Porous substrates for chemical reactors

Abstract

Disclosed herein is a porous substrate configured to separate a reaction chamber from a product chamber in a chemical reactor. The porous substrate comprises a reaction chamber facing surface and a product chamber facing surface, wherein a size of pores in the porous substrate decreases between the reaction chamber facing surface and the product chamber facing surface. The pore size at the product chamber facing surface is such that chemical species larger than a predetermined size are excluded from passing through the porous substrate into the product chamber.

Description

POROUS SUBSTRATES FOR CHEMICAE REACTORSTechnical Field

[0001] The present invention relates to porous substrates for use in chemical reactors. The present invention also relates to catalysts for use in chemical reactors.Background Art

[0002] The growth of renewable energy continues at a dramatic rate. Indeed, some studies estimate that, by 2026, global renewable-electricity capacity will rise more than 80 percent from 2020 levels (to more than 5,022 gigawatts). While generation capacity has grown rapidly, storage and transport of renewable energy remains a challenge. Renewable energy is periodic, seasonal and geographically unevenly distributed. Thus, strategies and technologies to transport energy from locations of high energy generation intensity to places lean in renewables with high energy demand need to be developed.

[0003] In this regard, green hydrogen produced using renewables is a potential renewable energy storage and transport media. However, storage and long-distance transport of hydrogen remains a challenge due to energy-intensive compression or liquefaction processes and storage. One solution to this problem involves the conversion of hydrogen into other molecules for use as intermediates, often referred to as “Hydrogen carriers”.

[0004] One such hydrogen carrier is ammonia, which may be produced from green hydrogen and nitrogen from the air, and hence without the need for carbon feedstocks as are required by liquid fuels such as methanol. Ammonia’s hydrogen energy content is relatively high, and it remains in liquid form under nominal conditions (compared to H2, which requires extreme conditions for liquefaction). Furthermore, ammonia transport and handling infrastructure is well established, with millions of tons of ammonia already being transported and stored across the world.

[0005] The process of converting liquid ammonia back to hydrogen is, however, challenging due to reaction endothermicity and the need for downstream separation of N2, H2 and unreacted ammonia. Indeed, the process is estimated to utilise about 10-12 kWh of energy (approximately 35% of the stored hydrogen’s energy content). Further, the separation process requires rare and costly palladium-based membranes to achieve a purity of hydrogen suitable for use in many state-of-the-art fuel cells. A separate process is therefore preferred, in which the nitrogen andhydrogen produced by the cracking of ammonia are subsequently separated using membrane separation, with the pure hydrogen then being fed into fuel cells in order to generate electricity.

[0006] It would be advantageous to provide alternative processes via which streams of hydrogen having a purity compatible with use in state-of-the-art fuel cells can directly be produced by the cracking of ammonia.Summary of Invention

[0007] In a first aspect, the present invention provides a porous substrate configured to separate a reaction chamber from a product chamber in a chemical reactor. The porous substrate comprises: a reaction chamber facing surface and a product chamber facing surface, wherein a size of pores in the porous substrate decreases between the reaction chamber facing surface and the product chamber facing surface, the pore size at the product chamber facing surface being such that chemical species larger than a predetermined size are excluded from passing through the porous substrate into the product chamber.

[0008] The inventor of the invention the subject of the present application has discovered a unique solution to the problems associated with the cracking of ammonia and the production of a hydrogen stream having a purity that allows for its subsequent use in fuel cells (i.e. without requiring a purification step). The inventor’s solution utilises a reaction substrate having a porous structure with gradually decreasing pore size, where the pores on the inlet side (i.e. at the reaction chamber facing surface) of a cracker are relatively bigger, and those on the outlet side (i.e. at the product chamber facing surface) relatively smaller. The purpose of this graded porosity is to allow effective separation of hydrogen from nitrogen and any unreacted ammonia. Hydrogen is a smaller molecule than nitrogen and ammonia and hence can permeate through finer pores. Thus, hydrogen egress on the outlet side of the cracker can occur, whist nitrogen and any unreacted ammonia can egress no further than pores on the inlet side.

[0009] The inventor contemplates that this invention will also be useful for cracking other compounds including hydrocarbons such as methane to produce substantially pure hydrogen. In such cases, hydrogen may be separated from the relatively larger CO and CO2 molecules produced by the methane reforming reactions (e.g. steam methane reforming (SMR) reactions or dry methane reforming with CO2). Other applications of this invention will be apparent to those skilled in the art.

[0010] In some embodiments, the porous substrate may comprise a plurality of layers of porous substrates, each layer of porous substrate having a different pore size. Each of the porous substrates may, for example, be a different substance.

[0011] In some embodiments, the porous substrate may comprise a ceramic material, a metal, an alloy, a metal oxide or a composite material. These materials may be selected to provide a comprehensive spectrum of thermal stability, mechanical strength and chemical resistance, ensuring the substrate can perform under diverse operating conditions. The inclusion of such a broad range of substrate materials ensures adaptability of the present invention to different industrial environments.

[0012] In some embodiments, the porous substrate may comprise a catalyst (e.g. to catalyze cracking of ammonia into nitrogen and hydrogen). The catalyst may be distributed on or around the reaction chamber facing surface of the porous substrate and / or distributed throughout the porous substrate. The catalyst may be an existing catalyst, for example, selected from nickel, cobalt or iron, with or without oxide supports. Alternatively, and as discussed below, a novel catalyst may be used.

[0013] In some embodiments, the chemical reactor may be a cracker, such as an ammonia cracker or a methane cracker.

[0014] In some embodiments, the porous substrate may be tubular or planar in shape, and hence configured to separate the reaction / product chambers in crackers having such configurations of reaction chamber. The planar or tubular porous supports can be fabricated using a variety of methods such as powder pressing or extrusion or injection molding.

[0015] In a second aspect, the present invention provides a chemical reactor comprising the porous substrate of the first aspect of the present invention.

[0016] In a third aspect, the present invention provides a fuel cell comprising the porous substrate of the first aspect of the present invention.

