Solid materials, their uses and preparation

Abstract

A solid material comprising, or alternatively composed of, the following: (i) at least one metal selected from Fe, Co, Ni, Mo, Ru, V, and Mn; (ii) at least one support for said at least one metal (i), said support being an oxide of Ti, Si, Ce, Al, Zr, La, Eu, Pr, or Nb; (iii) at least an alkali metal or alkaline earth metal hydride; and (iv) at least a nitride. The use of said solid material as a catalyst and a method for preparing the solid material are also disclosed.

Description

Technical Field

[0001] This invention relates to solid materials, the use of said solid materials as catalysts, and methods for preparing said solid materials. Background Technology

[0002] Ammonia is industrially synthesized using the Haber-Bosch process, in which molecular nitrogen and hydrogen react at elevated temperatures and pressures in the presence of a suitable catalyst.

[0003] During synthesis, catalysts perform two functions: activating molecular hydrogen and molecular nitrogen to form reactive atomic species. These activations typically involve electron transfer reactions facilitated by high temperatures and the presence of promoters with electron-donating properties.

[0004] Several catalysts are active for ammonia synthesis.

[0005] Historically, iron (Fe)-based catalysts, containing Fe3O4 and a few percentage points of Al2O3 and K2O, have been used for ammonia synthesis in the temperature range of 400°C to 500°C and the pressure range of 150 bar to 300 bar. More recently, ruthenium (Ru)-based catalysts have made ammonia synthesis possible under milder conditions, such as at temperatures of 250°C to 400°C and pressures of approximately 110 bar.

[0006] Today, the catalysts commonly used for ammonia synthesis are supported catalysts, in which active catalytic elements are dispersed on a support to reduce manufacturing costs, increase the dispersion of active species, and, in some cases, promote nitrogen activation through electron supply.

[0007] For example, known supported catalysts for ammonia synthesis include Ru / C, Ru / MgO, and Ru / CaO.

[0008] There is a growing interest in the search for ammonia synthesis catalysts characterized by high activity and capable of operating at temperatures and / or pressures below those typically used for Fe-based industrial catalysts. This is particularly important for green ammonia applications where energy is intermittent. Furthermore, such catalysts should be produced inexpensively and with low energy consumption. Summary of the Invention

[0009] The present invention aims to overcome the above-mentioned defects of the prior art.

[0010] The object of this invention is a solid material comprising, or alternatively composed of, the following: (i) at least one metal selected from Fe, Co, Ni, Mo, Ru, V, Mn; (ii) at least one support for the metal (i), the support being an oxide of Ti, Si, Ce, Al, Zr, La, Eu, Pr or Nb; (iii) At least alkali metal or alkaline earth metal hydrides; (iv) At least nitrides, preferably nitrides selected from Li, La, Ti, Zr, V, Ca, Ba, Nb, Ce and mixtures thereof.

[0011] Another object of the present invention is the use of the solid material as a catalyst.

[0012] Another object of the present invention is a method for preparing solid materials. The method includes the following steps: (I) Providing at least one salt or complex of a metal selected from Fe, Co, Ni, Mo, Ru, V, Mn, and contacting the metal salt or complex with a solution or solvent to form a metal-containing solution. (II) Providing at least a support, said support being an oxide of Ti, Si, Ce, Al, Zr, La, Eu, Pr or Nb, and contacting said support with said metal-containing solution to form a suspension. (III) The suspension from step (II) is dried to obtain a solid powder (also known as “supported metal”). (IV) Optionally, the solid powder of step (III) is subjected to a purification step to obtain purified solid powder. (V) The solid powder of step (III) or the purified solid powder of step (IV) is mixed with at least an alkali metal or alkaline earth metal hydride and a nitride to obtain the solid material, wherein the nitride is preferably selected from nitrides of Li, La, Ti, Zr, V, Ca, Ba, Nb, Ce and mixtures thereof.

[0013] Definitions used in this specification "Support" refers to a material in solid form, which is typically characterized by a high surface area, allowing metals to adhere to or be deposited on its surface.

[0014] "Reducing agent" refers to a substance that loses electrons to other substances and is oxidized to a higher oxidation state in a redox reaction.

[0015] A "precipitation agent" is a substance added to a medium to cause precipitation of other substances present in the medium. Such precipitation can be selective precipitation of substances that need to be precipitated from the medium.

[0016] An "inert atmosphere" refers to an atmosphere that does not contain reactive gases (such as oxygen). More specifically, an inert atmosphere does not affect the synthesis of solid materials; for example, it does not cause chemical or electrochemical reactions or physical interactions between the gases present in the atmosphere and the solid materials being synthesized. Inert atmospheres can be obtained using nitrogen, argon, or helium as the inert gas.

[0017] "Nanoparticles" refers to particles with an average particle size distribution of 1 nanometer (nm) to 100 nm. Preferably, the average particle size distribution is 2 nm to 80 nm, more preferably 3 nm to 70 nm, and still more preferably 4 nm to 30 nm. Such an average particle size distribution can be determined by known analytical methods, such as electron microscopy.

[0018] "BET" is an abbreviation for Brunauer–Emmett–Teller, which is a known analytical method for measuring specific surface area by utilizing the physical adsorption of gas molecules (nitrogen molecules) on a solid surface.

[0019] "BJH" is an abbreviation for Barrett-Joyner-Halenda, which is another known analysis used to determine pore volume and pore diameter using gas (nitrogen) adsorption and desorption techniques.

