A method for preparing a noble metal catalyst based on a precipitation reduction method

Abstract

The application discloses a method for preparing a noble metal catalyst based on a precipitation reduction method, and comprises the following steps: preparing a precipitation mixed slurry; preparing a reducing agent solution; under a water bath at 0-90 DEG C, the reducing agent solution is added dropwise into the precipitation mixed slurry, and stirring reduction is carried out for 1-12 hours to obtain a noble metal catalyst slurry; the noble metal catalyst slurry, a binder, an acid solution, an additive and a thickening agent are mixed, and stirring is carried out for 5-30 minutes to obtain a coating slurry; the coating slurry is sprinkled on the end face of a ceramic or metal substrate to perform quantitative coating; after the substrate coated with the coating slurry is dried, calcination is carried out, and the coating slurry is solidified on the substrate to obtain the noble metal catalyst. In application, the method avoids migration or precipitation of noble metals in the process of drying or slurry preparation, and migration of noble metals in a mixed slurry of multiple noble metals, improves the dispersion state of active components after use in a high-temperature environment, and further improves the anti-aging performance of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically a method for preparing noble metal catalysts based on precipitation-reduction. Background Technology

[0002] Existing automotive exhaust treatment technologies primarily utilize catalysts to remove CO, HC, and NO from vehicle exhaust. X These catalysts convert harmful substances into harmless substances such as CO2, H2O, and N2. They are typically made by loading noble metals (such as Pt, Pd, Rh, etc.) onto a metal oxide support. Currently, easily industrialized preparation methods mainly involve applying the noble metal to the metal oxide support via impregnation, reduction, or precipitation, followed by drying and high-temperature calcination to decompose it into oxides that are then fixed onto the support.

[0003] Chinese Patent Publication No. CN105148908A, published on December 16, 2015, discloses an invention entitled "A Preparation Method of a Supported Noble Metal Catalyst and Its Application." This method uses a noble metal as the active component to prepare a precursor solution, which is then uniformly mixed with a support. A protective agent and a liquid reducing agent are added to reduce the noble metal ions adsorbed or free on the surface or within the pores of the support, allowing the noble metal to be applied to the support in a reduced state, resulting in a mixed slurry. This slurry is then coated onto a cordierite matrix or a metal matrix, and dried and calcined to obtain the supported noble metal catalyst. While this method is simple, energy-efficient, and ensures the dispersion of the noble metal, for catalysts with high coating amounts, the addition of a large amount of high-polymer organic protective agent during preparation can cause rapid decomposition and heat release during calcination, potentially leading to the rupture of the catalytic unit.

[0004] Chinese Patent Publication No. CN112691660B, published on July 26, 2022, discloses an invention entitled "A Method for Preparing Ammonia Oxidation Catalyst Based on Deposition and Precipitation." In this method, a noble metal oxide support is heat-treated in a reducing atmosphere to obtain a defective support, which is then dispersed in deionized water. An ammonium carbonate solution is added for alkalization, followed by the addition of a noble metal precursor solution. After aging at room temperature, the solution is centrifuged, washed, and dried. The noble metal is then calcined and solidified in a reducing atmosphere to obtain the ammonia oxidation catalyst. This method requires a hydrogen reduction device and a centrifugal washing device, making the process complex. Furthermore, the noble metal solidification process also suffers from high energy consumption during drying and calcination, resulting in high industrial-scale costs. Additionally, the precipitated noble metal is not yet solidified, and the drying process can lead to migration of the noble metal, resulting in decreased dispersion and poorer anti-aging properties.

[0005] Chinese Patent Publication No. CN113600188A, published on November 5, 2021, discloses an invention entitled "A Gasoline Vehicle Exhaust Gas Purification Catalyst and Its Preparation Method." In this method, an alkaline solution is added dropwise to a Pt precursor solution until the pH of the mixture reaches 10-12. This solution is then applied to a support, and an acidic solution is added dropwise until the pH of the mixture reaches 3-5, forming a mixed coating slurry. This slurry is then coated onto a honeycomb support, dried, and calcined to obtain a supported noble metal catalyst. This method addresses the problem of noble metal migration in mixed slurries containing multiple amounts or types of noble metals, and the issue that the lack of solidification of noble metals during the slurry preparation process leads to migration during drying, resulting in decreased dispersion and poorer anti-aging performance.

