Comparative study of the oxidative decomposition of trichloroethylene overH-type zeolites under dry and humid conditions

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 degre esC. The: activity order was found to be: H-MOR > H-ZSM-5 > H-Y. Temperatur e-programmed desorption of ammonia and diffuse reflectance FT-IR measuremen ts of adsorbed pyridine revealed that strong Bronsted acidity plays an impo rtant role in controlling the oxidative activity of the H-type zeolites. Th e main oxidation products were CO, CO2, HCl and Cl-2. Small amounts of tetr achloroethylene were also detected. The addition of water to the feed stream did not alter the activity order o f the zeolites observed in dry conditions. Better conversions were anticipa ted over H-MOR and H-ZSM-5 at low temperatures and excess of water concludi ng that both oxygen and water accounted for the TCE destruction. In contras t, H-Y showed a low activity in humid air due to its strong hydrophilic cha racter. It was found that water promoted the formation of CO2 and limited t he generation of undesired chlorinated by-products (Cl-2 and C2Cl4). XRD an alysis indicated that H-ZSM-5 was the most resistant zeolite to dealuminati on by chlorination. (C) 2001 Elsevier Science B,V. All rights reserved.