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Showing papers by "Fritz Haber Institute of the Max Planck Society published in 2008"


Journal ArticleDOI
TL;DR: In this paper, high resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif of graphitic carbon nitride, and a new family of metal nitride nanostructures can also be accessed from the corresponding oxides.
Abstract: Graphitic carbon nitride, g-C3N4, can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.

2,746 citations


Journal ArticleDOI
03 Oct 2008-Science
TL;DR: It is shown that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene, and a high selectivity to alkenes was achieved for periods as long as 100 hours.
Abstract: Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O2/butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene. For low O2/butane ratios, a high selectivity to alkenes was achieved for periods as long as 100 hours. This process is mildly catalyzed by ketonic CO groups and occurs via a combination of parallel and sequential oxidation steps. A small amount of phosphorus greatly improved the selectivity by suppressing the combustion of hydrocarbons.

754 citations


Journal ArticleDOI
TL;DR: In this paper, the conditions for suitable experimental arrangements are characterized and examples show spectral sensitization of photocurrents due to electron or hole injection into inorganic or organic solids.
Abstract: — Spectral photosensitization is discussed from an electrochemical point of view, as caused by electron transfer from or to excited molecules. General principles for a description of electron transfer processes at semiconductor or insulator electrodes are reviewed and applied to reactions which involve excited electronic states. The conditions for suitable experimental arrangements are characterized. Illustrations for the application of these techniques are given. The examples show spectral sensitization of photocurrents due to electron or hole injection into inorganic or organic solids.

250 citations


Journal ArticleDOI
TL;DR: In this paper, a series of catalysts with Au:Pd ratios varying from 9.5:0.5 to 2:8 were prepared and characterized by TEM, HRTEM, EDX, and X-ray mapping techniques to obtain morphological information, particle size distributions, crystalline structure and distribution of the two metals.
Abstract: Au nanoparticles are known to be a good catalyst or an effective promoter for a wide range of catalytic reactions. Bimetallic Au−Pd nanoparticles supported on activated carbon were synthesized following a two-step procedure: immobilization of Au sol onto activated carbon followed by immobilization of Pd(0). The catalysts showed superior activities compared to monometallic Pd or Au nanoparticles on the same support. A series of catalysts with Au:Pd ratios varying from 9.5:0.5 to 2:8 were prepared. These catalysts were characterized by TEM, HRTEM, EDX, and X-ray mapping techniques to obtain morphological information, particle size distributions, crystalline structure, and distribution of the two metals. Correlating with the result from catalytic tests of selective oxidation of glycerol to glyceric acid, we found that the surface configuration of Pd monomers isolated by Au atoms has a substantial effect on activity and stability. The Au:Pd ratio on the surface of the particles is the key parameter and can be...

227 citations


Journal ArticleDOI
TL;DR: This paper aims to demonstrate the efforts towards in-situ resolution of the stationary phase of proton-proton collisions that have been reported in the literature on high-resolution X-ray diffraction analysis.
Abstract: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany, Institute of Isotopes, Hungarian Academy of Sciences, Post Office Box 77, Budapest H-1525, Hungary WestCHEM, Department of Chemistry, University of Glasgow, Glasgow G128 QQ, Scotland, UK Universite de Lyon, Institut de Chimie, Laboratoire de Chimie, Ecole Normale Superieure de Lyon and CNRS 46 Allee d’Italie, 69364 Lyon, Cedex 07 (France)

194 citations


Journal ArticleDOI
TL;DR: These experiments demonstrate that conformer-selected samples of large molecules can be prepared, offering new possibilities for the study of gas-phase biomolecules.
Abstract: During the last decades, the properties of biomolecules in the gas phase have been studied in ever greater detail [1‐3]. Although the study of biomolecules outside of their natural environment was met with skepticism in the beginning, spectroscopic studies on isolated species in a molecular beam have proven to be very powerful to understand their intrinsic properties. Moreover, their native environment can be mimicked by adding solvent molecules one by one. These studies on well-defined biomolecular systems are particularly relevant to benchmark theoretical calculations. Even in the cold environment of a molecular beam, biomolecules exist in various conformational structures. The existence of multiple conformers (structural isomers) has been observed in the study of jetcooled glycine for the first time [4] and in numerous experiments since then. In many cases, the individual conformers are identified via their different electronic spectra [5, 6]. This has been exploited in multiple-resonance techniques to measure, for instance, conformer-specific infrared spectra from which the conformational structures can be deduced [7, 8].

