Chemical looping synthesis of amines from N2 via iron nitride as a mediator

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In this study, we present an alternative route to make amines using iron nitride (Fe 2.5 N) as the nitrogen source. Without any additional catalyst, Fe 2.5 N reacts with a range of alcohols at 250 °C under 1 or 10 bar H 2 to produce amines as major products. Mechanistic investigations indicate that hydrogen activates the nitrogen species within iron nitride, converting them into surface NH and NH 2 groups that then react with alcohols to form amines. Building on this foundation, we further demonstrated an iron nitride-mediated chemical looping pathway that utilizes N 2 as the nitrogen source to synthesize octylamines. In this process, N 2 first reacts with iron to form Fe x N by a ball-milling method at ambient temperature and 6 bar N 2 . The as-prepared Fe x N subsequently reacts with alcohols to yield amines, transferring over 80% of the nitrogen to organic compounds. This looping process proved stable across four cycles. Physical sciences/Chemistry/Green chemistry/Sustainability Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis Nitrogen activation Organoamines production Transition metal nitride Iron nitride Amination Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Nitrogen-containing chemicals, particularly amines, are key building blocks for chemical industries. 1-10 Currently, the primary nitrogen source for synthesizing these compounds, ammonia, is produced from the Haber-Bosch process—the single most energy-intensive processes globally operating at 400-500 °C and 200-250 bar. 11,12 Additionally, amination reactions using ammonia often require noble metal catalysts because many substrates do not efficiently react with ammonia. Even with catalysts, the single-pass conversion of NH 3 remains low, typically ranging from 0.2~7% (Table S1 and Scheme 1). Given these challenges, there has been a sustained effort to develop alternative pathways that enable the production of nitrogen-containing organic compounds starting from N 2 , bypassing the Haber-Bosch process. Exciting progresses have been made in the synthesis of organonitrogen chemicals directly from N 2 , primarily utilizing Li in metallic or other highly reactive states. For instance, Li has been employed as the reductant for the synthesis of N 2 -transition metal complexes as key intermediates 13 or for the direct conversion of N 2 to organonitrogen chemicals. 14 Li also reacts with N 2 to form Li 3 N, which further interacts with reactive species such as aromatic halides or aromatic acyl chlorides to construct C–N bonds. 15 Additionally, key synthons like Li 2 CN 2 have been synthesized from LiH and N 2 , serving as precursors for accessing organonitrogen chemicals. 16 Despite these elegant studies, the high redox potential of Li makes the preparation and regeneration of metallic Li energy-intensive, 15 and its high reactivity also necessitates precautions in wide application. Beyond Li, organometallic complexes of Mo and Ti have also been explored, showing potential in activating N 2 17-19 and leading to the formation of organonitrogen chemicals in the presence of Pd catalysts. 20,21 Nevertheless, no studies have yet harnessed inexpensive 3-d metals as effective mediators to synthesize organonitrogen chemicals from N 2 . We propose that 3-d metal nitrides could serve as promising candidates to bridge N 2 to organonitrogen compounds. Investigations into the release of nitrogen atoms from 3-d transition metal nitrides under H 2 , 22-25 CO, 26 and mixed atmosphere of CO 2 and H 2 , 27 have shown that lattice nitrogen is labile and reactive, potentially facilitating C–N bond formation. Furthermore, a range of 3-d metals, including Ti, 28 Cr, 29 Mn, 30,31 and Fe 32 have reacted with N 2 to form metal nitrides. 33,34 With a moderate nitrogen binding energy that enable both the fixation of N 2 to nitride, as well as the transfer of nitrogen in the nitride into organonitrogen chemicals, 3-d transition metal nitrides may thus serve as effective nitrogen carriers. 35 In this study, we report our advances in the chemical looping synthesis of organonitrogen compounds using iron nitride as the nitrogen carrier (Scheme 1). We first investigated the reactivity of iron nitride (Fe 2.5 N) in converting isopropanol to isopropylamine and di-isopropylamine, demonstrating that iron nitride is a superior nitrogen source for amine synthesis compared to ammonia (Scheme 1b, left). We then expanded our investigation to include a range of alcohols—primary, secondary, and tertiary—to broaden the applicability of this method. Finally, we demonstrated the effectiveness of the N 2 -nitridated iron powder (Fe x N), made at ambient temperature and low pressure, as a nitrogen source for amine synthesis, during which itself is converted back to metallic iron. Through these efforts, we establish a cheap 3d metal-based chemical looping process for organonitrogen synthesis beginning with N 2 (Scheme 1b). Results Synthesis and reactivity of Fe 2.5 N We initially prepared iron nitride with stoichiometric Fe:N ratio (2.5:1, terms as Fe 2.5 N) 36 for reactivity study, while the more challenging synthesis of Fe x N from N 2 and metallic iron was explored later. The fresh Fe 2.5 N sample exhibited aggregates of 100 nm ~ 1µm particles with irregular shapes (Fig. 1 a, S1a-e, S2a-f) and small surface area (14 m 2 ∙g -1 , Table S3). The XRD pattern of the sample matches that of Fe 2 N (PDF #73-2102) and Fe 3 N phase (PDF #72-2125) (Fig. 1 c). The lattice fringe spacing (d value) was 0.210 nm, 0.239 nm, and 0.302 nm, corresponding to the (-1 -1 1), (1 1 0), and (1 0 1) crystal plane of ε-phase 37 Fe 2 N/Fe 3 N hexagonal structure, respectively (Fig. 1 a and S2). The N content of was 9.1 wt.% (Table S5), confirming a Fe:N ratio of ~ 2.5:1. In the Mössbauer spectra (Fig. 1 e), a doublet peak corresponding to ε-Fe 2.1 N is the major phase while a low-intensity sextet corresponding to γ-Fe 4 N coexists. 38 , 39 In the XPS spectra (Fig. 1 d and Figure S3), the peaks at around 397.6 eV, 396.7 eV and 399.1 eV corresponded to Fe-O-N, Fe-N and adsorbed NH 3 , respectively. 40 – 42 The adsorption edge of the fresh Fe 2.5 N in the XANES spectrum (Fig. 1 f) was in between the reference Fe foil and FeO. Fourier transform of Fe K-edge EXAFS of the Fe 2.5 N was also performed: the peaks centered at ~ 1.56 Å and ~ 2.27 Å correspond to Fe-N and Fe-Fe shells, respectively, 43 , 44 consistent with the interstitial structure of iron nitride. Fe 2.5 N was thermally stable under inert atmosphere below 400°C, after which it decomposes, releasing N 2 (Figure S5). Next, amination of isopropanol was conducted in a continuous fixed-bed reactor, with Fe 2.5 N placed inside the reactor while a mixture of H 2 and Ar carried isopropanol vapor through the sample bed (Fig. 2 a). The study focuses on the conversion of nitrogen in Fe 2.5 N, so that the product yields were calculated on nitrogen basis. Fe 2.5 N was inactive at 150°C, but a notable productivity towards amines, including isopropylamine and di-isopropylamine, was observed at 200°C. The best performance was achieved at 250°C, resulting in a high organonitrogen selectivity of 23% under 5 bar H 2 (Fig. 2 b). At this temperature, the conversion of isopropanol remained relatively stable in the first 5 h (Figure S6), while the yield of organonitrogen compounds gradually decreased, indicating the nitrogen consumption led to the decrease amine production. Hydrocarbons and oxygenates (C 6 -C 9 ) were the major non-nitrogen containing products (Figure S7-S8). When the temperature further increased to 300°C, the most favorable reaction became hydrodeoxygenation. At optimum temperature (250°C), the variation of H 2 partial pressure from 0 to 10 bar significantly influenced amine formation (Fig. 2 c). Without H 2 , only a minor fraction of organonitrogen compounds was formed, likely through the hydrogen-borrowing pathway as observed in catalytic amination of alcohols. 45 – 47 Increasing the hydrogen partial pressure to 1 bar substantially enhanced amine production. Further increasing the H 2 partial pressure led to reduced amine yields, attributable to the enhanced formation of ammonia, thereby limiting the nitrogen available to form the organonitrogen products. Additionally, H 2 is known to hinder the dehydrogenation of isopropanol. 