Porous γ-Al2O3 Research Articles

Preparation of flexible porous γ-Al2O3 nanofibers by electrospinning and its application in supercapacitor separator

Preparation of flexible porous γ-Al2O3 nanofibers by electrospinning and its application in supercapacitor separator

Aerosol fluidized bed coating: Exploring the impact of process conditions on process yield, coating coverage and thickness

Aerosol droplets are used to coat fluidized particles in this work. Coating experiments utilizing aerosol droplets (with a mean diameter of around 1μm) were performed under different process conditions to explore their impact on process yield, as well as on coating coverage. Core materials were glass and porous γ-Al2O3, which had mean diameters of 653μm and 610μm, respectively. Sodium benzoate (NaB) solution and silicon dioxide (SiO2) nanosuspension were used as the coating liquid. After sampling, particle pictures were taken by a scanning electron microscope and analyzed using image processing to determine the coating coverage. To simulate the coating process and determine, for each experiment, a factor for preferential deposition on already occupied positions, Monte Carlo simulations were used. Also, some particles were cut in the middle to measure coating layer thickness. Intraparticle coating thickness distribution from Monte Carlo simulations coarsely matches the measured thickness from cut particles. Results show that the process yield, coating coverage, and preference factor are affected by experimental conditions such as expanded bed height, fluidization air temperature, atomizing pressure, the number of aerosol inlets, as well as the surface potential of core particles. This study is first to examine the impact of surface charge of different core materials on droplet deposition. In an experiment with SiO2 nanosuspension, γ-Al2O3 cores could be coated quite uniformly with SiO2 nanoparticles with a layer thickness of ca. 1.1μm. This shows the potential of aerosol droplet deposition as a novel semi-wet method for coating large particles with nanoparticles without using any binders.

Effect of Fe/Mn Ratio on the Catalytic Oxidation of Toluene over Porous γ-Al2O3 Supported Fe and Mn Bimetal Catalysts

Effect of Fe/Mn Ratio on the Catalytic Oxidation of Toluene over Porous γ-Al2O3 Supported Fe and Mn Bimetal Catalysts

Ammonium salt-assisted preparation of porous high-purity γ-Al2O3 with a high specific surface area

γ-Al2O3 with a high density of active sites has been widely used. In this study, γ-Al2O3 powder with a high specific surface area and a high purity is prepared through facile ammonium salt-assisted calcination. During the calcination process, the gases (NH3 and CO2) generated from ammonium salts can manipulate the pore and crystal structures to obtain active γ-Al2O3 with a high purity of above 99.99 %. The results demonstrate that the specific surface areas of γ-Al2O3 obtained by the use of ammonium carbonate (AC), ammonium bicarbonate (AB), and ammonium acetate (AA) are 441.35, 459.23, and 427.32 m2 g−1, respectively. Moreover, the γ-Al2O3 obtained with ammonium salt shows a higher content of AlO6 than the blank group, contributing to the formation of a sponge-like morphology and more active sites. Furthermore, the active γ-Al2O3 exhibits good performance in adsorption and desorption, making it highly valuable in various applications.

Atomic-level mechanism of CO2-promoted oxidation of alumina-forming alloys

The high-temperature oxidation of the NiAl alloy in the CO2 and O2 atmospheres is comparatively studied by a combination of electron microscopy characterization and first-principles calculations. It is shown that CO2 accelerates the oxidation of NiAl alloy by the formation of a highly porous γ-Al2O3 scale that is non-protective and follows the linear growth law. By contrast, the NiAl oxidation in O2 results in a double-layered oxide scale consisting of an outer columnar γ-Al2O3 layer and an inner equiaxed α-Al2O3 layer, which is protective and follows parabolic growth law. Our first-principles calculations show that this accelerated NiAl oxidation in the CO2 can be attributed to more ready decomposition of adsorbed CO2 than adsorbed O2 into atomic oxygen on defective γ-Al2O3 surfaces, which leads to the inward γ-Al2O3 growth by the infiltration of gaseous CO2 through the cracked oxide scale toward the exposed NiAl alloy. These results provide new insights into the atomic origin of CO2-promoted alloy oxidation.

