Anionic PGM carboxylate assisted PGM nanoparticle synthesis for exhaust gas treatment applications

Abstract

A method of making a catalyst article, the method comprising: providing an anionic complex comprising a PGM and a carboxylate ion; providing a support material; applying the anionic 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] Platinum group metals (PGMs) are used in exhaust gas catalysts, such as three-way catalysts (TWCs), diesel oxidation catalysts (DOCs) and NO x PGMs are key components in trap catalysts. To maximize efficiency, it is desirable to selectively and / or reliably locate PGMs on target support materials. Conventional catalyst article preparation methods use simple PGM salts, typically PGM nitrate, as the PGM source. However, using such conventional methods, it is difficult to locate PGMs on a particular support material. This is due to the weak interaction between the support material and the PGMs when preparing the washcoat. To overcome this problem, methods have been explored that include pre-fixing PGMs on the target support material by impregnation followed by calcination, spray drying, and reduction precipitation. However, all of these approaches require multiple / additional processing steps. Furthermore, during calcination to fix PGMs on the support material, decomposition of nitrates can result in the release of harmful NO. x This may result in the release of by-products.

[0003] When using nitrate PGM precursors, metal migration can occur due to the lack of strong interactions between the PGMs and the support material, which means that certain separate layer arrangements within the catalyst article may intermix, which may cause deactivation of the layers, for example if the layers are included for specific different purposes. Furthermore, such catalyst articles may be susceptible to excessive wicking of the supported PGM catalyst through the substrate when exposed to further wet applications of washcoats, particularly when palladium is used.

[0004] There is therefore a need to provide improved methods of producing catalyst articles including PGMs supported on a support material, specifically methods that can more reliably bind the PGMs to the support material to avoid migration and / or wicking, that emit fewer harmful by-products during manufacture, and that require fewer steps to simplify manufacture and reduce manufacturing costs.

[0005] WO 96 / 31275 relates to PGM carboxylates, in particular PGM lactate, for use as precursors for the manufacture of catalytic articles. However, anionic PGM complexes are not described.

[0006] "Free rhodium(II) citrate and rhodium(II) citrate magnetic carriers as potential strategies for breast cancer therapy" Carneiro et al., Journal of Nanobiotechnology, 2011, 9:11, "Carboxylates of Palladium, Platinum, and Rhodium, and their Adducts" Stephenson et al., Journal of the Chemical Society, 1965, 667, 3632-3640, and "Preparation and Properties of Anhydrous Rhodium(II) acetate and Some Adducts Thereof" Johnson et al., Inorganic Chemistry, 1963, 2, 5, 960-962 each describe PGM carboxylate complexes. However, none of these publications are in the field of preparing catalytic articles for applications such as exhaust gas treatment. Summary of the Invention

[0007] One aspect of the present disclosure relates to a method of making a catalyst article, the method including providing an anionic complex including a PGM and a carboxylate ion, providing a support material, applying the anionic 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.

[0010] The present invention also encompasses a method of treating an exhaust gas, the method comprising providing a catalytic article of the second aspect and contacting the catalytic article with the exhaust gas. [Brief description of the drawings]

[0011] [Figure 1] EPMA shows the palladium distribution on palladium citrate coated cores (Example 6). [Diagram 2] EPMA shows the distribution of palladium on palladium nitrate coated cores (Example 6). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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.

[0013] In a first aspect, the present invention provides a method of making a catalyst article, the method comprising: providing an anionic complex comprising a PGM and a carboxylate ion; Providing a carrier material; applying the anionic complex to a support material to form a supported support material; placing a substrate-supported carrier material thereon; and heating the supported support material to form nanoparticles of the PGMs on the support material.

[0014] 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.

[0015] Surprisingly, when used in an emission treatment system, the catalyst articles produced by the method of the present invention may exhibit significantly less wicking of the washcoat layer through or into the substrate and / or mixing of the washcoat layer compared to catalyst articles prepared by conventional methods. In other words, the catalyst articles produced by the method of the present invention may exhibit stronger / more secure fixation of the PGMs to the support material compared to catalyst articles produced by conventional methods. Thus, the catalyst articles produced by the method of the present invention may exhibit improved catalytic activity as well as improved aesthetics in such catalyst articles. This is at least because mixing of catalytically active PGMs between any separate washcoat layers in the catalyst article may be reduced, thereby reducing the likelihood that any of the washcoat layers will be deactivated. This, in turn, may help to maintain the catalytic activity of the entire catalyst article high as intended when the catalyst article is unused and after aging. Keeping the PGMs of any separate washcoat layers within their intended respective layers may be important to maintain their respective intended catalytic purpose (e.g., either oxidation or reduction). For example, it is known that direct interactions between Pd and Rh can reduce the catalytic activity of the individual components, especially the catalytic function of the Rh component.

[0016] Without wishing to be bound by theory, it is believed that these surprising and advantageous properties exhibited by the catalyst articles produced by the method of the present invention may be achieved due to strong electrostatic interactions between the support material and the anionic complexes. The interactions may be particularly strong when the method is carried out at low pH, e.g., pH 8 or less. The anionic complexes of the present invention may generally be electrostatically attracted to the support material, which may have a (slight) positive charge in solution. Thus, the anionic complexes may be less likely to leave the supported support material due to such electrostatic interactions. Furthermore, when preparing the washcoat solution, the anionic complexes may be attracted to the support material, thereby actively gathering in solution to form the supported support material. Thus, this may result in a higher percentage of PGMs actually being supported (i.e., "fixed" or "loaded") on the support material. This is in contrast to, for example, conventional washcoating methods using neutral nitrate PGMs and / or nitrate PGM precursors, where the PGM cations are "free" in solution, i.e., do not have a significant electrostatic attraction to the support material. It is also believed that due to such stronger interactions between the anionic complexes and the support material, a more uniform distribution of the PGMs supported on the support material may be obtained throughout the catalyst article.

