Catalytic properties of copper chromite ferrites in water gas shift reaction and hydrogen oxidation

The catalytic properties of a series of copper chromite ferrite samples with the composition CuCr2–x Fe x O4 (where x = 0–2) and a spinel-type structure in reactions with reducing (water gas shift reaction, WGSR) and oxidizing (the oxidation of hydrogen) reaction atmospheres were studied. The samples were obtained by the thermal decomposition of mixed hydroxo compounds. The distribution of Cu2+ ions in the tetrahedral and octahedral crystallographic positions of spinel, which depends on the Cr3+/Fe3+ ratio, affects the apparent activation energy (E a) in both of the reactions. In WGSR, E a is ∼33 kJ/mol for CuCr2O4, in which Cu2+ ions mainly occupy tetrahedral positions, whereas E a ≈ 100 kJ/mol for CuFe2O4, in which Cu2+ ions mainly occupy octahedral positions. In the reaction of hydrogen oxidation, E a is ∼71 kJ/mol for CuCr2O4 or ∼42 kJ/mol for CuFe2O4. The value of E a for the mixed chromite ferrites changes with the replacement of chromium ions by iron ions and, hence, with a ratio between the amounts of copper ions in the tetrahedral and octahedral oxygen positions of spinel.