[0006] Given the limitations of existing methods for preparing supported catalysts, it is imperative to develop a novel method for preparing supported noble metals. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing noble metal catalysts based on precipitation-reduction. This method regulates the state of noble metals on the catalyst material by adding a precipitant to precipitate the noble metals on the catalyst material, and then stabilizes the noble metals precipitated on the catalyst material by reduction. This avoids the migration or precipitation of noble metals during drying or slurry preparation, as well as the migration of noble metals in mixed noble metal slurries. It also improves the dispersion state of active components after use at high temperatures, thereby enhancing the anti-aging performance of the catalyst.

[0008] The objective of this invention is mainly achieved through the following technical solutions:

[0009] A method for preparing noble metal catalysts based on precipitation-reduction includes the following steps:

[0010] Under stirring, the catalyst material with D50 in the range of 1-10 μm, the noble metal solution, water and the precipitant are mixed and dispersed. The pH of the mixture is controlled at 8-14, and the mixture is stirred and matured at room temperature for 1-12 h to obtain a precipitated mixed slurry.

[0011] Dissolve a reducing agent with a molar mass of 1.1-5 times that of the precious metal in deionized water to obtain a reducing agent solution;

[0012] Under a water bath at 0-90℃, the reducing agent solution is added dropwise to the precipitated mixed slurry and stirred for 1-12 hours to obtain the noble metal catalyst slurry.

[0013] The precious metal catalyst slurry is mixed with binder, acid solution, additives and thickener, and stirred for 5 to 30 minutes to obtain a coating slurry. The solid content of the coating slurry is 25% to 40% and the viscosity is 1000 to 3500 mPa·s.

[0014] The coating slurry is applied quantitatively to the end face of a ceramic or metal substrate;

[0015] The substrate coated with the coating slurry is dried and then calcined until the coating slurry solidifies on the substrate to obtain the noble metal catalyst.

[0016] Furthermore, the noble metal is one or a combination of several of Pt, Pd, Rh, Ir, Ru, and Au, and the noble metal exists in the form of nitrate, chlorate, or organic complex salt.

[0017] Furthermore, the catalytic material is Al2O3, CeO2, ZrO2, Y2O3, La2O3, or Pr6O. 11 One or more of Nd2O3 mixed oxides or composite oxides, with a fresh specific surface area ≥20m² 2 / g.

[0018] Furthermore, the precipitant is one or a combination of several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and iminourea.

[0019] Furthermore, the reducing agent is one or a combination of several of ascorbic acid, glucose, fructose, maltose, formaldehyde, formic acid, ethylene glycol, and glycerol.

[0020] Furthermore, the acid solution is one or more of glacial acetic acid, dilute nitric acid, and oxalic acid.

[0021] Furthermore, the binder is one or a mixture of two of aluminum sol and zirconium sol, with a binder mass fraction of 20%-25%, a D50 of 2-20 nm, and a pH of 2-5.

[0022] Furthermore, the auxiliary agent is one or a mixture of two of barium salts and strontium salts.

[0023] Furthermore, the thickener is one or a mixture of more than one of methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose.

[0024] Furthermore, the coating slurry is a mixture of one or more precious metal catalyst slurries, and the coating dry basis coating amount is 10-350 g / L.

[0025] In summary, the present invention has the following advantages compared with the prior art:

[0026] 1. Compared with existing processes, the catalyst prepared by the present invention can fix the precious metal in situ at the pre-precipitation position, avoiding the migration or precipitation of precious metals during the drying or slurrying process, as well as the migration of precious metals in multi-precious metal mixed slurry. It can improve the dispersion state of the active components after use in high temperature environment, thereby improving the anti-aging performance of the catalyst.

[0027] 2. In the method of the present invention, no high polymer organic matter is added during the catalyst preparation process, thus avoiding the rupture of the support during the calcination process of the catalytic unit.

[0028] 3. This invention adopts a one-step slurry forming process, which reduces the drying and calcination fixation process after loading precious metals. The operation process is simple, the energy consumption is low, and it is easy to realize industrial-scale production. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0030] Figure 1 This is a schematic diagram showing the change in CO conversion rate of fresh catalysts with temperature in Examples 1 and 1 of the present invention.

[0031] Figure 2 This is a schematic diagram showing the change in NO conversion rate of fresh catalysts with temperature in Examples 1 and 1 of the present invention.

