Alumina Aerogel Research Articles

Tailoring porosity: Unveiling the ideal alumina support (aerogel, xerogel, cryogel) for high-performance CO2 capture with polyethylene glycol

This study investigates enhancing CO2 capture through high polyethylene glycol (PEG) loading on alumina aerogel (Al2O3-A), comparing it with alumina cryogel (Al2O3-C) and xerogel (Al2O3-X). Focusing on sustainable carbon capture and storage (CCS), the research optimizes PEG’s CO2 adsorption by adjusting the porosity of these alumina supports. Key characterization techniques, including XRD, FESEM, FTIR, and N2 adsorption-desorption analysis, were utilized. The study evaluated the effects of pressure, temperature, and PEG loading on CO2 capture capacity using response surface methodology (RSM). Optimal conditions (25 °C, 9.0 bar, 61.0 % PEG) achieved a CO2 adsorption capacity of 443 mg/g. The Hill model was most effective in describing the CO2 adsorption, while the fractional order model accurately depicted the kinetics. Thermodynamic analysis confirmed that the adsorption process is spontaneous, exothermic, and physical. The results underscore the potential of PEG/Al2O3-A for effective CO2 capture, highlighting its high stability, capacity, and reusability, and advancing sustainable carbon capture technologies.

Comparative catalytic performance of PGM-nanoparticle-doped alumina Xerogels and aerogels for potential application in automotive pollution mitigation

The structural (low density, high porosity), thermal (low thermal conductivity, high temperature stability), and chemical (high degree of tailorability) properties of aerogels make them attractive in a range of applications, including catalysis. The automotive industry relies on three-way-catalysts (TWCs) for automotive pollution mitigation, and TWCs in turn depend heavily on the use of platinum group metals (PGMs). Reduction of the use of PGMs in TWCs would be advantageous. To investigate the effect of aerogel structure and processing on three-way catalytic performance we prepared alumina wet gels doped with ca. 15 nm rhodium and palladium nanoparticles and dried them (1) supercritically to form aerogels and (2) under ambient conditions to form xerogels. Nanoparticle concentration was adjusted to ensure that both forms of the catalyst (aerogel and xerogel) had the same volumetric concentration of PGM after calcination to 800°C. Powder x-ray diffraction and transmission electron microscopy (TEM) confirmed the presence of PGMs. TEM images showed PGM particle agglomeration on the order of 40 to 200 nm in both the aerogel and xerogel materials. Gas adsorption analysis indicated that the aerogels have a surface area of 460 m2/g with most pores in the 2- to 100-nm range, whereas the xerogel surface area was 170 m2/g with a narrow pore distribution around 10 nm. Catalytic performance tests under a range of simulated automotive operating conditions show that, in all cases, the aerogels outperformed the xerogels. The aerogel light-off temperatures (the temperature at which a 50 % conversion is achieved) were 45 to 120 °C lower for the conversion of HCs, 25 to 55 °C lower for the conversion of CO and 40 to 145 °C lower for the conversion of NO. This study provides direct evidence that aerogel processing of catalysts provides catalytic performance benefits separate from the underlying chemistry of the catalysts.

Fiber-Reinforced Coal Gangue-Based Alumina Aerogel Composites with Highly Thermal Stability by Ambient Pressure Drying

Fiber-Reinforced Coal Gangue-Based Alumina Aerogel Composites with Highly Thermal Stability by Ambient Pressure Drying

High transmittance and ultra-low thermal conductivity ZrO2 aerogel via zirconium hydroxyacetate precursor

Zirconia (ZrO2) aerogels have the potential to service at temperatures exceeding 1000 °C, exhibiting superior insulation performance over those of silica, alumina and carbon aerogels, etc., but the zirconium chloride based salts, such as zirconium oxychloride, with overfast phase separation rate and indelible chlorine impurities, impede the development of an economic and environmentally benign synthesis. Besides, the stabilities of ZrO2 aerogels toward high temperature exposure need to be further improved. With these regards, in this work, zirconium hydroxyacetate was brought up for the first time to produce ZrO2 aerogel with the aid of a tailor-made sol-gel chemistry. Polar solvents were found to be efficient in manipulating the phase separation. After depositing silica to the gel network, ZrO2 aerogels with a maximum visible light transmittance of up to 90 %, compressive strength of 0.24 MPa (0.159 g‧cm−3) were successfully obtained. The thermal conductivity of the aerogel reached a recorded value of 9.67 mW‧m−1‧K−1 at room temperature. The resultant aerogels possess a uniform skeleton structure with pore distribution below 20 nm, and can retain their mesoporous structure at 1000 °C, keeping a specific surface area of 200 cm2‧g−1. This work presents a well-established procedure for synthesizing high-quality ZrO2 aerogels and promotes their utilization in optics, thermal insulation, and other related fields.

