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Identification and quantification of functional groups in activated carbons by means of a multi-technique approach.

The adsorption of H2 and CO over Pt/Al2O3 was studied in gas and in liquid phase by FT-IR and ATR-IR spectroscopies under otherwise similar conditions. The solvent competes with hydrogen and CO for terrace and kink metal sites.

The effect of nanosize and structural disorder on the MgCl2 support of Ziegler–Natta catalysts has been investigated in terms of induced changes to their vibrational spectroscopic fingerprint. In p...

The all-inorganic perovskite barium zirconate, BaZrO3, is a widely used material in a range of different technological applications. However, fundamental questions surrounding the crystal structure of BaZrO3, especially in regard to its ground-state structure, remain. While diffraction techniques indicate a cubic structure all the way down to T = 0 K, several first-principles phonon calculation studies based on density functional theory indicate an imaginary (unstable) phonon mode due to the appearance of an antiferrodistortive transition associated with rigid rotations of ZrO6 octahedra. The first-principles calculations are highly sensitive to the choice of exchange-correlation functional and, using six well-established functional approximations, we show that a correct description about the ground-state structure of BaZrO3 requires the use of hybrid functionals. The ground-state structure of BaZrO3 is found to be cubic, which is corroborated by experimental results obtained from neutron powder diffraction, inelastic neutron scattering, and neutron Compton scattering experiments.

Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxide ion conductivity at low temperatures. This is the longest time scale neutron scattering study of any fluorite-type solid electrolyte, and it represents only the second case of oxide ion dynamics in any material observed on a nanosecond time scale by quasielastic neutron scattering. Ab initio molecular dynamics simulations reveal two mechanisms that contribute to the oxide ion dynamics in the material: a slower diffusion process through the Bi-O sublattice and a faster process which corresponds to more localized dynamics of the oxide ions within the VO x coordination spheres. The length of the trajectories simulated and the validation of the simulations by neutron scattering experiments provide for the first time a quantitative insight into the relative contributions of the two processes to the oxide ion conduction in this exceptional solid electrolyte, which can be used to derive design principles for the preparation of related oxide ion conductors with even better properties.

We report an inelastic neutron scattering study on the magnetic excitations of ${\mathrm{Pr}}_{2}{\mathrm{NiO}}_{4+\ensuremath{\delta}}$ ($\ensuremath{\delta}\ensuremath{\sim}0.24\ifmmode\pm\else\textpm\fi{}0.01$) at $T=10$ K. Spin stripe ordering becomes pronounced below $\ensuremath{\sim}220$ K with an incommensurability $\ensuremath{\epsilon}\ensuremath{\approx}0.346$, and a strong influence of interstitial oxygen is identified on establishing a long-range spin stripe ordering. Apart from the Goldstone modes emerging from the magnetic satellites (${\mathbf{q}}_{m}$), multiple homologous modes are observed along the spin stripe modulation separated by $\mathrm{\ensuremath{\Delta}}{\mathbf{q}}_{m}\ensuremath{\approx}0.076$ in reciprocal lattice units, which is interpreted by the internal periodicity of the long-range ordered discommensurated spin stripes.

We have successfully grown centimeter-sized layered $$\textit{R}\mathrm{SrNiO}_{4}$$ R SrNiO 4 single crystals under high oxygen pressures of 120–150 bar by the floating zone technique. This enabled us to perform neutron scattering experiments where we observe close to quarter-integer magnetic peaks below $$\sim 77~\mathrm{K}$$ ∼ 77 K that are accompanied by steep upwards dispersing spin excitations. Within the high-frequency Ni–O bond stretching phonon dispersion, a softening at the propagation vector for a checkerboard modulation can be observed. We were able to simulate the magnetic excitation spectra using a model that includes two essential ingredients, namely checkerboard charge disproportionation and nano phase separation. The results thus suggest that charge disproportionation is preferred instead of a Jahn–Teller distortion even for this layered $$\mathrm{Ni}^{3+}$$ Ni 3 + system.

