Enhancing sulfur tolerance of cryptomelane MnO2 for benzene oxidation via binary Ag-V decoration: The role of Ag-V sacrificial sites in oxygen and benzene activation.

α-MnO2 is widely used in catalytic combustion of volatile organic compounds (VOCs), but resistance to SO2 poisoning still poses significant challenge for industrial application. To tackle this problem, bimetallic modification strategy was herein employed via Ag and V incorporation (AgVMn). The AgVMn achieved 80 % benzene-to-CO2 conversion at 150 °C under an air velocity of 120 L/g/h and completely mineralized all fed benzene at ≥ 175 °C. More importantly, the AgVMn also demonstrated significantly improved resistance to SO2 poisoning as compared with MnO2, AgMn, VMn and two commercial VOCs catalysts (Hopcalite and Pt/Al2O3). Over the sulfurized AgVMn, the activity loss relative to the situation of fresh AgVMn was 18 % at 150 °C and only 3 % at 175 °C, whereas the activity reduction caused by sulfur poisoning was 36 % at 150 °C & 24 % at 175 °C for MnO2, 30 % at 150 °C & 12 % at 175 °C for AgMn, and 27 % at 150 °C & 10 % at 175 °C for VMn. Characterization studies confirmed that the key factors determining benzene oxidation capability included mass transfer, Mn-O bond strength, defect site content, adsorptive O2 dissociation and benzene activation by surface oxygen. In addition, the Ag and V heteroatoms strictly limited the combination of sulfur oxides with Mn by preferentially capturing sulfur oxides to form sulfates, thus allowing for higher accessibility of active site on the surface. Compared with the single Ag or V, the Ag-V cooperation strengthened both the activation of O2 and benzene and the protection of Mn from sulfur poisoning.