Catalysis to discriminate single atoms from subnanometric ruthenium particles in ultra-high loading catalysts

We report a procedure for preparing ulta-high metal loading (10-20 % w/w Ru) Ru@C60 nanostructured catalysts comprising exclusively Ru single atoms. We show that by changing the Ru/C60 ratio and the nature of the solvent used during the synthesis, it is possible to increase the Ru loading up to 50% w/w, and to produce hetero-structures containing subnanometric Ru nanoparticles. Several techniques such as high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy – high angle annular dark field (STEM-HAADF), Raman spectroscopy, wideangle X-ray scattering (WAXS), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS) together with theoretical calculations were used to characterize these materials. At such high metal loading, the distinction between Ru single atoms and clusters is not trivial, even with this combination of techniques. We evaluated the catalytic properties of these materials for the hydrogenation of nitrobenzene and 2,3-dimethyl-2-butene. The catalysts containing only Ru single atoms are much less active for these reactions than the ones containing clusters. For nitrobenzene hydrogenation, this is because electro-deficient Ru single atoms and few atom Run clusters are not performant for H2 activation compared to larger clusters (n ≥ 13), as shown by density functional theory (DFT) calculations. For the more crowded substrate 2,3-dimethyl-2-butene, DFT calculations have shown that this is due to steric hindrance. These simple tests can thus been used to distinguish samples containing metallic sub-nanometer nanoparticles. These novel catalysts are also extremely active for the hydrogenation of -substituted 2,3-dimethyl-2-butene

Polymer versus phosphine stabilized Rh nanoparticles as components of supported catalysts : implication in the hydrogenation of cyclohexene model molecule

The solution synthesis of rhodium nanoparticles (Rh NPs) was achieved from the organometallic complex [Rh(η³-C₃H₅)₃] under mild reaction conditions in the presence of a polymer (PVP), a monophosphine (PPh₃) and a diphosphine (dppb) as a stabilizer, leading to very small Rh NPs of 2.2, 1.3 and 1.7 nm mean size, with PVP, PPh3 and dppb, respectively. The surface properties of these nanoparticles were compared using a model catalysis reaction namely, hydrogenation of cyclohexene, first under colloidal conditions and then under supported conditions after their immobilization onto an amino functionalized silica-coated magnetite support. PVP-stabilized Rh NPs were the most active catalyst whatever the catalytic conditions as a result of a strong coordination of the phosphine ligands at the metal surface that blocks some surface atoms even after several recycles of the supported nanocatalysts and limit the reactivity of the metallic surface

"Brace Technology" Thematic Series - The Lyon approach to the conservative treatment of scoliosis

<p>Abstract</p> <p/> <p>The Lyon Brace, or adjustable multi-shell brace, has been used for more than 60 years.</p> <p>The use and function of the Lyon Brace includes:</p> <p>- The utilization of one or two corrective plaster casts, which enables a true lengthening of the concave ligaments.</p> <p>- An oriented CAD-CAM moulding in 3D auto correction after the removal of the plaster cast.</p> <p>- A blueprint adapted to Lenke's classification.</p> <p>- A specific physiotherapy program.</p> <p>Background</p> <p>Pierre Stagnara created the Lyon Brace in 1947. The brace has the following characteristics:</p> <p>- It adjusts to allow for a child's growth of up to seven centimetres and for an increase in weight of up to seven kilograms.</p> <p>- It is 'active' in that the rigidity of the PMM (polymetacrylate of methyl) structure stimulates the user to auto-correct. The active axial auto-correction decreases the pressures of the brace on the trunk.</p> <p>- It is decompressive in that the effect of extension between the two pelvic and scapular girdles decreases the pressure on the intervertebral disc allowing for more effective pushes in the other planes.</p> <p>- It is symmetrical making it both more aesthetically pleasing and easier to build.</p> <p>- It is stable at both shoulders and pelvic girdle, facilitating the intermediate 3D corrections.</p> <p>- It is transparent. The pressure of the shells on the skin can be directly controlled so "pads" are usually not necessary.</p> <p>Brace description</p> <p>Two metal bars are fixed vertically, one anterior the other posterior and all shells are attached from the bottom to the top in this order:</p> <p>- Two pelvic shells ensure an optimal stability of the brace.</p> <p>- One lumbar shell T12-L4, which can be either independent or extending, at the abdominal chondrocostal level.</p> <p>- One thoracic shell at the level of the thoracic convexity.</p> <p>- One opposite thoracic shell used as a counter push.</p> <p>- One shoulder balance shell on the side of the thoracic convexity.</p> <p>Long term follow up results</p> <p>This is a retrospective study of 1,338 completed treatments checked a minimum of two years after weaning from the brace.</p> <p>Only 5% of the curves progressed more than 5° from the initial magnitudes. This translates to an effectiveness index of 0.95.</p> <p>A subset of 174 subjects who started treatment at Risser 0 was isolated. The global progressive angular mean curve was superimposed on the statistic general curve and the effectiveness index was calculated at 0.80.</p> <p>The Surgery rate was just 2% of the patients presenting with an initial curve below 45°.</p> <p>Conclusion</p> <p>The Lyon Brace is the historical reference of bracing AIS. To be fully effective, it requires the patient to wear a plaster cast for at least one month and receive specific physiotherapy training. Although this is a retrospective study, the results are very positive, and clearly indicate a need for a prospective study.</p

