Method for specifically equipping a subregion of a throughflow body with precious metal, and one-piece throughflow body equipped with precious metal

Abstract

The present invention relates to a method for equipping a throughflow body with at least one precious metal, wherein only a subregion of the throughflow body is equipped with the at least one precious metal. The method comprises non-immersive coating with a composition that contains a precious metal component and a solvent, wherein the entire quantity of applied composition initially remains on the subregion of the throughflow body. The invention also relates to a one-piece throughflow body having at least one subregion equipped with at least one precious metal, wherein the at least one subregion is at least partially surrounded by one or more further subregions of the throughflow body. The invention also relates to a catalytic converter, comprising a one-piece throughflow body according to the invention or a throughflow body equipped according to the invention, an exhaust silencer comprising such a one-piece throughflow body or a throughflow body equipped in such a way, and also a method for exhaust gas aftertreatment using such a one-piece throughflow body or a throughflow body equipped in such a way.

Description

[0001] Method for the targeted equipping of a portion of a flow-through body with precious metal and one-piece flow-through body equipped with precious metal

[0002] The present invention relates to a method for equipping a flow-through body with at least one precious metal, wherein only a partial region A of the flow-through body is equipped with the at least one precious metal. The method comprises non-immersive coating with a composition containing a precious metal component and a solvent, wherein initially the entire amount of the applied composition remains on the partial region A of the flow-through body. The invention also relates to a one-piece flow-through body with at least one partial region A equipped with at least one precious metal, wherein the at least one partial region A is at least partially enclosed by one or more further partial regions B of the flow-through body.Furthermore, the invention relates to a catalyst comprising a one-piece flow-through body according to the invention or a flow-through body equipped according to the invention, an exhaust silencer comprising such a one-piece flow-through body or a flow-through body equipped according to the invention, and a method for exhaust gas aftertreatment with such a one-piece flow-through body or a flow-through body equipped according to the invention.

[0003] Flow-through bodies, for example in the form of wire bodies, are used in catalysts where a large surface area is crucial for bringing a material to be treated into contact with a catalytically active component. Such catalysts are typically used in the purification of exhaust gases, for example, from internal combustion engines. JP 2009156158 A proposes the use of such flow-through bodies as catalysts in mufflers.

[0004] Precious metals, in particular, have proven to be effective catalytically active components. Flow-through bodies are usually coated using a washcoat process, as described, for example, in CN 104588036 A. The flow-through body to be coated is brought into contact, either completely or partially, with a suspension containing a solvent, at least one carrier component, and optionally a precious metal component, for example by immersion or suction. If a precious metal-free washcoat suspension is applied first, the precious metal is added in a subsequent process step in which a precious metal-containing solution is applied to the pre-coated flow-through body. The suspension or precious metal-containing solution is used in excess, meaning that more solution volume is required than would be necessary to wet the surface of the flow-through body to be coated.In both cases, this leads to higher costs for the precious metal used in the manufacturing process.

[0005] Furthermore, such processes cannot fully account for the flow conditions prevailing under the operating conditions of a catalyst with such a flow-through body. For example, it may be the case that catalytic activity is only desirable in the core region of the flow-through body. Isolating the catalytically active zone from the peripheral regions can be advantageous, as this prevents the heat generated during the catalytic reaction from affecting the possible fixation of the flow-through body in the catalyst housing.

[0006] A targeted and partial coating of flow-through bodies with precious metal is therefore desirable. Flow-through bodies consisting of multiple sub-regions are known from the prior art to solve this problem. For example, US 2012183460 A1 discloses a flow-through body consisting of a stack of multiple layers forming different zones.

[0007] However, the production of such bodies requires additional steps and / or the modular equipment of the individual sub-bodies.

[0008] The object of the present invention is to provide a method for producing a body equipped with at least one precious metal, which allows for the precise placement of the catalytically active components and minimizes the precious metal inventory of the flow-through body. Furthermore, it is the object to reduce the amount of precious metal used during the manufacturing process.

[0009] Surprisingly, it has been found that the object underlying the present invention is at least partially achieved by a method for equipping a partial area A of a flow-through body with at least one precious metal, the method comprising the following steps:

[0010] (i) providing the flow-through body, (ii) providing a composition containing a precious metal component and a solvent,

[0011] (iii) non-immersive coating of the partial area A of the flow-through body with the composition, wherein the non-immersive coating is carried out by applying the composition to the partial area A and the entire amount of the composition applied to the partial area A initially remains on the partial area A,

[0012] (iv) removing the volatile components of the composition from the portion A.

[0013] The process according to the invention thus makes it possible to produce a flow-through body having at least two subregions (hereinafter referred to as subregion A and subregion B), wherein at least one of the subregions is provided with at least one precious metal. The further subregion(s) (subregion B) can be provided with no precious metal component, a different precious metal component, or fewer precious metal components. Such flow-through bodies are typically used in catalysts, wherein the precious metal acts as a catalytically active species.

[0014] The method according to the invention is particularly advantageous because it allows the selective design of flow-through bodies. Furthermore, the targeted and partial application of the precious metal-containing composition allows the amount of the required composition to be minimized. This allows the amount of precious metal component to be used to be reduced compared to processes in which an excess of composition is used. This advantage is particularly evident compared to immersive processes, particularly dipping processes. Furthermore, by using a suitable composition, a three-dimensional sub-region of the flow-through body can be selectively equipped, in contrast to coating processes intended for the layer-by-layer buildup of coatings.A further advantage lies in the simple implementation of the method according to the invention, which does not require any additional aids such as masks or covers in order to coat specific partial areas.

[0015] In the process according to the invention, a flow-through body is partially coated with precious metal. A flow-through body is understood to be a body through which gas can flow and which has a continuous network of channels and / or pores. In other words, the flow-through body can be described as a porous matrix with a multitude of irregularly or regularly shaped passages.

[0016] Flow bodies are characterized by a large surface area per total volume.

[0017] Preferably, the flow-through body is a one-piece body. Advantageously, the flow-through body is dimensionally stable.

[0018] The shape of the flow body is not further restricted. The flow body can be designed, for example, in the form of a cube, a cuboid, a sphere, a pyramid, a cone, or a cylinder.

[0019] Typically, the flow body has at least one end face, preferably exactly two end faces, such as in the case of a cylinder or cuboid. Advantageously, the flow body has a circumferential surface extending from the at least one end face; in the case of a cuboid, the cylinder, the circumferential surface extends from the first end face to the second end face. The at least one end face and the circumferential surface form the edge regions of the flow body, or more precisely, they form the surfaces of the edge regions of the flow body.

[0020] The geometry of the flow body is determined by a central longitudinal axis and a perpendicular transverse axis. Typically, the longitudinal axis is longer than the transverse axis, as in a cuboid or cylinder. In these cases, the longitudinal axis extends from the first to the second end face.

[0021] The total volume of the flow body can be, for example, 10 cm 3 up to 200 cm 3 , especially 20 cm 3 up to 100 cm 3 The density of the flow body is advantageously 0.6 g / cm 3 up to 2 g / cm 3 , especially 0.9 g / cm 3 up to 1.7 g / cm 3 .

[0022] For the purposes of this application, the area boundaries are deemed to be included if areas are mentioned.

