Vapour pressure of guest and thermodynamic stability of inclusion compounds [Ni(DBM)2Py2]*2G (DBM = dibenzoylmethanate anion, G = pyridine, tetrahydrofurane and chloroform)

Temperature dependences of the equilibrium vapour pressure of the guest molecules (G) over inclusion compounds [Ni(DBM)₂Py₂]*2G (DBM = C₆H₅COCHCOC₆H₅ ^?—dibenzoylmethanate anion; Py = pyridine; G = pyridine, tetrahydrofurane and chloroform) were investigated by means of the static membrane procedure. It was established using TGA and DTA methods that both of two guest molecules get detached at the first step of decomposition 1/2[Ni(DBM)₂Py₂]*2G_s = 1/2[Ni(DBM)₂Py₂]_s + G_gas. The changes of thermodynamic parameters $ (\Updelta {\text{H}}^{0}_{\text{av}} , \Updelta {\text{G}}^{0}_{ 2 9 8} \;{\text{and}}\;\Updelta {\text{S}}^{0}_{\text{av}} ) $ in this process were determined on the basis of the experimental data.     

Vapour pressure of 4-methylpyridine (MePy) over [Ni(MePy)4(NCS)2]·y(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy) clathrates during their dissociation

Strain measurement and quasiequilibrium thermogravimetry were used to study the dissociation processes of two clathrates, [Ni(MePy)₄(NCS)₂]·(MePy) and [Cu(MePy)₄(NCS)₂]·2/3(MePy), accompanied by the liberation of MePy into the gaseous phase. In the Ni clathrate dissociation process in the temperature range 298–368 K the liberated MePy was redistributed between the solid clathrate and gaseous phases; the MePy vapour pressure over the clathrate is a function of temperature and the guest contenty, which agrees with the presence in the MePy-[Ni(MePy)₄(NCS)₂] system of a wide range of -clathrate solutions, [Ni(MePy)₄(NCS)₂]·y(MePy). The same methods used to study the Cu clathrate dissociation resulted in conclusions different from those obtained for the dissociation process of the above clathrate: the process is described by the equation [Cu(MePy)₄(NCS)₂]·2/3(MePy)_solid =[Cu(MePy)₂(NCS)₂]_solid+22/3(MePy)_gas; the temperature dependence of the Mepy vapour pressure over the solid sample does not depend on its composition, which points to the absence from the system of solid solutions based on the clathrate. Standard changes of the enthalpy, entropy, and isobaric-isothermal reaction potential for the temperature range 292–325 K are equal to 178.6±1.7 kJ (mole of clathrate)^–1, 463±5.6 J (mole of clathrate)^–1 K^–1, and 40.4±2.4 kJ (mole of clathrate)^–1, respectively.     

X-ray diffraction study of the clathrate [MnPy4(NO3)2)]·2Py and complex [MnPy3(NO3)2] formed in the pyridine (Py)-manganese nitrate system

A clathrate compound [MnPy₄(NO₃)₂]·2Py was synthesized and studied by single-crystal X-ray diffraction analysis (KM-4 diffractometer, CuK_α,ω/2? scan mode,? _max=78°). The unit cell is base-centered orthorhombic, space group Ccca, a=12.097(4), b=15.197(4), c=17.213(4) Å, V=3164(2) ų, Z=4, R=0.072, for 632 reflections and 107 parameters in the least-squares analysis. The host molecule has 222 symmetry. Two monodentate nitrato groups and four pyridine ligands are coordinated to Mn(II) along the symmetry axes (the former via O). The pyridine guest molecules lie in the cavities of the crystal framework. For [MnPy₃(NO₃)₂)], only unit cell parameters were determined: a=12.467(5), b=9.514(2), c=16.383(5) Å,β=108.93(4), V=1838(1) ų space group C2/c or Cc (according to extinctions). The pyridine-manganese nitrate system is shown to be analogous to the previously investigated Co, Ni, Cu, Zn, and Cd systems.     