[0020] Preferred embodiments of the present invention The solid material is preferably in the form of powder, granule, or shaped body (e.g., cylinder, pellet, or bead).

[0021] According to one embodiment, the weight ratio (iii):(iv) is 3:1 to 1:10, preferably 2:1 to 1:7, more preferably 1:1 to 1:5, and even more preferably 1:1 to 1:3.

[0022] According to another embodiment, the weight ratio [(i) + (ii)]:[(iii) + (iv)] is 15:1 to 1:1, preferably 10:1 to 1:1, more preferably 5:1 to 1:1, and even more preferably 3:1 to 1:1.

[0023] Preferably, the solid material, expressed as a weight percentage (%wt) of each component (i), (ii), (iii), and (iv) relative to the total weight of the solid material, comprises: (i) The amount is 5%wt to 25%wt, preferably 7%wt to 20%wt, more preferably 10%wt to 18%wt, and even more preferably 12%wt to 15%wt; (ii) The amount is 25%wt to 70%wt, preferably 30%wt to 65%wt, more preferably 40%wt to 60%wt, and even more preferably 45%wt to 58%wt; (iii) The amount is 3%wt to 20%wt, preferably 5%wt to 18%wt, more preferably 7%wt to 15%wt, and even more preferably 8%wt to 12%wt; (iv) The amount is 8%wt to 35%wt, preferably 10%wt to 30%wt, more preferably 15%wt to 25%wt, and even more preferably 18%wt to 22%wt.

[0024] The weight percentage refers to the total weight of a single component (i), (ii), (iii), or (iv) in the solid material. This means that if, for example, more metal is present in the solid material as component (i), the total weight of such metal in the solid material is within the range or subrange mentioned above. This also applies independently to supports (ii), hydrides (iii), and / or nitrides (iv).

[0025] The metal (i) is preferably dispersed on the support (ii) in the form of nanoparticles.

[0026] Preferably, the solid material is characterized in that: — BET specific surface area is 45 m² 2 / g to 800 m 2 / g, preferably 50 m 2 / g to 500 m 2 / g, more preferably 55m 2 / g to 200m 2 / g, or even more preferably 57m 2 / g to 78m 2 / g; and / or — The pore volume determined by the BJH method is 0.05 cm³. 3 / g to 1.50 cm 3 / g, selected as 0.06 cm 3 / g to 1.00cm 3 / g, more preferably 0.08 cm 3 / g to 0.50 cm 3 / g, or even more preferably 0.10 cm 3 / g to 0.30 cm 3 / g; and / or — The pore size determined by the BJH method is 5 nm to 30 nm, preferably 10 nm to 25 nm, more preferably 12 nm to 20 nm, and even more preferably 13 nm to 19 nm.

[0027] According to a preferred embodiment, the solid material comprises at least two metals (i) (e.g., only two metals or two or more metals), which are preferably non-sinterisable with each other.

[0028] Preferably, the solid material comprises at least two metals in a weight ratio of 5:1 to 1:5, more preferably 4:1 to 1:4, even more preferably 3:1 to 1:3, and still more preferably 2:1 to 1:2, for example 1.5:1 to 1:1.5, or 1:1.

[0029] More preferably, the metal (i) is Fe and / or Co.

[0030] According to another preferred embodiment, the metal (i) is Mo and / or Co.

[0031] According to some different embodiments, the at least support (ii) is selected from: TiO2, doped TiO2, SiO2, doped-SiO2, CeO2, SiO2-Al2O3, Al2O3, γ-Al2O3, ZrO2, doped ZrO2, La2O3, Eu2O3, Pr2O3, Nb2O5, zeolite; preferably selected from TiO2, doped TiO2, SiO2, doped SiO2, and mixtures thereof; even more preferably selected from TiO2 and / or SiO2.

[0032] The combination of Fe and / or Co as metals (i) with TiO2 and / or SiO2 as supports (ii) is particularly preferred.

[0033] According to another embodiment, (iii) is a hydride of Li, Na, K, Ca, Ba or Sr, preferably a hydride of Li, Ca, Na or K; even more preferably a hydride of Li or Ca.

[0034] According to another implementation scheme, (iv) is lithium nitride (Li3N) or lanthanum nitride (LaN).

[0035] The solid material is preferably selected from at least one of the following, contains at least one of the following, or is composed of at least one of the following: — Co / TiO2 / LiH / Li3N; — Co / SiO2 / LiH / Li3N; — Fe / TiO2 / LiH / Li3N; — Fe / SiO2 / LiH / Li3N; — Fe-Co / TiO2 / LiH / Li3N; — Fe-Co / SiO2 / LiH / Li3N; — Fe-Co / CeO2 / LiH / Li3N; — Fe-Co / γ-Al2O3 / LiH / Li3N; — Fe-Co / ZrO2 / LiH / Li3N; — Fe-Co / TiO2 / CaH2 / Li3N; — Mo-Co / TiO2 / LiH / Li3N.

[0036] In a preferred embodiment of the application, the catalyst is an ammonia synthesis catalyst, wherein the ammonia synthesis is carried out in the presence of a makeup gas containing nitrogen and hydrogen under ammonia-forming conditions.

