Catalytic structures with metal oxide substrates, their preparation and their use - Patents.com

Abstract

The catalytic structure includes a substrate and a plurality of high entropy alloy (HEA) nanoparticles. At least a surface layer of the substrate is formed from a metal oxide. The HEA nanoparticles can be formed on the surface layer. Each HEA nanoparticle can include a homogenous mixture of at least four different elements that form a single-phase solid solution alloy. The catalytic structure can be used for catalysis in chemical reactions, such as an ammonia oxidation reaction, an ammonia synthesis reaction, or an ammonia decomposition reaction.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 261,557, filed September 23, 2021, entitled "Supported Multi-Element Nanoparticle Catalysts and Methods for Making and Using the Same," which is incorporated by reference in its entirety herein.

[0002] (Statement Regarding Federally Sponsored Research) This invention was made with United States Government support under DEAR0001239 awarded by the U.S. Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E). The United States Government has certain rights in this invention.

[0003] The present disclosure relates generally to catalysts, and more particularly to catalyst structures comprising high entropy alloy (HEA) nanoparticles formed on and / or within a metal oxide substrate. [Background technology]

[0004] In traditional supported catalysts, metal catalysts are distributed on a porous solid substrate. The synthesis of supported catalysts typically involves impregnation, drying, and calcination. Traditional supported catalysts are mainly limited to single-component, two-component, or three-component catalysts by calcination in a furnace (e.g., continuous heating at about 500-600 °C for a long time). Summary of the Invention [Problem to be solved by the invention]

[0005] However, such heating techniques make it difficult to produce high entropy alloy (HEA) nanoparticles. In particular, due to the high temperature and long period of time in conventional furnaces, the metals can react with the substrate to form impurities or second phases, thereby affecting the formation and dispersion of high-quality metals at the nanoscale level. Embodiments of the disclosed subject matter may address, among other things, one or more of the problems and shortcomings mentioned above. [Means for solving the problem]

[0006] An embodiment of the disclosed subject matter system provides a catalytic structure including a plurality of high entropy alloy (HEA) nanoparticles, each formed on and supported by a substrate, as well as a method of making and using the same. In some embodiments, at least a portion of the substrate is formed from a metal oxide, such as, but not limited to, aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, or perovskite. In some embodiments, each HEA nanoparticle can be formed from at least five elements that can be used to catalyze an ammonia oxidation reaction, an ammonia synthesis reaction, or an ammonia decomposition reaction. For example, a catalytic structure having HEA nanoparticles made of platinum, palladium, rhodium, cobalt, and rare earth elements can be used for an ammonia oxidation reaction, and / or a catalytic structure having HEA nanoparticles made of cobalt, molybdenum, iron, nickel, and copper or manganese can be used for an ammonia synthesis reaction.

[0007] In one or more embodiments, the catalyst structure includes a substrate and a plurality of high entropy alloy (HEA) nanoparticles. At least a surface layer of the substrate can be formed from a metal oxide. A plurality of HEA nanoparticles can be formed on the surface layer of the substrate. Each HEA nanoparticle can have a maximum cross-sectional dimension of 1 μm or less. Each HEA nanoparticle can include a homogenous mixture of at least four different elements that form a single-phase solid solution alloy.

[0008] In one or more embodiments, the method can include providing one or more catalytic structures. Each catalytic structure can include a substrate and a plurality of HEA nanoparticles. At least a surface layer of the substrate can be formed from a metal oxide. A plurality of HEA nanoparticles can be formed on the surface layer of the substrate. Each HEA nanoparticle can have a maximum cross-sectional dimension of 1 μm or less. Each HEA nanoparticle can include a homogenous mixture of at least four elements that form a single-phase solid solution alloy. The method can further include contacting one or more reactants with the one or more catalytic substrates such that a chemical reaction converts the one or more reactants to one or more products at a first temperature.

[0009] In one or more embodiments, a method for producing a catalyst structure can include coating a substrate with a solution including a plurality of precursor metal salts. The plurality of precursor metal salts can include at least four different elements. At least a surface layer of the substrate can be formed from a metal oxide. The method can further include drying the substrate with the plurality of precursor metal salts. The method can also include subjecting the dried substrate to a thermal shock to form the catalyst structure. The thermal shock can include exposure to a peak temperature of at least 1500K for a duration of 1 second or less. After the thermal shock, the catalyst structure can include a plurality of HEA nanoparticles formed on the surface layer of the substrate. Each HEA nanoparticle can have a maximum cross-sectional dimension of 1 μm or less and can include a homogenous mixture of at least four different elements forming a single-phase solid solution alloy.

[0010] In one or more embodiments, the Pt-based catalyst and the NO removal catalyst can be removed from a nitric acid production reactor. The nitric acid production reactor has (i) one or more inlets for ammonia, oxygen, and nitrogen, and (ii) one or more inlets for NO xand one or more outlets for the product. The Pt-based catalyst may be in a first location between the one or more inlets and the one or more outlets prior to the removal. The N2O removal catalyst may be in a second location after the first location prior to the removal. The method may further include installing one or more catalyst structures in the nitric acid production reactor. Each catalyst structure may include a substrate and a plurality of HEA nanoparticles. At least a surface layer of the substrate may be formed from a non-conductive metal oxide. The plurality of HEA nanoparticles may be formed on the surface layer of the substrate. Each HEA nanoparticle may have a maximum cross-sectional dimension of 1 μm or less. Each HEA nanoparticle may include a homogenous mixture of at least four elements forming a single-phase solid solution alloy.

[0011] Any of the various innovations of the present disclosure can be used in combination or separately. This summary is provided to introduce in a simplified form a selection of concepts that are further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. [Brief description of the drawings]

[0012] The embodiments will now be described with reference to the accompanying drawings, which are not necessarily drawn to scale. Where applicable, some elements may be simplified or otherwise not shown to help illustrate and explain the underlying features. Like reference numbers refer to like elements throughout the drawings. [Figure 1A] FIG. 1A is a simplified schematic diagram illustrating aspects of high entropy alloy (HEA) nanoparticles in accordance with one or more embodiments of the disclosed subject matter. [Figure 1B]FIG. 1B is a simplified schematic diagram of a catalyst structure including HEA nanoparticles formed on a metal oxide substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 1C] FIG. 1C is a macroscopic image of a catalyst structure fabricated using an extruded aluminum oxide substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 1D] FIG. 1D is a microscope image of a catalyst structure fabricated using an extruded aluminum oxide substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 1E] FIG. 1E is a simplified schematic diagram of a catalyst structure including HEA nanoparticles formed on a metal oxide coated substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 1F] FIG. IF is a microscope image of a fabricated catalyst structure using an aluminum oxide coated carbon nanofiber substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 2A] FIG. 2A is a simplified schematic diagram of HEA nanoparticles formed on a metal oxide surface of a substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 2B] FIG. 2B shows transmission electron microscope (TEM) elemental mapping of the interface between the fabricated HEA nanoparticles (PtPdRhCoCe) and an aluminum oxide substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 2C] FIG. 2C is a simplified schematic diagram of HEA and other nanoparticles formed on a metal oxide surface of a substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 2D] FIG. 2D shows TEM elemental mapping of HEA (PtPdRhCoCe) and other nanoparticles formed on an aluminum oxide substrate in accordance with one or more embodiments of the disclosed subject matter. [Figure 2E] FIG. 2E shows TEM elemental mapping of HEA (PtPdCoNiFe) nanoparticles formed on a carbon nanofiber substrate. [Figure 2F]FIG. 2F is a simplified schematic diagram of a cross-sectional view of a metal oxide substrate illustrating the gradient distribution of formed HEA nanoparticles, in accordance with one or more embodiments of the disclosed subject matter. [Figure 2G] FIG. 2G shows scanning electron microscope (SEM) images of the surface and cross-sectional portion of an aluminum oxide substrate with a gradient distribution of HEA nanoparticles. [Figure 3A] FIG. 3A is a simplified schematic diagram of various stages for producing a catalyst structure in accordance with one or more embodiments of the disclosed subject matter. [Figure 3B] FIG. 3B is a simplified schematic diagram of a closed thermal shock apparatus for producing a catalyst structure in accordance with one or more embodiments of the disclosed subject matter. [Figure 3C] FIG. 3C is a simplified schematic diagram of an open thermal shock setup for fabricating a catalyst structure in accordance with one or more embodiments of the disclosed subject matter. [Figure 3D] FIG. 3D illustrates an alternative heater configuration for a thermal shock setup for fabricating catalyst structures in accordance with one or more embodiments of the disclosed subject matter. [Figure 3E] FIG. 3E illustrates an alternative heater configuration for a thermal shock setup for fabricating catalyst structures in accordance with one or more embodiments of the disclosed subject matter. [Figure 3F] FIG. 3F illustrates a generalized example of a computing environment in which the disclosed technology can be implemented. [Figure 4A] FIG. 4A is a process flow diagram of a method for making a catalyst structure according to one or more embodiments of the disclosed subject matter. [Figure 4B] FIG. 4B is a graph of an exemplary temperature profile of a thermal shock for forming HEA nanoparticles on a substrate in accordance with one or more embodiments of the disclosed subject matter. [Diagram 5] FIG. 5 is a process flow diagram of a generalized method for the use of a catalytic structure in a chemical reaction in accordance with one or more embodiments of the disclosed subject matter. [Figure 6A]FIG. 6A illustrates an exemplary ammonia oxidation reaction in accordance with one or more embodiments of the disclosed subject matter. [Figure 6B] FIG. 6B illustrates the retrofitting of an existing nitric acid production reactor to include a catalyst structure having HEA nanoparticles in accordance with one or more embodiments of the disclosed subject matter. [Figure 6C] FIG. 6C is a process flow diagram of a method for retrofitting an existing nitric acid production reactor in accordance with one or more embodiments of the disclosed subject matter. [Figure 7] FIG. 7 illustrates an exemplary ammonia synthesis reaction in accordance with one or more embodiments of the disclosed subject matter. [Figure 8A] FIG. 8A is a graph of product selectivity versus reaction temperature obtained from an ammonia oxidation reaction using the catalyst structure. [Figure 8B] FIG. 8B is a graph of product selectivity and ammonia conversion versus time on-stream for an ammonia oxidation reaction using the catalyst structure. [Figure 8C] FIG. 8C is a graph of mass-dependent catalytic performance for catalyst structures in powder and bulk form. [Figure 9A] FIG. 9A is a graph of the temperature-dependent catalytic activity of Co25Mo45-HEA nanoparticles on aluminum oxide coated carbon paper in an ammonia synthesis reaction operated at 10 bar and a reactant gas flow of 50 standard cubic centimeters per minute (sccm). [Figure 9B] FIG. 9B is a graph of temperature dependent catalytic activity of Co25Mo45-HEA nanoparticles on extruded aluminum oxide substrate in an ammonia synthesis reaction operated at 10 bar and a reactant gas flow of 50 sccm. [Figure 9C] FIG. 9C is a graph of temperature dependent catalytic activity of powder form of Co25Mo45-HEA nanoparticles on aluminum oxide substrate in an ammonia synthesis reaction operated at 10 bar and a reactant gas flow of 50 sccm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] General Considerations For the purposes of this specification, certain aspects, advantages, and novel features of the embodiments of the present disclosure are described herein. The disclosed methods and systems should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, both alone and in various combinations and subcombinations with each other. The methods and systems are not limited to any particular aspects, features, or combinations thereof, and the disclosed embodiments do not require that any one or more particular advantages exist or problems be solved. The technology from any embodiment or example can be combined with the technology described in any one or more of the other embodiments or examples. In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely illustrative and should not be construed as limiting the scope of the disclosed technology.

[0014] Although some operations of the disclosed methods are described in a particular order for convenient presentation, it should be understood that this method of description encompasses reordering, unless a particular ordering is required by the specific language described below. For example, operations described in sequence may be reordered or performed simultaneously in some cases. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed methods may be used in conjunction with other methods. Furthermore, the description may use terms such as "provide" or "achieve" to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the specific implementation and are readily discernible by those of ordinary skill in the art.

[0015] The disclosure of a numerical range should be understood to refer to each discrete point within the range, including the endpoints, unless otherwise indicated. Unless otherwise indicated, all numbers expressing amounts of ingredients, molecular weights, percentages, temperatures, times, etc., used in this specification or claims should be understood to be modified by the term "about". Thus, unless otherwise implicitly or explicitly indicated, or unless the context is properly understood by those skilled in the art to have a clearer configuration, the numerical parameters described are approximations that may depend on the desired properties sought and / or the limits of detection under standard test conditions / methods, as known to those skilled in the art. When directly and explicitly distinguishing the embodiments from the prior art discussed, the numbers of the embodiments are not approximations unless the word "about" is recited. Whenever "substantially", "approximately", "about", or similar language is expressly used in conjunction with a particular value, a variation of up to 10% of that value is intended, unless expressly stated otherwise.

