Electrocatalytically Activating and Reducing N2 Molecule by Tuning Activity of Local Hydrogen Radical

Decarbonizing N₂ conversion is particularly challenging, but essential for sustainable development of industry and agriculture. Herein, we achieve electrocatalytic activation/reduction of N₂ on X/Fe−N−C (X=Pd, Ir and Pt) dual-atom catalysts under ambient condition. We provide solid experimental evidence that local hydrogen radical (H*) generated on the X site of the X/Fe−N−C catalysts can participate in the activation/reduction of N₂ adsorbed on the Fe site. More importantly, we reveal that the reactivity of X/Fe−N−C catalysts for N₂ activation/reduction can be well adjusted by the activity of H* generated on the X site, i.e., the interaction between the X−H bond. Specifically, X/Fe−N−C catalyst with the weakest X−H bonding exhibits the highest H* activity, which is beneficial to the subsequent cleavage of X−H bond for N₂ hydrogenation. With the most active H*, the Pd/Fe dual-atom site promotes the turnover frequency of N₂ reduction by up to 10 times compared with the pristine Fe site.     

One-Step Preparation of Fe/N/C Single-Atom Catalysts Containing Fe−N4 Sites from an Iron Complex Precursor with 5,6,7,8-Tetraphenyl-1,12-Diazatriphenylene Ligands

Fe/N/C single-atom catalysts containing Fe−N_x sites prepared by pyrolysis are promising cathode materials for fuel cells and metal-air batteries due to their high oxygen reduction reaction (ORR) activities. We have developed iron complexes containing N2- or N3-chelating coordination structures with preorganized aromatic rings in a 1,12-diazatriphenylene framework tethering bromo substituents as precursors to precisely construct Fe−N₄ sites in an Fe/N/C catalyst. One-step pyrolysis of the iron complex with carbon black forms atomically dispersed Fe−N₄ sites without iron aggregates. X-ray absorption spectroscopy (XAS) and electrochemical measurements revealed that the iron complex with N3-coordination is more effectively converted to Fe−N₄ sites catalyzing ORR with a TOF value of 0.21 e site⁻¹ s⁻¹ at 0.8 V vs. RHE. This indicates that the formation of Fe−N₄ sites is controlled by precise tuning of the chemical structure of the iron complex precursor.     

Rational Synthesis of Iron/Nitrogen-Doped Carbon Catalyst through a Spatial Isolation Strategy for Efficient Oxygen Reduction in Acidic and Alkaline Media

It remains challenging to rationally synthesize iron/nitrogen-doped carbon (Fe/N-C) catalysts with rich Fe−N_x atomic active sites for improved oxygen reduction reaction (ORR) electrocatalysis. A highly efficient Fe/N-C catalyst, which has been synthesized through a spatial isolation strategy, is reported. Derived from bioinspired polydopamine (PDA)-based hybrid microsphere precursors, it is a multifunctional carrier that loads atomically dispersed Fe³⁺/Zn²⁺ ions through coordination interactions and N-rich melamine through electrostatic attraction and covalent bonding. The Zn²⁺ ions and melamine in the precursor efficiently isolate Fe³⁺ atoms upon pyrolysis to form rich Fe−N_x atomic active sites, and generate abundant micropores during high-temperature treatment; as a consequence, the resultant Fe-N/C catalyst contains rich catalytically active Fe−N_x sites and a hierarchical porous structure. The catalyst exhibits improved ORR activity that is superior to and close to that of Pt/C in alkaline and acidic solutions, respectively.     

Ni/Fe物质的量的比对Ni-Fe催化剂表面性质和二硝基甲苯加氢活性的影响

采用Fe粉置换氯化镍溶液中的Ni²⁺制备了Ni-Fe催化剂, 并应用于催化二硝基甲苯加氢合成甲苯二胺的反应中。运用XRD、低温氮吸附-脱附、H₂-TPD、XPS和TEM等技术手段对不同Ni/Fe物质的量的比(n_Ni/n_Fe)下催化剂进行了表征。结果表明, n_Ni/n_Fe对Ni-Fe催化剂表面性质影响显著。当n_Ni/n_Fe为1:4时, Fe抑制Ni氧化的作用达到最大, Ni-Fe催化剂化学氢吸附量和活性物种Ni的分散度分别达到了0.16 mmol·g^-1和23%, 催化剂性能得到较大的提升。在优化的催化剂制备条件下, DNT(二硝基甲苯)的转化率和TDA(甲苯二胺)的选择性分别达到了~100%和99%。另外, 对Ni-Zn漆原镍(Urushibara Ni)催化剂和Ni-Fe催化剂催化DNT加氢反应进程进行了研究, 发现它们有相同的加氢中间产物, 但反应不同阶段的催化速率存在差异。     

