Rational design of single-atom catalysts for efficient hydrogenation of nitro compounds

Abstract

The catalytic reduction of nitro compounds to amines is crucial in the fine and bulk chemical industries. Single-atom catalysts (SACs), featuring high atomic utilization and unique unsaturated coordination structures, hold significant promise in this field and have garnered considerable attention in recent years. Despite notable advancements, their performance remains insufficient for industrial applications. Therefore, it is imperative to develop strategies to enhance their catalytic performance, particularly in terms of activity. This review comprehensively summarizes recent progress in the application of SACs for the hydrogenation of nitro compounds. Firstly, the synthesis and characterization of SACs are briefly discussed. Secondly, strategies to enhance the catalytic activity of SACs are highlighted, including the design of single-atom sites. This involves optimizing the metal center and its microenvironment to improve intrinsic activity, as well as increasing the loading and utilization efficiency of single-atom sites to enhance apparent activity. Key insights from the reviewed works are summarized. Third, the hydrogenation mechanism on some SACs is briefly discussed. Finally, the challenges and prospects of SAC applications in the hydrogenation of nitro compounds are discussed.

Keywords

Single-atom catalysts / nitro hydrogenation / designing strategies / catalytic activity / hydrogenation mechanisms

References

[1] Formenti D,Scharnagl FK.Reduction of nitro compounds using 3d-non-noble metal catalysts.Chem Rev2019;119:2611-80

[2] Ono N.The nitro group in organic synthesis. Weinheim: Wiley-VCH; 2001.

[3] Blaser H,Studer M.Selective catalytic hydrogenation of functionalized nitroarenes: an update.ChemCatChem2009;1:210-21

[4] Yu M,Wang L.Catalytic reduction of aromatic nitro compounds to phenylhydroxylamine and its derivatives.Molecules2024;29:4353 PMCID:PMC11433948

[5] Wang H,Liu Y,Lei M.First-Principles study on the mechanism of nitrobenzene reduction to aniline catalyzed by a N-doped carbon-supported cobalt single-atom catalyst.J Phys Chem C2021;125:19171-82

[6] Corma A.Chemoselective hydrogenation of nitro compounds with supported gold catalysts.Science2006;313:332-4

[7] Lin L,Gao R.A highly CO-tolerant atomically dispersed Pt catalyst for chemoselective hydrogenation.Nat Nanotechnol2019;14:354-61

[8] Gao R,Wang B,Sun M.Co based N, S co-doped carbon hybrids for catalytic hydrogenation: role of cobalt salt and doped S.Appl Catal A-Gen2019;579:99-105

[9] Gao R,Wang J.Pd/Fe₂O₃ with electronic coupling single-site Pd-Fe pair sites for low-temperature semihydrogenation of alkynes.J Am Chem Soc2022;144:573-81

[10] Liu F,Shi C.Avoiding Sabatier’s limitation on spatially correlated Pt-Mn atomic pair sites for oxygen electroreduction.J Am Chem Soc2023;145:25252-63

[11] Qiao B,Yang X.Single-atom catalysis of CO oxidation using Pt1/FeO_x.Nat Chem2011;3:634-41

[12] Yang XF,Qiao B,Liu J.Single-atom catalysts: a new frontier in heterogeneous catalysis.Acc Chem Res2013;46:1740-8

[13] Wang H,Pu M.Theoretical study on nitrobenzene hydrogenation by N-doped carbon-supported late transition metal single-atom catalysts.ACS Catal2022;12:11518-29

[14] Zhang L,Wang A.Selective hydrogenation over supported metal catalysts: from nanoparticles to single atoms.Chem Rev2020;120:683-733

[15] Greeley J.Alloy catalysts designed from first principles.Nat Mater2004;3:810-5

[16] Deng P,Liu F.Atomic insights into synergistic nitroarene hydrogenation over nanodiamond-supported Pt₁-Fe₁ dual-single-atom catalyst.Angew Chem Int Ed Engl2023;62:e202307853

[17] Macino M,Althahban SM.Tuning of catalytic sites in Pt/TiO₂ catalysts for the chemoselective hydrogenation of 3-nitrostyrene.Nat Catal2019;2:873-81

[18] Li X,Huang Y,Liu B.Supported noble-metal single atoms for heterogeneous catalysis.Adv Mater2019;31:e1902031