Synthesis of alumina aerogel enriched carboxymethyl cellulose with polymodal pore size distribution by ambient pressure drying

Synthesis of alumina aerogel enriched carboxymethyl cellulose with polymodal pore size distribution by ambient pressure drying

Production of high-carbon-number bio-aviation fuels from furans using sulfated zirconia and silica-alumina aerogel catalysts

Lignocellulose can help produce fuels in biorefineries through its fractionated components such as cellulose, hemicelluloses, and lignin. For instance, hemicellulose-derived xylose has been studied for obtaining petroleum-substituting fuels. Therefore, in this study, catalytic hydroalkylation/alkylation (HAA) of xylose-derived 2-methylfuran (2-MF) with butanal was targeted to selectively produce high-carbon-number diesel fuels. To that end, silica–alumina (SiAl) aerogels with different Si/Al ratios and a series of sulfated zirconia (SZ) compounds calcined at various temperatures were prepared as catalysts to overcome the limitations of conventional hazardous homogeneous acid catalysts. The activity of the SiAl catalysts in forming the desired HAA product, 5,5-bissylvylbutane (denoted as BB), was found to be directly related to the number of acid sites and acid density. Moreover, increasing the Si/Al molar ratio, which reduced the acid density and number of acid sites, led to lower 2-MF conversions and BB yields. The optimal 2-MF conversion and BB yield with the SiAl catalysts (67 % and 45 %, respectively) were achieved using a Si/Al ratio of 8:2 mol/mol. Furthermore, SZ calcined at 700 °C (denoted as SZ-700) exhibited the highest activity among the SZ catalysts (72 % 2-MF conversion, 63 % BB yield), despite having the fewest acid sites and lowest acid density. This was presumably because of the physical structure of SZ-700, which featured mixed monoclinic and tetragonal phases, many oxygen vacancies, and a large accessible external surface area, which facilitated the HAA reactions. Hydrogenation and hydrodeoxygenation (HDO) of BB were performed thereafter using Pd/C and Ru/SiO2–Al2O3 catalysts, respectively. The resulting deoxygenated hydrocarbons comprised 15.1 % light hydrocarbons (C4–C8) and 83.1 % heavier hydrocarbons (C9–C20). Simulated distillation analysis of the post-HDO product distribution indicated that the liquid-phase product contained 70 % high-carbon-number bio-aviation fuels.

Investigation of novel expandable polystyrene/alumina aerogel composite thermal insulation material

Expandable polystyrene (EPS) foam is one of the most commonly used building thermal insulation materials due to its low thermal conductivity, apparent density as well and low cost. However, its high flammability and the release of a large number of toxic gases during combustion hinder its application. In this paper, using EPS foam and alumina aerogel (Al2O3) as insulation components, epoxy resin (EP) as a binder, and expandable graphite (EG) and ammonium polyphosphate (APP) as composite flame-retardant, a novel organic-inorganic composite thermal insulation material (EPS-AEA) was designed and fabricated. Experiment results showed that adding Al2O3 to EPS could further reduce the thermal conductivity of the obtained composite, and improve its mechanical properties. The addition of EG and APP composite flame-retardant could markedly enhance flame-retardant performance. With the addition of 4.17% Al2O3, and 50% EG/APP (1/1 mass ratio), the obtained EPS-AEA-1/1 composite showed superior fire resistance (reaching UL-94 V-0 rating and limiting oxygen index (LOI of 40.6%), high thermal insulation (thermal conductivity of 0.0487 W/(m·K)and applicable mechanical properties. In addition, EPS-AEA had excellent anti-hygroscopic properties (moisture ab-desorption rate within 0.5%) and fairly low toxic gas emissions during combustion, indicating its potential in practical application.

