Polymaleic acid assisted synthesis of metal nanoparticles for three-way catalytic applications

Abstract

A method of making a catalyst article, the method including providing a complex of a maleic acid-containing polymer and a PGM, 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 Catalyst (TWC) is a catalytic converter that removes CO, HC, and NO from the exhaust of a gasoline engine at a stoichiometric air-fuel ratio. x The oxidation of CO and HC to CO2 and water vapor (HO) is primarily catalyzed by Pd, while the oxidation of NO x The reduction of N2 to N2 is primarily catalyzed by rhodium (Rh). Modern TWCs use supported platinum group metal (PGM) catalysts (e.g., palladium (Pd), rhodium (Rh), platinum (Pt)) 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 supports.

[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. To improve TWC performance, promoter salts are often added to the washcoat formulation. Once the monolith support is washcoated with the as-prepared slurry, drying and calcination steps are subsequently performed to decompose the inorganic salts and fix the PGMs and promoter elements onto the support material. It is well 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 interactions is essential in optimizing TWC performance. Furthermore, homogenized PGM particle size distribution can contribute to reducing the degree of metal sintering due to Ostwald ripening, such as occurs during the fuel cut-off process, which is an engine strategy often 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. Catalyst articles with lower light-off temperatures are needed.

[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, the 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 maleic acid-containing polymer and a PGM, 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 that includes the catalytic article of the second aspect. [Brief description of the drawings]

[0010] [Figure 1a] 4 shows the results of NO conversion in a perturbation light-off performance test of the example catalyst article and the reference example catalyst article produced according to the method of the present invention. [Figure 1b]4 shows the results of CO conversion in a perturbation ignition performance test of the catalyst article of the example and the catalyst article of the reference example produced according to the method of the present invention. [Figure 1c] 1 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 2a] 4 shows the results of NO conversion in a perturbation light-off performance test of the example catalyst article and the reference example catalyst article produced according to the method of the present invention. [Figure 2b] 4 shows the results of CO conversion in a perturbation ignition performance test of the catalyst article of the example and the catalyst article of the reference example produced according to the method of the present invention. [Figure 2c] 1 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 3a] 4 shows the results of NO conversion in a perturbation light-off performance test of the example catalyst article and the reference example catalyst article produced according to the method of the present invention. [Figure 3b] 4 shows the results of CO conversion in a perturbation ignition performance test of the catalyst article of the example and the catalyst article of the reference example produced according to the method of the present invention. [Figure 3c] 1 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 4] 1 shows the rhodium incorporation of 1 wt. % rhodium on La-doped alumina based on rhodium nitrate, and the in-situ modification of rhodium with various rhodium-PMAs. 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 catalytic article, the method comprising: providing a complex of a maleic acid-containing polymer and a PGM; Providing a support material; applying the complex to a 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 PGMs on the support material.

[0013] Each aspect or embodiment defined in this specification may be combined with any other aspect(s) or embodiment(s) unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature(s) 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 superior to that exhibited by a conventional catalyst article having the same / similar PGM type(s), loading(s), support(s), and configuration(s). 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 may facilitate the use of lower loadings of PGMs compared to conventional catalyst articles without compromising catalytic performance, which may be beneficial given the high cost of such metals, particularly rhodium. Furthermore, such superior performance may facilitate partial / complete replacement 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 the complexation of the PGM with the maleic acid-containing polymer, the ions of the PGM may react with the carboxyl functional groups, and the same predictable amount of PGM ions is "uptaken" by each polymer unit structure, but the total amount of PGM "uptaken" is determined by the molecular structure / size of the polymer and the PGM-polymer coordination ratio. Each complex may then react / interact with surface functional groups (e.g., hydroxyl groups) or surface charges, allowing the PGM-polymer complex to "anchore" onto the support material surface. The "anchored" PGM-polymer complex may 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 complex and the support material functional groups may increase the PGM uptake by the support compared to catalysts prepared by conventional 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 US 2012 / 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 US 2012 / 0077669(A1), only a limited amount of polymer molecules 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, in particular, as a three-way catalyst for stoichiometric gasoline emission reduction. In contrast, the catalyst article produced by the method of US 2012 / 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 within 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 maleic acid-containing polymer with a PGM typically involves providing the complex in a solution, for example an aqueous or alcoholic solution. Providing a complex of a maleic acid-containing polymer with a PGM typically involves mixing the inorganic PGM precursor(s) in pure form or in solution with the maleic acid-containing polymer in an aqueous medium, for example mixing nitric acid PGM with the maleic acid-containing polymer in water.