102 citations


Journal ArticleDOI
TL;DR: The ALD-coated tubes are used as active component in gas-sensing devices and show electric responses that are directly related to the peculiar structure, i.e., the p-n heterojunction formed between the support and the film.
Abstract: A new atomic layer deposition (ALD) process was applied for the homogeneous coating of carbon nanotubes with vanadium oxide. It permits the coating of the inner and outer surface with a highly conformal film of controllable thickness and, hence, the production of high surface area hybrid materials at a so far unprecedented quality. The ALD-coated tubes are used as active component in gas-sensing devices. They show electric responses that are directly related to the peculiar structure, i.e., the p-n heterojunction formed between the support and the film.

101 citations


Journal ArticleDOI
TL;DR: It is indicated that the reduction of soot emission in terms of mass does not automatically lead to a reduction of the toxic effects toward humans when the structure and functionality of the soot is changed, and thereby the biological accessibility and inflammatory potential ofSoot is increased.
Abstract: We evaluated, in vitro, the inflammatory and cytotoxic potential of soot particles from current low-emission (Euro IV) diesel engines toward human peripheral blood monocyte-derived macrophage cells. The result is surprising. At the same mass concentration, soot particles produced under low-emission conditions exhibit a much higher toxic and inflammatory potential than particles from an old diesel engine operating under black smoke conditions. This effect is assigned to the defective surface structure of Euro IV diesel soot, rendering it highly active. Our findings indicate that the reduction of soot emission in terms of mass does not automatically lead to a reduction of the toxic effects toward humans when the structure and functionality of the soot is changed, and thereby the biological accessibility and inflammatory potential of soot is increased.

98 citations


Journal ArticleDOI
TL;DR: In this paper, the de Broglie wavelength of the scattered photoelectron in units of the bond length is used to show that the transition from two-centre to one-center coherence occurs.
Abstract: In molecular double-slit experiments, the interference between emitted core electrons of diatomic molecules gives rise to oscillations in the observed electron intensity. Here, we explore this behaviour for photoelectrons emitted from CO and N_2 by soft X-ray ionization in the molecular frame, and we argue that in addition to the undisturbed emission process, intramolecular scattering can lead to electron interference between the scattered and unscattered wave in two ways: two-centre interference between two spatially coherent emitters and one-centre self-interference. The latter is the signature of a loss of spatial coherence. The spatial scale over which the transition from two-centre to one-centre coherence occurs is the de Broglie wavelength of the scattered photoelectron in units of the bond length. These results highlight the fact that the molecular double slit is based on two independent uncertainty principles, Δp_xΔx and ΔEΔt, the second of which causes ongoing tunnelling between the two centres, even after the collapse of the electron wavefunction in real space.

94 citations


Journal ArticleDOI
TL;DR: The average Pt-Pt bond length is enlarged in agreement with experimental results and an overall shift to lower values as well as a loss of the well-defined peak structure in the bond-order distribution is found.
Abstract: Molecular dynamics simulations have been performed with two reactive force fields to investigate the structure of a Pt100 cluster adsorbed on the three distinct sides of a carbon platelet. A revised Reax force field for the carbon−platinum system is presented. In the simulations, carbon platelet edges both with and without hydrogen termination have been studied. It is found that the initial mismatch between the atomic structure of the platelet egde and the adsorbed face of the Pt100 cluster leads to a desorption of a few platinum atoms from the cluster and the subsequent restructuring of the cluster. Consequently, the average Pt−Pt bond length is enlarged in agreement with experimental results. This change in the bond length is supposed to play an important role in the enhancement of the catalytic activity, which is demonstrated by studying the changes in the bond order of the platinum atoms. We found an overall shift to lower values as well as a loss of the well-defined peak structure in the bond-order d...

