Ruthenium-containing catalytically active compositions for exhaust gas aftertreatment catalysts

Abstract

The present invention relates to a ruthenium-containing catalytically active composition for an exhaust gas aftertreatment catalyst, the composition comprising: a doped refractory oxide, a metal oxide which is provided with at least ruthenium and is selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof, and composite oxides of two or more thereof; and a cerium-zirconium oxide comprising at least one element other than cerium from the rare earth family. The invention also relates to formulations containing the catalytically active composition, methods for their preparation, catalysts having the catalytically active composition, and methods of using the composition.

Description

[0001] The invention relates to a ruthenium-containing catalytically active composition for exhaust gas aftertreatment catalysts, a preparation containing the catalytically active composition, a process for the preparation thereof, a catalyst containing the catalytically active composition and a process for using the composition.

[0002] Many hazardous or environmentally harmful compounds are found in exhaust gas emissions from chemical, industrial or fuel-consuming processes, for example from incinerators, gas turbines, industrial facilities or internal combustion engines. Exhaust gases from internal combustion engines, especially in motor vehicles, have long been treated by three-way catalysts. The task of the catalyst is to convert the pollutants produced during combustion, in particular hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO x )) into non-toxic substances carbon dioxide (CO2), water (H2O) and nitrogen (N2). In addition to the three-way catalyst, the oxidation catalyst and NO x Storage of catalysts is most commonly used.

[0003] Such catalysts typically contain at least one catalytically active noble metal component. The noble metal is applied to a support material and forms active centers on the surface of the catalyst. For example, catalysts for oxidation reactions in exhaust gas aftertreatment typically contain platinum, palladium, iridium and rhodium on a heat-resistant support (such as alumina), which is usually mixed with an oxygen storage material and applied to an inert substrate. The substrate is typically a honeycomb made of a ceramic material (e.g., cordierite) or a metallic material (e.g., FeCrAl).

[0004] However, due to the high cost of a large number of noble metals, efforts are being made to reduce the noble metal content in catalysts, in particular to at least partially replace rhodium with substitutes. In addition, there is a need for catalysts that are less expensive but are equally capable of removing pollutants from exhaust gases of combustion reactions, such as from emissions from chemical plants or motor vehicles. Ruthenium represents a more cost-effective alternative to rhodium as an active catalytic substance.

[0005] Reduction of NO using ruthenium-containing catalysts x As well as oxidizing CO and hydrocarbons are known in principle. One problem with the use of ruthenium is that the noble metal tends to form volatile and toxic oxides, which affects the durability of such systems. For example, US2017107880A1 discloses a ruthenium-containing exhaust gas catalyst for reducing NO x However, in order to achieve high activity and selectivity of the catalyst, the exhaust gas must be conditioned to ensure reducing conditions.

[0006] US2006034740 A1 discloses a combination of ruthenium and another noble metal on an alumina support material for stabilization purposes. US2003144143 A1 proposes the use of zirconium oxide and tin oxide to stabilize a ruthenium-containing alumina-based catalyst.

[0007] US2018229220 A1 discloses a catalyst for removing volatile organic compounds (VOCs) from industrial waste gases, which contains tin oxide and silicon dioxide and optionally other oxide stabilizers to stabilize the catalyst system in addition to ruthenium and a heat-resistant mixed oxide. The catalyst is produced using a washcoat process, in which ruthenium is applied uniformly to all support materials as an active catalytic substance.

[0008] The object of the present invention is to provide ruthenium-containing catalytically active compositions for exhaust gas aftertreatment catalysts which have a favorable light-off behavior and increased stability. In particular, the object is to provide catalytically active compositions which enable the use of low-cost metal substances in catalyst systems intended to eliminate toxic emissions such as carbon monoxide, hydrocarbons and other volatile organic compounds, in particular nitrogen oxides.

[0009] The "light-off temperature" denotes the temperature at which 50% of at least one of the compounds to be decomposed or of a group of compounds to be decomposed is converted. Below this minimum temperature, the catalytic effect is too low to ensure sufficient effectiveness of the catalytic oxidation reaction.

[0010] Furthermore, it is an object to provide a process for the preparation of such catalytically active compositions, preparations containing the catalytically active compositions and processes for their preparation as well as catalysts containing the catalytically active compositions.

[0011] Surprisingly, it was found that the objects solved by the present invention are achieved by a catalytically active composition, which contains: a doped refractory oxide, which is provided with at least ruthenium and is selected from the group consisting of: aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof; and a cerium-zirconium oxide, which contains at least one element from the rare earth group other than cerium.

[0012] In particular, it has been found that the combination of a doped refractory oxide on which at least ruthenium is loaded as a catalytically active component and a doped cerium-zirconium oxide leads to an unexpected stabilization of ruthenium in a catalytically active composition. In addition, the composition exhibits an unexpectedly high catalytic activity, which allows particularly low loadings of catalytically active substances. Thus, the specific combination of different components makes it possible to provide a relatively inexpensive but active and stable catalytically active composition.

[0013] The catalytically active composition according to the invention is suitable for exhaust gas aftertreatment, in particular the aftertreatment of oxygen-containing combustion exhaust gases. Examples of combustion exhaust gases include exhaust gases from mobile and stationary internal combustion engines, which contain nitrogen oxides reduced from the exhaust gas in addition to hydrocarbons and carbon monoxide that are oxidized during the aftertreatment process. Other possible sources of treatable exhaust gases are combustion facilities, gas turbines or industrial facilities, such as refineries, chemical plants, sewage plants or waste incinerators. The composition is particularly preferably used to treat exhaust gases from internal combustion engines, in particular small engines, 2-stroke engines and engines operating in the "rich" λ range. λ (Lambda) refers to the air-fuel ratio. This establishes the relationship between the air mass that is actually available for combustion and the minimum stoichiometric air mass required for complete combustion of the fuel. With respect to the stoichiometric fuel ratio, there is just the right amount of air that can be used to completely burn the fuel. This is indicated as λ=1. If more fuel is available, it is called a rich mixture (λ<1), and if there is an excess of air, it is called a lean mixture (λ>1).

[0014] The catalytically active composition comprises a doped refractory oxide. As used herein, the term "refractory oxide" refers to metal-containing oxides that are chemically and physically stable at high temperatures, particularly those associated with gasoline and diesel engine exhaust. Refractory oxides are also commonly referred to as heat-resistant oxides.

