Preparation method of sub-micron monodisperse spherical palladium powder with controllable particle size

Abstract

The present application relates to the technical field of noble metal powder preparation, and particularly relates to a preparation method of submicron monodisperse spherical palladium powder with controllable particle size. The present application adopts a multi-process parameter coordination and precision regulation idea, and can precisely and controllably prepare submicron spherical palladium powder with monodispersity, narrow particle size distribution and high sphericity; the overall process parameters have strong adjustability and wide process window, and can flexibly prepare and output palladium powder products with different target particle size specifications according to the performance requirements of different application scenarios such as MLCC and electronic paste, are more suitable for wider application scenarios, and have more excellent process stability and industrialization batch production adaptability.

Description

Technical Field

[0001] This invention relates to the field of precious metal powder preparation technology, and in particular to a method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size. Background Technology

[0002] Submicron-sized (100 nm~1 μm) spherical palladium powder possesses a suitable specific surface area, excellent flowability, and high sintering activity, making it a core functional material in high-end electronics and catalysis fields such as multilayer ceramic capacitors (MLCCs), high-palladium silver pastes, thick-film electronic pastes, and catalytic electrodes. The particle size uniformity, sphericity, and dispersion stability of palladium powder directly determine the sintering density, conductivity uniformity, performance consistency, and reliability of end-device components.

[0003] Currently, the mainstream methods for preparing submicron-sized palladium powder mainly include liquid-phase reduction, vapor deposition, electrochemical methods, and high-temperature reduction. However, existing palladium powder preparation processes generally struggle to achieve effective separation and precise control of crystal nucleation and growth processes, and the reduction reaction rate is uncontrollable, easily leading to problems such as excessively rapid local reduction and uneven reaction. This makes it impossible to stably and accurately control the palladium powder particle size within the submicron range. This directly results in palladium powder products exhibiting defects such as a narrow adjustable particle size range, irregular particle morphology, wide particle size distribution, poor dispersibility, and poor process repeatability. Consequently, this leads to unstable rheological properties of electronic pastes, high porosity in sintered films, and poor density. Furthermore, existing processes cannot flexibly adjust the palladium powder particle size according to the needs of different application scenarios, limiting the versatility and applicability of the products. They can no longer meet the stringent requirements for powder particle size uniformity and precision in the development of microelectronic devices towards miniaturization, high integration, and high performance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size. This invention achieves precise control over the particle size and morphology of palladium powder, resulting in palladium powder with controllable particle size, uniform particle size, narrow particle size distribution, high sphericity, and good dispersibility. Furthermore, the process is simple, has a short cycle time, and can be mass-produced.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size, comprising the following steps: The pH of the palladium source solution was adjusted to 7.5-8.5 using an inorganic alkali solution to obtain an alkaline palladium-containing solution. An oxidizing agent solution is obtained by mixing a surfactant solution and an alkaline palladium-containing solution; the mass ratio of surfactant to palladium ions in the oxidizing agent solution is (0.05~0.2):1; the mass content of surfactant in the oxidizing agent solution is 0.02~0.2%. The reducing agent solution is added dropwise to the oxidizing agent solution under stirring conditions to carry out a reduction reaction, followed by solid-liquid separation, to obtain the submicron-sized monodisperse spherical palladium powder with controllable particle size; The concentration of the reducing agent in the reducing agent solution is 0.6~2.5 mol / L; the molar ratio of the reducing agent to the palladium ions in the oxidizing agent solution is (1~4):1; the dropping rate of the reducing agent solution is 1~4 mL / s; the temperature of the reduction reaction is 20~40℃; and the stirring speed is 200~300 rpm.

[0006] Preferably, the surfactant comprises one or more of polyvinylpyrrolidone K30, gum arabic, gelatin, sodium dodecylbenzenesulfonate, and hexadecyltrimethylammonium bromide.

[0007] Preferably, the mass concentration of the surfactant solution is 0.1~0.5%.

[0008] Preferably, the reducing agent is hydrazine hydrate.

[0009] Preferably, the reduction reaction takes 30 to 60 minutes.

[0010] Preferably, the inorganic alkaline solution is one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution.