[0037] Preferably, the ammonia formation conditions include a reaction temperature of 200°C to 500°C, more preferably 210°C to 400°C, more preferably 220°C to 380°C, and even more preferably 250°C to 370°C; and a reaction pressure of 1 bar to 150 bar, preferably 2 bar to 100 bar, more preferably 3 bar to 80 bar, and even more preferably 5 bar to 40 bar.

[0038] The salt or complex in step (I) is preferably selected from FeCl3, Fe(NO3)3, Fe(acac)3 (Iron(III) acetylacetonate), CoCl2, and mixtures thereof.

[0039] Preferably, no capping agent is used in step (I) to prevent nanoparticle aggregation. In fact, the applicant has found through electron microscopy that no capping agent is needed in step (I) to form metal nanoparticles. Widely used capping agents in the literature (but not in this invention) are cetyltrimethylammonium chloride and citric acid.

[0040] According to one embodiment, after step (I) and before step (II), the method may further include contacting the metal-containing solution with a reducing agent and / or a precipitating agent (e.g., a complexing agent).

[0041] According to another embodiment, the method may further include contacting the suspension in step (II) with a reducing agent and / or a precipitating agent (e.g., a complexing agent), preferably before step (III).

[0042] According to another implementation scheme, when no reducing agent is used in the method, the reduction of solid materials can be carried out in situ during the ammonia synthesis process.

[0043] Suitable reducing agents include, for example, sodium borohydride (NaBH4) or potassium borohydride (KBH4).

[0044] Suitable precipitants include, for example, aqueous solutions of urea or carbonates. Preferably, the carbonate is (NH4)2CO3, Na2CO3, or K2CO3.

[0045] In the prior art, it is known that boron can be incorporated, for example, using NaBH4, during catalyst preparation to enhance the catalytic activity of the synthesized catalyst. In this invention, when sodium borohydride or potassium borohydride is used as a reducing agent, such a reducing agent is essentially not present in the solid material, but is only used to induce the precipitation of metal (i) onto the support (ii). In other words, the reducing agent is only used to precipitate metal ions (e.g., Co²⁺). + It is converted into metal nanoparticles (e.g., cobalt) on the surface of the support, instead of being used to dope boron into them.

[0046] Preferably, optional step (IV) includes at least one washing operation. The washing operation may use distilled water as the washing agent and is carried out at a temperature of 40°C to 100°C or preferably at a temperature of 80°C to 95°C.

[0047] Particularly preferably, the washing operation in step (IV) is performed to remove any excess boron. This washing operation can be performed to remove the excess boron from the support surface and / or from the support bulk, leaving only the metal nanoparticles.

[0048] Preferably, the residual boron content in the purified solid powder after step (IV) is equal to or less than 1%wt, preferably equal to or less than 0.5%wt, relative to the total weight of the purified solid powder. The residual boron content in the purified solid powder (and preferably in the solid material) may be from 0.001%wt to 0.8%wt, or from 0.01%wt to 0.7%wt, or from 0.1%wt to 0.5%wt.

[0049] According to the above, step (IV) in one embodiment includes at least partially reducing the boron content in the purified solid powder.

[0050] In a preferred embodiment of the method, step (V) is not performed in an inert controlled atmosphere, but rather in atmospheric air.

[0051] In another preferred embodiment, step (V) includes dry mechanical mixing of the solid powder or purified solid powder with the at least one hydride and the at least one nitride, wherein both the hydride and the nitride are in powder form.

[0052] Step (III) is preferably carried out by filtration on a membrane, more preferably by a membrane with a pore size of 0.10 μm to 0.40 μm, even more preferably 0.20 μm to 0.30 μm, and still more preferably about 0.22 μm.

[0053] Preferably, the method is used to prepare a solid material according to any of the foregoing embodiments. Therefore, the preferred embodiments of the solid material are modified as necessary ( mutatis mutandis This applies to the method.

[0054] Advantages of the present invention Advantageously, the combination of hydrides and nitrides allows for the production of solid materials for ammonia synthesis that exhibit improved catalytic activity at lower temperatures and / or pressures compared to known catalysts.

[0055] Advantageously, the support (ii) ensures good dispersion of the metal (i), and the combination of hydride and nitride allows for a synergistic improvement in performance as an ammonia synthesis catalyst: on the one hand, ammonia production at lower temperatures is significantly improved, and on the other hand, the solid material can be prepared in a simple and energy-intensive manner.

[0056] Advantageously, the presence of at least two non-sinterisable metals (i) allows for higher performance and a longer service life of solid materials.

[0057] Advantageously, the solid material of the present invention exhibits improved on-stream stability because the support further promotes resistance against sintering, which typically occurs when metal is deposited directly on hydrides.

[0058] Advantageously, solid materials are synthesized with low energy consumption because the mixing of the loaded metal, hydride and nitride is preferably carried out in the open air and at room temperature, thus eliminating the need for pressure-sealed vessels or synthesis in chemically and thermally controlled environments.

[0059] Advantageously, this method does not require a pressure-sealed container, thus enabling excellent control over the metal load, suppression of metal leaching phenomena, and optimal dispersion of the metal on the support.

[0060] This method is therefore particularly suitable for large-scale production.

[0061] Advantageously, the solid material of the present invention provides improved production flexibility because it can operate in atmospheres with different hydrogen to nitrogen ratios.

[0062] Advantageously, simple mechanical mixing of the components can unexpectedly yield enhanced catalytic activity.

[0063] Advantageously, low levels of hydrides and nitrides are necessary to achieve significant improvements in catalysis.