Inelastic neutron scattering has been used to study the in-plane Cu-O bond-stretching mode in oxygen-doped ${\mathrm{La}}_{1.94}{\mathrm{Sr}}_{0.06}{\mathrm{CuO}}_{4.035}$ $({T}_{c}=38\phantom{\rule{0.28em}{0ex}}\text{K})$ and ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ $({T}_{c}=43\phantom{\rule{0.28em}{0ex}}\text{K})$. Similar to results from optimally doped ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ $({T}_{c}=35\phantom{\rule{0.28em}{0ex}}\text{K})$, we observe anomalous features in the dispersion of this half-breathing mode in the form of a softening halfway through the Brillouin zone. Considering the differences in electronic structure and local environment between the oxygen- and strontium-doped compounds with similar ${T}_{\text{c}}$, we rule out a connection between the phonon anomaly and structural instabilities related to the specific dopant type. We interpret the phonon anomaly as a signature of correlated charge fluctuations ubiquitous in optimally doped superconductors.

Introduction of Bi(III) into apatite-type germanate oxide ion conductors can improve the conductivity by up to two orders of magnitude. To account for these experimental findings, we have carried out the first ab initio molecular dynamics simulations study of the conduction mechanisms in lone pair-containing apatite-type oxide ion conductors. These calculations were performed on the series La10−xBixGe6O27 (x = 0, 2, 4) and were supported by neutron scattering experiments. We observe four types of oxide ion exchange mechanisms and describe the effects that the introduction of lone-pair cations has on the O2− migration pathways and on the overall conductivity.

The material class of rare earth nickelates with high Ni$^{3+}$ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO$_3$ thin films has also triggered intensive research efforts. LaNiO$_3$ seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimetre-sized impurity-free single crystal growth has not been reported for the rare earth nickelates material class since elevated oxygen pressures are required for their synthesis. Here, we report on the successful growth of centimetre-sized LaNiO$_3$ single crystals by the floating zone technique at oxygen pressures of up to 150 bar. Our crystals are essentially free from Ni$^{2+}$ impurities and exhibit metallic properties together with an unexpected but clear antiferromagnetic transition., Nature Communications 9 (1), 43, S. 1 - 7 (2018)

Fe x Mn1−x S belongs to the group of strong electron correlations compounds MnO. We present here experimental results for the antiferromagnetic iron–manganese sulfide system, based on X-ray and neutron diffraction studies. The neutron diffraction investigations were carried out at ambient conditions and at hydrostatic pressures up to 4.2 GPa in the temperature range from 65 to 300 K. Our results indicate that the Neel temperature of α-MnS increases up to room temperature by applying chemical (x Fe) or weak hydrostatic pressure P. In Fe0.27Mn0.73S, the Neel temperature increases from 205(2) K (P = 0 GPa) to 280(2) K (P = 4.2 GPa) and the magnetization at 100 K decreases by a factor of 2.5 when the hydrostatic pressure increases from 0 to 4.2 GPa.

This work is focused on the determination of the most likely border morphologies in the H-terminated graphenic domains that constitute activated carbons, focusing on four different carbons and six supported-metal catalysts. Among the available characterization techniques, Inelastic Neutron Scattering spectroscopy provides detailed vibrational spectra containing the fingerprint of the terminal C-H groups of carbon materials. From the experimental spectra, we observed clear differences among carbons having different origin, and a systematic decrease in the integrated area upon metal deposition that linearly scales with the nanoparticles dispersion. Density Functional Theory simulations are fundamental to assign the experimental bands to specific species. Thus, an extended simulation work on both regular and defective aromatic models was carried out, providing the inelastic neutron scattering fingerprint of a large number of different C-H terminations. By fitting the experimental spectra with a linear combination of the simulated spectra, it was possible to quantify the concentration of each terminal C-H geometry in the samples, and to identify the species most affected by the metal nanoparticles deposition. Specific benzene rings exposing a single C-H group appear to have a decisive role in the interaction with the metal nanoparticles and their deposition procedure.

