Improved TWC activity using rhodium / platinum and tannic acid as complexing and reducing agents.

Abstract

A method for producing a catalyst article, the method comprising: providing a complex of a polyphenol and a PGM, wherein the PGM comprises rhodium and / or platinum and the polyphenol comprises an ester functional group; providing a support material; applying the complex to the support material to form a supported support material; disposing the supported support material on a substrate; and heating the supported support material to form nanoparticles of the PGM on the support material.

Description

[Technical field]

[0001] The present invention relates to a method for producing a catalytic article, a catalytic article obtainable by this method, an emission treatment system, and a method for treating exhaust gases. [Background technology]

[0002] Three-way catalysts (TWCs) are used to remove CO, HC and NO from the exhaust gas of a gasoline engine at a stoichiometric air-fuel ratio. x to harmless compounds (about 98%). Specifically, the oxidation of CO and HC to CO2 and water vapor (HO) is primarily catalyzed by Pd, while NO x The reduction of N2 to N2 is primarily catalyzed by Rh. Modern TWCs use supported platinum group metal (PGM) catalysts (Pd, Rh, Pt, etc.) deposited on single, bi- or multi-layer supports, with the support material consisting of high surface area metal oxides, primarily stabilized gamma alumina, and ceria-containing oxygen storage materials. The supported catalysts are washcoated onto ceramic monolith substrates.

[0003] Conventional preparation of TWC washcoat slurries generally involves depositing the PGM elements onto oxide supports by incipient wetness or wet impregnation using solutions of inorganic PGM precursors, such as nitrates, acetates, or chloride salts. Promoter salts are often added to the washcoat formulation to enhance TWC performance. Once the monolith substrate is washcoated with the as-prepared slurry, it is followed by drying and calcination steps to decompose the inorganic salts and fix the PGMs and promoter elements onto the support material. It is known that the performance of supported metal catalysts depends on the structure and composition of the metal nanoparticles and the nature of the support. Conventional TWCs prepared using the above methods often offer limited control over the structure of the catalytically active species (i.e., average PGM particle size and composition, location of the active components, and metal-support interactions). This is mainly due to metal migration and particle growth during the high-temperature calcination process.

[0004] With increasingly stringent environmental regulations, TWCs with higher emission reduction efficiency are required. Meanwhile, with increasing PGM costs, there is an urgent need to reduce PGM loading without TWC performance. Better control of PGM particle size and metal-support interaction is essential to optimize TWC performance. Furthermore, homogenized PGM particle size distribution can contribute to reducing the degree of metal sintering due to Ostwald ripening, as often occurs during the fuel cut-off process, an engine strategy used to improve fuel economy.

[0005] Catalytic light-off is the minimum temperature required to initiate a catalytic reaction. Specifically, the light-off temperature is the temperature at which 50% conversion is reached. There is a need for catalyst articles with lower light-off temperatures.

[0006] US 2012 / 0077669(A1) describes the polymer-assisted synthesis of supported metal catalysts for automotive applications. The polymers used in the examples include poly(vinylpyrrolidone), poly(acrylic acid), and poly(ethyleneimine). In the described synthesis procedure, a support (alumina powder) is first impregnated with a polymer-containing aqueous solution. The impregnated support is then separated from the solution by filtration and drying steps. The dried impregnated support is further impregnated with a PGM precursor solution by incipient wetness impregnation. The described process involves multiple steps for the formation of the claimed supported metal catalysts, which increases the cost and difficulty for commercial-scale production. US 2012 / 0077669(A1) indicates that lean-burn engines, such as diesel engines or lean-burn gasoline engines, are preferably used to apply the technology. Summary of the Invention

[0007] One aspect of the present disclosure relates to a method of making a catalyst article, the method including providing a complex of a polyphenol and a PGM, where the polyphenol comprises an ester functional group and the PGM comprises rhodium and / or platinum, providing a support material, applying the complex to the support material to form a supported support material, disposing the supported support material on a substrate, and heating the supported support material to form nanoparticles of the PGM on the support material.

[0008] Another aspect of the present disclosure relates to a catalyst article obtainable by the method of the first aspect.

[0009] The present invention also includes an exhaust system for an internal combustion engine, comprising the catalytic article of the second aspect. [Brief description of the drawings]

[0010] STEM Rh elemental mapping image and Rh particle size distribution [Figure 1a]1 shows a STEM Rh elemental mapping image of reference virgin Rh / alumina (Reference Example 1). [Figure 1b] 1 shows a STEM Rh elemental mapping image of virgin Rh / alumina (Example 1) with tannic acid modification. [Diagram 2] 1 shows the Rh particle size distribution for reference virgin Rh / alumina (Reference Example 1) and virgin Rh / alumina modified with tannic acid (Example 1). [Diagram 3] 1 shows the Rh dispersion measured by CO chemisorption for the reference catalyst and the TA modified catalyst described in Examples 1 and 2. [Figure 4a] FIG. 2 is a diagram showing the results of NO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 4b] FIG. 2 is a graph showing the results of CO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 4c] FIG. 2 shows the THC conversion results of a perturbation ignition performance test of an example catalyst article and a reference example catalyst article produced according to the method of the present invention. [Figure 5a] FIG. 2 is a diagram showing the results of NO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 5b] FIG. 2 is a graph showing the results of CO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 5c] FIG. 2 shows the THC conversion results of a perturbation ignition performance test of an example catalyst article and a reference example catalyst article produced according to the method of the present invention. [Figure 6a] FIG. 2 is a diagram showing the results of NO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 6b] FIG. 2 is a graph showing the results of CO conversion in a perturbation ignition performance test of the catalyst article of the embodiment produced according to the method of the present invention and the catalyst article of the reference example. [Figure 6c]FIG. 2 shows the THC conversion results of a perturbation ignition performance test of an example catalyst article and a reference example catalyst article produced according to the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention aims to address at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution.

