Thermodynamics of cation exchange on natural heulandite

Microcalorimetric measurements were carried out on the heat effects of ion exchange in a system containing natural heulandite and aqueous solutions of pairs of electrolytes at 303.15 K. The electrolytes studied were NaCl, KCl, RbCl, CsCl, and NH ₄ Cl. The ion exchange enthalpy decreases in the cation series: Na⁺ > NH₄ ⁺ > K⁺ > Rb⁺ > Cs⁺.Institute of the Chemistry of Carbon Materials, Siberian Branch, Russian Academy of Sciences, 650099 Kemerovo. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 754–756, March, 1992.     

Generalized gradient approximation adjusted to transition metals properties: Key roles of exchange and local spin density

Perdew-Burke-Ernzerhof (PBE) and PBE adapted for solids (PBEsol) are exchange-correlation (xc) functionals widely used in density functional theory simulations. Their differences are the exchange, μ, and correlation, β, coefficients, causing PBEsol to lose the Local Spin Density (LSD) response. Here, the μ/β two-dimensional (2D) accuracy landscape is analyzed between PBE and PBEsol xc functional limits for 27 transition metal (TM) bulks, as well as for 81 TM surfaces. Several properties are analyzed, including the shortest interatomic distances, cohesive energies, and bulk moduli for TM bulks, and surface relaxation degree, surface energies, and work functions for TM surfaces. The exploration, comparing the accuracy degree with respect experimental values, reveals that the found xc minimum, called VV, being a PBE variant, represents an improvement of 5% in mean absolute percentage error terms, whereas this improvement reaches ~11% for VVsol, a xc resulting from the restoration of LSD response in PBEsol, and so regarded as its variant.     

洗涤剂用沸石的钙离子交换性能的研究

作为洗涤剂助剂,沸石的主要作用是通过离子交换降低水中的钙镁离子浓度、软化洗涤用水以提高洗涤剂中的表面活性剂的洗涤效率。因此,沸石对钙镁离子交换容量的大小和交换速率的快慢是评价洗涤用沸石的重要质量指标［１,２］。目前,使用最多的沸石类助剂为ＮａＡ沸石。为了弥补ＮａＡ型沸石镁离子交换能力的不足,先后又出现了Ａ、Ｘ型沸石混合使用［３］、高铝Ｘ型沸石(ＭＡＸ)［４～５］和高铝Ｐ型沸石(ＭＡＰ)等技术［１,２］。ＭＡＸ型和ＭＡＰ型沸石与ＮａＡ型沸石一样具有最小的硅铝比(ＳｉＯ２／Ａｌ２Ｏ３＝２)。因此,这三种沸石的…     

Aryloxide-based multidentate ligands for early transition metals and f-element metals

This article presents an overview of the chemistry of early transition metal and f-element complexes stabilized by aryloxide-based multidentate ligands. Preparations and reactivity studies of these compounds are discussed. The presence of the bridging units in this ligand system imposes a strong geometry constraint to the aryloxide groups, which leads the way to novel patterns of structure and reactivity.     

Thermal explosion of nitrophenates of transition metals

The thermal decomposition studies on nitrophenates of copper, nickel and cobalt have been undertaken,-t curves show dehydration of these compounds at lower temperatures whereas dehydration cum decomposition seem to occur at higher temperatures leading to oxidative combustion of aromatic part. NO₂ gas is evolved during decomposition which seems to be responsible for oxidative reactions leading to detonation. The explosion temperature and velocity of detonation have been found to be linearly related with the number of nitro groups. The mechanism of thermal explosion has also been discussed.Thanks are due to Prof. S. Giri for providing laboratory facilities; and Aeronautics R&D Board, Ministry of Defence for financial assistance. Authors are also grateful to Shri I. P. S. Kapoor for helpful discussions.     

