High-thermal-stability noble metal catalyst and preparation method thereof

Abstract

The application relates to the technical field of catalyst preparation, and particularly discloses a high-thermal-stability noble metal catalyst and a preparation method thereof. The catalyst comprises a catalyst matrix and a coating. The coating comprises a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material. The porous protective layer is silicon dioxide, the thickness of the porous protective layer is 2-50 nm, and the pore size of the porous protective layer is 2-10 nm. In the process of using the catalyst or when the catalyst is subjected to high-temperature calcination, the porous protective layer of silicon dioxide can isolate the noble metal, can effectively control the size of the noble metal nanoparticles after aging, can prevent the migration and agglomeration of the noble metal in a large area, can improve the thermal stability of the noble metal catalyst, can guarantee the durability of the catalyst, can effectively repel SO2 in tail gas, can prevent SO2 from combining with the noble metal nanoparticles or the catalytic material to cause sulfur poisoning and reduce performance, and can further improve the catalytic performance and sulfur resistance of the catalyst.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalyst preparation, in particular to a high-thermal-stability noble metal catalyst and a preparation method thereof. BACKGROUND

[0002] Most of the existing automobile exhaust aftertreatment catalysts are mainly supported noble metal catalysts, and the number of effective active centers determines the activity of the catalysts. In particular, in the fierce competitive environment, the loading amount of noble metal in the noble metal catalysts is getting lower and lower. GB 17691-2018 stipulates that the endurance mileage of heavy-duty vehicles is 700,000 kilometers, and GB 18352-2016 stipulates that the endurance mileage of light-duty vehicles is 200,000 kilometers, which is a great challenge to the endurance performance of the aftertreatment catalysts. The noble metal catalysts are in the exhaust pipe of the engine, and are prone to high-temperature sintering of noble metals or collapse of catalytic materials, agglomeration or burying of active centers, thereby reducing the performance of the catalysts, because they are in the high-temperature exhaust for a long time. Meanwhile, various chemical elements such as S, P and Ca in the exhaust due to engine oil or fuel can also cause chemical poisoning or sulfur poisoning of the active centers, thereby reducing the performance of the catalysts. In order to not reduce the initial activity of the noble metal catalysts, high dispersion technology is needed to ensure sufficient active centers, and the higher the dispersion degree of noble metals in the catalysts, the smaller the noble metal nanoparticles. According to the principle of thermodynamics, the smaller the nanoparticles, the higher the surface chemical potential, and the more prone to agglomeration in the use process or high-temperature environment. Therefore, in addition to using high dispersion technology to ensure the activity of the catalysts, noble metal stabilization technology is also needed to ensure the endurance performance of the catalysts, and it is extremely challenging to improve the endurance performance of the automobile exhaust aftertreatment catalysts.

[0003] The sintering of the active centers of the noble metal catalysts is mainly affected by thermodynamic and kinetic factors, and the main ways to control the sintering of noble metals are: 1. Controlling the uniformity of the size of noble metal particles to reduce the migration of particles caused by thermodynamic factors; 2. Using the strong interaction between the metal and the carrier to improve the stability of the noble metal particles, which is to prevent the migration of noble metals by using the strong chemical bonding effect between the metal and the carrier; 3. Using mechanical confinement to control the migration of noble metal particles; 4. Using energy barriers to prevent the migration of noble metal particles. Among them, the strong interaction between the metal and the carrier. The mechanical confinement mode is to confine the noble metal nanoparticles in a fixed position, and the reactants and products can normally diffuse in and out, but the noble metal nanoparticles cannot migrate due to the interception of surrounding atoms at high temperatures, thereby preventing the growth of noble metal particles. Especially in the use environment of automobile exhaust catalysts, the exhaust temperature is high, and the noble metal nanoparticles are prone to migration and sintering. If the mechanical confinement mode is adopted, the noble metal nanoparticles are locked in fixed adsorption sites, and the migration probability is reduced at high temperatures, thereby improving the stability of the catalysts.

[0004] The noble metal catalyst active center sintering prevention by mechanical confinement mode needs to limit the noble metal nanoparticles in fixed position, and then protect the noble metal nanoparticles from migration at high temperature by protective layer, and the protective layer needs to enable the reactants and products to diffuse in and out normally, but the existing catalysts cannot achieve the above. SUMMARY

[0005] The present application aims to overcome the above-mentioned deficiencies in the prior art, and provides a high-thermal-stability noble metal catalyst and a preparation method thereof.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] A high-thermal-stability noble metal catalyst, comprising a catalyst substrate and a coating layer coated on the catalyst substrate, the coating layer comprising a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material, wherein the porous protective layer is a silica layer, the thickness of the porous protective layer is 2-50 nm, and the pore size of the porous protective layer is 2-10 nm.

