Catalytic combustion of PVOCs on MnOx catalysts

• MnOx oxide catalysts with different structures were successfully synthesized.
• Correlated physicochemical properties of MnOx catalyst were across-the-board investigated.
• Benzene, toluene, xylene, and ethylbenzene were used as the air pollutants to be studied.
• Catalytic activity is related with the chemical composition and structure of MnOx catalysts.

In this study, manganese oxide (MnOx) catalysts were prepared by using hard-template (MnOx-HT) and precipitation (MnOx-PC) methods. The prepared MnOx catalysts were systematically characterized by XRD, TEM, BET, XPS, O2-TPD, and H2-TPR analyses. The activity of the catalysts was investigated in the catalytic combustion of PVOCs, such as benzene, toluene, xylene, and ethylbenzene, in air. Results indicate that the chemical composition and structure of the prepared MnOx oxide catalysts are obviously affected by the preparation methods. The T90 corresponding to the catalytic combustion of xylene, ethylbenzene, toluene, and the T60 of benzene over the MnOx-HT catalyst are 200 °C, 205 °C, 210 °C, and 225 °C, which are much lower than that over MnOx-PC. The catalytic combustion of the PVOCs over the MnOx-HT catalyst follows the order xylene > ethylbenzene > toluene > benzene. Both the MnOx-HT and MnOx-PC catalysts exhibit stable catalytic performance during the combustion of toluene. Therefore, the superior catalytic performance of the MnOx-HT catalyst can be attributed to the high MnO2 content, high concentration of surface reactive oxygen, highly ordered mesopores, large specific surface area, good oxygen mobility, and low-temperature reducibility. In addition, the catalytic combustion of the phenyl compounds is affected by their inherent characteristics such as structural stability, molecular polarity, and dimensions.

The orderly developed mesoporous structure extremely facilitates the reactant and product molecules to move throngh the MnOx-HT catalyst, which is very benetful to the PVOCs combustion. The aggreated bulk structure badly handicaps the movement and transfer of the reactant and product molecules through the MnOx-PC catalyst, thus go against the PVOCs combustion. The PVOCs catalytic combustion over both MnOx-HT and MnOx-PC catalysts follows Mars Van Krevelen mechanism, the PVOC molecules are adsorbed and activated on the catalyst surface, and then react with the reactive oxygen species on the catalyst surface to form CO2 and H2O to realize PVOC molecules complete combustion. As the reactive oxygen species comsumed, the molecular oxygen can be adsorbed and activated on the catalyst surface to form reacttive oxygen species, and it can also be effectively supplied by the lattice oxygen. After the lattice oxygen converts to the reactive oxygen species being comsumed, the adsorbed oxygen species on the catalyst surface can convert to supply it in time.Figure optionsDownload high-quality image (231 K)Download as PowerPoint slide