GB2589890A - Catalytic converters - Google Patents

Abstract

A catalytic core for an exhaust catalytic converter has a network structure defining a plurality of fluid flow channels for receiving a flow of fluid for catalytic conversion. A catalytically active surface of the network structure has a surface topography defined by a repeating pattern of surface features 13 extending from a body 7 of the network structure. Each surface feature has a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm, and preferably no less than 1 nm or 10 µm. A dimension of the surface features locally parallel to the profile of the body may be no greater than about 250 µm or 100 µm. The surface features may be the same or different in size and/or shape. The surface features may be of micron-scale and may further comprise nano-scale secondary surface features 14. The catalytic core may be manufactured using an additive manufacturing (3D printing) process such as selective laser melting or electro-beam melting.

Description

CATALYTIC CONVERTERS

Field of the Disclosure

The present disclosure concerns catalytic cores for catalytic converters, catalytic converters, methods of manufacturing catalytic cores for catalytic converters, and associated digital design models.

Background of the Disclosure

Catalytic converters are reactors in which the rate of a chemical conversion reaction (i.e. a reaction in which at least one chemical substance is transformed into another chemical substance) is accelerated through use of a catalyst. In particular, catalytic converters are commonly used to change the chemical composition of input fluids by catalysing one or more chemical reactions. For example, catalytic converters are commonly used to reduce levels of toxic or pollutant chemicals in exhaust gases exiting internal combustion engines of motor vehicles, trains or aircraft. Catalytic converters are also used in industry, for example in processing of fluids produced during petroleum processing or in the production of polymers and pharmaceuticals.

Catalytic converters may be used to catalyse many different types of chemical reaction. The chemical reactions catalysed by catalytic converters in motor vehicles are commonly redox reactions. For example, catalytic converters for use with diesel-based internal combustion engines commonly catalyse the conversion of carbon monoxide (CO), or unburnt or partially unburnt hydrocarbons, to carbon dioxide (CO2). Another example chemical reaction which can be catalysed by catalytic converters is the conversion of nitrogen oxides (NO.) to nitrogen (N2). Catalytic converters enable such conversion reactions to occur more rapidly, at lower temperatures, and in line with exhaust systems.

Due to our increased understanding of the potential environmental effects of many exhaust gases, more effective catalytic converters are desirable.

Summary of the Disclosure

According to a first aspect, there is provided a catalytic core for a catalytic converter, the catalytic core having a network structure defining a plurality of fluid flow channels for receiving a flow of fluid for catalytic conversion, wherein a catalytically active surface of the network structure has a surface topography defined by a repeating pattern of surface features extending from a body of the network structure, each surface feature having a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm.

The skilled person will appreciate that a catalytic converter is a device in which the chemical composition of a fluid is changed by catalysis of one or more chemical reactions. That is to say, a catalytic converter is a reactor (i.e. a reaction vessel) in which catalysis of said one or more chemical reactions takes place. The catalysis which takes place inside the catalytic converter is generally heterogeneous catalysis, i.e. catalytically active material (i.e. catalyst) present inside the catalytic converter is in a different physical state than the fluid. For example, the catalytically active material (i.e. catalyst) may be solid.

Catalytic converters are commonly used to reduce levels of unwanted components (such as toxic or pollutant components) in exhaust gases exiting internal combustion engines (of, for example, motor vehicles, trains or aircraft). The chemical reactions catalysed by such catalytic converters are commonly redox reactions. For example, catalytic converters for use with diesel-based internal combustion engines commonly catalyse the conversion of carbon monoxide (CO), or unburnt or partially unburnt hydrocarbons, to carbon dioxide (CO2). Another example chemical reaction which can be catalysed by catalytic converters is the conversion of nitrogen oxides (N0x) to nitrogen (N2). Catalytic converters are also used to catalyse chemical reactions in industrial processes, for example in the processing of petroleum, the synthesis of polymers, or the manufacture of pharmaceuticals. The design and scale of the reactor (i.e. reaction vessel), and the type of catalytically active material used, can be tailored to the particular application.

Throughout this specification and the appended claims, the term "catalytic core" is used to refer to the catalytically active region of a catalytic converter where catalytic conversion of fluid takes place in use. For example, the catalytic core may be an interior region of a reactor (i.e. a reaction vessel) where catalysis takes place. The catalytic core is therefore the region of the catalytic converter where catalytically active material (i.e. catalyst) is located.

The fluid flow channels provide pathways for flow of fluid through the catalytic core. In use, fluid is exposed to the catalytically active surface of the network structure as it flows through the fluid flow channels and chemical conversion of the fluid generally takes places at said catalytically active surface.

It will be appreciated that the term "fluid" takes its normal meaning in the art, i.e. a substance which has negligible or zero shear modulus and which therefore flows continuously under any applied shear stress. Fluids have no fixed shape but may flow to take on the shape of a container. The fluid may be a liquid or a gas.

The inventors have found that, by providing the catalytically active surface of the network structure with a surface topography defined by a repeating pattern of surface features extending from a body of the network structure, each surface feature having a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm, the geometric surface area of the catalytically active surface can be increased, as compared to a network structure which has the same body profile but lacks the repeating pattern of surface features (for example, as compared to a network structure having a catalytically active surface having a generally flat, featureless surface topography). By increasing the geometric surface area of the catalytically active surface for a given body profile, the overall catalytic activity of the catalytic core is also increased. Catalytic converters including the catalytic core of the present invention are therefore more effective (for example, they have a greater catalytic efficiency) than known catalytic converters.

In addition, by restricting the characteristic dimension, in the direction locally perpendicular to the profile of the body, of each surface feature to being less than about 1 mm, the geometric surface area of the catalytically surface is increased without significantly impacting the overall shape of the network structure and therefore without significantly obstructing the flow of fluid through the catalytic core (for example, without generating substantial turbulent flow).

