Post plasma-catalysis for total oxidation of trichloroethylene over Ce–Mn based oxides synthesized by a modified “redox-precipitation route”

Abstract

Two CeMnxOy (CeMnx) catalysts (x=1, CeMn; x=4; CeMn4) were synthesized via a modified “redox-precipitation” route followed by calcination at 500°C. XRD analysis showed only the presence of ceria. Raman spectroscopy gave a featureless spectrum for CeMn while peaks characteristic of a birnessite-type structure were observed for CeMn4 oxide. A large surface area of 165m2/g was obtained for CeMn which decreased to 95m2/g with x=4. Furthermore XPS characterizations showed homogeneous distribution of the active phase. Trichloroethylene (TCE) abatement was investigated at 150°C with catalyst alone, non-thermal plasma (NTP) alone at ambient conditions and with a post plasma-catalytic (PPC) system using these cerium–manganese oxides as well as a reference Mn oxide as catalysts positioned downstream of the plasma. At 150°C, without NTP, MnOy converted specifically 5% of TCE into CO2 while volatile organic compound (VOC) adsorption mainly occurred over the other catalysts. With NTP alone, 87% TCE removal was achieved at 240J/L but formation of unwanted polychlorinated by-products, such as phosgene, dichloroacetylchloride and trichloroacetaldehyde occurred resulting in a low COx (x=1, 2) selectivity of about 27%. In comparison, a significant improvement was observed in TCE abatement performance when using the PPC configuration. Indeed, TCE conversion up to about 100% as well as COx selectivity up to 56% were achieved thanks to the high efficiency of the catalysts to completely decompose O3 leading to the production of active oxygen species which are able to oxidize the by-products. The best plasma-assisted catalyst performance observed for CeMn4 may be linked to the presence of residual potassium allowing to avoid the poisoning of catalytic sites with chlorinated organic species as well as slowing down the formation of chlorinated mineral phases.