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

Abstract

A method of making a catalyst article, the method comprising: providing a complex of a compound of formula (I) # imgabs0 # and PGM, R1 being H or C1-C6 alkyl, R2 being H, OH or O-C1-C4 alkyl, the PGM comprising rhodium and / or platinum; providing a carrier material; applying the complex to a support material to form a supported support material; disposing the loaded carrier material on a substrate; and heating the loaded support material to form nanoparticles of the PGM on the support material.

Description

Technical Field

[0001] The present invention relates to a method of manufacturing a catalyst article, a catalyst article obtainable by the method, an emission treatment system, and a method of treating exhaust gas. Background Art

[0002] Three-way catalysts (TWCs) convert CO, HC, and NO from gasoline engine exhaust x to non-toxic compounds simultaneously at a stoichiometric air-fuel ratio (about 98%). Specifically, the oxidation of CO and HC to CO2 and steam (H2O) is mainly catalyzed by Pd, while NO x to N2 reduction is mainly catalyzed by Rh. Modern TWCs use supported platinum group metal (hereinafter referred to as "PGM") catalysts (Pd, Rh, Pt, etc.) deposited on a single layer, double layer, or multi-layer carrier, where the carrier material consists of metal oxides with a high specific surface area, mainly stable γ-alumina and ceria-containing oxygen storage materials. The supported catalyst carrier coating is applied to a ceramic monolithic substrate.

[0003] The conventional preparation of TWC carrier coating slurries typically involves using solutions of inorganic PGM precursors (such as nitrates, acetates, or chloride salts) to deposit the PGM elements on the oxide carrier via an incipient wetness impregnation method or a wet impregnation method. Promoter salts are usually also added to the carrier coating formulation to obtain enhanced TWC performance. Once a monolithic substrate is coated with the slurry carrier coating thus prepared, drying and calcination steps are then used to decompose the inorganic salts and fix the PGM and promoter elements to the carrier material. It is known that the performance of supported metal catalysts depends on the structure and composition of the metal nanoparticles and the nature of the carrier. Conventional TWCs prepared using the above methods typically provide only limited control over the structure of the catalytically active substances (i.e., the average PGM particle size and composition, the location of the active components, and the metal-carrier interaction). This is mainly due to metal migration and grain growth during the high-temperature calcination process.

[0004] With increasingly stringent environmental regulations, there is a need for TWCs with higher emission reduction efficiency. On the other hand, with the increasing cost of PGM, there is an urgent need to reduce the PGM loading without compromising TWC performance. Better control of the PGM particle size and the metal-carrier interaction is crucial for optimizing TWC performance. In addition, a uniform PGM particle size distribution can help reduce the extent of metal sintering due to Ostwald ripening that often occurs during fuel cut-off processes (an engine strategy for enhancing fuel economy).

[0005] Catalyst light-off is the minimum temperature required to initiate a catalytic reaction. In particular, the light-off temperature is the temperature at which the conversion rate reaches 50%. There is a need for catalyst articles with a reduced light-off temperature.

[0006] US2012 / 0077669 A1 describes the polymer-assisted synthesis of a supported metal catalyst for automotive applications. The polymers used in the examples include poly(vinylpyrrolidone), poly(acrylic acid), and poly(ethyleneimine). In the synthesis process, the support (aluminum oxide powder) is first impregnated with an aqueous solution containing the polymer. Then, through filtration and drying steps, the impregnated support is separated from the above solution. By incipient wetness impregnation, the dried impregnated support is further impregnated with a PGM precursor solution. The method includes multiple steps for forming the claimed supported metal catalyst, which increases the cost and difficulty of commercial-scale production. US2012 / 0077669 A1 indicates that for the application of this technology, lean-burn engines, such as diesel engines or lean-burn gasoline engines, are preferably used. Summary of the Invention

[0007] One aspect of the present disclosure relates to a method for manufacturing a catalyst article, the method comprising: providing a complex of a compound of formula (I): with PGM, where R1 is H or C1-C6 alkyl, R2 is H, OH, or O-C1-C4 alkyl, and the PGM comprises rhodium and / or platinum; providing a support material; applying the complex to the support material to form a loaded support material; disposing the loaded support material on a substrate; and heating the loaded support material to form nanoparticles of the PGM on the support material.

[0008] Another aspect of the present invention relates to a catalyst article obtained by the method in the first aspect.

[0009] The present invention also encompasses an exhaust system for an internal combustion engine, the exhaust system comprising the catalyst article in the second aspect. Brief Description of the Drawings

[0010] Figure 1A Shows the NO conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B; Figure 1B Shows the THC conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B; Figure 1C Shows the CO conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B.

[0011] Figure 2A Shows the NO conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B; Figure 2B Shows the THC conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B; Figure 2C Shows the CO conversion results of the perturbation light-off performance tests of Comparative Example 1A and Example 1B.

[0012] Figure 3A Shows the CO conversion results of the perturbation λ-scan performance test for Comparative Example 1A and Example 1B; Figure 3B Shows the THC conversion results of the perturbation λ-scan performance test for Comparative Example 1A and Example 1B; Figure 3C Shows the NO of the perturbation λ-scan performance test for Comparative Example 1A and Example 1B x conversion results.