[0008] In the technical solution of the present application, the coating layer on the catalyst comprises a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material, wherein the silica is uniformly distributed on the catalytic material containing noble metal, forming a porous silica protective layer, and the thickness of the porous protective layer is limited to 2-50 nm and the pore size is limited to 2-10 nm, which can ensure that the reactant gas and product can smoothly pass through the porous protective layer. During the use of the catalyst or after high-temperature calcination, the porous silica protective layer can isolate the noble metal, effectively control the size of the noble metal nanoparticles after aging, prevent the migration and agglomeration of the noble metal in a large area, improve the thermal stability of the noble metal catalyst, and ensure the durability of the catalyst. At the same time, the uniformly distributed porous silica protective layer is acidic, and the addition of silica can improve the acidity of the catalyst, promote the adsorption of the reactants, enhance the interface interaction between silica and the noble metal active component, effectively repel SO2 in the tail gas, prevent SO2 from combining with noble metal nanoparticles or catalytic material to cause sulfur poisoning and reduce performance, and further improve the performance and sulfur resistance of the catalyst.

[0009] As a preferred scheme of the present application, the noble metal in the noble metal active component is one or more of Pt, Pd, Rh, Ru, Au, and Ag.

[0010] As a preferred scheme of the present application, the content of the noble metal active component is 1-100 g / ft 3 . More preferably, the content of the noble metal active component is 10-60 g / ft 3 .

[0011] As a preferred scheme of the present application, the catalytic material is a metal oxide, and the metal oxide is one or more composite element oxides of aluminum oxide, cerium oxide, zirconium oxide, and silicon oxide. In the above technical scheme, the noble metal active component is distributed on the metal oxide catalytic material, the SiO2 protective layer is uniformly distributed on the surface of the metal oxide loaded with the noble metal, does not combine with the noble metal, is adsorbed on part of the adsorption sites of the metal oxide, and exists in a reticular structure.

[0012] As a preferred scheme of the present application, the thickness of the porous protective layer is 10-30 nm. More preferably, the thickness of the porous protective layer is 20-25 nm.

[0013] As a preferred scheme of the present application, the pore size of the porous protective layer is 2-6 nm. More preferably, the pore size of the porous protective layer is 4-5 nm.

[0014] As a preferred scheme of the present application, the SiO2 of the porous protective layer accounts for 0.1% to 10% of the total mass of the catalyst. More preferably, the SiO2 of the porous protective layer accounts for 1% to 4% of the total mass of the catalyst.

[0015] As a preferred scheme of the present application, the catalyst is a diesel oxidation type catalyst (DOC).

[0016] Another aspect of the present application provides a preparation method of a high-thermal-stability noble metal catalyst, comprising the following steps:

[0017] Step S1, preparation of a noble metal catalytic material: dispersing a noble metal precursor solution on the catalytic material, stirring for 0.5-4 hours after adding a dispersing agent, then adding a reducing agent and stirring for 1-5 hours to obtain the noble metal catalytic material;

[0018] Preparation of a silicone sol: adding a surfactant to water, heating and stirring to dissolve, continuously adding a silicon source to the solution, and stirring to form a light blue silicone sol;

[0019] Step S2, slurry preparation of the noble metal catalytic material, then adding the silicone sol, stirring uniformly, adding a first binder and adjusting the pH of the slurry to 4-8 to obtain a first slurry;

[0020] Step S3, coating the first slurry on the catalyst substrate, drying, and calcining to obtain a noble metal catalyst with a porous protective layer.

[0021] In the technical scheme, the noble metal active component is first prepared to be dispersed on the surface of the catalytic material, then a porous silica protective layer is coated on the surface of the noble metal catalytic material, and then coating and calcination are performed to obtain the noble metal catalyst. The high dispersion technology is used to ensure the initial activity of the low noble metal catalyst, the mechanical confinement mode is used to prevent the migration and sintering of the noble metal, the pore size and thickness of the porous silica protective layer are controlled to ensure the diffusion of the reactant and product gas, and thus the good initial activity and durability of the catalyst are ensured.

[0022] As a preferred scheme of the present application, the noble metal precursor solution is one of noble metal nitrate, chlorate and organic salt, such as platinum nitrate, tetraamine platinum nitrate, platinum chloride, palladium nitrate, tetraamine palladium nitrate and palladium chloride.

[0023] As a preferred scheme of the present application, the noble metal precursor solution is dispersed on the catalytic material by using an excess impregnation method in step S1.

[0024] As a preferred scheme of the present application, the dispersant is one or more of polyvinyl alcohol, polyvinylpyrrolidone and carboxymethyl cellulose. More preferably, the molar ratio of the dispersant (calculated as monomer) to the noble metal catalytic material ranges from 1 to 10.

[0025] As a preferred scheme of the present application, the reducing agent is one or more of NaBH4, hydrazine hydrate, citric acid and formaldehyde. More preferably, the molar ratio of the reducing agent to the noble metal catalytic material ranges from 1 to 10.

[0026] As a preferred scheme of the present application, the surfactant is one of polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, cetyltrimethylammonium chloride and cetyltrimethylammonium bromide (CTAB).

[0027] As a preferred scheme of the present application, the silicon source is one of tetraethyl orthosilicate (TEOS), sodium metasilicate nonahydrate and silica sol.

[0028] As a preferred scheme of the present application, the molar ratio of the noble metal catalytic material to the silicon source ranges from 100 to 10:1, and the molar ratio of the surfactant to the silicon source ranges from 10:1 to 1:10. In the preparation of the catalyst, the thickness and pore size of the porous protective layer are adjusted by controlling the amount and ratio of the surfactant and the silicon source.

