Method for producing a precious metal mesh on a flat knitting machine

Abstract

The invention relates to a method for producing a double-layered precious metal mesh on a flat-bed knitting machine having a first needle bed and a second needle bed. The method comprises providing at least one precious metal containing thread and knitting the precious metal mesh. A first layer and a second layer of the precious metal mesh are knitted simultaneously on the first needle bed and the second needle bed and a support mesh is knitted on the first needle bed and the second needle bed using a support thread. Adjacent edges of the support mesh are connected to the two layers of the precious metal mesh via a connecting stitch and are knitted in a knitting row containing the connection via both needle beds.

Description

Technical Field

[0001] This invention relates to a method for producing a double-layer precious metal mesh on a flat knitting machine including a first needle bed and a second needle bed. The method includes providing at least one precious metal-containing filament and knitting the precious metal mesh. The first and second layers of the precious metal mesh are knitted simultaneously on the first and second needle beds, and a support mesh is knitted on the first and second needle beds using support yarns. Thus, adjacent edges of the support mesh are connected to the two layers of the precious metal mesh via connecting knitting stitches, and the knitting is performed across the two needle beds in a knitting row containing the connection. Background Technology

[0002] The heterogeneous noble metal catalytic oxidation of ammonia (NH3) to nitric acid (HNO3) (Ostwald process) or the production of hydrogen cyanide (HCN) (Androusso process) is extremely important due to the central relevance of the products to the chemical industry. Catalyst systems for this purpose are typically introduced into the reaction zone of a flow reactor in the form of a breathable fabric in a plane perpendicular to the direction of fresh gas flow. Collection or trapping systems for recovering catalytically active components from evaporation are also often based on this mesh structure. Typically, multiple meshes are advantageously arranged one after another and combined to form a catalyst mesh stack. Individual meshes consist of fine noble metal wires primarily containing platinum (Pt), palladium (Pd), rhodium (Rh), or alloys of these metals. Specifically, trapping meshes may also contain additional components, such as nickel.

[0003] Several methods are known for producing this type of knitted fabric, such as machine weaving, warp knitting, and weft knitting. Machine weaving and warp knitting are particularly suitable for producing rectangular webs with a homogeneous material distribution and structure. They offer little flexibility in terms of the shape and material variability of the product to be manufactured. In an additional process step, the web must be cut from the manufactured web to fit the size and shape of the reactor, resulting in edge material containing precious metal components. Furthermore, the machines used require long setup times and high material input.

[0004] In comparison, weft knitting offers greater flexibility: the knitting pattern, the yarn (in terms of both thickness and material), the needles, and the yarn tension can be used to change both the weight per unit area and the available structure, elasticity, and strength of the knitted fabric. Another advantage is a significantly shorter machine setup time. It is also possible to use different materials in a single knitted fabric; in so-called intarsia knitting, for example, different areas can be made from different yarns or silks. In principle, the length of a knitted fabric is unlimited; however, in the case of a flat knitting machine, the maximum width is determined by the width of the needle bed.

[0005] Knitting can be performed using either flat knitting machines or circular knitting machines. In a circular knitting machine, needles are arranged in a circular needle bed, and the yarn or filament is supplied in a circular motion. These machines are primarily used for the production of tubular knitted fabrics. However, on a flat knitting machine, the shape and size of the knitted fabric can be varied. Flat knitting machines may also include more than one needle bed, with yarn or filament being guided back and forth between the needle beds during production using a guide wire.

[0006] The use of two needle beds allows for the production of single-layer or double-layer knitted fabrics. In principle, single-layer knitted fabrics can be produced in two ways: in one way, only one needle bed is in operation, i.e., stitches are formed and knitted together only on one needle bed. In another way, stitches produced on the first needle bed can be knitted together with stitches produced on the second needle bed, i.e., the yarn is guided back and forth between the two needle beds in the right and / or wrong rows. Therefore, when knitting is performed in parallel on two needle beds, a double-layer knitted fabric is produced, and the stitches produced on the first needle row are not knitted or are selectively knitted together with the stitches produced on the second needle bed only via edge stitches. In this production method, two single-layer knitted fabrics or knitted layers can also be produced in parallel on the first and second needle beds.

[0007] Knitting of precious metal mesh is described in EP 0544710 A1. For this purpose, EP 3795728 A1 uses a flat knitting machine. It is described that individual layers produced on different needle beds can be interconnected on one side of two knitted surfaces by means of connecting knitting rows. This allows the production of knitted surfaces with a greater width than previously possible.

[0008] EP 0364153 A1 describes the use of additional, precious metal-free yarns during the knitting of precious metal webs, which improves process stability. The additional yarns are knitted in parallel with the precious metal and, if necessary, can be removed from the homogeneous knitted fabric produced from the precious metal and yarn materials after the knitting process. In EP 3779005 A1, this method is further developed so that the additional yarns and precious metal are knitted simultaneously, not in parallel. This means that areas free of precious metals can be retained in the finished knitted fabric, resulting in a reduction in the amount of precious metal used.

