Activated alumina is an excellent desiccant. Spherical particles with diameters of 3 ~ 5 and 4 ~ 6mm are widely used. It can adsorb a large amount of water vapor, and the water saturated alumina is easy to remove the physically adsorbed water by drying and reuse. In addition to dry air, it is also used to remove water from various gases and organic liquids, such as alcohol dehydration. It is also a good adsorbent for the oxides of ammonia, hydrogen fluoride and arsenic. As a high-quality fluoride remover for high fluoride drinking water and arsenic remover for acid industry, it has been widely used. Among its various forms, it is called activated alumina because of its excellent surface properties, such as large specific surface area, uniform dispersion of active sites, wide crystal phase temperature range, acidic surface and so on. However, its thermal stability has plagued people for a long time, especially in high-temperature reaction systems, such as automobile exhaust purification, catalytic combustion and other high-temperature and harsh environments, the specific surface area of the catalyst carrier decreases greatly due to phase transformation and thermal combustion, resulting in the serious deactivation of the supported catalyst. Therefore, how to prevent the phase transformation of activated alumina and improve its thermal stability is of great significance to prolong the service life of industrial catalysts, and it is also an important topic in the research of activated alumina support.
Because of its excellent specific area, suitable pore structure and acidic surface, it can also be widely used as catalyst and its support. However, in some high-temperature reaction systems, its high-temperature sintering is easy to lead to catalyst deactivation, so its high-temperature sintering resistance and phase denaturation resistance need to be further solved.
The introduction of some cations on the surface of activated alumina has a significant effect on its sintering and phase transformation. For improving its thermal stability, additives can be basically divided into four categories, namely rare earth metal alumina, alkaline earth metal alumina, silica and other oxides. After modification, alumina can still maintain a large specific surface area at high temperature.