Studies of the methanation catalysts ThNi5 and ZrNi5 by Auger and Characteristic Energy Loss Spectra

ThNi₅ and ZrNi₅ (fresh, used, and H₂S poisoned) have been examined by Auger spectroscopy (AES) and Characteristic Energy Loss Spectroscopy (CELS) to elucidate the strikingly different behavior of these materials as methanation catalysts. With use ZrNi₅ is transformed into Ni supported on ZrO₂ and ThNi₅ into Ni supported on ThO₂. AES indicates that the Ni on ZrO₂ is heavily overlaid with graphite. This does not occur with Ni and ThO₂, accounting for the exceptional activity of this catalyst compared to Ni on ZrO₂. Plasmon excitation energy determined from CELS are consistent with this picture. The large amount of surface Ni for the transformed ThNi₅ catalyst accounts for its high resistance to H₂S poisoning compared to that of ZrNi₅. A strong CELS peak is observed at 6.5 eV in ZrNi₅ and ThNi₅ as well as in elemental Ni, suggesting a very similar band structure for these materials. In this respect Ni and the Ni intermetallics are similar to Co and Co intermetallics as deduced from photoemission studies and recent APW band calculations.     

Study of the performances of an oxygen carrier: Experimental investigation of the binder's contribution and characterization of its structural modifications

The aim of this work is to investigate the contribution of the binder (NiAl₂O₄) on the performances of the oxygen carrier NiO/NiAl₂O₄. To this purpose, oxidation/reduction cycles have been performed in a fixed bed reactor using CO as a fuel. The results reveal that the binder can react with the fuel to form CO₂, and that its total reduction capacity increases with temperature. XRD characterizations performed on the binder (on the fresh and after several cycles) show a shift of the diffraction peaks of NiAl₂O₄ toward the ones of γ-alumina, which can be attributed to a progressive decomposition of NiAl₂O₄ to alumina and NiO.     

The analysis of inorganic and organometallic antimony,arsenic and tin compounds using an on-column hydride generation method

A novel method of analysis of inorganic and organometallic compounds is reported. Essentially this utilizes the well-documented hydride generation technique, but in the present method the hydrides are generated from their involatile precursors (e.g. chlorides) on a GC column and separated from each other and from extraneous materials on the same GC column in a single process. Using the method, a solution of butyltin chlorides can be directly injected into a GC AA system to yield the volatile hydrides for separation, detection and quantification. To date, species analysed by this method include inorganic As(III), Me₂AsOOH, inorganic Sb(III) and Sb(V), MeSnCl₃, Me₂SnCl₂, Me₃SnCl, Et₂SnCl₂, Et₃SnCl, BuSnCl₃, Bu₂SnCl₂, Bu₃SnCl and Pr₃SnCl. With the use of the internal standard Pr₃SnCl and with the almost complete hydridization afforded by the technique, the procedure is shown to eliminate errors and to reduce the time involved in the analysis. The use of on-column derivatization also allows for the possibility that, in some cases, organotin hydrides reported to be found in the natural environment may, in fact, be organotin chlorides being reported as hydrides owing to inadvertent hydride production on the column. Some reports of successful gas chromatography for organotin halides could also conceivably be due to on-column hydride generation.     

A simple and scalable procedure for TiCl4-promoted aldol reaction

TiCl₄-promoted aldol reaction was carried out by adding TiCl₄ to a solution of the aldol reaction substrates and (i-Pr)₂NEt (DIPEA) in CH₂Cl₂. Compared to the conventional order of addition (sequentially adding TiCl₄, DIPEA, and piperonal to the lactone 2 in CH₂Cl₂), this simplified procedure, gave a much cleaner reaction that could be executed on large scale and without cryogenic cooling. However this procedure provided no stereoselectivity.     

Composition and rheology of polyamide-6 obtained by using bi- and tri-functional coupling agents

A statistical approach is developed, based on a Monte Carlo method, in order to determine the statistical composition of a polyamide-6 sample composed of caprolactam (an AB-type monomer) and of a di-acid (A2 type) or a tri-acid (A3 type) as coupling agents. For this composition, the linear rheological behavior of these systems is predicted using a tube-based theory. This allows us to show that while coupling agents of type A2 can be seen as flow improver, the effect of branching agents of type A3 , depending on the synthesis recipe and the conversion level, can lead either to an increase or to a decrease of the viscosity. By adding specific amount of these agents, we also show that it is possible to obtain materials with the same zero-shear viscosity but with different shear thinning behavior. Furthermore, the polydispersity of linear samples of the same average number molecular weight, M n , is discussed in function of the amount of A2 monomers they contain. Ranging from 2 to 1.5, this difference in polydispersity is expected to have a significant influence on the processing behavior of such materials.     