[0011] Preferably, the palladium source solution is a chloropalladium acid solution or a palladium nitrate solution.

[0012] Preferably, the palladium source solution contains 5-20% palladium by mass.

[0013] Preferably, after solid-liquid separation, the resulting solid is further washed and dried.

[0014] Preferably, the drying temperature is 40~60℃.

[0015] This invention provides a method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size, comprising the following steps: adjusting the pH of a palladium source solution to 7.5-8.5 with an inorganic alkaline solution to obtain an alkaline palladium-containing solution; mixing a surfactant solution and the alkaline palladium-containing solution to obtain an oxidant solution; wherein the mass ratio of surfactant to palladium ions in the oxidant solution is (0.05-0.2):1; and the mass concentration of surfactant in the oxidant solution is 0.02-0.2%; adding a reducing agent solution dropwise to the oxidant solution under stirring conditions to carry out a reduction reaction, followed by solid-liquid separation to obtain the submicron-sized monodisperse spherical palladium powder with controllable particle size; wherein the concentration of reducing agent in the reducing agent solution is 0.6-2.5 mol / L; the molar ratio of reducing agent to palladium ions in the oxidant solution is (1-4):1; the dropping rate of the reducing agent solution is 1-4 mL / s; the temperature of the reduction reaction is 20-40℃; and the stirring speed is 200-300 rpm.

[0016] This invention precisely controls the particle size of palladium powder through the synergistic control of multiple process parameters. The core control conditions include: the pH value of the palladium source solution, the amount and concentration of the reducing agent, the dropping rate of the reducing agent, the amount and concentration of the surfactant, the temperature of the reaction system, and the stirring rate. Specifically, higher reducing agent concentration, faster dropping rate, higher reaction temperature, greater stirring rate, and a moderately increased surfactant concentration generally result in smaller palladium powder particle size, and vice versa.

[0017] Existing preparation methods mostly employ fixed formulations and solidified process parameters, lacking a systematic particle size control logic. This results in a narrow adjustable particle size range, enabling the preparation of palladium powder with only a single, fixed particle size, and failing to achieve flexible particle size customization. This invention adopts a multi-process parameter synergistic and precise control approach, enabling the precise and controllable preparation of monodisperse, narrow-size, and highly spherical submicron spherical palladium powder. The overall process parameters are highly adjustable with a wide process window, allowing for the flexible preparation and output of palladium powder products with different target particle size specifications based on the performance requirements of various applications such as MLCCs and electronic pastes. This broadens the applicability of the method while also exhibiting superior process stability and suitability for industrial-scale mass production.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Precise control of particle size and monodispersity are achieved: By synergistically controlling the nucleation kinetics and grain growth process of the reaction system, this invention successfully achieves precise control of the submicron-sized palladium powder particle size and morphology. The average particle size of the palladium powder is adjustable in the range of 100 nm to 1 μm, and it has a narrow particle size distribution, high sphericity, and excellent dispersibility. This effectively solves the problems of wide particle size distribution and poor sphericity caused by the difficulty in separating the nucleation and growth processes and the uncontrollable reduction rate in traditional processes.

[0019] Significantly Improved Application Performance and Material Quality: The palladium powder prepared by this invention features a wide adjustable particle size range, good particle size uniformity, narrow particle size distribution, high sphericity, and excellent dispersibility. When used in electronic pastes, it can significantly improve the rheological properties of the pastes, increase the density of the sintered film, and reduce porosity, which is beneficial to improving the performance stability of microelectronic devices. Furthermore, the palladium powder particle size can be flexibly adjusted according to the needs of different application scenarios, greatly expanding the product's versatility and applicability, and better adapting to the differentiated needs of high-end electronic materials in various fields such as MLCCs, thick-film circuits, and sensors.

