Humic acid assisted metal nanoparticle synthesis for three-way catalytic applications

Abstract

1. A method of producing a catalyst article, the method comprising: providing a complex of humic acid or a derivative thereof and a PGM; providing a support material; applying the complex to the support material to form a supported support material; disposing the supported support material on a substrate; and heating the supported support material to form nanoparticles of the PGM on the support material.

Description

[Technical field]

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

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

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

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

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

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

[0007] One aspect of the present disclosure is directed to a method of making a catalytic article, the method including providing a complex of humic acid, or a derivative thereof, and a PGM, providing a support material, applying the complex to the support material to form a supported support material, disposing the supported support material on a substrate, and heating the supported support material to form nanoparticles of the PGM on the support material.

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

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

[0010] [Figure 1A] FIG. 1 shows NO conversion results of perturbation ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 1 and Catalyst 1. [Figure 1B]FIG. 1 shows the CO conversion results of perturbation ignition performance tests under stoichiometric TWC conditions for Reference Catalyst 1 and Catalyst 1. [Figure 1C] FIG. 1 shows THC conversion results of perturbed ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 1 and Catalyst 1. [Figure 2A] FIG. 1 shows NO conversion results of perturbation ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 2.1, Reference Catalyst 2.2, and Catalyst 2. [Figure 2B] FIG. 1 shows the CO conversion results of perturbation ignition performance tests under stoichiometric TWC conditions for Reference Catalyst 2.1, Reference Catalyst 2.2, and Catalyst 2. [Figure 2C] FIG. 1 shows THC conversion results of perturbed ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 2.1, Reference Catalyst 2.2 and Catalyst 2. [Figure 3A] FIG. 1 shows NO conversion results of perturbation ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 3 and Catalyst 3. [Figure 3B] FIG. 1 shows the CO conversion results of perturbation ignition performance tests under stoichiometric TWC conditions for Reference Catalyst 3 and Catalyst 3. [Figure 3C] FIG. 13 shows THC conversion results of perturbed ignition performance tests at stoichiometric TWC conditions for Reference Catalyst 3 and Catalyst 3. [Figure 4] FIG. 1 shows ethane conversion during ethane hydrogenolysis tests for a fresh mono-supported Rh catalyst and an aged mono-supported Rh catalyst of Example 1. [Diagram 5] FIG. 13 is a graph showing ethane conversion in an ethane hydrogenolysis test of the aged fully blended Rh-TWC of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] In a first aspect, the present invention provides a method of making a catalytic article, the method comprising: providing a complex of humic acid or a derivative thereof (preferably humic acid) and a PGM; Providing a carrier material; applying the complex to the support material to form a supported support material; placing the supported support material on a substrate; and heating the supported support material to form nanoparticles of the PGM on the support material.

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

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

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

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

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

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

[0019] Providing a complex of humic acid or a derivative thereof with a PGM typically involves providing the complex in a solution, for example an aqueous or alcoholic solution. Providing a complex of humic acid or a derivative thereof with a PGM typically involves mixing inorganic PGM precursor(s) in pure form or in solution with humic acid or a derivative thereof in an aqueous medium, for example mixing nitrate PGM with humic acid (such as CAS number 1415-93-6) in water. The humic acid or derivative thereof may be in the form of a salt, such as an alkali metal salt.

[0020] Humic acids are known to be able to strongly bind heavy metal ions and have been used in radiation techniques for removing heavy metals from wastewater, however this is an entirely different field and application to its use in the present invention.

[0021] The term "humic acid" as used herein corresponds to terms known in the art. For example, humic acid can be described as a brown polymeric product of the decomposition of organic matter, especially dead vegetation. This polymeric combination may contain aromatic and heterocyclic structures, carboxyl groups, and nitrogen. The functional groups that contribute most to the surface charge and reactivity of humic materials are phenolic and carboxyl groups. Molecules that contain humic acid may form supramolecular structures that are held together by non-covalent forces, for example. Humic acid as traditionally produced in the laboratory may not be a single acid. Rather, it may be a complex mixture of many different acids that contain carboxyl and phenolate groups, such that the mixture behaves functionally as a dibasic acid, and in some cases, as a tribasic acid. Humic acid may, for example, contain a fulvic acid component.

