Influence of the nature of molybdenum compounds on the activity of Mo/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and NiMo/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalysts

The influence of the nature of molybdenum compounds on the catalytic activity of sulfided NiMo/γ-Al₂O₃ catalysts was studied. The samples were prepared by impregnating the support with mixed aqueous solutions of nickel nitrate and molybdenum-containing compounds: ammonium paramolybdate and the 6-series heteropoly compounds (HPCs) ammonium 6-molybdonickelate (NiMo₆-HPC) and ammonium 6-molybdoaluminate (AlMo₆-HPC). Complexing agents (tartaric acid or a solution of NH₃) were used for stabilizing mixed aqueous ammonium paramolybdate and nickel nitrate solutions and for simultaneously producing an acidic or alkaline medium. The starting molybdenum compounds and catalysts in the oxide form were characterized using IR spectroscopy and x-ray diffraction analysis. The activity of catalysts based on NiMo₆-HPC in the hydrogenolysis of thiophene and in the hydrotreating of the diesel fraction was higher than that of catalysts based on ammonium paramolybdate: at 320°C, the degree of sulfur removal from the diesel fraction was higher by 13–16% and the average degree of hydrogenation of polycyclic aromatic hydrocarbons was higher by 14–15%. It was also found that the use of AlMo₆-HPC does not cause such an effect.     

Effect of chelating agents on catalytic performance of Cr/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dehydrogenation catalysts

Chromia/alumina (Cr₂O₃/γ-Al₂O₃) catalysts with addition of chelating agents (citric acid or oxalic acid) were prepared by the incipient impregnation method. The resulting catalysts with different citric acid (CA) or oxalic acid (OA) contents were applied to the dehydrogenation of isobutane to isobutene. The influence of chelating agents on the catalysts was investigated by means of BET, SEM, H₂-TPR, NH₃-TPD, and TG-DTG. The results showed that the Cr₂O₃/γ-Al₂O₃ catalysts with addition of CA or OA exerted slightly increase on specific surface area. The addition of the chelating agents as expected, determined a general decrease in the surface acidity. The catalysts with CA or OA have a better anti-coking ability by inhibiting the side reaction of cracking and carbon formation. The addition of CA or OA for preparing these catalysts resulted in a beneficial effect on the reducibility of the Cr species to diminish the reduction temperature. The appropriate content of chelating agents could improve dispersion of metal species in the γ-Al₂O₃ support. The catalytic activity showed an important enhancement when the metal species was impregnated in the presence of CA or OA.     

Compositional control of electrical transport properties in the new series of defect thiospinels, Ga1−xGexV4S8−δ (0≤x≤1)

A new series of non-stoichiometric sulfides Ga_1−xGe_xV₄S_8−δ (0≤x≤1; δ≤0.23) has been synthesized at high temperatures by heating stoichiometric mixtures of the elements in sealed quartz tubes. The samples have been characterized by powder X-ray diffraction, SQUID magnetometry and electrical transport-property measurements. Structural analysis reveals that a solid solution is formed throughout this composition range, whilst thermogravimetric data reveal sulfur deficiency of up to 2.9% in the quaternary phases. Magnetic measurements suggest that the ferromagnetic behavior of the end-member phase GaV₄S₈ is retained at x≤0.7; samples in this composition range showing a marked increase in magnetization at low temperatures. By contrast Ga_0.25Ge_0.75V₄S_8−δ appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x≠1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing Ga content, whilst the end-member phase GeV₄S_8−δ is a p-type semiconductor. The results demonstrate that the physical properties are determined principally by the degree of electron filling of narrow-band states arising from intracluster V-V interactions.     

Synthesis of TCPP–Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@S/RGO and its application for purification of water

A one-step green-chemistry method was applied to prepare sulfur/reduced graphene oxide (S/RGO). The synthesized S/RGO was modified by 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and Fe₃O₄ nanoparticles to form TCPP–Fe₃O₄@S/RGO. The prepared composites were investigated by X-ray diffraction (XRD) analysis, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX) mapping, and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) imaging. Diffuse reflectance spectroscopy (DRS) was used to determine the photocatalytic ability of S/RGO and TCPP–Fe₃O₄@S/RGO. In addition, photocatalytic degradation of a hazardous dye (methylene blue) by the TCPP–Fe₃O₄@S/RGO composite under visible-light irradiation is reported. The results demonstrate synthesis of TCPP–Fe₃O₄@S/RGO by an environmentally friendly method with excellent degradation effect.     