[0017] In a fourth aspect, the present invention provides a catalyst having the formula:Ce(0.99 x [1-a-b-c]) XaYb RucO(2+ / -5) where:X represents a trivalent element selected from the group consisting of: samarium (Sm), europium (Eu), neodymium (Nd), dysprosium (Dy), gadolinium (Gd), lanthanum (La), praseodymium (Pr), lanthanum and yttrium (Y),Y represents a transition metal selected from the group consisting of: cobalt (Co), nickel (Ni) and iron (Fe), a, b, and c denote the molar fractions of X, Y and Ru, respectively, where: a is between zero and about 0.4, b is between zero and about 0.2 and c is between about 0.01 and about 0. 1, and8 indicates the deviation from stoichiometry due to oxygen vacancies, where:8 is between zero and about 0.05.

[0018] The present invention thus also provides a series of innovative catalyst compositions for efficient ammonia or methane decomposition, each formulated with a distinct chemical composition to enhance catalytic performance. Specifically, the invention provides a set of novel metal oxide catalysts for ammonia or methane cracking with an A-site deficient perovskite structure (i.e. where the molar percentage of the atom at the A site, in this case Ce, is less than stoichiometric) having a base matrix of cerium oxide (CeCh) with a substitution of rare earth and transition metal elements. The catalyst may also be oxygen deficient or oxygen excessive, potentially further enhancing its catalytic activity.

[0019] The inventor has found that these catalysts can be used at temperatures of 400°C to 600°C (e.g. 500°C) and at pressures of 1 to 10 bar, conditions that are ideal for the cracking of ammonia or methane, as well as numerous other industrial reactions.

[0020] The catalyst may, for example, have the formula: Ceo.85Pro.iCoo.o3Ruo.o20(2+ / -8), Ceo.77Pro.l5Coo.05Ruo.020(2+ / -8), Ceo.82Yo.iCoo.o5Ruo.o20(2+ / ^), Ceo.54Yo.3Coo.iRuo.o50(2+ / -5), Ceo.77Lao.i5Coo.o5Ruo.o20(2+ / -8), Ceo.77Lao.i5Feo.o5Ruo.o20(2+ / -8) or Ceo.77Feo.i5Coo.o5Ruo.o20(2+ / -8).

[0021] In some embodiments, the porous substrate of the first aspect of the present invention may comprise the catalyst of the fourth aspect of the present invention

[0022] In a fifth aspect, the present invention provides an ammonia cracker or a methane cracker comprising the porous substrate of the first aspect of the present invention, with the catalyst of the fourth aspect of the present invention being distributed on the porous substrate.

[0023] Other aspects, features and advantages of the present invention will be described below.Brief Description of the Drawings

[0024] Embodiments of the present invention will be described in further detail below with reference to the following drawings, in which:

[0025] Figure 1 shows a schematic diagram illustrating a bilayer porous substrate in accordance with an embodiment of the present invention in planar form. Layer 2 has finer pore size compared to Layer 1, and both Layer 1 and Layer 2 are coated with an ammonia cracking catalyst;

[0026] Figure 2 shows a schematic diagram illustrating a bilayer porous substrate in accordance with an embodiment of the present invention in tubular form. Layer 2 has finer pore size compared to Layer 1, and both Layer 1 and Layer 2 are coated with an ammonia cracking catalyst;

[0027] Figure 3 shows a schematic diagram illustrating a bilayer porous substrate in accordance with an embodiment of the present invention inside a jacked counterflow heat exchanger;

[0028] Figure 4 shows a schematic diagram illustrating how a bilayer porous substrate in accordance with an embodiment of the present invention would be positioned inside of a cracker bundle, where a jacket is used to flow hot gas inside of container used for H2 / N2 collection and the tubes used to carry unreacted NH3 and N2 mix;

[0029] Figure 5 shows a schematic diagram showing perspective and cross-sectional illustrations of a bilayer porous substrate in accordance with an embodiment of the present invention in the form of a tube inside of a tubular shaped solid oxide fuel cell;

[0030] Figure 6 shows a schematic diagram illustrating a planar bilayer porous substrate in accordance with an embodiment of the present invention inserted in a solid oxide fuel cell stack;

[0031] Figure 7 shows a schematic diagram illustrating the bilayer porous substrate in accordance with an embodiment of the present invention as fabricated in the Examples;

[0032] Figure 8 shows a TEM image of the catalyst coating (Ceo.TvPro.isCoo.osRuo.oiCh-s); and

[0033] Figure 9 shows a surface SEM of the catalyst coating on a porous substrate.Detailed Description of the Invention

[0034] The overarching purpose of the present invention is to provide alternative apparatus and processes which can be used to produce substantially pure streams of hydrogen (and indeed, other reaction products) by the cracking of ammonia, hydrocarbons or other molecules.

[0035] The present invention will be described below primarily in the context of the cracking of hydrocarbons (such as methane) or ammonia. It is to be appreciated, however, that the present invention is equally applicable for use with any relevant industrial chemical reactions known to those skilled in the art.

[0036] The present invention provides a porous substrate configured to separate a reaction chamber from a product chamber in a chemical reactor. The porous substrate comprises a reaction chamber facing surface and a product chamber facing surface, wherein a size of pores in the porous substrate decreases between the reaction chamber facing surface and the product chamber facing surface. The pore size at the product chamber facing surface is such that chemical species larger than a predetermined size are excluded from passing through the porous substrate into the product chamber.

[0037] The present invention also provides reaction chambers for use in chemical reactors (e.g. fuel cells, methane or ammonia crackers, hydrocarbon cracker including methanol or ethanol crackers, etc.) which incorporate the porous substrates and / or catalysts disclosed herein.