[0029] As a preferred scheme of the present application, in the preparation of the first slurry, the first binder includes one or more of aluminum sol, silica sol, zirconium sol and self-made sol, and the mass ratio of the first binder is 2-10%.

[0030] As a preferred scheme of the present application, in step S3, the dry coating layer has a loading of 50-150 g / L, and then is dried. Further, the drying condition is 60-150℃ for 1-2h.

[0031] As a preferred scheme of the present application, in step S3, the drying condition after coating the slurry is 120-150℃ for 5-20min.

[0032] As a preferred scheme of the present application, in step S3, the calcination condition is 400-600℃ for 1-2h.

[0033] Compared with the prior art, the present application has the following advantages:

[0034] 1. The present application provides a high-thermal-stability noble metal catalyst, the coating layer on the catalyst comprises a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material, wherein the silica is uniformly distributed on the catalytic material containing noble metal, and is a porous silica protective layer, and the thickness of the porous protective layer is limited to 2-50nm, and the pore size is 2-10nm, so that the reactant gas and product can smoothly pass through the porous protective layer, and the porous silica protective layer can isolate the noble metal during the use of the catalyst or during the high-temperature calcination, so as to effectively control the size of the noble metal nanoparticles after aging, prevent the migration and agglomeration of the noble metal in a large area, improve the thermal stability of the noble metal catalyst, and ensure the durability of the catalyst.

[0035] 2. The uniformly distributed silica porous protective layer on the catalyst is acidic, and the addition of silica can improve the acidity of the catalyst, promote the adsorption of the reactants, enhance the interface interaction between the silica and the noble metal active component, and also effectively repel SO2 in the tail gas, prevent SO2 from combining with the noble metal nanoparticles or the catalytic material to cause sulfur poisoning and reduce performance, and further improve the performance and sulfur resistance of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 SEM image of the noble metal catalyst with a silica protective layer of Example 1;

[0037] Figure 2 SEM image of the noble metal catalyst without a silica protective layer of Comparative Example 1;

[0038] Figure 3 Catalytic schematic diagram of the noble metal catalyst with a silica protective layer of Example 1;

[0039] Figure 4 Aging schematic diagram of the noble metal catalyst with a silica protective layer of Example 1;

[0040] Figure 5 Schematic diagram of sulfur resistance of noble metal catalyst with silica protective layer for Example 1;

[0041] Figure 6 XRD comparison diagram of noble metal catalyst with and without silica protective layer for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0042] In order to more clearly describe the purposes, technical solutions and technical effect advantages of the application in the specific implementation cases of the application, the solutions in the specific examples will be described in detail below in combination with the drawings of the specification of the application. The specific technical solutions involved in the following specific examples are only for clearly and completely describing the innovative technical solutions of the application, and they are only a part of the specific implementation examples that can be adopted by the application, not all the examples, and should not be understood as a limitation on the innovative solutions of the application. Any solution that adopts the same inventive concept of the application should be included in the protection scope of the application.

[0043] Secondly, the related description of the drawings in the specific examples of the application is only for the convenience of the technicians to understand the solutions of the application, and some details in the drawings are shown for the convenience of clearly presenting the technical solutions, and should not be considered that all the technical features in the drawings must be included in the specific implementation cases, and even more cannot be considered as additional limitations on the innovative technical solutions of the application. The components in each of the examples described and shown in the drawings can be combined and arranged in different configurations, and these combinations and arrangements should be considered as part of all the examples of the innovative solutions of the application and included in the scope to be protected by the application.

[0044] In summary, the solutions or descriptions presented in the specific examples and drawings of the application are not intended to limit the scope of protection, but only to represent selected examples / cases to help technicians understand the related innovative solutions. Based on these examples, all other equivalent or parallel examples obtained by those skilled in the art without making creative efforts are within the scope of protection claimed by the application.

[0045] Example 1

[0046] The present embodiment provides a high-thermal-stability noble metal catalyst, which comprises a catalyst substrate and a coating layer coated on the catalyst substrate, the coating layer comprising a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material, the porous protective layer being silica.

[0047] The preparation method of the catalyst comprises the following steps:

[0048] S1, noble metal slurry configuration: take 7.4333g of platinum chloride and 3.7167g of palladium chloride (in terms of metal elements), add deionized water to a total of 1500ml, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85g of lanthanum modified alumina as a catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1h; take 100g of polyvinylpyrrolidone (PVP) dissolved in 200ml of water, and add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1h; take 10.87g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950g (dry basis) of the above slurry to a ball mill tank;

[0049] Take 50g of CTAB and dissolve it in 1000ml of water, heat to 60°C until completely dissolved, add 50g of TEOS dropwise to the CTAB solution, stir at 60°C for 4h, then stand overnight, after completion, a light blue sol is formed;

[0050] S2, add the light blue sol obtained in S2 to the noble metal catalytic material, stir at room temperature for 2h, and evaporate the excess water at 80°C; take 19.23g of silica sol (dry basis) and add it, ball mill, control D50 at 3-5 microns, solid content 40%, pH 4.5, to obtain a first slurry SA1.

