated with the redox properties of CeO\({}_{2}\), which has a well-known oxygen storage and mobilization capacity [26]; this characteristic allowed it to capture and release oxygen easily, generating vacancies in the structure. Incorporating CeO\({}_{2}\) into the SBA-15 support facilitates the surface migration and oxygen transfer from cobalt oxides, thus favoring the reduction processes. Furthermore, in these samples, the peak centered at 472 \({}^{\circ}\)C shifts toward slightly higher temperatures, suggesting a stronger metal-support interaction (MSI) between the cobalt oxide species and the support. It is associated with the smaller Co crystallite formation, increasing the interfacial contact area, leading to the surface chemical bonding [49]. This highlights the significant role of metal-support interaction in catalyst design since a suitable support will interact effectively with the metallic species, minimizing its surface migration and preventing sinterization. In contrast, scarce metal-support interaction would promote particle agglomeration, leading to a negative impact on the catalytic performance [50]. The Co/10 CeO\({}_{2}\)-SBA-15 catalyst exhibited the most strongly pronounced reduction feature associated with strong metal-support interactions, while this peak was almost absent in the Co/30 CeO\({}_{2}\)-SBA-15 catalyst. It could be attributed to the slight modification of the mesoporous structure. A further decrease in surface area could probably promote CeO\({}_{2}\) agglomeration, hindering the effective cobalt oxide species dispersion. Consequently, the metal-support interaction effect between the cobalt phase and the SBA-15 structure was reduced. Additionally, reduction features at higher temperatures (735-769 \({}^{\circ}\)C) arise in all Co/xCeO\({}_{2}\)-SBA-15 catalysts, ascribed to the partial reduction of CeO\({}_{2}\) to CeO\({}_{2-x}\)[25; 51].