ZnO Al2O3 Research Articles

Co-Based Catalysts Derived from Layered-Double-Hydroxide Nanosheets for the Photothermal Production of Light Olefins.

Solar-driven Fischer-Tropsch synthesis represents an alternative and potentially low-cost route for the direct production of light olefins from syngas (CO and H2 ). Herein, a series of novel Co-based photothermal catalysts with different chemical compositions are successfully fabricated by H2 reduction of ZnCoAl-layered double-hydroxide nanosheets at 300-700 °C. Under UV-vis irradiation, the photothermal catalyst prepared at 450 °C demonstrates remarkable CO hydrogenation performance, affording an olefin (C2-4= ) selectivity of 36.0% and an olefin/paraffin ratio of 6.1 at a CO conversion of 15.4%. Characterization studies using X-ray absorption fine structure and high-resolution transmission electron microscopy reveal that the active catalyst comprises Co and Co3 O4 nanoparticles on a ZnO-Al2 O3 mixed metal oxide support. Density functional theory calculations further demonstrate that the oxide-decorated metallic Co nanoparticle heterostructure weakens the further hydrogenation ability of the corresponding Co, leading to the high selectivity to light olefins. This study demonstrates a novel solar-driven catalyst platform for the production of light olefins via CO hydrogenation.

The effect of UV exposure and heat treatment on crystallization behavior of photosensitive glasses

In this study, photosensitive glasses in the Na2O–ZnO–Al2O3–SiO2 system with photosensitizing agents (cerium, silver, tin, antimony) and halogenides (NaF and KBr) were synthesized through a conventional melt-quenching technique. The crystallization mechanism was investigated for solely heat-treated and UV-exposed + heat-treated samples using differential thermal analysis (DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques to understand the effect of UV exposure on crystallization behavior of photosensitive glasses. Accordingly, non-isothermal DTA measurements were performed at different heating rates to determine crystallization peak, Tp, and onset, Tc, temperatures. For solely heat-treated samples, the kinetic parameters such as the Avrami constant, n, and morphology index, m, were calculated as 1 from the Ozawa method indicating surface crystallization and the value of crystallization activation energy was calculated as 944 kJ/mol using modified Kissinger method. On the contrary, bulk crystallization was found to be predominant for UV exposed + heat-treated samples revealing that UV exposure is the primary cause of bulk crystallization in photosensitive glasses.

Highly thermally stable single-component warm-white-emitting ZANP glass: Synthesis, luminescence, energy transfer, and color tunability

Luminescent glass demonstrates potential for applications as color converters in white-light-emitting diodes (W-LEDs). In this study, solution combustion synthesis combined with low-temperature melt quenching was employed as a novel route for preparing new white-light fluorescent glasses (rare-earth-doped ZnO–Al2O3–Na2O–P2O5, ZANP). The developed solution combustion synthesis can considerably decrease the reaction temperature and time, with several advantages such as energy and time savings. X-ray diffraction and photoluminescence spectroscopy, as well as decay curves, CRI, and CCT, as well as the Commission Internationale de I′Eclairage (CIE) 1931 chromaticity coordinates, were assessed to examine the microstructure and photoluminescence properties of Tm3+/Dy3+ co-doped and Tm3+/Dy3+/Eu3+ tri-doped ZANP glasses for use in W-LEDs. Experimental results revealed that ZANP glass co-doped with Tm3+ and Dy3+ exhibits blue- and yellow-light emissions based on the energy transfer of dipole-dipole interaction between Tm3+ and Dy3+, which can realize the adjustment of color in a wide range. The emitting color coordinate (0.343, 0.344) of ZANP: 1.0Tm3+, 0.75Dy3+ approach ideal white light. Also, by the introduction of additional Eu3+ doping, ZANP:1.0Tm3+, 0.75Dy3+, 0.1%Eu3+ glass emit warm-white light (CCT = 3198 K) under an excitation of 361 nm. Moreover, the tri-doped ZANP glasses exhibit good thermal stability, where the luminous intensity at 498 K remains exceeding 50% of that at room temperature, and the color coordinate offset is only 2.87 × 10−2 relative to room temperature.

