DEACTIVATION OF METAL EXCHANGED ZEOLITE CATALYSTS DURING EXPOSURE TO CHLORINATED HYDROCARBONS UNDER OXIDIZING CONDITIONS

Deactivation of modified cation exchanged zeolite catalysts was studied during complete oxidation of methylene chloride, trichloroethylene and carbon tetrachloride over a temperature range of 175 to 400-degrees-C. Coking was found to be the cause of deactivation. However, the catalysts could be completely regenerated by oxidation in air at 450-degrees-C. Two different formulations of modified cobalt exchanged Y zeolite catalysts were tested to determine the coking and deactivation rates. Increased cation content increased deactivation and coking over a period of about 1000 hours. Changing the type of zeolite from larger pore Y to medium pore mordenite increased deactivation. The type of chlorinated feed also affected coking and deactivation with the rate of deactivation increasing in the order of trichloroethylene > methylene chloride > carbon tetrachloride. Both coking and deactivation increased with decreasing temperature. Higher space velocity produced more deactivation for trichloroethylene oxidation at 275-degrees-C. Based on these results a mechanism for coking is proposed with CO as the possible reaction intermediate that leads to the formation of coke.