[0051] S3, apply the first slurry SA1 to the catalyst substrate, the catalyst substrate uses a cordierite substrate, the substrate specification is ø25.4mm*25.4mm / 400cpsi-4mil, the loading amount is 100g / L, the noble metal loading amount is 30g / ft 3 , the noble metal ratio is 2:1, dry and calcine to obtain a noble metal catalyst S1 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 20-25nm, and the pore size of the porous protective layer is 4-5nm.

[0052] Example 2

[0053] This example provides a high-thermal-stability noble metal catalyst, and the catalyst structure is similar to that of Example 1, the difference being the porous protective layer.

[0054] The preparation method of the catalyst comprises the following steps:

[0055] S1, noble metal slurry configuration: take 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (in terms of metal elements), add deionized water to a total of 1500 ml, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85 g of lanthanum modified alumina as a catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1 h; take 100 g of polyvinylpyrrolidone (PVP) dissolved in 200 ml of water, and add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1 h; take 10.87 g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950 g (dry basis) of the above slurry to a ball mill tank;

[0056] Take 100 g of CTAB and dissolve it in 1000 ml of water, heat to 60°C until completely dissolved, add 100 g of TEOS dropwise to the CTAB solution, stir at 60°C for 4 h, then stand overnight, after completion, a light blue sol is formed;

[0057] S2, add the light blue sol obtained in S2 to the noble metal catalytic material, stir at room temperature for 2 h, and evaporate the excess water at 80°C; take 19.23 g of aluminum sol (dry basis) and add it, ball mill, control D50 at 3-5 microns, solid content 40%, pH 4.5, to obtain a first slurry SA2.

[0058] S3, apply the first slurry SA2 to the catalyst substrate, the catalyst substrate uses a cordierite substrate, the substrate specification is ø25.4mm*25.4mm / 400cpsi-4mil, the loading amount is 108 g / L, the noble metal loading amount is 30 g / ft 3 , the noble metal ratio is 2:1, dry, calcine at 500°C for 1 h, to obtain a noble metal catalyst S2 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 45-50 nm, and the pore size of the porous protective layer is 4-5 nm.

[0059] Example 3

[0060] This example provides a high-thermal-stability noble metal catalyst, the catalyst structure is similar to that of Example 1, the difference lies in the porous protective layer.

[0061] The preparation method of the catalyst comprises the following steps:

[0062] S1, noble metal slurry configuration: take 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (in terms of metal elements), add deionized water to a total of 1500 ml, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85 g of lanthanum modified alumina as a catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1 h; take 100 g of polyvinylpyrrolidone (PVP) dissolved in 200 ml of water, and add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1 h; take 10.87 g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950 g (dry basis) of the above slurry to a ball mill tank;

[0063] Take 25 g of CTAB and dissolve it in 1000 ml of water, heat to 60°C until completely dissolved, add 50 g of TEOS dropwise to the CTAB solution, stir at 60°C for 4 h, then stand overnight, after completion, a light blue sol is formed;

[0064] S2, add the light blue sol obtained in S2 to the noble metal catalytic material, stir at room temperature for 2 h, and evaporate the excess water at 80°C; take 19.23 g of silica sol (dry basis) and add it, ball mill, control D50 at 3-5 microns, solid content 40%, pH 4.5, to obtain a first slurry SA3.

[0065] S3, apply the first slurry SA3 to the catalyst substrate, the catalyst substrate uses a cordierite carrier, the carrier specification is ø25.4mm*25.4mm / 400cpsi-4mil, the loading is 100 g / L, the noble metal loading is 30 g / ft 3 , the noble metal ratio is 2:1, dry and calcine to obtain a noble metal catalyst S3 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 20-25 nm, and the pore size of the porous protective layer is 2-3 nm.

[0066] Example 4

[0067] This example provides a high-thermal-stability noble metal catalyst, and the catalyst structure is similar to that of Example 1, the difference being the porous protective layer.

[0068] The preparation method of the catalyst comprises the following steps:

[0069] S1, noble metal slurry configuration: take 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (in terms of metal elements), add deionized water to a total of 1500 ml, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85 g of lanthanum modified alumina as a catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1 h; take 100 g of polyvinylpyrrolidone (PVP) dissolved in 200 ml of water, and add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1 h; take 10.87 g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950 g (dry basis) of the above slurry to a ball mill tank;

[0070] Take 10 g of CTAB dissolved in 400 ml of water, heat to 60°C to completely dissolve, add 10 g of TEOS dropwise to the CTAB solution, stir at 60°C for 4 h, and then stand overnight, after completion, a light blue sol is formed;

[0071] S2, add the light blue sol obtained in S2 to the noble metal catalytic material, stir at room temperature for 2 h, and evaporate the excess water at a temperature of 80°C; take 19.23 g of silica sol (dry basis) and add it, ball mill, control D50 at 3-5 microns, solid content 40%, pH 4.5, to obtain a first slurry SA4.

[0072] S3, apply the first slurry SA4 to the catalyst substrate, the catalyst substrate uses a cordierite substrate, the substrate specification is ø25.4 mm*25.4 mm / 400 cpsi-4 mil, the loading amount is 97.4 g / L, the noble metal loading amount is 30 g / ft 3 , the noble metal ratio is 2:1, dry and calcine to obtain a noble metal catalyst S4 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 3-6 nm, and the pore size of the porous protective layer is 4-5 nm.

