Aluminum hydroxide, also known as hydrated alumina, has the chemical formula Al2O3 · NH2O. When n=1, Al2O3 · H2O is called monohydrate alumina, which can be divided into three types: boehmite, boehmite, and pseudo boehmite. The primary difference between boehmite and pseudo boehmite is their large and fine grain size.

Aluminum oxide has multiple crystal forms. The crystal shapes of alumina prepared by calcining aluminum hydroxide under different conditions are different. Among them, γ - Al2O3 is the most widely used transition state alumina in industry, also known as activated alumina. Gamma Al2O3 has a large specific surface area and can be used as a carrier for more metals or metal oxides. Its pore size can be adjusted, and it has good thermal stability. It is often used as a catalyst carrier for hydrogenation, reforming, methanol synthesis and other reactions. Currently, most industrial activated alumina is obtained by calcining pseudo boehmite and is widely used in the refining and automotive industries.

In order to prepare alumina with a large specific surface area and pore size, the primary requirement is to prepare precursors of boehmite or pseudo boehmite with a large specific surface area. The characterization and particle size of pseudo boehmite determine the characterization and specific surface area of alumina. The main methods for preparing pseudo boehmite now include acid precipitation, alkali precipitation, alcohol aluminum method, and sodium aluminate carbon dioxide neutralization method.

The acid precipitation method involves the addition of strong acid in a sodium aluminate solution, primarily the nitric acid method. This method involves the neutralization reaction between sodium aluminate and nitric acid to obtain pseudo boehmite, which facilitates the manipulation of reaction conditions. The pore size of the product is relatively concentrated, but the resulting composition is unstable, the purity is low, and the quality is greatly affected. Nitric acid is relatively expensive and difficult to use on a large scale in industry. The alkaline deposition method for preparing pseudo boehmite involves adding a sedimentation agent (ammonia, sodium aluminate, or sodium hydroxide) to an acidic aluminum salt solution, followed by sedimentation, filtration, washing, and drying to prepare pseudo boehmite. The product quality obtained by alkali precipitation method is stable, impurities are easy to separate, and trihydrate alumina is not easily generated. However, the material purity requirements are high, and anion removal is difficult. Both acid deposition and alkali deposition methods will undergo acid-base neutralization reactions. During acid-base differentiation, harmful gases can occur, causing pollution to both the human body and the environment. The aluminum alcohol hydrolysis method involves the reaction of aluminum with ethanol under the effect of a catalyst to produce aluminum alcohol. The product has high purity, but the cost of organic alcohols is high and difficult to recover, resulting in a high price of pseudo boehmite and high toxicity of organic alcohols. During the reaction process, a lot of wastewater will occur, causing significant pollution to the environment.