CATALYTIC DECOMPOSITION OF CFC-12 ON TRANSITION-METAL CHLORIDE PROMOTED GAMMA-ALUMINA

The activity of gamma-alumina and gamma-alumina promoted with transiti on metal chlorides for the hydrolytic decomposition of dichlorodifluor omethane was investigated in the temperature range 250-400 degrees C, It was found that the hydrolysis of dichlorodifluoromethane occurs on the acid sites of the gamma-alumina. Carbon dioxide was the main produ ct formed. gamma-alumina was deactivated by reaction with hydrogen flu oride formed by the hydrolysis reaction. The fresh catalysts and catal ysts after the reaction were characterized by X-ray photoelectron spec troscopy and X-ray diffraction. Surface chloride was found to be repla ced by fluoride during catalytic reaction. After prolonged reaction, r hombohedral aluminum fluoride was detected in the aged catalysts. The deactivated catalyst also catalyzed the formation of chlorotrifluorome thane. Transition metal chlorides were dispersed on the surface of gam ma-alumina and reduced the hydrolytic activity of the fresh catalyst. Transition metal fluoride phase formed by reaction of the chlorides wi th HF during reaction, especially that formed from CrCl3, reduced the rate of fluorination of gamma-alumina and thus its deactivation. (C) 1 998 Elsevier Science B.V.