bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal‐metal interactions in improved Pt‐Co‐Cr catalysts used in phosphoric acid fuel cells
Authors: Tröger Larc , Freund Andreas , Albers Peter , Seibold Klaus , Prescher Günter 
Published: July 2012

AbstractMetal‐metal interactions were studied on high performance Pt‐Co‐Cr catalysts used in commercial phosphoric acid fuel cell power plants by means of X‐ray absorption fine‐structure spectroscopy (XAFS), X‐ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry. In addition, samples were characterized by transmission electron microscopy and X‐ray diffraction. The XAFS measurements of the alloy catalyst revealed different kinds of interactions between the metal atoms as well as between the metal and carbon atoms. A Pt‐Pt distance considerably shorter than in Pt metal indicated a complete alloying of that metal. There was no evidence for local atomic arrangements including all three metals. On the other hand, the Co XAFS data suggest a tetragonal‐ordered structure of PtCo in HgMn arrangement. Missing Cr‐Cr interactions are likely to be a consequence of a highly disordered Pt‐Cr alloy partially depleted from Cr. Upon annealing a surface segregation and preferential oxidation of Cr was observed by XPS measurements and supported by the SIMS results. The segregational tendency of Cr and the favorable reduction behavior of Co promotes the formation of a tetragonal PtCo structure while cooling down to ambient temperature.
Ab initio study of structural properties of stage‐1 alkali graphite intercalation compounds
Authors: Hartwigsen C. , Witschel W. , Spohr E. 
Published: July 2012

AbstractFirst‐principles electronic structure calculations are carried out for the stage‐1 alkali graphite intercalation compounds LiC6 and XC8 (X = Li, Na, K, Rb and Cs). Lattice constants and atomic positions are determined by total energy minimization. It is demonstrated that the experimentally observed AA stacking order of the graphite host is partly a consequence of the electronic charge transfer from the alkali atoms to the graphite host.
Change of the resonance frequency of a quartz crystal microbalance in contact with an aqueous dispersion of solid particles
Authors: Bell J. , Köhler T. , Woermann D. 
Published: July 2012

AbstractThe change of resonance frequency of shear oscillations of an AT‐cut quartz crystal with a resonance frequency f0 of f0 = 5 MHz operated with one face in contact with air and the other in contact with an aqueous suspension of non‐porous solid particles is studied. The experiments are carried out as function of the concentration of the colloidal particles at constant temperature. The aqueous suspensions are prepared with three kinds of particles of different size (radius r ≈︁ 500, 200, 5 nm). It is found that the resonance frequency is independent of the concentration of the colloidal particles with r ≈︁ 500 and 200 nm. It has approximately the value of the resonance frequency of the fluid medium in the absence of the colloidal particles. For the colloidal particles with r ≈︁ 5 nm a small change of the resonance frequency with the concentration of the colloidal particles is observed. An attempt is made to rationalize this finding. The observation could be of importance to practical applications of the quartz crystal microbalance as a sensor in fluids.
A differential anomalous X‐ray scattering study of the formation of lead zirconate titanate via sol‐gel process
Authors: Beudert R. , Bertagnolli H. , Gutwerk D. , Kolb U. , Weigelt J. 
Published: July 2012

AbstractA differential anomalous X‐ray scattering (DAS) investigation on gels, produced by hydrolysis of a mixture of lead(II)acetate and zirconium‐ and titanium‐n‐propoxides, and calcinated at the temperatures 200, 300, and 450 °, is presented. Anomalous X‐ray scattering was applied to get more precise information on the structural changes of the gel during calcination. Two different scattering experiments for each sample were performed with synchroton radiation of the energy below the L3 edge of lead, namely at 11500 and 13025 eV. The data were corrected for absorption, fluorescence radiation and multiple scattering. The Compton and atomic scattering were subtracted after normalization to absolute units with values for the anomalous dispersion corrections, determined by an absorption experiment. The Fourier transform of the total and differential scattering intensities yields the total and differential atom pair correlation functions (TAPCF, DACPF), which provide information on the local structure of lead and its changes during the calcination process. The analysis of the TAPCF's and DAPCF's indicates a structure, similar to that existing in the pyrochlore or perovskite phase of lead zirconate titanate (PZT), even at low temperatures. By comparison of the corresponding atom pair correlation functions (APCF's) it can be deduced that the near range as well as the long range order in the local environment of lead nearly remains unaltered during the calcination process.
State of copper species during N2O decomposition over Cu‐ZSM‐5
Authors: Bossmann Stefan H. , Ottaviani M. Francesca , Turek Thomas 
Published: July 2012