[0020] Process advantages: The preparation method of this invention operates under mild conditions, requiring no expensive specialized equipment or extreme reaction conditions. The operation process is simple, the reaction cycle is short, and batch reproducibility is good. Furthermore, the preparation process of this invention exhibits excellent scale-up effects, facilitating the transition from laboratory preparation to large-scale industrial production, thus combining economic efficiency with engineering practicality. Attached Figure Description

[0021] Figure 1 This is a SEM image of the palladium powder prepared in Example 1 of the present invention; Figure 2 This is a particle size distribution diagram of the palladium powder prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the palladium powder prepared in Example 2 of the present invention; Figure 4 This is a particle size distribution diagram of the palladium powder prepared in Example 2 of the present invention; Figure 5 This is a SEM image of the palladium powder prepared in Example 3 of the present invention; Figure 6 This is a particle size distribution diagram of the palladium powder prepared in Example 3 of the present invention; Figure 7 This is a SEM image of the palladium powder prepared in Example 4 of the present invention; Figure 8 This is a particle size distribution diagram of the palladium powder prepared in Example 4 of the present invention; Figure 9 This is a SEM image of the palladium powder prepared in Example 5 of the present invention; Figure 10 This is a particle size distribution diagram of the palladium powder prepared in Example 5 of the present invention; Figure 11 This is a SEM image of the palladium powder prepared in Example 6 of the present invention; Figure 12 This is a particle size distribution diagram of the palladium powder prepared in Example 6 of the present invention; Figure 13 This is a SEM image of the palladium powder prepared in Comparative Example 1 of this invention. Figure 14 This is a particle size distribution diagram of the palladium powder prepared in Comparative Example 1 of the present invention; Figure 15 This is a SEM image of the palladium powder prepared in Comparative Example 2 of this invention; Figure 16 This is a particle size distribution diagram of the palladium powder prepared in Comparative Example 2 of the present invention; Figure 17 This is a SEM image of the palladium powder prepared in Comparative Example 3 of this invention. Figure 18 This is a particle size distribution diagram of the palladium powder prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0022] This invention provides a method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size, comprising the following steps: The pH of the palladium source solution was adjusted to 7.5-8.5 using an inorganic alkali solution to obtain an alkaline palladium-containing solution. An oxidizing agent solution is obtained by mixing a surfactant solution and an alkaline palladium-containing solution; the mass ratio of surfactant to palladium ions in the oxidizing agent solution is (0.05~0.2):1; the mass concentration of surfactant in the oxidizing agent solution is 0.02~0.2%. The reducing agent solution is added dropwise to the oxidizing agent solution under stirring conditions to carry out a reduction reaction, followed by solid-liquid separation, to obtain the submicron-sized monodisperse spherical palladium powder with controllable particle size; The concentration of the reducing agent in the reducing agent solution is 0.6~2.5 mol / L; the molar ratio of the reducing agent to the palladium ions in the oxidizing agent solution is (1~4):1; the dropping rate of the reducing agent solution is 1~4 mL / s; the temperature of the reduction reaction is 20~40℃; and the stirring speed is 200~300 rpm.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0024] This invention uses an inorganic alkaline solution to adjust the pH of the palladium source solution to 7.5-8.5 to obtain an alkaline palladium-containing solution.

[0025] In this invention, the inorganic alkaline solution is preferably one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution; in specific embodiments, the pH value of the palladium source solution can be adjusted to 7.5, 8.0, or 8.5 using the inorganic alkaline solution. Adjusting the pH value to the above range provides a suitable alkaline environment for the reduction reaction.

[0026] In this invention, the palladium source solution is preferably a chloropalladium acid solution or a palladium nitrate solution, more preferably a chloropalladium acid solution. In this invention, the mass fraction of palladium in the palladium source solution is preferably 5-20%, and in specific embodiments it can be 5%, 10%, 15%, 18%, or 19.8%.

[0027] After obtaining the alkaline palladium-containing solution, the present invention mixes the surfactant solution and the alkaline palladium-containing solution to obtain the oxidant solution.