The effect of surfactant type and concentration on the pore structure of alumina aerogels

Alumina aerogels are excellent materials for thermal insulators used at high temperatures due to the good thermal stability of aluminum oxide. In this study, alumina aerogels treated with various types of surfactants (non-ionic (Triton X-100), cationic (cetyltrimethylammonium bromide), or anionic (sodium dodecyl sulfate)). The effect of the surfactant depended on the charge-charge interactions between it and the cationic inorganic species in the aluminum precursor. As determined by using small-angle scattering and pore volume change measurements, these interactions induced a change in the pore structure that could be controlled by controlling the concentration of the surfactant. The hindrance effect due to the ionic interference was more pronounced at a higher surfactant concentration than at a lower one. Thus, the concentration of surfactant plays an important role in determining the pore structure of the alumina aerogel.

Water-Assisted Transformation of Aluminum Alloys to Ceramic Nanowires and Aerogels

Ceramic nanowires (NWs) and their-based aerogels hold great promise for manufacturing and applications of polymer nanocomposites with otherwise unattainable mechanical and thermal properties. Unfortunately, conventional routes for the synthesis of ceramic NWs commonly suffer from the use of costly or toxic chemicals, low production rate, and complex and expensive procedures. Here, we report on a water-assisted route for the cost-effective, scalable transformation of bulk aluminum–lithium alloys into ceramic alumina NWs and aerogels. In this study, we employ water as the intermediary solvent for dealloying to form monolithic porous Li-doped aluminum metal, which can then be converted to ultralong metal–organic NWs, then to hydroxide NWs after hydrolysis and finally to NW aerogels after freeze-drying. As a high-performance thermal interface material for electronic devices, the oxidized alumina NW aerogels infiltrated with epoxy show significantly improved thermal properties. Our study shows great potential for the scalable production of ceramic NWs using a low-cost and environmental-friendly route for various applications.

Alpha Al2O3 Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Alumina aerogels are desirable for lightweight and highly efficient thermal insulation. However, they are typically constrained by brittleness and structural collapse at high temperatures. The manufacture of alumina aerogels with ultralow thermal conductivity and excellent thermal stability at high temperatures beyond 1300 °C is still challenging. Herein, alumina aerogels with superior ultrahigh-temperature-resistant and thermal insulation were successfully prepared by assembling the α-Al2O3 nanosheets with silica sols as the high-temperature binders. Benefiting from the generation of the mullite-covered alumina biphasic structure, the α-Al2O3 nanosheet-based aerogels (ANSAs) exhibit excellent thermal and chemical stabilities even after calcination at as high as 1600 °C. The ANSAs had a low thermal conductivity (0.029 W·m-1·K-1 at room temperature), structural stability with a measured compressive strength of 0.6 MPa, and good thermal shock resistance. Furthermore, the 2D α-alumina@mullite core-shell sheets were also prepared as assembly units to construct aerogels (AMSAs). This core-shell structure can improve temperature resistance through inter-lattice suppression under continuous energy input at high temperatures. The AMSAs have a linear shrinkage of only 2.7% after calcination at 1600 °C for 30 min, further improving the temperature resistance, making them an ideal super-insulating material for applications at extremely high temperatures.

Superhydrophobic, heat-resistant alumina-methylsilsesquioxane hybrid aerogels with enhanced thermal insulating performance in high humidity

Heat-resistant alumina aerogels serve as prospective thermal insulating materials in the high-temperature fields, whereas the inherent hydrophilicity and thermal coarsening restrict their thermal insulating application. In this study, superhydrophobic, heat-resistant alumina-methylsilsesquioxane hybrid aerogels (AlMSAs) were prepared via in-situ sol-gel method combined with supercritical drying to overcome the aforesaid obstacles. The transformation from hydrophilicity to hydrophobicity is achieved by regulating the molar ratio of methyltriethoxysilane. The aerogel exhibits homogenous superhydrophobicity with contact angle reaching up to 152.6° when the molar ratio of Al to Si is 2 (AlMSA2). AlMSAs show superior heat resistance up to 1300 °C, suffering no α-Al2O3 transition and minor grain growth. Quartz fiber reinforced alumina-based aerogel composite (QFAlMSA2) is prepared to study the thermal insulating performance in practical application. The thermal conductivity of QFAlMSA2 reversibly increases by 5.0% subject to 90% relative humidity (36 °C) for one month due to the superhydrophobicity. QFAlMSA2 exhibits a low thermal conductivity of 0.0542 W/(m·K) after being calcined at 1200 °C and a moderate temperature of 113 °C when exposed to a butane flame for 30 min. This study offers meaningful insights into developing alumina-based aerogel materials for high-moisture and high-temperature thermal insulations.