[0012] In a first aspect, the present invention provides a method of making a catalyst article, the method comprising: providing a complex of a polyphenol and a PGM, the polyphenol comprising an ester functional group and the PGM comprising rhodium and / or platinum; Providing a support material; applying the complex to a support material to form a supported support material; placing the supported support material on a substrate; and heating the supported support material to form nanoparticles of the PGMs on the support material.

[0013] Each aspect or embodiment defined in this specification may be combined with any other aspect or embodiment, unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0014] Surprisingly, when used in an emission treatment system, the catalyst article produced by the method of the present invention may exhibit favorable catalytic activity, particularly favorable three-way catalytic activity. For example, the catalyst article may exhibit favorable light-off performance, particularly NO, CO and total hydrocarbon conversion, during three-way catalytic emission reduction of a stoichiometric gasoline engine. Such favorable catalytic activity and light-off performance may be better than that exhibited by a conventional catalyst article having the same / similar PGM type, loading, support, and configuration. The catalyst article may be more durable compared to a conventional catalyst article. In other words, such favorable catalytic activity may be exhibited even after aging.

[0015] Advantageously, such superior performance can facilitate the use of lower loadings of PGMs compared to conventional catalyst articles without compromising catalytic performance, which can be beneficial in view of the high cost of such metals, particularly rhodium. Furthermore, such superior performance can facilitate partial / complete substitution of high cost PGMs with lower cost PGMs or other transition metals without compromising catalytic performance.

[0016] Without being bound by theory, it is hypothesized that such superior performance may be provided by the favorable particle size distribution of the PGM nanoparticles on the support material. During PGM-polyphenol complex formation, the ions of the PGMs can react with the ester functional groups, and the same predictable amount of PGM ions is "taken up" by each polymer unit structure. The total amount of PGM "taken up" is determined by the molecular structure / size of the polymer and the PGM-polyphenol coordination ratio. Each complex can then react / interact with surface functional groups (e.g., hydroxyl groups) or surface charges to allow the PGM-polyphenol complexes to "anchor" onto the support material surface. The "anchor" PGM-polyphenol complexes can be separated due to the steric effect of the polymer and the available amount of surface functional groups / charges of the support material. The interaction between the complexes and the support material functional groups may increase the PGM uptake by the support compared to catalysts prepared by traditional methods. Without wishing to be bound by theory, it is hypothesized that such uniform separation may result in a narrower particle size distribution (more uniform particle size) of the PGM nanoparticles upon heating (calcination), which in turn may result in less excessive agglomeration and / or sintering of the PGM particles during aging and / or fuel cut events. In other words, a more sintering resistant catalyst article can be obtained by using the method of the present invention compared to conventional catalysts.

[0017] Compared with the method of US2012 / 0077669(A1), the method of the present invention is a simpler and more efficient "one-pot" method. The method of the present invention does not require separate impregnation, filtration, and drying steps to deposit polymer molecules on the support material. By using the method of the present invention, the occurrence of polymer-support and PGM-polymer interactions can be increased, since each added polymer molecule is available for interaction. In contrast, in US2012 / 0077669(A1), only a limited amount of polymer can remain on the support after the filtration and washing steps. Furthermore, the catalyst article prepared by the method of the present invention can be used as a three-way catalyst, especially for stoichiometric gasoline emission reduction. In contrast, the catalyst article produced by the method of US2012 / 0077669(A1) has particular application in lean-burn diesel or gasoline engines.

[0018] The term "catalyst article" as used herein may include an article on or in which a catalyst is supported. The article may take the form of, for example, a honeycomb monolith, or a filter, such as a wall-flow filter or a flow-through filter. The catalyst article may be for use in an emission treatment system, particularly an emission treatment system for a gasoline engine, preferably a stoichiometric gasoline engine. The catalyst article may be for use in three-way catalysis.

[0019] Providing a complex of a polyphenol and a PGM typically involves providing the complex in a solution, for example an aqueous or alcoholic solution. Providing a complex of a polyphenol and a PGM typically involves mixing an inorganic PGM precursor in pure form or in solution with a polyphenol in an aqueous medium, for example mixing nitrate PGM with a polyphenol in water.