[0032] Figure 3 This is a schematic diagram showing the change in the conversion rate of THC by fresh catalysts as a function of temperature in Examples 1 and 1 of the present invention.

[0033] Figure 4 This is a schematic diagram showing the change in CO conversion rate of the aged catalysts in Example 1 and Comparative Example 1 as a function of temperature in the present invention.

[0034] Figure 5 This is a schematic diagram showing the change in NO conversion rate of the aged catalysts in Example 1 and Comparative Example 1 as a function of temperature in the present invention.

[0035] Figure 6 This is a schematic diagram showing the change in the conversion rate of THC to THC by the aged catalysts of Example 1 and Comparative Example 1 as a function of temperature in the present invention.

[0036] Figure 7 This is a process flow diagram of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0038] like Figure 7 As shown, a method for preparing noble metal catalysts based on precipitation-reduction includes the following steps: a catalyst material with a D50 of 1-10 μm, a noble metal solution, water, and a precipitant are mixed and dispersed under stirring, the pH of the mixture is controlled at 8-14, and the mixture is stirred and matured at room temperature for 1-12 hours to obtain a precipitated slurry; a reducing agent with a molar mass of 1.1-5 times the amount of noble metal is dissolved in deionized water to obtain a reducing agent solution; the reducing agent solution is added dropwise to the precipitated slurry under a water bath at 0-90℃. In a process involving stirring and reduction for 1-12 hours, a noble metal catalyst slurry is obtained. The noble metal catalyst slurry is then mixed with a binder, acid solution, additives, and thickener, and stirred for 5-30 minutes to obtain a coating slurry. The solid content of the coating slurry is 25%-40%, and the viscosity is 1000-3500 mPa·s. The coating slurry is then applied quantitatively to the end face of a ceramic or metal substrate. After drying the substrate coated with the coating slurry, it is calcined until the coating slurry is cured on the substrate to obtain the noble metal catalyst.

[0039] Furthermore, the noble metal is one or a combination of several of Pt, Pd, Rh, Ir, Ru, and Au, and the noble metal exists in the form of nitrate, chlorate, or organic complex salt.

[0040] Furthermore, the catalytic material is Al2O3, CeO2, ZrO2, Y2O3, La2O3, or Pr6O. 11 One or more of Nd2O3 mixed oxides or composite oxides, with a fresh specific surface area ≥20m² 2 / g.

[0041] Furthermore, the precipitant is one or a combination of several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and iminourea.

[0042] Furthermore, the reducing agent is one or a combination of several of ascorbic acid, glucose, fructose, maltose, formaldehyde, formic acid, ethylene glycol, and glycerol.

[0043] Furthermore, the acid solution is one or more of glacial acetic acid, dilute nitric acid, and oxalic acid.

[0044] Furthermore, the binder is one or a mixture of two of aluminum sol and zirconium sol, with a binder mass fraction of 20%-25%, a D50 of 2-20 nm, and a pH of 2-5.

[0045] Furthermore, the auxiliary agent is one or a mixture of two of barium salts and strontium salts.

[0046] Furthermore, the thickener is one or a mixture of more than one of methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose.

[0047] Furthermore, the coating slurry is a mixture of one or more precious metal catalyst slurries, and the coating dry basis coating amount is 10-350 g / L. It should be noted that the coating dry basis coating amount is the same as the coating amount after the substrate is calcined.

[0048] To further illustrate this application, more specific embodiments and comparative examples are provided below.

[0049] Example 1:

[0050] Fresh material with a specific surface area of ​​80m² under stirring conditions. 2 99g of Ce-Zr material with a density of / g and a D50 of 6μm was completely dispersed in deionized water. Palladium nitrate solution (1g as palladium oxide) was dissolved in deionized water. The treated palladium nitrate solution and tetramethylammonium hydroxide were added to the above mixed slurry using a peristaltic pump to adjust the pH of the mixture to 11. After stirring and maturing at room temperature for 3 hours, a precipitated mixed slurry was obtained. Formic acid solution (stoichiometric ratio of formic acid to precious metal 2:1) was diluted with deionized water to obtain a reducing agent solution. The reducing agent solution was added to the above precipitated mixed slurry using a peristaltic pump. A noble metal catalyst slurry was obtained by stirring and reducing at room temperature for 2 hours. 6.25 g of dilute nitric acid, 24.3 g of barium acetate, 0.5 g of carboxymethyl cellulose, and 25 g of aluminum sol (25% by mass, D50 10 nm, pH 3) were added to the noble metal catalyst slurry and stirred for 20 minutes. Water was added to adjust the solid content, resulting in a coating slurry with a solid content of 35% and a viscosity of 2690 mPa·s. The coating slurry was coated onto a cordierite substrate, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours to obtain catalyst 1. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours. Samples were taken to test the content of the noble metal palladium (denoted as A). Samples from the other group were taken to test the dispersion of the noble metal palladium (denoted as B).