It may be that the characteristic dimension of each surface feature, in the direction locally perpendicular to the profile of the body, is no less than about 1 nm, for example no less than about 50 nm, or no less than about 100 nm, or no less than about 500 nm, or no less than about 1 pm, or no less than about 10 pm, or no less than about 25 pm, or no less than about 50 pm, or no less than about 100 pm, or no less than about 150 pm. It may be that the characteristic dimension of each surface feature, in the direction locally perpendicular to the profile of the body, is no greater than about 999 pm, for example, no greater than about 900 pm, or no greater than about 750 pm, or no greater than about 500 pm, or no greater than about 250 pm, or no greater than about 100 pm, or no greater than about 50 pm. It may be that the characteristic dimension of each surface feature, in the direction locally perpendicular to the profile of the body, is from about 1 nm to about 999 pm, for example, from about 1 nm to about 900 pm, or from about 1 nm to about 750 pm, or from about 1 nm to about 500 pm, or from about 1 nm to about 250 pm, or from about 1 nm to about 100 pm, or from about 1 nm to about 50 pm, or from about 50 nm to about 999 pm, or from about 50 nm to about 900 pm, or from about 50 nm to about 750 pm, or from about 50 nm to about 500 pm, or from about 50 nm to about 250 pm, or from about 50 nm to about 100 pm, or from about 50 nm to about 50 pm, or from about 100 nm to about 999 pm, or from about 100 nm to about 900 pm, or from about 100 nm to about 750 pm, or from about 100 nm to about 500 pm, or from about 100 nm to about 250 pm, or from about 100 nm to about 100 pm, or from about 100 nm to about 50 pm, or from about 500 nm to about 999 pm, or from about 500 nm to about 900 pm, or from about 500 nm to about 750 pm, or from about 500 nm to about 500 pm, or from about 500 nm to about 250 pm, or from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 999 pm, or from about 1 pm to about 900 pm, or from about 1 pm to about 750 pm, or from about 1 pm to about 500 pm, or from about 1 pm to about 250 pm, or from about 1 pm to about 100 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 999 pm, or from about 10 pm to about 900 pm, or from about 10 pm to about 750 pm, or from about 10 pm to about 500 pm, or from about 10 pm to about 250 pm, or from about 10 pm to about 100 pm, or from about 10 pm to about 50 pm, or from about 25 pm to about 999 pm, or from about 25 pm to about 900 pm, or from about 25 pm to about 750 pm, or from about 25 pm to about 500 pm, or from about 25 pm to about 250 pm, or from about 25 pm to about 100 pm, or from about 25 pm to about 50 pm, or from about 50 pm to about 999 pm, or from about 50 pm to about 900 pm, or from about 50 pm to about 750 pm, or from about 50 pm to about 500 pm, or from about 50 pm to about 250 pm, or from about 50 pm to about 100 pm, or from about 100 pm to about 999 pm, or from about 100 pm to about 900 pm, or from about 100 pm to about 750 pm, or from about 100 pm to about 500 pm, or from about 100 pm to about 250 pm, or from about 150 pm to about 999 pm, or from about 150 pm to about 900 pm, or from about 150 pm to about 750 pm, or from about 150 pm to about 500 pm, or from about 150 pm to about 250 pm.

It may be that each surface feature has a characteristic dimension, in a direction locally parallel to the profile of the body, of no greater than about 250 pm, for example no greater than about 200 pm, or no greater than about 150 pm, or no greater than about 100 pm. It may be that each surface feature has a characteristic dimension, in a direction locally parallel to the profile of the body, of no less than about 1 pm, for example, no less than about 50 pm, or no less than about 100 pm. It may be that each surface feature has a characteristic dimension, in a direction locally parallel to the profile of the body, from about 1 pm to about 250 pm, for example, from about 1 pm to about 200 pm, or from about 1 pm to about 150 pm, or from about 1 pm to about 100 pm, or from about 50 pm to about 250 pm, or from about 50 pm to about 200 pm, or from about 50 pm to about 150 pm, or from about 50 pm to about 100 pm, or from about 100 pm to about 250 pm, or from about 100 pm to about 200 pm, or from about 100 pm to about 150 pm.

It may be that each surface feature has first and second characteristic dimensions, in first and second mutually orthogonal directions, each being locally parallel to the profile of the body, of no greater than about 250 pm, for example no greater than about 200 pm, or no greater than about 150 pm, or no greater than about 100 pm. It may be that each surface feature has first and second characteristic dimensions, in first and second mutually orthogonal directions, each being locally parallel to the profile of the body, of no less than about 1 pm, for example, no less than about 50 pm, or no less than about 100 pm. It may be that each surface feature has first and second characteristic dimensions, in first and second mutually orthogonal directions, each being locally parallel to the profile of the body, from about 1 pm to about 250 pm, for example, from about 1 pm to about 200 pm, or from about 1 pm to about 150 pm, or from about 1 pm to about 100 pm, or from about 50 pm to about 250 pm, or from about 50 pm to about 200 pm, or from about 50 pm to about 150 pm, or from about 50 pm to about 100 pm, or from about 100 pm to about 250 pm, or from about 100 pm to about 200 pm, or from about 100 pm to about 150 pm.

It may be that each surface feature has characteristic dimensions, in any direction (e.g. all directions) locally parallel to the profile of the body, of no greater than about 250 pm, for example no greater than about 200 pm, or no greater than about 150 pm, or no greater than about 100 pm. It may be thate each surface feature has characteristic dimensions, in any direction (e.g. all directions) locally parallel to the profile of the body, of no less than about 1 pm, for example, no less than about 50 pm, or no less than about 100 pm. It may be the each surface feature has characteristic dimensions, in any direction (e.g. all directions) locally parallel to the profile of the body, from about 1 pm to about 250 pm, for example, from about 1 pm to about 200 pm, or from about 1 pm to about 150 pm, or from about 1 pm to about 100 pm, or from about 50 pm to about 250 pm, or from about 50 pm to about 200 pm, or from about 50 pm to about 150 pm, or from about 50 pm to about 100 pm, or from about 100 pm to about 250 pm, or from about 100 pm to about 200 pm, or from about 100 pm to about 150 pm.

The skilled person will appreciate that many different surface feature shapes are possible. For example, the surface features may comprise (i.e. one or more of) columns, cylinders, truncated cylinders, cones, conical frusta, prisms, truncated prisms, pyramids, cuboids, walls, fins, gratings, domes, spirals, helices or clavates, or any combination thereof.

A characteristic dimension of a surface feature, in a direction locally perpendicular to the profile of the body, may be a height or thickness of said surface feature, dependent on the particular shape of the surface feature. A characteristic dimension of a surface feature, in a direction locally parallel to the profile of the body, may be a width, breadth, length (e.g. an axial length, for example a major axial length or a minor axial length) or diameter of said surface feature, dependent on the particular shape of the surface feature.