[0016] Directions and other relative references may be used to facilitate the description of the figures and principles herein, but are not intended to be limiting. For example, certain terms such as "inside," "outside," "top," "bottom," "inner," "outer," "left," "right," "front," "rear," "rear side," and the like may be used. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. However, such terms are not intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, a "top" portion may become a "bottom" portion by simply flipping the object over. Nevertheless, it is still the same portion, and the object remains the same.

[0017] As used herein, "comprising" means "including," and the singular forms "a" or "an" or "the" include plural references unless the context clearly dictates otherwise. The term "or" refers to a single element or a combination of two or more elements of the referenced alternative elements, unless the context clearly dictates otherwise.

[0018] There are alternatives for the various components, parameters, operating conditions, etc. described herein, but these alternatives are not necessarily equivalent and / or function equally well. Nor are the alternatives listed in order of preference unless otherwise indicated. Unless otherwise indicated, any of the groups defined below may be substituted or unsubstituted.

[0019] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs.Methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, but suitable methods and materials are described below.The materials, methods, and examples are illustrative only and are not intended to be limiting.Features of the subject matter of this disclosure will become apparent from the following detailed description and the appended claims.

[0020] Terminology Overview The following is provided to facilitate a description of various aspects of the disclosed subject matter and to guide those of ordinary skill in the art in practicing the disclosed subject matter.

[0021] Thermal shock: application of a thermal shock temperature for a period having a duration of about 1 second or less. In some embodiments, the duration of the thermal shock temperature application period is less than 500 milliseconds, e.g., 100 milliseconds or less. For example, in some embodiments, the duration of the thermal shock can range from about 1 microsecond to about 100 milliseconds, inclusive, e.g., about 55 milliseconds. In some embodiments, the thermal shock is applied for at least 10 seconds prior to the heating period.3 K / s (e.g., about 10 5 and / or heating to the thermal shock temperature at a ramp rate of at least 10 3 K / s (e.g., about 10 5 The method may include cooling from the thermal shock temperature at a ramp rate of 100 K / s.

[0022] Thermal shock temperature: the peak or maximum temperature at the surface of one or more heating elements when energized (e.g., by application of a current pulse) and / or at the surface of the material being heated. In some embodiments, the thermal shock temperature is at least about 1500 K, e.g., in the range of about 1500 K to about 2500 K (e.g., 1700 to 2300 K). In some embodiments, the temperature of the material being heated in the furnace (e.g., precursors on a substrate) can match or substantially match (e.g., within 10%) the temperature of the heating elements.

[0023] Particle size: The largest cross-sectional dimension (e.g., diameter) of one or more particles. In some embodiments, the specified particle size represents the average particle size (e.g., the average of the largest cross-sectional dimension) of all particles. In some embodiments, particle size can be measured according to one or more known standards, such as, but not limited to, ASTM B214-16, entitled "Standard Test Method for Sieve Analysis of Metal Powders," ASTM B330-20, entitled "Standard Test Method for Estimating the Average Particle Size of Metal Powders and Related Compounds Using Air Permeability," ASTM B822-20, entitled "Standard Test Method for Particle Size Distribution of Metal Powders and Related Compounds by Light Scattering," and ASTM B922-20, entitled "Standard Test Method for Metal Powder Specific Surface Area by Physical Adsorption," all of which are incorporated herein by reference.

[0024] Nanoparticle: An engineered particle formed from a plurality of elements (e.g., at least four elements, at least five elements, or at least eight elements) and having a maximum cross-sectional dimension (e.g., diameter when the particle is spherical, e.g., D in FIG. 1A, about 1 μm or less, e.g., about 100 nm or less). In some embodiments, each nanoparticle has a maximum cross-sectional dimension of about 25 nm or less, e.g., in the range of 1-20 nm.

[0025] High-entropy alloy (HEA) nanoparticles: nanoparticles that contain a homogeneous mixture of at least four elements that form a single-phase solid solution.

[0026] Non-HEA particles: particles consisting of three or fewer elements (e.g., nanoparticles or smaller), e.g., single-element particles (e.g., atoms) or binary element particles. In some embodiments, non-HEA particles formed simultaneously on a common substrate with HEA nanoparticles may have a particle size smaller than that of the HEA nanoparticles (e.g., 25% or less of the diameter of the HEA nanoparticles).

[0027] Noble Metals: Gold (Au), platinum (Pt), and other platinum group metals, including iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), and ruthenium (Ru).

[0028] Rare Earth Elements: Scandium (Sc), Yttrium (Y), Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), and Lu (Lu).

[0029] Transition metals: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Lanthanum (La), Hafnium (Hf), Any element selected from Tantalum (Ta), Tungsten (W), Rhenium (Re), Osnium (Os), Platinum (Pt), Iridium (Ir), Gold (Au), Mercury (Hg), Actinium (Ac), Ruthenium (Rf), Dubnium (Db), Seaborgium (Sg), Borium (Bh), Hassium (Hs), Methinerium (Mt), Darmstadium (Ds), Roentgenium (Rg), and Copernicium (Cn).

[0030] Introduction High entropy alloy (HEA) nanoparticles can be formed on porous substrates to form catalytic structures. HEA nanoparticles can be formed from a homogenous mixture of at least four elements (e.g., five or more) in a single solid solution phase. The large number of elements available for inclusion in HEA nanoparticles (e.g., 20 possible transition and / or main group metals) can allow for tuning and / or optimization of material composition and / or surface properties, for example, to maximize or at least improve catalytic activity, durability, or any other desirable properties. In some embodiments, HEA nanoparticles also have a large entropy of mixing that reduces the chemical potential of dealloying (ΔGmix=ΔHmix-T*ΔSmix). Alternatively or additionally, HEA nanoparticles can exhibit a highly distorted lattice that can reduce or inhibit atomic diffusion, which can give rise to enhanced thermodynamic and kinetic stability compared to pure metals or simple alloys.

[0031] Such features may enable high catalytic activity and durability, which may be particularly advantageous for catalytic applications in harsh reaction conditions, such as ammonia reactions and / or exhaust conversion. For example, catalysts according to embodiments of the disclosed subject matter may be used in ammonia (NH3) synthesis, ammonia oxidation, ammonia decomposition, and / or NO x Reduction (e.g., de-NO x ), but are not limited to, in thermochemical or thermocatalytic reactions.

[0032] In some embodiments, the substrate is a non-conductive solid metal oxide or has an outermost non-conductive metal oxide layer on which the HEA nanoparticles are formed. For example, the metal oxide can be aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, and / or perovskite. In some embodiments, the catalyst structure including a plurality of HEA nanoparticles on the substrate can have a low precious metal content, e.g., 30% or less by weight of the catalyst structure (e.g., in the range of 2-10% by weight). For example, a HEA catalyst supported on a metal oxide substrate (e.g., alumina extrudates) can have less than 5% by weight of precious metal, which represents a more than 20-fold reduction in precious metal content compared to conventional platinum-rhodium gauze catalysts used in ammonia oxidation.

[0033] catalyst structure Referring to FIG. 1A, a simplified diagram of a HEA nanoparticle 102 is shown. The nanoparticle 102 can be formed from a plurality of 104 elements, e.g., four or more different element atoms 106a-106d, in a single particle having a maximum cross-sectional dimension D of 1 μm or less, e.g., in the range of 1-20 nm. The atoms in the nanoparticle can form a homogenous mixture as a single-phase solid solution (e.g., having a face-centered cubic (FCC) phase). In some embodiments, the atoms 106a-106d are selected from transition metals, lanthanides, actinides, and post-transition metals.

[0034] In some embodiments, HEA nanoparticles can be formed from platinum (Pt), palladium (Pd), rhodium (Rh), cobalt (Co), and a promoter (e.g., a rare earth element such as cerium). For example, HEA nanoparticles for use as ammonia oxidation catalysts can be formed from Pt, which exhibits high selectivity, high conversion, and excellent stability. 63 Pd 15 Rh4Co 15 Alternatively, in some embodiments, HEA nanoparticles formed from Pt, Pd, Rh, Co, and a promoter can have a reduced Pt content (e.g., in the range of 50-60 atomic %) and an increased content of non-precious metals (e.g., Co and / or promoters) (e.g., ≧20 atomic %).

[0035] Alternatively, in some embodiments, the HEA nanoparticles can be formed from at least two elements from the group of cobalt (Co), molybdenum (Mo), and transition metal elements (e.g., 3d transition metals such as iron (Fe), nickel (Ni), copper (Cu), and manganese (Mn)). In some embodiments, the atomic elements 106a-106d form an HEA or are graded to form an HEA, have an atomic size difference δ, and / or a mixing enthalpy ΔH. mix For example, δ≦6.6% and / or −11.6<ΔH mix <3.2 kJ / mol. For example, the atomic elements can be selected so that the ammonia decomposition nanoparticles are Co x Mo y Fe a Ni b M´ c where x+y=100-(a+b+c), 10≦a, b, c≦20, and M′ is Cu or Mn. In some embodiments, a, b, and c can be the same as each other (e.g., a=b=c=10) or can be different from each other.

[0036] In some embodiments, a plurality of HEA nanoparticles 102 are integrally formed on and supported by a substrate to form a catalytic structure. For example, FIG. 1B shows a catalytic structure 110 including a solid substrate 112 and a plurality of HEA nanoparticles 102. The solid substrate 112 may be composed of (e.g., consists essentially of) a metal oxide, such as, but not limited to, aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolites, spinels, and / or perovskites. The plurality of HEA nanoparticles 102 may be randomly disposed on and / or within the substrate 112, for example, with a minimum spacing S between adjacent nanoparticles 102 in the range of about 10-100 nm. In some embodiments, the substrate 112 can be porous (e.g., having a pore volume in the range of 0.6-0.8 mL / g, e.g., as determined by Brunauer-Emmett-Teller (BET) measurements) such that the reactants 114 can flow through the catalyst structure 110, thereby generating a flow of the products 126 (and / or carrier gas and / or potentially unreacted reactants) under appropriate reaction conditions (e.g., reaction temperature).

[0037] In FIG. 1B, the substrate 112 is shown as a rectangular prism for convenience. However, in actual implementations, the substrate may have a different shape than that shown in FIG. 1B. In some embodiments, the substrate may be an extruded metal oxide support having any shape, such as, but not limited to, irregular granules, spheres, hollow rings, cubes, rectangular prisms, cylinders, bilobes, trilobes, or tetralobes. For example, in some embodiments, the substrate may be an aluminum-based extrudate pellet, as disclosed in European Patent No. 0 455 307 B1, issued Aug. 10, 1994, and entitled "Method of Preparation of Alumina-Based Extrudates," or U.S. Patent No. 6,656,875 B1, issued Dec. 2, 2003, and entitled "Alumina Extrudates, Method of Preparation, and Use as Catalyst Supports," both of which are incorporated herein by reference. For example, in some embodiments, the substrate may be a multi-lobe cylindrical pellet, as disclosed in U.S. Patent No. 4,028,227, issued June 7, 1977, and entitled "Hydroprocessing of Petroleum Residues Using Small Pore Shaped Catalyst Particles," which is incorporated herein by reference. Alternatively or additionally, in some embodiments, the substrate having nanoparticles therein may be ground into a powder, e.g., having a particle size of 1 mm or less.

[0038] In some embodiments, the substrate 110 is an extruded metal oxide support, for example as shown in Figures 1C-1D. The extruded metal oxide support can have a maximum cross-sectional dimension of 20 mm or less, for example a length in the range of 4-6.5 mm, and a diameter in the range of 2.1-3.2 mm. In some embodiments, the substrate 110 is an extruded metal oxide support having a diameter of 175-225 mm. 2 The porous structure may exhibit a surface area of ​​about 1 / g (inclusive).

[0039] In the examples of Figures 1B-1D, the substrate 110 is formed entirely of a metal oxide. Alternatively, in some embodiments, only a portion of the substrate may be formed of a metal oxide, e.g., the outermost layer on which HEA nanoparticles are formed. For example, Figure 1E shows a catalyst structure 120 having a plurality of nanoparticles 102 formed on a composite substrate, in particular having a base layer 124 and a metal oxide coating 122. In some embodiments, the metal oxide coating 122 can be formed of aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, and / or perovskite, while the base layer 124 can be formed of a different material, such as a carbon-based material (e.g., carbon nanofibers). For example, Figure 1F is an image of a fabricated catalyst structure having HEA nanoparticles formed on an alumina-coated carbon nanofiber. In some embodiments, the metal oxide coating 122 can be formed on all of the interior and / or exterior surfaces of the base layer 124, e.g., as a conformal coating (e.g., via atomic layer deposition). For example, the metal oxide coating 122 can have a thickness of about 100 nm or less.

