Both acid-base activation methods use physical or chemical means to re-expand the pore structure and restore activity. However, thermal treatment plays an important role.
During the thermal treatment process, the physical and chemical changes of activated alumina can be attributed to three processes: thermal decomposition, recrystallization, and sintering.
Firstly, volatile components and chemically-bound water in the waste alumina material are removed through a thermal decomposition reaction, converting the waste activated alumina balls into the desired chemical composition and forming a stable structure.
Secondly, through the recrystallization process, the carrier obtains a certain crystal size, grain size, pore structure, and specific surface area; at the same time, through microcrystalline sintering, the mechanical strength of the catalyst can be improved.
Waste activated alumina is a dense whole with very small pores, high density, closely packed particles and ions, and most of the pores are filled with adsorbate, forming a smooth and non-continuous gas. At the same time, particle and cluster deformation is evident, and the interface is obvious, causing a significant decrease in specific surface area, resulting in loss of material activity.
However, activated alumina particles that have undergone high-temperature activation have uniform and irregular pores formed between particles, resulting in larger sample specific surface area and higher activity.