Photon interaction parameters for some ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Some photon interaction parameters such as mass attenuation coefficient, effective atomic number, half value layer, mean free path and electron density for 15ZnO–(17.5–x)Al₂O₃–xFe₂O₃–67.5P₂O₅ glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO–(25–x)Al₂O₃–xFe₂O₃–60P₂O₅ glass system (x = 0, 25) have been investigated in the photon energy range of 1 keV to 100 GeV. It has been observed that all the photon interaction parameters for the selected glass systems vary with the photon energy. Among the selected glass systems, the sample 15ZnO–25Fe₂O₃–60P₂O₅ glass system shows maximum values for mass attenuation coefficients, effective atomic numbers, electron densities and minimum values for mean free path and half value layer in the entire energy grid.     

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.     

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.     

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.     

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.

Graphical Abstract

Open image in new window

     

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.     

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.     

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.     

Bimetallic Pd–Cu/ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pd–Cu/ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for methanol synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO–Al₂O₃ and ZrO₂–Al₂O₃ were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, X-ray, TPR-H₂, TPD-NH₃ techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd–Cu alloy formation.     

Synthesis and physicochemical properties of a solid oxide nanocomposite based on a ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–MgO system

A highly dispersive powder with a (ZrO₂)_0.92(Y₂O₃)_0.03(Gd₂O₃)_0.03(MgO)_0.02 composition and specific surface area of 150 m²/g has been synthesized via a method of coprecipitation of hydroxides with the subsequent cryochemical treatment of the gel. Nanoceramics based on the cubic modification of zirconium dioxide with the grain size of ~40–45 nm have been obtained. The temperature dependence of the specific electrical conductance of the nanoceramics within a temperature range of 350–870°C in air has been studied, and the ratio of the ionic and electronic parts of the conductance has been determined. Recommendations for the use of the obtained oxide nanocomposite as an electrolyte for a high-temperature fuel cell have been given.     

Notable Reactivity of Acetonitrile Towards Li<Subscript>2</Subscript>O<Subscript>2</Subscript>/LiO<Subscript>2</Subscript> Probed by NAP XPS During Li–O<Subscript>2</Subscript> Battery Discharge

One of the key factors responsible for the poor cycleability of Li–O₂ batteries is a formation of byproducts from irreversible reactions between electrolyte and discharge product Li₂O₂ and/or intermediate LiO₂. Among many solvents that are used as electrolyte component for Li–O₂ batteries, acetonitrile (MeCN) is believed to be relatively stable towards oxidation. Using near ambient pressure X-ray photoemission spectroscopy (NAP XPS), we characterized the reactivity of MeCN in the Li–O₂ battery. For this purpose, we designed the model electrochemical cell assembled with solid electrolyte. We discharged it first in O₂ and then exposed to MeCN vapor. Further, the discharge was carried out in O₂?+?MeCN mixture. We have demonstrated that being in contact with Li–O₂ discharge products, MeCN oxidizes. This yields species that are weakly bonded to the surface and can be easily desorbed. That’s why they cannot be detected by the conventional XPS. Our results suggest that the respective chemical process most probably does not give rise to electrode passivation but can decrease considerably the Coulombic efficiency of the battery.     

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.     

Monte Carlo Design and Experiments on the Neutron Shielding Performances of B<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass System

Neutron shielding properties of (90 – x)B₂O₃–10ZnO–xBi₂O₃ glass systems (where x = 15, 20, 25 and 30 mol %) were investigated by Monte Carlo simulations (FLUKA and GEANT4) and experiments. Neutron mass removal cross sections, number of inelastic scattering, elastic scattering, and capture interactions were estimated by simulations. ²⁴¹Am/Be neutron source was used for the neutron equivalent dose rate measurements. As a result, produced glass samples have fine neutron shielding capacity.     

Change of the thermal behavior of 55Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 45B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass at annealing close to the vitrification temperature

The characteristic properties of relaxation processes for 55Bi₂O₃ ? 45B₂O₃ glass were described. The pattern of changes of the vitrification temperature (T _g ) is found to be quasi-periodic; the value of the endothermic effect near T _g (ΔC’ _p ) and the difference between the softening point and the vitrification temperature (T _m –T _g ) were determined. The temperature-time parameters of the transition from quasi-periodic to the continuous change of the properties were determined and an explanation of such behavior of the system was offered.     

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.     

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.     

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.