Nanostructured silica-gel doped with TiO₂ for mercury vapor control

A novel high surface area SiO₂-TiO₂ composite has been developed for elemental mercury vapor removal from combustion sources. The composite exhibits synergistic adsorption and photocatalytic oxidation. Mercury vapor in the gas stream is adsorbed, oxidized and stays on the composite. The composite has demonstrated a high mercury capacity (1512 μg/g) although in its current 3-mm pellet form only the outer layer is effectively utilized. The loading of 13% TiO₂ shows the best removal, both with and without UV irradiation. Increasing TiO₂ loading beyond this level does not enhance the removal further. It has also been observed that the composite after being 'activated' by photocatalytic oxidation has better performance, probably due to the change of surface functional groups. The examination of the effects of flow velocity reveals that mass transfer is the rate limiting step. Relative humidity has been found to impede adsorption therefore decreasing the overall removal efficiency. By rinsing with acid, both the deposited mercury and composite can be regenerated.