[0013] Figure 4A Shows the NO conversion results of the perturbation light-off performance test for Comparative Example 2A and Example 2B; Figure 4B Shows the THC conversion results of the perturbation light-off performance test for Comparative Example 2A and Example 2B; Figure 4C Shows the CO conversion results of the perturbation light-off performance test for Comparative Example 2A and Example 2B. Detailed Description of the Invention

[0014] The present invention attempts to solve at least some of the problems associated with the prior art or at least provide a commercially acceptable alternative solution thereto.

[0015] In a first aspect, the present invention provides a method for manufacturing a catalyst article, the method comprising:

[0016] Providing a complex of a compound of formula (I): with PGM, where R1 is H or C1-C6 alkyl, R2 is H, OH or 0-C1-C4 alkyl, and the PGM comprises rhodium and / or platinum;

[0017] Providing a carrier material;

[0018] Applying the complex to the carrier material to form a loaded carrier material;

[0019] Setting the loaded carrier material on a substrate; and

[0020] Heating the loaded carrier material to form nanoparticles of the PGM on the carrier material.

[0021] Unless explicitly indicated to the contrary, each aspect or embodiment as defined herein can be combined with any other aspect or embodiment. In particular, any feature indicated as preferred or advantageous can be combined with any other feature indicated as preferred or advantageous.

[0022] Surprisingly, when used in an emissions treatment system, the catalyst article made by the method of the present invention can exhibit favorable catalytic activity after aging, especially favorable three-way catalytic activity. For example, the aged catalyst article can exhibit favorable light-off performance during three-way catalytic reduction of a stoichiometric gasoline engine, especially the conversion rates of NO, CO, and total hydrocarbons. Such favorable catalytic activity and light-off performance can be superior to those exhibited by conventional catalyst articles having the same / similar PGM species, loading, support, and configuration.

[0023] Advantageously, compared with conventional catalyst articles, such excellent performance can facilitate the use of a lower loading of PGM without compromising catalytic performance. Given the high cost of such metals (especially rhodium), this can be advantageous. In addition, such excellent performance can facilitate the partial or complete replacement of high-cost PGM with lower-cost PGM or other transition metals without compromising catalytic performance.

[0024] Compared with the method of US2012 / 0077669 A1, the method of the present invention is a simpler and more efficient "one-pot" method. The method of the present invention does not require separate impregnation, filtration, and drying steps for depositing polymer molecules onto the support material. In contrast, in US2012 / 0077669 A1, only a limited amount of polymer can remain on the support after the filtration and washing steps. In addition, the catalyst article prepared by the method of the present invention can specifically be used as a three-way catalyst for stoichiometric gasoline emissions reduction. In contrast, the catalyst article prepared by the method of US2012 / 0077669 A1 has specific applications in lean-burn diesel or gasoline engines.

[0025] As used herein, the term "catalyst article" can encompass an article on or in which a catalyst is loaded. The article can 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 can be used in an emissions treatment system, especially for a gasoline engine, preferably an emissions treatment system for a stoichiometric gasoline engine. The catalyst article can be used in three-way catalysis.

[0026] Providing a complex of a compound of formula (I): with PGM generally involves providing the complex in solution form, such as an aqueous solution or an alcohol solution. Providing a complex of a compound of formula (I) with PGM generally involves mixing an inorganic PGM precursor and a compound of formula (I) in pure form or in solution in an aqueous medium, such as mixing PGM nitrate and a compound of formula (I) in water.

[0027] Preferably, R1 is H. Preferably, R2 is OH.

[0028] The PGM contains rhodium and / or platinum. Such metals can be particularly suitable for performing three-way catalysis. In addition, such metals are expensive, meaning that it would be advantageous to be able to provide a similar level of catalytic activity for the same amount of metal. Furthermore, using such metals in the method of the present invention can result in particularly advantageous perturbation light-off performance. The PGM can be in the form of an alloy. In addition to rhodium and / or platinum, the PGM can also include other PGMs, such as one or more of ruthenium, palladium, osmium, and iridium.

[0029] The ratio of the PGM atoms of the complex to the ester groups can be from 2:1 to 1:10, preferably from 1:1 to 1:8, more preferably from 1:2 to 1:5. The ratio of the rhodium atoms of the complex to the ester groups can be from 2:1 to 1:10, preferably from 1:1 to 1:8, more preferably from 1:2 to 1:5. The ratio of the platinum atoms of the complex to the ester groups can be from 2:1 to 1:10, preferably from 1:1 to 1:8, more preferably from 1:2 to 1:5. The ratio of the rhodium atoms plus platinum atoms of the complex to the ester groups can be from 2:1 to 1:10, preferably from 1:1 to 1:8, more preferably from 1:2 to 1:5.

[0030] The carrier material can be any material capable of loading the complex and the nanoparticles thereon or therein. The carrier material can take any form, but is usually in the form of a powder, more usually a high-surface area powder. When preparing a catalytic filter such as a wall-flow filter or a flow-through filter using the method of the present invention, the carrier material will usually be in the form of a powder having a D50 of, for example, 0.1 μm to 25 μm, more usually 0.5 μm to 5 μm, as measured using TEM. Such particle sizes can be beneficial for the desired rheology of the slurry used for coating the filter. The carrier material can be used as a washcoat. The carrier material can be a washcoat or can be part of a washcoat.