48 – 51 The consumption of nitrogen in Fe 2.5 N at optimal condition over time is illustrated in Fig. 2 d. The 5 hours of reaction at 250°C with 1 bar H 2 led to almost total loss of nitrogen, where 37% of the initial nitrogen had been transformed into amines, and the remaining amount was present as gaseous NH 3 . After 32-hour reaction (Table S5), N was completely depleted. The data indicate a positive correlation between the amination rate and the nitrogen content in Fe 2.5 N. The spent Fe 2.5 N remained similar shape (Fig. 1 b, Figure S1 f-j, and Figure S2g-k) and surface area (12 m 2 ∙g -1 , Table S3) compared with fresh Fe 2.5 N. The lattice fringe spacing of 32-hour spent Fe 2.5 N corresponds to the (1 1 0) crystal plane of metallic iron, and the XRD patterns of both 2-hour and 32-hour spent Fe 2.5 N also corresponded well with metallic Fe phase (Fig. 1 c). For the 2 h and 32 h spent Fe 2.5 N, the Mössbauer spectrum showed only the sextet corresponding to α-Fe. 38 , 52 In XPS analysis, the presence of N could still be observed in the 2-hour spent Fe 2.5 N (Fig. 1 d and Figure S3), but no nitrogen was seen in the 32-hour spent Fe 2.5 N. These results consistently suggest that the lattice nitrogen in Fe 2.5 N was gradually consumed during the reaction while Fe species are transformed into metallic Fe. Reaction mechanism and substrate scope Figure 3 a displays the in-situ DRIFTS spectra of isopropanol adsorption on fresh Fe 2.5 N under H 2 atmosphere at 250°C. The peak at 3656 cm - 1 is attributed to the O-H stretching of isopropanol. 53 More importantly, the peak at 2655 cm - 1 corresponds to characteristic peak of isopropylamine (Figure S10), indicating the formation of the desired product. The peak at 1738 cm - 1 is assigned to C = O stretching, 54 , 55 revealing the presence of acetone. 56 The peaks at 1651 and 1642 cm - 1 are ascribed to C = N stretching, 57 and the peak at 1246 cm - 1 arises from C-N stretching. 58 , 59 Vibrations of NH x species bonded to Fe sites are also observed. 60 Further assignments of peaks are provided in the supporting information (Table S7). Using ammonia as a probe molecule, Lewis acid sites was identified on Fe 2.5 N (Figure S9), 54 , 61 , 62 which are known to be beneficial for dehydrogenation of alcohol, 63 activation of C = O, 64,65 and hydrogenation of C = N. 64 Acetone was further employed as a substrate to react with Fe 2.5 N (Fig. 3 b). At both 200°C and 250°C, acetone generated the same types of products as isopropanol did, such as isopropylamine, di-isopropylamine, and Schiff base (Figure S8), demonstrating that acetone is a viable intermediate for amine formation. Compared to using alcohol, the production of amine compounds is much more prominent at a lower 200°C, indicating that the dehydrogenation of isopropanol to acetone is likely to be rate-limiting. The reduction behavior of Fe 2.5 N was investigated under H 2 (Fig. 3 c). A prominent peak, identified as NH 3 , appeared at 520°C, demonstrating the transformation of lattice nitrogen in Fe 2.5 N to form NH 3 . The NH 3 signal below 335°C was minimal, supporting the notion that the chosen amination reaction temperature of 250°C reduced the undesirable side reaction of producing ammonia. We propose the following mechanism for the reaction (Fig. 3 d). Initially, isopropanol is adsorbed on the Lewis acid sites of the iron nitride and undergoes dehydrogenation to yield acetone. Subsequently, the NH x present on Fe 2.5 N surface transform acetone into imine, which is then hydrogenated to isopropylamine. As surface nitrogen is progressively consumed, the lattice nitrogen migrates to the surface for further amination, during which Fe 2.5 N is gradually converted to metallic iron. This reaction pathway is analogous to the conventional amination mechanism, but the nitrogen source is lattice nitrogen. Given that hydrogen also reacts with Fe 2.5 N to produce ammonia, the existence of conventional amination pathway cannot be entirely excluded. To validate the wide applicability of amine production using iron nitride as the nitrogen source, we evaluated the reaction between Fe 2.5 N and a range of alcohols in a batch reactor. The findings revealed that primary alcohols (Fig. 4 ) react more effectively than secondary alcohols, while tertiary alcohols show no reactivity in forming amines. This variation in reactivity is attributed to the steric hindrance in secondary alcohols and the absence of α-H in tertiary alcohols, which prevents the formation of the crucial C = O intermediate. Additionally, primary alcohols exhibited a higher selectivity for producing tertiary amines, likely due to the greater stability of tertiary amines. The highest amine yield achieved is 95.2% with 1-decanol as substrate. These results suggest that Fe 2.5 N has broad applicability and adaptability across different alcohol substrates and add supporting evidence for the proposed mechanism of alcohol dehydrogenation followed by solid N (in Fe 2.5 N)-dominated amination. N 2 -to-amine via Fe x N as a mediator To enable an iron nitride-mediated looping pathway to make amines using N 2 as nitrogen source, we synthesized iron nitride from N 2 following an elegant recent report based on a mechanochemical approach. 66 Typically, iron powder was loaded into ball-mill jar with iron balls and charged with 6 bar of N 2 for the ball milling to synthesize iron nitride (Fe x N) without heat supply. N 1s XPS spectra of the as-prepared Fe x N clearly showed the existence of N on the surface (Fig. 5 a). The XRD patterns of the as-prepared Fe x N and commercial iron powder are shown in Fig. 5 b. A peak shift towards lower angel caused by N insertion is observed after ball milling under N 2 atmosphere. The presence of N in the as-prepared Fe x N was further ambiguously confirmed by EDX mapping of SEM and TEM (Figure S11, Table S2) and CHN elemental analysis (Table S5). Based on acid treatment method (Table S8), the N content in the as-prepared Fe x N was 0.4 wt.%. The as-prepared Fe x N was subsequently reacted with octanol in the same manner as described in the previous session. Encouragingly, around 80% N in the as-prepared Fe x N was transferred to octylamines, majority of which was trioctylamine due to its higher stability. Post-reaction Fe x N was washed with methanol and freeze-dried before taking to the next round looping synthesis. The nitrogen content of the spent Fe x N was not detected by acid treatment and elemental analysis, (Table S5 and Table S8) indicating the N in Fe x N was depleted during the reaction. The excellent activity maintained throughout the 4 cycles, highlighting the high N utilization efficiency and durability of the proposed N 2 -to-amine looping strategy. The overall activity and specific selectivity towards dioctylamine both increased with increasing cycles, which could be explained by enriched H species on iron nitride surface during repeated use, which facilitates reaction and product desorption. Discussion In conclusion, this study provides an entry point into the broader potential for transition metal nitrides as the nitrogen carrier bridging the looping synthesis of organonitrogen chemicals from N 2 . We confirmed the donation of nitrogen from iron nitride to alcohols, with the concurrent transformation of Fe species metal nitride into metallic Fe. When Fe 2.5 N was used as a nitrogen carrier, more than 85% of the nitrogen was extracted to produce amines from C 6 ~ C 10 primary alcohols in a batch reactor at 250°C and 10 bar H 2 . More importantly, Fe x N, produced by nitridating iron powder with N 2 at ambient temperature and low pressure, has proven to be an effective nitrogen source for the catalyst-free production of organic amines. High N utilization efficiency of over 80% was consistently achieved over 4 cycles. This study unlocks the previously untapped potential of using inexpensive 3d-transition metal nitrides to produce organonitrogen compounds with N 2 as the nitrogen source. Methods Materials 2-propanol (≥ 99.5%) and phenol (99%) were purchased from Fisher Scientific Pte. Ltd. Iron (≥ 99%, reduced, fine powder), concentrated sulfuric acid (ACS reagent, 95.0–98.0%), concentrated hydrochloric acid (ACS reagent, 37%), potassium hydroxide (ACS reagent, ≥ 85%, pellets), isopropylamine (≥ 99.5%), acetone (anhydrous, ≥ 99.5%), cyclohexanol (99%), 1-butanol (99.8%), 1-hexanol (≥ 99%), 1-octanol (≥ 99%), 1-decanol (98%), and tert-butanol (≥ 99.5%) were provided by Sigma-Aldrich Pte. Ltd. (Singapore). Fe 3 O 4 (≥ 97%) was purchased from Shanghai Macklin Biochemical Co., Ltd. Typical activity test The catalytic performance tests were carried out in a vertical, fixed-bed tube reactor (SS316), with the reactor tube length of 0.5 m and the diameter of 7.6 mm. A furnace (1.2 kW, 220 V, up to 