Mechanistic features of reduction of copper chromite and state of absorbed hydrogen in the structure of reduced copper chromite

Abstract

The review discusses the experimental data on the unusual mechanism of the reduction of copper cations from the copper chromite, CuCr2O4, structure. Treatment of copper chromite in hydrogen at 180–370°C is not accompanied by water formation but leads to absorption of hydrogen by the oxide structure with simultaneous formation of metallic copper as small flat particles which are epitaxially bound to the oxide. This process is due to the redox reaction Cu2+ + H2 → Cu0 + 2H+; the protons are stabilized in the oxide phase, which is confirmed by neutron diffraction studies. The reduced copper chromite which contains absorbed hydrogen in its oxidized state and the metallic copper particles epitaxially bound to the oxide phase structure exhibit catalytic activity in hydrogenation reactions.