I-I-type zeolites (H-Y, H-ZSM-5, and H-MOR) have been investigated for the catalytic oxidative decomposition of trichloroethylene under dry and humid (1000, 7500 and 15,000 ppmv of water) conditions, between 200 and 550 degreesC. The: activity order was found to be: H-MOR > H-ZSM-5 > H-Y. Temperature-programmed desorption of ammonia and diffuse reflectance FT-IR measurements of adsorbed pyridine revealed that strong Bronsted acidity plays an important role in controlling the oxidative activity of the H-type zeolites. The main oxidation products were CO, CO2, HCl and Cl-2. Small amounts of tetrachloroethylene were also detected. The addition of water to the feed stream did not alter the activity order of the zeolites observed in dry conditions. Better conversions were anticipated over H-MOR and H-ZSM-5 at low temperatures and excess of water concluding that both oxygen and water accounted for the TCE destruction. In contrast, H-Y showed a low activity in humid air due to its strong hydrophilic character. It was found that water promoted the formation of CO2 and limited the generation of undesired chlorinated by-products (Cl-2 and C2Cl4). XRD analysis indicated that H-ZSM-5 was the most resistant zeolite to dealumination by chlorination. (C) 2001 Elsevier Science B,V. All rights reserved.