Equilibria and heats of ion exchange in the system of mordenite-alkali and alkaline earth cations

A concurrent absorption analytical study of the ion exchange equilibria and direct microcalorimetric measurement of the heat of ion exchange absorption of K⁺ and Ca²⁺ cations for the sodium forms of two mordenites (NaM) obtained from naturally occurring samples rich in Na⁺ and Ca²⁺ cations has been carried out for the first time. The free energies and entropies of exchange have been calculated. It was shown that the free energy of exchange in the K⁺-NaM system is determined by the enthalpy, whereas in the Ca²⁺-NaM system it is determined by the entropy of solvation. The measured thermodynamic characteristics of exchange were analyzed taking into account the preferred localization of sorption for the cations in the structure. A memory effect in natural mordenites has been established for extra-skeletal K⁺ and Ca²⁺ cations, in the presence of which these zeolites crystallized in nature. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 312–317, September–October, 2006.     

Role of Ion exchange in permeation processes

The single ion transport of transition metal ions like Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ were carried out through the H⁺ and alkali metal ion forms of Nafion membrane. These studies showed that the ion exchange selectivity coefficient of the permeating ion had an effect on its transport process. It was found that the diffusion coefficient values (D) were directly proportional to the selectivity coefficient (K). This shows that the initial stage of permeation is governed by ion exchange process (effect of K on D).     

Effect of ion exchange by an organic cation on platinum immobilization on clays

Clay-supported platinum catalysts were prepared by ion exchange. The platinum precursor has been reduced either in the presence or in the absence of cinchonidinium cations introduced in the interlamellar space of the cationic clay. The samples were characterized by XRD and TEM. Reduction by NaBH₄ in the absence of cinchonidinium cations and the subsequent introduction of this latter ensured the formation of monodispersed, small platinum crystallites immobilized mostly between the clay sheets. On the other hand, reduction in the presence of the organic cations resulted in migration of the platinum particles on the external surface of the clay.     

Diene complexes of early transition metals: ideas and progresses at Osaka University

Historical perspectives for the chemistry of diene complexes of early transition metals developed at Osaka University in the period after 1970s were reviewed briefly and personally. Preparative chemistry of this field commenced from the magnesium-diene 1:1 compounds and quickly extended to almost all the early transition metals. By the studies operated together with other researchers, unique features of these diene complexes, especially their bonding and structure, selective reactions, and catalysis performances are described.     

Gaussian basis sets for transition metals of the second series

A Gaussian basis set consisting of (15s, 9p, 8d) Gaussian functions has been optimized for the transition metal atoms of the second series (fourth-row atoms).     

Sorption of transition metal cations on natural heulandite

The cation exchange equilibrium in the systems of natural heulandite-binary aqueous solutions of NaCl, NiCl₂, CuCl₂, ZnCl₂, and MnCl₂ was studied. The corrected coefficients of the selectivity (k ^a _M/Na) and thermodynamic constants (K _M/Na) of the cation exchange of Na⁺ cations for transition metal cations were determined. The selectivity of the cation exchange on natural heulandite increases in the following order: Ni²⁺ < Cu²⁺ < Zn²⁺ < Na²⁺ < Mn²⁺.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1101–1103, May, 1996.     

NEB与过渡金属元素二元配合物的pH电位法研究

用精密pH电位法测定了在甲醇 水混合溶剂中配体氨三乙氧基三苯甲酸 (NEB)质子化常数 (2 5℃ ,I =0 .2 0mol·L- 1 NaCl) ,讨论了溶剂对质子化常数的影响 ,结果表明溶剂对质子化常数的影响呈线性关系。测定了NEB与部分过渡金属M(Ⅱ) (M =Cd、Co、Ni、Cu及Zn)二元配合物的稳定常数 ,实验数据处理用程序MINIQUAD - 82和MIQUV完成。在二元体系中存在的配合物物种有 112、111、110及 2 10型 (M2 + ∶NEB3- ∶H+ ) ,并且 111及 110型配合物稳定常数的变化规律Cd(Ⅱ) Zn(Ⅱ)符合Irving Williams序列     

Thermodynamic and structural features of chloro-complex formation of bivalent transition metals in dimethylsulfoxide

Heats of formation of complexes of the type MCl⁺ have been determined calorimetrically for M=Mn, Co, Ni, and Cu in dimethylsulfoxide (DMSO), at 25°C. Combined with the stability constants of the complexes they complete the thermodynamic characteristics of these systems. It appears that the complexes are formed in markedly endothermic reactions and owe their considerable stabilities to the large positive reaction entropies. The exceptionally large entropy of formation of the CuCl⁺ complex indicates its essentially pentacoordinate structure, CuCl(DMSO) ₄ ⁺ , while the other complexes are octahedral, MCl(DMSO) ₅ ⁺ , with a probable contribution of the outer-sphere ion-pair for CuCl⁺. The characteristic features of complex formation in dimethylsulfoxide, as compared with water, are discussed and ascribed to the relatively large molar entropy of this liquid.Deceased.     