[0028] In this invention, the mass concentration of the surfactant solution is preferably 0.1-0.5%, and in specific embodiments it can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%. In this invention, the mass ratio of surfactant to palladium ions in the oxidant solution is (0.05-0.2):1, and in specific embodiments it can be 0.05:1, 0.1:1, 0.15:1, or 0.2:1. In this invention, the mass concentration of surfactant in the oxidant solution is preferably 0.02-0.2%, and in specific embodiments it can be 0.02%, 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, 0.17%, or 0.2%. In this invention, as the amount and concentration of surfactant increase within the above ranges, the particle size of the prepared palladium powder becomes smaller. In this invention, the surfactant preferably includes one or more of polyvinylpyrrolidone K30, gum arabic, gelatin, sodium dodecylbenzenesulfonate, and hexadecyltrimethylammonium bromide.

[0029] After obtaining the oxidant solution, the present invention adds the reducing agent solution dropwise to the oxidant solution under stirring conditions to carry out a reduction reaction, and separates the solid and liquid to obtain the submicron-sized monodisperse spherical palladium powder with controllable particle size.

[0030] In this invention, the stirring speed is 200-300 rpm, and in specific embodiments, it can be 200, 230, 250, 270, or 300 rpm. In this invention, the solvent of the reducing agent solution is preferably water; the concentration of the reducing agent in the reducing agent solution is 0.6-2.5 mol / L, and in specific embodiments, it can be 0.6, 0.75, 1, 1.4, 1.6, 1.8, 2, 2.2, or 2.5 mol / L; the molar ratio of the reducing agent to palladium ions in the oxidizing agent solution is (1-4):1, and in specific embodiments, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. In this invention, the dropping rate of the reducing agent solution is 1-4 mL / s, and in specific embodiments, it can be 1, 2, 3, or 4 mL / s. In this invention, as the amount and concentration of reducing agent, the drop rate of reducing agent, and the stirring speed increase, the resulting palladium powder particle size is generally smaller, and vice versa. Those skilled in the art can make adjustments according to their needs.

[0031] During the slow dripping of the reducing agent into the oxidizing agent solution, the instantaneous concentration and amount of the reducing agent in the system gradually increase. Palladium ions preferentially and uniformly nucleate first under low reducing agent concentration conditions. As the reducing agent concentration in the system continues to increase, palladium ions are further directionally deposited and epitaxially grown on the surface of the already generated crystal nuclei, realizing the stepwise process of crystal nucleus formation and particle growth.

[0032] In this invention, the temperature of the reduction reaction is 20~40℃, and in specific embodiments it can be 20, 25, 30, 35 or 40℃; the time of the reduction reaction is preferably 30~60 min, and in specific embodiments it can be 30, 40, 50 or 60 min. In this invention, the time of the reduction reaction refers to the time starting from when the reducing agent solution is completely added. Within the above range, the smaller the particle size of the palladium powder obtained, the higher the reduction reaction temperature.

[0033] In this invention, the solid-liquid separation is preferably performed by centrifugation. The centrifugation speed is preferably 4000~8000 rpm, and in specific embodiments it can be 4000, 5000, 6000, 7000 or 8000 rpm.

[0034] After solid-liquid separation, the present invention preferably further includes washing and drying the obtained solid. In the present invention, the washing preferably includes sequential water washing and ethanol washing; the washing method is preferably: after adding water or ethanol, ultrasonic vibration is performed first, followed by centrifugation. In an embodiment of the present invention, the number of water washings is 3 times, and the number of ethanol washings is 3 times.

[0035] In this invention, the drying temperature is preferably 40~60℃, and in specific embodiments it can be 40, 50 or 60℃.

[0036] The palladium powder prepared by this invention has an adjustable average particle size in the submicron range (100 nm to 1 μm), good particle size uniformity, narrow particle size distribution, high sphericity, and excellent dispersibility.