[0020] The term "polyphenol" as used herein includes polymers containing several hydroxyl groups on aromatic rings. Polyphenols are generally moderately water-soluble compounds. Polyphenols may be natural or synthetic, but in the present invention, they are preferably naturally occurring, to make the process more environmentally friendly. The term "polyphenol" as used herein may include polymers having a weight average molecular weight of 500-4,000 g / mol, 13 or more hydroxyl groups, and 5-7 aromatic rings per 1,000 g / mol. Polyphenols may be, for example, phenolic acids (e.g., tannic acid, caffeic acid), flavonoids (e.g., flavones, flavonols, flavanols, flavanones, isoflavones), stilbenes, or lignin (polyphenols derived from phenylalanine, found in flaxseed and other cereals).

[0021] The polyphenol comprises an ester functionality, typically a carboxylic acid ester functionality. The polyphenol preferably comprises two or more ester and / or carboxylic acid ester functional groups. The terms "ester functionality" and "carboxylic acid ester functionality" may include functional groups that comprise a carboxyl group bonded to an OR group.

[0022] [ka]

[0023] The PGMs include rhodium and / or platinum. Such metals may be particularly suitable for performing three-way catalysis. In addition, such metals are expensive, which means that it is advantageous to be able to provide a similar level of catalytic activity for the same amount of metal. Furthermore, the use of such metals in the method of the present invention may result in particularly favorable perturbation ignition performance. The PGMs may be in the form of alloys. In addition to rhodium and / or platinum, the PGMs may include other PGMs, such as, for example, one or more of ruthenium, palladium, osmium and iridium.

[0024] The complexes may have a PGM atom to ester group ratio of 2:1 to 1:10, preferably 1:1 to 1:8, more preferably 1:2 to 1:5. The complexes may have a rhodium atom to ester group ratio of 2:1 to 1:10, preferably 1:1 to 1:8, more preferably 1:2 to 1:5. The complexes may have a platinum atom to ester group ratio of 2:1 to 1:10, preferably 1:1 to 1:8, more preferably 1:2 to 1:5. The complexes may have a rhodium and platinum atom to ester group ratio of 2:1 to 1:10, preferably 1:1 to 1:8, more preferably 1:2 to 1:5.

[0025] The support material may be any material capable of supporting the complexes and nanoparticles thereon or therein. The support material may take any form, but is typically in the form of a powder, more typically a high surface area powder. When the method of the present invention is used to prepare a catalyzed filter, such as a wall-flow filter or a flow-through filter, the support material will typically be in the form of a powder having a D50, e.g., of 0.1 to 25 μm, more typically 0.5 to 5 μm, as measured using TEM. Such particle size may promote desirable rheological properties of the slurry used to coat the filter. The support material may function as a washcoat. The support material may be the washcoat or may be part of the washcoat.

[0026] The support material may also function as an oxygen storage material to store and release oxygen under fuel-lean and fuel-rich conditions, respectively, to promote three-way catalytic conversion.

[0027] The application of the complex to the support material typically involves contacting the complex with the support material in the presence of a solvent, typically water, to produce a slurry. The term "slurry" as used herein can include a liquid containing insoluble materials, e.g., insoluble particles. The slurry may include (1) the solvent, (2) soluble contents, e.g., unreacted polyphenol polymer, inorganic PGM and cocatalyst precursor, and PGM-polymer complex (outside the support), and (3) insoluble contents, e.g., support particles that may or may not interact with the polymer and metal precursor. The slurry is typically stirred, more typically for at least 10 minutes, more typically for at least 30 minutes, and even more typically for at least 1 hour. The amount of complex supported on the support material can be increased by increasing the contact time and / or stirring time.

[0028] As used herein, the term "supported support material" can include support materials having PGM-polyphenol complexes supported thereon (e.g., on the surface of a high surface area metal oxide support material) and / or supported therein (e.g., within the pores of a zeolite support material). The complexes are typically immobilized on the support by, for example, electrostatic forces, hydrogen bonding, coordination bonds, covalent bonds, and / or ionic bonds. For example, in the case of oxides, ester functional groups in the polyphenols (e.g., carboxylate functional groups) and surface hydroxyl groups on the support can interact via electrostatic forces or hydrogen bond formation.

[0029] The term "substrate" as used herein may include, for example, ceramic or metal honeycombs, or filter blocks, such as wall-flow or flow-through filters. Substrates may include ceramic monolith substrates. Substrates may vary in their material composition, size and configuration, cell shape and density, and wall thickness. Suitable substrates are well known in the art.

[0030] The placement of the supported carrier material on the substrate can be performed using techniques known in the art. Typically, the supported carrier material is placed on the substrate by pouring a slurry of the supported carrier material into the inlet of the substrate in a predetermined amount using a specific forming tool. Subsequent vacuum and drying steps may be used during the placement step, as discussed in more detail below. If the carrier is a filter block, the supported carrier material may be placed on the filter wall, within the filter wall (if porous), or both.

[0031] Heating of the supported support material is typically carried out in an oven or furnace, more typically in a belt or static oven or furnace, typically in a specific flow of hot air from one direction. Heating may include calcination. Heating may also include drying. The drying and calcination steps may be continuous or sequential. For example, a separate washcoat may be applied after the substrate has already been washcoated and dried together with the previous washcoat. The washcoated substrate may also be dried and calcined using one continuous heating program once coating is complete. During heating, the complex may at least partially, substantially or completely decompose. In other words, the ligands of the complex, i.e., the polyphenols, are at least partially, substantially or completely removed or separated from the PGM and removed from the final catalyst article. The particles of PGM so separated can then begin to form metal-metal and metal-oxide bonds. As a result of heating (calcination), the substrate is typically substantially free of polyphenols, more typically completely free of polyphenols.