[0015] The refractory oxide is selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixed oxides thereof, and composite oxides of two or more thereof.

[0016] The term "mixed oxide" as used herein generally refers to a mixture of oxides in a single phase, as is generally known in the relevant technical field. It is not used for physical mixtures of oxides, but rather refers to a "solid solution" with a uniform crystal lattice in which individual metal oxides may not be distinguished. The term "complex oxide" as used herein refers to an aggregate of metal oxides that does not have a uniform crystal lattice and in which phases of individual metal oxides can be distinguished.

[0017] In a preferred embodiment, the refractory oxide is alumina or a mixed oxide or composite oxide of alumina.

[0018] The refractory oxide is doped, in other words, the refractory oxide contains a dopant. The refractory oxide doped with a dopant can be obtained using methods known in the relevant technical field.

[0019] 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) and neodymium (Nd). Preferably, the dopant comprises La, Ba, Sr, Zr or Mn. The dopant is preferably in the form of an oxide.

[0020] Particularly preferably, the doped refractory oxide is lanthanum oxide-doped aluminum oxide, a mixed oxide of lanthanum oxide-doped aluminum oxide or a composite oxide of lanthanum oxide-doped aluminum oxide.

[0021] The total amount of dopant can be 0.2 to 6 wt. % (wt. %) of the doped refractory oxide, preferably 0.5 to 5 wt. %, particularly preferably 1 to 4 wt. %. The total amount of dopant used here refers to the weight of the doped refractory oxide.

[0022] Preferably, the doped refractory oxide layer has a large BET surface area, preferably at least 30 m 2 / g, especially at least 80m 2 / g, particularly preferably at least 100m 2 Typically, the BET surface area of ​​the doped refractory oxide layer is between 30 m 2 / g and 300m 2 / g, preferably between 50m 2 / g and 200m 2 The BET surface area is also referred to as specific surface area and can be determined according to ISO 9277:2010 using nitrogen as the adsorbate.

[0023] The proportion of the doped refractory oxide in the catalytically active composition can be in the range of 10% to 95% by weight, preferably in the range of 20% to 90% by weight, in particular in the range of 30% to 85% by weight, based on the total amount of the catalytically active composition.

[0024] The doped refractory oxide is preferably a porous material. The pore volume is typically in the range of 0.2 mL / g to 10.0 mL / g, in particular in the range of 0.3 mL / g to 0.8 mL / g. The average pore radius is 5 nm to 40 nm, in particular 10 nm to 30 nm. The pore volume and pore size distribution can be determined by mercury intrusion according to ISO 15901-1:2022.

[0025] Preferably, the particle size of the doped refractory oxide is 90In the range of 10 μm to 35 μm, preferably in the range of 15 μm to 30 μm, particularly preferably in the range of 19 μm to 24 μm. 90 The value indicates that 90% of the particles have a diameter below this value. The particle size distribution can be determined according to ISO 13320 by laser diffraction.

[0026] The doped refractory oxide is provided with at least ruthenium. Ruthenium forms at least part of the catalytically active component of the catalytically active composition.

[0027] The term "ruthenium" used does not contain any information about the oxidation state of ruthenium. In other words, it does not indicate the presence of an elemental state with an oxidation state of 0. Ruthenium can be present on the doped refractory oxide in elemental form, i.e. in oxidation state (0) or in higher oxidation states. The term "oxidation state" as used herein and known to those skilled in the art refers to the formal charge of an atom within a compound or the actual charge of a monatomic ion. By definition, an atom in an elemental state has an oxidation state of 0.

[0028] The provision of a doped refractory oxide with ruthenium is understood to mean that ruthenium is supported on the doped refractory oxide, i.e. ruthenium is present in or on the doped refractory oxide, for example in the form of particles or a layer, whereby this layer is preferably a non-enclosed layer. The terms "provided" and "supported" are used synonymously and interchangeably in the present application. The provision of the doped refractory oxide may occur on the surface and inside the doped refractory oxide. The term "surface" includes both the outer surface and the inner surface, i.e. also the inner surface formed by the pores.

[0029] Typically, the doped refractory oxide provides 0.1 wt. % to 25 wt. %, preferably 0.1 wt. % to 20 wt. %, more preferably 0.5 wt. % to 15 wt. %, particularly preferably 1.0 wt. % to 10 wt. % ruthenium, based on the total amount of doped refractory oxide and ruthenium.

[0030] Preferably, the catalytically active composition comprises ruthenium in an amount of 0.05 to 20% by weight, preferably 0.5 to 18% by weight, more preferably 1.0 to 13% by weight, for example 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 15%, 18%, 20% by weight or intermediate values ​​thereof, based on the total amount of doped refractory oxide, ruthenium, cerium-zirconium oxide and optionally further noble metals.

[0031] The doped refractory oxide with ruthenium can be provided using methods known to those skilled in the art, for example by impregnation, precipitation, chemical vapor deposition (CVD), a coating process or a spraying process. The providing can be carried out in one or more steps.

[0032] The provision typically comprises combining the doped refractory oxide with at least one ruthenium compound, which is generally provided in a composition comprising at least one solvent. After combining them together, precipitation and / or reduction and drying and / or calcining steps of at least one ruthenium compound may be performed.

[0033] For example, the composition may be absorbed into or within the doped refractory oxide driven by capillary forces such that the volume of the composition roughly corresponds to the intrapore volume of the doped refractory oxide, which is known to those skilled in the art as "incipient wetness".

[0034] In this case, "solvent" means that the solvent comprises at least one liquid substance in which the at least one ruthenium compound is soluble. The at least one solvent may comprise a plurality of chemical substances, ie the solvent may also be a solvent mixture.

[0035] At least one solvent may be selected from the group consisting of water and an organic solvent. The organic solvent may be selected from a variety of commercially available organic solvents. Advantageously, the organic solvent is substantially volatile under the processing conditions of the composition. The organic solvent may be, for example, an alcohol, such as methanol or ethanol.

[0036] In a preferred embodiment, the composition comprises 20% to 99.5% by weight, preferably 30% to 95% by weight, of solvent, based on the total weight of the composition. Advantageously, the composition comprises at least 50% by weight, particularly preferably at least 80% by weight, very particularly preferably at least 90% by weight of solvent.

[0037] The composition also contains at least one ruthenium compound.