AbstractThe state of copper species in Cu‐ZSM‐5 during isothermal oscillations in nitrous oxide decomposition was monitored by CW‐ESR. A change in the copper oxidation state could not be observed. The prevailing species in the state of low activity is Cu2+ (O6) · NO while in the more active state Cu2+ (O6) · O2 could be identified as intermediate. A simple set of reactions involving these species was proposed, which is able to explain the occurrence of oscillations and is in agreement with the experimental observations.
Rh(III)/Rh(I)‐Catalyzed homogeneous oxidation of hypophosphite by water
Authors: Jusys Z. , Lenkaitiene J. , Genutiene I. , Jurevičius A. 
Published: July 2012

AbstractHomogeneous hydrolytic oxidation of hypophosphite in HCl solutions catalyzed by Rh(III)/Rh(I) has been studied by cyclic voltammetry and on‐line mass spectrometry. The effect of H/D substitution in both hypophosphite and water on the kinetics of the process has been studied. A deuterium tracer evidenced hydrogen to evolve entirely from water in the course of Rh(III)/Rh(I)‐catalyzed homogeneous oxidation of hypophosphite. No kinetic H/D isotope effect (kH/kD) has been found for H/D substitution in hypophosphite. kH/kD = 1.4 ± 0.1 has been found for H/D substitution in water. Possible transformations in both structure and composition of Rh(III) and Rh(I) complexes occurring during homogeneous catalytic hypophosphite oxidation by water are discussed.
Application of spin trapping in the study of the electrochemical and photochemical synthesis of phenylated C60 derivatives with iodonium salts
Authors: Fedurco Milan , Rapta Peter , Kurán Pavel , Dunsch Lothar 
Published: July 2012

AbstractA spin trap technique was used to investigate the fullerene phenylation both electrochemically and photochemically using the reactions of iodonium salts. Phenyl radicals, produced in the cathodic reduction as well as during the photolysis of iodonium salts, were trapped by nitroso‐tert‐butane (BuNO) and nitrosodurene (ND) spin traps. However, no phenyl radicals could be detected by ESR during the irradiation of diphenyliodonium iodide, or during its electrochemical reduction, in the presence of C60. This indicates that prior trapping of phenyl radicals to d̊BuNO and ND spin trap agents, their trapping by fullerenes occurred. The radical mechanism of electrochemical and photochemical phenylation of C60 using iodonium salts are discussed and these two phenylation techniques are compared.
Effect of adsorbed S‐benzylisothiouronium cation on hydrogen evolution reaction at mild steel electrode
Authors: Pillai K. Chandrasekara 
Published: July 2012

AbstractS‐benzylisothiouronium (SBTU) chloride and S‐methylisothiouronium (SMTU) sulphate retard the hydrogen evolution reaction (HER) on mild steel in HCl solutions, and increase the cathodic Tafel slope (‐bc) of HER to different extent depending on their concentration. The cause for the occurrence of high ‐bc values, and the dependence on additive concentration (cA), of the two parameters ‐bc and the electrochemical reaction order with respect to additive concentration (zA), have been explained in terms of a mechanism based on blocking of the electrode surface by the additive and its dependence on cA and the electrode potential. According to this treatment ‐bc of HER is a function of the interaction parameter rA‐A of the adsorbate and y, the parameter which measures the change of free energy of adsorption of the adsorbate with potential. Basing on the two sets of values for rA‐A and y by SBTU at lower and higher concentrations, effects by SBTU on zSBTU and ‐bc have been suggested as a result of different orientations the molecule adopts at two concentration regions, y and rA‐A have been interpreted in terms of adsorbate‐electric field and adsorbate‐solvent interactions at the interphase. The general applicability of the equation for calculating surface coverage (θHA) from polarisation measurements has been discussed.
Time‐resolved laser‐induced thermal grating experiments induced by short pulse CO2‐laser radiation
Authors: Latzel H. , Dreier T. , Giorgi M. , Fantoni R. 
Published: July 2012

AbstractUsing a high pressure carbon dioxide laser with pulse lengths of 80 ns laser‐induced thermal grating spectroscopy (LITGS) experiments have been carried out in gas mixtures consisting of an absorbing species (ethylene) and buffer gases (nitrogen/helium) at various temperatures and pressures. The grating structure is written into the medium by absorption and subsequent collisional relaxation of CO2‐laser radiation. Transport properties in these mixtures such as thermal conductivity and the speed of sound have been determined from the time‐resolved signal generated by Bragg scattering of a continuous wave HeNe‐laser beam off the grating structure. Accurate numerical values for transport coefficients are obtained from fitting analytical expressions to the measured oscillating signal traces and are compared with literature values.
Electrochemical scanning tunnelling microscopy (EC‐STM) study of silver electrodeposition from a room temperature molten salt
Authors: Endres Frank , Freyland Werner , Gilbert Bernard 
Published: July 2012

