Structure Sensitivity of Ceria-Supported Au Catalysts for CO Oxidation

Atomically dispersed Au anchored on CeO2to enhancing the antioxidant activity

The modification of Au nanoparticles can improve the antioxidant activity of CeO₂, however, nano Au/CeO₂has also met some problems such as low atomic utilization, the limit of reaction conditions, and high cost. Au single atom catalysts can well solve the above-mentioned problems, but there are some contradictory results about the activity of single atom Au₁/CeO₂and nano Au/CeO₂. Here, we synthesized rod-like Au single atom Au/CeO₂(0.4% Au₁/CeO₂) and nano Au/CeO₂(1% Au/CeO₂, 2% Au/CeO₂and 4% Au/CeO₂), and their antioxidant activity from strong to weak is 0.4% Au₁/CeO₂, 1% Au/CeO₂, 2% Au/CeO₂and 4% Au/CeO₂, respectively. The higher antioxidant activity of 0.4% Au₁/CeO₂is mainly due to the high Au atomic utilization ratio and the stronger charge transfer between Au single atoms and CeO₂, resulting in the higher content of Ce³⁺. Due to the coexistence of Au single atoms and Au NPs in 2% Au/CeO₂, the antioxidant activity 2% Au/CeO₂is higher than that of 4% Au/CeO₂. And the enhancement effect of Au single atoms was not affected by the concentration of ·OH and material concentration. These results can promote the understanding of the antioxidant activity of 0.4% Au₁/CeO₂and promote its application.

In Situ Spectroscopy and Microscopy Insights into the CO Oxidation Mechanism on Au/CeO2(111)

In this work, we prepared and investigated in ultra-high vacuum (UHV) two stoichiometric CeO₂(111) surfaces containing low and high amounts of step edges decorated with 0.05 ML of gold using synchrotron-radiation photoelectron spectroscopy (SRPES) and scanning tunneling microscopy (STM). The UHV study helped to solve the still unresolved puzzle on how the one-monolayer-high ceria step edges affect the metal-substrate interaction between Au and the CeO₂(111) surface. It was found that the concentration of ionic Au⁺ species on the ceria surface increases with increasing number of ceria step edges and is not correlated with the concentration of Ce³⁺ ions that are supposed to form on the surface after its interaction with gold nanoparticles. We associated this with an additional channel of Au⁺ formation on the surface of CeO₂(111) related to the interaction of Au atoms with various peroxo oxygen species formed at the ceria step edges during the film growth. The study of CO oxidation on the highly stepped Au/CeO₂(111) model sample was performed by combining near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), UHV-STM, and near-ambient-pressure STM (NAP-STM). This powerful combination provided comprehensive information on the processes occurring on the Au/CeO₂(111) surface during the interaction with CO, O₂, and CO + O₂ (1:1) mixture at conditions close to the real working conditions of CO oxidation. It was found that the system demonstrates high stability in CO. However, the surface undergoes substantial chemical and morphological changes as the O₂ is added to the reaction cell. Already at 300 K, gold nanoparticles begin to grow using a mechanism that involves the disintegration of small gold nanoparticles in favor of the large ones. With increasing temperature, the model catalyst quickly transforms into a system of primarily large Au particles that contains no ionic gold species.

Effects of the Crystalline Properties of Hollow Ceria Nanostructures on a CuO-CeO2 catalyst in CO Oxidation

The development of an efficient and economic catalyst with high catalytic performance is always challenging. In this study, we report the synthesis of hollow CeO2 nanostructures and the crystallinity control of a CeO2 layer used as a support material for a CuO-CeO2 catalyst in CO oxidation. The hollow CeO2 nanostructures were synthesized using a simple hydrothermal method. The crystallinity of the hollow CeO2 shell layer was controlled through thermal treatment at various temperatures. The crystallinity of hollow CeO2 was enhanced by increasing the calcination temperature, but both porosity and surface area decreased, showing an opposite trend to that of crystallinity. The crystallinity of hollow CeO2 significantly influenced both the characteristics and the catalytic performance of the corresponding hollow CuO-CeO2 (H-Cu-CeO2) catalysts. The degree of oxygen vacancy significantly decreased with the calcination temperature. H-Cu-CeO2 (HT), which presented the lowest CeO2 crystallinity, not only had a high degree of oxygen vacancy but also showed well-dispersed CuO species, while H-Cu-CeO2 (800), with well-developed crystallinity, showed low CuO dispersion. The H-Cu-CeO2 (HT) catalyst exhibited significantly enhanced catalytic activity and stability. In this study, we systemically analyzed the characteristics and catalyst performance of hollow CeO2 samples and the corresponding hollow CuO-CeO2 catalysts.

Confinement of nano-gold in 3D hierarchically structured gadolinium-doped ceria mesocrystal: synergistic effect of chemical composition and structural hierarchy in CO and propane oxidation

Gadolinium-doped ceria hierarchical gold catalyst shows four-fold TOF increase compared to undoped non-hierarchical system, proving the synergistic effect of doping and structural hierarchy in propane oxidation.