Selective deoxygenation of vegetable oils in the presence of Pt–Sn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

We studied deoxygenation of individual fatty esters and fatty acid triglycerides from vegetable oils and lipid extracts from microalgae in the presence of catalysts prepared by deposition of Pt–Sn-containing compounds onto the γ-aluminum oxide surface. Using individual esters as an example, selective reduction of oxygen into water was demonstrated for the first time to proceed on a catalytic system at the 5 : 1 molar ratio of Sn and Pt active components to afford hydrocarbon components of substrates in virtually quantitative yield. Transformation of vegetable oil in the presence of this catalyst affords the C₃–C₁₈ hydrocarbon fraction in yield up to 99% at the content of C₃ and C₁₈ hydrocarbons up to 90%. The fraction of C₁ and C₂ hydrocarbons and carbon oxides is not higher than 0.5%. The possibility of carbon weight loss minimization during transformation of lipids was shown for the first time.     

Selective Hydrogenation of Acetylene and Physicochemical Properties of Pd–Fe/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Bimetallic Catalysts

The selective hydrogenation of acetylene on Pd–Fe/Al₂O₃ catalysts prepared by decomposition of ferrocene on reduced Pd/Al₂O₃ was studied. The effect of the conditions of treatment of the Pd–ferrocene/ Al₂O₃ precursor on the catalyst activity and selectivity was investigated, and the optimum conditions were determined at which the Pd–Fe/Al₂O₃ catalyst has higher selectivity than Pd/Al₂O₃ without any loss of activity.     

Effects of TiO<Subscript>2</Subscript> on the hydrophilicity of сotton/polyester (50/50) blend fabric under UV irradiation

Alkaline TiO₂ nanoparticles treated cotton/polyester (50/50) blend fabric were prepared, and then exposed to UV irradiation. It was found that the addition of a small amount of TiO₂ nanoparticles to the coating solution improves the hydrophilicity and mechanical strength of the fabrics. The treated fabrics exhibited high water absorption as well as better hydrophilicity compared to the untreated sample. Compared to the surface of untreated blend fabric, scanning electron microscopy showed that the surface of the modified blend fabric becomes rough and covered by a layer of other materials. Furthermore, X-ray diffraction demonstrated the formation of crystalline material. In addition, thermograms showed that the modification process improved the thermostability of blend fabric.     

Spectroscopic study of the properties of surface compounds in methanol conversions on Cu/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The reactions of methanol on the (10% Cu)/γ-Al₂O₃ surface were studied by the spectrokinetic method (simultaneous measurements of the conversion rates of surface compounds and the product formation rates). Bridging and linear methoxy groups result from the interaction of methanol with surface hydroxyl groups. Formate and aldehyde-like complexes form by the oxidative conversion of the linear methoxy groups. Hydrogen forms via the recombination of hydrogen atoms on copper clusters, and the hydrogen atoms result from interconversions of surface compounds. The source of CO₂ in the gas phase is the formate complex, and the source of CO is the aldehyde complex. In the absence of methanol in the gas phase, dimethyl ether forms by the interaction between two bridging methoxy groups. When present in the gas phase, methanol reacts with methoxy groups on the surface. The roles of oxygen and water vapor in the conversions of surface compounds are discussed.     

p(O2)-stability of LaFe1−xNixO3−δ solid solutions at 1100 °C

LaFe_1−xNi_xO_3−δ (x=0.1−1.0) perovskites were synthesized via citrate route. The p(O₂)-stability of the perovskite phases LaFe_1−xNi_xO_3−δ has been evaluated at 1100 °C based on the results of XRD analysis of powder samples annealed at various p(O₂) and quenched to room temperature. The isothermal LaFeO_3−δ-“LaNiO_3−δ” cross-section of the phase diagram of the La-Fe-Ni-O system has been proposed in the range of oxygen partial pressure −15<log p(O₂)/atm≤0.68. The unit cell parameters of orthorhombic perovskites O-LaFe_1−xNi_xO_3−δ increase with decrease in p(O₂) at fixed composition x. This behavior is explained on the basis of size factor. The decomposition temperatures of rhombohedral phases R-LaFe_1−xNi_xO_3−δ for x=0.7, 0.8, 0.9 and 1.0 in air were determined as 1137, 1086, 1060 and 995 °C, respectively.     

Synthesis and structural characterization of LaxSr1−xMnO2.6+δ (0.1<x<0.4) compounds displaying compressed octahedral coordination of Mn

La_xSr_1−xMnO_2.6+δ (x=0.1-0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La_0.1Sr_0.9MnO_2.6+δ (δ=0.15) and La_0.3Sr_0.7MnO_2.6, tetragonal (P4/m), and La_0.2Sr_0.8MnO_2.6, pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr₅Mn₅O₁₃ (, c≈a_P). La_0.4Sr_0.6MnO_2.6 shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (La_xSr_1−x)₅Mn₅O₁₃ phases four out of five Mn cations are Mn³⁺ and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn^(4−5x)+, in octahedral environment, shows decreasing formal charge from Mn⁴⁺ (x=0) to Mn^2.5+x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn^(4−5x)+ and, in the case of (La_0.2Sr_0.8)₅Mn₅O₁₃, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d_x²-y² orbital is occupied, which would be a rare example of inverted occupancy of e_g orbitals in manganites, or that disordered Mn³⁺ apically elongated MnO₆ octahedra are present with normal electronic configuration , and the observed bond distances are the average of the long and intermediate in-plane Mn-O bonds. Several structural features favor the second case.     

