Mechanistic insight into Mn-Ce synergy drives efficient low-temperature SCR over fly ash

Abstract

Fly ash (FA) is rich in SiO₂ and Al₂O₃, exhibiting potential as a catalyst support for selective catalytic reduction (SCR) reactions. However, its practical application is restricted due to inert oxygen species and insufficient acidic sites. Herein, a series of fly ash-based catalysts were prepared via a sequential method combining acid pretreatment and wet impregnation. The synthesized Mn-Ce/AFA catalyst exhibited outstanding low-temperature denitration performance, reaching a NO_x conversion rate of 100% at 150 °C. Additionally, the Mn-Ce/AFA catalyst showed satisfactory H₂O vapor tolerance, with the NO_x conversion rate maintaining approximately 95% when exposed to 5 vol% water vapor. Compared with the Mn-Ce/Ti catalysts, the Mn-Ce/AFA catalyst exhibited elevated levels of Mn⁴⁺ and Ce³⁺, indicating enhanced electron transfer in the Mn³⁺ + Ce⁴⁺ ⇌ Mn⁴⁺ + Ce³⁺ cycle. Results from H₂-temperature-programmed reduction (H₂-TPR) and NH₃-temperature-programmed desorption (NH₃-TPD) suggested that Ce-Mn co-doping enhanced the catalyst’s reducibility and the adsorption strength of NH₃ on Lewis acid sites. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results and NO oxidation tests revealed that the enhanced NO oxidation capacity promoted the generation of key monodentate nitrite species, while the strengthened Lewis acidity facilitated the NH₃ activation process. This work introduces an innovative approach to convert fly ash into efficient catalysts for environmental remediation, demonstrating waste valorization in green chemistry.

Graphical abstract

Keywords

Air pollution control / Selective catalytic reduction / NO_x / Fly ash / Acid sites

Highlight

	● The Mn-Ce/AFA catalyst is a low-cost substitution of commercial SCR catalysts.
	● Enhanced Mn3+/Ce4+ redox cycling drives the superior SCR activity.
	● The enhanced redox ability and oxygen adsorption generate key nitrite species.
	● The strengthened Lewis acidity promotes NH3 adsorption and activation process.
	● A method for high-value utilization of solid waste is proposed.

References

[1] Chen J , Zhou L , Deng X , Liu W , Liu J Y , Ji H W , Wu S H , Liang J X , Ou J H , Liu B Y . (2020). Role of Co content on the gradient microstructure evolution and mechanical properties of bilayer functionally graded cemented carbides. Materials Chemistry and Physics, 248: 122910

[2] Chen Z CRen SWang M MYang JChen LLiu W ZLiu Q CSu B X (2022). Insights into samarium doping effects on catalytic activity and SO₂ tolerance of MnFeO_x catalyst for low-temperature NH₃-SCR reaction. Fuel. 321: 124113

[3] Duan X X , Dou J X , Zhao Y Q , Rish S K , Yu J L . (2020). A study on Mn-Fe catalysts supported on coal fly ash for low-temperature selective catalytic reduction of NO_x in flue gas. Catalysts, 10(12): 1399

[4] Fang J , Bi X Z , Si D J , Jiang Z Q , Huang W X . (2007). Spectroscopic studies of interfacial structures of CeO₂–TiO₂ mixed oxides. Applied Surface Science, 253(22): 8952–8961

[5] Feng X B , Zhu J R , Song K L , Zeng J L , Zhou X Y , Guo X L , Lin K X , Zhang C H , Xie C , Shi J W . (2024). Insight into the reasons for enhanced NH₃-SCR activity and SO₂ tolerance of Mn-Co layered oxides. Separation and Purification Technology, 336: 126285

[6] Gao C , Shi J W , Fan Z Y , Gao G , Niu C M . (2018). Sulfur and water resistance of Mn-based catalysts for low-temperature selective catalytic reduction of NO_x: a review. Catalysts, 8(1): 11

