Activated alumina is a highly porous, synthetically manufactured form of aluminum oxide (Al₂O₃). It is used primarily as a desiccant to remove moisture from gases and liquids, such as compressed air. It’s also used to filter water and to purify gas streams by selectively adsorbing certain molecules. In industrial processes, it's commonly used as a catalyst or catalyst support, such as in the Claus process for removing sulfur from natural gas.