New catalysts of dry reforming of methane into synthesis gas

New catalysts have been developed for the production of synthesis gas via a resource-saving and environmentally friendly process—dry reforming of methane. The catalysts are fabricated from NdCaCo_1–xNi _x On precursors (x = 0, 0.2, 0.4, 0.6, 0.8, 1) synthesized by a ceramic method. According to X-ray powder diffraction, when reacting with an equimolar CH₄/CO₂ mixture at 800–900°С, the precursors are converted into a mixture of neodymium and calcium oxides and cobalt and nickel metals. The catalyst based on NdCaNiO _n at 850°С has ensured high conversions of methane (91%) and CO₂ (86%) at СО and hydrogen yields of 88 and 78%, respectively. At 940°С, the yield of CO is close to the quantitative one (97%).     

CO oxidation by oxygen of the catalyst and by gas-phase oxygen over (0.5–15)%CoO/ZrO<Subscript>2</Subscript>

CO adsorption on (0.5–15)%CoO/ZrО₂ catalysts has been investigated by temperature-programmed desorption and IR spectroscopy. At 20°С, carbon monoxide forms carbonyl and monodentate carbonate complexes on Co _m ²⁺ O _n ^2- clusters located on the surface of crystallites of tetragonal ZrO₂. With an increasing CoO content of the clusters, the amount of these complexes increases and the temperature of carbonate decomposition, accompanied by CO₂ desorption, decreases from 400 to 304°С. On the 5%CoO/ZrО₂ sample, the carbonyls formed on the Со²⁺ and Со⁺ cations and Со⁰ atoms decompose at 20, 90, and 200–220°С, respectively, releasing CO. At 20°С, they are oxidized by oxygen to monodentate carbonates, which decompose at 180°С. Adsorbed oxygen decreases the temperature of their decomposition on oxidation sites by ~40°C, and the sample remains in an oxidized state ensuring the possibility of subsequent CO adsorption and oxidation. The rate of the oxidation of 5%CoO/ZrО₂ containing adsorbed CO by oxygen is higher than the rate of the oxidation of the same sample reduced by carbon monoxide, because the latter reaction is an activated one. In view of the properties of the complexes, it can be concluded that the carbonates decomposing at 180°С are involved in CO oxidation by oxygen from the gas phase in the presence of hydrogen, a process occurring at 50–200°С. The rate-limiting step of this process the decomposition of the carbonates, which is characterized by an activation energy of 77–94 kJ/mol.     

Electrolyte systems for primary lithium-fluorocarbon power sources and their working efficiency in a wide temperature range

New compositions of liquid organic electrolytes with working temperatures of up to–50°С were developed for low-temperature primary Li/CF _x power sources. Five different compositions of organic electrolytes with a 15-crown-5 (2 vol %) addition and without it were studied on laboratory Li/CF _x power sources. 1МLiBF₄ (LiPF₆) in an ethylene carbonate/dimethyl carbonate/methyl propionate/ethylmethyl carbonate (EC/DMC/MP/EMC) (1: 1: 1: 2) mixture and 1 М LiPF6 in an EC/DMC/EMC (1: 1: 3) mixture each with a 15-crown-5 (2 vol %) addition were found to be the best compositions of organic electrolytes with working temperatures of up to–50°С. The electrochemical tests at 20 and–50°С in the Li/CF _x system showed that the 15-crown-5 addition increased the length of the discharge plateau at–50°С three- or fourfold. The mechanisms responsible for the increase in the discharge capacity of the CF _x cathode in the presence of a crown ether addition were suggested.     

Neutron diffraction study of dehydrogenation of titanium carbohydrides TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The possibility of the synthesis of hydrogen-nonstoichiometric cubic titanium carbide ТiС _х of high purity from powdery nonstoichiometric cubic titanium carbohydride ТiС _х H _y or nonstoichiometric titanium carbide with admixture hydrogen by annealing in a continuously maintained vacuum of no worse than 1.33 × 10^–3 Pa at temperatures of 600–750°C for several hours has been shown. Similar annealing at higher temperatures (T ≥ 800°C) does not lead to the complete removal of hydrogen from a sample due to intensive sintering. In this case, it seems that pores between sintered particles are hydrogen traps, and the release of hydrogen through the surface of sintered particles is hindered.     