A study on the reduction behavior of silica supported iron and platinum-iron catalysts

The reduction behavior of silica supported iron and platinum-iron catalysts were studied by combinedin situ temperature programmed reduction (TPR)-M?ssbauer Spectroscopy (MBS). The results indicated that the TPR profiles of the supported Fe catalysts were different from that of bulk α-Fe₂O₃. There existed an interaction between the Pt and Fe metals and the SiO₂ support for the Pt−Fe/SiO₂ catalyst. On the supported iron-containing catalysts, the Fe³⁺ species were highly dispersed on the SiO₂ supported before reduction. No Fe⁰ and Fe²⁺ in octahedral vacancy were found in the reduction of SiO₂ supported iron-containing catalysts. Addition of Pt to the Fe/SiO₂ catalyst could promote the reduction of the iron species.     

Boosting the Proton-coupled Electron Transfer via Fe−P Atomic Pair for Enhanced Electrochemical CO2 Reduction

Single-atom catalysts exhibit superior CO₂-to-CO catalytic activity, but poor kinetics of proton-coupled electron transfer (PCET) steps still limit the overall performance toward the industrial scale. Here, we constructed a Fe−P atom paired catalyst onto nitrogen doped graphitic layer (Fe₁/PNG) to accelerate PCET step. Fe₁/PNG delivers an industrial CO current of 1 A with FE_CO over 90 % at 2.5 V in a membrane-electrode assembly, overperforming the CO current of Fe₁/NG by more than 300 %. We also decrypted the synergistic effects of the P atom in the Fe−P atom pair using operando techniques and density functional theory, revealing that the P atom provides additional adsorption sites for accelerating water dissociation, boosting the hydrogenation of CO₂, and enhancing the activity of CO₂ reduction. This atom-pair catalytic strategy can modulate multiple reactants and intermediates to break through the inherent limitations of single-atom catalysts.     

Ni/Fe物质的量的比对Ni-Fe催化剂表面性质和二硝基甲苯加氢活性的影响

采用Fe粉置换氯化镍溶液中的Ni²⁺制备了Ni-Fe催化剂,并应用于催化二硝基甲苯加氢合成甲苯二胺的反应中。运用XRD、低温氮吸附-脱附、H₂-TPD、XPS和TEM等技术手段对不同Ni/Fe物质的量的比(n_Ni/n_Fe)下催化剂进行了表征。结果表明,n_Ni/n_Fe对Ni-Fe催化剂表面性质影响显著。当n_Ni/n_Fe为1:4时,Fe抑制Ni氧化的作用达到最大,Ni-Fe催化剂化学氢吸附量和活性物种Ni的分散度分别达到了0.16 mmol·g^-1和23%,催化剂性能得到较大的提升。在优化的催化剂制备条件下,DNT(二硝基甲苯)的转化率和TDA(甲苯二胺)的选择性分别达到了~100%和99%。另外,对Ni-Zn漆原镍(Urushibara Ni)催化剂和Ni-Fe催化剂催化DNT加氢反应进程进行了研究,发现它们有相同的加氢中间产物,但反应不同阶段的催化速率存在差异。     

Boosting Benzene Oxidation with a Spin-State-Controlled Nuclearity Effect on Iron Sub-Nanocatalysts

A fundamental understanding of the nature of nuclearity effects is important for the rational design of superior sub-nanocatalysts with low nuclearity, but remains a long-standing challenge. Using atomic layer deposition, we precisely synthesized Fe sub-nanocatalysts with tunable nuclearity (Fe₁–Fe₄) anchored on N,O-co-doped carbon nanorods (NOC). The electronic properties and spin configuration of the Fe sub-nanocatalysts were nuclearity dependent and dominated the H₂O₂ activation modes and adsorption strength of active O species on Fe sites toward C−H oxidation. The Fe₁-NOC single atom catalyst exhibits state-of-the-art activity for benzene oxidation to phenol, which is ascribed to its unique coordination environment (Fe₁N₂O₃) and medium spin state (t_2g⁴e_g¹); turnover frequencies of 407 h⁻¹ at 25 °C and 1869 h⁻¹ at 60 °C were obtained, which is 3.4, 5.7, and 13.6 times higher than those of Fe dimer, trimer, and tetramer catalysts, respectively.     