[0073] Comparative Example 1

[0074] This comparative example provides a high-thermal-stability noble metal catalyst, which is different from Example 1 in that no porous protective layer is provided on the catalyst of this comparative example.

[0075] The preparation method of the catalyst comprises the following steps:

[0076] S1, noble metal slurry configuration: take 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (calculated as metal elements), add a total of 1500 ml of deionized water, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85 g of lanthanum modified alumina as a first catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1 h; take 100 g of polyvinylpyrrolidone PVP dissolved in 200 ml of water, add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1 h; take 10.87 g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950 g (calculated on a dry basis) of the above slurry to a ball mill tank;

[0077] S2, take 19.23 g of silica sol (calculated on a dry basis) and add it to the noble metal catalytic material, ball mill, control the D50 at 3-5 microns, the solid content is 40%, and the pH is 4.5, to obtain a first slurry DA1.

[0078] S3, apply the first slurry DA1 to a catalyst substrate, the catalyst substrate uses a cordierite substrate, the substrate specification is ø25.4 mm*25.4 mm / 400 cpsi-4 mil catalyst substrate, the loading is 97 g / L, the noble metal loading is 30 g / ft 3 , the noble metal ratio is 4:1, dry and calcine to obtain a noble metal catalyst D1.

[0079] Comparative Example 2

[0080] This comparative example provides a high-thermal-stability noble metal catalyst, which is different from Example 1 in that the thickness of the porous protective layer on the catalyst of this comparative example is different.

[0081] The preparation method of the catalyst comprises the following steps:

[0082] S1, noble metal slurry configuration: take 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (calculated as metal elements), add a total of 1500 ml of deionized water, stir and mix uniformly to obtain a prepared first noble metal precursor solution; take 986.85 g of lanthanum modified alumina as a first catalytic material in a stirring tank, add the noble metal precursor solution to it, use an excess impregnation method, and stir for 1 h; take 100 g of polyvinylpyrrolidone PVP dissolved in 200 ml of water, add it to the suspension of the first noble metal precursor solution and the catalytic material, and stir for 1 h; take 10.87 g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is 37%; transfer 950 g (calculated on a dry basis) of the above slurry to a ball mill tank;

[0083] Take CTAB 150 g dissolved in 1000 ml water, heated to 60℃ completely dissolved, to the CTAB solution drop TEOS 150 g, keep 60℃ stirring 4h after standing overnight, complete after the formation of light blue sol;

[0084] S2, the light blue sol obtained in S2 is added to the noble metal catalytic material, stirred at room temperature for 2h, and the excess water is evaporated by heating to 80℃; take 19.23g silica sol (dry basis) and add, ball mill, D50 control in 3-5 microns, solid content 40%, pH 4.5, get the first slurry DA2.

[0085] S3, the first slurry DA2 is coated on the catalyst substrate, the catalyst substrate adopts cordierite substrate, the substrate specification is catalyst substrate ø25.4mm*25.4mm / 400cpsi-4mil, the loading capacity is 105g / L, the noble metal loading capacity is 30g / ft 3 , the noble metal ratio is 2:1, dried and calcined, to get the noble metal catalyst D2 with porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 65-75nm, and the pore size of the porous protective layer is 4-5nm.

[0086] Comparative example 3

[0087] This comparative example provides a high thermal stability noble metal catalyst, which is different from example 1 in that the pore size of the porous protective layer on the catalyst of this comparative example is different.

[0088] The preparation method of the catalyst comprises the following steps:

[0089] S1, noble metal slurry configuration: take 7.4333g of platinum chloride and 3.7167g of palladium chloride (calculated as metal), add deionized water to a total of 1500ml, stir and mix uniformly to obtain the prepared first noble metal precursor solution; take 986.85g of lanthanum modified alumina as the first catalytic material in the stirring tank, add the noble metal precursor solution to it, use the excess impregnation method, stir for 1h; take 100g of polyvinylpyrrolidone PVP dissolved in 200ml of water, add it to the suspension of the first noble metal precursor solution and the catalytic material, stir for 1h; take 10.87g of hydrazine hydrate, after stirring is completed, the solid content of the slurry is measured to be 37%; transfer 950g (dry basis) of the above slurry to a ball mill tank;

[0090] Take CTAB 150 g dissolved in 1000 ml water, heated to 60℃ completely dissolved, to the CTAB solution drop TEOS 150 g, keep 60℃ stirring 4h after standing overnight, complete after the formation of light blue sol;

[0091] S2, the light blue sol obtained in S2 is added to the noble metal catalytic material, stirred at room temperature for 2 h, and the excess water is evaporated at 80°C; 19.23 g of silica sol (calculated on a dry basis) is weighed and added, ball milled, D50 is controlled at 3-5 microns, solid content is 40%, pH is 4.5, to obtain a first slurry DA3.

[0092] S3, the first slurry DA3 is coated onto the catalyst substrate, the catalyst substrate uses a cordierite substrate, the substrate specification is a catalyst substrate ø25.4 mm*25.4 mm / 400 cpsi-4 mil, the loading amount is 100 g / L, the noble metal loading amount is 30 g / ft 3 , the noble metal ratio is 2:1, dried and calcined to obtain a noble metal catalyst D3 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 20-25 nm, and the pore size of the porous protective layer is 13-15 nm.

