Praseodymium Hydroxide/Gold-Supported Precursor: A New Strategy For Preparing Stable And Active Catalyst For The Water-Gas Shift Reaction

Praseodymium oxide with a mixed-valence state (Pr4+/Pr3+) has the highest O mobility among the rare earth oxides (REOs) and holds great promise in the field of heterogeneous catalysis. Herein, a rod-shaped praseodymium hydroxide (Pr(OH)(x)) support was obtained via hydrothermal method and used for the immobilization of Au nano-species by a modified deposition-precipitation (MDP) method. The resulting Au/Pr(OH)(x_)M catalyst was tested for water-gas shift reaction (WGSR) and CO oxidation and exhibited high activity and stability in both reactions with a TOF of 0.55 s(-1) for WGSR, which is high compared with the reported ceria-support Au catalysts. HAADF-STEM measurements combined with the elemental composition distribution maps verified Au sub-nanospecies formed on the surface. The EXAFS and XPS studies demonstrated the transformation of the chemical state of Au from ionic Au (Au3+) to metallic Au (Au-0) after the WGSR. The photoemission spectra of Pr 3d and O 1s indicate high number of O vacancies on Au/Pr(OH)(x_)M, which facilitate the H2O dissociation and contribute to the improved WGSR. This study shows that praseodymium hydroxide, as a hydroxyl- and O vacancy-rich support can promote the dispersion and stabilization of Au species, thus providing useful concepts for the design and preparation of active and stable catalysts for heterogeneous catalysis.