Activated Alumina

Activated alumina is not simply alumina powder, but a porous solid material prepared through a special process, possessing high specific surface area, controllable pore structure, and rich surface chemical properties. It typically exists in transition states such as γ-Al₂O₃ alumina, and its "active" nature accurately summarizes its high surface energy and strong surface reactivity.

Key Structural Characteristics

Large Specific Surface Area: Typically 200-400 m²/g, with some products reaching over 500 m²/g, providing a vast reaction area for various physicochemical processes.

Controllable Pore Size Distribution: Through process control, materials dominated by micropores (<2 nm) and mesopores (2-50 nm) can be prepared to meet the needs of substances with different molecular sizes.

Abundant Surface Functional Groups: The presence of numerous hydroxyl groups (-OH) on the surface gives it amphoteric surface properties, exhibiting both weak acidity and weak basicity.

Good thermal stability: It can work at 500-600°C for a long time and can withstand higher temperatures for a short period of time.

Three Core Functional Roles

Activated alumina plays three main roles in industry:

As an Adsorbent:

Deep Drying: Used for drying compressed air, industrial gases, etc., lowering the dew point to below -70°C. It has a large adsorption capacity, high intensity, and is thermally regenerable.

Environmental Purification: Used for defluorination of drinking water, removal of acidic gases (such as HCl and SO₂), and adsorption and separation of impurities in solvents.

As a Catalyst Support (Highest Value-Added Field):

Petrochemical Industry: Loaded with active components such as Co-Mo and Ni-Mo, used in oil hydrorefining, cracking, and reforming. Its function is to disperse active components, stabilize the active phase, and control mass diffusion.

Environmental Catalysis: Used as the main coating material for three-way catalytic converters for automotive exhaust and diesel oxidation catalysts, loading precious metals (Pt, Pd, Rh, etc.).

Diverse Forms: Can be made into spherical, strip-shaped, and other fixed-bed supports, or used as a honeycomb ceramic coating for automotive exhaust purification.

As a (co)catalyst

Activated alumina possesses inherent catalytic activity, primarily stemming from the Lewis acid and weak Brønsted acid centers on its surface.

Alcohol dehydration reactions: such as the dehydration of ethanol to ethylene, are classic acid-catalyzed reactions.

Claus process: used to convert H₂S to elemental sulfur, activated alumina is a key catalyst in this process.

CFCs conversion: promotes their isomerization or disproportionation reactions.

In this role, it often works synergistically with the main catalyst to modulate the reaction pathway or improve selectivity.

Key selection parameters

Specific surface area and pore size: selected based on the size of the adsorbate molecules or the requirements of the catalytic reaction.

Bulk density and strength: affect the packing density and bed pressure drop.

Sodium and other impurity content: requires extremely low levels for sensitive catalytic applications.

Thermal and hydrothermal stability: crucial, especially in high-temperature, water-containing environments such as tail gas catalysis.

Summary

Activated alumina is a perfect example of the integration of porous materials science and industrial catalytic engineering. Starting as a high-performance adsorbent, it has ultimately become an indispensable material in modern industrial catalysis due to its unparalleled structural tunability, surface modifiability, and morphological plasticity. We are a Chinese industrial ceramics manufacturer. For more information, please contact us via email at annayu@169chem.net or WhatsApp at +8618909016373.