Mesoporous γ-Al2O3 Research Articles

Highly Dispersed HKUST-1 on Milimeter-Sized Mesoporous γ-Al2O3 Beads for Highly Effective Adsorptive Desulfurization

HKUST-1 was impregnated effectively on millimeter-sized mesoporous γ-Al2O3 beads under hydrothermal conditions, resulting in formation of a composite material HKUST-1@γ-Al2O3 that features high specific surface area, remarkable enhanced mechanical strength, chemical and thermal stability, and low cost. The composite material exhibited excellent performance with the adsorptive desulfurization capacity of 59.7 mg S/g MOF (versus 49.1 mg S/g MOF for bare HKUST-1) for a model oil composed of dibenzothiophene (with the initial S-content being 1000 ppmwS) and n-octane. Experimental results also revealed that HKUST-1@γ-Al2O3 could reduce 35 ppmwS sulfur content of the model oil lower than 9.6 ppmwS at a ratio of HKUST-1@γ-Al2O3 to oil over 30 wt %, indicating effectiveness for deep adsorptive desulfurization. The Gibbs free energy for DBT adsorption by HKUST-1@γ-Al2O3 was found smaller than that by HKUST-1 due to efficient utilization of active centers, shorter diffusion channels and larger specific surface area...

Hierarchically micro-/mesoporous Pt/KL for alkane aromatization: Synergistic combination of high catalytic activity and suppressed hydrogenolysis

Pt/KL is a highly active and selective monofunctional catalyst for aromatization of n-alkanes due to its 1-dimensionally connected cage-like micropores. The unique micropore structure of the KL zeolite, however, can also inhibit the diffusion of bulky aromatic products out of the catalyst, which can cause unwanted side reactions that can decrease the aromatic yields. In this work, we investigated the effect of secondary mesoporosity, which can substantially facilitate molecular diffusion in Pt/KL during C6–C8 alkane aromatizations. The results showed that the hierarchically micro-/mesoporous Pt/KL synthesized with a subsequent dealumination/desilication method exhibited enhanced aromatic yields, compared with a conventional Pt/KL. In particular, in C7 and C8 aromatizations, the hierarchical Pt/KL showed substantially less formation of dealkylated aromatic products than the Pt/KL due to suppressed secondary hydrogenolysis. Pt supported on a solely mesoporous γ-Al2O3 also showed significantly suppressed secondary hydrogenolysis (dealkylation), which indicates that fast diffusion of alkylated aromatics out of the catalyst structure is important for suppressing the secondary hydrogenolysis. However, the solely mesoporous Pt/γ-Al2O3 showed markedly lower aromatization activities than the KL-supported catalysts, which indicates that Pt located inside the zeolite micropores is crucial for obtaining high catalytic activity due to the preorganization of n-alkanes in the micropores. The present results showed that the hierarchical Pt/KL provides the synergistically combined benefits of the Pt/KL and the mesoporous Pt catalyst, namely high aromatization activity and suppressed secondary hydrogenolysis, respectively.

Phosphotungstic acid immobilized on amino functionalized spherical millimeter-sized mesoporous γ-Al2O3 bead and its superior performance in oxidative desulfurization of dibenzothiophene

The composite material HPW/NH2–Al2O3 was successfully prepared by immobilization of phosphotungstic acid H3PW12O40 (HPW) on the surface of amino functionalized spherical millimeter-sized mesoporous γ-Al2O3 beads (NH2–Al2O3), that featured high specific surface area, remarkable enhanced mechanical strength, chemical stability and low cost. This composite material was characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Brunner−Emmet−Teller (BET) and mechanical strength measurements. The experimental results showed that introduction of NH2 group in between HPW and Al2O3 surface not only provide strong binding sites for catalytic centers HPW to get high dispersion on the carrier surface but also prevent HPW from structural decomposition. As a consequence, the prepared HPW/NH2–Al2O3 exhibited excellent catalytic performance in the oxidative desulfurization of model oil composed of dibenzothiophene (DBT) and n-octane. The 350ppmwS of sulfur content in 20mL of n-octane can be dropped down to 2.8ppmwS in 2h using 60mg of HPW/NH2–Al2O3 catalyst under the optimal conditions. Remarkably, the catalyst can be conveniently recycled by simple decantation method. After 10 times recycling, the oxidation desulfurization efficiency just dropped down slightly from 99.2% to 98.6%. The results indicate that synthesized HPW/NH2–Al2O3 beads have great potential as a catalyst in oxidative desulfurization for special practical applications.

