Catalyst for ammonia synthesis

Abstract

The present invention relates to a catalyst for low energy production of ammonia; a process for preparing the catalyst; and a process for the low energy production of ammonia comprising the use of the catalyst.

Description

Technical Field

[0001] The present invention relates to a catalyst for low-energy preparation of ammonia; a process for preparing the catalyst; and a process for low-energy preparation of ammonia, the process comprising using the catalyst. Background Art

[0002] The industrial synthesis of ammonia has allowed the global population to surge from 1.6 billion in the early 1900s to about 7.7 billion today. This expansion would not have been possible without the rapid development of food production driven by the widespread use of ammonia-based fertilizers. Current ammonia production is 176 million tons (Mt) per year, which in turn generates about 500 million tons of CO2 (~1.8% of global CO2 emissions). The Haber-Bosch process for ammonia production (early 20th century), although considered one of the key chemical reactions ever developed, accounts for about 2% of our planet's energy consumption. In addition to the importance of ammonia as a fertilizer, it is also of great interest in energy storage and transportation - a way to store and transport hydrogen fuel. It can be stored in the liquid phase under mild conditions, has a much higher volumetric energy density than hydrogen, and can be transported as it is currently done. In addition, ammonia has also attracted attention as an alternative source of carbon-free fuel that does not contribute any CO2 emissions.

[0003] The main challenge in ammonia synthesis is to activate N2, since the N-N triple bond is one of the most stable chemical bonds in all of chemistry. The current industrial process for producing ammonia is the Haber process (N2+3H2→2NH3), which requires high pressure (>15MPa (150 bar)) and high temperature (>400°C) reaction conditions, associated with a large centralized infrastructure. However, considering the environmental need to reduce dependence on fossil fuels, a sustainable ammonia synthesis process is desirable, which can occur under low pressure and low temperature conditions and rely exclusively on renewable energy sources and feedstocks.

[0004] Typically, industry has used iron as a catalyst for ammonia synthesis, although it is well understood that a variety of alternative transition metals, in particular Pt, Mo, Re, Co, Ru and / or Rh, are equally suitable catalysts.

[0005] Ammonia synthesis at low temperature and low pressure is a well-known academic topic [1-3]. Many catalysts have been invented for low-energy thermal ammonia synthesis. For example, Masashi Hattori and his colleagues found that CaFH is an excellent catalyst for ammonia synthesis at 0.1 MPa (1 bar) and 50°C [4]. However, the preparation of such complex systems remains challenging.

[0006] Another alternative technology is electrochemical ammonia synthesis at room temperature and atmospheric pressure. However, the current technology is at a very early stage and there are no electrocatalysts available that can produce ammonia in significant yields and with high Faradaic efficiency [5].

[0007] We disclose herein novel catalysts and processes for low-energy ammonia synthesis via heterogeneous catalysis. This is achieved by novel atomic metal catalysts comprising at least one single metal atom or metal atom cluster (e.g., diiron atom catalyst) supported on the surface of a substrate, which is unreactive to N2 reduction and, in a typical but non-limiting embodiment, prepared by cluster beam deposition technology [6].

[0008] Using the catalysts and methods disclosed herein, ammonia can be synthesized at low temperatures (i.e., ≤250°C and preferably ≤50°C) and low pressures (i.e., ≤30 bar and preferably ≤0.1 MPa (1 bar)). In this way, this catalyst and preparation process paves the way for combination with green hydrogen feedstocks (such as water electrolysis) and powered by renewable energy (such as solar energy) to provide a near-zero carbon process for ammonia synthesis. Further, the simplicity of the setup offsets the need for complex infrastructure typically associated with high-energy existing preparation processes, providing the possibility of simple and local green ammonia preparation at the point of use (such as on a farm) using machines powered by renewable energy; in this way, ammonia can be generated as needed and introduced into an irrigation system, or stored as an ammonia solution for use as a fertilizer. Summary of the invention

[0009] The invention in its various aspects is set out in the accompanying claims.

