THE OXIDATION OF CHROMIUM(III) TO CHROMIUM(VI) IN THE PRESENCE OF PLATINUM METALS

BS>Ruthenium, either as soluble salts, powdered metal, or oxide, catalyzed the oxidation of Cr(III) to Cr(VI) in dilute oxygenated sulfuric acid solutions. Under the same conditions, in the absence of ruthenium, Cr(Vl) was not produced. In a 2 M Al(NO/sub 3/)/sub 3/-1 M HNO/sub 3/ solution at atmospheric boiling point, ruthenium and compounds of ruthenium, platinum, palladium, rhodium, and osmium very markedly increased the rate at which Cr(III) was oxidized to Cr(VI). Very low concentrations of ruthenium were capable of causing the oxidation to proceed at an appreciable rate. In boiling 65% nitric acid, Cr(HI) was oxidized to Cr(VI) if reduced oxides of nitrogen were removed from solution either m the presence or absence of ruthenium; without removal of the oxides of nitrogen, detectable quantities of Cr(VI) were not formed in either case. Cr(VI) was not produced in boiling and aerated uranyl sulfate solutions containing ruthenium. (auth