81 citations


Journal ArticleDOI
TL;DR: Mixed quantum-classical molecular dynamics simulations based on first-principles potential-energy surfaces demonstrate that the scattering of a beam of singlet O2 molecules at Al(111) will enable an unambiguous assessment of the role of spin-selection rules for the adsorption dynamics.
Abstract: We perform mixed quantum-classical molecular dynamics simulations based on first-principles potential-energy surfaces to demonstrate that the scattering of a beam of singlet ${\mathrm{O}}_{2}$ molecules at Al(111) will enable an unambiguous assessment of the role of spin-selection rules for the adsorption dynamics. At thermal energies we predict a sticking probability that is substantially less than unity, with the repelled molecules exhibiting characteristic kinetic, vibrational and rotational signatures arising from the nonadiabatic spin transition.

Journal ArticleDOI
TL;DR: The adsorption of H2 on a series of gas-phase transition metal clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations to give information on hydrogen-bonding geometries.
Abstract: The adsorption of H2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the experimental and calculated spectra gives information on hydrogen-bonding geometries. The adsorption of H2 is found to be exclusively dissociative on ScnO+, Vn+, Fen+, and Con+, and both atomic and molecularly chemisorbed hydrogen is present in NinHm+ complexes. It is shown that hydrogen adsorption geometries depend on the elemental composition as well as on the cluster size and that the adsorption sites are different for clusters and extended surfaces. In contrast to what is observed for extended metal surfaces, where hydrogen has a preference for high coordination sites, hydrogen can be both 2- or 3-fold coordinated to cationic metal clusters.

Journal ArticleDOI
TL;DR: The worlds of nanotechnology and energy meet to unveil a realm of functional materials for fuelling the challenge of low-carbon, sustainable energy.
Abstract: The worlds of nanotechnology and energy meet to unveil a realm of functional materials for fuelling the challenge of low-carbon, sustainable energy.

Journal ArticleDOI
TL;DR: The role of the (001) crystallographic plane of the M1 phase of MoVTeNb mixed-oxide catalysts in selective oxidation of propane to acrylic acid was addressed by investigating a phase-pure M1 material preferentially exposing this surface.


Journal ArticleDOI
TL;DR: In this paper, a detailed investigation of the preparation of MoVTeNbO x 3 catalysts by hydrothermal synthesis is presented. But the results of this work are restricted to phase-pure materials.
Abstract: This work presents a detailed investigation of the preparation of MoVTeNbO x catalysts by hydrothermal synthesis. Phase-pure synthesis of M1 has been achieved applying the metals in a molar ratio Mo/V/Te/Nb = 1/0.25/0.23/0.12. Raman, UV/Vis spectroscopy, and SEM/EDX analysis show that the elements are inhomogeneously distributed in the initial suspension that is formed after mixing the metal salts in an aqueous medium. Iso- and heteropoly anions of molybdenum, free telluric acid as well as supra-molecular polyoxometalate clusters are observed in the solution, whereas all metals have been found in the precipitate. Complete rearrangement of molecular building blocks under hydrothermal conditions is essential for formation of phase-pure materials. Optimized synthesis conditions with respect to temperature and time result in the formation of a precursor consisting of nano-structured M1 characterized by an extended periodic organization in the [001] direction and a fairly homogeneous distribution of the elements. Residual ammonium containing supra-molecular species in the precursor result in the formation of phase mixtures during the subsequent crystallization by heat treatment in inert gas. Phase-pure M1 exhibits a distinct degree of flexibility with respect to the chemical composition that becomes obvious by incorporating Nb not exclusively into pentagonal bi-pyramidal units, but also into octahedral coordinated positions as shown by EXAFS. Anisotropic growth of the needle-like M1 crystals has been observed during the final heat treatment performed at 873–923 K in inert atmosphere disclosing a potential method to control the catalytic properties of MoVTeNbO x catalysts.