[0038] The porous substrate (and chemical reactor) of the present invention may take any convenient shape and configuration, primarily dependent on the purpose of the chemical reactor. Specific embodiments described in further detail below include porous substrates that are tubular or planar in shape and which, in these embodiments, are configured to be part of a reaction chamber for incorporation into a tubular solid oxide fuel cell or a planar solid oxide fuel cell stack, respectively. For example, a porous support formed in a tubular shape can be conveniently inserted inside an anode supported or cathode supported solid oxide fuel cell, or an electrolyte supported solid oxide fuel cell (discussed in further detail below with reference to Figure 5). In this manner, hydrogen gas (i.e. produced by cracking ammonia or methane) within the reaction chamber can pass through the porous substrate directly into the fuel cell, where it reacts to produce electricity in a conventional manner. Conventional ammonia crackers cannot be used in this maimer because the presence of significant amounts of N2 and NH3 in the reaction products preclude use in the fuel cell (instead, the hydrogen produced in the cracker needs to be purified using membrane separation before presenting to the fuel cell).

[0039] The porous substrate may have any suitable thickness (i.e. between its reaction chamber facing surface and its product chamber facing surface), given its intended applications. For example, the inventors envisage porous substrates having a thickness of between about 0.5mm and about 1cm. Thicknesses outside of this range might be possible, although the inventors note that substrates thicker than about 1cm are probably mechanically wasteful and would result in a slower diffusion of gas (e.g. hydrogen) therethrough, whilst substrates thinner than about 0.5mm would likely be difficult to fabricate and perhaps not have an appropriate mechanical strength.

[0040] The size of the pores in the porous substrate become smaller moving from the reaction chamber facing surface to the product chamber facing surface. The size of the pores at or proximal to the product chamber facing surface is such that chemical species larger than apredetermined size cannot pass through the porous substrate into the product chamber. In this manner, only species that are small enough can pass all the way through the support will reach the product chamber, with all other chemical species being rejected.

[0041] The purpose of varied / graded porosity is to enable the effective separation of species in the chemical reactor. For example, ammonia gas cracking produces hydrogen and nitrogen. The varied porosity in the support allows for the effective separation of hydrogen from nitrogen and any unreacted ammonia. Hydrogen is a smaller molecule than nitrogen and ammonia, and hence its permeation rate through the finer pores is favored, enabling hydrogen egress on the outlet side of the substrate / reactor, with nitrogen and any unreacted ammonia egressing through the pores on the inlet side of the substrate / reactor. In embodiments where a cracker is used in a methane reforming reaction, hydrogen can similarly be separated from CO and CO2.

[0042] In some embodiments, for example, the pore size at the product chamber facing surface is such that chemical species larger than hydrogen are excluded from passing through the porous substrate into the product chamber. For example, the size of pores in the porous substrate may range from about 5 to 10 microns at the reaction chamber facing surface to about 5 to 500 nm at the product chamber facing surface. In some embodiments, the size of the pores at the reaction chamber facing surface may be about 5microns, 6 microns, 7 microns, 8 microns, 9 microns or 10 microns. In some embodiments, the size of the pores at the product chamber facing surface may be about 5nm, 50nm, lOOnm, 200nm, 300nm, 400nm or 500 nm. The pore size may decrease in a linear manner (i.e. through the cross section of the substrate) or may decrease stepwise between the reaction and product chambers.

[0043] In a specific embodiment, the porous substrate may be part of a methane cracker, and the size of pores in the porous substrate range from about 5 to 10 microns at the reaction chamber facing surface to about 5 nm to 500 nm at the product chamber facing surface.

[0044] In another specific embodiment, the porous substrate may be part of an ammonia cracker and the size of pores in the porous substrate range from about 1 to 2 microns at the reaction chamber facing surface to about 1 to 100 nm at the product chamber facing surface (N2 is smaller than CO2, and the pore size thus correspondingly smaller).

[0045] The porous substrate may comprise, or consist of, a single material having the required pore size gradient. Alternatively, the pore size gradient may be provided by a porous substrate including a plurality of layers of porous substrates, each layer having a different pore size. Typically, each of the layered porous substrates would be a different substance, but this need not be the case - e.g. different synthetic techniques might result in the same material having adifferent pore size. As noted above, the pore size may be consistent throughout each of the porous substrates in the plurality of layers of porous substrates, or the porous substrate may have a pore size that shrinks at a particular (even or uneven) gradient moving from its reaction chamber facing surface to its product chamber facing surface.

[0046] Figure 1 shows a conceptual drawing of a bilayer porous substrate 10 in planar form. The porous support is characterized by graded porosity. Layer 2 (on the outlet side) 12 has a finer pore size compared to layer 1 (on the inlet side) 14 and, in this embodiment, both layers 12 and 14 are coated with an ammonia cracking catalyst.

[0047] As shown in Figure 2, the porous support 16 may instead be tubular. The outermost layer 18 has a finer pore size compared to the innermost layer 20. In use, ammonia is fed into the central chamber 22, where it is cracked to form nitrogen and hydrogen. Only hydrogen is small enough to pass through the pores in outermost layer 18, where it can be collected for downstream use.

[0048] The porous substrate may be formed from any suitable material, or combinations of materials. The porous substrate may, for example, comprise (or consist of) a ceramic material (such as yttria stabilized zirconium oxide (YSZ), undoped zirconium oxide, lanthanum doped alumina, or just alumina and silica), a metal (such as SS316 or nickel), an alloy (such as a nickeliron or nickel-cobalt alloy), a metal oxide or a composite material (such as a cermet of nickel and YSZ or nickel and alumina). These materials are selected to provide a comprehensive spectrum of thermal stability, mechanical strength, and chemical resistance, ensuring the substrate can perform under diverse operating conditions. Such a broad range of substrate materials provides for a high degree of adaptability to different industrial environments and enhances the utility and commercial value of the substrate.

[0049] In some embodiments, the porous substrate may comprise a bi-layer of two porous substrates, e.g. nickel and zirconium or cerium oxide.

[0050] The porous substrates (e.g. planar or tubular porous substrates) can be fabricated using a variety of methods such as powder pressing or extrusion or injection molding.

