Effect of copper source on the structure–activity of CuAl2O4 spinel catalysts for CO hydrogenation

Due to the complexity of the structure–activity relationship of the CuAl₂O₄ spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl₂O₄ spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl₂O₄ spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl₂O₄ spinel catalyst was characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The activity of CO hydrogenation over the CuAl₂O₄ spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl₂O₄ spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu⁺/Cu⁰ and thus affected the catalytic performance, especially the alcohol distribution. The CuAl₂O₄ spinel, employing copper hydroxide as the copper source, showed better selectivity of C₂₊OH, which was assigned to a higher ratio of Cu⁺/Cu⁰, along with larger pore size and pore volume. Moreover, the synergistic effect between Cu⁰ and γ-Al₂O₃ improved the selectivity of dimethyl ether.     

Review of the quantitative structure–activity relationship modelling methods on estimation of formation constants of macrocyclic compounds with different guest molecules

There is an increasing interest in the use of quantitative structure–activity relationship (QSAR) approaches as a progressive tool in modelling and prediction of many physicochemical properties in host–guest interactions of macrocyclic complexes. A review is presented on the QSAR modelling of macrocyclic compounds formation constants, which focus on two most interesting macrocycles, e.g. crown ethers and cyclodextrins (CDs), with different guest molecules. The review starts with a short overview on experimental methods of stability constant measurement, followed by a short explanation of the QSAR methodologies. In the next section, we focus on and discuss QSAR techniques that used to predict the stability (binding) constants or free energy complexation of some most interesting macrocyclic compounds, e.g. CDs and crown ethers, with different guest molecules including anionic, cationic and neutral molecules.     

Thermal conductivity enhancement of copper–diamond composites by sintering with chromium additive

The thermal diffusivity (TD) and thermal conductivity (TC) of Cu–Cr–diamond composite materials were examined in the temperature range from 50 to 300 °C for diamond volume fractions of 22, 40, 50, 55, and 60 %. The samples were fabricated by the plasma pulse sintering (PPS) method. TC does not increase proportionally with the diamond fraction in the particular composite materials. The highest TD was determined for 50 % diamond volume fraction, and the evaluated TC reached 658 W m^?1 K^?1 at 50 °C. This article complements earlier articles concerning synthesis and characterization of the diamond–copper composites produced by the PPS method.     

Investigation of the factors affecting the carbohydrate–lectin interaction by ITC and QCM-D

Although the carbohydrate–lectin interactions have been intensively investigated, there is little report concerning the factors that affect the carbohydrate–lectin interaction. The interactions between concanavalin A (Con A) and glycopolymers, namely poly(2-(methacrylamido)-glucopyranose) and poly(2-methacrylamido-2-deoxy-glucitol) containing pyranose ring form and open form of glucosamine, respectively, have been investigated by a combination of isothermal titration calorimetry and quartz crystal microbalance-dissipation. Our results show that not only the pyranose ring form of glucosamine but also the open form can bind to Con A. Moreover, we investigate the influence of temperature on the carbohydrate–lectin interaction. As the temperature increases, the carbohydrate–lectin interaction is enhanced.     

Mechanisms of the action of alkali metal admixtures on the properties of copper–zinc–aluminum water–gas shift catalysts

The effect of alkali metal (Cs, Na) admixtures on the catalytic and physicochemical properties of coprecipitated Cu–Zn–Al catalysts for the low-temperature water–gas shift reaction has been investigated. The inhibition of the formation of methanol, an undesired by-product, by alkali metals is accompanied by a decrease in the activity of the catalyst in the main, water–gas shift reaction ion. The alkali metals exert an adverse effect on the thermal stability of the catalyst. Experimental data are explained in a consistent way on the basis of the following conceptions of the mechanism of the action of alkali metals: (1) the alkali metals stimulate sintering of the crystal structure of the main components of the catalyst, diminishing the activity of the catalyst in the water–gas shift reaction and in methanol formation; (2) the alkali metals directly or indirectly accelerate methanol conversion into other chemical products.     