[19] Deelen TW, Hernández Mejía C, de Jong KP. Control of metal-support interactions in heterogeneous catalysts to enhance activity and selectivity.Nat Catal2019;2:955-70

[20] Xu D,Li J,Ma J.Atomically dispersed Co-N₄ sites anchored on N-doped carbon for aqueous phase transfer hydrogenation between nitroarenes and saturated N-heterocycles.Appl Catal B Environ2021;299:120681

[21] Liu J.Catalysis by supported single metal atoms.ACS Catal2017;7:34-59

[22] Xing L,Weng Y.Top-down synthetic strategies toward single atoms on the rise.Matter2022;5:788-807

[23] Chen R,Wang L.Nanoscale metal particle modified single-atom catalyst: synthesis, characterization, and application.Adv Mater2024;36:e2304713

[24] He T,Ni B.Zirconium-porphyrin-based metal-organic framework hollow nanotubes for immobilization of noble-metal single atoms.Angew Chem Int Ed Engl2018;57:3493-8

[25] Xi J,Xu Y,Bae JW.Single-atom catalysts: synthesis strategies, catalytic applications, and performance regulation of single-atom catalysts Adv Funct Mater 2021;31:2170081.

[26] Huang Y,Zou Z.Emerging strategies for the synthesis of correlated single atom catalysts.Adv Mater2025;37:e2312182

[27] Xue K,Long B.Single-atom catalysts supported on ordered porous materials: Synthetic strategies and applications.InfoMat2022;4:e12296

[28] Ding S,Pérez-ramírez J.Transforming energy with single-atom catalysts.Joule2019;3:2897-929

[29] Cheng N,Doyle-davis K.Single-atom catalysts: from design to application.Electrochem Energ Rev2019;2:539-73

[30] Li L,Lin X,Gong J.Theoretical insights into single-atom catalysts.Chem Soc Rev2020;49:8156-78

[31] Xue Z,Zhang H.Single-atom catalysts for photocatalytic energy conversion.Joule2022;6:92-133

[32] Xiong H,Wang Y.Thermally stable single-atom heterogeneous catalysts.Adv Mater2021;33:e2004319

[33] Singh B,Kute AD.Single-atom (iron-based) catalysts: synthesis and applications.Chem Rev2021;121:13620-97

[34] Ye Y,Gao L.CuO/CeO₂ catalysts prepared by modified impregnation method for ethyl acetate oxidation.Chem Eng J2023;471:144667

[35] Li Y,He H.In situ photodeposition of platinum clusters on a covalent organic framework for photocatalytic hydrogen production.Nat Commun2022;13:1355 PMCID:PMC8924255

[36] Zhang Z,Zhou L.The simplest construction of single-site catalysts by the synergism of micropore trapping and nitrogen anchoring.Nat Commun2019;10:1657 PMCID:PMC6458126

[37] Ji D,Li L.Atomically transition metals on self-supported porous carbon flake arrays as binder-free air cathode for wearable zinc-air batteries.Adv Mater2019;31:e1808267

[38] Sun G,Mu R.Breaking the scaling relationship via thermally stable Pt/Cu single atom alloys for catalytic dehydrogenation.Nat Commun2018;9:4454 PMCID:PMC6203812

[39] Zhang Z,Liu C.Electrochemical deposition as a universal route for fabricating single-atom catalysts.Nat Commun2020;11:1215 PMCID:PMC7058015

[40] Wenderich K.Methods, mechanism, and applications of photodeposition in photocatalysis: a review.Chem Rev2016;116:14587-619

[41] Oros-ruiz S,Guzmán C.Effect of gold particle size and deposition method on the photodegradation of 4-chlorophenol by Au/TiO₂.Top Catal2011;54:519-26

[42] Liu P,Qin R.Photochemical route for synthesizing atomically dispersed palladium catalysts.Science2016;352:797-801

[43] George SM.Atomic layer deposition: an overview.Chem Rev2010;110:111-31

[44] Libera J,Pellin M.Conformal ZnO coatings on high surface area silica gel using atomic layer deposition.Thin Solid Films2008;516:6158-66

[45] Elam JW,Mardilovich PP.Conformal coating on ultrahigh-aspect-ratio nanopores of anodic alumina by atomic layer deposition.Chem Mater2003;15:3507-17

[46] Lu J,Kung MC.Coking- and sintering-resistant palladium catalysts achieved through atomic layer deposition.Science2012;335:1205-8