[0051] The porous substrate may also be used in a configuration shown in Figure 3, where a cracker tube 24, or bundle of such tubes (see Figure 4, described below), is placed inside the jacket enclosure 26 for integration with a fuel cell system (not shown). The hot gases or steam produced in downstream processes can be circulated in the jacket 26 to enable heating of the catalyst in the porous support 28 to optimal temperature of 400 to 600°C. Ammonia fed into a proximal end of the porous support 28 (on the right in Figure 3) is cracked into nitrogen andhydrogen. The hydrogen is small enough to pass through the porous support 28 and into the product chamber 30 of the reactor. The nitrogen and any unreacted ammonia cannot pass through the porous support 28 and exits at the distal end of the porous support 28 (on the left in Figure 3).

[0052] In Figure 4, a cracker bundle 32 is shown where a jacket 34 is used to flow hot gas around a container that includes a number of porous supports 28. Ammonia fed into a proximal end of the cracker bundle 32 via inlet 36 is distributed across the porous supports 28, where it is cracked into nitrogen and hydrogen. The nitrogen and any unreacted ammonia exits the cracker bundle 32 via outlet 38, whilst the produced Ph collects in the interior chamber 40 and can be removed from the cracker bundle 32 via hydrogen 42.

[0053] The inventors envisage that chemical reactors including a (tubular or planar) porous substrate can be incorporated within existing fuel cell systems. In specific embodiments, for example, cracking of ammonia and conversion into hydrogen may occur in accordance with the present invention within the fuel cell itself. Hydrogen passing through the porous substrate is substantially uncontaminated (e.g. with NH3 or N2) and is immediately available for reaction in the fuel cell to produce electricity. Referring to Figure 5, for example, a cracker cartridge 44 formed in a tubular shape can conveniently be housed inside of an anode supported, cathode supported or electrolyte supported solid oxide fuel cell 46, for operation in a conventional manner. The cracker cartridge 44 (or multiple cracker cartridges that are bundled together, not shown) can thus be used as standalone reactors for cracking ammonia (or methane) to produce hydrogen for immediate use in the fuel cell.

[0054] Alternatively, a cracker including a planar porous substrate can be placed in a planar solid oxide fuel cell stack, such as that depicted in Figure 6. Figure 6 shows a conventional planar solid oxide fuel cell stack 48, as well as a planar solid oxide fuel cell stack 50 incorporating a porous cracker cartridge in accordance with embodiments of the present invention. The conventional planar solid oxide fuel cell stack 48 included alternating layers of solid oxide cells (electrolyte, anode and cathode) 52, separated by interconnects with flow fields 54. In the planar solid oxide fuel cell stack 50, a porous cracker cartridge 56 is located between layers 52 and 54. This configuration can be easily scaled up, making the present invention suitable for integration with commercial solid oxide fuel cells stacks. A planar cracker provides several benefits for hydrogen production, including high energy efficiency due to effective heat transfer, ease of scalability for various application sizes, and straightforward integration with other planar systems. Its uniform temperature distribution promotes consistent hydrogen output, and the design's simplicity can lead to lower manufacturing and maintenance costs. Additionally,its compact, space-efficient form factor and modular nature allow for flexible operation and easy capacity adjustments.

[0055] The inventors also speculate that a cracker including the porous substrate of the present invention might also be integrated at the inlet of fuel injection port inside of an internal combustion engine running on ammonia or methane. In such a configuration, the reactant will be cracked at entry and the product fuel gas fed directly into the internal combustion engine.

[0056] As will be described in further detail below, the porous support may be coated with a variety of catalysts required for target reactions (e.g. which enable cracking of the supplied compound like ammonia into nitrogen and hydrogen). Any existing catalyst, having known catalytic properties, may be used in the invention, provided it does not detrimentally affect its performance. The catalyst may be present on the surfaces of the porous substrate, as well as inside the substrate (i.e. within the pores), particularly at the reaction chamber facing surface.

[0057] For ammonia cracking, specially adapted catalysts are typically required. The present invention also provides a series of innovative catalyst compositions designed for efficient ammonia or methane decomposition, each formulated with a distinct chemical composition to enhance catalytic performance. Specifically, the invention comprises a set of novel metal oxide catalysts for ammonia or methane cracking with the notional and non-stoichiometric composition characterized by a base matrix of cerium oxide (CcCE). with a substitution of rare earth and transition metal elements to form a unique series of mixed-oxide catalysts.

[0058] The present invention also provides a catalyst having the formula:Ce(0.99 x [1-a-b-c]) XaYb RucO(2+ / -5) where:X represents a trivalent element selected from the group consisting of: samarium (Sm), europium (Eu), neodymium (Nd), dysprosium (Dy), gadolinium (Gd), lanthanum (La), praseodymium (Pr), lanthanum and yttrium (Y),Y represents a transition metal selected from the group consisting of: cobalt (Co), nickel (Ni) and iron (Fe), a, b, and c denote the molar fractions of X, Y and Ru, respectively, where: a is between zero and about 0.4, b is between zero and about 0.2 and c is between about 0.01 and about 0. 1, and5 indicates the deviation from stoichiometry due to oxygen vacancies, where:8 is between zero and about 0.05.

[0059] Specific embodiments of the catalyst produced by the inventors include:Ceo.85Pro.iCoo.o3Ruo.o20(2+ / ^),Ceo.77Pro.l5Coo.05Ruo.020(2+ / -8),Ceo.82Yo.lCoo.05Ruo.020(2+ / -8),Ceo.54Yo.3Coo.lRuo.050(2+ / -8),Ceo.77Lao.l5Coo.05Ruo.020(2+ / -8),Ceo.77Lao.i5Feo.o5Ruo.o20(2+ / -8), andCeo.77Feo,15Coo.05Ruo.020(2+ / -8).

[0060] These catalysts can be used at temperatures of about 400°C to 600°C, with 500°C being preferred, at a pressure of between about 1 to 10 bar. As described below, these temperatures and pressures are significantly lower than those required by many prior art ammonia cracking processes.

[0061] The proposed catalyst may be used in combination with the porous support / chemical reactor of the present invention, as well as in conventional catalyst reactors, such as packed bed reactors, where the catalyst powder is loosely packed inside a metallic or non-metallic pipe. It can also be used for standard honeycomb structures, where an alumina honeycomb is coated using a slurry of catalyst particles.