Kinetic patterns in the formation of nanosized manganese–manganese oxide systems

Transformations in nanosized manganese films are studied by means of optical spectroscopy, microscopy, and gravimetry at different film thicknesses (d = 4–108 nm) and temperatures of heat treatment (T = 373–673 K). It is found that the kinetic curves of conversion are satisfactorily described in the terms of linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference is measured for Mn and MnO films, and photo EMF is measured for Mn–MnO systems. An energy band diagram is constructed for Mn–MnO systems. A model for the thermal transformation of Mn films is proposed that includes stages of oxygen adsorption, the redistribution of charge carriers in the contact field of Mn–MnO, and manganese(II) oxide formation.     

Synthesis of a new bismuth oxide fluoride with the γ-Bi2O3 structure type

A new bismuth compound with the γ-Bi₂O₃ structure type has been synthesized by a hydrothermal method. The experimental results show that only the solution or starting materials which contain fluorine ions are effectual for the synthesis of the compound. Chemical analysis proved that the new compound contains a small amount of fluorine. We comment the stabilization of the γ-form by partial replacement of oxygen atoms with fluorine atoms and assume Bi₂₆O₃₈F₂ as its constitution. The measured dimension of the unit cell is 10.183(2) Å. Its thermal stability is also studied by differential thermal analysis.     

Modification of aluminum alkoxides with β-ketoesters: new insights into formation,structure and stability

[Al(OⁱPr)₂(β-ketoesterate)]₂ and Al(β-ketoesterate)₃ (β-ketoesterate = methyl, ethyl, iso -propyl, tert-butyl, allyl and 2-(methacryloyloxy)ethyl acetoacetate) were prepared by reaction of [Al(OⁱPr)₃]₄ with the corresponding β-ketoesters. Al(β-ketoesterate)₃ derivatives were exclusively formed at room temperature, whereas elevated reaction temperatures, causing thermal de-oligomerization of [Al(OⁱPr)₃]₄, were necessary for the formation of [Al(OⁱPr)₂(β-ketoesterate)]₂. All compounds were characterized by NMR spectroscopy, and [Al(OⁱPr)₂(tert-butyl acetoacetate)]₂ by a single crystal structure analysis. The [Al(OⁱPr)₂(β-ketoesterate)]₂ derivatives are asymmetrically substituted dimers with one octahedrally and one tetrahedrally substituted aluminum atom, bridged by two iso -propoxo groups, whereas the Al(β-ketoesterate)₃ derivatives are monomers with octahedrally coordinated aluminum. Transesterification as a possible side reaction was only observed at elevated temperatures for Al(tert-butyl acetoacetate)₃ in the presence of liberated iso -propanol. Dedicated to David Avnir on the occasion of his 60th birthday.     

Formation of calcium in the products of iron oxide–aluminum thermite combustion in air

The composition of condensed products resulting from the combustion of thermite mixtures (Al + Fe₂O₃) in air is studied by precise methods. It is shown that during combustion, calcium is formed and stabilized in amounts of maximal 0.55 wt %, while is missing from reactants of 99.7 wt % purity. To explain this, it is hypothesized that a low-energy nuclear reaction takes place alongside the reactions of aluminum oxidation and nitridation, resulting in the formation of calcium (Kervran–Bolotov reaction).     

Structure of compounds of chromium with 2,2′-bipyridyl that participate in the Belousov-Zhabotinskii oscillating reaction

It was shown that a binuclear complex of composition [Cr₂(OH)₂(bpy)₄]³⁺ acts as a reaction catalyst in the oscillating chemical system bromate-malonic acid-compound of chromium with 2,2 bipyridyl. The catalytically active compound was investigated by fast-atom-bombardment mass spectrometry, electron and EPR spectroscopies, and cerimetric analysis. The formal redox potential of such a complex E⁰ was obtained by cyclic voltammetry as +0.72 V.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 266–270, May–June, 1992.     