[0038] The amount of ruthenium in the composition can vary widely and is determined by the expected loading of the doped refractory oxide and ruthenium. "The amount of ruthenium" refers to the proportion of ruthenium in the composition, in other words, it therefore does not refer to the amount of the entire ruthenium compound. Preferably, the composition comprises 0.5% to 80% by weight of ruthenium, based on the total weight of the composition comprising at least one solvent and the ruthenium compound. In one embodiment, the composition comprises 1% to 60% by weight, preferably 5% to 50% by weight of ruthenium. Particularly good results are obtained when the composition contains ruthenium in an amount of at least 0.5% by weight, in particular at least 1% by weight, preferably at least 5% by weight, preferably at least 10% by weight.

[0039] The composition may contain only one ruthenium compound or a plurality of ruthenium compounds. Suitable ruthenium compounds are, for example, Ru salts, Ru complex compounds or Ru organometallic compounds, such as nitrates, acetylacetonates or acetates, and a variety of other salts known to those skilled in the art or that can be found by simple experiments. The ruthenium compound is preferably a ruthenium compound that does not contain halogens. Examples of suitable ruthenium compounds include ruthenium nitrate, ruthenium acetate, pentacarbonyl ruthenium, ruthenium acetylacetonate, ruthenium oxalate, bis(oxadiazole) ruthenium and nitrosyl ruthenium nitrate.

[0040] Preferably, providing the doped refractory oxide with ruthenium involves a drying step in which at least some of the solvent is removed from the composition.

[0041] Preferably, providing the refractory oxide doped with ruthenium can involve a calcination step. "Calcination" is understood by a person skilled in the art to mean a heat treatment in which the metal component is preferably fixed to the support material. The calcination step is particularly advantageous if the temperature is in the range of 150° C. to 700° C., in particular 200° C. to 600° C. In a preferred embodiment, the temperature is greater than 200° C., particularly preferably greater than 300° C. In a preferred embodiment, the calcination step is carried out for a period of 1 hour to 24 hours, preferably 2 hours to 12 hours.

[0042] The doped refractory oxide can be provided with at least one further noble metal selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh) and combinations thereof. In such a case, ruthenium and the at least one further noble metal form at least part of the catalytically active component of the catalytically active composition. The combination of ruthenium with at least one further noble metal has proven to be particularly advantageous with regard to the long-term stability and the light-off temperature of the catalytically active composition.

[0043] The terms "metal", "noble metal" or, for example, "platinum" as used herein do not contain any information about their oxidation state. In other words, it does not indicate the presence of an elemental state with an oxidation state of 0. A metal, a noble metal or, for example, platinum can be in elemental form, i.e. in oxidation state (0) or in higher oxidation states.

[0044] In particular, it has proven to be advantageous that the doped refractory oxide is provided with a combination of: ruthenium and iridium; ruthenium and platinum; ruthenium and palladium; ruthenium, platinum and iridium; ruthenium, palladium and iridium; or ruthenium, palladium and platinum. In a particularly preferred embodiment, the doped refractory oxide is provided with ruthenium and iridium or ruthenium, platinum and iridium.

[0045] Preferably, the doped refractory oxide provides ruthenium and at least one other precious metal in an amount of 0.2% to 30% by weight, preferably 0.5% to 25% by weight, more preferably 1% to 20% by weight, and particularly preferably 5% to 15% by weight, based on the total amount of the doped refractory oxide, ruthenium and at least one other precious metal.

[0046] If the doped refractory oxide has at least one further noble metal, ruthenium and the at least one further noble metal are preferably present in a molar ratio in the range from 1:20 to 20:1, in particular in a ratio of 1:10 to 10:1.

[0047] In the case where the doped refractory oxide is to be provided with ruthenium and at least one other noble metal, it may be preferred to provide the doped refractory oxide with ruthenium and at least one other noble metal simultaneously. In this case, the composition for providing ruthenium may contain at least one other noble metal compound. The provision is carried out in the manner already described for providing ruthenium. It is also advantageous if at least one other noble metal is provided in a separate composition, which is contacted with the doped refractory oxide simultaneously with the composition containing the ruthenium compound. The doped refractory oxide may also be provided with another noble metal in a separate step, which step may be carried out after or before the provision of ruthenium.

[0048] The amount of at least one other precious metal compound in the composition can vary widely and is determined by the expected loading of the refractory oxide doped with at least one other precious metal. "The amount of at least one other precious metal" refers to the proportion of at least one other precious metal in the composition, in other words, it does not refer to the amount of at least one precious metal compound. Preferably, based on the total weight of the composition comprising at least one solvent and at least one precious metal compound, the composition comprises 0.5 wt % to 80 wt % of at least one other precious metal. In one embodiment, the composition comprises 1 wt % to 60 wt %, preferably 5 wt % to 50 wt % of at least one other precious metal. Particularly good results are obtained when the composition contains at least 0.5 wt %, particularly at least 1 wt %, preferably at least 5 wt %, preferably at least 10 wt % of at least one other precious metal.

[0049] The composition may contain only one noble metal compound or a plurality of noble metal compounds. Suitable noble metal compounds are complexes, organometallic compounds or salts of noble metals, such as nitrates, halides, acetylacetonates or acetates, as well as a variety of other salts known to those skilled in the art or discoverable by simple experiments.

[0050] In the case where the at least one noble metal comprises iridium, the at least one noble metal compound may be, for example, an Ir salt, an Ir complex compound or an Ir organometallic compound. Examples of suitable iridium compounds are iridium chloride, iridium acetate, iridium acetylacetonate, iridium sulfate and dihydrogen hexachloroiridate.

[0051] In the case where at least one noble metal comprises platinum, the at least one noble metal compound may be, for example, a Pt salt, a Pt complex compound or a Pt organometallic compound. As examples of suitable platinum compounds, the following may be mentioned: platinum halides such as platinum(II) chloride or platinum(IV) chloride or their acids, hexachloroplatinic acid or its salts, platinic acid or its salts, hydroxyethylammonium hexahydroxyplatinate, ammonium hexachloroplatinate, ammonium tetrachloroplatinate, potassium tetrachloroplatinate, potassium hexachloroplatinate, sodium tetrachloroplatinate, potassium tetrahydroxyplatinate, platinum nitrate, platinum sulfite, ethanolamine platinum, platinum acetylacetonate, platinum oxalate or a mixture of at least two of these compounds.