[0009] However, it has been shown that simultaneous knitting of yarns or threads containing and without precious metals presents specific challenges to the knitting process and is likely to cause warping of the knitted fabric due to the different material properties, thus leading to instability in the production process. This instability can manifest itself as yarn breakage and irregularities in structural and mechanical properties during the knitting process, both of which can result in products of poor quality.

[0010] Therefore, the problem solved by the present invention is to provide a method with high process stability for producing precious metal mesh on a flat knitting machine using filaments containing precious metals and yarns without precious metals. Summary of the Invention

[0011] The problem is addressed by a method for producing a double-layer precious metal mesh on a flat knitting machine, the flat knitting machine comprising a first needle bed and a second needle bed, the method comprising the following steps:

[0012] - Provide at least one wire containing a precious metal.

[0013] - Provide at least one support line that does not contain precious metals.

[0014] - Knit the first layer of the precious metal mesh on the first needle bed and knit the second layer of the precious metal mesh on the second needle bed.

[0015] The first layer includes adjacent edges S11 and S12, and the second layer includes adjacent edges S21 and S22, wherein adjacent edge S11 is at least partially adjacent to adjacent edge S21, and adjacent edge S12 is at least partially adjacent to adjacent edge S22.

[0016] - A support mesh is knitted on the first and second needle beds using at least one support yarn that does not contain precious metals. The support mesh includes an adjacent edge SH and an edge KH opposite to the adjacent edge SH, the adjacent edge SH being adjacent to the adjacent edges S11 and S21 of each of the two layers of the precious metal mesh.

[0017] All knitting processes occur simultaneously.

[0018] The method is characterized in that the adjacent edge SH of the support net is connected to the corresponding adjacent edges S11 and S21 of the two layers of the precious metal net via at least one knitting stitch, and the method is characterized in that the support net is knitted in a knitting row by two needle beds using connecting stitches on which the adjacent edge SH of the support net is connected to the corresponding adjacent edges S11 and S21 of the two layers of the precious metal net.

[0019] In the context of this invention, it is surprising to note that knitting the support mesh across two needle beds in the region where the support mesh is connected to the precious metal mesh has a stabilizing effect on the knitting process. In other words, the precious metal mesh, at least partially embedded in the single-layer support structure, has the effect of reducing process disturbances in the form of breakage of precious metal-containing threads or irregularities in precious metal knitted fabrics.

[0020] The method according to the invention relates to knitting on a flat knitting machine comprising a first needle bed and a second needle bed.

[0021] Knitting is characterized by the row-by-row production of the resulting knitted fabric, in which interlocking stitches are formed. During the knitting process on a flat knitting machine comprising two needle beds, a knitted row is first formed on at least one of the needle beds. Then, the next knitted row is formed in the knitting direction, wherein the portion of the knitted fabric containing the first knitted row is referred to hereinafter as the "bottom". Thread or yarn is guided from one side of one or more needle beds to the other and back. If "thread" is referred to hereinafter, the relevant description is also intended to apply to the corresponding "yarn". Thus, a knitted row comprises a right-side row and a wrong-side row, which is produced by a guide wire. In this case, the thread can be guided in the knitted row on only one needle bed or on two needle beds. Typically, the thread for the entire knitted row can be guided first on the first needle bed (right-side row) and then guided in the opposite direction on the same needle bed or the second needle bed (wrong-side row). However, the thread can also be guided alternately on both needle beds in the right-side row and / or the wrong-side row, wherein a connection is created between the stitches within a knitted row on the two needle beds. Guide lines can be drawn across the entire width of one or more needle beds, but it is also possible to knit only a portion of the width of the needle bed. The width and shape of the knitted fabric can be determined based on the width of the needle bed.

[0022] In the method according to the invention, all knitting processes occur simultaneously. This means that multiple sub-regions of the knitted fabric to be produced are knitted simultaneously on two needle beds, i.e., these sub-regions are not produced one after another in multiple knitting steps.

[0023] The method involves providing at least one wire containing a precious metal.

[0024] The term "precious metal-containing wire" is understood to mean a wire composed of or containing a significant proportion (>50% by weight) of at least one precious metal. In the context of this invention, "precious metal" is understood to mean a metal selected from platinum, gold, and silver. Platinum should be understood to mean the so-called platinum group metals, namely platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), and ruthenium (Ru).

[0025] At least one wire containing a precious metal is preferably composed of platinum, a platinum alloy, palladium, or a palladium alloy. The platinum-based alloy contains more than 50% by weight of platinum, and other alloying components particularly include palladium, rhodium, and ruthenium. The palladium-based alloy contains more than 50% by weight of palladium.