[0010] According to a first aspect, an atomic metal catalyst is provided, which comprises a plurality of metal atom clusters supported on the surface of a solid substrate, wherein each metal atom cluster independently comprises or consists of: about 1 to about 500, preferably about 1 to about 100, more preferably about 1 to about 50, still more preferably about 1 to about 10, and most preferably about 1 to about 6 metal atoms.

[0011] Preferably, each of the metal atom clusters comprises one or more metals selected from the following or consists of one or more metals selected from the following: lead (Pb), silver (Ag), gold (Au), platinum (Pt), molybdenum (Mo), tungsten (W), rhenium (Re), cobalt (Co), ruthenium (Ru), rhodium (Rh) and iron (Fe). More preferably, the metal atom clusters comprise one or more metals selected from the following or consist of one or more metals selected from the following: Pt, Mo, Re, Co, Ru, Rh and Fe, and more preferably comprise one or more metals selected from the following or consist of one or more metals selected from the following: Mo, Re, Fe and Pt atoms. In a particularly preferred embodiment, the metal atom clusters comprise Fe atoms or consist of Fe atoms.

[0012] The atomic cluster may comprise a single atom or may comprise a mixture or alloy comprising multiple atoms. The metal atom may be covalently or non-covalently modified and / or may be in oxidized or reduced form. Preferably, substantially all metal atom clusters comprise the metal atoms of the same number and / or type or are composed of the metal atoms of the same number and / or type.

[0013] In a preferred embodiment, the metal atom cluster comprises a single metal atom, two metal atoms or three metal atoms, or is composed of a single metal atom, two metal atoms or three metal atoms. Such metal atom clusters are respectively referred to as single atom catalysts (SAC), diatomic catalysts (DAC) and triatomic catalysts (TAC).

[0014] A metal atom cluster comprising two metal atoms, in particular a metal atom cluster comprising two Fe atoms, ie, FeDAC, is particularly preferred.

[0015] It is obvious to those skilled in the art that the surface coverage of the metal atom clusters on the surface of the substrate can be measured or calculated by a variety of methods. For example, surface coverage is usually measured by projected surface area derived from deposition beam current and X-ray photoelectron spectroscopy (XPS).

[0016] Preferably, the metal atom clusters cover 0.1 to 20%, more preferably 1 to 10%, and still more preferably 2 to 5% of the surface of the substrate.

[0017] The solid substrate on which the metal ion clusters are deposited and loaded is not particularly limited, except that the substrate is generally unreactive to N2 reduction. It is readily appreciated that suitable solid substrates include, but are not limited to, silicon or carbon-based materials, oxides, hydrides, nitrides, or MXenes. However, in a preferred embodiment, the substrate is a carbon material, which may be doped with a dopant containing one or more heteroatoms (i.e., nitrogen, sulfur, or oxygen).

[0018] Preferably, the dopant comprises one or more nitrogen heteroatoms. More preferably, the substrate comprises a carbon material doped with pyridinic nitrogen and / or pyrrolic nitrogen atoms. The inclusion of such a dopant prevents surface diffusion of the metal atom catalyst on the substrate.

[0019] Preferably, when a doped carbon material is used as a substrate, the dopant preferably covers 0.1 to 20%, more preferably 1 to 10%, and still more preferably 2 to 5% of the surface of the substrate. It is obvious to those skilled in the art that the dopant surface coverage can be measured or calculated by a variety of methods. Examples of suitable methods include electron microscopy, surface spectroscopy (such as XPS), and inductively coupled plasma mass spectrometry (ICP-MS) in the case of a powder substrate.

[0020] It is obvious to one of ordinary skill in the art that the atomic metal catalyst of the first aspect of the invention may be formed via any conventional physical vapor deposition (PVD) process, such as by evaporation, sputtering or pulsed laser deposition. Such PVD processes may include cluster deposition processes, in which metal atom clusters are formed (such as via condensation in the gas phase) and then deposited on the surface of the substrate. Alternatively, the PVD technique may include an atomic deposition process, in which single metal atoms are deposited on the surface of the substrate and then metal atom clusters are formed.

