Activated alumina is used as a catalyst for removing hydrocarbons from gaseous pollutants in a combustion unit.

Activated Alumina as a Catalyst:
Activated alumina is a highly porous form of aluminum oxide that has a large surface area, high adsorption capacity, and excellent thermal stability. It is commonly used as a catalyst in various chemical processes, including the removal of hydrocarbons from gaseous pollutants.

Mechanism of Hydrocarbon Removal:
When hydrocarbons are present in gaseous pollutants, they can contribute to air pollution and pose a threat to human health and the environment. Therefore, it is essential to remove these hydrocarbons before releasing the gases into the atmosphere. Activated alumina acts as a catalyst to facilitate the conversion of hydrocarbons into carbon dioxide and water through the process of catalytic oxidation.

Adsorption:
Activated alumina has a high affinity for hydrocarbons and other volatile organic compounds (VOCs). The porous structure of activated alumina provides a large surface area, allowing for efficient adsorption of hydrocarbon molecules onto its surface.

Oxidation:
Once the hydrocarbon molecules are adsorbed onto the surface of activated alumina, oxidation reactions take place. The catalyst provides active sites where oxygen molecules can react with the adsorbed hydrocarbons, leading to their conversion into carbon dioxide (CO2) and water (H2O). This process is known as catalytic oxidation.

Regeneration:
Over time, the adsorption capacity of activated alumina may decrease as it becomes saturated with hydrocarbons. Therefore, periodic regeneration is required to restore its adsorption capacity. This can be achieved by heating the activated alumina at high temperatures, which removes the adsorbed hydrocarbons and allows the catalyst to be reused.

Advantages of Activated Alumina Catalyst:
- High adsorption capacity: Activated alumina has a large surface area, allowing for efficient adsorption of hydrocarbons.
- Thermal stability: The catalyst can withstand high temperatures without losing its effectiveness.
- Regenerability: Activated alumina can be regenerated, making it suitable for long-term use.
- Versatility: Activated alumina can be used for the removal of various pollutants, including hydrocarbons and VOCs.

In conclusion, activated alumina is an effective catalyst for removing hydrocarbons from gaseous pollutants in a combustion unit. Its high adsorption capacity, thermal stability, and regenerability make it a suitable choice for this application.