Preparation method of noble metal catalyst and noble metal catalyst
By employing hydrothermal treatment and a titanium-zirconium composite support, the problems of migration and sintering of noble metal catalysts at high temperatures were solved, the pore structure and noble metal dispersion were optimized, and the stability and efficiency of the catalyst were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING DEPURATE ENVIRONMENTAL TECH CO LTD
- Filing Date
- 2026-02-09
- Publication Date
- 2026-04-17
AI Technical Summary
Existing precious metal catalysts are prone to migration and sintering in high-temperature and complex reaction media, resulting in a reduction in active surface area and a decline in catalytic performance. Furthermore, the pore structure limits the efficiency of macromolecular reactions.
A titanium-zirconium composite was introduced into an alumina support by hydrothermal treatment to form a titanium-zirconium-aluminum composite support. This support was then mixed with noble metals and oxygen storage materials to prepare a noble metal catalyst, thereby optimizing the pore structure and the dispersion of the noble metals.
It significantly improves the catalytic efficiency and high-temperature stability of precious metal catalysts, and enhances the performance of catalysts throughout their entire life cycle.
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Figure CN121869352A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of motor vehicle exhaust purification technology, specifically to a method for preparing a precious metal catalyst and the precious metal catalyst itself. Background Technology
[0002] In the field of industrial catalysis, noble metal catalysts are widely used in many important chemical reactions due to their superior catalytic activity, such as automobile exhaust purification, petrochemical processing, and the synthesis of fine chemicals. Among them, noble metal components such as platinum, palladium, and rhodium are the core sources of activity in the catalytic system.
[0003] However, these precious metal resources are scarce and expensive. At the same time, catalysts often face harsh environments such as high temperature and complex reaction media in practical applications. It is necessary to maximize the utilization efficiency of precious metals, maintain the stability of active sites and optimize the reaction mass transfer process, so as to synergistically improve the activity, selectivity and service life of the catalyst.
[0004] In traditional approaches, noble metal nanoparticles are directly loaded onto porous supports with high specific surface areas (such as γ-alumina). However, the pore structure of alumina supports is mainly composed of micropores and small-to-medium-sized mesopores, which may restrict diffusion when processing large molecular reactants or products, affecting the overall reaction efficiency. More importantly, at high temperatures, noble metal nanoparticles on the support surface are prone to migration and sintering, leading to a reduction in active area and a decline in catalyst performance.
[0005] Therefore, improving the catalytic efficiency and stability of precious metal catalysts has become a key technical challenge in the existing technology. Summary of the Invention
[0006] The purpose of this application is to provide a method for preparing a noble metal catalyst and a noble metal catalyst that can improve the catalytic efficiency and stability of the noble metal catalyst. To achieve the above objective, one aspect of this application is a method for preparing a noble metal catalyst, comprising the following steps: Step S1: Hydrothermally heating, drying, and calcining alumina to obtain modified alumina powder; Step S2: Mixing titanium salt and zirconium salt in a predetermined ratio, adding a diluent to obtain a precursor solution; impregnating and mixing the alumina powder and the precursor solution at a predetermined first mass ratio, then rinsing, drying, and calcining to obtain a titanium-zirconium-aluminum composite support; Step S3: Mixing and grinding the titanium-zirconium-aluminum composite support, a noble metal, and an oxygen storage material at a predetermined second mass ratio to obtain a coating slurry; the noble metal includes one or more of platinum, palladium, and rhodium; Step S4: Coating the coating slurry onto the target support, then drying and calcining to obtain the noble metal catalyst.
[0007] As a preferred embodiment, in step S1, the solvent used for hydrothermal treatment of the alumina is one of deionized water, ammonia, or ammonium carbonate solution; wherein the weight ratio of the alumina to the solvent is 1:4-1:5, and / or the hydrothermal temperature is 300℃-350℃.
[0008] As a preferred method, in step S1, the drying temperature is 200℃-220℃ and the drying time is 8 hours-12 hours.
[0009] As a preferred method, in step S1, the calcination temperature is 350℃-450℃ and the duration is 2 hours-4 hours.
[0010] As a preferred embodiment, in step S2, the molar ratio of the titanium salt to the zirconium salt is 3:1 to 2:1.
[0011] As a preferred embodiment, in step S2, the diluent is one or more of ethanol, isopropanol, acetylacetone, and acetic acid; and / or, the total concentration of the titanium salt and the zirconium salt in the solution after dilution is 0.1-0.4 mol / L.
[0012] As a preferred embodiment, in step S2, the mass ratio of the alumina powder to the precursor solution is 4:1 to 3:1.
[0013] As a preferred embodiment, in step S3, the oxygen storage material is one or more oxides of cerium, zirconium, lanthanum, yttrium, barium, and europium.
[0014] As a preferred embodiment, in step S3, the titanium-zirconium-aluminum composite carrier accounts for 42%-51% of the solid components of the coating slurry by mass; and / or, the oxygen storage material accounts for 48%-57% by mass.
