High-performance water gas shift induced by asymmetric oxygen vacancies: Gold clusters supported by ceria-praseodymia mixed oxides

• Published in: Applied catalysis. B, Environmental Environmental, 2022-02, Vol.301, p.120789, Article 120789
• Main Authors: Shi, Junjie, Li, Hailian, Genest, Alexander, Zhao, Weixuan, Qi, Pengfei, Wang, Tao, Rupprechter, Günther
• Format: Article
• Language: English
• Subjects: Absorption; Asymmetric oxygen vacancy; Asymmetry; Catalysis; Catalytic activity; Ceria-praseodymia mixed oxides; Cerium oxides; Clusters; Density functional theory; Fine structure; Free energy; Gold; Heat of formation; Mixed oxides; Nanoparticles; Oxygen; Photoelectron spectroscopy; Photoelectrons; Photoemission; Raman spectroscopy; Shift reaction; Spectroscopy; Spectrum analysis; Supported gold clusters; Ultrastructure; Vacancies; Volcanoes; Water gas; Water gas shift reaction; X ray absorption; X ray photoelectron spectroscopy
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2021.120789

Modifying and controlling sites at the metal/oxide interface is an effective way of tuning catalytic activity, beneficial for bifunctional catalysis by reducible oxide supported metal nanoparticles. We employed mixed ceria-praseodymia supported Au clusters for the water gas shift reaction (WGSR). Varying the Ce: Pr ratio (4:1, 2:1, 1:4) not only allows to control the number of oxygen vacancies but, even more important, their local coordination, with asymmetrically coordinated O# being most active for water activation. These effects have been examined by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, temperature programmed desorption/reduction (TPD/TPR), and density functional theory (DFT). Using the WGSR performance of Au/CeOx as reference, Au/Ce4Pr1Ox was identified to exhibit the highest activity, with a CO conversion of 75% at 300°, which is about 5-times that of Au/CeOx. Au/Ce4Pr1Ox also showed excellent stability, with the conversion still being 70% after 50 h time-on-stream at 300 °. Although a higher Pr content leads to more O vacancies, the catalytic activity showed a “volcano behavior”. Based on DFT, this was rationalized via the formation energy of oxygen vacancies, the binding energy of water, and the asymmetry of the O# site. The presented route of creating active vacancy sites should also be relevant for other heterogeneous catalytic systems. The activity of ceria-praseodymia supported Au clusters in WGSR does not simply depend on the number of oxygen vacancies, but specifically on the presence of asymmetric O# sites. [Display omitted] •Ceria-praseodymia mixed oxide supported Au cluster catalysts were prepared by a combined hydrothermal and deposition-precipitation method.•In water gas shift, Au/Ce4Pr1Ox exhibited high activity (TOF 2.0 s−1, 360 °C) and long-term stability (50 h, 300 °C).•Combined experimental and theoretical studies reveal the effect of Pr doping on the chemical environment of O#.•The high catalytic activity of Au/Ce4Pr1Ox is attributed to asymmetric O vacancies which facilitate H2O dissociation.