[0026] Preferably, at least one of the precious metal-containing wires is composed of an alloy selected from platinum with 1 to 15 wt% rhodium, platinum with 1 to 15 wt% rhodium and 0.1 to 20 wt% palladium, platinum with 1 to 15 wt% rhodium, 0.1 to 20 wt% palladium and 0.1 to 5 wt% ruthenium, platinum with 1 to 15 wt% rhodium, 0.1 to 40 wt% palladium and 0.001 to 5 wt% iridium, platinum with 1 to 15 wt% rhodium, 0.1 to 20 wt% palladium and 0.001 to 5 wt% iridium, and platinum with 1 to 15 wt% rhodium, 0.1 to 20 wt% palladium and 0.001 to 5 wt% iridium. % tantalum, platinum and 1% to 15% rhodium, 0.001% to 5% iridium and 0.001% to 5% tantalum, palladium and 1% to 25% platinum, palladium and 1% to 20% platinum and 1% to 15% rhodium, palladium and 1% to 25% tungsten, palladium and 1% to 15% nickel, palladium and 0.001% to 5% rhodium, palladium and 1% to 15% copper, palladium and 1% to 15% copper and 1% to 15% nickel, and palladium and 1% to 30% cobalt.

[0027] Preferably, a precious metal-containing wire with a diameter of 40µm to 150µm, preferably 50µm to 130µm, is used.

[0028] At least one wire containing a precious metal may be designed as a round wire, i.e., having a circular cross-section. In another embodiment, the wire may be designed as a flat round wire or as a wire with a different cross-section.

[0029] At least one precious metal-containing wire may comprise multiple wires, also referred to in this case as filaments, which are preferably twisted together. The filaments may all be composed of the same material, i.e., all containing precious metals, or they may be composed of different materials, and the different materials need not all contain precious metals.

[0030] In many cases, it may be advantageous to knit two or more precious metal-containing filaments together. In other words, multiple precious metal-containing filaments can be guided together when forming a stitch. When knitting with multiple filaments, in one embodiment, the precious metal-containing filaments are composed of the same material, and in another embodiment, precious metal-containing filaments composed of at least two different materials can be used. The multiple filaments may have the same or different diameters.

[0031] In the method according to the invention, a first layer of a double-layer precious metal mesh is knitted on a first needle bed while a second layer of the precious metal mesh is simultaneously knitted on a second needle bed. In other words, during the knitting process, the two parts of the precious metal mesh to be produced are each knitted simultaneously on a separate needle bed, so the two layers are not produced one after the other.

[0032] In the context of this invention, "double-layer precious metal mesh" is understood to mean a precious metal mesh comprising two layers, wherein these layers may be interconnected via one or more adjacent edges of their respective adjacent edges or may not be connected at their adjacent edges. The two layers lie on top of each other, i.e., they at least partially overlap in a region of their surface area. As in the case of this invention, a precious metal mesh interconnected on one side via adjacent edges of two layers is also referred to as a double-layer precious metal mesh. A single-layer precious metal mesh can be obtained by folding along a common adjacent edge.

[0033] The first and second layers of the double-layer precious metal mesh each include two adjacent edges; that is, each layer includes one adjacent edge on one side and another adjacent edge on the other side. The first layer includes adjacent edges S11 and S12, and the second layer includes adjacent edges S21 and S22. The sides of the precious metal layers should be understood in relation to the positions of the adjacent edges perpendicular to the knitting direction on the two needle beds. Depending on the shape of the relevant layers, the adjacent edges of the layers may not intersect, as in the case of rectangular layers, or they may intersect, as in the case of semi-circular layers.

[0034] Adjacent edges may be interconnected, preferably by at least one connecting knitted stitch. However, adjacent edges may also be adjacent to each other without being connected. Adjacent edges are formed from bottom to top in the knitting direction during the knitting process. The two noble metal layers may also include an upper edge or adjacent edge and / or a lower edge or adjacent edge; the presence of these edges depends on the shape of the associated layers. For example, a rectangular layer includes a lower edge or adjacent edge and an upper edge or adjacent edge in addition to two lateral adjacent edges, while a semi-circular layer does not include any additional edges or adjacent edges.

[0035] The lower edge is understood as the edge that forms first in the knitting direction, that is, at the bottom of the knitted fabric. Therefore, the upper edge is understood as the edge that forms later in the knitting direction.

[0036] The adjacent edge S11 of the first layer of the precious metal mesh is at least partially adjacent to the adjacent edge S21 of the second layer of the precious metal mesh. Additionally, the corresponding other adjacent edges of the first and second layers of the precious metal mesh, namely adjacent edges S12 and S22, are at least partially adjacent to each other. In this context, "at least partially adjacent to each other" is understood to mean that the adjacent edges are adjacent to each other along a portion of their length in the knitting direction, i.e., along the portion of the knitted row that forms them. In other words, the adjacent edges may also be at least partially offset from each other.

