Hydrogenation of ethylene over palladium: evolution of the catalyst structure by operando synchrotron-based techniques.

Palladium-based catalysts are exploited on an industrial scale for the selective hydrogenation of hydrocarbons. The formation of palladium carbide and hydride phases under reaction conditions changes the catalytic properties of the material, which points to the importance of operando characterization for determining the relation between the relative fractions of the two phases and the catalyst performance. We present a combined time-resolved characterization by X-ray absorption spectroscopy (in both near-edge and extended regions) and X-ray diffraction of a working palladium-based catalyst during the hydrogenation of ethylene in a wide range of partial pressures of ethylene and hydrogen.

Local Structures of Oxygen-Deficient Perovskite SrScGaO Polymorphs Explored by Total Neutron Scattering and EXAFS Spectroscopy.

Depending on the synthesis route, the oxygen ion electrolyte SrScGaO shows two polymorphs, a brownmillerite and a cubic perovskite framework. In order to better explore oxygen diffusion pathways and mechanisms, we report here on a multitechnical approach to characterize local structural changes for SrScGaO polymorphs as a function of temperature, using a neutron pair distribution function (PDF) analysis together with an extended X-ray absorption fine structure (EXAFS) analysis. While for the brownmillerite type structure PDF and Rietveld refinements yield identical structural descriptions, considerable differences are found for the cubic oxygen-deficient polymorph.

Phase Transformations in the CeO-SmO System: A Multiscale Powder Diffraction Investigation.

The structure evolution in the CeO-SmO system is revisited by combining high resolution synchrotron powder diffraction with pair distribution function (PDF) to inquire about local, mesoscopic, and average structure. The CeO fluorite structure undergoes two phase transformations by Sm doping, first to a cubic (C-type) and then to a monoclinic (B-type) phase. Whereas the C to B-phase separation occurs completely and on a long-range scale, no miscibility gap is detected between fluorite and C-type phases.

Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory.

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1  nm length scale that differ substantially from the low-temperature long-range spin arrangement.

Percolating hierarchical defect structures drive phase transformation in Ce1-x Gd x O2-x/2: a total scattering study.

A new hierarchical approach is presented for elucidating the structural disorder in Ce1-x Gd x O2-x/2 solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materials via an analysis of disorder on the mesocopic scale. Real-space (pair distribution function) and reciprocal-space (Rietveld refinement and microstructure probing) analysis of X-ray powder diffraction data and electron spin resonance (ESR) investigations were carried out following this approach.

Crystal structures of eight mono-methyl alkanes (C26-C32) via single-crystal and powder diffraction and DFT-D optimization.

The crystal structures of eight mono-methyl alkanes have been determined from single-crystal or high-resolution powder X-ray diffraction using synchrotron radiation. Mono-methyl alkanes can be found on the cuticles of insects and are believed to act as recognition pheromones in some social species, e.g.

Reducing the dehydrogenation temperature of lithium hydride through alloying with germanium.

LiH is a highly stable light metal hydride with a hydrogen capacity of 12.5 wt%. However, having a dehydrogenation enthalpy, ΔH(dehy), of 181.

In situ pair distribution function study on lanthanum doped ceria.

Doped ceria materials are widely studied for their application in solid oxide fuel cell devices. In this work we report on the average and local structure evolution of La-doped ceria (Ce(1-x)La(x)O(2-x/2), x = 0.25) under fuel cells' operating conditions.

Inclusion properties of volatile organic compounds in a calixarene-based organic zeolite.

The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients.

Acetylene and argon adsorption in a supramolecular organic zeolite.

The adsorption properties of a new nanoporous organic zeolite with respect to acetylene and Ar were studied by volumetric adsorption analysis, microcalorimetric experiments, and synchrotron high-resolution X-ray powder diffraction. This allowed us to locate the guest molecules inside the host channels and characterize the host-guest interactions.

Magnesium imide: synthesis and structure determination of an unconventional alkaline earth imide from decomposition of magnesium amide.

Magnesium imide (MgNH) was produced by monitoring the decomposition process of magnesium amide with in situ neutron diffraction. Significant changes in the structure of magnesium amide are detected during heat treatment and eventually result in the formation of crystalline MgNH. A model for the crystal structure of magnesium imide (MgNH) is presented for the first time.