[0040] In the illustrated example in FIG. 1A, the HEA nanoparticles 102 are shown as being substantially spherical in shape. However, in some embodiments, interactions between elements of the HEA nanoparticles and metal oxides of the substrate (e.g., between metals of the HEA nanoparticles and oxygen of the substrate) can cause the HEA nanoparticles to have a non-spherical shape. For example, FIG. 2A shows a catalyst structure 200 in which HEA nanoparticles 202 formed on a substrate metal oxide substrate 204 assume a truncated spherical shape. FIG. 2B shows an example of the preparation of HEA nanoparticles having a truncated spherical shape, specifically HEA nanoparticles composed of Pt, Pd, Rh, Co, and Ce formed on an aluminum oxide substrate. In some embodiments, the non-spherical shape and / or interactions between the HEA nanoparticles and the metal oxide can result in improved adhesion, reliability, and / or durability, as compared to spherical nanoparticles formed on, for example, a carbon substrate.

[0041] In some embodiments, the use of metal oxides for the substrate surface may inhibit the complete formation of HEA nanoparticles, such that at least some of the elements in the precursor starting material form non-HEA particles on the substrate surface, for example, interposed between the formed HEA nanoparticles. For example, FIG. 2C shows a catalyst structure 210 in which a plurality of non-HEA particles 214 are formed on the metal oxide surface 204 in the interstitial regions 212 between adjacent HEA nanoparticles 202. The non-HEA particles 214 may be formed simultaneously and / or by the same process as the HEA nanoparticles 202, for example, due to interactions between the elements and the metal oxide of the substrate, inhibiting the mobility of the elements during the thermal shock process. In some embodiments, the number of non-HEA particles formed on / in the substrate may be greater than the number of HEA nanoparticles formed on / in the substrate, and / or the size of the non-HEA particles (e.g., D2 in FIG. 2C) may be smaller than the size of the HEA nanoparticles. In some embodiments, some or all of the non-HEA particles may be single element particles (e.g., atoms). FIG. 2D shows an example of the preparation of a catalyst structure with HEA nanoparticles composed of Pt, Pd, Rh, Co, and Ce and non-HEA particles (shown as dots) formed together on an aluminum oxide substrate. In contrast, FIG. 2E shows an example of the preparation of a catalyst structure with HEA nanoparticles composed of Pt, Pd, Co, Ni, and Fe formed on a carbon-based substrate. Because the carbon-based substrate does not inhibit HEA nanoparticle formation, FIG. 2E shows no evidence of non-HEA particle formation (e.g., no dots outside the HEA nanoparticles).

[0042] In some embodiments, a plurality of HEA nanoparticles may be formed on and within a porous solid substrate such that the distribution of nanoparticles varies throughout a cross-section of the substrate, e.g., such that the particle density of HEA nanoparticles is less in regions closer to the outer surface of the substrate and further from the outer surface of the substrate (e.g., closer to the center). For example, FIG. 2F shows a catalyst structure 230 having a plurality of HEA nanoparticles 202 formed on and within a metal oxide substrate 204. The distribution of HEA nanoparticles 202 may follow a gradient 236, where the density and / or number of nanoparticles 202 is greater at the outer surface 232 compared to a central region proximate the center 234. In some embodiments, the gradient 236 may be substantially linear or nonlinear. Alternatively or additionally, in some embodiments, the central interior region (e.g., proximal to the center 234) may have a mass loading of HEA nanoparticles 202 that is 0-80% (e.g., ≦50%) of the mass loading of HEA nanoparticles 202 at the outer surface 232 of the substrate 204. 2G shows a fabricated example of a catalyst structure in which HEA nanoparticles are distributed in a gradient across the cross section of an aluminum oxide substrate. In some embodiments, a non-uniform distribution of HEA nanoparticles can be beneficial for some reactions, for example, by providing a higher density of HEA nanoparticles closer to the substrate surface where reactants are more likely to interact with the nanoparticles.

[0043] In some embodiments, the HEA nanoparticle gradient can be a function of precursor loading on and into the porous solid substrate. For example, in some embodiments, the precursor can be loaded using a dry impregnation method, where the volume of the precursor solution (e.g., metal salt in organic solvent or water) is equal to or less than the pore volume of the substrate. Capillary action can draw the precursor solution into the pores of the substrate until it is absorbed. The concentration profile of the precursor-loaded sample can depend on the mass transfer conditions in the pores during impregnation, such that the precursor can be limited or confined to the surface region rather than the central interior region of the substrate. Exposure to thermal shock heating can convert the precursor to HEA nanoparticles, e.g., primarily in the proximal region of the surface with few HEA nanoparticles present in the interior region. Alternatively, in some embodiments, the precursor can be loaded using a wet impregnation method, where the volume of the precursor solution is greater than the pore volume of the substrate. For example, the metal oxide substrate can be immersed in the precursor solution (e.g., for several hours, such as 24 hours) such that the precursor is absorbed into the substrate. The precursor loading can be substantially uniform. However, when exposed to thermal shock heating, HEA nanoparticles may be formed in a non-uniform distribution, for example such that the particle density gradually decreases from the surface to the interior of the substrate.

[0044] Catalyst Structure Manufacturing System 3A, a generalized setup 301 for forming a catalyst structure can include a substrate fabrication and preparation stage 303, a precursor loading or impregnation stage 307, a drying stage 311, and a thermal shock heating stage 315. In the substrate fabrication and / or preparation stage 303, a substrate formed partially or entirely from a metal oxide can be provided. In some embodiments, stage 303 can include fabrication of the substrate via, for example, extrusion and / or calcination of a metal oxide, formation of a carbon-based layer, and / or coating with a metal oxide. Alternatively or additionally, in some embodiments, stage 303 can include preparation of the substrate for subsequent precursor loading, for example, by removing moisture, altering crystallinity and / or porosity, and / or improving surface wettability.

[0045] The substrate can be provided to a precursor loading / impregnation stage 307, where the substrate can be combined, coated, and / or mixed with a solution 305 containing one or more precursors (e.g., metal salts such as chlorides, nitrates, and / or alkoxides in an organic solvent or water). In some embodiments, the precursor loading / impregnation stage 307 can use dry impregnation, wet impregnation, or both. In some embodiments, mixing of the substrate and the precursor solution can be performed using a rotating drum mixer. Other methods for combining, coating, and / or mixing are also possible according to one or more contemplated embodiments. In some embodiments, the precursor-loaded substrate 309 can be provided to a drying stage 311, for example, to remove the solvent (e.g., organic solvent or water) therefrom. In some embodiments, the drying stage 311 can use freeze drying or critical point drying, which can avoid or at least reduce precursor loss and / or disruption of the distribution of the precursor. For example, lyophilization or critical point drying can maintain a substantially uniform distribution of the precursor salts in the solid state, which in turn can affect the subsequent HEA particle size and / or distribution. Other methods for drying are also possible, according to one or more contemplated embodiments.

[0046] The dried, precursor-loaded substrate 313 may be provided to a thermal shock heating stage 315, for example, to convert the precursors into HEA nanoparticles, thereby providing catalytic structures for subsequent use 317. In some embodiments, the thermal shock heating stage 315 exposes the precursor-loaded substrate to a short time pulse (e.g., less than 1 second) of high temperature (e.g., a thermal shock temperature of at least 1200 K) such that the precursors self-assemble into a plurality of isolated HEA nanoparticles on and within the substrate. In some embodiments, the short time pulse of high temperature can be achieved by moving the substrate through a spatially confined heating zone (e.g., the duration of heating is determined by the size of the heating zone and the speed of the substrate through the heating zone). Alternatively or additionally, in some embodiments, the short time pulse of high temperature can be achieved by pulsing a heating element.

[0047] In some embodiments, the thermal shock heating step can use Joule heating elements similar to any of those disclosed in, for example, U.S. Patent Application Publication No. 2018 / 0369771 entitled "Nanoparticles and Systems and Methods for Synthesizing Nanoparticles via Thermal Shock," U.S. Patent Application Publication No. 2019 / 0161840 entitled "Thermal Shock Synthesis of Multi-Element Nanoparticles," International Publication No. WO 2020 / 236767 entitled "High Temperature Sintering System and Method," or International Publication No. WO 2020 / 252435 entitled "Systems and Methods for High Temperature Synthesis of Mono- and Polyatomic Dispersions." Alternatively or additionally, in some embodiments, the thermal shock heating step can use microwave heating, laser heating, electron beam heating, spark discharge heating, or a joule heating element similar to any of those disclosed in, for example, U.S. Patent Application Publication No. 2018 / 0369771 entitled "Thermal Shock Synthesis of Multi-Element Nanoparticles via Thermal Shock," International Publication No. WO 2020 / 236767 entitled "High Temperature Sintering System and Method," or International Publication No. WO 2020 / 252435 entitled "System and Method ... 3 K / s heating rate, a maximum temperature of at least 1200 K, and / or a 3 Any other heating mechanism capable of providing a cooling rate of 100 K / s can be used.

[0048] In some embodiments, a system for forming a catalyst structure according to the setup 301 of FIG. 3A can be provided. In some embodiments, the system can include one or more process stations or systems corresponding to the different stages 303, 307, 311, and 315. For example, the system can include a substrate fabrication station for extruding a metal oxide substrate, an impregnation station for loading a precursor onto the substrate, a drying station for removing solvent from the substrate, and a heating station for performing a thermal shock (e.g., furnace system 300 of FIG. 3B or furnace system 330 of FIG. 3C). In some embodiments, the system can include a controller or control module configured to control various components of the system to perform the fabrication of the catalyst structure.

[0049] FIG. 3B illustrates a furnace 300 for thermal shock heating using a sealed or enclosed setup. In the illustrated example, the various components of the furnace 300 (including an input queue or hopper 306, a transport assembly 310 having rollers 312 (e.g., drive rollers and / or passive support rollers), a pair of heating elements 316a, 316b, and an output collection bin 320) can be disposed within an interior volume 304 of a sealed (e.g., airtight) enclosure 302. In some embodiments, the interior volume 304 of the enclosure 302 can be filled with a static or flowing inert gas (e.g., argon, nitrogen, or combinations thereof). The pair of heating elements 316a, 316b can be disposed on either side of the transport assembly 310 and together can define a heating zone 314 of length L (e.g., 1-2 inches). In some embodiments, the transport assembly 310 can be formed of a flexible material, e.g., carbon cloth, that can be exposed to high temperatures (e.g., >1200K) without substantial degradation.

[0050] During operation, a dry substrate 308 loaded with precursor is deposited from an input hopper 306 onto a transport assembly 310, which transports the substrate 308 through a heating zone 314 between heating elements 316a, 316b, thereby exposing the substrate 308 to a thermal shock that converts the precursor to HEA nanoparticles. The resulting catalyst structure 318 (having HEA nanoparticles formed on the metal oxide surface) is further transported from the heating zone 314 by conveying the assembly 310 into an output collection bin 320. In some embodiments, the operation of the furnace 300 can be semi-continuous, for example, with the substrate 308 being dispensed, transported by the transport assembly 310, heated by the heating elements 316a, 316b, and the catalyst structure 318 being collected until the supply of substrates 308 in the input hopper 306 is exhausted. Alternatively, in some embodiments, operation of the furnace 300 may be continuous, for example, with the supply of substrates 308 being continuously or periodically replenished (e.g., by introducing new substrates into the input hopper 306 via an airlock or other mechanism).

[0051] In some embodiments, the duration of the thermal shock may be the product of the length L of the heating region 314 and the velocity v of the transport assembly 310 (e.g., t1=L / v). The velocity of the transport assembly 310 (e.g., 60 in / min) is determined by the desired duration of the thermal shock (e.g., ≦1 sec, e.g., ≦500 ms or ≦100 ms) and / or the desired heating or cooling ramp rate (e.g., ≧10 3 The heating elements 316a, 316b may be selected to achieve a constant or substantially constant temperature (e.g., ≧1200 K / s) within the heating zone 314. In such a configuration, the heating elements 316a, 316b may be continuously energized, for example, to provide a constant or substantially constant temperature (e.g., ≧1200 K) within the heating zone 314. Alternatively or additionally, in some embodiments, the heating elements 316a, 316b may be operated in a pulsed mode, for example, to provide a time-varying temperature profile within the heating zone 314.

[0052] In some embodiments, the heating elements 316a, 316b can be joule heating elements formed of, for example, a carbon-based material (e.g., carbon felt). For example, the joule heating elements can be similar to any of the heating elements disclosed in U.S. Patent Application Publication No. 2018 / 0369771, entitled "Systems and Methods for Synthesizing Nanoparticles via Thermal Shock," U.S. Patent Application Publication No. 2019 / 0161840, entitled "Thermal Shock Synthesis of Multi-Element Nanoparticles," International Publication No. WO2020 / 236767, entitled "High Temperature Sintering System and Method," and International Publication No. WO2020 / 252435, entitled "Systems and Methods for High Temperature Synthesis of Single-Atomic and Multi-Atomic Dispersions." Instead of or in addition to Joule heating, in some embodiments, the heating elements can comprise any other heating source capable of generating a thermal shock profile, such as a microwave heating source, a laser, an electron beam device, a spark discharge device, or any combination thereof.