[0037] The first and second layers of the double-layer precious metal mesh can be at least partially connected at their adjacent edges by connecting knitted stitches. This means that the two layers are interconnected at their edge stitches via stitches formed from at least one precious metal-containing wire. This connection between the first and second layers of the double-layer precious metal mesh can be made on only one side or on both sides. One or more connections can be made along the entire length of the adjacent edges or a portion of its length. It may be advantageous to make the connection on one side along the entire length of the adjacent edges.

[0038] In another embodiment, connections can be made on both sides of the first and second layers of the double-layer precious metal mesh, at least at the corresponding adjacent edges of the two layers. These partial connections can be made at the same height, i.e., in one or more identical knit rows, or at different heights. Partial connections can be made on both sides along the same length of the adjacent edges, i.e., along the same number of knit rows. However, partial connections can also be made on both sides along the length of the adjacent edges. In a preferred embodiment, the partial connections are made at least partially on the same knit rows. In this embodiment, the knitting is therefore completed at least partially in a circle, i.e., circular knitting; in other words, a loop structure is created via these knit rows. It has been shown that knitting such a partially loop structure can have a further positive impact on the stability of the knitting process.

[0039] The reference point for the height of a knitted fabric is the bottom row of the fabric. Even if the knitting of layers begins in different rows, the overall height of the knitted fabric remains the same; in other words, layers of knitted fabric can include different numbers of rows at different heights.

[0040] The first and second layers of the double-layer precious metal mesh can preferably be knitted from a single precious metal-containing filament or multiple precious metal-containing filaments having the same composition. However, the two layers can also be knitted from a single precious metal-containing filament or multiple precious metal-containing filaments with different compositions.

[0041] Precious metal-containing filaments of the same or different diameters can be used to knit the first and second layers of a double-layer precious metal mesh. It has been shown that it is advantageous for the first and second layers of the precious metal mesh to be knitted from a single precious metal-containing filament or multiple precious metal-containing filaments of the same diameter.

[0042] The first and second layers of the double-layer precious metal mesh can be knitted with the same or different knitting patterns. For example, different knitting patterns can be produced from different stitch lengths, floats, or pleats. In a preferred embodiment, the first and second layers of the precious metal mesh are knitted with the same knitting pattern.

[0043] The first and second layers of the double-layer precious metal mesh may have the same or different lengths in the knitting direction and / or the same or different widths perpendicular to the knitting direction. Preferably, the first and second layers of the precious metal mesh have the same length and the same width.

[0044] The first and second layers of the double-layer precious metal mesh may have the same shape or different shapes. It is particularly preferable that the first and second layers of the double-layer precious metal mesh have the same shape. It may be advantageous for the first and second layers of the double-layer precious metal mesh to have a semi-circular shape. It may be particularly advantageous for the two semi-circles to have the same width and the same length.

[0045] In a preferred embodiment, the first and second layers of the double-layer precious metal mesh are congruent; in other words, the two layers may have the same length, the same width, and the same shape.

[0046] The method involves providing at least one support wire that does not contain precious metals.

[0047] Considering the ultimate purpose of the double-layer precious metal mesh and any additional steps in the manufacturing process, suitable precious metal-free support wires can be selected through routine testing. Preferred precious metal-free support wires can be removed after the production of the precious metal mesh, for example, by dissolving, cutting, melting, or burning in an acidic or alkaline medium. Such support wires can have natural or synthetic organic or inorganic properties. Examples of suitable materials are polyamides, polyesters, cellulose fibers, cotton, acrylic-styrene polymers, nylon, PVA and other vinyl polymers, alginates, copper, silver, aluminum, or even metals with low melting points such as tin alloys and lead alloys.

[0048] At least one support wire without precious metals may consist of only a single wire element; such a single wire element is also referred to as a filament in the case of a wire without precious metals. A support wire without precious metals may also consist of more than one filament, which may advantageously be twisted together. These multiple filaments may be made of the same or different materials.

[0049] In the method according to the invention, at least one support yarn without precious metals is used to knit the support mesh simultaneously with the first and second layers of the double-layer precious metal mesh on the first and second needle beds. In other words, the support mesh is knitted simultaneously with the two layers of the precious metal mesh to be produced, so the two layers and the support mesh are not produced one after the other.

[0050] The term "support web" refers to an area of ​​a knitted fabric that is at least partially knitted using support yarns that do not contain precious metals. Support webs may also include other yarns or filaments.

[0051] The knitted fabric comprises all the knitted rows formed during the method. The knitted fabric includes at least a first and second layer of double-layered precious metal mesh and a support mesh. However, the knitted fabric may also include other sections or areas. Preferably, all the knitted rows of the knitted fabric are knitted on the same width of the needle bed; in other words, the knitted fabric is preferably rectangular.

[0052] The support mesh consists of adjacent edges SH and opposite edges KH. Depending on the shape of the support mesh, the adjacent edges SH and opposite edges KH may not intersect, as in the case of a rectangular support mesh, or they may intersect, as in the case of a semi-circular support mesh. The adjacent edges SH and edges KH are formed from the bottom to the top in the knitting direction during the knitting process.