[0015] As a preferred embodiment, in step S3, the mass percentage of the precious metal in the solid component of the coating slurry is 0.1%-0.5%.
[0016] As a preferred method, in step S4, after the coating slurry is coated onto the target carrier, it is dried at 105℃-120℃ for more than 0.5 hours and calcined at 650℃-750℃ for more than 2 hours.
[0017] In addition, another aspect of this application is a noble metal catalyst, which is prepared by the aforementioned method for preparing noble metal catalysts.
[0018] The preparation method and the noble metal catalyst of the above embodiments of this application can significantly improve the catalytic efficiency and structural stability of the noble metal catalyst at high temperature, thereby improving its entire life cycle. Attached Figure Description
[0019] To more clearly illustrate this application, the accompanying drawings will be described and explained below. Obviously, the drawings described below only illustrate certain aspects of some exemplary embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.
[0020] Figure 1 This is an electron microscope image of the sample obtained in Example 1.
[0021] Figure 2 The N2 adsorption-desorption curves and pore size distribution diagrams of the obtained noble metal catalysts are shown.
[0022] Figure 3 These are ignition test diagrams of the noble metal catalysts obtained in Examples 1, 2, and 1.
[0023] Figure 4 These are ignition test diagrams of the noble metal catalysts obtained in Examples 3, 4 and Comparative Example 2. Detailed Implementation
[0024] Various exemplary embodiments of this application are described in detail below with reference to the accompanying drawings. The descriptions of the exemplary embodiments are merely illustrative and are in no way intended to limit the application or its application or use. This application can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the application thorough and complete, and to fully express the scope of the application to those skilled in the art. It should be noted that, unless otherwise stated, the relative arrangement of components and steps, numerical expressions, and values set forth in these embodiments should be interpreted as merely exemplary and not as limiting.
[0025] As used in this application, the words “including” or “comprising” or similar terms mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility that it may also cover other elements.
[0026] All terms used in this application (including technical or scientific terms) have the same meaning as understood by one of ordinary skill in the art to which this application pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as being interpreted with idealized or highly formalized meanings, unless explicitly defined herein.
[0027] For components, specific model numbers and other parameters of components not described in detail in this section, the interrelationships between components and control circuits, these may be considered as techniques, methods and devices known to those skilled in the art, but where appropriate, such techniques, methods and devices should be considered part of the specification.
[0028] It should be noted that although the operations of the method described in this application are given a specific order, this does not require or imply that these operations must be performed in that specific order, or that all of the operations shown must be performed to achieve the desired result. On the contrary, the steps described in this application may be performed in a different order. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.
[0029] The technical solution, technical effects and principles of the present invention will be described in detail below through specific embodiments, comparative examples and test data.
[0030] The method for preparing the noble metal catalyst of this application includes the following steps: Step S1: Alumina is subjected to hydrothermal treatment, drying, and calcination to obtain alumina powder; Step S2: After mixing titanium salt and zirconium salt in a predetermined ratio, the mixture is diluted and inhibited to obtain a precursor solution; the alumina powder is impregnated and mixed with the precursor solution in a predetermined first mass ratio, and then rinsed, dried and calcined to obtain a titanium-zirconium-aluminum composite carrier. Step S3: Mix and grind the titanium-zirconium-aluminum composite carrier, the precious metal, and the oxygen storage material at a predetermined second mass ratio to obtain a coating slurry; the precious metal is one or more of platinum, palladium, and rhodium. Step S4: The coating slurry is coated onto the target support, followed by drying and calcination to obtain the noble metal catalyst. It should be noted that the target support can be different catalyst supports such as metal honeycomb supports or ceramic honeycomb supports; here, only a metal honeycomb support is used as an example.
[0031] Preferably, in step S1, the solvent used for hydrothermal treatment of the alumina is one of deionized water, ammonia, or ammonium carbonate solution; wherein the weight ratio of the alumina to the solvent is 1:4-1:5, and / or the hydrothermal temperature is 300℃-350℃.
[0032] Preferably, in step S1, the drying temperature is 200℃-220℃ and the drying time is 8-12 hours.
[0033] Preferably, in step S1, the calcination temperature is 350℃-450℃ and the duration is 2 hours-4 hours.
[0034] Preferably, in step S2, the molar ratio of the titanium salt to the zirconium salt is 3:1 to 2:1.
[0035] Preferably, in step S2, the diluent is one or more of ethanol, isopropanol, acetylacetone, and acetic acid; and / or, the total concentration of the titanium salt and the zirconium salt in the solution after dilution is 0.1-0.4 mol / L. Here, the diluent is preferably an organic solvent, which can both dissolve the mixture of titanium salt and zirconium salt and inhibit the precipitation of titanium salt and zirconium salt.
[0036] Preferably, in step S2, the mass ratio of the alumina powder to the precursor solution is 4:1-3:1, which is the first mass ratio.
[0037] Preferably, in step S3, the oxygen storage material is one or more oxides of cerium, zirconium, lanthanum, yttrium, barium, and europium.