Journal ArticleDOI
TL;DR: A combination of low temperature scanning tunneling microscopy (STM) and theoretical calculations is used to investigate Au dimers, supported on thin MgO(001) films, whose thickness was chosen such that charge transfer from the Ag substrate to the deposited Au is possible.
Abstract: A combination of low temperature scanning tunneling microscopy (STM) and theoretical calculations is used to investigate Au dimers, supported on thin MgO(001) films, whose thickness was chosen such that charge transfer from the Ag substrate to the deposited Au is possible. Au dimers exist not only in an upright geometry--as theoretically predicted to be the most stable configuration--but also as flat lying dimers which populate a manifold of different azimuthal orientations. Apart from the difference in adsorption configurations, these two isomers exhibit rather different electronic structures: while upright dimers are neutral, flat ones are charged.

Journal ArticleDOI
TL;DR: In all cases, the vibrational spectroscopy of the electronically closed-shell cations finds global minimum structures that differ considerably from those derived from known modifications of bulk alumina.
Abstract: The vibrational spectroscopy of the electronically closed-shell (Al 2O 3) n (AlO) (+) cations with n = 1-4 is studied in the 530-1200 cm (-1) range by infrared predissociation spectroscopy of the corresponding ion-He atom complexes in combination with quantum chemical calculations. In all cases we find, assisted by a genetic algorithm, global minimum structures that differ considerably from those derived from known modifications of bulk alumina. The n = 1 and n = 4 clusters exhibit an exceptionally stable conical structure of C 3 v symmetry, whereas for n = 2 and n = 3, multiple isomers of lower symmetry and similar energy may contribute to the recorded spectra. A blue shift of the highest energy absorption band is observed with increasing cluster size and attributed to a shortening of Al-O bonds in the larger clusters. This intense band is assigned to vibrational modes localized on the rim of the conical structures for n = 1 and n = 4 and may aid in identifying similar, highly symmetric structures in larger ions.

Journal ArticleDOI
TL;DR: The experimental mid- and far-IR spectra of six conformers of phenylalanine in the gas phase are presented and a simple model to describe the observed conformer abundances based on quasi-equilibria near the barriers is presented and it appears to describes the experimental observation reasonably well.
Abstract: The experimental mid- and far-IR spectra of six conformers of phenylalanine in the gas phase are presented. The experimental spectra are compared to spectra calculated at the B3LYP and at the MP2 level. The differences between B3LYP and MP2 IR spectra are found to be small. The agreement between experiment and theory is generally found to be very good, however strong discrepancies exist when –NH2 out-of-plane vibrations are involved. The relative energies of the minima as well as of some transition states connecting the minima are explored at the CCSD(T) level. Most transition states are found to be less than 2000 cm−1 above the lowest energy structure. A simple model to describe the observed conformer abundances based on quasi-equilibria near the barriers is presented and it appears to describe the experimental observation reasonably well. In addition, the vibrations of one of the conformers are investigated using the correlation-corrected vibrational self-consistent field method.

Journal ArticleDOI
TL;DR: In this article, the surface properties of oxide catalysts were characterized using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectrographs, infrared spectrograms, and thermal desorption spectroscopic analysis.
Abstract: Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V2O5(001) to V2O3(0001) via V6O13(001). V2O3(0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxy-dehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models.

Journal ArticleDOI
TL;DR: In this article, the authors used density functional theory to analyze the nature of the Ar-Co-n^+ bond and its role for the vibrational spectra of small cationic cobalt clusters.
Abstract: Far-infrared vibrational spectroscopy by multiple photon dissociation has proven to be a very useful technique for the structural fingerprinting of small metal clusters. Contrary to previous studies on cationic V, Nb and Ta clusters, measured vibrational spectra of small cationic cobalt clusters show a strong dependence on the number of adsorbed Ar probe atoms, which increases with decreasing cluster size. Focusing on the series Co_4^+ to Co_8^+ we therefore use density-functional theory to analyze the nature of the Ar-Co_n^+ bond and its role for the vibrational spectra. In a first step, energetically low-lying isomer structures are identified through first-principles basin-hopping sampling runs and their vibrational spectra computed for a varying number of adsorbed Ar atoms. A comparison of these fingerprints with the experimental data enables in some cases a unique assignment of the cluster structure. Independent of the specific low-lying isomer, we obtain a pronounced increase of the Ar binding energy for the smallest cluster sizes, which correlates nicely with the observed increased influence of the Ar probe atoms on the IR spectra. Further analysis of the electronic structure motivates a simple electrostatic picture that not only explains this binding energy trend, but also why the influence of the rare-gas atom is much stronger than in the previously studied systems.