[0064] Advantageously, the hydride and nitride are mixed only after the preparation of the loaded metal to prevent any degradation of the hydride in subsequent preparations.

[0065] Furthermore, in the initial preparation stage of the ammonia catalyst, the powder can be generated with the desired mechanical and structural properties before the addition of hydrides and nitrides. This is advantageous because once hydrides have been added, processing the powder to obtain the desired performance becomes more challenging.

[0066] Advantageously, performing a washing operation during step (IV) has been shown to be beneficial to the catalyst performance in the ammonia synthesis process. Attached Figure Description

[0067] Figure 1(a): Solid material according to the present invention at 5 bar, GHSV=40000 h - ¹ and the catalytic performance at different temperatures with H2 / N2=3 (as normalized productivity relative to Comparative Example 3 at 350℃). Figure 1(b): Solid material according to the present invention at 5 bar, GHSV=40000 h - ¹ and the catalytic performance at different temperatures with H2 / N2=1 (as normalized productivity relative to Comparative Example 3 at 350℃). Figure 1(c): The Fe-Co / TiO2 / LiH / Li3N (Example 4) sample according to the present invention at 5 bar and GHSV=40000 h - ¹And the effect of temperature on catalytic performance at H2 / N2=1 (as normalized productivity relative to Comparative Example 3 at 350℃). Figure 2: Samples of the solid material obtained in Example 4 at 350°C, H2 / N2=3, and 40000 h. - ¹The effect of measured pressure on ammonia production (as normalized productivity relative to ammonia production at 10 bar in Example 4); Figure 3: Diffractogram: (a) P25 TiO2 (Degussa P25 titanium dioxide nanopowder; CAS N. 13463-67-7; Rutile:Anatase / 85:15; 99.9%, 20 nm), (b) Fresh sample (bottom) and spent sample (top) 20% Co / TiO2, (c) Fresh sample (bottom) and spent sample (top) Fe-Co / TiO2, (d) Fresh sample (bottom) and spent sample (top) Fe / TiO2; Figure 4: Nitrogen (N2) physisorption isotherm: (a) P25 TiO2, (b) 20% Co / TiO2 in Example 1 (top curve) and Co / TiO2 / LiH / Li3N (bottom curve), (c) 10% Fe-10% Co / TiO2 in Example 4 (top curve) and Fe-Co / TiO2 / LiH / Li3N (bottom curve), (d) 20% Fe / TiO2 in Example 3 (top curve) and Fe / TiO2 / LiH / Li3N (bottom curve).

[0068] The invention will now be described in more detail with reference to the following non-limiting embodiments.

[0069] Example 1. Example 1 (Invention): Synthesis of Co / TiO2 / LiH / Li3N In a 150 mL container, 0.55 g of CoCl2 (Alfa Aesar 98%, 20% wt Co) was dissolved in 48 mL of distilled water. The resulting solution was magnetically stirred for 20 minutes at room temperature. Subsequently, 1 g of commercially available TiO2 (P25 provided by Degussa) was added to the container to form a suspension. The TiO2 particles were redispersed for 5 minutes under magnetic stirring.

[0070] Meanwhile, in a second container, 2.4 g of NaBH4 (Merck, >99%) was dissolved in 52 mL of distilled H2O and magnetically stirred for 5 minutes at room temperature. Then, the NaBH4 aqueous solution was added dropwise to the CoCl2-TiO2 suspension to avoid Co²⁻ contamination. +An explosion occurs during the exothermic reduction of ions to cobalt nanoparticles. Upon addition of NaBH4 aqueous solution, the pink suspension turns deep blue and subsequently foams. This new suspension is magnetically stirred at room temperature for 1 h to allow the cobalt nanoparticles to fully deposit on the support (i.e., TiO2).

[0071] Subsequently, the solid labeled 20% Co / TiO2 was recovered from the suspension by vacuum filtration using a 220 nm (Merck) filter membrane. The solid was then washed three times with 25 mL of warm distilled H2O preheated to 90 °C. During vacuum filtration, the solid was stirred with hot water using a spatula to promote the removal of borides and other impurities (i.e., Cl) present on the solid surface. - The solid was dissolved (by ions). Then, it was placed in a fume hood and left to stand overnight, and then dried under vacuum at 60°C for 2 h to obtain ~1.45 g of 20% Co / TiO2.

[0072] Finally, 20% Co / TiO2 powder was mixed with Li3N (Sigma-Aldrich, >99.5%) and LiH (Sigma-Aldrich, 95%) at a weight ratio of 70:20:10 using an agate mortar. The resulting powder (Co / TiO2 / LiH / Li3N) was placed in a desiccator before use.

[0073] 2. Example 2 (Invention): Synthesis of Co / SiO2 / LiH / Li3N The catalyst was prepared according to the steps reported in Example 1 above. In this case, the TiO2 support was replaced with SiO2.

[0074] 3. Example 3 (Invention): Synthesis of Fe / TiO2 / LiH / Li3N In a 150 mL container, 0.74 g of FeCl3 (Alfa Aesar 98%, 20% wt Fe) was dissolved in 48 mL of distilled water. The resulting solution was magnetically stirred for 20 minutes at room temperature. Next, 1 g of commercially available TiO2 (P25 provided by Degussa) was added to the container to form a suspension. The TiO2 particles were redispersed for 5 minutes under magnetic stirring.