[0017] Advantageously, when the supported support material is heated and / or calcined to form nanoparticles of PGM on the support material, the composition of the anionic complexes, i.e., carboxylate ion ligands, results in a higher NO 3 content compared to conventional methods using, for example, nitric acid PGM precursors. x Without wishing to be bound by theory, this is because the nitrate releases less NO when heated. xIt is believed that this is because the anionic complexes of the present invention may decompose to PGM metals, whereas the carboxylate ion ligands of the present invention may decompose to less harmful or "cleaner" by-products, e.g., just carbon dioxide and water. In other words, upon heating, the anionic complexes of the present invention are believed to decompose / reduced to only the PGM metals (or metal oxides / hydroxides), CO2 and HO. Furthermore, it has been found that the anionic complexes of the present invention self-reduce the PGM centres upon heating. In other words, upon heating, the ligands are capable of decomposing and reducing the PGMs to the PGM metals without the need for any additional process steps, such as chemical or gas phase reduction, to produce a catalyst having the PGM metals in active form, i.e., supported, nanoparticles.

[0018] Advantageously, the anionic complexes of the present invention may also have high water solubility, which is beneficial as it allows for the use of conventional aqueous washcoating techniques without the need to significantly modify them, i.e., by modifying the precursors.

[0019] Thus, for example, compared to WO 96 / 31275, in which the PGM precursors are not anionic complexes, catalyst articles produced by the methods of the present invention may exhibit the above-mentioned advantageous properties due, at least in part, to increased electrostatic attraction between the PGM precursors and the support material.

[0020] The term "catalytic article" as used herein may include an article on which 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 catalytic 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 catalytic article may be for use in three-way catalysis, i.e., for use as a three-way catalyst (TWC). Alternatively, the catalytic article may be for use in an emission treatment system for a diesel engine. The catalytic article may be for use in diesel oxidation catalysis, i.e., for use as a diesel oxidation catalyst (DOC). The catalytic article may also be for use in an emission treatment system for a NO 3 engine. x For use in trap catalysis, i.e., NO x It may be for use as a trap catalyst.

[0021] Providing an anionic complex comprising a PGM and a carboxylate ion typically involves providing the anionic complex in a solution, for example an aqueous or alcoholic solution, preferably an aqueous solution.

[0022] The term "anionic complex" as used herein includes any complex containing at least one metal center and at least one ligand, where the total charge of the at least one metal center and at least one ligand is less than zero. Thus, anionic complexes are typically associated with a positive counterion. Possible positive counterions are further described below.

[0023] As used herein, the term "PGM" means "platinum group metals" and may include, for example, one or more of platinum, palladium, rhodium, ruthenium, osmium, and iridium. Preferably, the PGMs are TWC, DOC, or NO xDepending on the intended application, such as for use as a trap catalyst, the anionic complex may include one or more of platinum, palladium, and rhodium. The anionic complex may include one or more PGM metal centers. For example, the anionic complex may include two or more metal centers, such as two or three metal centers.

[0024] As used herein, the term "carboxylate ion" takes its ordinary meaning in the art, i.e., a carboxylate ion having the general formula RCOO - where R is any group, typically any organic group. Thus, typically, a carboxylate ion is -COO - However, the carboxylate ion may alternatively and / or additionally be linked to another -COO - The anionic complex may be coordinated via another functional group, such as a -OH group, or a different functional group, such as a -OH group. The anionic complex may contain one or more carboxylate ions, depending, for example, on the size and / or number of the functional groups of the carboxylate ion. R preferably consists of C, H and O. This may advantageously result in anionic complexes that decompose only to the PGM metal (or metal oxide / hydroxide), CO2 and HO. Preferred carboxylate ions for use in the present invention are discussed further below.

[0025] The support material may be any material capable of supporting the anionic complex 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 facilitate three-way catalytic conversion or other catalytic applications.

[0027] The application of the anionic complex to the support material typically involves contacting the anionic 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 material, e.g., insoluble particles. The slurry may include (1) the solvent, (2) soluble content, e.g., "free" uncomplexed carboxylate ions or carboxylic acid molecules, inorganic PGMs and cocatalyst precursors, and the anionic complex (excluding the support, i.e., unsupported anionic complex), and (3) insoluble content, e.g., support particles that may or may not interact with the anionic complex and metal precursor. Preferably, the slurry comprises predominantly (1) and (3), such as 70% by weight or more of (1) and (3), such as 80% by weight or more of (1) and (3), or even 90% by weight or more of (1) and (3), based on the total weight of (1), (2) and (3). 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 may increase the amount of anionic complex loaded onto the support material in addition to that achieved by possible theorized electrostatic interactions.

[0028] As used herein, the term "supported support material" may include a support material having an anionic complex 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 anionic complex is typically fixed to the support by, for example, electrostatic forces, hydrogen bonds, coordinate bonds, covalent bonds, and / or ionic bonds. For example, in the case of oxides that may have a positive charge, strong electrostatic forces may exist between the anionic complex and the support material. However, there may also be other interactions due to the functional groups of the (carboxylate ion) ligands, such as electrostatic forces or hydrogen bond formation due to carboxylic acid functional groups and / or other functional groups such as hydroxyl groups interacting with hydroxyl groups on the support.

[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 performed 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 anionic complex may at least partially, substantially, or completely decompose. In other words, the ligands of the complex, i.e., the carboxylate ions, 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 carboxylate ions, more typically completely free of carboxylate ions.

