A divalent rare earth-graphyne composite material, a preparation method thereof and a thermal catalytic ammonia production application thereof

Abstract

This invention discloses a divalent rare earth-graphyne composite material, its preparation method, and its application in thermocatalytic ammonia production, belonging to the field of catalyst materials technology. The divalent rare earth-graphyne composite material comprises rare earth ions, iodide ions, and graphyne material. The rare earth ions are selected from at least one divalent ion of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium. The rare earth ions and iodide ions exist on the surface of the graphyne material in the form of nanoparticles. This divalent rare earth-graphyne composite material achieves thermocatalytic ammonia production under mild conditions through the interaction of rare earth nanoparticles and oxygen-containing functional groups on the graphyne surface, and is expected to become a new generation of high-performance thermocatalytic ammonia production catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, and in particular to a divalent rare earth-graphyne composite material, its preparation method, and its application in the thermal catalytic production of ammonia under mild conditions. Background Technology

[0002] Against the backdrop of accelerated global energy transition, renewable energy has surpassed traditional fossil fuels in several key dimensions, including new installed capacity, levelized cost of electricity (LCOE), annual investment scale, and policy support. Notably, in 2025, renewable energy generation accounted for a historic first time, exceeding coal-fired power generation in global electricity generation, marking a significant turning point in the structural transformation of the power system (T. Appenzeller, 2025 breakthrough of the year, Science, 2025, 390, 1208-1209). However, the inherent intermittency and geographical dispersion of renewable energy pose serious challenges to long-term energy storage and cross-regional transmission, necessitating the development of efficient green energy carriers compatible with existing energy infrastructure. Green ammonia is an ammonia synthesized by electrolyzing water using renewable energy sources such as wind and solar power to produce green hydrogen, which is then reacted with nitrogen separated from the air. Due to its high hydrogen content (17.6 wt%), low liquefaction pressure, and mature storage and transportation infrastructure, it is an ideal carrier for absorbing green hydrogen and storing renewable energy.

[0003] Currently, the mainstream synthesis routes for green ammonia mainly include three categories: thermocatalysis, electrocatalysis, and photocatalysis. While electrocatalysis and photocatalysis possess the potential for mild reactions, they are limited by bottlenecks such as low reaction efficiency, poor selectivity, and lack of stability, and are still in the laboratory exploration stage. In contrast, the thermocatalytic route, with its high technological maturity and good scale-up feasibility, remains the preferred route for the industrialization of green ammonia at this stage. The ammonia synthesis process currently used industrially is still the Haber-Bosch process proposed in the early 20th century. This process uses first-generation iron-based catalysts, which must operate at 300-500 °C and 150-200 atm, resulting in high energy consumption and high emissions. While second-generation ruthenium-based catalysts exhibit higher catalytic activity, they are limited by factors such as the high cost of metallic ruthenium and hydrogen poisoning, preventing them from completely replacing iron-based catalysts (VS Marakatti, et al., Recent advances in heterogeneous catalysis for ammonia synthesis. ChemCatChem, 2020, 12, 5838-5857). Therefore, developing novel catalysts for efficient thermocatalytic ammonia production under mild conditions has been a long-term vision for the synthetic ammonia industry. Crucially, green ammonia production is rapidly shifting towards distributed, small-scale operations, typically in areas rich in wind and solar resources. The traditional Haber-Bosch process, however, is inherently centralized, continuous, and ultra-large-scale, making the two technologies structurally incompatible. This further underscores the urgency and strategic value of developing efficient and flexible thermocatalytic ammonia production technologies adapted to the new energy landscape.