Synthesis and characterisation of new copper(II) coordination polymers constructed from pyrazine–tetrazole ligands with the formation of a water cluster

Three novel bis-tetrazole ligands (1–3) containing carboxylate functional groups on the tetrazole rings and a rigid pyrazine linker unit, for the construction of coordination polymers when coordinated to copper(II) ions, were synthesised and structurally characterised. The use of pyrazine as a rigid linker between the two tetrazole units was expected to increase the dimensionality of the solid phase polymeric network of the resulting copper(II)-containing compounds. X-ray structures of the ligands revealed the effect of the substitution position on the tetrazole ring of the ester/carboxylate groups. Higher solid phase dimensionality was successfully achieved as shown by the layered two-dimensional (2-D) coordination structure being formed when the pyrazine bis-tetrazole systems were reacted with copper(II) chloride, although not in the expected manner. There was no interaction between the pyrazine nitrogen atoms and the metal ion. Computational studies showed that this was probably due to the geometry, required by the copper ion, to be involved in the close packing between the layers. The 2-D coordination polymer based on the asymmetric substituted pyrazine bis-tetrazole, [Cu(4)(H₂O)](H₂O)₂, was further connected into a three-dimensional (3-D) coordination network through hydrogen bonding between H₂O molecules. These H₂O molecules were connected as a unique 1-D chain throughout the structure.     

Use of SEC–ICP–MS with a collision cell for determining the interaction of chromium with DNA extracted from metal-contaminated soils

The potential of chromium to bind to DNA isolated directly from soil microbial communities was investigated in this study. An analytical scheme was developed to distinguish between chromium bound to DNA and its fragments or chromium contained elsewhere in an environmental DNA extract. DNA was extracted from chromium-contaminated soils and purified using DNA clean-up resins. Size-exclusion chromatography was employed due to its advantages in the separation and molecular weight approximation of large biomolecules. It was coupled with two on-line detection systems (spectrophotometric and inductively coupled plasma mass spectrometric) to study the binding of chromium to DNA or other components in a DNA extract. A collision cell was pressurized with helium to remove diatomic and polyatomic interferents resulting from the chosen mobile phase. Chromium peaks were observed in both the large and small molecular weight regions of the chromatogram; to further confirm that the environmentally extracted DNA contained Cr, the subsequently purified DNA was examined for total Cr using flow injection ICP–MS to accommodate small sample volumes. DNA samples isolated from the two soils examined contained 0.5–0.7 ppb Cr, indicating that DNA isolated directly from a chromium-contaminated soil has chromium bound to the nucleic acids.     

Crystal structure of a cyanide-bridged heptanuclear manganese(III)–chromium(III) complex with a ground state S = 21/2

K₃[Cr(CN)₆] reacts with the mononuclear Mn^III complex Mn(salen)ClO₄ · 2H₂O [salen: N,N-ethylenebis(salicylideneiminato)dianion] to give a bimetallic heptanuclear complex cation salt [Cr{(CN)Mn(salen · H₂O)}₆][Cr(CN)₆]6H₂O. In the complex anion, [Cr{(CN)Mn(salen · H₂O)}₆]³⁺, six Mn^III ions coordinate to a Cr^III center via cyano bridges, forming a spherical species with 3 symmetry. A study of magnetic properties shows the presence of antiferromagnetic interaction through the cyanide bridge between Cr^III (S = 3/2) and Mn^III (S = 4/2) and results in a ground state S = 21/2.     

Agar: a natural and environmentally-friendly support composed of copper oxide nanoparticles for the green synthesis of 1,2,3–triazoles

ABSTRACT

A novel, green and cost-effective heterogeneous nanocatalyst was synthesized by supporting copper (I) oxide nanoparticles on magnetic agar (Cu₂O/Agar@Fe₃O₄). Then, it was characterized with multiple techniques, such as scanning electron microscopy and transmission electron microscopy images, energy-dispersive X-ray analysis, Fourier-transform infrared (FT–IR) spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction pattern, vibrating sample magnetometer curve, and inductively coupled plasma analysis. The catalytic activity of the newly designed catalyst was investigated in a one-pot three-component reaction of alkyl halides, sodium azide, and alkynes to obtain 1,4–disubstituted 1,2,3–triazoles in high yields in water–ethanol media. The present catalyst was simply separated from the reaction media by an external magnet and reused at least five subsequent runs without significant activity loss.     

