Iron Catalyst Research Articles

Ammonia Synthesis Over an Iron Catalyst with an Inverse Structure.

Achieving a substantial increase in the ammonia productivity of the Haber-Bosch (HB) process at low temperatures has been a significant challenge for over 100 years. However, the iron catalyst designed over 100 years ago remains at the forefront of this process because it is difficult to exceed the industrial iron catalyst in terms of the ammonia synthesis rate/catalyst volume that determines ammonia productivity in a reactor. Here, a new catalyst with an inverse structure of a supported metal catalyst that consists of metallic iron particles loaded with an aluminum hydride species is reported. The iron catalyst is readily prepared from an α-Fe2O3 precursor and ammonia could be synthesized at more than twice the ammonia synthesis rate/catalyst volume of the conventional industrial iron catalyst, even though the specific surface area of the former is only half that of the latter. In addition, ammonia synthesis over the catalyst is observed with a small apparent activation energy at 50 °C. Mechanistic studies suggested that an increase in the active sites with strong electron-donating capability on the iron catalyst significantly increased the ammonia synthesis rate/catalyst surface area, which resulted in high catalytic activity/catalyst volume.

Enhanced FeIV═O Generation via Peroxymonosulfate Activation by an Edge-Site Engineered Single-Atom Iron Catalyst.

As an oxidant, the ferryl-oxo complex (FeIV═O) offers excellent reactivity and selectivity for degrading recalcitrant organic contaminants. However, enhancing FeIV═O generation on heterogeneous surfaces remains challenging because the underlying formation mechanism is poorly understood. This study introduces edge defects onto a single-atom Fe catalyst (FeNC-edge) to promote FeIV═O generation via peroxymonosulfate (PMS) activation. In the presence of PMS, the FeNC-edge catalyst at a low dose (20 mg L-1, equivalent to 0.14 mg L-1 Fe) exhibits unprecedented activity for organic contaminant degradation. Electrochemical analysis, in situ Raman spectroscopy, and FeIV═O probe experiments confirm that FeIV═O generation is enhanced on the surface of FeNC-edge. Density functional theory calculations reveal that the introduced edge sites concentrate electron density on active Fe atoms, facilitating charge transfer from Fe to PMS. Notably, FeNC-edge immobilized on a polymeric membrane functioned as a continuous-flow oxidation system with efficient catalyst recycling and minimal Fe leaching.

Methane Decomposition over a Titanium-Alumina and Iron Catalyst Assisted by Lanthanides to Produce High-Performance COx-Free H2 and Carbon Nanotubes

COx-free H2, along with uniform carbon nanotubes, can be achieved together in high yield by CH4 decomposition. It only needs a proper catalyst and reaction condition. Herein, Fe-based catalyst dispersed over titania-incorporated-alumina (Fe/Ti-Al), with the promotional addition of lanthanides, like CeO2 and La2O3, over it, is investigated for a methane decomposition reaction at 800 °C with GHSV 6 L/(g·h) in a fixed-bed reactor. The catalysts are characterized by temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The promoted catalysts are facilitated with higher surface area and enhanced dispersion and concentration of active sites, resulting in higher H2 and carbon yields than unpromoted catalysts. Ceria-promoted 20Fe/Ti-Al catalyst had the highest concentration of active sites and always attained the highest activity in the initial hours. The 20Fe-2.5Ce/Ti-Al catalyst attains >90% CH4 conversion, >80% H2-yield, and 92% carbon yield up to 480 min time on stream. The carbon nanotube over this catalyst is highly uniform, consistent, and has the highest degree of crystallinity. The supremacy of ceria-promoted catalyst attained >90% CH4 conversion even after the second cycle of regeneration studies (against 87% in lanthanum-promoted catalyst), up to 240 min time on stream. This study plots the path of achieving catalytic and carbon excellence over Fe-based catalysts through CH4 decomposition.

Coordination-induced axial chirality controls the metal-centred configuration in a stereogenic-at-iron catalyst.