We investigated the magnetic structure and dynamics of YbMnBi$_2$, with elastic and inelastic neutron scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We confirm C-type antiferromagnetic ordering of the Mn spins below $T_{\rm N} = 290$ K, and determine that the spins point along the $c$-axis to within about $3^\circ$. The observed magnon spectrum can be described very well by the same effective spin Hamiltonian as was used previously to model the magnon spectrum of CaMnBi$_2$. Our results show conclusively that the creation of Weyl nodes in YbMnBi$_2$ by the time-reversal-symmetry breaking mechanism can be excluded in the bulk.

Inelastic neutron scattering measurements on the molecular dimer-Mott insulator $\ensuremath{\kappa}\text{\ensuremath{-}}(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF}{)}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Cl}$ reveal a phonon anomaly in a wide temperature range. Starting from ${T}_{\mathrm{ins}}\ensuremath{\sim}50--60\text{ }\text{ }\mathrm{K}$ where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature ${T}_{\mathrm{N}}=27\text{ }\text{ }\mathrm{K}$, where also a ferroelectric ordering at ${T}_{\mathrm{FE}}\ensuremath{\approx}{T}_{\mathrm{N}}$ occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below ${T}_{\mathrm{N}}$, while no change of the lattice symmetry is observed across ${T}_{\mathrm{N}}$ in neutron diffraction measurements. We assign the phonon anomalies to structural fluctuations coupled to charge and spin degrees of freedom in the BEDT-TTF molecules.

Here, we reinvestigate the underlying charge and magnetic correlations in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{4}$ within a combined study of muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), x-ray photon correlation spectroscopy, synchrotron radiation single-crystal x-ray diffraction, and neutron-scattering measurements. For ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{4}$ around 1/3 hole-doping, the significant charge correlations that are responsible for the emergence of hour-glass magnetic spectra are found to be slowly fluctuating checkerboard charge ordering (CBCO) correlations with an onset temperature being independent of hole-doping. This reveals a local origin of the CBCO correlations in the rather ionic cobaltates, thus being distinct from the more covalent nickelates. Moreover, we report the observation of a very similar temperature dependence of the intensities of in-plane high- and low-energy excitations within the ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{4}$ hour-glass spectrum. This observation shows that nano phase separation is distinct from conventional phase separation and that there is a coupling between nanometer-sized undoped and hole-doped islands. Based on this, it is possible to propose a microscopic scenario for the suppression of the outwards-dispersing branches in hour-glass magnetic spectra.

Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxide ion conductivity at low temperatures. This is the longest time scale neutron scattering study of any fluorite-type solid electrolyte, and it represents only the second case of oxide ion dynamics in any material observed on a nanosecond time scale by quasielastic neutron scattering. Ab initio molecular dynamics simulations reveal two mechanisms that contribute to the oxide ion dynamics in the material: a slower diffusion process through the Bi–O sublattice and a faster process which corresponds to more localized dynamics of the oxide ions within the VOx coordination spheres. The length of the trajectories simulated and the validation of the simulations by neutron scattering experiments provide for the first time a quantitative insight into the relative contributions of the two processes to the oxide ion conduction in this exceptional solid electrolyte, which can be used to derive design principles for the preparation of related oxide ion conductors with even better properties.

Inelastic neutron scattering measurements on the molecular dimer-Mott insulator κ-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl reveal a phonon anomaly in a wide temperature range. Starting from T_{ins}∼50-60 K where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature T_{N}=27 K, where also a ferroelectric ordering at T_{FE}≈T_{N} occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below T_{N}, while no change of the lattice symmetry is observed across T_{N} in neutron diffraction measurements. We assign the phonon anomalies to structural fluctuations coupled to charge and spin degrees of freedom in the BEDT-TTF molecules.

