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

The destruction mechanisms of C-2-chlorinated hydrocarbons have been invest igated. The adsorption of 1,2-dichloroethane (DCE) and trichloroethylene (T CE) on alumina and alumina supported catalysts was studied by FTIR-spectros copy. Interpretation of the spectra suggests that the destruction of DCE oc curs via HCl elimination to vinyl chloride, followed by an attack of a hydr ogen and a surface oxygen on the double bond resulting in acetyl chloride. Subsequent elimination of a chloride ion gives acetaldehyde that can be fur ther oxidized into acetate. With regard to the destruction of TCE, the spec tra indicate that TCE is attacked by a basic oxygen and a hydrogen accordin g to Markovnikov's rule. This results in the formation of acyl chloride, wh ich is further converted into acetate like species. In addition, the oxidat ion of TCE was examined over alumina supported catalysts. While alumina its elf is not very active, palladium and chromium containing catalysts are. In the absence of water, the formation of tetrachloroethylene (PCE) was obser ved. 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 palladi um it inhibited the oxidation reaction over chromium oxide. The activity of the chromia catalyst compared to alumina might be due to the supply of bas ic 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.