[0031] The carrier material can also be used as an oxygen storage material, which stores and releases oxygen under lean fuel and rich fuel conditions, respectively, to promote three-way catalytic conversion.

[0032] Applying the complex to the support material generally 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 encompass a liquid containing insoluble materials, such as insoluble particles. The slurry can contain (1) a solvent; (2) soluble contents, such as unreacted compound of formula (I), inorganic PGM, promoter precursors, and PGM-compound of formula (I) complex (outside the support); and (3) insoluble contents, such as support particles with and without interaction with the compound of formula (I) and metal precursors. The slurry is typically stirred, more typically stirred for at least 10 minutes, more typically stirred for at least 30 minutes, and even more typically stirred for at least one hour. Increasing the contact and / or stirring time can increase the amount of complex loaded onto the support material.

[0033] As used herein, the term "loaded support material" can encompass a support material having a PGM-compound of formula (I) complex loaded thereon (e.g., on the surface of a high-surface-area metal oxide support material) and / or loaded therein (e.g., within the pores of a zeolite support material). The complex is typically immobilized on the support, for example, by electrostatic forces, hydrogen bonds, coordination bonds, covalent bonds, and / or ionic bonds. For example, in the case of an oxide, the ester functional group (e.g., carboxylic acid ester functional group) in the compound of formula (I) can interact with the surface hydroxyl groups on the support through electrostatic or hydrogen bond formation.

[0034] As used herein, the term "substrate" can encompass, for example, a ceramic or metal honeycomb or filter block (e.g., a wall-flow filter or a flow-through filter). The substrate can include a ceramic monolithic substrate. The substrate can vary in its material composition, dimensions and configuration, pore shape and density, and wall thickness. Suitable substrates are known in the art.

[0035] Techniques known in the art can be used to dispose the loaded support material on the substrate. Generally, the slurry of the loaded support material is poured into the inlet of the substrate in a predetermined amount using a specific molding tool to dispose the loaded support material on the substrate. As discussed in more detail below, subsequent vacuum and drying steps can be employed during this disposal step. When the support is a filter block, the loaded support material can be disposed on the filter walls, within the filter walls (if porous), or both.

[0036] The carrier material for the heating load is typically carried out in an oven or furnace, more typically in a belt or static oven or furnace, usually in hot air with a specific flow from one direction. This heating may include calcination. This heating may also include drying. The drying step and the calcination step can be continuous or sequential. For example, a separate carrier coating can be applied after the substrate has been coated with a previous carrier coating and dried. If the coating is complete, a continuous heating program can also be used to dry and calcine the substrate with the coated carrier coating. During heating, the complex can decompose at least partially, substantially, or completely. In other words, the ligands of the complex (i.e., the compound of formula (I)) are at least partially, substantially, or completely removed or separated from the PGM and removed from the final catalyst article. Then the particles of such separated PGM can begin to form metal-metal bonds and metal-oxide bonds. As a result of heating (calcination), the substrate is typically substantially free of the compound of formula (I), more typically completely free of the compound of formula (I).

[0037] As used herein, the term "nanoparticle" can encompass particles having a diameter of 0.01 nm to 100 nm as measured by TEM. The nanoparticles can be of any shape, such as spherical, plate-shaped, cubic, cylindrical, hexagonal, or rod-shaped, but are typically spherical. The maximum size of the nanoparticles (i.e., the diameter if the nanoparticles are spherical) will typically be 0.5 nm to 10 nm, more typically 1 nm to 5 nm, as measured by TEM.

[0038] After the heating step, the substrate is typically cooled, more typically to room temperature. Cooling is typically carried out in air with or without a coolant / medium, usually without a coolant.

[0039] In some preferred embodiments, the compound of formula (I) is gallic acid:

[0040]

[0041] Gallic acid can coordinate with metal ions through hydrogen bonds or covalent bonds. The PGM-gallic acid complex can be immobilized on a carrier (such as a metal oxide carrier) in the carrier coating, where the carboxylate functional group in the gallic acid ligand and the surface hydroxyl groups on the carrier can form interactions through electrostatic forces or hydrogen bonds.

[0042] The PGM preferably contains rhodium, consists essentially of rhodium, or consists of rhodium. Rhodium is a particularly expensive PGM and forms a particularly suitable complex with the compound of formula (I), especially gallic acid. The PGM preferably contains platinum, consists essentially of platinum, or consists of platinum. Platinum is a particularly expensive PGM and forms a particularly suitable complex with the compound of formula (I), especially gallic acid.

[0043] In a preferred embodiment, the PGM comprises rhodium and platinum, consists essentially of rhodium and platinum, or consists of rhodium and platinum. The use of such metals in the process of the present invention can result in particularly advantageous light-off performance.