[0022] The exact chemical structure of humic acid may not be well defined or well understood, but the definition is often well understood, as it can include many similar compounds of varying functionality. Humic acid is obtained from natural sources, which can make it more environmentally friendly than methods that use synthetic polymers. In some literature, humic acid is also referred to as urmic acid.

[0023] Humic acid may be defined by the internationally recognized CAS number 1415-93-6. CAS numbers 68514-28-3 and 68131-04-4 are also known potassium and sodium salts of humic acid, respectively. A CAS number (or CAS Registry Number) is a unique numerical identifier for a particular substance. The identification numbers are assigned by the Chemical Abstract Service (CAS), and a registry is maintained by CAS.

[0024] Humic acid may also be supplied as the potassium salt, a typical composition of which is, for example, as follows: Potassium oxide (KO), 12 w / w% in natural samples; Total humic extract, more than 85% w / w or more than 75% w / w based on the dry sample; Humic acid, 82 w / w% or 72 w / w% based on dry sample; Fulvic acid, 3% or more w / w based on dry sample; Organic nitrogen (N), 1 w / w% for natural samples; Ash content: 31 w / w% for natural samples; Dry matter, >85w / w%, Total carbon, 36w / w%.

[0025] Such compositions may have a pH of 8.45±1 (in a 1% solution) or 8.95±1 (in a 10% solution) and a solubility of 250 g / L.

[0026] Humic acid may also be supplied as a mixture of potassium humate and fulvic acid, a typical composition of which is, for example, as follows: Potassium oxide (K2O), 4+ / -0.5w / w% or 4.4+ / -0.6w / v%, Total humic extract, 15% w / w or more than 16.6% w / v; Humic acid, 12 w / w% or 13.3 w / v%, Fulvic acid, 3 w / w% or 3.3 w / v%, Organic matter, 13.1 w / w% or 14.4 w / v%.

[0027] The pH of such a composition may be greater than 10.

[0028] A typical example of a humic acid can have, for example, the following structure:

[0029] [ka]

[0030] Preferably, providing a complex of humic acid or a derivative thereof with PGM comprises contacting PGM with a mixture of humic acid or a derivative thereof with fulvic acid. In such a method, there may be a further complex comprising fulvic acid and PGM. Preferably, providing a complex of humic acid or a derivative thereof with PGM comprises contacting PGM with a substance defined by one or more of CAS numbers 1415-93-6, 68514-28-3 and 68131-04-4. That is, humic acid or a derivative thereof may preferably comprise a substance defined by one or more of CAS numbers 1415-93-6, 68514-28-3 and 68131-04-4. Preferably, humic acid or a derivative thereof comprises a substance defined by CAS number 1415-93-6.

[0031] The term PGM as used herein includes one or more platinum group metals selected from ruthenium, rhodium, palladium, osmium, iridium, and platinum. Preferably, the PGM comprises one or more of palladium, rhodium, and platinum, more preferably rhodium and / or platinum, and even more preferably rhodium. Such metals may be particularly suitable for performing three-way catalysis. In addition, such metals are expensive, which means that it is advantageous to be able to provide a similar level of catalytic activity for the same amount of metal. Furthermore, the use of such metals in the method of the present invention can result in particularly favorable perturbation ignition performance. The PGM may be in the form of an alloy.

[0032] The complex may comprise a humic acid to PGM atomic mass ratio (i.e. mass of humic acid / mass of PGM atoms in the complex) of 0.5 to 5, preferably 0.8 to 4, more preferably 0.9 to 3, even more preferably 1 to 2, and still more preferably 1.3 to 1.8. When the PGM is rhodium, the mass ratio of humic acid to PGM is preferably about 1.68. When the PGM is platinum, the mass ratio of humic acid to PGM is preferably about 1.4. Such mass ratios can achieve a particularly desirable PGM nanoparticle distribution on the final catalyst article, which can contribute to the improved light-off and catalytic performance demonstrated by catalyst articles produced by the methods of the present invention.

[0033] The support material may be any material capable of supporting the complexes and nanoparticles thereon or therein. The support material may take any form, but is typically in the form of a powder, more typically a high surface area powder. When the method of the present invention is used to prepare a catalyzed filter, such as a wall-flow filter or a flow-through filter, the support material will typically be in the form of a powder having a D50, e.g., of 0.1 to 25 μm, more typically 0.5 to 5 μm, as measured using TEM. Such particle size may facilitate 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.

