Morphology effects of nanocrystalline CeO2 on the preferential CO oxidation in H2-rich gas over Au/CeO2 catalyst

Hierarchical Au/CeO2 systems – influence of Ln3+ dopants on the catalytic activity in the propane oxidation process

The catalytic activity of the hierarchical tube-like Au/Ce1−xLnxO2−x/2 in the propane oxidation process depends not only on the presence of Au nanoparticles on the support surface but also on the type of deformation in the CeO2 network.

Morphology effect of ceria supports on gold nanocluster catalyzed CO oxidation

The interfacial perimeter is generally viewed as the catalytically active site for a number of chemical reactions over oxide-supported nanogold catalysts. Here, well-defined CeO₂ nanocubes, nanorods and nanopolyhedra are chosen to accommodate atomically precise clusters (e.g. Au₂₅(PET)₁₈) to give different Au cluster-CeO₂ interfaces. TEM images show that Au particles of ∼1.3 nm are uniformly anchored on the ceria surface after annealing in air at 120 °C, which can rule out the size hierarchy of nanogold in CO oxidation studies. The gold nanoclusters are only immobilized on the CeO₂(200) facet in Au₂₅/CeO₂-C, while they are selectively loaded on CeO₂(002) and (111) in the Au₂₅/CeO₂-R and Au₂₅/CeO₂-P catalysts. X-ray photoelectron spectroscopy (XPS) and in situ infrared CO adsorption experiments clearly demonstrate that the gold species in the Au₂₅/CeO₂ samples are similar and partially charged (Au ^δ+, where 0 < δ < 1). It is observed that the catalytic activity decreases in the order of Au/CeO₂-R ≈ Au/CeO₂-P > Au/CeO₄-C in the CO oxidation. And the apparent activation energy over Au₂₅/CeO₂-C (60.5 kJ mol^-1) is calculated to be about two-fold of that over the Au₂₅/CeO₂-R (28.6 kJ mol^-1) and Au₂₅/CeO₂-P (31.3 kJ mol^-1) catalysts. It is mainly tailored by the adsorbed [O] species on the ceria surface, namely, Au₂₅/CeO₂(002) and Au₂₅/CeO₂(111) which were more active than the Au₂₅/CeO₂(200) system in the CO oxidation. These insights at the molecular level may provide guidelines for the design of new oxide-supported nanogold catalysts for aerobic oxidations.

Atomic Scale Characterization of Fluxional Cation Behavior on Nanoparticle Surfaces: Probing Oxygen Vacancy Creation/Annihilation at Surface Sites

Oxygen vacancy creation and annihilation are key processes in nonstoichiometric oxides such as CeO₂. The oxygen vacancy creation and annihilation rates on an oxide's surface partly govern its ability to exchange oxygen with the ambient environment, which is critical for a number of applications including energy technologies, environmental pollutant remediation, and chemical synthesis. Experimental methods to probe and correlate local oxygen vacancy reaction rates with atomic-level structural heterogeneities would provide significant information for the rational design and control of surface functionality; however, such methods have been unavailable to date. Here, we characterize picoscale fluxional behavior in cations using time-resolved in situ aberration-corrected transmission electron microscopy to locate atomic-level variations in oxygen vacancy creation and annihilation rates on oxide nanoparticle surfaces. Low coordination number sites such as steps and edges, as well as locally strained sites, exhibited the greatest number of cation displacements, implying enhanced surface oxygen vacancy activity at these sites. The approach has potential applications to a much wider class of materials and catalysis problems involving surface and interfacial transport functionalities.

Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide

We reviewed recent advances in catalysts for PROX with emphasis on synergistic effects that contribute to enhanced catalytic performance.

Divergent influence of {1 1 1} vs. {1 0 0} crystal planes and Yb3+ dopant on CO oxidation paths in mixed nano-sized oxide Au/Ce1−xYbxO2−x/2 (x = 0 or 0.1) systems

In this paper, the fundamental information on interactions in systems concerning nanocrystalline gold disperses on the shaped (octahedron-like or cube-like) Ce_1−xYb_xO_2−x/2 (x = 0 or 0.1) support has been discussed.

Oxygen vacancies on nanosized ceria govern the NOxstorage capacity of NSR catalysts

The oxygen vacancies on Pt/BaO/CeO₂govern the NO_xstorage capacity by creating efficient sites or channels for nitrate formation and its further transformation to Ba-based storage sites.

High oxygen storage capacity and enhanced catalytic performance of NiO/NixCe1−xO2−δ nanorods: synergy between Ni-doping and 1D morphology

NiO/Ni-doped ceria nanorods have been synthesized. Their unique structure combines specific composition and 1D morphology, which provide great improvements in their physical chemical properties.

Catalytic oxidation of CO on metals involving an ionic process in the presence of H2O: the role of promoting materials

A new catalytic oxidation of CO is enhanced by H₂O molecule on the Pt and Au with specific promoting materials where the rate-determining reaction of HCOO(a) + OH → CO₂ + H₂O is promoted by repeated contribution of OH⁻ anion via messenger molecule H₂O.

Morphological effects of the nanostructured ceria support on the activity and stability of CuO/CeO2 catalysts for the water-gas shift reaction

Three CuO/CeO2 catalyst with different morphologies of ceria, namely nanospheres, nanorods and nanocubes, were synthesized and used to catalyze the water-gas shift (WGS) reaction. The reactivity tests showed that the Cu supported on the ceria nanospheres exhibited both the highest activity and superior stability when compared with the nanocube and nanorod ceria catalysts. Operando X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) methods were used to characterize these catalysts in their working state. High resolution electron microscopy (HRTEM, STEM) was used to look at the local atomic structure and nano-scale morphology. Our results show that the morphology of the ceria support, which can involve different crystal faces and concentrations of defects and imperfections, has a critical impact on the catalytic properties and influences: (1) the dispersion of CuO in the as-synthesized catalyst; (2) the particle size of metallic Cu upon reduction during the WGS reaction, (3) the stability of the metallic Cu upon variations of temperature, and (4) the dissociation of water on the ceria support. The nanosphere ceria catalyst showed an excellent water dissociation capability, the best dispersion of Cu and a strong Cu-Ce interaction, therefore delivering the best performance among the three WGS catalysts. The metallic Cu, which is the active species during the WGS reaction, was more stabilized on the nanospheres than on the nanorods and nanocubes and thus led to a better stability of the nanosphere catalyst than the other two architectures. Each catalyst exhibited a distinctive line-shape in the 800-1600 cm(-1) region of the DRIFTS spectra, pointing to the existence of different types of carbonate or carboxylate species as surface intermediates for the WGS.

Exposed surfaces on shape-controlled ceria nanoparticles revealed through AC-TEM and water-gas shift reactivity

Aberration-corrected transmission electron microscopy and high-angle annular dark field imaging was used to investigate the surface structures and internal defects of CeO2 nanoparticles (octahedra, rods, and cubes). Further, their catalytic reactivity in the water-gas shift (WGS) reaction and the exposed surface sites by using FTIR spectroscopy were tested. Rods and octahedra expose stable (111) surfaces whereas cubes have primarily (100) facets. Rods also had internal voids and surface steps. The exposed planes are consistent with observed reactivity patterns, and the normalized WGS reactivity of octahedra and rods were similar, but the cubes were more reactive. In situ FTIR spectroscopy showed that rods and octahedra exhibit similar spectra for -OH groups and that carbonates and formates formed upon exposure to CO whereas for cubes clear differences were observed. These results provide definitive information on the nature of the exposed surfaces in these CeO2 nanostructures and their influence on the WGS reactivity.