Bamboo-like MnO₂ ?Co₃ O₄ : High-performance catalysts for the oxidative removal of toluene

The manganese-cobalt mixed oxide nanorods were fabricated using a hydrothermal method with different metal precursors (KMnO4 and MnSO4H2O for MnOx and Co(NO3)(2)& sdot;6H(2)O and CoCl2 & sdot;6H(2)O for Co3O4). Bamboo-like MnO2 & sdot;Co3O4 (B-MnO2 & sdot;Co3O4 (S)) was derived from repeated hydrothermal treatments with Co3O4@MnO2 and MnSO4 & sdot;H2O, whereas Co3O4@MnO2 nanorods were derived from hydrothermal treatment with Co3O4 nanorods and KMnO4. The study shows that manganese oxide was tetragonal, while the cobalt oxide was found to be cubic in the crystalline arrangement. Mn surface ions were present in multiple oxidation states (e.g., Mn4+ and Mn3+) and surface oxygen deficiencies. The content of adsorbed oxygen species and reducibility at low temperature declined in the sequence of B-MnO2 & sdot;Co3O4 (S) > Co3O4@MnO2 > MnO2 > Co3O4, matching the changing trend in activity. Among all the samples, B-MnO2 & sdot;Co3O4 (S) showed the preeminent catalytic performance for the oxidation of toluene (T-10% = 187 degrees C, T-50% = 276 degrees C, and T-90% = 339 degrees C). In addition, the B-MnO2 & sdot;Co3O4 (S) sample also exhibited good H2O-, CO2-, and SO2-resistant performance. The good catalytic performance of B-MnO2 & sdot;Co3O4 (S) is due to the high concentration of adsorbed oxygen species and good reducibility at low temperature. Toluene oxidation over B-MnO2 & sdot;Co3O4 (S) proceeds through the adsorption of O-2 and toluene to form O*, OH*, and H2C(C6H5)* species, which then react to produce benzyl alcohol, benzoic acid, and benzaldehyde, ultimately converting to CO2 and H2O. The findings suggest that B-MnO2 & sdot;Co3O4 (S) has promising potential for use as an effective catalyst in practical applications. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.