Toluene oxidation over Co³⁺-rich spinel Co₃O₄: Evaluation of chemical and by-product species identified by in situ DRIFTS combined with PTR-TOF-MS

Series of Co³⁺-rich spinel Co₃O₄ catalysts were synthesized and evaluated by toluene catalytic oxidation. An outstanding activity was achieved over Co₃O₄-N utilizing Co(NO₃)₂·6H₂O as precursor (T₅₀ = 211 °C, T₉₀ = 217 °C at conditions: 1000 ppm(v), WHSV = 60 000 mL g^-1 h^-1). Results of comparative characterizations demonstrated that such excellent performance was mainly attributed to large surface area, high reducibility at low temperature, high abundance of Co³⁺ ions and structure defects, as well as highly active surface oxygen. The results of in situ DRIFTS revealed that in the air or N₂ atmosphere, the by-products were almost the same. The reaction pathway of toluene oxidation can be described as follow: transformation of toluene from benzyl alcohol, benzaldehyde, benzoate, benzene, phenol, benzoquinone, maleic acid and to final products, which were fully confirmed by PTR-TOF-MS. Besides, ring opened by-products, such as acetone, acetic acid, acetaldehyde, etc. were also detected. In this work, the combination of in situ DRIFTS and PTR-TOF-MS provided a promising approach for further understanding of the mechanism of VOCs elimination.