Effects of Cu2+ ion incorporation into ZnTe nanocrystals dispersed within a glass matrix

This paper reports on the optical, morphological, structural and magnetic properties of Zn1-xCuxTe nanocrystals, doped with Cu (x varying from 0.000 to 0.100) and grown by thermal annealing at 500 °C in a P2O5–ZnO–Al2O3–BaO–PbO glass system that had been synthesized by fusion. At higher levels of Cu-doping, optical absorption (OA) showed that Cu2+ ions were incorporated within and dispersed throughout the lattice of the ZnTe semiconductor. The OA spectra also showed that the growth kinetics of these NCs were influenced by the Cu2+ magnetic ions. Transmission electron microscopy (TEM) images revealed that the lattice parameter of the nanocrystals was not affected by the incorporation of Cu2+ ions. Finally, electron paramagnetic resonance (EPR) spectra of the Cu2+ ions showed asymmetrical hyperfine lines as well as proved a substitutive incorporation of Cu2+ in ZnTe NCs.

Synthesis, Luminescence and Thermal Properties of PVA–ZnO–Al2O3 Composite Films: Towards Fabrication of Sunlight-Induced Catalyst for Organic Dye Removal

Poly(vinyl alcohol) (PVA)–ZnO–Al2O3 composite films have been prepared by the addition of different compositions of ZnO and Al2O3 through solvent casting method. Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis) and photoluminescence spectroscopy (PL) spectra revealed the successful incorporation of ZnO and Al2O3 onto PVA and interactions among ZnO, Al2O3 and PVA molecules. PL data indeed showed the enhanced luminescence property of composite films compared with the PVA. Thermogravimetric analysis (TGA) data showed that thermal stability of PVA–ZnO–Al2O3 composite films could be greatly improved by the incorporation of ZnO and Al2O3 into the system. The glass transition temperature (Tg) were increased for the composite samples using ZnO and Al2O3. Differential scanning calorimetry (DSC) measurements revealed that the melting temperature (Tm) of PVA–ZnO–Al2O3 composite films are significantly higher (~ 12 to 25 °C) than PVA. The photocatalytic measurements exhibited better photocatalytic degradation ability of PVA–ZnO–Al2O3 composites over PVA. Such photocatalytic capacity makes the PVA–ZnO–Al2O3 composite films promising candidates for the removal of organic dyes for water purification.

Scintillation and optical properties of TiO2–ZnO–Al2O3–B2O3 glasses and glass-ceramics

13TiO2–xZnO–17Al2O3–(70 − x)B2O3 (x = 17, 26, and 35) glasses were prepared by a melt-quenching method, and the obtained glass samples were heated at temperatures 30 °C above the glass transition temperature of corresponding glass in order to obtain glass-ceramics. The obtained glass-ceramic samples were confirmed to have anatase (x = 17) and rutile (x = 26 and 35) phases from X-ray diffraction analysis. Then, the scintillation and optical properties were evaluated and discussed the difference between the glass-ceramic and glass samples. In the scintillation spectra under X-ray irradiation, a broad emission peak was observed around 450 nm in all the samples, and the new peak around 500 nm appeared in the anatase-precipitated glass-ceramic. The intensities of the glass-ceramic samples were enhanced in comparison with the corresponding glasses because the glass-ceramics includes TiO2 crystallites with defect centers which act as effective emission centers. The scintillation decay curves of the glass and glass-ceramic samples were approximated by one and a sum of two exponential decay functions, respectively. The faster component of glass and glass-ceramic samples would be caused by the host emission, and the slower component of glass-ceramic sample would be ascribed to the emission of Ti3+.

Epitaxial Growth of Bandgap Tunable ZnSnN2 Films on (0001) Al2O3 Substrates by Using a ZnO Buffer

Growth of ZnSnN2 films on (0001) Al2O3 substrates is performed by plasma-assisted molecular-beam epitaxy by changing the growth temperatures from 350 to 650 °C. Single crystal ZnSnN2 films have been grown by using ZnO buffer while the film grown without the ZnO buffer has shown amorphous-like disordered characteristics addressed by no observation of any diffraction from reflection high-energy electron diffraction. All the grown crystalline ZnSnN2 films with ZnO buffer show a pseudowurtzite structure without the formation of an orthorhombic structure. Epitaxial relationships between Al2O3 substrate, ZnO buffer, and ZnSnN2 film are determined to be [1120] ZnSnN2//[1120] ZnO//[1010] Al2O3 and [0001] ZnSnN2//[0001] ZnO//[0001] Al2O3. The bandgaps of ZnSnN2 films could be tuned from 1.85 to 2.15 eV, simply by increasing the growth temperatures from 350 to 650 °C. The carrier concentrations and carrier mobilities were investigated and compared. Since the growth of single crystal ZnO films has been reported o...