1000°C) was utilized to heat the reactor, and a thermocouple was inserted into the catalyst bed to monitor the temperature in real time. The temperature was regulated by a temperature controller that was inserted into the reactor. The samples were diluted with quartz sand and held in place with quartz wool to form a sample bed in the middle of the reactor. The liquid substrates were first introduced into a three-way autoclave, which had dedicated paths for the addition of liquid substrates, gas supply, and gas outlet connected to the reactor tube. The autoclave was maintained in water bath at 25°C, and the pressure inside was regulated using a back pressure valve. The gas inlet path of the autoclave was submerged at the bottom of the liquid for bubbling so that the liquid vapor can be carried by the gas to enter the reactor and go through the sample bed, while the hydrogen gas and argon gas were supplied to the autoclave controlled by gas flow meters. After loading Fe 2.5 N in the middle of reactor and increasing the temperature to the reaction temperature, substrates mixed with H 2 and Ar were supplied into the reactor at desired flow rates. The products were collected and analyzed by an online GC-FID system equipped with an Agilent CAM capillary column. The outlet flow could also be collected by passing through a bottle of methanol in ice bath to obtain the organic chemicals for off-line GC or GC-MS analysis. Activity test for substrate scope (Autoclave batch reactor) The transformation of alcohols with Fe 2.5 N was also performed in an autoclave. For example, 50 mg Fe 2.5 N, 70 µL dodecane (internal standard), and 1 mL alcohol substrates were added to the reactor in the glovebox. After that, the autoclave was introduced with 9 bar H 2 , and placed in a metal jacket wafer on an electronic hotplate (typically 250°C). After 6 hours of reaction, the reactor was immediately terminated by cooling the reactor in ice. The gas phase products were collected by gas bag, and the gas was then bubbled into the diluted sulfuric acid solution. The obtained solution was detected by IC (ion chromatography). The liquid products were collected and tested by GC and GC-MS for qualification and quantification analysis. The synthesis and activity test of N 2 -nitridated Fe (Fe x N) Specifically, iron powder (5 g) and iron balls (50 g, 5 mm diameter) were loaded into the ball-mill jar (50 mL) inside an Ar-atmosphere glovebox. The ball-mill jar was then evacuated and charged to 6 bar using N 2 before being taken to the planetary ball mill machine for 30 h 2000 rpm ball milling. The ball milling was stopped for 10 min every 30 min to release the heat. The as-prepared Fe x N powder was transferred into an autoclave, together with 1 mL octanol and 70µL dodecane (internal standard). The autoclave was purged with 10 bar H 2 for more than 10 times carefully to exchange the Ar inside. After purging, the batch reactor was charged with 10 bar H 2 , and reacted at 250°C for 6 h on an electronic hotplate with metal jacket. Similarly, the reactor was instantly cooled with ice after 6 hours of reaction, and the gas phase was carefully released into a 0.5 M sulfuric acid solution. The liquid products were washed with 1 mL methanol and tested by GC-FID and GC-MS. The remaining spent Fe x N powder was further washed with 50 mL methanol for 3 times inside the glovebox before taken to ball-mill reaction with nitrogen gas again. N content determination The nitrogen content of iron nitride samples was determined by dissolving 0.1 g of the sample in 30 mL 0.2 M hydrochloric acid at 80°C overnight. After that, 50 mL of 5 M KOH solution was injected to the clear aliquot under continuous N 2 purging at 80°C. The outlet gas was bubbled through 10 mL of 0.5 M sulfuric acid for 2 hours, which was taken to IC analysis for NH 4 + concentration. Characterization The crystal structure of iron nitride was tested by a Bruker D8 Advance X-Ray diffractometer, equipped with a Cu Kα source (40 kV, 30 mA). BET surface areas were calculated from nitrogen adsorption isotherms obtained by N 2 adsorption and desorption at 77 K in a Micromeritics ASAP 2020 surface area. Scanning electron microscopy (SEM) was performed with a JEOL JSM-7610F. Transmission electron microscopy images were acquired on a JEM 2100F (JEOL, Japan) microscope operated at 200 kV. XPS spectra were recorded on a VG Escalab MKII spectrometer, using a mono Al Kα X-ray source (hv = 1486.71 eV, 5 mA, 15 kV), and the calibration was done by setting the C1s peak at 284.5 eV. Elemental mappings of iron nitride were obtained using an JEOL microscope equipped with a Bruker Quantax energy-dispersive X-ray spectrometer (EDXS). CHN elemental analysis was conducted on Thermo Scientific Flashsmart CHNS analyzer. The room temperature 57 Fe Mössbauer spectrum was observed on a Topologic 500A spectrometer, which equipped 57 Co(Rh) as the radioactive source. Fitted by the MössWinn 4.0, all of the spectra were distinguished by different parameters, such as quadrupole splitting (QS) and isomer shift (IS). Besides, an α-iron foil was used to calibrate the IS values and Doppler velocities. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectra were acquired on a Thermo Scientific Nicolet iS50 FT-IR. The measurement was under atmospheric pressure, with ZnSe window and MCT-A detector cooled by liquid nitrogen. The solid Fe 3 O 4 powder was treated at 550°C under 30 mL/min NH 3 flow for 30 minutes in the cell to in situ form iron nitride, and then the temperature was changed to the required temperature under the H 2 flow or the Ar flow for the in-situ observation. The background was recorded under Ar before testing samples. The vapor of the liquid substrate was carried by the Ar gas flow into the cell. The NH 3 gas was supplied by the gas sample bag injection and degassed under Ar gas flow. The spectra were recorded with 4 cm − 1 resolution of 32 scans. H 2 -TPR-MS measurements were performed using a Quantachrome instrument coupled with a quadrupole mass spectrometer (Hidden Analytical). Prior to the measurements, the sample was pretreated in a flow of pure He gas at 150°C to remove the moisture and any contaminants. The H 2 -TPR profile was obtained by heating the sample from 30°C to 800°C at the rate of 10°C/min in a 5% H 2 /He atmosphere, while Ar-TPD (decomposition) measurements were conducted under pure He flow when heating the sample at the rate of 10°C/min to 800°C. The mass spectrometer was set to record the gas outlet composition. Ex situ Fe K-edge XAS measurements were conducted at a public beamline, BL01B1, Spring-8 (Japan Synchrotron Radiation Research Institute, Hyogo, Japan). (Proposal number: 2023A1533) The incident X-rays were monochromatized with a Si (111) double crystal monochromator. 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Activity and selectivity control in reductive amination of butyraldehyde over noble metal catalysts. Catal. Lett. 104, 23-28 (2005). Jamil, M. A. R. et al. Selective transformations of triglycerides into fatty amines, amides, and nitriles by using heterogeneous catalysis. ChemSusChem 12, 3115-3125 (2019). Luo, D. et al. Intrinsic mechanism of active metal dependent primary amine selectivity in the reductive amination of carbonyl compounds. J. Catal. 395, 293-301 (2021). Chatterjee, M., Ishizaka, T. & Kawanami, H. Reductive amination of furfural to furfurylamine using aqueous ammonia solution and molecular hydrogen: an environmentally friendly approach. Green Chem. 18, 487-496 (2016). Ruiz, D. et al. Direct amination of dodecanol with NH 3 over heterogeneous catalysts. Catalyst screening and kinetic modelling. Chem. Eng. J. 307, 739-749 (2017). Li, M., Pischetola, C., Cárdenas-Lizana, F. & Keane, M. A. Production of benzylamine by tandem dehydrogenation/amination/reduction over Cu and Au catalysts. Appl. Catal., A 590, (2020). Ibáñez, J., Kusema, B. T., Paul, S. & Pera-Titus, M. Ru and Ag promoted Co/Al 2 O 3 catalysts for the gas-phase amination of aliphatic alcohols with ammonia. Catal. Sci. Technol. 8, 5858-5874 (2018). Jagadeesh, R. V. et al. MOF-derived cobalt nanoparticles catalyze a general synthesis of amines. Science 358, 326-332 (2017). Dong, C. et al. Facile and efficient synthesis of primary amines via reductive amination over a Ni/Al 2 O 3 Catalyst. ACS Sustainable Chem. Eng. 9, 7318-7327 (2021). Hu, Q. et al. Ambient-temperature reductive amination of 5-Hydroxymethylfurfural over Al 2 O 3 -supported carbon-doped Nickel catalyst. ChemSusChem 15, e202200192 (2022). Brzezinski, B. & Zundel, G. An intramolecular charge relay system via easily polarizable hydrogen bonds in the N-(4-methyl-2-pyridyl)amide of 6-methylpicolinic acid N-oxide. J.Phys.Chem. 83, 1787-1789 (1979). Yang, X. et al. DRIFTS Study of Ammonia Activation over CaO and Sulfated CaO for NO Reduction by NH 3 . Environ. Sci. Technol. 