[0020] The term "maleic acid" as used herein may include cis-butenedioic acid, i.e.,

[0021] [ka]

[0022] As used herein, the term "maleic acid-containing polymer" may encompass a class of polymers formed at least in part from maleic acid. The polymer may comprise a homopolymer, i.e., polymaleic acid. Alternatively, the polymer may comprise a copolymer formed from maleic acid and at least one other monomer. The polymer may be linear or branched, but is preferably branched. The polymer may be in the form of a dendrimer.

[0023] As used herein, the term "platinum group metals" or "PGMs" may include ruthenium, rhodium, palladium, osmium, iridium, and platinum. The PGMs may include one of these metals. Alternatively, the PGMs may include two or more of these metals. The PGMs may be in the form of an alloy.

[0024] The complexes may have a PGM to carboxyl group ratio of from 1:1 to 1:10, preferably from 1:2 to 1:8, more preferably from 1:5 to 1:7.

[0025] The support material can be any material capable of supporting the complexes and nanoparticles thereon or therein. The support material can be in 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 is typically in the form of a powder having a D50, for example, of 0.1 to 25 μm, more typically 0.5 to 5 μm, as measured using TEM (Transmission Electron Microscopy). Such particle sizes can facilitate desirable rheological properties of the slurry used to coat the filter. The support material can function as a washcoat. The support material can be a washcoat or can be part of a washcoat.

[0026] The support material may also act as an oxygen storage material, storing and releasing oxygen under fuel-lean and fuel-rich conditions, respectively, to facilitate 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. As used herein, the term "slurry" can include a liquid containing insoluble materials, e.g., insoluble particles. The slurry can include (1) the solvent, (2) soluble inclusions, e.g., unreacted maleic acid-containing polymer, inorganic PGM and cocatalyst precursor(s), and PGM-polymer complex (outside the support), and (3) insoluble inclusions, 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. Increasing the contact time and / or stirring time can increase the amount of complex supported on the support material.

[0028] As used herein, the term "loaded support material" can include support materials having a PGM-polymer complex supported thereon (e.g., on the surface of a high surface area metal oxide support material) and / or within it (e.g., within the pores of a zeolite support material). The complex is 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, carboxyl functional groups in the maleic acid-containing polymer 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 monolithic carriers. 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] Placing the supported carrier material on the substrate can be performed using techniques well 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 can be used during the placement step, as discussed in more detail below. If the carrier is a filter block, the supported carrier material can 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 drying. Heating may also include calcination. 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 when the coating is complete. During heating, the complex may at least partially, substantially, or completely decompose. In other words, the ligand of the complex, i.e. the maleic acid-containing polymer, is at least partially, substantially, or completely removed or separated from the PGM and removed from the final catalyst article. The particles of PGM thus separated may then begin to form metal-metal and metal-oxide bonds. As a result of heating (calcining), the substrate is typically substantially free of maleic acid-containing polymer, and more typically completely free of maleic acid-containing polymer.

[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., spherical, plate-like, cubic, cylindrical, hexagonal, or rod-like, but are typically spherical. The maximum dimension of a nanoparticle (i.e., the diameter, if the nanoparticle is spherical) is typically 0.5 to 10 nm, more typically 1 to 5 nm, as measured by TEM.

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

[0034] The maleic acid-containing polymer preferably comprises one or more of polymaleic acid (i.e., homopolymer), poly(methyl vinyl ether-alt-maleic acid), and poly(acrylic acid-co-maleic acid). Such polymers may be linear or branched, but are preferably branched and may be in dendrimeric form. Use of such species may result in particularly favorable perturbation ignition performance.

