Abstract:Developing low-temperature catalytic mineralization technology has become an importantEnergy Environmental Protectionresearch direction for the treatment of volatile organic pollutants (VOCs). Using toluene as the modelpollutant, we combine MnO, which has both catalytic oxidation activity and microwave absorptionability, with microwave irradiation to mineralize toluene into CO and HO at low temperatures rangingfrom 100 ℃ to 200 ℃. Four different crystalline phases of MnO catalysts (α-MnO, β-MnO, δ-MnO,and γ-MnO) were successfully synthesized by the hydrothermal method. The catalytic oxidationactivity and microwave utilization potential of the different catalysts were evaluated quantitatively,considering both physicochemical and microwave properties. XRD results confirm the successfulsynthesis of the four distinct crystalline phases. SEM and BET results show that δ-MnO has a higherspecific surface area (115.3 m/g) and larger pore volume (0.458 cm/g) due to its porous structure.Through the heating experiment, it was found that δ-MnO shows better microwave conversion ability.When the microwave output power was 400 W, 600 s was required for δ-MnO to rise from roomtemperature to 300 ℃, which was lower than that of α-MnO, β-MnO, and γ-MnO. Combined with thevector network test results, we found that δ-MnO exhibits the strongest reflection loss, impedancematching, and maximum attenuation constant, indicating better microwave absorption and utilizationability. By comparing the mineralization performance under microwave irradiation, we conclude thatthe crystalline structure significantly affects the catalytic activity of MnO. δ-MnO exhibits a superiorlow-temperature mineralization performance, achieving complete mineralization temperature at 195 ℃with a gas hourly space velocity (GHSV) of 18 000 h. The order of toluene mineralization activity isdetermined to be: δ-MnO > α-MnO > γ-MnO > β-MnO. Moreover, δ-MnO shows an outstandingstability, whose toluene mineralization efficiency remains stable with increasing reaction time.Moreover, we used GC-MS to analyze the degradation products of toluene at different catalytictemperatures. GC-MS results reveal that the main by-products of toluene degradation are esters,ketones, and other organic compounds. The type of toluene degradation by-products decreases as thereaction temperature increases. At a temperature of 200 ℃, toluene is completely oxidized to CO andHO without the generation of organic products. Through comprehensive characterization, analysis ofelectromagnetic properties, and experimental results, we found that the excellent low-temperatureoxidation characteristics of δ-MnO are related to its unique microstructure, including crystallinity,specific surface area, pore volume, and pore size. The rich void structure of δ-MnO enhances theabsorption and attenuation of microwaves, exhibiting optimal microwave absorption and utilizationproperties. Close-