An integral design and synthesis approach to heterogeneous catalysts: Tailoring the surface characteristics and mass and heat transport properties

A novel integrated approach to designing and synthesizing heterogeneous catalysts with customized surface characteristics and improved heat and mass transport properties is studied. This unique approach utilizes hydrothermal reactions of aluminum (Al) metal substrates with controlled interfacial chemistry, manipulating the kinetics of aluminum hydroxide crystal growth to develop Al@Al2O3 core–shell metal-ceramic composite micro-architectures. The shapes, spatial orientation, and surface-exposed crystal facets of the porous γ-Al2O3 crystallites of the Al@Al2O3 core–shell are effectively tailored via modulation of the specific charge interaction of the boehmite crystallites with heteroatom ions in the solution. The reaction chemistry and formation mechanism of the Al@Al2O3 core–shell micro-composites with morphologically modulated γ-Al2O3 crystallites are studied in detail, along with their physicochemical and catalytic properties. For the acid-catalyzed ethanol dehydration reaction, the Al@Al2O3 catalysts with tailored morphologies and exposed γ-Al2O3 crystal facets demonstrate the high effectiveness of the integrated design and synthesis approach to heterogeneous catalysts, modulating the intrinsic catalytic activities with enhanced mass and heat transport properties at the same time.

Experimental gas-fluidized bed drying study on the segregation and mixing dynamics for binary and ternary solids

Fluidized bed drying is an evolving process: The bed hydrodynamics, including the segregation and mixing tendencies, and its interplay with mass and heat transfer change in time. In this study, pseudo-2D fluidized bed experiments are performed using binary (50/50%) and ternary (33.3/33.3/33.3%) solids mixtures. A coupled particle image velocimetry infrared thermography technique provides local solids velocity and temperature fields. Furthermore, a machine learning algorithm is applied to characterize the bed segregation and mixing dynamics. Significant hydrodynamic changes and various segregation and mixing tendencies due to the evaporation of water from the porous γ-Al2O3 material were observed. A competition between size and density-based segregation and mixing dynamics resulted in changing bed configurations, which are correlated to the local solids drying behavior. Besides, it showed that drying of wider size distributions could lead to more complex efficient process operation.

MOF/Al2O3 composites obtained by immobilization of MIL-53(Cr) or MIL-101(Cr) on γ-alumina: Preparation and characterization

The synthesis of hierarchical MOFs/γ-Al2O3 composites under hydrothermal conditions by deposition of either MIL-53(Cr), or MIL-101(Cr) on the surface of porous alumina supports has been studied. The influence of different parameters (reaction temperature, synthesis duration, reactants/alumina ratio, volume of water, the type of alumina support) on the nature and the quality of the composites were systematically investigated by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), optical microscopy, scanning electron microscopy (SEM), and N2 adsorption-desorption. The research results showed that the best synthesis conditions for the formation of MIL-53(Cr)/γ-Al2O3 composites were 150 °C, 12 h for the optimum molar ratio (1)CrCl3·6H2O/(1)H2BDC/(0.7)γ-Al2O3/(64)H2O. In contrast, in all the cases, the deposition of MIL-101(Cr) on the γ-Al2O3 support was not surface-selective at all. Thus, to increase the quality of the deposited MOF on the selected alumina support, successive depositions of MIL-53 or MIL-101 under solvothermal conditions have been explored on two types of porous γ-Al2O3, (S, particles size <2.0 mm, SBET = 110 m2/g) and (S1, 0.5–2.0 mm particle size, SBET = 247 m2/g). The experimental results show that MIL-101(Cr) formation on alumina S1 is initiated after the second deposition under the synthesis conditions used in this study.