Synthesis and structure of N-arylimines of β-tellurocyclohexenals with the intramolecular coordination N → Te bonds

A series of N-arylimines of β-tellurocyclohexenals 11 have been synthesized and the molecular and crystal structures of the compounds 11a-e and also β-(dimethyltelluronium)cyclohexenal perchlorate 12 studied by X-ray crystallography. All the compounds contain strong intramolecular coordination N → Te (O → Te) bonds of the hypervalent type. In 11a-e, the lengths of the N → Te bonds are within the range of 2.690-2.147 Å and are 1.0-1.5 Å shorter than the sum of the van der Waals radii of respective atoms. In the N-arylimines 11b-e with the electronegative groups attached to the tellurium center, the lengths of the N → Te bonds are very close to that characteristic of a standard covalent N-Te bond. The experimental observed geometries are well reproduced by the DFT calculations performed at B3LYP/LanL2DZ level of approximation. The energies of the intramolecular coordination N → Te bonds vary from 23 kJ mol⁻¹ for 11a to 119 kJ mol⁻¹ for 11e. The calculated energy of the O → Te bond in 12 was found to be 50 kJ mol⁻¹. The ¹²⁵Te NMR chemical shifts of compounds 11 span the wide range of 734.3-1622.4 ppm. The largest downfield ¹²⁵Te NMR chemical shifts are observed in the case of the compounds 11e, f in which the most electronegative atoms are attached to the tellurim centers.     

Unexpected cleavage of the Cpy–Cpy bond in the reaction of 2,2′-bipyridine N,N′-diimines with acetylenes

An unusual cleavage of the C_py–C_py bond in the reaction of 2,2′-bipyridine N,N′-diimine and its C-methyl substituted derivatives with acetylenes is described. The effect of the solvent on the yield of 7,7′-bipyrazolo[1,5-a]pyridine-2,2′,3,3′-tetracarboxylates and the products of cleavage of the C_py–C_py bond has been studied. The mechanism of the cleavage reaction is discussed on the basis of DFT calculations.     

Variation of the activity of СuO·ZnO·K<Subscript>2</Subscript>O/SiO<Subscript>2</Subscript> catalysts during generation in dehydrogenation of methanol to formaldehyde

The development of the catalytic properties of supported model catalysts СuO·ZnO·K₂O/SiO₂ with different component ratios in methanol dehydrogenation was studied. In the temperature interval 400–500°С, the formation of the target product, formaldehyde, is accompanied by the formation of surface polymeric hydrocarbons, which undergo gradual condensation to coke with the evolution of hydrogen and carbon dioxide. By properly combining the concentrations of the supported components and the sequence of the deposition of zinc, copper, and potassium oxides, it is possible to reduce the time in which the steady-state catalyst operation mode is reached and to improve the catalyst selectivity with respect to formaldehyde formation.     

Hydrocracking of vacuum gas oil in the presence of catalysts NiMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates and NiW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates

Supported nickel–molybdenum and nickel–tungsten hydrocracking catalysts prepared using a support that consists of 70% Al₂O₃ and 30% amorphous aluminosilicate were characterized by nitrogen and mercury porosimetry, IR spectroscopy of adsorbed CO, and high-resolution electron microscopy. The catalytic tests in hydrocracking of vacuum gas oil containing 3.39% sulfur showed that the nature of the hydrogenating component (NiMo or NiW) only slightly influences the vacuum gas oil conversion and the diesel fraction yield, but noticeable influences the properties of the diesel fraction obtained. The catalyst NiMo/Al₂O₃–amorphous aluminosilicates, compared to NiW/Al₂O₃–amorphous aluminosilicates, ensures lower sulfur content in the diesel fraction obtained, whereas the catalyst NiW/Al₂O₃–amorphous aluminosilicates allows obtaining a diesel fraction with lower content of polyaromatic compounds.     