[47] Yan H,Yi H.Single-atom Pd₁/graphene catalyst achieved by atomic layer deposition: remarkable performance in selective hydrogenation of 1,3-butadiene.J Am Chem Soc2015;137:10484-7

[48] Zwiener L,Brennecke D.Evolution of zincian malachite synthesis by low temperature co-precipitation and its catalytic impact on the methanol synthesis.Appl Catal B Environ2019;249:218-26

[49] Behrens M.Coprecipitation: an excellent tool for the synthesis of supported metal catalysts - from the understanding of the well known recipes to new materials.Catal Today2015;246:46-54

[50] Sun L,Su Y,Lin J.Ru₁/FeO_x single-atom catalyst with dual active sites for water gas shift reaction without methanation.Appl Catal B Environ2022;318:121841

[51] Peng J,Jia Z,Jiang H.Axial coordination regulation of MOF-based single-atom Ni catalysts by halogen atoms for enhanced CO₂ electroreduction.Nano Res2022;15:10063-9

[52] Qi H,Liu F.Highly selective and robust single-atom catalyst Ru₁/NC for reductive amination of aldehydes/ketones.Nat Commun2021;12:3295 PMCID:PMC8172939

[53] Deng D,Chen X.Iron encapsulated within pod-like carbon nanotubes for oxygen reduction reaction.Angew Chem2013;52:371-5.

[54] Yang J,Zhao C.In situ thermal atomization to convert supported nickel nanoparticles into surface-bound nickel single-atom catalysts.Angew Chem Int Ed Engl2018;57:14095-100

[55] Yao Y,Xie P.High temperature shockwave stabilized single atoms.Nat Nanotechnol2019;14:851-7

[56] Li R,Zhao Q.Cathodic corrosion as a facile and universal method for the preparation of supported metal single atoms.Nano Res2022;15:1838-44

[57] Deng D,Yu L.A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature.Sci Adv2015;1:e1500462 PMCID:PMC4672762

[58] Cui X,Wu Y.A graphene composite material with single cobalt active sites: a highly efficient counter electrode for dye-sensitized solar cells.Angew Chem Int Ed Engl2016;55:6708-12

[59] Khan K,Arif M.Laser-irradiated holey graphene-supported single-atom catalyst towards hydrogen evolution and oxygen reduction.Adv Energy Mater2021;11:2101619

[60] James SL,Bolm C.Mechanochemistry: opportunities for new and cleaner synthesis.Chem Soc Rev2012;41:413-47

[61] Yang J,Wang D.Electronic Metal-support interaction of single-atom catalysts and applications in electrocatalysis.Adv Mater2020;32:e2003300

[62] Ouyang R,Li WX.Atomistic theory of Ostwald ripening and disintegration of supported metal particles under reaction conditions.J Am Chem Soc2013;135:1760-71

[63] Xu H,Liu J.Entropy-stabilized single-atom Pd catalysts via high-entropy fluorite oxide supports.Nat Commun2020;11:3908 PMCID:PMC7413391

[64] Liu J,Zang L.Supported single-atom catalysts: synthesis, characterization, properties, and applications.Environ Chem Lett2018;16:477-505

[65] Wu M,Wang W.Electronic metal-support interaction modulation of single-atom electrocatalysts for rechargeable zinc-air batteries.Small Methods2022;6:e2100947

[66] Qi P,Djitcheu X,Liu H.Techniques for the characterization of single atom catalysts.RSC Adv2021;12:1216-27 PMCID:PMC8978979

[67] Li X,Zhang J,Liu B.In situ/operando techniques for characterization of single-atom catalysts.ACS Catal2019;9:2521-31

[68] Jiang J,Shen D.Utilizing molybdenum to tailor the electronic structure of iron through electron complementary effect for promoting oxygen reduction activity.Adv Funct Mater2025;35:2500065

[69] Guo W,Xie Q.Achieving pH-universal oxygen electrolysis via synergistic density and coordination tuning over biomass-derived Fe single-atom catalyst.Nat Commun2025;16:2920 PMCID:PMC11937382

[70] Zhang L,Lu F.Metal-saloph complexes pre-coordination for Fe single atom catalyst towards oxygen reduction reaction in rechargeable quasi-solid-state Zn-air battery.Appl Catal B Environ2025;370:125189

[71] Zhang S,Liao K.Boosting oxygen reduction reaction performance of Fe single-atom catalysts via precise control of the coordination environment.Adv Funct Mater2025;35:2425640