45, 1147-1151 (2011). Scheme Scheme 1 is available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files SI.docx Scheme.png Scheme 1. (a) Catalytic amination of alcohols/aldehydes using NH 3 (b) The proposed Fe x N-mediated chemical looping pathway to synthesize organoamines. (Left) Organoamines synthesis using Fe x N, (Right) Preparation of stable Fe x N using N 2 . Cite Share Download PDF Status: Published Journal Publication published 02 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4394450","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":307534813,"identity":"ebec02ec-5c68-4b92-ad0c-e5c302f819c7","order_by":0,"name":"Ning Yan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYDACZijNj8olRotkA9FaYMDgALFazNl5D79gbLPLM77dY/yBocI6sYH/+AW8Wiyb+dIsGNuSi83unDGTYDiTntggkVOA3z2HecwMGNuYE7fdyDFjYGw7DNTCk0CMlvrEzTNyjD8w/gNq4T9DUIvxA5DhGyRyDCQYG4BaGNIPELSFIeHc8cQZN9LKJBKOpRu3SeTg1cFgcP6M8YcPZdWJ/TOSN3/4UGMt289//AF+PQwMbBKJbFAmyBNsDDwGhLQwf2D4gyLATtCWUTAKRsEoGFkAAIFIRRWEqoTMAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-1877-9206","institution":"National University of Singapore","correspondingAuthor":true,"prefix":"","firstName":"Ning","middleName":"","lastName":"Yan","suffix":""},{"id":307534814,"identity":"f6b9621b-7223-4f57-b49f-7235162c5726","order_by":1,"name":"Haoyue Li","email":"","orcid":"https://orcid.org/0009-0002-2981-9733","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Haoyue","middleName":"","lastName":"Li","suffix":""},{"id":307534815,"identity":"34c2816f-6db9-401c-a0d1-5700e9f68fda","order_by":2,"name":"Tie Wang","email":"","orcid":"https://orcid.org/0009-0002-4505-8700","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Tie","middleName":"","lastName":"Wang","suffix":""},{"id":307534816,"identity":"fa0300e0-7eeb-4035-ae58-af6de2c37c78","order_by":3,"name":"Shifu Wang","email":"","orcid":"","institution":"State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Shifu","middleName":"","lastName":"Wang","suffix":""},{"id":307534817,"identity":"90647887-1138-4117-b0b3-a9d04d63d83d","order_by":4,"name":"Xuning Li","email":"","orcid":"https://orcid.org/0009-0009-7353-842X","institution":"Dalian Institute of Chemical Physics","correspondingAuthor":false,"prefix":"","firstName":"Xuning","middleName":"","lastName":"Li","suffix":""},{"id":307534818,"identity":"8fe2569a-0977-42c4-a626-df788aac696e","order_by":5,"name":"Yanqiang Huang","email":"","orcid":"https://orcid.org/0000-0002-7556-317X","institution":"Dalian Institute of Chemical Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yanqiang","middleName":"","lastName":"Huang","suffix":""}],"badges":[],"createdAt":"2024-05-09 10:17:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4394450/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4394450/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-024-55511-4","type":"published","date":"2025-01-02T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":60887020,"identity":"e06192a9-0ac5-4393-884f-c4ac3e510db6","added_by":"auto","created_at":"2024-07-23 08:10:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":701387,"visible":true,"origin":"","legend":"\u003cp\u003eHR-TEM image of fresh (a) Fe\u003csub\u003e2.5\u003c/sub\u003eN and (b) spent Fe\u003csub\u003e2.5\u003c/sub\u003eN (32 h reaction), (c) XRD patterns and (d) XPS high-resolution N 1s spectra of the fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN, 2 h spent, 5 h spent, and 32 h spent Fe\u003csub\u003e2.5\u003c/sub\u003eN, (e) \u003csup\u003e57\u003c/sup\u003eFe-Mössbauer spectra of fresh, 2 h spent, 5 h spent and 32 h spent Fe\u003csub\u003e2.5\u003c/sub\u003eN obtained at 298 K (f) Fe K-edge XANES spectra and FT-EXAFS spectra of fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN, reference FeO, and reference Fe foil.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/f2e34005749417f944410ae9.png"},{"id":60886371,"identity":"23fe0d34-850f-44a1-8992-3b0f5ea9577d","added_by":"auto","created_at":"2024-07-23 08:02:43","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":270179,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/061beee90c2dc80697debd5f.png"},{"id":60886375,"identity":"1371a701-8bc2-410c-8eb2-05f2408a4f54","added_by":"auto","created_at":"2024-07-23 08:02:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":461459,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/b69037eebe3e535723bd4cd0.png"},{"id":60887022,"identity":"aafc165c-0ab1-4776-8098-b84afd358012","added_by":"auto","created_at":"2024-07-23 08:10:43","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":412360,"visible":true,"origin":"","legend":"\u003cp\u003eThe extraction of N in Fe\u003csub\u003e2.5\u003c/sub\u003eN with different alcohols.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/fad6db41ac0af6c022a4b4cb.png"},{"id":60886377,"identity":"a861639d-0a9a-4e38-9e90-338850daae6e","added_by":"auto","created_at":"2024-07-23 08:02:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":421323,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XPS spectra of as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN and spent Fe\u003csub\u003ex\u003c/sub\u003eN, (b) XRD patterns of as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN and commercial Fe, (c) Organonitrogen products amount and organonitrogen yield (N basis) within 4 cycles of the N\u003csub\u003e2\u003c/sub\u003e-to-amines synthesis system. The as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN was prepared by ball milling in N\u003csub\u003e2\u003c/sub\u003e (6 bar) at rotation speed of 2000 r.p.m. for 30 h. Octylamine production reaction condition: 1 mL octanol, 5 g Fe\u003csub\u003ex\u003c/sub\u003eN, 10 bar H\u003csub\u003e2\u003c/sub\u003e, 250℃, 6 h. Organonitrogen yield [%] = the amount of organonitrogen products / the amount of input N in Fe\u003csub\u003ex\u003c/sub\u003eN.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/9a3b6b2697fa5b42437cd7be.png"},{"id":72949903,"identity":"b97ecdba-fc3c-4861-979e-07e1508cc32a","added_by":"auto","created_at":"2025-01-04 08:12:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3154496,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/84a4c157-5442-4969-ab95-d700f294840a.pdf"},{"id":60886373,"identity":"c6edc7a3-0ba0-48f1-a337-4e1565aca777","added_by":"auto","created_at":"2024-07-23 08:02:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2674959,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/a707cd8d2eeb47a13d72846a.docx"},{"id":60887021,"identity":"25da8c4e-c2b1-4264-bc52-6e2ffb4aea27","added_by":"auto","created_at":"2024-07-23 08:10:43","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":219662,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1.\u003c/strong\u003e (a) Catalytic amination of alcohols/aldehydes using NH\u003csub\u003e3\u003c/sub\u003e (b) The proposed Fe\u003csub\u003ex\u003c/sub\u003eN-mediated chemical looping pathway to synthesize organoamines. (Left) Organoamines synthesis using Fe\u003csub\u003ex\u003c/sub\u003eN, (Right) Preparation of stable Fe\u003csub\u003ex\u003c/sub\u003eN using N\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"Scheme.png","url":"https://assets-eu.researchsquare.com/files/rs-4394450/v1/e2a7d1015895c1c23b1702c4.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eChemical looping synthesis of amines from N\u003csub\u003e2\u003c/sub\u003e via iron nitride as a mediator\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNitrogen-containing chemicals,\u0026nbsp;particularly\u0026nbsp;amines, are key building blocks for chemical industries.\u003csup\u003e1-10\u003c/sup\u003e Currently, the\u0026nbsp;primary nitrogen source for synthesizing these compounds, ammonia, is produced from the Haber-Bosch process\u0026mdash;the single most energy-intensive processes globally operating at 400-500 \u0026deg;C\u0026nbsp;and\u0026nbsp;200-250 bar.\u003csup\u003e11,12\u003c/sup\u003e Additionally, amination reactions\u0026nbsp;using\u0026nbsp;ammonia often require noble metal catalysts because many substrates do not efficiently react with ammonia. Even with catalysts, the single-pass conversion of NH\u003csub\u003e3\u003c/sub\u003e remains low, typically ranging from 0.2~7% (Table S1 and Scheme 1).\u0026nbsp;Given these challenges, there has been a sustained effort to develop alternative pathways that enable the production of nitrogen-containing organic compounds starting from N\u003csub\u003e2\u003c/sub\u003e, bypassing the Haber-Bosch process.