Correlation between the porosity of γ-Al2O3 and the performance of CuO–ZnO–Al2O3 catalysts for CO2 hydrogenation into methanol

The influence of the porosity of γ-Al2O3 on the performance of CuO–ZnO–Al2O3 catalysts for methanol synthesis from H2 + CO2 mixture was studied. Various types of γ-Al2O3 with different surface areas (from 130 to 280 m2/g) and pore sizes (from 3 to 11 nm) were investigated. N2 adsorption, XRD, TPR studies and grand canonical Monte Carlo simulation were utilized to determine the correlation between their physico-chemical properties and catalytic performance. It was shown that the crystallite size of CuO (determined by XRD) and BET surface area of supports are not the key factors for methanol productivity. The TPR profiles of catalysts demonstrated a direct relationship between CuO–ZnO interaction with their catalytic performance. Interestingly, samples with the uniform pore size of 5 nm exhibit a higher CuO–ZnO interaction and the highest methanol yield. In addition, at this pore size, simulation results showed that the ratio of H2 and CO2 inside the γ-Al2O3 pore was 1.5, which could be an appropriate feed ratio for high methanol productivity.

ZnO-Al2O3-promoted CuO/ZrO2 catalyst prepared by oxalate gel-coprecipitation for the conversion of water-bearing materials

Generally, ZrO2 facilitates the reactions of O-containing species, which result in the loss of activity or the sintering of Cu species via intimate interaction between water and CuO/ZrO2 catalysts. Indeed, the CuO/ZrO2 catalysts (CZo) prepared by oxalate gel-coprecipitation technique possessed a high dispersion of Cu and a certain degree of alkalinity. Unfortunately, it exhibited inferior catalytic activity in conversion of bio-ethanol (37.6% conversion). In contrast, the CuO–ZnO–Al2O3–ZrO2 catalysts (CZAZo) with extra addition of ZnO and Al2O3 showed a good catalytic performance and stability (>600 h on line). For example, the 92.5% selectivity of ethyl acetate based on 62.2% conversion of ethanol, was achieved. Besides, it performed better in hydrogenation of hydrous ethyl acetate than CZo. Evidently, the excellent performance in conversion of water-bearing materials was mainly due to the addition of ZnO and Al2O3 to CuO/ZrO2 catalysts. Besides, the uniform combination of each component could be achieved successfully by the employment of oxalate gel-coprecipitation. As a result, the surface electronic properties are tuned effectively and the affinity for water decreases sharply. Most importantly, the associated loss of active sites could be effectively avoided because of the reduced water coverage over CZAZo.

Effect of ZnO/MgO ratio on the crystallization and optical properties of spinel opaque glazes

AbstractThe effect of the ZnO/MgO ratio on the crystallization and optical properties of glass‐ceramic glazes from the SiO2–Al2O3–ZnO–MgO–CaO–K2O–Na2O–B2O3 system was studied. The glazes with different ZnO/MgO ratios were characterized by differential scanning calorimetry, X‐ray powder diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy analysis and a spectrophotometer. The results reveal that the A glaze without ZnO content contains forsterite and sapphirine. The B and C glazes with intermediate ZnO/MgO ratio contain enstatite and spinel solid solution. The D to F glazes with higher ZnO/MgO ratio crystallize spinel solid solution as the only crystalline phase. The amount of spinel solid solution, lightness values (L*), gloss values and the reflectance of the studied glazes increase with the ZnO/MgO ratio.

Inclusion of Zn into Metallic Ni Enables Selective and Effective Synthesis of 2,5-Dimethylfuran from Bioderived 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) is an important platform chemical derived from C6 sugars and cellulose. The formed 2,5-dimethylfuran (DMF) via hydrogenolysis of HMF was denoted as a promising and sustainable fuel candidate. The further improvement of DMF yield is the central premise of this work, which is based on the elucidation of the relationship between catalytic performance and active sites. Herein, a NiZn alloy catalyst was formed through Zn inclusion to Ni by controllable reduction of the NiZnAl hydrotalcite-derived NiO–ZnO–Al2O3 mixed oxide. The combination of temperature-programmed reduction (TPR), in situ X-ray diffraction (XRD), CO-adsorbed infrared spectroscopy (CO–IR), and X-ray photoelectron spectroscopy (XPS) revealed that the surface of the NiZn catalyst was composed of β1-NiZn while the bulk was composed of α-NiZn. Moreover, the surface Ni atoms were geometrically isolated by Zn atoms and modulated to be electron-rich. Finally, the rate of C═O/C—O hydrogenolysis over C═C/C—C hydrogenation f...

