Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Calculation of the formation enthalpies,standard entropies,and standard heat capacities of alkali and alkaline-earth germanates

The formation enthalpies, standard entropies, and standard heat capacities of alkali and alkaline-earth germanates were determined by regression analysis with allowance for error in the initial data (weights). The potentialities of the presented method of calculation appreciably grew due to the possibility to enhance the array of initial data independently of the crystal structure of compounds. The thermodynamic properties of alkali germanates were estimated for the first time and could be used in the physicochemical models of magmatic melts.     

Theoretical study of V<Subscript>20</Subscript>O<Subscript>50</Subscript> oxovanadate cluster compounds with alkali metal atoms

The energies and structural and spectroscopic characteristics of model М _n V₂₀O₅₀ systems corresponding to compounds of the V₂₀O₅₀ oxovanadate cluster with alkali metal atoms (M = Li, K; n = 1–20) have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, in the K _n V₂₀O₅₀ compounds, all the metal atoms are coordinated in the outer sphere to the edges of the hollow dodecahedral V₂₀O₅₀ cage to form three-center O_t?K?O_t bridges with terminal oxygen atoms. In the Li _n V₂₀O₅₀ compounds, the metal atoms can be coordinated both outside and inside the V₂₀O₅₀ cage. At n = 4, the most favorable isomer is endohedral Li₄O₄@V₂₀O₄₆ in the quintet state (S = 5), in which the four Li atoms are located in the inner cavity of the inverted O₄@V₂₀O₄₆ isomer of the oxovanadate cluster with four O atoms oriented to the cage center and form with them a corrugated eight-membered ring Li₄O₄. The decrease in energy caused by the formation of the endohedral isomer (4Li + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆) is estimated at ~377 kcal/mol. The exohedral isomer 4Li ? V₂₀O₅₀ (S = 5), in which the Li atoms are coordinated to the outside of the V₂₀O₅₀ cage, is ~23 kcal/mol less favorable. For the other members of the Li series with n from 4 to 20, the endohedral isomers with the inner Li₄O₄ ring remain preferable. At n > 4, the extra Li atoms fill the outer sphere of the cage, being coordinated to its edges to form three-center O_t?Li?O_t bridges with terminal oxygen atoms. The specific energy of formation of Li _n V₂₀O₅₀ (by the scheme nLi + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆Li_n-4) per Li atom monotonically decrease from ~98 (n = 2) to ~80 kcal/mol (n = 20). For K _n V₂₀O₅₀, these energies are ~20?25 kcal/mol lower than for the lithium analogues and decrease from ~80 (n = 2) to ~64 kcal/mol (n = 12). The atoms of both alkali metals in the M _n V₂₀O₅₀ systems have large positive effective charges (0.85e?0.92e for K and 0.65e?0.78e for Li), which also monotonically decrease with increasing n. The addition of each alkali metal atom is accompanied by its ionization (М → М⁺) along with the reduction of one of the neighboring pentavalent vanadium atoms to the tetravalent state (V^V → V^IV) and localization of the unpaired electron in its 3d shell. For all Li _n V₂₀O₅₀ complexes, the states with maximal multiplicity and parallel spins are the most preferable.     

Crystal structure of EuLnAgS<Subscript>3</Subscript> (Ln = Gd and Ho) compounds

The crystal structures of the first prepared EuLnAgS₃ (Ln = Gd and Ho) compounds, which have two polymorphs, were determined by X-ray powder diffraction. α-EuLnAgS₃ phases are isostructural to BaErAgS₃ (monoclinic crystal system, space group C2/m): a = 17.3168(10) Å, b = 3.9683(2) Å, c = 8.3174(4) Å, β = 103.94° (EuGdCuS₃); a = 17.1729(12) Å, b = 3.9367(3) Å, c = 8.2905(6) Å, β = 103.9° (EuHoCuS₃). β-EuLnAgS₃ phases belong to the AgBiS₂ structure type (cubic crystal system, space group Fm-3m): a = 5.739(2) Å (EuGdCuS₃) and a = 5.678 Å (EuHoCuS₃). In the α-EuLnAgS₃ crystal structure, LnS₆ octahedra and AgS₅ trigonal bipyramids share edges to form a three-dimensional (3D) structure with channels accommodating Eu²⁺ ions. A decrease in Ln³⁺ ionic radius gives rise to the crystal-chemical contraction of the 3D structure.     