[0038] Preferably, in step S3, the titanium-zirconium-aluminum composite carrier accounts for 42%-51% of the solid components of the coating slurry by mass; and / or, the oxygen storage material accounts for 48%-57% of the solid components. More preferably, in step S3, the precious metal accounts for 0.1%-0.5% of the solid components of the coating slurry by mass. Here, the mass percentages of the titanium-zirconium-aluminum composite carrier, the precious metal, and the oxygen storage material constitute the second mass ratio.
[0039] Preferably, in step S4, after the coating slurry is coated onto the target carrier, it is dried at 105℃-120℃ for more than 0.5 hours and calcined at 650℃-750℃ for more than 2 hours.
[0040] The following describes the embodiments and comparative examples.
[0041] Example 1
[0042] The preparation method of noble metal catalysts includes the following steps: (1) Alumina powder and deionized water were mixed at a weight ratio of 1:4, and after hydrothermal treatment at 350°C, dried at 200°C for 12 hours, and then calcined at 400°C for 2 hours to obtain modified alumina powder.
[0043] (2) Tetraisopropyl titanate and tetran-n-propyl zirconate were mixed in a molar ratio of 2:1 and the total molar amount was calculated. The mixture was then dissolved in ethanol to a concentration of 0.2 mol / L, and 1% of the metal molar amount of acetic acid was added to obtain a precursor solution. The alumina powder modified in step (1) and the precursor solution were impregnated and mixed in a mass ratio of 4:1. The mixture was then slowly rinsed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5 μS / cm. After drying at 120°C for 10 hours, the mixture was placed in a muffle furnace and calcined at 650°C in air for 3 hours to obtain a titanium-zirconium-aluminum composite carrier.
[0044] (3) The titanium-zirconium-aluminum composite support, precious metals, oxygen storage materials, and deionized water were mixed for 2 hours, ground to a particle size of D90 = 8 μm ± 1 μm, and then homogenized to obtain a coating slurry for the precious metal catalyst. The solid components of this coating slurry comprise 43% by mass of the titanium-zirconium-aluminum composite support, 0.9% by mass of the precious metals, and 54% by mass of the oxygen storage materials. The precious metals are platinum, palladium, and rhodium, comprising 65%, 25%, and 10% by mass, respectively. The oxygen storage materials are oxides of cerium, zirconium, and lanthanum, comprising 56%, 42%, and 2% by mass, respectively. The solid content of the coating slurry is 35%.
[0045] (4) A metal honeycomb carrier (target carrier) with a diameter of 46 mm, a length of 110 mm, and a pore density of 400 cpi was selected for slurry coating. The loading amount was 104 g / L. After coating, the substrate was dried at 120 °C for 0.5 hours and then calcined at 700 °C for 2 hours in air atmosphere to obtain a precious metal catalyst.
[0046] Example 2 The preparation method of noble metal catalysts includes the following steps: (1) Alumina powder and deionized water are mixed in a weight ratio of 1:4, subjected to hydrothermal treatment at 350℃, dried at 200℃ for 12 hours, and then calcined at 400℃ for 2 hours to obtain modified alumina powder.
[0047] (2) Tetraisopropyl titanate and tetran-n-propyl zirconate were mixed in a molar ratio of 3:1 and the total molar amount was calculated. The mixture was then dissolved in ethanol to a concentration of 0.2 mol / L, and 1% of the metal molar amount of acetic acid was added to obtain a precursor solution. The modified alumina powder and the precursor solution were impregnated and mixed in a mass ratio of 3:1, and then slowly washed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5 μS / cm. After that, it was dried at 120°C for 10 hours, and then placed in a muffle furnace and calcined in air at 650°C for 3 hours to obtain a titanium-zirconium-aluminum composite carrier.
[0048] (3) The titanium-zirconium-aluminum composite support, precious metals, oxygen storage materials, and deionized water were mixed for 2 hours, ground to a particle size of D90 = 8 μm ± 1 μm, and then homogenized to obtain a coating slurry for the precious metal catalyst. The solid components of this coating slurry comprise 43% by mass of the titanium-zirconium-aluminum composite support, 0.9% by mass of the precious metals, and 54% by mass of the oxygen storage materials. The precious metals are platinum, palladium, and rhodium, comprising 65%, 25%, and 10% by mass, respectively. The oxygen storage materials are oxides of cerium, zirconium, and lanthanum, comprising 56%, 42%, and 2% by mass, respectively. The solid content of the coating slurry is 35%.
[0049] (4) A metal honeycomb carrier with a diameter of 46 mm, a length of 110 mm, and a pore density of 400 cpi was selected for coating the precious metal catalyst slurry. The loading was 104 g / L. After coating, the slurry was dried at 120°C for 0.5 hours and then calcined at 700°C in air for 2 hours to obtain the precious metal catalyst.
[0050] Example 3 The same precious metal catalyst was obtained in Example 1. The precious metal catalyst was then calcined at 1100°C for 4 hours to obtain an aged precious metal catalyst.