[0035] The polymaleic acid may have the general formula:

[0036] [ka]

[0037] Poly(methyl vinyl ether-alt-maleic acid) (aka maleic acid-methyl vinyl ether copolymer, vinyl methyl ether-maleic acid copolymer, poly(maleic acid-methyl vinyl ether), methoxyethylene-maleic acid copolymer) can have the general formula:

[0038] [ka]

[0039] Poly(acrylic acid-co-maleic acid) may have the general formula:

[0040] [ka]

[0041] In a preferred embodiment, the maleic acid-containing polymer comprises polymaleic acid. The use of polymaleic acid can provide particularly favorable perturbation ignition performance.

[0042] The polymaleic acid preferably has a weight average molecular weight M of 100 to 6,000,000, more preferably 10,000 to 4,000,000 g / mol, even more preferably 100,000 to 2,000,000 g / mol, still more preferably 190,000 to 400,000 g / mol, as measured by light scattering. w The weight average molecular weight Mw is represented by the following formula:

[0043]

number

[0044] In other preferred embodiments, the maleic acid-containing polymer comprises a copolymer. The copolymer preferably comprises poly(acrylic acid-co-maleic acid).

[0045] The copolymers and / or poly(acrylic acid-co-maleic acid) may be linear or branched, but are preferably branched. The copolymers and / or polymaleic acid may be in dendrimeric form. The use of copolymers, particularly poly(acrylic acid-co-maleic acid), may provide particularly favorable perturbation ignition performance.

[0046] The poly(acrylic acid-co-maleic acid) preferably has a weight average molecular weight M of 1,000 to 5,000, more preferably 2,000 to 4,000 g / mol, and even more preferably 2,500 to 3,500 g / mol, as measured by light scattering. w The weight average molecular weight Mw is determined by the above formula. The use of such a weight average molecular weight can result in particularly favorable perturbation ignition performance.

[0047] The poly(acrylic acid-co-maleic acid) preferably has a molar ratio of acrylic acid to maleic acid of from 1.5:1 to 1:1.5, more preferably from 1.25:1 to 1:1.25, even more preferably from 1.1:1 to 1:1.1, and still more preferably about 1:1. Use of such ratios can result in particularly favorable perturbation ignition performance.

[0048] The PGM is preferably selected from one or more of rhodium, palladium and platinum, more preferably from rhodium and platinum. Such metals may be particularly suitable for performing three-way catalysis. However, 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.

[0049] The PGM more preferably comprises rhodium. Rhodium is a particularly expensive PGM. The use of rhodium in the method of the present invention may result in particularly favorable perturbation ignition performance.

[0050] In a preferred embodiment, the PGMs include rhodium and palladium. The use of such metals in the methods of the present invention can result in particularly favorable perturbation ignition performance.

[0051] 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 zirconia. The alumina and / or zirconia are preferably doped, more preferably 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 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 zirconia in an amount of from 0.001% to 20% by weight, and more preferably, from 0.5% to 10% by weight.

[0052] 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. D90 can be measured by TEM.

[0053] The supporting may include a washcoating.

[0054] 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.

[0055] Providing the complex of the PGM and the maleic acid-containing polymer preferably involves synthesizing the complex in situ in a slurry.

[0056] In a preferred embodiment, the slurry is contacting a PGM salt with a maleic acid containing polymer in water to form said complex of the maleic acid containing polymer and the PGM in aqueous solution; applying the complex to the support material by contacting the support material with an aqueous solution to form a supported support material; Optionally, the oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or base, a thickener, and / or a reducing agent are added to the aqueous solution.

[0057] Such a "one-pot" preparation method may be simplified and less costly than conventional methods, and may also maximize polymer utilization.

[0058] In other words, the steps of providing a complex of a maleic acid-containing polymer 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 can be performed by: contacting a PGM salt with a maleic acid containing polymer in water to form a complex of the maleic acid containing polymer with the PGM in an aqueous solution; adding a support material to the 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; disposing the slurry on a substrate.

[0059] In another preferred embodiment, the slurry comprises: contacting a PGM salt with a support material in water to form a support material suspension; contacting the support material suspension with a maleic acid containing polymer to form a supported support material, the supported support material comprising a support material having a complex supported thereon, the complex comprising a complex of the maleic acid containing polymer and a PGM; Optionally, the carrier material suspension is prepared by a process 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 carrier material suspension.

[0060] Such a "one-pot" preparation method may be simplified and less costly than conventional methods, and may also maximize polymer utilization.