AbstractPreliminary results by in situ EC‐STM on the electrodeposition of silver on highly oriented pyrolytic graphite (HOPG) from a room temperature molten salt are presented. The molten salt was composed of 55 mol‐% AlCl3 and 45 mol‐% 1‐methyl‐3‐butyl‐imidazolium chloride — this mixture is liquid at ambient temperature — and contained AgCl in a concentration of 0.025 mol/l. The results show for the first time that HOPG can be imaged at this interface with atomic resolution and that the silver deposition/dissolution process can be viewed in situ.
An X‐ray diffraction study on the kinetics of the cation redistribution in the spinel NiAl2O4
Authors: Röttger R. , Schmalzried H. , Günter M. 
Published: July 2012

AbstractA study of the relaxation kinetics in the partially inverse NiAl2O4 spinel after temperature jumps T1 T2 is reported. The change of the lattice parameter was measured by high temperature X‐ray diffraction at T2 (695–760°C) using NiAl2O4 powder samples equilibrated with NiO in air. For the temperature range of T1 under study (1100–1450°C), the kinetics can be well described by an equation which is formally equivalent to a third‐order rate law. Changes of the diffraction line widths occur during the relaxation which are due to elastic stresses, strongly dependent on the initial temperature T1. Comparison with recent results from optical spectroscopy indicates that the process observed by lattice parameter measurements is not the homogeneous exchange reaction between the two cation sublattices. The nature of the various relaxation phenomena occurring on different time scales is discussed taking concentration inhomogeneities of structure elements and elastic stress fields on different length scales into account.
Effect of barium and cesium promoters on copper/zirconia methanol synthesis catalysts: An FTIR investigation
Authors: Weigel J. , Wokaun A. , Horbaschek K. , Baiker A. 
Published: July 2012

AbstractHydrogenation reactions occurring on the surface of a copper/zirconia (Cu: Zr = 50: 50 at.%) catalyst, as well as on Cs and Ba promoted (1 at.%) Cu/Zr samples, have been investigated by means of in situ diffuse reflectance FTIR spectroscopy. Both carbon monoxide and carbon dioxide hydrogenation reactions are monitored with the aim of acquiring information on the methanol synthesis mechanism, and on the role of the promoter components.The promoter metals are found to enhance the surface concentrations of both methoxy and surface‐bound formaldehyde species, as compared to the unpromoted catalyst. On the surface of the promoted samples, the stretching frequency of singly surface‐bound CO is red shifted by 10cm−1, demonstrating that the C‐O bond is weakened. This behavior is interpreted in terms of an interaction between the promoter ion and the 1π orbital of the adsorbed CO species.
A comparison of metal/vacuum and metal/electrolyte interfaces : The Au(100)/(dimethylsulfoxide) and (dimethylsulfoxide + acetonitrile) systems
Authors: Roelfs B. , Schröter C. , Solomun T. 
Published: July 2012

AbstractMetal/vacuum and metal/electrolyte Au(100)/dimethylsulfoxide (DMSO) and Au(100)/(DMSO+acetonitrile) interfaces were studied by means of thermal desorption (TDS), photoelectron spectroscopy (XPS), work function change (Δø), differential capacitance and interfacial infrared spectroscopy (SNIFTIRS) measurements. The adsorptive properties of DMSO in gas phase experiments are scrutinized for their relevance to the electrochemical systems. At monolayer coverages DMSO desorbs from Au(100) from two states that are situated at relatively high temperatures of 240 and 275 K. The adsorbed molecule, however, shows no chemical shifts in its core levels, indicating that the chemical contribution to the surface bond is small. Only extra‐atomic relaxation of the O(1s) and S(2p) electron holes were observed in the XPS spectra. This is rationalized by a bonding model that involves a bidentate DMSO interaction with the surface through the electron lone‐pairs on the O and S atoms. The adsorption geometry agrees also with the behavior of the work function (ΔøDMSO = −770mV). Despite the large dipole moment of DMSO, the differential capacitance of the Au/DMSO interface is found to be rather low. It is argued that this is due to the molecule‐surface interaction that is sufficiently strong to hinder a reorientation of DMSO in the interfacial field. The adsorptive properties of DMSO and acetonitrile under competitive conditions provide a further support for this. Since DMSO bonds to Au(100) significantly stronger than acetonitrile (Tdes = 172 K), DMSO displaces acetonitrile from the surface in UHV, as well as under electrochemical conditions. In the latter case this results in a large decrease in the differential capacitance.
Molecular level interface designs using self‐assembling technique for stabilizing Langmuir‐Blodgett films
Authors: Liu Zhong‐Fan , Zhao Chun‐Xia , Zhang Jin , Tang Ming , Zhu Tao , Cai Sheng‐Min 
Published: July 2012