[0093] Comparative Example 4

[0094] This comparative example provides a high-thermal-stability noble metal catalyst, which is different from Example 1 in that the porous protective layer on the catalyst of this comparative example is cerium dioxide.

[0095] The preparation method of the catalyst comprises the following steps:

[0096] S1, noble metal slurry preparation: 7.4333 g of platinum chloride and 3.7167 g of palladium chloride (calculated on the basis of metal elements) are weighed and added to 1500 ml of deionized water, and stirred and mixed uniformly to obtain a prepared first noble metal precursor solution; 986.85 g of lanthanum modified alumina is weighed as a catalytic material in a stirring tank, and the noble metal precursor solution is added thereto, and an excess impregnation method is used to stir for 1 h; 100 g of polyvinylpyrrolidone (PVP) is dissolved in 200 ml of water, and the first noble metal precursor solution and the catalytic material suspension are added thereto, and stirred for 1 h; 10.87 g of hydrazine hydrate is weighed, and after stirring is completed, the solid content of the slurry is determined to be 37%; 950 g (calculated on a dry basis) of the above slurry is transferred to a ball mill tank;

[0097] 77.7 g of cerium nitrate is weighed and dissolved in 1000 ml of water, 20 g of citric acid is added, stirred, and then ammonium bicarbonate is added to adjust the pH to 3.5-4, and a light yellow sol is formed after completion;

[0098] S2, the light yellow sol obtained in S2 is added to the noble metal catalytic material, stirred at room temperature for 2 h, and the excess water is evaporated at 80°C; 19.23 g of silica sol (calculated on a dry basis) is weighed and added, ball milled, D50 is controlled at 3-5 microns, solid content is 40%, pH is 4.5, to obtain a first slurry DA3.

[0099] S3, the first slurry DA4 is applied to the catalyst substrate, the catalyst substrate adopts a cordierite substrate, the substrate specification is a catalyst substrate ø25.4mm*25.4mm / 400cpsi-4mil, the loading is 100g / L, the noble metal loading is 30g / ft 3 , the noble metal ratio is 2:1, drying and calcination are performed, and a noble metal catalyst D4 with a porous protective layer is obtained. The thickness of the porous protective layer of the obtained catalyst is 20-25nm, and the pore size of the porous protective layer is 4-5nm.

[0100] Comparative Example 5

[0101] The present comparative example provides a high-thermal-stability noble metal catalyst, which is different from the catalyst of Example 1 in that the preparation method of the porous protective layer on the catalyst of the present comparative example is different.

[0102] The preparation method of the catalyst comprises the following steps:

[0103] S1, noble metal slurry preparation: 7.4333g of platinum chloride and 3.7167g of palladium chloride (calculated as metal elements) are weighed, and a total of 1500ml of deionized water is added, and the mixture is stirred and mixed uniformly to obtain a prepared first noble metal precursor solution; 986.85g of lanthanum-modified alumina is weighed as a catalyst material in a stirring tank, and the first noble metal precursor solution is added to the catalyst material, and an excess impregnation method is used to stir for 1h; 100g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 200ml of water, and the first noble metal precursor solution and the catalyst material suspension are added to the stirring tank, and stirring is performed for 1h; 10.87g of hydrazine hydrate is weighed, and after stirring is completed, the solid content of the slurry is determined to be 37%; 950g (calculated as dry basis) of the above slurry is transferred to a ball mill tank;

[0104] S2, 19.23g of silica sol (calculated as dry basis) is weighed and added, and ball milling is performed; the slurry after ball milling is applied to the catalyst substrate, the loading is 100g / L, and the noble metal loading is 97g / ft 3 , the noble metal ratio is 2:1; after drying, a preliminary catalyst is obtained;

[0105] S3, 50g of CTAB is dissolved in 1000ml of water, heated to 60°C to completely dissolve, and 50g of TEOS is added dropwise to the CTAB solution; after stirring at 60°C for 4h and standing overnight, a light blue sol is formed after completion;

[0106] S4, the light blue sol is applied to the preliminary catalyst, and drying and calcination are performed to obtain a noble metal catalyst D5 with a porous protective layer. The thickness of the porous protective layer of the obtained catalyst is 20-25nm, and the pore size of the porous protective layer is 4-5nm.

[0107] Test Example 1

[0108] The catalysts of Example 1 and Comparative Example 1 were subjected to SEM testing, as shown in Figure 1 The test results of the catalyst of Example 1 are shown in Table 1, and the test results of the catalyst of Comparative Example 1 are shown in Table 2. Figure 2 The test results of the catalyst of Example 1 are shown in Table 1, and the test results of the catalyst of Comparative Example 1 are shown in Table 2.

