Density functional studies of hydrogen-bonded systems: II. Solvation of the H2O–CO complex by a nonpolar solvent

A dielectric continuum approach (SCIPCM) in the framework of density functional theory has been applied to study the structures, energetics and vibrational spectra of hydrogen-bonded H₂O–CO and H₂O–OC complexes in a non-polar solvent. The dielectric constants for Ar (1.63), Kr (1.83) and Xe (2.19) were used in order to mimic the low-temperature matrix isolation experiments. We have found that calculations which include a dielectric reaction field around the complexes are able to reproduce the experimentally observed spectral changes. The correction of the calculated interaction energy for the basis set superposition error is discussed in the framework of the self-consistent reaction field approach.     

Kinetics of decomposition of the liquid phase of the ternary system LiOH-H2O2-H2O in the presence of the solid phase of Li2O2 · H2O

The kinetics of decomposition of hydrogen peroxide in the liquid phase of the ternary system LiOH-H₂O₂-H₂O was studied in the presence the solid phase of Li₂O₂·H₂O and without it. The main kinetic parameters of the processes studied were determined.     

Kinetics of nonisothermal crystallization of Cs2O–Fe2O3–P2O5 glasses

The crystallization kinetics of Cs₂O–Fe₂O₃–P₂O₅ glasses containing 12.5–27 mol% Cs₂O were studied by using differential scanning calorimetry under nonisothermal conditions. Strong dependence of activation energy with temperature was observed, indicating the complex nature of the crystallization process. The various crystallization products were identified by X-ray diffraction technique. CsFeP₂O₇ was found to be the major crystalline phase in all cases. The overall activation energy obtained by classical model-free kinetic method was compared with that of isoconversional method; and from the results, the dependence of activation energy on extent of reaction and average temperature was delineated.     

Parameters of Li2O2 · H2O crystallization from the LiOH-H2O2-H2O ternary system

The decomposition kinetics of peroxide products contained in the liquid phase of the LiOH-H₂O₂-H₂O ternary system were studied, and the applicability of the solubility method to studying this system was demonstrated for hydrogen peroxide concentrations in the liquid phase from 2 to 6 wt % and temperatures of 21–33°C. The stabilizing influence of solid Li₂O₂ · H₂O on hydrogen peroxide decomposition was demonstrated. The temperature and concentration boundaries of existence were determined for the Li₂O₂ · H₂O phase, whose identity was verified by chemical analysis and qualitative X-ray powder diffraction analysis.     

Adsorption of several gases on flexible metal organic framework [Cu(dhbc)2(4,4'-bpy)]·H2O

The adsorption of ten gases on the flexible metal organic framework material [Cu(dhbc)(2)(4,4'-bpy)]·H(2)O (Cu(db)) has been measured over a wide range of temperatures and pressures. The gate opening condition and driving force behind gate adsorption for Cu(db) were discussed by examining the adsorption isotherms. The adsorption isotherms for each adsorbate can be generalized to a characteristic curve using the adsorption potential energy (ε) and the adsorption volume. The adsorption potential (ε(gate)) at gate opening is almost constant over a wide range of temperatures; thus, the gate pressure at a desired temperature can be deduced using the ε(gate) evaluated from one adsorption isotherm. The gate opening capacity of the gases was arranged in the order: CO(2)≒N(2)O>C(2)H(4)≒Xe>CH(4)>CO>O(2)>Ar≒N(2)>H(2), which is governed by the interaction energy between the outer surface of Cu(db) and the adsorbate. It is suggested that the gate effect is brought about when the integral interaction energy of adsorbates with the Cu(db) surface exceeds a defined limit correlating with the π-π stacking energy of Cu(db) layers.     

Molecular simulation of vapor–liquid equilibria of toxic gases

In this paper, we derived the potential parameters for three toxic gases, hydrogen sulfide, phosgene and nitrous oxide, modeled by the effective Stockmayer potential model proposed by Gao et al. [Fluid Phase Equilib. 137 (1997) 87]. The vapor–liquid equilibria (VLE) of these substances have been extensively investigated over a wide range of temperatures by the Gibbs ensemble Monte Carlo (GEMC) technique. The simulated saturated densities and pressures are in good agreement with experimental data. The critical properties obtained by regression of the simulated data also agree well with the experimental values. The present work demonstrates that the effective Stockmayer potential can describe well the toxic gases concerned.     