[7] Gao G , Shi J W , Fan Z Y , Gao C , Niu C M . (2017). MnM₂O₄ microspheres (M = Co, Cu, Ni) for selective catalytic reduction of NO with NH₃: comparative study on catalytic activity and reaction mechanism via in-situ diffuse reflectance infrared Fourier transform spectroscopy. Chemical Engineering Journal, 325: 91–100

[8] Gollakota A R K , Volli V , Shu C M . (2019). Progressive utilisation prospects of coal fly ash: a review. Science of the Total Environment, 672: 951–989

[9] Gu T T , Liu Y , Weng X L , Wang H Q , Wu Z B . (2010). The enhanced performance of ceria with surface sulfation for selective catalytic reduction of NO by NH₃. Catalysis Communications, 12(4): 310–313

[10] Jin L Y , Xu X T , Wang Y H , Li J Y , Fan K H , Hu B , Shen Y , Liu X S . (2023). Study on H₂O₂, Ce, W modified MnO_x/TiO₂ based NH₃-SCR catalyst: the status and effect of doped promoters and synergies. Materials Research Bulletin, 168: 112494

[11] Kong M , Liu Q C , Jiang L J , Tong W , Yang J , Ren S , Li J L , Tian Y M . (2019). K⁺ deactivation of V₂O₅-WO₃/TiO₂ catalyst during selective catalytic reduction of NO with NH₃: effect of vanadium content. Chemical Engineering Journal, 370: 518–526

[12] Larachi F , Pierre J , Adnot A , Bernis A . (2002). Ce 3d XPS study of composite Ce_xMn_1−xO_2−y wet oxidation catalysts. Applied Surface Science, 195(1−4): 236–250

[13] Lee K JKumar P AMaqbool M SRao K NSong K HHa H P (2013). Ceria added Sb-V₂O₅/TiO₂ catalysts for low temperature NH₃ SCR: physico-chemical properties and catalytic activity. Applied Catalysis B: Environmental, 142–143: 142–143

[14] Li G H , Mao D S , Chao M X , Li G , Yu J , Guo X M . (2020). Significantly enhanced Pb resistance of a Co-modified Mn–Ce–O_x/TiO₂ catalyst for low-temperature NH₃-SCR of NO_x. Catalysis Science & Technology, 10(18): 6368–6377

[15] Li L , Chen L , Kong M , Liu Q C , Ren S . (2019). New insights into the deactivation mechanism of V₂O₅-WO₃/TiO₂ catalyst during selective catalytic reduction of NO with NH₃: synergies between arsenic and potassium species. RSC Advances, 9(65): 37724–37732

[16] Liang Y J , Wang B , Xuan Y , Fan W J , An P H , Meng S , Zhu X , Yun Y , Luan T , Wang D . et al. (2025). Significant promoting effect of toluene oxidation by CO on CuMnO_x catalysts: heterostructure and CO co-accelerated active oxygen cycling. Applied Catalysis B: Environment and Energy, 373: 125325

[17] Liu F D , He H , Ding Y , Zhang C B . (2009). Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH₃. Applied Catalysis B: Environmental, 93(1−2): 194–204

[18] Liu H , Fan Z X , Sun C Z , Yu S H , Feng S , Chen W , Chen D Z , Tang C J , Gao F , Dong L . (2019). Improved activity and significant SO₂ tolerance of samarium modified CeO₂-TiO₂ catalyst for NO selective catalytic reduction with NH₃. Applied Catalysis B: Environmental, 244: 671–683

[19] Liu J , Li X Y , Zhao Q D , Ke J , Xiao H N , Lv X J , Liu S M , Tadé M , Wang S B . (2017). Mechanistic investigation of the enhanced NH₃-SCR on cobalt-decorated Ce-Ti mixed oxide: in situ FTIR analysis for structure-activity correlation. Applied Catalysis B: Environmental, 200: 297–308

[20] Liu YYao W YCao X LWeng X LWang YWang H QWu Z B (2014). Supercritical water syntheses of Ce_x/TiO₂ nano-catalysts with a strong metal-support interaction for selective catalytic reduction of NO with NH₃. Applied Catalysis B: Environmental, 160–161: 160–161