AbstractSelf‐assembled monolayers (SAMs) of HS‐(CH2)2‐X with X being ‐COOH, ‐OH, ‐NH2, and ‐CH2SO3Na were fabricated on Au surfaces for deposition of C8H17‐C6H4‐N=N‐C6H4O‐(CH2)3‐COOH(ABD) LB films. Thus‐created SAM/LB interfaces were studied by the grazing‐angle incident reflection absorption FTIR technique. For ‐NH2 group, the interface was proved to be dominated by ‐NH3+‐ OOC‐ ionic bonding structure. When X was ‐COOH, an eight‐membered face‐to‐face hydrogen bond was observed at the SAM/LB interface. With the ‐OH terminated interface, two types of hydrogen bond were created: one is the face‐to‐face hydrogen bond and the other one is the side‐by‐side hydrogen bond. In the case of Au/‐CH2SO3Na/HOOC‐ interface, two terminal groups seem to exchange their cations, forming a ‐CH2SO3H/NaOOC‐structure. The stability of these monolayer assemblies was investigated using Atomic Force Microscopy (AFM). It is found that all these films showed a greatly improved structural stability and the destructive three‐dimensional rearrangement of ABD molecules has been effectively prohibited. The sequence of film stability was ‐NH2>‐COOH>‐OH>‐CH2SO3Na, with the first two interfaces exhibiting even nice stability in aqueous solution, strong enough for tolerating the interfacial electron transfer studies.
Micellar solutions of octyl monoglucoside in the presence of butanol: A small angle and light scattering study
Authors: Möller A. , Lang P. , Findenegg G. H. , Keiderling U. 
Published: July 2012

AbstractAqueous solutions of β‐D‐octyl‐monoglucoside (β‐C8G1) with different amounts of 1‐butanol have been studied using static and dynamic light scattering and small angle X‐ray and neutron scattering. Analysis of the small angle scattering data reveals that in the absence of butanol the size and shape of the β‐C8G1 micelles is nearly independent of the surfactant concentration in the experimental range (up to 10 wt‐%). The micelles can be represented by a core‐shell model of a prolate ellipsoid of revolution with a ratio of the minor to major semi‐axis of 3:1. Although the micelles do not change in size, their apparent molar mass and the apparent hydrodynamic radius exhibit a pronounced concentration dependence in this range, which indicates attractive intermicellar interactions. Addition of butanol to the solution causes the micelles to grow with respect to the longer axis (the minor semi‐axis), whereas the cross‐sectional radius (the major semi‐axis) remains constant. Near the solubility limit S of butanol in the micellar solution the scattering particles become apparently larger. Here, the core‐shell model of a prolate ellipsoid of revolution fails to fit the experimental results.
Activity coefficients and solubilities of the system (Ag/Cs)NO3‐H2O from vapour pressure measurements
Authors: Geerlings Jürgen , Richter Joachim , Rørmark Lisbeth , Øye Harald A. 
Published: July 2012

AbstractVapour pressures of water over (Ag/Cs)NO3‐H2O (0, 40, 60, and 100% AgNO3) are reported at three temperatures: 152,179, and 218 °C. The water activities derived from these data are fitted with equations for multicomponent electrolyte solutions developed by Van Laar and Pitzer (three models: Van Laar model, Pitzer‐Van Laar model, Pitzer‐Simonson model). With these models the mean activity coefficients of the salts and the solubilities of the pure salt components (AgNO3 or CsNO3) in the ternary mixture are calculated. The advantages of the Pitzer‐Simonson model are underlined.
Thermodynamic study of the NaCl + MgCl2 + H2O mixed system by emf measurements at different temperatures
Authors: Hernández‐Luis Felipe , Fernández‐Mérida Luis , Esteso Miguel A. , Galleguillos‐Castro Héctor R. 
Published: July 2012