[0053] In some embodiments, only a portion of the furnace may be enclosed in an inert environment, for example, to simplify loading and / or unloading of materials and to reduce manufacturing and / or operating costs of the system. For example, FIG. 3C shows a furnace 330 for thermal shock heating using an open setup. In the illustrated example, the heating elements 316a, 316b are disposed within an interior volume 334 of a protective enclosure 332, while the remaining components of the furnace 330, including an input hopper 336, a transport assembly 310 with rollers 312, and an output collection bin 346, are disposed outside the enclosure 332 (e.g., in an ambient environment, such as air). In the illustrated example, the protective enclosure 332 may be open to allow the transport assembly 310 to pass through. Alternatively or additionally, in some embodiments, a flow of shielding gas (e.g., an inert gas, such as argon, nitrogen, or both) may be introduced into the protective enclosure 332, for example, via an inlet flow 338, to protect the heating elements 316a, 316b. After passing through the heating zone, the shielding gas may exit the protective enclosure 332 , for example, as exit stream 340 .

[0054] In the illustrated example of FIGS. 3B-3C, heating is provided by a pair of heating elements 316a, 316b on both sides (e.g., top and bottom) of the transport assembly 310. However, in some embodiments, a different number of heating elements can be used. In some embodiments, a single heating element 316 can be disposed on top of the transport assembly 310, for example, as shown in setup 350 of FIG. 3D. Alternatively, in some embodiments, two pairs of heating elements can be disposed in an arrangement surrounding the transport assembly 310, for example, as shown in FIG. 3E, with a first pair of heating elements 316a, 316b on the top and bottom of the transport assembly 310 and a second pair of heating elements 316c, 316d on the left and right of the transport assembly 310. In some embodiments, one, some, or all of the heating elements can be disposed in close proximity (e.g., ≦5 mm) to the substrate 308 and / or the transport assembly 310, for example, to achieve a high temperature and uniform temperature profile.

[0055] Although the illustrated example shows each heating element extending the length of the heating zone, embodiments of the disclosed subject matter are not so limited. Rather, multiple heating elements can be positioned along the length of the heating zone. Alternatively or additionally, in some embodiments, a portion of the transport assembly 310 can be energized to function as a bottom heating element, for example, by electrically contacting a portion of the transport assembly in the heating zone when the transport assembly is formed of carbon. Other furnace setups and heating configurations are also possible according to one or more contemplated embodiments. For example, embodiments of the disclosed subject matter can use any of the furnace setups or heating configurations disclosed in International Application No. PCT / US22 / 21915, entitled "High Temperature Sintering Furnace System and Method," filed March 25, 2022, which is incorporated herein by reference.

[0056] Method for producing catalyst structure FIG. 4A illustrates a method 400 for producing a catalyst structure. The method 400 can begin at an initial step 402 and proceed to a decision step 404, where a decision is made between a solid substrate or a coated substrate. If a solid substrate is desired, the method 400 can proceed to a processing step 406, where a porous solid substrate formed of a metal oxide (e.g., consisting essentially of one or more metal oxides) can be provided. In some embodiments, the solid substrate can be comprised of aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolites, spinels, and / or perovskites. For example, the solid substrate can be a metal oxide extrudate pellet, such as a multi-lobed cylindrical pellet. In some embodiments, providing the processing step 406 can include producing a solid substrate, for example, by extrusion and calcination.

[0057] Alternatively, if a coated substrate is instead desired, method 400 can proceed to process step 408, where a base layer can be provided. In some embodiments, the base layer can be formed of a conductive material such as conductive carbon (e.g., a network of carbon nanofibers (CNFs)). In some embodiments, providing process step 408 can include fabricating the base layer. For example, a polymer nanofiber network (e.g., polyacrylonitrile) can be formed by electrospinning and then carbonized (e.g., by heating at 900° C. for 2 hours) to produce a network of CNFs for subsequent use as a base layer. Method 400 can proceed from process step 408 to decision step 410, where it is determined whether any pretreatment is desired for the base layer. If pretreatment is desired, method 400 can proceed to process step 412, where a surface treatment (e.g., thermal activation to increase surface defect concentration) can be performed. In some embodiments, the surface treatment can be effective to create surface defects in the carbon-based layer (e.g., for more effective nanoparticle dispersion). For example, when using a CNF film as the base layer, the surface treatment can be at least 1 hour (eg, ~2 hours) in a carbon dioxide atmosphere at 600°C (eg, 600-1000°C, eg, 750°C) or higher.

[0058] If pretreatment is not desired at determining step 410 or after completion of the surface treatment at treating step 412, method 400 can proceed to treating step 414, where the base layer can be coated with one or more metal oxide layers. For example, the coating can be comprised of aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolites, spinels, and / or perovskites. In some embodiments, the metal oxide coating on the base layer can have a thickness of 100 nm or less, e.g., ∼20 nm. In some embodiments, the metal oxide coating can be a conformal coating that covers all interior (within pores) and exterior surfaces of the base layer, e.g., via atomic layer deposition (ALD).

[0059] From treating step 414 or treating step 406, method 400 can proceed to determining step 416, where it is determined whether another optional pretreatment is desired. If pretreatment is desired, method 400 can proceed to treating step 418, where a treatment to enhance the wettability of the exposed metal oxide surface is performed. In some embodiments, the treatment to enhance wettability can include a plasma treatment and / or an acid treatment, for example, as disclosed in the article by Achour et al., “Effect of Plasma Functionalization Treatment and Gold Nanoparticles on Surface Chemistry and Wettability of Reactively Sputtered TiO2 Thin Films,” Applied Surface Science (July 2018, No. 458, pp. 678-85). Other metal oxide surface treatments are also possible according to one or more contemplated embodiments.

[0060] If pre-treatment is not desired at determining step 416 or after completion of treatment at treatment step 418, method 400 can proceed to determining step 420, where it is determined whether pre-heating of the substrate is desired. If pre-heating is desired, method 400 can proceed to treatment step 422, where the substrate can be heated. For example, in some embodiments, the substrate can be heated to 100-200° C. (e.g., 105° C. for 4 hours) to remove moisture. Alternatively, or in addition, in some embodiments, the substrate can be heated at a temperature of 800-1500° C. in an inert gas atmosphere (e.g., argon, nitrogen, or both) to increase crystallinity. For example, increased crystallinity can reduce the surface area of ​​the substrate, which can in turn alter (e.g., decrease) the precursor loading capacity and / or alter (e.g., enhance) the catalytic effect of the final structure. Other pre-heating regimes and effects are also possible according to one or more contemplated embodiments.

[0061] If pre-heating was not desired in determining step 420 or after pre-heating in process step 422 is completed, method 400 can proceed to process step 424, where HEA particle precursors can be loaded onto the substrate, e.g., onto the interior or exterior metal oxide surface. The loading of precursors can reflect the desired composition of the resulting mixture of HEA nanoparticles, e.g., such that a desired atomic ratio of elements is achieved. However, evaporation of elements can occur during the thermal shock heating stage. Thus, in some embodiments, the loaded precursor content can be adjusted (e.g., increased) to compensate for any elemental losses and achieve the desired HEA nanoparticle composition.

[0062] In some embodiments, loading can include coating, impregnating, and / or infiltrating the precursor onto and / or into the substrate, for example, via wet impregnation techniques (e.g., when the volume of the precursor solution is greater than the pore volume of the substrate) or dry impregnation techniques (e.g., when the volume of the precursor solution is equal to or less than the pore volume of the substrate). In some embodiments, loading can be performed by mixing the precursor (e.g., metal salts such as chlorides, nitrates, or alcoholides) with the substrate in solution (e.g., organic solvent or water), for example, using a rotating drum mixer. For example, the precursor can be MCl x H y where M is a metal (e.g., Pt, Pd, Ni, Fe, Co, Au, Cu, Sn, etc.), x is 1 or greater, and y is 0 or greater. Other loading methods are possible according to one or more contemplated embodiments. For example, precursor loading can include dip coating, brushing, spraying, printing, rolling, incipient wetness spray impregnation, agitation drying, or any combination of the foregoing.

[0063] The method 400 can proceed to processing step 426, where the precursor-loaded substrate can be dried, e.g., to remove solvent therefrom. In some embodiments, the drying can be controlled to avoid precursor agglomeration, desorption, and / or precipitation, e.g., to enhance or ensure uniform precursor distribution. In some embodiments, the substrate can be dried by freeze drying or critical point drying. Alternatively, in some embodiments, the substrate can be oven dried, e.g., at 20-120° C.

[0064] The method 400 can proceed to process step 428, where the dried substrate with loaded precursor can be subjected to thermal shock heating by a pulsed heating profile 450, for example, as shown in FIG. H (For example, ≥ 10 3 K / s, e.g. 10 4 -10 5 (ii) a short residence time, t1 (e.g., 1 μs to 10 s, such as ≦500 ms), at or near the maximum temperature, T H (e.g., 1200–3000 K, such as 1500–2300 K), and (iii) a rapid cooling ramp, R C (For example, ≥ 10 3 K / s, e.g., 10-10 4 A thermal shock process 428 may be performed more than once (e.g., by undergoing multiple pulsed temperature profiles). In some embodiments, the peak temperature may be sufficient to melt all of the components and / or induce high temperature homogeneous mixing, while the rapid cooling may allow crystallization of the liquid elements into substantially uniform and homogeneous alloy nanoparticles without being subject to agglomeration, clumping, element segregation, or phase separation. Thus, a substrate and a catalyst structure including HEA nanoparticles thereon may be fabricated by the thermal shock process.

[0065] In some embodiments, the temperature profile 450 includes a low temperature TL or to and / or from elevated ambient temperature (e.g., 100-200°C), the maximum temperature T H A rapid transition to and / or from the heating zone can be provided. In some embodiments, the heating of the thermal shock process can be provided by Joule heating, microwave heating, laser heating, electron beam heating, spark discharge heating, or any other heating mechanism capable of providing the desired heating rate and temperature. In some embodiments, the thermal shock process can be terminated by removing the substrate from the heating zone and / or by deactivating, deactivating, or otherwise terminating operation of the heating elements. Alternatively or additionally, in some embodiments, cooling can be achieved using one or more passive cooling features (e.g., a heat sink thermally coupled to the heating elements and / or substrate, etc.), one or more active cooling features (e.g., a fluid flow directed at the substrate and / or heater, a fluid flow through the substrate, or a heat sink thermally coupled thereto, etc.), or any combination thereof.

[0066] After the thermal shock of process step 428, the method 400 can proceed to process step 430, where the catalyst structure can be used (e.g., as described below with respect to FIG. 5) or otherwise adapted for subsequent use. In some embodiments, the catalyst structure can be subjected to crushing and / or grinding, for example, to convert the catalyst structure from a bulk material to a powder (e.g., having a particle size ≦1 mm). Alternatively or additionally, the catalyst structure or multiple catalyst structures can be assembled together in a suitable holding structure (e.g., an array of Raschig rings) for installation in a reactor. In some embodiments, the catalyst can be used to perform ammonia (NH3) synthesis, ammonia oxidation, ammonia decomposition, and / or NO2 synthesis. x Reduction (e.g., de-NO x ) and can be used in, but not limited to, thermochemical or thermocatalytic reactions.

[0067] Although shown separately, it is contemplated that the various processing steps may occur simultaneously or iteratively. Additionally, certain processing steps shown as occurring after other processing steps may actually occur beforehand. Although some of the steps 402-430 of method 400 have been described as being performed once, in some embodiments, multiple iterations of a particular processing step may be used before proceeding to the next decision or processing step. Additionally, although the steps 402-430 of method 400 are shown and described separately, in some embodiments, the processing steps may be combined and performed together (concurrently or sequentially). Additionally, while FIG. 4A shows a particular order of steps 402-430, embodiments of the disclosed subject matter are not limited thereto. Indeed, in certain embodiments, the steps may occur in a different order than that shown, or simultaneously with other steps.

[0068] Computer implementation 3F illustrates a generalized example of a suitable computing environment 331 in which the described innovations may be implemented, such as, but not limited to, method 400, method 500, method 650, a controller of furnace system 300, a controller of furnace system 330, and / or a controller of a chemical reaction system. The computing environment 331 is not intended to suggest any limitation as to scope of use or functionality, as the innovations may be implemented in a variety of general purpose or special purpose computing systems. For example, the computing environment 331 may be any of a variety of computing devices (e.g., a desktop computer, a laptop computer, a server computer, a tablet computer, etc.).

[0069] Referring to FIG. 3F, the computing environment 331 includes one or more processing units 335, 337 and memory 339, 341. In FIG. 3F, this basic configuration 351 is included within the dashed line. The processing units 335, 337 execute computer-executable instructions. The processing units may be a central processing unit (CPU), a processor in an application specific integrated circuit (ASIC), or any other type of processor (e.g., hardware processor, graphics processing unit (GPU), virtual processor, etc.). In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. For example, FIG. 3F shows a central processing unit 335 and a graphics processing unit or co-processing unit 337. The tangible memory 339, 341 may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two accessible by the processing units. The memories 339, 341 store software 333 implementing one or more innovations described herein in the form of computer-executable instructions suitable for execution by a processing unit(s).