Phase stability of La1−xCaxCrO3−δ in oxidizing atmosphere

The chemical stability of perovskite-type La_1−xCa_xCrO_3−δ (x=0.1, 0.2, 0.3) in high oxygen partial pressure, P_O2, was investigated with three methods: thermogravimetry, XRD analysis, and thermodynamic calculation. The second phase, CaCrO₄ was observed by XRD analysis on the powder equilibrated in high P_O2. Thermogravimetry under fixed temperatures sensitively detected the segregation of the second phase in the form of oxygen incorporation, because oxidation of chromium ion accompanies the segregation. The second phase tended to appear in high P_O2 and at low temperature. The single-phase regions of La_1−xCa_xCrO_3−δ obtained from the two experimental methods well agreed with each other. The results of thermodynamic calculation on the assumption of ideality of the solid solution also agreed with the experimental results. These results suggested the sufficient chemical stability of La_1−xCa_xCrO_3−δ in high P_O2 concerning the application to an interconnector of high-temperature solid oxide fuel cells; for example, La_0.7Ca_0.3CrO_3−δ is stable at 1273 K in air.     

Conversion of bio-oxygenates into hydrocarbons in the presence of a commercial Pt–Re/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

It was found that the preliminarily reduced commercial platinum–rhenium catalyst PR-71 exhibited high activity in the conversion of ethanol into C₄–C₁₂ olefins and in the cross-condensation reactions of ethanol with glycerol, acetone, n-propanol, and isopropanol. Acetone and glycerol exhibited the highest reactivity in the cross-condensation reactions; this manifested itself in an increase in the total yield of the target fraction of C₄–C₁₂ hydrocarbons and in a more than 10-fold increase in the yield of products containing the odd numbers of carbon atoms, as compared with the conversion of individual ethanol. The structural studies performed by extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy showed that the high selectivity of PR-71 can be caused by the formation of bimetallic Pt–Re and Pt–Al clusters in the course of the prolonged preliminary reduction of the catalyst.     

Electrochemical characterization of polypyrrole–LiNi<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>O<Subscript>2</Subscript> composite cathode material for aqueous rechargeable lithium batteries

A series of polypyrrole (PPy)–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrodes are formed by physical mixing of polypyrrole with LiNi_1/3Mn_1/3Co_1/3O₂ cathode material. LiNi_1/3Mn_1/3Co_1/3O₂ is synthesized by reaction under autogenic pressure at elevated temperature method. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide an evidence to well-ordered layered structure of the compound. The ratios of the intensities of 003 and 104 peaks are found to be >1, which indicate no pronounced mixing of the cation. Cyclic voltammetry and AC impedance studies revealed that the addition of polypyrrole significantly decreases the charge-transfer resistance of LiNi_1/3Mn_1/3Co_1/3O₂ electrodes. The electrochemical reactivity of PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode is examined during lithium ion insertion and de-insertion by galvanostatic charge–discharge testing; 10 wt.% PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode exhibits better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiNi_1/3Mn_1/3Co_1/3O₂ electrode. The cell with 10 wt.% PPy added cathode shows significant improvement in the electrochemical performance compared with that having pristine cathode. The capacity remains about 70% of the initial value after 50 cycles while for cell with pristine cathode only about 28% of initial capacity remains after 40 cycles.     

Effect of potassium addition on bimetallic PtSn/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for dehydrogenation of propane to propylene

PtSn/θ-Al₂O₃ catalysts with different amounts of K (0.14, 0.22, 0.49, 0.72, and 0.96 wt%) are prepared to investigate the K effects on the PtSn catalyst in propane dehydrogenation (PDH). KPtSn catalyst with 0.xx wt% K, 0.5 wt% Pt and 0.75 wt% Sn is designated as xx-KPtSn. PDH was performed at 873 K and a gas hourly space velocity (GHSV) of 53,000 mL/g_cat h. The temperature-programmed desorption (NH₃-TPD), temperature-programmed reduction (TPR) and CO chemisorption of the KPtSn catalysts with K added revealed the potassium addition blocked the acid sites, promoted the reduction of Sn oxide and decreased the Pt dispersion. The formations of cracking products and higher hydrocarbons on acid sites were suppressed by the K effect of blocking the acid sites. In contrast, K addition at more than 0.72 wt% rather increased cracking products and the amount of coke, resulting in the severe deactivation of catalysts. The high cracking products on the KPtSn catalysts with the high amount of K should not be related to the acid sites, because the acid sites were monotonously decreased with an increase in the amount of K. Instead, the potassium affected the characteristics of PtSn. The interaction between Pt and Sn could be weakened by enriching the reduced Sn, because the K component promoted the reduction of Sn oxide in the TPR experiments. Therefore, the 14-KPtSn catalyst with the low amount of K exhibits the highest stability and selectivity among the prepared KPtSn catalysts due to the compromise of the advantageous (blocking the acid sites) and bad (weakening the interaction between Pt and Sn) effects of the K addition in PDH.