Light on: Impact of Reaction Conditions and Catalyst Synthesis in Co ₃ O ₄ -Catalyzed Aerobic Oxidation of Ethylene Glycol

The transition to a sustainable chemical industry necessitates processes that utilize renewable feedstocks and energy sources. The selective oxidation of biobased ethylene glycol (EG) to valuable chemicals like glycolic acid as a precursor for bioplastics and formic acid as a hydrogen carrier represents a promising pathway. However, conventional methods often rely on noble metals or unsustainable oxidants. This study explores the potential of non-noble Co3O4 catalysts, synthesized via coprecipitation (CP), hard templating (HT), and spray-flame synthesis (SF), for the thermal and photothermal oxidation of EG. We demonstrate that the synthesis method profoundly impacts catalytic performance and catalyst stability. The SF-derived catalyst exhibited superior initial activity, while the HT catalyst showed exceptional reusability without or only minor deactivation. In addition, it is highlighted that the introduction of light as an additional stimulus significantly enhanced EG conversion by direct utilization of photogenerated charge carriers. Moreover, using illumination, C–C bond cleavage leading to the formation of formic acid appears to be less dominant compared to rate enhancements obtained by higher reaction temperatures. Thus, higher selectivity for the formation of glycolic acid is maintained. Postcatalytic characterization of the catalyst revealed that catalyst deactivation is linked to structural changes and the catalyst’s inability to reoxidize Co2+ sites back to active Co3+. This work provides fundamental insight into the rational design of robust, non-noble metal oxide catalysts and demonstrates photothermal catalysis as a powerful strategy for advancing sustainable liquid-phase oxidation reactions.