\u003c/p\u003e\n\u003cp\u003eExciting progresses have been made in the synthesis of organonitrogen chemicals directly from N\u003csub\u003e2\u003c/sub\u003e, primarily utilizing Li in metallic or other highly reactive states. For instance, Li has been employed as the reductant for the synthesis of N\u003csub\u003e2\u003c/sub\u003e-transition metal complexes as key intermediates\u003csup\u003e13\u003c/sup\u003e or for the direct conversion of N\u003csub\u003e2\u003c/sub\u003e to organonitrogen chemicals.\u003csup\u003e14\u003c/sup\u003e Li also reacts with N\u003csub\u003e2\u003c/sub\u003e to form Li\u003csub\u003e3\u003c/sub\u003eN, which further interacts with reactive species such as aromatic halides or aromatic acyl chlorides to construct C\u0026ndash;N bonds.\u003csup\u003e15\u003c/sup\u003e Additionally, key synthons like Li\u003csub\u003e2\u003c/sub\u003eCN\u003csub\u003e2\u003c/sub\u003e have been synthesized from LiH and N\u003csub\u003e2\u003c/sub\u003e, serving as precursors for accessing organonitrogen chemicals.\u003csup\u003e16\u003c/sup\u003e Despite these elegant studies, the high redox potential of Li makes the preparation and regeneration of metallic Li energy-intensive,\u003csup\u003e15\u003c/sup\u003e and its high reactivity also necessitates precautions in wide application. Beyond Li, organometallic complexes of Mo and Ti have also been explored, showing potential in activating N\u003csub\u003e2\u003c/sub\u003e \u003csup\u003e17-19\u003c/sup\u003e and leading to the formation of organonitrogen chemicals in the presence of Pd catalysts.\u003csup\u003e20,21\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eNevertheless, no studies have yet harnessed inexpensive 3-d metals as effective mediators to synthesize organonitrogen chemicals from N\u003csub\u003e2\u003c/sub\u003e. We propose that 3-d metal nitrides could serve as promising candidates to bridge N\u003csub\u003e2\u003c/sub\u003e to organonitrogen compounds.\u0026nbsp;Investigations into the release of nitrogen atoms from 3-d transition metal nitrides under\u0026nbsp;H\u003csub\u003e2\u003c/sub\u003e,\u003csup\u003e22-25\u003c/sup\u003e CO,\u003csup\u003e26\u003c/sup\u003e and mixed atmosphere of CO\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e,\u003csup\u003e27\u003c/sup\u003e have shown that lattice nitrogen is labile and reactive, potentially facilitating C\u0026ndash;N bond formation.\u0026nbsp;Furthermore,\u0026nbsp;a range of 3-d metals, including Ti,\u003csup\u003e28\u003c/sup\u003e Cr,\u003csup\u003e29\u003c/sup\u003e Mn,\u003csup\u003e30,31\u003c/sup\u003e and Fe\u003csup\u003e32\u003c/sup\u003e have reacted with N\u003csub\u003e2\u003c/sub\u003e to form metal nitrides.\u003csup\u003e33,34\u003c/sup\u003e With a moderate nitrogen binding energy that enable both the fixation of N\u003csub\u003e2\u003c/sub\u003e to nitride, as well as the transfer of nitrogen in the nitride into organonitrogen chemicals, 3-d transition metal nitrides may thus serve as effective nitrogen carriers.\u003csup\u003e35\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eIn this study, we report our advances in the chemical looping synthesis of organonitrogen compounds using iron nitride as the nitrogen carrier (Scheme 1).\u0026nbsp;We first investigated the reactivity of iron nitride (Fe\u003csub\u003e2.5\u003c/sub\u003eN) in converting isopropanol to isopropylamine and di-isopropylamine, demonstrating that iron nitride is a superior nitrogen source for amine synthesis compared to ammonia\u0026nbsp;(Scheme 1b, left). We then expanded our investigation to include a range of alcohols\u0026mdash;primary, secondary, and tertiary\u0026mdash;to broaden the applicability of this method. Finally, we demonstrated the effectiveness of the N\u003csub\u003e2\u003c/sub\u003e-nitridated iron powder (Fe\u003csub\u003ex\u003c/sub\u003eN), made at ambient temperature and low pressure, as a nitrogen source for amine synthesis, during which itself is converted back to metallic iron. Through these efforts, we establish a cheap 3d metal-based chemical looping process for organonitrogen synthesis beginning with N\u003csub\u003e2\u003c/sub\u003e (Scheme 1b).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and reactivity of Fe\u003csub\u003e2.5\u003c/sub\u003eN\u003c/h2\u003e \u003cp\u003eWe initially prepared iron nitride with stoichiometric Fe:N ratio (2.5:1, terms as Fe\u003csub\u003e2.5\u003c/sub\u003eN)\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e for reactivity study, while the more challenging synthesis of Fe\u003csub\u003ex\u003c/sub\u003eN from N\u003csub\u003e2\u003c/sub\u003e and metallic iron was explored later. The fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN sample exhibited aggregates of 100 nm\u0026thinsp;~\u0026thinsp;1\u0026micro;m particles with irregular shapes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, S1a-e, S2a-f) and small surface area (14 m\u003csup\u003e2\u003c/sup\u003e∙g\u003csup\u003e-1\u003c/sup\u003e, Table S3). The XRD pattern of the sample matches that of Fe\u003csub\u003e2\u003c/sub\u003eN (PDF #73-2102) and Fe\u003csub\u003e3\u003c/sub\u003eN phase (PDF #72-2125) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). The lattice fringe spacing (d value) was 0.210 nm, 0.239 nm, and 0.302 nm, corresponding to the (-1 -1 1), (1 1 0), and (1 0 1) crystal plane of ε-phase\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e Fe\u003csub\u003e2\u003c/sub\u003eN/Fe\u003csub\u003e3\u003c/sub\u003eN hexagonal structure, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and S2). The N content of was 9.1 wt.% (Table S5), confirming a Fe:N ratio of ~\u0026thinsp;2.5:1. In the M\u0026ouml;ssbauer spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee), a doublet peak corresponding to ε-Fe\u003csub\u003e2.1\u003c/sub\u003eN is the major phase while a low-intensity sextet corresponding to γ-Fe\u003csub\u003e4\u003c/sub\u003eN coexists.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e In the XPS spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and Figure S3), the peaks at around 397.6 eV, 396.7 eV and 399.1 eV corresponded to Fe-O-N, Fe-N and adsorbed NH\u003csub\u003e3\u003c/sub\u003e, respectively.\u003csup\u003e\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e The adsorption edge of the fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN in the XANES spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef) was in between the reference Fe foil and FeO. Fourier transform of Fe K-edge EXAFS of the Fe\u003csub\u003e2.5\u003c/sub\u003eN was also performed: the peaks centered at ~\u0026thinsp;1.56 \u0026Aring; and ~\u0026thinsp;2.27 \u0026Aring; correspond to Fe-N and Fe-Fe shells, respectively,\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e consistent with the interstitial structure of iron nitride. Fe\u003csub\u003e2.5\u003c/sub\u003eN was thermally stable under inert atmosphere below 400\u0026deg;C, after which it decomposes, releasing N\u003csub\u003e2\u003c/sub\u003e (Figure S5).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNext, amination of isopropanol was conducted in a continuous fixed-bed reactor, with Fe\u003csub\u003e2.5\u003c/sub\u003eN placed inside the reactor while a mixture of H\u003csub\u003e2\u003c/sub\u003e and Ar carried isopropanol vapor through the sample bed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The study focuses on the conversion of nitrogen in Fe\u003csub\u003e2.5\u003c/sub\u003eN, so that the product yields were calculated on nitrogen basis. Fe\u003csub\u003e2.5\u003c/sub\u003eN was inactive at 150\u0026deg;C, but a notable productivity towards amines, including isopropylamine and di-isopropylamine, was observed at 200\u0026deg;C. The best performance was achieved at 250\u0026deg;C, resulting in a high organonitrogen selectivity of 23% under 5 bar H\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). At this temperature, the conversion of isopropanol remained relatively stable in the first 5 h (Figure S6), while the yield of organonitrogen compounds gradually decreased, indicating the nitrogen consumption led to the decrease amine production. Hydrocarbons and oxygenates (C\u003csub\u003e6\u003c/sub\u003e-C\u003csub\u003e9\u003c/sub\u003e) were the major non-nitrogen containing products (Figure S7-S8). When the temperature further increased to 300\u0026deg;C, the most favorable reaction became hydrodeoxygenation.