Catalysts prepared from solid wastes for efficient removal of NO_x in NH₃-SCR process: A review

The increase of solid wastes exerted great pressure on the environment and even damaged human health. Given this, the resource utilization of solid wastes became an inevitable trend of the industrial development. However, many researchers recognized that solid wastes with the component of Fe₂O₃, SiO₂, Al₂O₃, TiO₂, etc., could be utilized as the low-cost materials for preparing NH₃-SCR catalysts, which could solve both the accumulation of solid wastes and the emission of NO_x in industrial processes. Herein, some typical solid wastes, such as blast furnace slag (BFS), red mud (RM), coal fly ash (CFA), Fenton sludge (FS), etc., were extensively studied for their potential in NH₃-SCR catalysts. Although the presence of some harmful components in solid wastes led to catalysts deactivation, they could still be excellent supports applied on NH₃-SCR catalysts after proper pretreatment. In fact, these catalyst supports derived from solid wastes provided larger specific surface areas, thereby enhancing the NH₃ adsorption and redox capacity and facilitating the active ingredients loaded uniformly. Meanwhile, some useful impurities in solid wastes might also facilitate the NH₃-SCR performance, achieving denitrification efficiency comparable to other catalysts made from costly materials. Moreover, most of these NH₃-SCR catalysts performed significant SO₂ and/or H₂O tolerance via metal oxides-doping, which would expand their potential for practical application in industry. Finally, the prospects for the application of solid wastes in NH₃-SCR catalysts were also proposed.