[0032] The term "nanoparticle" as used herein can include particles having a diameter of 0.01 nm to 100 nm as measured by TEM. Nanoparticles can be of any shape, e.g., spheres, plates, cubes, cylinders, hexagons, or rods, but are typically spherical. The maximum dimension of a nanoparticle (i.e., the diameter if the nanoparticle is spherical), as measured by TEM, is typically 0.5 to 10 nm, more typically 1 to 5 nm.

[0033] After the heating step, the substrate is typically cooled, more typically to room temperature, typically in air with or without a coolant / cooling medium, typically without a coolant.

[0034] The polyphenol preferably comprises tannic acid. The term "tannic acid" as used herein may include mixtures of polygalloyl glucose or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 to 12, depending on the plant source used to extract the tannic acid. Tannic acid may be a natural phenolic compound and may be extracted from the bark of oak, hemlock, chestnut and mangrove trees, certain sumac leaves, and the fruits of many plants, among others. The term "tannic acid" as used herein may include compounds consisting of a central glucose ring and 10 galloyl groups, i.e., decagalloyl glucose, as shown by the following structural formula:

[0035] [ka]

[0036] Such compounds have the IUPAC name 1,2,3,4,6-penta-O-{3,4-dihydroxy-5-[(3,4,5-trihydroxybenzoyl)oxy]benzoyl}-D-glucopyranose or 2,3-dihydroxy-5-({[(2R,3R,4S,5R,6R)-3,4,5,6-tetrakis({3,4-dihydroxy-5-[(3,4,5-trihydroxyphenyl)carbonyloxy]phenyl}carbonyloxy)oxan-2-yl]methoxy}carbonyl)phenyl 3,4,5-trihydroxybenzoate. Each of the five hydroxyl groups of the glucose molecule is esterified with a molecule of digallic acid.

[0037] Tannic acid may coordinate with metal ions through hydrogen bonds or covalent bonds. The PGM-tannic acid complex may be immobilized on a support, such as a metal oxide support, in a washcoat, and the carboxylate functional groups in the tannic acid ligand and the surface hydroxyl groups on the support may interact through electrostatic forces or hydrogen bond formation.

[0038] Because tannic acid is naturally occurring, its use to form PGM complexes may be more environmentally friendly compared to the use of other non-naturally occurring ligands. Tannic acid preferably has a decomposition point in the range of 210-215°C. It is also water soluble (1g of tannic acid dissolves in 0.35ml of water at standard temperature and pressure). The use of tannic acid may result in particularly favorable perturbation ignition performance.

[0039] The polyphenols preferably have a weight average molecular weight M of 500 to 4,000, more preferably 1,000 to 2,000 g / mol, and even more preferably 1,600 to 1,800 g / mol, as measured by light scattering. w The weight average molecular weight Mw is expressed by the following formula:

[0040]

number

[0041] The polyphenol preferably has a number average molecular weight M of 500 to 4,000 g / mol as measured by gel permeation chromatography (GPC). n The number average molecular weight M w is expressed by the following formula:

[0042]

number

[0043] The PGM preferably comprises, consists essentially of, or consists of rhodium. Rhodium is a particularly expensive PGM and forms particularly suitable complexes with polyphenols, especially tannic acid. The PGM preferably comprises, consists essentially of, or consists of platinum. Platinum is a particularly expensive PGM and forms particularly suitable complexes with polyphenols, especially tannic acid.

[0044] In a preferred embodiment, the PGM comprises, consists essentially of, or consists of rhodium and platinum. The use of such metals in the methods of the present invention can result in particularly favorable perturbation ignition performance.

[0045] The support material preferably comprises an oxide, preferably one or more of Al2O3 (aluminum oxide or alumina), SiO2, TiO2, CeO2, ZrO2, V2O5, La2O3 and zeolites. The oxide is preferably a metal oxide. The support material more preferably comprises alumina, even more preferably gamma-alumina. The support material preferably comprises ceria-zirconia. The support material preferably comprises alumina and ceria-zirconia. The alumina and / or ceria-zirconia are preferably doped, more preferably doped with one or more oxides of lanthanum, neodymium, yttrium, niobium, praseodymium, hafnium, molybdenum, titanium, vanadium, zinc, cadmium, manganese, iron, copper, calcium, barium, strontium, cesium, magnesium, potassium or sodium, even more preferably doped with oxides of lanthanum, neodymium or yttrium. Such doped oxides are particularly useful as support materials. Preferably, the dopant is present in the alumina and / or ceria-zirconia in an amount of from 0.001% to 20% by weight, more preferably from 0.5% to 10% by weight.

[0046] The support material is preferably in the form of a powder having a D90 of 0.1 to 25 μm, more preferably 0.5 to 5 μm.

