The interaction of chlorinated ethylenes (vinyl chloride, 1,1 dichloroethylene, trichloroethylene, and perchloroethylene) with the surface of chromium exchanged zeolite Y (Cr-Y) catalyst has been studied by in situ FT-IR spectroscopy. The adsorptions were carried out on the in situ oxidized Cr-Y pellet at temperatures between 25 and 300 degrees C in a dry nitrogen stream as a means of studying possible decomposition intermediates. The adsorption at 25 degrees C was chiefly physical in nature although some dechlorination of the molecule was evident even at this temperature. At higher temperatures, between 100 and 300 degrees C, an oxygen attack on the adsorbed molecule led to the formation of partially and/or fully oxygenated (but still adsorbed) species. These oxygenated species, including carboxylate and carbonate, were found to contain fewer chlorine atoms than the original feed molecule. The catalytic activity for the formation of these intermediates was found to diminish with increasing chlorine content of the feed molecule. Based on these results, a reaction pathway for the progressive catalytic oxidation of chlorinated ethylenes has been proposed.