Substrate-dependent valency of Yb chemisorbed onto Si(111)7&#215;7, Si(100)2&#215;1, and a-Si surfaces

Yb chemisorption at monolayer coverages onto Si substrates is the precursor stage of Yb/Si interface formation. Ytterbium is divalent as a metal but forms mixed-valent intermetallic compounds with silicon. L-edge x-ray-absorption resonance measurements show that at the early stage of the Yb/Si interface formation the Yb-Si chemisorption on different Si substrates induces mixed valency in the Yb atoms chemisorbed on the a-Si surface sites and a lower mixed valency in those on the Si(100) sites, but leaves purely divalent Yb ions on the Si(111) surface. This has direct consequences on the kinetics of the interface formation that develops for higher Yb coverages. Delocalization of Yb 4f electrons appears to be a unique electron probe of the bonding at semiconductor surfaces, and the Yb/Si interface can be viewed as a prototype case for understanding the kinetics of metal-semiconductor interface formation

THE GROWTH OF THE Pt/Si (111) 7 x 7 INTERFACES AS PROBED BY Pt L3 SEXAFS

SEXAFS and XARS on the Pt, L2, 3 edges for submonolayer and monolayer coverages on Si (111) 7 x 7 allow to recognize the growth mode of the Pt/Si silicide like interface, at room temperature. Chemisorption into sixfold interstitial sites in the top Si (111) double layer is followed by intermixing, and likely nucleation of Pt2Si coordinated clusters

Interstitial chemisorption and interface formation of Pt on Si(111) observed by surface extended x-ray-absorption fine-structure and L2,3-edge x-ray-absorption resonance spectroscopies

The first structural description of the Pt/Si(111)7\uc3\u977 interface formation at room temperature is derived from Pt L3-edge surface extended x-ray-absorption fine-structure spectroscopy and x-ray-absorption resonance spectroscopy. Pt chemisorbs in the top Si double-layer sixfold interstitial sites, introducing stress in the surface and subsurface. Above monolayer thicknesses Pt diffuses within the silicon substrate and, upon Pt enrichment of the intermixed phase, clusters with Pt2Si local coordination nucleate

X-ray absorption resonance spectroscopy as a local probe of the electronic structure at metal-semiconductor interfaces and silicide: Pt/Si, Pd/Si, and Yb/Si

Measurement of the distribution of the empty band states is one of the key problems for reaching a more complete understanding of the electronic structure of metal/semiconductor systems. X-ray absorption resonance on transition-metal (TM) L2,3edges are a probe of the presence and of the approximate distribution of d-like empty states. The results provide evidence of the existence of empty antibonding d-like states in the electronic structure of near-noble-metal/silicon interfaces and silicides; Yb L2.3resonances provide evidence of mixed valency in the Yb/Si system even for thin underreacted Yb/Si interfaces