[0047] The supported support material is preferably disposed on the substrate in the form of a slurry, which is particularly effective in disposing the material on the substrate, particularly for maximizing gas diffusion and minimizing pressure drop during catalytic conversion.

[0048] Providing the complex of polyphenol and PGM preferably comprises synthesizing the complex in situ in the slurry.

[0049] The slurry preferably comprises contacting a PGM salt with a polyphenol in water to form a complex of the polyphenol with the PGM in an aqueous solution, the PGM salt comprising rhodium and / or platinum; applying the complex to the support material by contacting the support material with an aqueous solution to form a supported support material; Optionally, it is prepared by a method comprising adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent to the aqueous solution.

[0050] Such a "one-pot" preparation method can be simplified and less costly than conventional methods, and can also maximize polymer utilization.

[0051] In other words, providing a complex of a polyphenol and a PGM, providing a support material, applying the complex to the support material to form a supported support material, and disposing the supported support material on a substrate comprises: contacting a PGM salt with a polyphenol in water to form a complex of the polyphenol with the PGM in an aqueous solution, the PGM salt comprising rhodium and / or platinum; adding the support material to an aqueous solution to form a slurry of supported support material; Optionally, adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent to the slurry; and disposing the slurry on a substrate.

[0052] The support may include a washcoating.

[0053] The slurry preferably has a solids content of 10-40%, preferably 15-35%. Such solids content may allow suitable slurry rheology for disposing the supported carrier material on the substrate. For example, if the substrate is a honeycomb monolith, such solids content may allow deposition of a thin layer of washcoat on the inner wall of the substrate. If the substrate is a wall-flow filter, such solids content may allow the slurry to enter the channels of the wall-flow filter and may allow the slurry to enter the walls of the wall-flow filter.

[0054] Preferably, the slurry comprises: an oxygen storage material, preferably ceria-zirconia; cocatalyst salt, Binder, Acid or base, Thickeners, and Further comprising one or more of the following reducing agents:

[0055] The other promoters may include, for example, non-PGM transition metal elements, rare earth elements, alkali group elements, and / or combinations of two or more of the above elements in the same or different groups of the periodic table. The promoter salt may be a salt of such elements.

[0056] The binder may include, for example, an oxide material having a small particle size to bind together individual insoluble particles in the washcoat slurry. The use of binders in washcoats is well known in the art.

[0057] The thickener may include, for example, a natural polymer with functional hydroxyl groups that interact with insoluble particles in the washcoat slurry. It serves the purpose of thickening the washcoat slurry for improved coating profile during washcoat coating on a substrate. The thickener is usually baked off during washcoat baking. Examples of specific thickeners / rheology modifiers for washcoats include glactoma gum, guar gum, xanthan gum, curdlan schizophyllan, scleroglucan, diutan gum, wheylan gum, hydroxymethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, and ethylhydroxycellulose.

[0058] The term "reducing agent" as described herein may include compounds capable of reducing PGM cations to their metallic state particles in situ during washcoat preparation.

[0059] Organic acids can be added to act as reducing agents for the PGMs and / or create a reducing environment during the subsequent calcination step. Examples of suitable organic acids can include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof.

[0060] In a preferred embodiment, the PGMs comprise rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia. In another preferred embodiment, the PGMs comprise rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina. In another preferred embodiment, the PGMs comprise rhodium, and the support material comprises alumina and ceria-zirconia.

[0061] The method preferably further comprises disposing a further slurry on the substrate, the further slurry comprising one or more of a further support material, an oxygen storage material, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent, prior to disposing the support material on the substrate and / or after heating the supported support material to form nanoparticles of PGM on the support material. This can result in a catalyst article having multiple layers of different washcoats, for example a bottom washcoat containing, inter alia, rhodium nanoparticles supported on alumina, and a top washcoat containing, inter alia, rhodium nanoparticles supported on alumina. Further examples of such multiple layers are discussed in more detail below.

[0062] Placing the supported support material on the substrate preferably includes contacting a slurry with the substrate (e.g., injecting the slurry into an inlet of the substrate) and, optionally, applying a vacuum to the substrate; and / or Drying the slurry on the substrate.

[0063] This can result in a preferred distribution of the supported support material on the substrate.

[0064] Drying is preferably carried out as follows: At a temperature between 60°C and 200°C, preferably between 70°C and 130°C, and / or 10 to 360 minutes, preferably 15 to 60 minutes.

[0065] The substrate may be a "blank", i.e., an unwashcoated substrate. Alternatively, the substrate may have one or more washcoats already supported thereon. In such a situation, the final catalyst article may include multiple layers of different washcoats.

[0066] The substrate preferably comprises cordierite. Cordierite substrates are particularly suitable for use in catalytic articles.

[0067] The substrate is preferably in the form of a honeycomb monolith, a wall-flow filter or a flow-through filter.

[0068] The heating is preferably carried out as follows: At a temperature of 400°C to 700°C, preferably 400°C to 600°C, more preferably 450°C to 600°C, and / or The reaction is carried out for 10 to 360 minutes, preferably 35 to 120 minutes.