For example, where a surface feature is a cylinder arranged such that a longitudinal axis thereof is locally perpendicular to the profile of the body, a characteristic dimension of the surface feature locally perpendicular to the profile of the body may be an axial length of the cylinder and a characteristic dimension of the surface feature locally parallel to the profile of the body may be a cross-sectional diameter of the cylinder measured in a plane perpendicular to the longitudinal axis.

A characteristic dimension of a surface feature, in a direction locally perpendicular to the profile of the body, may be the maximum dimension (i.e. maximum extent) of the surface feature in the direction locally perpendicular to the profile of the body. Similarly, a characteristic dimension of a surface feature, in a direction locally parallel to the profile of the body, may be a maximum dimension (i.e. maximum extent) of the surface feature in the direction locally parallel to the profile of the body.

The characteristic dimensions of the surface features may be determined, at least in part, by the manufacturing method. For example, it may not be feasible to form a surface feature having a characteristic dimension, in a direction locally perpendicular to the profile of the body, of less than about 1 nm. If the network structure is manufactured using an additive manufacturing method such as powder bed fusion, in which regions of a layer of powder are selectively melted by application of heat (for example, by a laser), the characteristic dimensions of the surface features may be determined, at least in part, by the minimum dimensions of a melt pool or the particle size of a powder feedstock achievable in the manufacturing method. Characteristic dimensions in directions locally parallel to the profile of the body may be particularly limited by the minimum dimensions of the melt pool achievable in such methods.

It may be that the surface features are micron-scale surface features. That is to say, it may be that the surface features have one or more characteristic dimensions On directions locally perpendicular to and/or locally parallel to the profile of the body) from about 1 pm to about 999 pm. It may be that all characteristic dimensions of the micron-scale surface features are from about 1 pm to about 999 pm.

It may be that the surface features are nanoscale surface features. That is to say, it may be that the surface features have one or more characteristic dimensions On directions locally perpendicular to and/or locally parallel to the profile of the body) from about 1 nm to about 999 nm. It may be that all characteristic dimensions of the nanoscale surface features are from about 1 nm to about 999 nm.

It may be that the surface features are micron-scale primary surface features and that a plurality of (e.g. a majority of, for example all of) said micron-scale primary surface features each further comprise one or more nanoscale secondary surface features.

The primary surface features may be surface features which protrude from the body of the network structure. The secondary surface features may be surface features which in turn protrude from the primary surface features. Accordingly, the surface topography of the network structure may be patterned on multiple length scales.

It may be that the catalytically active surface has an arithmetic mean surface roughness, Ra, of no less than about 50 pm, for example no less than about 100 pm. It may be that the catalytically active surface has an arithmetic mean surface roughness, Ra, of no greater than about 200 pm, for example no greater than about 100 pm. It may be that the catalytically active surface has an arithmetic mean surface roughness, Ra, from about 50 pm to about 200 pm, for example from about 50 pm to about 100 pm, or from about 100 pm to about 200 pm. The skilled person will appreciate that the arithmetic mean surface roughness, Ra, of a surface is defined as Ii Ra = XIYtI 1=1 where Ra is measured along a roughness profile containing n ordered, equally spaced data points and yi is the vertical distance between a mean line to the ith data point. Ra may be measured using any suitable profilometer and the surface roughness determined according to ISO 4287:1997.

It may be that at least some of the surface features (e.g. neighbouring surface features) cooperate to direct fluid flow across a region (for example, a majority or the entirety) of the catalytically active surface. For example, it may be that at least some of the surface features (e.g. neighbouring surface features) are aligned with one another to direct fluid flow across the region of the catalytically active surface. Surface features such as walls or fins may be aligned with one another to direct fluid flow across the region of the catalytically active surface. By directing fluid flow across the region of the catalytically active surface, turbulent fluid flow may be reduced (for example, by increasing the thickness of a viscous boundary layer and reducing surface drag). Additionally or alternatively, it may be that some surface features (e.g. neighbouring surface features) cooperate to disrupt fluid flow across a region (for example, a majority or the entirety) of the catalytically active surface, thereby promoting turbulent flow in the fluid. It may be that some surface features cooperate to direct fluid flow across a first region of the catalytically active surface so as to reduce turbulent flow in said first region and that some other surface features cooperate to disrupt fluid flow across a second region of the catalytically active surface so as to increase turbulent flow in said second region.

It will be understood that the term "repeating pattern" refers to a periodic array of repeating units. Each repeating unit may comprise (e.g. consist of) one or more surface features. The repeating pattern may be a one-dimensionally repeating pattern or a two-dimensionally repeating pattern. The repeating pattern may consist predominantly (for example, entirely) of surface features having the same shape and/or size. Alternatively, the repeating pattern may comprise surface features having two or more different shapes and/or sizes. The spacing between neighbouring surface features (i.e. the distance between adjacent surface features) may be uniform across the repeating pattern. For example, the surface features may be arranged on a lattice.

It may be that the catalytically active surface comprises (e.g. is formed from (e.g. predominantly or entirely formed from)) catalytically active material. The skilled person will appreciate that catalytically active material comprises (e.g. is) material which catalyses a chemical reaction which takes place in the catalytic converter when in use.

The catalytically active material may be selected based on the chemical reaction to be catalysed. Catalytically active material may comprise (e.g. be) catalytically active metal, such as platinum (Pt), palladium (Pd), rhodium (Rh), copper (Cu), nickel (Ni), cerium (Ce), iron (Fe) and/or manganese (Mn). Accordingly, catalytically active material may comprise (e.g. be) catalytically active precious metal, such as platinum (Pt), palladium (Pd) and/or rhodium (Rh). The catalytically active metal (e.g. catalytically active precious metal) may be present in the form of one or more elemental metals, alloys and/or compounds. The catalytically active metal (e.g. catalytically active precious metal) may be in the form of particles, for example nanoparticles, or a thin film.

It may be that the network structure comprises (e.g. is formed from (e.g. predominantly or entirely formed from)) a catalyst support having a catalytically active coating. It may be that the catalyst support comprises catalytically inactive material. The skilled person will appreciate that catalytically inactive material comprises (e.g. is) material which does not catalyse a chemical reaction which takes place in the catalytic converter when in use. The catalytically inactive material may be unreactive under the standard operating conditions of the catalytic converter.

