Key Takeaways & Executive Findings
- •• • The Mn7-Cu3-Nb0.05/BCN catalyst, with a Nb doping amount of 0.05%, achieves a NO conversion efficiency of ≥94% in the temperature window of 150–275 °C, demonstrating superior low-temperature activity for biomass flue gas denitration. • • The catalyst exhibits dual E-R and L-H reaction pathways at low temperatures, with DFT calculations showing that the E-R pathway involves NH3 adsorption on the Mn-2 site (adsorption energy: −299.1 kJ/mol) and dehydrogenation with a low energy barrier of 15.5 kJ/mol, while the rate-determining step (NH2NO decomposition) has an energy barrier of 22.5 kJ/mol. • • In the L-H pathway, NO is adsorbed on the Mn-1 site and oxidized to NO2 with a low energy barrier, rapidly forming bridged nitrate species that react with NH4+ to produce NH4NO3, which decomposes into N2 and H2O; no transition state is observed in key steps, confirming the rapid reaction characteristics. • • The catalyst shows improved resistance to alkali metal K poisoning, a critical advantage for real-world biomass combustion flue gas containing potassium, thereby extending catalyst lifetime and reducing operational costs.
Abstract
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.
1. Introduction
Commercial vanadium-based SCR catalysts dominate the market due to their excellent N2 selectivity, thermal stability, and sulfur resistance, yet they suffer from a narrow active temperature window, high light-off temperature, and potential biotoxicity of vanadium, which may cause secondary pollution. These drawbacks are particularly problematic for biomass combustion flue gas, which is typically low in temperature, necessitating the development of novel, high-performance, and eco-friendly low-temperature SCR catalysts.
Biochar-based supports have emerged as promising candidates due to their high surface area and tunable surface chemistry. This study addresses the bottleneck by doping the Mn7-Cu3/BCN catalyst with Nb, aiming to enhance low-temperature activity and resistance to alkali metal poisoning. The systematic investigation using SCR activity tests, in situ DRIFTS, and DFT calculations provides a mechanistic understanding of the dual E-R and L-H pathways, offering a foundation for rational catalyst design.
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LIU Bingbing, JI Ke, LU Zhibin, ZHANG Fangfang, BI Xuejun (2026). Low-Temperature NH3-SCR Denitration Mechanism of Biochar-Supported Mn-Cu-Nb Catalyst. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(25)60619-0
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Frequently Asked Questions
What is the optimal Nb doping amount for the Mn7-Cu3/BCN catalyst, and what NO conversion efficiency does it achieve?
The optimal Nb doping amount is 0.05%, achieving a NO conversion efficiency of ≥94% in the temperature range of 150–275 °C.
What are the key reaction pathways and energy barriers for the Mn7-Cu3-Nb0.05/BCN catalyst in low-temperature NH3-SCR?
The catalyst follows both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) pathways. In the E-R pathway, NH3 adsorbs on the Mn-2 site with an adsorption energy of −299.1 kJ/mol, dehydrogenates with a barrier of 15.5 kJ/mol to form −NH2, which reacts with NO to produce NH2NO; the decomposition of NH2NO (barrier 22.5 kJ/mol) is rate-determining. In the L-H pathway, NO adsorbs on Mn-1, oxidizes to NO2, and forms bridged nitrate that reacts with NH4+ to yield NH4NO3, which decomposes to N2 and H2O without a transition state.
How does Nb doping improve the catalyst's resistance to alkali metal poisoning, specifically potassium (K)?
The study reports that the Nb-doped catalyst demonstrates improved resistance to K poisoning, although the exact mechanism is not detailed in the provided text. This is likely due to Nb modifying the surface acidity and redox properties, which mitigates the detrimental effects of K on active sites.
What is the significance of the dual E-R and L-H pathways for industrial application?
The dual pathways ensure high NO conversion efficiency across a broad temperature window (150–275 °C) by providing alternative routes for NH3 and NO activation. This is industrially beneficial as it accommodates fluctuations in flue gas temperature and composition, enhancing process robustness.
What are the implications of the DFT findings for catalyst design?
DFT calculations reveal low energy barriers and exothermicity for both pathways, confirming the thermodynamic and kinetic feasibility of the low-temperature reaction. This provides a theoretical basis for optimizing active site composition and support interactions to further enhance catalytic performance.
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