ON THE MECHANISM OF CATALYTIC-OXIDATION OF CH2CL2 ON GAMMA-AL2O3 AND ITS OSCILLATORY BEHAVIOR

Adsorption of CH2Cl2 and its oxidation with dioxygen have been investi gated on pure gamma-Al2O3 by means of infrared spectroscopy and gas ch romatographic analysis. Infrared spectroscopy showed that CH2Cl2 may b e adsorbed on the alumina surface through chlorine ions either on two adjacent exposed Al ions at the (111) plane of Al2O3, or on the isoloa ted Lewis acid sites. The oxidation of CH2Cl2 at temperatures below 45 0 degrees C yields an intermediate product CH3Cl with 50% of selectivi ty whereas the other half of the CH2Cl2 amount is totally oxidized to CO2 and HCl. At temperatures higher than 450 degrees C practically tot al conversion of CH2Cl2 to CO2 and HCl takes place. Selfsustained osci llations of the CH2Cl2 conversion in a broad range are observed when w ater vapour is added to the feed. The mechanism explaining the nature of the activity of alumina in the CH2Cl2 oxidation and selectivity to CH3Cl as well as a possible reason of oscillations of the conversion a re proposed.