[0052] In the case where the at least one noble metal comprises palladium, the at least one noble metal compound may be, for example, a Pd salt, a Pd complex compound or a Pd organometallic compound. As examples of suitable palladium compounds, the following may be mentioned: palladium halides such as palladium(II) chloride, palladium(II) bromide or palladium(IV) chloride or their acids, palladium acetate, palladium nitrate, palladium acetylacetonate, palladium sulfate, palladium oxalate, hydroxyethylammonium hexahydroxypalladate, ammonium hexachloropalladate, ammonium tetrachloropalladate, potassium tetrachloropalladate, potassium hexachloropalladate, sodium tetrachloropalladate, potassium tetrahydroxypalladate, dichlorodiamminepalladium, tetraamminepalladium nitrate, tetraamminepalladium chloride, tetraamminepalladium hydroxide, tetraamminepalladium sulfate or a mixture of at least two of these compounds.

[0053] In order to remove oxygen from the nitrogen oxides of the exhaust gas to be treated and to oxidize hydrocarbons and carbon monoxide at the same time, the catalytically active composition comprises a cerium-zirconium oxide which contains at least one element from the rare earth group other than cerium. Such cerium-zirconium oxides are known to those skilled in the art as oxygen storage components. Cerium-zirconium oxides can be mixed oxides or mixtures of cerium oxide (CeO2) and zirconium oxide (ZrO2). According to the invention, the cerium-zirconium oxide comprises both an oxide rich in cerium and an oxide rich in zirconium.

[0054] The cerium-zirconium oxide preferably contains 10 to 90 wt %, preferably 15 to 80 wt %, of zirconium oxide, based on the total weight of the cerium-zirconium oxide.

[0055] The cerium-zirconium oxide comprises at least one element from the rare earth group except cerium. At least one element from the rare earth group is preferably present in the form of an oxide. Preferably, at least one rare earth element is selected from the group consisting of neodymium (Nd), praseodymium (Pr), lanthanum (La) and hafnium (Hf). The cerium-zirconium oxide may, for example, comprise cerium-zirconium-lanthanum oxide, cerium-zirconium-yttrium oxide, cerium-zirconium-lanthanum-yttrium oxide, cerium-zirconium-neodymium oxide, cerium-zirconium-praseodymium oxide, cerium-zirconium-lanthanum-neodymium oxide, cerium-zirconium-lanthanum-praseodymium oxide, cerium-zirconium-lanthanum-neodymium-praseodymium oxide or a combination thereof. Based on the total weight of the oxygen storage component, the proportion of each of the rare earth oxides may be 2 wt % to 20 wt %, preferably 5 wt % to 15 wt %.

[0056] The catalytically active composition preferably comprises cerium-zirconium oxide in a proportion of 5% to 50% by weight, particularly preferably in a proportion of 10% to 40% by weight, based on the total weight of the catalytically active composition.

[0057] Preferably, the BET surface area of ​​ceria-zirconia is at least 10 m 2 / g, especially at least 20m 2 Typically, the BET surface area of ​​ceria-zirconia is between 10 m 2 / g and 150m 2 / g, preferably between 30m 2 / g and 100m 2 / g.

[0058] The cerium-zirconium oxide is preferably a porous material. The pore volume is usually in the range of 0.2 mL / g to 1.0 mL / g, especially in the range of 0.3 mL / g to 0.8 mL / g. The average pore radius is about 5 nm to 20 nm, especially 7 nm to 12 nm.

[0059] Preferably, the particle size of the cerium-zirconium oxide is 90 In the range of 10 μm to 35 μm, preferably in the range of 15 μm to 30 μm, particularly preferably in the range of 19 μm to 24 μm.

[0060] The cerium-zirconium oxide can be provided with at least one noble metal, which is preferably selected from the group consisting of ruthenium (Ru), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh) and combinations thereof. In order to avoid any misunderstanding, it should be pointed out at this point that ruthenium therefore also belongs to the noble metal family. In such cases, the ruthenium provided by the doped refractory oxide and optionally the other noble metals and the noble metal provided by the cerium-zirconium oxide form the catalytically active components of the catalytically active composition.

[0061] In particular, if the total proportion of noble metals in the catalytically active composition is greater than 5% by weight, in particular greater than 10% by weight, it is advantageous if the cerium-zirconium oxide is provided with at least one noble metal. The total proportion of noble metals is understood to mean all noble metals present in the catalytically active composition, in other words both ruthenium and any other noble metals provided by the doped refractory oxide, and the noble metal provided by the cerium-zirconium oxide.

[0062] The cerium-zirconium oxide preferably provides the at least one noble metal in an amount of 0.05 to 15% by weight, in particular 0.1 to 10% by weight, very particularly 0.5 to 5% by weight, based on the total amount of cerium-zirconium oxide and the at least one noble metal.

[0063] In particular, it has proven to be advantageous if the cerium-zirconium oxide is provided with ruthenium, ruthenium and iridium, ruthenium and platinum, ruthenium and palladium or ruthenium, iridium and platinum.

[0064] Providing the cerium-zirconium oxide with at least one noble metal can be carried out using methods known to those skilled in the art, such as when providing a doped refractory oxide with at least one noble metal, for example by impregnation, precipitation, chemical vapor deposition (CVD) or spraying processes. The above statements about providing a doped refractory oxide also apply to providing a cerium-zirconium oxide.

[0065] The noble metal provision of cerium-zirconium oxide can be the same or different from the noble metal provision of the refractory oxide of doping. In a preferred embodiment, the noble metal provision of the refractory oxide of doping and cerium-zirconium oxide is different. In other words, the catalytically active components loaded on the refractory oxide of doping and cerium-zirconium oxide are different. For example, the shape or size of the noble metal particles provided by the refractory oxide of doping and cerium-zirconium oxide may be different. It should be noted at this point that in the case where cerium-zirconium oxide is not provided with any catalytically active components, the provision of the refractory oxide of doping and cerium-zirconium oxide is also different. Providing refractory oxides and cerium-zirconium oxides with doping of different noble metals makes it possible to specifically combine noble metals and carrier materials in order to realize the maximum efficiency of different substances and the separation of different noble metal substances from each other. This can lead to a further increase in catalytic activity. In particular, in the case where the catalytically active composition is provided with at least one other noble metal in addition to ruthenium, different provision may be advantageous.

