What is gamma activated alumina and material pseudoboehmite do you know? In here, we will explain it. Gamma activated alumina and material pseudoboehmite are in here.
Alumina has been found to exist at least 8 form, they are α- Al2O3, θ-Al2O3, γ- Al2O3, δ- Al2O3, η- Al2O3, χ- Al2O3, κ- Al2O3 and ρ- Al2O3, their respective macroscopic structure properties are also different. Gamma -Al2O3 is a cubic close packed crystal, insoluble in water, but soluble in acid and alkali. Gamma Al2O3 carrier is weak acidic support, has a high melting point 2050 ℃, alumina gel in hydrate form can be made into the oxide with high porosity and high specific surface, it has transition phases in a wide temperature range. At higher temperature, due to dehydration and dehydroxylation, the Al2O3surface appears coordination unsaturated oxygen (alkali center) and aluminum (acid center), with catalytic activity. Therefore, alumina can be used as carrier, catalyst and cocatalyst.
γ-Al2O3, was called “ activated alumina”, is a kind of porous high dispersion solid materials, because of its adjustable pore structure, large specific surface area, good adsorption performance, surface with the advantages of acidity and good thermal stability, microporous surface with requisite properties of catalytic action, therefore become the most widely used catalyst, catalyst carrier and chromatography carrier in the chemical and oil industry, and plays an important role in the oil hydrocracking, hydrogenation refining, hydrogenation reforming, dehydrogenation reaction and automobile exhaust purification process.
γ-Al2O3 is widely used as catalyst carrier because of the adjustability of its pore structure and surface acidity. When γ- Al2O3 is used as a carrier, besides can have the effects to disperse and stabilize active components, also can provide acid alkali active center, synergistic reaction with the catalytic active components. The pore structure and surface properties of catalyst depend on γ-Al2O3 carrier, so high performance carrier would be found for specific catalytic reaction by controlling the properties of γ-Al2O3carrier.
alumina catalyst carriers
Gamma Al2O3 is generally made of its precursor pseudo-boehmite through 400~600℃ high temperature dehydration, so the surface physicochemical properties is largely determined by its precursor pseudo-boehmite, but there are many ways to make pseudo-boehmite, and different sources of pseudo-boehmite leads to the diversity of gamma – Al2O3. However, to those catalysts with special requirements to alumina carrier, only rely on the control of precursor pseudo-boehmite is difficult to achieve, must be taken to prophase preparation and post processing combining approaches to adjust the properties of alumina to meet different requirements. When the temperature is higher than 1000 ℃ in use, alumina occurs following phase transformation: γ→δ→θ→α-Al2O3, among them γ、δ、θ are cubic close packing, the difference only lies in the distribution of aluminum ions in tetrahedral and octahedral, so these phase transformation does not cause much variation of the structures. Oxygen ions in alpha phase are hexagonal close packing, aluminum oxide particles are grave reunion, specific surface area declined considerably.