[0044] The support material preferably comprises an oxide, preferably one or more of Al2O3 (aluminum oxide or alumina), SiO2, TiO2, CeO2, ZrO2, V2O5, La2O3, and zeolite. The oxide is preferably a metal oxide. The support material more preferably comprises alumina, even more preferably γ-alumina. The support material preferably comprises cerium-zirconium oxide. The support material preferably comprises alumina and cerium-zirconium oxide. The alumina and / or cerium-zirconium oxide is preferably doped, more preferably doped with an oxide of one or more of the following: lanthanum, neodymium, yttrium, niobium, praseodymium, hafnium, molybdenum, titanium, vanadium, zinc, cadmium, manganese, iron, copper, calcium, barium, strontium, cesium, magnesium, potassium, or sodium; even more preferably doped with an oxide of lanthanum, neodymium, or yttrium. Such doped oxides are particularly effective as support materials. Preferably, the dopant is present in the alumina and / or cerium-zirconium oxide in an amount of 0.001 wt% to 20 wt%, still more preferably 0.5 wt% to 10 wt%.

[0045] The support material is preferably in the form of a powder having a D90 of 0.1 μm to 25 μm, more preferably 0.5 μm to 5 μm.

[0046] The supported support material is preferably provided on the substrate in the form of a slurry. The slurry is particularly effective in setting the material on the substrate, especially for maximizing gas diffusion and minimizing pressure drop during catalytic conversion.

[0047] Providing a complex of the compound of formula (I) with the PGM preferably comprises in-situ synthesizing the complex in the slurry.

[0048] The slurry is preferably prepared by a method comprising the steps of:

[0049] Contacting a PGM salt with the compound of formula (I) in water to form a complex of the compound of formula (I) with the PGM in an aqueous solution, the PGM salt comprising rhodium and / or platinum; and

[0050] Applying the complex to the support material by contacting the support material with the aqueous solution to form a supported support material;

[0051] Optionally adding one or more of the following to the aqueous solution: an oxygen storage material, preferably cerium-zirconium oxide; a promoter salt; a binder; an acid or a base; a thickening agent; and a reducing agent.

[0052] Compared with conventional methods, such "one-pot" preparation methods can be simplified and are less costly. It also maximizes the utilization rate of the compound of formula (I).

[0053] In other words, the steps of providing a complex of the compound of formula (I) and PGM; providing a support material; applying the complex to the support material to form a loaded support material; and disposing the loaded support material on a substrate may include:

[0054] Contacting a PGM salt with the compound of formula (I) in water to form a complex of the compound of formula (I) and PGM in an aqueous solution, the PGM salt comprising rhodium and / or platinum;

[0055] Adding the support material to the aqueous solution to form a slurry of the loaded support material;

[0056] Optionally adding one or more of the following to the slurry: an oxygen storage material, preferably cerium-zirconium oxide; a promoter salt; a binder; an acid or a base; a thickening agent; and a reducing agent; and

[0057] Drying the slurry on the substrate.

[0058] Loading may include coating with a support coating.

[0059] The solids content of the slurry is preferably 10% to 40%, preferably 15% to 35%. Such a solids content renders the slurry rheology suitable for disposing the loaded support material onto the substrate. For example, if the substrate is a honeycomb monolith, such a solids content can cause a thin layer of the support coating to deposit on the inner walls of the substrate. If the substrate is a wall-flow filter, such a solids content enables the slurry to enter the channels of the wall-flow filter and enables the slurry to enter the walls of the wall-flow filter.

[0060] Preferably, the slurry further comprises one or more of the following:

[0061] An oxygen storage material, preferably cerium-zirconium oxide;

[0062] A promoter salt;

[0063] A binder;

[0064] An acid or a base;

[0065] A thickening agent; and

[0066] A reducing agent.

[0067] The promoter may comprise, for example, a non-PGM transition metal element, a rare earth element, an alkali group element, and / or a combination of two or more of the above elements within the same or different groups of the periodic table. The promoter salt may be a salt of such an element.

[0068] The binder may comprise, for example, an oxide material having a small particle size to bind together the individual insoluble particles in the carrier coating slurry. The use of a binder in the carrier coating is well known in the art.

[0069] The thickener may include, for example, a natural polymer having functional hydroxyl groups that interact with the insoluble particles in the carrier coating slurry. It is used for the purpose of thickening the carrier coating slurry to improve the coating profile during the application of the carrier coating to the substrate. It is typically burned off during the calcination of the carrier coating. Examples of specific thickeners / rheology modifiers for the carrier coating include guar gum, gum arabic, xanthan gum, gellan gum, schizophyllan, scleroglucan, diutan gum, welan gum, hydroxyethyl methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, and ethyl hydroxyethyl cellulose.

[0070] The term "reducing agent" as described herein may encompass compounds of particles that can reduce PGM cations in situ to their metallic state during the preparation of the carrier coating.

[0071] Organic acids may be added, which serve as reducing agents for the PGM and / or create a reducing environment during subsequent heating / calcination steps. Examples of suitable organic acids may include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, tannic acid, and combinations thereof.

[0072] In a preferred embodiment, the PGM comprises rhodium, the carrier material comprises alumina, and the slurry further comprises cerium-zirconium oxide. In another preferred embodiment, the PGM comprises rhodium, the carrier material comprises cerium-zirconium oxide, and the slurry further comprises alumina. In another preferred embodiment, the PGM comprises rhodium, and the carrier material comprises alumina and cerium-zirconium oxide.