[0051] Example 4 The same precious metal catalyst was obtained in Example 2. The precious metal catalyst was calcined at 1100°C for 4 hours to obtain an aged precious metal catalyst.
[0052] Comparative Example 1 The preparation method of noble metal catalysts includes the following steps: (1) Unmodified oxide powder, precious metal, oxygen storage material, and deionized water were mixed for 2 hours, ground to a particle size of D90 = 8 μm ± 1 μm, and then homogenized to obtain a coating slurry for the precious metal catalyst. The solid components of the coating slurry comprised alumina powder, precious metal, and oxygen storage material at mass percentages of 43%, 0.9%, and 54%, respectively. The precious metals were platinum, palladium, and rhodium, with mass percentages of 65%, 25%, and 10%, respectively. The oxygen storage material consisted of oxides of cerium, zirconium, and lanthanum, with mass percentages of 56%, 42%, and 2%, respectively. The solid content of the coating slurry was 35%.
[0053] (3) A metal honeycomb carrier with a diameter of 46 mm, a length of 110 mm, and a pore density of 400 cpi was selected for slurry coating with a loading of 104 g / L. After coating, it was dried at 120°C for 0.5 hours and then calcined at 700°C for 2 hours in air atmosphere to obtain a precious metal catalyst.
[0054] Comparative Example 2 The same as in Comparative Example 1, a noble metal catalyst was obtained. The catalyst was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0055] To verify the effectiveness of the present invention, this application provides Examples 1-4 and Comparative Examples 1-2 as described above. Examples 1-2 demonstrate the preparation of fresh catalysts at different titanium-zirconium molar ratios (2:1 and 3:1); Examples 3-4 are samples of the catalysts obtained in Examples 1-2 after aging at 1100°C for 4 hours, used to evaluate their anti-aging performance; Comparative Example 1 is a catalyst prepared by directly supporting noble metals and oxygen storage materials on unmodified alumina; Comparative Example 2 is a sample of Comparative Example 1 after aging under the same conditions.
[0056] Comparative Example 3 The same steps were used to obtain the noble metal catalyst as in Example 1. The difference was that in step (1), the modified alumina powder and the precursor solution were impregnated and mixed at a mass ratio of 4.2:1, and then slowly washed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5μS / cm. After that, it was dried at 120°C for 10 hours and then placed in a muffle furnace and calcined at 650°C in an air atmosphere for 3 hours to obtain the titanium-zirconium-aluminum composite support.
[0057] Comparative Example 4 The noble metal catalyst was obtained using the same steps as in Example 1. The difference was that in step (1), the modified alumina powder and the precursor solution were impregnated and mixed at a mass ratio of 4.5:1, and then slowly washed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5μS / cm. After that, it was dried at 120°C for 10 hours and then placed in a muffle furnace and calcined at 650°C in an air atmosphere for 3 hours to obtain the titanium-zirconium-aluminum composite support.
[0058] Comparative Example 5 The same steps were used to obtain the noble metal catalyst as in Example 1. The difference was that in step (1), the modified alumina powder and the precursor solution were impregnated and mixed in a mass ratio of 2.8:1, and then slowly washed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5μS / cm. After that, it was dried at 120°C for 10 hours and then placed in a muffle furnace and calcined at 650°C in an air atmosphere for 3 hours to obtain the titanium-zirconium-aluminum composite support.
[0059] Comparative Example 6 The same steps were used to obtain the noble metal catalyst as in Example 1. The difference was that in step (1), the modified alumina powder and the precursor solution were impregnated and mixed at a mass ratio of 2.5:1, and then slowly washed with deionized water at 70°C until the filtrate was neutral and the conductivity was ≤5μS / cm. After that, it was dried at 120°C for 10 hours and then placed in a muffle furnace and calcined at 650°C in air atmosphere for 3 hours to obtain the titanium-zirconium-aluminum composite support.
[0060] Comparative Example 7 The same as Comparative Example 3 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0061] Comparative Example 8 The same as Comparative Example 4 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0062] Comparative Example 9 The same as Comparative Example 5 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0063] Comparative Example 10 The same as Comparative Example 6 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0064] Comparative Example 11 The same steps were used to obtain the noble metal catalyst as in Example 1. The difference was that in step (1), alumina powder and deionized water were mixed in a weight ratio of 1:3.5, hydrothermally treated at 350°C, dried at 200°C for 12 hours, and then calcined at 400°C for 2 hours to obtain the modified alumina powder.
[0065] Comparative Example 12 The same steps were used to obtain the noble metal catalyst as in Example 1. The difference was that in step (1), alumina powder and deionized water were mixed in a weight ratio of 1:5.5, hydrothermally treated at 350°C, dried at 200°C for 12 hours, and then calcined at 400°C for 2 hours to obtain the modified alumina powder.