[0062] Despite the advantages of the catalysts of the present invention, it is envisaged that commercially available catalysts (e.g. ammonia or methane decomposition catalysts, etc.) can also be used with the porous supports of the present invention. For example, in some applications, the invention may be used to crack methane or perform another chemical reaction, and a catalyst for ammonia cracking might not be appropriate. Other catalysts which may be incorporated in the present invention include metal oxides, mixed metal oxides, precious metal catalysts, zeolites and transition metal-based materials.

[0063] In embodiments of the invention where the porous substrate comprises a catalyst, the catalyst may be associated with the porous support in any functionally effective manner. The catalyst may, for example, be distributed on the surface of the porous substrate. Alternatively (or in addition), the catalyst may be distributed throughout the porous substrate (e.g. with the porous structure being filled with catalyst).

[0064] Catalysts for use in the present invention may be synthesized using a variety of traditional catalyst synthesis methods such as coprecipitation or wet impregnation. Alternatively, the catalyst may be synthesized in situ using the following method.

[0065] A thin fdm of catalyst-precursor may be deposited onto the porous substrate by dipping the substrate into a viscous precursor made by chelating stoichiometric amounts of the metal cations which form the catalyst, the viscous precursor optionally including a plasticizer such as ethylene glycol or urea (which can help assist in producing continuous thin films). The viscous precursor can be formed by dissolving the source of metal cations in water, adding a chelating agent (e.g. glycine, gelatin, ketones, amines, ethylenediamine, 1-ascorbic acid and / or D-sorbitol) and then heating the resultant mixture. Heat-treating of the coated substrate is then performed, whereby the metal oxide catalyst forms. This method has been found by the inventors to be more efficient and cost-effective, allowing for a near 100% efficiency in transferring the catalyst from its synthesis to the substrate. In contrast, many prior art methods use expensive and hard to maintain equipment such as ultrasonic spray coating machines.

[0066] In some embodiments, the viscosity of the viscous precursor may be adjustable in order to produce a catalyst layer having a predetermined thickness (e.g. when dip coating) and depth of penetration into the pores of the porous substrate. Viscosity may, for example, be adjusted by adding more or less plasticiser and / or chelating agent, changing the volume of solvent used, changing the polymerisation time or temperature, or any suitable combination thereof.

[0067] The catalyst may otherwise be coated on the porous support using any suitable technique, including spraying or screen printing, slurry dip coating or nitrate impregnation.

[0068] The amount of catalyst applied to the porous substrate can be carefully controlled, with loading densities ranging from approximately 0.01 mg / cm2to 5 mg / cm2Examples

[0069] The inventor has conducted proof of concept trials using prototype porous substrates and catalysts in accordance with embodiments of the present invention. Some of these trials are described below.Example 1Step 1: Fabrication of bilayer substrate

[0070] A porous UNS 430 stainless steel filter tube purchased from Mott Corporation was used as a starting substrate. Following a cleaning step, the SS tube was subjected to an electroless nickel plating procedure using a commercially available plating solution, allowing for a uniform layer of metal deposition. To create a bilayer structure, a cerium oxide layer was then formed onthe nickel-plated SS tube. For fabrication of the cerium oxide layer, a cerium oxide paste was prepared using ball milling of ceria nano powder using terpinol and polyethylene butyryl and starch pore formers. The surface of SS tube was then brush painted using the ceramic paste and dried in oven at 80°C followed by sintering at 1100°C in argon atmosphere. A two-layer structure was formed, with the smaller pores on the ceria layer (the outer layer) having a target pore size of 10 to 100 nm, and the larger pores on the nickel plating (the inner layer) being up to about 2 micron. Figure 7 schematically illustrates the bilayer structure fabricated in this manner.Step 2: Preparation of catalyst coating

[0071] To prepare the catalyst precursor, high-purity metal nitrates (including nitrosyl nitrate for Ruthenium) were dissolved in 50 millilitres of deionised water. This was done in precise molar ratios to achieve a 0.05 M solution, corresponding to the desired target formula (in this example Ceo.77Pro.i5Coo.o5Ruo o202-8). To this nitrate solution, add 50 millilitres of ethylene glycol (sourced from Sigma Aldrich) as a plasticiser, which aids in fdm formation. Then, add 0.5 grams of glycine (also from Sigma Aldrich) into the mixture. The glycine acts as a chelating agent, helping to form a stable metal-glycinate complex that facilitates the creation of a three- dimensional network structure. Adjust the pH of the solution with nitric acid until a precipitate- free solution is obtained. Transfer this solution to an oven preheated to 80°C and allow it to incubate for 48 hours. During this period, the solution will undergo chelation and evaporation, resulting in a viscous polymeric catalytic precursor ready for subsequent coating applications.Step 3: Dip coating

[0072] The next stage involves the fabrication of a catalyst layer using dip coating, where the substrate from Step 1 is immersed into the catalyst coating solution from Step 2.

[0073] In brief, the dip coating process involves immersing the bi-layer porous substrate, as detailed in Step 1, into the viscous polymeric catalyst precursor formulated in step 2. This step is performed using either an automatic or semi-automatic dip coater to maintain precision and control during the coating process. After dip coating, the catalyst is bound to the porous substrate using a vacuum oven and placing it in a muffle furnace at high temperature. The muffle furnace is programmed to ramp at 1 °C per minute, till 300 °C. The temperature then stays at 300 °C for 60 minutes, before cooling back down to room temperature.Preliminary Results - hydrogen egress

[0074] Gas Chromatography analysis on the product gas of cracked ammonia which passed through the ceria layer of the porous support produced in Step 1, and which included a Ce0.85Y0.1Co0.05Ru0.02O2 catalyst, showed a purity of 95% H2. In a comparative experiment wherethe porous support used was the nickel -plated SS tube initially prepared in Step 1 (i.e. which does not have a bilayer structure), the purity of H2 in the product gas was 81%. As described above, product gas having a hydrogen purity of less than 90% would need to undergo further purification steps before it could be used in a fuel cell.Preliminary results - enhanced ammonia cracking

[0075] Figure 8 depicts the Transmission Electron Microscopy (TEM) image of a catalyst coating (CeojvPro.isCoo.osRuo.cnCh-a) on a porous substrate. The image provides a detailed view of a catalyst nanostructure, revealing particle morphology, size, crystallinity and porosity.