Synchronously enhanced electromagnetic wave absorption and heat conductance capabilities of flower-like porous γ-Al2O3@Ni@C composites

Efficient multifunction materials with strong electromagnetic wave (EMW) absorption and high thermal conductance play a pivotal role in addressing the heat accumulation and EM interference problems in miniaturized and integrated electronics. However, incompatibility between EMW absorption and heat conductance makes their simultaneous improvement a major challenging issue. In this work, flower-like porous γ-Al2O3@Ni@C composites are successfully formulated via a hydrothermal-soaking-calcining route. The original findings of the concerted improvement in EMW absorption and heat conductance are reported. By controlling [Ni2+] and sintering temperature (Ts), the interfaces, components, and defects are modified to achieve synergistic enhancement in the performance of the target composites. Results show that the γ-Al2O3@Ni@C composites formed at [Ni2+] = 2.0 M and Ts = 700 °C present an optimal thermal conductance of 2.84 W/(m⋅K) at a low filling ratio of 30 % due to the phonon/electron relay transmiss on in the 3D network of unique flower-like porous structures, clearly superior to γ-Al2O3 and most of the other γ-Al2O3-based composites. Meanwhile, the composites synchronously present a broad absorption band (4.24 GHz, beyond 90 % damping over 15.75 ∼ 18.00 GHz) and strong absorption (-42.43 dB) relative to a 1.7 mm-thick specimen owing to the enhanced damping coefficient and EM parameters. The outstanding properties exhibited by the flower-like porous γ-Al2O3@Ni@C composites suggest that they have promising prospects for application in EMW absorption and thermal management.

Fluidized-bed plasma enhanced atomic layer deposition of Pd catalyst for low-temperature CO oxidation

A fluidized-bed plasma-enhanced atomic layer deposition (FP-ALD) process is reported to fabricate Pd nanoparticles using palladium hexafluoroacetylacetonate and H2 plasma. The process successfully deposits Pd nanoparticles over porous γ-Al2O3 (30 wt. %), amorphous aluminum silicate (50 wt. %), and molecular sieve (20 wt. %) (ASM) powders. Pd loading on ASM is increased linearly with increasing the number of FP-ALD cycle with a growth rate of 0.34 mg/1 g ASM/cycle. Transmission electron microscopy reveals that high-density Pd nanoparticles are uniformly distributed over the entire ASM powders and the average Pd particle size is sensitive to the number of FP-ALD cycle. By increasing the number of FP-ALD cycles from 25 to 150, the average Pd particle size rises from 0.9 to 5.8 nm, indicating the particle size can be tuned easily by varying the number of FP-ALD cycles. The catalytic activities of different particle sizes and Pd loading samples are evaluated for CO oxidation. With the metal loading amount of 2% for Pd and the average particle size of 2.9 nm, the deposited Pd/ASM sample shows an excellent catalytic activity for the oxidation of CO. Under the condition of a gas mixture of 0.5 vol. % CO and 21 vol. % O2 balanced with N2, and gas hourly space velocity of 24 000 h−1, 100% CO conversion temperature is as low as 140 °C.

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h−1 and T = 560 K, while the inlet temperature (Tinlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al2O3 heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and −102.1 kJ/mol, respectively.

Experimental investigation of monodisperse solids drying in a gas-fluidized bed

Fluidized bed drying is an unsteady process where particle and gas properties evolve in time. The bed hydrodynamics and its interplay with mass and heat transfer changes in time. In this study, experiments in a pseudo-2D fluidized bed setup are performed to obtain insight in this complex behavior. A coupled particle image velocimetry infrared thermography technique provides solids velocity and temperature fields in the bed. Significant hydrodynamic changes due to the evaporation of water from the porous γ-Al2O3 material for three superficial velocities were observed. The 1.25 umf case resulted in an fixed bed state, but after drying for 580 s a bed inversion took place. The 1.50 and 1.75 umf experiments showed an increase in bed expansion over time. Furthermore, clear asymmetrical solids volume fluxes were observed for the wet material that became more symmetrical over time when the material dried.