[72] Li S,Wang H.Single-atom photo-catalysts: synthesis, characterization, and applications.Nano Mater Sci2024;6:284-304

[73] Dai H,Zhu S,Zhou W.Regulating the Fe-N_x coordination structure of Fe single-atom catalysts for efficient catalytic degradation of methylparaben.Chem Eng J2025;507:160462

[74] Lan L,Pei Y.High-density accessible iron single-atom catalyst for durable and temperature-adaptive laminated zinc-air batteries.Adv Mater2025;37:e2417711

[75] Wang C,Ren H.Stabilizing Ni single-atom sites through introducing low-valence Ni Species for durably efficient electrochemical CO₂ reduction.Appl Catal B Environ2025;368:125151

[76] Zhang ZQ,Bai CW,Wang J.Surface-hydroxylated single-atom catalyst with an isolated Co-O-Zn configuration achieves high selectivity in regulating active species.Nat Commun2025;16:2376 PMCID:PMC11897339

[77] Gallenkamp C,Proppe J.Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction.Int J Quantum Chem2021;121:e26394

[78] Bates JS,Hall MN.Chemical kinetic method for active-site quantification in Fe-N-C catalysts and correlation with molecular probe and spectroscopic site-counting methods.J Am Chem Soc2023;145:26222-37

[79] Wu B,Li L.Integrating PtCo intermetallic with highly graphitized carbon toward durable oxygen electroreduction in proton exchange membrane fuel cells.Adv Mater2025;37:e2500096

[80] Zhao J,Avdoshenko SM,Eckert J.Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges.Proc Natl Acad Sci U S A2014;111:15641-6 PMCID:PMC4226114

[81] Guo X,Liu W.Oxidative dehydrogenation on nanocarbon: revealing the catalytic mechanism using model catalysts.ACS Catal2017;7:1424-7

[82] Pan L,Lu F.Single-atom or dual-atom in TiO₂ nanosheet: which is the better choice for electrocatalytic urea synthesis?.Angew Chem Int Ed Engl2023;62:e202216835

[83] Li X,Ren X,Huang Y.Microenvironment modulation of single-atom catalysts and their roles in electrochemical energy conversion.Sci Adv2020;6 PMCID:PMC7531890

[84] Wei H,Wang A.FeO_x-supported platinum single-atom and pseudo-single-atom catalysts for chemoselective hydrogenation of functionalized nitroarenes.Nat Commun2014;5:5634

[85] Ren Y,Zhang L.Unraveling the coordination structure-performance relationship in Pt₁/Fe₂O₃ single-atom catalyst.Nat Commun2019;10:4500 PMCID:PMC6776505

[86] Vilé G,Nachtegaal M.A stable single-site palladium catalyst for hydrogenations.Angew Chem Int Ed Engl2015;54:11265-9

[87] Li J,Tong L.Atomic Pd on graphdiyne/graphene heterostructure as efficient catalyst for aromatic nitroreduction.Adv Funct Mater2019;29:1905423

[88] Dasgupta A,Gong R.Atomic control of active-site ensembles in ordered alloys to enhance hydrogenation selectivity.Nat Chem2022;14:523-9

[89] Yang J,Zhang L.Hydrogenation reactions with synergistic catalysis of Pd single atoms and nanoparticles under near-ambient conditions.Chemistry2023;29:e202203108

[90] Shen X.Discrete Au₁(0) stabilized by 15-crown-5 for high-efficiency catalytic reduction of nitrophenol and nitroaniline.Catalysts2023;13:776

[91] Fu H,Yang G.Highly dispersed rhodium atoms supported on defect-rich Co(OH)₂ for the chemoselective hydrogenation of nitroarenes.New J Chem2022;46:1158-67

[92] Wang W,Qi H.MIL-53 (Al) derived single-atom Rh catalyst for the selective hydrogenation of m-chloronitrobenzene into m-chloroaniline.Chinese J Catal2021;42:824-34

[93] Wu B,Yang R.Ru single atoms for efficient chemoselective hydrogenation of nitrobenzene to azoxybenzene.Green Chem2021;23:4753-61

[94] Ma Y,Zhou Y.High-density and thermally stable palladium single-atom catalysts for chemoselective hydrogenations.Angew Chem Int Ed Engl2020;59:21613-9

[95] Campbell CT.Physics. The active site in nanoparticle gold catalysis.Science2004;306:234-5