[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 carboxylate ion preferably contains two or more carboxyl functional groups, for example, two to four carboxyl functional groups. In some preferred embodiments, the carboxylate ion contains two carboxyl functional groups. In other preferred embodiments, the carboxylate ion contains three carboxyl functional groups. When the carboxylate ion contains two or more carboxyl functional groups, for example, at least one of the carboxyl functional groups may coordinate to one or more metal centers of the anionic complex. For example, without wishing to be bound by theory, in some embodiments, two or more of the carboxyl functional groups may coordinate to one or more metal centers of the anionic complex, such as to form chelating or bridging ligands. In other embodiments, for example, without wishing to be bound by theory, it is believed that one or more of the carboxyl functional groups may interact with the support material, such as to form electrostatic interactions and / or hydrogen bonds with any exposed hydroxyl groups on the (oxide) support material. These interactions may be in addition to the coordination of one or more of the carboxyl functional groups to one or more metal centers of the anionic complex. Without wishing to be bound by theory, it is believed that in this case these additional interactions, i.e. in addition to any electrostatic interactions as described above due to being an anionic complex, may also contribute to the above-mentioned advantageous properties of the anionic complexes of the invention, e.g. providing a stronger interaction or "bonding" with the support material.

[0035] In a preferred embodiment, the carboxylate ion comprises 2 to 6 carbon atoms, such as 2, 3, 4, 5 or 6 carbon atoms. The number of carbon atoms in the carboxylate ion may not be particularly limited in achieving the present invention. However, without wishing to be bound by theory, it is believed that the higher the number of carbon atoms in the carboxylate ion, the lower the water solubility of the resulting anionic complex. It may be desirable for the anionic complex to have high water solubility. It is therefore believed that it may be desirable for the number of carbon atoms in the carboxylate ion, for example, not to exceed 6. It may be desirable for the anionic complex to have high water solubility, at least since conventional washcoating techniques are carried out in aqueous solutions. It may therefore be desirable for the anionic complex to have high water solubility in order to use the PGM precursors of the present invention, i.e., the anionic complex, in conventional washcoating techniques, i.e., so that the conventional techniques do not have to be substantially adapted. Furthermore, it may therefore be desirable for the carboxylate ions used in the anionic complexes of the present invention to have a good balance between high water solubility, such as by having fewer carbon atoms, and having stronger interactions or "bonds" with the support material, such as by having more negative charges on the anionic complex, such as due to the carboxylate ion having more functional groups, such as carboxyl or hydroxyl functional groups, and / or having more interactions, such as electrostatic or hydrogen bonds, with the support material.

[0036] Thus, in some preferred embodiments, the carboxylate ion contains a hydroxyl group, preferably an alpha-hydroxy acid functional group. Without wishing to be bound by theory, it is believed that such functional groups may increase the number and / or strength of attractions or interactions between the anionic complex and the support material.

[0037] Preferably, the carboxylate ion comprises one or more of citrate, malate, malonate, succinate, tartrate, glutarate, tartronate, oxalate, lactate and glycolate, more preferably comprises one or more of citrate, malate, malonate, succinate, tartrate, glutarate, tartronate and oxalate, and even more preferably comprises citrate and / or malonate. It has been found that such carboxylate ions, when used in the anionic complex of the present invention, surprisingly show a strong interaction with the carrier material and therefore show the advantageous effects described herein particularly well.

[0038] Preferably, the PGMs are selected from one or more of rhodium, palladium, platinum and ruthenium. More preferably, the PGMs comprise, consist essentially of or consist of rhodium, palladium, platinum or a combination thereof, preferably rhodium and / or palladium. In some preferred embodiments, the PGMs comprise, consist essentially of or consist of rhodium. In some preferred embodiments, the PGMs comprise, consist essentially of or consist of platinum. In some preferred embodiments, the PGMs comprise, consist essentially of or consist of palladium. The selection of each of platinum, palladium and / or rhodium for use in the present invention may depend on the particular purpose of the catalytic article, i.e., whether for reduction or oxidation, such as, for example, TWC or DOC applications. Different applications of each of platinum, palladium and / or rhodium are known to those skilled in the art.

[0039] Particularly preferred anionic complexes include one or more of Pt(IV) malonate, Pt(IV) succinate, Pt(II, IV) oxalate, Pd(II) citrate, Pd(II) lactate, Pd(II) oxalate, Pd(II) glycolate, Pd(II) malate, Rh(II) citrate, Rh(III) citrate, Rh(II) lactate, Rh(III) lactate and Ru(III) oxalate, more preferably, for example, one or more of Pt(IV) malonate, Pd(II) citrate, Rh(II) citrate and Rh(III) citrate.

[0040] In a preferred embodiment, the anionic complex is provided in the form of an aqueous solution comprising the anionic complex, preferably the aqueous solution has a pH of 8 or less, more preferably a pH of 7 or less. The use of an aqueous solution can provide a simple and low-cost process, for example following more conventional wash-coating processes, such that the use of the PGM precursors of the invention, i.e. the anionic complexes, does not require significant changes in known techniques and additives. This can therefore allow for an easy transition from the use of conventional methods of producing catalytic articles to the improved method of the invention. As a result of the method of providing the anionic complexes for use in the method of the invention, such aqueous solutions can contain other components such as "free" or non-coordinating ligands (e.g. carboxylate ions or carboxylic acids). For example, the aqueous solution can also contain additional acetic acid and / or acetate ions due to the method of providing the anionic complexes.

[0041] Preferably, at least 70% by weight of the PGMs present in the aqueous solution are present in the form of anionic complexes as described herein, more preferably at least 80%, even more preferably at least 90% by weight, and most preferably substantially all or even all of the PGMs present in the aqueous solution are present in the form of anionic complexes as described herein, in other words, preferably no other PGM complexes are present in the aqueous solution, and no uncomplexed PGM particles, atoms and / or ions are present.