Using waste to treat waste: Red mud induced hierarchical porous γ-AlOOH and γ-Al2O3 microspheres as superior Pd support for catalytic reduction of 4-nitrophenol

Toward the imperative treatment of the industrial wastewater containing 4-nitrophenol (4-NP) and industrial solid waste red mud (RM), an innovative approach of “Using waste to treat waste” is developed. Valuable element Al is leached from the RM first, the resultant NaAlO2 solution is hydrothermally converted to γ-AlOOH hierarchical porous microspheres (RM γ-AlOOH HPMSs, average diameter: 2.0 μm, SBET: 77.81 m2 g−1, pore volume: 0.38 cm3 g−1) in the presence of urea. The subsequent mild thermal conversion results in γ-Al2O3 hierarchical porous microspheres (RM γ-Al2O3 HPMSs). Both of the RM γ-AlOOH and RM γ-Al2O3 HPMSs are employed as the Pd catalyst support for the catalytic reduction of 4-NP. Particularly, the as-obtained composite Pd/RM γ-AlOOH and Pd/RM γ-Al2O3 exhibit excellent catalytic activities with superior knor as 8204.5 and 4831.4 s−1 g−1, respectively, significantly higher than that of most Pd based catalysts. Moreover, the excellent catalytic stability and durability of the Pd/RM γ-AlOOH and Pd/RM γ-Al2O3 within 10 successive cycles of reduction enable the present industrial solid waste RM induced γ-AlOOH and γ-Al2O3 HPMSs as great promising Pd catalyst support for the reduction of the industrial wastewater containing 4-NP.

In Situ Identification of NNH and N2H2 by Using Molecular-Beam Mass Spectrometry in Plasma-Assisted Catalysis for NH3 Synthesis

Ammonia synthesis at 533 K and atmospheric pressure was investigated in a coaxial dielectric barrier discharge (DBD) plasma reactor without packing and with porous γ-Al2O3, 5 wt % Ru/γ-Al2O3, or 5 ...

Model-based control of iron- and copper oxide particle distributions in porous γ-Al2O3 microspheres through careful tuning of the interactions during impregnation

Up until now, the key phenomena steering metal particle distributions within macroscopically shaped porous supports has not yet been fundamentally understood. In this work, the embedment, upon incipient wetness impregnation, of iron- and copper oxide particles into porous γ-Al2O3 microspheres has been carefully studied. In both cases, specific electrostatic interactions between the dissolved metal ions and accessible support surface were found to be paramount in determining the macroscopic metal oxide distribution in the final material. For copper, these interactions resulted in a homogeneous macroscopic distribution, under the form of a coating directly on the alumina surface. This was contrasted with the more complex iron/γ-Al2O3 system, where competition between dissolved iron species and other dissolved species occurred, which drastically altered the obtained macroscopic and microscopic distribution. Modifying the impregnation procedure, either by altering the pH or ion concentration of the precursor solution, by pretreatment of the support material or by the use of a complexing agent, resulted in particles sizes ranging from 5 nm up to a few μm, and macroscopic distributions varying from homogeneous to egg-white or egg-yolk, all within the context of simple and scalable impregnation-based syntheses. Based on the systematic study of the effects of different impregnation solutions, competitive adsorption of both positively charged iron species and protons on the support surface, and shielding interactions by the negative counter-ions in solution could be identified as main determining factors for the macroscopic distribution. These insights have been validated and quantified within a model, which allows accurate predictions of the metal distribution in porous γ-Al2O3 microspheres for a broad range of synthesis conditions. This model or simulation tool could prove to be a useful tool to guide future catalyst design.

Ordered Mesoporous Alumina with Tunable Morphologies and Pore Sizes for CO2 Capture and Dye Separation.