In this work we investigated in detail the effects of nitric acid on the surface chemistry of two carbons, activated by steam and by phosphoric acid, meant to identify the nature and the concentration of the oxidized surface species. To this aim, the oxidized carbons were characterized by means of a large number of complementary techniques, including micro-Raman spectroscopy, N2 physisorption, Boehm titration method, 13C solid state nuclear magnetic resonance, X-ray photoelectron spectroscopy, diffuse reflectance infrared and inelastic neutron scattering spectroscopy. Carboxylic and carboxylate groups are mainly formed, the latter stabilized by the extended conjugation of the π electrons and being more abundant on small and irregular graphitic platelets. We demonstrated that the presence of oxygen-containing groups acts against the palladium dispersion and causes the appearance of an appreciable induction time in hydrogenation reactions. The carbon with more oxygenated surface species (and in particular more carboxylate groups) must be chosen in the hydrogenation of polar substrates, while it is detrimental to the hydrogenation of nonpolar substrates.

The effect of a graphitization treatment on the phyisico-chemical properties of an activated carbon have been studied by means of multi-technical approach. Inelastic neutron scattering and DRIFT spectroscopy revealed the modifications occurring at the material borders, involving H-containing species and O-containing functional groups. Information on the structural modifications were obtained by means of Raman spectroscopy and X-Ray Powder Diffraction.

We investigated moderate-temperature oxygen diffusion mechanisms in Sr2ScGaO5 with Brownmillerite structure type. From oxygen isotope 18O−16O exchange experiments we determined that oxygen mobility sets in above 550 °C. Temperature-dependent neutron and X-ray (synchrotron) diffraction experiments allowed us to correlate the oxygen mobility with a subtle phase transition of the orthorhombic room-temperature structure with I2mb space group toward Imma, going along with a disorder of the (GaO4)∞-tetrahedral chains. From lattice dynamical simulations we could clearly evidence that dynamic switching of the (GaO4)∞-tetrahedral chains from its R to L configuration sets in at 600 °C, thus correlating oxygen diffusion with the dynamic disorder. Oxygen ion diffusion pathways are thus constrained along the onedimensional oxygen vacancy channels, which is a different diffusion mechanism compared to that of the isostructural CaFeO2.5, where diffusion of the apical oxygen atoms into the vacant lattice sites are equally involved in the diffusion pathway. The proposed ordered room-temperature structure in I2mb is strongly supported by 17O, 45Sc, and 71Ga NMR measurements, which indicate the presence of crystallographically unique sites and the absence of local disordering effects below the phase transition. The electric field gradient tensor components measured at the nuclear sites are found to be in excellent agreement with calculated values using the WIEN2k program. The oxygen site assignment has been independently confirmed by 17O{45Sc} transfer of adiabatic populations double-resonance experiments.

We looked for the active hydrogen species in a highly dispersed and very homogeneous 5 wt% Pt/C industrial catalyst (Pt particle mean diameter of 2.0 ± 0.5 nm) for hydrogenation reactions, by coupling H2 adsorption measurements with Inelastic Neutron Scattering (INS). Taking advantage of the enormous progress undergone by INS instruments, we succeeded in collecting INS spectra of unprecedented quality that allowed us to: (1) demonstrate that the Pt nanoparticles are mainly located at the regular edges of the sp2 graphitic domains on the activated carbon; (2) validate that most of the H2 physisorbed on the carbon is side-on adsorbed; (3) detect for the first time H2 molecules adsorbed on hydride-covered Pt nanoparticles; (4) observe Pt-hydrides (on the Pt/C catalyst with the lowest Pt loading among those investigated by INS so far) and (5) provide evidence for the occurrence of spillover of atomic hydrogen from the Pt surface to unsaturated reactive sites located at the irregular borders of the sp2 domains on the activated carbon.

Wave excitations (magnons) along the helical arrangement of magnetic moments in helimagnets generally travel along this helix, while orthogonal magnons are thought to require much higher energy. New experiments reveal the existence of low-energy orthogonal magnons that could lead to a new understanding of a broad class of magnetic materials.