[0053] In each case, the adjacent edge SH of the support mesh is adjacent to the adjacent edges S11 and S21 of the first and second layers of the double-layer precious metal mesh. In other words, the edge of the support mesh adjacent to the two layers of the double-layer precious metal mesh is called the adjacent edge SH. Therefore, the adjacent edge SH comprises the knitted rows in which both the layer of the double-layer precious metal mesh and the support mesh are knitted. Thus, the opposite edge KH is the edge of the support mesh opposite to the adjacent edge SH in the same knitted row; that is, the adjacent edge SH and edge KH have the same length in the knitting direction. Edge KH does not adjoin either of the two layers of the double-layer precious metal mesh.

[0054] The shape of the edges and adjacent edges of the support mesh is not further restricted. However, it has proven advantageous to design the shape of the support mesh in such a way that the overall shape of the knitted fabric is rectangular. In other words, the support mesh complements the layers of the precious metal mesh in such a way that the overall shape of the knitted fabric, comprising one or more precious metal layers and the support mesh, is rectangular. Therefore, the shape of the support mesh is preferably related to the shape of the first and second layers of the precious metal mesh. For example, if the first and second layers of the precious metal mesh have convex shapes, then the support mesh preferably has a concave shape.

[0055] In a preferred embodiment, the adjacent edge SH has the same length as adjacent edges S11 and S12. In other words, the adjacent edge SH includes the same knitted rows as adjacent edges S11 and S12, and therefore, the support mesh abuts the adjacent edges of the double-layer precious metal mesh over the entire length of the precious metal mesh layer.

[0056] The adjacent edges SH of the support mesh and the corresponding adjacent edges S11 and S21 of the first and second layers of the double-layer precious metal mesh are interconnected via at least one knitting stitch. In other words, the support mesh is at least partially connected to both layers of the double-layer precious metal mesh during the knitting process. This stabilizes the knitting process. It is preferable that the adjacent edges SH of the support mesh are connected to the corresponding adjacent edges S11 and S21 of the first and second layers of the double-layer precious metal mesh along their entire length.

[0057] One or more connecting knitting stitches may be formed from at least one support yarn containing precious metals or not containing precious metals. Preferably, one or more connecting knitting stitches are formed from a support yarn that does not contain precious metals.

[0058] The support mesh is knitted in a knitting row via two needle beds using connecting stitches in which the adjacent edges SH of the support mesh are connected to the corresponding adjacent edges S11 and S21 of the two layers of the precious metal mesh. The term "connecting stitch" is understood to refer to the knitting stitch formed between the first and second needle beds. In other words, the support mesh is at least partially knitted as a single layer. It has been shown that a single-layer design of the support mesh in one or more areas of the layers connected to the precious metal mesh results in improved process stability.

[0059] A support yarn without precious metals can be knitted in parallel with at least one filament containing precious metals; that is, during knitting, a stitch comprising both the filament containing precious metals and the support yarn can be formed. In these cases, the relevant portion of the resulting knitted fabric contains both the material of the precious metal and the support yarn. In other embodiments, the support yarn can also be used in portions or areas of the knitted fabric that do not contain the filament containing precious metals; that is, in these cases, the resulting knitted fabric contains areas with the filament containing precious metals and areas without the filament containing precious metals.

[0060] The support mesh may include multiple regions. For example, the support mesh may also include knitted rows in which no precious metal-containing yarns are used, i.e., only support yarns without precious metals are used for knitting. In other words, the knitted fabric may include regions that do not contain precious metal-containing yarns. In this case, the support mesh may include other edges besides adjacent edges SH and KH. These edges may be formed in knitted rows of stitches in which layers without precious metal mesh are knitted. In other words, the knitted fabric may also include knitted rows formed solely by regions of the support mesh.

[0061] It may be preferable for the support mesh to be knitted into two layers in areas including knitted rows that do not contain yarns containing precious metals. In other words, the support mesh in these knitted rows cannot be knitted using connecting stitches between the first and second needle beds. The two layers can be connected at the edge stitches via connecting knitted stitches; therefore, it may be advantageous for the support mesh to have a tubular structure in these areas. It may also be preferable for the support mesh to be knitted into a single layer in areas that do not contain yarns containing precious metals.

[0062] In a preferred embodiment, the support mesh includes a single-layer knitted area and a double-layer knitted area excluding the precious metal-containing yarn.

[0063] In a preferred embodiment, the support mesh abuts the two layers of the double-layer precious metal mesh only at adjacent edges S11 and S21. It is also preferable that the support mesh abuts the two layers of the double-layer precious metal mesh at corresponding other edges or adjacent edges S12 and S22 of the two layers. The adjacent edges of the support mesh SH and the two adjacent edges S12 and S22 of the two layers of the double-layer precious metal mesh may be interconnected via at least one knitted stitch of the support thread. However, this connection is not mandatory; in such embodiments, these adjacent edges are not interconnected by knitted stitches.