[0042] It may be desirable for the aqueous solution to have a pH of 8 or less, preferably a pH of 7 or less, and more preferably a pH of 6 or less. Without wishing to be bound by theory, it is believed that such a low pH may serve to increase the electrostatic attraction between the anionic complex and the support material. This is because the support material may, for example, dissolve associated H in the aqueous solution. + This may be due to the fact that the anionic complex and the carrier material have a higher electrostatic attraction, and therefore ...

[0043] Preferably, the aqueous solution does not include PGM nitrate. This may be at least due to the above-mentioned properties associated with PGM nitrate that the present invention seeks to improve upon, such as, for example, greater specificity for locating the PGM on the support material, stronger fixation of the PGM to the support material, and the production of "less harmful" by-products upon decomposition of the PGM precursor. In other words, the present invention seeks to improve upon conventional methods of producing catalyst articles that use PGM nitrate precursors, and therefore the method of the present invention preferably does not include the use of PGM nitrate.

[0044] When the anionic complex is provided in the form of an aqueous solution containing the anionic complex, the anionic complex preferably has a counterion, which is preferably H + , H3O + and NH4 +and preferably, H + and / or H3O + Preferably, the aqueous solution does not include elemental inorganic cations. For example, the counterions preferably do not include elemental inorganic cations. This may be, for example, to prevent the resulting catalyst article from being contaminated with such inorganic elements. Such an aqueous solution may also help achieve a desirable "clean" decomposition of the anionic complex during the heating step. Such elemental inorganic cations may include, for example, one or more cations of sodium, potassium, magnesium and / or calcium (not exhaustive).

[0045] Anionic complexes include, for example, water, OH - , acetate ions and bridging O atoms. Preferably, the ligands of the anionic complex are carboxylate ions, water, OH, depending on the particular carboxylate ion used. - and bridging O atoms. Preferably, the anionic complex does not include phosphorus-containing ligands / or nitrogen-containing ligands. Thus, such anionic complexes can help achieve the desired "green" decomposition upon heating, e.g., to form only PGM nanoparticles and released CO2 and water upon heating. This is in contrast to conventional methods that use, e.g., nitrate PGM precursors.

[0046] In some embodiments, the anionic complexes include more than one PGM center, for example, two or three PGM centers. Thus, such anionic complexes may contain bridging ligands, such as bridging O atoms and / or bridging carboxylate ions, which may have more than one functional group, such as more than one carboxyl functional group and / or additional hydroxyl groups.

[0047] The support material comprises an oxide, preferably one or more of Al2O3, SiO2, TiO2, CeO2, ZrO2, CeO2-ZrO2, V2O5, La2O3 and zeolite. 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 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, praseodymium 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 0.001% to 20% by weight, more preferably 0.5% to 10% by weight. Such support materials may be particularly suitable for use in the method of the present invention in preferred embodiments where the anionic complex is provided in the form of an aqueous solution comprising the anionic complex, preferably the aqueous solution having a pH of 8 or less, more preferably a pH of 7 or less. This may be because such support materials as described above may desirably acquire a positive charge in such circumstances, resulting in a strong electrostatic attraction between the support material and the anionic complex.

[0048] In certain preferred embodiments, the support material comprises a molecular sieve such as a zeolite. Zeolite support materials may be more prone to migration of PGM atoms / cations, especially palladium, due to, for example, their porous structure. Migration may be, for example, from the surface of the substrate into the substrate, which may result in deactivation of the catalytic article. Reducing the likelihood of migration may therefore be beneficial as it may mean that a higher concentration of PGMs may remain on or near the surface of the substrate after aging, thereby maintaining a desired level of catalytic activity for longer. Thus, the method of the present invention may also be particularly beneficial for zeolite support materials. This is because the method of the present invention may reduce the likelihood of such PGM migration, due in part to increased electrostatic attraction between the anionic complexes and the support material. In aqueous solutions with low pH, for example, zeolite support materials may also acquire a positive charge, and any functional groups, such as carboxyl and / or hydroxyl functional groups, may also interact with the zeolite framework, which in turn may reduce the likelihood of PGM migration.

[0049] The support material is preferably in the form of a powder having a D90, eg measured by TEM, of 0.1-25 μm, preferably 0.5-20 μm, more preferably 1-15 μm.

[0050] Providing the anionic complex preferably comprises providing a hydroxide PGM and / or a water-insoluble PGM salt, preferably an acetate PGM, contacting the hydroxide PGM and / or the water-insoluble PGM salt with an aqueous carboxylic acid solution, and optionally recovering the anionic complex in the form of an aqueous solution comprising the anionic complex. In other words, the anionic complex may be provided in situ in the method of the invention or, alternatively, the anionic complex may be prepared at a separate time and stored prior to use in the invention, such as for use as a preformed precursor. The term "water-insoluble PGM salt" as used herein encompasses salts of PGMs that do not substantially dissociate in water, e.g., less than 5%, less than 3% or less than 1% by weight of the PGM salt dissociates in water, and / or salts that have very low water solubility (such as less than 10 mg / L). When acetate PGM is used, for example, any remaining acetate or acetate ions may remain in solution. Without wishing to be bound by theory, it is not believed that such substances remaining in the solution will adversely affect the effectiveness of the method of the present invention. Preferably, the aqueous solution containing the anionic complex has a pH of 8 or less, more preferably a pH of 7 or less. Preferably, the counter ion of the anionic complex is H + and / or H3O + Preferably, the PGM of the PGM hydroxide is rhodium and / or platinum and / or the PGM of the water insoluble PGM salt, preferably PGM acetate, is palladium. It has been found that such combinations may be particularly suitable for use in the present invention.