A high thermal stability core–shell aerogel structure for high-temperature solar thermal conversion

Silica aerogel can be applied to the concentrated solar power (CSP) plants to achieve a high operation temperature due to the high optical transparency and thermal insulation properties. However, the insulation capacity of aerogel at high-temperature will deteriorate rapidly due to the damage of the porous structure. In present study, a transparent aerogel consisting of SiO2/Al2O3 core–shell particles was proposed. The structure-dependent radiative properties were predicted through the combination of Discrete Dipoles Approximation (DDA) and Monte Carlo (MC) method. The core–shell aerogel achieves a higher solar transmittance than the alumina aerogel. The evaluation parameter of greenhouse selectivity was introduced to assess the aerogel performance by considering the solar transmission and infrared extinction simultaneously. An optimal design of SiO2/Al2O3 core–shell aerogel at different temperatures was conducted. Compared with the pure alumina aerogel, a maximum enhancement of 22.6% in greenhouse selectivity was achieved by the core–shell aerogel with ϕ = 95% and r1/r2 = 0.4 at 700 °C. This work provides a promising method to achieve a high-efficient transparent thermal insulating aerogel for high-temperature CSP plants with high thermal stability.

PGM nanoparticle-based alumina aerogels for three-way catalyst applications

Alumina aerogels doped with PGM nanoparticles are prepared and characterized as candidates for three-way catalysts (TWCs). After heat-treatment at 800 °C the materials maintain low density (∼0.1 g/mL), high surface area (290–460 m2/g) and high pore volume (1.4–3.6 g/m3), but show some agglomeration of the nanoparticles. Pt-, Pd- and Rh-alumina aerogels show TWC activity comparable to a commercial catalyst. Light-off temperatures for CO and propene by Pd/Al2O3 aerogels are 190 and 220 °C (respectively) while for NO by Rh/Al2O3 aerogel is 250 °C. These materials are loaded at 0.08–0.16 g/L (2–3 g/ft3), considerably lower than typical TWC PGM loadings of 1.8–2.8 g/L (50–80 g/ft3).

Effect of Sol Concentration on Properties of Alumina Aerogels

Effect of Sol Concentration on Properties of Alumina Aerogels

Transient thermal performance of multilayer thermal protection systems doped with phase change materials

In this article, the transient heat transfer process of the multilayer thermal protection system (TPS) doped with the phase change materials (PCM) is studied. The multilayer TPS consists of the C/SiC composite material, alumina aerogel, silica aerogel, and silica aerogel doped with the PCM. A thermal lattice Boltzmann model is adopted to consider the effect of interlayer thermal contact resistance on the transient thermal response of the TPS. An enthalpy-based lattice Boltzmann model is adopted to solve the solid–liquid phase change problem. The transient heat transfer characteristics of two kinds of TPSs in different layouts are analyzed in detail. The results show that whether the doped PCM enhances the thermal insulation performance of the TPS depends on the layout design of the multiple layers and service time. There exists an optimal layer thickness of the PCM that makes a TPS have the best thermal insulation performance, and the optimal value increases with the service time. The interlayer thermal contact resistance can have a significant effect on the transient thermal response of the TPS, and the optimal value of the PCM thickness will reduce.

Novel silica-modified boehmite aerogels and fiber-reinforced insulation composites with ultra-high thermal stability and low thermal conductivity

Alumina–silica composite aerogels have drawn vast attention due to their enhanced thermal stability compared to pristine alumina aerogels. However, they are generally weakly-crystallized and tend to experience inevitable sintering and significant surface area loss especially above 1200 °C. In this study, we developed a hydrothermal treatment and supercritical drying strategy for synthesizing novel, well-crystallized, silica-modified boehmite aerogels and fiber-reinforced composites. For the prepared aerogel, network coarsening was significantly hindered and the α-Al2O3 transition was completely prevented even at 1400 °C. As a result, the aerogel exhibits extremely high surface area maintenance (87 % and 53 % after 1300 °C and 1400 °C calcination, respectively) and low linear shrinkage (14 % after 1300 °C calcination) at elevated temperatures. The composite with good toughness shows excellent heat resistance and thermal insulating performance up to 1500 °C. These findings provide a general, direct new idea to improve the thermal tolerance of alumina-based aerogels and extend their applications to higher temperatures.

