Valérie Paul-Boncour

Bio: Valérie Paul-Boncour is an academic researcher from University of Paris. The author has contributed to research in topics: Hydride & Neutron diffraction. The author has an hindex of 28, co-authored 183 publications receiving 2580 citations. Previous affiliations of Valérie Paul-Boncour include Centre national de la recherche scientifique.

Pt/CeO2 catalysts in crotonaldehyde hydrogenation: Selectivity, metal particle size and SMSI states

Abstract: Pt/CeO2 catalysts with different metal particle sizes were prepared by impregnation of chlorine-free precursor, Pt(NH3)4(NO3)2, with different Pt loadings (1, 3, 5, 10 wt%), on a commercial ceria. These catalysts and a CePt5 powder, which was regarded as a reference catalyst, were tested in the hydrogenation of crotonaldehyde as a function of the reduction treatment (from 473–973 K). A dramatic difference in the influence of the reduction temperature on the reactivity was observed between the high and low loaded metal catalysts: after reduction at 973 K, high selectivity to crotyl alcohol (83%) was observed on the high loaded catalyst while on the 1% Pt/CeO2, crotyl alcohol selectivity was below 35%. Characterization by TEM, XPS and XRD showed differences in the particle size distributions and the presence of various nanostructural modifications during the increase of the reduction temperature. On the other hand, the reactivity of CePt5 powder indicates no ability of this compound for the carbonyl bond hydrogenation. The different SMSI states which could influence the reactivity are discussed: formation of epitaxial Pt (1 1 1) layer on CeO2 instead of Pt–CeOx interfacial sites or CePt5 sites, has been retained to be responsible for the increase in crotyl alcohol selectivity.

Size-Dependent Hydrogen Sorption in Ultrasmall Pd Clusters Embedded in a Mesoporous Carbon Template

Abstract: Hydrogen sorption properties of ultrasmall Pd nanoparticles (2.5 nm) embedded in a mesoporous carbon template have been determined and compared to those of the bulk system. Downsizing the Pd particle size introduces significant modifications of the hydrogen sorption properties. The total amount of stored hydrogen is decreased compared to bulk Pd. The hydrogenation of Pd nanoparticles induces a phase transformation from fcc to icosahedral structure, as proven by in situ XRD and EXAFS measurements. This phase transition is not encountered in bulk because the 5-fold symmetry is nontranslational. The kinetics of desorption from hydrogenated Pd nanoparticles is faster than that of bulk, as demonstrated by TDS investigations. Moreover, the presence of Pd nanoparticles embedded in CT strongly affects the desorption from physisorbed hydrogen, which occurs at higher temperature in the hybrid material compared to the pristine carbon template.

Catalytic Properties of Ceria and CeO2-Containing Materials

Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Energy storage applications of activated carbons: supercapacitors and hydrogen storage

Abstract: Porous carbons have several advantageous properties with respect to their use in energy applications that require constrained space such as in electrode materials for supercapacitors and as solid state hydrogen stores. The attractive properties of porous carbons include, ready abundance, chemical and thermal stability, ease of processability and low framework density. Activated carbons, which are perhaps the most explored class of porous carbons, have been traditionally employed as catalyst supports or adsorbents, but lately they are increasingly being used or find potential applications in the fabrication of supercapacitors and as hydrogen storage materials. This manuscript presents the state-of-the-art with respect to the preparation of activated carbons, with emphasis on the more interesting recent developments that allow better control or maximization of porosity, the use of cheap and readily available precursors and tailoring of morphology. This review will show that the renewed interest in the synthesis of activated carbons is matched by intensive investigations into their use in supercapacitors, where they remain the electrode materials of choice. We will also show that activated carbons have been extensively studied as hydrogen storage materials and remain a strong candidate in the search for porous materials that may enable the so-called Hydrogen Economy, wherein hydrogen is used as an energy carrier. The use of activated carbons as energy materials has in the recent past and is currently experiencing rapid growth, and this review aims to present the more significant advances.