Thermogravimetric study of the dehydration reaction of LiCl·H<Subscript>2</Subscript>O

The dehydration of LiCl·H₂O was studied under inert helium atmosphere by DTA/TG for different heating rates. The dehydration of LiCl·H₂O proceeds through a two step reaction between 99–110 and 160–186°C, respectively. It leads to the formation of LiCl·0.5H₂O as intermediate compound. The proposed mechanism is: and Based on the temperature peak of the DTA signals the activation energies of the two reactions were determined to be 240 kJ mol⁻¹ (step 1) and 137 kJ mol⁻¹ (step 2), respectively.     

A computational study of the radical–radical reaction of O(<Superscript>3</Superscript>P) + C<Subscript>2</Subscript>H<Subscript>5</Subscript> with comparisons to gas-phase kinetics and crossed-beam experiments

We present density functional theory (DFT) and complete basis set (CBS) calculations of the prototypical radical–radical reaction of ground–state atomic oxygen [O(³P)] with ethyl (C₂H₅) radicals. The respective reaction mechanisms and dynamics were investigated on the doublet potential energy surfaces using the DFT method and CBS model. In the title reaction, the barrierless addition of O(³P) to C₂H₅ led to the formation of energy-rich intermediates that underwent subsequent isomerization and decomposition to yield various products. The products predicted to be found were: H₂CO + CH₃, CH₃CHO + H, c–CH₂OCH₂ + H, ^1,3CH₃COH + H, ^1,3HCOH + CH₃, CH₂CHOH + H, C₂H₃ + H₂O, and CH₂CH₂ + OH. In particular, unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, two distinctive pathways to the formation of CH₂CH₂ + OH were predicted to be in competition: direct, barrierless H-atom abstraction mechanism versus addition process. The competition was consistent with the recent crossed-beam investigations, and their microscopic dynamic characteristics are discussed at the molecular level.     

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 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.     

New bimetallic Mo<Subscript>2</Subscript>C–WC/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane catalysts in the dry reforming of methane

Bimetallic membrane catalysts based on the Mo₂C–WC binary carbides were obtained. Their structural characteristics and catalytic properties in a reaction of dry reforming of methane were compared with those of monocarbide catalysts. The advantage of the use of the mixed carbide catalysts was established.     

Polytherm of the CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>–KNO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O phase diagram

The crystallization polytherm of the ternary CO(NH₂)₂–KNO₃–H₂O system is plotted for the first time via visual polythermal analysis and calculating ternary eutonics characteristics from data on the boundary elements of two-component systems. The ternary eutonics modeling error does not exceed 3.5%. In addition to the crystallization fields of individual components, the field of the redox reaction that occurs in the system between potassium nitrate and carbamide is shown in the CO(NH₂)₂–KNO₃–H₂O diagram by a dashed outline.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Catalytic partial oxidation of methanol over Au–Pd bimetallic catalysts: a comparative study of SBA-16, SBA-16-CeO<Subscript>2</Subscript>, and CeO<Subscript>2</Subscript> as supports

Au–Pd catalysts supported on SBA-16, SBA-16-CeO₂, and CeO₂ had been studied for partial oxidation of methanol to produce H₂. The physicochemical characteristics of the catalysts prepared by deposition–precipitation using urea hydrolysis were examined by inductively coupled plasma atomic emission spectroscopy (ICP-AES), Brunauer-Emmett-Teller (BET), X-ray powder diffraction (XRD), Temperature-programmed reduction (TPR), and H₂ temperature-programmed desorption (H₂-TPD) analyses. The results show that Au_xPd_y alloys are observed in Au–Pd/SBA-16 and Au–Pd/SBA-16-CeO₂ catalysts. The catalytic results demonstrate that both Au–Pd/SBA-16 and Au–Pd/SBA-16-CeO₂ catalysts exhibit higher activity and lower CO selectivity than the Au–Pd/CeO₂ catalyst. This could be ascribed to the formation of Au_xPd_y alloys. The comparison of the Au–Pd/SBA-16 and Au–Pd/SBA-16-CeO₂ catalysts reveals that the Au–Pd/SBA-16-CeO₂ shows the lower CO selectivity, probably due to the presence of CeO₂.     