AbstractMean activity coefficients of NaCl in NaCl + MgCl2 + H2O mixed system were determined from the emf measurements of galvanic cells without transport and at 15, 25, 35 and 45 °C. The measurements were carried out at total ionic strengths of 0.1, 0.3, 0.5, 1, 2, 3, 4 and 6 mol·kg−1 and at ionic strength fractions for MgCl2 between 0 and 0.8 mol·kg−1. These activity coefficient values were analysed by using the Harned rule and the treatments of Scatchard‐Rush‐Johnson and Pitzer. From these, it can be deduced that binary ionic interactions are only significant in this mixed system and hence triple ionic interactions are negligible (except for the mixture of 6 mol·kg−1 for which these high‐order interactions probably cannot be considered irrelevant). Moreover, a decrease in the ion‐ion interaction (and therefore an increase in the ion‐solvent interaction) takes place by the simultaneous presence of Na* and Mg2+ ions in the mixture, specially when the ionic strength increases, probably as a consequence of the larger hydration of the Mg2+ ions. Finally, the excess properties of the mixtures were determined and qualitatively analysed against the composition of the mixed system.
Kinetics of the photochemical reaction of C2F5I and C4F9I with C2F4
Authors: Linyang Zhang , Xiaoyu Zhang , Weihua Yang , Xudong Lou , Fuß W. 
Published: July 2012

AbstractAlthough the formal insertion of C2F4 into the CI bond of iodides is a chain reaction, we found quantum yields clearly below 1. We show that this is due to an inhibition reaction: the very rapid reaction of the radicals with molecular iodine, which accumulates during the reaction in amounts equal to the radical dimers. The corresponding kinetic model quantitatively describes the quantum yields and product distributions, if we assume for the rate constants kn for the addition of the F(C2F4)n radicals to C2F4 (in 107 cm3 mol−1 s−1 at 373 and 303 K, respectively): k1 = 19 and 3.6. k2 = 8.0 and 1.9, k3 = 1.6 (303 K).
The v1, v2, 2v3, v2 + v3 band systems and the overtone region of HCNO above 4000 cm−1: A Network of Resonance Systems
Authors: Albert Sieghard , Winnewisser Manfred , Winnewisser Brenda P. 
Published: July 2012

AbstractThe v2, 2v3, v1, v2 + v3, 3v3, 2v2, v1 + v3, v2, + 2v3, v1 + v2 and 2v2 + v3 band systems of HCNO could be identified between 1800 and 5800 cm−1. In addition, new transitions in the v5, v4 and v3 band systems could be assigned. The determination of spectroscopic power series coefficients shows that every assigned vibrational level is perturbed. Most of the interactions are part of resonance systems which are embedded in a grand network of interacting states. This network can be built up on the basis of the resonance systems 00010/00002, 00100/00004 and 01000/00015. In this paper the 01010/01002/00201/00113/[00025] and the 01110/01102/00301/00213/[01014]/[00125] resonance systems are presented. Vibrational quantum numbers in brackets indicate that the vibrational term value of the vibrational state is only estimated. The 10003/10011/00205 and 10005/01201 resonance systems, which do not fit into this network, are also discussed. The effect of excitation of the stretching modes v1, v2 and v3 on the v5 manifold and the quasilinear parameter y0 are examined.
Size dependence of structural and dynamic properties of CdS‐nanoparticles
Authors: Rockenberger Jörg , Tröger Larc , Kornowski Andreas , Voßmeyer Tobias , Eychmüller Alexander , Feldhaus Josef , Weller Horst 
Published: July 2012

AbstractTemperature‐dependent EXAFS (Extended X‐ray Absorption Fine Structure) measurements between 5 and 290 K show that structural and dynamic properties of CdS nanoparticles with 13‐120 Å diameter depend on their particle size and the way of surface stabilization. The mean Cd‐S distance of thiolcapped CdS nanoparticles (13‐40 Å) increases with decreasing particle size with respect to CdS bulk. In contrast, mean interatomic distances in polyphosphate‐stabilized particles (30‐120 Å) are slightly contracted. This demonstrates that the covalently bound thiol ligands induce the nanocluster lattice expansion. From the temperature dependence of the mean‐square relative displacement (MSRD), a slight stiffening of the Cd‐S bond can be observed with decreasing particle size. The static part of the MSRD, reflecting static disorder of the Cd‐S bond, exhibits a maximum at cluster sizes of about 30 Å. For particles larger than 30 Å diameter, the increase of the static disorder follows the change of the surface to volume ratio. This ratio also determines the size dependence of the asymmetry of the interatomic Cd‐S pair potential. Furthermore, in CdS bulk and CdS nanoparticles with the thermodynamically favored wurtzite structure this asymmetry is significantly enlarged in comparison to nanoparticles with zincblende structure.