\u003c/p\u003e \u003cp\u003eAt optimum temperature (250\u0026deg;C), the variation of H\u003csub\u003e2\u003c/sub\u003e partial pressure from 0 to 10 bar significantly influenced amine formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Without H\u003csub\u003e2\u003c/sub\u003e, only a minor fraction of organonitrogen compounds was formed, likely through the hydrogen-borrowing pathway as observed in catalytic amination of alcohols.\u003csup\u003e\u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e Increasing the hydrogen partial pressure to 1 bar substantially enhanced amine production. Further increasing the H\u003csub\u003e2\u003c/sub\u003e partial pressure led to reduced amine yields, attributable to the enhanced formation of ammonia, thereby limiting the nitrogen available to form the organonitrogen products. Additionally, H\u003csub\u003e2\u003c/sub\u003e is known to hinder the dehydrogenation of isopropanol.\u003csup\u003e\u003cspan additionalcitationids=\"CR49 CR50\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe consumption of nitrogen in Fe\u003csub\u003e2.5\u003c/sub\u003eN at optimal condition over time is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. The 5 hours of reaction at 250\u0026deg;C with 1 bar H\u003csub\u003e2\u003c/sub\u003e led to almost total loss of nitrogen, where 37% of the initial nitrogen had been transformed into amines, and the remaining amount was present as gaseous NH\u003csub\u003e3\u003c/sub\u003e. After 32-hour reaction (Table S5), N was completely depleted. The data indicate a positive correlation between the amination rate and the nitrogen content in Fe\u003csub\u003e2.5\u003c/sub\u003eN.\u003c/p\u003e \u003cp\u003eThe spent Fe\u003csub\u003e2.5\u003c/sub\u003eN remained similar shape (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ef-j, and Figure S2g-k) and surface area (12 m\u003csup\u003e2\u003c/sup\u003e∙g\u003csup\u003e-1\u003c/sup\u003e, Table S3) compared with fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN. The lattice fringe spacing of 32-hour spent Fe\u003csub\u003e2.5\u003c/sub\u003eN corresponds to the (1 1 0) crystal plane of metallic iron, and the XRD patterns of both 2-hour and 32-hour spent Fe\u003csub\u003e2.5\u003c/sub\u003eN also corresponded well with metallic Fe phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). For the 2 h and 32 h spent Fe\u003csub\u003e2.5\u003c/sub\u003eN, the M\u0026ouml;ssbauer spectrum showed only the sextet corresponding to α-Fe.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e In XPS analysis, the presence of N could still be observed in the 2-hour spent Fe\u003csub\u003e2.5\u003c/sub\u003eN (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and Figure S3), but no nitrogen was seen in the 32-hour spent Fe\u003csub\u003e2.5\u003c/sub\u003eN. These results consistently suggest that the lattice nitrogen in Fe\u003csub\u003e2.5\u003c/sub\u003eN was gradually consumed during the reaction while Fe species are transformed into metallic Fe.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eReaction mechanism and substrate scope\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea displays the in-situ DRIFTS spectra of isopropanol adsorption on fresh Fe\u003csub\u003e2.5\u003c/sub\u003eN under H\u003csub\u003e2\u003c/sub\u003e atmosphere at 250\u0026deg;C. The peak at 3656 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is attributed to the O-H stretching of isopropanol.\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e More importantly, the peak at 2655 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e corresponds to characteristic peak of isopropylamine (Figure S10), indicating the formation of the desired product. The peak at 1738 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is assigned to C\u0026thinsp;=\u0026thinsp;O stretching,\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e,\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e revealing the presence of acetone.\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e The peaks at 1651 and 1642 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e are ascribed to C\u0026thinsp;=\u0026thinsp;N stretching,\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e and the peak at 1246 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e arises from C-N stretching.\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e,\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e Vibrations of NH\u003csub\u003ex\u003c/sub\u003e species bonded to Fe sites are also observed.\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e Further assignments of peaks are provided in the supporting information (Table S7). Using ammonia as a probe molecule, Lewis acid sites was identified on Fe\u003csub\u003e2.5\u003c/sub\u003eN (Figure S9),\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e,\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e,\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e which are known to be beneficial for dehydrogenation of alcohol,\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e activation of C\u0026thinsp;=\u0026thinsp;O,\u003csup\u003e64,65\u003c/sup\u003e and hydrogenation of C\u0026thinsp;=\u0026thinsp;N.\u003csup\u003e64\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAcetone was further employed as a substrate to react with Fe\u003csub\u003e2.5\u003c/sub\u003eN (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). At both 200\u0026deg;C and 250\u0026deg;C, acetone generated the same types of products as isopropanol did, such as isopropylamine, di-isopropylamine, and Schiff base (Figure S8), demonstrating that acetone is a viable intermediate for amine formation. Compared to using alcohol, the production of amine compounds is much more prominent at a lower 200\u0026deg;C, indicating that the dehydrogenation of isopropanol to acetone is likely to be rate-limiting.\u003c/p\u003e \u003cp\u003eThe reduction behavior of Fe\u003csub\u003e2.5\u003c/sub\u003eN was investigated under H\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). A prominent peak, identified as NH\u003csub\u003e3\u003c/sub\u003e, appeared at 520\u0026deg;C, demonstrating the transformation of lattice nitrogen in Fe\u003csub\u003e2.5\u003c/sub\u003eN to form NH\u003csub\u003e3\u003c/sub\u003e. The NH\u003csub\u003e3\u003c/sub\u003e signal below 335\u0026deg;C was minimal, supporting the notion that the chosen amination reaction temperature of 250\u0026deg;C reduced the undesirable side reaction of producing ammonia.\u003c/p\u003e \u003cp\u003eWe propose the following mechanism for the reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Initially, isopropanol is adsorbed on the Lewis acid sites of the iron nitride and undergoes dehydrogenation to yield acetone. Subsequently, the NH\u003csub\u003ex\u003c/sub\u003e present on Fe\u003csub\u003e2.5\u003c/sub\u003eN surface transform acetone into imine, which is then hydrogenated to isopropylamine. As surface nitrogen is progressively consumed, the lattice nitrogen migrates to the surface for further amination, during which Fe\u003csub\u003e2.5\u003c/sub\u003eN is gradually converted to metallic iron. This reaction pathway is analogous to the conventional amination mechanism, but the nitrogen source is lattice nitrogen. Given that hydrogen also reacts with Fe\u003csub\u003e2.5\u003c/sub\u003eN to produce ammonia, the existence of conventional amination pathway cannot be entirely excluded.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo validate the wide applicability of amine production using iron nitride as the nitrogen source, we evaluated the reaction between Fe\u003csub\u003e2.5\u003c/sub\u003eN and a range of alcohols in a batch reactor. The findings revealed that primary alcohols (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) react more effectively than secondary alcohols, while tertiary alcohols show no reactivity in forming amines. This variation in reactivity is attributed to the steric hindrance in secondary alcohols and the absence of α-H in tertiary alcohols, which prevents the formation of the crucial C\u0026thinsp;=\u0026thinsp;O intermediate. Additionally, primary alcohols exhibited a higher selectivity for producing tertiary amines, likely due to the greater stability of tertiary amines. The highest amine yield achieved is 95.2% with 1-decanol as substrate. These results suggest that Fe\u003csub\u003e2.5\u003c/sub\u003eN has broad applicability and adaptability across different alcohol substrates and add supporting evidence for the proposed mechanism of alcohol dehydrogenation followed by solid N (in Fe\u003csub\u003e2.5\u003c/sub\u003eN)-dominated amination.