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

The mixed oxide of zirconium and titanium was investigated for the catalytic hydrolysis of dichlorodifluoromethane. The mixed oxide was further promoted by doping with sulfate ions. It was found by both powder X-ray diffraction and Raman spectroscopy that addition of hydrogen peroxide to the methanol solution of ZrOCl₂ and TiCl₄ before gelation was induced by ammonia addition promoted the formation of the mixed oxide phase with the anatase structure in addition to the expected phase of columbite structure. This increased 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 concentration of the acid used, in addition to sulfate deposition on the oxide surface, occurred. The treatment with 96% sulfuric acid resulted in a catalyst with nearly entirely the anatase structure. This catalyst was found to be the most active, capable of complete conversion of CFC-12 and 100% selectivity to carbon dioxide at 280°C. Prolonged reaction of this catalyst at 280°C for 211 h resulted neither in reduction of activity nor reduction in CO₂ selectivity. The performance of this catalyst is among the highest reported in the literature.