An in situ iron-57 Mössbauer spectroscopic investigation of the reduction of ironcerium oxide catalysts in different gaseous reducing agents

The formation of iron-cerium oxide catalysts by the treatment in hydrogen or carbon monoxide of air-dried precipitates has been monitored in situ by⁵⁷Fe Mössbauer spectroscopy. The results show that the initial calcination of the precipitates in air induces phase segregation and the formation of small concentrations of large particle α-iron(III) oxide in combination with cerium dioxide. Treatment of the solid in hydrogen at 450°C results in the facile reduction of α-Fe₂O₃ to metallic iron which is unaffected by exposure to a reactant gaseous mixture of carbon monoxide and hydrogen. Exposure of the biphasic material formed in air to carbon monoxide at similar temperatures induces the reduction of α-Fe₂O₃ to Fe₃O₄ and metallic iron and the subsequent formation of iron carbide. The carbided catalyst is not changed by exposure to a mixture of carbon monoxide and hydrogen. In distinct contrast the cerium orthoferrite of composition CeFeO₃ suffers only slight reduction when treated in hydrogen and shows a very limited amenability to carbide formation when treated in carbon monoxide.