Selective oxidation of glycerol on morphology controlled ceria nanomaterials

Ceria has attracted great interest in heterogeneous catalysis due to its facile exchange between Ce3+ and Ce4+. In particular, in this work it is reported, for the first time, that morphology controlled ceria without any addition of other metal exhibits catalytic activity for the selective oxidation of glycerol. Singularly, ceria nanorods present the highest catalytic activity among all tested materials, which can be attributed to their highest surface area. Nevertheless, surface crystallography plays a key role in determining the catalytic activity and selectivity of these nanocatalysts, as proven by TEM, Raman and XPS analyses. In particular, the development of {111} ceria nanofacets on ceria nanocubes strongly affects both activity and selectivity in the selective oxidation of glycerol. On the other hand, Ce3+ surface content cannot be discarded as an important factor in the catalytic activity of ceria nanoparticles for this specific redox reaction.Ministerio de Ciencia, Innovación y Universidades (España)Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

Low-Lanthanide-Content CeO2/MgO Catalysts with Outstandingly Stable Oxygen Storage Capacities: An In-Depth Structural Characterization by Advanced STEM Techniques

International audienceA novel CeO2/MgO catalyst with low ceria loading has been synthesized. This catalyst showed unique redox properties compared with conventional high and low surface area CeO2. Advanced (scanning) transmission electron microscopy techniques revealed the presence of a variety of highly dispersed ceria nanostructures: isolated CeOx entities, CeO2 clusters, as well as fairly small (<5nm) CeO2 nanoparticles. More interestingly, this CeO2/MgO catalyst showed outstanding stability in its redox response against high temperature aging treatments. Thus, after reduction in hydrogen at 950 degrees C and further oxidation at 500 degrees C, CeO2 reduction effects took still place at low temperatures, and no significant loss of oxygen storage capacity (OSC) was detected. Unique ceria-bilayer nanostructures were found and characterized in the aged catalyst. Their peculiar structural and chemical properties seem to be responsible for the large improvement observed in the stability of the redox response

Enhanced Hydroxyl Radical Scavenging Activity by Doping Lanthanum in Ceria Nanocubes

Ceria nanoparticles have been reported to possess special antioxidant and catalytic properties due to their unique redox characteristics. In this study, single-crystalline CeO₂ nanocubes were synthesized which demonstrated hydroxyl radical scavenging properties. In order to further enhance such activity, 10% lanthanum (La) was doped into the nanocubes by a hydrothermal method. The as-synthesized, La-modified ceria nanocubes presented improved radical scavenging activity spanning a range of concentrations and durations. The structure and redox behavior of the nanocubes were characterized using X-ray diffraction (XRD), inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), high resolution electron microscopy (HREM), temperature-programmed reduction (TPR), oxygen storage capacity (OSC), etc. A mechanism was proposed on how the incorporation of La could affect the redox as well as scavenging properties of CeO₂ nanocubes. This new nanomaterial may be potentially used as protective agent in bioapplications

Improved Oxidase Mimetic Activity by Praseodymium Incorporation into Ceria Nanocubes

Ceria nanocubes (NC) modified with increasing concentrations of praseodymium (5, 10, 15, and 20 mol %) have been successfully synthesized by a hydrothermal method. The as-synthesized Pr-modified ceria nanocubes exhibit an enhanced oxidase-like activity on the organic dye TMB within a wide range of concentrations and durations. The oxidase activity increases with increasing Pr amounts in Pr-modified ceria nanocubes within the investigated concentration range. Meanwhile, these Pr-modified ceria nanocubes also show higher reducibility than pure ceria nanocubes. The kinetics of their oxidase mimetic activity is fitted with the Michaelis–Menten equation. A mechanism has been proposed on how the Pr incorporation could affect the energy level of the bands in ceria and hence facilitate the TMB oxidation reaction. The presence of Pr³⁺ species on the surface also contributes to the increasing activity of the Pr-modified ceria nanocubes present higher oxidase activity than pure ceria nanocubes

Local Distortions in Nanostructured Ferroelectric Ceramics through Strain Tuning

Ferroelectric materials are highly sensitive to grain size reduction because strain and ferroelectric polarization have a direct connection. Using 15 nm (Ba,Sr)TiO3 particles obtained by advanced supercritical synthesis and their densification by high-pressure spark plasma sintering under air, reproducible and dense nanostructured ceramics are achieved. Taking advantage of the high pressure (up to 600 MPa) applied during the sintering step, the internal stress generated at the grain scale can be monitored to compensate for the particle surface stress due to size effect. Both the local dynamics observed by Raman scattering and the overall dielectric behavior consistently indicate a recovery of the ferroelectric properties as the sintering pressure is increased. This unique behavior shows that low-temperature and high-pressure processing enables designing nanostructured functional ceramics exhibiting original properties.Corrélations entre Architecture, Interfaces et Fonctionnalités dans les multi-matériaux Ferroélectriques :Frittage Flash et caractérisations multi-échelle 3