[0073] The method preferably further comprises disposing an additional slurry on the substrate, the additional slurry comprising one or more of the following: additional carrier material; oxygen storage material; promoter salt; binder; acid or base; thickener; and reducing agent, wherein disposing the additional slurry on the substrate is performed before disposing the carrier material on the substrate and / or after heating the loaded carrier material to form the nanoparticles of the PGM on the carrier material. This can result in a catalyst article having multiple layers of different carrier coatings, such as a bottom carrier coating containing, in particular, rhodium nanoparticles supported on alumina and a top carrier coating containing, in particular, rhodium nanoparticles supported on alumina. Additional embodiments of such multiple layers are discussed in more detail below.

[0074] Setting the carrier material of the load on the substrate preferably includes contacting the slurry with the substrate (e.g., pouring the slurry into the inlet of the substrate) and optionally:

[0075] Applying a vacuum to the substrate, and / or

[0076] Drying the slurry on the substrate.

[0077] This can result in a favorable distribution of the carrier material of the load on the substrate.

[0078] Drying is preferably carried out under the following conditions:

[0079] At a temperature of 60 °C to 200 °C, more preferably 70 °C to 130 °C; and / or

[0080] For a duration of 10 minutes to 360 minutes, preferably 15 minutes to 60 minutes.

[0081] The substrate can be "blank", i.e., a substrate without a carrier coating. Alternatively, the substrate can have one or more carrier coatings already loaded thereon. In this case, the final catalyst article can comprise multiple layers of different carrier coatings.

[0082] The substrate preferably comprises cordierite. A cordierite substrate is particularly suitable for catalyst articles.

[0083] The substrate is preferably in the form of a honeycomb monolith, a wall-flow filter, or a flow-through filter.

[0084] Heating is preferably carried out under the following conditions:

[0085] At a temperature of 400 °C to 700 °C, preferably 400 °C to 600 °C, more preferably 450 °C to 600 °C; and / or

[0086] For a duration of 10 minutes to 360 minutes, preferably 35 minutes to 120 minutes.

[0087] Lower temperatures and / or shorter heating times may result in incomplete decomposition of the complex and / or may result in a high level of the compound of formula (I) remaining in the substrate. Higher temperatures and / or longer heating times may result in an unfavorable large particle size of the PGM particles, presumably due to sintering. Higher temperatures and longer heating times may also cause damage to the catalyst article.

[0088] Heating preferably includes calcination. As used herein, the term "calcination" can encompass a heat treatment process in the absence or limited supply of air or oxygen to effect thermal decomposition.

[0089] The nanoparticles preferably have a D50 of from 0.1 nm to 10 nm, more preferably from 0.2 nm to 5 nm, and even more preferably from 0.2 nm to 4 nm. The D50 can be measured by TEM. Such particle sizes can result in favorable levels of catalytic activity.

[0090] In another aspect, the present invention provides a catalyst article obtainable by the method described herein for use in an emissions treatment system.

[0091] Compared to conventional catalyst articles, the catalyst articles obtainable by the method described herein can contain PGM particles having a favorable small particle size and a favorable particle size distribution (e.g., D50 from 0.2 nm to 4 nm). Additionally, compared to conventional catalyst articles, the catalyst articles obtainable by the method described herein can exhibit a more uniform dispersion of the PGM particles throughout the substrate.

[0092] When used in an emissions treatment system, the catalyst article can exhibit favorable light-off performance, particularly for NO, CO, and total hydrocarbons during three-way catalytic conversion for stoichiometric gasoline emission reduction.

[0093] The catalyst is preferably used for three-way catalysis.

[0094] The catalyst article can have a washcoat loading of from 1 g / in 3 to 3 g / in 3 Compared to conventional catalyst articles, such catalyst articles can exhibit similar or higher catalytic activity but lower cost in view of the use of lower levels of PGM.

[0095] The substrate preferably comprises a wall-flow filter substrate or a flow-through substrate.

[0096] In a preferred embodiment, the catalyst article comprises a bottom layer of carrier material having rhodium thereon and a top layer of carrier material having palladium thereon. In another preferred embodiment, the catalyst article comprises a bottom layer of carrier material having palladium thereon and a top layer of carrier material having rhodium thereon. As used herein, the term "bottom layer" can encompass the layer (e.g., washcoat) closest to or in contact with the substrate (i.e., the substrate wall). As used herein, the term "top layer" can encompass the layer (e.g., washcoat) further away from the substrate (i.e., the substrate wall) than the bottom layer and located on top of the bottom layer.

[0097] In such preferred embodiments, the carrier material preferably comprises alumina and ceria-zirconia.

[0098] The catalyst article, particularly in such preferred embodiments, preferably comprises from 2 g / ft 3 to 15 g / ft3 Rhodium, more preferably 5 g / ft 3 to 10 g / ft 3 rhodium. Advantageously, such rhodium levels can be lower than those of conventional catalyst articles without compromising catalytic activity.

[0099] The catalyst article, particularly in such preferred embodiments, preferably comprises 50 g / ft 3 to 200 g / ft 3 palladium, more preferably 80 g / ft 3 to 150 g / ft 3 palladium. Advantageously, such palladium levels can be lower than those of conventional catalyst articles without compromising catalytic activity.