Preparation of HfB<Subscript>2</Subscript>/SiC composite powders by sol–gel technology

Sol–gel technology was used to chemically modify the surface of HfB₂ powders with highly dispersed silicon carbide using two carbothermy protocols: (1) under heating to 1500°С in flowing argon (100 mL/min) without exposure and (2) under dynamic vacuum conditions (p ~ 1 × 10^–5–1 × 10^–6 MPa) at 1400°С with 4-h exposure. The phase composition and microstructural features of the thus-prepared HfB₂/xSiC (x = 10–65 vol %) composite powders were studied. The products prepared by the second protocol showed an enhanced oxidation resistance in the range 20–1400°C in flowing air compared to individual HfB₂.     

Dependence of the properties of Ce-Zr-Y-La-M-O systems on synthetic conditions and on the nature of the transition metal M (Mn,Fe, Co)

The effects of synthetic conditions, component ratios, and the nature of the transition metal on the physicochemical and catalytic properties of Ce-Zr-Y-La-M-O (M = Mn, Fe, Co) systems are studied. The Ce-Zr-Y-La-M-O samples precipitated at ～23°C and calcined at 600°C are single-phase and are solid solutions with a fluorite structure, which persists upon calcination at 1150°C. The Ce-Zr-Y-La-Fe(Co)-O samples precipitated at 70°C and calcined at 1150°C consist of two solid solutions, one cubic, and the other tetragonal. The specific surface area (S _sp) of the samples precipitated at ～23°C and calcined at 600°C increases in the order Ce-Zr-Y-La-O < Ce-Zr-Y-La-Mn-O < Ce-Zr-Y-La-Co-O ≈ Ce-Zr-Y-La-Fe-O. The specific surface area of the samples precipitated at 70°C is independent of M and is ～110 m²/g. Calcination at 1150°C reduces S _sp approximately by two orders of magnitude. The TPR of the unpromoted systems in H₂ proceeds in two steps at 600–650 and 750–840°C. The introduction of M decreases the reduction temperatures and gives rise to a lower temperature peak between 150 and 300°C. The most effective promoter is cobalt. The fluorite-type catalysts containing no noble metal are active in NO reduction (X _NO ≈ 100%) at T _react = 400–450°C. The cobalt-containing catalysts are the most active in the oxidation of CO (X _max = 28%) and hydrocarbons (X _max = 4.3%).     

3D Computer Models of <Emphasis Type="Italic">T</Emphasis>–<Emphasis Type="Italic">x</Emphasis>–<Emphasis Type="Italic">y</Emphasis> Diagrams,Forming the Fe–Ni–Co–FeS–NiS–CoS Subsystem

3D computer models of Fe–Ni–Co, Fe–Ni–FeS–NiS, Fe–Co–FeS–CoS, Ni–Co–NiS–CoS T–x–y diagrams have been designed. The geometric structure (35 surfaces, two-phase surface of the reaction type change, 17 phase regions) of the Fe–Ni–FeS–NiS T–x–y diagram is investigated in detail. The liquidus hypersurfaces prediction of the Fe–Ni–Co–FeS–NiS–CoS subsystem is represented.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

Surface modification of single-walled carbon nanotubes by functional nitrogen-containing groups and study of their properties

Treatment of single-walled carbon nanotubes (SWCNT) in a gaseous 40%NH₃–1%С₂Н₂–C₂H₄ mixture at 600 and 700°С led to “nitrogen-containing carbon coating–single-wall carbon nanotubes” composites. Single-walled carbon nanotubes after etching in aqua regia (SWCNTetch) and doped with nitrogen (N-SWCNT) were studied by XPS, electron microscopy, and IR spectroscopy. It was found that the initial SWCNTetch surface contains various oxygen-containing functional groups. Treatment of SWCNTetch in a 40%NH₃–1%С₂Н₂–C2H₄ mixture led to the formation of a thin carbon coating on the carbon nanotube surface due to polymerization and condensation of hydrocarbons. After treatment at 600°C, the formation of nitrogen-containing functional groups is insignificant; however, when the treatment temperature is increased to 700°C, the nitrogen content reaches 0.5 at % of the weight of the N-SWCNT sample.     