Journal ArticleDOI
TL;DR: In this article, supported vanadium oxide catalysts were studied by high-frequency EPR for determination of the paramagnetic vanadium oxidation states vanadium (IV) and vanadium(III).
Abstract: Supported vanadium oxide catalysts were studied by high-frequency EPR for determination of the paramagnetic vanadium oxidation states vanadium(IV) and vanadium(III). TiO2-, γ-Al2O3-, and SiO2 (SBA-...

Journal ArticleDOI
TL;DR: The Pb/Si(557) system exhibits a strong anisotropy in conductance below 78 K, with the evolution of a characteristic chain structure, and the domain structure along the chains forms split-off valence bands with mesoscopic Fermi wavelengths which induce the 1D conductance without further instabilities at low temperatures.
Abstract: The Pb/Si(557) system exhibits a strong anisotropy in conductance below 78 K, with the evolution of a characteristic chain structure. Here we show, using angle-resolved photoemission, that chain ordering results in complete Fermi-like nesting in the direction normal to the chains; in addition, the domain structure along the chains forms split-off valence bands with mesoscopic Fermi wavelengths which induce the 1D conductance without further instabilities at low temperatures.

Journal ArticleDOI
TL;DR: The adsorption of a metallo-supramolecular coordination polymer (Fe-MEPE) in the cylindrical pores of SBA-15 silica with pure and carboxylic acid carrying pore walls has been studied and it is shown that the average chain length of Fe-M EPE is reduced when the complex is incorporated in the pores.
Abstract: The adsorption of a metallo-supramolecular coordination polymer (Fe−MEPE) in the cylindrical pores of SBA-15 silica with pure and carboxylic acid (CA) carrying pore walls has been studied. Fe−MEPE is an intrinsically stiff polycation formed by complexation of Fe(II)−acetate with an uncharged ditopic bis-terpyridine ligand. The adsorption affinity and kinetics of the Fe−MEPE chains is strongly enhanced when the pore walls are doped with CA, and when the pH of the aqueous medium or temperature is increased. The initial fast uptake is connected with a decrease of pH of the aqueous solution, indicating an ion-exchange mechanism. It is followed by a slower (presumably diffusion-controlled) further uptake. The maximum adsorbed amount of Fe−MEPE in the CA-doped material corresponds to a monolayer of Fe−MEPE chains disposed side-by-side along the pore walls. The stoichiometry of Fe−MEPE in the pores (determined by XPS) was found to be independent of the loading and similar to that of the starting material. The me...

Journal ArticleDOI
TL;DR: Comparison with their well-known neutral analogues reveals that ionization of the neutral compounds destabilizes bridge bound CO ligands in Rh2(CO)8 and Rh4( CO)12, leading to cationic complexes with only terminally bound CO.
Abstract: The structures of cationic rhodium carbonyl cluster compounds containing one to six Rh atoms are established by infrared multiple photon dissociation spectroscopy. Comparison with their well-known neutral analogues reveals that ionization of the neutral compounds destabilizes bridge bound CO ligands in Rh2(CO)8 and Rh4(CO)12, leading to cationic complexes with only terminally bound CO. The destabilization is associated with removal of charge from a highest occupied molecular orbital that is bonding with respect to bridge-bound CO. Density functional theory calculations support this conclusion. The results provide a possible insight into electronic promoter effects in catalysis.