Electron localisation function (ELF) calculations have been used to provide the first computational location of the cation lone pairs in apatite materials. We show that the orientation of the lone pairs varies depending on the identity and positions of the channel anions. The results represent a new platform for interpreting experimentally observed structure-property relationships in functional apatites. In particular, they have significant implications for ionic conductivity and suggest that structure-property relationships in lone-pair containing apatite-type solid electrolytes are more complex than previously thought.

Quasielastic neutron scattering (QENS), underpinned by ab initio molecular dynamics (AIMD) simulations, has been used to directly observe oxide ion dynamics in solid electrolyte La2Mo2O9 on the nanosecond timescale, the longest timescale probed in oxide ion conductors by neutron scattering to date. QENS gives the activation energy of 0.61(5) eV for this process, while AIMD simulations reveal that the exchange processes, which ultimately lead to long-range oxide ion diffusion in La2Mo2O9, rely on the flexibility of the coordination environment around Mo6+, with oxide ions jumps occurring between vacant sites both within and between Mo coordination spheres. Simulations also differentiate between the crystallographic sites which participate in the oxide ion exchange processes, offering the first atomic-level understanding of the oxide ion dynamics in La2Mo2O9, which is consistent with the macroscopic experimental observations on this material.

Nanoparticles research represents one of the most active fields in science due to the importance of nanosized materials in a wide variety of applications. Their characterization needs the comparison of data coming from different experimental techniques, but the peculiar properties of the nanosystem that each technique points out are not always properly taken into account and misleading results have been often reported. In this work, we generated transmission electron microscopy like (TEM-like) data to predict the extended X-ray absorption fine structure (EXAFS) and chemisorption-like typical outputs as the average coordination numbers up to fourth shell of the particles distribution and the surface area. The aim of the simulations is to explore the dependence of the calculated average coordination number (ACN) and average dispersion (AD) values from each parameter characterizing a particle size distribution (PSD), as the mean diameter, the width, the shape, and the profile, and shows that a range of distr...

In a number of hydrogenation reactions, palladium nanoparticles may undergo a transition to the hydride or the carbide phase, which affects the catalytic properties. In the current work, we determine the structural evolution of an industrial Pd/C catalyst in the presence of hydrogen and acetylene by means of in situ X-ray absorption spectroscopy and X-ray powder diffraction. We observe reversible hydride phase formation and irreversible formation of the carbide phase. The near-edge structure of the absorption spectra (XANES) plays the key role in distinguishing between hydride and carbide phases. We show that the presence of hydrogen and carbon atoms have a direct effect on the near-edge region which is reproduced by theoretical simulations performed in the Monte-Carlo approach.