A new approach is introduced to control the metal-centred configuration of stereogenic-at-iron catalysts by utilizing axial ligand chirality, which becomes locked upon metal coordination. This strategy is applied to an iron catalyst containing two chelating N-(2-pyridyl)-substituted triazol-5-ylidene mesoionic carbenes (MICs) resulting in a helical topology with a stereogenic iron centre.

Utilizing an Oil-soluble Iron and Sodium-based Catalyst for Catalytic Hydrogenation of Carbon Dioxide in Heavy Oil

Utilizing an Oil-soluble Iron and Sodium-based Catalyst for Catalytic Hydrogenation of Carbon Dioxide in Heavy Oil

Depolymerization of PET with ethanol by homogeneous iron catalysts applied for exclusive chemical recycling of cloth waste

The acid-, base-free exclusive depolymerization of PET with ethanol catalyzed by FeCl3 affording DET and EG, and the selective depolymerization of PET from textile waste have been demonstrated.

Assembly-foaming synthesis of hierarchically porous nitrogen-doped carbon supported single-atom iron catalysts for efficient oxygen reduction.

High-performance electrocatalysts are highly concerned in oxygen reduction reaction (ORR) related energy applications. However, facile synthesis of hierarchically porous structures with highly exposed active sites and improved mass transfer is challenging. Herein, we develop a novel assembly-foaming strategy for synthesizing hierarchically porous nitrogen-doped carbon supported single-atom iron catalysts. Incorporation of a Fe3+/histidine complex into the block copolymer F127/resol assembly system not only enables an assembly-foaming process forming hierarchical pores, but also promotes the creation of abundant nitrogen-coordinated single-atom Fe (FeNX) sites on well-graphitized carbon skeletons. The obtained materials possess interconnected macropores (1.5-11.5µm), large mesopores (5-30nm) and rich micropores, high surface areas (534-970m2 g-1), large pore volumes (0.68-1.04cm3 g-1) and rich FeNX sites. The optimized sample exhibits a superior ORR activity (onset potential 1.03V and half-wave potential 0.89V) to the commercial 20wt% Pt/C catalyst, a high kinetic current density and excellent stability and methanol tolerance.The prominent performance stems from the coeffects of the hierarchical pore structure and the rich accessible FeNX sites. The significance of the pore structure is revealed by the positive linear relationship between the double-layer capacitances of the obtained materials and their ORR activities.

Engineering Robust Triazine Crosslinked and Pyridine Capped Anion Exchange Membrane for Advanced Water Electrolysis.

Exploring high-performance anion exchange membranes (AEM) for water electrolyzers (AEMWEs) is significant for green hydrogen production. However, the current AEMWEs are restricted by the poor mechanical strength and low OH- conductivity of AEMs, leading to the low working stability and low current density. Here, we develop a robust AEM with polybiphenylpiperidium network by combining the crosslinking with triazine and the capping with pyridine for advanced AEMWEs. The AEM exhibits an excellent mechanical strength (79.4 MPa), low swelling ratio (19.2 %), persistent alkali stability (≈5,000 hours) and high OH- conductivity (247.2 mS cm-1) which achieves the state-of-the-art AEMs. Importantly, when applied in AEMWEs, the corresponding electrolyzer equipped with commercial nickel iron and nickel molybdenum catalysts obtained a current density of up to 3.0 A cm-2 at 2 V and could be stably operated ~430 h at a high current density of 1.6 A cm-2, which exceeds the most of AEMWEs. Our results suggest that triazine crosslinking and pyridine capping can effectively improve the overall performance of the AEMWEs.

Sulfur-Bridged Iron and Molybdenum Catalysts for Electrocatalytic Ammonia Synthesis.