Catalytically inactive material may comprise (e.g. be) catalytically inactive ceramic, such as cordierite (i.e. magnesium iron aluminium cyclosilicate) or alumina. Additionally or alternatively, catalytically inactive material may comprise (e.g. be) catalytically inactive metal, such as an iron-based alloy, for example steel (e.g. stainless steel) or Kanthal (i.e. an iron-chromium-aluminium alloy). Additionally or alternatively, catalytically inactive material may comprise (e.g. be) catalytically inactive polymeric material.

The catalytically active coating may comprise (e.g. consist of) any catalytically active material disclosed herein.

The catalytically active coating may further comprise catalytically inactive material. For example, the catalytically active coating may comprise one or more catalytically inactive oxides, such as titania (i.e. titanium dioxide, Ti02), alumina (i.e. aluminium oxide, A1203) and/or silica (i.e. silicon dioxide, Si02). The catalytically active coating may be a catalytically active washcoat.

The catalytically active coating may be substantially uniform in thickness, for example across a majority (e.g. all) of the network structure.

It will be appreciated that, in embodiments in which the network structure comprises a catalyst support having a catalytically active coating, the catalytically active surface may be the surface of the catalytically active coating. Nevertheless, it may be that the catalyst support defines (i.e. determines) the shape and/or dimensions of the surface features. It may be that the catalyst support defines the shape of the surface features such that the surface features have any of the shapes and/or characteristic dimensions disclosed herein.

The catalytically active material in the catalytically active coating may be any catalytically active material capable of being applied to the catalyst support in a gaseous, liquid or colloidal phase and/or using chemical vapour deposition or physical 5 I vapour deposition methods.

The network structure may be a cellular structure. For example, the network structure may be a foam structure or a honeycomb structure. Alternatively, the network structure may be a lattice structure.

It may be that the network structure is a least partially additively manufactured such that the surface features are defined by additive manufacture.

In a second aspect, there is provided a catalytic converter comprising a catalytic core according to the first aspect, the catalytic core being provided within a housing defining a fluid flow passage from a fluid inlet, through the catalytic core, to a fluid outlet. The catalytic converter may be a catalytic converter for a vehicle, for example for a motor vehicle, train or aircraft. The housing may be substantially tubular. For example, the housing may be a jacket tube.

In a third aspect, there is provided a method of manufacturing a catalytic core for a catalytic converter, the method comprising: depositing material, by additive manufacturing apparatus, to form a network structure defining a plurality of fluid flow channels for receiving a flow of fluid for catalytic conversion, the network structure comprising a surface having a surface topography defined by a repeating pattern of surface features extending from a body of the network structure, each surface feature having a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm.

The network structure may have any features disclosed herein with regard to the first aspect. In particular, the surface features may have any shapes and/or dimensions as disclosed herein with regard to the first aspect.

The method may comprise: depositing catalytically active material, by additive manufacturing apparatus, to form at least a surface portion of the network structure such that at least a portion of the surface of the network structure is a catalytically active surface. The method may comprise: depositing catalytically active material, by additive manufacturing apparatus, to form at least a surface portion of the network structure such that the majority (for example, the entirety) of the surface of the network structure is a catalytically active surface. The method may comprise: depositing catalytically active material, by additive manufacturing apparatus, to form the majority (for example, the entirety) of the network structure.

The method may comprise: depositing catalytically inactive material, by additive manufacturing apparatus, to form a catalyst support of the network structure; and coating at least a portion of the catalyst support with catalytically active material. The method may comprise: coating the majority (for example, the entirety) of the catalyst support with catalytically active material.

The catalytically inactive material and the catalytically active material may have any properties or compositions disclosed herein with regard to the first aspect.

The skilled person will appreciate that any suitable coating method known in the art may be used to coat the catalyst support with catalytically active material. Suitable methods may include electrodeposifion (e.g. electroplating or electrophorefic coating) or washcoating, or other methods selected from chemical vapour deposition methods or physical vapour deposition methods.

It will be appreciated that the term "additive manufacture" refers to the computer-controlled deposition of materials to build up a three-dimensional component structure and can be contrasted with "subtractive manufacturing" in which material is sequentially removed by machining to arrive at the desired component structure. Additive manufacture may sometimes be referred to as "3D printing".

The skilled person will also appreciate that any suitable additive manufacturing apparatus or methods known in the art may be used to form the network structure, dependent on the chosen catalytically active material and/or catalytically inactive material. Suitable methods may include selective laser sintering, selective laser melting (i.e. laser powder bed fusion) or electron-beam additive manufacturing (i.e. electron-beam melting). Such methods may comprise selectively melting or sintering regions of sequential layers of powdered material (for example, metal or ceramic powder) using a laser or an electron beam to fuse the material.

The method may comprise: providing or producing a digital design model for the network structure; and controlling the additive manufacturing apparatus using the digital design model to form the network structure. The digital design model may be provided in the form of a Computer-aided Design (CAD) file such as an Additive Manufacturing File (AMF) or a stereolithography (STL) file.

In a fourth aspect, there is provided a digital design model for the network structure of the catalytic core according to the first aspect. The digital design model may be provided in the form of a Computer-aided Design (CAD) file such as an Additive Manufacturing File (AMF) or a stereolithography (STL) file.

In a fifth aspect, there is provided a computer program comprising instructions to cause an additive manufacturing apparatus to carry out the method according to the third aspect and/or to produce the network structure of the catalytic core according to the first aspect. For example, it may be that the additive manufacturing apparatus comprises or is in electronic communication with a computer (for example, a processor in a controller) and that the computer program comprises instructions which, when the program is executed by the computer (for example, by the processor), cause the additive manufacturing apparatus to carry out the method according to the third aspect and/or to produce the network structure according to the first aspect.

In a sixth aspect, there is provided a non-transitory computer-readable medium storing the digital design model according to the fourth aspect and/or the computer program according to the fifth aspect.

In a seventh aspect, there is provided a data carrier signal carrying the digital design model according to the fourth aspect and/or the computer program according to the fifth aspect.

In an eighth aspect, there is provided a non-transitory computer-readable medium storing instructions to cause an additive manufacturing apparatus to carry out the method according to the third aspect and/or to produce the network structure of the catalytic core according to the first aspect.