The effect of silver on the optical, spectral-luminescent, and crystallization properties of bromide photo-thermo-refractive glasses

The effect of silver on the optical, spectral-luminescent, and crystallization properties of bromide photo-thermo-refractive glasses is studied. Multicomponent photosensitive glasses of the Na2O–ZnO–Al2O3–SiO2 system with photosensitizing agents (cerium, antimony, silver) and halogenides (fluorine and bromine) are synthesized. Ultraviolet irradiation and thermal treatment below the glass-transition temperature of the glasses cause the formation of silver molecular clusters, which exhibit luminescence in the visible and infrared regions. UV irradiation and thermal treatment of glasses above the glass-transition temperature lead to the growth of silver nanoparticles with plasmon resonance peak in the region of 420 nm. Further thermal treatment of glasses above the glass-transition temperature shifts the plasmon-resonance maximum by 70 nm to longer wavelengths, which is related to the growth of a crystalline shell consisting of mixed silver and sodium bromides on nanoparticles. This formation of a crystalline phase on colloidal centers results in a local increase in the refractive index of the irradiated region by +Δn ~ 900 ppm compared to the nonirradiated region. Photo-thermo-refractive glasses with increased silver concentration are promising photosensitive materials for creating holographic optical elements and devices for line narrowing and stabilizing filters, spectral beam combiners, and filters for increasing the spectral brightness of laser diodes. A positive change in the refractive index of Photo-thermo-refractive glasses provides the possibility of recording in them 3D waveguide and integrated-optical structures.

Structural evolution of CaF2 nanoparticles during the photoinduced crystallization of a Na2O–K2O–CaO–CaF2–Al2O3–ZnO–SiO2 glass

A glass in the system Na2O–SiO2–Al2O3–K2O–CaO–CaF2–ZnO was doped with Ce, Ag, Sn, Sb and Br. Homogeneous and transparent glass ceramics are obtained from this glass by the precipitation of CaF2 nanoparticles. An interface-controlled crystallization mechanism hinders crystal growth after some time. By adding photosensitive agents, a tailored photoinduced CaF2 crystallization was achieved. Structural evolution during irradiation and heat treatment was investigated by different electron microscopic techniques, e.g., scanning transmission electron microscopy (STEM) including energy-dispersive X-ray analysis (EDXS) and scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). Agglomerated structures with a size of ca. 35 nm were observed after the first thermal treatment at 530 °C. The Ag nucleation is accompanied by clustering of several components within the glass. CaF2 particles with diameters of ca. 300 nm with a spherulitic structure are observed in the glass ceramic after the second heat treatment step at 560 °C. Calcium and fluoride are depleted from the glass matrix during crystallization, while SiO2 is enriched. From (S)TEM micrographs, supplemented by selected area diffraction (SAD), outward growth of CaF2 from a central point is observed. STEM–EDXS analyses show residual glass within the spherulitic structure.

Influence of the oxide support reducibility on the CO2 methanation over Ru-based catalysts

Catalysts consisting of 5wt.% ruthenium dispersed on four different metal oxide supports were synthesized with single-step flame spray pyrolysis and assessed for the hydrogenation of CO2. The chosen supports covered a variety of characteristics expected to alter the catalytic performance, ranging from amphoteric and irreducible Al2O3, to amphoteric and reducible ZnO and MnOx, to basic and reducible CeO2. For the pristine metal oxide supports, the catalytic activity correlated with the oxide basicity and ZnO showed the highest CO2 conversion. However, CO formation through the reverse water-gas shift reaction dominated over the CO2 methanation due to a lack of H2 dissociation sites. The addition of Ru created such H2 dissociation sites and a significant increase in CO2 conversion and CH4 selectivity was observed. Combining the results of H2 temperature-programmed reduction, quantitative H2 and CO chemisorption, in situ DRIFTS, and the CO2 hydrogenation reaction kinetics revealed that the Ru coverage with CO decreased with the support reducibility. For the irreducible Al2O3 support, the Ru particles were quasi-saturated with CO at low temperatures and the reaction was limited by the competitive Langmuir-type co-adsorption of H2. The ZnO support lead to the lowest Ru-CO coverage associated with a weak CO adsorption and the reaction was dominated by the reverse water-gas shift reaction. CeO2 showed a Ru-CO coverage in between Al2O3 and ZnO, which ensured the presence of H2 dissociation sites while the Ru-CO adsorption strength remained sufficiently high.