We describe a versatile and scalable strategy toward long-range and periodically ordered mesoporous alumina (Al2O3) structures by evaporation-induced self-assembly of a structure-directing ABA triblock copolymer (F127) mixed with aluminum tri-sec-butoxide-derived sol additive. We found that the separate preparation of the alkoxide sol-gel reaction before mixing with the block copolymer enabled access to a relatively unexplored parameter space of copolymer-to-additive composition, acid-to-metal molar ratio, and solvent, yielding ordered mesophases of two-dimensional (2D) lamellar, hexagonal cylinder, and 3D cage-like cubic lattices, as well as multiscale hierarchical ordered structures from spinodal decomposition-induced macro- and mesophase separation. Thermal annealing in air at 900 °C yielded well-ordered mesoporous crystalline γ-Al2O3 structures and hierarchically porous γ-Al2O3 with 3D interconnected macroscale and ordered mesoscale pore networks. The ordered Al2O3 structures exhibited tunable pore sizes in three different length scales, <2 nm (micropore), 2-11 nm (mesopore), and 1-5 μm (macropore), as well as high surface areas and pore volumes of up to 305 m2/g and 0.33 cm3/g, respectively. Moreover, the resultant mesoporous Al2O3 demonstrated enhanced adsorption capacities of carbon dioxide and Congo red dye. Such hierarchically ordered mesoporous Al2O3 are well-suited for green environmental solutions and urban sustainability applications, for example, high-temperature solid adsorbents and catalyst supports for carbon dioxide sequestration, fuel cells, and wastewater separation treatments.

Effect of multiple laser shock peening on microstructure, crystallographic texture and pitting corrosion of Aluminum-Lithium alloy 2060-T8

This study investigated the influence of multiple laser shock peening on microstructure, crystallographic texture, and pitting corrosion behavior of Aluminum-Lithium alloy 2060-T8 (in 3.5% NaCl) using EBSD, SEM and XPS techniques. Results show that microstructure and crystallographic texture were noticeably influenced by the peening passes. At single peening, plastic strain accommodation was homogenous, resulting in higher fraction of low Σ CSL boundaries, and significant crystallographic texture transformation from fibre (unpeened) into Cube {001}〈100〉 component (corresponding to dynamic recovery as plastic deformation mode) was induced. In contrast, repetitive peening (3 & 5 passes) induced heterogeneous plastic strain accommodation, developed random and low angle grain boundaries, and texture transformation from fibre to Goss {011}〈100〉, implying recrystallization as corresponding plastic deformation mode. As a result of dense atomic structured microstructures/textures, pitting corrosion after single peening was significantly lowered than that of multiple peening. Major reason for the improved corrosion behavior at single peening pass was the formation of dense and uniform α-Al2O3 type oxide film, which significantly lowered the materials dissolution. Whereas, multiple peening led to the formation of porous γ-Al2O3, θ-Al2O3 oxides and Cu-rich regions, which activated the deeper and wider pitting. Besides, the effect of precipitates (Al2CuLi, θ′ (Al2Cu) and β′ (Al3Zr)) on pitting corrosion is quantitatively examined.

Corrosion of the WC-12Co and enamel coatings in liquid Zn-55Al alloy at 640 °C

Corrosion behavior of the WC-12Co and enamel coatings in liquid Zn-55Al alloy is investigated comparatively. Serious corrosion consumes over 40 μm of the WC-12Co coating after 100 h immersion. Co dissolution occurs firstly by forming Zn-Co solid solution and then intermetallic compounds. WC is decarburized and reacts with Al to form WAl5 at high temperature. The enamel coating suffers quite slight corrosion. Porous γ-Al2O3 layer develops at surface, which then reacts with the enamel to form a continuous CaAl4O7 interlayer that prevents the further invasion of Al and provides the high corrosion resistance.

Morphology Controlled Synthesis of γ-Al2O3 Nano-Crystallites in Al@Al2O3 Core-Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates.

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core–shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl−, NO3−, and SO42−), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl−, NO3−, SO42−) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods.

Preparation of High-surface-area Hierarchically Porous γ-Al2O3 by One-step Hydrolysis of Metal Alkoxide and Performance

Preparation of High-surface-area Hierarchically Porous γ-Al2O3 by One-step Hydrolysis of Metal Alkoxide and Performance