A Facile Method for Fabricating a Monolithic Mullite Fiber-Reinforced Alumina Aerogel with Excellent Mechanical and Thermal Properties.

Alumina aerogels are considered to have good application prospects in the high-temperature field. In this study, monolithic mullite fiber-reinforced alumina aerogels with excellent mechanical and thermal properties were synthesized via a facile method without the use of any chelating agents. This method successfully avoids the introduction of impurities during the use of catalysts and chelating agents while greatly reducing gelation time, and thus helps mullite fibers to uniformly disperse in the sol. The compressive stress at 80% strain of the obtained mullite fiber-reinforced alumina aerogels was as high as 16.04 MPa—426% higher than that of the alumina aerogel without the addition of mullite fibers. Regarding thermal properties, the shrinkage of the mullite fiber-reinforced alumina aerogels (AM) samples was less than 1% after heat treatment at 1300 °C for 2 h. Furthermore, the rear-surface temperature of the AM samples burned by a butane blow torch was only 68 °C. These outstanding properties make AM samples promising for application in thermal insulation materials in high-temperature fields such as aerospace and industrial thermal protection in the future.

Organic/inorganic double-precursor cross-linked alumina aerogel with high specific surface area and high-temperature resistance

Alumina aerogel has drawn a great research interest in the aerogel community owing to its great high-temperature heat resistance. The typical preparation can be divided into two approaches depending on the type of precursors. However, the alumina aerogel derived from organic aluminum alkoxides suffers from poor monolithic integrity, whereas the one from inorganic aluminum salts presents unsatisfied thermal stability. In this work, we develop a novel organic/inorganic double-precursor cross-linking method to prepare alumina aerogels. Aluminum chloride hexahydrate is used to provide an acid condition for the hydrolysis and condensation reaction of aluminum sec-butoxide (ASB), and serves as a reactant to co-condensate with the hydrolyzed ASB to form an interpenetrating chain structure. The resulting alumina aerogel exhibits a high specific surface area (SSA) of 667 m2/g and good high-temperature thermal insulation performance. Moreover, it can still retain SSA of 224 and 105 m2/g after heating at 1000 and 1300°C, respectively.

Hydrothermal assisted synthesis of heat resistant, well-crystallized aerogels constructed by boehmite nano rods

Alumina aerogels in previous studies which are generally weakly-crystallized tend to experience framework coarsening and corundum formation above 1000 °C. In this work, a straightforward strategy, including hydrothermal treatment and supercritical drying, is developed for tailoring the crystallinity of boehmite colloid and for synthesizing heat resistant, well-crystallized alumina aerogels. Thermal evolution of the aerogel and factors influencing the thermal stability were investigated and discussed in detail. Compared to reported pristine alumina aerogels, the aerogel after calcination at 1300 °C for 2 h shows quite high specific surface area (95 m2/g) and pore volume (0.28 cm3/g), which are 38% and 61% of the corresponding maintenance of the samples at 300 °C, respectively, with α-Al2O3 transition significantly retarded. These findings represent a general rule towards the improvement of heat-resistance of alumina aerogels.

Non-supercritical drying synthesis and characterization of monolithic alumina aerogel from secondary aluminum dross

In the present study, the pure and monolithic alumina aerogel is synthesized from secondary aluminum dross as a common waste of the aluminum smelting industry. The process includes the extraction of aluminum content of the waste as sodium aluminate liquor through a multi-stage hydrometallurgical treatment, gelation, removal of the salt by-product by washing, three-stage solvent exchange, aging, non-supercritical drying, and calcination. No chemical additives are used to strengthen the gel structure. It is worth mentioning that the drying step of the hydrogel, which has the main effect on the integrity of the aerogel, is performed at ambient pressure and a relatively low temperature (50 °C). The characterization of the obtained alumina aerogel revealed a density of 0.25 g/cm3, a total pore volume of 1.4 cm3/g, a specific surface area of 148.5 m2/g, and a purity of more than 97%.