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eN\u003csub\u003e2\u003c/sub\u003e-to-amine via Fe\u003csub\u003ex\u003c/sub\u003eN as a mediator\u003c/h2\u003e \u003cp\u003eTo enable an iron nitride-mediated looping pathway to make amines using N\u003csub\u003e2\u003c/sub\u003e as nitrogen source, we synthesized iron nitride from N\u003csub\u003e2\u003c/sub\u003e following an elegant recent report based on a mechanochemical approach.\u003csup\u003e\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e Typically, iron powder was loaded into ball-mill jar with iron balls and charged with 6 bar of N\u003csub\u003e2\u003c/sub\u003e for the ball milling to synthesize iron nitride (Fe\u003csub\u003ex\u003c/sub\u003eN) without heat supply. N 1s XPS spectra of the as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN clearly showed the existence of N on the surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The XRD patterns of the as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN and commercial iron powder are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. A peak shift towards lower angel caused by N insertion is observed after ball milling under N\u003csub\u003e2\u003c/sub\u003e atmosphere. The presence of N in the as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN was further ambiguously confirmed by EDX mapping of SEM and TEM (Figure S11, Table S2) and CHN elemental analysis (Table S5). Based on acid treatment method (Table S8), the N content in the as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN was 0.4 wt.%.\u003c/p\u003e \u003cp\u003eThe as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN was subsequently reacted with octanol in the same manner as described in the previous session. Encouragingly, around 80% N in the as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN was transferred to octylamines, majority of which was trioctylamine due to its higher stability. Post-reaction Fe\u003csub\u003ex\u003c/sub\u003eN was washed with methanol and freeze-dried before taking to the next round looping synthesis. The nitrogen content of the spent Fe\u003csub\u003ex\u003c/sub\u003eN was not detected by acid treatment and elemental analysis, (Table S5 and Table S8) indicating the N in Fe\u003csub\u003ex\u003c/sub\u003eN was depleted during the reaction. The excellent activity maintained throughout the 4 cycles, highlighting the high N utilization efficiency and durability of the proposed N\u003csub\u003e2\u003c/sub\u003e-to-amine looping strategy. The overall activity and specific selectivity towards dioctylamine both increased with increasing cycles, which could be explained by enriched H species on iron nitride surface during repeated use, which facilitates reaction and product desorption.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn conclusion, this study provides an entry point into the broader potential for transition metal nitrides as the nitrogen carrier bridging the looping synthesis of organonitrogen chemicals from N\u003csub\u003e2\u003c/sub\u003e. We confirmed the donation of nitrogen from iron nitride to alcohols, with the concurrent transformation of Fe species metal nitride into metallic Fe. When Fe\u003csub\u003e2.5\u003c/sub\u003eN was used as a nitrogen carrier, more than 85% of the nitrogen was extracted to produce amines from C\u003csub\u003e6\u003c/sub\u003e\u0026thinsp;~\u0026thinsp;C\u003csub\u003e10\u003c/sub\u003e primary alcohols in a batch reactor at 250\u0026deg;C and 10 bar H\u003csub\u003e2\u003c/sub\u003e. More importantly, Fe\u003csub\u003ex\u003c/sub\u003eN, produced by nitridating iron powder with N\u003csub\u003e2\u003c/sub\u003e at ambient temperature and low pressure, has proven to be an effective nitrogen source for the catalyst-free production of organic amines. High N utilization efficiency of over 80% was consistently achieved over 4 cycles. This study unlocks the previously untapped potential of using inexpensive 3d-transition metal nitrides to produce organonitrogen compounds with N\u003csub\u003e2\u003c/sub\u003e as the nitrogen source.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003e2-propanol (\u0026ge;\u0026thinsp;99.5%) and phenol (99%) were purchased from Fisher Scientific Pte. Ltd. Iron (\u0026ge;\u0026thinsp;99%, reduced, fine powder), concentrated sulfuric acid (ACS reagent, 95.0\u0026ndash;98.0%), concentrated hydrochloric acid (ACS reagent, 37%), potassium hydroxide (ACS reagent, \u0026ge;\u0026thinsp;85%, pellets), isopropylamine (\u0026ge;\u0026thinsp;99.5%), acetone (anhydrous, \u0026ge;\u0026thinsp;99.5%), cyclohexanol (99%), 1-butanol (99.8%), 1-hexanol (\u0026ge;\u0026thinsp;99%), 1-octanol (\u0026ge;\u0026thinsp;99%), 1-decanol (98%), and tert-butanol (\u0026ge;\u0026thinsp;99.5%) were provided by Sigma-Aldrich Pte. Ltd. (Singapore). Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (\u0026ge;\u0026thinsp;97%) was purchased from Shanghai Macklin Biochemical Co., Ltd.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eTypical activity test\u003c/h2\u003e \u003cp\u003eThe catalytic performance tests were carried out in a vertical, fixed-bed tube reactor (SS316), with the reactor tube length of 0.5 m and the diameter of 7.6 mm. A furnace (1.2 kW, 220 V, up to 1000\u0026deg;C) was utilized to heat the reactor, and a thermocouple was inserted into the catalyst bed to monitor the temperature in real time. The temperature was regulated by a temperature controller that was inserted into the reactor. The samples were diluted with quartz sand and held in place with quartz wool to form a sample bed in the middle of the reactor. The liquid substrates were first introduced into a three-way autoclave, which had dedicated paths for the addition of liquid substrates, gas supply, and gas outlet connected to the reactor tube. The autoclave was maintained in water bath at 25\u0026deg;C, and the pressure inside was regulated using a back pressure valve. The gas inlet path of the autoclave was submerged at the bottom of the liquid for bubbling so that the liquid vapor can be carried by the gas to enter the reactor and go through the sample bed, while the hydrogen gas and argon gas were supplied to the autoclave controlled by gas flow meters.\u003c/p\u003e \u003cp\u003eAfter loading Fe\u003csub\u003e2.5\u003c/sub\u003eN in the middle of reactor and increasing the temperature to the reaction temperature, substrates mixed with H\u003csub\u003e2\u003c/sub\u003e and Ar were supplied into the reactor at desired flow rates. The products were collected and analyzed by an online GC-FID system equipped with an Agilent CAM capillary column. The outlet flow could also be collected by passing through a bottle of methanol in ice bath to obtain the organic chemicals for off-line GC or GC-MS analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eActivity test for substrate scope (Autoclave batch reactor)\u003c/h2\u003e \u003cp\u003eThe transformation of alcohols with Fe\u003csub\u003e2.5\u003c/sub\u003eN was also performed in an autoclave. For example, 50 mg Fe\u003csub\u003e2.5\u003c/sub\u003eN, 70 \u0026micro;L dodecane (internal standard), and 1 mL alcohol substrates were added to the reactor in the glovebox. After that, the autoclave was introduced with 9 bar H\u003csub\u003e2\u003c/sub\u003e, and placed in a metal jacket wafer on an electronic hotplate (typically 250\u0026deg;C). After 6 hours of reaction, the reactor was immediately terminated by cooling the reactor in ice. The gas phase products were collected by gas bag, and the gas was then bubbled into the diluted sulfuric acid solution. The obtained solution was detected by IC (ion chromatography). The liquid products were collected and tested by GC and GC-MS for qualification and quantification analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eThe synthesis and activity test of N\u003csub\u003e2\u003c/sub\u003e-nitridated Fe (Fe\u003csub\u003ex\u003c/sub\u003eN)\u003c/h2\u003e \u003cp\u003eSpecifically, iron powder (5 g) and iron balls (50 g, 5 mm diameter) were loaded into the ball-mill jar (50 mL) inside an Ar-atmosphere glovebox. The ball-mill jar was then evacuated and charged to 6 bar using N\u003csub\u003e2\u003c/sub\u003e before being taken to the planetary ball mill machine for 30 h 2000 rpm ball milling. The ball milling was stopped for 10 min every 30 min to release the heat.