[0100] In a preferred embodiment, the supported carrier material is provided on a substrate in the form of a slurry, the PGM comprises rhodium, the carrier material comprises alumina, and the slurry further comprises cerium-zirconium oxide. In another preferred embodiment, the supported carrier material is provided on a substrate in the form of a slurry, the PGM comprises rhodium, the carrier material comprises cerium-zirconium oxide, and the slurry further comprises alumina. In another preferred embodiment, the supported carrier material is provided on a substrate in the form of a slurry, the PGM comprises rhodium, and the carrier material comprises alumina and cerium-zirconium oxide.

[0101] In yet another aspect, the present invention provides an emissions treatment system comprising the catalyst article described herein.

[0102] The emissions treatment system is preferably for a gasoline engine.

[0103] The gasoline engine is preferably operated under stoichiometric conditions.

[0104] In yet another aspect, the present invention provides a method of treating exhaust gas, the method comprising:

[0105] providing a catalyst article as described herein; and

[0106] contacting the catalyst article with the exhaust gas.

[0107] The exhaust gas is preferably exhaust gas from a gasoline engine. The catalyst article is particularly suitable for treating such exhaust gas. The gasoline engine is preferably operated under stoichiometric conditions.

[0108] The present invention will now be described in connection with the following non-limiting examples.

[0109] A plurality of catalyst articles were prepared according to the following examples:

[0110] Comparative Example 1A: Catalyst coated with a Pt-TWC (containing platinum nitrate) washcoat

[0111] 1. Prepare a slurry of platinum nitrate (Pt loading is 11 g / ft 3 ).

[0112] 2. Add a slurry of a stabilized alumina support (0.5 g / in 3 ), and mix for 1 h.

[0113] 3. Add a cerium-zirconium oxide support (0.8 g / in 3 ), and mix for 30 minutes.

[0114] 4. Adjust the solids to the target (such as approximately 23%).

[0115] 5. Add an appropriate amount of thickener and mix overnight.

[0116] 6. Coat a single-dose target from an inlet of 1.2 inches

[0117] 7. Place the brick in a static oven and calcine at 500 °C for 30 min.

[0118] Example 1B: Catalyst coated with a Pt-TWC (containing Pt modified with gallic acid) washcoat

[0119] 1. Prepare a slurry of platinum nitrate (Pt loading is 11 g / ft 3 ).

[0120] 2. Add a slurry of a stabilized alumina support (0.5 g / in 3 ), and mix for 1 h.

[0121] 3. Add a cerium-zirconium oxide support (0.8 g / in 3 ), and mix for 30 minutes.

[0122] 4. Add the required amount of gallic acid with a target GA:Pt mass ratio of 18:1.

[0123] 5. Adjust the solids to the target (such as approximately 23%).

[0124] 6. Add an appropriate amount of thickener and mix overnight.

[0125] 7. Coat a single-dose target from an inlet of 1.2 inches

[0126] 8. Place the brick in a static oven and calcine at 500 °C for 30 min.

[0127] Ignition performance under disturbance

[0128] Aging conditions: Rich-burn long-term redox aging

[0129] Figures 1A - 1CSeparate comparisons of the light-off conversion rates of NO, THC, and CO between Comparative Example 1A and Example 1B are shown after redox aging at 1000 °C for 40 hours. After rich fuel pretreatment, and at light-off temperatures between 150 °C and 600 °C, at a perturbation λ = 0.96 - 1.04 (frequency of 1 Hz), and a GHSV of 200,000 h -1 -1, the catalyst is evaluated. Compared with the formulated Pt reference catalyst without gallic acid modification (Comparative Example 1A), Example 1B of the present invention shows significantly improved TWC light-off performance. The maximum T 50 reductions of THC and CO for the Pt catalyst modified by GA are 21 °C and 35 °C, respectively. The maximum T 20 reduction of NO is 73 °C because for the Pt reference catalyst, the NO conversion rate does not exceed 25%.

[0130] Aging conditions: Lean-burn long-term redox aging

[0131] Figures 2A - 2C Separate comparisons of the light-off conversion rates of NO, THC, and CO between Comparative Example 1A and Example 1B are shown after redox aging at 1000 °C for 40 hours. After lean fuel pretreatment, and at light-off temperatures between 150 °C and 600 °C, at a perturbation λ between 0.96 and 1.04 (frequency of 1 Hz), and a GHSV of 200,000 h -1 -1, the catalyst is evaluated. Compared with the formulated Pt reference catalyst without gallic acid modification (Comparative Example 1A), Example 1B of the present invention shows significantly improved TWC light-off performance. The maximum T 50 reductions of NO, THC, and CO for the Pt catalyst modified by GA are 30 °C, 24 °C, and 32 °C, respectively.

[0132] λ-scan performance under disturbance

[0133] Figures 3A - 3C Separate comparisons of the conversion rates of NO, THC, and CO between Comparative Example 1A and Example 1B are shown under λ-scan conditions between λ = 0.98 - 1.04 after redox aging at 1000 °C for 40 hours. Compared with the formulated Pt reference catalyst without gallic acid modification (Comparative Example 1A), Example 1B of the present invention shows significantly improved TWC performance, with the highest improvement occurring under more lean fuel conditions. The maximum decreases of CO, THC, and NO at λ 1.04 are 15%, 10%, and 12%, respectively. The maximum decreases of CO, THC, and NO at λ 1.01 are 13%, 20%, and 3%, respectively. The maximum decreases of CO, THC, and NO at λ 0.98 are -3%, 0%, and 2%, respectively.

