Enhancing water resistance of α-MnO2 catalyst for efficient airborne benzene oxidation at mild temperatures via facile Ag incorporation

Abstract

Facile structural modification of α-MnO2via single incorporation of Ag element was applied to achieve high-efficiency oxidation removal of benzene, particularly under wet gas. Ag+ ions could enter the MnO2 structure by partially replacing the tunnel K+ ions, leading to lower crystallinity, smaller crystallite and distorted lattice arrangement. Due to electron transfer from Ag+ to lattice oxygen, Ag decoration weakened Mn-O bonds and the bulk lattice oxygen became more mobile to migrate towards the Ag-MnO2 surface, resulting in the larger number of surface lattice oxygen. Along with the abundance of oxygen species, the reactivity of surface adsorbed oxygen and lattice oxygen was significantly improved as well by Ag modification. All these factors were favorable to the complete C6H6-to-CO2 conversion. Gaseous benzene could be directly oxidized by oxygen species over the pristine MnO2 catalyst, while the adsorptive activation of gaseous benzene was required for the Ag-MnO2 before further oxidation. As to the Ag-MnO2’s endurability of moisture-aroused inactivation, Ag species oppressed water adsorption in the form of strong adsorbate, thus preventing structural damage of the catalyst during humid benzene oxidation. Moreover, water molecules could enhance the “Ag-MnO2vs. adsorbed benzene” interaction, which increased the oxidation efficiency of adsorbed benzene. However, the strong binding of water vapor with the MnO2 surface would cause strong restriction of gaseous benzene from approaching the surface oxygen species, resulting in much less benzene being oxidized under wet gas.