[96] Sun Q,Zhang T.Inside cover: zeolite-encaged single-atom rhodium catalysts: highlyefficient hydrogen generation and shape-selective tandem hydrogenation of nitroarenes.Angew Chem Int Ed2019;58:18300

[97] Li H,Fan Y.Enhancing hydride formation and transfer for catalytic hydrogenation via electron-deficient single-atom silver.J Colloid Interface Sci2025;682:751-9

[98] Junge K,Shaikh N.Iron-catalyzed selective reduction of nitroarenes to anilines using organosilanes.Chem Commun (Camb)2010;46:1769-71

[99] Liu W,Yan W.Single-atom dispersed Co-N-C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes.Chem Sci2016;7:5758-64 PMCID:PMC6021980

[100] Zhou P,Wang F,Lv K.High performance of a cobalt-nitrogen complex for the reduction and reductive coupling of nitro compounds into amines and their derivatives.Sci Adv2017;3:e1601945 PMCID:PMC5315448

[101] Cheng T,Peng F,Zhang B.Identifying active sites of CoNC/CNT from pyrolysis of molecularly defined complexes for oxidative esterification and hydrogenation reactions.Catal Sci Technol2016;6:1007-15

[102] Wei X,Li C.High-density atomically dispersed CoN_x catalysts supported on nitrogen-doped mesoporous carbon materials for efficient hydrogenation of nitro compounds.Catal Today2022;405-406:92-100

[103] Sheng Y,Yue S,Zou X.In situ synthesized silica-supported Co@N-Doped carbon as highly efficient and reusable catalysts for selective reduction of halogenated nitroaromatics.ChemCatChem2020;12:4632-41

[104] Li M,Jiang Q.Origin of the activity of Co-N-C catalysts for chemoselective hydrogenation of nitroarenes.ACS Catal2021;11:3026-39

[105] Liu X,Meng J.Single-atom cobalt catalysts for chemoselective hydrogenation of nitroarenes to anilines.Chin Chem Lett2023;34:108745

[106] Li AY,Feng J.From haemoglobin to single-site hydrogenation catalyst.Green Chem2022;24:7574-83

[107] Zhang T,Jiang L.Selective transfer hydrogenation coupling of nitroaromatics to azoxy/azo compounds by electron-enriched single Ni-N₄ sites on mesoporous N-doped carbon.Chem Eng J2022;443:136416

[108] Liang J,Wu J.Anchoring copper single atoms on porous boron nitride nanofiber to boost selective reduction of nitroaromatics.ACS Nano2022;16:4152-61

[109] Yang F,Liu W.Atomically dispersed Ni as the active site towards selective hydrogenation of nitroarenes.Green Chem2019;21:704-11

[110] Liu W,Qi H.A durable nickel single-atom catalyst for hydrogenation reactions and cellulose valorization under harsh conditions.Angew Chem Int Ed Engl2018;57:7071-5

[111] Qin L,Lai C.Highly efficient reduction of nitrophenols by Fe-N-C single-atom catalyst: performance and mechanism insights.J Environl Chem Eng2023;11:110278

[112] Cheong WC,Zhang J.Isolated iron single-atomic site-catalyzed chemoselective transfer hydrogenation of nitroarenes to arylamines.ACS Appl Mater Interfaces2019;11:33819-24

[113] Lu G,Lin Y.Single-atomic-site iron on N-doped carbon for chemoselective reduction of nitroarenes.Nano Res2022;15:603-11

[114] Song Y,Feng B.Coordination number engineering of Zn single-atom sites for enhanced transfer hydrogenation performance.Chem Eng J2023;465:142920

[115] Yang X,Li Y.Do we achieve “1 + 1 > 2” in dual-atom or dual-single-atom catalysts?.Coord Chem Rev2024;516:215961

[116] Zhou D,Wang L.The d-p electron coupling over the unsaturated oxygen coordinated CuCo alloy surface for enhanced N-heteroarenes hydrogenation under mild conditions.J Energy Chem2025;106:671-80

[117] Yang Y,Wu G.Electronic structure tuning in Cu-Co dual single atom catalysts for enhanced COOH* spillover and electrocalytic CO₂ reduction activity.Angew Chem Int Ed Engl2025;64:e202504423

[118] Liu H,Yang D.Pd-Mn/NC dual single-atomic sites with hollow mesopores for the highly efficient semihydrogenation of phenylacetylene.J Am Chem Soc2024;146:2132-40

