Mesostructured Forms of the Transition Phases η‐ and χ‐Al 2 O 3

Green synthesis of mesoporous γ-Al2O3 from coal fly ash with simultaneous on-site utilization of CO2

Mesoporous Al₂O₃ with crystalline framework walls has expanded all over the world due to the various potential applications especially in catalysis. Here, we develop a green and facile approach for the conversion of coal fly ash (CFA) into ordered mesoporous γ-Al₂O₃. The practical and promising lime-sinter method was comprehensively studied for the extraction of aluminum from CFA as a first step. The extraction efficiency of aluminum could reach up to 87.42%, through calcining with CaCO₃ at 1390°C for 1 h and then dissolving in Na₂CO₃ solution at 70°C for 0.5 h. Combined with the urgent demand for CO₂ emission reduction, simulated purified flue gas was introduced to precipitate the Al(OH)₃ precursors without structure-directing agents for just 1 h, followed by calcining at only 400°C or 550°C. A series of characterizations were conducted to discuss the effect of precipitation temperature and calcination temperature, resulting the superior product (Al₂O₃-65/550) with high surface area (230.3 m² g^-1), crystalline γ-Al₂O₃ phase and ordered mesostructure. This proposed strategy, integrating the on-site recycling of CFA and utilization of CO₂, appears to be promising for scalable production of mesoporous γ-Al₂O₃.

Room-temperature synthesis of χ-Al2O3 and ruby (α-Cr:Al2O3)

In this work, we present a unique crystal growth synthesis of χ-Al₂O₃ accompanied with α-Cr:Al₂O₃ at room temperature.

Kinetics and mechanisms of alcohol dehydration pathways on alumina materials

Ethanol dehydration on α,γ,η-alumina mechanistically and kinetically described by the same rate expression implicating similar active sites on all alumina materials.

Nickel-induced morphology change of mesostructured alumina with enhanced catalytic activity for selective CO methanation

Nickel-induced morphology change of mesostructured alumina with amorphous walls to bayerite tetrahedra when treated in water, and then to γ-alumina with worm-like mesopores topologically after it was calcined at 400 °C is reported. The catalytic activity for selective CO methanation increased significantly after this treatment.

Atomic structure of a spinel-like transition Al2O3(100) surface

We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies, exhibiting a strong preference for surface hydroxyl group formation in two configurations. The transition alumina films are crystalline and perfectly stable in ambient atmospheres, a quality which is expected to open the door to new fundamental studies of the surfaces of transition aluminas.

Synthesis and Characterization of Mesoporous Alumina-Zirconia as Catalyst Support for Suzuki Coupling Reaction

One pot facile synthesis of ordered mesoporous alumina-supported zirconia with high thermal stability and large pore sizes by evaporation-induced method was systematically investigated. The strategy based on a sol-gel process associated with nonionic triblock copolymers PPO-PEO-PPO as templates in ethanolic solution. Small-angle XRD, TEM, and nitrogen adsorption and desorption results showed that these composites possessed an ordered 2D hexagonal mesostructure, resisted to high temperature up to 1000 °C, and had large surface areas and narrow pore-size distributions. Loaded with palladium, the mesoporous alumina-zirconia composite exhibited high catalytic activity in Suzuki coupling of 2-bromotoluene with phenylboronic acid.

Obtaining of transition phases of alumina starting from sodium aluminate in Bayer process

Transition (active) phases of alumina were synthesized starting from sodium aluminate solution prepared out of Bayer liquor. The neutralisation of sodium aluminate solution was performed by sulphuric acid. Powder X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and low-temperature nitrogen absorption studies were employed to trace the formation of the transition phases of alumina. The results show that the properties of the powders (phase composition, morphology and specific surface area) are strongly influenced by the initial pH value of the system, as well as by the duration of neutralisation step. It is possible to obtain powders with heterogeneous structure with dominant phase of bayerite, gibbsite or boehmit by tuning the pH and concentration of the starting sodium aluminate solution. The transition (active) phases of alumina (?- and ?-alumina) with high specific surface area (264-373 m2/g) are formed through the thermal dehydratation of aluminium hydroxide (bayerite and gibbsite) and aluminium oxyhydroxide (boehmite or pseudoboehmite) at the temperature of 500?C. Namely, bayerite and pseudoboehmite transforms to ?-phase of alumina upon heating, while gibbsite transforms to ?-phase, maintaining the parent morphology.

Synthesis of mesoporous alumina from boehmite in the presence of triblock copolymer

Mesoporous alumina was synthesized using commercial boehmite in the presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer Pluronic P123. Its calcination at 400 degrees C yielded gamma-alumina, in contrast to the ordered mesoporous alumina (OMA) obtained by hydrolysis of aluminum alkoxide in the presence of the same triblock copolymer. This synthesis afforded boehmite-based mesoporous alumina (BMA) with better adsorption properties and higher thermal stability in comparison to the alkoxide-based OMA, which remained amorphous after calcination below 900 degrees C. The BMA materials also exhibited higher amount of acidic and basic sites as evidenced by ammonia (NH(3)) and carbon dioxide (CO(2)) temperature programmed desorption (TPD), respectively. Dispersion of commercial boehmite precursor under microwave irradiation afforded BMA materials with similar surface characteristics as those of the corresponding BMA samples obtained under conventional conditions, but showing slightly lower acidity and better basic properties. Thus, the dispersion method of boehmite can be used to modify the surface properties of the resulting BMA samples without sacrificing their porosity.

Shaping colloidal rutile into thermally stable and porous mesoscopic titania balls

High crystallinity and controlled porosity are advantageous for many applications such as energy conversion and power generation. Despite many efforts in the last decades, the direct synthesis of organic-inorganic composite materials with crystalline transition metal oxides is still a major challenge. In general, molecules serve as inorganic precursors and heat treatment is required to convert as-synthesized amorphous composites to stable crystalline materials. Herein, an alternative approach to the direct synthesis of crystalline polymer-metal oxide composites by using a spherical polyelectrolyte brush as the template system is presented. Pre-synthesized electrostatically stabilized rutile nanocrystals that carry a positive surface charge are used as inorganic precursors. In this approach, the strong Coulomb interactions between anionic polyelectrolyte brush chains and cationic crystalline rutile colloids, whose surfaces are not capped and therefore reactive, are the key factors for the organic-inorganic crystalline composite formation. Stepwise calcination first under argon and followed with a second calcination in air lead to the complete removal of the polymer template without collapse and porous rutile balls are obtained. The results suggest that any colloids that carry a surface charge might serve as inorganic precursors when charged templates are used. It is expected that this hierarchical route for structuring oxides at the mesoscale is generally applicable.

Ordered mesoporous alumina-supported metal oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.