[0069] Lower temperatures and / or shorter heating times may result in insufficient decomposition of the complexes and / or high levels of polyphenols may remain in the substrate. Higher temperatures and / or longer heating times may result in particles of PGMs with undesirably large particle sizes, possibly due to sintering. Higher temperatures and longer heating times may also result in damage to the catalyst article.

[0070] Heating preferably includes calcining. As used herein, the term "calcining" may include a heat treatment process in the absence or limited supply of air or oxygen to cause pyrolysis.

[0071] The nanoparticles preferably have a D50 of 0.1 nm to 10 nm, more preferably 0.2 to 5 nm, and even more preferably 0.2 to 4 nm. D50 can be measured by TEM. Such particle size can provide a preferred level of catalytic activity.

[0072] In a further aspect, the present invention provides a catalyst article obtainable by the methods described herein, the catalyst article being for use in an emission treatment system.

[0073] Compared to conventional catalyst articles, catalyst articles obtainable by the methods described herein can contain PGM particles having advantageously small particle size and favorable particle size distribution (e.g., D50 of 0.2 to 4 nm). Furthermore, compared to conventional catalyst articles, catalyst articles obtainable by the methods described herein can exhibit a more uniform distribution of PGM particles throughout the substrate.

[0074] When used in emissions treatment systems, the catalyst articles can exhibit favorable light-off performance, particularly for NO, CO and total hydrocarbons, during three-way catalytic conversion for stoichiometric gasoline emission reduction.

[0075] The catalyst is preferably for a three-way catalyst.

[0076] The catalyst article is 1 g / in 3 ~3g / in 3 Such catalyst articles may exhibit similar or higher catalytic activity compared to conventional catalyst articles, but may be less expensive given the lower levels of PGMs used.

[0077] The substrate preferably comprises a wall-flow filter substrate or a flow-through substrate.

[0078] In a preferred embodiment, the catalytic article includes a bottom layer of a support material having rhodium thereon and a top layer of a support material having palladium thereon. In another preferred embodiment, the catalytic article includes a bottom layer of a support material having palladium thereon and a top layer of a support material having rhodium thereon. As used herein, the term "bottom layer" may include a layer (e.g., a washcoat layer) that is closest to or in contact with the substrate (i.e., substrate wall). As used herein, the term "top layer" may include a layer (e.g., a washcoat layer) that is further from the substrate (i.e., substrate wall) than the bottom layer and may be located above the bottom layer.

[0079] In such preferred embodiments, the support material preferably comprises alumina and ceria-zirconia.

[0080] The catalyst article, in particular in such preferred embodiments, preferably has a coating weight of 2 g / ft 3 ~15g / ft 3 of rhodium, more preferably 5g / ft 3 ~10g / ft 3 Advantageously, such rhodium levels can be lower than those of conventional catalyst articles, yet without impairing catalytic activity.

[0081] The catalyst article, in particular in such preferred embodiments, preferably has a coating weight of 50 g / ft 3 ~200g / ft 3 of palladium, more preferably 80 g / ft 3 ~150g / ft 3 Advantageously, such palladium levels can be lower than those of conventional catalyst articles, yet do not impair catalytic activity.

[0082] In a preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia. In another preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina. In another preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, and the support material comprises alumina and ceria-zirconia.

[0083] In a further aspect, the present invention provides an emissions treatment system comprising a catalytic article as described herein.

[0084] The emission treatment system is preferably for a gasoline engine.

[0085] Gasoline engines preferably operate under stoichiometric conditions.

[0086] In a further aspect, the present invention provides a method for treating an exhaust gas, the method comprising: Providing a catalyst article as described herein; contacting the catalytic article with the exhaust gas.

[0087] The exhaust gas is preferably exhaust gas from a gasoline engine. The catalytic article is particularly suitable for treating such exhaust gas. The gasoline engine preferably operates under stoichiometric conditions.

[0088] The invention will now be described with reference to the following non-limiting examples.

[0089] Manufacturing of catalytic articles A number of catalyst articles were prepared according to the following examples.

[0090] Reference Example 1: 0.3% Rh / gamma alumina (containing Rh nitrate) washcoat catalyst 1. Required amount of RhN (5.2g / ft 3 ) and water to dissolve and mix for 1 hour. 2. Milled gamma alumina (1 g / in 3 ) slurry and mix for 1 hour. 3. Adjust solids to approximately 20% by adding DI water. 4. Adjust batch solids to 30% by adding activated 4% by weight thickener in water. Mix vigorously with a VWR vortex mixer until a homogenous gel is formed. 5. Coat 1x3 inch core under vacuum aiming at 1.2 inches from the inlet and allow to air cure and dry. 6. Fire the bricks in a static oven at 500°C for 30 minutes.

[0091] Example 1: 0.3% Rh / gamma alumina (with Rh modified by tannic acid) washcoat catalyst 1. Required amount of RhN (5.2g / ft 3 ) and water to dissolve and mix for 1 hour. 2. Add the required amount of Tannic Acid (Sigma Aldrich product #403040) to target a TA:Rh mass ratio of 2.1. Mix for 1 hour. 3. Add the ground gamma alumina slurry and mix for 1 hour. 4. Adjust solids to approximately 20% by adding DI water. 5. Activated 4 wt.% thickener in water (1 g / in 3 ) to adjust batch solids to 30%. Mix vigorously with a VWR vortex mixer until a homogenous gel is formed. 6. Coat 1x3 inch core under vacuum aiming to dos 1.2 inches from the inlet and allow to air cure and dry. 7. Fire the bricks in a static oven at 500°C for 30 minutes.