Carbon zero electrocatalytic nitrogen reduction reaction (NRR), converting N2 to NH3 under ambient temperature and pressure, offers a sustainable alternative to the energy-intensive Haber-Bosch process. Nevertheless, NRR still faces major challenges due to direct dissociation of the strong N≡N triple bond, poor selectivity, as well as other issues related to the inadequate adsorption, activation and protonation of N2. In nature's nitrogen fixation, microorganisms are able to convert N2 to ammonia at ambient temperature and pressure, and in aqueous environment, thanks to the nitrogenase enzymes. The core NRR performance is achieved with sulfur-rich Fe transition metal clusters as active site cofactors to capture and reduce N2, with optimum performance found for Fe-Mo clusters. Because of this reason, artificial analogs in Fe-Mo coordination chemistry have been explored. However, the studies of sulfur coordinated Fe, Mo catalysts for electrocatalytic ammonia synthesis are scarce. In this review, the recent progress of Fe-Mo sulfur-bridged catalysts (including sulfur-coordinated single-site catalysts in carbon frameworks and MoS2-based catalysts) and their activities for the ammonia synthesis from nitrate reduction reaction (NO3 -RR) and nitrogen reduction reaction (NRR) are summarized. Further existing challenges and future perspectives are also discussed.

Initiators for Continuous Activator Regeneration (ICAR) Depolymerization.

Chemical recycling of polymers synthesized by atom transfer radical polymerization (ATRP) typically requires high temperatures (i.e., 170 °C) to operate effectively, not only consuming unnecessary energy but also compromising depolymerization yields due to unavoidable end-group deterioration. To overcome this, the concept of initiators for continuous activator regeneration (ICAR) depolymerization is introduced herein as a broadly applicable approach to significantly reduce reaction temperatures for ATRP depolymerizations. Addition of commercially available free radical initiators enables the on-demand increase of depolymerization efficiency from <1% to 96%, achieving monomer generation at 120 °C, with conversions on par with thermal reversible addition-fragmentation chain transfer (RAFT) depolymerizations. Incubation studies confirm the elimination of deleterious side reactions at the milder temperatures employed, while the methodology can be scaled up to 1 g. The robustness and versatility of ICAR depolymerization is further demonstrated by the possibility to effectively depolymerize both chlorine and bromine terminated polymers and its compatibility with both copper and iron catalysts.

Nonheme iron catalyst mimics heme-dependent haloperoxidase for efficient bromination and oxidation.

The [Fe]/H2O2 oxidation system has found wide applications in chemistry and biology. Halogenation with this [Fe]/H2O2 oxidation protocol and halide (X-) in the biological system is well established with the identification of heme-iron-dependent haloperoxidases. However, mimicking such halogenation process is rarely explored for practical use in organic synthesis. Here, we report the development of a nonheme iron catalyst that mimics the heme-iron-dependent haloperoxidases to catalyze the generation of HOBr from H2O2/Br- with high efficiency. We discovered that a tridentate terpyridine (TPY) ligand designed for Fenton chemistry was optimal for FeBr3 to form a stable nonheme iron catalyst [Fe(TPY)Br3], which catalyzed arene bromination, Hunsdiecker-type decarboxylative bromination, bromolactonization, and oxidation of sulfides and thiols. Mechanistic studies revealed that Fenton chemistry ([Fe]/H2O2) might operate to generate hydroxyl radical (HO•), which oxidize bromide ion [Br-] into reactive HOBr. This nonheme iron catalyst represents a biomimetic model for heme-iron-dependent haloperoxidases with potential applications in organic synthesis, drug discovery, and biology.

Thermally robust bis(imino)pyridyl iron catalysts for ethylene polymerization: Synergy effects of weak π-π interaction, steric bulk, and electronic tuning

Thermally robust bis(imino)pyridyl iron catalysts for ethylene polymerization: Synergy effects of weak π-π interaction, steric bulk, and electronic tuning

Conversion of glycerol into renewable hydrocarbons employing platinum and iron catalysts supported on mixed zirconium and aluminum oxides

Conversion of glycerol into renewable hydrocarbons employing platinum and iron catalysts supported on mixed zirconium and aluminum oxides

Insights into pore structure-activity relationships of iron catalysts supported on fluorine–cerium nanosheets for heterogeneous Fenton oxidation

