Influence of heat treatment conditions on the physicochemical and catalytic properties of a chromium-containing catalyst for tetrachloroethylene hydrofluorination to pentafluoroethane

The physicochemical properties of coprecipitated 95% Cr₂O₃-5% Al₂O₃ oxide systems obtained by heat treatment of the precursor in nitrogen and air between 110 and 600°C and their influence on the catalytic activity in tetrachloroethylene hydrofluorination were studied by thermal and X-ray diffraction analyses, diffuse reflectance spectroscopy, and specific surface are measurements. The CrO_1.9 compounds are more active than CrO_1.5, but their preparation in the finely divided state is difficult because of the high exothermicity of the oxidation stage, which results in the decomposition of the oxides CrO_1.9 and CrO_1.5 followed by the crystallization and sintering of the decomposition products. Fine-powder and highly active chromium-containing oxides with CrO_1.9 stoichiometry can be obtained by two-stage heating of hydroxides first in nitrogen and then in air at comparatively low temperatures.