[0061] The slurry preferably has a solids content of 10-40%, preferably 15-35%. Such a solids content may allow suitable slurry rheology for disposing the supported support material on a substrate. For example, if the substrate is a honeycomb monolith, such a 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 a solids content may allow the slurry to enter the channels of the wall-flow filter and allow the slurry to enter the walls of the wall-flow filter.

[0062] Preferably, the slurry comprises: an oxygen storage material, preferably ceria-zirconia; cocatalyst salt, Binder, Acid or base, Thickeners, and Further comprising one or more reducing agents.

[0063] 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.

[0064] 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.

[0065] The thickener may include, for example, a natural polymer with functional hydroxyl groups that interact with insoluble particles in the washcoat slurry. The thickener serves the purpose of thickening the washcoat slurry for improved coating profile during washcoat coating on the substrate. The thickener is usually baked off during the washcoat bake. Examples of specific thickeners / rheology modifiers for washcoats include galactomannan gum, guar gum, xanthan gum, curdlan schizophyllan, scleroglucan, deutan gum, wheelan gum, hydroxymethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, and ethylhydroxycellulose.

[0066] The term "reducing agent" as used herein may include compounds that can reduce PGM cations to their metallic state particles in situ during washcoat preparation.

[0067] Organic acids may 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 may include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof.

[0068] In a preferred embodiment, the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

[0069] 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, the further slurry being disposed on the substrate 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 may 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, palladium nanoparticles supported on alumina. Optionally, an OSC (Oxygen Storage Capacity) type support may be added to either or both of the layers. Further examples of such multiple layers are discussed in more detail below.

[0070] Placing the supported support material on the substrate preferably comprises contacting the 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 and drying the slurry on the substrate.

[0071] This may result in a preferred distribution of the supported support material on the substrate.

[0072] Drying is preferably carried out as follows: At a temperature of 60°C to 200°C, more preferably 70°C to 130°C, and / or 10 to 360 minutes, preferably 15 to 60 minutes.

[0073] The substrate may be a "blank", i.e., an unwashcoated substrate. Alternatively, the substrate may have a pre-support or washcoat already thereon. In such a situation, the final catalyst article may include multiple layers of different washcoats.

[0074] The substrate preferably comprises cordierite. Cordierite substrates are particularly suitable for use in catalytic articles.

[0075] The substrate is preferably in the form of a honeycomb monolith, a wall-flow filter or a flow-through filter.

[0076] 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 10 to 360 minutes, preferably 35 to 120 minutes.

[0077] Lower temperatures and / or shorter heating times may result in insufficient decomposition of the complex and / or high levels of maleic acid-containing polymers may remain in the substrate. Higher temperatures and / or longer heating times may result in particles of PGM with undesirably large particle sizes, possibly due to sintering. Higher temperatures and longer heating times may also result in damage to the catalyst article.

[0078] 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.

[0079] 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 may be measured by TEM. Such particle size may provide a preferred level of catalytic activity.

[0080] In a further aspect, the present invention provides a catalyst article obtainable by the process described herein, the catalyst article being for use in an emission treatment system.

[0081] Compared to conventional catalyst articles, catalyst articles obtainable by the methods described herein may contain PGM particles having an advantageously small particle size and a 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 may exhibit a more uniform distribution of PGM particles throughout the substrate.

[0082] When used in emissions treatment systems, the catalyst articles may exhibit favorable light-off performance, particularly for NO, CO and total hydrocarbons, during three-way catalytic conversion for stoichiometric gasoline emission reduction.

[0083] The catalyst is preferably for a three-way catalyst.

[0084] 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.

[0085] The substrate preferably comprises a wall-flow filter substrate or a flow-through substrate.

[0086] In a preferred embodiment, the catalyst article includes a bottom layer of support material having rhodium thereon and a top layer of support material having palladium thereon. In another preferred embodiment, the catalyst article includes a bottom layer of support material having palladium thereon and a top layer of 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. In another preferred embodiment, either or both layers may be further layered with different catalyst compositions containing the same or different PGM species.

[0087] In such preferred embodiments, the support material preferably comprises alumina.

