Biomedical subjects

P Sautet

Publications and source records attributed to P Sautet.

14 recordsLinked to original sources

PubMed2005

A combined experimental and theoretical evaluation of the structure of hydrated microporous aluminophosphate AlPO4-18.

Water adsorption in the microporous aluminophosphate AlPO4-18 is studied by a combination of solid-state NMR, X-ray diffraction, and density functional theory calculations. The change of the framework structure upon hydration is moderate, and NMR gives local information on the environment of Al and P atoms. The structural distribution of water molecules in the channels has been explored by a combination of first-principle molecular dynamics simulations and of static geometry optimizations. Two starting points have been considered for the calculations. If the structure of the dehydrated aluminophosphate is used, the simulation result is not satisfactory with an incomplete hydration and no agreement with NMR results. Starting from a partial refinement of the aluminophosphate framework for the hydrated system, a structure with six tetrahedral and six octahedral Al atoms in the unit cell is obtained, involving twelve water molecules coordinated to Al atoms and twelve others in the channels, and in good agreement with experimental data.

Journal Article↗

PubMed2005

First-principles study of CO adsorption and vibration on Au surfaces.

A CO stretching frequency analysis is presented for the adsorption of CO on various Au(110) surfaces from density functional theory calculations. The structure sensitivity of the adsorption has been studied by considering the unreconstructed (1 x 1) surface, the missing-row reconstructed (1 x 2) surface, the vicinal stepped (20) surface, and the adsorption on adatoms deposited on the (110)-(1 x 2) surface. The calculated CO stretching frequencies are compared with infrared reflection-absorption spectroscopy (IRAS) measurements carried out at room temperature and pressure below 1 atm. The overall stability of the systems is discussed within the calculations of surface free energies at various coverages. At room temperature, the adsorption of CO on the ridge of the missing-row reconstructed surface competes in the high pressure regime with more complex adsorption structures where the molecule coadsorbs on the ridge and on adatoms located along the empty troughs of the reconstruction. This result is supported by the CO stretching frequency analysis.

Journal Article↗

PubMed2004

Understanding the high activity of a nanostructured catalyst obtained by a deposit of Pd on Ni: first principle calculations.

The catalytic activity of a 4 monolayer deposit of Pd on a Ni(110) surface toward the hydrogenation of ethylene is investigated by using gradient-corrected periodic density functional calculations. The Pd/Ni(110) surface is strongly nanostructured, due to the anisotropic stress induced by the Ni(110) substrate on the Pd layer. A kinetic analysis, based on the investigation of the optimal reaction pathway for the hydrogenation of ethylene to ethane, is presented, allowing a comparison between Pd/Ni(110) and pure Pd(110) surfaces. The calculated activation energies allow one to reproduce the experimental result, which shows that the Pd/Ni(110) surface is about 30 times more active than the pure Pd(110) surface. This marked increase of the catalytic activity is a consequence of the specific nanostructure of the Pd/Ni(110) surface. By examining the structure of the adsorbed species and of the transition states and by analyzing the electronic properties, we show that this rate increase can be associated to the fact that the ethylene adsorption energy in the first hydrogenation step and the ethyl-hydrogen coadsorption energy in the second step are both much lower on Pd/Ni(110) than on pure Pd(110).

Journal Article↗

PubMed2002

Highly strained structure of a four-layer deposit of Pd on Ni(110): a coupled theoretical and experimental study.

The structure of a four monolayer deposit of Pd on Ni(110) has been determined by a combination of x-ray diffraction experiments and density-functional theory calculations. This Pd film presents, after annealing at 500 K, a (Nx2) reconstruction associated with a large enhancement of its catalytic activity. The N superstructure, along the dense [11;0] direction, comes from periodic edge dislocations initiated by a vacancy in the first Pd layer. In the perpendicular direction, the doubling of the period originates in a pairing-buckling displacement of the rows. This study evidences a new Pd atoms arrangement with quasi-four-fold hollow sites on the surface, which could play an important role in the exceptional catalytic activity.

Journal Article↗

PubMed2001

Surface temperature dependence of rotational excitation of H(2) scattered from Pd(111).

Classical dynamics simulations are performed to study rotational excitation of H(2) scattered from Pd(111), taking into account energy exchange with surface phonons through a 3D surface oscillator model. We show that dynamic trapping, identified recently in the study of dissociation dynamics, plays a prominent role. The corresponding long interaction time due to several recollisions allows an efficient energy exchange between H(2) molecules and surface phonons. This microscopic mechanism explains the puzzling experimental finding on the role of surface temperature in H(2)(nu = 0,J = 1-->3) excitation.

Journal Article↗

PubMed2001

Stability of chiral domains produced by adsorption of tartaric acid isomers on the Cu(110) surface: a periodic density functional theory study.

In the present work the interaction of different bitartrate isomers on the Cu(110) surface has been investigated systematically by using the Vienna Ab-initio Simulation Package (VASP), which performs periodical density functional theory (DFT) calculations. Among all bitartrate isomers the R,R-configuration is the most stable under the (3 1, 1 2) domain on the Cu surface. Its optical isomer, the S,S-bitartrate, is 10 kJ mol(-)(1) less stable in the same domain. This energy difference is sufficient to produce the distinct chiral assemblies observed after the adsorption of each optical isomer on the Cu surface. The calculations also showed that these domains are not formed due to intermolecular H-bonds, in contrast with the previous proposal by Raval et al.(Nature 2000, 23, 376). In fact, there is a formation of optimal intramolecular H-bonds in the chemisorption structures. A favorable packing orientation is also needed for the respective chiral domains. For instance, the S,S-configuration suffers from a destabilizing packing energy of 21 kJ mol(-)(1) under the same domain, due to a short contact between the H atoms of the hydroxy groups. These intramolecular H-bonds cause also some distortions on the bitartrate molecule, which appear to be dependent on the relative position of the alpha-hydroxy groups. The stability of the extended asymmetric domains, when the surface is modified by a chiral additive, might have important consequences for understanding and optimizing the properties of enantioselective heterogeneous catalysts.

Journal Article↗

PubMed2000

Imaging the surface and the interface atoms of an oxide film on Ag111 by scanning tunneling microscopy: experiment and theory

High-resolution images of the vacuum oxide surface atomic structure of Ag111-p(4x4)-O reveal large terraces of a perfect (4x4) reconstruction. Under certain conditions, the surface Ag atoms at the interface between the reconstructed oxide layer and the underlying Ag111 lattice are also imaged, providing the structural registry. Scanning tunneling microscopy simulations reveal a strong sensitivity to structure and comparison with the experimental images, therefore providing an atom-by-atom model for the entire metal-oxide-vacuum structure.

Journal Article↗

PubMed1996