[0075] Meanwhile, in a second container, 2.5 g of NaBH4 (Merck, >99%) was dissolved in 52 mL of distilled H2O and magnetically stirred for 5 minutes at room temperature. Subsequently, the NaBH4 aqueous solution was added dropwise to the FeCl3-TiO2 suspension to avoid Fe³⁺... +An explosion occurs during the exothermic reduction of ions to iron nanoparticles. Upon addition of NaBH4 aqueous solution, the suspension changes from orange to black, thus forming foam. This new suspension is magnetically stirred at room temperature for 1 h to allow the iron nanoparticles to fully deposit on the support (i.e., TiO2).

[0076] Subsequently, the solid labeled 20% Fe / TiO2 was recovered from the suspension by vacuum filtration using a 220 nm filter membrane (Merck). The solid was then washed three times with 25 mL of warm distilled H2O preheated to 90 °C. During vacuum filtration, the solid was stirred with hot water using a spatula to promote the removal of borides and other impurities (i.e., Cl-) present on the solid surface. - (Ionic) dissolution. Next, the solid was placed in a fume hood and left to stand overnight, then dried under vacuum at 60°C for 2 h to obtain ~1.45 g of 20% Fe / TiO2.

[0077] Finally, 20% Fe / TiO2 powder was mixed with Li3N (Sigma-Aldrich, >99.5%) and LiH (Sigma-Aldrich, 95%) at a weight ratio of 70:20:10 using an agate mortar. The resulting powder (Fe / TiO2 / LiH / Li3N) was placed in a desiccator before use.

[0078] 4. Example 4 (Invention): Synthesis of Fe-Co / TiO2 / LiH / Li3N In a 150 mL container, 0.25 g of CoCl2 (Alfa Aesar 98%, 10% wt Co) and 0.33 g of FeCl3 (Alfa Aesar 98%, 10% wt Fe) were dissolved in 48 mL of distilled water. The solution containing these two metal ions was magnetically stirred at room temperature for 20 minutes. Subsequently, 1 g of commercially available TiO2 (P25 provided by Degussa) was added to the container to form a suspension. The TiO2 particles were then redispersed under magnetic stirring for 5 minutes.

[0079] Meanwhile, in a second container, 2.2 g of NaBH4 (Merck, >99%) was dissolved in 52 mL of distilled H2O and magnetically stirred for 5 minutes at room temperature. Subsequently, the NaBH4 aqueous solution was added dropwise to the CoCl2-FeCl3-TiO2 suspension to avoid Fe³⁺. + and Co² + An explosion occurs during the exothermic reduction of ions to metal nanoparticles. Upon addition of an aqueous NaBH4 solution, the orange suspension turns dark blue, thus forming foam. This new suspension is stirred magnetically at room temperature for 1 h to allow the metal nanoparticles to fully deposit on the support (i.e., TiO2).

[0080] Subsequently, the solid labeled 10% Fe-10% Co / TiO2 was recovered from the suspension by vacuum filtration using a 220 nm filter membrane (Merck). The solid was then washed three times with 25 mL of warm distilled H2O preheated to 90 °C. During vacuum filtration, the solid was stirred with hot water using a spatula to promote the removal of borides and other impurities (i.e., Cl-) present on the solid surface. - (Ionic) dissolution. Next, the solid was placed in a fume hood and left to stand overnight, then dried under vacuum at 60°C for 2 h to obtain ~1.45 g of 10% Fe-10% Co / TiO2.

[0081] Finally, using an agate mortar, 10% Fe-10% Co / TiO2 powder was mixed with Li3N (Sigma-Aldrich, >99.5%) and LiH (Sigma-Aldrich, 95%) at a weight ratio of 70:20:10. The resulting powder (Fe-Co / TiO2 / LiH / Li3N) was placed in a desiccator before use.

[0082] 5. Comparative Example 1: Synthesis of Fe / TiO2-LiH In a container, 7.14 g of tetradecyltrimethylammonium bromide (TTAB, TCI > 98%) was dissolved in 47.34 g of distilled water. The solution was magnetically stirred at room temperature for 20 min. 0.74 g (20 wt.% Fe) FeCl3 was added to the TTAB aqueous solution, and the mixture was magnetically stirred at room temperature for 10 min. Subsequently, 1.0 g of TiO2 (P25, produced by Degussa) was added as a support, and the suspension was magnetically stirred at room temperature for 5 min.

[0083] In a separate container, 1.6 g of NaBH4 (Merck) was dissolved in 52 g of distilled water and magnetically stirred for 5 min at room temperature. The NaBH4 solution was then added dropwise to an aqueous suspension containing TTAB, FeCl3, and TiO2 support. The resulting mixture was allowed to react at room temperature with magnetic stirring for 1 h. The suspension was then filtered through a 220 nm membrane filter, and the solid was washed three times with 25 mL of hot distilled water (approximately 90 °C). The resulting solid was finally air-dried for 48 h. The yield of Fe / TiO2 powder was approximately 1.4 g.

[0084] Subsequently, Fe / TiO2 powder and LiH powder were mechanically mixed at a weight ratio of 50:50 for 2 min using a porcelain mortar, and the resulting powder (Fe / TiO2 / LiH) was stored in a desiccator before use. The Fe loading obtained in the Fe / TiO2 / LiH powder was 10 wt.%.