[0004] Rare earth elements include the 15 lanthanides in the periodic table, as well as scandium (Sc) and yttrium (Y), which have similar chemical properties, totaling 17 elements. For a long time, due to the strong shielding of the outer electrons of the 4f orbitals of lanthanides, it was traditionally believed that their contribution to the activation of small molecules (such as N2) was limited. Compared with transition metals, there are relatively few research examples of lanthanide metal complexes in the activation and conversion of nitrogen, one of the main reasons being the weak activation ability of the lanthanide metal center for nitrogen molecules. Normally, nitrogen is only reduced to [N2]. 2-It is difficult for them to undergo further derivatization reactions with electrophilic reagents (Chen Xiao et al., Study on nitrogen activation and conversion promoted by rare earth and actinide complexes. Acta Chimica Sinica, 2022, 80 (9), 1299-1308). In the subsequent nitrogen conversion process, nitrogen molecules tend to dissociate rather than form functionalized nitrogen-containing products. It is worth noting that the current application of lanthanides in the field of ammonia synthesis is mainly as a carrier or functional component, especially lanthanide metal oxides (such as CeO2, La2O3, etc.). These oxides have both intrinsic Lewis basicity and defect-mediated electron transport characteristics: on the one hand, the surface O 2- or OH ⁻ The lanthanide sites can act as electron donors, injecting electrons into the π* antibonding orbitals of adsorbed N₂, thus weakening the N≡N bond. On the other hand, oxygen vacancies and adjacent variable-valence cations significantly promote the directional migration of electrons from the support to the supported metal active centers (such as Fe and Ru), thereby increasing the electron density and reducing power of the interfacial active sites. However, recent studies have found that lanthanides can achieve highly efficient activation of nitrogen in heterogeneous catalytic systems under suitable reaction conditions. For example, some lanthanide hydrides can achieve N≡N bond breaking and efficiently generate nitrides under relatively mild conditions (such as ball milling at room temperature at 200°C or atmospheric pressure). Furthermore, research has shown that under high vacuum conditions, various lanthanide metal (such as Sm, Gd, Dy, Er, and Tb) films can react with nitrogen at room temperature, breaking the N≡N bond and generating the corresponding lanthanide nitrides. These nitrides can further react with water to release ammonia. These findings confirm that the potential of lanthanides for nitrogen conversion has not yet been fully understood. Meanwhile, although scandium and yttrium do not belong to the lanthanides, their electronic configuration (Sc: [Ar]3d) 1 4s 2 ;Y: [Kr]4d 1 5s 2 ) and ionic radius (Sc 3+ 74.5 pm; Y 3+ Scandium (90 pm) and yttrium (Yttrium) highly overlap with lanthanide ions, and the modulation by the lanthanide contraction effect gives them chemical properties highly consistent with lanthanides in terms of coordination environment and redox behavior. Therefore, incorporating scandium and yttrium into the rare earth nitrogen activation research system has sufficient structural and functional basis. In summary, the multi-scale action mechanism of rare earth elements (including Sc, Y, and all lanthanides) in nitrogen activation and directed conversion urgently needs to be systematically elucidated. Developing novel heterogeneous catalytic systems based on the intrinsic activity of rare earth elements has both important basic scientific significance and potential application value.

[0005] Graphdiyne (GDY), as a novel nanomaterial, possesses numerous advantages, including an intrinsically tunable band gap, a naturally porous structure, high specific surface area, uneven surface charge distribution, and excellent charge separation efficiency, making it an ideal platform for designing novel catalytic materials. Current research on the catalytic ammonia production of GDY mainly focuses on transition metals and noble metals, and primarily on electrocatalytic and photocatalytic systems. CN116809052A discloses an actinide ion-graphdiyne composite material and its preparation method, achieving catalytic ammonia production under mild conditions by supporting actinide single ions on few-layer GDY. Furthermore, CN119633798A discloses a class of actinide-graphdiyne aerogel composite materials with high specific surface area, further optimizing the catalytic ammonia production performance of the material through monomer structure regulation. However, while previous patents focused on actinides, which possess good catalytic activity, most actinides (such as Pu, Am, and Cm), except for uranium and thorium, have strong radioactivity and are subject to strict regulations, severely limiting their practical application. Furthermore, the strong reducing properties of low-valence actinides necessitate stringent requirements for catalyst storage and transportation, further raising the barrier to entry for their use. In contrast, among rare earth elements, only promethium (Pm) is an artificially radioactive element; the remaining 16 elements (Sc, Y, and La-Lu) are stable and non-radioactive, possessing excellent safety and potential for large-scale application. Compared to actinides, although the 4f orbitals of lanthanides are strongly shielded by outer electrons, studies have shown that through appropriate coordination regulation, the 4f orbitals can still participate in and influence the metal center to some extent. The unique electronic structure of GDY holds promise for partially unshielding the 4f orbitals through interfacial charge transfer and orbital hybridization effects, thereby enhancing its π-coupling effect on N2 molecules. * The electron-donating ability of antibonding orbitals. Most importantly, the lanthanide 4f-GDY interaction differs significantly from the actinide 5f-GDY and transition metal 3d-GDY systems in terms of orbital symmetry, spatial extension, and energy matching. This mechanistic difference not only expands the theoretical understanding of synergistic catalysis between GDY and lanthanides, but also provides a unique pathway for designing novel lanthanide metal catalysts for mild-condition ammonia production.