Synthesis and characterization of ion-exchangeable titanate nanotubes

Titanate nanotubes were synthesized under hydrothermal conditions. The optimized synthesis (100-180 degrees C, longer than 48 h), thermal and hydrothermal stability, ion exchangeability and consequent magnetic and optical properties of the titanate nanotubes were systematically studied in this paper. First, nanotubes with monodisperse pore-size distribution were prepared. The formation mechanism of the titanate nanotubes was also studied. Second, the thermal and hydrothermal stability were characterized with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), and Raman spectroscopy. Results showed that sodium ions played a significant role in the stability of the frameworks. Third, the selective ion exchangeability was demonstrated with a series of ions. The ion substitution also enlarged the BET surface area of the titanate nanotubes to 240 m(2) x g(-1). Combination of these two features implied that these nanotubes might be functionalized by substitution of different transitional-metal ions and consequently used for selective catalysis. Magnetism, photoluminescence, and UV/Vis spectra of the substituted titanate nanotubes revealed that the magnetic and optical properties of the nanotubes were modifiable.     

Thermodecomposition ofo-benzoquinone complexes of transition metals

Thermodecomposition of 3,5- and 3,6-di-tert-butyl-o-benzoquinone complexes of Cu, Fe, Co, Cr, Mo, and W has been investigated in the solid phase by the thermogravimetric method. The relative stability of a series of complexes has been determined from the temperatures at which their decomposition begins. Detachment of a neutral electron-donor ligand takes place in the first stage. Detachment of ano-quinone ligand and decomposition of theo-benzoquinone formed occur in the next stage. Thermodecomposition of Fe, Co, Cr, Mo, and W complexes gives oxides or carbides, while copper complexes decompose to pure metal.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 327–329, February, 1994.     

Thermodynamics of the solution equilibria of 3-hydroxypyridine and pyridoxine in water-dioxane mixtures

The thermodynamics of tautomeric and microscopic ionization equilibrium constants of 3-hydroxypyridine and pyridoxine have been determined in waterdioxane mixtures (0–70% weight fraction in dioxane) ranging from 10°C to 50°C. Generally, for both types of processes, the entropic contributions to the Gibbs energy predominate and this tendency increase concomitantly with the dioxane content in the media. The thermodynamic parameters are consistent with the corresponding values obtained from macroscopic ionization processes. An equation for the equilibrium constant K as a function of temperature and a solvent characteristic parameter is proposed to predict the K values throughout the whole range of the temperature and solvent compositions studied.     

Secondary ion emission of selected transition metals under nitrogen oxides

The emission of various positive secondary ions has been investigated for polycrystalline targets of Ti, V, Cr, Nb, Ta, Co, Ni, Cu, Pd and Pt, which were bombarded by Ar⁺ ions under dynamic SIMS (DSIMS) conditions in the presence of the gaseous nitrogen oxides N₂O, NO and NO₂ at fixed pressure and under residual gas. Besides ions of the Me⁺ type several fragmentary ions (e.g. N⁺, O⁺, NO⁺, MeN⁺ and MeO⁺) and also cluster ions Me _x O _y ⁺ (x 2, 0 y 2) were detected. Signals of a more molecular type with respect to the reactant gas, e.g. MeNO⁺, were only found for Co, Ni, Cu, Pd and Pt. From this, one may infer that for the other targets the nitrogen oxides will exist preferentially in a dissociatively adsorbed state at the metal surface. Several aspects of secondary ion emission can be explained assuming a different degree of oxidation for the metals under the influence of reactant gas.Part of the dissertation     

磺酸型阳离子交换树脂催化合成肉桂酸甲酯

以磺酸型阳离子交换树脂为催化剂，由肉桂酸和甲醇合成了肉桂酸甲酯。考察了反应条件对酯化反应的影响和树脂的催化稳定性。结果表明，肉桂酸的转化率可达９５．５％，且催化剂的性能稳定。