[0023] The flow-through body typically comprises a ceramic material or a metallic material. The flow-through body can preferably comprise cordierite (SiO2-Al2O3-MgO), silicon carbide (SiC), titanium, an iron alloy such as an Fe-Cr-Al alloy or a heat-resistant steel, in particular 1.4767 or a nickel alloy such as a Ni-Cr alloy, a Ni-Cr-Al alloy, a Ni-Cr-Fe alloy, in particular 2.4851. The flow-through body can be a foam, a body consisting of irregularly arranged fibers, a body made of expanded metal or a wire body; flow-through bodies in the form of a wire body are particularly preferred. A wire body is understood to be a body formed from one wire or multiple wires. A wire body formed from multiple wires can also be a one-piece flow-through body. A wire is a thin, elongated, flexible piece of metal.The wire preferably has a round cross-section. A square cross-section can also be advantageous. The cross-section of the wire is advantageously constant along its length within the usual manufacturing tolerances.

[0024] In particular, the wire body may be a knitted wire mesh, a wire cloth, a shaped metal wire, a wire mat or a wound wire mat.

[0025] The diameter of the wire of the wire body or, in the case of a non-circular cross-section, the greatest extension of the wire in cross-section is advantageously from 0.1 mm to 2 mm, in particular from 0.2 mm to 1 mm. A diameter of 0.3 mm to 1 mm is considered particularly advantageous. The wire diameter is particularly preferably no more than 0.5 mm.

[0026] The present invention relates to a method for equipping the flow-through body with at least one precious metal. In the context of the present invention, a precious metal is understood to be a metal selected from the group consisting of platinum group metals, gold, and silver. Platinum group metals are understood to be the metals of the so-called platinum group, i.e., platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), and ruthenium (Ru).

[0027] The terms "metal," "precious metal," or, for example, "platinum" used here do not imply any information about their oxidation state. In other words, they do not indicate the presence of the elemental state with oxidation state 0. The metal, precious metal, or, for example, platinum can exist in elemental form, i.e., in oxidation state (0), or in a higher oxidation state.

[0028] Precious metals often exhibit catalytic activity for certain reactions, such as the decomposition of exhaust gas components. The at least one precious metal therefore represents a catalytically active component of a correspondingly equipped flow body.

[0029] The at least one precious metal is preferably selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru) and combinations thereof, in particular the at least one precious metal is platinum, palladium, rhodium, a combination of platinum and rhodium or a combination of platinum, palladium and rhodium.

[0030] In step (ii) of the process according to the invention, a composition containing a precious metal component and a solvent is provided. The precious metal component is a component of the at least one precious metal with which the partial region of the flow-through body is to be provided.

[0031] In this context, a "noble metal component" is understood to mean a component that consists at least partially of at least one noble metal. The noble metal component can be a precursor component of a catalytically active species, for example in the form of a corresponding noble metal compound. Suitable noble metal compounds are complexes, organometallic compounds, or salts of the noble metal, for example nitrates, halides, acetylacetonates, or acetates, but also a multitude of other salts known to the person skilled in the art. The noble metal component can also already be present in the form of a catalytically active species. The noble metal component can also be at least partially metallic noble metal, for example in the form of particles, in particular in the form of nanoparticles.

[0032] The composition may also contain multiple precious metal components. In this case, these may be multiple components of the same precious metal or different precious metals. The at least one precious metal component is preferably a component of a precious metal selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru), and, in the case of multiple precious metal components, from combinations thereof. Combinations of platinum, palladium, or rhodium are particularly preferred, for example platinum and palladium, platinum and rhodium, or platinum, palladium, and rhodium. The amount of the precious metal component of the at least one precious metal in the composition can vary within wide ranges and is determined by the intended loading of the flow-through body with the at least one precious metal. In particular, the amount of the at least one precious metal is determined by the intended loading.The “amount of the at least one precious metal” refers to the proportion of the at least one precious metal in the composition and not necessarily to the amount of the precious metal component. In the case that the precious metal component is a noble metal compound, this does not refer to the amount of the noble metal compound, but rather the amount of the precious metal in the noble metal compound. The composition preferably comprises 0.5 to 90 wt.% of the at least one precious metal, based on the total weight of the composition comprising the at least one solvent and the at least one noble metal component. In one embodiment, the composition comprises 1 to 80 wt.% of the at least one precious metal, preferably 5 to 70 wt. Particularly good results are obtained when the composition contains the at least one precious metal in an amount of at least 0.5 wt.%, in particular at least 1 wt.%, preferably at least 5 wt.-%, preferably at least 10 wt.%.

[0033] In the case where the at least one noble metal comprises iridium, the noble metal component can be an Ir(IV) compound, e.g., an Ir(IV) salt, an Ir(IV) complex, or an Ir organometallic compound. Examples of suitable iridium compounds are iridium chloride, iridium acetate, iridium acetylacetonate, iridium sulfate, and dihydrogen hexachloroiridate.

[0034] In the case that the at least one precious metal comprises platinum, the precious metal component can be a platinum(II) or a platinum(IV) compound, e.g. a Pt(II) or Pt(IV) salt, a Pt(II) or Pt(IV) complex compound, or a Pt(II) or Pt(IV) organometallic compound. Examples of suitable platinum compounds include platinum halides, such as platinum(II) chloride or platinum(IV) chloride or an acid thereof, hexachloroplatinic acid or a salt of this acid, platinic acid or a salt of this acid, hydroxyethylammonium hexahydroxoplatinate, ammonium hexachloroplatinate, ammonium tetrachloroplatinate, potassium tetrachloroplatinate, potassium hexachloroplatinate, sodium tetrachloroplatinate, potassium tetrahydroxyplatinate, platinum nitrate, platinum sulfite, platinum ethanolamine, platinum acetylacetonate, platinum oxalate, or a mixture of at least two of these compounds.In the case that the at least one precious metal comprises palladium, the precious metal component may be a palladium(II) or a palladium(IV) compound, e.g. a Pd(II) or Pd(IV) salt, a Pd(II) or Pd(IV) complex compound or a Pd(II) or Pd(IV) organometallic compound. As exemplary palladium compounds, palladium halides such as palladium(II) chloride, palladium(II) bromide or palladium(IV) chloride or an acid thereof, palladium acetate, palladium nitrate, palladium acetylacetonate, palladium sulfate, palladium oxalate, hydroxyethylammonium hexahydroxopalladate, ammonium hexachloropalladate, ammonium tetrachloropalladate, potassium tetrachloropalladate, potassium hexachloropalladate, sodium tetrachloropalladate, potassium tetrahydroxypalladate, diaminedichloropalladium, tetraaminepalladium nitrate, tetraaminepalladium chloride, tetraaminepalladium hydroxide, tetraaminepalladium sulfate or a mixture of at least two of these compounds may be mentioned.

[0035] In the case where the at least one noble metal comprises ruthenium, the noble metal component can be a ruthenium(III) or a ruthenium(IV) compound, e.g., Ru(III) or Ru(IV) salts, Ru(III) or Ru(IV) complex compounds, or Ru(III) or Ru(IV) organometallic compounds. Examples of ruthenium compounds include nitrates, acetylacetonates or acetates, and halides. Examples of suitable ruthenium compounds include ruthenium nitrate, ruthenium acetate, ruthenium pentacarbonyl, ruthenium acetylacetonate, ruthenium oxalate, ruthenocene, and ruthenium nitrosyl nitrate, or a mixture of at least two of these compounds.