[0037] The following detailed description of the preparation method of submicron-sized monodisperse spherical palladium powder with controllable particle size provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1 (1) Take 100 mL of chloropalladium acid solution with a palladium mass fraction of 19.8%, add a certain amount of sodium hydroxide solution to adjust the pH value of the solution to 8, and make the total volume of the solution 1 L to prepare an alkaline palladium-containing solution; (2) Dissolve 2 g of polyvinylpyrrolidone K30 completely in 500 mL of deionized water to prepare a surfactant solution with a mass concentration of 0.4%, and mix it thoroughly with the above alkaline palladium-containing solution to prepare an oxidant solution. The mass ratio of polyvinylpyrrolidone K30 to palladium ions is 0.1:1, and the mass concentration of surfactant in the oxidant solution is 0.13%. (3) Take 35 g of hydrazine hydrate with a mass fraction of 80%, add it to 400 mL of deionized water, stir and mix well to prepare a reducing agent solution with a molar concentration of 1.4 mol / L; (4) The reducing agent solution was added to the oxidizing agent solution at a dropping rate of 3 mL / s, and the reduction reaction was carried out continuously for 30 min under stirring conditions of 30℃ and 250 rpm. After the reaction was completed, a suspension containing palladium powder was obtained. (5) The suspension containing palladium powder was centrifuged at 6000 rpm to separate the solid and liquid components. The precipitated palladium powder was washed with deionized water and ethanol in sequence. After being ultrasonically vibrated and homogenized, it was centrifuged again. The washing was repeated 6 times (3 times with water and 3 times with ethanol) to remove residual ions and surfactants. The washed palladium powder was placed in a forced-air drying oven and dried at 50°C to obtain the desired submicron-sized monodisperse spherical palladium powder.

[0039] Example 2 The difference from Example 1 is that the molar concentration of hydrazine hydrate is 1.8 mol / L.

[0040] Example 3 The difference from Example 1 is that the molar concentration of hydrazine hydrate is 1 mol / L.

[0041] Example 4 The difference from Example 1 is that the molar concentration of hydrazine hydrate is 0.75 mol / L.

[0042] Example 5 The difference from Example 1 is that the amount of polyvinylpyrrolidone K30 used is 1.8 g.

[0043] Example 6 The difference from Example 1 is that the dropping rate of the reducing agent solution is 2 mL / s.

[0044] Comparative Example 1 The difference from Example 1 is that the molar concentration of hydrazine hydrate is 3 mol / L.

[0045] Comparative Example 2 The difference from Example 1 is that the molar concentration of hydrazine hydrate is 0.25 mol / L.

[0046] Comparative Example 3 The difference from Example 1 is that the reduction reaction temperature is 50°C.

[0047] Morphology and particle size analysis Morphology analysis was performed on the palladium powder samples obtained in Examples 1-6 and Comparative Examples 1-3. Figure 1 This is a SEM image of the palladium powder obtained in Example 1. Figure 2 This is a particle size distribution diagram of the palladium powder obtained in Example 1. Figure 1 and Figure 2 It can be seen that the palladium powder prepared by the present invention has high sphericity, good dispersibility, uniform particle size, and narrow particle size distribution, with an average particle size of 357 nm.

[0048] Figure 3 This is a SEM image of the palladium powder obtained in Example 2. Figure 4 This is a particle size distribution diagram of the palladium powder obtained in Example 2. Figure 3 and Figure 4 It can be seen that the preparation method of the present invention can control the particle size of palladium powder in the submicron range by adjusting the concentration of the reducing agent solution, while ensuring the characteristics of uniform particle size, high sphericity, monodispersity, and narrow particle size distribution of palladium powder. Compared with Example 1, the concentration of the reducing agent solution in Example 2 is increased, and the average particle size of the resulting palladium powder is reduced to 212 nm.

[0049] Figure 5 This is a SEM image of the palladium powder obtained in Example 3. Figure 6 This is a particle size distribution diagram of the palladium powder obtained in Example 3. Figure 7 Here is a SEM image of the palladium powder obtained in Example 4. Figure 8 This is a particle size distribution diagram of the palladium powder obtained in Example 4. Figures 5-8 It can be seen that, compared with Example 1, as the concentration of the reducing agent solution gradually decreases, the average particle size of palladium powder gradually increases. The average particle size of palladium powder obtained in Example 3 is 542 nm, and the average particle size of palladium powder obtained in Example 4 is 861 nm.

[0050] Figure 9 This is a SEM image of the palladium powder obtained in Example 5. Figure 10 This is a particle size distribution diagram of the palladium powder obtained in Example 5. Figure 9 and Figure 10 It can be seen that, compared with Example 1, the amount of surfactant used was reduced by 10%, and the average particle size of palladium powder increased from 357 nm to 417 nm.

