Oxygen Vacancy in CeO₂ Enhanced Low-Temperature Ammonia Synthesis over Fe-Based Catalysts

Abstract

Ammonia is essential for agriculture and, as a next-generation carbon-free fuel, typically produced through the Haber–Bosch method. This process requires high temperature and pressure, leading to significant energy consumption and greenhouse gas emissions. Therefore, achieving ammonia synthesis under milder conditions has been a long-standing goal. In this study, we design and synthesize a series of CeO₂-modified Fe/carbon-based catalysts with varying amounts of CeO₂ (Ce_xFe_y/C). The catalyst Ce₂Fe₅/C demonstrates an ammonia yield rate of 3.5 mmol/(g·h), which is 44 times greater than that of Fe/C and 8 times greater than that of commercial Fe-based catalysts at 300 °C and 1 MPa. Temperature-programmed desorption experiments show that Ce₂Fe₅/C has enhanced nitrogen adsorption capabilities. Multiple analyses confirm that the CeO₂ in Ce₂Fe₅/C is rich in oxygen vacancies, which can provide electrons to Fe, facilitating nitrogen adsorption, dissociation, and activity in low-temperature ammonia synthesis.

Keywords

Ammonia synthesis / Iron catalyst / Oxygen vacancy / Cerium dioxide

References

[1] WangB, NiM, JiaoK. Green ammonia as a fuel. Sci Bull, 2022, 67(15): 1530-1534

[2] SmilV. Detonator of the population explosion. Nature, 1999, 400(6743): 415-415

[3] ErismanJW, SuttonMA, GallowayJ, et al.. How a century of ammonia synthesis changed the world. Nat Geosci, 2008, 1(10): 636-639

[4] ČorićI, HollandPL. Insight into the iron–molybdenum cofactor of nitrogenase from synthetic iron complexes with sulfur, carbon, and hydride ligands. J Am Chem Soc, 2016, 138(23): 7200-7211

[5] KandemirT, SchusterME, SenyshynA, et al.. The Haber-Bosch process revisited: on the real structure and stability of “ammonia iron” under working conditions. Angew Chem Int Ed, 2013, 52(48): 12723-12726

[6] PoolJA, LobkovskyE, ChirikPJ. Hydrogenation and cleavage of dinitrogen to ammonia with a zirconium complex. Nature, 2004, 427(6974): 527-530

[7] GambarottaS, ScottJ. Multimetallic cooperative activation of N₂. Angew Chem Int Ed, 2004, 43(40): 5298-5308

[8] LiC, WangT, GongJ. Alternative strategies toward sustainable ammonia synthesis. Trans Tianjin Univ, 2020, 26(2): 67-91

[9] ChenY, MaA, ChenL, et al.. Accelerating electrocatalytic nitrate reduction to ammonia via weakening of intermediate adsorption on Cu-based catalyst. Trans Tianjin Univ, 2024, 30(6): 488-497

[10] MaC, ZhangH, XiaJ, et al.. Screening of intermetallic compounds based on intermediate adsorption equilibrium for electrocatalytic nitrate reduction to ammonia. J Am Chem Soc, 2024, 146(29): 20069-20079

[11] ZhuX, MaC, WangY-C, et al.. Mott-Schottky contact synergistically boosts the electroreduction of nitrate to ammonia under low-nitrate concentration. Energy Environ Sci, 2024, 17(8): 2908-2920

[12] HanQ, WuC, JiaoH, et al.. Rational design of high-concentration Ti³⁺ in porous carbon-doped TiO₂ nanosheets for efficient photocatalytic ammonia synthesis. Adv Mater, 2021, 3392008180

[13] YeT-N, ParkS-W, LuY, et al.. Contribution of nitrogen vacancies to ammonia synthesis over metal nitride catalysts. J Am Chem Soc, 2020, 142(33): 14374-14383

[14] BoettcherSW. Introduction to green hydrogen. Chem Rev, 2024, 124(23): 13095-13098

[15] ChenH-Y, ChenS-Y, ReyesYIA, et al.. Promotion effects in ammonia synthesis over ruthenium catalysts: a review. EnergyChem, 2024, 66100140

[16] OoyaK, LiJ, FukuiK, et al.. Ruthenium catalysts promoted by lanthanide oxyhydrides with high hydride-ion mobility for low-temperature ammonia synthesis. Adv Energy Mater, 2021, 1142003723