Structural-dynamic properties of infinitely dilute ionic liquid–nonpolar compound systems

The effect of nonpolar solvents (argon, methane, and benzene) on the structural-dynamic properties of an ionic liquid (IL), dimethylimidazolium chloride, is studied at 400 K by the method of molecular dynamics using DL_POLY _4.05 software package. The energy and structural-dynamic parameters of infinitely dilute liquid ternary systems are calculated and analyzed. The pattern of motion of the molecules of dilute compound in the IL is described. It is demonstrated that increased size of a solvent molecule enhances the effect on the ionic liquid structure, which also influences the solubility of nonpolar compounds and IL.     

Dimerization of cobalt-substituted Keggin phosphotungstate, [PW11O39Co(X)]5−, in nonpolar solvents

The tetraheptylammonium (THA) salt of cobalt-substituted polyoxotungstate with Keggin-like structure, (THA)₅[PW₁₁O₃₉Co^II(X)], was investigated by ³¹P NMR and UV/VIS spectroscopies in toluene. A solution obtained after transferring PW₁₁Co from aqueous solution into toluene, using THABr as a transfer agent, and rigorous drying, gives multiple peaks in the ³¹P NMR spectrum. The spectrum in dry toluene significantly simplifies, after extracting a hexane solution several times with water, which removes simple inorganic ions. However, even the dry toluene solution after purification has ³¹P NMR and UV/VIS spectra which cannot be explained using the known equilibrium between (THA)₅[PW₁₁O₃₉Co(H₂O)] and (THA)₅[PW₁₁O₃₉Co(__)]. Both ³¹P NMR and UV/VIS spectroscopies indicate the existence of dimers in dry toluene solutions, (THA)₁₀[(PW₁₁O₃₉Co)₂]. Pure (THA)₅[PW₁₁O₃₉Co(_)] with five-coordinate cobalt can, however, be obtained in dry toluene in the presence of excess inert salt (high ionic strength conditions). Quantum mechanical/molecular mechanical calculations also support dimer formation in toluene.     

Synthesis and thermochemical characteristics of Na2O · Al2O3 · 2.5H2O

A pure phase of monosodium aluminate hydrate Na₂O · Al₂O₃ · 2.5H₂O (MAH) is synthesized and characterized by means of XRD, IR, SEM, TGA, and DSC. The heat capacity of the compound is measured in the temperature range of ?100 to 100°C, and the thermal contributions to enthalpy and entropy are calculated. The standard entropy, enthalpy, and Gibbs energy of formation of MAH at 298 K are estimated.     

Theoretical Study of the Dehydration Process of MgCl_2·4H_2O to MgCl_2·2H_2O

Density functional theory was employed to study the dehydration mechanism of MgCI_2·4H_2O. Analysis of potential energy surface(PES) of possible pathways indicated that the most possible way was one of the water molecules halfly dissociated with an elongated bond distance with Mg~(2+),where electrostatic interaction played a leading role; another water molecule dissociated sequentially. It was in agreement with the result from differencial thermal analysis. The dehydration process of MgCI_2·4H_2O was clarified theoretically,promoting the theoretical study of dehydration of MgCI_2·2H_2O.     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

TG Study of the Dispersion Threshold of Mn2O3 on γ-Al2O3

Mn₂O₃/-Al₂O₃ catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn₂O₃ on the surface of -Al₂O₃ was determined to be 13.08% from the decomposition mass loss of supported Mn(NO₃)₂ in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn₂O₃ on the surface of -Al₂O₃.This revised version was published online in November 2005 with corrections to the Cover Date.     

Enhancement of Activity of SnO2-doped In2O3/Al2O3 Catalyst for NO Reduction with Propene in the Presence of H2O and SO2

The selective catalytic reduction of nitrogen oxides by hydrocarbons (HC-SCR) has attracted much attention as an efficient way to remove NO in the presence of excess oxygen1-2. The metal oxides are the most promising catalysts for the SCR of NO because of their high activity and selectivity3-5. In the previous work, the metal oxides such as Ag, Sn, In, Co supported on alumina for NO reduction were investigated6-8, however, the HC-SCR is usually suppressed in the presence of H2O and S…     

The effect of mechanical activation on the thermal reactions of P2O5–Al2O3–Fe2O3–Na2O phosphate glasses

The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T _g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.