Gamma alumina (γ - Al ₂ O3) is an important crystalline form of alumina, widely used in industry due to its unique physical and chemical properties. The following is a comprehensive analysis of its core characteristics, preparation methods, and application fields:

1、 Structural characteristics and physicochemical properties

Porosity and high specific surface area

Gamma alumina has a tightly packed oxygen ion structure with cubic faces, and Al ³ ⁺ is irregularly distributed in octahedral and tetrahedral voids, forming a rich pore structure. Its specific surface area can reach 200-300 m ²/g, or even higher (such as nano level γ - Al ₂ O3 specific surface area ≥ 230 m ²/g), providing a large number of active sites for catalyst loading and adsorption reactions.

Surface acidity and thermal stability

The surface of γ - Al ₂ O3 has both B acid and L acid sites, which can be adjusted by doping negative ions such as halogens to promote reactions such as cracking and isomerization. It has good thermal stability and can maintain structural stability at 400-600 ℃, but it will completely transform into α - Al ₂ O ∝ 134 at 1200 ℃.

Adjustable pore size and morphology

By adjusting the preparation process, γ - Al ₂ O3 can form a composite structure of micropores, mesopores, and macropores, and be shaped into spherical, strip-shaped, honeycomb, and other forms to meet the needs of different reactors such as fixed beds and fluidized beds.

2、 Main preparation methods

Precursor conversion method

Acid/alkali precipitation method: Using aluminum salts (such as aluminum nitrate, aluminum sulfate) or sodium aluminate as raw materials, pseudo boehmite (AlOOH) is generated through neutralization reaction, and then calcined at 400-600 ℃ to obtain γ - Al ₂ O3. The pore size distribution of acid method products is narrow, and the alkaline method (double aluminum method) has low cost and is suitable for industrial production.

Carbonization method: Injecting CO ₂ into sodium aluminate solution to generate pseudo boehmite, which has low process cost but is prone to producing impurities.

Preparation of Nanoscale γ - Al ₂ O3

Aluminum alcohol hydrolysis method: High purity nano - γ - Al ₂ O3 is prepared by hydrolysis of aluminum isopropoxide and other raw materials, which is suitable for high-end fields such as electronic ceramics.

Spray granulation method: spray drying molding is used to obtain microspheres with uniform particle size, which is suitable for catalyst carrier 8.

Special structural regulation technology

Preparation of Macroporous Structure: Utilizing the decomposition of ammonium aluminum carbonate to produce NH3 and CO ₂ gases for pore formation, or adding template agents (such as polystyrene microspheres) to form gradient pore structures.

Spherical carrier forming: High strength spherical γ - Al ₂ O3 is produced using hot oil column method, oil ammonia column method or rolling ball method, and is used in processes such as petroleum hydrogenation.

3、 Core application areas

Catalyst and Carrier

Petrochemical industry: used for hydrogenation desulfurization, cracking, reforming and other reactions, accounting for more than 80% of the catalyst carrier dosage.

Environmental protection field: As a carrier for automotive exhaust purification catalysts (such as three-way catalysis), it reduces pollutants such as NOx.

Adsorption and Separation

Gas/liquid purification: adsorption of fluoride ions (fluoride removal from drinking water), drying of gases (such as hydrogen and acetylene), removal of acidic substances from transformer oil.

Industrial wastewater treatment: removes pollutants such as phosphorus and heavy metals, and suppresses eutrophication of water bodies.

Functional materials

Electronics and Ceramics: Used for high-pressure sodium lamp tubes, integrated circuit substrates, transparent ceramics, etc. Alpha phase gamma Al ₂ O3 can also be used as a far-infrared emitting material.

Reinforcement materials: added to plastics, rubber, and coatings to improve wear resistance, hardness, and water resistance.

New energy and energy storage

Battery material: As a component of lithium-ion battery electrodes or solid electrolytes (β - Al ₂ O ∝).

Supercapacitors: Use high specific surface area to store charges.

4、 Regeneration and Sustainability

Gamma Al ₂ O3 can be removed from pollutants through high-temperature calcination (such as heating at 175 ℃ for 6-8 hours) or solvent washing, achieving multiple regenerations and significantly reducing usage costs.