Thermal reactivity of jadeite and nephrite

The thermal reactivity of the naturally occurring silicates jadeite, NaAl[Si₂O₆], and nephrite, a variety of actinolite, Ca₂ (Mg,Fe)₅[(OH,F)Si₄O₁₁]₂, have been investigated by thermogravimetric and thermomechanical analysis as well as temperature-dependent X-ray diffraction and analytical electron microscopy. TG shows that nephrite undergoes a weight loss at around 900°C. Mass spectrometry reveals that this irreversible reaction corresponds to the evolution of H₂O, and XRD shows that a phase related to diopside CaMg[Si₂O₆] is formed. Jadeite does not undergo and observable weight changes up to 1000°C. Thermomechanical analysis indicates a reversible phase transition at about 950°C. Temperature-dependent X-ray diffraction shows that jadeite is again present on cooling (peak temperature: 1000°C), but that this is accompared by an additional unidentified phase. The mechanism of this process is not yet clear although it has been observed in several samples from different origins and with different metal impurities.     

Single and Combined Effects of Continuous and Discontinuous O3 and SO2 Immission on Norway Spruce Needles: II. Metabolic Changes

Abstract

The analysis of the cytological effects of SO₂, O₃ or SO₂/O₃ exposure on the structure of spruce needles (Picea abies Karst.) revealed an extremely high amount of phenolic compounds in the vacuoles of the mesophyll cells of primary needles (see part 1 of this study). This observation prompted us to identify and quantify different spruce needle phenolics, their changing amount during SO₂, O₃, or SO₂/O₃ exposure as well as their effect on the adenylate energy charge (AEC) as an integrate stress index of the plant cell.

Discontinuous fumigation with O₃ combined with low constant-concentration exposure to SO₂, overlapped by occasional peak concentration of SO₂, seems to affect the phenolic metabolism and the adenylate energy charge the most. The high phytotoxicity of this fumigation pattern is indicated by a drastically reduced adenylate energy charge and extremely high levels of distinct intermediates of the phenolic pathway.     

Lattice Pressure Creating and Annihilating Superconducting Subperoxides

The involvement of O⁻ in oxide superconductivity is indicated in a variety of phenomenological rules such as a universal scaling of T_c with stoichiometric holes per O. Here, a crystal chemistry of O⁻ creation and placement is developed, based on the competition of various types of planes (CuO₂, E, B1). Generally, cuprate structural stability is dictated by slab matching, conventionally expressed in tolerance factors (t). Electronic liquefaction through subperoxide formation can ameliorate t, indicating a decisive influence of lattice pressure on the limits of O⁻ formation. Comparison of calculation with experiment indicates trends to lattice commensurable hole patterns, of which the one responsible for optimal T_c is an alternate hole charge order (P2), for both simple and complex cuprates. For complex cuprates, tension on the layers containing M=Bi, Hg, T1 leads to additional reductive self-dopings. Calculations indicate that in optimally doped materials this leads universally to P2. The T_c decreases beyond this optimal doping, usually referred to as “overdoping,” are here related to overfilling of this pattern. An extreme case of this occurs with nonsuperconducting Bi₂Sr₂CuO₆, which appears to be P1. This overdoping is caused by severe lattice pressure causing the annihilation of superconducting pairs. A distinction has to be made with a second type of “early” T_c decreases. They occur before attainment of P2 and are due to an unfavorable hole placement crystal chemistry. An example is the disorder in [(LaSr)₂CuO₄]. T_c optimization involves navigating between these antagonistic principles.     