NiCo/C nanocomposites: Synthesis and magnetic properties

NiCo/C metal–carbon nanocomposites were prepared using NiCl₂–CoCl₂–polyacrylonitrile (PAN) precursors using IR-laser heating. The characterization of these NiCo/C nanocomposites by X-ray powder diffraction, transmission electron microscopy, and vibration magnetometry showed that the structure and properties of NiCo/C nanocomposites depended on the nickel concentration in the precursor and the synthesis temperature. The magnetization of NiCo/C nanocomposites increased from 0.46 to 17 A m²/kg as the synthesis temperature changed from 500 to 800°С.     

Charge Transfer and Defect Structure in BaCeO<Subscript>3</Subscript>

Electrical conductivity (at 460–990°С) and ion and proton transference numbers (at 550–950°С) of nominally undoped BaCeO₃ have been studied as dependent on temperature, pO₂ (2.1 × 10^–4 to 10–15 Pa), and pН₂O (40–2340 Pa). For determining the defect model, small additives of aliovalent dopants Nd³⁺ (up to 1 at %) and Ta⁵⁺ (up to 0.5 at %) were used. The effect of cationic nonstoichiometry of barium cerate on the electrical conductivity and reaction with the gas phase has been considered. Charge transfer in ВаСеО₃ is explained using the model of defect formation in the reaction of ВаСеО₃ with the gas phase.     

Influence of ZrO<Subscript>5</Subscript> treatment temperature on the interaction with titanium tetrachloride

The data on phase and chemical transformations of nanosized zirconium dioxide upon annealing at 25–1300°С are presented. The in situ interaction of titanium tetrachloride with nanosized zirconia annealed at 200–800°С has been studied. The revealed regularities of the change of titanium content and the Cl/Ti ratio in the chemisorbed groups have confirmed that TiCl₄ predominantly reacts with zirconia treated at up to 400°С via the hydroxyl groups to yield the TiCl_4–n fragments. In the case of zirconia treated at higher temperature, the interaction with TiCl₄ involves the coordination-unsaturated Zr⁺ and Zr–O^– centers as well.     

A comparative FMR study of the reduction of Co-containing catalysts for the Fischer–Tropsch process in hydrogen and supercritical isopropanol

An in situ comparative study of the reduction of Co-containing catalysts for the Fischer–Tropsch process in hydrogen and supercritical (SC) isopropanol is performed by ferromagnetic resonance (FMR) spectroscopy. According to the FMR data, the reduction of cobalt-containing oxide particles to metal in hydrogen starts at temperatures of ~360°C, which is substantially lower than a temperature of the formation of metal particles of the active phase according to powder X-ray diffraction and differential thermogravimetry data (Т ~ 450°C). In SC isopropanol, the reduction to Co metal occurs at lower temperatures (T ~ 245°C) as compared with the reduction temperature for these catalysts in hydrogen. It is shown that the reduction in SC isopropanol can lead to the formation of superparamagnetic Co nanoparticles with a narrow particle size distribution.     

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.     

Synthesis of Highly Dispersed Zirconium Carbide

The reduction of zirconium oxide with nanofibrous carbon to obtain highly dispersed zirconium carbide was studied. The optimum reduction conditions were determined. The reaction products were identified using modern physicochemical methods (scanning electron microscopy, low-temperature nitrogen adsorption, sedimentation analysis, differential scanning calorimetry). The product obtained appeared to be single-phase zirconium carbide containing no more than 2 wt % impurities. The powder particles are aggregated (mean diameter 14.9–15.0 μm, specific surface area 1.5–1.7 m² g^–1). The oxidation of zirconium carbide starts at 480°С and is complete at 800°С.     

Performance of a zeolite-containing catalyst and catalysts based on noble metals in intermolecular hydrogen transfer between С<Subscript>6</Subscript> hydrocarbons

The activities of a zeolite-containing catalyst and catalysts containing a noble metal in intermolecular hydrogen transfer between С₆ hydrocarbons are compared. The zeolite-containing catalyst is ineffective in hydrogen transfer from cyclohexane to 1-hexene and in cyclohexene conversion at <400°С. Cyclohexene disproportionation at Т < 200°С takes place only over catalysts containing a noble metal. The cyclohexene conversion selectivity depends strongly on the support type. Using deuterated compounds, it has been demonstrated that intermolecular hydrogen transfer via the dehydrogenation–hydrogenation mechanism involves only the initial cyclohexene.     

