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.     

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.     

Synthesis and research of nanopowders composed of 0.97ZrO<Subscript>2</Subscript> · 0.03La<Subscript>2</Subscript>O<Subscript>3</Subscript>

This work is devoted to the preparation of zirconium oxide nanopowders stabilized by lanthanum oxide using the method of codeposition in the presence of hydrogen peroxide. Nanopowders composed of 0.97ZrO₂ · 0.03La₂O₃ with particles of 10–20 nm are obtained. It is found that in the temperature interval of 500–1100°C the tetragonal and monoclinic points of the zirconium oxide phase crystallize at the same time.     

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.     

Structural analyses of RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti and IrO<Subscript>2</Subscript>–RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti anodes used in industrial chlor-alkali membrane processes

The morphology and composition of RuO₂–TiO₂/Ti and IrO₂–RuO₂–TiO₂/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO₂–TiO₂/Ti anode. For the IrO₂–RuO₂–TiO₂/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.     

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.     

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.     

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.     

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.     

Synthesis and Physicochemical Properties of Nanopowders and Ceramics in a CeO<Subscript>2</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.     

Conversion of 4-Methylanisole Catalyzed by Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and by Pt/SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>: Reaction Networks and Evidence of Oxygen Removal

Abstract  

The conversion of 4-methylanisole, a prototypical bio-oil compound, was catalyzed by Pt/Al₂O₃, Pt/SiO₂-Al₂O₃, or HY zeolite at 573 K and atmospheric pressure. More than a dozen products were formed with each catalyst, the most abundant being 4-methylphenol, 2,4-dimethylphenol, and 2,4,6-trimethylphenol; toluene was also a major product when the catalyst was supported platinum with H₂ as a co-reactant. 4-Methylphenol was the only methylphenol isomer formed in significant yields, which indicates that migration of the methyl group on the aromatic ring is not significant under the selected reaction conditions. The data determine approximate reaction networks including reactions forming 4-methylphenol, 2,4-dimethylphenol, and toluene as primary products. The kinetically significant reaction classes were transalkylation, observed with all three catalysts, and hydrogenolysis (including hydrodeoxygenation) and hydrogenation, observed only with the platinum-containing catalysts operating in the presence of H₂. Data such as those reported here provide a starting point for predicting the conversion of whole bio-oils for removal of oxygen and upgrading of fuel properties.     

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.     

Effect of preparation procedure of Iro<Subscript>2</Subscript>–Nb<Subscript>2</Subscript>o<Subscript>5</Subscript> anodes on surface and electrocatalytic properties

The influence of the electrode manufacturing procedure on surface and electrocatalytic properties for oxygen and ozone evolution at electrodes of nominal composition Ti/[IrO₂–Nb₂O₅] (45:55 mol%) was investigated. Thermal decomposition at 450 °C (1 h, air stream) was adopted as standard procedure. Metal support pretreatment, solvent mixture, method of applying the precursor mixture and calcination procedure were all investigated. X-ray diffraction, scanning electronic microscopy, voltammetric and differential capacity analysis show the use of HCl 1:1 as solvent and applying the mixture by brush led to fragile rugged/porous oxide coatings. However, for the same conditions, but controlled calcination (heating/cooling rates), the coating becomes more compact. Using isopropanol as solvent results in a more homogeneous coating, presenting the lowest morphology factor. Kinetic investigation shows the rugged/porous coating presents the lowest Tafel slopes and the highest global electrocatalytic activity for OER. The more compact the coating the lower the electrochemically active surface area and the global OER activity. Ozone efficiency depends on the electrochemically active area while support pretreatment strongly influences the lifetime of the electrode. Application of a Pt interlayer between the oxide and Ti base improves the service life.     

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.     

Ultrafast Spectroscopy and Red Emission from β-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>/β-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> Nanowires

Ultrafast pump-probe and transient photoluminescence spectroscopy were used to investigate carrier dynamics in β-Ga₂O₃ nanowires converted to β-Ga₂O₃/Ga₂S₃ under H₂S between 400 to 600 °C. The β-Ga₂O₃ nanowires exhibited broad blue emission with a lifetime of 2.4 ns which was strongly suppressed after processing at 500–600 °C giving rise to red emission centered at 680 nm with a lifetime of 19 μs. Differential absorption spectroscopy reveals that state filling occurs in states located below the conduction band edge before sulfurization, but free carrier absorption is dominant in the β-Ga₂O₃/Ga₂S₃ nanowires processed at 500 to 600 °C for probing wavelengths >500 nm related to secondary excitation of the photo-generated carriers from the mid-gap states into the conduction band of Ga₂S₃.     

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.     

Synthesis and comparative studies of xerogels,aerogels, and powders based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> system

The technology of liquid-phase synthesis of mesoporous xerogels and aerogels based on ZrO₂–Y₂O₃–CeO₂ is developed. Xerogels are obtained by the coprecipitation of hydroxides, while aerogels are obtained in accordance with the sol–gel technology: the average pore size is 1.5–17.2 nm and the specific surface area is 120–878 m²/g. Aerogels are characterized by a high degree of porosity: the pore volume attains 1–4 cm³/g. Based on precursor xerogels, nanopowders of a tetragonal solid solution of the (ZrО₂)_0.92(Y₂О₃)_0.03(CeО₂)_0.05 composition with a particle size of 5–9 nm and S _spec = 74 m²/g were fabricated. Due to the high values of their specific surface area, the synthesized xerogels and aerogels are promising as sorbents, catalysts, or catalyst supports.     

Zn<Superscript>2+</Superscript>-exchange kinetics and antimicrobial properties of synthetic zirconium umbite (K<Subscript>2</Subscript>ZrSi<Subscript>3</Subscript>O<Subscript>9</Subscript>·H<Subscript>2</Subscript>O)

Zirconium umbite, K₂ZrSi₃O₉·H₂O, is a microporous framework ion exchanger whose potential as a carrier for Zn²⁺ ions in antimicrobial formulations has not yet been investigated. Accordingly, batch Zn²⁺-exchange kinetics of synthetic zirconium umbite (K-UM) and the subsequent antimicrobial action of the zinc-bearing phase (Zn-UM) against Staphylococcus aureus and Escherichia coli are reported. Nonstoicheiometric over-exchange of Zn²⁺ for K⁺ was observed and attributed to hydrolysis and complexation reactions of Zn²⁺ within the umbite framework. The exchange process, which was described by a simple pseudo-first-order model (k ₁ = 2.69 × 10⁻⁴ min⁻¹, R ² = 0.992), did not achieve equilibrium within 120 h at 25 °C, by which time the uptake of zinc was found to be 1.04 mmol g⁻¹. The minimal bactericidal concentrations of Zn-UM for E. coli and S. aureus were found to be >10 g cm³ and <1.0 g cm³, respectively.     

Physical–chemical properties and conductivity of Na<Subscript>2</Subscript>O–SnO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> glass systems

The effect of tin(IV) oxide on the conductivity and chemical stability of sodium–silicate glass has been studied for five different glass compositions. Dilatometry and DSC were used to investigate the thermal behavior of the glass. The research into transport characteristics of the glass has shown that its conductivity is in the range of 2 × 10^–8–5 × 10^–7 S/cm at 25°C and 10^–3 S/cm at 300°C.