[0034] The support material may also act as an oxygen storage material, storing and releasing oxygen under fuel-lean and fuel-rich conditions, respectively, to facilitate three-way catalytic conversion.

[0035] The application of the complex to the support material typically involves contacting the complex with the support material in the presence of a solvent, typically water, to produce a slurry. As used herein, the term "slurry" can include a liquid containing insoluble material, e.g., insoluble particles. The slurry may include (1) the solvent, (2) soluble content, e.g., unreacted humic acid, inorganic PGM and cocatalyst precursor(s), and PGM-humic acid complexes (outside the support), and (3) insoluble content, e.g., support particles that may or may not interact with the humic acid and metal precursors. 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. By increasing the contact time and / or stirring time, the amount of complex loaded onto the support material can be increased.

[0036] As used herein, the term "supported support material" can include support materials having PGM-humic acid complexes supported thereon (e.g., on the surface of a high surface area metal oxide support material) and / or supported therein (e.g., within the pores of a zeolite support material). The complexes are typically immobilized on the support by, for example, electrostatic forces, hydrogen bonding, coordinate bonds, covalent bonds, and / or ionic bonds. For example, in the case of oxides, amine and / or carboxyl(rate) functional groups in humic acid and surface hydroxyl groups on the support can interact through electrostatic forces or hydrogen bond formation.

[0037] The term "substrate" as used herein can include, for example, ceramic or metal honeycombs, or filter blocks, such as wall-flow or flow-through filters. Substrates can include ceramic monolith substrates. Substrates can vary in their material composition, size and configuration, cell shape and density, and wall thickness. Suitable substrates are known in the art.

[0038] 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, air knife and / or drying steps can be used during the placement step, as discussed in more detail below. If the carrier is a filter block, the supported carrier material can be placed on the filter wall, within the filter wall (if porous), or both.

[0039] 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 complex may at least partially, substantially or completely decompose. In other words, the ligand of the complex, i.e., humic acid or its derivative, is 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 may then begin to form metal-metal and metal-oxide bonds. As a result of heating (calcination), the substrate is typically substantially free of humic acid or its derivatives, and more typically is completely free of humic acid or its derivatives.

[0040] 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.

[0041] After the heating step, the substrate is typically cooled, more typically to room temperature. Cooling is typically performed in air with or without a coolant / cooling medium, typically without a coolant.

[0042] The PGM preferably comprises, consists essentially of or consists of one or more of palladium, rhodium and platinum, more preferably comprises, consists essentially of or consists of rhodium and / or platinum, and even more preferably comprises, consists essentially of or consists of rhodium. In particular, rhodium is an expensive PGM and forms a particularly suitable complex with humic acid or a derivative thereof. In particular, platinum is an expensive PGM and forms a particularly suitable complex with humic acid or a derivative thereof.

[0043] In a preferred embodiment, the PGM comprises, consists essentially of, or consists of rhodium and platinum. The use of such metals in the methods of the present invention can result in particularly favorable perturbation ignition performance.

[0044] Preferably, the humic acid or derivative thereof further comprises fulvic acid. In some cases, it is common to obtain humic acid as such a mixture. Fulvic acid can, for example, form further complexes with PGMs and contribute to achieving advantageous distribution properties in the final catalytic article.

[0045] Preferably, providing a complex of humic acid or a derivative thereof and PGM comprises contacting PGM with a material defined by one or more of CAS numbers 1415-93-6, 68514-28-3 and 68131-04-4, more preferably CAS number 1415-93-6. These particular compositions may work particularly well in the methods of the invention.

[0046] The support material preferably comprises an oxide, preferably one or more of Al2O3 (aluminum oxide or alumina), SiO2, TiO2, CeO2, ZrO2, V2O5, La2O3 and zeolites. The oxide is preferably a metal oxide. The support material more preferably comprises alumina, even more preferably gamma-alumina. The support material preferably comprises ceria-zirconia. The support material preferably comprises alumina and ceria-zirconia. The alumina and / or ceria-zirconia are preferably doped, more preferably doped with one or more oxides of lanthanum, neodymium, yttrium, niobium, praseodymium, hafnium, molybdenum, titanium, vanadium, zinc, cadmium, manganese, iron, copper, calcium, barium, strontium, cesium, magnesium, potassium or sodium, even more preferably doped with oxides of lanthanum, neodymium or yttrium. Such doped oxides are particularly useful as support materials. Preferably, the dopant is present in the alumina and / or ceria-zirconia in an amount of from 0.001% to 20% by weight, and more preferably from 0.5% to 10% by weight.