[0134] Comparative Example 2A: Catalyst coated with a Pt-Rh TWC (containing Pt and Rh nitrates) washcoat

[0135] 1. Prepare a slurry of cerium dioxide - zirconium oxide support (1 g / in 3 )。

[0136] 2. Add the required amount of rhodium nitrate (Rh loading 2 g / ft 3 ) and platinum nitrate (Pt loading 2 g / ft 3 )。

[0137] 3. Adjust the pH of the support coating to a pH target of approximately 6 - 7.

[0138] 4. Add a slurry of stable alumina support (1 g / in 3 ) and mix for 1 h.

[0139] 5. Adjust the solids to the target (such as approximately 30%).

[0140] 6. Add an appropriate amount of thickener and mix overnight.

[0141] 7. Coating a single - dose target from an inlet of 1.2 inches

[0142] 8. Place the brick in a static oven and calcine at 500 °C for 30 min.

[0143] Example 2B: Catalyst coated with a Pt-Rh TWC (containing Pt modified with gallic acid) washcoat

[0144] 1. Prepare a slurry of cerium dioxide - zirconium oxide support (1 g / in 3 )。

[0145] 2. Add the required amount of platinum nitrate (Pt loading 2 g / ft 3 ) to the slurry.

[0146] 3. Add the required amount of gallic acid with a target GA:Pt mass ratio of 15:1.

[0147] 4. Add the required amount of rhodium nitrate (Rh loading 2 g / ft 3 ) to the slurry.

[0148] 5. Adjust the pH of the support coating to a pH target of approximately 6 - 7.

[0149] 6. Add a slurry of stable alumina support (1 g / in 3 ) and mix for 1 h.

[0150] 7. Adjust the solids to the target (such as approximately 30%).

[0151] 8. Add an appropriate amount of thickener and mix overnight.

[0152] 9. Coating a single - dose target from an inlet of 1.2 inches

[0153] Place the bricks in a static oven and calcine them at 500 °C for 30 min.

[0154] After aging, test the light-off performance of the catalyst articles of Example 2B and Comparative Example 2A against TWC conversion perturbations under simulated gasoline exhaust conditions. (Aging conditions: 1000 °C / redox / 40 h. Reaction conditions: after rich pretreatment, 150 °C - 700 °C, λ = 0.96 - 1.04, GHSV = 200,000 h -1 ). The results of the NO, CO, and THC conversion rates are shown in Figures 4A - 4C . In each case, the TWC activity of Example 2B is greater than that of Comparative Example 2A. The maximum T x reductions of NO, CO, and THC in Example 2B are 15 °C, 22 °C, and 33 °C, respectively. 50

[0155] The foregoing detailed description has been presented by way of illustration and example, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated 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 producing a catalyst product, the method comprising: Provided is formula (I): A complex of a compound and PGM, wherein R1 is H or a C1-C6 alkyl group, R2 is H, OH or a 0-C1-C4 alkyl group, and the PGM contains rhodium and / or platinum; providing carrier materials; applying the complex to the support material to form a supported support material; disposing the loaded carrier material on a substrate; as well as The loaded support material is heated to form nanoparticles of the PGM on the support material.

2. The method according to claim 1, wherein R2 is OH.

3. The method according to claim 1 or claim 2, wherein R1 is H.

4. A method according to any preceding claim, wherein the PGM comprises rhodium.

5. A method according to any preceding claim, wherein the PGM comprises platinum.

6. A method according to any preceding claim, wherein the PGM comprises rhodium and platinum.

7. A method according to any preceding claim, wherein the support material comprises an oxide, preferably one or more of Al2O3, SiO2, TiO2, CeO2, ZrO2, CeO2-ZrO2, V2O5, La2O3 and zeolite.

8. A method according to any preceding claim, wherein the support material comprises alumina, preferably gamma-alumina.

9. A method according to any preceding claim, wherein the support material comprises ceria-zirconia.

10. A method according to any preceding claim, wherein the support material comprises alumina and ceria-zirconia.

11. The method according to any one of claims 8 to 10, wherein the alumina and / or ceria-zirconia is doped.

12. The method of claim 11, wherein the alumina and / or ceria-zirconia is doped with oxides of one or more of lanthanum, neodymium, yttrium, niobium, praseodymium, hafnium, molybdenum, titanium, vanadium, zinc, cadmium, manganese, iron, copper, calcium, barium, strontium, cesium, magnesium, potassium and sodium, preferably one or more of lanthanum, neodymium and yttrium.

13. A method according to claim 11 or claim 12, wherein the dopant is present in the alumina and / or ceria-zirconia in an amount of 0.001 to 20 wt%, preferably 0.5 to 10 wt%.

14. A method according to any preceding claim, wherein the support material is in the form of a powder having a D90 of 0.1 to 25 μm, preferably 0.5 to 5 μm.

15. A method according to any preceding claim, wherein the supported support material is provided on the substrate in the form of a slurry.