[0036] In the case where the at least one precious metal comprises rhodium, the precious metal component can be a Rh(III) compound, e.g., a Rh(III) salt, a Rh(III) complex, or a Rh organometallic compound. Examples of suitable rhodium compounds are rhodium halides, such as rhodium(III) chloride, or an acid thereof, rhodium nitrate, rhodium acetylacetonate, rhodium sulfate, or a mixture of at least two of these compounds.

[0037] In addition to the at least one precious metal component, the composition contains a solvent. The solvent is preferably an aqueous solvent, acetone, or an alcohol; advantageously, the solvent comprises water. It has proven advantageous if the solvent consists primarily of water; in particular, the solvent comprises at least 70% by weight of water, more preferably at least 80% by weight, and most preferably at least 90% by weight of water. It can also be advantageous if the solvent comprises only water, i.e., consists entirely of water.

[0038] The composition is preferably a non-solid composition. In particular, the composition can be liquid or viscous, for example in the form of a solution, an emulsion, a suspension, a dispersion, or a paste. A suspension, within the meaning of the present invention, is a mixture of a solid and a liquid, wherein the solid is present in the form of finely divided solids uniformly distributed throughout the liquid.

[0039] Preferably, the composition exhibits thixotropic properties. As known to those skilled in the art, thixotropic properties are said to exist when a fluid exhibits a lower viscosity under constant and sustained force (shear stress phase) than under static conditions, and the static viscosity returns to normal once the force is removed (complete recovery of viscosity in the rest phase).

[0040] In preferred embodiments, the composition has a static viscosity of at least 500 mPa*s, more preferably at least 1000 mPa*s, especially at least 20,000 mPa*s. Suitable compositions have, for example, a static viscosity in the range of 500 to 100,000 mPa*s, preferably in the range of 1000 to 50,000 mPa*s, especially preferably in the range of 2000 to 30,000 mPa*s. The static viscosity of a composition can be determined according to a measurement described later. The determination of static viscosity is also known to those skilled in the art as a CS measurement (controlled stress).

[0041] In preferred embodiments, the composition has a dynamic viscosity of no more than 2500 mPa*s, more preferably no more than 1500 mPa*s, in particular no more than 1000 mPa*s. By using a composition with a minimum dynamic viscosity, it can be ensured that the composition can be applied specifically to the flow-through body. Suitable compositions have, for example, a dynamic viscosity in the range of 50 to 2500 mPa*s, preferably in the range of 100 to 1500 mPa*s, particularly preferably in the range of 200 to 1000 mPa*s. The dynamic viscosity of a composition can be determined according to a measurement described later. The determination of dynamic viscosity is also known to those skilled in the art as a CR measurement (constant shear rate, controlled rate).

[0042] The composition preferably has a thixotropy index (TI) of at least 5, in particular at least 10, and particularly preferably at least 20. The thixotropy index (TI) is understood to be the ratio of static to dynamic viscosity. Within the scope of the present invention, it was surprisingly discovered that the use of such compositions allows for a particularly efficient, targeted treatment of flow body sections.

[0043] The viscosity of the composition can be specifically adjusted using methods known to those skilled in the art. The composition preferably contains a thickener, for example a polyvinyl alcohol, an oxide and / or hydroxide of aluminum such as boehmite, a nitrate of cerium, aluminum or zirconium, or a hydrocolloid. A person skilled in the art understands a hydrocolloid to be a substance that can dissolve in water as a colloid and exhibits a high gel-forming capacity. Hydrocolloids are typically polymers, in particular proteins or polysaccharides, obtained from natural sources such as plants, algae, or animals. The hydrocolloid can be, for example, a cellulose, in particular a methylcellulose or a hydroxycellulose, a pectin, an alginate, gelatin, agar, or carrageenan.

[0044] The composition preferably contains at least 0.5% by weight of the thickener, based on the total weight of the composition, in particular at least 1.5% by weight, particularly preferably at least 2% by weight. The composition preferably contains less than 10% by weight of the thickener, in particular less than 8% by weight, particularly preferably less than 5% by weight. If the proportion of thickener is greater, the viscosity of the composition is too high to be able to use it according to the invention. It has proven advantageous if the composition contains the thickener in a range from 0.5 to 10% by weight, in particular in a range from 2 to 8% by weight.

[0045] The composition may be a washcoat suspension. The term "washcoat" is familiar to those skilled in the art. A distinction must be made between a washcoat suspension and a washcoat layer that can be applied or has been applied to a macroscopic support, such as a flow-through body. As is known to those skilled in the art, washcoat suspensions are used to coat catalyst supports with a washcoat layer. The flow-through bodies that are coated using the process according to the invention are such catalyst supports. The washcoat suspension preferably contains at least one microscopic support, typically an oxidic support material. The microscopic support must be distinguished from the macroscopic support, in the case of the present invention, from the flow-through body to be coated.

[0046] The oxidic support material may comprise a refractory oxide, preferably selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, their mixed oxides, and composite oxides of two or more thereof. The refractory oxide may be doped; in other words, the refractory oxide may contain a dopant. Refractory oxides doped with a dopant are obtainable using methods known in the relevant art. Suitable dopants may be selected from the group consisting of rare earth metals, transition metals, alkaline earth metals, and mixtures thereof. In particular, the dopant may be at least one element selected from the group consisting of cerium (Ce), zirconium (Zr), titanium (Ti), silicon (Si), manganese (Mn), yttrium (Y), lanthanum (La), barium (Ba), praseodymium (Pr), gadolinium (Gd), samarium (Sm), neodymium (Nd) and their oxides.Preferably, the dopant comprises La, Ba, Sr, Zr or Mn. More preferably, the refractory oxide is an aluminum oxide doped with lanthanum or lanthanum oxide, a mixed oxide of aluminum oxide doped with lanthanum or lanthanum oxide, or a composite oxide of aluminum oxide doped with lanthanum or lanthanum oxide.

[0047] The washcoat suspension preferably comprises the oxidic carrier material in a proportion of 5 to 50 wt.%, particularly preferably in a proportion of 10 to 40 wt.%, based on the total weight of the washcoat suspension.

[0048] The oxidic support material can also comprise an oxygen storage component, preferably a cerium oxide and / or a cerium-zirconium oxide. The cerium-zirconium oxide can be a mixed oxide or a mixture of cerium oxide (CeOs) and zirconium oxide (ZrCh). The oxidic support material can comprise a refractory oxide and an oxygen storage component. In the case of a cerium-zirconium oxide, it can be either a cerium-rich oxide or a zirconium-rich oxide. The cerium-zirconium oxide can preferably contain 10 to 50 wt.% zirconium oxide, preferably 15 to 40 wt.%, based on the total weight of the cerium-zirconium oxide. The cerium-zirconium oxide preferably contains cerium oxide in an amount of 20 to 90 wt.%, particularly preferably 40 to 85 wt.%, in each case based on the total weight of the cerium-zirconium oxide.

[0049] The oxygen storage component can comprise at least one element other than cerium from the group of rare earths. The at least one element from the group of rare earths is preferably present as an oxide. Preferably, the at least one rare earth element is selected from the group consisting of neodymium (Nd), praseodymium (Pr), lanthanum (La), and hafnium (Hf). The oxygen storage component can comprise, for example, a cerium-zirconium-lanthanum oxide, a cerium-zirconium-yttrium oxide, a cerium-zirconium-lanthanum-yttrium oxide, a cerium-zirconium-neodymium oxide, a cerium-zirconium-praseodymium oxide, a cerium-zirconium-lanthanum-neodymium oxide, a cerium-zirconium-lanthanum-praseodymium oxide, a cerium-zirconium-lanthanum-neodymium-praseodymium oxide, or a combination thereof. The proportion of the respective rare earth oxides can be 2 wt.% to 20 wt.%, preferably 5 wt.% to 15 wt.%, based on the total weight of the oxygen storage component.

