Plasma-catalytic removal of a low concentration of acetone in humid conditions

Abstract

A coaxial dielectric barrier discharge (DBD) plasma reactor has been developed for plasma-catalytic removal of low concentration acetone over MO_x/γ-Al₂O₃ (M=Mn, Co, or Cu) catalysts. The effect of relative humidity of air (RH) on the discharge characteristics, acetone removal efficiency, CO₂ selectivity, and byproduct formation with and without catalyst has been investigated. The results show that increasing the RH leads to a decrease of the specific energy density (SED) of the DBD, while packing γ-Al₂O₃ supported metal oxide catalysts into the discharge gap enhances the SED of the discharge. The maximum acetone removal of 75.3% is achieved at an optimum RH of 10% using CoO_x/γ-Al₂O₃ beyond which the removal efficiency of acetone decreases with the increase of the RH. Higher RH inhibits the formation of energetic electrons while water can be adsorbed onto the catalyst surface and block active sites on the catalyst surface. It is found that increasing the air humidity enhances both CO₂ selectivity and carbon balance, but decreases the formation of ozone. However, the formation of NO_x slightly increases with increasing the gas humidity. In addition, the presence of these catalysts in the discharge significantly decreases the formation of unwanted byproducts (O₃ and NO_x) and promotes the deep oxidation of acetone towards CO₂ with an increased carbon balance.