[0066] For example,

[0067] - the doped refractory oxide may be provided with ruthenium and the cerium-zirconium oxide may be provided without any noble metal,

[0068] -doped refractory oxides may be provided with ruthenium and cerium-zirconium oxides may be provided with ruthenium,

[0069] -doped refractory oxides may be provided with ruthenium and cerium-zirconium oxides may be provided with platinum,

[0070] - the doped refractory oxide may be provided with ruthenium and the cerium-zirconium oxide may be provided with iridium,

[0071] -doped refractory oxides may be provided with ruthenium, and cerium-zirconium oxides may be provided with ruthenium and platinum,

[0072] - the doped refractory oxide may be provided with ruthenium and the cerium-zirconium oxide may be provided with ruthenium and iridium,

[0073] - the doped refractory oxide may be provided with ruthenium and the cerium-zirconium oxide may be provided with platinum and iridium,

[0074] - the doped refractory oxide may be provided with ruthenium, and the cerium-zirconium oxide may be provided with ruthenium, platinum and iridium,

[0075] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided without any noble metal,

[0076] -doped refractory oxides may be provided with ruthenium and platinum, and cerium-zirconium oxides may be provided with ruthenium,

[0077] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided with platinum,

[0078] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided with iridium,

[0079] -doped refractory oxides may be provided with ruthenium and platinum, and cerium-zirconium oxides may be provided with ruthenium and platinum,

[0080] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided with ruthenium and iridium,

[0081] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided with platinum and iridium,

[0082] - the doped refractory oxide may be provided with ruthenium and platinum, and the cerium-zirconium oxide may be provided with ruthenium, platinum and iridium,

[0083] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided without any noble metal,

[0084] - doped refractory oxides may be provided with ruthenium and iridium, and cerium-zirconium oxides may be provided with ruthenium,

[0085] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with platinum,

[0086] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with iridium,

[0087] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with ruthenium and platinum,

[0088] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with ruthenium and iridium,

[0089] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with platinum and iridium,

[0090] - the doped refractory oxide may be provided with ruthenium and iridium, and the cerium-zirconium oxide may be provided with ruthenium, platinum and iridium,

[0091] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided without any noble metal,

[0092] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with ruthenium,

[0093] - doped refractory oxides may be provided with ruthenium, platinum and iridium, and cerium-zirconium oxides may be provided with platinum,

[0094] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with iridium,

[0095] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with ruthenium and platinum,

[0096] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with ruthenium and iridium,

[0097] - the doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with platinum and iridium, or

[0098] The -doped refractory oxide may be provided with ruthenium, platinum and iridium, and the cerium-zirconium oxide may be provided with ruthenium, platinum and iridium.

[0099] Furthermore, it has been shown that it is advantageous for the stability of the catalytically active composition if, in particular, the ruthenium is predominantly supported on the doped refractory oxide. In a preferred embodiment, at least 60%, particularly preferably more than 75%, very particularly preferably more than 95% of the total ruthenium contained in the catalytically active composition is supported on the doped refractory oxide.

[0100] Preferably, the catalytically active composition comprises the precious metal in an amount of 0.5 to 35% by weight, preferably 1 to 30% by weight, more preferably 5 to 25% by weight, for example 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35% by weight or intermediate values ​​thereof, based on the total amount of doped refractory oxide, ruthenium, cerium-zirconium oxide and optionally further precious metals.

[0101] The catalytically active composition may also contain other components, such as fillers, binders, pore formers, stabilizers or rheology modifiers. Such additional components generally do not exhibit catalytic activity for the desired reaction, but rather improve the effectiveness of the catalytically active composition, for example by increasing the operating temperature range, increasing the contact surface, improving the adhesion properties of the catalytically active composition to the substrate, etc.

[0102] Preferably, the catalytically active composition is prepared by a process comprising the following steps:

[0103] i) providing a doped refractory oxide provided with at least ruthenium and selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof,

[0104] ii) providing a cerium-zirconium oxide comprising at least one element from the rare earth group other than cerium,

[0105] iii) A doped refractory oxide provided with at least ruthenium is mixed with a cerium-zirconium oxide.

[0106] The invention also relates to a process for preparing a catalytically active composition according to the invention, comprising the steps described above. With regard to preferred embodiments of the individual components, reference is made to the statements made above.

[0107] Surprisingly, it has been found that providing the doped refractory oxide with ruthenium before preparing the catalytically active composition improves the long-term stability of the catalytic activity of the composition. Furthermore, surprisingly, a positive influence on the light-off temperature of the catalytically active composition prepared according to the invention was observed.

[0108] In particular, the provision of doped refractory oxides in processes using halogen-free ruthenium compounds has proven to be advantageous with regard to the long-term stability and efficiency of the catalytically active composition. For examples of suitable ruthenium compounds, reference is made to the above statements.

[0109] In step iii), a doped refractory oxide provided with at least ruthenium is mixed with a cerium-zirconium oxide. The mixing is carried out according to methods known to those skilled in the art or in systems known to those skilled in the art, with the aim of mixing the components as uniformly as possible. For example, the mixing is carried out in a screw mixer, ribbon mixer, paddle mixer, blade mixer, rotor mixer, drum mixer, double cone mixer or V-type mixer.

[0110] The present invention also relates to a preparation comprising

[0111] a) a catalytically active composition according to the invention, and

[0112] b) a liquid, preferably water.

[0113] The preparation is preferably in the form of a suspension. A suspension in the sense of the present invention is a mixture of a solid and a liquid, wherein the solid is in the form of finely divided solids which are uniformly distributed in the liquid.

[0114] Such preparations are also referred to as "washcoat suspensions". The term "washcoat" is known to the person skilled in the art. A distinction must be made between washcoat suspensions and washcoat layers which are applied or can be applied to a macroscopic support.

[0115] At this point, it should be emphasized that the preparation according to the invention already contains at least one catalytically active substance, namely at least ruthenium applied to the doped refractory oxide. This distinguishes the preparation according to the invention from preparations known in the art that contain precursor compounds of catalytically active substances.

[0116] The preparation may also contain other components, such as acids or bases for pH adjustment, binders, adhesion promoters or stabilizers. Based on the total mass of solid components and liquid, the preparation preferably contains between 10% by weight and 70% by weight, particularly preferably between 30% by weight and 50% by weight of solid components.

[0117] The preparation according to the invention can preferably be prepared by a process comprising the following steps:

[0118] i) providing a doped refractory oxide provided with at least ruthenium and selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof,

[0119] ii) providing a cerium-zirconium oxide comprising at least one element from the rare earth group other than cerium,

[0120] iii) providing a liquid, preferably water,

[0121] iv) mixing a doped refractory oxide provided with at least ruthenium, a cerium-zirconium oxide, with a liquid.

