Praseodymium hydroxide/gold-supported precursor: a new strategy for preparing stable and active catalyst for the water-gas shift reaction

Abstract

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 (Au⁰) 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.