Effect of Viscosity of Dimethacrylate Ester-Based Compositions on the Kinetics of Their Photopolymerization in Presence of <Emphasis Type="Italic">o</Emphasis>-Quinone Photoinitiators

The kinetics of photopolymerization of compositions based on dimethacrylate oligomers with viscosities ranging from 1.5 to 376.7 cSt under the action of visible light (9,10-phenanthrenquinone and a mixture of 3,6-di-tert-butyl-1,2-benzoquinone with N,N-dimethylcyclohexylamine as initiators) is studied. Dimethacrylates of poly(ethylene glycols) with the number of ethoxy fragments of n = 1–4 and 8, dimethacrylates of OKM-2 and MDF-2 trademarks, and solvents (benzene, acetonitrile, and dinonyl ester of phthalic acid) are used. At the initial stages of the reaction, the dependence of the reduced rate of photopolymerization of such compositions on their initial viscosity is described by a curve attaining a plateau at a viscosity of 100 cSt or above. The dependences of viscosity of all dimethacrylates on temperature ranging from –10 to +80°С are determined, the effective activation energies of monomer viscous flow are calculated, and the temperature dependences of the number of molecules in associates for each of the oligomers are ascertained. At Т = 20°С, the number of molecules in the associates of poly(ethylene glycol) dimethacrylates with n = 1–4 does not exceed 10, for n = 8 the number of molecules in the associates is ～10², and for dimethacrylates of OKM-2 and MDF-2 trademarks this value is above 10⁴.     

Reactive Oligomeric Protic Cationic Linear Ionic Liquids with Different Types of Nitrogen Centers

Reactive linear oligo(ethylene oxides) containing terminal secondary hydroxyl groups and secondary amino groups combined with nitrogen heterocyclic fragments are synthesized by the reaction of oligo(oxyethylene glycol) α,ω-diglycidyl ether (М = 1.0 × 10³) with 1-(3-aminopropyl)imidazole, 2-aminopyridine, or 2-amino-3-methylpyridine. Protonation of the synthesized compounds by ethanesulfonic acid and p-toluenesulfonic acid at their different ratios is studied. This process makes it possible to obtain oligomeric linear protic cationic ionic liquids capable of condensation. The proton conductivity of oligomeric ionic liquids is investigated under anhydrous conditions in the temperature range of 40–120°С. The highest conductivity (1.36 × 10^–3 S/cm) is attained in the case of methylpyridinium ethanesulfonate oligomeric ionic liquid at 120°С. These compounds are thermally stable to a temperature of 250–290°С. They show promise for the synthesis of polymeric analogs of block ionic liquids suitable in the production of electrochemical devices for various purposes.     

Synthesis and van Alphen–Hüttel rearrangement of substituted 3<Emphasis Type="Italic">H</Emphasis>-pyrazoles,adducts of 1,3-dipolar cycloaddition of 9-diazofluorene and diphenyldiazomethane to trimethyl(tosylethynyl)silane

Trimethyl(tosylethynyl)silane reacted in ethyl ether at 20°С with diphenyldiazomethane affording 3Н-pyrazole, a product of 1,3-dipolar cycloaddition against Auwers rule. The reaction with 9-diazofluorene is less selective, but its regioselectivity is also governed by the steric effect of the bulky trimethylsilyl substituent at the triple bond С≡С. The adduct with diphenyldiazomethane at boiling in methanol or keeping in glacial acetic acid in the presence of a catalytic quantity of conc. H₂SO₄ undergoes the Van Alphen–Hüttel rearrangement by the migration of the phenyl substituent to the atom N² in the 1Н-pyrazole. The same 1Н-pyrazole together with a product of nitrogen elimination, trimethylsilyl substituted cyclopropane, is formed in the 2: 1 ratio at boiling in benzene. A similar behavior is observed in the glacial acetic acid for the anti-Auwers adduct of 9-diazofluorene. It suffers nitrogen elimination at boiling in benzene converting in spirocyclic cyclopropene. The Auwers adduct of 9-diazofluorene at boiling in methanol transforms due to the van Alphen–Hüttel rearrangement into the corresponding 4Н-pyrazole that undergoes a hydrodesilylation to give a derivative of 1Н-pyrazole, 3-tosyl-1(2)H-dibenzo[e,g]indazole.