Two-dimensional (2D) structural materials as catalyst supports is crucial for improving the heterogeneous catalytic activity, while the relationships between their porous structure and catalytic performance are still not very clear. Herein, four kinds of porous 2D Fluorine-Cerium (F-Ce) nanosheets were fabricated and used as catalyst support, aiming to investigate the effect of porous structure on the catalytic properties by heterogeneous Fenton oxidation and unveil the structure-activity relationships. Compared with 2D non-porous GO, Ti3C2, and porous g-C3N4, F-Ce nanosheets exhibited superior catalytic activity. Specifically, FeOOH/F-Ce-3 catalysts achieved 95.5 % phenol removal within 40 minutes, with the deposition sites and electronic structures of the loaded Fe-active species being modulated by tuning the pore structures. In addition, we demonstrated that large pore size and high pore volume are more conducive to high catalytic performance, as well as the uniform pore shape and well-ordered pore distribution are more favorable for mass transfer during catalysis. This work emphasizes the great advantage of using porous 2D F-Ce nanosheets as support in the construction of heterogeneous Fenton catalysts while elaborating the relationship between pore structure and catalytic activity.

Stereoselective Glycosylation for 1,2-cis-Aminoglycoside Assembly by Cooperative Atom Transfer Catalysis.

We report here a new catalytic method for exclusively 1,2-cis-α-selective glycosylation that assembles a wide variety of 1,2-cis-aminoglycosidic linkages in complex glycans and glycoconjugates. Mechanistic studies revealed a unique glycosylation mechanism in which the iron catalyst activates a glycosyl acceptor and an oxidant when it facilitates the cooperative atom transfer of both moieties to a glycosyl donor in an exclusively cis-selective manner. This catalytic approach is effective for a broad range of glycosyl donors and acceptors, and it can be operated in a reiterative fashion and scaled up to the multigram scale.

Protonic Ceramic Membranes: Up-Scaling and Application to E-Fuels Synthesis

The production of synthetic fuels / chemicals relies on the availability of the reactants: low-carbon H2, CO2 valorization from various CO2 sources, N2. In addition, the value chains are not enough mature to be considered as commercial and still need improvement. The main levers are high production costs of conversion processes, access to biologic or fatal CO2 sources and issues related to the H2 supply chain (H2 cost, heat recovery, etc.). The main streams for improving current e-fuels conversion technologies being explored by industry are focused on new catalyst materials and new reactor architectures to enhance CO2 / N2 and H2 conversion and selectivity towards the desired molecule.However, new low TRL innovations are developing around protonic ceramic-based technology. It offers the advantage of being able to intensify the process by integrating hydrogen supply (electrolysis of water, then transfer of protons through the membrane) and conversion to the desired molecule (catalytic effect) in the same electro-catalytic reactor. Based on its extensive experimental and collaborative experience, EIFER is now focusing its research in the ENERMAT laboratory on the development of protonic ceramic cells for a variety of applications, including NH3 production and the direct conversion of CO2 into CH4, up to the integration in an SRU/stack environment. Manufacture and characterization of samples Using a multi-step manufacturing wet chemical route, hydrogen electrode supported samples from 10 to 50 cm² have been achieved. The hydrogen electrode substrate is firstly manufactured by tape-casting from a slurry containing NiO and BaCe1-x-YZrxYyO3-δ (BCZY). The BCZY-based electrolyte is coated by screen-printing, and the bilayer assembly is co-sintered at a temperature around 1300°C to limit the effect of shrinkage and diffusion. The last electrode layer is also coated by screen-printing and fired at a lower temperature to keep its structure and ensure a good bonding with the membrane.The final microstructure results in a thin (below 10 µm) and dense membrane, whereas the electrodes remain porous to ease the gas diffusion. In order to enhance the activity of samples, catalysts are either infiltrated or directly incorporated in the electrode layer(s). As an example, the figure 1 shows the composition of a protonic ceramic multilayer assembly for the synthesis of ammonia. The iron catalyst is introduced into a sintered backbone layer by infiltration or by direct embedding into a composite structure.The multi-layered assemblies are tested in adapted laboratory-scale reactors. The gas produced are analyzed using mass spectrometry and the electrochemical behavior of the samples is analyzed by impedance spectroscopy. Finally, the microstructure of the layers is observed and compared before and after electrochemical measurements.Here, EIFER’s main achievements for the manufacture of large multi-layered assemblies and the synthesis of hydrogen derivatives will be discussed. Figure 1