[0064] It is preferable that the support mesh also adjoins the respective lower and / or upper edges of the two layers of the double-layer precious metal mesh. Therefore, the support mesh may only adjoin the lower or upper edges of the two layers of the precious metal mesh, or it may adjoin both the lower and upper edges of the two layers of the precious metal mesh. In such embodiments, the support mesh surrounds the two layers of the double-layer precious metal mesh on at least two sides.

[0065] It may be advantageous for the support mesh to surround both layers of the double-layer precious metal mesh on more than two sides. In a preferred embodiment, the support mesh surrounds at least 50% of the sides of both layers of the double-layer precious metal mesh. This means that at least 50%, preferably at least 60%, and even more preferably at least 80% of the perimeter of both layers of the double-layer precious metal mesh is surrounded by the support mesh. It may be particularly preferred that the support mesh completely surrounds both layers of the double-layer precious metal mesh.

[0066] Preferably, all areas of the support mesh can be knitted from support yarns of the same composition that do not contain precious metals. However, different areas can also be knitted from support yarns of different compositions that do not contain precious metals. Different areas of the support mesh can be knitted using the same or different knitting patterns.

[0067] The method according to the invention may include additional steps.

[0068] The method may include providing at least one additional filament or thread. The appropriate additional filament or thread may be selected depending on its intended use and / or function in the manufacturing process or for subsequent applications to the precious metal mesh. For example, the additional filament may be a non-precious metal filament suitable for stabilizing the precious metal mesh when used in a reactor, such as steel or stainless steel wire. In these cases, the method includes using at least one additional filament or thread to simultaneously knit various areas of the knitted fabric. In this case, the knitted fabric may include portions or areas containing only the additional filament or thread, or portions or areas containing both the additional filament or thread and a precious metal-containing filament, or portions or areas containing both the additional filament or thread and a non-precious metal support thread, or portions or areas containing both the additional filament or thread and a precious metal-containing filament and a non-precious metal support thread.

[0069] Preferably, the support mesh can be removed in a separate step. Suitable methods are known in principle to those skilled in the art and depend on the type of support wire used (either non-precious metal or precious metal-containing). The support mesh can be, for example, decomposed, dissolved, melted, burned, or cut.

[0070] In a further step, one or more connecting stitches between the first and second layers of the double-layer precious metal mesh may be removed on at least one side; in other words, the connection formed between the two layers via edge stitches may be separated on at least one side. This allows the production of a single-layer precious metal mesh that is at least partially connected on only one side of the two layers, i.e., only via one adjacent edge of the two layers. In other words, a single-layer precious metal mesh can thus be obtained. Attached Figure Description

[0071] The invention will be explained in more detail below with reference to the accompanying drawings and examples. However, the invention is not limited to these embodiments.

[0072] Figure 1 This is a schematic diagram of a flow reactor used for heterogeneous catalytic combustion of ammonia.

[0073] Figure 2 This is a schematic diagram of an exemplary front row guide between two needle beds of a flat knitting machine.

[0074] Figure 2 Example A illustrates a wire guide for the front row of lines or wires 12.

[0075] Figure 2 B shows the front row of a single-layer knitted fabric, in which stitches are knitted on the first and second needle beds.

[0076] Figure 3 An embodiment of a double-layer precious metal mesh produced on a flat knitting machine comprising two needle beds using the method according to the invention is shown.

[0077] Figure 3 A and Figure 3 B illustrates a double-layered precious metal mesh 100 consisting of two rectangular layers 101 and 102, wherein... Figure 3 In the front view of A, only the first layer 101 is visible.

[0078] Figure 3 C shows a double-layered precious metal mesh 200 surrounded by a support mesh on both sides.

[0079] Figure 3 D shows a view of a double-layered precious metal mesh 300 surrounded by a support mesh on adjacent sides.

[0080] Figure 3 E shows a view of a double-layered precious metal mesh 400 surrounded by a support mesh on all four sides.

[0081] Figure 3 F shows a double-layered precious metal mesh 500 surrounded by support mesh areas (530, 531, 532, 533) on four sides.

[0082] Figure 3 G shows a view of a double-layer precious metal mesh 600 consisting of two semi-circular layers (only the first layer 601 is visible).

[0083] Figure 3 H shows a double-layered precious metal mesh 700 formed by two semi-circular layers. Detailed Implementation

[0084] Figure 1 This is a schematic diagram of a vertically positioned flow reactor 1 used for the heterogeneous catalytic combustion of ammonia. A catalyst system 2 forms the actual reaction zone of the flow reactor 1. This catalyst system includes catalyst packing 3 and a downstream trapping mesh 4. The catalyst system 3 includes multiple catalyst meshes 6 arranged one after another in the direction of fresh gas flow 5.

[0085] Typically, the catalyst mesh 6 is a knitted mesh, which is produced, for example, from various platinum-rhodium alloys by knitting filaments with a diameter of 76µm. A trapping mesh 4 may also be provided.