[21] Ma H Y , Xia S W , Liang Y J , Jiang H Y , Wang B , Ma K , Wang D. . (2025). Iron-driven framework engineering in fly ash zeolites: boosting pore diffusion and efficient removal of polar VOCs. Chemical Engineering Journal, 522: 167938

[22] Meng D M , Zhan W C , Guo Y , Guo Y L , Wang L , Lu G Z . (2015). A highly effective catalyst of Sm-MnO_x for the NH₃-SCR of NO_x at low temperature: promotional role of Sm and its catalytic performance. ACS Catalysis, 5(10): 5973–5983

[23] Meng S , Wang Y , Wang B , Xuan Y , Liang Y J , Zhu X , Yun Y , Wang D , Peng Y. . (2025). The strong Fe-Mn interaction over red mud accelerating the activation of key oxygen species for toluene oxidation. Chemical Engineering Journal, 509: 161265

[24] Murugan B , Ramaswamy A V . (2008). Chemical states and redox properties of Mn/CeO₂−TiO₂ nanocomposites prepared by solution combustion route. The Journal of Physical Chemistry C, 112(51): 20429–20442

[25] Niu C H , Wang B R , Xing Y , Su W , He C , Xiao L , Xu Y R , Zhao S Q , Cheng Y H , Shi J W . (2021). Thulium modified MnO_x/TiO₂ catalyst for the low-temperature selective catalytic reduction of NO with ammonia. Journal of Cleaner Production, 290: 125858

[26] Perumal S K , Samidurai U , Balashanmugam V G , Kim H S , Aghalayam P . (2023). Superior catalytic performance of Zr-incorporated MnCu/SBA-15 catalyst for low-temperature NH₃-SCR of NO: effect of support. Separation and Purification Technology, 322: 124181

[27] Qi G , Yang R T , Chang R . (2004). MnO_x-CeO₂ mixed oxides prepared by co-precipitation for selective catalytic reduction of NO with NH₃ at low temperatures. Applied Catalysis B: Environmental, 51(2): 93–106

[28] Qi K , Xie J L , Mei D , He F , Fang D . (2018). The utilization of fly ash-MnO_x/FA catalysts for NO_x removal. Materials Research Express, 5(6): 065526

[29] Sun P , Guo R T , Liu S M , Wang S X , Pan W G , Li M Y . (2017). The enhanced performance of MnO_x catalyst for NH₃-SCR reaction by the modification with Eu. Applied Catalysis A: General, 531: 129–138

[30] Wang M M , Guo R T , Ren S , Sun S , Chen Z C , Yang J , Chen L , Li X D . (2022a). Revealing M (M = Cu, Co and Zr) oxides doping effects on anti-PbCl₂ poisoning over Mn-Ce/AC catalysts in low-temperature NH₃-SCR reaction. Applied Catalysis A: General, 643: 118749

[31] Wang M M , Ren S , Jiang Y H , Su B X , Chen Z C , Liu W Z , Yang J , Chen L . (2022b). Insights into co-doping effect of Sm and Fe on anti-Pb poisoning of Mn-Ce/AC catalyst for low-temperature SCR of NO with NH₃. Fuel, 319: 123763

[32] Wei L , Cui S P , Guo H X , Ma X Y , Zhang L J . (2016). DRIFT and DFT study of cerium addition on SO₂ of manganese-based catalysts for low temperature SCR. Journal of Molecular Catalysis A: Chemical, 421: 102–108

[33] Xing X , Li Z , Wang Y X , Tian Z H , Cheng J , Hao Z P . (2025). Exploration of the interaction mechanism in the synergistic degradation of benzene and toluene over MnCoO_x catalysts. Frontiers of Environmental Science & Engineering, 19(2): 22

[34] Xu R Y , Shen Q H , Chen L J . (2025). The γ-MnO₂/NF mediated peroxymonosulfate activation for expeditious 2,4,6-trichloro-phenol degradation: performance, pathways, and mechanism. Frontiers of Environmental Science & Engineering, 19(8): 108