Among zeolites containing highly dispersed transitions metal ions, iron-substituted zeolites represent an important family of materials with well-established catalytic activity in reactions such as N2O decomposition, [3,4] N2O reduction by CO, [5] hydroxylation of benzene to phenol with N2O, [5] oxidation of methane and higher hydrocarbons with N2O, [6] selective catalytic reduction (SCR) of NO by ammonia and hydrocarbons, and oxidation of substrates with H2O2. [8] The high level of industrial interest in these processes has led to the appearance of a remarkable number of scientific studies, as reviewed in Ref. [9] . Despite such intense study, understanding of the local structure of the active sites is still somewhat lacking. For the sites active in N2O decomposition reaction, there is agreement on the fact that the activity increases with Fe dilution and with activation temperature. On this basis, it has been concluded that the catalytic sites are constituted by single Fe atoms or FexOy clusters of extremely low nuclearity in extra-framework positions. Concerning the sites active in the SCR reaction, both isolated and clustered species have been taken into consideration. Understanding of the structure of the active centers and of the mechanism of partial oxidation reactions is vitally dependent upon the elucidation of many factors: a) the concentration, the oxidation state, the structure and nuclearity of the extra-framework sites; b) the role of framework Fe and Al in determining the nuclearity of the active species in extra-framework position; c) the role of thermal treatments in influencing the migration of iron from framework to extraframework sites; d) the propensity of the Fe sites to undergo redox processes. The investigation of the structure and properties of diluted Fe sites represents a difficult task for experimental techniques. In particular the discrimination between extra-framework clustered and isolated Fe resulted problematic. Among all employed methods, FTIR spectroscopy of adsorbed NO and Raman spectroscopy under resonant conditions have emerged as tools of choice because they are sensitive enough to give information on very diluted species. Raman spectroscopy under controlled atmospheric conditions has not been extensively applied to zeolites because of the low sensitivity of the method and because of difficulties associated with strong fluorescence interference caused by organic templates, impurities, and surface defects. However, the fluorescence problem can be avoided if the laser wavelength is moved from the visible to the UV range. Furthermore, when the UV laser frequency falls in the range of the chargetransfer transitions between the framework oxygen ions and the transition metal centers, the resonance effect conditions are realized and the sensitivity problems associated with conventional Raman spectroscopy are surmounted. The study reported herein concerns Raman spectroscopy of an isomorphously Fe-substituted MFI sample (silicalite), that is, a sample not containing Al in the framework. The motivation of this apparently limited approach is based on the idea that, to understand the properties of Fe-ZSM-5 systems and the role of framework Al, it is useful to proceed in a stepwise manner, starting from a system not containing Al at all, where the iron species are initially all in framework positions as tetrahedrally coordinated Fe ions and then are forced to migrate partially or totally in extra-framework positions. In this system, the total migration of iron from framework to extra-framework positions is possible. For this reason it represents the ideal system to investigate the migration process and structure of extra-framework species (both clustered or mononuclear) and their interaction with a fully siliceous matrix. The structure of iron species in Fe–silicalite treated at increasing temperatures and hence containing an increasing fraction of extra-framework iron has been investigated in the past by means of IR spectroscopy of adsorbed NO, which is a sensitive probe of the structure and valence state of extra-framework iron species. It was concluded that, in samples treated at high temperature in vacuo, the extra-framework iron is prevalently in the divalent state, and is anchored to the siliceous framework. Upon NO dosage, the mononuclear species and polynuclear (clustered) species form poly and mononitrosyls, characterized by intense IR bands in the 1900–1700 cm 1 interval. When compared with the results obtained on Fe-ZSM-5 treated under similar conditions, the obtained data shows that the presence of Al in the structure enhances the iron dispersion and influences the nNO frequency of the nitrosyl species, the shape of which is, however, substantially similar in both cases. The aim of this study was to investigate the potential utility of Raman spectroscopy in a) the study of iron migration from framework to extra-framework position, b) the investigation of the structure of isolated and clustered iron species interacting with a siliceous and crystalline framework, and c) the study of the adsorbed species formed on coordinatively unsaturated Fe sites upon NO contact. To overcome the usual sensitivity [a] Dr. F. Bonino , Dr. A. Damin , A. Piovano , Prof. Dr. C. Lamberti , Prof. Dr. S. Bordiga , Prof. A. Zecchina Department of Inorganic, Physical and Materials Chemistry University of Torino, via Giuria 7, I-10125 Torino (Italy) [b] Dr. F. Bonino , Dr. A. Damin , A. Piovano , Prof. Dr. C. Lamberti , Prof. Dr. S. Bordiga , Prof. A. Zecchina NIS Centre of Excellence and INSTM Centro di Riferimento via Quarello 11, I-10135, Torino (Italy) Fax: (+39)011-6707855 E-mail : francesca.bonino@unito.it Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201000265.