In a ninth aspect, there is provided an electrode for an electrochemical cell, the electrode comprising an electrode surface having a surface topography defined by a repeating pattern of surface features extending from a body of the electrode, each surface feature having a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm. The surface features may have any configurations, dimensions and/or shapes described hereinabove with regard to the surface features of the first aspect.

The electrode may be an anode. The electrode may be a cathode. The electrode may comprise (e.g. be made of) any suitable electrode material (e.g. anode material or cathode material). The electrode material (e.g. anode material or cathode material) may be electrically conductive. For example, the electrode material (e.g. anode material or cathode material) may be a metal, metal alloy, metalloid or electrically-conductive non-metal (e.g. carbon), or any combination thereof.

The electrode may comprise (e.g. be formed from (e.g. predominantly or entirely formed from)) an electrode support having an electrode coating. The electrode support may comprise (e.g. be formed from) a first electrode material and the electrode coating may comprise (e.g. be formed from) a second electrode material, the first and second electrode materials being different. For example, it may be that the first electrode material is a first metal or metal alloy and the second electrode material is a second metal or metal alloy. In some examples, the first electrode material is a metal or metal alloy and the second electrode material is an electrically-conductive non-metal, e.g. carbon.

In a tenth aspect, there is provided an electrochemical cell comprising an electrode according to the ninth aspect. The electrochemical cell may comprise an anode and a cathode separated by an electrolyte. The electrode according to the ninth aspect may be the anode or the cathode. The surface topography of the electrode may determine an interfacial topography of an interface between the electrode and the electrolyte. Accordingly, the repeating pattern of surface features may correspond to a repeating pattern of interfacial features which define the interfacial topography.

In some examples, the electrochemical cell comprises both first and second electrodes according to the ninth aspect, the first electrode corresponding to (i.e. being) the anode and the second electrode corresponding to (i.e. being) the cathode.

In an eleventh aspect, there is provided a method of manufacturing an electrode for an electrochemical cell, the method comprising: depositing material, by additive manufacturing apparatus, to form an electrode comprising a surface having a surface topography defined by a repeating pattern of surface features extending from a body of the electrode, each surface feature having a characteristic dimension, in a direction locally perpendicular to a profile of the body, of less than about 1 mm.

The method may comprise: depositing electrode material, by additive manufacturing apparatus, to form at least a surface portion of the electrode. The method may comprise: depositing electrode material by additive manufacturing apparatus, to form the majority (for example, the entirety) of the electrode.

The method may comprise: depositing a first electrode material, by additive manufacturing apparatus, to form an electrode support; and coating at least a portion of the electrode support with a second electrode material; wherein the first and second electrode materials are different. The method may comprise: coating the majority (for example, the entirety) of the electrode support with the second electrode material.

The electrode may have any features disclosed hereinabove with regard to the ninth aspect. The method may include or make use of, mutatis mutandis, any steps or features (including apparatus, digital design models, computer programs, non-transitory computer-readable media and/or data carrier signals) disclosed hereinabove with regard to the third, fourth, fifth, sixth, seventh and/or eighth aspects.

The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Brief Description of the Drawings

Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a schematic cross-sectional view of a catalytic converter; Figure 2 is a schematic cross-sectional view of a catalytic core of the catalytic converter of Figure 1; Figure 3 is a magnified view of region A of Figure 2 showing a surface topography of part of the catalytic core; Figure 4 is a schematic cross-sectional view of an alternative surface topography; Figure 5 is a schematic cross-sectional view of a further alternative surface topography; Figure 6 is a schematic cross-sectional view of a further alternative surface topography; Figure 7 is a schematic view of additive manufacturing apparatus in use, Figure 8 is a schematic illustration of a processor in communication with a computer readable medium storing computer executable instructions for controlling a laser of the additive manufacturing apparatus of Figure 7; Figure 9 is a flowchart illustrating a first method of manufacturing a catalytic core for a catalytic converter; Figure 10 is a flowchart illustrating a second method of manufacturing a catalytic core for a catalytic converter; Figure 11 is an SEM image of a first surface formed by additive manufacture, Figure 12 is an SEM image of a second surface formed by additive manufacture; Figure 13 is a schematic cross-sectional view of an electrochemical cell comprising a cathode, an electrolyte and an anode; Figure 14 is a magnified view of region B of Figure 13 showing an interfacial topography of an interface between the cathode and the electrolyte, Figure 15 is a schematic cross-sectional view of an alternative interfacial topography; and Figure 16 is a schematic cross-sectional view of a further alternative interfacial topography.

Detailed description

With reference to Figure 1, a catalytic converter 1 comprises a housing 2 extending between a fluid inlet 3 and a fluid outlet 4. The housing 2 contains a catalytic core 5.

The catalytic core 5 is shown in cross-section in more detail in Figure 2. The catalytic core 5 has a honeycomb structure 6 comprising a plurality of walls 7 defining a plurality of fluid flow channels 8 between a fluid inlet end 9 and a fluid outlet end 10. The surfaces of the walls 7 of the honeycomb structure 6 are catalytically active, that is to say they comprise catalytic material selected to catalyse a chemical reaction which takes place within the catalytic converter 1 when in use.

A region A (indicated by dashed lines in Figure 2) of a surface of a wall 7 of the honeycomb structure 6 is shown in more detail in cross-section in Figure 3. The surface of the wall 7 has a surface topography defined by a repeating pattern of pyramidal surface features 11 extending from a body of the wall 7. The pyramidal surface features 11 are micron-scale in size. That is to say, one or more of the characteristic dimensions of the pyramidal surface features 11 (e.g. the height, h, of the surface features, measured in a direction locally perpendicular to the profile of the body of the wall,7 and the base width, w, of the surface features, measured in a direction locally parallel to the profile of the body of the wall 7) are micron-scale, i.e. between about 1 pm and about 999 pm.

In use, fluid for catalytic conversion (such as exhaust gas exiting an internal combustion engine) flows sequentially into the catalytic converter through the fluid inlet 3, through the catalytic core 5 (from the fluid inlet end 9 to the fluid outlet end 10 by way of the fluid flow channels 8) and out through the fluid outlet 4. As the fluid flows along the fluid flow channels 8 inside the catalytic core 5, catalytic conversion of the fluid takes place by virtue of the catalytically active material on the surfaces of the walls 7. In particular, catalysis of the catalytic conversion reaction(s) takes places at the surfaces of the walls. Because the walls 7 have surfaces having surface topographies defined by pyramidal surface features 11, the overall geometric surface area of catalytically active wall surface exposed to the fluid flow is substantially greater than it would be if the walls 7 had flat surface topographies. Catalysis of the catalytic conversion reaction(s) in the fluid flowing through the fluid flow channels 8 is therefore enhanced in comparison to known catalytic converters which generally include catalytic cores containing structures having flat or smooth surfaces.