[0047] The support material is preferably in the form of a powder having a D90 of 0.1 to 25 μm, more preferably 0.5 to 5 μm.

[0048] The supported support material is preferably disposed on the substrate in the form of a slurry, which is particularly effective in disposing the material on the substrate to maximize gas diffusion and minimize pressure drop during catalytic conversion.

[0049] Providing a complex of humic acid or a derivative thereof and a PGM preferably comprises synthesizing the complex in situ in the slurry.

[0050] The slurry preferably comprises contacting a PGM salt with humic acid or a derivative thereof in water to form a complex between the humic acid or derivative thereof and the PGM in the aqueous solution; applying the complex to the support material by contacting the support material with the aqueous solution to form a supported support material; Optionally, adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent to the aqueous solution.

[0051] Such a "one-pot" preparation method may be simplified and less costly than conventional methods, and may also maximize the utilization of the polymer / humic acid.

[0052] In other words, providing a complex of humic acid or a derivative thereof and a PGM, providing a support material, applying the complex to the support material to form a supported support material, and disposing the supported support material on a substrate comprises: contacting a PGM salt with humic acid or a derivative thereof in water to form a complex between the humic acid or derivative thereof and the PGM in the aqueous solution; adding the support material to an aqueous solution to form a slurry of supported support material; Optionally, adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or base, a thickener, and a reducing agent to the slurry; and disposing the slurry on a substrate.

[0053] In an alternative preferred embodiment, the slurry comprises: contacting a PGM salt with a support material in water to form a support material suspension; contacting the support material suspension with humic acid or a derivative thereof to form a supported support material, the supported support material comprising a support material having a complex supported thereon, the complex comprising a complex of humic acid or a derivative thereof and the PGM; 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 support material suspension.

[0054] Such a "one-pot" preparation method may be simplified and less costly than conventional methods, and may also maximize the utilization of the polymer / humic acid.

[0055] The support may include a washcoating.

[0056] The slurry preferably has a solids content of 10-40%, preferably 15-35%. Such solids content can provide a suitable slurry rheology for disposing the loaded support material on a substrate. For example, if the substrate is a honeycomb monolith, such solids content can allow deposition of a thin layer of washcoat on the inner walls of the substrate. If the substrate is a wall-flow filter, such solids content can allow the slurry to enter the channels of the wall-flow filter and can allow the slurry to enter the walls of the wall-flow filter.

[0057] 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:

[0058] 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.

[0059] 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.

[0060] The thickener may include, for example, a natural polymer with functional hydroxyl groups that interact with insoluble particles in the washcoat slurry. The thickener serves the purpose of thickening the washcoat slurry for improved coating profile during washcoat coating on the substrate. The thickener is usually burned off during washcoat calcination. Examples of specific thickeners / rheology modifiers for washcoats include glactoma gum, guar gum, xanthan gum, curdlan schizophyllan, scleroglucan, diutan gum, wheylan gum, hydroxymethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, and ethylhydroxycellulose.

[0061] 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.

[0062] Organic acids can be added to act as reducing agents for the PGMs and / or create a reducing environment during the subsequent heating / calcination steps. Examples of suitable organic acids can include citric acid, succinic acid, oxalic acid, ascorbic acid, acetic acid, formic acid, and combinations thereof.

[0063] In a preferred embodiment, the PGMs comprise rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia. In another preferred embodiment, the PGMs comprise rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina. In another preferred embodiment, the PGMs comprise rhodium, and the support material comprises alumina and ceria-zirconia.

[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 support material on the substrate and / or after heating the supported support material to form nanoparticles of the PGM on the support material. This can result in a catalyst article having multiple layers of different washcoats, for example a bottom washcoat containing, inter alia, rhodium nanoparticles supported on alumina, and a top washcoat containing, inter alia, rhodium nanoparticles supported on alumina. Further examples of such multiple layers are discussed in more detail below.

[0065] 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 and drying the slurry on the substrate.

[0066] This can result in a preferred distribution of the supported support material on the substrate.