[0021] Therefore, according to a second aspect of the present invention, there is provided a method for preparing the catalyst of the first aspect of the present invention by PVD, wherein the metal atom clusters are formed by a cluster deposition process, or wherein the metal atom clusters are formed after being deposited as single atoms on the surface of a substrate.

[0022] In some embodiments, the PVD process is selected from: cluster deposition, evaporative deposition, sputtering deposition, or pulsed laser deposition.

[0023] The atomic metal catalyst is advantageously deposited by a cluster deposition process, preferably a cluster beam deposition process, because such a process allows strict control of the size of the deposited metal atom clusters. Therefore, according to a preferred embodiment of the second aspect of the present invention, there is provided a method for preparing the catalyst of the first aspect by depositing a plurality of metal atom clusters onto a substrate of a solid substrate, wherein the metal ion clusters comprise 1 to 10 metal atoms or consist of 1 to 10 metal atoms, and wherein the method comprises the following steps:

[0024] (i) providing a cluster beam deposition source including a plasma sputtering and gas condensation chamber, a mass filtration chamber, and a deposition chamber;

[0025] (ii) arranging a metal catalyst target including or consisting of metal atoms in the condensation chamber;

[0026] (iii) disposing a solid substrate in a deposition chamber;

[0027] (iv) performing a magnetron sputtering step in the condensation chamber, which includes sputtering the metal catalyst target with plasma to eject metal atoms; and then performing a condensation step, wherein

[0028] The ejected atoms are cooled in an inert gas to form positively charged metal ion clusters;

[0029] (v) separating and selecting metal ion clusters based on size in the mass filtration chamber; and

[0030] (vi) depositing the metal ion clusters of a selected size on the surface of the substrate in the deposition chamber.

[0031] It is obvious to those skilled in the art that in step (iv), the metal catalyst target can be sputtered with a plasma derived from any one or a combination of an inert gas (such as argon) and / or a reactive gas. If a reactive gas such as O2 or N2 is used, the sputtered particles from the metal catalyst target can undergo a chemical reaction during the sputtering and deposition process, resulting in, for example, metal oxide or metal nitride clusters deposited on the surface of the substrate.

[0032] In a preferred embodiment, the metal catalyst target is sputtered using an inert gas (eg, helium, neon, argon) plasma, most preferably an argon plasma.

[0033] Preferably, the clusters are formed in step (iv) by condensation under helium pressure cooled to about 80 to about 120K.

[0034] Preferably, the metal catalyst target comprises one or more metals selected from the following or consists of one or more metals selected from the following: lead (Pb), silver (Ag), gold (Au), platinum (Pt), molybdenum (Mo), tungsten (W), rhenium (Re), cobalt (Co), ruthenium (Ru), rhodium (Rh) and iron (Fe). The metal catalyst target can be a single element or can be a mixture or alloy containing multiple elements. The metal catalyst target can include covalently or non-covalently modified metal atoms and / or can be in an oxidized or reduced form. More preferably, the metal catalyst target comprises one or more metals selected from the following or consists of one or more metals selected from the following: Pt, Mo, Re, Co, Ru, Rh and Fe, and more preferably comprises one or more metals selected from the following or consists of one or more metals selected from the following: Mo, Re, Fe or Pt atoms, and most preferably comprises Fe atoms or consists of Fe atoms.

[0035] In a preferred embodiment, a metal ion cluster comprising 1, 2 or 3 metal atoms (most preferably Fe atoms) or consisting of 1, 2 or 3 metal atoms (most preferably Fe atoms) is deposited on the surface of the substrate, i.e., a SAC, DAC or TAC is formed. Most preferably, a DAC is formed by the deposition of a metal ion cluster comprising 2 Fe atoms or consisting of 2 Fe atoms.

[0036] Preferred features relating to the substrate are as set out above in relation to the first aspect.

[0037] In a preferred embodiment, the cluster beam deposition source provided in step (i) further comprises an ion optical chamber disposed between the gas condensation chamber and the mass filtration chamber. In such embodiments, between steps (iv) and (v), the method comprises extracting and focusing the metal ion clusters in the optical chamber.

