Removal of NO_x Using the Reductive Properties of TiO_x (0<x<2)

Abstract

Removal of NO_x is one of the most urgent environmental issues. NO decomposition has been carried out utilizing the reductive properties of TiO_x (0<x<2) (i.e., low valence materials of titanium oxides), as represented by Ti-coated Al₂O₃ balls prepared by fine particle bombardment, or TiO_x powders (for example, so-to-speak Ti-black powders used for liquid crystal displays as the black matrix). In the absence of oxygen, NO is found to mostly decompose into NH₃ by means of Ti-coated Al₂O₃ balls or TiO_x powders at approximately 150°C, accompanied by traces of N₂O. A similar result is also obtained even in the presence of about 20% oxygen. The formation of NH₃ is further effective in reducing NO to give water and N₂ as shown by the urea-SCR (selective catalytic reduction) system used currently in practice in diesel engines.