Storage of reactive hydrogen species in CeMxOy (M = Cu, Ni; 0≤x≤1) mixed oxides

Abstract

Interaction of hydrogen with a series of mixed oxides CeM x O y (M = Cu, Ni; 0 ⩽ x ⩽ 1) has been studied in the 300–1073 K temperature range. A dynamic method of titration has been used to provide evidence for reactive hydrogen H∗ present in the solids. This method of titration involves hydrogenation at 423 K of isoprene under helium flow in the absence of gaseous hydrogen. The hydrogen reservoir capacity depends on the pretreatment temperature under H 2 and is related to the creation of anionic vacancies in the solid. All the CeM x O y mixed oxides are large catalytic hydrogen reservoirs with marked diffusion properties of hydrogen species (H∗, OH −). In the series studied, the highest amount of hydrogen H∗ (29.5 10 −3 mol g −1) is stored by CeNi 0.7O y pretreated under H 2 at 523 K (H 6.8CeNi 0.7O y ). In the conditions in which the incorporation of hydrogen in the solid occurs, X-ray diffraction analysis under H 2 shows shifts depending on the treatment temperature and corresponding to non-negligeable expansion of the ceria-based lattice attributed to the insertion of hydrogen species of hydridic nature in the anionic vacancies.