Kinetics and mechanism of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl<Subscript>2</Subscript>–CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A systematic study of the kinetics of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl₂–CuCl₂/γ-Al₂O₃ supported catalyst was carried out over a wide range of the partial pressures of oxygen, water, and CO in order to test hypotheses on the reaction mechanism. It was shown that, as the temperature was increased from 20 to 38°C, rate of formation of CO₂ decreased and the apparent activation energy was about–40 kJ/mol. The hypotheses of different degrees of complexity concerning the reaction mechanism were formulated based on physicochemical data and a Langmuir–Hinshelwood model. Mechanisms in which carbon dioxide is formed on the interaction of the surface Pd(I) and Pd(II) complexes that include carbon monoxide and water with the surface complex of Cu(I) that coordinates oxygen were recognized as the most probable.     

State of active components on the surface of the PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the low-temperature oxidation of carbon monoxide

The state of the active constituents of the freshly prepared PdCl₂-CuCl₂/γ-Al₂O₃ catalyst for the low-temperature oxidation of the carbon monoxide by molecular oxygen was studied by X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance IR Fourier transform spectroscopy (DRIFTS). It was shown that copper in the form of a crystalline phase of Cu₂Cl(OH)₃ with the structure of the mineral paratacamite and palladium chloride in an amorphous state occurred on the surface of γ-Al₂O₃. According to XAS data, the local environment of palladium consisted of four chlorine atoms, which formed a flat square with an increased distance between palladium and one of the chlorine atoms. The evolution of the local environments of copper and palladium upon a transition from the initial salts to the impregnating solutions and chlorides on the surface of γ-Al₂O₃ was considered. The role of γ-Al₂O₃ in the formation of the Cu₂Cl(OH)₃ phase was discussed. It was found by the DRIFTS method that linear (2114 cm⁻¹) and bridging (1990 and 1928 cm⁻¹) forms of coordinated carbon monoxide were formed upon the adsorption of CO on the catalyst surface. The formation of CO₂ upon the interaction of coordinated CO with atmospheric oxygen was detected. Active sites including copper and palladium were absent from the surface of the freshly prepared catalyst.     

Identification of iron oxidation states in the products of interaction of Na<Subscript>2</Subscript>O<Subscript>2</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> by Mössbauer absorption spectroscopy

The first stage of the solid-phase reaction of Na₂O₂ and Fe₂O₃ yields a tetravalent iron derivative. The product is unstable and disproportionates to form compounds with different oxidation states of iron. Analysis of their Mössbauer spectra was performed with the DISCVER program based on the Afanas’ev-Chuev method. At the early stage of analysis, the program identifies the maximal possible number of well-defined lines in the spectrum with a specified statistical quality and, thus, discerns a large number of known and unknown iron derivatives (phases) in samples of complex composition. Previously unknown highest oxidation states of iron from +5 to +8 were identified.     

A magnetic CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite fabricated by the sol-gel method for electrocatalytic oxidation and determination of L-cysteine

Magnetic CoFe₂O₄/SiO₂ spinel-type nanocomposites have been fabricated by a sol-gel method in the presence of various acids. Their structural, morphological and magnetic properties were characterized by XRD, SEM, TEM, FTIR, VSM and EDX which revealed that they are formed in the presence of all precursors. TEM analysis indicates homogeneous and porous spherical morphology with nanosize grains 10–20 nm in diameter in the presence of salicylic acid. Electrochemical sensor application of nanocrystalline CoFe₂O₄/SiO₂ synthesized by salicylic acid for determination of L-cysteine was investigated using differential pulse voltammetry (DPV) and cyclic voltammetry (CV). DPV indicates that the sensor shows remarkable sensitivity for the determination of L-Cys. The response of a glassy carbon electrode modified with CoFe₂O₄/SiO₂ is linear in the 0.02–425 μM L-Cys concentration range, with a 0.20 μM detection limit (at an S/N ratio of 3). The electrode produces a negligible current response for tryptophan, glutamic acid and citric acid at the working potential applied (+0.748 V vs Ag/AgCl). The electrode is reliable, simple, rapidly prepared, precise, and the method does not require extensive sample treatment.

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Graphical abstract A CoFe₂O₄/SiO₂ magnetic nanocomposite was synthesized by a sol-gel auto combustion method in the presence of various acids as precursors. A highly sensitive electrochemical sensor was fabricated for determination of trace amount of L-cysteine using a glassy carbon electrode modified with the nanocomposite.