[0085] 6. Comparative Example 2: Synthesis of Co / TiO2-LiH In a container, 7.14 g of tetradecyltrimethylammonium bromide (TTAB, TCI > 98%) was dissolved in 47.34 g of distilled water. The solution was magnetically stirred at room temperature for 20 min. Subsequently, 0.55 g (20 wt.% Co)CoCl2 (AlfaAesar, 99.7%, anhydrous) was added to the TTAB aqueous solution, and the mixture was magnetically stirred at room temperature for 10 min. Then, 1 g of TiO2 (P25, produced by Degussa) was added as a support, and the suspension was magnetically stirred at room temperature for 5 min.

[0086] In a separate container, 1.52 g of NaBH4 (Merck) was dissolved in 52 g of distilled water and magnetically stirred for 5 min at room temperature. The NaBH4 solution was then added dropwise to an aqueous suspension containing TTAB, CoCl2, and TiO2 supports. The resulting mixture was allowed to react at room temperature with magnetic stirring for 1 h. The suspension was then filtered using a 220 nm membrane filter, and the solid was washed three times with 25 mL of hot distilled water (approximately 90 °C). The resulting solid was finally air-dried for 48 h and further vacuum-dried for 3 h at room temperature. The resulting Co / TiO2 powder weighed approximately 1.4 g.

[0087] Subsequently, the Co / TiO2 powder and LiH powder were mechanically mixed in a porcelain mortar at a weight ratio of 50:50 for 2 min. The resulting powder was stored in a desiccator before use. The Co loading obtained in the Co / TiO2-LiH powder was 10 wt.%.

[0088] 7. Comparative Example 3: Synthesis of Fe / LiH Fe / LiH powder was synthesized according to the protocol described in Nature Chem 2017, 9, 64-70. 2 g of LiH (Alfa Aesar, >97%) was mixed with 0.659 g (10 wt.% Fe) FeCl3 (Alfa Aesar, 98%, anhydrous) in a 45 mL stainless steel grinding bowl. Five 10 mm diameter beads (bead-to-sample mass ratio of 10) were then added, and the bowl was sealed. The bowl was then placed in a Pulverisette 7 Premium line (Fritsch) planetary ball mill at 200 rpm. The sample was ball-milled for 3 h (6 cycles of 30 min each, with the rotation direction reversed between cycles), and then washed three times with 50 mL THF (Roth, 99.5%) to remove LiCl. The sample was vacuum-dried at room temperature for 3 h and stored in a desiccator before use. The obtained Fe / LiH powder was approximately 2.3 g.

[0089] 8. Comparative Example 4: Fe / CeO2-Li3N Fe / CeO2-Li3N powder was synthesized in the same manner as in Example 4, except that LiH was replaced with Li3N (Sigma Aldrich, >99.5%, 60 mesh).

[0090] 9. Comparative Example 5: Synthesis of Cs-Ru / CeO2 Ru / CeO2 powder was synthesized in a similar manner to Fe / CeO2 in Example 4, except that Ru(NO)(NO3)3 (Alfa Aesar, Ru 31.3% min.) was used instead of FeCl3 as the metal precursor. Specifically, 0.1651 g of Ru(NO)(NO3)3 (5 wt.% Ru) was introduced into an aqueous TTAB solution and the resulting mixture was magnetically stirred at 30°C for 30 min. After adding 1 g of CeO2, a solution prepared by dissolving 0.8852 g of NaBH4 in 52 g of distilled water was added dropwise, and the resulting suspension was stirred at room temperature for 1 h. The rest of the synthesis was consistent with Example 4. The resulting Ru / CeO2 powder was approximately 1.05 g.

[0091] The Cs promoter was introduced using a wet impregnation method with a Cs to Ru molar ratio of 2. First, 0.2050 g of CsNO3 (Sigma Aldrich, 99%) (Cs to Ru molar ratio of 2) was dissolved in 50 g of distilled water, and the solution was magnetically stirred at room temperature for 10 min. Then, Ru / CeO2 powder was added to the CsNO3 aqueous solution, and the resulting suspension was magnetically stirred at room temperature for 15 min, followed by sonication at room temperature for 30 min. The solvent was then removed by evaporation using a Büchi Rotavapor R-200 apparatus at 50 °C and 80 rpm. The resulting Cs-Ru / CeO2 powder, approximately 1.2 g, was placed in a desiccator before use.

[0092] 10. Comparative Example 6: Synthesis of Cs-Ru / Al2O3 Cs-Ru / Al2O3 powder was synthesized in the same manner as in Comparative Example 4, except that the CeO2 support was replaced with Al2O3 (Alfa Aesar) and the molar ratio of Cs to Ru was adjusted to 10.

[0093] 11. Comparative Example 7: Ru / C Ru / C is a standard commercially available catalyst, namely 5% Ru / activated carbon from Thermo Fisher Scientific.

[0094] Example 5: Ammonia productivity calculation After synthesis, the catalyst was placed in a reactor for gaseous ammonia production testing, and the ammonia production rate of each catalyst was calculated according to the process reported below.

[0095] 0.12 mL of catalyst powder was mixed with 0.12 mL of glass beads (350–500 μm in diameter) and arranged in a stainless steel fixed bed reactor.

[0096] Nitrogen (N2, Air Liquide, 5.0 purity) and hydrogen (H2, Air Liquide, 5.0 purity) were supplied to the fixed-bed reactor. The gas hourly space velocity (GHSV) was then maintained at 20,000 to 40,000 h⁻¹. - ¹.