[0122] The individual components can also be mixed with the liquid separately from one another; in other words, the refractory oxide and the cerium-zirconium oxide provided with the doping of ruthenium can each be mixed separately with the liquid, and these mixtures can then be mixed. In a further embodiment, one of the two components can also be mixed with the liquid first, and then the other component can be added to the mixture obtained. It can also be preferred to first mix the two oxides together, and then mix this mixture with the liquid.

[0123] Optionally, the method for preparing the formulation may further comprise additional steps.

[0124] For example, the method may include a pH adjustment step or a grinding step. The grinding step may include grinding the doped refractory oxide and / or cerium-zirconium oxide provided with at least ruthenium. The grinding may be performed before or after mixing the doped refractory oxide provided with at least ruthenium with the cerium-zirconium oxide and the liquid.

[0125] The invention also relates to a process for preparing the preparation according to the invention.

[0126] Typically, the catalytically active composition is in the form of a catalytically active coating. As known to those skilled in the art, the catalytically active composition is present on a macroscopic support, in this case typically on a refractory support. In this context, the term "macroscopic support" is to be understood in a manner that distinguishes it from a "microscopic support" that supports one or more catalytically active components. In the present invention, the microscopic support therefore comprises doped refractory oxides and cerium-zirconium oxides.

[0127] The invention also relates to a catalytically active coating comprising:

[0128] a) a doped refractory oxide provided with at least ruthenium selected from the group consisting of:

[0129] Aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof, and composite oxides of two or more thereof, and

[0130] b) Cerium-zirconium oxide comprising at least one element from the rare earth group other than cerium.

[0131] With regard to preferred embodiments of the catalytically active coating, reference is made to the statements above regarding the catalytically active composition, which also applies to the catalytically active coating according to the invention.

[0132] In principle, the heat-resistant carrier can have any shape or size. Typically, the heat-resistant carrier has a plurality of channels or open-cell foam structures arranged side by side, which have interconnected cavities through which gases can flow. The shape and size of the heat-resistant carrier are generally selected so that the catalytically active composition or catalytically active coating in the catalyst has an optimized effect on the exhaust gas. Examples of suitable shapes of heat-resistant carriers include bulk materials, integral honeycombs or honeycomb bodies, layered fibrous bodies or warp knitted fabrics, foams, nets, weft knitted fabrics, porous bodies or particles. In the case of bulk material catalysts, the heat-resistant carrier is preferably in the form of a molded body (such as a particle, a pellet or an extrudate, such as a cylinder, a ring, a sphere, a cuboid, a platelet). The diameter or size of such a bulk material molded body can be, for example, in the range of about 1 mm to 20 mm.

[0133] The heat-resistant carrier typically comprises a ceramic material or a metal material. Preferably, the heat-resistant carrier may be cordierite (SiO2-Al2O3-MgO), silicon carbide (SiC), titanium, an iron alloy (such as Fe-Cr-Al alloy or Ni-Cr-Al alloy) or a stainless steel alloy.

[0134] Methods for preparing catalytically active coatings are known to those skilled in the art. For example, they can be prepared by applying the formulation according to the invention to a suitable heat-resistant support. The application process can involve spraying the formulation or immersing the heat-resistant support in the carrier coating suspension.

[0135] For example, this method includes the following steps:

[0136] i) providing a preparation comprising

[0137] a) a catalytically active composition according to the invention, and

[0138] b) a liquid, preferably water,

[0139] ii) providing a heat-resistant carrier,

[0140] iii) applying the formulation to a heat-resistant carrier.

[0141] The present invention also relates to a method comprising the above steps. In this method, a coated heat-resistant support is obtained.

[0142] If the process comprises only steps i), ii) and iii), a liquid-containing catalytically active coating is obtained, in other words the catalytically active coating may be in the form of a “wet washcoat layer”.

[0143] The formulation can be applied to the heat-resistant support in one or more steps.

[0144] The method for producing a catalytically active coating may also comprise further steps.

[0145] Preferably, the coated refractory support can be dried and / or calcined in a further step. In such a case, the catalytically active coating is obtained as a dried or calcined support coating layer.

[0146] The drying step is preferably carried out at a temperature in the range of 50 to 200° C., particularly preferably between 80 and 150° C. In a preferred embodiment, the drying step is carried out for a period of 0.5 to 10 hours, preferably 2 to 8 hours.

[0147] The calcination step is particularly advantageous if the temperature is in the range from 100 to 700° C., in particular from 150 to 500° C. In a preferred embodiment, the temperature is greater than 200° C., particularly preferably greater than 300° C. In a preferred embodiment, the calcination step is carried out for a period of 1 to 12 hours, preferably 2 to 10 hours.

[0148] The amount of formulation applied to the refractory support can be determined based on the desired loading of the macroscopic support with the catalytically active components. As known to those skilled in the art, the loading of the refractory support can be controlled, for example, by the rheological properties of the formulation.

[0149] Furthermore, the process steps of applying the formulation and optionally drying and / or calcining the refractory support to produce a washcoat layer may be repeated as necessary to achieve a desired degree of loading or a desired thickness.

[0150] The invention furthermore relates to a catalyst comprising the catalytically active composition or the catalytically active coating according to the invention and a heat-resistant support.

[0151] The catalyst may be in the form of, for example, a monolithic catalyst coated with a washcoat layer, a bulk material coated with a washcoat layer, or a metal honeycomb or weft-knitted metal catalyst coated with a washcoat layer. In such cases, the washcoat layer comprises a catalytically active composition or a catalytically active coating.

[0152] Methods for preparing catalysts having a catalytically active coating are known in principle to those skilled in the art. For example, such methods may comprise the following steps:

[0153] i) providing a preparation comprising

[0154] a) a catalytically active composition according to the invention, and

[0155] b) a liquid, preferably water,

[0156] ii) providing a heat-resistant carrier,

[0157] iii) applying the preparation to a heat-resistant carrier,

[0158] iv) drying and / or calcining the coated refractory support.

[0159] With regard to preferred embodiments, reference is made to the statements above regarding the preparation of the catalytically active coating, which also apply to the preparation of the catalyst according to the invention.