[0006] In summary, constructing a rare earth-graphyne composite catalytic system not only helps to elucidate the role mechanism of 4f electrons in heterogeneous catalysis and expand the application boundaries of rare earth elements in the field of energy catalysis, but also, relying on the rich variety of rare earth elements, can provide a broad material screening space for high-performance, low-cost, and scalable green ammonia catalysts. Summary of the Invention

[0007] The purpose of this invention is to provide a rare earth-graphyne composite material that maintains good stability in air and can achieve efficient thermocatalytic ammonia production under mild conditions, thereby breaking through the energy efficiency bottleneck of green ammonia synthesis and promoting the conversion of renewable energy.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A divalent rare earth-graphyne composite material includes rare earth ions, iodide ions, and graphyne material. The rare earth ions are selected from at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium ions. The rare earth ions and iodide ions are attached to the surface of the graphyne material in the form of nanoparticles with a size of 4-5 nm, and the rare earth ions are in the +2 valence state.

[0010] In some embodiments of the present invention, the morphology of the graphyne material is a nanowall structure.

[0011] In some embodiments of the present invention, the rare earth ion of the divalent rare earth-graphyne composite material is Sm, and its valence is +2.

[0012] The present invention also provides a method for preparing the above-mentioned divalent rare earth-graphyne composite material, comprising: immersing the graphyne material in a solution containing divalent rare earth ion iodides under conditions of isolation from water, oxygen and nitrogen, and drying it after a period of adsorption to obtain the divalent rare earth-graphyne composite material.

[0013] Preferably, the rare earth ion iodide is samarium diiodide.

[0014] Furthermore, the solvent for the solution containing rare earth ion iodides can be tetrahydrofuran, diethyl ether, dioxane, toluene, etc., preferably tetrahydrofuran.

[0015] In some embodiments of the present invention, the solution containing rare earth ion iodides is a tetrahydrofuran solution containing 50 ppm to 1000 ppm samarium diiodide, and the graphyne material is immersed in the solution at room temperature for 6-12 hours.

[0016] The present invention further provides the application of the above-mentioned divalent rare earth-graphyne composite material in thermocatalytic ammonia production.

[0017] In some embodiments of the present invention, the divalent rare earth-graphyne composite material is used as a catalyst for thermocatalytic ammonia production using a nitrogen-hydrogen mixture.

[0018] The nitrogen-hydrogen mixture contains 25-90 vol% nitrogen, preferably 10-40 vol% nitrogen; the temperature for thermocatalytic ammonia production is 90-200℃; and the pressure required for thermocatalytic ammonia production is 1-20 bar, preferably 10-15 bar.

[0019] In some embodiments of the present invention, the amount of the divalent rare earth-graphyne composite material used is such that the surface area is 2-6 cm². 2 The corresponding nitrogen-hydrogen mixed gas volume for the divalent rare earth-graphyne composite material is 100-200 mL.

[0020] The beneficial effects of this invention are:

[0021] This invention provides a divalent rare earth-graphyne composite material, in which nanoparticles formed by divalent rare earth ions and iodine ions are loaded onto the surface of graphyne material. Compared with the actinide-graphyne composite materials prepared by CN116809052A and CN119633798A, the use of non-radioactive rare earth elements in this invention is not only beneficial for the practical application of catalysts, but also provides more choices for catalyst optimization and iteration due to the abundance of selectable rare earth elements. Through the charge transfer interaction between graphyne and divalent rare earth ions, the valence state of rare earth ions can be effectively stabilized, allowing them to remain stably at +2 valence after exposure to air. This divalent rare earth-graphyne composite material exhibits excellent water and oxygen stability, which is beneficial for storage and transportation in practical applications. This divalent rare earth-graphyne composite material achieves highly efficient thermocatalytic ammonia production under mild conditions through the combined action of surface nanoparticles and oxygen-containing functional groups on the graphyne surface, which has important theoretical significance and practical application value for breaking through the energy efficiency bottleneck of green ammonia synthesis and promoting the conversion of renewable energy. Attached Figure Description

[0022] To provide a clearer and more detailed explanation of the technical solutions in the embodiments of the present invention, the accompanying drawings related to the embodiments of the present invention will be briefly introduced.