The skilled person will appreciate that many different surface topographies, which increase the overall geometric surface area of catalytically active wall surface exposed to fluid flow, are possible. For example, Figure 4 shows an alternative structure for region A (indicated by dashed lines in Figure 2) of a surface of the wall 7 which has a surface topography defined by a repeating pattern of surface features 12. The surface features 12 may take any suitable shape (as indicated by the use of dashed lines), such as columns, cylinders, truncated cylinders, cones, conical frusta, prisms, truncated prisms, pyramids, cuboids, walls, fins, gratings, domes, spirals, helices or clavates, or any combination thereof.

The surface features 12 may be arranged (e.g. grouped and aligned with one another) to direct fluid flow along the wall surface and/or to disrupt fluid flow along the wall surface. The design and arrangement of the surface features 12 may therefore be tailored to reduce and/or increase turbulence in the fluid flow, dependent on the particular application.

It will also be appreciated that the dimensions of the surface features 12 can vary. Generally, however, the characteristic dimensions of the surface features 12, in a direction locally perpendicular to the profile of the body of the wall, should be less than about 1 mm. Restricting the maximum characteristic dimensions of the surface features 12 in a direction locally perpendicular to the profile of the body of the wall ensures that the surfaces features do not obstruct fluid flow along the fluid flow channels.

In some examples, the surface features 12 are micron-scale surface features (i.e. where one or more or all of the characteristic dimensions of the surface features 12 are between about 1 pm and about 999 pm). In some examples, the surface features 12 are nanoscale surface features (i.e. where one or more or all of the characteristic dimensions of the surface features 12 are between about 1 nm and about 999 nm).

In some examples, the surface features 12 are micron-scale primary surface features and at least some of the micron-scale primary surface features further comprise nanoscale secondary surface features. For example, Figure 5 shows an alternative structure for region A (indicated by dashed lines in Figure 2) of a surface of the wall 7 which has a surface topography defined by a repeating pattern of generally pyramidal surface features 13. The surface features 13 have micron-scale characteristic dimensions overall, but also include nanoscale secondary surface features 14 which protrude from one face of each generally pyramidal surface feature 13. Such a structure enables the overall geometric surface area of catalytically active wall surface exposed to fluid flow to be increased even further.

It will further be appreciated that the honeycomb structure 6 can be replaced by any suitable network structure known in the art, as long as the network structure provides fluid flow channels for exposing fluid to catalytically active material as fluid flows through the catalytically active core. The fluid flow channels are preferably configured to provide a torturous path for fluid flow. Alternatives to honeycomb structures include foam structures and lattice structures.

The network structure (i.e. the honeycomb, foam or lattice structure) may be manufactured from any suitable catalytically active material known in the art. The skilled person will appreciate that a catalytically active material is selected for the chosen application of the catalytic converter, i.e. for the specific reaction(s) which the catalytic converter is designed to catalyse. Suitable catalytically active materials may include catalytically active metals (such as platinum (Pt), palladium (Pd), rhodium (Rh), copper (Cu), nickel (Ni), cerium (Ce), iron (Fe) and/or manganese (Mn)). More specifically, catalytically active precious metals (platinum (Pt), palladium (Pd) and/or rhodium (Rh)) may be used. The catalytically active material may be in the form of particles, for example nanoparticles, or a thin film.

In some examples, the network structure is manufactured from both catalytically inactive material and catalytically active material. For example, Figure 6 illustrates an embodiment in which a body 15 includes a catalyst support 16 made of catalytically inactive material and a catalytically active coating 17 containing catalytically active material. The thickness of the catalytically active coating is relatively uniform across the catalyst support. As can be seen in Figure 6, the shape of the catalyst support defines the shape and size of pyramidal surface features 18.

The catalyst support may be made of any suitable catalytically inactive material known in the art. Suitable catalytically inactive materials include catalytically inactive ceramics, such as cordierite or alumina, catalytically inactive metals, such as an iron-based alloys (e.g. stainless steel or Kanthal), or catalytically inactive polymers. The catalytically active coating may contain any suitable catalytically active material and, optionally, catalytically inactive material, such as titania, alumina or silica.

The catalytic core may be manufactured using any suitable manufacturing methods known in the art. However, additive manufacturing methods are particularly suitable for forming complex network structures having surface topographies defined by repeating patterns of micron-scale and/or nanoscale surface features. Suitable manufacturing methods include selective laser melting (i.e. laser powder bed fusion) and selective electron-beam melting (i.e. electron-beam additive manufacturing). Such additive manufacturing methods enable particularly complex surface topographies to be manufactured, such complex topographies not being achievable using conventional catalytic core manufacturing methods such as the extrusion of metals or the shaping and sintering of metal or ceramic powders.

Figure 7 illustrates schematically additive manufacturing apparatus 100 for carrying out selective laser melting. The apparatus 100 includes a substrate 101 and a processor-controlled laser 102. In use, a layer of powdered material (e.g. powdered metal) 103 is applied to the substrate 101. As illustrated in Figure 8, a processor 106 of the laser 102 communicates with a computer readable medium 107 storing computer executable instructions 108 for controlling the behaviour of the laser. The laser 102 is controlled by the processor 106 to direct a laser beam 104 to selectively fuse regions 105 of the layer of powdered material 103. Following selective fusion of regions of the layer of powdered material 103, a fresh layer of powdered material is applied on top of the previous layer and the fusion process is repeated. By sequentially applying and selectively fusing layers of powdered material, it is possible to build up a complex, three-dimensional fused structure. In selective electron-beam melting, the laser beam is replace by an electron beam.

Figure 9 illustrates schematically a method for manufacturing a catalytic core using additive manufacturing apparatus. At step 200, the additive manufacturing apparatus deposits material to form a network structure defining a plurality of fluid flow channels and comprising a surface having a surface topography defined by a repeating pattern of micron-scale and/or nanoscale surface features extending from a body of the network structure.