[0160] After drying and / or calcination, the catalytically active coating is considered to be substantially free of solvent.The resulting loading of the refractory support can therefore be determined by determining the difference between the weight of the coated and uncoated refractory support.

[0161] The loading of the catalyst with the catalytically active composition or the catalytically active coating is selected so that the device as a whole is used as efficiently as possible. The catalyst is preferably loaded with 30 g / L to 250 g / L, particularly preferably 50 g / L to 200 g / L, particularly preferably 75 g / L to 150 g / L of the catalytically active composition. The loading indicates the amount of coating applied based on the empty volume of the heat-resistant support.

[0162] By using the catalytically active composition according to the invention or the catalytically active coating according to the invention, catalysts having a particularly low total ruthenium loading are possible, for example in the range from 0.1 g / L to 15 g / L, more preferably from 0.5 g / L to 12 g / L, particularly preferably from 1 g / L to 10 g / L.

[0163] In the case of catalytically active compositions which contain further noble metals in addition to ruthenium, the total loading is preferably in the range of 1 g / L to 30 g / L, more preferably 1.5 g / L to 25 g / L, particularly preferably 3 g / L to 20 g / L.

[0164] The catalysts according to the invention can be used, for example, in small engines, motorcycles, the automotive industry, commercial vehicles, industrial and special applications and also in marine applications.

[0165] The invention furthermore relates to a method for exhaust gas aftertreatment, in which the exhaust gas stream is brought into contact with a catalytically active composition according to the invention, a catalytically active coating according to the invention or a catalyst according to the invention.

[0166] The exhaust gas aftertreatment is preferably carried out at a temperature in the range of 150°C to 500°C.

[0167] The exhaust gases may, for example, come from incinerators, gas turbines, industrial facilities or internal combustion engines. Particular preference is given to treating exhaust gases from internal combustion engines, in particular small engines, 2-stroke engines and engines operating in the "rich" lambda range. Combustion exhaust gases typically contain carbon monoxide, hydrocarbons and / or other volatile organic compounds and / or nitrogen oxides.

[0168] Volatile organic compounds (VOC) are understood to mean gaseous or volatile organic compounds, such as organic compounds having a boiling point of, for example, up to 300° C. or having sublimation properties. Typical examples of such VOCs are hydrocarbons and organic solvents used, for example, in chemical production, paint or adhesive production or processing, cleaning processes, etc. For example, when fossil fuels are processed, for example during their production or distribution, hydrocarbons can also enter the exhaust gas. Other examples of VOCs are organic residual monomers from the production and processing of polymers or odorants, such as those produced in the food sector (food production, animal fattening, baking plants, fermentation processes, etc.).

[0169] The measurement methods used in the present invention are specified below. If no test method is specified, the appropriate ISO method in effect on the filing date of this application is used to determine the parameter in question. If no specific measurement conditions are specified, the measurements are made at room temperature (298.15K) and standard pressure (100 kPa).

[0170] BET surface area

[0171] The BET specific surface area was determined according to the BET theory (multipoint method, ISO 9277:2010) at 77 K using nitrogen as the adsorbate.

[0172] Pore ​​volume and pore size distribution

[0173] The pore volume and pore size distribution are determined by mercury porosimetry according to ISO 15901-1:2022.

[0174] Particle size distribution (d 90 )

[0175] Particle size was determined by laser diffraction according to ISO standard 13320 using a Mastersizer 2000 (Malvern).

[0176] Determination of precious metal content by ICP-MS

[0177] The noble metal content was determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS).For this purpose, each sample was digested in HF+HCl.

[0178] Long-term stability

[0179] Before testing the catalytic activity, the catalysts were treated in air at 1050°C for 16 hours. This resulted in artificial aging, thus simulating the exposure of the catalysts to typical application conditions.

[0180] Testing catalytic activity

[0181] The catalysts were tested in a specially constructed catalyst testing facility. x , 500 vol ppm propane and 0.3% oxygen in synthetic air for 70,000 h -1 The CO, NO and ions in the gas mixture were measured before and after the catalyst using FT-IR and FID. xThe ratio of propane to propane was determined and the oxygen content was measured using a paramagnetic detector. Based on this, the conversion (C) was determined in each case. To determine the light-off temperature (T50), the conversion curves obtained in this way were evaluated and the temperature at which 50% conversion occurred was determined each time.

[0182] The present invention is explained in more detail with reference to the following examples. However, these examples should not be construed as limiting.

[0183] For all examples, La2O3 doped Al2O3 and Nd2O and La2O3 doped CeZr oxides were used. Both oxides are commercially available.

[0184] CE-(Comparative Example: Ru / Al2O3+Ru / CeZr Oxide)

[0185] 80 g of Al2O3 were impregnated with a ruthenium nitrosyl nitrate (Ru-NN) solution containing 80% of the applied Ru and then dried, and 20 g of CeZr oxide were also treated with a Ru-NN solution containing 20% ​​of the applied Ru. For calcination, the previously dried material was treated in an oven at 500°C for 4 hours.

[0186] Al2O3 provided with Ru was slurried in water, and then CeZr oxide provided with Ru was added. The resulting suspension was ground. The ground suspension was applied to a ceramic honeycomb substrate. The coated honeycomb was calcined at 550°C for 4 hours. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 3.5 g / L.

[0187] Figure 1 The NO of the freshly prepared catalyst is shown x and temperature-dependent conversion of HC.

[0188] IE1(Ru / Al2O3)

[0189] 80 g of Al2O3 were impregnated with a Ru-NN solution containing 90% of the applied Ru and then dried, and 20 g of CeZr oxide were also treated with a Ru-NN solution containing 10% of the applied Ru. For calcination, the dried material was treated in an oven at 500°C for 4 hours.

[0190] Al2O3 provided with Ru was slurried in water, then CeZr oxide provided with Ru was added and the whole suspension was ground. The ground suspension was applied to a ceramic honeycomb substrate. The coated honeycomb was calcined at 550°C for 4 hours. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 10.6 g / L.

[0191] Use NO x and HC conversion rate, Figure 2 The catalyst performance of the catalyst prepared according to the present invention is illustrated.

[0192] IE2(Ru / Al2O3)

[0193] The preparation procedure was carried out analogously to the method given in IE1, but only the Al2O3 was treated with a Ru-NN solution containing 100% of the Ru to be applied. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 3.5 g / L.