[0088] The catalyst article, particularly in such preferred embodiments, preferably has a surface area of ​​2 g / ft 3 ~15g / ft 3 of rhodium, more preferably 3 g / ft 3 ~10g / ft 3 Advantageously, such rhodium levels can be lower than those of conventional catalyst articles, yet without impairing catalytic activity.

[0089] The catalyst article, particularly in such preferred embodiments, preferably has a surface roughness of 20 g / ft 3 ~200g / ft 3 of palladium, more preferably 30 g / ft 3 ~180g / ft 3 Advantageously, such palladium levels can be lower than those of conventional catalyst articles, yet do not impair catalytic activity.

[0090] In a preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

[0091] In a further aspect, the present invention provides an emission treatment system comprising the catalytic article described herein.

[0092] The emission treatment system is preferably for a gasoline engine.

[0093] Gasoline engines preferably operate under stoichiometric conditions.

[0094] 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.

[0095] 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.

[0096] The invention will now be described with reference to the following non-limiting examples.

[0097] Maleic Acid-Containing Polymers The following maleic acid-containing polymers, labeled PMA-a to PMA-d, were purchased directly from the supplier. PMA-a: Polymaleic acid, average Mw by LS is approximately 216,000. PMA-b: Polymaleic acid, average M by LS w is approximately 1,080,000. PMA-c: Polymaleic acid, mean M by LS w is approximately 1,980,000. PMA-d: poly(acrylic acid-co-maleic acid), AA:MA molar ratio 1:1, average Mw is 3,000.

[0098] Manufacturing of catalytic articles A number of catalyst articles were prepared according to the following examples.

[0099] Reference Example 1: 0.3% Rhodium / gamma alumina (containing rhodium nitrate) washcoat catalyst. The catalyst article was prepared by carrying out the following steps. 1. The required amount of rhodium nitrate (5.2g / ft 3 ) and water to dissolve and mix for 1 hour. 2. Milled gamma alumina (1 g / in 3 ) Add the slurry and mix for 1 hour. 3.Add DI water to adjust solids to approximately 20%. 4. Adjust batch solids to 30% by adding 4% by weight of activated thickener in water. Mix vigorously with a VWR vortex mixer until a homogenous gel is formed. 5. Under vacuum, coat 1×3 inch cores, targeting doses 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.

[0100] Example 2: 0.3% Rhodium / gamma alumina (containing rhodium modified with PMA-a, b, c, or d) washcoat catalyst. The catalyst article was prepared by carrying out the following steps. 1. The required amount of rhodium nitrate (5.2g / ft 3 ) and water to dissolve and mix for 1 hour. 2. Add the required amount of PMA to target a PMA:Rhodium mass ratio of 8.0 for PMA-a, PMA-b, and PMA-c, and a PMA:Rhodium mass ratio of 1.4 for PMA-d. Mix for 1 hour. 3. Add the ground gamma alumina slurry and mix for 1 hour. 4. Add DI water to adjust solids to approximately 20%. 5. 4% by weight of activated thickener in water (1 g / in 3 Adjust batch solids to 30% by adding 100% ethanol. Mix vigorously in a VWR vortex mixer until a homogenous gel is formed. 6. Under vacuum, coat 1×3 inch cores, targeting doses 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.

[0101] Reference Example 3: Rhodium-TWC (containing rhodium nitrate) washcoat catalyst. The catalyst article was prepared by carrying out the following steps. 1. Prepare a slurry of ground gamma alumina support (0.6 g / in 3 ). 2. Add an appropriate amount of rhodium nitrate solution (rhodium loading 4.8 g / ft 3 ) and mix until homogenous. 3. Add ammonium dropwise until a pH of 7.0-7.5 is reached. The washcoat will thicken as more ammonium is added. 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. In aqueous systems, add thickener, targeting approximately 1.0-1.2% by weight. 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 fired in a static oven at 500° C. for 30 minutes.