[0051] Applying the anionic complex to the support material preferably comprises contacting the support material with an aqueous solution comprising the anionic complex, and preferably contacting the support material with the aqueous solution is carried out at a pH of 8 or less, more preferably a pH of 7 or less.

[0052] The supported support material is preferably disposed on the substrate in the form of a slurry, preferably the slurry having a pH of 8 or less, more preferably a pH of 7 or less. The slurry is particularly effective in disposing the material on the substrate, particularly for maximizing gas diffusion and minimizing pressure drop during catalytic conversion. The slurry is preferably prepared by a method comprising applying an anionic complex to the support material according to the method described above, and 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 aqueous solution.

[0053] Such a "one-pot" preparation method can be simplified and less costly than conventional methods, and can also maximize the utilization of the anionic complex.

[0054] In other words, the steps of providing an anionic complex comprising a PGM and a carboxylate ion, providing a support material, applying the anionic complex to the support material to form a supported support material, and disposing the supported support material on a substrate can include: Providing a PGM hydroxide and / or a water insoluble PGM salt, preferably PGM acetate; contacting a hydroxide PGM and / or a water insoluble PGM salt with an aqueous carboxylic acid; Optionally, recovering the anionic complex in the form of an aqueous solution comprising the anionic complex; contacting the support material with an aqueous solution comprising an anionic complex to form a slurry, preferably wherein the contacting of the support material with the aqueous solution is carried out at a pH of 8 or less, more preferably a pH of 7 or less; 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 aqueous solution; and disposing the slurry on a substrate.

[0055] The deposition may include washcoating. Conventional washcoating techniques are well known in the art.

[0056] Preferably, each of the steps of applying the anionic complex to the support material, disposing the supported support material on a substrate, and heating the supported support material are carried out at a pH of not more than 8, preferably not more than 7. For the avoidance of doubt, for all process steps in which the anionic complex has not yet decomposed, it is preferred that the process steps are carried out at a pH of not more than 8, preferably not more than 7, for the reasons described herein.

[0057] The slurry preferably has a solids content of 10-40%, preferably 15-35%. Such solids content may allow suitable slurry rheology for disposing the loaded support material onto a substrate. For example, if the substrate is a honeycomb monolith, such solids content may allow deposition of a thin layer of washcoat onto the inner walls 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.

[0058] 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:

[0059] 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.

[0060] 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.

[0061] 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 galactomannan gum, guar gum, xanthan gum, curdlan schizophyllan, scleroglucan, diutan gum, wheylan gum, hydroxymethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, and ethylhydroxycellulose.

[0062] 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.

[0063] Additional organic acids can be added to act as reducing agents for the PGMs and / or to create a reducing environment during the subsequent calcination step. However, as noted above, additional organic acids are preferably not added as they may not be necessary due to the self-reducing properties of the anionic complexes. Examples of suitable organic acids include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof.

[0064] 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 supported support material on the substrate and / or after heating the supported support material to form nanoparticles of PGMs on the support material. In other words, the further slurry may form another catalyst layer or region on the substrate, thereby resulting in a catalyst article having multiple layers and / or regions of, for example, a washcoat. Due to the advantageous properties of the anionic complexes described herein, the supported PGMs may be more likely to remain in their intended layers and / or regions during such processes.

[0065] Alternatively, the method preferably further comprises disposing a further slurry on the substrate, the further slurry comprising one or more of a further anionic complex comprising a PGM and a carboxylate ion, a further support material, an oxygen storage material, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent, the disposing of the further slurry on the substrate occurring after disposing the support material on the substrate and prior to heating the supported support material to form nanoparticles of the PGM on the support material. In other words, with the method of the present invention it may be possible to eliminate the need for a further calcination step between the application of each washcoat layer.

[0066] 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.

[0067] This can result in a preferred distribution of the supported support material on the substrate.

[0068] 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.

[0069] 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.

[0070] The substrate preferably comprises cordierite. Cordierite substrates are particularly suitable for use in catalytic articles.

[0071] The substrate is preferably in the form of a honeycomb monolith, a wall-flow filter or a flow-through filter.

[0072] 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.

[0073] Lower temperatures and / or shorter heating times may result in insufficient decomposition of the anionic complexes and / or high levels of carboxylate ions 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.

[0074] 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.

[0075] Preferably, the nanoparticles have a D50 of 0.1 nm to 25 nm, preferably 0.2 to 10 nm, more preferably 0.2 to 5 nm. D50 can be measured by TEM. Such particle size can provide a favorable level of catalytic activity and can be less susceptible to agglomeration and sintering after aging, i.e., after use in exhaust systems.

[0076] In a further aspect, the present invention provides a catalyst article obtainable by the method described herein, the catalyst article being for use in an emission treatment system. Compared to conventional catalyst articles, for example, PGMs may be less likely to undergo migration between any catalyst layers and / or catalyst regions, which is believed to be due, at least in part, to stronger and more secure anchoring of the PGMs to the support material. Thus, each layer and / or each region of the catalyst article may maintain a desired level of activity for longer. Significant wicking is also less likely to occur.

[0077] The catalyst article is preferably for three-way catalysis.

[0078] The catalyst article is preferably for diesel oxidation catalysis.

[0079] The catalytic article preferably comprises a NO x This is for trap catalysis.

[0080] The catalyst article is 0.5 g / in 3 ~8g / in 3 or 1g / 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.

[0081] The substrate preferably comprises a wall-flow filter substrate or a flow-through substrate.

