Hydrogen adsorption kinetics on Pd/Ce0.8Zr0.2O2

Abstract

Hydrogen adsorption on Pd/Ce_0.8Zr_0.2O₂ was studied by temperature-programmed reduction, volumetric measurements and IR spectroscopy. Hydrogen uptake and reduction rate at 353 K are strongly dependent on the hydrogen pressure. At relatively high hydrogen partial pressure, reduction involves PdO, the surface and a significant fraction of the bulk of the ceria based oxide. Formation of oxygen vacancies even at low temperature (<373 K) is observed. The hydrogen adsorption process is mainly irreversible, as is shown by an increase in the ²F_5/2 → ²F_7/2 electronic transition of Ce³⁺ with hydrogen pressure and surface dehydroxylation. This “severe” reduction has a negative effect on the subsequent hydrogen adsorption capability. The decrease of hydrogen uptake capacity and rate during adsorption can be associated with the partial loss of superficial OH and the presence of Ce³⁺, which deactivates Pd electronically.