Preparation and characterization of mesoporous nanocrystalline La-, Ce-, Zr-, Sr-containing Ni[sbnd]Al2O3 methane autothermal reforming catalysts

The promotion effect of La, Ce, Sr and Zr on the catalytic and structural properties of nanocrystalline mesoporous γ-Al2O3 supported Ni catalysts was investigated in autothermal reforming of methane. Mesoporous nanocrystalline γ-Al2O3 powder and promoted ones with high specific surface area (>220 m2/g) were prepared by solid state reaction method and employed as the support for nickel catalysts. The prepared catalysts were subjected to autothermal reforming reaction and characterized by XRD, BET, DR-UV-Vis, TPR, TPO and SEM techniques before and/or after the reaction. The effect of experimental conditions, such as temperature was investigated on the catalysts. Ce promoted catalyst, containing small amounts of CeO2 as a separate phase, was found the most effective catalyst between both promoted and unpromoted ones.

Synthesis and application of highly dispersed ordered mesoporous silicon-doped Pd-alumina catalyst with high thermal stability

Employing P123 as a structure directing agent and acetic acid as an interfacial protector, ordered mesoporous silicon-doped γ-alumina with high thermal stability was synthesized through a modified sol–gel process by adding aluminum isopropoxide in batches to control the hydrolytic and condensation rate of Al3+. When the silicon content was 10–25wt%, the specific surface area of the as-obtained samples were higher than others. Especially when the silicon content up to 20wt%, the sample still maintained ordered mesoporous γ-Al2O3 phase with a large specific surface area of 139.8m2g−1 and narrow pore size distribution even the calcination temperature up to 1100°C. Taking as-synthesized ordered mesoporous alumina (OMA) as carrier, the catalysts with high thermal stability supported by Pd were obtained by a facile process of thermal incipient wetness impregnation, which shows highly dispersed nano-particles and ordered mesostructure. When applied the catalysts in the catalytic converters of simulated exhaust automobile gases, it was found that the ordered mesostructure and high surface area showed significant effects in promoting catalytic activity. The as-synthesized ordered mesoporous Pd-alumina catalyst exhibited an excellent catalytic activity for gas mixture including CO, NO and hydrocarbon (HC).

Microemulsion synthesis method for preparation of mesoporous nanocrystalline γ-Al2O3 powders as catalyst carrier for nickel catalyst in dry reforming reaction

Three large mesoporous alumina powders were prepared by microemulsion (ME) method with different microemulsion structures and compositions (various surfactants and oil phases) and employed as catalyst carrier for preparation of mesoporous nanocrystalline Ni/Al2O3 catalysts. The prepared catalysts were used in dry reforming reaction for production of synthesis gas. The samples were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller surface area analysis (BET), temperature programmed reduction (TPR) and scanning electron microscopy (SEM) techniques. The results showed that the prepared γ-Al2O3 with different microemulsion compositions possessed mesoporous structure with high surface area from 239.7 to 277.7 m2 g−1. In addition, the prepared 10wt.% Ni/γ-Al2O3 catalysts exhibited high activity and stability in dry reforming reaction. The results also revealed that the microemulsion composition have a significant effect on the textural properties and affected the catalytic performance.

Ni catalysts supported on nano-crystalline aluminum oxide prepared by a microemulsion method for dry reforming reaction

Mesoporous nano-crystalline γ-Al2O3 with high surface area prepared by a microemulsion (ME) method was employed as carrier for nickel catalysts in dry reforming of methane for syngas production. The structural properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, temperature programmed reduction and oxidation and scanning electron microscopy techniques. Microemulsion showed it to be a promising way for the production of nano-crystalline aluminum oxide, and the nickel catalysts prepared with this support have significant features and properties to use in the dry reforming reaction. The results revealed that the prepared γ-Al2O3 exhibited a nano-crystalline structure (crystal size: c.4.8 nm) with a high specific surface area (308 m2 g−1). In addition, the catalysts with different nickel contents exhibited high catalytic activity in the dry reforming reaction. The results also showed that an increase in Ni loading from 5 to 15 wt% caused a decrease in the specific surface area and nickel dispersion.

