Catalytic performance of Co-Mo-Ce-K/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the shift reaction of CO in coke oven gas

The catalytic performance of Co-Mo-Ce-K/γ-Al₂O₃ catalyst for the shift reaction of CO in coke oven gas is investigated using X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The results indicate that Ce and K have a synergistic effect on promoting the catalytic activity, and the Co-Mo-Ce-K/γ-Al₂O₃ catalyst with 3.0 wt-% CeO₂ and 6.0 wt-% K₂O exhibits the highest activity. CeO₂ favors Co dispersion and mainly produces an electronic effect. TPR characterization results indicate that the addition of CeO₂-K₂O in the Co-Mo-Ce-K/γ-Al₂O₃ catalyst decreases the reduction temperature of active components, and part of octahedrally coordinated Mo⁶⁺ transforms into tetrahedrally coordinated Mo⁶⁺, which has a close relationship with the catalytic activity.     

Preparation of Biodiesel by Transesterification of Rapeseed Oil with Methanol Using Solid Base Catalyst Calcined K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

We report here the preparation of biodiesel by transesterification of rapeseed oil with methanol using calcined K₂CO₃/γ-Al₂O₃ as a solid base catalyst. The prepared catalysts were characterized using SEM, IR and BET, and their catalytic activities were evaluated. The reaction conditions were optimized, and in particular, the conversion can be as high as 98.62% under the optimal reaction conditions. In addition, the effect of the presence of water in the reaction system on the catalytic activity was also studied.     

Catalytic effects of potassium on lignin steam gasification with <Emphasis Type="Italic">γ</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as a bed material

The effects of potassium on the reactivity of biomass-char steam gasification with the presence of a porous material were investigated by using a thermogravimetric reactor with high-heating rates. Lignin was employed as a char-rich biomass model compound. The potassium carbonate (K₂CO₃) was added to lignin and a mixture of lignin and γ-Al₂O₃ porous particles by means of aqueous impregnation. The effects of K₂CO₃ and γ-Al₂O₃ addition on pyrolysis of lignin and steam gasification of lignin-derived char were evaluated in terms of lignin conversion and the gaseous products. Results showed that K₂CO₃ slightly increased the steam gasification rate of lignin-derived char, but it did not influence the conversion in both the pyrolysis and steam gasification steps. In addition, tar was reduced by adding K₂CO₃ because of the increment of carbon conversion to gas product. The presence of γ-Al₂O₃ was found to induce the lower reactivity of resulting char after pyrolysis, reducing the gasification rate and conversion. A significant improvement in gasification conversion was observed with the presence of both K₂CO₃ and γ-Al₂O₃. Especially, almost complete gasification was achieved at a reaction temperature of 1,073 K.     

Thermal expansion and phase transitions in K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cs<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BSi<Subscript>2</Subscript>O<Subscript>6</Subscript> borosilicate solid solutions

Solid solutions K_{1 − x} Cs _x BSi₂O₆ (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization of glasses in the KBSi₂O₆-CsBSi₂O₆ borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I $ \bar 4 $ \bar 4 3d and I a $ \bar 3 $ \bar 3 d, respectively. The cubic-cubic phase transition I $ \bar 4 $ \bar 4 3d ai Ia $ \bar 3 $ \bar 3 d occurs in the composition range x = 0.35−0.40 at room temperature. In the series of solid solutions with x = 0−0.30, the reversible cubic-cubic polymorphic transition I $ \bar 4 $ \bar 4 3d ai ia $ \bar 3 $ \bar 3 d with an increase in the temperature has been revealed, the temperature of the polymorphic transition has been determined, and the thermal expansion in both polymorphic modifications has been studied using high-temperature X-ray diffraction and dilatometry. The solid solutions belonging to the space group Ia $ \bar 3 $ \bar 3 d are characterized by a lower thermal expansion than the solid solution belonging to the space group I $ \bar 4 $ \bar 4 3d. According to the calculations, the equivalents α/γ for the space groups I $ \bar 4 $ \bar 4 3d and Ia $ \bar 3 $ \bar 3 d are 0.03 and 0.02 (in cesium atomic fractions per degree Celsius), respectively.     

Role of CeO<Subscript>2</Subscript> in Rh/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Abstract  

The Rh/α-Al₂O₃ catalyst was modified by CeO₂ in order to improve the thermal stability and the carbon deposition resistance during the CO₂ reforming of methane The carbon formation was determined by TPO, TEM and Raman spectroscopy. Characterization results showed that the incorporation of Ce in the support inhibits the carbon deposition, increasing the useful life and the stability of the Rh base catalysts.     

Direct-hydrothermal synthesis of LiFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> cathode materials

Carbon free LiFe_1−x Mn _x PO₄ (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical performance of LiFePO₄ prepared in this manner showed to be positively affected by Mn²⁺-substitution. Among the Mn²⁺-substitution samples, the LiFe_0.9Mn_0.1PO₄ exhibited an initial discharge capacity of 141.4 mA h g⁻¹ at 0.1 C, and the capacity fading is only 2.7% after 50 cycles.     