[0082] In a preferred embodiment, the catalyst article comprises a first catalyst region comprising a first PGM component, and optionally further comprises a second catalyst region comprising a second PGM component. Preferably, the first catalyst region is supported / deposited directly on a substrate. Preferably, the second catalyst region is supported / deposited directly on a substrate. Preferably, the first PGM component and / or the second PGM component are selected from the group consisting of platinum, palladium, rhodium, and mixtures of two or more thereof. Preferably, the first PGM component and the second PGM component are different. Preferably, for example, the first PGM component is palladium and the second PGM component is rhodium.

[0083] The catalyst article preferably has a surface area of ​​2 g / ft 3 ~15g / ft 3 of rhodium, 0.1 g / ft 3 ~50g / ft 3 of rhodium, more preferably 0.5 g / ft 3 ~25g / ft 3 of rhodium, more preferably 1 g / ft 3 ~20g / ft 3 Contains rhodium.

[0084] The catalyst article preferably has a surface area of ​​10 g / ft 3 ~100g / ft 3 Platinum, etc., 1g / ft 3 ~300g / ft 3 of platinum, more preferably 2 g / ft 3 ~200g / ft 3 of platinum, more preferably 5 g / ft 3 ~150g / ft 3 Contains platinum.

[0085] The catalyst article preferably has a surface area of ​​10 g / ft 3 ~100g / ft 3 Palladium, etc., 1g / ft 3 ~300g / ft 3 of palladium, more preferably 2 g / ft 3 ~200g / ft 3 of palladium, more preferably 5 g / ft3 ~150g / ft 3 Contains palladium.

[0086] In a further aspect, the present invention provides an emissions treatment system comprising the catalytic article described herein.

[0087] In some embodiments, the emission treatment system may be for an internal combustion engine. The emission treatment system is preferably for a gasoline engine.

[0088] Gasoline engines preferably operate under stoichiometric conditions.

[0089] 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; and contacting the catalytic article with the exhaust gas.

[0090] In some embodiments, the emission treatment system may be for an internal combustion engine. The exhaust gas is preferably from a gasoline engine. The catalytic article is particularly suitable for treating such exhaust gas. The gasoline engine preferably operates under stoichiometric conditions.

[0091] definition As used herein, the term "region" refers to an area on a substrate that is typically obtained by drying and / or firing a washcoat. A "region" may be disposed or carried on a substrate as, for example, a "layer" or a "zone." The area or arrangement on the substrate is generally controlled during the process of applying the washcoat to the substrate. A "region" typically has a distinct boundary or edge (i.e., it is possible to distinguish one region from another using conventional analytical techniques).

[0092] Typically, a "region" has a substantially uniform length. Reference to a "substantially uniform length" in this context refers to a length that does not deviate from its average value by more than 10% (e.g., the difference between the maximum and minimum length), preferably a length that does not deviate from its average value by more than 5%, and more preferably a length that does not deviate from its average value by more than 1%.

[0093] Each "region" preferably has a substantially uniform composition (i.e., there is no substantial difference in the composition of the washcoat when comparing one portion of the region to another portion of the region). Substantially uniform composition in this context refers to a material (e.g., region) that has a compositional difference of 5% or less, usually 2.5% or less, and most usually 1% or less, when comparing one portion of the region to another portion of the region.

[0094] The term "washcoat" is well known in the art and typically refers to an adherent coating that is applied to a substrate during the preparation of a catalyst.

[0095] As used herein, the term "mixed oxide" generally refers to a mixture of oxides in a single phase, as is conventionally known in the art. As used herein, the term "complex oxide" generally refers to a composition of oxides having two or more phases, as is conventionally known in the art.

[0096] As used herein, the phrase "consisting essentially of" limits the scope of a feature to include the specified materials or steps and any other materials or steps, e.g., trace impurities, that do not substantially affect the basic properties of the feature. "Consisting essentially of" encompasses the phrase "consisting of."

[0097] By "slurry" is meant a liquid containing insoluble material, e.g., insoluble particles.

[0098] As used herein, any reference to an amount, particularly a total amount, of dopant expressed as a weight percent refers to the weight of the support material or refractory metal oxide thereof.

[0099] As used herein, the term "loading" refers to g / ft2 on a metal weight basis. 3 Refers to the measurement in units of .

[0100] When reference is made herein to "a" or "an," this includes the singular and the plural.

[0101] The invention will now be described with reference to the following non-limiting examples. EXAMPLES

[0102] Preparation of anionic complex precursors A number of anionic complex precursors were prepared according to the following examples.

[0103] Example 1: Pd Citrate Solid Pd acetate (6.33 g) was placed in a round bottom flask and 1.1 equivalents of citric acid (6.51 g) dissolved in 50 ml of water was added. The mixture was heated at 75° C. for 6 hours until complete dissolution. This gave a deep red solution. The solution was filtered using 542 filter paper to remove remaining solid impurities. The UV / VIS spectrum showed a peak at 388 nm. Inductively Coupled Plasma analysis (ICP) gave a Pd assay of 5.73 wt% Pd.

[0104] Example 2: Rh(III) citrate The RhCl3 solution (46.46 g, 21.52% Rh) was diluted with water (150 mL) and K2CO3 (5 M solution) was added dropwise over 15 min until the pH of the solution increased from 1.29 to 2.5 (to neutralize any free HCl present). Further 5 M K2CO3 solution was added dropwise until the pH reached 7.5. The mixture was heated at 40° C. At this stage the solution turned red in color. Further K2CO3 solution was added to raise the pH to 10.8 and then heated at 100° C. for 2 h during which a yellow-brown precipitate formed. The solid was filtered and washed with DI water until a conductivity of 60 mS was reached. The hydroxide was mixed with citric acid (40.84 g) and heated at 100° C. during which the hydroxide dissolved in less than 4 h. ICP gave an Rh assay of 6.52 wt % Rh and a Cl assay of 20 ppm Cl.