Facile synthesis of a mesoporous alumina and its application as a support of Ni-based autothermal reforming catalysts

Mesoporous nanocrystalline γ-Al2O3 powder with high specific surface area (>220 m2/g) was prepared by a “solid state” method and employed as the support for nickel catalysts. Ni catalysts supported on this alumina were prepared and investigated in autothermal reforming of methane. The prepared catalysts were characterized by XRD, BET, DR-UV-Vis, TPR and SEM techniques before and after the reaction. The effect of experimental conditions, such as temperature, space velocity, steam to carbon (S/C) and oxygen to carbon (O/C) ratio was investigated on the catalytic performance of the prepared catalysts. Catalyst with 25 wt.% of Ni content revealed high methane conversion (around 86% at 700 °C). The catalytic activity is reduced by calcination at 800 °C, which results in lower surface area and in the formation of bulk Ni aluminate spinel.

Template-free synthesis of mesoporous γ-alumina with tunable structural properties

Mesoporous γ-Al2O3 (MA) with agglomerated nanoparticles was successfully synthesized by using aluminum sulfate as inorganic Al resource, and hexamethylene tetramine (HMTA) as precipitant without using any surfactants, via a hydrothermal method. All the experimental processes experienced the hydrolysis, precipitation and calcination steps. The structural and morphological properties of uncalcined and calcined samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry differential thermal gravity (TG-DTG) and N2 adsorption–desorption. The bulk density of the sample is 0.682cm3g−1, and the specific surface area is 273.302m2g−1. The pore diameters (7.1nm and 9.7nm) indicate that a typical bimodal mesoporous structure was formed within MA. In order to tune the structural properties of MA, various kinds of inorganic aluminum sources and precipitating agents were employed to carry out contrast experiments, which leaded to regular variations in the specific surface area (200.898–273.302m2g−1), pore volume (0.121–1.327cm3g−1) and pore size (3.7–35.9nm). At the same time, the experimental results also demonstrated that the various kinds of Al resources and precipitants had no effects on the crystal structure of MA. However, the morphologies of samples, such as nanoparticles, short fibers, flower-like and block-shaped, can be controlled effectively. The present study provides a simple and effective approach for preparing MA, and the structural properties of MA can be controlled precisely by carefully choosing aluminum sources and precipitants. The approach of this work not only allows us to investigate the growth mechanism of the final product, but also reduces cost and the environmental pollution effectively than other template methods.

Catalytic Dehydration of Methanol to Dimethyl Ether Over Mesoporous γ-Al2O3

This study focused on the preparation of a high surface area mesoporous γ-Al2O3 as a catalyst for methanol dehydration. The catalysts were characterized using NH3- temperature-programmed desorption, X-ray diffraction, Brunauer-Emmett-Teller, and transmission electron microscopy techniques and evaluated in a fixed-bed reactor at 250°C at a gas hourly space velocity of 1,000 h−1 under atmospheric pressure. A three-factor uniform design was utilized to determine the optimal conditions. The catalyst prepared under optimal conditions showed a time-space yield of 0.659 g dimethyl ether/(g cat·h) with selectivity of about 99.99%. The activity showed a significant dependence on the textural properties and enhanced weak acid strength of the alumina.

Influence of coal power plant exhaust gas on the structure and performance of ceramic nanostructured gas separation membranes

In this work, we investigate the effect of coal power plant exhaust gas on amino-modified mesoporous ceramic membranes. The testing of ceramic membranes in the flue gas of coal-fired power plants represents a new approach, as testing under simulated flue gas conditions has already been undertaken, but not yet during direct exposure to exhaust gas. Flue gas exposure trials were carried out at a lignite-fueled power plant and a hard-coal-fueled power plant. Most experiments were conducted using a test rig designed to bring planar membrane samples in direct contact with unconditioned flue gas in the exhaust gas channel. Another test rig was designed to test membrane modules with pre-treated flue gas. The tested membranes had an asymmetrical structure consisting of a macroporous α-Al2O3 support coated with a mesoporous γ-Al2O3 or 8YSZ interlayer. The microporous functional top layer was made of amino-functionalized silica. The tests revealed different degradation mechanisms such as gypsum/fly ash deposition on the membrane surface, pore blocking by water condensation, chemical reactions and phase transformation. A detailed analysis was carried out to evaluate their impact on the membrane in order to assess membrane stability under real conditions. The suitability of these membranes for this application is critically discussed and an improved mode of membrane operation is proposed.