Theoretical study of reaction mechanism for Se + O<Subscript>3</Subscript>

The reaction mechanism of Se + O₃ on the singlet potential energy has been investigated at CCSD(T)/6-311++G(2df,2pd) level of theory based on the geometric parameters optimized at the B3LYP/6-311++G(3df,3pd) level of theory. The calculated results show that the reactants are firstly associated into the adduct Se–O₃ with any intrinsic barrier. Subsequently, through a variety of transformations of isomer Se–O₃, two kinds of products P₁(SeO₃(D_3h)) and P₂(SeO + ³O₂) are obtained. The breakage and formation of the chemical bonds in the reaction have been studied by the topological analysis of electronic density. The topological analysis results show that the ring transitional structure region does not only occur in cis-OSeOO → SeO₃(C_s) process but also occur in SeO₃(C_s) → SeO₃(D_3h).     

Selective hydrogenation of 1,3-pentadiene over mono- and bimetallic sulfidized Ni(Cu)—S/SiO<Subscript>2</Subscript> catalysts

The activity and selectivity of the Ni/SiO₂ catalyst, as well as the mono- and bimetallic Ni(Cu)—S/SiO₂ systems were investigated in the selective hydrogenation of 1,3-pentadiene to pentenes. The presulfiding of the catalysts in a hydrogen sulfide flow substantially increases the selectivity to olefins in gas mixtures with a range of H₂/diene molar ratio of 2.5–10. The samples activated in hydrogen at elevated temperatures turned out to be more active. The effect of modification of the nickel—sulfide catalysts with copper, resulting in an increase in the activity and selectivity to olefins, was found. The weight ratio Ni/Cu = 4 was shown to be optimum for achieving the maximum conversion and selectivity on the surface.     

Low-temperature catalytic oxidation of toluene over Mn–Co–O/Ce<Subscript>0.65</Subscript>Zr<Subscript>0.35</Subscript>O<Subscript>2</Subscript> mixed oxide catalysts

Ce_0.65Zr_0.35O₂ was prepared by co-precipitation method and a series of Mn_1-yCo_y/Ce_0.65Zr_0.35O₂ catalysts with different Mn/Co molar ratio were synthesized via the co-impregnation method. These catalysts were applied for gaseous toluene oxidation, which showed that the catalytic activity was significantly improved by the addition of Mn and Co. In particular, Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ with Mn/Co molar ratio of 1:1 displayed the best result with the lowest complete conversion temperature of 242 °C under a GHSV of 12,000 h^?1. The as-prepared catalysts were characterized by X-ray diffraction, H₂ temperature-programmed reduction, N₂ adsorption–desorption, X-ray photoelectron spectroscopy and O₂ temperature-programmed desorption. These characteristics revealed that the coexistence of Mn and Co could enhance the redox property and generate more surface adsorbed oxygen, thereby improving the performance of the catalysts for toluene low-temperature oxidation. The Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ exhibited the best catalytic activity and high stability. The excellent catalytic activity of the Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ could be ascribed to a greater amount of surface adsorbed oxygen species and Mn⁴⁺ on the catalyst surface.     

Promotion effect of nickel for Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the transfer dehydrogenation of primary aliphatic alcohols

Cu–Ni/γ-Al₂O₃ bimetallic catalysts were developed for anaerobic dehydrogenation of non-activated primary aliphatic alcohols to aldehydes. Systematic investigation about the promotion effect of nickel on the catalytic performance was carried out. Hydrogenation of C=C bond rather than C=O bond, was significantly improved over Cu–Ni/γ-Al₂O₃ catalyst by introducing nickel, which interprets the good conversion of primary aliphatic alcohols. This work would contribute to design new catalysts for dehydrogenation of primary aliphatic alcohols.     