[0050] The washcoat suspension preferably comprises the oxygen storage component in a proportion of 5 to 50 wt.%, particularly preferably in a proportion of 10 to 40 wt.%, based on the total weight of the washcoat suspension.

[0051] It is preferred that the oxidic support material has a large BET surface area, preferably the BET surface area is at least 30 m 2 / g, in particular at least 80 m 2 / g, particularly preferably at least 100 m 2 / g. Typically, the BET surface area of ​​the oxide support material is between 30 and 300 m 2 / g, preferably between 50 and 200 m 2 / g. The BET surface area is also called specific surface area and can be determined according to ISO 9277:2010 using nitrogen as the adsorbate.

[0052] The oxidic support material is preferably a porous material. The pore volume is typically in the range of 0.2 to 10.0 mL / g, in particular in the range of 0.3 to 0.8 mL / g. The average pore radii are 5 to 40 nm, in particular 10 to 30 nm. The pore volume and pore diameter distribution can be determined using mercury porosimetry according to ISO 15901-1:2022. If a washcoat suspension is used as the composition in the process according to the invention, the precious metal component can be supported on an oxidic support material, in particular on a refractory oxide and / or an oxygen storage component.This means that the oxide support material is provided with at least one precious metal component, i.e., the precious metal component is present on, in, or on the oxide support material, for example, in the form of an adsorbed precursor component, particles, or a layer. The oxide support material's features can be present both on the surface and inside the oxide support material. The term "surface" encompasses both the outer and inner surfaces; in other words, it also includes the internal surface formed by pores.

[0053] The coating of an oxidic support material with the at least one precious metal component can be carried out by methods known to those skilled in the art, for example by impregnation, precipitation, chemical vapor deposition (CVD), or spraying. The coating typically comprises combining the oxidic support material with at least one precious metal compound, which is usually provided in a preparation comprising at least one solvent. Following the combination, the precipitation and / or reduction of the at least one precious metal compound and a drying and / or calcination step can take place. For example, the preparation can be absorbed into or in the oxidic support material by capillary forces, so that the volume of the preparation approximately corresponds to the pore volume of the oxidic support material, known to those skilled in the art as the "incipient wetness method."

[0054] The washcoat suspension can also contain the precious metal component in the form of an unsupported precious metal compound, in particular a precious metal precursor component.

[0055] The composition may also contain additional components such as acids or bases for pH regulation, fillers, binders, pore formers, adhesion promoters, or stabilizers. Such additional components typically do not exhibit catalytic activity, but rather improve the processability of the composition or the properties of the coating produced therefrom, for example, by extending the operating temperature range, increasing the contact surface, improving adhesion properties, or similar.

[0056] In step (iii), the flow body is coated with the composition.

[0057] Non-immersive coating is carried out by applying the composition to a partial area A of the flow-through body. In other words, the coating is carried out only selectively on at least one partial area A of the flow-through body, thereby achieving a partial coating of the flow-through body. In particular, the coating is carried out by applying a predefined amount of the composition to the partial area A to be coated.

[0058] The coating is non-immersive, meaning that the coating is not applied by immersing the flow-through body into the composition. Coating techniques that rely on immersing the body to be coated do not allow for the intended selective and targeted application of the coating. Immersion processes are particularly unsuitable for partial areas A inside the flow-through body, i.e., those that are partially or completely enclosed by one or more partial areas B of the flow-through body.

[0059] The non-immersive coating is advantageously carried out by a method selected from the group consisting of pipetting, brushing, stamping, spreading, injecting, rolling or printing.

[0060] The volume of the coated partial area A is advantageously 5% to 90%, in particular 10% to 80% of the total volume of the flow-through body. Particularly advantageously, the volume of partial area A is at most 60%, in particular at most 50% of the total volume of the flow-through body. A volume of partial area A of 15% to 30% of the total volume of the flow-through body has proven particularly advantageous.

[0061] The spatial extent of the coated partial area A can also be specifically controlled by the method according to the invention. In particular, point-shaped, cylindrical, or spherical partial areas A can be coated. The method is particularly suitable for equipping point-shaped, cylindrical, or spherical partial areas A that are at least partially arranged inside the flow-through body, i.e., are partially or completely enclosed by one or more further partial areas B of the flow-through body and at least partially or completely do not form an edge region of the flow-through body.

[0062] The method is particularly advantageous if both the flow body and the partial area A equipped with at least one precious metal are cylindrical, cuboid or disc-shaped.

[0063] Preferably, the cross-sectional area of ​​the partial region A provided with at least one precious metal perpendicular to the longitudinal axis of the flow-through body amounts to no more than 80% of the total cross-sectional area of ​​the flow-through body perpendicular to the longitudinal axis in the direction of the longitudinal axis, in particular no more than 70%, preferably no more than 60%. In particular, the cross-sectional area of ​​the partial region A perpendicular to the longitudinal axis amounts to more than 30% of the total cross-sectional area of ​​the flow-through body perpendicular to the longitudinal axis in the direction of the longitudinal axis, preferably more than 40%.

[0064] The partial region A provided with at least one precious metal can extend along the entire length of the longitudinal axis of the flow-through body. Preferably, the length of the partial region A provided with at least one precious metal along the longitudinal axis of the flow-through body amounts to no more than 80% of the total length of the flow-through body along the longitudinal axis, in particular no more than 70%, preferably no more than 60%. In particular, the length of the partial region A along the longitudinal axis amounts to more than 30% of the total length of the flow-through body, preferably more than 40%.

[0065] Advantageously, at least 50% of the circumferential surface of the flow-through body is not formed by the partial area A provided with at least one precious metal, in particular at least 80%, particularly preferably the entire circumferential surface is not formed by the partial area A provided with at least one precious metal. In other words, it may be advantageous if the partial area A provided with at least one precious metal does not adjoin the circumferential surface.

[0066] Advantageously, at least 50%, in particular at least 80%, of at least one of the end faces is not formed by the partial region A provided with at least one precious metal. In a particularly preferred embodiment, this at least one end face is not completely formed by the partial region A provided with at least one precious metal. In other words, the partial region A provided with at least one precious metal does not border on at least one end face. The method is particularly advantageous if the partial region A provided with at least one precious metal does not border on any of the end faces of the flow-through body.

[0067] It may also be preferred for the non-immersive coating to be carried out on a central partial area A of the flow-through body, which at least partially does not border any edge area. The method according to the invention is particularly advantageous for such embodiments, since such inner partial areas A of the flow-through body can be coated with precious metal in a targeted manner.

[0068] The entire amount of the composition applied to sub-area A of the flow-through body initially remains on the flow-through body. The time limitation "initially" here means that the composition remains on sub-area A immediately after application, but can optionally be at least partially removed again in subsequent process steps. In the following process step (iv), at least the volatile components of the composition, in particular the solvent, are removed.

[0069] The total amount of the composition is understood to be the amount that reaches the partial area A of the flow body during application. Particularly in spray processes, for example, the amount of composition applied and the amount that actually reaches the substrate to be coated are not identical. Such losses can be caused, for example, by evaporation of components of the composition, especially the solvent.