[0038] The atomic metal catalysts of the first aspect of the present invention can be used to catalyze a variety of chemical reactions. Specifically, they can catalyze the synthesis of ammonia (NH3) by reducing N2 at low temperature and low pressure.

[0039] Therefore, according to a third aspect, there is provided a process for producing ammonia, the process comprising:

[0040] (i) arranging a catalyst bed comprising an atomic metal catalyst according to the first aspect of the present invention in a reactor;

[0041] (ii) passing one or more nitrogen (N2) sources and one or more hydrogen (H2) sources through the catalyst bed;

[0042] (iii) obtaining a product stream comprising ammonia (NH3).

[0043] Preferably, step (ii) is carried out at a temperature of 250°C or below, more preferably at 200°C or below, and still more preferably at 150°C or below. Alternatively or additionally, step (ii) is preferably carried out at a temperature of 20°C or above, and more preferably at a temperature of 30°C or above.

[0044] In an exemplary embodiment, step (ii) can be carried out at a temperature in the range of about 20°C to about 250°C, such as about 30°C to about 75°C, or about 30°C to less than about 50°C. Further, in a preferred embodiment, step (ii) is carried out at a pressure of no more than about 3 MPa (30 bar), more preferably no more than about 2 MPa (20 bar), still more preferably no more than about 1 MPa (10 bar), and even more preferably no more than about 0.5 MPa (5 bar). For example, step (ii) can be carried out under standard atmospheric pressure conditions, i.e., about 0.1 MPa (1 bar).

[0045] Step (ii) can also be carried out at a pressure lower than atmospheric pressure. For example, catalytic N2 reduction has been demonstrated at a pressure of about 250 to about 750 Pa (2.5 to 7.5 mbar), and more preferably about 500 Pa (5 mbar).

[0046] In a preferred embodiment, the catalyst bed is reduced prior to step (ii). Catalyst reduction may be achieved, for example, by exposure to H2 at elevated temperature (eg up to about 400°C).

[0047] Preferably, one or more hydrogen sources are prepared from green hydrogen feedstocks. For example, hydrogen can be prepared from water by electrolysis.

[0048] Preferably, the process of the present invention is driven by renewable energy, non-limiting examples of which include solar and wind energy. By combining the use of renewable energy and green hydrogen feedstock, ammonia can be produced via a zero-carbon process.

[0049] Preferred features of each aspect of the invention may be as described in connection with any other aspect.

[0050] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, such as "comprising" and "comprises", mean "including but not limited to" and do not exclude other parts, additives, components, integers or steps. Throughout the description and claims of this specification, the term "and / or" includes any and all combinations of one or more of the relevant listed elements. Throughout the description and claims of this specification, unless the context requires otherwise, the singular includes the plural. In particular, where the indefinite article is used, the specification is to be understood as contemplating the plural as well as the singular, unless the context requires otherwise. Throughout the description and claims of this specification, unless the context requires otherwise, the word "about" means ±5%, alternatively ±2%.

[0051] Throughout the description and claims of this specification, unless the context requires otherwise, the term "metal atom cluster" and variations thereof include single metal atoms and aggregates of multiple metal atoms.

[0052] All references cited in this specification, including any patents or patent applications, are incorporated herein by reference. No admission is made that any reference constitutes prior art. Furthermore, no admission is made that any prior art constitutes part of the common general knowledge in the art.

[0053] Other features of the invention will become apparent from the following examples. In general, the invention extends to any novel one or any novel combination of the features disclosed in this specification (including the attached claims and drawings). Therefore, features, integers, characteristics, compounds or chemical moieties described in conjunction with a particular aspect, embodiment or embodiment of the invention should be understood to be applicable to any other aspect, embodiment or embodiment described herein, unless incompatible therewith.

[0054] Furthermore, unless stated otherwise, any feature disclosed herein may be replaced by alternative features serving the same or similar purpose.