[0076] Figure 9 depicts SEM image clearly showing the catalyst coating on porous substrate.

[0077] Table 1 shows the preliminary testing results of the catalysts Ceo.vvPro.isCoo.osRuo.oiCh-a and Ceo.82Yo.iCoo.o5Ruo.o202-8. The measurements were performed using an Emerson online ammonia analyzer. For measuring ammonia decomposition, the porous supports were placed in the homemade reactor tube made up of stainless steel. The split tube furnace is used for heating fixture to 450°C.

[0078] The preliminary data confirms the superior performance of catalysts in accordance with the present invention, which facilitate robust ammonia decomposition into nitrogen and hydrogen (up to 92%) at a temperature of 450 °C. This represents a significant advancement over conventional technologies, which typically require operational temperatures ranging from 750 °C to 950 °C, thereby underscoring the potential for enhanced efficiency and reduced thermal energy demand in industrial applications. For example, Johnson Matthey’s KATALCO 27-2 catalyst is a nickel-based ammonia cracking catalyst that has been used for over 50 years. It is a highly active catalyst that typically operates in the range 700 - 950°C and hence requires significantly more energy.Table 1. Preliminary Results for ammonia crackingExample 2

[0079] Example 2 describes the synthesis and characterization of catalytic materials, the fabrication of porous substrates in tubular and disc geometries, and the performance evaluationof these substrates — both uncoated and coated with catalytic thin films. The experimental studies were primarily conducted using ammonia gas to assess decomposition and hydrogen production performance. Additional data is also presented for selected catalysts under steam methane reforming (SMR) conditions to further validate the versatility and efficacy of the catalytic system.Fabrication of bilayer substrate

[0080] Bi-layer porous substrates were developed to serve as support platforms for catalytic layers used in hydrogen separation and ammonia decomposition applications. These substrates were fabricated by pressing and sintering structured powder mixtures designed to create functionally distinct porosity gradients across the cross-section of the membrane body (e.g. as shown in Figures 1 and 2).

[0081] The substrate includes a lower-porosity support layer to provide mechanical strength and dimensional stability and an upper, higher-porosity surface layer to facilitate gas transport and integration with subsequent coatings. This gradient architecture was achieved through sequential powder loading and pressing using a uniaxial hydraulic press. The lower-porosity layer was compacted first using a ceramic matrix without or with minimal pore-former content. A second, high-porosity layer was then added and compacted in the same die to form a composite green body. The assembly was subsequently sintered using a controlled multistep heating schedule to promote densification and maintain structural integrity. The sintering cycle included a burnout phase at 600 °C to remove residual pore-forming agents, followed by high-temperature treatment at 1450 °C to achieve inter-grain necking and consolidation of the ceramic framework.

[0082] In addition to planar pellet substrates, tubular porous supports were also produced. These tubes were fabricated from sintered stainless steel with nominal pore sizes of approximately 10 pm and were subsequently coated with a ceramic membrane material using the same formulation as applied to the planar substrates.

[0083] Ceramic coatings were applied to the porous metallic substrates (disk and tubular) using a brush-assisted dip-coating technique, wherein a slurry comprising 8 mol% yttria-stabilized zirconia (8YSZ) dispersed in terpineol was uniformly deposited onto the substrate surface. Following application, the coated substrates were subjected to a controlled drying phase and subsequently sintered under an inert nitrogen atmosphere at temperatures up to approximately 1100 °C to promote densification, adhesion, and mechanical stability of the ceramic layer. While brush-assisted dip-coating was employed in the present example, it is contemplated that the ceramic coating may alternatively be applied using other deposition techniques such asconventional dip-coating, spray coating, or equivalent methods capable of producing a uniform fdm with sufficient substrate adhesion.

[0084] Gas-tightness, separation efficiency, and permeation flow rates were evaluated using a custom-built fixture rated for operation up to 850 °C.

[0085] Surface and cross-sectional morphology of the sintered bi-layer structures were examined by SEM. The cross-sectional SEM images reveal a distinct bi-layer structure comprising a dense, lower-porosity support layer and a higher-porosity surface layer. Surface images confirm the support layer’s compact morphology and the surface layer’s larger, interconnected pores. This tailored porosity gradient supports selective gas permeation while maintaining mechanical stability.

[0086] The cross-sectional SEM images show a continuous ceramic coating conformally applied to the internal structure of the nickel foam substrate. The surface image highlights the uniform morphology of the ceramic layer, which facilitates gas separation by providing a selective barrier. The coating’s adherence to the porous foam underscores the substrate’s durability under reactor conditions.

[0087] The combination of tuneable porosity, mechanical robustness, and integration with catalytic films renders these bi-layer substrates suitable for application in membrane-based hydrogen generation systems and gas reforming environments.Gas separation testing - hydrogen egress

[0088] Gas separation testing was conducted using a simulated ammonia mixture feed gas of 75% hydrogen and 25% nitrogen by volume, representative of ammonia decomposition output. Under test conditions at 400 °C, bi-layer ceramic pellets demonstrated selective hydrogen permeation, enriching the hydrogen content in the permeate by approximately 10.6% relative to the feed. Table 1 presents representative gas chromatographic results showing a rise from 68% to 76% hydrogen in the permeate, with a total flow rate of 600 mL / min.Table 2: Results of GC analysis and permeate flow rate at 400 °CCatalysts for ammonia cracking

[0089] Table 1, set out above, presents the inventors’ preliminary catalytic activity data for doped ceria-based catalysts, specifically Ceo.77Pro.i5Coo.osRuo.o202-8 and Ceo.82Yo.iCoo.o5Ruo.o20^-5, under ammonia decomposition conditions. As discussed above, these data confirmed that the catalysts significantly enhance ammonia cracking efficiency.Ceo.82Y0.1Co0.05Ru0.02O2— 8 achieved a conversion rate of 92% at 450 °C, while Ce0.77Pr0.15Co0.05Ruo.02O2— 8 reached 70% conversion under the same conditions.