[0066] Comparative Example 13 The same as Comparative Example 11 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0067] Comparative Example 14 The same as in Comparative Example 12, a noble metal catalyst was obtained. The catalyst was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0068] Comparative Example 15 The noble metal catalyst was obtained using the same steps as in Example 1. The difference was that in step (2), tetraisopropyl titanate and tetra-n-propyl zirconate were mixed in a molar ratio of 3.5:1 and the total molar amount was calculated. The mixture was then dissolved in ethanol to a concentration of 0.2 mol / L, and 1% of the metal molar amount of acetic acid was added to obtain the precursor solution.
[0069] Comparative Example 16 The noble metal catalyst was obtained using the same steps as in Example 1. The difference was that in step (2), tetraisopropyl titanate and tetra-n-propyl zirconate were mixed in a molar ratio of 2.5:1 and the total molar amount was calculated. The mixture was then dissolved in ethanol to a concentration of 0.2 mol / L, and 1% of the metal molar amount of acetic acid was added to obtain the precursor solution.
[0070] Comparative Example 17 The same as Comparative Example 15 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0071] Comparative Example 18 The same as Comparative Example 16 yielded a noble metal catalyst, which was then calcined at 1100℃ for 4 hours to obtain an aged noble metal catalyst.
[0072] Next, combined Figure 1-4 Tables 1-3 illustrate the technical effects and related principles of this application.
[0073] Figure 1 The image shown is an electron microscope image of the sample obtained in Example 1. Figure 2 The N2 adsorption-desorption curves and pore size distribution diagrams of the obtained noble metal catalysts are shown. Figure 3 The images show the ignition test results of the noble metal catalysts obtained in Examples 1, 2, and 1. Figure 4 The images show the ignition test results of the noble metal catalysts obtained in Examples 3, 4 and Comparative Example 2.
[0074] Table 1 shows the specific surface area and pore volume of the obtained noble metal catalyst; Table 2 shows the ignition temperature T50 and conversion rate C400 of the obtained noble metal catalyst; Table 3 shows the emission test results of the obtained noble metal catalyst. Details are as follows: Table 1
[0075] Table 2
[0076] Table 3
[0077] Electron microscopy was performed on Example 1 to observe the changes in the noble metal catalyst at different stages. Figure 1 (a) shows unmodified alumina powder, which has a smooth surface and no obvious defects. Figure 1 (b) is a partial magnified view of the alumina powder after the modification in step (1) of Example 1. It can be seen that after hydrothermal treatment, a large number of defects are generated on the surface of the alumina. Figure 1 (c) shows the titanium-zirconium-aluminum composite carrier obtained through step (2) of Example 1. Numerous tiny particles can be seen on the alumina surface. Upon magnification of a local area, such as… Figure 1 As shown in (d), the size of the tiny particles is approximately between 10 nm and 20 nm.
[0078] Figure 2 (a) and (b) show the nitrogen adsorption-desorption curves and particle size distribution diagrams for Examples 1-4 and Comparative Examples 1-2. The noble metal catalysts prepared in these examples and comparative examples are type I-IV mixed adsorption-desorption isotherms. When the relative pressure P / P0 (P / P0 represents the ratio of the current pressure P to the maximum pressure P0 that the gas can reach at that temperature, i.e., the liquefaction pressure. Its value ranges from 0 to 1. When P / P0=0, it represents a vacuum; when P / P0=1, it represents that the pressure has reached the liquefaction point of nitrogen at that temperature, and theoretically, bulk liquefaction will occur) is less than 0.30, the adsorption and desorption curves basically overlap. However, when P / P0 is in the range of 0.30-0.99, obvious hysteresis loops can be found, indicating that the noble metal catalysts prepared in the examples and comparative examples have certain micropores and mesopores.
[0079] like Figure 2 As shown in (a), the nitrogen adsorption-desorption curves of Examples 1, 2, and Comparative Example 1 show an increase around P / P0 = 0.99, indicating that a large number of macropores exist in all three catalysts. The specific surface area and pore volume results are shown in Table 1. The noble metal catalyst prepared from unmodified alumina has the largest specific surface area and pore volume. As the molar ratio of tetraisopropyl titanate to tetran-n-propyl zirconate decreases, the specific surface area and pore volume of the noble metal catalyst also decrease. In step (2) of Examples 1 and 2, the titanium-zirconium mixed solution is adsorbed into the pores and surface of the modified alumina. After being washed with deionized water, it undergoes a hydrolysis reaction and is then calcined to become titanium-zirconium oxide. These titanium-zirconium oxides occupy part of the pores, reducing the specific surface area of the catalyst.
[0080] like Figure 2 As shown in (b), in the nitrogen adsorption-desorption curves of Examples 3, 4, and Comparative Example 2, it can be seen that compared with Examples 1, 2, and Comparative Example 1, the hysteresis loops all show significant shrinkage, and the support of the noble metal catalyst collapses after aging. However, the shrinkage ratio of the titanium-zirconium-aluminum composite oxide is even lower. Figure 2(c) and Figure 2 This can also be seen in the pore size distribution of (d). The specific surface area and pore volume results are shown in Table 1. After titanium zirconium oxide occupies part of the pores, it improves the anti-sintering performance of the catalyst support. As the molar ratio of tetraisopropyl titanate to tetran-n-propyl zirconate decreases, the loss of specific surface area and pore volume of the noble metal catalyst also decreases. The higher the zirconium content, the stronger the effect of titanium zirconium oxide on the anti-sintering ability of the support.