[0051] Example 2:

[0052] Fresh material with a specific surface area of ​​80m² under stirring conditions. 2 49.5g Ce-Zr material with a density of / g and a D50 of 6μm and a fresh specific surface area of ​​140m 249.5 g of La-Al material with a density of / g and a D50 of 6 μm was completely dispersed in deionized water. Palladium nitrate solution (1 g as palladium oxide) was dissolved in deionized water and divided into two portions. The treated palladium nitrate solution and tetramethylammonium hydroxide were added to the Ce-Zr and La-Al material slurries respectively using a peristaltic pump to adjust the pH to 11. After stirring and maturing at room temperature for 3 hours, formic acid solution (stoichiometric ratio to precious metal 2:1) was diluted with deionized water and divided into two portions. These were then added to the Ce-Zr and La-Al material slurries respectively using a peristaltic pump. La-Al material slurry was prepared and reduced at room temperature for 2 hours to obtain mixed slurries E and F. Slurry E and slurry F were mixed, and 6.25 g of dilute nitric acid, 24.3 g of barium acetate, 0.5 g of carboxymethyl cellulose, and 25 g of aluminum sol with a mass fraction of 25%, a D50 of 10 nm, and a pH of 3 were added. The mixture was stirred for 20 minutes, and water was added to adjust the solid content, resulting in a coating slurry with a solid content of 35% and a viscosity of 3150 mPa·s. The coating slurry was coated onto a cordierite matrix, dried at 150 °C for 2 hours, and calcined at 550 °C for 2 hours to obtain catalyst 2. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150 °C for 2 hours, and calcined at 550 °C for 2 hours. Samples were taken to test the content of the precious metal palladium, denoted as A. Samples were taken from the other group to test the dispersion of the precious metal palladium, denoted as B.

[0053] Comparative Example 1:

[0054] The pH of the palladium nitrate solution (1 g based on palladium oxide) was adjusted to 11.0 by adding tetramethylammonium hydroxide. The treated palladium nitrate precursor solution was then loaded onto a fresh substrate with a specific surface area of ​​80 m² using the initial wet, equal-volume impregnation method. 2 The catalyst was dried at 120℃ for 2 hours and then calcined at 550℃ for 2 hours on 99g / g Ce-Zr material. The calcined catalyst was then mixed with 200g water, 6.25g dilute nitric acid, 24.3g barium acetate, 0.5g carboxymethyl cellulose, and 25g aluminum sol (25% by mass), with a D50 of 10nm and a pH of 3, and stirred for 20 minutes to obtain a coating slurry with a solid content of 35% and a viscosity of 1860mPa·s. This slurry was coated onto a cordierite matrix, dried at 150℃ for 2 hours, and then calcined at 550℃ for 2 hours to obtain catalyst R1. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150℃ for 2 hours, and then calcined at 550℃ for 2 hours. Samples were taken from this group to test the palladium content (denoted as A). Samples from the other group were taken to test the palladium dispersion (denoted as B).

[0055] Comparative Example 2:

[0056] Fresh material with a specific surface area of ​​80m² under stirring conditions. 299g of Ce-Zr material with a density of / g and a D50 of 6μm was dispersed in deionized water. Tetramethylammonium hydroxide was added using a peristaltic pump to adjust the pH to 11. Palladium nitrate solution (1g as palladium oxide) was dissolved in deionized water and added to the mixture using a peristaltic pump. The pH was finely adjusted to 11 with 0.1mol / L tetramethylammonium hydroxide solution, and the mixture was stirred and matured at room temperature for 5 hours. Then, 6.25g of dilute nitric acid, 24.3g of barium acetate, 0.5g of carboxymethyl cellulose, and 25g of aluminum sol (25% by mass, D50 10nm, pH 3) were added and stirred for 20 minutes. Water was added to adjust the solids content, resulting in a coating slurry with a solids content of 35% and a viscosity of 2730 Pa·s. The coating slurry was coated onto a cordierite substrate, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours to obtain catalyst R2. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours. The content of the precious metal palladium was then tested and recorded as A. The other group was sampled and the dispersion of the precious metal palladium was tested and recorded as B.

