Thermal investigation of ammonioborite (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>[B<Subscript>15</Subscript>O<Subscript>20</Subscript>(OH)<Subscript>8</Subscript>] · 4H<Subscript>2</Subscript>O

The thermal behavior of ammonioborite (NH₄)₃[B₁₅O₂₀(OH)₈] · 4H₂O is investigated using thermal X-ray diffraction, differential thermal analysis (DTA) in air and vacuum, and thermogravimetry. It is shown that the decomposition of the mineral (dehydration, dehydroxylation, deammoniation) proceeds in several stages, and the dehydration is accompanied by the amorphization. The thermal expansion of ammonioborite is sharply anisotropic. As in the case of other hydrous pentaborates, the thermal expansion is maximum in the direction in which pentaborate groups alternate with ammonium cations.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Synthesis of the study of solid solutions based on the ZrO<Subscript>2</Subscript>–HfO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>(CeO<Subscript>2</Subscript>) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO₂–HfO₂–Y₂O₃(CeO₂) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO₂ and the physical–chemical properties of these ceramics are studied.     

Vitreous region and properties of glasses of the Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–GeS<Subscript>2</Subscript>–PbF<Subscript>2</Subscript> system

Vitrification in the Ga₂S₃–GeS₂–PbF₂ system is considered. The physicochemical properties of glasses, such as density, microhardness, electroconductivity, refraction index, and transmission percentage of specimens in visible and IR ranges of spectrum are studied; differential thermal analysis is carried out; and Raman and electron paramagnetic resonance spectra are investigated.     

Effects of ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on sintering behaviors and microwave dielectric properties of Ba<Subscript>4</Subscript>Sm<Subscript>9.33</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript> ceramics

Effects of ZnO–B₂O₃ (ZB) addition on the densification, phase evolution and microwaves dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) ceramics for low-temperature fired applications have been investigated. The sintering temperature of BST ceramics can be effectively lowered to about 1000°C with introduction of ZB. Tungsten bronze like single phase is observed in the BST ceramics with 0.5 and 1.0% ZB. However, Sm₂Ti₂O₇ secondary phase appears when ZB addition reaches 2%, and Sm₂Ti₂O₇ phase gradually increases with the increase ZB addition. Microwave dielectric properties of the present ceramics are strongly dependent on phase constitution and density. Optimal microwave dielectric properties of ε = 63.4, Qf = 2830 GHz, τ _f =–8.8 ppm/°C is obtained for BST ceramics with 1% ZB addition.     

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.     

Vapor–Liquid Equilibrium of Binary Components of the BrCF<Subscript>2</Subscript>COOCH<Subscript>3</Subscript>–CF<Subscript>3</Subscript>COOH–BrCF<Subscript>2</Subscript>COOH–CF<Subscript>3</Subscript>COOCH<Subscript>3</Subscript> Quaternary System

Vapor–liquid equilibria of binary components of the BrCF₂COOCH₃–CF₃COOH–BrCF₂COOH–CF₃COOCH₃ quaternary system have been studied experimentally at constant pressure. The experiments have been carried out on a modified Sventoslavskii ebulliometer. Using the Aspen Plus software package, the appropriate models have been selected and the vapor–liquid equilibria for six binary systems have been simulated.     

Enhancement of the Activities of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Methane-SCR of NO by Treatment with NH<Subscript>3</Subscript>

Abstract  

The precursor particles for γ-Ga₂O₃–Al₂O₃ solid solutions were prepared by the coprecipitation method from aqueous solutions of Ga(NO₃)₃ and Al(NO₃)₃ with (NH₄)₂CO₃ as a precipitant. The γ-Ga₂O₃–Al₂O₃ solid solutions were obtained by calcination of the precursor at 700 °C. In this paper, the performance of the catalysts treated with NH₃ was investigated for the selective catalytic reduction (SCR) of NO with methane as a reducing agent, and it was found that γ-Ga₂O₃–Al₂O₃ catalysts treated with NH₃ and subsequently annealed in air showed higher activities than the γ-Ga₂O₃–Al₂O₃ catalysts without NH₃ treatment. NH₃ treatment of the catalyst caused partial rearrangement of Ga³⁺ and Al³⁺ ions and increased the population of tetrahedral Ga³⁺ ions in the defective spinel structure.     