[0086] Figure 2 This is a schematic diagram of a guide wire in an exemplary front row of a knitting row between two needle beds 10 and 11 on a flat knitting machine. The needles used during the knitting process are highlighted, and the direction of the guide wire is indicated by arrows. Each circle represents a needle. Figure 2Example A illustrates a guide wire for the thread or yarn 12 used in the right-side row, wherein the stitches are knitted only on the first needle bed. If the stitches are knitted only in one wrong-side row on the first needle bed 10 and in all other complete knitted rows, a single-layer knitted fabric is obtained. If the stitches are knitted in multiple wrong-side rows on the second needle bed 11, a double-layer knitted fabric is obtained. Figure 2 The knitting pattern used in A also contains floats: the stitches are formed only on every other needle in the needle bed. Figure 2 B shows the front row of a single-layer knitted fabric, in which stitches are knitted with thread or silk 12 on the first needle bed 10 and the second needle bed 11.

[0087] Figure 3 An embodiment of a double-layer precious metal mesh that can be produced using the method according to the invention on a flat knitting machine comprising two needle beds is shown.

[0088] Figure 3 A and Figure 3 B illustrates a double-layered precious metal mesh 100 consisting of two rectangular layers 101 and 102, wherein... Figure 3 In the front view of A, only the first layer 101 is visible. Figure 3 B shows a view of a precious metal mesh 100 with a slotted edge 111 along the adjacent edge 111 of the first layer 101 and the adjacent edge 112 of the second layer 102. The adjacent edge 112 of the first layer is congruent to the adjacent edge 113 of the second layer 102. The term "slotted" will indeed be understood at this point and used to provide a better understanding of the invention. The two layers 101 and 102 are connected along their adjacent edges 112 and 113 to the adjacent edge 120 of the support mesh 130 (in... Figure 3 In the illustration of B, for better visualization, the connection with adjacent edge 113 is not shown. The support mesh 130 is knitted into a single layer from the support thread, preferably cotton thread, using connecting stitches between two needle beds. The edge 121 of the support mesh 130 opposite to the adjacent edge 120 does not adjoin any other side or edge of the precious metal mesh 20'.

[0089] Figure 3 Figure C shows a double-layered precious metal mesh 200 surrounded on both sides by a support mesh. Only a front view of the first rectangular layer 201 is shown, which is congruently positioned above the other layer. The two layers are connected to two support mesh regions 230 and 231 via their respective adjacent edges (only the adjacent edges (210 and 211) of the first layer 201 are visible in the figure). The first region of the support mesh 230 is manufactured as a single layer. The second region 231 may be manufactured as one or two layers.

[0090] Figure 3 D shows a view of a double-layered precious metal mesh 300 surrounded by a support mesh on adjacent sides, which is consistent with... Figure 3 Similarly, in the case of the precious metal mesh in this embodiment, for example, knitting can begin with the lower region 331 of the support mesh, after which two layers of the precious metal mesh 300 and another region 330 of the support mesh are produced simultaneously. In the corresponding knitted rows, the stitches are thus formed by the support material and the precious metal-containing yarn. Advantageously, the two regions of the support mesh 330 and 331 can be interconnected.

[0091] Figure 3 E shows a view of a double-layered precious metal mesh 400 surrounded by a support mesh on all four sides, which is consistent with... Figure 3 Similarly, in Figure C, the support mesh is advantageously divided into regions 430, 431, 432, and 433; these regions are preferably interconnected. In the embodiment shown in Figure F, the double-layer precious metal mesh 500 is also surrounded on all four sides by support mesh regions (530, 531, 532, 533). One region of the support mesh region 532 is not adjacent to the precious metal mesh 500, but is spaced apart from it by gaps 534. In this embodiment, all regions are also produced simultaneously from bottom to top in the knitting direction (i.e., during a single knitting process).

[0092] Figure 3 G shows a view of a double-layered precious metal mesh 600 consisting of two semi-circular layers (only the first layer 601 is visible), which is consistent with... Figure 3 Similarly, in case C, the two layers are connected to the support net 630 on one side via the adjacent edge 620 of the associated adjacent edge (610 in the case of the first layer 601). Figure 3 H also shows a double-layered precious metal mesh 700 formed by two semi-circular layers, in which the layers are surrounded by two support mesh regions 730 and 731 at two adjacent edges.

[0093] Examples and Comparative Examples

[0094] In embodiments and comparative examples according to the invention, rectangular layers (100 cm wide and 200 cm long) were knitted on each needle bed using PtRh5 yarn (76 µm diameter) on a flat knitting machine comprising two needle beds, the two layers being interconnected on one side. Cotton yarn was used as the support yarn.

[0095] In the comparative example, cotton yarn was used to knit a single-layer support mesh area on the unconnected sides of the two layers. Thus, a single-layer knitted fabric comprising two areas (the precious metal layer and the support mesh) was knitted on each of the two needle beds.