Microstructure evolution during air bonding of Al2O3 to Al2O3 joints using bismuth–borate–zinc glass

Alumina ceramics with 95wt.% purity were sealed together using a bismuth based glass, 40Bi2O3–40B2O3–20ZnO (mol.%). The wettability of the glass on the Al2O3 substrate was investigated. The results showed a contact angle of≤36.5° was achieved when the temperature was≥630°C. Subsequently, sealing cycles were performed at temperatures of 520–700°C for 30min. The dependence of microstructure evolution of the joints on temperature was investigated. Bi24B2O39 was detected to be the product in the joints sealed at 530–580°C, while ZnAl2O4 was identified to be the main product when sealing at temperature of≥650°C due to the reaction between the Al2O3 substrate and ZnO from the glass. The influence of dwelling time at 700°C on microstructure evolution of the joints was also studied. The results showed that the size of ZnAl2O4 increased with increasing holding time.

Bimetallic Pd–Cu/ZnO–Al2O3 and Pd–Cu/ZrO2–Al2O3 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.

Mechanical, Structural and Thermal Properties of Transparent Bi2O3–Al2O3–ZnO–TeO2 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, Tg, onset, Tx, crystallization, Tp, and melting, Tm, temperatures were obtained by using DTA scan.

Characterization and Catalytic Performance of Cu/ZnO/Al2O3 Water–Gas Shift Catalysts Derived from Cu–Zn–Al Layered Double Hydroxides

Cu/ZnO/Al2O3 catalysts with different compositions were prepared from Cu–Zn–Al layered double hydroxides (LDHs) and tested for the water–gas shift reaction. LDHs were synthesized by the coprecipitation method, and Cu–Zn–Al LDHs or Cu–Al LDHs could be formed depending on the (Cu + Zn)/Al atomic ratio. Upon calcination, LDHs decomposed to form mixed metal oxides consisting of CuO, ZnO, ZnAl2O4, CuAl2O4, and/or amorphous Al2O3. After reduction, well dispersed Cu metal particles with 18–48% dispersion and 2–6 nm size were formed. It was observed that the initial activity of Cu/ZnO/Al2O3 catalysts was proportional to the number of surface Cu0 atoms and the 30%Cu/Zn1Al catalyst showed the highest activity. Moreover, this optimum catalyst exhibited better activity, thermal stability, and long-term stability than a commercial Cu/ZnO/Al2O3 catalyst. It was considered that a synergetic effect between Cu metal and ZnAl2O4 spinel might exist and play a key role for the high catalytic performance.

Microstructure evolution and mechanical properties of ZnAl2O4-reinforced Al2O3/Al2O3 joints brazed with a bismuth borate zinc glass

Amorphous bismuth borate zinc glass with a composition of 40Bi2O3–40B2O3–20ZnO (in mol.%) was used as a braze to join 95wt.% purity alumina ceramics (95Al2O3) in air. The interfacial phases in the brazed joints were characterized using scanning electron microscopy, transmission electron microscopy. Zinc aluminate (ZnAl2O4) was identified as the main reaction product in the joints due to the chemical reaction between the Al2O3 substrate and ZnO from the glass. Typical microstructure of the Al2O3/Al2O3 brazed joints was Al2O3 substrate/glassy matrix phase+ZnAl2O4 particles/Al2O3 substrate. The dependence of the microstructure and mechanical properties on brazing temperature was investigated. The size of ZnAl2O4 increased with an increase in brazing temperature. It was found the room lap shear strength of Al2O3/Al2O3 joints firstly increased and then declined with increasing brazing temperature. The maximum lap shear strength of 95MPa was obtained for the samples brazed at 675°C for 30min, which was mainly attributed to the formation of ZnAl2O4.

Glass structure of the CaO–B2O3–SiO2–Al2O3–ZnO glasses system with different Si content

The aim of the present work is to investigate the effects of SiO2 content on the structure of CaO–B2O3–SiO2–Al2O3–ZnO glass using the MAS-NMR, the fourier transform infrared spectrometer and differential scanning calorimetry (DSC). The results showed that the majority of Al existed in fourfold coordination and Zn acted as glass modifier in glass structure. With the increasing of SiO2 content, the relative amount of BIII units decreased while the BIV units increased and the proportion of Si–O–Si bridge oxygen bond in [SiO4] tetrahedrons increased obviously. The DSC curves revealed that the glass transition temperature increased from 732 to 773 °C with the increasing of SiO2 content, indicating that SiO2 generating more bridge oxygen can increase the degree of polymerization of glass structure.