A study on the effect of synthesis parameters on the size of nickel particles in sol–gel derived Ni–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

The present work deals with the synthesis of Ni–SiO₂–Al₂O₃ nanocomposites fabricated by embedding nickel oxide particles, obtained from hexahydrated nickel nitrate [Ni(NO₃)₂ · 6H₂O], in matrixes with different molar percents of Silica/Alumina, through sol–gel method based on hydrolysis and condensation of tetraethylorthosilicate (TEOS) and Aluminum Isopropoxide [Al(OC₃H₇)₃] alkoxides. Due to the various factors, e.g., pH, EtOH/TEOS/H₂O ratio, Si/Ni ratio etc., influencing the nickel grain size of the nanocomposites, Taguchi robust design method of system optimization was used to determine the percent of contribution (%ρ) of each factor. The nanocomposites were reduced in a flow of hydrogen and nitrogen gas at 700 °C for half an hour. The nickel grain size in the nanocomposites was determined by utilizing Scherrer`s method and XRD patterns. The smallest nickel grain size obtained from the Taguchi orthogonal array was about 24 nm, later confirmed by TEM observations. After optimization of the controlling factors, a nickel grain size of 15.4 nm was obtained. It was found that the SiO₂/Al₂O₃ molar ratio of the matrix had the most influence on the nickel grain size (29.22%) and the Water/TEOS molar ratio stood in second place (21.44%). It was illustrated that the starting temperature of the aluminum isopropoxide had the least influence on the nickel grain size.     

Oxidation of Adamantane with H<Subscript>2</Subscript>O<Subscript>2</Subscript>–CF<Subscript>3</Subscript>COCF<Subscript>3</Subscript> · 1.5 H<Subscript>2</Subscript>O in the Presence of VO(acac)<Subscript>2</Subscript>

The system hydrogen peroxide–hexafluoroacetone sesquihydrate effectively oxidizes adamantane in the presence of VO(acac)₂ to afford 64% of adamantan-1-ol in tert-butyl alcohol or 76% of adamantan-2-one in a mixture of acetic acid with pyridine.     

Solid-Liquid Equilibria in the Quaternary Systems KCl–MgCl<Subscript>2</Subscript>–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O and NaCl–KCl–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 348 K

Solid-liquid equilibria in the quaternary systems KCl–MgCl₂–SrCl₂–H₂O and NaCl–KCl–SrCl₂–H₂O at 348 K were measured by the isothermal solution saturation method. The composition of the equilibrium solid phase, solubilities of salts, and densities of saturated solution in the two systems were determined. Phase diagrams, water content diagrams and solution density diagrams of quaternary systems were plotted according to experimental data. The phase diagram of the quaternary system NaCl–KCl–SrCl₂–H₂O has one invariant point, three univariant curves as the boundary of NaCl, KCl and SrCl₂ · 2H₂O. This phase diagrams were simple co-saturation type without complex salt and solid solution. For the quaternary system KCl–MgCl₂–SrCl₂–H₂O, one complex salt KCl · MgCl₂ · 6H₂O (Car) had been found in this system, consisted of five univariant curves, two invariant points and four crystallization regions of MgCl₂ · 6H₂O (Bis), KCl, SrCl₂ · 2H₂O and KCl · MgCl₂ · 6H₂O. And the densities transformation rules were simply discussed. Simultaneously, the solubilities and densities data in invariant point of the quaternary system NaCl–KCl–SrCl₂–H₂O had been compared with the experimental data of previous researchers.     

Mechanochemical Activation of Cu–CeO<Subscript>2</Subscript> Mixture as a Promising Technique for the Solid-State Synthesis of Catalysts for the Selective Oxidation of CO in the Presence of H<Subscript>2</Subscript>

A new ecologically clean method for the solid-phase synthesis of oxide copper–ceria catalysts with the use of the mechanochemical activation of a mixture of Cu powder (8 wt %) with CeO₂ was developed. It was established that metallic copper was oxidized by oxygen from CeO₂ in the course of mechanochemical activation. The intensity of a signal due to metallic Cu in the X-ray diffraction analysis spectra decreased with the duration of mechanochemical activation. The Cu¹⁺, Cu²⁺, and Ce³⁺ ions were detected on the sample surface by X-ray photoelectron spectroscopy. The application of temperature-programmed reduction (TPR) made it possible to detect two active oxygen species in the reaction of CO oxidation in the regions of 190 and 210–220°C by a TPR-H₂ method and in the regions of 150 and 180–190°C by a TPR-CO method. It is likely that the former species occurred in the catalytically active nanocomposite surface structures containing Cu–O–Ce bonds, whereas the latter occurred in the finely dispersed particles of CuO on the surface of CeO₂. The maximum conversion of CO (98%, 165°C) reached by the mechanochemical activation of the sample for 60 min was almost the same as conversion on a supported CuO/CeO₂ catalyst.     