[0081] Figure 3 The images show the ignition test results of the noble metal catalysts obtained in Examples 1, 2, and 1. It can be seen that the noble metal catalysts obtained in Examples 1 and 2 have better ignition temperatures and conversion rates for CO, THC, and NOx than those in Comparative Example 1. Figure 4 The ignition test diagrams for the noble metal catalysts obtained in Examples 3, 4, and Comparative Example 2 show that after aging, the ignition temperature and conversion rate of the noble metal catalysts obtained in Examples 3 and 4 for CO, THC, and NOx decreased to a lesser extent than those in Comparative Example 2. Table 2 shows that, in their fresh state, the alumina supports in Examples 1 and 2 were modified. The presence of titanium zirconium oxide provided more sites for the uniform dispersion of the noble metals, forming channels more conducive to the diffusion of macromolecular reactants, helping to reduce internal diffusion resistance and improve the overall reaction rate. After aging, the unmodified alumina experienced significant increases in the ignition temperature (T50) and a decrease in the conversion rate (C400) for CO, THC, and NOx due to the collapse of large-area pores and the sintering of the noble metals. While the titanium zirconium oxide reduced the effective contact area of the catalyst, it provided more stable binding sites for the noble metal loading, resulting in a more uniform and stable dispersion of the noble metals.
[0082] Furthermore, as shown in Table 1, Comparative Examples 3-10 demonstrate that when the ratio of modified alumina to precursor solution is too high, only a small number of pores are occupied by titanium zirconium oxide, resulting in a specific surface area and pore volume close to that of unmodified alumina. Conversely, when the ratio of modified alumina to precursor solution is too low, titanium zirconium oxide occupies too many pores, leading to a decrease in specific surface area and pore volume. In contrast, samples with an excessively high ratio of alumina to precursor solution after high-temperature aging exhibit partial pore collapse, showing a specific surface area and pore volume close to that of unmodified alumina. In samples with an excessively low ratio of alumina to precursor solution after high-temperature aging, although cerium zirconium oxide provides support, its excessive occupation of pores further reduces the specific surface area and pore volume.
[0083] Comparative Examples 11-14 illustrate that when the ratio of deionized water to alumina is too low, the modification effect of deionized water is not significant, resulting in a specific surface area and pore volume close to that of unmodified alumina. After high-temperature aging, this also leads to a similar specific surface area and pore volume to unmodified alumina. However, when the ratio of deionized water to alumina is too high, the hydrothermal modification effect on the alumina surface is excessive, causing a large number of micropores to transform into mesopores and macropores, resulting in a decrease in specific surface area and an increase in pore volume. After high-temperature aging, the collapse of the pore structure and the supporting effect of cerium-zirconium compounds cause a sharp decrease in specific surface area and pore volume. This trend can also be seen in the ignition and emission data in Tables 2 and 3.
[0084] Comparative Examples 15-18 illustrate that when the molar ratio of tetraisopropyl titanate to tetran-n-propyl zirconate is too high or too low, the fresh state exhibits a specific surface area and pore volume similar to that of Example 1. However, after high-temperature aging, the titanium in the titanium-zirconium oxide is prone to phase change, easily transforming from the anatase phase to the rutile phase, resulting in a sharp decrease in specific surface area and pore volume. This trend can also be seen from the ignition and emission data in Tables 2 and 3.
[0085] As shown in Table 2, none of the comparative examples showed a significant difference from Example 1 when they were fresh. However, after aging, the structure of the modified alumina changed (supported by specific surface area and pore volume data), resulting in a sharp decrease in the ignition temperature T50 and conversion rate C400 after high-temperature aging.
[0086] All vehicle emission tests for the embodiments and comparative examples were conducted according to the WMTC cycle for motorcycles. The results are shown in Table 3. It can be seen that the emissions of CO, THC, and NOx from the fresh noble metal catalysts are similar. However, after high-temperature aging, the emissions from the noble metal catalyst in Comparative Example 2 without zirconium titanium oxide increased more significantly, indicating that the noble metal catalyst with zirconium titanium oxide showed improved anti-aging ability. Furthermore, data from Comparative Examples 7-8, 13-14, and 17-18 show that after high-temperature aging, the modified alumina structure changed, resulting in a sharp decline in emission performance after aging.
[0087] Through structural characterization (SEM, nitrogen adsorption-desorption, pore size distribution) and performance testing (ignition characteristics, vehicle emissions) of the catalysts in the examples and comparative examples, this application has achieved significant technical effects, the core principles of which are as follows: Firstly, the carrier structure was optimized, and the dispersion of noble metals was improved. Scanning electron microscopy (SEM) observations showed (see...). Figure 1 The hydrothermal treatment resulted in numerous defects on the alumina surface, see [link / reference]. Figure 1(b) These defects provide effective anchoring points for subsequently introduced titanium-zirconium species. Following permeation of the precursor solution and subsequent hydrolysis and calcination, titanium-zirconium oxide nanoparticles with a size of approximately 10-20 nm were generated in situ on the alumina surface and within the pores. See [link to relevant documentation]. Figure 1 (c) Figure 1 (d). These nanoparticles are highly dispersed, which significantly increases the surface roughness and active site density of the carrier.