Sol–gel derived nano zinc oxide for the reduction of zinc oxide level in natural rubber compounds

Zinc oxide (ZnO) nanoparticles are synthesized by polymeric sol–gel method and characterized by X-ray diffraction, field-emission scanning electron microscopy. The cure characteristics, mechanical properties and thermal behaviour of natural rubber (NR) systems containing nano ZnO are investigated and compared to those of NR with micro-sized (conventional) ZnO. The NR vulcanizate with 0.5 phr (parts per hundred parts of rubber) sol–gel derived nano ZnO shows improvement in the curing and mechanical properties in comparison to the NR vulcanizate with 5 phr conventional ZnO. Thermogravimetric analysis reveals that nano ZnO impose better thermal stability than conventional ZnO in the NR vulcanizates. Thus, nano ZnO not only acts as a curing activator but also nano filler to improve the resulting properties of the NR vulcanizates. More essentially nano ZnO leads to the reduction of ZnO level in the NR compounds. Therefore, sol–gel derived nano ZnO diminishes the pollution of aquatic environment due to higher amount of conventional ZnO in rubber compounds.     

Study of formation of metal–polymer complexes between copper (I) and polyamic acids by HPLC

Structural, molecular, and hydrodynamic characteristics of thermostable functionalized polymers [polyamic acids (PAAs) with biquinoline chelate groups in the main chain] were studied by high-performance liquid chromatography. Size exclusion mechanism of chromatography in conditions including suppression of polyelectrolyte swelling and ion-exclusion effects was proved. The influence of molecular and structural characteristics of PAAs on their ability to form metal–polymer complexes (MPCs) with copper(I) chloride was studied. The critical polymer concentration at which binding of two PAA macromolecules with Cu⁺ ion takes place to form MPCs was estimated.     

Energy release characteristics of impact-initiated energetic aluminum–magnesium mechanical alloy particles with nanometer-scale structure

Aluminum–magnesium alloys, fabricated by bi-directional rotation ball milling, were used as a kind of promising solid fuel in “reactive material” that can be ignited by impact to release a large quantity of heats. Different percentages of Mg were added to Al to yield Al_90%–Mg_10% and Al_70%–Mg_30% alloys in order to probe the effect of Mg content on the microstructure and thermal reactivity of Al–Mg alloys. Structural characterization revealed that a nanometer-scale structure was formed and oxidation of as-fabricated alloy powders was faint. Moreover, as the Mg percentage increased, the particle size of alloy decreased with increasing brittleness of Al–Mg. TGA/DSC curves of the [Al_70%–Mg_30%]–O₂ system exhibited an intense exothermic peak before melting with reaction heat of 2478 J g^?1 and its weight increase reached 90.16% of its theoretical value, which contrasted clearly with 181.2 J g^?1 and 75.35% of [Al_90%–Mg_10%]–O₂ system, respectively. In addition, other than [Al_90%–Mg_10%]–Fe₂O₃ system, the [Al_70%–Mg_30%]–Fe₂O₃ system exhibited a considerable solid–solid reaction and a low activation energy. Finally, target penetration experiments were conducted and the results confirmed that a projectile composed of [Al_70%–Mg_30%]–Fe₂O₃ displayed a more complete ignition of target than that of Al–Fe₂O₃ formulation.     

Study of the precision in the purge-and-trap–gas chromatography–mass spectrometry analysis of volatile compounds in honey

Data precision in the analysis by purge-and-trap coupled on-line to gas chromatography–mass spectrometry (P&T-GC–MS) of honey volatiles has been studied by statistical analysis. The contribution of non-random factors to dispersion of quantitative results was proven by comparing several statistical parameters (correlation coefficients, principal component analysis (PCA) eigenvalues and loadings) from both experimental and simulated data. PCA was also useful for grouping volatiles with similar dispersion behaviour; these groups being generally related to compounds with common properties or structural features. The use of area ratios improves data precision for compounds within the same group. Results from this study could be used for a better selection of internal standards in quantitative analysis of volatiles by P&T-GC–MS.