ALUMINA AND ZEOLITES AS CATALYSTS FOR DECOMPOSITION AND TRANSFORMATION OF CHLOROFLUOROCARBONS STUDIED BY MULTINUCLEAR NMR METHODS

摘要

The reactions of various chlorofluorocarbons were studied with solid reactants: zeolites an y-Al_2O_3. CC1_2F_2 led to the final product CO_2, while CO was the final product starting from CHC1F_2, proved by ~(13)C NMR technique. The fate of the solid reactants - aluminium extraction, A1F_3 formation, etc., ― was determined using ~(29)Si, ~(27)A1 and ~(19) NMR. On zeolites both Bronsted and Lewis acid sites were detected, while no dismutation reaction products were found. It means that in the case of zeolites immediate attack of the framework takes place. On alumina dismutation reaction take place as primary steps caused by the Lewis acid sites, exclusively identified by pyridine adsorption. For zeolites and alumina ~(27)A1 and ~(19)F NMR results proved that the Cl content of chlorofluorocarbons is released as A1C1_3 and HC1 (or NaCl), while the F content remains deposited as A1F_3 in the solid, because the sublimation point of A1F_3 is 1500 K.~(19)F resonances are different for the Al-F with zeolitic (― 163.4 ppm) and alumina (-172.8 ppm) origin.