Photocatalytic Removal of 17α-Ethinyl Estradiol Using the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>4</Subscript> Photocatalyst

A series of Bi₂O₃/Bi₂O₄ composites were prepared by calcining raw materials with different NaBiO₃/KOH mass ratios. The Bi₂O₃/Bi₂O₄ photocatalysts were characterized by the various measurements and their photocatalytic performance was assessed by degradation of 17α-ethinyl estradiol (EE2). The Bi₂O₃/Bi₂O₄ photocatalysts have wider visible light absorption and lower fluorescence emission intensity than the commercial Bi₂O₃. So, they displayed superior performance in the degradation of EE2. After the adsorption equilibrium of EE2 was reached, the degradation efficiency of Bi₂O₃/Bi₂O₄ for EE2 can reach a maximum value of ~?100% in 12 min under the visible-light illumination. Degradation analysis results indicated that both holes (h⁺) and superoxide radical (·O₂^?) can affect the degradation efficiency of EE2.

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Preparation and Photocatalytic Activity of an Inorganic–Organic Hybrid Photocatalyst Ag<Subscript>2</Subscript>WO<Subscript>4</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>

Ag₂WO₄/g-C₃N₄ composites with different Ag₂WO₄ concentration and calcination temperature were synthesized via a mixing and heating approach. Various techniques were used to investigate the characters of the as-prepared samples, such as thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The degradation of rhodamine B (20 ppm) under visible light was performed to investigate the photocatalytic activity of Ag₂WO₄/g-C₃N₄ composites. Results indicate that the Ag₂WO₄/g-C₃N₄ is actually Ag/Ag₂WO₄/g-C₃N₄ ternary system. 7.5 wt% Ag₂WO₄/g-C₃N₄ prepared at 300 °C presented the best photocatalytic performance in rhodamine B degradation. The degradation rate reaches 0.0679 min^?1, which is 3.25 times higher than the value of pure g-C₃N₄. The enhanced activity is attributed to the synergetic effect of Ag₂WO₄, g-C₃N₄ and metal Ag. Additionally, cycling experiments also proved that the Ag₂WO₄/g-C₃N₄ photocatalyst has good stability.     

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.     

Study on flame structures and emissions of CO and NO in Various CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript>–O<Subscript>2</Subscript>/N<Subscript>2</Subscript> counterflow premixed flames

An oxygen-diluted partially premixed/oxygen-enriched supplemental combustion (ODPP/OESC) counterflow flame is studied in this paper. Flame images are obtained through experiments and numerical simulations with the GRI-Mech 3.0 chemistry. The oxygen dilution effects are revealed by comparing the flame structures and emissions with those of a premixed flame and partially premixed flame (PPF) at the same equivalence ratio (?_Σ = 0.95 and ? _f = 1.4). The results show that both PPF and ODPP/OESC flames have distinct double flame structures; however, the location of the premixed combustion zone and the distance between premixed/nonpremixed combustion zone are significantly different for these two cases. For the ODPP/OESC flame, the temperature in the premixed combustion zone is lower and the premixed zone itself is located farther downstream from the fuel nozzle, which leads to reduction of NO and CO emissions, as compared to those of the PPF. Therefore, by adjusting the distribution of the oxygen concentration in the premixed and nonpremixed combustion zones, the ODPP/OESC can effectively balance the chemical reaction rate in the entire combustion zone and, consequently, reduce emissions.     