[0088] Specifically, hydrothermal treatment not only altered the surface morphology of alumina but also optimized its surface hydroxyl distribution, enhancing its interaction with the titanium-zirconium precursor. The in-situ generated titanium-zirconium oxide nanoparticles formed a tightly packed composite structure with the alumina support. This structure provided more and more uniform anchoring sites for the loading of noble metals, effectively suppressing the migration and aggregation of noble metal particles during preparation and use, thus achieving high dispersion and stabilization of the noble metals. Compared to the use of smooth, unmodified alumina directly in Comparative Example 1, see [link to Comparative Example 1]. Figure 1 (a) This application significantly improves the dispersion and stability of precious metals, which is the basis for the improvement of catalytic activity.
[0089] Secondly, the pore structure is controlled and diffusion performance is improved. See the test results for nitrogen adsorption / desorption and pore size distribution (see...). Figure 2 As shown in Table 1, all catalysts possess a mixed microporous and mesoporous structure. Compared to Comparative Example 1, the specific surface area and pore volume of Examples 1-2 decreased, which is attributed to the titanium zirconium oxide nanoparticles occupying part of the pore space. However, the appropriate amount of titanium zirconium oxide did not completely block the pores, but rather served as a modifier, acting as follows: (a) stabilizing the mesoporous structure and preventing its collapse during subsequent processing; and (b) forming a more permeable pore network that facilitates the diffusion of reactant and product molecules, reducing internal diffusion resistance. This is evident in the superior ignition performance of Examples 1-2 in the fresh state compared to Comparative Example 1 (lower ignition temperature T50 and higher conversion C400, see Table 1). Figure 3 This is confirmed by Table 2. This indicates that, despite a slight sacrifice in absolute specific surface area, the optimized pore structure greatly improves mass transfer efficiency, makes active sites more accessible, and thus enhances overall reaction kinetics.
[0090] Thirdly, it exhibits excellent high-temperature anti-aging (anti-sintering) properties. After aging at 1100℃, a comparison of the structure and performance of Examples 3-4 (corresponding to the aged samples of Examples 1-2) and Comparative Example 2 (the aged sample of Comparative Example 1) fully demonstrates that the stability of the noble metal catalyst in this application has been improved. The specific reasons are as follows: 1. Structural stability: After aging, the nitrogen adsorption-desorption hysteresis loops of all catalysts showed shrinkage, indicating that the pore structure underwent a certain degree of collapse and sintering. (Reference) Figure 2(b). However, the shrinkage of Examples 3-4 was significantly less than that of Comparative Example 2. Pore size distribution diagram ( Figure 2 (c) Figure 2 (d) Further, it is shown that the catalyst with the titanium-zirconium-aluminum composite support suffers less loss of pore structure. Table 1 data quantitatively demonstrates that the specific surface area and pore volume retention after aging in Examples 3-4 are significantly higher than those in Comparative Example 2. In particular, this anti-sintering effect is more pronounced with increasing zirconium content (comparing Example 2 and Example 1).
[0091] It should be noted that "hysteresis shrinkage" means a significant reduction in the amount of adsorbed / desorbed gas in the high-pressure zone (corresponding to larger pore sizes). This indicates that after aging at 1100℃, the pores of the catalyst support (especially mesopores and macropores) underwent severe collapse, fusion, or blockage, leading to a decrease in total pore volume and specific surface area (as shown in Table 1). Among them, compared with Comparative Example 2 without titanium-zirconium modification, Examples 3 and 4 showed less hysteresis shrinkage. This means that the titanium-zirconium oxide, acting as a "scaffold," effectively supported the pore structure of the alumina, significantly inhibiting sintering and collapse at high temperatures, thereby preserving more active surface area and pores. This is the main reason why the catalyst still exhibits superior performance after aging.
[0092] In short, the hysteresis loop is the core structural evidence in the complete logical chain connecting "preparation method (introducing titanium and zirconium)" → "formation of a special porous structure (generating and maintaining the hysteresis loop)" → "achieving anti-sintering performance (small hysteresis loop shrinkage)" → "ultimately improving catalytic activity and durability". It intuitively demonstrates the structural stability advantage of the titanium-zirconium-aluminum composite support prepared by this invention at high temperatures.
[0093] 2. Performance stability: Ignition test ( Figure 4 The results of the WMTC cycle emission test of the whole vehicle (Table 3) and Table 2 show that, after aging, the catalytic activity (T50 and C400) of Examples 3-4 decreased by much less than that of Comparative Example 2, and the emission indicators of the whole vehicle were also significantly better than those of Comparative Example 2.