[0057] Comparative Example 3:

[0058] Fresh material with a specific surface area of ​​80m² under stirring conditions. 2 99g of Ce-Zr material with a density of / g and a D50 of 6μm was dispersed in deionized water. Tetramethylammonium hydroxide was added using a peristaltic pump to adjust the pH to 11. Palladium nitrate solution (1g as palladium oxide) was dissolved in deionized water and added to the mixture using a peristaltic pump. The pH was then finely adjusted to 11 with 0.1mol / L tetramethylammonium hydroxide solution. After stirring and aging at room temperature for 5 hours, the mixture was filtered, washed, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours. The calcined catalyst was then mixed with 200g of water, 6.25g of dilute nitric acid, 24.3g of barium acetate, 0.5g of carboxymethyl cellulose, and 25g of aluminum sol (25% by mass), with a D50 of 10nm and a pH of 3. The mixture was stirred for 20 minutes to obtain a coating slurry with a solid content of 35% and a viscosity of 2050mPa·s. The coating slurry was coated onto a cordierite matrix, dried at 150°C for 2 hours, and calcined at 550°C for 2 hours to obtain catalyst R3. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150°C for 2 hours, and calcined at 550°C for 2 hours. Samples were taken to test the content of the precious metal palladium, denoted as A. Samples from the other group were taken to test the dispersion of the precious metal palladium, denoted as B.

[0059] Comparative Example 4:

[0060] Fresh material with a specific surface area of ​​80m² under stirring conditions. 299g of Ce-Zr material with a density of / g and a D50 of 6μm was dispersed in deionized water. Then, 1g of palladium nitrate solution (calculated as palladium oxide) was dissolved in deionized water. The treated palladium nitrate solution was added to the Ce-Zr material slurry using a peristaltic pump. After stirring for 3 hours, PVP (stoichiometric ratio of 3:1 with the noble metal) as a protective agent and formic acid (stoichiometric ratio of 2:1 with the noble metal) as a reducing agent were gradually added using a peristaltic pump. The mixture was stirred and reduced at room temperature for 2 hours. Then, 6.25g of dilute nitric acid, 24.3g of barium acetate, 0.5g of carboxymethyl cellulose, and 25g of aluminum sol (25% by mass, D50 10nm, pH 3) were added and stirred for 20 minutes. Water was added to adjust the solid content, resulting in a coating slurry with a solid content of 35% and a viscosity of 2250 mPa·s. The coating slurry was coated onto a cordierite substrate, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours to obtain catalyst R4. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours. The content of the precious metal palladium was then tested and recorded as A. The other group was sampled and the dispersion of the precious metal palladium was tested and recorded as B.

[0061] Comparative Example 5:

[0062] Fresh material with a specific surface area of ​​80m² under stirring conditions. 2 / g, D50 of 49.5g Ce-Zr material slurry and fresh specific surface area of ​​140m 2 49.5g of La-Al material slurry with a density of / g and a D50 of 6μm was completely dispersed in deionized water. Palladium nitrate solution (1g as palladium oxide) was dissolved in deionized water and divided into two portions. The treated palladium nitrate solution and tetramethylammonium hydroxide were added separately to the Ce-Zr and La-Al material slurries using a peristaltic pump to adjust the pH to 11. After stirring and maturing at room temperature for 5 hours, slurries C and D were obtained. Slurries C and D were mixed, and 6.25g of dilute nitric acid, 24.3g of barium acetate, 0.5g of carboxymethyl cellulose, and 25g of aluminum sol (25% by mass, D50 10nm, pH 3) were added. The mixture was stirred for 20 minutes, and water was added to adjust the solid content, resulting in a coating slurry with a solid content of 35% and a viscosity of 3100 mPa·s. The coating slurry was coated onto a cordierite substrate, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours to obtain catalyst R5. The remaining coating slurry was divided into two groups. One group was filtered, washed, dried at 150℃ for 2 hours, and calcined at 550℃ for 2 hours. The content of the precious metal palladium was then tested and recorded as A. The other group was sampled and the dispersion of the precious metal palladium was tested and recorded as B.

