After that, over a period of six days, the temperature was progressively increased to 215 °C, 230 °C, and 245 °C. Increasing the temperature above 200 °C did not enhance the yield to MEK, even though the conversion of 2-butanol increased at 245 °C (up to 17%). The concentration of CO2 in the gas-phase products increased, suggesting that, in these conditions, a larger fraction of MEK was further oxidized to CO2 and H2O. Hence, it appears that raising the temperature above 200 °C reduced the selectivity to the desired reaction product by its depletion via consecutive oxidation. Moreover, below 245 °C, the conversion does not significantly increase upon heating. The expected increase in activity at higher temperatures seemed to be counterbalanced by a simultaneous deactivation of the catalyst, which might be due to a rearrangement in the oxide including crystal growth and pore clogging, or by deactivation by deposition of deactivating carbonaceous and/or organic matter. Indeed, when the temperature was lowered again down to 200 °C (days 15 and 16), a lower activity (6% conversion) was observed with respect to days 7 and 8, when the reactor had been operated at the same conditions. Finally, the temperature was further reduced to 185 °C and 160 °C. As expected, this led to a drop in the catalytic performance, both in terms of conversion (6% and 3%) and yield (3% and 1%). At 160 °C, almost no CO2 was detected in the gas phase. This suggests that, at lower temperatures, the catalyst is less active, but more selective towards MEK. The chosen optimal conditions are a trade-off between catalyst activity and selectivity; 13% conversion and 8% yield were obtained on day 7, at 200 °C with 40 bar oxygen pressure and 0.1 mL/min liquid flowrate: these were selected as optimal operating conditions, and were used in the continuous flow catalytic tests to explore the influence of the catalyst, as described in the following paragraph. A brief catalytic test was conducted using an aqueous solution of MEK as the feed of the oxidation with the flow reactor loaded with Co3O4. The purpose of this experiment was to examine the formation of compounds resulting from the successive oxidation of MEK. The analysis of reaction products was performed qualitatively, revealing only CO2 as a detected product. Despite most of the MEK still being present at the reactor outlet, the production of CO2 appeared significantly higher compared to when the liquid feed was a 2-butanol solution. After selecting the optimal operating regime, we investigated the activity of Co3O4 and of other Cocontaining spinel oxides (CoFe2O4, ZnCo2O4, NiCo2O4, and MnCo2O4) in static conditions (Table -3).