Single-Atom or Dual-Atom in TiO2 Nanosheet: Which is the Better Choice for Electrocatalytic Urea Synthesis?

As rising star materials, single-atom and dual-atom catalysts have been widely reported in the electro-catalysis area. To answer the key question: single-atom and dual-atom catalysts, which is better for electrocatalytic urea synthesis? we design two types of catalysts via a vacancy-anchorage strategy: single-atom Pd₁−TiO₂ and dual-atom Pd₁Cu₁−TiO₂ nanosheets. An ultrahigh urea activity of 166.67 mol_urea mol_Pd⁻¹ h¹ with the corresponding 22.54 % Faradaic efficiency at −0.5 V vs. reversible hydrogen electrode (RHE) is achieved over Pd₁Cu₁−TiO₂, which is much higher than that of Pd₁−TiO₂. Various characterization including an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations demonstrate that dual-atom Pd₁Cu₁ site in Pd₁Cu₁−TiO₂ is more favorable for producing urea, which experiences a C−N coupling pathway with a lower energy barrier compared with Pd₁ in Pd₁−TiO₂.     

Understanding Synergistic Catalysis on Cu-Se Dual Atom Sites via Operando X-ray Absorption Spectroscopy in Oxygen Reduction Reaction

The construction and understanding of synergy in well-defined dual-atom active sites is an available avenue to promote multistep tandem catalytic reactions. Herein, we construct a dual-hetero-atom catalyst that comprises adjacent Cu-N₄ and Se-C₃ active sites for efficient oxygen reduction reaction (ORR) activity. Operando X-ray absorption spectroscopy coupled with theoretical calculations provide in-depth insights into this dual-atom synergy mechanism for ORR under realistic device operation conditions. The heteroatom Se modulator can efficiently polarize the charge distribution around symmetrical Cu-N₄ moieties, and serve as synergistic site to facilitate the second oxygen reduction step simultaneously, in which the key OOH*-(Cu₁-N₄) transforms to O*-(Se₁-C₂) intermediate on the dual-atom sites. Therefore, this designed catalyst achieves satisfied alkaline ORR activity with a half-wave potential of 0.905 V vs. RHE and a maximum power density of 206.5 mW cm⁻² in Zn-air battery.     

57Fe 穆斯堡尔谱研究 Ir-Fe 催化剂用于 CO 选择氧化反应

 采用不同浸渍顺序制备了三种 Ir-Fe 催化剂, 其 CO 选择氧化 (PROX) 反应活性差别很大, 其中共浸渍的 Ir-Fe 催化剂活性最高. 吸附量热研究表明, 三种催化剂的 H2 和 CO 吸附存在差别. 通过对三种催化剂还原后、再氧化和反应后准原位 57Fe 穆斯堡尔谱的研究, 得到各种 Fe 物种信息. 结果表明, 三种制备方法影响催化剂中 Ir-Fe 相互作用强度, 导致催化剂中 Fe 物种的氧化还原性能不同. 催化剂中 Fe²⁺(a) 的含量与 CO 转化率呈正比关系, Fe²⁺(a) 是 PROX 反应过程中活化氧的活性中心. 浸渍顺序改变了 Ir-Fe 间相互作用强度, 从而改变 Fe²⁺(a) 物种含量, 影响 PROX 反应活性. Ir-Fe 间的相互作用可以稳定活化氧的 Fe²⁺(a) 物种, 为今后研究金属-金属间的相互作用提供借鉴.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment-benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III-OH-Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III-OH-Pt interfaces. In situ IR, X-ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the -NO₂ group during hydrogenation catalysis. Benefitting from Fe^III-OH-Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