International audience; Activated carbons are widely used as supports for industrial catalysts based on metal nanoparticles. The catalytic performance of carbon-supported catalysts is strongly influenced by the carbon activation method. Notwithstanding this important role, the effect induced by different activation methods has been rarely investigated in detail. This work deals with two carbons of wood origin, activated either by steam or by phosphoric acid, and the corresponding catalysts based on supported Pd nanoparticles. We demonstrate that the catalysts perform in a different way in hydrogenation reactions depending on the nature of the carbon used as a support, being the palladium dispersion the same. We propose a multi-technique approach to fully characterize both carbons and catalysts at the micro-and nanoscale. In particular, we investigate how the activation procedure influences the texture (by N-2 physisorption), the morphology (by Scanning Electron Microscopy), the structure (by Solid State Nuclear Magnetic Resonance, Raman spectroscopy and X-ray Diffraction) and the surface properties (by X-ray Photoelectron Spectroscopy, Diffuse Reflectance Infrared Spectroscopy and Inelastic Neutron Scattering) of carbons and of the related catalysts. The comprehensive characterization approach proposed in this work allows the rationalization, at least in part, of the role of activated carbons in enhancing the performance of a hydrogenation catalyst

In order to investigate the on-site motion of the diffusive species in crystalline solids, we have implemented a code to perform a time-summation of displacements of specific atoms, involving symmetry and adapted projections. The resulting 2D maps have been called ‘positional recurrence maps’ (PRM). Only displacements are considered, instead of positions, so static deformations are filtered out. In this paper we present the PRM method and show the type of information on the dynamics of selected atoms that can be obtained. We take, as an example, the Nd2NiO4+d system in which we were able to characterize in detail the effects of the dynamical delocalization of the apical oxygen.

We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T > T* ~ 38 K the x-ray diffraction data can be satisfactorily refined using the space group Pm-3n. Below T* the crystal structure is modulated with a propagation vector of q = (1/2, 1/2, 0). This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Delta(120 K) = 1.05 meV. Using density functional theory the soft phonon mode is identified as a 'breathing' mode of the Sn12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single crystal diffraction data.

International audience; Periodic DFT calculations allow an understanding of the strong orientation-dependent Ramanspectra of oriented CaFeO2.5 single crystals. Modes involving the oscillation of the apical oxygen(Oap) atoms perturb the induced electric dipoles. These are formed by anisotropy in the chargedistribution and are found to be strongly enhanced when the electric field of the linearly polarizedlaser line is parallel to the b axis. For the CaFeO2.5 ordered system, strong polarizability of thesemodes corresponds to strong Raman intensities. Conversely, the apical oxygen disorder observedin low-temperature oxygen-conducting SrFeO2.5 destroys the long-range coherence of therespective Raman modes, which consequently show a strongly reduced intensity. This studyprovides a vibrational tool to discriminate between ordered and disordered isomorporphousABO2.5 Brownmillerite frameworks. Furthermore, in combination with DFT calculations, we havefound that the weakening of the interlayer interactions is responsible for the loss of ordering inBrownmillerite compounds

The single-layer perovskite cobaltates have attracted enormous attention due to the recent observation of hour-glass shaped magnetic excitation spectra which resemble the ones of the famous high-temperature superconducting cuprates. Here, we present an overview of our most recent studies of the spin and charge correlations in floating-zone grown cobaltate single crystals. We find that frustration and a novel kind of electronic and magnetic nano phase separation are intimately connected to the appearance of the hour-glass shaped spin excitation spectra. We also point out the difference between nano phase separation and conventional phase separation., * plenary talk SUPERSTRIPES conference 2015

The role of a catalyst in improving the activity and the selectivity of a given chemical reaction is provided, together with a discussion on the reasons why XAS and XES are so important techniques in the understanding, at the molecular level, of the structure and of the electronic configuration of a working catalyst. Two industrially relevant catalysts are described as key studies: (i) the combined XAS/XES in situ study on TS-1 catalyst provided the structure of the Ti active center in selective oxidation with \(\mathrm {H}_{2}\mathrm {O}_{2}\), and its evolution upon molecular coordination; (ii) the combined in situ/operando XAS study revealed the red-ox catalytic cycle of \(\mathrm {CuCl}_{2}/\mathrm {Al}_{2}\mathrm {O}_{3}\) during the ethylene oxychlorination reaction.