Cyclohexane oxidation with an O<Subscript>2</Subscript>–H<Subscript>2</Subscript> mixture in the presence of a two-component Pt/C–heteropoly acid catalyst and ionic liquids

Approaches to increase the efficiency of Pt/C–heteropoly acid catalyst in a liquid-phase oxidation of cyclohexane using an O₂–H₂ mixture were studied. It was shown that small additives of ionic liquid (BMImBr, Bu₄NBr, or Bu₄NHSO₄) significantly improve the catalytic effect of the Pt/C–H₃PMo₁₂O₄₀–CH₃CN system at 35°C, by slowing the rate of side reactions resulting in water formation, increasing the rate of oxygenate formation, and inhibiting their secondary oxidation reactions. The efficiency of H₂ consumption increases from 2 to 18–25%, while the selectivity of cyclohexane conversion is 92–98%. The substitution of one or two Mo(VI) ions by V(V) in the structure of the heteropoly acid decreases these parameters. In the presence of Bu₄NHSO₄, a Pt/C catalyst can be used many times. During the reaction, the heteropoly acid present in the solution is in a reduced state under the action of the reaction medium and undergoes reversible redox transformations. The nature of the catalytic action of the studied system is explained from the viewpoint of the effect of ionic liquids on the properties of a Pt/C catalyst in activating O₂, heteropoly molybdate chemistry, and the known mechanisms of the peroxide oxidation of hydrocarbons.     

Physicochemical Analysis of the System Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O at 25°С

The solubility in the quaternary water–salt system Zr(SO₄)₂ · 4Н₂О–Na₂SO₄–H₂SO₄–H₂O at 25°C was studied. It was found that, in the system, there is crystallization of not only Na₂SO₄ and Zr(SO₄)₄ · 4H₂O, but also sodium sulfate zirconates Na₂Zr(SO₄)₂(OH)₂ · 0.3H₂O, Na₄Zr(SO₄)₄ · 3H₂O, and Na₂Zr(SO₄)₂ · 3H₂O and two new compounds, S₁ and S₂, which are presumably Na₂ZrO(SO₄)₂ · 2H₂O and Na₂Zr₂O₂(SO₄)₃ · 6H₂O.     

Transformations of CO<Subscript>2</Subscript> in Two-Phase Systems C<Subscript>8</Subscript>F<Subscript>18</Subscript>–H<Subscript>2</Subscript>O and C<Subscript>6</Subscript>F<Subscript>6</Subscript>–H<Subscript>2</Subscript>O

The transformation of carbon dioxide in aqueous emulsions of perfluorons in the presence of oxygen in the air results in the formation of a mixture of oxalic acid and a minor set of organic compounds C₄–C₈. The maximum CO₂ consumption occurs in the emulsion with the C₈F₁₈: H₂O vol/vol ratio of 1: 0.42 at pH 2.4; the H₂C₂O₄ yield is 11 mol %.     

Phase and extraction equilibria in H<Subscript>2</Subscript>O–sulfonol–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) and H<Subscript>2</Subscript>O–sodium dodecyl sulfate–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) systems

Solubility isotherms of water–sulfonol–hydrochloric (or sulfuric) acid and water–sodium dodecyl sulfate–hydrochloric acid systems at 75°C and a water–sodium dodecyl sulfate–sulfuric acid system at 50°C are constructed. Regions of two-phase liquid equilibrium suitable for use in extraction are found. Concentration parameters for extraction are determined. The interfacial distribution of a series of metal ions with and without such additional complexing reagents as diantipyrylmethane and diantipyrylheptane is studied.