[0070] In step (iv), the volatile components of the composition are removed from subregion A. Volatile components are those components that are evaporable under normal conditions. Non-volatile components of the composition, in particular the precious metal component or parts of the precious metal component, remain on the subregion. The volatile components of the composition include, in particular, the solvent. Parts of the precious metal component may also be volatile. Removal can be carried out by methods known to those skilled in the art, such as, for example, by passive drying, heating, or removal under reduced pressure.

[0071] The process according to the invention may also comprise further steps, for example a step for precipitating and / or fixing a noble metal precursor component, a drying step and / or a step for converting a noble metal precursor component into a catalytically active noble metal component.

[0072] Preferably, equipping the flow-through body with at least one precious metal includes a calcination step. Those skilled in the art understand "calcination" to mean a thermal treatment in which a metallic component is fixed to a support material. The calcination step is particularly advantageous when the temperature is in the range of 150 to 700°C, in particular 200 to 600°C. In preferred embodiments, the temperature is more than 200°C, particularly preferably more than 300°C. In preferred embodiments, the drying step takes place over a period of 1 to 24 hours, preferably 2 to 12 hours.

[0073] The loading of the flow-through body with the at least one precious metal is selected so that the precious metal content can be used as efficiently as possible. The loading with the at least one precious metal is preferably in the range of 0.01 to 1 g / L, particularly preferably in the range of 0.05 to 0.8 g / L, and especially preferably in the range of 0.01 to 0.7 g / L. The loading indicates the amount of the at least one precious metal relative to the volume of the entire flow-through body.

[0074] Preferably, the sub-area A of the flow-through body is provided with precious metal in a range of 0.1 - 10 g / L, in particular in a range of 0.5 - 8 g / L. Preferably, the sub-area A of the flow-through body is provided with less than 8 g / L of the at least one precious metal, in particular with less than 5 g / L. In this case, the provision indicates the amount of the at least one precious metal relative to the volume of the sub-area A.

[0075] Compared to a homogeneously coated flow-through body, the process according to the invention can produce a flow-through body in which the catalytically active precious metal is used as efficiently as possible. In other words, the amount of precious metal can be reduced while maintaining the same catalytic performance, or the catalytic performance can be increased with the same amount of precious metal.

[0076] The method according to the invention can also be carried out several times, for example in order to equip different partial areas of the flow body with different amounts of the at least one precious metal or in order to equip different partial areas with different precious metals.

[0077] In an advantageous embodiment, the flow-through body can initially be completely coated with a precious metal-free washcoat suspension, i.e., with a precious metal-free washcoat layer. Preferred components of such a precious metal-free washcoat suspension are described above, which, with the exception of the information regarding the precious metal component, also apply here.

[0078] Subsequently, the method according to the invention is carried out to selectively equip partial regions of the thus pretreated flow-through body with the at least one precious metal. In such cases, the flow-through body comprises at least a first partial region equipped with a precious metal-free washcoat layer, i.e., one without a catalytically active component, and at least a second partial region equipped with a washcoat layer and at least one precious metal. Only this second partial region A thus has a catalytically active component.

[0079] In a further advantageous embodiment, the flow-through body can initially be partially coated with a precious metal-free washcoat suspension, i.e., coated in partial areas with a precious metal-free washcoat layer. The method according to the invention is then carried out to selectively coat partial areas of the thus pretreated flow-through body with the at least one precious metal. In such cases, the flow-through body comprises at least a first partial area that is neither coated with a washcoat coating nor with a precious metal, at least a second partial area that is coated only with a precious metal-free washcoat layer, and at least a third partial area that is coated with a washcoat layer and at least one precious metal. Only this third partial area therefore has a catalytically active component.It may also be preferred that parts of the flow body be coated neither with a washcoat nor with a precious metal. A combination of all variants is also possible.

[0080] The invention also relates to a one-piece flow-through body with at least one partial region A provided with at least one precious metal, wherein the at least one partial region A is at least partially enclosed by one or more further partial regions B of the one-piece flow-through body.

[0081] The flow-through body according to the invention is a one-piece flow-through body. In other words, the flow-through body is not composed of multiple individual bodies. However, the one-piece flow-through body can comprise multiple components; for example, in cases where it is a wire body, it can comprise multiple wires that form the one-piece flow-through body.

[0082] The one-piece design of the flow-through body according to the invention is particularly advantageous because it allows for a minimization of components to provide a flow-through body with a subregion A enclosed by at least one further subregion B. Subregions A and B differ particularly in their precious metal configuration, such as the precious metal loading, the type of precious metal, or the combination of several precious metals. Subregion or subregions B can, in particular, be precious metal-free.

[0083] The shape of the one-piece flow body is not further restricted. The one-piece flow body can be designed, for example, in the form of a cube, a cuboid, a sphere, a pyramid, a cone, or a cylinder.

[0084] Typically, the one-piece flow-through body has at least one end face, preferably exactly two end faces, such as in the case of a cylinder or cuboid. Advantageously, the one-piece flow-through body has a circumferential surface extending from the at least one end face; in the case of a cuboid or cylinder, the circumferential surface extends from the first end face to the second end face. The at least one end face and the circumferential surface form the edge regions of the one-piece flow-through body.

[0085] The geometry of the one-piece flow body is determined by a central longitudinal axis and a perpendicular transverse axis. Typically, the longitudinal axis is longer than the transverse axis, as in a cuboid or cylinder. In these cases, the longitudinal axis extends from the first to the second end face.

[0086] The total volume of the one-piece flow body can be, for example, 10 cm 3 up to 200 cm 3 be, in particular 20 cm 3 up to 100 cm 3 . The density of the one-piece flow body is advantageously 0.6 g / cm 3 up to 2 g / cm 3 , especially 0.9 g / cm 3 up to 1.7 g / cm 3 .

[0087] The one-piece flow-through body typically comprises a ceramic material or a metallic material. Preferably, the one-piece flow-through body can comprise cordierite (SiO2-Al2O3-MgO), silicon carbide (SiC), titanium, an iron alloy such as an Fe-Cr-Al alloy or a heat-resistant steel, in particular 1.4767, or a nickel alloy such as a Ni-Cr alloy, a Ni-Cr-Al alloy, or a Ni-Cr-Fe alloy, in particular 2.4851.

[0088] The one-piece flow body can be a foam, a body consisting of irregularly arranged fibers, a body made of expanded metal or a metal sheet, or a wire body. Flow bodies in the form of a wire body are particularly preferred. The wire preferably has a round cross-section. A square cross-section can also be advantageous. The cross-section of the wire is constant along its length within the usual manufacturing tolerances.

[0089] In particular, the wire body may be a knitted wire mesh, a knitted or woven wire mesh, a shaped metal wire, a wire mat or a wound wire mat.

[0090] The diameter of the wire of the wire body or, in the case of a non-circular cross-section, the greatest extension of the wire in cross-section is advantageously from 0.1 mm to 2 mm, in particular from 0.2 mm to 1 mm. A diameter of 0.3 mm to 1 mm is considered particularly advantageous. The diameter of the wire is particularly preferably at most 0.5 mm. At least one partial region A of the one-piece flow-through body is provided with at least one precious metal. The at least one partial region A can be provided with the precious metal using various methods, in particular using the method according to the invention as described above.

[0091] The at least one precious metal with which the partial region A is provided is preferably selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru) and combinations thereof, in particular the at least one precious metal is platinum, palladium, rhodium, a combination of platinum and rhodium or a combination of platinum, palladium and rhodium.