Theoretical and experimental studies on formation of diethylzinc-triphenylphosphine complex

This work is mainly focused on understanding the complex-forming behavior of diethylzinc with neutral phosphine ligands such as triphenylphosphine (PPh₃) to yield [Zn(PPh₃)₂Et₂]. The complex formation in solution is observed in the presence of a large excess of diethylzinc, but leaving an insoluble solid on aging. The product formed in solution was analyzed by spectroscopic data. ³¹P-NMR was also used as a tool to observe this behavior, i.e., the disappearance of the chemical shift of PPh₃ (δ -5.45) requires 14-fold excess of ZnEt₂ in solution. The alkyl chains reduce the Lewis acidity on Zn and thereby the formation of phosphine adducts is restricted. Results obtained from orbital analyses calculations reveal that the LUMO appears to be asymmetrically distributed, and localized on one of the PPh₃ ligands. The length of alkyl chains also influence the stability of [Zn(PPh₃)₂R₂] and the longer chains on Zn impart less stability.     

Structure and dynamics of the lowest triplet state in p-benzoquinone: I. An isotope effect study on the optical absorption,emission and ODMR spectra

The results of detailed spectroscopic experiments on the lowest nπ* triplet state of p-benzoquinone-h₄, -dh₃, 2,6-d₂h₂, -d₄ and -CH₃ in mixed and isotopic mixed crystals are presented and analyzed. The origin of the lowest B_1g (nπ*) singlet-triplet transition in p-benzoquinone-h₄ (PBQ-h₄) is shown to be induced by asymmetric isotopic substitution and the oscillator strength of this origin is seen to be accounted for by a corresponding decrease in intensity of a level 16.9 cm^?1 higher in energy in the pure PBQ-h₄ crystal. The combined oscillator strength of these close lying levels is measured and found to be almost independent of deuteration.These results are discussed in reference to the previously proposed double minimum potential model for the lowest nπ* triplet state in PBQ-h₄ and the applicability for this model is critically examined.Optical absorption experiments on heavily doped isotopic mixed crystals of PBQ-h₄ in PBQ-d₄ show hydrogen (deuterium) bounding effects between translational inequivalent molecules to be primarily responsible for the observed cluster states. These hydrogen bounding effects also induce the electronic origin of the B_1g (nπ*) triplet state in case of a translational inequivalent dimer.A detailed vibrational analysis of the phosphorescence spectrum of PBQ-h₄ in a PBQ-d₄ host crystal at 1.8 K is presented and it is shown that the unobserved origin of the B_1g (nπ*) triplet state of PBQ-h₄ is located at 18609 ± 1 cm^?1 and that the inversion splitting in this lowest excited state amounts to 21 ± 1 cm^?1 in this mixed crystal system. An isotope effect is study on the vibronic structure in the emission spectrum further indicates that the excited state structure of PBQ is isotope dependent.The observed large isotope effect on the ZFS parameters of the lowest triplet state of PBQ-h₄ is demonstrated to be an intramolecular phenomenon and explained as an isotope dependent spin-orbit contribution to the ZI-S parameters, induced by localization of the nπ* excitation on oxygen.Finally the dynamics of energy migration in the dilute PBQ-h₄ in PBQ-d₄ isotopic mixed crystal is probed by concentration and temperature dependent phosphorescence intensity measurements and it is suggested that trap-exciton band communication effects are of importance in this system.     

Topology and Equilibrium Analysis of the Monovalent Aluminum Compound Al4Cp*Ph4

The theoretical structure and thermochemistry of the tetrameric, low‐valence aluminum compound Al₄Cp*^Ph₄ (Cp*^Ph = C₅Me₄Ph) is discussed. The first synthesis of this compound was reported in 2005, but the compound failed to crystallize and experimental ²⁷Al NMR results were inconclusive in regard to the degree of association. Here density functional theory combined with a genetic algorithm is used to predict the expected structure and properties for Al₄Cp*^Ph₄. Synthesis efforts were repeated for this compound, resulting in a product with a ²⁷Al NMR chemical shift that differed from the previous report by nearly 20 ppm. However, calculated ²⁷Al NMR chemical shifts for the theoretically predicted structure are within one ppm of these new experimental results, strongly suggesting the tetrameric form has been synthesized. Previous work on five Al₄R₄ (R = C₅H₅, C₅Me₄H, C₅Me₅, C₅Me₄iPr, C₅Me₄Pr) compounds showed a general trend towards an increased likelihood of disassociation into monomeric species in solution as ligand bulk increased. Analysis of Al₄Cp*^Ph₄, the sixth and bulkiest compound in this series, indicates a departure from this trend. Bonding characteristics for monomer and tetramer forms in this series are examined in detail via topological analysis to understand this trend.     