[0023] Figure 1 The images show the Sm 3d X-ray photoelectron spectra (XPS) of samarium diiodide prepared in Example 1 and samarium trichloride standard used as a reference. (a) is the fine Sm 3d XPS spectrum of the prepared samarium diiodide, and (b) is the fine Sm 3d XPS spectrum of the samarium trichloride standard used as a reference.

[0024] Figure 2 The image shows the Raman spectrum of the Sm / GDY-NW composite material prepared in Example 1.

[0025] Figure 3 The image shows a scanning electron microscope (SEM) image of the Sm / GDY-NW composite material prepared in Example 1.

[0026] Figure 4 The images show low-resolution transmission electron microscopy (LRTEM) and high-resolution transmission electron microscopy (HRTEM) images of the Sm / GDY-NW composite material prepared in Example 1. (a) is the LRTEM image of Sm / GDY-NW, and (b) is the HRTEM image of Sm / GDY-NW.

[0027] Figure 5 The Sm 3d and N 1s XPS fine spectra of the Sm / GDY-NW composite material prepared in Example 1 are shown. Among them: (a) is the Sm 3d XPS fine spectrum of Sm / GDY-NW, and (b) is the N 1s XPS fine spectrum of Sm / GDY-NW.

[0028] Figure 6 The fine Sm3d XPS spectra of the Sm / GDY-NW composite material prepared in Example 1 after exposure to air for different times are shown.

[0029] Figure 7 The fine XPS spectra of the Sm / GDY-NW composite material prepared in Example 1 after catalytic ammonia production are shown as (a) Sm 3d and (b) N 1s. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific experiments and accompanying drawings, but the present invention is not limited thereto. Other embodiments obtained by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

[0031] Experimental materials:

[0032] Graphdiyne nanowalls (GDY-NW) were prepared according to the method reported in the literature (J. Zhou, et al., Synthesis of graphdiyne nanowalls using acetylenic coupling reaction. J. Am. Chem. Soc. 2015, 137 (24), 7596-7599.). Ultrapure iodine, samarium powder (99.9%, 200 mesh), and samarium trichloride (99.9%) were purchased from Beijing Innocare Technology Co., Ltd.; pyridine, tetramethylethylenediamine (99%), acetone (99%), and ultra-dry dioxane (99%) with water and oxygen content all below 50%. Solvents such as ppm, tetrahydrofuran (99%), and diethyl ether (99%) were purchased from Beijing Inokai Technology Co., Ltd., with a purity of 99%. Dioxane, tetrahydrofuran, and diethyl ether required further dehydration and deoxygenation by a solvent purification system and metallic sodium before use. Concentrated sulfuric acid (98%), hydrochloric acid, dimethylformamide, dichloromethane, anhydrous ethanol, and cuprous chloride were purchased from Xilong Scientific Co., Ltd., with a purity of 99%. A nitrogen-hydrogen mixture (volume ratio 1:3, 99.999%) was purchased from Sichuan Shunlong Xinteng Co., Ltd.

[0033] Experimental apparatus:

[0034] Raman spectroscopy was performed using a DXRxi micro-Raman imaging spectrometer (Thermo-Fisher, USA). Scanning electron microscopy (SEM) analysis was performed using a Merlin Compact field emission scanning electron microscope (ZEISS, Germany). X-ray photoelectron spectroscopy (XPS) was performed on an ESCALAB 250Xi spectrometer (Thermo-Fisher, USA) using Al-Kα rays (hν = 1486.6 eV) as the excitation source. Inductively coupled plasma atomic emission spectrometry (ICP-OES) was performed using a Leeman Prodigy 8 instrument. Ion chromatography analysis was performed on a Thermo-Fisher INTEGRION ion chromatograph (USA).