Figure 10 illustrates an alternative method for manufacturing a catalytic core using additive manufacturing apparatus. At step 300, the additive manufacturing apparatus deposits catalytically inactive material to form a catalyst support of a network structure.

At step 301, the catalyst support is coated with catalytically active material, for example by electrodeposition or washcoating methods, or by suitable chemical vapour deposition or physical vapour deposition methods.

Figure 11 is a Scanning Electron Microscope (SEM) image of a first example surface having a surface topography defined by a repeating pattern of surface features obtained by selective laser melting. In this example, the surface features are elongate walls spaced uniformly apart and arranged parallel to one another. Both the height and thickness of the elongate walls are on the micron-scale. The surface topography also includes smaller secondary surface features protruding from the elongate wall primary surface features. These smaller secondary surface features are a direct result of the selective laser melting process.

Figure 12 is a Scanning Electron Microscope (SEM) image of a second example surface having a surface topography defined by a repeating pattern of primary and secondary surface features obtained by selective laser melting. In this example, the primary surface features are elongate walls spaced uniformly apart and arranged parallel to one another. Both the height and thickness of the elongate walls are on the micron-scale. The primary surface features are decorated with smaller secondary surface features protruding from the elongate walls.

The skilled person will appreciate that additive manufacturing methods such as selective laser melting or electron-beam melting may be used to manufacture other types of component having surface topographies defined by repeating patterns of nanoscale and/or micron-scale surface features.

For example, Figure 13 shows an electrochemical cell 400 comprising a cathode 401 and an anode 403 separated by an electrolyte 402. The cathode 401 and the anode 403 are solid. In the example shown in Figure 13, the electrolyte 402 is also solid, but the skilled person will appreciate that liquid or gel electrolytes are also possible. The electrochemical cell 400 may also contain any other standard cell components known in the art, such as cathodic and/or anodic current collectors, membranes, a housing, sealant, etc. A region B (indicated by dashed lines in Figure 13) of an interface between the cathode 401 and the electrolyte 402 is shown in more detail in cross-section in Figure 14. The interface has an interfacial topography defined by a repeating pattern of interfacial features 404 extending from the cathode 401 into the electrolyte 402. The interfacial features 404 are micron-scale in size. That is to say, one or more of the characteristic dimensions of the interfacial features 404 are micron-scale, i.e. between about 1 pm and about 999 pm. The interfacial features 404 may take any suitable shape (as indicated by the use of dashed lines), such as columns, cylinders, truncated cylinders, cones, conical frusta, prisms, truncated prisms, pyramids, cuboids, walls, fins, gratings, domes, spirals, helices or clavates, or any combination thereof.

The electrochemical cell 400 may be manufactured by sandwiching electrolyte 402 between the cathode 401 and the anode 403. Accordingly, the interfacial features 404 may be surface features 404 which define a surface topography of a surface of the cathode 401 which contacts the electrolyte 402.

It will be appreciated that the presence of the surface features 404 increases the geometric interfacial area between the cathode 401 and the electrolyte 402 in comparison to electrochemical cells having smooth or flat interfaces. An increase in interfacial surface area can lead to an increase in the electrochemical cell's capacity to store charge (i.e. an increase in the stored energy density), an increase in electrochemical cell reaction rates, a reduction in charge time, improved mass and charge transfer and an increase in the maximum number of charge-discharge cycles possible.

In some examples, the interfacial or surface features 404 are micron-scale features (i.e. where one or more or all of the characteristic dimensions of the features 404 are between about 1 pm and about 999 pm). In some examples, the interfacial or surface features 404 are nanoscale features (i.e. where one or more or all of the characteristic dimensions of the features 404 are between about 1 nm and about 999 nm).

In some examples, the interfacial features 404 are micron-scale primary features and at least some of the micron-scale primary features further comprise nanoscale secondary features. For example, Figure 15 shows an alternative structure for region B of an interface, between the cathode 401 and the electrolyte 402, which has an interfacial topography defined by a repeating pattern of generally pyramidal interfacial features 405. The interfacial features 405 have micron-scale characteristic dimensions overall, but also include nanoscale secondary interfacial features 406 which protrude from one face of each generally pyramidal interfacial feature 405. Such a structure enables the overall geometric interfacial area between the cathode 401 and the electrolyte 402 to be increased even further.

The cathode may be manufactured from any suitable cathode material known in the art. The skilled person will appreciate that a cathode material is selected for the chosen type of electrochemical cell and typically depends on the materials selected for both the electrolyte and the anode. Nevertheless, cathode materials are generally electrically conductive and may therefore be made of metals or metalloids such as aluminium, copper, germanium, calcium, iron, lithium, magnesium, potassium, sodium, silicon, tin or zinc or electrically conductive non-metals such as carbon (for example, in the form of graphite).

The anode may be manufactured from any suitable anode material known in the art. The skilled person will appreciate that an anode material is selected for the chosen type of electrochemical cell and typically depends on the materials selected for both the electrolyte and the cathode. Nevertheless, anode materials are generally electrically conductive and may therefore be made of metals or metalloids such as aluminium, copper, germanium, calcium, iron, lithium, magnesium, potassium, sodium, silicon, tin or zinc or electrically conductive non-metals such as carbon (for example, in the form of graphite). In some examples, for example in which the electrochemical cell is a lithium-ion cell, the anode may be made of an intercalated compound, such as an intercalated lithium compound. Example intercalated lithium compounds include lithium cobalt oxide (LiCo02), lithium iron phosphate (LiFePO4), lithium-ion manganese oxide (LiMn204 or Li2Mn03), lithium nickel cobalt aluminium oxide (LiNiC0A102) and lithium nickel manganese cobalt oxide (LiNiMnC002)* In the examples shown in Figures 13 to 15, the cathode has a surface topography defined by a repeating pattern of micron-scale and/or nanoscale surface features. However, it will be appreciated that, in other examples, it is the anode which has a surface topography defined by a repeating pattern of micron-scale and/or nanoscale surface features. In some examples, both the cathode and anode have surface topographies defined by repeating patterns of micron-scale and/or nanoscale surface features. That is to say, the cathode-electrolyte interface and/or the anode-electrolyte interface has an interfacial topography defined by a repeating pattern of micron-scale and/or nanoscale interfacial features.