[0070] A computing system may have additional features. For example, computing environment 331 includes storage 361, one or more input devices 371, one or more output devices 381, and one or more communication connections 391. An interconnection mechanism (not shown), such as a bus, controller, or network, interconnects the components of computing environment 331. Typically, operating system software (not shown) provides an operating environment for other software executing in computing environment 331 and coordinates the activities of the components of computing environment 331.

[0071] Tangible storage 361 may be removable or non-removable and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium that can be used to store information in a non-transitory manner and that can be accessed within computing environment 331. Storage 361 may store instructions for software 333 that implements one or more of the innovations described herein.

[0072] The input device(s) 371 may be a touch input device such as a keyboard, a mouse, a pen, or a trackball, a voice input device, a scanning device, or another device that provides input to the computing environment 331. The output device 371 may be a display, a printer, speakers, a CD-writer, or another device that provides output from the computing environment 331.

[0073] The communications connection(s) 391 enable communication over a communications medium to another computing entity. The communications medium conveys information such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal that has one or more of its characteristics set up or changed in such a manner as to encode information in the signal. By way of example, and not limitation, the communications medium may use electrical, optical, radio frequency (RF), or another carrier.

[0074] Any of the disclosed methods may be implemented as computer-executable instructions stored on one or more computer-readable storage media (e.g., one or more optical media disks, volatile memory components (such as DRAM or SRAM), or non-volatile memory components (such as flash memory or hard drives)) and executed on a computer (e.g., any commercially available computer, including a smartphone or other mobile device that includes computing hardware). The term computer-readable storage medium does not include communication connections such as signals and carrier waves. Any computer-executable instructions for implementing the disclosed techniques, as well as any data created and used during the implementation of the disclosed embodiments, may be stored on one or more computer-readable storage media. The computer-executable instructions may be a dedicated software application or part of a software application that is accessed or downloaded, for example, via a web browser or other software application (such as a remote computing application). Such software may be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a networked environment using one or more networked computers (e.g., via the Internet, a wide area network, a local area network, a client-server network (such as a cloud computing network), or any other such network).

[0075] For clarity, only some selected aspects of the software-based implementation are described. Other details well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any particular computer language or program. For example, aspects of the disclosed technology can be implemented by software written in C++, Java™, Python™, and / or any other suitable computer language. Similarly, the disclosed technology is not limited to any particular computer or hardware type. Specific details of suitable computers and hardware are well known and need not be described in detail in this disclosure.

[0076] It should also be appreciated that any functionality described herein may be performed, at least in part, by one or more hardware logic components instead of software. For example, and without limitation, exemplary types of hardware logic components that may be used include field programmable gate arrays (FPGAs), program specific integrated circuits (ASICs), program specific standard products (ASSPs), systems on a chip (SOCs), complex programmable logic devices (CPLDs), etc.

[0077] Additionally, any of the software-based embodiments (e.g., including computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed via suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, an intranet, a software application, cable (including fiber optic cable), magnetic communication, electromagnetic communication (including radio frequency, microwave, and infrared communication), electronic communication, or other such communication means. In any of the above examples and embodiments, the provision of requests (e.g., data requests), instructions (e.g., data signals), commands (e.g., control signals), or any other communication between systems, components, devices, etc. can be by generation and transmission of appropriate electrical signals via wired or wireless connections.

[0078] Reactions using catalyst structures FIG. 5 illustrates a generalized method 500 for using a catalytic structure. The method 500 can begin with a process step 502 in which a catalytic structure is provided. The catalytic structure can include a substrate having a plurality of HEA nanoparticles. In some embodiments, the substrate can be formed entirely of a metal oxide, or can be formed at least of a metal oxide and have an outermost layer on which the HEA nanoparticles are formed. In some embodiments, the composition of the HEA nanoparticles can be selected for use in a particular chemical reaction. In some embodiments, providing the process step 502 can include fabricating the catalytic structure, for example, according to the method 400 of FIG. 4A. Alternatively or additionally, providing the process step 502 can include placing the catalytic structure in a suitable reactor for carrying out the chemical reaction.

[0079] The method 500 can proceed to process step 504, where the catalytic structure can be used in a chemical reaction, for example, by contacting a reactant (e.g., a gas) with the HEA nanoparticles of the catalytic structure. In some embodiments, the chemical reaction can include ammonia synthesis, ammonia oxidation, ammonia decomposition, or NOx Reduction (e.g., de-NO x ). In some embodiments, the substrate of the catalytic structure is porous and the contacting can include flowing the reactants through the porous substrate. Alternatively or additionally, in some embodiments, the contacting can include flowing the reactants parallel to the surface of the substrate on which the HEA nanoparticles are formed. In some embodiments, the catalytic structure, the reactants, and / or the environment containing the catalytic structure and the reactants can be subjected to heating, e.g., to provide energy to initiate and / or drive a chemical reaction. For example, the heating can be such that the reactants and / or HEA nanoparticles are exposed to (or maintained at) a maximum temperature of 300-600°C, e.g., ~500°C. For example, the reactant can be ammonia and the product can be hydrogen and nitrogen for a thermochemical reaction involving ammonia decomposition, or hydrogen and nitrogen for a thermochemical reaction involving ammonia synthesis, or vice versa.

[0080] For example, FIG. 6A shows a setup 600 for an ammonia oxidation reaction, where a reactor 602 employs a catalyst structure 604 having HEA nanoparticles formed on a metal oxide substrate. In some embodiments, the HEA nanoparticles of the catalyst structure 604 have at least Pt, Pd, and Rh, such as a combination of Pt, Pd, Rh, Co, and a promoter (e.g., a rare earth element). Ammonia 606 and oxygen and / or nitrogen 608 (e.g., air) can be provided as reactants in the reactor 602, which upon contact with the catalyst 604 at elevated temperatures (e.g., up to 800° C.), can react to form a product stream at an outlet 610. In some embodiments, the product outlet is NO x The product can include x=1 or 2. For example, the catalytic reaction can include at least 90% of the products at the outlet 610 being NO xproducts and / or 1% or less of the products at outlet 610 is N2O. Alternatively or additionally, the catalytic reaction may be such that at least 95% of the ammonia 606 may be converted to products. In some embodiments, the catalytic reaction may enable reactor 602 to operate without a de-N2O catalyst.

[0081] In some embodiments, the reactor 602 can be built as a slipstream device, for example, for operational testing within the configuration of an existing nitric acid plant. In some embodiments, the slipstream device can be skid mounted, for example, to allow the reactor to be built off of an existing plant and transported to / from the existing plant. In some embodiments, the slipstream device can utilize available plant ammonia and feed air, and the exhaust NO from the slipstream device can be used to generate the NO. x The stream can be sent back to the plant for conversion to nitric acid. For example, the slipstream device can operate at a pressure equal to or less than the ammonia vaporizer pressure of the existing plant. Alternatively or additionally, the slipstream device can operate at a pressure equal to or greater than the plant pressure downstream of the ammonia oxidation reactor. In some embodiments, the slipstream device includes an ammonia inlet nozzle, an air inlet nozzle, and a NO 2 inlet nozzle. x and a gas outlet nozzle, all of which may be connected via piping at the plant site.

[0082] In existing nitric acid plants, ammonia is vaporized and superheated to ensure that all ammonia is in a vapor state for accurate monitoring (e.g., via a flow meter). Downstream of the superheater is a flow control valve followed by an ammonia flow meter. In some embodiments, the ammonia source for the slipstream device may be provided downstream of the ammonia superheater but upstream of the ammonia control valve. This input stream may flow to the slipstream device in fully insulated electrically or steam traced piping so that the inlet ammonia temperature can remain in a vapor state for the slipstream device instrumentation. In some embodiments, the air inlet supply may be taken from the plant air compressor or may be supplied by a separate compressor dedicated to the slipstream device. In some embodiments, the slipstream device may have an analyzer to measure the reactant gas composition. The reactant gas may be returned from the slipstream device to the plant at any location between the ammonia oxidation reactor and the absorber.

[0083] Alternatively, in some embodiments, the reactor 604 can be accomplished by retrofitting an ammonia oxidation reactor in an existing nitric acid plant. Commercial nitric acid plants rely on Pt-Rh gauze catalysts for ammonia oxidation. Additionally, de-NO catalysts are typically used to remove the undesirable by-product NO, e.g., to mitigate polluting emissions. For example, an ammonia oxidation reactor 622 (e.g., a pancake reactor) in a conventional nitric acid plant facility 620 is shown in FIG. 6B. The ammonia oxidation reactor 622 has at least one inlet 624 for reactants (e.g., ammonia, nitrogen, and oxygen), one inlet 625 for products (e.g., NO), one inlet 626 for products (e.g., NO), and one inlet 628 for products (e.g., NO). xThe reactor has at least one outlet 630 for NO, nitrogen, and water, an upstream catalyst 626 (e.g., Pt-Rh gauze), and a downstream catalyst 628 for removing NO. The NO removal catalyst 628 is typically in the form of a cylindrical extrudate supported by an array of Raschig rings. In some embodiments, the ammonia oxidation reactor 622 can be subjected to a retrofit 632, for example, by removing the existing catalysts 626, 628 and replacing them with a catalyst structure 642 using HEA nanoparticles on a metal oxide substrate. The high activity and selectivity of the HEA catalyst for NO and NO minimizes the production of NO, so the retrofitted production facility 640 can operate without the need for additional de-NO catalysts.

[0084] Referring to FIG. 6C, a method 650 for retrofit operation of an ammonia oxidation reactor is shown. The method 650 can begin with a process step 652 in which an existing Pt-based catalyst (e.g., Pt-Rh gauze) is removed from the ammonia oxidation reactor. In step 654, an existing NO removal catalyst can also be removed from the ammonia oxidation reactor. In process step 656, one or more catalyst structures, each including HEA nanoparticles formed on a metal oxide substrate, can be installed in the ammonia oxidation reactor. In step 65, the ammonia oxidation reactor can continue to operate without the need for a separate NO removal catalyst.

[0085] Although shown separately, it is contemplated that various process steps may be performed simultaneously or iteratively. For example, process steps 652 and 654, removing existing catalyst, may be performed simultaneously, despite being shown as sequential process steps. Additionally, certain process steps shown as occurring after other processes may actually occur beforehand. Although some of steps 652-658 of method 650 have been described as being performed once, in some embodiments, multiple iterations of certain process steps may be used before proceeding to the next decision step or process step. Additionally, although steps 652-658 of method 650 are shown and described separately, in some embodiments, the process steps may be combined and performed together (concurrently or sequentially). Additionally, while FIG. 6C shows a particular order of steps 652-658, embodiments of the disclosed subject matter are not limited thereto. Indeed, in certain embodiments, the steps may occur in a different order than those shown, or simultaneously with other steps.

[0086] 7 shows a setup 700 for an ammonia synthesis reaction, where a reactor 702 employs a catalyst structure 704 having HEA nanoparticles formed on a metal oxide substrate. In some embodiments, the HEA nanoparticles of the catalyst structure 704 have at least Co and Mo, e.g., a combination of Co, Mo, and at least two transition metals. For example, a homogeneous mixture in each HEA nanoparticle has the formula Co x Mo y Fe a Ni b M´ c (where x+y=100-(a+b+c), 10≦a≦20, 10≦b≦20, 10≦c≦20, and M′ is Cu or Mn). Hydrogen 706 and nitrogen 708 can be provided as reactants in reactor 702, which upon contact with catalyst structure 704 at a temperature (e.g., 300-600° C., e.g., 450° C.) can react to form a product stream at outlet 710. In some embodiments, the product outlet can include ammonia. For example, the catalyzed reaction can have a mass specific reaction rate of the chemical reaction of at least 0.7 g ammonia gmetals -1 h -1 , e.g. ~1.52g ammonia g metals -1 h -1 It may be such that:

[0087] Example of fabrication and experimental results Alumina (Al2O3) extrudates were impregnated with metal salt solutions of designed concentrations. After drying, the precursor-loaded alumina substrates were loaded onto a carbon belt that manually transported the material through the HTS zone created by a Joule heater. The metal salts were directly converted to HEA nanoparticles in less than one second by radiant thermal shock. The color of the extrudates changed from tan (derived from the metal salt precursors) to black after HTS treatment. Elemental mapping analysis showed a uniform distribution of HEA elements across the alumina substrate, indicating the formation of a uniform alloy catalyst. The HEA nanoparticles were composed of Pt 63 Pd 15 Rh4Co 15 The pentane nanoparticles with the chemical moiety of Ce3 were formulated and used as ammonia oxidation catalysts. As shown in Figure 8A, the catalyst configuration showed approximately 100% conversion of ammonia and >99% NO oxidation at 700 °C. x Selectivity can be achieved at temperatures as high as 1000° C., whereas the commercial Pt-Rh gauze catalyst requires >900° C. to achieve similar performance. As shown in FIG. 8B, the catalyst structure containing HEA nanoparticles exhibits stable performance for extended operation.