[0067] 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 The heating is carried out for 10 to 360 minutes, preferably 15 to 60 minutes.

[0068] 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.

[0069] The substrate preferably comprises cordierite. Cordierite substrates are particularly suitable for use in catalytic articles.

[0070] The substrate is preferably in the form of a honeycomb monolith, a wall-flow filter or a flow-through filter.

[0071] 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.

[0072] Lower temperatures and / or shorter heating times may result in insufficient decomposition of the complex and / or high levels of humic acid or its derivatives 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.

[0073] Heating preferably involves calcination. As used herein, the term "calcination" can include a heat treatment process in the absence or limited supply of air or oxygen to cause pyrolysis. Typically, however, calcination in this context involves heating in air in an oven.

[0074] The nanoparticles preferably have a D50 of 0.1 nm to 10 nm, more preferably 0.2 to 5 nm, and even more preferably 0.2 to 4 nm. D50 can be measured by TEM. Such particle size can provide a preferred level of catalytic activity.

[0075] In a further aspect, the present invention provides a catalyst article obtainable by the methods described herein, the catalyst article being for use in an emission treatment system.

[0076] Compared to conventional catalyst articles, catalyst articles obtainable by the methods described herein can contain PGM particles having advantageously small particle size and favorable particle size distribution (e.g., D50 of 0.2 to 4 nm). Furthermore, compared to conventional catalyst articles, catalyst articles obtainable by the methods described herein can exhibit a more uniform distribution of PGM particles throughout the substrate.

[0077] When used in emissions treatment systems, the catalyst articles can exhibit favorable light-off performance, particularly for NO, CO and total hydrocarbons, during three-way catalytic conversion for stoichiometric gasoline emission reduction.

[0078] The catalyst is preferably for a three-way catalyst.

[0079] The catalyst article is 1 g / in 3 ~3g / in 3 Such catalyst articles may exhibit similar or higher catalytic activity compared to conventional catalyst articles, but may be less expensive given the lower levels of PGMs used.

[0080] The substrate preferably comprises a wall-flow filter substrate or a flow-through substrate.

[0081] In a preferred embodiment, the catalytic article includes a bottom layer of support material having rhodium thereon and a top layer of support material having palladium thereon. In another preferred embodiment, the catalytic article includes a bottom layer of support material having palladium thereon and a top layer of support material having rhodium thereon. As used herein, the term "bottom layer" may include a layer (e.g., a washcoat layer) that is closest to or in contact with the substrate (i.e., substrate wall). As used herein, the term "top layer" may include a layer (e.g., a washcoat layer) that is further from the substrate (i.e., substrate wall) than the bottom layer and may be located above the bottom layer.

[0082] In such preferred embodiments, the support material preferably comprises alumina and ceria-zirconia.

[0083] The catalyst article, in particular in such preferred embodiments, preferably has a surface area of ​​2 g / ft 3 ~15g / ft 3 of rhodium, more preferably 5 g / ft 3 ~10g / ft 3 Advantageously, such rhodium levels can be lower than those of conventional catalyst articles, yet without impairing catalytic activity.

[0084] The catalyst article, in particular in such preferred embodiments, preferably has a coating weight of 50 g / ft 3 ~200g / ft 3 of palladium, more preferably 80 g / ft 3 ~150g / ft 3 Advantageously, such palladium levels can be lower than those of conventional catalyst articles, yet without compromising catalytic activity.

[0085] In a preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia. In another preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, the support material comprises ceria-zirconia, and the slurry further comprises alumina. In another preferred embodiment, the supported support material is disposed on a substrate in the form of a slurry, the PGMs comprise rhodium, and the support material comprises alumina and ceria-zirconia.

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

[0087] 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 catalyst article with an exhaust gas.

[0090] The exhaust gas is preferably exhaust gas from a gasoline engine. The catalytic article is particularly suitable for treating such exhaust gas. The gasoline engine preferably operates under stoichiometric conditions.

[0091] The invention will now be described with reference to the following non-limiting examples.

[0092] A number of catalyst articles were prepared according to the following examples.

[0093] Example 1: Two washcoat catalysts containing Rh supported on a single alumina support were prepared by a conventional method and the method according to the present invention, respectively.