[0092] The at least one partial region A is at least partially enclosed by one or more further partial regions B of the one-piece flow-through body. In other words, the partial region A is at least partially arranged inside the one-piece flow-through body. In advantageous embodiments, the partial region A is completely enclosed by one or more further partial regions B; in other words, in such cases, the partial region A does not border any edge region of the one-piece flow-through body.

[0093] The further sub-area or sub-areas B may contain no precious metal or also contain at least one precious metal. The at least one precious metal may be the same as or different from the precious metal in sub-area A. In particular, sub-area B may contain less precious metal than sub-area A, in each case relative to the volume of the sub-area.

[0094] The volume of the partial area A equipped with at least one precious metal is advantageously 5% to 90%, in particular 10% to 80% of the total volume of the one-piece flow-through body. Particularly advantageously, the volume of partial area A is at most 60%, in particular at most 50% of the total volume of the one-piece flow-through body. A volume of partial area A of 15% to 30% of the total volume of the one-piece flow-through body has proven particularly advantageous.

[0095] The shape of the partial region A equipped with at least one precious metal is not further restricted; in particular, the partial region A can be point-shaped, cylindrical, or spherical. In particular, both the one-piece flow body and the partial region A equipped with at least one precious metal can be cylindrical, cuboid, or disc-shaped.

[0096] Preferably, the cross-sectional area of ​​the partial region A provided with at least one precious metal perpendicular to the longitudinal axis of the one-piece flow-through body amounts to no more than 80% of the total cross-sectional area of ​​the one-piece flow-through body perpendicular to the longitudinal axis in the direction of the longitudinal axis, in particular no more than 70%, preferably no more than 60%. In particular, the cross-sectional area of ​​the partial region A perpendicular to the longitudinal axis amounts to more than 30% of the total cross-sectional area of ​​the one-piece flow-through body perpendicular to the longitudinal axis in the direction of the longitudinal axis, preferably more than 40%.

[0097] The partial region A provided with at least one precious metal can extend along the entire length of the longitudinal axis of the one-piece flow-through body. Preferably, the length of the partial region A provided with at least one precious metal along the longitudinal axis of the one-piece flow-through body amounts to no more than 80% of the total length of the one-piece flow-through body along the longitudinal axis, in particular no more than 70%, preferably no more than 60%. In particular, the length of the partial region A along the longitudinal axis amounts to more than 30% of the total length of the one-piece flow-through body, preferably more than 40%.

[0098] Advantageously, at least 50% of the circumferential surface of the one-piece flow-through body is not formed by the partial area A provided with at least one precious metal, in particular at least 80%, particularly preferably the entire circumferential surface is not formed by the partial area A provided with at least one precious metal.

[0099] Advantageously, at least 50%, in particular at least 80%, of at least one of the end faces is not formed by the partial region A provided with at least one precious metal. In a particularly preferred embodiment, this at least one end face is not completely formed by the partial region A provided with at least one precious metal. In other words, the partial region A provided with at least one precious metal does not border on at least one end face. In particular, it can be the case that the partial region A provided with at least one precious metal does not border on any of the end faces of the one-piece flow-through body. The loading of the one-piece flow-through body with precious metal is selected such that the precious metal equipment can be used as efficiently as possible overall.Precious metal loading refers to the entire loading of the one-piece flow-through body with precious metal, thus also including any precious metal loading of other sub-areas. The precious metal loading is preferably in the range of 0.01 to 1 g / L, particularly preferably in the range of 0.05 to 0.8 g / L, and especially preferably in the range of 0.01 to 0.7 g / L. The loading indicates the amount of the at least one precious metal relative to the volume of the one-piece flow-through body.

[0100] Preferably, the partial area A of the one-piece flow-through body is provided with the at least one precious metal in a range of 0.1 - 10 g / L, in particular in a range of 0.5 - 8 g / L. Preferably, the partial area A of the one-piece flow-through body is provided with less than 8 g / L of the at least one precious metal, in particular with less than 5 g / L. In this case, the provision indicates the amount of the at least one precious metal relative to the volume of the partial area A.

[0101] The further sub-region(s) B of the one-piece flow-through body may have no coating or, for example, a washcoat coating. Regarding advantageous compositions of the washcoat coating, reference is made to the above statements, which also apply to the coating of the one-piece flow-through body. The one-piece flow-through body may also have multiple sub-regions provided with at least one precious metal. The multiple sub-regions may be provided with the same or different coatings and, in the case of different coatings, may differ in the precious metal, the combination of precious metals, or the quantity of precious metal(s). Furthermore, the one-piece flow-through body may have sub-regions provided with a precious metal-free washcoat layer.

[0102] For example, the one-piece flow-through body can have at least one first subregion or multiple subregions equipped with a precious metal-free washcoat layer and at least one second subregion equipped with at least one precious metal. The invention also relates to a catalyst comprising a one-piece flow-through body according to the invention or a flow-through body equipped with at least one precious metal produced by the method according to the invention, and a catalyst housing. For preferred embodiments of the method or the one-piece flow-through body, reference is made to the above explanations.

[0103] The catalyst according to the invention can be used, for example, in small engines, in particular two-stroke engines, mixture-lubricated four-stroke engines or separately lubricated internal combustion engines, in particular for exhaust gas aftertreatment.

[0104] Advantageously, the catalyst housing is made of steel, for example 1.4828, 1.4509 or 1.4767 steel.

[0105] The catalyst housing advantageously has at least one inlet opening and at least one outlet opening. In particular, the housing has more inlet openings than outlet openings.

[0106] The at least one inlet opening and the at least one outlet opening are preferably arranged on opposite end sides of the catalyst housing.

[0107] The at least one inlet opening and the at least one outlet opening are advantageously arranged at least partially offset from one another. In a preferred embodiment, the at least one inlet opening and the at least one outlet opening do not overlap with one another. The overlap of the inlet opening and outlet opening refers to the inflow direction of an exhaust gas through the respective inlet opening, i.e. to a direction perpendicular to the surface of the at least one inlet opening. The fact that the at least one inlet opening and the at least one outlet opening are at least partially offset from one another, in particular do not overlap with one another, ensures that an exhaust gas flow is deflected within the catalytic converter housing. This allows the flow path of the exhaust gas in the housing to be easily extended and thus the conversion to be improved.

[0108] The flow-through body is preferably arranged such that, for example, exhaust gases to be treated can flow into the catalyst housing through the inlet opening, flow through the flow-through body in the catalyst housing and then flow out through the outlet opening.

[0109] The catalyst housing can be manufactured in one piece or consist of several parts, preferably two half-shells. The two-half-shell design allows for particularly simple production of the catalyst.

[0110] Preferably, the volume of the flow-through body is at least 80% of the volume enclosed by the catalyst housing, in particular at least 90%. Particularly advantageously, the flow-through body completely fills the volume of the catalyst housing.

[0111] The flow-through body has a circumferential surface that is advantageously in contact with the catalyst housing. It is particularly advantageous if at least 50% of the circumferential surface of the flow-through body is in contact with the catalyst housing, even more advantageously at least 70%, and most advantageously the entire circumferential surface is in contact with the catalyst housing. It is particularly advantageous if the circumferential surface of the flow-through body does not have any portion coated with precious metal.

[0112] In a preferred design, the flow body is pressed into the catalyst housing or welded therein. Additional fastening elements may be provided, but are not mandatory.