Synthesis, Characterization and Shape-Dependent Catalytic CO Oxidation Performance of Ruthenium Oxide Nanomaterials: Influence of Polymer Surfactant

Ruthenium oxide nano-catalysts supported on mesoporous γ-Al2O3 have been prepared by co-precipitation method and tested for CO oxidation. The effect of polyethylene glycol (PEG) on the properties of the catalyst was studied. Addition of the PEG surfactant acted as a stabilizer and induced a change in the morphology of ruthenium oxide from spherical nanoparticles to one-dimensional nanorods. Total CO conversion was measured as a function of morphology at 175 °C and 200 °C with 1.0 wt.% loading for PEG-stabilized and un-stabilized catalysts, respectively. Conversion routinely increased with temperature but in each case, the PEG-stabilized catalyst exhibited a notably higher catalytic activity as compared to the un-stabilized equivalent. It can be assumed that the increase in the activity is due to the changes in porosity, shape and dispersion of the catalyst engendered by the use of PEG.

Enhanced Fenton Catalytic Efficiency of γ-Cu-Al₂O₃ by σ-Cu²⁺-Ligand Complexes from Aromatic Pollutant Degradation.

Mesoporous Cu-doped γ-Al2O3 (γ-Cu-Al2O3) was prepared via an evaporation-induced self-assembly process, in which Cu(+/2+) was co-incorporated into mesoporous γ-Al2O3 by chemical bonding of Al-O-Cu. The catalyst was found to be highly effective and stable for the degradation and mineralization of aromatic pollutants, as demonstrated with bisphenol A, 2,4-dichlorophenoxyacetic acid, ibuprofen, diphenhydramine, and phenytoin in the presence of H2O2 under neutral pH conditions. In addition, the high utilization efficiency of H2O2 was maintained at approximately 90% prior to the disappearance of the initial aromatic pollutants. On the basis of all of the characterization results, the pollutant degradation processes predominantly occurred on the surface of the catalyst due to the formation of σ-Cu-ligand complexes between the phenolic OH group and the surface Cu. In the reaction system, in addition to the unselective oxidation by (•)OH, H2O2 directly attacked the σ-Cu(2+)-complexes aromatic ring with the phenolic OH group, which resulted in the formation of (•)OH and HO-adduct radicals that were oxidized to hydroxylation products by reduction of Cu(2+) in the σ-Cu(2+)-complexes to Cu(+). The process prevented Cu(2+) from oxidizing H2O2 to form HO2(•)/O2(•-) or O2, and enhanced the Cu(+)/Cu(2+) cycle, the formation of (•)OH, and the utilization efficiency of H2O2. Therefore, an extraordinarily high degradation and mineralization of the aromatic pollutants was observed.

The effect of polyoxyethylene (40) stearate surfactant on novel synthesis of mesoporous γ-alumina from Kano kaolin

Mesoporous γ-alumina was synthesized by acid extraction of alumina from Kano kaolin using polyoxyethylene (40) stearate (PS) as a surfactant. The synthesized alumina was characterized using X-ray diffraction (XRD), N2 adsorption–desorption, Fourier transform infra-red spectroscopy (FTIR), field emission scanning electron microscopy attached with energy-dispersive X-ray (FESEM–EDX), and thermogravimetric analysis (TG–DTA). High-purity mesoporous γ-Al2O3 with relatively large surface area and narrow pore size distribution was obtained. For comparison the preparation in the absence of surfactant was also carried out. In this study mesoporous alumina was also obtained even in the absence of the surfactant, however, the addition of PS resulted in modification on physical properties and morphology. The surface area increased from 169.0m2/g to 222.7m2/g, pore size from 4.4nm to 5.6nm and pore volume from 0.32cm3/g to 0.45cm3/g. Crystallite size was also found to increase from 2.68nm to 3.33nm after the addition of the surfactant.

Solvothermal-assisted evaporation-induced self-assembly process for significant improvement in the textural properties of γ-Al2O3, and study dye adsorption efficiency

A comparative study of the textural properties of γ-Al2O3 prepared by solvothermal-assisted evaporation-induced self-assembly (SA-EISA) and conventional evaporation-induced self-assembly (EISA) processes has been carried out using aluminum isopropoxide, triblock copolymer-type nonionic surfactant (Pluronic P123) and ethanol. The solvothermal reaction was carried out at 100 °C for 24 h followed by slow drying at 60 °C for 48 h. The synthesized products were characterized by thermogravimetry analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) analysis, N2 adsorption–desorption study and transmission electron microscopy (TEM). The γ-Al2O3 prepared by SA-EISA process became stable up to 1000 °C. The powder prepared by SA-EISA process resulted in a significant increase in textural properties (BET surface area, pore volume and pore diameter) compared to that prepared by conventional EISA process. A better adsorption capacity for Congo red, a carcinogenic dye used in textile industry, was exhibited by the powders prepared by SA-EISA process. A proposed mechanism was illustrated for the formation of mesoporous γ-Al2O3 obtained by EISA and SA-EISA processes.