The depth of nanocrystallites of pyrocarbon deposition in pores of ultrafiltration membranes and its influence on their efficiency

Scanning electron microscopy and energy dispersion spectrometry were used to determine the depth of the deposition of pyrocarbon nanocrystals (PNCs) on the pore surface of TRUMEM inorganic ultrafiltration membranes (D _pore = 50 nm) depending on the pressure of the gas subjected to pyrolysis (methane). It was shown that, while the deposition of PNCs occurred over the whole pore length equal to the selective layer thickness (20 μm) at 4.9 kPa methane pressure, an increase in pressure to 40.0 kPa decreased the deposition depth to 5.0 μm. Simultaneously, the λ/D ratio decreased from 94 to 11. At a pressure increased to 100.0 kPa, the depth of PNC deposition was ～1.5 μm (λ/D = 5). Changes in the depth of PNC deposition and the λ/D ratio depending on pressure were similar in character and could be described by exponential dependences. With PNCs deposited ～1.5 nm deep (100 kPa), membranes with pore size 8–17 nm were obtained. Their efficiency, for instance, for ethanol, was 50–75% of that of the initial membranes. The diameter of pores decreased by 3–6 times.     

Phase equilibria in a system of aqueous arginine with an octane solution of sulfonic acid

The extraction of arginine (Arg) from aqueous salt (0.1 M NaCl) solutions with a sulfo extractant in a wide range of pH values and amino acid concentrations was studied. The 0.1 M solution of dinonylnaphthalenesulfonic acid (HD) in octane was used as an extractant. The degree of extraction was found to be high at pH 0.8–9.0. This can be explained by the effect of additional intermolecular interactions in the extractant phase involving the guanidine group of Arg.     

Phase and structural study of clathrate formation in the [Zn(MePy)2(NCS)2]-MePy system (MePy=4-methylpyridine)

A phase diagram of the [Zn(MePy)₂(NCS)₂]-MePy binary system has been studied by DTA and solubility methods. Two compounds melting incongruently (at 63 and 57°C) have been discovered in the system. They have been obtained as separate phases with crystals of different shape (needles and octahedra). Their composition has been determined by analytical methods and verified by X-ray structural analysis: [Zn(MePy)₄(NCS)₂]·0.67 MePy·xH₂O, wherex depends on the synthesis conditions, and [Zn(MePy)₄(NCS)₂]·MePy, respectively.The preliminary X-ray study of the first compound (at –100°C) has shown it to be isostructural with the known clathrates of the common formula [M(MePy)₄(NCS)₂]·0.67MePy·xH₂O, where M=Cu, Mn, Mg andx=0–0.33. The unit cell parameters are as follows:a=27.20(1),c=11.202(4) Å, space group ,Z=9.The X-ray study of [Zn(MePy)₄(NCS)₂]·MePy (at–50°C) has shown it to be analogous to the organic zeolite -phase with the guest MePy molecules located in the channels formed by molecular packing of the [Zn(MePy)₄(NCS)₂]host. The cell is tetragonal, the space groupI4₁/a,a=16.845(6),c=23.496(7) Å,V=6667(4) ų,Z=8,D _calc=1.289 g cm^–3,R=0.074. The zinc cation is surrounded by a slightly irregular octahedron of six nitrogen atoms of the MePy and NCS ligands. The crystallisation field of the host [Zn(MePy)₄(NCS)₂] complex in the temperature range concerned is absent in the phase diagram. It suggests contact stabilization of the [Zn(MePy)₄(NCS)₂] molecule by the guest in the clathrates. Supplementary Data relevant to this paper have been deposited with the British Library at Boston Spa, Wetherby, West Yorkshire, U.K. as Supplementary Publication No. SUP 82166 (15 pages).     

Research and application of inorganic selective sorbents at Mayak PA

This work has been performed in order to identify selective inorganic sorbents for caesium and strontium. Thin-layer sorbents with nickel ferrocyanide embedded in an inert matrix were found to be the best for caesium. Sorbents including non-stoichiometric manganese dioxide were selected for strontium. Bench tests have been carried out on the purification of desalted water of SNF storage-pool from ¹³⁷Cs, and on the purification of contaminated natural water from ⁹⁰Sr. The facility for synthesizing the ferrocyanide sorbent with the registered mark ‘Seleks-CFN’ has been brought into operation. The sorbent ISM-S seems promising for ⁹⁰Sr decontamination. To cite this article: M.V. Logunov et al., C. R. Chimie 7 (2004).