[0113] Press-fitting the flow-through body is particularly advantageous when the flow-through body is made of molded metal wire or wire mesh. The flow-through body then exhibits sufficiently high elasticity and is securely held in the catalyst housing after the press-fitting process.

[0114] Because the flow-through body of the catalyst has at least two sub-areas with different amounts of catalytically active precious metal, the catalytic reaction, for example, the conversion of an exhaust gas, takes place predominantly or entirely in sub-area A, which is equipped with at least one precious metal. This allows rapid and intense heating to occur in this sub-area. The sub-area equipped with at least one precious metal preferably serves predominantly to convert hydrocarbons, carbon oxides, and / or nitrogen oxides.

[0115] The further sub-region(s) of the flow-through body that are not equipped with, or contain fewer or no precious metal components can preferably serve predominantly to reduce the particulate matter in exhaust gases. Exhaust gases from mixture-lubricated internal combustion engines contain lubricating oil in droplet form, which is evaporated by the catalyst. This requires a sufficiently high catalyst temperature. In addition, a sufficiently long residence time of the oil droplets in the catalyst is necessary. The further sub-region(s) are preferably heated quickly by sub-region A. This improves the particle-reducing effect of the further sub-region(s). Oil droplets are evaporated as soon as the required temperatures are reached. For lubricating oils commonly used today, the evaporation temperature can, for example, be in the range of 600°C to 700°C.The additional sub-area(s) also serve to thermally insulate sub-area A. The additional sub-area(s) are therefore also advantageous for catalysts where particle reduction is not the primary focus.

[0116] The invention also relates to an exhaust silencer comprising a one-piece flow-through body according to the invention or a flow-through body equipped according to the invention according to the preceding embodiments, a first silencer chamber and a second silencer chamber and a partition wall, wherein the partition wall is arranged between the first and the second silencer chamber and has a connecting opening, wherein the flow-through body is arranged in the connecting opening.

[0117] The exhaust silencer may also include a catalyst as previously described.

[0118] An exhaust silencer typically comprises an exhaust inlet, an exhaust outlet, and a flow-through body arranged between the exhaust inlet and the exhaust outlet in the direction of exhaust flow. Advantageously, the entire exhaust gas flows through the flow-through body during use. The exhaust silencer is, in particular, the exhaust silencer of a two-stroke engine or a mixture-lubricated four-stroke engine. In such mixture-lubricated engines, the exhaust gas may contain oil. The specified design of an exhaust silencer with a catalytic converter is particularly advantageous for such internal combustion engines. The exhaust silencer can also be used for separately lubricated internal combustion engines, particularly for separately lubricated four-stroke engines.The exhaust silencer is particularly advantageous for power generators or hand-held tools such as a chainsaw, a power cutter, a brush cutter, a blower, a lawn mower, a sprayer or the like.

[0119] The requirements for such exhaust silencers in hand-held implements differ in many respects from those in the automotive sector, for example. Due to the limited space available, exhaust silencers in such hand-held implements must be comparatively small. At the same time, operator contact with hot parts of the implement must be avoided. Therefore, strict requirements also apply with regard to exhaust gas temperatures.

[0120] In advantageous embodiments in which the exhaust silencer comprises a catalyst according to the invention, the at least one inlet opening of the catalyst is arranged in or adjacent to the first silencer chamber and the at least one outlet opening of the catalyst is arranged in or adjacent to the second silencer chamber.

[0121] Preferably, the volume of the flow-through body is no more than 70% of the volume enclosed by the exhaust silencer, in particular no more than 50%. It may be particularly advantageous if the volume of the flow-through body is no more than 30% of the volume enclosed by the exhaust silencer, since this minimizes the pressure loss of the exhaust gas during flow.

[0122] The invention also relates to a method for exhaust gas aftertreatment, wherein an exhaust gas stream is brought into contact with a one-piece flow-through body according to the invention or a flow-through body equipped according to the invention in accordance with the preceding embodiments. The exhaust gases can originate, for example, from internal combustion engines, in particular two-stroke engines or mixture-lubricated four-stroke engines.

[0123] Preferably, the flow body or the catalyst can be arranged in an exhaust silencer as described.

[0124] The invention is explained in more detail with reference to the following figures and examples. However, the exemplary embodiments are not to be understood as limiting. Like reference numerals identify like elements in the different embodiments.

[0125] Figure 1 shows a section of a flow body made of a pressed metal wire.

[0126] Figure 2 shows different geometries of coated sections and flow body cross-sections.

[0127] Figure 3 shows possible embodiments of a catalyst in which a flow body is arranged in a catalyst housing.

[0128] Figure 4 shows an exhaust silencer in which a catalyst is arranged in a silencer housing.

[0129] Figure 5 shows a measurement curve for determining the viscosity of a thickened precious metal solution

[0130] Figure 6 shows the emission of HC and NOx of the differently coated wire meshes for different air-fuel mixtures.

[0131] Figure 7 compares the increase in exhaust gas temperature of two differently equipped flow bodies.

[0132] Figure 1 shows a section of a flow body (1) made of a shaped metal wire, in this case a shaped wire mesh, which can be advantageously coated by the method according to the invention.

[0133] Figure 2 shows various geometries of coated partial areas A (2) (represented by the hatched areas) and flow-through body cross-sections. In Fig. 2 A, the coated partial area A (2) is positioned centrally in a square cross-section of the flow-through body (1) and surrounded by two further partial areas (3). In Fig. 2 B, the coated rectangular partial area A (2) is completely surrounded by another partial area (3). The coated round partial areas A (2) in Fig. 2 C and Fig. 2 D are arranged centrally in flow-through bodies (1) with different geometries. Fig. 2 E shows the round cross-section of a flow-through body (1) in which a partial area A (2) with a square cross-section is arranged centrally. Several coated partial areas A (2) are also possible, as shown in the embodiment in Fig. 2 F. The coated partial area A (2) of an elongated flow-through body (1) in Fig.2 G also has a rectangular cross-section and is positioned centrally between further sub-regions (3). In Fig. 2 H a similar embodiment is shown, but the coated sub-region A (2) does not border on the end faces of the flow-through body. In the embodiment in Fig. 2 I the coated sub-region A (2) is placed on an outer side, as is the case in Fig. 2 J. The coated sub-region A (2) in Fig. 2 K extends over the entire thickness of the flow-through body (1). In the embodiment in Fig. 2 L the coated sub-region A (2) is placed on an outer side, without bordering on any of the end faces. The embodiment as in Fig. 2 M has several sub-regions A (2) placed centrally and on the inside.

[0134] In all embodiments, the further subregion (3) or the further subregions can also be provided with a precious metal-containing coating or with a precious metal-containing or precious metal-free washcoat layer. A combination of more than two different subregions is also possible. For example, an embodiment can be advantageous in which a first subregion of the flow-through body has no coating, a second subregion has a precious metal-free washcoat layer, and a third subregion has a precious metal-containing washcoat layer applied according to the invention. The third subregion A can be provided by providing it with a precious metal-containing washcoat suspension or by providing a precious metal-free washcoat layer with a precious metal-containing composition.