The role of the acidity of alumina prepared by aluminum-carbon black composite for CO hydrogenation to dimethyl ether on hybrid Cu–ZnO–Al2O3/alumina

The effects of surface area and the acidity of mesoporous γ-Al2O3, which is prepared by calcining aluminum-carbon black composite (Al/CB) of the precipitated aluminum nitrate on carbon black at different weight ratios, were investigated to verify the roles of carbon black in the surface properties and stability of Cu–ZnO–Al2O3 for the direct synthesis of dimethyl ether (DME) from syngas. A high surface area of ~100 m2/g with a large pore diameter of ~25 nm originated from the occupied spaces of carbon black enhanced the dispersion of the active Cu–ZnO–Al2O3 particles by forming a strong and stable interaction with mesoporous solid acid γ-Al2O3 surfaces. The enhanced dispersion of copper-containing particles, being strongly interacted with the acid sites of the hybrid Cu–ZnO–Al2O3/Al2O3 catalyst using γ-Al2O3 prepared at an optimal Al/CB weight ratio of 10, is mainly responsible for the high CO conversion with a high yield to oxygenates and a suppressed aggregation of active copper species during the direct synthesis of DME from syngas.

Synthesis of rod-like mesoporous γ-Al2O3 by an ionic liquid-assisted sol–gel method

Uniform rod-like mesoporous alumina has been successfully synthesized by an ionic liquid-assisted sol–gel method. The result shows that the morphology of the alumina is dependent on the molar ratio of [Bmim]PF6 to aluminum isopropoxide and the uniform alumina rods with the diameter of 200–400nm and the length of 2–5μm can be fabricated at the [Bmim]PF6/aluminum mole ratio 0.18. The hydrogen bond-co-π–π stack mechanism is used to explain the formation of the [Bmim]PF6/aluminum hydroxide hybrids rods. We believe that the ionic liquid plays the role of a capping agent in inhibiting the side growth of the [Bmim]PF6/aluminum hydroxide hybrids through the hydrogen bonds between PF6− and aluminum hydroxides, resulting in the construction of final alumina rods.

Facile synthesis of mesoporous Si-containing γ-Al2O3 nanofiber with enhanced thermal stability

Mesoporous γ-Al2O3 nanofiber was prepared via a simple reverse precipitation route using Si-containing Al(OH)3 and HNO3 as raw materials. The resultant Si-containing mesoporous γ-Al2O3 nanofiber exhibited high surface area of 320 m2/g, large pore volume of 1.17 cm3/g and large pore size of 10.5 nm. The introduction of Si element remarkably enhanced the thermal stability of mesoporous γ-Al2O3. The as-prepared nanofiber could maintain relative high surface area(110 m2/g) and pore volume(0.73 cm3/g) up to 1100 °C. The effects of various experimental conditions, such as pH value, reaction temperature and aging temperature on the structural properties of the mesoporous γ-Al2O3 were also investigated.

A facile strategy to fabricate well-defined mesoporous γ-Al2O3 microcubes with good adsorption performance towards Cr(VI) removal

A facile route is initiated to fabricate well-defined mesoporous γ-Al2O3, with a three-dimensional micro/nanostructure, using basic aluminum sulfate (BAS) microcubes as precursor. The as-synthesized γ-Al2O3 is cubic-like in morphology with an average size of ca. 6μm. Mesoporous γ-Al2O3 synthesized by this method is highly thermal stable and exhibits superior adsorption performance (maximum adsorption capacity 9.93mg/g) with good recycling efficiency (more than 76% of its original adsorption capacity after 4 cycles) as an adsorbent to remove the heavy metal ions Cr(VI) as a result of its unique structure, which made it to be a promising material for environmental remediation.

A non-template approach to fabricate mesoporous alumina with predefined morphology by solid-state transformation of Al-based metal–organic frameworks

Using different Al-MOFs as precursor, mesoporous γ-Al2O3 with special morphology and different textural properties were synthesized by thermal treatment method.