Oxidation of hydrogen on palladium: Chemicurrents in the Schottky nanodiode

The oxidation of hydrogen on palladium was studied by the chemicurrents method using the nanosized catalytic Pd/n-Si Schottky diode. The chemicurrent was found to be generated when the reactions H₂+O₂ and H + O + H₂ + O₂ occurred on the palladium surface, occasionally in the auto-oscillation mode. A model was created that describes the complex kinetic behavior of the reaction. Mathematical modeling was performed and showed the possibility of complex auto-oscillations of chemicurrent similar to those obtained in experiments. The catalytic Schottky nanodiode method was shown to be effective for reaction visualization and can be used as a new physical method for investigating the chemical processes on the catalyst surface.     

Utility of 2-(5-methyl-1-phenyl-1H-pyrazol-4-yl)-2-oxo-N′-phenylaceto-hydrazonoyl bromide as precursor for synthesis of new functionalized heterocycles

2-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-oxo-N′-phenylaceto-hydrazonoyl bromide was synthesized and used as precursor for synthesis of some new 1,3,4-thiadiazoles, pyrrolo[3,4-c]pyrazoles, and 1,2,4-triazolo[4,3-a]pyrimidines. The mechanisms that account for formation of products were discussed. Also, the structures of all the newly synthesized products were confirmed based on elemental analysis, spectral data and by alternative methods.     

Hybrid materials based on polymethylsilsesquioxanes containing Fe,Pt, and Fe–Pt metallic nanoparticles

New hybrid materials based on Pt, Fe, and Pt–Fe nanoparticles stabilized in a matrix of polymethylsilsesquioxane nanogel and ultrahigh molecular weight polyethylene (UHMWPE) were prepared. Metal vapor synthesis was used to produce mono- and bimetallic nanoparticles. It was shown that organosilicon nanogel effectively stabilizes Pt nanoparticles with an average size of 0.9 nm. Using the nanogel results in the formation of superparamagnetic Fe particles 3–5 nm in size that consist of ferromagnetic Fe⁰ core and antiferromagnetic shells of Fe oxides. It is established that using an organosilicon matrix in the formation of Pt-Fe/UHMWPE systems helps reduce the average particle size of Fe in the material from 6.5 to 4.5 nm and narrow their particle size distribution. The composition, magnetic and electronic characteristics of the nanocomposites are studied via transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, XANES, and EXAFS.     

Properties of methylammonium lead iodide perovskite single crystals

The technique for growing CH₃NH₃PbI₃ single crystals from saturated solutions in concentrated hydroiodic acid is improved by introducing a reducing agent (hypophosphorous acid). The structure of perovskite is confirmed by single crystal XRD. By energy dispersive spectroscopy and X-ray photoelectron spectroscopy it is established that the stoichiometry of the grown crystals corresponds to the CH₃NH₃PbI₃ compound. Changes in the photoluminescence intensity during in-air measurements show that the crystals synthesized using the reducing agent are more stable in the external environment with laser exposure than without it.     

Decomposition of pentaammineaquacobalt(III) perchlorate under laser radiation action

Photolytic decomposition of the complex [Co(NH₃)₅(H₂O)](ClO₄)₃ under the action of a laser with a wavelength of 355 nm, which is resonant in energy to the energy of the (¹ A _1g → ¹ T _2g ) d–d transition, was studied. Decomposition of the complex is accompanied by a release of ammonia with its subsequent oxidation to nitrogen oxides and by partial cobalt reduction with the formation of the mixed cobalt(II, III) oxide Co₃O₄.