16. The method of claim 15, wherein providing the complex of the compound of formula (I) and a PGM comprises synthesizing the complex in situ in the slurry.

17. The method of claim 15, wherein the slurry is prepared by a method comprising the steps of: contacting a PGM salt with a compound of formula (I) in water to form a complex of the compound of formula (I) and PGM in an aqueous solution, the PGM salt comprising rhodium and / or platinum; applying the complex to the support material by contacting the support material with the aqueous solution to form a supported support material; Optionally, one or more of the following are added to the aqueous solution: an oxygen storage material, preferably ceria-zirconia; a promoter salt; a binder; an acid or base; a thickener; and a reducing agent.

18. A method according to any preceding claim, wherein the supporting comprises a washcoat coating.

19. The method according to any one of claims 15 to 18, wherein the solids content of the slurry is from 10% to 40%, preferably from 15% to 35%.

20. The method according to any one of claims 15 to 19, wherein the slurry further comprises one or more of the following: an oxygen storage material, preferably ceria-zirconia; Accelerator salts; Binder; Acid or base; Thickeners; and reducing agent.

21. The method of any one of claims 15 to 20, wherein the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

22. The method of any one of claims 15 to 20, wherein the PGM comprises rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina.

23. The process of claims 15 to 20, wherein the PGM comprises rhodium and the support material comprises alumina and ceria-zirconia.

24. The method according to any one of claims 15 to 23, further comprising disposing an additional slurry on the substrate, the additional slurry comprising one or more of the following substances: an additional support material; an oxygen storage material; a promoter salt; a binder; an acid or a base; a thickener; and a reducing agent, wherein the additional slurry is disposed on the substrate before the support material is disposed on the substrate and / or after heating the loaded support material to form nanoparticles of the PGM on the support material.

25. The method of any one of claims 15 to 24, wherein disposing the supported support material on a substrate comprises contacting the slurry with the substrate, and optionally: applying a vacuum to the substrate, and / or The slurry on the substrate is dried.

26. The method of claim 25, wherein the drying occurs under the following conditions: At a temperature of 60°C to 200°C, preferably 70°C to 130°C; and / or The duration is from 10 minutes to 360 minutes, preferably from 15 minutes to 60 minutes.

27. A method according to any preceding claim, wherein the substrate comprises cordierite.

28. A method according to any preceding claim, wherein the substrate is in the form of a honeycomb monolith, a wall flow filter or a flow-through filter.

29. A method according to any preceding claim, wherein the heating is carried out under the following conditions: 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 duration is from 10 minutes to 360 minutes, preferably from 35 minutes to 120 minutes.

30. A method according to any preceding claim, wherein the heating comprises calcining.

31. A method according to any preceding claim, wherein the nanoparticles have a D50 of 0.1 nm to 10 nm, preferably 0.2 nm to 5 nm, more preferably 0.2 nm to 4 nm.

32. A catalyst article obtainable by a method according to any preceding claim, for use in an emission treatment system.

33. The catalyst article according to claim 32, which is used for three-way catalysis.

34. The catalyst product of claim 32 or claim 33, wherein the carrier coating loading of the catalyst product is 1 g / in 3 Up to 3g / in 3 .

35. The catalyst article of any one of claims 32 to 34, wherein the substrate comprises a wall flow filter substrate.

36. The catalyst article of any one of claims 32 to 34, wherein the substrate comprises a flow-through substrate.

37. The catalyst article of any one of claims 32 to 36 comprising a bottom layer of a support material having rhodium thereon and a top layer of a support material having palladium thereon.

38. The catalyst article of any one of claims 32 to 36 comprising a bottom layer of a support material having palladium thereon and a top layer of a support material having rhodium thereon.

39. The catalyst article of claim 37 or claim 38, wherein the support material comprises alumina and ceria-zirconia.

40. The catalyst article of any one of claims 32 to 39, comprising 2 g / ft 3 Up to 15g / ft 3 Rhodium, preferably 5g / ft 3 Up to 10g / ft 3 of rhodium.

41. The catalyst article of any one of claims 37 to 40, comprising 50 g / ft 3 Up to 200g / ft 3 of palladium, preferably 80 g / ft 3 Up to 150g / ft 3 of palladium.

42. The catalyst article of any one of claims 32 to 41, wherein the supported support material is disposed on the substrate in the form of a slurry, the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

43. The catalyst article of any one of claims 32 to 41, wherein the supported support material is disposed on the substrate in the form of a slurry, the PGM comprises rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina.

44. The catalyst article of any one of claims 32 to 41, wherein the supported support material is disposed on the substrate in the form of a slurry, the PGM comprises rhodium, and the support material comprises alumina and ceria-zirconia.

45. An emission treatment system comprising the catalyst article of any one of claims 32 to 44.

46. ​​The exhaust treatment system of claim 45 for use with a gasoline engine.

47. The emission treatment system of claim 46, wherein the gasoline engine operates under stoichiometric conditions.

48. A method for treating exhaust gas, the method comprising: Providing a catalyst article according to any one of claims 32 to 44; as well as The catalyst article is contacted with an exhaust gas.

49. The method of claim 48, wherein the exhaust gas is from a gasoline engine.

50. The method of claim 49, wherein the gasoline engine is operated under stoichiometric conditions.

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