Reductive Amination of Carbonyl Compounds with Amines or Ammonia Using a Single-Atom Iron Catalyst

Reductive Amination of Carbonyl Compounds with Amines or Ammonia Using a Single-Atom Iron Catalyst

Understanding the Effect of M(III) Choice in Heterodinuclear Polymerization Catalysts.

The ring-opening copolymerization (ROCOP) of epoxides with CO2 or anhydrides is a promising strategy to produce sustainable polycarbonates and polyesters. Currently, most catalysts are reliant on scarce and expensive cobalt as the active center, while more abundant aluminum and iron catalysts often suffer from lower activities. Here, two novel heterodinuclear catalysts, featuring abundant Al(III), Fe(III), and K(I) active centers, are synthesized, and their performance in the polymerization of four different monomer combinations is compared to that of their Co(III) analogue. The novel Al(III)K(I) catalyst exhibits outstanding activities in the cyclohexane oxide (CHO)/CO2 ROCOP, and at 1 bar CO2 pressure it is the fastest aluminum-based catalyst reported to date. The M(III) site electronics for all three catalysts, Al(III)K(I), Fe(III)K(I), and Co(III)K(I), are measured using IR and NMR spectroscopy, cyclic voltammetry, and single crystal X-ray diffraction. A correlation between M(III) electron density and catalytic activity is revealed and, based on the established structure-activity relationship, recommendations for the future catalyst design of abundant Al(III)- and Fe(III)-based catalysts are made. The catalytic performances of both Al(III)K(I) and Fe(III)K(I) are further contextualized against the relative elemental abundance and cost. On the balance of performance, abundance, and cost, the Al(III)K(I) complex is the better catalyst for the carbon dioxide/epoxide ROCOP, while Fe(III)K(I) is preferable for anhydride/epoxide ROCOP.

Iron-Catalyzed Perfluoroalkylarylation of Styrenes with Arenes and Alkyl Iodides Enabled by Halogen Atom Transfer.

A new iron-catalyzed three-component perfluoroalkylarylation of styrenes with alkyl halides and arenes has been established. Alkyl halides undergo halogen atom transfer with methyl radicals to form alkyl radicals in reactions initiated by a combination of tert-butyl peroxybenzoate and an iron catalyst, thus adducting to the olefins, which results in alkylarylation products. The protocol is compatible with a wide range of perfluoroalkyl and non-perfluoroalkyl halides, features excellent functional group tolerance, and enables the synthesis of structurally diverse 1,1-diaryl fluoro-substituted alkanes.

High-yield pentanes-plus production via hydrogenation of carbon dioxide: Revealing new roles of zirconia as promoter of iron catalyst with long-term stability

The metal oxide promoter decisively influences the overall performance of Fe catalysts in the direct hydrogenation of CO2 to C5+ hydrocarbons. However, the roles of metal oxide promoter for Fe catalysts, particularly ZrO2, have rarely been investigated. To plug this knowledge gap, a new Fe catalyst promoted with Na and partially reduced ZrOx (Na-FeZrOx-9) was developed in this study; the catalyst helped produce C5+ hydrocarbons in remarkably high yield (26.3% at 360 °C). In contrast to ZrOx-free Fe-oxide, Na-FeZrOx-9 exhibited long-term stability for CO2 hydrogenation (750 h on-stream). The findings revealed multiple roles of ZrOx. Notably, ZrOx decorated the Fe-oxide particles after calcination, thereby suppressing excess particle aggregation during the reaction, and acted as a “coke remover” to eliminate the carbon deposited on the catalyst surface. Additionally, oxygen vacancy (Ov) sites in ZrOx and electron transfer from ZrOx to Fe sites facilitated the adsorption of CO2 at the Zr-Fe interface.