[0096] In an embodiment of the invention, a single-layer support mesh is knitted across two needle beds on the unconnected sides of the two layers. Thus, each of the two noble metal layers is knitted on only one needle bed, while the support mesh is knitted on both needle beds.

[0097] The knitted fabric according to an embodiment of the invention has a more uniform structure than the knitted fabric of the comparative example. Such irregularities in the knitted fabric represent potential mechanical weaknesses that have a negative effect when the web is used in a reactor.

[0098] Definition of the symbols used in the illustrations

[0099]

Claims

1. A method for producing a double-layer precious metal mesh on a flat knitting machine, the flat knitting machine comprising a first needle bed and a second needle bed, the method comprising the following steps: - Provide at least one wire containing a precious metal. - Provide at least one support line that does not contain precious metals. - Knit a first layer of the precious metal mesh on the first needle bed and knit a second layer of the precious metal mesh on the second needle bed. The first layer includes adjacent edges S11 and S12, and the second layer includes adjacent edges S21 and S22, wherein adjacent edge S11 is at least partially adjacent to adjacent edge S21, and adjacent edge S12 is at least partially adjacent to adjacent edge S22. - A support mesh is knitted on the first and second needle beds using at least one support yarn that does not contain precious metals. The support mesh includes an adjacent edge SH and an edge KH opposite to the adjacent edge SH, the adjacent edge SH being adjacent to the adjacent edges S11 and S21 of each of the two layers of the precious metal mesh. All knitting processes occur simultaneously. The method is characterized in that, The adjacent edge SH of the support mesh is connected to the corresponding adjacent edges S11 and S21 of the two layers of the precious metal mesh via at least one knitted stitch, and The method is characterized in that the support mesh is knitted in a knitting row via two needle beds using connecting stitches on which the adjacent edges SH of the support mesh are connected to the corresponding adjacent edges S11 and S21 of the two layers of the precious metal mesh.

2. The method according to claim 1, wherein the at least one precious metal-containing wire is composed of platinum, a platinum alloy, palladium, or a palladium alloy.

3. The method according to claim 1, wherein the first layer and the second layer of the double-layer precious metal mesh are knitted from a single precious metal filament or multiple precious metal filaments having the same composition.

4. The method according to claim 2, wherein the first layer and the second layer of the double-layer precious metal mesh are knitted from a single precious metal filament or multiple precious metal filaments having the same composition.

5. The method according to any one of claims 1-4, wherein the first layer and the second layer of the precious metal mesh are knitted from a single precious metal filament or multiple precious metal filaments having the same diameter.

6. The method according to any one of claims 1-4, wherein the first layer and the second layer of the precious metal mesh are knitted with the same knitting pattern.

7. The method of claim 5, wherein the first layer and the second layer of the precious metal mesh are knitted with the same knitting pattern.

8. The method according to any one of claims 1-4, wherein the first layer and the second layer of the precious metal mesh are identical.

9. The method of claim 7, wherein the first layer and the second layer of the precious metal mesh are identical.

10. The method according to any one of claims 1-4, wherein the first layer and the second layer of the double-layer precious metal mesh are at least partially connected at their adjacent edges by at least one connecting knitted stitch.

11. The method of claim 9, wherein the first and second layers of the double-layer precious metal mesh are at least partially connected at their adjacent edges by at least one connecting knitted stitch.

12. The method according to any one of claims 1-4, wherein the adjacent edge SH of the support mesh has the same length as the adjacent edges S11 and S12 of the first and second layers of the double-layer precious metal mesh.

13. The method of claim 11, wherein the adjacent edge SH of the support mesh has the same length as the adjacent edges S11 and S12 of the first and second layers of the double-layer precious metal mesh.

14. The method according to any one of claims 1-4, wherein the shape of the support mesh is related to the shape of the first layer and the second layer of the double-layer precious metal mesh.

15. The method of claim 13, wherein the shape of the support mesh is related to the shapes of the first layer and the second layer of the double-layer precious metal mesh.

16. The method according to any one of claims 1-4, wherein the adjacent edge SH of the support mesh is connected over its entire length to the corresponding adjacent edges S11 and S21 of the first and second layers of the double-layer precious metal mesh.

17. The method of claim 15, wherein the adjacent edge SH of the support mesh is connected over its entire length to the corresponding adjacent edges S11 and S21 of the first and second layers of the double-layer precious metal mesh.

18. The method according to any one of claims 1-4, wherein the support mesh surrounds at least 50% of the sides of the first and second layers of the double-layer precious metal mesh.

19. The method of claim 17, wherein the support mesh surrounds at least 50% of the sides of the first and second layers of the double-layer precious metal mesh.

20. The method of claim 1, wherein the support network comprises a plurality of regions.

21. The method of claim 1, wherein the method includes the additional step of removing the support mesh.

22. The method according to any one of claims 1-4, wherein the method includes the additional step of removing one or more connecting stitches between the first layer and the second layer of the precious metal mesh on one side.

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