Integral structured Co-Mn composite oxides grown on interconnected Ni foam for catalytic toluene oxidation

Considering the three-dimensional ordered network of Ni foam-supported catalysts and the toxicity effects of volatile organic compounds (VOCs), the design of proper active materials for the highly efficient elimination of VOCs is of vital importance in the environmental field. In this study, a series of Co-Mn composite oxides with different Co/Mn molar ratios grown on interconnected Ni foam are prepared as monolithic catalysts for total toluene oxidation, in which Co_1.5Mn_1.5O₄ with a molar ratio of 1 : 1 achieves the highest catalytic activity with complete toluene oxidation at 270 °C. The Co-Mn monolithic catalysts are characterized by XRD, SEM, TEM, H₂-TPR and XPS. It is observed that a moderate ratio of Mn/Co plays significant effects on the textural properties and catalytic activities. From the XPS and H₂-TPR characterization results, the obtained Co_1.5Mn_1.5O₄ (Co/Mn = 1/1) favors the excellent low-temperature reducibility, high concentration of surface Mn³⁺ and Co³⁺ species, and rich surface oxygen vacancies, resulting in superior oxidation performance due to the formation of a solid solution between the Co and Mn species. It is deduced that the existence of the synergistic effect between Co and Mn species results in a redox reaction: Co³⁺-Mn³⁺ ↔ Co²⁺-Mn⁴⁺, and enhances the catalytic activity for total toluene oxidation.