[119] Park D,Han J.Insights into the synergy effect in dual single-atom catalysts on defective CeO₂ under CO₂ hydrogenation.Appl Catal B Environ2025;365:124987

[120] Gong L,Xing X.Coupling Fe-Co atomic pair to promote the selective reduction of nitroaromatics under mild conditions.Sci Total Environ2024;912:169161

[121] Mu Y,Zhang J,Zhang Y.Single-atom catalysts: advances and challenges in metal-support interactions for enhanced electrocatalysis.Electrochem Energy Rev2022;5:145-86

[122] Lin L,Chen W.Single atom catalysts by atomic diffusion strategy.Nano Res2021;14:4398-416

[123] Lou Y,Liu J.Nanocarbon-edge-anchored high-density Pt atoms for 3-nitrostyrene hydrogenation: strong metal-carbon interaction.iScience2019;13:190-8 PMCID:PMC6409412

[124] Zhang G,Wang X,Wang L.Co,N-codoped porous carbon-supported Co_y ZnS with superior activity for nitroarene hydrogenation.ACS Sustain Chem Eng2020;8:6118-26

[125] Wei X,Zhou M,Wu WD.Solid-state nanocasting synthesis of ordered mesoporous CoN_x-carbon catalysts for highly efficient hydrogenation of nitro compounds.Nanoscale2018;10:16839-47

[126] Li H,Liu J.Cobalt single atoms anchored on N-doped ultrathin carbon nanosheets for selective transfer hydrogenation of nitroarenes.Sci China Mater2019;62:1306-14

[127] Li J,Liu M.Self-template construction of high-performance Co, N-decorated carbon nanotubes from a novel cobalt dicyandiamide molecule.ChemCatChem2021;13:2609-17

[128] Yan X,Zhang F.Stable single-atom platinum catalyst trapped in carbon onion graphitic shells for improved chemoselective hydrogenation of nitroarenes.Carbon2019;143:378-84

[129] Gu Y,Wang L.A “competitive occupancy” strategy toward Co-N₄ single-atom catalysts embedded in 2D TiN/rGO sheets for highly efficient and stable aromatic nitroreduction.J Mater Chem A2020;8:4807-15

[130] Yan H,Guo N.Atomic engineering of high-density isolated Co atoms on graphene with proximal-atom controlled reaction selectivity.Nat Commun2018;9:3197 PMCID:PMC6107637

[131] Xi J,Wang D.Confined-interface-directed synthesis of Palladium single-atom catalysts on graphene/amorphous carbon.Appl Catal B Environ2018;225:291-7

[132] Ma T,Zhao Q.Template-oriented synthesis of Fe-N-codoped graphene nanoshells derived from petroleum pitch for efficient nitroaromatics reduction.Ind Eng Chem Res2020;59:129-36

[133] Wang C,Zhou R,Hou Z.Structure-activity relationship for the catalytic hydrogenation of nitrobenzene by single platinum atoms supported on nitrogen-doped carbon.ACS Appl Nano Mater2022;5:13601-11

[134] Chen J,Zhao J.A highly active non-precious metal catalyst based on Fe-N-C@CNTs for nitroarene reduction.RSC Adv2016;6:96203-9

[135] Jones J,DeLaRiva AT.Thermally stable single-atom platinum-on-ceria catalysts via atom trapping.Science2016;353:150-4

[136] Wang C,Wang Z.Insight into single-atom-induced unconventional size dependence over CeO₂-supported Pt catalysts.Chem2020;6:752-65

[137] Han B,Huang Y.Strong metal-support interactions between Pt single atoms and TiO₂.Angew Chem Int Ed Engl2020;59:11824-9

[138] Ye TN,Li J.Stable single platinum atoms trapped in sub-nanometer cavities in 12CaO·7Al₂O₃ for chemoselective hydrogenation of nitroarenes.Nat Commun2020;11:1020 PMCID:PMC7039943

[139] Li Z,Dong X.Strong electronic interaction of indium oxide with palladium single atoms induced by quenching toward enhanced hydrogenation of nitrobenzene.Appl Catal B Environ2022;313:121462

[140] Shi X,Shang X,Ding W.High performance and active sites of a ceria-supported palladium catalyst for solvent-free chemoselective hydrogenation of nitroarenes.ChemCatChem2017;9:3743-51