HREM Study of Nanostructured Molybdenum and Vanadium Doped Titania Catalysts

MoO₃/V₂O₅/TiO₂ (anatase) catalyst with 5 and 20 wt.% loadings of MoO₃ and V₂O₅ has been studied, using high resolution electron microscopy. Main structural peculiarity of this system was found to be the presence of nanometer size layers of a complex Mo-V-O phase on the surface of the titania support. The observed structure seems to be a metastable and may exist only on the surface of TiO₂ particles.     

Determination of Q 0 and k 0 factors for 75Se

Since the initial determination of the Q ₀ and k ₀ factors for ⁷⁵Se systematic errors in Se determination in various matrices have been noticed by several users of the k ₀ method. A number of publications have been made on this subject, resulting in different k ₀ and Q ₀ values for this radio-isotope. This work consists of a re-determination of Q ₀ and k ₀ values for ⁷⁵Se using the bare and Cd-ratio methods making use of three different irradiation channels from the BR1 reactor. For this re-determination three different kinds of standards were used: a pure Se powder standard, an ICP standard solution and pure Se shots. Results were compared with previously published literary data. Differences in k ₀ with the official published data ranging from 3.5 to 12 % were observed and potential reasons for this discrepancy are discussed. A good consistency with recent work was found. The impact on recent certification and intercomparison exercises demonstrates the effectiveness of the newly proposed values.     

Effect of Concentrated Salts Solutions on the Stability of Immobilized Enzymes: Influence of Inactivation Conditions and Immobilization Protocol

This paper aims to investigate the effects of some salts (NaCl, (NH₄)₂SO₄ and Na₂SO₄) at pH 5.0, 7.0 and 9.0 on the stability of 13 different immobilized enzymes: five lipases, three proteases, two glycosidases, and one laccase, penicillin G acylase and catalase. The enzymes were immobilized to prevent their aggregation. Lipases were immobilized via interfacial activation on octyl agarose or on glutaraldehyde-amino agarose beads, proteases on glyoxyl agarose or glutaraldehyde-amino agarose beads. The use of high concentrations of salts usually has some effects on enzyme stability, but the intensity and nature of these effects depends on the inactivation pH, nature and concentration of the salt, enzyme and immobilization protocol. The same salt can be a stabilizing or a destabilizing agent for a specific enzyme depending on its concentration, inactivation pH and immobilization protocol. Using lipases, (NH₄)₂SO₄ generally permits the highest stabilities (although this is not a universal rule), but using the other enzymes this salt is in many instances a destabilizing agent. At pH 9.0, it is more likely to find a salt destabilizing effect than at pH 7.0. Results confirm the difficulty of foreseeing the effect of high concentrations of salts in a specific immobilized enzyme.     

Ligand and Metal Effects on the Stability and Adsorption Properties of an Isoreticular Series of MOFs Based on T‐Shaped Ligands and Paddle‐Wheel Secondary Building Units

The synthesis of stable porous materials with appropriate pore size and shape for desired applications remains challenging. In this work a combined experimental/computational approach has been undertaken to tune the stability under various conditions and the adsorption behavior of a series of MOFs by subtle control of both the nature of the metal center (Co²⁺, Cu²⁺, and Zn²⁺) and the pore surface by the functionalization of the organic linkers with amido and N‐oxide groups. In this context, six isoreticular MOFs based on T‐shaped ligands and paddle‐wheel units with ScD_0.33 topology have been synthesized. Their stabilities have been systematically investigated along with their ability to adsorb a wide range of gases (N₂, CO₂, CH₄, CO, H_2, light hydrocarbons (C₁–C₄)) and vapors (alcohols and water). This study has revealed that the MOF frameworks based on Cu²⁺ are more stable than their Co²⁺ and Zn²⁺ analogues, and that the N‐oxide ligand endows the MOFs with a higher affinity for CO₂ leading to excellent selectivity for this gas over other species.     

