REDOX BEHAVIOR OF COPPER(II) SPECIES ON CUCE OXIDE CATALYSTS - ELECTRON-PARAMAGNETIC-RESONANCE (EPR) STUDY

Electron paramagnetic resonance (EPR) has been used to study the effec t of hear treatment under air or hydrogen on the behaviour of CuCe oxi de catalysts. Monomers, dimers and clusters of Cu2+ ions have been det ected in CeO2 after different calcination temperatures. Monomers and d imers are located in specific and similar sites of the ceria lattice i n place of Ce4+ ions. When two Cu2+ ions are situated at a distance of 3.6 +/- 0.3 Angstrom and bridged by an oxygen, the dimer signal is fo rmed. The reduction of dimers by hydrogen gives monomers in a first st ep and these transform into Cu+ or Cu-0 species in a second step.