[0090] To build upon the preliminary data, additional catalytic performance data were generated using a broader range of catalyst compositions and reaction temperatures, specifically between 400 °C and 500 °C. These extended experiments were conducted at a constant ammonia flow rate of 10 mL / rnin to allow for direct comparison of conversion efficiency across different dopant systems.

[0091] Catalytic testing was carried out using a fixed-bed reactor configuration, wherein each catalyst was placed in a stainless-steel tube reactor and subjected to a controlled thermal environment using a split-tube furnace. Ammonia gas was continuously supplied to the reactor, and the resulting product stream was directed into a medium capable of capturing unconverted ammonia. Following the reaction, the medium was analysed using a quantitative chemical titration method to determine residual ammonia content. The results were also confirmed using ammonia gas analyser for selected sample to ascertain accuracy of measurement using Agilent’s GC-MS system calibrated using calibration gases.

[0092] The conversion efficiency was then calculated by comparing the neutralisation capacity of the medium before and after exposure to the reaction stream. A summary of the resulting ammonia decomposition performance is provided in Table 3.Table 3: Results for ammonia cracking

[0093] These results reinforce the superior activity of the Ru-doped ceria systems, particularly when co-doped with rare earth and transition metals such as La, Y, Pr, and Fe. High catalytic conversion at 500 °C indicates excellent thermal stability and redox performance of these materials. Notably, Ceo.77Lao.isCoo.o5Ruo.o202-8 achieved complete ammonia decomposition (99.9-100%), confirming its suitability for practical hydrogen generation applications at moderate temperatures.

[0094] These expanded findings further demonstrate the potential for low-temperature ammonia cracking using tailored ceria-based catalysts. The data also validates the robustness and adaptability of the catalytic platform for future scale-up and integration into membrane -based reactor systems.Example 3Preparation of catalyst coating and application to porous substrate

[0095] To evaluate the catalytic functionality of the bi-layer porous substrates described above under representative reactor conditions, substrates having tubular and disc geometries were coated with a catalytic thin film comprising Ce0.82Y0.1Co0.05Ru0.02O2.-8. The coating was applied using a dip-coating technique, wherein a viscous polymeric precursor solution was deposited uniformly onto the surface of the substrates. The precursor formulation used for producing the catalytic fdm is that described in international (PCT) patent application no.PCT / AU2024 / 051250, entitled “METHODS OF PRODUCING CATALYTIC COATINGS ON SUBSTRATES”, briefly described below.

[0096] To prepare a viscous polymeric precursor for the catalyst composition Ceo.82Yo.iCoo.osRuo.o202-3, appropriate metal cation source compounds are dissolved in deionized water to achieve a ~0.1 M total metal ion concentration, followed by the addition of ethylene glycol and citric acid for chelation and network formation.

[0097] For example, the polymeric precursor for the Ce0.82Y0.1Co0.05Ru0.02O2.-8 catalyst was prepared by dissolving cerium (Ce), yttrium (Y), cobalt (Co), and ruthenium (Ru) cation source compounds, such as cerium(III) nitrate [CefNOs^ blW], yttrium(III) nitrate [YfNCEXblLO], cobalt(II) nitrate [Co(NOs)2-6H2O], and ruthenium(III) chloride [RuClrxEEO], in deionized water to achieve a total metal ion concentration of approximately 0. 1 M, with molar ratios of Ce:Y:Co:Ru = 0.82:0.1:0.05:0.02. Ethylene glycol was added as a plasticizer to facilitate fdm formation, and citric acid was introduced as a chelating agent to form a stable, three-dimensional metal-citrate complex network. The solution was stirred and incubated for 24 - 60 hours to allow chelation and water evaporation, resulting in a viscous precursor suitable for further processing.

[0098] The same precursor was employed for both the disc and tube substrates. Following deposition by simple dip coating, the coated substrates were thermally treated at 600°C to form a nanocrystalline thin fdm on the support.

[0099] Instead of dip coating, alternative techniques such as spraying and drying or flame spray pyrolysis are also viable options for applying the precursor onto substrates. Additionally, while physical vapor deposition (PVD) or chemical vapor deposition (CVD) could be adapted for layer formation, these methods are less suitable for achieving uniform coating inside porous structures, limiting their effectiveness for applications requiring the catalysts to penetrate into the pores of the porous substrate.

[0100] Ammonia decomposition testing was performed to assess catalytic activity across a temperature range of 400 °C to 500 °C. The experimental configuration comprised custom-built test fixtures, each housed within a programmable furnace. Distinct fixtures were employed for tubular and disc formats to ensure accurate gas sealing and flow dynamics.

[0101] In the tubular configuration, the coated porous tube was j oined to an alumina inlet tube via a high-temperature ceramic adhesive (Ceramabond 552), forming a sealed assembly. The seal was initially air set for four hours, followed by a two-hour cure at 93 °C and another two- hour cure at 260°C. Ammonia gas was introduced through the conical end of the tube, enabling longitudinal flow along the coated inner surface. For the disc configuration, ammonia was directed to one face of the coated disc, thereby enabling through-plane permeation across the catalytic layer. This arrangement corresponds to the gas-flow architecture illustrated in Figure 7.Measurement of Ammonia Conversion and Methane Conversion

[0102] Each coated substrate was subjected to a continuous ammonia gas flow at a fixed rate of lOOmL / min. The outlet stream was directed into a reactive medium, and the amount of hydrogen was quantified using GC-MS methods.Table 4: Purity of Hydrogen coming out Thin-Film-Coated Porous Tube and Disc Substrates for ammonia decomposition

[0103] To evaluate the broader applicability of the coated systems, additional tests were conducted under steam methane reforming (SMR) conditions. A feed mixture of methane and steam in a molar ratio of 1 :4 was introduced to the coated substrates under the same temperature regime at 5 bars pressure and 750°C.Table 5: Purity of Hydrogen coming out Thin-Film-Coated Porous Tube and Disc Substrates for methane decomposition

[0104] The results obtained from these decomposition and reforming studies demonstrate that coated porous substrates bearing thin catalytic films of Ceo.82Yo.iCoo.o5Ruo.o202-3 exhibit strong catalytic activity at relatively low temperatures. These findings support the suitability of the present invention for use in hydrogen production applications.