[0035] Example 1

[0036] (1) Preparation of samarium diiodide

[0037] 2.5 g of metallic samarium powder was added to a reaction tube. After the system was purged three times with argon, ultra-dry tetrahydrofuran (THF) solvent, which had been strictly dehydrated and deoxygenated, was added. Under continuous argon protection, 3.24 g of iodine was slowly added in portions to the reaction tube while stirring in an ice-water bath. After the addition was complete, the reaction tube was sealed and heated at 80 °C for 2 days. It was observed that the solution was purple immediately after the addition of iodine, turning brownish-yellow as the reaction proceeded with stirring. With continued heating, the solution eventually turned dark blue. After the reaction was completed, the reaction tube was transferred to an argon-filled glove box, where unreacted excess samarium powder was filtered using a sintered glass funnel. After the filtrate was placed at -31 °C and allowed to stand, crystals were observed to gradually precipitate. After filtration, samarium diiodide crystals were obtained, and the product was in the form of green crystals. The product was stored in a freezer at -31 °C in the glove box.

[0038] (2) Preparation of Sm / GDY-NW

[0039] The loading of samarium diiodide was carried out in an argon glove box. Copper foil with grown GDY-NW was cut into 1 cm × 1 cm pieces and placed in 1 mL of tetrahydrofuran solution containing 50 ppm samarium diiodide. After standing at room temperature for 12 hours, the solution was removed, washed with a small amount of tetrahydrofuran, and the residual solvent was removed to obtain the Sm / GDY-NW composite material loaded with samarium diiodide. The loading of samarium diiodide was controlled by... 2+ The concentration of the solution can be adjusted to obtain Sm / GDY-NW composite materials with different loadings.

[0040] (3) Catalytic ammonia production of Sm / GDY-NW composite material

[0041] Three 1 cm × 1 cm pieces of Sm / GDY-NW composite material were transferred into a 100 mL 316L stainless steel high-pressure reactor in an argon-filled glove box. The reactor was sealed and then removed from the glove box. The gas inside the reactor was purged using a vacuum pump and a double-row tube to completely convert it into a nitrogen-hydrogen mixture with a hydrogen content of 75%. After at least three gas purgings, the reactor was charged with a nitrogen-hydrogen mixture at an initial pressure of 10 bar. After charging, the reactor was sealed, and the system was heated to 150 °C for 24 hours. Heating was stopped after the reaction was complete. Once the gas inside the reactor cooled to room temperature, it was slowly introduced into 3 mL of 0.005 M (mol / L) dilute sulfuric acid to absorb the ammonia produced. After product collection, the reactor was vacuum-sealed and transferred back to the glove box. The ammonia-producing material was stored in the glove box for further characterization. Ion chromatography was used to quantitatively analyze the ammonium ions in the absorption solution to determine the ammonia production. The chromatographic conditions were as follows: the column was a Dionex IonPac 4 μm ion chromatography column, the column temperature was kept constant at 25℃, isocratic elution was performed at a flow rate of 1 mL / min, and the eluent was a 0.01 M aqueous solution of methanesulfonic acid.

[0042] Example 2

[0043] Except for changing the concentration of samarium diiodide solution in step (2) of Example 1 to 100 ppm, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0044] Example 3

[0045] Except for changing the concentration of samarium diiodide solution in step (2) of Example 1 to 150 ppm, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0046] Example 4

[0047] Except for changing the concentration of samarium diiodide solution in step (2) of Example 1 to 1000 ppm, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0048] Example 5

[0049] Except for changing the reaction temperature of step (3) in Example 1 to 130 °C, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0050] Example 6

[0051] Except for changing the reaction temperature of step (3) in Example 1 to 110 °C, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0052] Example 7

[0053] Except for changing the reaction temperature of step (3) in Example 1 to 90 °C, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0054] Example 8

[0055] Except for changing the reaction temperature of step (3) in Example 1 to 70 °C, the rest is the same as in Example 1, and the corresponding ammonia production is obtained.

[0056] Comparative Example 1

[0057] A blank experiment was conducted using a 100 mL empty reactor, with all other experimental conditions being the same as in Example 1, to obtain the corresponding catalytic ammonia production.