[0094] Reference catalyst 1 (0.3% Rh / gamma alumina (containing Rh nitrate) washcoat catalyst): 1.Nitric acid (5g / ft 3 ) was added to the water and mixed for 1 hour to dissolve. 2. Milled gamma alumina (1 g / in 3 ) slurry was added and allowed to mix for 1 hour. 3. Deionized water was added to adjust the solids content to approximately 20%. 4. Activated 4 wt% thickener in water was added to adjust the batch solids to 30%. This was mixed vigorously in a VWR vortex mixer until a homogenous gel was formed. 5. A 1x3 inch core was coated under vacuum aiming at a dose 1.2 inches from the inlet, then air cured and dried. 6. The bricks were then fired in a static oven at 500°C for 30 minutes.

[0095] Catalyst 1 (0.3% Rh / gamma alumina (containing Rh modified by humic acid) washcoat catalyst) 1.Nitric acid (5g / ft 3 ) was added to the water and mixed for 1 hour to dissolve. 2. Humic acid (HA) was then added aiming for a HA:Rh mass ratio of 1.7 and allowed to mix for 1 hour. 3. Milled gamma alumina (1 g / in 3 ) slurry was added and allowed to mix for 1 hour. 4. Deionized water was added to adjust the solids content to approximately 20%. 5. Activated 4 wt% thickener in water was added to adjust the batch solids to 30%. This was mixed vigorously in a VWR vortex mixer until a homogenous gel was formed. 6. A 1x3 inch core was coated under vacuum aiming at a dose 1.2 inches from the inlet and then air cured to dry. 7. The bricks were then fired in a static oven at 500°C for 30 minutes.

[0096] Each catalyst was then aged at 1000°C under redox for 40 hours and compared for perturbed ignition performance under simulated gasoline exhaust conditions. The results for NO, CO and THC (total hydrocarbon) conversion are shown in Figure 1. The reaction conditions were: sufficient pretreatment, 150-700°C, =0.96-1.04, GHSV=200,000hr -1 Compared with the reference catalyst 1, catalyst 1 prepared by complexing Rh with humic acid showed a significant effect in TWC activity. The maximum T of NO, CO, and THC of single alumina-supported Rh catalyst with HA modification was 50 (the temperature at which the catalyst converts 50% of the inlet concentration of the target pollutant) reduction rates were 34°C, 46°C, and 90°C, respectively.

[0097] Example 2: More complex washcoat catalysts were prepared by the conventional method and the method of the present invention, respectively.

[0098] Reference catalyst 2.1 (Rh-TWC (containing Rh nitrate) washcoat catalyst) 1. A slurry of crushed gamma alumina support was prepared (0.6 g / in 3 ). 2. Rhodium nitrate solution (Rh loading 5g / ft 3 ) was added and the slurry was mixed until homogenous. 3. Ammonium was added dropwise until the pH reached 7.0-7.5. Upon addition of ammonium, the washcoat thickened. 4. The washcoat was mixed for 15-20 minutes to allow the rhodium to precipitate throughout the washcoat. 5. Ceria-zirconia support (0.7 g / in 3 ) was added and the slurry was mixed for 30 minutes until homogenous. 6. Binder (0.03g / in 3 ) was added and the slurry was mixed for 30 minutes until homogenous. 7. Deionized water was added to adjust the solids content to approximately 23%. 8. Thickener was added aiming for about 1.0-1.2 wt.% of the water-based washcoat. The washcoat was mixed for at least 6 hours. 9. Cordierite substrates were coated with a single dose washcoat under vacuum at 1.2 inches from the inlet and allowed to air cure and dry. 10. The washcoated bricks were then fired in a static oven at 500°C for 30 minutes.

[0099] Reference catalyst 2.2 (Rh-TWC (containing Rh nitrate) washcoat catalyst) Another reference catalyst was prepared according to the method of Reference Catalyst 2.1, except that the catalyst had a molecular weight of 9 g / ft 3 A higher Rh loading was used.