[0063] It should be noted that in the embodiments and comparative examples of this application, the substrate for catalyst coating is... Cordierite with a density of 118.41*80 / 400 cpsi and a volume of 0.8805 L was used. The coating amount on a dry basis was 88.3 g / L, and the precious metal loading was 0.706 g / L. The precious metal content was determined by ICP testing to obtain the concentration of precious metals in the coating slurry, and the precious metal loading rate G was calculated. A comparison table of the precious metal content in the coatings of the examples and comparative examples is shown in Table 2. Precious metal loading rate (G) = Precious metal concentration in the coating after washing, drying, and calcination (A) / Theoretical precious metal concentration in the coating (H).

[0064] Table 1 Comparison of catalyst preparation processes between the examples and comparative examples

[0065]

[0066] Table 2 Comparison of precious metal content in coatings of the examples and comparative examples.

[0067]

[0068]

[0069] As shown in Tables 1 and 2, compared with Comparative Example 1, Example 1 adopted a one-step slurry-forming process, reducing the drying and calcination process of precious metal fixation and significantly reducing energy consumption. Compared with Comparative Example 2, Example 1 further fixed the precious metal onto the catalyst material through reduction on the basis of precipitation, solving the problem of precious metal precipitation during the slurry-forming process and significantly improving the precious metal loading rate in the coating. Compared with Comparative Example 3, Example 1 further fixed the precious metal onto the catalyst material through reduction on the basis of precipitation, solving the problem of high energy consumption in the precious metal curing process. Compared with Comparative Example 4, Example 1 fixed the precious metal onto the catalyst material through a precipitation-reduction method, avoiding the use of high-polymer organic protective agents and solving the risk of unit breakage during the calcination process of the catalyst unit. Compared with Comparative Example 5, Example 2 fixed the precious metal onto the corresponding catalyst material through a precipitation-reduction method, avoiding the precipitation and migration problems of precious metal during the slurry mixing process, improving the precious metal loading rate, and enabling better matching between the catalyst material and the corresponding precious metal.

[0070] In the embodiments and comparative examples of this application, two 1-inch * 1-inch cylinders were taken from each substrate for activity testing. The aging samples were obtained by aging at 950°C in air for 10 hours.

[0071] Dispersion test conditions:

[0072] Referring to Shen M's method for excluding CeO2, the dispersion of precious metals was determined by CO-Pulse after subtracting the interference of Ce on precious metals using CO2.

[0073] Literature: Shen M, Wei G, Yang H, et al. Different selections of active sites for CO, C3H6, and C10H22 oxidation on Pd / CeO2 catalysts[J]. Fuel, 2013, 103: 869-875.

[0074] Activity test conditions:

[0075] Atmosphere: CO 4500ppm, NO 1250ppm, CO2 11.0%, H2O 10.0%, O2 3800ppm, C3H6 220ppm, C3H8 110ppm, H2 1500ppm, N2 as balance gas, λ = 1, space velocity 40000h -1 After activation at 600℃ in a full atmosphere for 2 hours, the temperature was lowered to below 150℃ for a transient heating test at a rate of 5℃ / min. In the table below, T50 represents the temperature at which the conversion rate reaches 50%, also known as the ignition temperature, and T90 represents the temperature at which the conversion rate reaches 90%, also known as the complete conversion temperature. The simplified reaction formulas for each component are as follows:

[0076] CO+O2—CO2; HC+O2—H2O+CO2; NO+CO+HC—N2+CO2+H2O

[0077] Table 3 Comparison of precious metal dispersion between the examples and comparative examples

[0078]

[0079] Table 4 Comparison of catalyst activities in each example and comparative example

[0080]