[0105] The experimental data presented above validate the effectiveness of the disclosed porous substrates and various reactor configurations. Bilayer porous substrates with engineered pore gradients exhibit strong gas separation performance, while the doped ceria-based catalysts demonstrate high ammonia conversion efficiency at moderate temperatures. Furthermore, the integration of catalytic thin films on these substrates enables robust activity in both ammonia decomposition and steam methane reforming.

[0106] These results not only confirm the practicality of the invention for hydrogen production applications but also highlight its potential for use in membrane -integrated reactors and fuel cells. The materials and configurations presented here offer a lower-energy, scalable, and flexible platform for distributed hydrogen generation in next-generation energy systems.

[0107] As will be appreciated, the present invention provides a number of significant and commercially important advantages over conventional chemical reactors. Advantages include:• chemical reactors for cracking ammonia or methane to produce hydrogen can be incorporated into fuel cells, without risk of contamination due to an unacceptably high level of nitrogen, ammonia and carbon dioxide;• catalysts of the present invention can facilitate robust ammonia decomposition into nitrogen and hydrogen at lower temperatures than was previously possible.

[0108] It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. All such modifications are intended to fall within the scope of the following claims.

[0109] It is to be understood that any prior art publication referred to herein does not constitute an admission that the publication forms part of the common general knowledge in the art.

[0110] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS:

1. A porous substrate configured to separate a reaction chamber from a product chamber in a chemical reactor, the porous substrate comprising: a reaction chamber facing surface and a product chamber facing surface, wherein a size of pores in the porous substrate decreases between the reaction chamber facing surface and the product chamber facing surface, the pore size at the product chamber facing surface being such that chemical species larger than a predetermined size are excluded from passing through the porous substrate into the product chamber.

2. The porous substrate of claim 1, wherein the porous substrate comprises a plurality of layers of porous substrates, each layer of porous substrate having a different pore size.

3. The porous substrate of claim 2, wherein each of the porous substrates is formed of a different substance.

4. The porous substrate of any one of claims 1 to 3, wherein the porous substrate comprises a ceramic material, a metal, an alloy, a metal oxide or a composite material.

5. The porous substrate of any one of claims 1 to 4, wherein the porous substrate comprises a bi-layer of two porous substrates.

6. The porous substrate of claim 5, wherein the porous substrate comprises a first layer comprising nickel and a second layer comprising zirconium oxide or cerium oxide.

7. The porous substrate of any one of claims 1 to 6, wherein the size of pores in the porous substrate ranges from about 1 to 20 microns at the reaction chamber facing surface to about 1 to 500nm at the product chamber facing surface.

8. The porous substrate of any one of claims 1 to 7, wherein the pore size at the product chamber facing surface is such that chemical species larger than hydrogen are excluded from passing through the porous substrate into the product chamber.

9. The porous substrate of any one of claims 1 to 8, wherein the porous substrate comprises a catalyst.

10. The porous substrate of claim 9, wherein the catalyst is distributed on the reaction chamber facing surface of the porous substrate.

11. The porous substrate of claim 9 or claim 10, wherein the catalyst is distributed throughout the porous substrate.

12. The porous substrate of any one of claims 1 to 11, wherein the chemical reactor is a cracker.

13. The porous substrate of claim 12, wherein the cracker is a methane cracker and the size of pores in the porous substrate ranges from about 5 to 10 microns at the reaction chamber facing surface to about 5 to 500nm at the product chamber facing surface.

14. The porous substrate of claim 12, wherein the cracker is an ammonia cracker and the size of pores in the porous substrate ranges from about 1 to 2 microns at the reaction chamber facing surface to about 1 to lOOnm at the product chamber facing surface.

15. The porous substrate of any one of claims 1 to 14, wherein the porous substrate is tubular or planar in shape.

16. A chemical reactor comprising the porous substrate of any one of claims 1 to 15.

17. A fuel cell comprising the porous substrate of any one of claims 1 to 15.

18. A catalyst having the formula:Ce(0.99 x [1-a-b-c]) Xa Yb Rile O(2+ / -§) where:X represents a trivalent element selected from the group consisting of: samarium (Sm), europium (Eu), neodymium (Nd), dysprosium (Dy), gadolinium (Gd), lanthanum (La), praseodymium (Pr), lanthanum and yttrium (Y),Y represents a transition metal selected from the group consisting of: cobalt (Co), nickel (Ni) and iron (Fe), a, b, and c denote the molar fractions of X, Y and Ru, respectively, where: a is between zero and about 0.4, b is between zero and about 0.2 and c is between about 0.01 and about 0.1 and8 indicates the deviation from stoichiometry due to oxygen vacancies, where:8 is between zero and about 0.05.

19. The catalyst of claim 18, wherein the catalyst is: Ceo.85Pro.iCoo.o3Ruo.o20(2+ / -8), Ceo.77Pro.l5Coo.05Ruo.020(2+ / -8), Ceo.82Yo.lCoo.05Ruo.020(2+ / -8), Ceo.54Yo.3Coo.lRuo.050(2+ / -8), Ceo.77Lao.i5Coo.o5Ruo.o20(2+ / -8), Ceo.77Lao.i5Feo.o5Ruo.o20(2+ / -8) or Ceo.77Feo.i5Coo.o5Ruo.o20(2+ / -8).

20. The porous substrate of any one of claims 1 to 15, comprising the catalyst of claim 18 or claim 19.

21. An ammonia cracker or a methane cracker comprising the porous substrate of any one of claims 1 to 15, with the catalyst of claim 18 or claim 19 being distributed on the reaction chamber facing surface of the porous substrate.

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