     

Kinetics for the Oxygen Evolution Reaction and Application of the Ti/SnO<Subscript>2</Subscript> + RuO<Subscript>2</Subscript> + MnO<Subscript>2</Subscript> Electrode

A Ti/SnO₂ + RuO₂ + MnO₂ electrode was prepared by thermal decomposition of their salts. Results from SEM and XPS analyses, respectively, indicate that the coating layer exhibits a compact structure and the oxidation state of Mn in the coating layer is +IV. The experimental activation energy for the oxygen evolution reaction, which increased linearly with increasing overpotential, is about 8 kJ⋅mol⁻¹ at the equilibrium potential (η=0). The electrocatalytic characteristics of the anode are discussed in terms of ligand substitution reaction mechanisms (Sn1 and Sn2). It was found that the transition state for oxygen evolution at the anode in acidic solution follows a dissociative mechanism (Sn1 reaction). The Ti/SnO₂ + RuO₂ + MnO₂ anode in conjunction with UV illumination was used to degrade phenol solutions, where the concentration of phenol remaining was determined by high-performance liquid chromatography (HPLC). The results indicate that the degradation efficiency of phenol on the anode can reach 96.3% after photoelectrocatalytic oxidation for 3 h.     

Influence of the temperature and cation nature on the EPR spectra of salts with the [Ni<Superscript>III</Superscript>(η<Superscript>5</Superscript>-1,2-B<Subscript>9</Subscript>C<Subscript>2</Subscript>H<Subscript>11</Subscript>)<Subscript>2</Subscript>]- anion

The influence of specific features of the structure and nature of the cations (Ph₄P⁺, H(Phen)⁺, Cs⁺, and (CH₃)₄N⁺) on the ERP spectra of the nickel ions in salts with the dicarbollylnickelate anion [Ni(B₉C₂H₁₁)₂]⁻ is studied. It is shown that the change in the cation type in these compounds results in the electron density redistribution, which affects the change in the main and average values of the g factor. The g _av value increases over that observed in frozen solutions upon the localization of the positive charge of the cation on one atom and in the absence of the screening effect of the solvent and large functional groups of the cation. The exception is the compound (Ph₄P⁺)NiCb₂⁻ (Cb is B₉C₂H₁₁) with solvated CCl₄ molecules. For all compounds studied, the temperature dependence of the linewidths in the EPR spectra is described by the equation ΔH = αT + βT⁷ with different α and β values and is defined by the temperature dependence of the relaxation process caused by the Raman interaction.     

Calorimetric study of the acidic character of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–TiO<Subscript>2</Subscript>/SO<Subscript>4</Subscript><Superscript>2−</Superscript> catalysts used in methanol oxidation to dimethoxymethane

The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated samples resulted in a decrease in surface area from 402 to 57 m² g⁻¹ and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination temperature appeared to be around 673 K.     

Reaction of the [B<Subscript>10</Subscript>H<Subscript>9</Subscript>O<Subscript>2</Subscript>C<Subscript>4</Subscript>H<Subscript>8</Subscript>]<Superscript>–</Superscript> anion with C-nucleophiles

The reactions of 1,4-dioxane-substituted closo-decaborate anion ([B₁₀H₉O₂C₄H₈]^–) with metal acetylenides, diethyl malonate, ethyl acetoacetate, triethyl orthoformate, acetylacetone, and malonodinitrile were studied. The reactions were shown to be accompanied with substituent ring opening and attachment of the corresponding pendant functional group. The obtained compounds were characterized by various physicochemical methods (IR and polynuclear NMR spectroscopy, ESI mass spectrometry).     

Calorimetric study of molecular superconductor κ-(BEDT-TTF)<Subscript>2</Subscript>Ag(CN)<Subscript>2</Subscript>H<Subscript>2</Subscript>O which contains water in the anion layers

Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)₂Ag(CN)₂H₂O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition was observed at 5 K. The existence of residual γ^* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)₂Cu(NCS)₂, and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is considered to give low-energy phonon excitations reflected in the heat capacity.     

On the Control of Plasma Parameters and Active Species Kinetics in CF<Subscript>4</Subscript> + O<Subscript>2</Subscript> + Ar Gas Mixture by CF<Subscript>4</Subscript>/O<Subscript>2</Subscript> and O<Subscript>2</Subscript>/Ar Mixing Ratios

The effects of both CF₄/O₂ and Ar/O₂ mixing ratios in three-component CF₄ + O₂ + Ar mixture on plasma parameters, densities and fluxes of active species determining the dry etching kinetics were analyzed. The investigation combined plasma diagnostics by Langmuir probes and zero-dimensional plasma modeling. It was found that the substitution of CF₄ for O₂ at constant fraction of Ar in a feed gas produces the non-monotonic change in F atom density, as it was repeatedly reported for the binary CF₄/O₂ gas mixtures. At the same time, the substitution of Ar for O₂ at constant fraction of CF₄ results in the monotonic increase in F atom density toward more oxygenated plasmas. The natures of these phenomena as well as theirs possible impacts on the etching/polymerization kinetics were discussed in details.     

