Advances in CO-SCR Catalysts and Reaction Mechanisms

Driven by increasingly stringent nitrogen oxides (NOx) control requirements, and the limitations of NH3-selective catalytic reduction (NH3-SCR) technology, CO-selective catalytic reduction (CO-SCR) technology is attracting considerable attention. This technology utilizes the carbon monoxide (CO), naturally present in industrial flue gas from processes like ferrous metallurgy and waste incineration, as a reducing agent. It selectively reduces NOx, simultaneously removing both NOx and CO, thereby addressing secondary pollution and high costs while achieving waste utilization for pollution control. This approach offers substantial environmental and economic benefits. Currently, research on CO-SCR technology is receiving considerable attention in the fields of energy conservation and environmental protection. However, research primarily focuses on optimizing catalyst performance and structure, while the underlying reaction mechanisms in diverse environments remain unclear. Overall, the technology is in its early stages and requires the development of efficient catalysts tailored for industrial applications. The development of catalysts for CO-SCR primarily focuses on reducing the use of precious metals while enhancing the simultaneous removal of NOx and CO. Synergistic effects can be achieved through methods such as doping with transitional metals like copper (Cu), manganese (Mn), and iron (Fe), or by selecting suitable carriers and innovative structural designs. Furthermore, maintaining high activity in complex environments is critical for practical applications. Factors such as oxygen-rich conditions, water vapor (H2O), sulfur dioxide (SO2), and alkali metal poisoning can significantly affect catalytic performance. Investigating the deactivation process through simulations of industrial flue gas and in situ characterization techniques is crucial for understanding catalyst resistance to poisoning. This review elucidates the fundamental reaction processes of CO-SCR and the challenges of its practical application. It provides a detailed summary of the performance advantages and fabrication methods of three catalyst types currently under investigation. These include precious metal catalysts, metal oxide catalysts, and molecular sieve catalysts. It also analyzes the reaction mechanisms and approaches for mitigating catalyst poisoning under different reaction conditions, such as oxygen-rich, water-containing, sulfur-containing, and various complex environments. Furthermore, it presents prospects for the future development of CO-SCR catalysts. This research offers theoretical guidance for developing more efficient industrial catalysts for simultaneous pollutant removal.