[0055] The present invention will now be described by way of example only with reference to the following Examples and the following Figures, in which:

[0056] Figure 1 . Schematic diagram of a cluster beam source of selected size, which combines magnetron sputtering technology and gas condensation technology;

[0057] Figure 2 STEM image of Fe dimer deposited on graphene oxide-coated TEM grid.

[0058] Figure 3 N1s XPS spectra of Fe dimer on N-doped carbon (Fe2-NC), N-doped carbon (NC) alone, and Fe dimer on carbon (Fe2-C);

[0059] Figure 4 .N1s XPS spectra of Fe2-NC system under different conditions;

[0060] Figure 5 .Fe L-edge NEXAFS of Fe2-NC system and Fe2-C system under different conditions;

[0061] Figure 6 N1s peak of N-doped carbon under different conditions. The temperature (T) is at room temperature (rt), and the flow rates of H2 and N2 are in sccm;

[0062] Figure 7 Partial mass spectra of the Fe2-NC system (top spectrum) and the Fe2-C system (bottom spectrum). The flow rates of H2 and N2 are expressed in sccm, and the partial pressures of the mass signals are expressed in mbar.

[0063] Figure 8 Catalytic activity of Fe-TiH2 powder for ammonia production (200°C; 10 bar). The metal loading of Fe clusters on TiH2 powder was standardized to 0.1%. The products were analyzed every hour by gas chromatography.

[0064] Materials and methods

[0065] The metal catalysts generated for this project were produced using cluster beam deposition technology, a Swansea-built instrument, at the new Swansea Satellite Nanolab at Diamond Light Source (B07).

[0066] Cluster deposition source ( Figure 1 ) is a vacuum-type, magnetron sputtering, gas condensation source equipped with a transverse time-of-flight mass filter [7]. The metal target is sputtered by a DC Argon plasma; the hot metal atoms are condensed into clusters under helium pressure cooled to ~100K by liquid nitrogen; the positively charged clusters are extracted and focused into the mass filter by ion optics for size selection. The resolution of the mass filter is about 1 / 20 atom, and the transmission efficiency of the selected mass is >50%. In this project, a series of atomic metal catalysts (Fe and Pt) including single atoms, dimers and trimers of metals were prepared. The atomic catalysts were deposited on transmission electron microscopy (TEM) grids (graphene oxide coated grids, 3 mm diameter) for TEM characterization [8] (1% surface coverage), as well as XPS and near-edge X-ray absorption fine structure (NEXAFS) studies [9] (3%-4% surface coverage). In order to prevent surface diffusion of the atomic catalyst, N-doping of carbon (graphene oxide) (5% surface coverage) was also performed before Fe deposition. The materials were imaged using scanning transmission electron microscopy (STEM) at Swansea University and Diamond Light Source.

[0067] XPS and NEXAFS experiments were performed at near-ambient pressure at beamline B07 at Diamond Light Source. -4 The samples were exposed to pure N2 and N2+H2 in the pressure range of 10 to 10 mbar. Ambient pressure XPS and NEXAFS were performed together with a multi-mass spectrometry system to verify the catalytic activity of different atomic catalysts for thermochemical ammonia synthesis. The adsorbed reactive intermediates (e.g., *NHx) and molecules were monitored in real time via chemical shifts at the N1s core level. The chemical / oxidation state was studied by monitoring the Fe 2p core level, etc.

[0068] In a further embodiment, a thin layer of iron clusters (about 1 nm in maximum cluster size) was deposited onto TiH2 particles (average particle size 20 μm) enclosed in a metal cup with a stirring function using a magnetron sputtering technique. The catalytic activity of the iron cluster-coated TiH2 particles for ammonia production was then measured using a high pressure reactor, and the products were analyzed using gas chromatography or liquid chromatography. Specifically, the reaction was tested in a mixture of N2 (10 ml / min) and H2 (30 ml / min) at a temperature of 200°C and a pressure of 1 MPa (10 bar), after diluting the catalyst with SiC powder to improve heat transfer.