[0058] Experimental results:

[0059] Figure 1 The Sm 3d XPS spectra are those of samarium diiodide prepared in Example 1 and samarium trichloride standard used as a reference. Figure 1 As shown, the synthesized samarium diiodide has a Sm 3d 5 / 2 and Sm 3d 3 / 2 The binding energies are 1083.8 and 1110.9 eV, respectively, while the Sm 3d of the samarium trichloride standard used as a reference has a lower binding energy of 1083.8 and 1110.9 eV. 5 / 2 and Sm 3d 3 / 2 The values ​​are 1084.5 and 1111.6 eV, respectively. For XPS, a higher metal ion binding energy indicates a higher oxidation state. This result demonstrates the successful preparation of samarium diiodide.

[0060] Figure 2 The image shows the Raman spectrum of the Sm / GDY-NW synthesized in Example 1. Figure 2 As shown in the figure, four sharp characteristic peaks can be clearly observed, located at 1384 cm⁻¹. -1 1554 cm -1 1920 cm -1 And 2170 cm -1 The vibrations are sequentially attributed to the D band, G band, monoyne stretching vibration, and diyne skeletal vibration of GDY-NW, which are highly consistent with the Raman spectrum of GDY-NW. The spectral characteristics showed no significant changes, indicating that the introduction of Sm species did not disrupt the skeletal structure of graphodyne, and the overall structural stability of the material was maintained.

[0061] Figure 3 The image shows a SEM image of the Sm / GDY-NW synthesized in Example 1. It can be seen that after loading Sm, the material surface still exhibits a clear nanowall structure, indicating that the loading process did not damage the material's morphology.

[0062] Figure 4 This is a TEM image of the Sm / GDY-NW synthesized in Example 1. Figure 4 As shown in (a), the material remains a relatively thick layered structure after loading. Figure 4 (b) is an HRTEM image, in which nanoparticles with a diameter of approximately 4-5 nm can be observed distributed on the surface of the material. This indicates that Sm mainly exists in the form of nanoparticles on the surface of GDY-NW after loading, and the interplanar spacing d of these nanoparticles is 0.209 nm.

[0063] Figure 5 The images show the fine XPS spectra of Sm 3d and N 1s of the Sm / GDY-NW synthesized in Example 1. Figure 5 As shown in (a), after loading divalent Sm, the 3d saturation of Sm on the Sm / GDY-NW surface... 5 / 2 and 3D 3 / 2 The binding energies are 1083.5 and 1110.7 eV, respectively. The Sm 3d XPS fine spectra of the bound samarium divalent and trivalent samarium standards are shown below. Figure 1 As can be seen, the oxidation state of Sm on the material surface is still +2 at this time. However, compared with samarium diiodide, the oxidation state of Sm on the Sm / GDY-NW material surface is 3d. 5 / 2 The binding energy decreased by 0.3 eV. This indicates that in the Sm / GDY-NW system, GDY-NW transferred electrons to Sm, thus causing the binding energy of Sm to decrease. Figure 5 As shown in (b), the N 1s spectrum of Sm / GDY-NW exhibits a single peak signal at a binding energy of 399.9 eV, which corresponds to the nitrogen signal in the adsorbed state, mainly originating from the nitrogen signal adsorbed from the air before the material is loaded with Sm.

[0064] Figure 6 This study aimed to obtain the fine XPS spectra of Sm 3d samarium (Sm / GDY-NW) synthesized in Example 1 after exposure to air for different durations. Samarium divalent is typically unstable in air and is rapidly oxidized to yellow samarium trivalent. In this study, freshly prepared Sm / GDY-NW samples were exposed to air for 2, 12, 24, and 48 hours, and then immediately transferred to a glove box. XPS spectroscopy was used to characterize the valence state changes of the Sm / GDY-NW samples. Figure 6 As shown, for each exposure duration, Sm 3d 5 / 2 and 3D 3 / 2 The binding energies were stable around 1083.5 and 1110.7 eV, respectively, compared to the binding energies of the original samples not exposed to air. Figure 5The results in (a) are completely consistent. This indicates that the valence state of Sm on the surface of Sm / GDY-NW did not change significantly after exposure to air. This is mainly because the charge transfer effect of GDY-NW on the divalent samarium center effectively stabilized the valence state of samarium, preventing it from changing significantly in room temperature air.