[0109] The sintering of the active centers of the noble metal catalyst is mainly affected by thermodynamic and kinetic factors. The essence of the sintering of the metal catalyst is the reduction of the chemical potential of the system, and the temperature is the main physical inducing factor causing sintering. The high temperature increases the kinetic energy of the metal, and regardless of the sintering mechanism, the higher temperature will affect the stability of the metal catalyst, causing the breaking of the atomic-atomic bond on the surface of the metal particles or the breaking of the related bond between the metal atoms and the support surface, thereby significantly affecting the sintering rate and accelerating the sintering process. The main sintering modes are particle migration and Ostwald ripening. The catalyst of the present application limits the noble metal nanoparticles to a fixed position by a mechanical confinement mode, and the reactants and products can normally diffuse in and out, as shown in FIG. 1. The silicon coating layer is uniformly distributed on the surface of the noble metal catalyst, and no separate silicon dioxide particles are formed, which does not cause embedding of the noble metal nanoparticles of the catalyst and does not affect the initial activity of the catalyst. During the use of the catalyst or after high-temperature calcination, the aging of the noble metal nanoparticles is only the sintering and agglomeration of the noble metal in the porous silicon dioxide cage, and no large-area migration occurs, as shown in FIG. 2. Therefore, the noble metal nanoparticles will grow slightly after aging, but will not grow indefinitely. The porous protection layer of silicon dioxide can effectively prevent the large-area migration and agglomeration of the noble metal, effectively control the size of the noble metal nanoparticles after aging, and prevent the sintering of the active centers of the noble metal catalyst. The noble metal is isolated by the porous protection layer of silicon dioxide, which can effectively control the size of the noble metal nanoparticles after aging, prevent the migration and agglomeration of the noble metal in a large area, improve the thermal stability of the noble metal catalyst, and ensure the durability of the catalyst. Figure 3 Figure 4 At the same time, the uniformly distributed porous protection layer of silicon dioxide is acidic, and the addition of silicon dioxide can improve the acidity of the catalyst, promote the adsorption of the reactants, and enhance the interface interaction between the silicon dioxide and the active components of the noble metal, as shown in FIG. 3. It can also effectively repel SO2 in the tail gas, prevent SO2 from combining with the noble metal nanoparticles or the catalytic material to cause sulfur poisoning and reduce the performance, and further improve the performance and sulfur resistance of the catalyst.

[0110] At the same time, the uniformly distributed porous protection layer of silicon dioxide is acidic, and the addition of silicon dioxide can improve the acidity of the catalyst, promote the adsorption of the reactants, and enhance the interface interaction between the silicon dioxide and the active components of the noble metal, as shown in FIG. 3. It can also effectively repel SO2 in the tail gas, prevent SO2 from combining with the noble metal nanoparticles or the catalytic material to cause sulfur poisoning and reduce the performance, and further improve the performance and sulfur resistance of the catalyst. Figure 5

[0111] Test Example 2

[0112] The catalysts of Example 1 and Comparative Example 1 were subjected to XRD testing, and the test results are shown in FIG. 4. It can be seen that: Figure 6 The catalysts of Example 1 and Comparative Example 1 were subjected to XRD testing, and the test results are shown in FIG. 4. It can be seen that:​​

[0113] After thermal aging of catalyst S1 relative to catalyst D1, the Pt characteristic peak half-peak width is smaller, and the nanoparticles are smaller. In the SEM pictures described above, the noble metal particle distribution of catalyst S1 is more uniform relative to catalyst D1, and the particle size is smaller, further confirming the conclusion of XRD.

[0114] Test Example 3

[0115] The catalysts of Examples 1-4 and Comparative Examples 1-3 were subjected to aging tests under the following conditions: 650°C, 100h, 10% H2O with Air, and the fresh and aged catalysts were subjected to catalytic performance tests under the following conditions: C3H6: 333.3ppm, CO: 1000ppm, NO: 1000ppm, O2: 8%, CO2: 8%, H2O: 7%, and the balance being N2, at a test space velocity of 120000h-1 -1 , and the test temperature was increased from 120°C to 450°C at a rate of 5°C / min, and the test results are shown in Table 1.

[0116] Table 1 Comparison of catalytic performance of catalysts of Examples 1-4 and Comparative Examples 1-3

[0117]

[0118] As can be seen from the data in Table 1, when the thickness of the silica protective layer is 2-50nm and the pore size is 2-10nm, the fresh and aged catalysts of Examples 1-4 have good performance. When the thickness of the silica protective layer exceeds 50nm, the thickness of the protective layer is too large, affecting the mass transfer of pollutants, so the activity of the fresh catalyst is reduced, and the relative degradation rate of the aged catalyst is not significantly increased; when the pore size of the silica protective layer exceeds 10nm, the pore size of the protective layer is too large, and during hydrothermal aging, the noble metal particles migrate severely, so the degradation of the aged catalyst is severe; using ceria as a protective layer, because the oxygen electron binding energy of Ce element itself is weak, the noble metal is easy to form a high valence state, and the activity is low during the reaction. However, after aging, the noble metal is not easy to migrate due to the formation of Ce-O-Pt bond, so the degradation rate of the catalyst is low, and thus it can be seen that the effect of using ceria as a protective layer is not as good as that of using silica; the catalyst D5 of Comparative Example 5 has an additional silica layer on the catalyst coating, and the preparation method is different from that of the silica layer of the present application, which has a small effect on the fresh performance of the catalyst, but the performance of the aged catalyst is severely degraded, and the reason is that the silica layer is not effectively distributed on the surface of the noble metal catalytic material, and has not effectively protected the noble metal nanoparticles.