Résumé

Recherches et applications sur l’utilisation de sorbants spécifiques à Mayak. Des sorbants sélectifs du césium et du strontium ont été identifiés. Pour le césium, le meilleur s’avère être le ferrocyanure de nickel, s’il est utilisé sous forme de couche mince. Pour le strontium, on a sélectionné des composés non stœchiométriques de dioxyde de manganèse. On a mené des tests visant à épurer en césium l’eau des piscines d’entreposage des combustibles nucléaires usagés, et en strontium des eaux contaminées. Une installation industrielle permettant de préparer le sorbant à base de ferrocyanure de marque « Seleks-CFN » a été réalisée. Le sorbant ISM-S semble prometteur pour la décontamination en strontium. Pour citer cet article : M.V. Logunov et al., C. R. Chimie 7 (2004).     

Revisiting the nature of Cu sites in the activated Cu-SSZ-13 catalyst for SCR reaction

Cu-SSZ-13 is a highly active NH₃-SCR catalyst for the abatement of harmful nitrogen oxides (NO_x, x = 1, 2) from the exhausts of lean-burn engines. The study of Cu-speciation occurring upon thermal dehydration is a key step for the understanding of the enhanced catalytic properties of this material and for identifying the SCR active sites and their redox capability. Herein, we combined FTIR, X-ray absorption (XAS) and emission (XES) spectroscopies with DFT computational analysis to elucidate the nature and location of the most abundant Cu sites in the activated catalyst. Different Cu species have been found to be dominant as a function of the dehydration temperature and conditions. Data analysis revealed that the dehydration process of Cu cations is essentially completed at 250 °C, with the formation of dehydrated [CuOH]⁺ species hosted in close proximity to 1-Al sites in both d6r and 8r units of the SSZ-13 matrix. These species persist at higher temperatures only if a certain amount of O₂ is present in the gas feed, while under inert conditions they undergo virtually total “self-reduction” as a consequence of an OH extra-ligand loss, resulting in bi-coordinated bare Cu⁺ cations. Synchrotron characterization supported by computational analysis allowed an unprecedented quantitative refinement of the local environment and structural parameters of these Cu(ii) and Cu(i) species.     

Noncatalytic hydrogenation of decene-1 with hydrogen accumulated in a hybrid carbon nanostructure in nanosized membrane reactors

Studies on the creation of nanosized membrane reactors (NMRs) of a new generation with accumulated hydrogen and a regulated volume of reaction zone were continued at the next stage. Hydrogenation was performed in the pores of ceramic membranes with hydrogen preliminarily adsorbed in mono- and multilayered orientated carbon nanotubes with graphene walls (OCNTGs)—a new hybrid carbon nanostructure formed on the inner pore surface. Quantitative determination of hydrogen adsorption in OCNTGs was performed using TRUMEM ultrafiltration membranes with D _av = 50 and 90 nm and showed that hydrogen adsorption was up to ～1.5% of the mass of OCNTG. The instrumentation and procedure for noncatalytic hydrogenation of decene-1 at 250–350°C using hydrogen accumulated and stored in OCNTG were developed. The conversion of decene-1 into decane was ～0.2–1.8% at hydrogenation temperatures of 250 and 350°C, respectively. The rate constants and activation energy of hydrogenation were determined. The latter was found to be 94.5 kJ/mol, which is much smaller than the values typical for noncatalytic hydrogenations and very close to the values characteristic for catalytic reactions. The quantitative distribution of the reacting compounds in each pore regarded as a nanosized membrane reactor was determined. The activity of hydrogen adsorbed in a 2D carbon nanostructure was evaluated. Possible mechanisms of noncatalytic hydrogenation were discussed.     

X-ray structural analysis of the dinitratotetrapyridinecopper(II) complex and its clathrates with tetrahydrofuran and chloroform

Journal of Structural Chemistry - The structure of the [CuPy4(NO3)2] complex (Py = pvridine) and its clathrates with tetrahydrofuran and chloroform (both with a host:guest molar ratio of 1:2) were...