Thermal expansion and phase transitions in K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BSi<Subscript>2</Subscript>O<Subscript>6</Subscript> leucite borosilicate solid solutions

Continuous solid solutions and the reversible phase transition from the I-43d cubic phase to the Ia-3d cubic phase are revealed in the borosilicate series K_{1 ? x} Rb _x BSi₂O₆. Samples in the KBSi₂O₆-RbBSi₂O₆ system are prepared by solid-phase synthesis and crystallization of glasses and investigated using the annealing and quenching technique, high-temperature X-ray diffraction, and dilatometry. The above polymorphic phase transition is observed in all solid solutions at temperatures in the range from 330 to 430°C depending on the composition: an increase in the rubidium content in the solid solution leads to a gradual decrease in the phase transition temperature. The linear thermal expansion coefficients α are determined for solid solutions of different crystalline modifications and glasses. The linear thermal expansion coefficients α for the I-43d low-temperature phase are equal to (20–23) × 10^?6 K^?1 according to the X-ray diffraction data and (21–24) × 10^?6 K^?1 according to the dilatometric data. The values of α for the Ia-3d high-temperature phase lie in the range (4–9) × 10^?6 K^?1 according to the X-ray diffraction data and in the range (6–9) × 10^?6 K^?1 according to the dilatometric data. The linear thermal expansion coefficients for both modifications decrease with an increase in the rubidium content in the solid solutions. The linear thermal expansion coefficients for glasses α = (10–11) × 10^?6 K^?1 are close to those for the high-temperature modification and virtually independent of the sample composition. The I-43d (cubic) ai I4₁/a (tetragonal) o Ia-3d (cubic) polymorphic phase transitions in the KBSi₂O₆ compound are revealed by differential scanning calorimetry (DSC) and dilatometry. Their reversibility is confirmed by the DSC data.     

Fabrication of Coaxial Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Heterostructure Nanowires by O<Subscript>2</Subscript> Flow-Induced Bifurcate Reactions

We report on bifurcate reactions on the surface of well-aligned Si_1−x Ge _x nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si_1−x Ge _x nanowires were grown in a chemical vapor transport process using SiCl₄ gas and Ge powder as a source. After the growth of nanowires, SiCl₄ flow was terminated while O₂ gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized into SiO₂ by the O₂ gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O₂ pressure without any intermediate region and enables selectively fabricated Ge/Si_1−x Ge _x or SiO₂/Si_1−x Ge _x coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion of oxygen through the oxide layer, respectively.     

Enhancement of combustion of a hydrogen-air mixture by excitation of O<Subscript>2</Subscript> molecules to the <Emphasis Type="Italic">a</Emphasis><Superscript>1</Superscript>Δ<Subscript><Emphasis Type="Italic">g</Emphasis></Subscript> state

The possibility of increasing the laminar flame velocity in a hydrogen-air mixture by excitation of O₂ molecules into the a ¹Δ _g singlet state. The presence of 10% of O₂(a ¹Δ _g ) molecules in oxygen is demonstrated to result in noticeable (up to 50%) enhancement of mixture burning. The temperature of combustion products and also the concentrations of H₂O, NO, and other constituents increase. The greatest effect of O₂(a ¹Δ _g ) molecules is manifested in combustion of lean mixtures; the least pronounced effect is observed in rich mixtures. These effects are caused by intensification of the chain mechanism in the presence of a super-equilibrium amount of excited O₂(a ¹Δ _g ) molecules in a hydrogen-air mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 3–12, July–August, 2008.     

Mesoporous ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZA) mixed metal oxide as an efficient and reusable catalyst for the liquid phase <Emphasis Type="Italic">O</Emphasis>-methoxymethylation reaction under solvent free conditions

Mixed metal oxide based solid acids like ZrO₂–Al₂O₃ (ZA) with Al₂O₃ different loadings (2, 4, 6, 8 and 10 mol%) were prepared by wet impregnation method and characterized by PXRD, NH₃-TPD, BET, ICP-OES, SEM, and TEM techniques. These solid acids were evaluated for their catalytic activity in the synthesis of a series of O-methoxymethylated products under solvent-free conditions at a moderate temperature in shorter reaction time (~20 min). This is achieved by various substituted alcohols and dimethoxy methane in good yields. Solid acids containing ZA used in this study exhibited good catalytic activity in the reaction. In case of 6 mol% ZA which has highest surface acidity, surface area and catalytically active tetragonal phase was found to be highest active in the O-methoxymethylation reaction up to ~99% yield. These catalysts were found to be reactivable and reusable.     

Synthesis and proton incorporation in BaCe<Subscript>0.9−<Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>

BaCe_0.9−x Zr _x Y_0.1O_3−δ powders were synthesized by a solid-state method at 1,400 °C. Two compositions were studied (x = 0.3 and x = 0.7). Pellets were prepared and conventionally sintered in air at 1,700 °C. Then, the samples were heated at 600 °C for 3 h in different reducing atmospheres: dry hydrogen, wet hydrogen and wet deuterium. After each treatment, the proton diffusion depth profile was obtained using Secondary Ion Mass Spectroscopy (SIMS). Protons were not incorporated in the material when the gas was not wet, and the isotope effect suggests that protons present in the pellet come from water and not from hydrogen.     