In general, therefore, one or more of the electrodes of the electrochemical cell has a surface topography defined by a repeating pattern of micron-scale and/or nanoscale surface features or, equivalently, one or more electrode-electrolyte interfaces of the electrochemical cell has an interfacial topography defined by a repeating pattern of micron-scale and/or nanoscale interfacial features.

In some examples, the electrode having a surface topography defined by a repeating pattern of micron-scale and/or nanoscale surface features is manufactured from two or more electrode materials. For example, Figure 16 illustrates an embodiment in which a cathode 401 includes a cathode support 407 made of a first cathode material, such as a metal, and a coating 408 of a second cathode material, such as carbon. The thickness of the coating is relatively uniform across the cathode support. As can be seen in Figure 16, the shape of the cathode support defines the shape and size of pyramidal surface features 409. Such an electrode design may be beneficial when it is challenging to manufacture complex surface topographies accurately from the second cathode material alone, or where the second cathode material is more expensive than the first cathode material. For example, additive manufacturing methods (such as selective laser melting or electron-beam melting) may be used to form the cathode support 407 from the first cathode material (e.g. metal), while the second cathode material (e.g. carbon) may subsequently be applied as a coating (for example, using chemical vapour deposition or physical vapour deposition methods). It will be appreciated that similar structures may be applied to anodes.

It will be understood that the invention is not limited to the embodiments described above and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims (22)

1. Claims 1. A catalytic core (5) for a catalytic converter (1), the catalytic core (5) having a network structure (6) defining a plurality of fluid flow channels (8) for receiving a flow of fluid for catalytic conversion, wherein a catalytically active surface of the network structure (6) has a surface topography defined by a repeating pattern of surface features (11, 12, 13, 18) extending from a body (7, 15) of the network structure, each surface feature (11, 12, 13, 18) having a characteristic dimension, in a direction locally perpendicular to a profile of the body (7, 15), of less than about 1 mm.
2. 2. The catalytic core (5) according to claim 1, wherein the characteristic dimension of each surface feature (11, 12, 13, 18), in the direction locally perpendicular to the profile of the body (7, 15), is no less than about 1 nm, for example no less than about 1 pm, or no less than about 10 pm.
3. 3. The catalytic core (5) according to claim 1 or claim 2, wherein each surface feature (11, 12, 13, 18) has characteristic dimensions, in any direction locally parallel to the profile of the body (7, 15), of no greater than about 250 pm, for example no greater than about 100 pm.
4. 4. The catalytic core (5) according to any preceding claim, wherein the surface features (13) are micron-scale primary surface features (13) and a plurality of said micron-scale primary surface features (13) further comprise nanoscale secondary surface features (14).
5. The catalytic core (5) according to any preceding claim, wherein the surface features (11, 12, 13, 18) comprise columns, cylinders, truncated cylinders, cones, conical frusta, prisms, truncated prisms, pyramids, cuboids, walls, fins, gratings, domes, spirals, helices and/or clavates.
6. The catalytic core (5) according to any preceding claim, wherein at least some of the surface features (11, 12, 13, 18) cooperate to direct fluid flow across a region of the catalytically active surface.
7. The catalytic core (5) according to any preceding claim, wherein the catalytically active surface comprises catalytically active material, for example catalytically active metal, such as platinum, palladium, rhodium, copper, nickel, cerium, iron and/or manganese.
8. 8. The catalytic core (5) according to claim 7, wherein the network structure (6) comprises a catalyst support (16) having a catalytically active coating (17), the catalyst support (16) comprising catalytically inactive material and the catalytically active surface being a surface of the catalytically active coating (17).
9. 9. The catalytic core (5) according to claim 8, wherein the catalyst support (16) defines the shape of the surface features (18) such that the surface features (18) each have the characteristic dimensions according to any of claims 1 to 3.
10. 10. The catalytic core (5) according to claim 8 or claim 9, wherein the catalytically inactive material is a catalytically inactive ceramic or a catalytically inactive metal.
11. 11 The catalytic core (5) according to any preceding claim, wherein the network structure (6) is a cellular structure, such as a foam structure or a honeycomb structure, or a lattice structure.
12. 12. The catalytic core (5) according to any preceding claim, wherein the network structure (6) is a least partially additively manufactured such that the surface features (11, 12, 13, 18) are defined by additive manufacture.
13. 13. A catalytic converter (1) comprising a catalytic core (5) according to any preceding claim, the catalytic core (5) being provided within a housing (2) defining a fluid flow passage from a fluid inlet (3), through the catalytic core (5), to a fluid outlet (4).
14. 14. A method of manufacturing a catalytic core (5) for a catalytic converter (1), the method comprising: depositing material, by additive manufacturing apparatus (100), to form a network structure (6) defining a plurality of fluid flow channels (8) for receiving a flow of fluid for catalytic conversion, the network structure (6) comprising a surface having a surface topography defined by a repeating pattern of surface features (11, 12, 13, 18) extending from a body (7, 15) of the network structure (6), each surface feature (11, 12, 13, 18) having a characteristic dimension, in a direction locally perpendicular to a profile of the body (7, 15), of less than about 1 mm.
15. 15. The method according to claim 14 comprising: depositing catalytically active material, by additive manufacturing apparatus (100), to form at least a surface portion of the network structure (6) such that at least a portion of the surface of the network structure (6) is a catalytically active surface.
16. 16. The method according to claim 14 comprising: depositing catalytically inactive material, by additive manufacturing apparatus (100), to form a catalyst support (16) of the network structure (6); and coating at least a portion of the catalyst support (16) with catalytically active material.
17. 17. The method according to any of claims 14 to 16 comprising: providing or producing a digital design model for the network structure (6); and controlling the additive manufacturing apparatus (100) using the digital design model to form the network structure (6).
18. 18. The method according to any of claims 14 to 17, wherein the additive manufacturing apparatus is selective laser melting apparatus or electron-beam melting apparatus.
19. 19. A digital design model for the network structure (6) of the catalytic core (5) of any of claims 1 to 12.
20. 20. A computer program comprising instructions (108) to cause an additive manufacturing apparatus (100) to carry out the method according to any of claims 14 to 18 and/or to product the network structure (6) of the catalytic core (5) of any of claims 1 to 12.
21. 21 A non-transitory computer-readable medium (107) storing the digital design model according to claim 19 and/or the computer program according to claim 20.
22. 22. A data carrier signal carrying the digital design model according to claim 19 and/or the computer program according to claim 20.