[0119] The catalysts of Example 1 and Comparative Example 1 were subjected to sulfurization test, and the anti-sulfur performance test procedure was as follows: (1) fresh activity test; (2) sulfurization, sulfurization conditions: 250℃, 350ppm SO2, 100000h-1, 10%O2, 7%H2O, 1h; (3) direct test of catalytic performance after sulfurization; (4) desulfurization, desulfurization conditions: 550℃ 1h; (5) performance test after desulfurization, test atmosphere: C3H6: 333.3ppm, CO: 1000ppm, NO: 1000ppm, O2: 8%, CO2: 8%, H2O: 7%, the rest was N2, test space velocity 120000h-1, test temperature was from 120℃ to 450℃ at a rate of 5℃ / min, and the test results were shown in Table 2. -1 , test temperature was from 120℃ to 450℃ at a rate of 5℃ / min, and the test results were shown in Table 2.

[0120] Table 2 Comparison of anti-sulfur performance of catalysts of Example 1 and Comparative Example 1

[0121]

[0122] As can be seen from the data in Table 2, the catalyst S1 with a silica protective layer has better anti-sulfur performance than the catalyst D1 of Comparative Example 1, the performance degradation of the catalyst after sulfurization is lower, and the performance of the catalyst after desulfurization by heat treatment is basically completely restored, but the performance of the catalyst D1 after desulfurization is not completely restored, and part of the sulfur has formed a difficult-to-decompose sulfate; the catalyst D4 has poor anti-sulfur performance relative to the catalyst S1, mainly because the Ce element is alkaline and is more prone to absorb acidic SO2 to form a sulfate, and even heat treatment can only partially restore the performance reduction caused by physical adsorption of sulfite.

[0123] For those skilled in the art, when understanding the scheme described in the embodiments of the present application, reference can be made to the conventional technical manuals in the art, and for the above-mentioned terms, appropriate understanding or adjustment can be made by reference, and the same or similar technical scheme implementation conditions can be derived without creative labor.

[0124] The above embodiments only describe the basic principles, main features and / or advantages of the present application, and those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and the description of the inventive content part only describe the principles or specific cases of the present application, and various changes and improvements of the present application can be made without departing from the essence of the innovative idea of the present application, and these changes and improvements all fall within the scope of the present application.

Claims

1. A high-thermal-stability noble metal catalyst, the catalyst comprising a catalyst substrate and a coating layer coated on the catalyst substrate, characterized in that, The coating comprises a catalytic material, a noble metal active component dispersed on the surface of the catalytic material, and a porous protective layer coated on the surface of the catalytic material, wherein the porous protective layer is a silica layer, the thickness of the porous protective layer is 2-50 nm, and the pore size of the porous protective layer is 2-10 nm.

2. The high-thermal-stability noble metal catalyst according to claim 1, characterized by, The noble metal in the noble metal active component is one or more of Pt, Pd, Rh, Ru, Au, Ag, and the content of the noble metal active component is 1-100 g / ft 3 .

3. The high-thermal-stability noble metal catalyst according to claim 1, wherein The catalytic material is a metal oxide, and the metal oxide is one or more of a composite element oxide composed of aluminum oxide, cerium oxide, and zirconium oxide.

4. The high-thermal-stability noble metal catalyst according to claim 1, characterized by, The thickness of the porous protective layer is 10-30 nm.

5. The high-thermal-stability noble metal catalyst of claim 1, wherein, The pore size of the porous protective layer is 2-6 nm.

6. The high-thermal-stability noble metal catalyst of claim 1, wherein, The SiO2 in the porous protective layer accounts for 0.1%-10% of the total mass of the catalyst.

7. A method for producing a high-thermal-stability noble metal catalyst as claimed in any one of claims 1 to 6, characterized by, The method comprises the following steps: Step S1: noble metal catalytic material preparation: dispersing a noble metal precursor solution on the catalytic material, stirring after adding a dispersant, then adding a reducing agent and stirring again to obtain a noble metal catalytic material; Organic silicon sol preparation: adding a surfactant to water, heating and stirring to dissolve, continuously adding a silicon source to the solution, and stirring to form a light blue organic silicon sol; Step S2: slurry preparation of the noble metal catalytic material, then adding the organic silicon sol, stirring uniformly, adding a first adhesive and adjusting the pH of the slurry to 4-8 to obtain a first slurry; Step S3: coating the first slurry on the catalyst substrate, drying, and calcining to obtain a noble metal catalyst with a porous silica protective layer.

8. The method of claim 7, wherein the high thermal stability noble metal catalyst is prepared by the steps of: The surfactant is one of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, cetyltrimethylammonium chloride, and cetyltrimethylammonium bromide, and / or the silicon source is one of tetraethyl orthosilicate, sodium metasilicate nonahydrate, and silica sol.

9. The method of claim 7, wherein the high thermal stability noble metal catalyst is prepared by the steps of: The molar ratio of the noble metal catalytic material to the silicon source ranges from 100:1 to 10:1, and the molar ratio of the surfactant to the silicon source ranges from 10:1 to 1:10.

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