[0105] Example 3: Rh(III) citrate (alternative method) A solution of RhCl3 (106.27 g, 19.29% Rh) was diluted with water (300 mL). NaOH (5 M solution) was added dropwise over 15 min until the pH of the solution increased from 1.29 to 2.5 (to neutralize the free HCl present). 5 M NaOH solution was added dropwise until the pH reached 7.5. The mixture was heated at 40° C. to obtain a cloudy red solution. The NaOH solution was added continuously until the pH reached 10 and stirred for 4 h while maintaining the temperature at 40° C., which resulted in the formation of a Rh(OH)3 precipitate. After cooling, the precipitate was filtered and washed with DI H2O until the conductivity of the solution reached 70 mS. A solution of citric acid (83.72 g) in water (400 ml) was prepared. To this was added the Rh(OH)3 precipitate and the mixture was stirred and heated at 100° C. The hydroxide dissolved within 3 h. The solution was filtered through a 542 filter and concentrated by evaporation to approximately 8% Rh concentration. An Rh assay of 8.01% Rh was obtained by ICP.

[0106] Manufacturing and testing of catalytic articles A number of catalyst articles were prepared according to the following examples.

[0107] Example 4: Comparison of Pd uptake to conventional methods Table 1 compares the Pd uptake values ​​on alumina supported CeZrO2 mixed oxide (ACZ with composition Al2O3:CeO2:ZrO2 = 64:21:15) using palladium citrate or palladium nitrate as Pd precursor. The experiments were carried out by adding the Pd precursor to a slurry of ACZ support, targeting a Pd loading of 2.3 wt.%. After mixing for 90 min, the mixture was centrifuged and the Pd content in the supernatant was analyzed. The Pd uptake values ​​were calculated by the percentage of Pd adsorbed on the surface of the ACZ support. The results show that Pd citrate resulted in 90% Pd adsorption on the ACZ support, compared to 60% Pd adsorption when Pd nitrate was used.

[0108] [Table 1]

[0109] Example 5: Performance comparison of catalyst articles of the present invention with conventional PGM precursors Comparison catalyst A: A single-layer PdRh TWC with only one catalytic region was prepared. The catalytic region consists of both Pd and Rh mixed in one slurry and supported on washcoats of CeZr mixed oxide, ceria-zirconium-alumina, and alumina sol as binder, and Pd nitrate solution as Pd source is used during the preparation of the washcoat slurry. The total washcoat loading of the catalytic region is 48 g / ft. 3 Pd loading and 2g / ft 3 The Rh loading is about 3.5 g / in 3 It was.

[0110] This washcoat was then coated onto each side of a ceramic substrate (400 cpsi, 6 mil wall thickness, 4.16 inch diameter and 4 inch length) using standard coating procedures with a coating depth targeted to be 50% of the substrate length per coating, dried at 100°C, and fired at 500°C for 45 minutes.

[0111] Catalyst B: Catalyst B was prepared following a similar procedure as Comparative Catalyst A, except that Pd citrate solution was used as the Pd source during the preparation of the washcoat slurry in the catalyst zone. Both Comparative Catalyst A and Catalyst B had the same composition, but used different palladium precursors.

[0112] Catalyst B and Comparative Catalyst A were bench aged for 100 hours at an average close coupled brick temperature of 875°C. A commercial vehicle equipped with a 3.5L GTDI engine and turbocharger was run under Federal Testing Procedure (FTP) with the catalyst bricks installed in the underfloor position paired with a common close coupled (CC) catalyst brick to run the vehicle exhaust. NO emissions from all systems under the FTP test cycle were measured. x The CO emissions are summarized in Table 2. The system with Pd citrate had a significantly lower (NO x +NMHC) and 65 mg / mile of CO.

[0113] [Table 2]

[0114] Example 6: Performance comparison of catalyst articles of the present invention with conventional PGM precursors (when using zeolite support materials) Comparative Catalysts C and D, with identical components except for using different Pd precursors, were prepared by using the same washcoat slurries as described for Catalysts A and B and coated onto monolithic extruded zeolite substrates (4.16" x 4", 400 / 11, 55% beta zeolite). The 11 / 16" x 1" cores were aged on a laboratory pulsator for 50 hours in a four-mode cycle at temperatures ranging from 740°C to 840°C. The Pd distribution on the aged cores was characterized by Electron Probe MicroAnalysis (EPMA) method. The cores made by Pd citrate in Figure 1 have a relatively lower Pd concentration inside the substrate compared to Pd nitrate in Figure 2, proving a lower degree of Pd migration.

[0115] A full size catalyst was placed in the bottom position in the system and each system was aged for 100 hours at an average close-coupled brick temperature of 875°C. The aged UB catalyst was then paired (0:78:2) with a common close-coupled catalyst to form a new system and tested in a Ford Flex vehicle equipped with a 3.5L GTDI engine and turbocharger. The NO of all systems under the FTP test cycle was x The CO emissions are summarized in Table 3. The system with Pd citrate had a significantly lower (NO x +NMHC) and 104 mg / mile of CO.

[0116] The results clearly show that the use of Pd citrate can minimize the migration of Pd into the zeolite substrate, resulting in a catalyst with improved performance.

[0117] [Table 3]

[0118] Example 7: Light-off performance and OSC test in synthetic catalyst activity test Comparison catalyst E: First catalytic region: The first catalyst zone consisted of Pd supported on a washcoat of CeZr mixed oxide, La-stabilized alumina and Ba-promoter, using Pd nitrate solution as the Pd source during the preparation of the washcoat slurry. The washcoat loading of the first catalyst zone was 24 g / ft 3 The Pd loading is about 1.8 g / in 3 It was.