[0088] Pt on alumina substrate for ammonia oxidation reaction 63 Pd 15 Rh4Co 15 The performance of Ce3 nanoparticles was optimized by varying, among other things, temperature, flow rate, O2 feed concentration (6000 ppm), substrate morphology (bulk extruded alumina vs. powdered extruded alumina) and catalyst loading, based on an ammonia feed concentration of 1000 ppm. In the ammonia oxidation reaction, excess catalyst reduced NO x Secondary conversion of products, i.e. NO to N x The reduction of NH3, and NO xThe efficiency of HEA catalyst can be reduced by reacting with the decomposition of NO to N2 and O2. The powder form of the HEA catalyst was used to study the catalyst loading optimization. As shown in Figure 8C, the catalyst loading was determined to be about 50 mg. To compare the effect of the substrate morphology, 100 mg of the bulk form of HEA catalyst was used to keep the metal loading constant. The bulk form of the HEA catalyst reduces the NO x It was demonstrated that the selectivity was improved. The reduction in the bulk form to 50 mg of catalyst used resulted in NO x The selectivity was further improved. At 750°C, Pt 63 Pd 15 Rh4Co 15 Ce3@Al2O3 showed approximately 100% conversion of NH3 and NO x A yield of about 93% or more of (NO+NO2) was achieved, but the N2O selectivity (undesirable) was about 0.1% or less. This catalyst allowed a reduction in reaction temperature of about 200 °C compared to the commercial Pt-Rh gauze catalyst, but the selectivity was improved.

[0089] Pt on alumina substrate (metal content 5-10 wt%) 63 Pd 15 Rh4Co 15 A tubular reactor with Ce nanoparticles was used to study the catalyst as an ammonia oxidation catalyst. Elemental mapping analysis showed that the HEA remained homogeneous after the reaction and exhibited great stability under harsh reaction conditions. In comparison, the commercially available Pt 95 Rh5 gauze is approximately 95% NO at 850℃. x yields and has a similar catalyst loading (with 100 wt% precious metal content), but the reactivity was obviously reduced. These results indicate that the HEA catalyst has enhanced activity, selectivity and durability compared to the state-of-the-art Pt-Rh gauze for the oxidation of NH3 to NO by 100-200 °C. xThe reduction in reaction temperature required for efficient conversion to CO, together with the demonstrated increased durability and high catalyst stability, is expected to provide significant benefits to industrial operations by improving catalyst life, reducing precious metal losses, and reducing downtime for catalyst replacement. These benefits, as well as the direct cost savings resulting from reduced precious metal usage (>80%), can improve the energy efficiency and economics of nitric acid plants.

[0090] CoMo-HEA nanoparticles dispersed on Al2O3-coated carbon paper were prepared and heated at 500 °C and 10 bar for 0.40 g. NH3 g metal -1 h -1 It was used for ammonia synthesis, showing catalytic activity of 1000 nm. Substrates with large specific surface area can improve nanoparticle loading. In some embodiments, CO2 activation can be used to increase the specific surface area of ​​the carbon paper substrate, which can result in higher loading of HEA dispersed on the Al2O3-coated carbon paper. As the activation temperature increases, the fiber diameter of the carbon paper can decrease, for example, to 2 μm for carbon paper activated at 1000 °C for 3 hours, thereby significantly increasing the surface area. Carbon paper with and without CO2 activation was coated with an oxide layer (~20 nm) using atomic layer deposition (ALD). As a result, a uniform Al2O3 layer was obtained on the surface of the carbon paper substrate.

[0091] Metal precursor salts (CoN2O6·6H2O, MoCl3, FeN3O9·9H2O, NiN2O6·6H2O, and CuN2O6·6H2O) were dissolved in ethanol to a concentration of 0.05 mol L -1 The composition was Co 25 Mo 45 Fe 10 Ni 10 Cu 10The solution was loaded onto Al2O3-coated carbon paper with the designed loading amount and then dried at room temperature before high-temperature heating. High-temperature thermal shock synthesis (~1700 K, ~55 ms) was performed to in situ heat the film in argon atmosphere, leading to the formation of ultrafine HEA nanoparticles dispersed on carbon paper substrates. A uniform and dense dispersion of CoMo-HEA nanoparticles on Al2O3-coated carbon paper with CO2 activation was achieved, and the nanoparticle size was reduced when using carbon paper substrates activated at 1000 °C due to their high specific surface area. Furthermore, the CoMo-HEA precursor was uniformly dispersed on extruded alumina (Al2O3) substrates. After high-temperature shock treatment, CoMo-HEA nanoparticles were formed on the alumina substrates. High-resolution EDX mapping confirmed the presence of five elements (Co, Mo, Fe, Ni, Cu) in the HEA nanoparticles on the Al substrates.

[0092] Precursor deposition and / or nanoparticle formation on extruded alumina substrates may differ from those on other substrates, such as Al2O3-coated carbon paper. In particular, metal elements may be more soluble in extruded alumina substrates, hindering the subsequent formation of nanoparticles by thermal shock heating. To address this, precursor loading can be varied (e.g., in the range of 2.5-10 wt%) and / or by introducing substrate treatments (e.g., annealing at high temperatures and / or functionalization of the substrate) to promote HEA nanoparticle formation.

[0093] The catalyst was first activated in situ at 500 °C under standard reaction conditions, where activity initializes after ~1 h under these conditions. As shown in Figure 9A, the optimum temperature for this catalyst was observed at about 450 °C at 10 bar and a reactant gas flow of 50 sccm, and the catalytic ammonia synthesis rate was 1.52 g NH3 g metal -1 hr -1Higher flow rates and pressures could further improve the catalytic activity. Compared with the Al2O3-coated carbon paper substrate, the extruded Al2O3 substrate showed much better thermal stability, relatively larger surface area, and easier large-scale synthesis without / with CO2 activation.

[0094] For the extruded Al2O3 substrates, two forms were evaluated for catalytic activity: bulk form and powder form (prepared by crushing the bulk form prior to impregnation). NH3 g metal -1 hr -1 9C) under the same conditions, whereas the powder form was slightly less active, at 0.71 g NH3 g metal -1 hr -1 These catalysts also did not require any pretreatment before catalytic activity testing. They were activated in the same way as the HEA, i.e., on Al2O3-coated carbon paper at 500 °C and 10 bar.

[0095] Further examples of the disclosed technology In view of the above implementations of the disclosed subject matter, the present application discloses additional examples in the appendices listed below. It should be noted that any feature of the appendices alone, or two or more features of the appendices in combination, and optionally in combination with one or more features of one or more additional appendices, are also included within the scope of the disclosure of the present application.

[0096] Appendix 1. A substrate having at least a surface layer formed of a metal oxide; a plurality of high entropy alloy (HEA) nanoparticles formed on the surface layer of the substrate, each HEA nanoparticle having a maximum cross-sectional dimension of 1 μm or less, each HEA nanoparticle comprising a homogenous mixture of at least four distinct elements forming a single-phase solid solution alloy; A catalyst structure comprising:

[0097] Appendix 2. The catalyst structure according to any of the sections or examples herein, particularly Appendix 1, wherein the entire substrate is formed from a metal oxide.

[0098] Appendix 3. The catalyst structure according to any of the sections or examples herein, particularly any one of Appendices 1-2, wherein the substrate comprises a base layer formed from a material other than a metal oxide.

[0099] Appendix 4. The catalyst structure of any of the sections or examples herein, in particular the catalyst structure described in Appendix 3, wherein the base layer is formed of carbon.

[0100] Appendix 5. The catalyst structure described in any section or example herein, particularly any one of Appendices 1-4, wherein the maximum cross-sectional dimension of each HEA nanoparticle is 25 nm or less.

[0101] Appendix 6. The catalyst structure according to any section or example herein, in particular any one of Appendices 1-5, wherein the maximum cross-sectional dimension of each HEA nanoparticle is in the range of 1 to 20 nm, inclusive.

[0102] Appendix 7. The catalyst structure according to any of the sections or examples herein, in particular any one of Appendices 1 to 6, wherein the metal oxide comprises an aluminum oxide, a titanium oxide, a cerium oxide, a silicon oxide, a zeolite, a spinel, a perovskite, or any combination of the foregoing.

[0103] Appendix 8. The catalyst structure according to any of the sections or examples herein, in particular any one of Appendices 1 to 7, wherein the precious metal content of the catalyst structure is 30 wt % or less.

[0104] Appendix 9. The catalyst structure according to any of the paragraphs or examples herein, in particular any one of appendices 1 to 8, wherein the precious metal content of the catalyst structure is in the range of 2 to 10 wt. % (both end values ​​included). Appendix 10. The catalyst structure described in any section or example herein, particularly any one of Appendices 1-9, wherein the homogenous mixture of each HEA nanoparticle is at least four elements selected from the group consisting of transition metals, lanthanides, actinides, and post-transition metals.

[0105] Appendix 11. Catalyst structure according to any section or example herein, in particular any one of Appendices 1 to 10, wherein the single phase solid solution comprises a face-centered cubic phase.

[0106] Appendix 12. Catalyst structure according to any of the sections or examples herein, particularly any one of Appendices 1 to 11, wherein each HEA nanoparticle has at least five different elements.

[0107] Appendix 13. The catalyst structure described in any section or example herein, particularly any one of Appendices 1-12, wherein the plurality of HEA nanoparticles are effective as a catalyst for ammonia oxidation, and the homogenous mixture in each HEA nanoparticle is a combination of platinum (Pt), palladium (Pd), rhodium (Rh), cobalt (Co), and a promoter, and the promoter is a rare earth element.

[0108] Appendix 14. The catalyst structure described in any section or example herein, particularly any one of Appendixes 1-12, wherein a plurality of HEA nanoparticles are effective as a catalyst for ammonia decomposition, and the homogenous mixture in each HEA nanoparticle is a combination of (i) cobalt (Co), (ii) molybdenum (Mo), and (iii) at least two transition metals.

[0109] Appendix 15. A homogeneous mixture of Co in each HEA nanoparticle was obtained. x Mo y Fe aNi b Cu c The catalyst structure of any of the sections or examples herein, particularly Appendix 14, wherein x+y=100-(a+b+c), 10≦a≦20, 10≦b≦20, and 10≦c≦20.

[0110] Appendix 16. The catalyst structure according to any of the sections or examples herein, particularly any one of Appendices 1-2 and 5-15, wherein the substrate comprises an extruded metal oxide pellet.

[0111] Appendix 17. The catalyst structure according to any of the paragraphs or examples herein, particularly paragraph 16, wherein the extruded metal oxide pellets are multi-lobal cylindrical pellets having a maximum cross-sectional dimension of 20 mm or less.

[0112] Appendix 18. The catalyst structure according to any of the sections or examples herein, particularly any one of Appendices 1 to 17, wherein the substrate comprises powder particles having a maximum cross-sectional dimension of 1 mm or less.

[0113] Appendix 19. The catalyst structure according to any of the sections or examples herein, in particular any one of Appendices 1 to 18, wherein the substrate has a plurality of pores, each pore having a diameter of 50 nm or less, and / or the substrate has a pore volume in the range of 0.6 mL / g to 0.8 mL / g.

[0114] Appendix 20. 20. The catalyst structure according to any of the sections or examples herein, in particular any one of appendices 1 to 19, wherein each HEA nanoparticle has a truncated spherical shape.

[0115] Appendix 21. The catalyst structure described in any section or example herein, particularly any one of Appendices 1 to 20, further comprising a plurality of non-HEA nanoparticles formed on a surface layer of the substrate between the HEA nanoparticles.

[0116] Appendix 22. The catalyst structure as described in any of the sections or examples herein, in particular as described in Appendix 21, wherein the number of HEA nanoparticles on the substrate is less than the number of non-HEA nanoparticles on the substrate.

[0117] Appendix 23. The catalyst structure according to any of the sections or examples herein, particularly any one of appendices 1 to 22, wherein the plurality of HEA nanoparticles are distributed in a gradient across the cross-section of the substrate.

[0118] Appendix 24. The catalyst structure as described in any of the sections or examples herein, in particular as described in Appendix 23, wherein the gradient is such that the particle density of the HEA nanoparticles in the outer portion of the substrate is greater than the particle density in the inner portion of the substrate.

[0119] Appendix 25. The catalyst structure according to any of the clauses or examples herein, in particular as described in Appendix 24, wherein the particle density at the inner portion of the substrate is in the range of 0 to 80% (inclusive) of the particle density at the outer portion of the substrate.