[0092] Reference Example 2: Rh-TWC (containing Rh nitrate) washcoat catalyst 1. Prepare a slurry of ground gamma alumina support (0.6 g / in 3 ). 2. Add an appropriate amount of rhodium nitrate solution (Rh loading 4.8 g / ft 3 ) and mix until homogenous. 3. Add ammonium hydroxide solution dropwise until a pH of 7.0-7.5 is reached. The washcoat will thicken with the addition of ammonium. 4. Mix for 15-20 minutes to allow the rhodium to precipitate throughout the washcoat. 5. Ceria-zirconia support (0.65 g / in 3 ) and mix for 30 minutes until homogenous. 6. Binder material (0.03g / in 3 ) and mix for 30 minutes. 7. Add DI water to adjust solids to approximately 23%. 8. Add thickener aiming for approximately 1.0-1.2% by weight based on water. Mix for at least 6 hours. 9. Coat the cordierite substrate with a single dose washcoat under vacuum 1.2 inches from the inlet and allow to dry by air curing. 10. The washcoated bricks are baked in a static oven at 500°C for 30 minutes.

[0093] Example 2: Rh-TWC (with Rh modified by tannic acid) washcoat catalyst. 1. Prepare a slurry of rhodium nitrate (Rh loading: 4.8 g / ft 3 ). 2. Add the required amount of Tannic Acid (Sigma Aldrich product #403040) to target a TA:Rh mass ratio of 2.1. Mix for 1 hour. 3. Crushed gamma alumina support (0.6 g / in 3 ) slurry and mix for 1 hour. 4. Ceria-zirconia support (0.65 g / in 3 ) and mix for 30 minutes. 5. Add binder material (0.03g / in 3 ) and mix for 30 minutes. 6. Adjust solids to approximately 23% by adding DI water. 7. Add thickener aiming for approximately 1.0-1.2% by weight on a water basis. Mix for at least 6 hours. 8. Coat the cordierite substrate with a single dose washcoat under vacuum 1.2 inches from the inlet and allow to dry by air curing. 9. The washcoated bricks are baked in a static oven at 500°C for 30 minutes.

[0094] Reference Example 3: Rh-Pt bimetallic (with Pt nitrate) TWC washcoat catalyst. 1. Ceria-zirconia support (1.1 g / in 3 ) and add at least 50% of the planned amount of water. 2. Rh nitrate (Rh loading 3.6g / ft 3 ) is added to the ceria-zirconia slurry and mixed for at least 15 minutes. 3. Add ammonium hydroxide to adjust the pH to greater than 6 and mix for at least 1 hour. 4. Gamma alumina (0.4g / in 3 ) slurry and platinum nitrate (Pt loading 1.8 g / ft 3 ) and mix for at least 15 minutes. 5. Adjust pH to greater than 5.8 with ammonia. Mix for at least 30 minutes. 6. Add binder (0.03g / in 3 ) and mix for at least 30 minutes. 7. Adjust washcoat to target % solids (suggested about 25%) and add thickener (suggested about 0.8-1.0%). Mix overnight. 8. Coat 50-55% from the inlet under vacuum, dry with air cure, then coat 50-55% DL from the outlet. 9. Fire the bricks in a static oven at 500°C / 30min.

[0095] Example 3: Rh-Pt bimetallic TWC (with Pt modified by tannic acid) washcoat catalyst 1. Prepare a solution containing the required amount of Tannic Acid (Sigma Aldrich product #403040) needed to complex with both Rh and Pt. Target a TA:Rh mass ratio of 2.1. Target a TA:Pt mass ratio of 0.7. 2. Rh nitrate (Rh loading 3.8g / ft 3 ) and mix for 1 hour. 3. Ceria-zirconia support (1.1 g / in 3 ) slurry and mix for 1 hour. 4. Gamma alumina (0.4g / in 3 ) slurry and platinum nitrate (Pt loading 1.8 g / ft 3 ) and mix for 1 hour. 5. Add binder (0.03g / in 3 ) and mix for at least 30 minutes. 6. Adjust washcoat to target % solids (suggested around 25%) and add thickener (suggested around 0.8-1.0%). Mix overnight. 7. Coat 50-55% from the inlet under vacuum, dry with air cure, then coat 50-55% DL from the outlet. 8. Fire the bricks in a static oven at 500℃ / 30min.

[0096] STEM Rh elemental mapping image and Rh particle size distribution Figures 1a and 1b show STEM Rh elemental mapping images of reference virgin Rh / alumina (Reference Example 1) and virgin Rh / alumina with tannic acid modification (Example 1). Figure 2 shows the Rh particle size distribution of reference virgin Rh / alumina (Reference Example 1) and virgin Rh / alumina with tannic acid modification (Example 1). Compared to the reference sample, the tannic acid modified sample shows smaller Rh particle size with a narrower distribution.