Fullerenium salts: a new class of C60-based compounds.

We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF(5). The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice.

Molecular and crystalline structures of three (S)-4-alkoxycarbonyl-2-azetidinones containing long alkyl side chains from synchrotron X-ray powder diffraction data.

The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active beta-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-beta-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase density-functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD.

Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculations.

The molecular and crystalline structure of ethyl 1',2',3',4',4a',5',6',7'-octahydrodispiro[cyclohexane-1,2'-quinazoline-4',1''-cyclohexane]-8'-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006).

From average to local structure: a Rietveld and an atomic pair distribution function (PDF) study of selenium clusters in zeolite-NdY.

The structure of Se particles in the approximately 13 A diameter alpha-cages of zeolite NdY has been determined by Rietveld refinement and pair distribution function (PDF) analysis of X-ray data. With the diffuse scattering subtracted an average structure comprised of an undistorted framework containing nanoclusters of 20 Se atoms is observed. The intracluster correlations and the cluster-framework correlations which give rise to diffuse scattering were modeled by using PDF analysis.

trans-Decahydronaphthalene (decalin) from powder diffraction data.

The title compound, C(10)H(18), a decalin stereoisomer, crystallizes with Z' = 0.5 in the space group P2(1)/n. The trans-decalin molecule is located on an inversion centre with both rings in a chair conformation, making for a quasi-flat overall shape.

Electron diffraction, X-ray powder diffraction and pair-distribution-function analyses to determine the crystal structures of Pigment Yellow 213, C23H21N5O9.

The crystal structure of the nanocrystalline alpha phase of Pigment Yellow 213 (P.Y. 213) was solved by a combination of single-crystal electron diffraction and X-ray powder diffraction, despite the poor crystallinity of the material.

Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between squaric acid and 4,4'-bipyridine.

We have applied a combination of spectroscopic and diffraction methods to study the adduct formed between squaric acid and bypridine, which has been postulated to exhibit proton transfer associated with a single-crystal to single-crystal phase transition at ca. 450 K. A combination of X-ray single-crystal and very-high flux powder neutron diffraction data confirmed that a proton does transfer from the acid to the base in the high-temperature form.

Structure and superconductivity of LiFeAs.

Lithium iron arsenide phases with compositions close to LiFeAs exhibit superconductivity at temperatures at least as high as 16 K, demonstrating that superconducting [FeAs](-) anionic layers with the anti-PbO structure type occur in at least three different structure types and with a wide range of As-Fe-As bond angles.

Molecular and crystalline structure of cycloheptanespiro-3'(4'H)-6',7',8',9'-tetrahydrocyclohexa[b][1,4]thiazole-2'(5'H)-thione from powder synchrotron X-ray diffraction data.

A series of bidentate nitrogen-sulfur pro-ligands has been designed and synthesized with the purpose of introducing a structural modification that favours the tetrahedral site distortions of metalloprotein systems with metallic centers surrounded by ligands containing two N atoms and two S atoms as donor groups. Some of these new pro-ligands were obtained only as powders. Here we present the molecular and crystalline structure of cycloheptanespiro-3'(4'H)-6',7',8',9'-tetrahydrocyclohexa[b][1,4]thiazole-2'(5'H)-thione (I) solved and refined from powder synchrotron X-ray diffraction data.

Reversible gas uptake by a nonporous crystalline solid involving multiple changes in covalent bonding.

Hydrogen chloride gas (HCl) is absorbed (and reversibly released) by a nonporous crystalline solid, [CuCl2(3-Clpy)2] (3-Clpy = 3-chloropyridine), under ambient conditions leading to conversion from the blue coordination compound to the yellow salt (3-ClpyH)2[CuCl4]. These reactions require substantial motions within the crystalline solid including a change in the copper coordination environment from square planar to tetrahedral. This process also involves cleavage of the covalent bond of the gaseous molecules (H-Cl) and of coordination bonds of the molecular solid compound (Cu-N) and formation of N-H and Cu-Cl bonds.