The activation of a copper-chromium system in H2 is accompanied by an accumu­lation of H2, which can become active for hydrogenation reactions, in the absence of H2 in the gas phase. This sorption of H2 is due to a specific mechanism of Cu2+ reduction from the CuCr2O4 structure, a reaction which does not release water. The reduction leads to the formation of metallic copper and to protons substituting for copper cations in the vicinity of O2 anions. INS spectra of copper chromite as prepared and reduced at various temperatures are shown in Fig. 2.1. The initial catalyst shows bands at low frequencies, due to the mass of the atoms, these bands having a low intensity because no proton motion is involved. Upon reduction, a large intensity

increase can be measured and OH-groups bending modes are observed in the energy range displayed in Fig. 2.1. Increasing the reduction temperature yields a shift of these bending modes to higher frequencies (from 700-800 to 1,220 cm-1), while the stretching modes shift to lower energy. This indicates that hydrogen bonding strength with neighbouring anions increases with the rise in temperature. The band around 400 cm-1 was assigned to librations of two geminal protons (i. e. HOH-groups) [6].