Journal ArticleDOI
TL;DR: An ab initio molecular dynamics simulation of a nanoscale liquid water film on NaCl shows a pronounced layering, with the density exhibiting a damped oscillatory behavior in the direction of the surface normal.
Abstract: The salt-water interface is one of the most important and common on earth, playing a prominent role in disciplines such as atmospheric science and biology. Despite the apparent simplicity of such interfaces, arguably the most fundamental question of what the nature and structure of the liquid water/salt interface is under ambient conditions remains unclear. Here we address this issue with an ab initio molecular dynamics simulation of a nanoscale liquid water film on NaCl. A pronounced layering is observed in the film, with the density exhibiting a damped oscillatory behavior in the direction of the surface normal. In addition, water molecules in the contact layer are preferentially adsorbed at specific adsorption sites, involved in about 20% fewer hydrogen bonds with each other, and carry considerably reduced dipole moments compared to bulk liquid water.

Journal ArticleDOI
TL;DR: This work shows that Dicarboxystilbene forms long-range "handed" structures when adsorbed on Cu(110) as revealed by scanning tunnelling microscopy, and interprets the formation of these structures in terms of a balance between hydrogen bond mediated intermolecular interactions and the adsorbate-surface structural relationship.
Abstract: Dicarboxystilbene, a molecule that becomes chiral in the adsorbed state through the loss of its improper axis of rotation, forms long-range "handed" structures when adsorbed on Cu(110) as revealed by scanning tunnelling microscopy. We show that these structures are created from chiral "adsorption complex" building blocks, giving rise to a complete set of racemic and enantiomerically pure structural assemblies. We interpret the formation of these structures in terms of a balance between hydrogen bond mediated intermolecular interactions and the adsorbate-surface structural relationship and discuss the reasons for temperature-induced conversion from the metastable enantiomerically pure to the racemic structure.

Journal ArticleDOI
TL;DR: In this paper, the NH3 + O2 reaction on a Pt(533) surface has been studied in the 10−4 mbar range and close to 1 mbar pressure with in situ X-ray photoelectron spectroscopy using synchrotron radiation.
Abstract: The NH3 + O2 reaction on a Pt(533) surface has been studied in the 10−4 mbar range and close to 1 mbar pressure with in situ X-ray photoelectron spectroscopy using synchrotron radiation. The coverages of the various O- and N-containing surface species have been followed in T-cycling experiments with varying mixing ratios O2/NH3 and varying total pressure. In heating/cooling cycles hysteresis of ∼50−100 K width occur. Adsorbed NOad already decomposes at T > 350 K. Under stationary conditions, no adsorbed NO could be detected. At no time during the experiments were Pt bulk oxides formed. A shift in the surface core level component of the Pt 4f spectrum by more than 0.5 eV toward higher binding energy is attributed to Pt atoms of the (100) step edges which are coordinated to more than one oxygen atom similar to the model proposed by Wang et al. Phys. Rev. Lett. 2005, 95, 256102.

Journal ArticleDOI
TL;DR: The new method, in situ PGAA, was used to determine the hydrogen-to-palladium molar ratio under various conditions of palladium-catalyzed alkyne hydrogenation, which successfully measured in the range of 0.1-1.0.
Abstract: Prompt γ activation analysis (PGAA) has been further developed to analyze reacting components inside a chemical reactor. The new method, in situ PGAA, was used to determine the hydrogen-to-palladium molar ratio under various conditions of palladium-catalyzed alkyne hydrogenation. The H/Pd molar ratio was successfully measured in the range of 0.1−1.0 in an ∼2-g catalytic reactor containing a few milligrams of palladium catalyst. The amount of hydrogen was only a few tens of micrograms, and the detection limit was ∼5 μg, i.e., at ppm level compared to the whole reactor. The description of the device, methodological developments, a feasibility study, and results of a series of catalytic measurements are presented.

Book ChapterDOI
01 Jan 2008
TL;DR: In this article, the results of spectroscopic measurements of adsorption and sorption kinetics of binary mixtures are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques.
Abstract: Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir–Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion .