Comparative study of Mn oxide catalysts on toluene oxidation: The effect of Mn valence electronic structures

Abstract

Understanding the structure-activity relationship of Mn-based oxide catalysts is of great importance for the rational development of highly performance catalysts for VOCs catalytic oxidation. However, the knowledge of the electronic structure-catalytic oxidation activity relationship over Mn-based oxide catalysts is still limited. Herein, we investigated the typical MnxOy (Mn3O4, MnO2, and Mn2O3) with different valence electronic structures by using various characterizations and DFT calculations. The MnO2 exhibits superior intrinsic activities (RS, 1.14×10−9 mol·m−2·s−1) when compared with Mn3O4 (0.54×10−9 mol·m−2·s−1) and Mn2O3 (0.45×10−9 mol·m−2·s−1) for toluene catalytic oxidation. The solid experimental and DFT calculation results show that the d-band center of Mn determines the intrinsic activity. The superior catalytic oxidation activity of MnO2 can be attributed to its higher d-band center (-1.03 eV) in comparison with that of Mn3O4 (-1.25 eV) and Mn2O3 (-1.59 eV). The higher d-band center can weaken the surface Mn-O bonds strength (k = 290.9 N/m) and strengthen the gaseous O2 adsorption simultaneously, then enhancing the mobility of surface lattice oxygen and the amount of adsorbed oxygen species. This work firstly reveals the intrinsic relationship between catalytic oxidation activity and d electronic structure over Mn-based oxide catalysts and provides knowledge that will advance the design of high-performance catalysts for catalytic oxidation.