[0097] The pressure in the reactor was maintained at 5 bar, and the catalyst was initially treated at 350 °C for 3 h in an N2:H2 gas mixture. The temperature was then lowered to 300 °C and 250 °C, and held at each temperature plateau for at least 1 h.

[0098] In different processes, 0.5 mL of catalyst particles were arranged in a stainless steel fixed-bed reactor. After reduction, the temperature was maintained at 350 °C, and the pressure was changed from 10 bar to 80 bar. Each pressure stage was maintained for 6 hours. The ammonia production rate at different pressures under this process is shown in Figure 2.

[0099] The reactor effluent gas from the flow system was analyzed using gas chromatography (GC) with the absolute calibration curve method. The analytical equipment and conditions are summarized in Table 1.

[0100] Table 1 Productivity was then calculated at 350°C.

[0101] The calculated productivity value of Comparative Example 3 (Fe / LiH) was then used to normalize the productivity values ​​of the remaining samples, and the percentage productivity (% Productivity) of these subsequent samples was calculated as reported in Table 2.

[0102] More specifically, the percentage productivity value for each catalyst is calculated according to the following formula: in: The calculated productivity of the catalyst; The calculated productivity of the catalyst reported in Comparative Example 3.

[0103] For Figure 2, the productivity of Example 4 at 10 bar is used as a reference.

[0104] Table 2 .

[0105] Table 2 shows that the percentage productivity of the solid material according to the present invention is significantly higher than the productivity value calculated for the comparative example.

[0106] The productivity of Example 1 must be compared with that of Comparative Example 2 because both examples used the same metal, the same support, and the same hydride. The only difference between these examples is the presence of a nitride in Example 1 according to the invention. The same applies to Example 3, which needs to be compared with Comparative Example 1.

[0107] This enhancement in catalytic activity was clearly unexpected and can only be explained by synergistic interactions between components (i)-(iv) of the solid material. Furthermore, the positive role of the oxide (ii) in the catalytic mechanism appears to be clearly indicated.

[0108] Example 6: Reaction temperature and pressure for ammonia synthesis The solid material according to the invention has been shown to be quite active as a catalyst for ammonia production under various conditions (e.g., temperatures from 250°C to 400°C). Figures 1(a) and 1(b) confirm that the sample of Example 4 exhibited the highest catalytic activity, and the catalyst was also tested under two different reaction atmospheres (H2 / N2=1; H2 / N2=3). Furthermore, as reported in Figure 2, the latter remains active for NH3 production over a wide pressure range of 5 bar to 80 bar.

[0109] To verify the limits of the catalyst in Example 4, catalytic tests were conducted at temperatures up to 380°C. Figure 1(c) shows the increased NH3 formation rate due to increased temperature.

[0110] In addition, activity screening under different pressures was conducted, and the results are reported in Figure 2. The catalyst activity increased across the entire pressure range of 10 bar to 80 bar with increasing pressure.

[0111] Example 7: Sintering resistance of solid materials containing more than one metal (i) X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed on three different loaded metals (20% Co / TiO2, Fe-Co / TiO2, and 20% Fe / TiO2) before and after catalytic testing to assess the feasibility of sintering metal nanoparticles. Figure 3(a) shows the diffraction pattern of the oxide support (i.e., TiO2), which shows the peaks corresponding to the anatase and rutile phases. The loaded metal before catalytic testing exhibited peaks consistent with TiO2, indicating good dispersion of metal nanoparticles on the support surface. Conversely, the loaded metal after catalytic testing showed additional peaks in addition to the aforementioned anatase and rutile peaks. 20% Co / TiO2 showed a small peak at 44.4° corresponding to hexagonal cobalt nanoparticles. On the other hand, Fe-Co / TiO2 (see Figure 3(c)) shows an intermetallic Fe-Co alloy with a cubic geometry.

[0112] Table 3 shows the crystallite size obtained using Sherer's equation, confirming that Fe-Co / TiO2 contains nanoparticles smaller than those in pure cobalt or pure iron catalysts (≈25 nm) (average particle size distribution ≈16 nm). Therefore, the intermetallic Fe-Co nanoparticles on the Fe-Co / TiO2-supported metal are more resistant to sintering under reaction conditions than those on pure supported metal.

[0113] Table 3 .

[0114] Solid materials can be in the form of powder, granules, or molded articles. This invention is characterized in relation to solid materials in powder form.

[0115] Table 4 summarizes the textural properties of the catalyst. Furthermore, Figure 5 shows the N2 physisorption isotherms for both the supported metal and the solid material.

[0116] Table 4 .

[0117] * BJH Method See Figures 4(a) to 4(d) for the N2 physical adsorption isotherms.

Claims

1. A solid material comprising, or alternatively composed of, the following: (i) at least one metal selected from Fe, Co, Ni, Mo, Ru, V, Mn; (ii) at least one support for the at least one metal (i), said support being an oxide of Ti, Si, Ce, Al, Zr, La, Eu, Pr or Nb; (iii) At least alkali metal or alkaline earth metal hydrides; (iv) At least nitrides, preferably nitrides selected from Li, La, Ti, Zr, V, Ca, Ba, Nb, Ce and mixtures thereof.

2. The solid material according to the preceding claims, wherein the weight ratio (iii):(iv) is 3:1 to 1:10, preferably 2:1 to 1:7, more preferably 1:1 to 1:5, and even more preferably 1:1 to 1:

3.