K6[Fe8.27(HPO3)12]: a new mixed‐valence iron phosphite

The title compound, hexapotassium octairon(II,III) dodecaphosphonate, exhibiting a two‐dimensional structure, is a new mixed alkali/3d metal phosphite. It crystallizes in the space group Rm, with two crystallographically independent Fe atoms occupying sites of m (Fe1) and 3m (Fe2) symmetry. The Fe2 site is fully occupied, whereas the Fe1 site presents an occupancy factor of 0.757 (3). The three independent O atoms, one of which is disordered, are situated on a mirror and all other atoms are located on special positions with 3m symmetry. Layers of formula [Fe₃(HPO₃)₄]²⁻ are observed in the structure, formed by linear Fe₃O₁₂ trimer units, which contain face‐sharing FeO₆ octahedra interconnected by (HPO₃)²⁻ phosphite oxoanions. The partial occupancy of the Fe1 site might be described by the formation of two [Fe(HPO₃)₂]⁻ layers derived from the [Fe₃(HPO₃)₄]²⁻ layer when the Fe1 atom is absent. Fe²⁺ is localized at the Fe1 and Fe2 sites of the [Fe₃(HPO₃)₄]²⁻ sheets, whereas Fe³⁺ is found at the Fe2 sites of the [Fe(HPO₃)₂]⁻ sheets, according to bond‐valence calculations. The K⁺ cations are located in the interlayer spaces, between the [Fe₃(HPO₃)₄]²⁻ layers, and between the [Fe₃(HPO₃)₄]²⁻ and [Fe(HPO₃)₂]⁻ layers.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment‐benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III‐OH‐Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III‐OH‐Pt interfaces. In situ IR, X‐ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the ‐NO₂ group during hydrogenation catalysis. Benefitting from Fe^III‐OH‐Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

Fe/Fe3C Nanoparticles Encapsulated in N-Doped Hollow Carbon Spheres as Efficient Electrocatalysts for the Oxygen Reduction Reaction over a Wide pH Range

Nonprecious-metal-based electrocatalysts with low cost, high activity, and stability are considered as one of the most promising alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR). Herein, an economical and easy-to-fabricate catalyst is developed, that is, Fe/Fe₃C embedded in N-doped hollow carbon spheres (Fe/Fe₃C/NHCS), which gave the half-wave potential of 0.84 V in 0.1 m KOH, similar to the commercial Pt/C catalyst. Surprisingly, the favorable ORR performance of the as-prepared catalyst was obtained in both acidic and neutral conditions with almost a four-electron pathway and low H₂O₂ yield, which desirable the development of the proton exchange membrane (PEM) and microbial electrolysis cell (MEC) technology. Additionally, the obtained catalyst demonstrated better long-term stability and high methanol tolerance over a wide range of pH. These features could be mainly attributed to the synergistic effect between Fe/Fe₃C and Fe-N_x sites, the hollow structure with mesopores, and the well-dispersed Fe/Fe₃C nanoparticles owing to the existence of the abundant hydrophilic groups within the HCS precursor. As such, designing an efficient and cheap ORR catalyst that can operate at alkaline, acidic, and neutral solutions is highly desirable, yet challenging.     

Catalytic Hydrogenation of Acetic Acid to Acetaldehyde: Synergistic Effect of Bifunctional Co/Ce‐Fe Oxide Solid Solution Catalysts

The large‐scale industrial production of acetic acid (HAc) from carbonylation of methanol has enabled intense research interest from direct hydrogenation of HAc to acetaldehyde (AA). Herein, a series of cerium‐iron oxide solid solution supported metallic cobalt catalysts were prepared by modified sol‐gel method and were applied in gas‐phase hydrogenation of HAc to AA. A synergistic effect between the hydrogenation metal cobalt and Ce‐Fe oxide solid solution is revealed. Specifically, oxygen vacancies provide the active sites for adsorption of HAc, while highly uniformly dispersed metallic Co adsorbs H₂ and activates the reduction of HAc into AA. Moreover, the metallic Co can also assist the cyclical conversion between Fe³⁺/Fe²⁺ and Ce³⁺/Ce⁴⁺ on the surface of Ce_1‐xFe_xO_2‐δ supports. The unique effect substantially enhances the ability of the support material to rapidly capture oxygen atoms from HAc. It is found that the catalyst of 5% Co/Ce_0.8Fe_0.2O_2‐δ with the highest concentration of oxygen vacancy presents the best catalytic performance (i.e. acetaldehyde yield reaches 49.9%) under the optimal reaction conditions (i.e. 623 K and H₂ flow rate = 10 mL/min). This work indicates that the Co/Ce‐Fe oxide solid solution catalyst can be potentially used for the selective hydrogenation from HAc to AA. The synergy between the metallic Co and Ce_1‐xFe_xO_2‐δ revealed can be extended to the design of other composite catalysts.     