[0065] Figure 7 The images show the fine XPS spectra of Sm 3d and N 1s of the Sm / GDY-NW synthesized in Example 1 after the catalytic reaction. Figure 7 As shown in (a), compared to before the reaction, the binding energy of Sm in Sm / GDY-NW after the catalytic reaction is significantly increased, and the valence state of Sm is between +2 and +3. Figure 7 As shown in (b), the number of nitrogen species on the material surface significantly increased after the catalytic reaction, and can be divided into four peaks at 399.4, 400.4, 401.8, and 402.5 eV, corresponding to *NH2, adsorbed N2, NH3, and *NH2-OH species, respectively. The presence of NH3 and other nitrogen-containing intermediates is direct evidence that a catalytic ammonia production reaction occurred on the material surface. These results collectively demonstrate that Sm participates in the catalytic ammonia production reaction, and that Sm is involved in the ammonia production process. 2+ With Sm 3+ The valence state transformations between them. *NH2-OH species originate from the nucleophilic attack of nitrogen-containing intermediates by oxygen-containing functional groups on the surface of GDY-NW, which stabilizes the nitrogen-containing intermediates in the catalytic reaction and accelerates the catalytic reaction process.

[0066] Table 1. Ammonia production in Examples 1-8 and Comparative Example 1

[0067]

[0068] The ammonia production in the table represents the total ammonium content detected in the solution after the ammonia produced is absorbed by 3 mL of 0.005 M sulfuric acid solution. r is the ammonia production rate normalized to the Sm loading, in units of... .

[0069] Table 1 shows the total ammonium content measured in Examples 1-8 and Comparative Example 1. Under mild conditions, thermocatalytic ammonia production experiments were conducted in a 100 mL sealed reactor. Sm / GDY-NW consistently showed significantly higher ammonia production than the blank control, indicating that the material catalytically converted nitrogen. Under the same GDY support conditions, the samarium diiodide solution concentration primarily affected the size of the supported nanoparticles. The results of Examples 1-4 demonstrate that the catalytic performance of Sm / GDY-NW is closely related to the size of the metal particles. Example 7 shows that when the reaction temperature was 90°C, the measured ammonium content was twice that of the blank control, indicating that the material already possessed significant catalytic ammonia production performance at this temperature. These results demonstrate that the divalent rare earth-graphyne composite material of the present invention exhibits excellent catalytic ammonia production performance.

[0070] In summary, this invention provides a type of divalent rare earth-graphyne composite material that exhibits excellent thermocatalytic ammonia production performance under mild conditions, and is expected to become a new generation of thermocatalytic ammonia production catalyst.

Claims

1. A divalent rare earth-graphdiyne composite material comprising rare earth ions, iodine ions and a graphdiyne material, characterized in that, The rare earth ions are selected from at least one of the +2 valence ions of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium, and are attached to the surface of the graphyne material in the form of nanoparticles with a size of 4-5 nm, together with iodine ions.

2. The divalent rare earth-graphyne composite of claim 1, wherein, The morphology of the graphdiene material is a nanowall structure.

3. The divalent rare earth-graphyne composite of claim 1, wherein, The rare earth ion is a samarium ion with a valence of +2.

4. The method for producing the divalent rare earth-graphyne composite material according to any one of claims 1 to 3, characterized by, Under conditions where water, oxygen, and nitrogen are excluded, graphyne material is immersed in a solution containing divalent rare earth ion iodides. After a period of adsorption, it is dried to obtain the divalent rare earth-graphyne composite material.

5. The production method according to claim 4, wherein The divalent rare earth ion iodide is samarium diiodide.

6. The production method according to claim 4, wherein The solvent for the solution containing divalent rare earth ion iodides is selected from one or more of tetrahydrofuran, diethyl ether, dioxane, and toluene.

7. The production method according to claim 4, wherein The solution containing divalent rare earth ion iodides is a tetrahydrofuran solution containing 50 ppm-1000 ppm samarium diiodide, and the graphyne material is immersed in this solution at room temperature for 6-12 hours.

8. The application of the divalent rare earth-graphyne composite material according to any one of claims 1 to 3 in thermocatalytic ammonia production.

9. Use according to claim 8, wherein the compound is ###0002### The divalent rare earth-graphyne composite material is used as a catalyst for thermocatalytic ammonia production using a nitrogen-hydrogen mixture.

10. Use according to claim 9, wherein The nitrogen-hydrogen mixture contains 25-90 vol% nitrogen, the reaction temperature is 90-200℃, and the pressure is 1-20 bar.

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