Abstract
Chemical dealumination by (NH4)2SiF6 treatment has been investigated as an effective method for improving the catalytic behaviour of Y zeolites for chlorinated hydrocarbon combustion. Hence, the deep catalytic oxidation of dichloromethane (DCM), 1,2-dichloroethane (DCE), and trichloroethylene (TCE) was evaluated over two Y zeolites with different Si/Al ratios, at conditions of lean chlorocarbon concentration (around 1000 ppm) in dry and humid (15,000 ppm of water) air between 200 and 550°C. Catalyst-subjected to dealumination exhibited a higher activity in CVOC oxidation compared with that of the untreated one. The activity increase was attributed to the strong Brønsted acidic sites formed during catalyst dealumination. The ease of destruction was found to decrease in the following order: DCE>DCM>TCE. The main oxidation products formed were CO, CO2, HCl, and Cl2. In addition, some other chlorinated by-products/intermediates were detected, namely vinyl chloride, methyl chloride, and tetrachloroethylene in the oxidation of DCE, DCM, and TCE, respectively. The addition of water slightly diminished the zeolite activity and markedly changed the product distribution. Hence, by-product generation was found to be significantly reduced. Water also promoted somewhat the CO2 selectivity and led to complete reaction of chlorine to HCl by the Deacon reaction.
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