[0120] Appendix 26. providing one or more catalyst structures, each catalyst structure comprising a substrate and a plurality of high entropy alloy (HEA) nanoparticles, at least a surface layer of the substrate being formed from a non-conductive metal oxide, a plurality of HEA nanoparticles being formed on the surface layer of the substrate, each HEA nanoparticle having a maximum cross-sectional dimension of 1 μm or less, each HEA nanoparticle comprising a homogenous mixture of at least four elements forming a single-phase solid solution alloy; flowing one or more reactants into contact with one or more catalytic substrates and converting the one or more reactants into one or more products at a first temperature via a chemical reaction; The method includes:

[0121] Appendix 27. The method of any of the sections or examples herein, in particular the method of appendix 26, wherein the chemical reaction comprises an oxidation reaction, a synthesis reaction, or a decomposition reaction.

[0122] Appendix 28. the one or more reactants include ammonia, oxygen, and nitrogen; The chemical reaction involves ammonia oxidation, One or more of the products is NO x The product includes The method described in any section or example herein, in particular any one of appendices 26 to 27.

[0123] Appendix 29. The method according to any of the sections or examples herein, particularly Appendix 28, wherein the homogenous mixture in each HEA nanoparticle is a combination of platinum (Pt), palladium (Pd), rhodium (Rh), cobalt (Co), and a promoter, and the promoter is a rare earth element.

[0124] Appendix 30. At least 90% of one or more products are NO x The product is At least 95% of the ammonia is converted to one or more products; 1% or less of one or more products is NO; the first temperature is less than or equal to 800° C.; or Any combination of the above. The method described in any section or example herein, in particular any one of appendices 28 to 29.

[0125] Appendix 31. The method according to any of the sections or examples herein, particularly any one of appendices 28 to 30, wherein the ammonia oxidation reaction is carried out without a catalyst for removing N2O.

[0126] Appendix 32. the one or more reactants include hydrogen and nitrogen; Chemical reactions include ammonia synthesis, one or more of the products include ammonia; The method described in any section or example herein, in particular any one of appendices 26 to 27.

[0127] Appendix 33. The method of any section or example herein, particularly Appendix 32, wherein the homogenous mixture in each HEA is a combination of (i) cobalt (Co), (ii) molybdenum (Mo), and (iii) at least two transition metals (e.g., iron (Fe), nickel (Ni), and copper (Cu) or manganese (Mn)).

[0128] Appendix 34. The first temperature is between 300° C. and 600° C., inclusive, and the mass specific reaction rate of the chemical reaction is at least 0.7 g / mol. ammonia g metals -1 h -1 The method according to any of the sections or examples herein, particularly any one of Appendices 32 to 33, wherein

[0129] Appendix 35. The first temperature is about 450° C. and the mass specific reaction rate of the chemical reaction is about 1.52 g ammonia g metals -1 h -1 The method according to any of the sections or examples herein, particularly any one of Appendices 32 to 34, wherein

[0130] Appendix 36. The method according to any of the paragraphs or examples herein, particularly any one of Appendices 26 to 35, wherein the entire substrate of each catalyst structure is formed from a metal oxide.

[0131] Appendix 37. The method according to any of the paragraphs or examples herein, particularly any one of appendices 26 to 35, wherein the substrate of each catalyst structure comprises a base layer formed from a material other than a metal oxide.

[0132] Appendix 38. The method according to any of the clauses or examples herein, in particular clause 37, wherein the base layer is formed of carbon.

[0133] Appendix 39. The method according to any of the paragraphs or examples herein, particularly any one of appendices 26 to 38, wherein the maximum cross-sectional dimension of each HEA nanoparticle of each catalyst structure is 25 nm or less.

[0134] Appendix 40. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 26 to 39, wherein the maximum cross-sectional dimension of each HEA nanoparticle of each catalyst structure is in the range of 1 to 20 nm (inclusive).

[0135] Appendix 41. The method according to any one of the paragraphs or examples of the present specification, particularly any one of appendices 26 to 40, wherein the metal oxide of each catalyst structure comprises aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, perovskite, or any combination thereof.

[0136] Appendix 42. The method according to any of the sections or examples herein, in particular any one of Appendices 26 to 41, wherein the precious metal content of each catalyst structure is 30 wt % or less.

[0137] Appendix 43. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 26 to 42, wherein the precious metal content of each catalyst structure is in the range of 2 to 10 wt. % (both end values ​​included).

[0138] Appendix 44. The method according to any of the paragraphs or examples herein, particularly any one of appendixes 26 to 43, wherein the homogenous mixture of each HEA nanoparticle of each catalyst structure is at least four elements selected from the group consisting of transition metals, lanthanides, actinides, and post-transition metals.

[0139] Appendix 45. The method according to any of the paragraphs or examples herein, in particular any one of appendices 26 to 44, wherein the single-phase solid solution of each HEA nanoparticle of each catalyst structure comprises a face-centered cubic phase.

[0140] Appendix 46. The method according to any of the paragraphs or examples herein, particularly any one of appendices 26 to 45, wherein each HEA nanoparticle of each catalyst structure has at least five different elements.

[0141] Appendix 47. The method according to any of the paragraphs or examples herein, in particular any one of paragraphs 26-36 and 39-46, wherein the substrate of each catalyst structure comprises an extruded metal oxide pellet.

[0142] Note 48. The method according to any of the paragraphs or examples herein, particularly paragraph 47, wherein each extruded metal oxide pellet is a multi-lobal cylindrical pellet having a maximum cross-sectional dimension of 20 mm or less.

[0143] Appendix 49. The method according to any of the paragraphs or examples herein, particularly any one of appendices 26 to 48, wherein the substrate of each catalyst structure comprises powder particles having a maximum cross-sectional dimension of 1 mm or less.

[0144] Note 50. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 26 to 49, wherein for each catalyst structure, the substrate has a plurality of pores, each pore having a diameter of 50 nm or less, and / or the substrate has a pore volume of 0.6 mL / g to 0.8 mL / g (inclusive).

[0145] Note 51. The method according to any of the sections or examples herein, particularly any one of appendices 26 to 50, wherein each HEA nanoparticle has a truncated spherical shape.

[0146] Appendix 52. The method according to any of the sections or examples herein, particularly any one of Appendices 26 to 51, wherein each catalyst structure further comprises a plurality of non-HEA nanoparticles formed on a surface layer of the substrate between the HEA nanoparticles.

[0147] Note 53. The method according to any of the sections or examples herein, in particular appendix 52, wherein for each catalyst structure, the number of HEA nanoparticles on the substrate is less than the number of non-HEA nanoparticles on the substrate.

[0148] Note 54. The method according to any of the sections or examples herein, particularly any one of appendices 26 to 53, wherein for each catalyst structure, a plurality of HEA nanoparticles are distributed in a gradient across the cross section of the substrate.

[0149] Note 55. The method according to any of the sections or examples herein, in particular appendix 54, wherein for each catalyst structure, the gradient is such that the particle density of HEA nanoparticles in the outer portion of the substrate is greater than the particle density in the inner portion of the substrate.

[0150] Note 56. The method according to any of the clauses or examples herein, particularly appendix 55, wherein for each catalyst structure, the particle density at the inner portion of the substrate is within the range of 0 to 80% (inclusive) of the particle density at the outer portion of the substrate.

[0151] Note 57. coating a substrate with a solution comprising a plurality of precursor metal salts, the plurality of precursor metal salts comprising at least four different elements, and at least a surface layer of the substrate being formed from a non-conductive metal oxide; drying the substrate with a plurality of precursor metal salts; subjecting the dried substrate to a thermal shock to form a catalytic structure, the thermal shock comprising exposing the substrate to a peak temperature of at least 1200K for a period of time of 1 second or less; A method for producing a catalyst structure, wherein after thermal shock, the catalyst structure comprises a plurality of high entropy alloy (HEA) nanoparticles formed on a surface layer of a substrate, each HEA nanoparticle having a maximum cross-sectional dimension of 1 μm or less and comprising a homogenous mixture of at least four distinct elements that form a single-phase solid solution alloy.

[0152] Note 58. The thermal shock further includes a heat ramp to a maximum temperature, the heat ramp being heated for at least 10 3 The method according to any of the clauses or examples herein, particularly appendix 57, wherein K / s.

[0153] Note 59. The thermal shock further includes a cooling ramp from the maximum temperature, the cooling ramp being at least 10 3 The method according to any of the sections or examples herein, particularly any one of appendices 57 to 58, wherein K / s.

[0154] Note 60. The method according to any of the sections or examples herein, particularly any one of Appendices 57 to 59, wherein the solution comprises an organic solvent or water.

[0155] Appendix 61. The method according to any of the paragraphs or examples herein, particularly any one of appendices 57 to 60, wherein each precursor metal salt comprises a chloride, a nitrate, or an alkoxide.

[0156] Appendix 62. The method according to any of the paragraphs or examples herein, in particular any one of appendices 57 to 61, wherein the coating includes wet impregnation or dry impregnation.

[0157] Appendix 63. The method according to any of the sections or examples herein, particularly any one of paragraphs 57-62, wherein the coating comprises combining the solution and the substrate using a rotating drum mixer.

[0158] Note 64. The method according to any of the sections or examples herein, in particular any one of appendices 57 to 63, wherein the drying comprises freeze-drying or critical point drying.

[0159] Note 65. The method according to any of the sections or examples herein, in particular any one of appendices 57 to 64, wherein the duration of the thermal shock is less than 500 ms.

[0160] Note 66. The method according to any of the sections or examples herein, in particular any one of appendices 57 to 65, wherein the duration of the thermal shock is less than 100 ms.

[0161] Note 67. The method of any section or example herein, in particular the method of any one of Appendices 57 to 66, wherein the peak temperature of the thermal shock is in the range of 1200 to 3000 K (inclusive).

[0162] Note 68. The method of any section or example herein, in particular the method of any one of Appendices 57 to 67, wherein the peak temperature of the thermal shock is in the range of 1500 to 2300 K (inclusive).

[0163] Note 69. The method according to any of the paragraphs or examples herein, particularly any one of appendices 57 to 68, further comprising treating the substrate prior to coating to improve its surface wettability.

[0164] Appendix 70. The method according to any of the clauses or examples herein, particularly appendix 69, wherein the treatment comprises a plasma treatment or an acid treatment.

[0165] Appendix 71. The method according to any of the paragraphs or examples herein, in particular any one of paragraphs 57 to 70, wherein the substrate is heated before or during coating.

[0166] Appendix 72. The method according to any of the sections or examples herein, particularly any one of Appendices 57 to 71, wherein the entire substrate is formed from a metal oxide.

[0167] Appendix 73. The method of any of the paragraphs or examples herein, particularly any one of appendices 57 to 71, wherein the substrate comprises a base layer formed from a material other than the metal oxide, and the method further comprises forming a metal oxide surface layer on the base layer.

[0168] Note 74. The method according to any of the paragraphs or examples herein, in particular paragraph 73, wherein the base layer is formed of carbon.

[0169] Appendix 75. The method according to any of the paragraphs or examples herein, particularly any one of appendices 73 to 64, further comprising maintaining the base layer at a temperature of 700° C. or higher in a carbon dioxide atmosphere for at least 1 hour to generate surface defects in the base layer prior to forming the metal oxide surface layer.

[0170] Appendix 76. The method according to any of the paragraphs or examples herein, particularly any one of paragraphs 73 to 75, wherein forming a metal oxide surface layer comprises atomic layer deposition.

[0171] Appendix 77. The method according to any of the sections or examples herein, particularly any one of Appendices 73 to 76, wherein the thickness of the metal oxide surface layer is 100 nm or less.

[0172] Appendix 78. The method according to any section or example herein, particularly any one of appendices 57-77, wherein the maximum cross-sectional dimension of each HEA nanoparticle is 25 nm or less.

[0173] Appendix 79. The method according to any of the clauses or examples herein, particularly any one of appendices 57-78, wherein the maximum cross-sectional dimension of each HEA nanoparticle is in the range of 1 to 20 nm, inclusive.

[0174] Note 80. The method according to any of the paragraphs or examples herein, particularly any one of paragraphs 57 to 79, wherein the metal oxide comprises aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, perovskite, or any combination of the foregoing.

[0175] Appendix 81. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 57 to 80, wherein the precious metal content of the catalyst structure is 30 wt % or less.

[0176] Note 82. The method according to any of the paragraphs or examples herein, in particular any one of paragraphs 57 to 81, wherein the precious metal content of the catalyst structure is in the range of 2 to 10 wt. % (both end values ​​included).

[0177] Appendix 83. The method according to any of the paragraphs or examples herein, particularly any one of appendixes 57 to 82, wherein the homogenous mixture of each HEA nanoparticle is at least four elements selected from the group consisting of transition metals, lanthanides, actinides, and post-transition metals.

[0178] Note 84. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 57 to 83, wherein the single-phase solid solution comprises a face-centered cubic phase.