[0102] Example 4: Rhodium-TWC (containing rhodium modified with PMA-a, b, c, or d) washcoat catalysts. The catalyst article was prepared by carrying out the following steps. 1. Prepare a slurry of rhodium nitrate (rhodium loading 4.8 g / ft 3 ). 2. Add the required amount of PMA to target a PMA:Rhodium mass ratio of 8.0 for PMA-a, PMA-b, and PMA-C, and a PMA:Rhodium mass ratio of 1.4 for PMA-d. Mix for 1 hour. 3. Crushed gamma alumina support (0.6 g / in 3 ) Add the slurry and mix for 1 hour. 4. Ceria-zirconia support (0.7 g / in 3 ) and mix for 30 minutes. 5. Add binder material (0.03g / in 3 ) and mix for 30 minutes. 6. Add DI water to adjust solids to approximately 23%. 7. In aqueous systems, add thickener, targeting approximately 1.0-1.2% by weight. 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 fired in a static oven at 500° C. for 30 minutes.

[0103] Reference Example 5: Rhodium-Platinum Bimetallic (with platinum nitrate) TWC washcoat catalyst. The catalyst article was prepared by carrying out the following steps. 1. Ceria-zirconia support (1.1 g / in 3 ) and add at least 50% of the planned amount of water. 2. Rhodium nitrate (rhodium loading 3.6g / ft 3 ) is added to the above ceria-zirconia slurry and mixed for at least 15 minutes. 3. Adjust pH to greater than 6 with ammonia. Mix for at least 1 hour. 4. Gamma alumina (0.4g / in 3 ) slurry and platinum nitrate (platinum 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 around 25%) and add thickener (suggested around 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 for 30 minutes.

[0104] Example 6: Rhodium-Platinum Bimetallic TWC (containing platinum modified with PMA-a, b, c, or d) washcoat catalysts. The catalyst article was prepared by carrying out the following steps. 1. Prepare a solution containing the required amount of PMA needed to complex with both rhodium and platinum. Target a PMA:rhodium mass ratio of 8.0 for PMA-a, PMA-b and PMA-C, and a PMA:rhodium mass ratio of 1.4 for PMA-d. Target a PMA:platinum mass ratio of 2.8 for PMA-a, PMA-b and PMA-C, and a PMA:platinum mass ratio of 0.5 for PMA-d. 2. Rhodium nitrate (rhodium loading 3.6g / ft 3 ) and mix for 1 hour. 3. Ceria-zirconia support (1.1 g / in 3 ) Add the slurry and mix for 1 hour. 4. Gamma alumina (0.4g / in 3 ) slurry and platinum nitrate (platinum 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°C for 30 minutes.

[0105] Perturbed ignition performance After aging, the single supported catalyst articles of Example 2 and Reference Example 1 were tested for perturbed light-off performance versus TWC conversion under simulated gasoline exhaust conditions. Aging conditions: 1000°C / Redox / 40 hours. Reaction conditions: enrichment pretreatment, 150-700°C, λ=0.96-1.04, GHSV=200,000 hours. -1 The results are shown in Figure 1a-c for NO, CO, and THC conversion, respectively (PMA-a = squares, PMA-b = dots, PMA-c = diamonds, PMA-d = triangles, rhodium nitrate reference = line). Compared to the reference catalyst, the catalyst prepared by complexing rhodium with PMA shows a significant advantage in TWC activity. The NO, CO, and THC conversions for the single alumina-supported rhodium catalyst with PMA modification are shown in Figure 1b. x , CO, THC max T 50 The decreases were at 35°C, 45°C, and 94°C, respectively.

[0106] Similar improvements were observed with more complexed rhodium catalysts (Example 4 and Reference Example 3), the results of which are shown in Figures 2a-c for NO, CO, and THC conversion, respectively (PMA-a = squares, PMA-b = dots, PMA-c = diamonds, PMA-d = triangles, rhodium nitrate reference = line). Aging conditions: 1000°C / redox / 40 hours. Reaction conditions: enrichment pretreatment, 150-700°C, λ = 0.96-1.04, GHSV = 200,000 hours. -1 The rhodium-PMA catalyst performed significantly better than the reference catalyst, with NOx , CO, and THC max T 50 The decreases were at 33°C, 40°C, and 37°C, respectively.

[0107] Similar improvements were observed in aged platinum / rhodium bimetallic catalysts where both rhodium and platinum were modified by PMA (Example 6 and Reference Example 5). The results are shown in Figures 3a-c for NO, CO, and THC conversion, respectively (PMA-a = squares, PMA-b = dots, PMA-c = diamonds, PMA-d = triangles, rhodium nitrate reference = line). Aging conditions: 1050°C / hot water / 4 hours. Reaction conditions: enrichment pretreatment, 150-700°C, λ = 0.96-1.04, GHSV = 200,000 hours. -1 The rhodium / platinum-PMA catalyst performed significantly better than the reference catalyst, with NO x , CO, and THC max T 90 The decreases were 51°C, 25°C, and 55°C, respectively.

