An advanced MC-type oxidation process — the role of carbon dioxide Original Research Article

The MC-type O2 oxidation of xylenes to the corresponding dicarboxylic acids with Co/Mn/HBr in the liquid phase was remarkably improved in the co-presence of carbon dioxide in O2 feed stream. This striking phenomenon became even more prominent when the catalyst was modified with an alkali/transition metal additive. A synergistic interaction of CO2 and O2 molecules generated an active cyclic peroxocarbonate complex. This complex appears to play a key role in promoting hydrogen abstraction, which has been reported to be the rate-determining step for the kinetic oxidation pathway. In short, the introduction of CO2 into the O2 feed stream brought about an advanced oxidation process, which resulted in an increase in the yield and selectivity towards the acid product, a reduction of partially oxidized intermediates, and an enhancement of the product quality over the conventional MC-type O2 oxidation process.