Modulating Coordination of Iron Atom Clusters on N,P,S Triply-Doped Hollow Carbon Support towards Enhanced Electrocatalytic Oxygen Reduction

Constructing atom-clusters (ACs) with in situ modulation of coordination environment and simultaneously hollowing carbon support are critical yet challenging for improving electrocatalytic efficiency of atomically dispersed catalysts (ADCs). Herein, a general diffusion-controlled strategy based on spatial confining and Kirkendall effect is proposed to construct metallic ACs in N,P,S triply-doped hollow carbon matrix (M_ACs/NPS−HC, M=Mn, Fe, Co, Ni, Cu). Thereinto, Fe_ACs/NPS−HC with the best catalytic activity for oxygen reduction reaction (ORR) is thoroughly investigated. Unlike the benchmark sample of symmetrical N-surrounded iron single-atoms in N-doped carbon (Fe_SAs/N−C), Fe_ACs/NPS−HC comprises bi-/tri-atomic Fe centers with engineered S/N coordination. Theoretical calculation reveals that proper Fe gathering and coordination modulation could mildly delocalize the electron distribution and optimize the free energy pathways of ORR. In addition, the triple doping and hollow structure of carbon matrix could further regulate the local environment and allow sufficient exposure of active sites, resulting in more enhanced ORR kinetics on Fe_ACs/NPS−HC. The zinc-air battery assembled with Fe_ACs/NPS−HC as cathodic catalyst exhibits all-round superiority to Pt/C and most Fe-based ADCs. This work provides an exemplary method for establishing atomic-cluster catalysts with engineered S-dominated coordination and hollowed carbon matrix, which paves a new avenue for the fabrication and optimization of advanced ADCs.     

Effect of Fe2O3 Content on the Local Structure and Crystallization Mechanism of Calcium Gallate Glasses

⁵⁷Fe Mössbauer and FT-IR of 60CaO·(40-x)Ga₂O₃·xFe₂O₃ glasses revealed that Fe(III)O₄ tetrahedra occupy substitutional sites of Ga(III)O₄ tetrahedra. The activation energy for crystallizaation (E _a) obtained from DTA study decreases distinctly from 8.9 to 4.8 eV with an increase in the Fe₂O₃ content. In the case of 40CaO·(60-x)Ga₂O₃·xFe₂O₃ glasses, a week doublet due to Fe(II)O₄ tetrahedra or Fe(III)O₆ octahedra was observed in addition to Fe(III)O₄ tetrahedra. The E _avalue decreases gradually from 7.1 to 5.6 eV with an increasing Fe₂O₃ content. These results indicate that a large amount of Fe₂O₃ in the network structure is favorable for the crystallization of calcium gallate glass, since it reduces the chemical bond strength.     

Generation of FeIV=O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron−N−C Catalyst

Generating Fe^IV=O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the Fe^IV=O generation pathway and oxidation behavior remain obscure. Employing an Fe−N−C catalyst with a typical Fe−N₄ moiety to activate peroxymonosulfate (PMS), we demonstrate that generating Fe^IV=O is mediated by an Fe−N−C−PMS* complex—a well-recognized nonradical species for induction of electron-transfer oxidation—and we determined that adjacent Fe sites with a specific Fe₁−Fe₁ distance are required. After the Fe atoms with an Fe₁-Fe₁ distance <4 Å are PMS-saturated, Fe−N−C−PMS* formed on Fe sites with an Fe₁-Fe₁ distance of 4–5 Å can coordinate with the adjacent Fe^II−N₄, forming an inter-complex with enhanced charge transfer to produce Fe^IV=O. Fe^IV=O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential.     

Non-planar Nest-like [Fe2S2] Cluster Sites for Efficient Oxygen Reduction Catalysis

Metal-nitrogen-carbon catalysts, as promising alternative to platinum-based catalysts for oxygen reduction reaction (ORR), are still highly expected to achieve better performance by modulating the composition and spatial structure of active site. Herein, we constructed the non-planar nest-like [Fe₂S₂] cluster sites in N-doped carbon plane. Adjacent double Fe atoms effectively weaken the O−O bond by forming a peroxide bridge-like adsorption configuration, and the introduction of S atoms breaks the planar coordination of Fe resulting in greater structural deformation tension, lower spin state, and downward shifted Fe d-band center, which together facilitate the release of OH* intermediate. Hence, the non-planar [Fe₂S₂] cluster catalyst, with a half-wave potential of 0.92 V, displays superior ORR activity than that of planar [FeN₄] or [Fe₂N₆]. This work provides insights into the co-regulation of atomic composition and spatial configuration for efficient oxygen reduction catalysis.