Spatial localization of holes in La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4</Subscript>

The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La_{2 ? x} Sr _x CuO₄ lattice have been determined by the method of emission Mössbauer spectroscopy on ⁵⁷Co(^57m Fe), ⁶⁷Cu(⁶⁷Zn), ⁶⁷Ga(⁶⁷Zn), and ¹⁵⁵Eu(¹⁵⁵Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V _zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe³⁺, Zn²⁺, and Gd³⁺ ions. Based on the comparison of the calculated and experimental dependences of V _zz on x it was shown that the holes appearing during the substitution of La³⁺ for Sr²⁺ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La_{2 ? x} Sr _x CuO₄ is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy.     

Hydroisomerization of Benzene-Containing Gasoline Fraction on Pt/B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pt/WO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

The effect of the hydroisomerization conditions of the benzene-containing fraction of catalytic reforming gasoline on the yield and composition of products is studied on Pt/B₂O₃–Al₂O₃ and Pt/WO₃–Al₂O₃ catalysts. These catalysts allow benzene to be completely removed from the raw material. At the same time, the greatest yields of liquid products are obtained with minimal losses of the octane number at 2 MPa, a mass feedstock hourly space velocity (MFHSV) of 2 h^?1, and 325°C: 96.3 and 95.4 wt % on Pt/B₂O₃–Al₂O₃ and Pt/WO₃–Al₂O₃ catalysts, respectively. The activity of the catalysts is maintained for 100 h during their operation.     

Features of the Growth of Thread-Like <Emphasis Type="Italic">x</Emphasis>InSe(1 – <Emphasis Type="Italic">x</Emphasis>)In<Subscript>2</Subscript>O<Subscript>3</Subscript> Crystals of Two-Layer PbSe and In Films

Lead and indium selenide films with an area of 3 × 3 mm² and thickness of ~1 μm each are deposited successively by thermal vacuum deposition on C-29 glass substrates. The films are heat-treated in a dry air atmosphere at a temperature of 550°С. X-ray microanalysis and scanning electron microscopy show the possibility of the formation of the thread-like nanocrystals of a xInSe(1 – x)In₂O₃ composite from two-layer PbSe and In films deposited on glass substrates in the process of heat treatment in an air atmosphere.     

Catalytic Methane Combustion over Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/CeO<Subscript>2</Subscript> Composite Oxides Prepared by Modified Citrate Sol–Gel Method

Abstract  

Co–Ce–O composite oxides with high surface areas were firstly prepared by a modified citrate sol–gel method with N₂ thermal treatment prior to calcination in air. The prepared Co–Ce–O catalysts have higher Brunauer–Emmett–Teller surface areas than those prepared by conventional calcination in air, and thus exhibit more effective catalytic activities. Adding CeO₂ into Co₃O₄ can not only increase the activity of Co₃O₄ but also greatly enhance its thermal stability. When the bulk atomic ratio of Co/Ce is 3/1, Co–Ce–O composite oxide possesses the best activity and stability for the methane combustion.     

CeO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> Mixed Oxides for the Selective Catalytic Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> by NH<Subscript>3</Subscript> Over a Wide Temperature Range

Abstract  

A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO _x by ammonia (NH₃-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H₂-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO₂–WO₃ with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH₃-SCR reactions, N₂ selectivity and SO₂ durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h⁻¹. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO₂–WO₃ mixed oxide catalyst.     

Electrochemical properties of amorphous Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>2</Subscript>O<Subscript>5−<Emphasis Type="Italic">y</Emphasis></Subscript> thin film deposited by r.f.-sputtering

The electrochemical properties of amorphous vanadium pentoxide (V₂O₅) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic intermittent titration technique (GITT). As x in Li _x V₂O_5−y increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO₄–propylene carbonate∣Li _x V₂O_5−y cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li _x V₂O_5−y thin film measured using GITT was determined to be 4 × 10⁻¹³–7 × 10⁻¹⁴ cm² s⁻¹ in the Li content range investigated.     

Synthesis of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3 + δ</Subscript> manganites by pyrohydrolysis of nitrates

Single-phase finely dispersed perovskite-like manganites La_{1 ? x} Sr _x MnO_{3 + δ} (0 ≤ x ≤ 0.33) with an average particle size of approximately 3μm were synthesized by the pyrohydrolytic method from a stoichiometric mixture of the corresponding metal nitrates at a temperature of 500°C in a water vapor atmosphere. The parameter δ was changed as a result of the subsequent heat treatment. It was established that the manganite La_0.67Sr_0.33MnO_{3 + δ} synthesized by the pyrohydrolytic method is characterized by a more pronounced change in the magnetoresistance as compared to the manganite that had the same composition but was synthesized according to the conventional ceramic technique.