INTERACTION OF HYDROGEN WITH COPPER-CONTAINING OXIDE CATALYSTS .4. STRUCTURE OF HYDROGEN-CONTAINING COPPER CHROMITE

The cation distribution and the forms and localization of dissolved hy drogen in the structure of copper chromite reduced in a hydrogen flow at 320 degrees C are studied by in situ powder X-ray and neutron diffr action. It is shown that copper ions are partially reduced to Cu-0 due to the exchange interaction with hydrogen and migrate to the surface of spinel crystals; another part of copper ions are reduced to Cu+ ion s that diffuse into the octahedral positions. The Cr3+ ions do not int eract with hydrogen, and their position does not change during reducti on. The dissolved hydrogen occurs in two states: (I) atomic hydrogen i ncorporated in the octahedral interstices and (2) protons in the tetra hedra whose centers were occupied by the copper ions before reduction. The protons interact with the lattice oxygen forming the covalent O-H bonds. Due to these peculiarities of the structure, the reduced chrom ite can be transformed to the initial state of the stoichiometric spin el upon hydrogen removal.