Research progress of red mud as catalysts for NH₃-SCR denitrification: A review

Red mud (RM) is a strongly alkaline solid waste generated from alumina production. It is rich in Fe₂O₃, Al₂O₃, TiO₂, and SiO₂. Due to its intrinsic acid-base properties and redox activity, RM has been widely explored as a catalyst for NH₃-selective catalytic reduction (NH₃-SCR) of NO_x. This review summarizes recent progress on RM-based NH₃-SCR catalysts, including acid modification, metal loading, and composite design strategies. Acid treatment can increase the specific surface area of RM from below 30 m² g^-1 to over 200 m² g^-1, and significantly enhance surface acidity and redox ability. RM-supported catalysts loaded with metals such as Ce, Cu, and Mn usually achieve NO_x conversion above 80-90% in the temperature range of 200-400 °C. The catalytic roles and synergistic effects of Fe, Ce, and Cu species are discussed with a focus on low-temperature activity. Current challenges, including limited activity below 200 °C, sulfur and water deactivation, and difficulties in catalyst shaping, are also summarized. Finally, future directions are proposed, such as multi-metal coupling, RM-carbon hybrid systems, and structured monolithic catalyst design, to promote the high-value utilization of RM in NH₃-SCR applications.