[0069] result

[0070] Figure 2 An image of Fe dimers prepared by cluster beam deposition after deposition is shown. Since the landing energy of those dimers is 9 eV per atom, they can break into single atoms upon surface collision. The bright spots shown in the STEM image are Fe dimers and single atoms.

[0071] Three samples were tested for ammonia synthesis, namely, Fe dimer on N-doped carbon (graphene oxide) support (Fe2-NC), N-doped carbon support itself (NC), and Fe dimer on undoped carbon support (Fe2-C). Figure 2 N1s XPS spectra of those samples under vacuum conditions are shown. After cluster deposition, the deposition chamber of the cluster source was ventilated with N2 gas, and the samples were then transferred (in air) to the beamline for measurement. The N in the bare NC system comes from the N doping process. Both pyridinic and pyrrolic N are found on the surface of this support. The addition of Fe dimers on N-doped carbon introduces Fe-N x The new peak of the species. This means that the Fe dimer is very active for N2 fixation. Once the NC system is modified by Fe dimer, N2 molecules are adsorbed on the surface of those dimers. This can also be confirmed by experiments with Fe2-C systems without N2 dosing in the chamber. There is no N doping here, and the surface N comes from the chamber ventilation process and air transport.

[0072] After sample reduction at temperatures up to 400 °C in H2, all samples were tested for ammonia synthesis under a mixed N2 and H2 atmosphere. Figure 4 The evolution of the N1s peak of the Fe2-NC system under different conditions is shown. Once N2 is introduced into the chamber, the Fe-NC x / NH x The strength of the Fe-N x or NH x Speciation. As N2 is depleted in the chamber, the intensity of this peak decreases.

[0073] like Figure 5 As shown, the reduction process of Fe dimer catalysts on N-doped carbon and bare carbon was monitored by Fe L-edge NEXAFS spectroscopy. After the deposition of metal atom clusters, Fe 2+ and Fe 3+ Two states. 3+ It can be rapidly reduced to Fe in a H2 atmosphere (e.g. 500Pa (5mbar), at a temperature of 300°C or above) 2+ For the Fe2-NC system, the Fe 2+ In the case of the Fe2-C system, in the subsequent reduction cycle, Fe 3+ It becomes more difficult to reduce to Fe 2 + , which means that the surface morphology (such as sintering) or atomic configuration changes during the heating process.

[0074] Figure 6 The presence of the N1s peak (NC sample) shown in Figure 1 before reduction indicates that N was successfully doped into carbon (graphene oxide). This peak disappeared during the reduction process. The formation of ammonia was detected during the process, which means that the bond between the doped N atoms and the carbon support is not strong enough to prevent N from forming NH3 in the H2 atmosphere. Since there is no catalyst for the cleavage of the N-N bond, the N peak cannot be restored by reintroducing the N2 gas.

[0075] like Figure 7 As shown, the catalytic activity of Fe dimer was monitored by mass spectrometry. The mass of ammonia is 17amu. However, water (18amu) also causes the secondary signal of 17amu, so 17amu is not a good indicator for ammonia formation. Because ammonia forms a strong signal when 16amu in mass spectrum, we use 16amu as the indication of ammonia here. The " NH3 " signal shown in pink is obtained from the contribution of water at 17amu. Mass spectrum is carried out with a pressure of 5mbar in the main chamber. In Fe2-NC system, it can be seen that the N2 (1sccm) of the minimum flow introduced into the chamber of temperature <50°C can trigger the ammonia synthesis reaction. The successful synthesis of ammonia can be confirmed (as described above) by the signal increase of 16amu and " NH3 " signal. Under high temperature test, Fe2-C system shows the behavior similar to the Fe2-NC system formed for ammonia.

[0076] Figure 8 The catalytic activity of the Fe-TiH2 particle system towards ammonia production is shown. Notably, the catalyst was observed to stabilize during the first two hours of reaction (as indicated by a decrease in catalytic activity) and then stabilized for the remaining measurement duration (7 hours).