[0135] Figure 3 shows possible embodiments of catalytic converters (4), in which a flow body (1) is arranged in a catalytic converter housing (5), each of which has an inlet opening (6) and an outlet opening (7). The catalytic converter housing (5) in Fig. 3 B consists of two half-shells (8). Figure 4 shows an exhaust silencer (9) in which a catalytic converter (4) is arranged in a silencer housing (10). Typically, an exhaust silencer comprises several metal shells that are connected to one another at a circumferential edge and enclose the exhaust silencer chamber (11). The metal shells can, for example, be deep-drawn parts made of sheet metal. The silencer housing (10) has an inlet opening (12) and an outlet opening (13), as well as a partition wall (14) with an opening (15). The partition wall (14) separates the two exhaust silencer chambers from one another.In the illustrated embodiment, the catalyst (4) is arranged in the opening (15) such that flowing exhaust gas is guided completely through the catalyst (4) along the flow direction (16). The catalyst housing (5) has an inlet opening (6) and two outlet openings (7). A different arrangement of the catalyst in the flow path can also be provided.

[0136] The measurement methods used in the present invention are listed below. If no test method is specified, the corresponding ISO method was used to determine the respective parameter, as valid at the time of filing this application. If no specific measurement conditions are specified, the measurement was performed at room temperature (298.15 K) and atmospheric pressure (100 kPa).

[0137] Viscosity and thixotropy index

[0138] The static and dynamic viscosity of samples were determined using a cone-and-plate rheometer (ThermoFisher "Haake Rheostress 600", MPC60 Ti plate, 60 mm diameter, cone C 20 / 0.5° Ti, cone-to-plate distance 0.026 mm). Prior to measurement, the sample was heated to 20 °C for 3 min under a controlled shear rate (CRS) of 100 s' 1 .

[0139] The measurement was carried out in several stages: static viscosity (CS) oscillating at controlled shear stress (CSS) of 1 Pa for 20 s dynamic viscosity (CR) rotating at CRS of 500 s -1 for 30 seconds

[0140] The measurements were evaluated using the software “HAAKE RheoWin”.

[0141] The thixotropy index TI of the samples indicates the ratio between static viscosity and dynamic viscosity (TI = CS / CR). BET specific surface area

[0142] The BET specific surface area was determined using nitrogen as adsorbate at 77 K according to BET theory (multipoint method, ISO 9277:2010).

[0143] Pore ​​volume and pore diameter distribution

[0144] The pore volume and pore diameter distribution were determined using mercury porosimetry according to ISO 15901-1:2022.

[0145] Examples

[0146] For all examples, a cuboid wire body (45 x 25 x 15 mm) made of a steel wire (1 .4767, 0.35 mm diameter) was first homogeneously coated with a precious metal-free washcoat layer. The wire body was immersed in the washcoat suspension (aqueous suspension of Al2O3 and cerium hydroxide), centrifuged, and calcined at 800 °C (VB0).

[0147] The pretreated wire bodies were treated with a solution of Pt nitrate in water (3.5 wt% Pt). The untreated solution showed no thixotropic behavior and a static and dynamic viscosity of <1 mPa*s.

[0148] The aqueous precious metal solution was thickened with 2 wt.% Natrosol and 0.5% triethylamine. The dynamic viscosity of the solution was 350 mPa*s, and the thixotropy index was 86. The measurement curve for determining the viscosity of the thickened solution is shown in Figure 5.

[0149] VB1 - Homogeneous equipment with precious metal

[0150] A pretreated wire body was completely immersed in the aqueous platinum solution. The impregnated wire body was then calcined in air at 800 °C.

[0151] The total platinum content was 60 mg.

[0152] VB2 - Selective treatment with untreated precious metal solution

[0153] The aqueous platinum solution was pipetted into the pretreated wire body in a channel-like fashion. Reproducible coating of the wire body was not possible because the solution partially permeated the wire body and, moreover, capillary action prevented it from being applied in a targeted manner. EB1 - Selective coating with a customized precious metal solution

[0154] The thickened platinum solution was pipetted into the pretreated wire body in a channel-shaped manner. A weighing check ensured that the entire solution remained on the wire body. The wire body was then calcined as described in VB1.

[0155] The platinum dose was 15 mg.

[0156] The coated wire bodies were installed downstream of an engine in the exhaust pipe. A two-stroke engine was used for the tests, operating with varying air-fuel ratios (lambda values ​​below 1). The temperature and composition of the exhaust gases from the exhaust pipe were measured while the engine was running.

[0157] Figure 6 shows the reduction in HC and NOx emissions of the differently coated wire meshes for different air-fuel mixtures. The percentage emissions are shown compared to an uncoated catalyst (VBO). Although the wire mesh selectively coated according to the invention (EB1) contained only a quarter of the precious metal inventory, it sufficiently reduced the pollutant concentration by half across the lambda range compared to the uniformly coated wire mesh (VB1).

[0158] Figure 7 compares the increase in exhaust temperature when using the wire mesh (EB1) equipped according to the invention with the fully coated wire mesh (VB1) compared to a wire mesh without catalytically active precious metal (VBO). The exhaust temperature with EB1 was significantly lower than with the comparable homogeneously coated wire mesh VB1. A lower temperature generally means an improvement in long-term stability.

[0159] The combination of sufficient efficiency with reduced precious metal inventory together with the improved long-term stability demonstrates the advantageous properties of the wire meshes equipped according to the invention.

Claims

CLAIMS 1. A method for equipping a partial area A of a flow body with at least one precious metal, the method comprising the following steps: (i) Provision of the flow body, (ii) providing a composition comprising a precious metal component and a solvent, (iii) non-immersive coating of the partial area A of the flow-through body with the composition, wherein the non-immersive coating is carried out by applying the composition to the partial area A and the entire amount of the composition applied to the partial area A initially remains on the partial area A, (iv) removing the volatile components of the composition from the portion A.

2. Method according to claim 1, wherein the flow-through body is a one-piece body.

3. Method according to claim 1 or 2, wherein the total volume of the flow body is 10 cm 3 up to 200 cm 3 amounts.

4. Method according to one of the preceding claims, wherein the flow-through body is a foam, a body consisting of irregularly arranged fibers, a body made of expanded metal or a wire body.

5. A process according to any one of the preceding claims, wherein the composition has thixotropic properties.

6. The method according to claim 5, wherein the composition has a dynamic viscosity of not more than 2500 mPa*s.

7. A process according to any one of claims 5 or 6, wherein the composition has a thixotropy index TI of at least 5.

8. A process according to any one of the preceding claims, wherein the composition contains a thickener.

9. The method according to any one of the preceding claims, wherein the non-immersive coating is carried out by a method selected from the group consisting of pipetting, brushing, stamping, spreading, injecting, rolling or printing.

10. Method according to one of the preceding claims, wherein the volume of the coated partial region A is 5% to 90% of the total volume of the flow-through body.

11. Method according to one of the preceding claims, wherein at least 50% of the circumferential surface of the flow-through body is not formed by the partial region A provided with at least one precious metal.

12. Method according to one of the preceding claims, wherein the non-immersive coating is carried out on a central partial region A of the flow-through body which is at least partially not adjacent to any edge region.

13. One-piece flow-through body with at least one partial area A provided with at least one precious metal, wherein the at least one partial area A is at least partially enclosed by one or more further partial areas B of the one-piece flow-through body.

14. A catalyst comprising a catalyst housing and a one-piece flow-through body according to claim 13 or a flow-through body equipped with at least one precious metal and manufactured according to any one of claims 1-12.

15. A method for exhaust gas aftertreatment, wherein an exhaust gas stream is brought into contact with a one-piece flow-through body according to claim 13 or a flow-through body equipped with at least one precious metal and produced according to one of claims 1-12.

Images