Plasma Catalytic Removal of p-Xylene from Air Stream Using γ-Al₂O₃ Supported Manganese Catalyst

The abatement of dilute p-xylene (500 ppm) from a contaminated air stream (2 L min⁻¹) by the non-thermal plasma in combination with an ozone decomposing catalyst (pelleted Mn/γ-Al₂O₃) was investigated. The reactor performance was evaluated in terms of p-xylene conversion, CO _x selectivity and ozone emission with and without external heating. Generally, the removal of p-xylene gradually increased with increasing the applied voltage from 16 to 22 kV (peak height). As the catalyst was used (i.e., packed inside the plasma active region), the reactor was able to remove ca. 82% of p-xylene at 22 kV, compared to 54% done by plasma alone. Under the same plasma-catalytic condition, the removal of p-xylene was successfully achieved (ca. 96%) by heating up the reactor to 150 °C. Not only was the conversion improved, but also the mineralization of p-xylene was also enhanced considerably by the mild thermal heating, increasing the CO₂ selectivity from ca. 41 to 59%. The ozone emission measurement showed that ozone formed in plasma was readily catalytically decomposed on Mn/γ-Al₂O₃ at above 16 kV, even without external heating. As revealed by the reactor infrared thermographic images, the plasma-induced surface temperature of the catalyst was far higher than the external heating temperature (i.e., 150 °C), facilitating the catalytic degradation of ozone and reducing the formation of byproducts. Additionally, no organic compounds have been found on the spent catalyst, avoiding the possibility of catalyst deactivation during the course of experiment.