3. The solid material according to any of the preceding claims, comprising (expressed as a weight percentage (%wt) of each component relative to the total weight of the solid material): (i) The amount is 5%wt to 25%wt, preferably 7%wt to 20%wt, more preferably 10%wt to 18%wt, and even more preferably 12%wt to 15%wt; (ii) The amount is 25%wt to 70%wt, preferably 30%wt to 65%wt, more preferably 40%wt to 60%wt, and even more preferably 45%wt to 58%wt; (iii) The amount is 3%wt to 20%wt, preferably 5%wt to 18%wt, more preferably 7%wt to 15%wt, and even more preferably 8%wt to 12%wt; (iv) The amount is 8%wt to 35%wt, preferably 10%wt to 30%wt, more preferably 15%wt to 25%wt, and even more preferably 18%wt to 22%wt.

4. The solid material according to any of the preceding claims, wherein (i) it is dispersed on the support (ii) in the form of nanoparticles, said nanoparticles being particles with an average particle size distribution of 1 nanometer (nm) to 100 nm, said average particle size distribution being determined by electron microscopy.

5. The solid material according to any of the preceding claims, characterized in that: — BET specific surface area is 45 m² 2 / g to 800 m 2 / g, preferably 50 m 2 / g to 500 m 2 / g, more preferably 55m 2 / g to 200m 2 / g, or even more preferably 57m 2 / g to 78m 2 / g; — The pore volume determined by the BJH method is 0.05 cm³. 3 / g to 1.5 cm 3 / g, preferably 0.06 cm 3 / g to 1.00 cm 3 / g, more preferably 0.08 cm 3 / g to 0.50 cm 3 / g, or even more preferably 0.10 cm 3 / g to 0.30 cm 3 / g; and — The pore size determined by the BJH method is 5 nm to 30 nm, preferably 10 nm to 25 nm, more preferably 12 nm to 20 nm, and even more preferably 13 nm to 19 nm.

6. The solid material according to any of the preceding claims, wherein (i) is Fe and / or Co.

7. The solid material according to any of the preceding claims, wherein the at least support (ii) is selected from: TiO2, doped TiO2, SiO2, doped SiO2, CeO2, SiO2-Al2O3, Al2O3, γ-Al2O3, ZrO2, doped ZrO2, La2O3, Eu2O3, Pr2O3, Nb2O5, zeolite; preferably selected from TiO2, doped TiO2, SiO2, doped SiO2, and mixtures thereof; even more preferably selected from TiO2 and / or SiO2.

8. The solid material according to any of the preceding claims, wherein: — (iii) is a hydride of Li, Na, K, Ca, Ba or Sr, preferably a hydride of Li, Na or K, and even more preferably a hydride of Li or Ca; and / or — (iv) is lithium nitride or lanthanum nitride.

9. The solid material according to any of the preceding claims, wherein the solid material comprises or is composed of at least one selected from the group consisting of: — Co / TiO2 / LiH / Li3N; — Co / SiO2 / LiH / Li3N; — Fe / TiO2 / LiH / Li3N; — Fe / SiO2 / LiH / Li3N; — Fe-Co / TiO2 / LiH / Li3N; — Fe-Co / SiO2 / LiH / Li3N; — Fe-Co / CeO2 / LiH / Li3N; — Fe-Co / γAl2O3 / LiH / Li3N; — Fe-Co / ZrO2 / LiH / Li3N; — Fe-Co / TiO2 / CaH2 / Li3N; — Mo-Co / TiO2 / LiH / Li3N.

10. Use of the solid material according to any of the preceding claims as a catalyst.

11. The use according to the preceding claim, wherein the catalyst is an ammonia synthesis catalyst, and the ammonia synthesis is carried out under ammonia-forming conditions in the presence of a supplementary gas containing nitrogen and hydrogen.

12. The use according to the preceding claim, wherein the ammonia formation conditions include: The reaction temperature is 200°C to 500°C, preferably 210°C to 400°C, more preferably 220°C to 380°C, and even more preferably 250°C to 370°C; and the reaction pressure is 1 bar to 150 bar, preferably 2 bar to 100 bar, more preferably 3 bar to 80 bar, and even more preferably 5 bar to 40 bar.

13. A method for preparing solid materials, the method comprising the following steps: (I) Providing at least one salt or complex of a metal selected from Fe, Co, Ni, Mo, Ru, V, Mn, and contacting the metal salt or complex with a solution or solvent to form a metal-containing solution; (II) Providing at least a support, said support being an oxide of Ti, Si, Ce, Al, Zr, La, Eu, Pr or Nb, and contacting said support with said metal-containing solution to form a suspension; (III) Dry the suspension from step (II) to obtain a solid powder; (IV) Optionally, the solid powder of step (III) is subjected to a purification step to obtain a purified solid powder; (V) The solid powder of step (III) or the purified solid powder of step (IV) is mixed with at least an alkali metal or alkaline earth metal hydride and a nitride to obtain the solid material, wherein the nitride is preferably selected from nitrides of Li, La, Ti, Zr, V, Ca, Ba, Nb, Ce and mixtures thereof.

14. The method of claim 13, wherein step (V) is carried out in atmospheric air, and wherein step (V) comprises dry mechanically mixing the solid powder or purified solid powder with the at least one hydride and the at least one nitride, wherein the hydride and the nitride are in powder form.

15. The method according to claim 13 or 14, wherein the solid material in step (V) is described in any one of claims 1 to 9.

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