Plasma-catalytic removal of formaldehyde over Cu–Ce catalysts in a dielectric barrier discharge reactor

In this study, a coaxial dielectric barrier discharge (DBD) reactor has been used for plasma-catalytic removal of low concentration formaldehyde over a series of Cu–Ce oxide catalysts prepared by the citric acid sol–gel method. The effect of the Cu/Ce molar ratio on the removal of formaldehyde and CO2 selectivity has been investigated as a function of specific energy density (SED). In comparison to the plasma-only process, the combination of plasma with the Cu–Ce binary oxide catalysts significantly enhances the reaction performance, while the presence of CuO or CeO2 in the DBD reactor has a negative effect on the removal of HCHO. This suggests that the interactions between Cu and Ce species change the properties of the catalysts and consequently affect the performance of the plasma-catalytic process. The highest removal efficiency of 94.7% and CO2 selectivity of 97.3% were achieved when the Cu1Ce1 catalyst (Cu/Ce = 1:1) was placed in the DBD reactor at the SED of 486 J L−1. The interaction between Cu and Ce species results in a larger specific surface area and pore volume, along with a greater formation of surface adsorbed oxygen (Oads), which favors the oxidation of formaldehyde in the plasma process. In addition, the redox cycles between Cu and Ce species facilitate the formation of additional active oxygen atoms and contribute to the plasma-catalytic oxidation reactions. Plausible reaction mechanisms involved in the plasma-catalytic oxidation of HCHO have been proposed.