[0100] Catalyst 2 (Rh-TWC (containing Rh modified by humic acid) washcoat catalyst) 1. Rhodium nitrate slurry was prepared (Rh loading: 5 g / ft 3 ). 2. Humic acid (HA) was then added aiming for a HA:Rh mass ratio of 1.68 and allowed to mix for 1 hour. 3. Next, crushed gamma alumina support (0.6 g / in 3 ) was added to the slurry, which was allowed to mix for 1 hour. 4. Ceria-zirconia support (0.7 g / in 3 ) was added and the slurry was mixed for 30 minutes until homogenous. 5. Binder (0.03g / in 3 ) was added and the slurry was mixed for 30 minutes until homogenous. 6. Deionized water was added to adjust the solids content to approximately 23%. 7. Thickener was added aiming for approximately 1.0-1.2 wt.% of the water-based washcoat. The washcoat was mixed for at least 6 hours. 8. Cordierite substrate was coated with a single dose washcoat under vacuum at 1.2 inches from the inlet and allowed to dry by air curing. 9. The washcoated bricks were then fired in a static oven at 500°C for 30 minutes.

[0101] Next, each catalyst was aged at 1000℃ under redox conditions for 40 hours, and their perturbed ignition performance under simulated gasoline exhaust conditions was compared. The reaction conditions were: sufficient pretreatment, 150-700℃, =0.96-1.04, GHSV=200,000hr -1 Similar improvements were observed with the more complexed loaded Rh catalyst (Example 2), and the results are shown in Figure 2 for NO, CO, and THC conversion. Rh-HA catalyst 2 was used at the same 5 g / ft 3 The maximum T50 reductions of NO, CO and THC were 25°C, 33°C and 48°C, respectively. Furthermore, Catalyst 2 performed significantly better than the reference Catalyst 2.1 at a Rh loading of 9 g / ft 3 The TWC light-off performance was similar to or better than that of the reference catalyst 2.2, which had a 1.8-fold higher Rh loading.

[0102] Example 3: Bimetallic (Rh-Pt) washcoat catalysts were prepared by the conventional method and the method of the present invention, respectively.

[0103] Reference catalyst 3 (Rh-Pt bimetallic (containing Pt nitrate) TWC washcoat catalyst) 1. Add at least 50% of the planned amount of water to the ceria-zirconia support (1.1 g / in 3 ) was prepared. 2. Rh nitrate (Rh loading 4g / ft 3 ) was added to the ceria-zirconia slurry and mixed for at least 15 minutes. 3. The pH was adjusted to >6 with ammonia and the slurry was mixed for at least 1 hour. 4. Next, gamma alumina (0.4 g / in 3 ) slurry was added, followed by platinum nitrate (Pt loading 2 g / ft 3 ) was added. The slurry was mixed for at least 15 minutes. 5. The pH was adjusted to above 5.8 with ammonia and the slurry was mixed for at least 30 minutes. 6. Binder (0.03g / in 3 ) was added and the slurry was mixed for at least 30 minutes. 7. The washcoat was adjusted to the target % solids (approximately 25%) and thickener was added (approximately 0.8-1.0%). The slurry was mixed overnight. 8. Cordierite substrate was coated with a single dose washcoat under vacuum at 1.2 inches from the inlet and allowed to dry by air curing. 9. The bricks were then fired in a static oven at 500°C for 30 minutes.

[0104] Catalyst 3 (Rh-Pt bimetallic TWC (containing Pt modified by humic acid) washcoat catalyst) 1. Add at least 50% of the planned amount of water to the ceria-zirconia support (1.1 g / in 3 ) was prepared. 2. Rh nitrate (Rh loading 4g / ft 3 ) was added to the ceria-zirconia slurry and mixed for at least 15 minutes. 3. The pH was adjusted to >6 with ammonia and the slurry was mixed for at least 1 hour. 4. Next, gamma alumina (0.4 g / in 3 ) slurry was added, followed by platinum nitrate (Pt loading 2 g / ft 3 ) was added. The slurry was mixed for at least 15 minutes. 5. Next, humic acid (HA) was added aiming for a HA:Pt mass ratio of 1.4. 6. Binder (0.03g / in 3 ) was added and the slurry was mixed for at least 30 minutes. 7. The washcoat was adjusted to the target % solids (approximately 25%) and thickener was added (approximately 0.8-1.0%). The slurry was mixed overnight. 8. Cordierite substrate was coated with a single dose washcoat under vacuum at 1.2 inches from the inlet and allowed to dry by air curing. 9. The bricks were then fired in a static oven at 500°C for 30 minutes.