[17] LiJ, JiangY, ZhangZ, et al.. Barium oxynitride electride as highly enhanced promotor for ruthenium catalyst in ammonia synthesis: comparative study with barium oxide. Adv Energy Mater, 2023, 13452302424

[18] KitanoM, InoueY, YamazakiY, et al.. Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store. Nat Chem, 2012, 4(11): 934-940

[19] KitanoM, KanbaraS, InoueY, et al.. Electride support boosts nitrogen dissociation over ruthenium catalyst and shifts the bottleneck in ammonia synthesis. Nat Commun, 2015, 616731

[20] YanP, GuoW, LiangZ, et al.. Highly efficient K-Fe/C catalysts derived from metal-organic frameworks towards ammonia synthesis. Nano Res, 2019, 12(9): 2341-2347

[21] WangZ, GongY, EvansML, et al.. Machine learning-accelerated discovery of A₂BC₂ ternary electrides with diverse anionic electron densities. J Am Chem Soc, 2023, 145(48): 26412-26424

[22] MaZ, ZhaoS, PeiX, et al.. New insights into the support morphology-dependent ammonia synthesis activity of Ru/CeO₂ catalysts. Catal Sci Technol, 2017, 7(1): 191-199

[23] NiwaY, AikaK-I. The Effect of lanthanide oxides as a support for ruthenium catalysts in ammonia synthesis. J Catal, 1996, 162(1): 138-142

[24] ZhaoH, YinJ, XiP. High-efficiency catalytic interface IrO_x/CeO₂ with adsorbate evolution mechanism boosts oxygen evolution reaction in acid media. Trans Tianjin Univ, 2023, 29(5): 395-405

[25] ErtlG. Primary steps in catalytic synthesis of ammonia. J Vac Sci Technol A, 1983, 1(2): 1247-1253

[26] HibbittsD, IglesiaE. Prevalence of bimolecular routes in the activation of diatomic molecules with strong chemical bonds (O₂, NO, CO, N₂) on catalytic surfaces. Acc Chem Res, 2015, 48(5): 1254-1262

[27] BêcheE, CharvinP, PerarnauD, et al.. Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CeTiO). Surf Interface Anal, 2008, 40(3–4): 264-267

[28] TomishigeK, SakaihoriT, IkedaY, et al.. A novel method of direct synthesis of dimethyl carbonate from methanol and carbon dioxide catalyzed by zirconia. Catal Lett, 1999, 58(4): 225-229

[29] ParkHR, PawarAU, PalU, et al.. Enhanced solar photoreduction of CO₂ to liquid fuel over rGO grafted NiO-CeO₂ heterostructure nanocomposite. Nano Energy, 2021, 79105483

[30] GongZ-J, LiY-R, WuH-L, et al.. Direct copolymerization of carbon dioxide and 1,4-butanediol enhanced by ceria nanorod catalyst. App Catal B Environ, 2020, 265118524

[31] SunW, ZhengL, WangY, et al.. Direct synthesis of dimethyl carbonate from CO₂ and methanol in dual supercritical phases over Y_xFe_1−xO_δ catalysts. J CO Util, 2022, 58101912

[32] WeberWH, HassKC, McbrideJR. Raman study of CeO₂: second-order scattering, lattice dynamics, and particle-size effects. Phys Rev B Condens Matter, 1993, 48(1): 178-185

[33] LiuJ, TangQ, ZhuY, et al.. Assisting Ni catalysis by CeO₂ with oxygen vacancy to optimize the hydrogen storage properties of MgH₂. J Mater Sci Technol, 2023, 159: 62-71

[34] HuF, ChenJ, PengY, et al.. Novel nanowire self-assembled hierarchical CeO₂ microspheres for low temperature toluene catalytic combustion. Chem Eng J, 2018, 331: 425-434

[35] FengZ, RenQ, PengR, et al.. Effect of CeO₂ morphologies on toluene catalytic combustion. Catal Today, 2019, 332: 177-182

[36] DongF, XiongT, SunY, et al.. Synergistic integration of thermocatalysis and photocatalysis on black defective (BiO)₂CO₃ microspheres. J Mater Chem A, 2015, 3(36): 18466-18474

[37] WuS, TanX, LeiJ, et al.. Ga-doped and Pt-loaded porous TiO₂–SiO₂ for photocatalytic nonoxidative coupling of methane. J Am Chem Soc, 2019, 141(16): 6592-6600

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