[0094] Specifically, the main mechanisms by which high-temperature aging leads to catalyst failure are support sintering (pore collapse, sharp drop in specific surface area) and the aggregation and growth of noble metal particles. In this application, titanium zirconium oxide nanoparticles firmly anchored on the alumina surface play a crucial "pillar" and "pinning" role: (a) Inhibiting support sintering: High-melting-point titanium zirconium oxide (especially zirconium oxide) nanoparticles can effectively block direct contact between alumina particles, inhibiting the migration and growth of alumina grains at high temperatures, thereby significantly slowing down the collapse of the support structure and the loss of specific surface area. (b) Stabilizing noble metals: As mentioned above, titanium zirconium oxide provides strongly interacting loading sites, fixing noble metal particles like an "anchor" and greatly inhibiting their migration and aggregation at high temperatures. (c) The key role of zirconium: Data shows that the higher the zirconium content, the stronger the anti-aging effect. This is attributed to the excellent thermal stability of zirconium oxide and the strong metal-support interaction formed between it and noble metals (especially platinum and rhodium), further locking in the noble metals. Therefore, the titanium-zirconium-aluminum composite support structure of the present invention synergistically improves the overall thermal stability of the catalyst from both physical spatial barrier and chemical bonding aspects.
[0095] In summary, this application utilizes a "hydrothermal modification of alumina-in-situ titanium-zirconium composite" support construction process to prepare a titanium-zirconium-aluminum composite support with a unique structure and excellent performance. This support not only enhances the activity and diffusion performance of the fresh catalyst by optimizing its surface structure and pores, but more importantly, it significantly strengthens the overall high-temperature sintering resistance of the catalyst from both physical and chemical perspectives by introducing highly stable titanium-zirconium oxide nanoparticles, thereby achieving a simultaneous and significant improvement in catalytic activity and durability. This solves the technical problem of traditional alumina-based catalysts being prone to deactivation under high-temperature environments, making it particularly suitable for applications with stringent durability requirements, such as automotive exhaust purification.
[0096] It should be understood that the specific embodiments described above are only used to explain this application, and the scope of protection of this application is not limited thereto. Any changes, substitutions, or combinations made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and inventive concept of this application, should be covered within the scope of protection of this application.
Claims
1. A method for preparing a noble metal catalyst, characterized in that, It includes the following steps: Step S1: The alumina is subjected to hydrothermal treatment, drying, and calcination to obtain modified alumina powder; Step S2: After mixing titanium salt and zirconium salt in a predetermined ratio, a diluent is added to obtain a precursor solution; the alumina powder is impregnated and mixed with the precursor solution in a predetermined first mass ratio, and then rinsed, dried and calcined to obtain a titanium-zirconium-aluminum composite carrier. Step S3: Mix and grind the titanium-zirconium-aluminum composite carrier, the precious metal, and the oxygen storage material at a predetermined second mass ratio to obtain a coating slurry; the precious metal includes one or more of platinum, palladium, and rhodium; Step S4: The coating slurry is coated onto the target support, and then dried and calcined to obtain the noble metal catalyst.
2. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S1, the solvent used when hydrothermally treating the alumina is one of deionized water, ammonia, or ammonium carbonate solution. Wherein, the weight ratio of alumina to solvent is 1:4-1:5, and / or, the hydrothermal temperature is 300℃-350℃.
3. The method for preparing the noble metal catalyst according to claim 2, characterized in that: In step S1, the drying temperature is 200℃-220℃ and the drying time is 8-12 hours.
4. The method for preparing the noble metal catalyst according to claim 3, characterized in that: In step S1, the calcination temperature is 350℃-450℃ and the duration is 2 hours-4 hours.
5. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S2, the molar ratio of the titanium salt to the zirconium salt is 3:1 to 2:
1.
6. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S2, the diluent is one or more of ethanol, isopropanol, acetylacetone, and acetic acid; And / or, after dilution, the total concentration of the titanium salt and the zirconium salt in the solution is 0.1-0.4 mol / L.
7. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S2, the mass ratio of the alumina powder to the precursor solution is 4:1 to 3:
1.
8. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S3, the oxygen storage material is one or more oxides of cerium, zirconium, lanthanum, yttrium, barium, and europium.
9. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S3, the titanium-zirconium-aluminum composite carrier accounts for 42%-51% of the mass of the solid components in the coating slurry. And / or, the oxygen storage material accounts for 48%-57% of the total mass.
10. The method for preparing the noble metal catalyst according to claim 9, characterized in that: In step S3, the mass percentage of the precious metal in the solid component of the coating slurry is 0.1%-0.5%.
11. The method for preparing the noble metal catalyst according to claim 1, characterized in that: In step S4, after the coating slurry is coated onto the target carrier, it is dried at 105℃-120℃ for more than 0.5 hours and calcined at 650℃-750℃ for more than 2 hours.
12. A noble metal catalyst, characterized in that: The noble metal catalyst is prepared by any one of claims 1 to 11.