[0077] summary

[0078] A small number of atomic Fe catalysts (1, 2 and 3 atoms) have been successfully synthesized and deposited using cluster beam deposition techniques. To date, Fe dimers have been tested for ammonia synthesis on two different supports, including carbon and N-doped carbon. Both the Fe2-NC system and the Fe2-C system show catalytic activity for the reduction of N2 to ammonia. Compared to the Fe2-C system, the Fe2-NC system is more stable when subjected to high temperature reduction cycles, as shown. Fe dimers can catalyze the reaction at pressures as low as 5 mbar and temperatures of <50°C, with higher pressures expected to achieve higher yields.

[0079] Fe clusters (~1 nm maximum cluster size) were also deposited onto TiH2 particles by magnetron sputtering, and the resulting Fe catalyst was shown to be catalytically active for the production of ammonia under milder conditions than those conventionally used in the Haber process.

[0080] References

[0081] [1]Rod, T. H., Logadottir, A., & JKThe Journal of ChemicalPhysics,2000,112(12),5343-5347.

[0082] [2]Wang,P.,Chang,F.,Gao,W.,Guo,J.,Wu,G.,He,T.,&Chen,P.Naturechemistry,2017,9(1),64-70.

[0083] [3]Ogura, Y., Tsujimaru, K., Sato, K., Miyahara, SI, Toriyama, T., Yamamoto, T., & Nagaoka, K. ACS Sustainable Chemistry & Engineering, 2018, 6 (12), 17258-17266.

[0084] [4] Hattori, M., Iijima, S., Nakao, T., Hosono, H., & Hara, M. Nature communications, 2020, 11(1), 1-8.

[0085] [5]Singh,AR;Rohr,BA;Schwalbe,JA;Cargnello,M.;Chan,K.;Jaramillo,TF;Chorkendorff,I.; JKACS Catalysis 2016,7,(1),706-709.

[0086] [6]Palmer,R.E.,Cai,R.,&Vernieres,J.Accounts of Chemical Research,2018,51(9),2296-2304.

[0087] [7]Pratontep,S.,Carroll,SJ,Xirouchaki,C.,Streun,M.,&Palmer,REReview of Scientific Instruments,2005,76(4),045103.

[0088] [8]Niu,Y.,Schlexer,P.,Sebok,B.,Chorkendorff,I.,Pacchioni,G.,&Palmer,RENanoscale,2018,10(5),2363-2370.

[0089] [9]Held,G.,Venturini,F.,Grinter,DC,Ferrer,P.,Arrigo,R.,Deacon,L.,...&Scott,S.Journal of synchrotron radiation,2020,27(5),1153-1166.

Claims

1. An atomic metal catalyst comprising a plurality of metal atom clusters supported on the surface of a solid substrate, wherein each metal atom cluster independently comprises or consists of about 1 to about 500 metal atoms.

2. The atomic metal catalyst of claim 1, wherein each metal atom cluster independently comprises or consists of about 1 to about 10 metal atoms.

3. The atomic metal catalyst according to claim 1 or 2, wherein each of the metal atom clusters comprises or consists of one or more metals selected from the following: Lead (Pb), silver (Ag), gold (Au), platinum (Pt), molybdenum (Mo), tungsten (W), rhenium (Re), cobalt (Co), ruthenium (Ru), rhodium (Rh) and iron (Fe).

4. The atomic metal catalyst according to claim 3, wherein each of the metal atom clusters comprises or consists of one or more metals selected from the following: Pt, Mo, Re, Co, Ru, Rh and Fe. 5 . The atomic metal catalyst according to claim 4 , wherein each of the metal atom clusters comprises or consists of an Fe atom.

6. The atomic metal catalyst according to any one of the preceding claims, wherein the metal atom clusters cover 0.1 to 20% of the surface of the substrate.

7. The atomic metal catalyst according to any one of the preceding claims, wherein the substrate is a silicon or carbon-based material, an oxide, a hydride, a nitride or a MXene.

