# Exploring CeO\({}_{2}\)-Doped Co/SBA-15 Catalysts for Acetic Acid Oxidative Steam Reforming
## 3 Results and Discussion
### Oxidative Steam Reforming of Acetic Acid
Consequently, Co/10 CeO\({}_{2}\)-SBA-15 and Co/20 CeO\({}_{2}\)-SBA-15 catalysts demonstrate potential as suitable catalysts for hydrogen production through AAOSR. Product distribution includes not only hydrogen but also several by-products detected in the output stream. In this context, the relations between (a) acetone, (b) methane, (c) carbon dioxide, and (d) carbon monoxide selectivities and the reaction temperature are graphically displayed in Figure 7. Acetone (Figure 7a) is an intermediate product that mainly was obtained at temperatures between 400 \({}^{\circ}\)C and 550 \({}^{\circ}\)C. Acetone would have been formed by adding acetyl (CH\({}_{3}\)CO\({}^{\circ}\)) and methyl (CH\({}_{3}\)*) groups that come from the acetic acid decomposition on the Co surface, according to [PERSON] et al. [54]. Acetone selectivity was significantly enhanced after the addition of CeO\({}_{2}\) to the Co/SBA-15 catalyst, reaching values between 65% and 70% at 400 \({}^{\circ}\)C with Co/10 CeO\({}_{2}\)-SBA-15, Co/20 CeO\({}_{2}\)-SBA-15, and Co/30 CeO\({}_{2}\)-SBA-15 catalysts. These results align with the findings reported by [PERSON] et al. [55] and [PERSON] et al. [56], who experimented with CeO\({}_{2}\)-supported catalysts in the steam reforming (Equation (1)) and ketonization of acetic acid (Equation (5)); they concluded that CeO\({}_{2}\) promotes the ketonization of acetic acid. The mechanism of acetic acid ketonization proposed by [PERSON] et al. [57] suggests that acetone formation takes place via the ketene intermediate, proceeding from acetic acid decomposition to the acyl group, which occurs on the CeO\({}_{2}\) support surface, predominating at low reaction temperatures (<250-350 \({}^{\circ}\)C). This would suggest that the acetic acid ketonization pathway has been thermodynamically unfavored, given that it is an exothermic reaction (\(\Delta\)H\({}_{\text{25}\,^{\circ}\text{C}}\) =16.7 KJ/mol). Moreover, by increasing the reaction temperature, the acetone selectivity decreases, dropping to near 0% above 550 \({}^{\circ}\)C alongside increasing CO\({}_{2}\) (Figure 7c) and CO (Figure 7d) selectivity, which could imply that acetone steam reforming is undergoing. Accordingly, above 550 \({}^{\circ}\)C, a slight enhancement in CO\({}_{2}\) selectivity alongside a CO selectivity decrease was observed on Ce-doped catalysts. Conversely, in the Co/SBA-15 catalyst, the CO selectivity increased alongside a slight CO\({}_{2}\) selectivity decrease. One of the possible reaction pathways for the Co/SBA-15 catalyst is the reverse water-gas shift (RWGS), which was thermodynamically favored as the temperature increased. By contrast, Ce-doped catalysts would be kinetically favoring the gas-water shift reaction (WGS) (Equation (3)), as stated above. Specifically, CeO\({}_{2}\) incorporation enhances the oxygen vacancy density on the catalyst surface [51]; thus, these vacancies promote the WGS reaction efficiently, oxidizing CO into CO\({}_{2}\). In addition, the improved cobalt dispersion leads to a greater number of active sites, evenly distributed, which further facilitates the CO oxidation. Finally, the methane selectivity (Figure 7b) remained at very low values (<5%) from 400 to 700 \({}^{\circ}\)C, suggesting that the thermal decomposition of acetic acid to methane (Equation (4)) is not a kinetically or thermodynamically relevant pathway. [PERSON] et al. [58] reported that one possible pathway to methane generation is the hydrogenation of CH\({}_{3}\)* species, proceeding from the breaking of C-C bonds, which could be kinetically disfavored when using cobalt-based catalysts as well as catalysts supported on metal oxides such as CeO\({}_{2}\). There has been speculation that this effect could be caused by the ease of cleavage of C-H bonds, thus limiting the formation of CH\({}_{3}\)* species, or also by the oxidation of CH\({}_{3}\)* species to CO\({}_{x}\) due to the oxygen mobility.