The strong Fe-Mn interaction over red mud accelerating the activation of key oxygen species for toluene oxidation

Red mud (RM) contains a high content of Fe2O3, which provides an ample supply of acid sites and moderate reducibility. These properties have made RM a viable candidate for catalytic reactions such as the selective catalytic reduction of NOx. However, the inert nature of surface oxygen species limits its application in catalytic oxidation. Here we report that the MnOx introduction reconstructs the surface electronic structure of RM and activates the key oxygen species efficiently. The synthesized Mn-doped acid-pretreated RM (Mn/ARM) catalyst exhibited excellent low-temperature toluene oxidation activity, in which T90 (temperature at which 90 % toluene conversion is achieved) decreased by 26 degrees C and 37 degrees C compared to that of conventional Mn/TiO2 and Mn/Al2O3 catalysts, respectively. The comprehensive characterization results revealed that the strong Fe-Mn interaction results in an enhanced electron transfer by Mn4+ + Fe2+ Mn3+ + Fe3+. The reconstruction of the surface electronic structure not only activated the chemisorbed oxygen over Fe2O3 but also enhanced the mobility of lattice oxygen of MnOx. The in-situ diffuse reflectance infrared Fourier transform spectra further revealed that the improvement mechanism, in which the active chemisorbed oxygen species accelerated the toluene adsorption and methyl group activation, and the enhanced lattice oxygen are responsible for the aromatic ring breakage during deep oxidation. Findings from this study provide valuable insights for the high-value utilization of solid waste and low-cost substitution of commercial environmental catalysts.