[35] Xuan Y , Wang B , Gao C , Zhang K H , Li B , Wang M X , Wang D , Li J H , Lu C M . (2022). Substantially enhanced anti-lead poisoning performance on the CeO₂-WO₃ pairs supported by red mud: sacrificial effect of Fe₂O₃. Chemical Engineering Journal, 450: 138165

[36] Xuan Y , Zhu X , Wang B , Liang Y J , Gao C , Li B , Wang D , Peng Y . (2025). Ultrahigh alkali resistance and regeneration capacity of the birnessite deNO_x catalysts: a recyclable extraction-insertion strategy. Separation and Purification Technology, 368: 133017

[37] Yang C , Yang J , Jiao Q R , Zhao D , Zhang Y X , Liu L , Hu G , Li J L . (2020). Promotion effect and mechanism of MnO_x doped CeO₂ nano-catalyst for NH₃-SCR. Ceramics International, 46(4): 4394–4401

[38] Yin Z Z , Wang G , Wang L , Ren P Y , Sun J , Zhao H H , Ji P H . (2024). An effective way to utilize solid waste resources: the application of modified fly ash in removing Cu²⁺ and Pb²⁺ in wastewater. Separation and Purification Technology, 350: 127948

[39] Zhang H , Li H N , Zhang P Y , Hu T X , Wang X J . (2024a). Highly active copper-intercalated weakly crystallized δ-MnO₂ for low-temperature oxidation of CO in dry and humid air. Frontiers of Environmental Science & Engineering, 18(5): 62

[40] Zhang L , Chen J H , Lei Z , He H B , Wang Y S , Li Y H . (2019). Preparation of soybean oil factory sludge catalyst and its application in selective catalytic oxidation denitration process. Journal of Cleaner Production, 225: 220–226

[41] Zhang L X , Liang L S , Ma H Y , Mi H , Zhang Z H , Li Y , Xu Q , Zhao C , Chen J , Qiao J Y . et al. (2024b). Study on the effect of Fe doping on SCR activity and reaction mechanism of Mn–TiO₂ catalysts. Catalysis Letters, 154(6): 2777–2789

[42] Zhang X , Xuan Y , Wang B , Gao C , Niu S L , Zhao G J , Wang D , Li J H , Lu C M , Crittenden J C . (2022a). Precise regulation of acid pretreatment for red mud SCR catalyst: targeting on optimizing the acidity and reducibility. Frontiers of Environmental Science & Engineering, 16(7): 88

[43] Zhang X X , Cao J , Tian S H , Zhao Y C , Long L L , Yao X J . (2024c). Mechanistic insights into the influence of preparation methods and Fe³⁺ doping on the low-temperature performance of MnCeO_x catalyst for NH₃-SCR reaction. Separation and Purification Technology, 347: 127519

[44] Zhang X Y , Liu W Q , Peng P , Zhang Z J , Du Q L , Shi J Y , Deng L D . (2023). A dual functional sorbent/catalyst material for in-situ CO₂ capture and conversion to ethylene production. Fuel, 351: 128701

[45] Zhang X Y , Liu W Q , Zhou S M , Li Z X , Sun J , Hu Y C , Yang Y D . (2022b). A review on granulation of CaO-based sorbent for carbon dioxide capture. Chemical Engineering Journal, 446: 136880

[46] Zhu X , Yuan X , Song Z J , Peng Y , Li J H . (2024). A dual-balance strategy via phosphate modification on MnO₂-CeO₂ for NO_x and chlorobenzene synergistic catalytic control. Applied Catalysis B: Environmental, 342: 123364

[47] Zhu Y S , Xu M Z , Li M Z , Zhu J Q , Wei Y F , Lei L C , Li Y R , Yu T , Li Z J , Hou Y . et al. (2025). Sustainable utilization of fly ash in crafting shell structure for the reduction of iron sludge in Fenton oxidation via enhanced core-shell interaction. Separation and Purification Technology, 361: 131320

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