[0081] As shown in Table 3, compared with Comparative Examples 1-4, and with Comparative Example 2, the fresh dispersion of noble metals in the prepared slurry coatings did not differ significantly. However, after effectively controlling and solidifying the state of the noble metals on the catalyst material through precipitation-reduction, the aging dispersion of noble metals in the prepared slurry coatings was improved to some extent. Further, the performance data in Table 4 show that the examples reduced both the fresh and aged ignition temperatures and the complete conversion temperature of CO / THC / NO, indicating improved catalytic conversion efficiency. Comparative Example 1, due to the lack of control over the size of the precious metal during the loading process, resulted in the embedding of the precious metal after high-temperature aging, leading to poor anti-aging performance. Comparative Examples 2 and 5, due to the lack of effective fixation of the precious metal, resulted in the aggregation of precious metal particles after high-temperature aging, further deteriorating anti-aging performance. Comparative Example 3 fixed the precious metal onto the catalyst material through drying and calcination, but the drying process caused the migration of the precious metal, resulting in poor anti-aging performance. Comparative Example 4 controlled the size of the precious metal and fixed it onto the catalyst material through reduction, resulting in better anti-aging performance, but the process required the addition of a large amount of organic matter. In contrast, all examples first controlled the size of the precious metal through pre-precipitation to precipitate it onto the catalyst material, and then fixed the precious metal through in-situ reduction. The entire process effectively controlled the precious metal, improved the aging dispersion of the precious metal, and thus further improved the anti-aging performance of the catalyst.

[0082] like Figures 1 to 3 As shown, the conversion rates of CO, NO, and THC by the fresh catalysts of Example 1 and Comparative Example 1 vary with temperature; where the vertical axis represents the conversion rate in % and the horizontal axis represents the temperature in °C; curves A and B represent the changes in the fresh samples of Example 1 and Comparative Example 1, respectively. Figures 4 to 6 The conversion rates of CO, NO, and THC by the aged catalysts of Example 1 and Comparative Example 1 as a function of temperature are shown. The vertical axis represents the conversion rate in % and the horizontal axis represents the temperature in °C. Curves Aa and Ba represent the changes in the aged samples of Example 1 and Comparative Example 1, respectively.

[0083] from Figures 1-6 It is evident that, compared to Comparative Example 1, both the fresh and aged catalysts in Example 1 exhibit superior ignition performance and high-temperature conversion rates for CO, NO, and THC. This demonstrates that the catalyst of the present invention possesses excellent ignition performance and anti-aging properties.

[0084] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing noble metal catalysts based on precipitation-reduction, characterized in that, Includes the following steps: Under stirring, the catalyst material with D50 in the range of 1-10 μm, the noble metal solution, water and the precipitant are mixed and dispersed. The pH of the mixture is controlled at 8-14, and the mixture is stirred and matured at room temperature for 1-12 h to obtain a precipitated mixed slurry. Dissolve a reducing agent with a molar mass of 1.1-5 times that of the precious metal in deionized water to obtain a reducing agent solution; Under a water bath at 0-90℃, the reducing agent solution is added dropwise to the precipitated mixed slurry and stirred for 1-12 hours to obtain the noble metal catalyst slurry. The precious metal catalyst slurry is mixed with binder, acid solution, additives and thickener, and stirred for 5 to 30 minutes to obtain a coating slurry. The solid content of the coating slurry is 25% to 40% and the viscosity is 1000 to 3500 mPa·s. The coating slurry is applied quantitatively to the end face of a ceramic or metal substrate; The substrate coated with the coating slurry is dried and then calcined until the coating slurry solidifies on the substrate to obtain the noble metal catalyst.

2. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The noble metal is one or a combination of several of Pt, Pd, Rh, Ir, Ru, and Au, and the noble metal exists in the form of nitrate, chlorate, or organic complex salt.

3. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The catalyst is Al2O3, CeO2, ZrO2, Y2O3, La2O3, Pr6O 11 One or more of Nd2O3 mixed oxides or composite oxides, with a fresh specific surface area ≥20m² 2 / g.

4. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The precipitant is one or a combination of several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and iminourea.

5. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The reducing agent is one or a combination of several of the following: ascorbic acid, glucose, fructose, maltose, formaldehyde, formic acid, ethylene glycol, and glycerol.

6. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The acid solution is one or more of glacial acetic acid, dilute nitric acid, and oxalic acid.

7. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The binder is one or a mixture of two of aluminum sol and zirconium sol, with a binder mass fraction of 20%-25%, a D50 of 2-20 nm, and a pH of 2-5.

8. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The additive is one or a mixture of two of barium salts and strontium salts.

9. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The thickener is one or a mixture of more than one of methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose.

10. The method for preparing noble metal catalysts based on precipitation-reduction according to claim 1, characterized in that, The coating slurry is a mixture of one or more precious metal catalyst slurries, and the coating dry basis coating amount is 10-350 g / L.

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