[0194] Figure 3 The catalytic performance of this catalyst according to the invention is shown. In addition to the catalytic performance of the freshly prepared catalyst (T before ), the performance after artificial aging (T after ) is also compared. The almost identical curves illustrate the particular stability of the catalyst.

[0195] IE3(Ru / Al2O3)

[0196] The preparation procedure was carried out similarly to the method given in IE2, but using less Ru-NN in solution. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 1.8 g / L.

[0197] Figure 4 The catalytic performance of this catalyst according to the invention is shown.

[0198] IE4(RuIr / Al2O3)

[0199] The preparation procedure was carried out analogously to the method given in IE2. For the impregnation of Al2O3, a solution of Ru-NN and iridium as iridium chloride in water was used. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 1.8 g / L.

[0200] Figure 5 The catalytic performance of this catalyst according to the invention is shown.

[0201] IE5(RuPt / Al2O3)

[0202] The preparation procedure was carried out analogously to the method given in IE2. For the impregnation of Al2O3, a solution of Ru-NN and platinum as platinum nitrate in water was used. The resulting washcoat loading was 100 g / L, which corresponds to a ruthenium content of 1.8 g / L.

[0203] Figure 6 The catalytic performance of this catalyst according to the invention is shown.

[0204] IE6 (RuIr / Al2O3+RuPt / CeZr oxide)

[0205] Al2O3 was slurried in water and mixed with Ru-NN containing solution and iridium chloride in water. The suspension was heated, then NaOH solution was added and the solid phase was separated from the liquid phase by filtration.

[0206] CeZr oxide was slurried in water and mixed with Ru-NN solution and platinum nitrate in water. The suspension was heated, then NaOH solution was added and the solid phase was separated from the liquid phase by filtration.

[0207] The two oxides with the precipitated noble metals were mixed, dried and treated in an oven at 400° C. for 2 hours for calcination. The calcined material was slurried in water and ground.

[0208] The coating of the ceramic honeycomb was carried out in a manner similar to that described in IE 2. The resulting loading was 100 g / L, which corresponds to a ruthenium content of 1.8 g / L.

[0209] Figure 7 The catalytic performance of this catalyst according to the invention is shown.

[0210] Table 1 summarizes the characteristics of the tested catalysts and the corresponding total noble metal loadings.

[0211]

[0212] The results of IE1 to IE6 show that various embodiments of the catalyst according to the present invention are functional in removing nitrogen oxides. Even relatively low noble metal loadings (such as in IE3) are sufficiently effective. In particular, the combination of ruthenium with another noble metal also shows a beneficial reduction in T50.

[0213] Figure 8 The NO2 content of the catalysts before (Tbefore) and after (Tafter) temperature treatment was compared based on CE, IE1 and IE2 containing only Ru. x Before the temperature treatment, the catalyst performance was similar. However, the catalytic activity of the catalyst according to the invention, in particular the light-off temperature, showed only slight changes after this artificial aging, while the catalyst of the comparative example (CE) clearly lost catalytic activity. In particular, the comparison between the catalysts of CE and IE2 with the same ruthenium loading demonstrates the increased stability of the catalyst according to the invention. The loading of ruthenium on Al2O3 presumably increases its stability and therefore increases the catalytic effectiveness under operating conditions, making it possible to minimize the precious metal supply in the catalyst.

[0214] Fig. 9 The NO2 xDetermination of the T50 value for the conversion. The T50 value could no longer be determined for the catalyst of the comparative example. In addition to reducing the light-off temperature, the combination of ruthenium with another noble metal, in particular iridium, proved to be beneficial for the stability of the catalyst.

Claims

1. A catalytically active composition comprising a) a doped refractory oxide provided with at least ruthenium and selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof, and b) Cerium-zirconium oxide, the cerium-zirconium oxide comprising at least one element from the rare earth group other than cerium. 2 . The catalytically active composition according to claim 1 , wherein the doped refractory oxide is aluminum oxide or a mixed oxide or a composite oxide of aluminum oxide. 3 . The catalytically active composition according to claim 1 , wherein the doped refractory oxide is lanthanum oxide-doped aluminum oxide, a mixed oxide of lanthanum oxide-doped aluminum oxide or a composite oxide of lanthanum oxide-doped aluminum oxide. 4 . The catalytically active composition according to claim 1 , wherein the proportion of the doped refractory oxide is in the range from 10% to 95% by weight.

5. The catalytically active composition according to claim 1, wherein the doped refractory oxide is provided with 0.1% to 25% by weight of ruthenium, based on the total amount of doped refractory oxide and ruthenium. 6 . The catalytically active composition according to claim 1 , wherein the catalytically active composition comprises ruthenium in an amount of 0.05% to 20% by weight, based on the total amount of doped refractory oxide, ruthenium and cerium-zirconium oxide.

7. The catalytically active composition according to any of the preceding claims, wherein the doped refractory oxide is provided with at least one further noble metal selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh) and combinations thereof.

8. The catalytically active composition according to claim 7, wherein the doped refractory oxide is provided with a combination of: ruthenium and iridium; ruthenium and platinum; ruthenium and palladium; ruthenium, platinum and iridium; Ruthenium, palladium and iridium; or ruthenium, palladium and platinum.

9. The catalytically active composition according to claim 7 or 8, wherein the doped refractory oxide provides ruthenium and the at least one other noble metal in an amount of 0.2% to 30% by weight, based on the total amount of doped refractory oxide, ruthenium and the at least one other noble metal. 10 . The catalytically active composition according to claim 1 , wherein the cerium-zirconium oxide is provided with at least one noble metal. 11 . The catalytically active composition according to claim 1 , wherein the noble metal contributions of the doped refractory oxide and the cerium-zirconium oxide are different.

12. A method for preparing a catalytically active composition according to any one of claims 1 to 11, comprising the following steps: i) providing a doped refractory oxide provided with at least ruthenium and selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof, ii) providing a cerium-zirconium oxide comprising at least one element from the rare earth group other than cerium, iii) mixing said doped refractory oxide provided with at least ruthenium with said cerium-zirconium oxide.

13. A preparation comprising: a) a catalytically active composition according to any one of claims 1 to 11, and b)Liquids.

14. A catalyst comprising the catalytically active composition according to any one of claims 1 to 11 and a heat-resistant support.

15. A method for exhaust gas aftertreatment, wherein the exhaust gas stream is contacted with a catalytically active composition according to any one of claims 1 to 11 or with a catalyst according to claim 14.

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