Mechanism of catalytic destruction of 1,2-dichloroethane and trichloroethylene over γ-Al2O3 and γ-Al2O3 supported chromium and palladium catalysts

The destruction mechanisms of C-2-chlorinated hydrocarbons have been investigated. The adsorption of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) on alumina and alumina supported catalysts was studied by FTIR-spectroscopy. Interpretation of the spectra suggests that the destruction of DCE occurs via HCl elimination to vinyl chloride, followed by an attack of a hydrogen and a surface oxygen on the double bond resulting in acetyl chloride. Subsequent elimination of a chloride ion gives acetaldehyde that can be further oxidized into acetate. With regard to the destruction of TCE, the spectra indicate that TCE is attacked by a basic oxygen and a hydrogen according to Markovnikov's rule. This results in the formation of acyl chloride, which is further converted into acetate like species. In addition, the oxidation of TCE was examined over alumina supported catalysts. While alumina itself is not very active, palladium and chromium containing catalysts are. In the absence of water, the formation of tetrachloroethylene (PCE) was observed. Addition of water to the feed resulted in a decrease in the amount of PCE produced. Although water did not affect the TCE conversion over palladium it inhibited the oxidation reaction over chromium oxide. The activity of the chromia catalyst compared to alumina might be due to the supply of basic oxygen which can attack the double bond. The inhibitive effect of water on the conversion of TCE is probably due to blocking of active oxygen sites. (C) 1999 Elsevier Science B.V. All rights reserved.