Phase relationships in the Na<Subscript>2</Subscript>ZnP<Subscript>2</Subscript>O<Subscript>7</Subscript>–LiKZnP<Subscript>2</Subscript>O<Subscript>7</Subscript> system

The phase relationships in the Na₂ZnP₂O₇–LiKZnP₂O₇ system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP₂O₇. The phase formation of this system is compared with the previously studied NaKZnP₂O₇–LiKZnP₂O₇ system. It is shown that a structural factor affects the geometry of the state diagrams.     

Fe-doping effects on the structural and electrochemical properties of 0.5Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·0.5LiMn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>2</Subscript> electrode material

With the aim of achieving a high-performance 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ material, a series of 0.5Li₂MnO₃·0.5LiMn _x Ni _y Fe_(1−x−y)O₂ (0.3 ≤ x ≤ 0.5, 0.4 ≤ y ≤ 0.5) samples with low Fe content was synthesized via coprecipitation of carbonates. Its crystal structure and electrochemical performance were characterized by means of powder X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, galvanostatic charge/discharge testing, cyclic voltammetry, and electrochemical impedance spectra. Rietveld refinements with a model integrating R [`3] \overline{3} m and Fm [`3] \overline{3} m indicate that a low concentration of Fe incorporated in 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ decrease a disordered cubic domain of the composite structure. The preferential distribution of Fe in cubic rock-salt contributes to an unimaginable decrease of c-axis parameter of the predominant layered structure as the Fe content increases. Moreover, including Fe as a dopant can kinetically improve crystallization and also change the ratio of Mn³⁺/Mn⁴⁺ and Ni³⁺/Ni²⁺. As a result, 0.5Li₂MnO₃·0.5LiMn_0.4Ni_0.5Fe_0.1O₂ exhibits lower Warburg impedance and higher reversible capacity than the undoped material.     

Effects of the geometry and operating temperature on the stability of Ti/IrO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> electrodes for O<Subscript>2</Subscript> evolution

Ternary IrO₂–Sb₂O₅–SnO₂ anode has shown its superiorities over IrO₂ and many other electrocatalysts for O₂ evolution, in terms of electrochemical stability, activity and cost. The performance of IrO₂–Sb₂O₅–SnO₂ anodes is affected by its electrochemical properties and operating conditions. In this paper, the electrochemical stability and activity of the Ti/IrO₂–Sb₂O₅–SnO₂ anodes prepared with three different geometries were investigated under different operating conditions. It was found that anodes with large mean curvature have high electrochemical stability. Although increasing temperature results in a decrease in the stability of Ti/IrO₂–Sb₂O₅–SnO₂, the anode with a mean curvature of 200 m⁻¹ still shows acceptable service life even at 70 °C. This tolerance of high temperature was attributed to the thermal expansion difference between the substrate and the coating layer, the redox window for Ir(V)/Ir(IV) conversion, and the redox reversibility of Sb and Sn species in the coating layer.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.     

Catalytic activation of C<Subscript>1</Subscript>—C<Subscript>3</Subscript> alkanes

The conversion of CH₄ and the C₆H₆—C₃H₈ mixture over (M, ReO _x )/Al₂O₃ (M = Ni, Co, Pt) analogues of industrial low-octane gasoline reforming catalysts containing 0.5 wt % M in a finely divided state and 0.3–1.0 wt % Re is reported. The unreduced catalysts activate the conversion of CH₄ into C₆H₆ at 650°C. Using (M, ReO _x )/Al₂O₃ + HZ catalytic mixtures (HZ = H-form of zeolite Y, M, or ZSM-5), it is possible to carry out low-temperature C₆H₆ alkylation or C₃H₈ dehydrogenation at 180–350°C. These processes are aimed at involving oil refining waste into obtaining valuable hydrocarbons. The processes can be commercial- ized at low-octane reforming and gas-phase benzene alkylation plants and can be intensified by separating the resulting H₂ in membrane reactors.