\u003c/p\u003e \u003cp\u003eThe as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN powder was transferred into an autoclave, together with 1 mL octanol and 70\u0026micro;L dodecane (internal standard). The autoclave was purged with 10 bar H\u003csub\u003e2\u003c/sub\u003e for more than 10 times carefully to exchange the Ar inside. After purging, the batch reactor was charged with 10 bar H\u003csub\u003e2\u003c/sub\u003e, and reacted at 250\u0026deg;C for 6 h on an electronic hotplate with metal jacket. Similarly, the reactor was instantly cooled with ice after 6 hours of reaction, and the gas phase was carefully released into a 0.5 M sulfuric acid solution. The liquid products were washed with 1 mL methanol and tested by GC-FID and GC-MS. The remaining spent Fe\u003csub\u003ex\u003c/sub\u003eN powder was further washed with 50 mL methanol for 3 times inside the glovebox before taken to ball-mill reaction with nitrogen gas again.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eN content determination\u003c/h2\u003e \u003cp\u003eThe nitrogen content of iron nitride samples was determined by dissolving 0.1 g of the sample in 30 mL 0.2 M hydrochloric acid at 80\u0026deg;C overnight. After that, 50 mL of 5 M KOH solution was injected to the clear aliquot under continuous N\u003csub\u003e2\u003c/sub\u003e purging at 80\u0026deg;C. The outlet gas was bubbled through 10 mL of 0.5 M sulfuric acid for 2 hours, which was taken to IC analysis for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe crystal structure of iron nitride was tested by a Bruker D8 Advance X-Ray diffractometer, equipped with a Cu Kα source (40 kV, 30 mA). BET surface areas were calculated from nitrogen adsorption isotherms obtained by N\u003csub\u003e2\u003c/sub\u003e adsorption and desorption at 77 K in a Micromeritics ASAP 2020 surface area. Scanning electron microscopy (SEM) was performed with a JEOL JSM-7610F. Transmission electron microscopy images were acquired on a JEM 2100F (JEOL, Japan) microscope operated at 200 kV. XPS spectra were recorded on a VG Escalab MKII spectrometer, using a mono Al Kα X-ray source (hv\u0026thinsp;=\u0026thinsp;1486.71 eV, 5 mA, 15 kV), and the calibration was done by setting the C1s peak at 284.5 eV. Elemental mappings of iron nitride were obtained using an JEOL microscope equipped with a Bruker Quantax energy-dispersive X-ray spectrometer (EDXS). CHN elemental analysis was conducted on Thermo Scientific Flashsmart CHNS analyzer. The room temperature \u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003eFe M\u0026ouml;ssbauer spectrum was observed on a Topologic 500A spectrometer, which equipped \u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003eCo(Rh) as the radioactive source. Fitted by the M\u0026ouml;ssWinn 4.0, all of the spectra were distinguished by different parameters, such as quadrupole splitting (QS) and isomer shift (IS). Besides, an α-iron foil was used to calibrate the IS values and Doppler velocities.\u003c/p\u003e \u003cp\u003eIn situ diffuse reflectance infrared Fourier transform (DRIFT) spectra were acquired on a Thermo Scientific Nicolet iS50 FT-IR. The measurement was under atmospheric pressure, with ZnSe window and MCT-A detector cooled by liquid nitrogen. The solid Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e powder was treated at 550\u0026deg;C under 30 mL/min NH\u003csub\u003e3\u003c/sub\u003e flow for 30 minutes in the cell to in situ form iron nitride, and then the temperature was changed to the required temperature under the H\u003csub\u003e2\u003c/sub\u003e flow or the Ar flow for the in-situ observation. The background was recorded under Ar before testing samples. The vapor of the liquid substrate was carried by the Ar gas flow into the cell. The NH\u003csub\u003e3\u003c/sub\u003e gas was supplied by the gas sample bag injection and degassed under Ar gas flow. The spectra were recorded with 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e resolution of 32 scans.\u003c/p\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003e-TPR-MS measurements were performed using a Quantachrome instrument coupled with a quadrupole mass spectrometer (Hidden Analytical). Prior to the measurements, the sample was pretreated in a flow of pure He gas at 150\u0026deg;C to remove the moisture and any contaminants. The H\u003csub\u003e2\u003c/sub\u003e-TPR profile was obtained by heating the sample from 30\u0026deg;C to 800\u0026deg;C at the rate of 10\u0026deg;C/min in a 5% H\u003csub\u003e2\u003c/sub\u003e/He atmosphere, while Ar-TPD (decomposition) measurements were conducted under pure He flow when heating the sample at the rate of 10\u0026deg;C/min to 800\u0026deg;C. The mass spectrometer was set to record the gas outlet composition.\u003c/p\u003e \u003cp\u003eEx situ Fe K-edge XAS measurements were conducted at a public beamline, BL01B1, Spring-8 (Japan Synchrotron Radiation Research Institute, Hyogo, Japan). (Proposal number: 2023A1533) The incident X-rays were monochromatized with a Si (111) double crystal monochromator. Conventional Fe K-edge XAS spectra of a Fe metal foil, FeO, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e were collected as reference data. Data were reduced using the Athena and Artemis software ver. 0.9.26 included in the Demeter package. The 7 mm catalyst pellets were made from a thoroughly ground mixture of 1.1 mg Fe\u003csub\u003ex\u003c/sub\u003eN with 60 mg boron nitride.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eWe thank the NRF Investigatorship (NRF-NRFI07–2021–0006) for the financial support.\u003c/p\u003e\n\u003cp\u003eSupporting Information\u003c/p\u003e\n\u003cp\u003eMaterials, experimental details, and supplementary data were provided. The authors have cited additional references within the Supporting Information.\u003csup\u003e48,65,67-82\u003c/sup\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eStankiewicz, B. A. \u0026amp; Van Bergen, P. 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Technol.\u003c/em\u003e \u003cstrong\u003e45,\u003c/strong\u003e 1147-1151 (2011).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Nitrogen activation, Organoamines production, Transition metal nitride, Iron nitride, Amination","lastPublishedDoi":"10.21203/rs.3.rs-4394450/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4394450/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAmines are commonly synthesized through the amination of organooxygenates using ammonia, frequently involving the use of noble metal catalysts. In this study, we present an alternative route to make amines using iron nitride (Fe\u003csub\u003e2.5\u003c/sub\u003eN) as the nitrogen source. Without any additional catalyst, Fe\u003csub\u003e2.5\u003c/sub\u003eN reacts with a range of alcohols at 250 °C under 1 or 10 bar H\u003csub\u003e2\u003c/sub\u003e to produce amines as major products. Mechanistic investigations indicate that hydrogen activates the nitrogen species within iron nitride, converting them into surface NH and NH\u003csub\u003e2\u003c/sub\u003e groups that then react with alcohols to form amines. Building on this foundation, we further demonstrated an iron nitride-mediated chemical looping pathway that utilizes N\u003csub\u003e2\u003c/sub\u003e as the nitrogen source to synthesize octylamines. In this process, N\u003csub\u003e2\u003c/sub\u003e first reacts with iron to form Fe\u003csub\u003ex\u003c/sub\u003eN by a ball-milling method at ambient temperature and 6 bar N\u003csub\u003e2\u003c/sub\u003e. The as-prepared Fe\u003csub\u003ex\u003c/sub\u003eN subsequently reacts with alcohols to yield amines, transferring over 80% of the nitrogen to organic compounds. This looping process proved stable across four cycles.\u003c/p\u003e","manuscriptTitle":"Chemical looping synthesis of amines from N2 via iron nitride as a mediator","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-23 08:02:38","doi":"10.21203/rs.3.rs-4394450/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"37e9f47a-2463-40c5-a36b-c1d9ce9a59e9","owner":[],"postedDate":"July 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":34993510,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"},{"id":34993511,"name":"Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis"}],"tags":[],"updatedAt":"2025-01-04T08:12:18+00:00","versionOfRecord":{"articleIdentity":"rs-4394450","link":"https://doi.org/10.1038/s41467-024-55511-4","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-01-02 05:00:00","publishedOnDateReadable":"January 2nd, 2025"},"versionCreatedAt":"2024-07-23 08:02:38","video":"","vorDoi":"10.1038/s41467-024-55511-4","vorDoiUrl":"https://doi.org/10.1038/s41467-024-55511-4","workflowStages":[]},"version":"v1","identity":"rs-4394450","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4394450","identity":"rs-4394450","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}