[0108] PGM Import The rhodium uptake on alumina containing rhodium nitrate and various rhodium-PMAs was measured. For this purpose, firstly a number of supported support materials (La-doped alumina) were prepared.

[0109] Reference: 1% Rhodium / Alumina with Rhodium Nitrate: The supported carrier material was prepared according to the following method. 1. Add the required amount of rhodium nitrate and alumina to water to target 1 wt % rhodium on alumina and 30% batch solids. 2. Mix for 1 hour.

[0110] 1% Rhodium / Alumina with in situ Rhodium-PMA-a, b, c, or d modification: The supported carrier material was prepared according to the following method. 1. Add the required amount of rhodium nitrate and PMA into water. 2. Mix for 30 minutes. 3. Add the required amount of alumina to target 1 wt. % rhodium on alumina and 30% batch solids. 4. Mix for 1 hour.

[0111] In each case, the final suspension was centrifuged and the supernatant was collected. The supernatant was then analyzed by ICP-OES to determine the amount of free rhodium still remaining in solution. Rhodium incorporation into the support material was determined using the following equation:

[0112]

number

[0113] The results of the rhodium incorporation experiments are summarized in Figure 4. Correlation of the rhodium incorporation results (rhodium-PMA-a ≈ rhodium-PMA-c > rhodium-PMA-b ≈ rhodium-PMA-d) with the TWC performance from Figure 2 (rhodium-PMA-a ≈ rhodium-PMA-c > rhodium-PMA-b ≈ rhodium-PMA-d) suggests that all PMAs provide improved TWC performance over rhodium, but with increasing benefit as rhodium-PMA incorporation on the alumina support increases.

[0114] 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. 1. A method of making a catalyst article, said method comprising: providing a complex of a maleic acid-containing polymer and a PGM; Providing a carrier material; applying the complex to the support material to form a supported support material; placing the supported support material on a substrate; and heating the loaded support material to form nanoparticles of the PGM on the support material.

2. 10. The method of claim 1, wherein the maleic acid-containing polymer comprises one or more of polymaleic acid, poly(methyl vinyl ether-alt-maleic acid), and poly(acrylic acid-co-maleic acid).

3. The method of claim 1 , wherein the maleic acid-containing polymer comprises polymaleic acid.

4. The method of claim 1 , wherein the maleic acid-containing polymer comprises a copolymer.

5. The method of claim 4, wherein the copolymer comprises poly(acrylic acid-co-maleic acid).

6. 6. The method of claim 5, wherein the poly(acrylic acid-co-maleic acid) has a molar ratio of acrylic acid to maleic acid of 1.5:1 to 1:1.

5.

7. 3. The method of claim 1, wherein the PGM is selected from one or more of rhodium, palladium, and platinum.

8. The support material is an oxide, preferably Al ２ O ３ , SiO ２ , TiO ２ , CeO ２ , ZrO ２ , CeO ２ -ZrO ２ , V ２ O ５ , La ２ O ３ and zeolite.

9. The method of claim 1, wherein the support material comprises alumina, preferably gamma-alumina.

10. The method of claim 1 , wherein the support material comprises zirconia.

11. 11. The method of claim 9 or claim 10, wherein the alumina and / or the zirconia is doped.

12. 12. The method according to claim 11, wherein the alumina and / or the zirconia are 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 with one or more oxides of lanthanum, neodymium, and yttrium.

13. The method of claim 1 , wherein the supported support material is disposed on the substrate in the form of a slurry.

14. The slurry contacting a PGM salt with a maleic acid-containing polymer in water to form said complex of maleic acid-containing polymer and PGM in aqueous solution; applying the complex to the support material by contacting the support material with the aqueous solution to form a supported support material; and optionally adding to the aqueous solution 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.

15. The method of claim 13 or claim 14, wherein the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

16. A catalytic article obtainable by the method of claim 1 or 2, said catalytic article being for use in an emission treatment system.

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