8. The atomic metal catalyst according to claim 7, wherein the substrate is a carbon material.

9. The atomic metal catalyst of claim 8, wherein the carbon material is doped with a dopant comprising one or more heteroatoms, optionally wherein the dopant covers 0.1 to 20% of the surface of the substrate.

10. A method for preparing a catalyst according to any one of the preceding claims, wherein the method is a cluster deposition process, in which clusters of metal atoms are formed and then deposited on the surface of the substrate; or wherein the method is an atomic deposition process, in which single metal atoms are deposited on the surface of the substrate and then metal atom clusters are formed.

11. The method of claim 10, comprising depositing a plurality of metal atoms and / or metal atom clusters onto the surface of a solid substrate by cluster deposition, evaporative deposition, sputtering deposition, or pulsed laser deposition processes, wherein each metal atom cluster independently comprises or consists of about 1 to about 500 metal atoms.

12. The method of claim 11, wherein each metal atom cluster independently comprises or consists of about 1 to about 10 metal atoms.

13. The method according to any one of claims 10 to 12, wherein the method is a cluster deposition process, the method comprising the following steps: (i) providing a cluster beam deposition source including a plasma sputtering and gas condensation chamber, a mass filtration chamber, and a deposition chamber; (ii) arranging a metal catalyst target including or consisting of metal atoms in the condensation chamber; (iii) disposing a solid substrate in a deposition chamber; (iv) performing a magnetron sputtering step in the condensation chamber, which comprises sputtering the metal catalyst target with plasma to eject metal atoms, followed by a condensation step, wherein The ejected atoms form positively charged metal ion clusters by cooling in an inert gas; (v) separating and selecting metal ion clusters based on size in the mass filtration chamber; and (vi) depositing the metal ion clusters of a selected size on the surface of the substrate in the deposition chamber.

14. The method according to claim 13, wherein the metal atom target comprises or consists of one or more metals selected from the group consisting of: Lead (Pb), silver (Ag), gold (Au), platinum (Pt), molybdenum (Mo), tungsten (W), rhenium (Re), cobalt (Co), ruthenium (Ru), rhodium (Rh) and iron (Fe).

15. The method according to claim 14, wherein the metal atom target comprises or consists of one or more metals selected from the group consisting of: Pt, Mo, Re, Co, Ru, Rh and Fe. The method according to claim 15 , wherein the metal atom target comprises or consists of Fe atoms.

17. The method according to any one of claims 10 to 16, wherein the substrate is a silicon or carbon-based material, an oxide, a hydride, a nitride or a MXene.

18. The method of claim 17, wherein the substrate is a carbon material, optionally doped with a dopant comprising one or more heteroatoms.

19. The method according to any one of claims 13 to 18, wherein in step (iv), the metal catalyst target is sputtered with an inert gas plasma, preferably an argon plasma, and / or wherein the clusters are formed in step (iv) by condensation in a pressure of helium gas cooled to about 80 to about 120 K.

20. The method according to any one of claims 13 to 19, wherein in step (vi), metal ion clusters comprising 1, 2 or 3 metal atoms are deposited on the surface of the substrate.

21. A method for producing ammonia, the method comprising: (i) arranging a catalyst bed comprising an atomic metal catalyst according to any one of claims 1 to 9 in a reactor; (ii) passing one or more nitrogen (N2) sources and one or more hydrogen (H2) sources through the catalyst bed; (iii) obtaining a product stream comprising ammonia (NH3).

22. The process of claim 21, wherein step (ii) is carried out at a temperature in the range of about 20°C to about 250°C and / or at a pressure not exceeding about 3 MPa (30 bar).

23. The process of claim 22, wherein step (ii) is carried out at a temperature in the range of about 30°C to about 75°C and / or at a pressure of no more than about 1 MPa (10 bar).

24. A process according to any one of claims 21 to 23, wherein the catalyst bed is reduced prior to step (ii), optionally by exposure to H2 at a temperature up to about 400°C.

25. A method according to any one of claims 21 to 24, wherein one or more hydrogen sources are produced from green hydrogen feedstocks, and / or the method is driven by renewable energy.

Images