Self-molten-polymerization synthesis of highly defected Mn/Sm binary oxides with mesoporous structures for efficient removal of toluene and chlorobenzene

Abstract

A simple and effective self-molten-polymerization strategy utilizing the molten metal salts from heated solid metal salt sources as the solvents to dissolve a self-polymerizable monomer, which acted as a mingling agent, was successfully applied to homogeneously synthesize a series of highly defected manganese/samarium (Mn/Sm-x, where x represents the molar ratio of Mn to Sm) hybrid bimetallic oxides with a mesoporous structure. The values of T₅₀ and T₉₀ over Mn/Sm-2 were 206 °C and 247 °C, respectively, for toluene conversion, as well as 213 °C and 273 °C for CO₂ yield under saturated vapor with a weight hourly space velocity of 60 000 ml g⁻¹ h⁻¹, which were far superior to the performances of Mn/Cu-2 (233 °C and 274 °C; 237 °C and 300 °C) and MnO_x (242 °C and 294 °C; 255 °C and 315 °C). Meanwhile, the most active catalyst Mn/Sm-4 exhibited complete mineralization of chlorobenzene under saturated vapor and a weight hourly space velocity of 60 000 ml g⁻¹ h⁻¹ at 350 °C. In addition, the Mn/Sm-4 catalyst also showed a high TOF_Mn value (8.35 × 10⁻⁶ s⁻¹) at 140 °C for toluene oxidation and good stability for the catalytic oxidation of toluene and chlorobenzene under a long-term test running for 200 h of uninterrupted reaction. The XRD, Raman, N₂ adsorption–desorption, FESEM, XPS, O₂-TPD and H₂-TPR results confirmed that more surface defects and surface oxygen vacancies were introduced into MnO_x using proper doping with Sm. Combined with the in situ DRIFTS and on-line MS measurements, the mechanism for chlorobenzene oxidation over Mn/Sm-4 was also revealed. This work presents an important interpretation for developing improved catalysts to control air pollution.