International audience; In this study we demonstrate the feasibility of following up a chemical reaction by single crystal x-ray (synchrotron) diffraction under operando conditions, carried out in a specially designed electrochemical cell mounted on the BM01A at the European Synchrotron Radiation Facility (ESRF). We investigated in detail the electrochemical oxidation of SrFeO 2.5 to SrFeO 3 on a spherical single crystal of 70 µ m diameter by in situ diffraction at an ambient temperature. Complete data sets were obtained by scanning the whole reciprocal space using a 2M Pilatus detector, resulting in 3600 frames with a resolution of 0.1° per data set, each obtained in 18 min. The crystal was mounted in a specially designed electrochemical cell with 1N KOH used as the electrolyte. During the electrochemical oxidation, the reaction proceeds following the phase sequence SrFeO 2.5 /SrFeO 2.75 /SrFeO 2.875 /SrFeO 3 , structurally accompanied by establishing a complex series of long-range oxygen vacancy ordering, which gets instantly organized at ambient temperature. The topotactic reaction pathway is discussed in terms of the evolution of the twin domain structure. The formation of SrFeO 2.875 is accompanied by the formation of diffuse streaks along the [1 0 0]-direction of the perovskite cell, reaching high d -spacings. The diffuse streaks are discussed and are thought to originate from a modified twin structure induced by the SrFeO 2.75 to SrFeO 2.875 transition, and the associated changes in the domain structure, developed during the oxygen intercalation. We equally analysed and discussed in detail the twin structure of all the title compounds. We confirm the ground state of SrFeO 2.5 is able to adopt the Imma space group symmetry, showing stacking faults of the tetrahedral layers along the stacking axis of the brownmillerite unit cell, indicated by the 1D diffuse rods. We showed that in situ single crystal diffraction has huge potential in the study of non-stoichiometric compounds under operando conditions, in order to obtain structural information i.e. about diffuse scattering, and microstructural information related to domain effects such as twinning—information far beyond that which powder diffraction methods allow us to obtain

International audience; Nonstoichiometric Nd2NiO4+δ shows oxygen ion mobility already at roomtemperature and as such is a promising material in the field of solid state ionic conductors.The present work aims to understand the impact of oxygen overstoichiometry on the lattice dynamics of the Nd2NiO4 framework and to correlate dynamic instabilities to the anionic mobility at room temperature. We performed neutron time-of-flight spectroscopy experiments coupled with DFT-based molecular dynamics calculations on the phases Nd2NiO4.0, Nd2NiO4.10, and Nd2NiO4.25. Specific signatures in the phonon density of states gave evidence that excess oxygen on interstitial lattice sites activates large displacements of the apical oxygen atoms along the [110] direction, thus favoring their diffusion toward interstitial sites within the rock salt-type layer already at ambient temperature. We implemented a position recurrence method to analyze apical oxygen displacements during the 40 ps time scale of molecular dynamics simulations. The resultshighlighted that dynamical delocalization of apical oxygen atoms along [110] is necessary to observe diffusion at room temperature, and thus ionic mobility at room temperature is activated by lattice dynamics

The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity. In these cuprate superconductors the magnetic excitation spectrum resembles an hour-glass and certain resonant magnetic excitations within are believed to be connected to the pairing mechanism, which is corroborated by the observation of a universal linear scaling of superconducting gap and magnetic resonance energy. So far, charge stripes are widely believed to be involved in the physics of hour-glass spectra. Here we study an isostructural cobaltate that also exhibits an hour-glass magnetic spectrum. Instead of the expected charge stripe order we observe nano phase separation and unravel a microscopically split origin of hour-glass spectra on the nano scale pointing to a connection between the magnetic resonance peak and the spin gap originating in islands of the antiferromagnetic parent insulator. Our findings open new ways to theories of magnetic excitations and superconductivity in cuprate superconductors.