Activated alumina is made by heating and dehydrating aluminum hydrate. Its properties depend on the structural state of the initial hydroxide. Generally, it is not pure Al2O3, but a partially hydrated amorphous porous structure, in which there are not only amorphous gel, and hydroxide crystals. Because of its high activity on the surface of capillary channels, it is also called activated alumina. It has a strong affinity for water and is an adsorbent for deep drying of trace water. Under certain operating conditions, its drying depth can reach below the dew point -70°C.

Specialty adsorbents are solid substances that can effectively adsorb certain components from a gas or liquid.

Adsorbents generally have the following characteristics: large specific surface, suitable pore structure and surface structure; strong adsorption capacity for adsorbate; generally do not chemically react with adsorbate and medium; easy to manufacture and easy to regenerate; good mechanical properties strength etc.

Adsorbents can be classified according to pore size, particle shape, chemical composition, surface polarity, etc., such as coarse-pore and fine-pore adsorbents, powdery, granular, strip-shaped adsorbents, carbonaceous and oxide adsorbents, polar and non-polar polar adsorbents, etc.