Catalytic destruction of chlorinated C1 volatile organic compounds (CVOCs) reactivity, oxidation and hydrolysis mechanisms

LaCoO3 and LaMnO3+delta prove to be good catalysts for the total oxidation of chlorinated volatile organic compounds (CVOCs) to CO2 and HCl. Total destruction of CH2Cl2, CHCl3 and CCl4 is possible below 550 degrees C. Different by-products are obtained in function of the nature of the catalysts and the chlorinated compounds. Conventional T-50 and T-90 values are replaced by T-50(COx) and T-90(COx) corresponding to the temperature at which CO+CO2 yields are equal to 50 and 90%, respectively. The proposed presentation of the catalytic results have the advantage to take into account the formation of by-products. The difference in behaviour depending upon the mixture of gases showed that the reaction mechanism is different for different chloromethanes. CCl4 reacts mainly by a hydrolysis mechanism. CHCl3 and CH2Cl2 react in two steps, hydrolysis and oxidation. These molecules result in a large number of intermediate chlorinated by-products. It is suggested, based on known chemistry of the reaction in liquid phase, that CCl4 reacts by a mechanism with formation of a +CCl3 cation. A substitution by concerted mechanism is in line with the kinetic studies for CH2Cl2. The role of water partly that of a reaction partner in CCl4 - and partly that of a polar solvent - increases the mobility of the Cl- anion. (C) 2000 Elsevier Science B.V. All rights reserved.