[141] Wang J,Xu X.Oxygen vacancy-rich Ni-CeO₂ heterojunction catalyst for hydrogenating halogenated nitroarenes with high activity and selectivity.ACS Appl Mater Interfaces2023;15:8149-56

[142] Liu R,Yu C,Liu JF.Atomic-level-designed catalytically active palladium atoms on ultrathin gold nanowires.Adv Mater2017;29

[143] Ji P,Lin Z.Single-site cobalt catalysts at new Zr₁₂(μ₃-O)₈(μ₃)-OH)₈(μ₂-OH)₆ metal-organic framework nodes for highly active hydrogenation of nitroarenes, nitriles, and isocyanides.J Am Chem Soc2017;139:7004-11

[144] Antil N,Akhtar N.Aluminum metal-organic framework-ligated single-site nickel(II)-hydride for heterogeneous chemoselective catalysis.ACS Catal2021;11:3943-57

[145] Sun X,Oar-arteta L.Metal-organic framework mediated cobalt/nitrogen-doped carbon hybrids as efficient and chemoselective catalysts for the hydrogenation of nitroarenes.ChemCatChem2017;9:1854-62

[146] Zhang M,Zhao H.Pd anchored on a phytic acid/thiourea polymer as a highly active and stable catalyst for the reduction of nitroarene.ACS Appl Mater Interfaces2021;13:19904-14

[147] He J,Li Z.Strategic defect engineering of metal-organic frameworks for optimizing the fabrication of single-atom catalysts.Adv Funct Mater2021;31:2103597

[148] Peng Y,Zhao S.Pt single atoms embedded in the surface of Ni nanocrystals as highly active catalysts for selective hydrogenation of nitro compounds.Nano Lett2018;18:3785-91

[149] Chugh V,Chang WC.An adaptive rhodium catalyst to control the hydrogenation network of nitroarenes.Angew Chem Int Ed Engl2022;61:e202205515 PMCID:PMC9544374

[150] Zhang H,Sun Q,Ji H.Boosting hydrogenation properties of Pt single-atom catalysts via tailoring the electronic structures by coordination number regulation.Chem Eng J2023;455:140808

[151] Zhao X,Zhang G.Breaking the trade-off between CO tolerance and intrinsic activity in hydrogenation on metal oxide-supported noble metal single atoms through coordination environment engineering.ACS Catal2024;14:15325-35

[152] Feng B,Cai Q.Construction of isolated Ni sites on nitrogen-doped hollow carbon spheres with Ni-N₃ configuration for enhanced reduction of nitroarenes.Nano Res2022;15:6001-9

[153] Wang L,Xu M.Boosting activity and stability of metal single-atom catalysts via regulation of coordination number and local composition.J Am Chem Soc2021;143:18854-8

[154] Tian S,Xu Q.Single-atom Fe with Fe₁N₃ structure showing superior performances for both hydrogenation and transfer hydrogenation of nitrobenzene.Sci China Mater2021;64:642-50

[155] Li X,Wang J,Li G.Highly efficient N-doped carbon supported FeS_x-Fe₂O₃ catalyst for hydrogenation of nitroarenes via pyrolysis of sulfurized N,Fe-containing MOFs.Appl Organomet Chem2021;35:e6294

[156] Jin H,Cui P.Unprecedentedly high activity and selectivity for hydrogenation of nitroarenes with single atomic Co₁-N₃P₁ sites.Nat Commun2022;13:723 PMCID:PMC8821636

[157] Cao F,Zhao Q.Precisely manipulating the local coordination of cobalt single-atom catalyst boosts selective hydrogenation of nitroarenes.Appl Catal B Environ2024;346:123762

[158] Zhang G,Wang X,Liu Y.Atomically dispersed Co-S-N active sites anchored on hierarchically porous carbon for efficient catalytic hydrogenation of nitro compounds.ACS Catal2022;12:5786-94

[159] Zhao Q,Wang L.A core-shell confinement strategy towards single-atom Fe-N/S-C bifunctional catalyst for selective nitroarene reduction and olefin epoxidation.J Alloy Compd2025;1012:178488

[160] Tang F,Wang L,Liu Y.Unsymmetrically N, S-coordinated single-atom cobalt with electron redistribution for catalytic hydrogenation of quinolines.J Catal2022;414:101-8

[161] Chen G,Gong W.Precisely tailoring the second coordination sphere of a cobalt single-atom catalyst for selective hydrogenation of halogenated nitroarenes.Angew Chem Int Ed Engl2025;64:e202421277