[0179] Note 85. The method according to any of the sections or examples herein, particularly any one of paragraphs 57 to 84, wherein each HEA nanoparticle comprises at least five different elements.

[0180] Note 86. The method of any of the sections or examples herein, particularly any one of paragraphs 57-72 and 78-85, wherein the substrate comprises an extruded metal oxide pellet.

[0181] Appendix 87. The method according to any of the paragraphs or examples herein, particularly paragraph 86, wherein the extruded metal oxide pellets are multi-lobal cylindrical pellets having a maximum cross-sectional dimension of 20 mm or less.

[0182] Note 88. (a) after coating the substrate and prior to thermal shock, grinding the substrate into powder particles, each having a maximum cross-sectional dimension of 1 mm or less; (b) prior to said coating, heating said substrate to 100-200° C. to remove moisture from said substrate; (c) heating the substrate at 800 to 1500° C. in an inert gas atmosphere to increase the crystallinity of the substrate; Including, (d) the coating has a loading of at least one of the precursor salts for the first metal that is greater than the loading of the first metal in the HEA nanoparticles formed by thermal shock, such that at least a portion of the first metal is lost during thermal shock; or Any combination of (a) to (d), The method described in any section or example herein, in particular any one of appendices 57 to 87.

[0183] Appendix 89. The method of any of the appendices or examples herein, in particular any one of appendices 57 to 88, wherein the substrate has a plurality of pores with a diameter of 50 nm or less, and / or the substrate has a pore volume in the range of 0.6 to 0.8 mL / g (inclusive).

[0184] Appendix 90. The method according to any of the sections or examples herein, particularly any one of appendices 57 to 89, wherein each HEA nanoparticle has a truncated spherical shape.

[0185] Appendix 91. The method according to any of the sections or examples herein, particularly any one of appendices 57 to 90, wherein after the thermal shock, the catalyst structure further comprises a plurality of non-HEA nanoparticles formed on the surface layer of the substrate between the HEA nanoparticles.

[0186] Appendix 92. The method according to any of the sections or examples herein, particularly appendix 91, wherein after the thermal shock, the number of HEA nanoparticles on the substrate is less than the number of non-HEA nanoparticles on the substrate.

[0187] Appendix 93. The method according to any of the sections or examples herein, particularly any one of appendices 57-92, wherein after thermal shock, a plurality of HEA nanoparticles are distributed gradiently across the cross-section of the substrate.

[0188] Appendix 94. The method of any section or example herein, particularly paragraph 93, wherein the gradient is such that the particle density of the HEA nanoparticles in the outer portion of the substrate is greater than the particle density in the inner portion of the substrate.

[0189] Appendix 95. The method according to any of the clauses or examples herein, in particular appendix 94, wherein the particle density in the inner portion of the substrate is in the range of 0 to 80% (inclusive) of the particle density in the outer portion of the substrate.

[0190] Appendix 96. Removing the Pt-based catalyst and the N2O removal catalyst from a nitric acid production reactor, the nitric acid production reactor having (i) one or more inlets for ammonia, oxygen, and nitrogen, and (ii) one or more inlets for NO x and one or more outlets for a product, the Pt-based catalyst being in a first location between the one or more inlets and the one or more outlets prior to the removing step, and the N2O removal catalyst being in a second location downstream of the first location prior to the removing step; placing one or more catalyst structures within the nitric acid production reactor, each catalyst structure comprising a substrate and a plurality of high entropy alloy (HEA) solid solution alloys, at least a surface layer of the substrate being formed of a non-conductive metal oxide, a plurality of HEA nanoparticles having a maximum cross-sectional dimension of 1 μm or less, each HEA nanoparticle comprising a homogenous mixture of at least four elements forming a single-phase solid solution alloy; The method includes:

[0191] Appendix 97. Ammonia, oxygen, and nitrogen form NO x flowing ammonia, oxygen, and nitrogen through one or more inlets into contact with one or more catalyst compositions in a nitric acid production reactor for conversion to products; The nitric acid production reactor operates without an N2O removal catalyst; The method according to any of the clauses or examples herein, including, in particular, the method according to paragraph 96.

[0192] Appendix 98. The method according to any of the paragraphs or examples herein, particularly any one of paragraphs 96-97, wherein the nitric acid production reactor comprises a pancake reactor.

[0193] Appendix 99. (a) The Pt-based catalyst is a PtRh gauze catalyst; (b) the homogenous mixture in each HEA nanoparticle is a combination of platinum (Pt), palladium (Pd), rhodium (Rh), cobalt (Co), and a promoter, the promoter being a rare earth element; or (c) Both (a) and (b) above; The method described in any section or example herein, in particular any one of appendices 96 to 98.

[0194] Appendix 100. The method according to any section or example herein, particularly any one of Appendices 96 to 99, wherein the entire substrate is formed from a metal oxide.

[0195] Appendix 101. The method of any of the paragraphs or examples herein, particularly any one of paragraphs 96-99, wherein the substrate includes a base layer formed of a material other than a metal oxide.

[0196] Appendix 102. The method of any section or example herein, particularly the method of paragraph 101, wherein the base layer is formed of carbon.

[0197] Note 103. The method according to any section or example herein, particularly any one of appendices 96-102, wherein the maximum cross-sectional dimension of each HEA nanoparticle is 25 nm or less.

[0198] Note 104. The method according to any of the paragraphs or examples herein, in particular any one of appendices 96-103, wherein the maximum cross-sectional dimension of each HEA nanoparticle is in the range of 1 to 20 nm (inclusive).

[0199] Note 105. The method of any section or example herein, particularly any one of paragraphs 96 to 104, wherein the metal oxide comprises aluminum oxide, titanium oxide, cerium oxide, silicon oxide, a zeolite, a spinel, a perovskite, or any combination of the foregoing.

[0200] Note 106. The method according to any of the paragraphs or examples herein, in particular any one of Appendices 96 to 105, wherein the precious metal content of the catalyst structure is 30% by weight or less.

[0201] Note 107. The method according to any of the paragraphs or examples herein, in particular any one of paragraphs 96 to 106, wherein the precious metal content of the catalyst structure is in the range of 2 to 10 wt. % (both end values ​​included).

[0202] Note 108. The method according to any of the paragraphs or examples herein, particularly any one of appendices 96-107, wherein the homogenous mixture of each HEA nanoparticle is at least four elements selected from the group consisting of transition metals, lanthanides, actinides, and post-transition metals.

[0203] Note 109. The method according to any of the paragraphs or examples herein, particularly any one of appendices 96 to 108, wherein the single-phase solid solution comprises a face-centered cubic phase.

[0204] Appendix 110. The method according to any of the sections or examples herein, particularly any one of paragraphs 96-109, wherein each HEA nanoparticle comprises at least five different elements.

[0205] Appendix 111. The method of any section or example herein, particularly any one of paragraphs 96-99 and 103-110, wherein the substrate comprises extruded metal oxide pellets.

[0206] Appendix 112. The method according to any of the paragraphs or examples herein, particularly paragraph 111, wherein the extruded metal oxide pellets are multi-lobal cylindrical pellets having a maximum cross-sectional dimension of 20 mm or less.

[0207] Note 113. The method of any of the paragraphs or examples herein, particularly any one of paragraphs 96-112, wherein the substrate comprises powder particles having a maximum cross-sectional dimension of 1 mm or less.

[0208] Appendix 114. The method according to any of the paragraphs or examples herein, particularly any one of paragraphs 96-113, wherein the one or more catalytic structures are disposed at a second location within the nitric acid production reactor.

[0209] Note 115. The method according to any of the paragraphs or examples of the present specification, in particular any one of Appendices 96 to 114, wherein the substrate of each catalyst structure has pores with a diameter of 50 nm or less and / or a pore volume in the range of 0.6 mL / g to 0.8 mL / g.

[0210] Note 116. The method according to any of the sections or examples herein, particularly any one of appendices 96 to 115, wherein for each catalyst structure, each HEA nanoparticle has a truncated spherical shape.

[0211] Note 117. The method according to any of the sections or examples herein, particularly any one of appendices 96 to 116, wherein each catalyst structure further comprises a plurality of non-HEA nanoparticles formed on a surface layer of the substrate between the HEA nanoparticles.

[0212] Note 118. The method described in any section or example herein, in particular in Appendix 117, wherein for each catalyst structure, the number of HEA nanoparticles on the substrate is less than the number of non-HEA nanoparticles on the substrate.

[0213] Appendix 119. The method according to any of the sections or examples herein, particularly any one of appendices 96 to 118, wherein for each catalyst structure, a plurality of HEA nanoparticles are distributed in a gradient across the cross section of the substrate.

[0214] Appendix 120. The method described in any section or example herein, particularly in Appendix 119, wherein for each catalyst structure, the gradient is such that the particle density of HEA nanoparticles in the outer portion of the substrate is greater than the particle density in the inner portion of the substrate.

[0215] Appendix 121. The method of any paragraph or example herein, particularly paragraph 120, wherein for each catalyst structure, the particle density at the inner portion of the substrate is within the range of 0 to 80% (inclusive) of the particle density at the outer portion of the substrate.

[0216] conclusion For example, any of the features shown or described herein with respect to Figures 1A-9C and Supplements 1-121 can be combined with any other features shown or described herein with respect to Figures 1A-9C and Supplements 1-121 to provide materials, systems, devices, structures, methods, and embodiments not otherwise shown or specifically described herein. All features described herein are independent of one another and can be used in combination with any other features described herein, except where structurally impossible. In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely examples and should not be construed as limiting the scope of the disclosed technology. Rather, the scope is defined by the following claims. Accordingly, we claim all that comes within the scope and spirit of these claims.

Claims

1. A catalyst structure for ammonia synthesis or ammonia decomposition, the catalyst structure comprising: a substrate comprising extruded metal oxide pellets having a maximum cross-sectional dimension of 20 mm or less; a plurality of high entropy alloy (HEA) nanoparticles formed on a surface layer of the substrate, each HEA nanoparticle having a maximum cross-sectional dimension of 1 μm or less, each HEA nanoparticle comprising a homogenous mixture of at least four different elements forming a single-phase solid solution alloy; Including, the homogeneous mixture in each HEA nanoparticle is a combination of (i) cobalt (Co), (ii) molybdenum (Mo), and (iii) at least two transition metals; Catalyst structure.

2. A homogeneous mixture of each HEA nanoparticle satisfies Co x Mo y Fe a Ni b Cu c , wherein: x+y=100-(a+b+c); 10 ≤ a ≤ 20; 10≦b≦20; and 10≦c≦20; The catalyst structure of claim 1.

3. 2. The catalyst structure of claim 1, wherein the entire substrate is formed of the metal oxide.

4. 10. The catalyst structure of claim 1, wherein the maximum cross-sectional dimension of each HEA nanoparticle is 25 nm or less.

5. 10. The catalyst structure of claim 1, wherein the extruded metal oxide pellets comprise aluminum oxide, titanium oxide, cerium oxide, silicon oxide, zeolite, spinel, perovskite, or any combination thereof.

6. The catalyst structure of claim 1, wherein the single-phase solid solution of each HEA nanoparticle comprises a face-centered cubic phase.

7. 10. The catalyst structure of claim 1, wherein said extruded metal oxide pellets are multi-lobe cylindrical pellets.

8. 10. The catalyst structure of claim 1, wherein the substrate has a plurality of pores and a pore volume of 0.6 mL / g to 0.8 mL / g, inclusive.

9. 10. The catalyst structure of claim 1, wherein each HEA nanoparticle has a truncated spherical shape.

10. 10. The catalyst structure of claim 1, wherein the plurality of HEA nanoparticles are distributed in a gradient across the cross section of the substrate.

11. 11. The catalyst structure of claim 10, wherein the gradient is such that the particle density of the HEA nanoparticles at an outer portion of the substrate is greater than the particle density at an inner portion of the substrate.

12. 12. The catalyst structure of claim 11, wherein the particle density at the inner portion of the substrate is in the range of 0 to 80% inclusive of the particle density at the outer portion of the substrate.

13. Providing one or more catalyst structures according to any one of claims 1 to 12; flowing one or more reactants into contact with one or more catalytic substrates and converting the one or more reactants into one or more products at a first temperature by chemical reaction; Including, the chemical reaction includes an ammonia synthesis reaction, the one or more reactants include hydrogen and nitrogen; the one or more products include ammonia; or the chemical reaction includes an ammonia decomposition reaction, one or more reactants include ammonia; the one or more products include hydrogen and nitrogen; method.

14. The first temperature is between 300°C and 600°C inclusive, and the mass specific reaction rate of the chemical reaction is at least 0.7g ａｍｍｏｎｉａ g ｍｅｔａｌｓ － h －１ The method of claim 13, wherein

15. The first temperature is about 450° C. and the mass specific reaction rate of the chemical reaction is 1.52 g ａｍｍｏｎｉａ g ｍｅｔａｌｓ －１ h －１ The method of claim 13, wherein

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