Study on low-temperature NH₃-SCR denitration mechanism of biochar-supported Mn-Cu-Nb catalyst

Under the context of global energy transition and carbon neutrality, controlling nitrogen oxide (NOx) emissions from biomass combustion is of great significance, and the development of high-efficiency low-temperature catalysts has become a current research focus. In this study, Nb was used to dope and modify the Mn7-Cu3/BCN catalyst to construct the Mn7-Cu3-Nbx/BCN system. The doping amount was optimized through selective catalytic reduction (SCR) activity tests. The reaction mechanism was explored by combining in situ DRIFTS and density functional theory (DFT) simulations. Experimental findings revealed that the catalyst doped with 0.05% Nb achieved the optimal performance, sustaining a NO conversion efficiency of ≥94% within the temperature window of 150−275 °C while demonstrating improved resistance to alkali metal K poisoning. Mechanistic analyses showed that at low temperatures, the catalyst facilitated the SCR reaction via both the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) pathways, with the synergistic interaction between multiple active sites driving the efficient conversion of NH3 and NO. DFT calculations further confirmed that both pathways had the characteristics of low reaction energy barriers and significant exothermicity, ensuring the high activity and feasibility of the low-temperature reaction. The findings provided foundational theoretical support for the design of Nb-doped Mn-Cu-supported catalysts and the exploration of the underlying working mechanisms.