Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) on unpromoted andsulfate promoted TiO2-ZrO2 mixed oxide catalysts

The mixed oxide of zirconium and titanium was investigated for the catalyti c hydrolysis of dichlorodifluoromethane. The mixed oxide was further promot ed by doping with sulfate ions. It was found by both powder X-ray diffracti on and Raman spectroscopy that addition of hydrogen peroxide to the methano l solution of ZrOCl2 and TiCl4 before gelation was induced by ammonia addit ion promoted the formation of the mixed oxide phase with the anatase struct ure in addition to the expected phase of columbite structure. This increase d the surface area and activity of the mixed oxide. Promotion with sulfate enhanced the acidity and activity of the catalysts. When sulfate was added by treatment with sulfuric acid, phase transformation, depending on the con centration of the acid used, in addition to sulfate deposition on the oxide surface, occurred. The treatment with 96% sulfuric acid resulted in a cata lyst with nearly entirely the anatase structure. This catalyst was found to be the most active, capable of complete conversion of CFC-12 and 100% sele ctivity to carbon dioxide at 280 degrees C, Prolonged reaction of this cata lyst at 280 degrees C for 211 h resulted neither in reduction of activity n or reduction in CO2 selectivity. The performance of this catalyst is among the highest reported in the literature. (C) 2000 Elsevier Science B.V. All rights reserved.