[0097] CO chemisorption 3 shows the Rh dispersion measured by CO chemisorption for the reference and TA-modified catalysts described in Examples 1 and 2. In both examples, the TA modification resulted in higher virgin Rh dispersion than the reference catalyst.

[0098] Perturbed ignition performance After aging, the catalyst articles of Example 1 and Reference Example 1 were tested for perturbation light-off performance versus TWC conversion under simulated gasoline exhaust conditions. (Aging conditions: 1000°C / redox / 40 hours. Reaction conditions: rich pretreatment, 150-700°C, λ=0.96-1.04, GHSV=200,000 hours) -1 The results for NO, CO, and THC conversion are shown in Figures 4a-4c. In each case, TWC activity was greater in Example 1 than in Reference Example 1. NO in Example 1 x , CO and THC max T 50 The reductions were 19°C, 26°C and 40°C, respectively.

[0099] After aging, the catalyst articles of Example 2 and Reference Example 2 were tested for perturbation light-off performance versus TWC conversion. (Aging conditions: 1000°C / redox / 40 hours. Reaction conditions: rich pretreatment, 150-700°C, λ=0.96-1.04, GHSV=200,000 hours) -1 The results for NO, CO, and THC conversion are shown in Figures 5a-5c. The TWC activity was greater in Example 2 than in Reference Example 2. The maximum TWC activity for NOx, CO, and THC in Example 2 was 50 The reductions were 10°C, 14°C and 15°C, respectively.

[0100] After aging, the catalyst articles of Example 3 and Reference Example 3 were tested for perturbation light-off performance versus TWC conversion. (Aging conditions: 1050°C / 10% H2O in air / 4 hours. Reaction conditions: rich pretreatment, 150-700°C, λ=0.96-1.04, GHSV=200,000 hours) -1 The results for NO, CO, and THC conversion are shown in Figures 6a-6c. The TWC activity was greater in Example 3 than in Reference Example 3. x , CO and THC max T 90 The reductions were 22°C, 12°C and 45°C, respectively.

[0101] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method for manufacturing a catalyst article, comprising providing a complex of a polyphenol and a PGM, wherein the polyphenol contains an ester functional group and the PGM contains rhodium and / or platinum; providing a carrier material; applying the complex to the carrier material to form a supported carrier material; disposing the supported carrier material on a substrate; and heating the supported carrier material to form nanoparticles of the PGM on the carrier material.

2. The method according to claim 1, wherein the polyphenol contains tannic acid.

3. The method according to claim 1 or 2, wherein the PGM contains rhodium.

4. The method according to claim 1 or 2, wherein the PGM contains platinum.

5. The method according to claim 1 or 2, wherein the carrier material contains alumina and ceria-zirconia.

6. The method according to claim 5, wherein the alumina and / or the ceria-zirconia is doped.

7. The method according to claim 6, wherein the alumina and / or the ceria-zirconia is doped with one or more oxides of lanthanum, neodymium, yttrium, niobium, praseodymium, hafnium, molybdenum, titanium, vanadium, zinc, cadmium, manganese, iron, copper, calcium, barium, strontium, cesium, magnesium, potassium, and sodium, preferably one or more oxides of lanthanum, neodymium, and yttrium.

8. The method according to claim 1, wherein the supported carrier material is disposed on the substrate in the form of a slurry.

9. the slurry is contacting a PGM salt with a polyphenol in water to form the complex of the polyphenol and PGM in an aqueous solution, wherein the PGM salt contains rhodium and / or platinum, and forming; applying the complex to the carrier material by contacting the carrier material with the aqueous solution to form a supported carrier material; Optionally, adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or a base, a thickener, and a reducing agent to the aqueous solution, and a method comprising: The method according to claim 8.

10. The method according to claim 8 or 9, wherein the PGM contains rhodium and the carrier material contains alumina and ceria-zirconia.

11. Placing the supported carrier material on a substrate comprises contacting the slurry with the substrate and optionally applying a vacuum to the substrate and / or drying the slurry on the substrate, and the method according to claim 8 or 9.

12. The method according to claim 1, wherein the substrate is in the form of a honeycomb monolith, a wall flow filter, or a flow through filter.

13. The heating is at a temperature of 400°C to 700°C, preferably 400°C to 600°C, more preferably 450°C to 600°C, and / or carried out for 10 to 360 minutes, preferably 35 to 120 minutes, and the method according to claim 1.

14. A catalyst article obtainable by the method according to claim 1, for use in an exhaust treatment system.

15. The catalyst article according to claim 14, comprising a lowermost layer of a carrier material having rhodium thereon and an uppermost layer of a carrier material having palladium thereon. **Claim 16** The catalyst article according to claim 14, comprising a lowermost layer of a carrier material having palladium thereon and an uppermost layer of a carrier material having rhodium thereon. **Claim 17** The catalyst article according to any one of claims 14 to 16, wherein the supported carrier material is disposed on the substrate in the form of a slurry, the PGM contains rhodium, and the carrier material contains alumina and ceria-zirconia.

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