Reactivity of the oxides in the ternary V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CuO-α-Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> system in air

In this work it has been established which compounds finally are formed in air in the two-component CuO-V₂O₅ and CuO-α-Sb₂O₄ systems. Unknown thermal properties of CuV₂O₆, Cu₂V₂O₇ and Cu₁₁V₆O₂₆ have been established. Reactivity of the oxides and phase relations in the ternary V₂O₅-CuO-α-Sb₂O₄ system in air have been studied by using XRD and DTA methods. The results have showed the reaction of V₂O₅, CuO with α-Sb₂O₄ does not produce any compound where all the three oxides would be involved. It has been established that the α-Sb₂O₄ reacts and forms binary phases independently with CuO or V₂O₅. On the base of these results the investigated system was divided into subsidiary subsystem in which CuSb₂O₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

Kinetics of α-olefin metathesis over the heterogeneous catalytic system (MoOCl<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>)-SnMe<Subscript>4</Subscript>

The kinetics of 1-hexene and 1-octene metathesis over the (MoOC_l4/SiO₂)-SnMe₄ catalytic system at 27 and 50°C has been investigated. The rate constants of the forward and reverse reactions and the catalyst deactivation constants have been measured. The number of active sites has been determined to be 10–13 mol % of the total number of molybdenum atoms.     

Magnetic phase diagrams of the Tm<Subscript>2</Subscript>Fe<Subscript>17</Subscript>–H system

The compound Tm₂Fe₁₇, the only one among R₂Fe₁₇ (where R is a rare earth metal), exhibits uniaxial magnetic anisotropy at cryogenic temperatures. Its Curie temperature is close to room temperature, T_C = 295 K. Magnetic phase diagrams for the Tm₂Fe₁₇–H system have been constructed on the basis of measuring the temperature and field dependences of magnetization performed for different crystallographic directions of single-crystalline samples of Tm₂Fe₁₇ and its hydrides Tm₂Fe₁₇H_x (x = 1, 2, 3, 4). It has been found that the hydrogen atoms, located in the interstices of the crystal lattice of this compound, have a significant effect on both its Curie temperature and the type of magnetic anisotropy.     

A new method of synthesis of the B<Subscript>3</Subscript>H<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack> anion

A new method of synthesis of the B₃H₈⁻ anion has been suggested. The method uses the reaction of some metal halides (CuCl, SnCl₂, CrCl₃, PbF₂, PbCl₂, PbBr₂, and BiCl₃) with sodium tetrahydroborate. It is characterized by high (up to quantitative) yields and simplicity of isolation of the target products ((n-C₄H₉)₄N)[B₃H₈] and Cs[B₃H₈].     

The ESCA analysis of the B<Subscript>3</Subscript>H<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack> anion

Compounds [Et₄N]₂B₃H₈ and CsB₃H₈ are studied using the ESCA method. The results of analysis of the B1s electron spectra and estimation of the effective charge differences in [Et₄N]₂B₃H₈ are compared to the data of theoretical calculations of the B₃H₈⁻ anion.     

Diagram of the PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript> system

A phase diagram of the PbF₂–SnF₂ system has been studied by differential thermal analysis and X-ray powder diffraction. The system forms Pb_1–хSn_хF₂ (х ≤ 0.33) solid solution and three compounds. Pb₂SnF₆ decomposes in solid state by a peritectoid reaction at 350°С; Pb₃Sn₂F₁₀ and PbSnF₄ melt by peritectic reactions at 565 and 380°С, respectively. The eutectic coordinates are 180°С, 90 mol % SnF₂.     

Crystal structure of Ba<Subscript>3</Subscript>[UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(NCS)]<Subscript>2</Subscript> · 9H<Subscript>2</Subscript>O

Single crystals of Ba₃[UO₂(C₂O₄)₂(NCS)]₂ · 9H₂O are synthesized and studied by X-ray diffraction. The crystals are orthorhombic, space group Fddd, Z = 16, and the unit cell parameters are a = 16.253(3) Å, b = 22.245(3) Å, c = 39.031(6) Å. The main crystal structural units are mononuclear complex groups [UO₂(C₂O₄)₂NCS]^3? of the crystal-chemical family (AB ₂ ⁰¹ M¹ (A = UO ₂ ²⁺ , B⁰¹ = C₂O ₄ ^2? , M¹ = NCS^?) of the uranyl complexes linked into a three-dimensional framework by electrostatic interactions and hydrogen bonds involving oxalate ions and water molecules.