[0105] Next, each catalyst was aged at 1050℃ / 10% H2O in air / 4 hours, and the perturbation ignition performance under simulated gasoline exhaust conditions was compared. The reaction conditions were: sufficient pretreatment, 150-700℃, =0.96-1.04, GHSV=200,000hr -1 Similar improvements were observed for Catalyst 3, where Pt was modified with HA, compared to Reference Catalyst 3, and the results for NO, CO, and THC conversion are shown in Figure 3. Catalyst 3 performed significantly better than Reference Catalyst 3, with maximum T values ​​of 34°C, 20°C, and 43°C for NO, CO, and THC, respectively. 90 A reduction was observed.

[0106] Example 4: Ethane conversion during ethane hydrogenolysis testing on fresh and aged single-supported Rh catalysts (prepared according to Example 1). Results are shown in Figure 4. Aging conditions: 1000°C / redox / 40 hours. Reaction conditions: with degassing pretreatment, 0.5% C2H6 and 2.8% H2 balanced with N2. Results allow a qualitative comparison of Rh active metal surface area, with an increase in ethane conversion indicating an increase in active Rh dispersion / metal surface area. Compared to reference catalyst 1, HA modification (catalyst 1) resulted in both an increase in the Rh active metal surface area of ​​fresh and aged catalysts, as well as a decrease in the difference between fresh and aged catalysts, indicating an improvement in Rh stability against aging at the relevant conditions.

[0107] Example 5: Ethane conversion during ethane hydrogenolysis testing for aged fully formulated Rh-TWC with and without Rh modification with humic acid (prepared according to Example 2). Results are shown in Figure 5. Aging conditions: 1000°C / redox / 40 hours. Reaction conditions: 0.5% C2H6 and 2.8% H2 balanced with N2 with degassing pretreatment. Results allow a qualitative comparison of Rh active metal surface area, with increased ethane conversion indicating increased active Rh dispersion / metal surface area. Compared to reference catalyst 2.1, HA modification (catalyst 2) resulted in increased aged Rh active metal surface area, resulting in more accessible Rh for TWC conversion.

[0108] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. 1. A method of making a catalyst article, said method comprising: Providing a complex of humic acid or a derivative thereof with PGM; Providing a carrier material; applying the complex to the support material to form a supported support material; placing the supported support material on a substrate; and heating the loaded support material to form nanoparticles of the PGM on the support material.

2. The method of claim 1 , wherein the PGM comprises one or more of palladium, rhodium, and platinum.

3. 3. The method of claim 2, wherein the PGM comprises rhodium and / or platinum, preferably rhodium.

4. The method according to any one of claims 1 to 3, wherein providing a complex of humic acid or a derivative thereof and PGM comprises contacting PGM with a mixture of humic acid or a derivative thereof and fulvic acid.

5. 3. The method of claim 1, wherein providing a complex of humic acid or a derivative thereof with PGM comprises contacting the PGM with a substance defined by one or more of CAS numbers 1415-93-6, 68514-28-3 and 68131-04-4.

6. 3. The method of claim 1 or 2, wherein the humic acid or derivative thereof comprises the substance defined by CAS number 1415-93-6.

7. 3. The method according to claim 1 or 2, wherein the complex comprises a humic acid to PGM atomic mass ratio of from 0.5 to 5, preferably from 0.8 to 4, more preferably from 0.9 to 3, even more preferably from 1 to 2, and still more preferably from 1.3 to 1.

8.

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

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

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

11. The method according to claim 9 or claim 10, wherein the alumina and / or the ceria-zirconia is doped.

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

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

14. The slurry contacting a PGM salt with humic acid or a derivative thereof in water to form a complex of humic acid or a derivative thereof with PGM in aqueous solution; applying the complex to the support material by contacting the support material with the aqueous solution to form a supported support material; and optionally adding one or more of an oxygen storage material, preferably ceria-zirconia, a promoter salt, a binder, an acid or a base, a thickener, and a reducing agent to the aqueous solution.

15. The slurry contacting a PGM salt with a support material in water to form a support material suspension; contacting the support material suspension with humic acid or a derivative thereof to form a supported support material, the supported support material comprising a support material having a complex supported thereon, the complex comprising a complex of humic acid or a derivative thereof and the PGM; 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 support material suspension.

16. The method of any one of claims 13 to 15, wherein the PGM comprises rhodium, the support material comprises alumina, and the slurry further comprises ceria-zirconia.

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

Images