[0119] The washcoat was then coated onto the ceramic substrate from the inlet face using standard coating procedures with a target coating depth of 80% of the substrate length (400 cpsi, 4.3 mil wall thickness, 4.66 inch diameter and 4.5 inch length) and dried at 100°C.

[0120] Second catalytic region: The second catalytic region is comprised of Rh supported on a washcoat of CeZr mixed oxide and La-stabilized alumina. The washcoat loading of the second catalytic region is about 1.3 g / in 3 The Rh loading is 4 g / ft 3 It was.

[0121] This second washcoat was then coated from the outlet face of the ceramic substrate containing the first catalytic region using standard coating procedures with a coating depth targeted to 80% of the substrate length, dried at 100°C, and calcined at 500°C for 45 minutes.

[0122] Catalyst F: Catalyst F was prepared according to a similar procedure as Comparative Catalyst E, except that in the first catalyst zone, Pd citrate solution was applied as the Pd source during the preparation of the washcoat slurry in the first catalyst zone.

[0123] Catalyst F and Comparative Catalyst E were tested separately in a Synthetic Catalyst Activity Test (SCAT) device. The light-off performance was tested in a gas flow of 10 vol.% H2O + 14 vol.% CO2 + 333 ppm C3H6 + 167 ppm C3H8 + 1.5 vol.% CO + 0.5 vol.% H2O + 1.15 vol.% O2 + 1000 ppm NO (balance with N2) at a space velocity of 60,000 h2. -1 The temperature gradient was 30°C / min. THC, CO, and NO x The conversion of was calculated by comparing the concentration of the feed gas with that of the gas at the catalyst outlet. The OSC was calculated using a gas flow of 10 vol.% H2O + 14 vol.% CO2 + 333 ppm C3H6 + 167 ppm C3H8 + 0.5 vol.% CO + 0.5 vol.% H2O + 0.5 vol.% O2 + 1000 ppm NO (balance by N2) at a space velocity of 60000 h -1 The catalysts were tested at 450° C. Comparative Catalysts E and F were hydrothermally aged at 980° C. for 4 hours in 2 vol.% O2 + 10 vol.% H2O (balance with N2) at a flow rate of 5 L / min.

[0124] HC, CO, and NO for aged Catalyst F and Comparative Catalyst E x T 50 The light-off temperatures and OSCs of the catalysts are shown in Table 4. The data surprisingly show that the inventive catalyst F has a significantly higher emission of CO, HC, and NO compared to the comparative catalyst E. x 23°C, 22.5°C, and 17.5°C lower, respectively. 50 (T 50 where t is the temperature at which the conversion rate reaches 50%), while the OSC of catalyst F is about 30% higher than that of comparative catalyst E.

[0125] [Table 4]

[0126] Example 8: Vehicle Testing Procedures and Results Catalyst F and comparative catalyst E were bench aged at a peak temperature of 980°C for 100 hours in a four-mode aging cycle. Vehicle emissions were measured with a brick placed in the CC position under the Worldwide Light Duty Testing Procedure (WLTP) for a 1.6L turbocharged commercial vehicle. Emissions were measured before and after the catalyst. Dilute bag emissions data from the tailpipe on the vehicle are shown in Table 5.

[0127] [Table 5]

[0128] The tailpipe bag data for test vehicle A is shown in Table 5. The catalyst F of the present invention had significantly lower emissions of THC, NMHC, CO and NO compared to the comparative catalyst E. x The results clearly show lower emissions (19%, 20%, 29%, and 17% reductions, respectively).

[0129] 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 an anionic complex comprising a PGM and carboxylate ions; providing a carrier material; applying the anionic complex to the carrier material to form a supported carrier material; disposing the supported carrier material on a substrate; heating the supported carrier material to form nanoparticles of the PGM on the carrier material.

2. The method according to claim 1, wherein the carboxylate ions comprise two or more carboxyl functional groups.

3. The method according to claim 1 or 2, wherein the carboxylate ions comprise 2 to 6 carbon atoms.

4. The method according to claim 1 or 2, wherein the carboxylate ions comprise a hydroxyl group, preferably an alpha-hydroxy acid functional group.

5. The method according to claim 1 or 2, wherein the carboxylate ions comprise one or more of citrate, malate, malonate, succinate, tartrate, glutarate, tartronate, oxalate, lactate, and glycolate.

6. The method according to claim 1 or 2, wherein the carboxylate ions comprise citrate and / or malonate.

7. The method according to claim 1 or 2, wherein the PGM is selected from one or more of rhodium, palladium, platinum, and ruthenium.

8. The method according to claim 1 or 2, wherein the anionic complex is provided in the form of an aqueous solution comprising the anionic complex, and preferably, the aqueous solution has a pH of 8 or less, more preferably a pH of 7 or less.

9. The method according to claim 8, wherein the aqueous solution does not contain PGM nitrate.

10. The carrier 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 one or more of zeolites, according to the method of claim 1 or 2.

11. Providing the anionic complex comprises: providing PGM hydroxide and / or a water-insoluble PGM salt, preferably PGM acetate; contacting the PGM hydroxide and / or the water-insoluble PGM salt with an aqueous carboxylic acid solution; and optionally, recovering the anionic complex in the form of an aqueous solution comprising the anionic complex.

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

13. The catalyst article according to claim 12 for three-way catalysis.

14. An exhaust gas treatment system comprising the catalyst article according to claim 12 or 13.

15. A method for treating exhaust gas, comprising: providing the catalyst article according to claim 12 or 13; and contacting the catalyst article with the exhaust gas.

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