[162] Duan Y,Ling Y.Regulating second-shell coordination in cobalt single-atom catalysts toward highly selective hydrogenation.ACS Nano2024;18:21326-35

[163] Wei H,Wang A.Remarkable effect of alkalis on the chemoselective hydrogenation of functionalized nitroarenes over high-loading Pt/FeO_x catalysts.Chem Sci2017;8:5126-31 PMCID:PMC5615215

[164] Iihama S,Komatsu T.Efficient catalytic system for chemoselective hydrogenation of halonitrobenzene to haloaniline using PtZn intermetallic compound.ACS Catal2016;6:742-6

[165] Zhang B,Zhang J,De S.Stabilizing a platinum1 single-atom catalyst on supported phosphomolybdic acid without compromising hydrogenation activity.Angew Chem Int Ed Engl2016;55:8319-23

[166] Zhang F,Liu P.Ultra-high loading single CoN₃ sites in N-doped graphene-like carbon for efficient transfer hydrogenation of nitroaromatics.J Catal2021;400:40-9

[167] Lin Y,Li Y.Highly efficient and anti-poisoning single-atom cobalt catalyst for selective hydrogenation of nitroarenes.Nano Res2022;15:10006-13

[168] Wang C,Han Y,Wang L.Carbon nanotube-supported Co-N-C with enriched mesopores for hydrogenation of nitro compounds.J Catal2025;447:116152

[169] Guo M,Gao ML.Single-atom Pt loaded on MOF-derived porous TiO₂ with maxim-ized Pt atom utilization for selective hydrogenation of halonitro-benzene.Angew Chem Int Ed Engl2025;64:e202418964

[170] Cao F,Tan X.A pre-coordinated strategy precisely tailors the coordination structure of single-atom sites toward efficient catalysis.Adv Funct Mater2025;35:2423398

[171] Sun X,Osadchii D,Kapteijn F.Single cobalt sites in mesoporous N-doped carbon matrix for selective catalytic hydrogenation of nitroarenes.J Catal2018;357:20-8

[172] Lian L,Zhao X,Wang L.Protein-metal ion networks coated carbon matrix as a precursor: to construct carbon-supported Mo-based catalysts with highly exposed active sites for hydrogenation of nitro compounds.New J Chem2024;48:8331-7

[173] Chen R,Dang J.Shedding light on the reversible deactivation of carbon-supported single-atom catalysts in hydrogenation reaction.Nano Res2024;17:4807-14

[174] Huang H,Zhao Q.An in-situ etching strategy toward fully exposed Fe-N₅ active sites for boosted nitroaromatic reduction.Appl Surf Sci2025;689:162592

[175] Gong X,Zhang Q.Cobalt single atoms supported on monolithic carbon with a hollow-on-hollow architecture for efficient transfer hydrogenations.Nano Res2023;16:11358-65

[176] Huang R,Liu J.Integration of metal single atoms on hierarchical porous nitrogen-doped carbon for highly efficient hydrogenation of large-sized molecules in the pharmaceutical industry.ACS Appl Mater Interfaces2020;12:17651-8

[177] Haber F.Über stufenweise Reduktion des Nitrobenzols mit begrenztem Kathodenpotential.Zeitschrift für Elektrochemie1898;4:506-14. (in German)

[178] Millán R,Boronat M.A new molecular pathway allows the chemoselective reduction of nitroaromatics on non-noble metal catalysts.J Catal2018;364:19-30

[179] Gelder EA,Lok CM.The hydrogenation of nitrobenzene to aniline: a new mechanism.Chem Commun (Camb)2005;:522-4

[180] Corma A,Serna P.A different reaction pathway for the reduction of aromatic nitro compounds on gold catalysts.Angew Chem Int Ed Engl2007;46:7266-9

[181] Yu M,Li K,Wang L.Ni nanoparticles decorated Ni-N-C catalyst: dual-site synergy for enhanced catalytic hydrogenation.AIChE J2025;71:e18830

[182] He T,Zhang L.Single Pt atom decorated graphitic carbon nitride as an efficient photocatalyst for the hydrogenation of nitrobenzene into aniline.Nano Res2019;12:1817-23

[183] Wang H,Du J,Lei M.First principles study on the mechanism of nitrobenzene hydrogenation by a Ni₁/CeO_2-x(111) single-atom catalyst.J Phys Chem C2023;127:16880-90