Comparison of Stress-Strain Relations of Polybutadiene Vulcanizates in Compression and in Extension

Abstract

According to elementary statistical theory of rubber elasticity, the modulus of rigidity τ/(λ - λ^?2) is constant. The phenomenological theory predicts that this modulus is in first approximation equal to the sum of a constant (2C₁) and a deformation-dependent term, 2C₂. The dependence on elongation of experimental modulus data of many elastomers agrees more or less with the C₂ term. Several attempts have been made to explain this dependence on the basis of molecular phenomena or by refinements of the statistical theory of elasticity. At present there is no consensus of opinion on the origin or interpretation of the deformation-dependent term. Almost all of the data on this dependence have been generated in extension experiments.     

Structure and Phase Transitions of SnP2O7

SnP₂O₇ is a member of the ZrP₂O₇ family of materials, several of which show unusual thermal expansion behavior over certain temperature ranges and which show a number of displacive phase transitions on cooling from high temperature. Here we describe the structural properties of SnP₂O₇ from 100 to 1243 K as determined by X-ray and neutron powder diffraction. These studies reveal that SnP₂O₇ shows two phase transitions in this temperature range. At room temperature the material has a pseudo-cubic 3×3×3× superstructure. Electron diffraction studies show that the symmetry of this structure is P2₁3 or lower. On warming to ∼560 K it undergoes a phase transition to a structure in which the subcell reflections show a triclinic distortion; above 830 K the subcell reflections show a rhombohedral distortion. Significant hysteresis in cell parameters is observed between heating and cooling. The structure of SnP₂O₇ is discussed with references to other members of the AM₂O₇ family of materials.     

Poly(Ionic Liquid)-Derived Carbon with Site-Specific N-Doping and Biphasic Heterojunction for Enhanced CO2 Capture and Sensing

CO₂ capture is a pressing global environmental issue that drives scientists to develop creative strategies for tackling this challenge. The concept in this contribution is to produce site-specific nitrogen doping in microporous carbon fibers. Following this approach a carbon/carbon heterojunction is created by using a poly(ionic liquid) (PIL) as a “soft” activation agent that deposits nitrogen species exclusively on the surface of commercial microporous carbon fibers. This type of carbon-based biphasic heterojunction amplifies the interaction between carbon fiber and CO₂ molecule for unusually high CO₂ uptake and resistive sensing.     

Bovine serum albumin stabilized iron oxide and gold bimetallic heterodimers: Synthesis,characterization and Stereological study

In this time researchers make a great efforts to develop new hybrid nanoparticles for medical and pharmaceutical applications. Fe₃O₄‐Au hybrid heterodimers have been prepared with superior properties for various claims. Unfortunately, Fe₃O₄‐Au heterodimers are not stable in the physiological medium. In this study, we employed the albumin macromolecules as a stabilizer of Fe₃O₄‐Au hybrid nanoparticles (noted as Fe₃O₄‐Au‐BSA hybrid nanoparticles). After characterization of synthesized nanoparticles by FTIR, UV–Vis, TEM, DLS, DSC, VSM and XRD techniques, the in vitro and in vivo biocompatibility of these nanoparticles were also evaluated. We encountered with an amazing result which confirmed nanoparticles could be stabilized by linking the BSA on the surface of Fe₃O₄‐Au heterodimers. Also, intravenous injection of Fe₃O₄‐Au‐BSA hybrid nanoparticles up to 400 mg/kg to Balb C mice show that these nanoparticles were non‐toxic. The biocompatibility and stereological study had been performed for more than 30 days after nanoparticles administration, using hystomorphometric analysis. Remarkably, to the best of our knowledge, it was the first time the biocompatibility and biodegradability of Fe₃O₄‐Au were studied and evaluated by stereological technique. Further promotion and biomedical usage of this type of hybrid nanoparticles are underway in our laboratory.     

One-dimensional WO3 and its hydrate: One-step synthesis,structural and spectroscopic characterization

We report on a one-step hydrothermal growth of one-dimensional (1D) WO₃ nanostructures, using urea as 1D growth-directing agent and a precursor free of metals other than tungsten. By decreasing the pH of the starting solution, the size of the nanostructures was reduced significantly, this development being accompanied by the realization of phase pure hexagonal WO₃ nanorods (elimination of monoclinic impurity phase) and a red shift in optical absorption edge. Surface analyses indicated the presence of reduced tungsten species in the WO₃ nanostructures, which increased two-fold in a hydrated WO₃ phase obtained with further decrease in pH. We suggest that oxygen vacancies are responsible for this defect state in WO₃, while protons are responsible or contribute significantly to the same in the hydrated phase.