[0051] Figure 11 Here is a SEM image of the palladium powder obtained in Example 6. Figure 12 This is a particle size distribution diagram of the palladium powder obtained in Example 6. Figure 11 and Figure 12It can be seen that, compared with Example 1, when the dropping rate of the reducing agent solution decreases, the average particle size of palladium powder increases by 553 nm.

[0052] Figure 13 The image shows a SEM image of the palladium powder obtained in Comparative Example 1. Figure 14 The particle size distribution diagram of the palladium powder obtained in Comparative Example 1 is shown. Figure 15 The image shows a SEM image of the palladium powder obtained in Comparative Example 2. Figure 16 The particle size distribution diagram of the palladium powder obtained in Comparative Example 2 is shown. Figure 17 The image shows a SEM image of the palladium powder obtained in Comparative Example 3. Figure 18 This is a particle size distribution diagram of the palladium powder obtained in Comparative Example 3. Figures 13-18 It can be seen that Comparative Examples 1 to 3 exceeded the reducing agent concentration and reduction temperature specified in this invention, and the resulting palladium powder had poor sphericity, wide particle size distribution, and severe particle agglomeration.

[0053] Table 1. Particle size distribution of Examples 1-6 and Comparative Examples 1-3

[0054] Note: Particle size deviation ratio = (standard deviation ÷ average particle size) × 100%. The larger the particle size deviation ratio, the wider the particle size distribution.

[0055] Depend on Figures 1-12 It is evident that the palladium powder particles prepared using the process parameters defined in this invention exhibit regular morphology, excellent sphericity, uniform dispersion, and concentrated particle size distribution. This allows for precise control of the palladium powder particle size within the submicron range (100 nm to 1 μm), fully demonstrating that the synergistic control of the preparation process in this invention plays a crucial role in regulating the nucleation and growth process of palladium powder and improving particle morphology and dispersibility. This further confirms the rationality and necessity of the process conditions in this invention.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing submicron-sized monodisperse spherical palladium powder with controllable particle size, characterized in that, Includes the following steps: The pH of the palladium source solution was adjusted to 7.5-8.5 using an inorganic alkali solution to obtain an alkaline palladium-containing solution. A surfactant solution and an alkaline palladium-containing solution are mixed to obtain an oxidizing agent solution; The mass ratio of surfactant to palladium ions in the oxidant solution is (0.05~0.2):1; the mass concentration of surfactant in the oxidant solution is 0.02~0.2%. The reducing agent solution is added dropwise to the oxidizing agent solution under stirring conditions to carry out a reduction reaction, followed by solid-liquid separation, to obtain the submicron-sized monodisperse spherical palladium powder with controllable particle size; The concentration of the reducing agent in the reducing agent solution is 0.6~2.5 mol / L; the molar ratio of the reducing agent to the palladium ions in the oxidizing agent solution is (1~4):1; the dropping rate of the reducing agent solution is 1~4 mL / s; the temperature of the reduction reaction is 20~40℃; and the stirring speed is 200~300 rpm.

2. The preparation method according to claim 1, characterized in that, The surfactant includes one or more of polyvinylpyrrolidone K30, gum arabic, gelatin, sodium dodecylbenzenesulfonate, and hexadecyltrimethylammonium bromide.

3. The preparation method according to claim 1 or 2, characterized in that, The mass concentration of the surfactant solution is 0.1~0.5%.

4. The preparation method according to claim 1, characterized in that, The reducing agent is hydrazine hydrate.

5. The preparation method according to claim 1, characterized in that, The reduction reaction takes 30 to 60 minutes.

6. The preparation method according to claim 1, characterized in that, The inorganic alkaline solution is one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution.

7. The preparation method according to claim 1, characterized in that, The palladium source solution is a chloropalladium acid solution or a palladium nitrate solution.

8. The preparation method according to claim 1 or 7, characterized in that, The palladium source solution contains 5-20% palladium by mass.

9. The preparation method according to claim 1, characterized in that, The solid-liquid separation process further includes washing and drying the resulting solid.

10. The preparation method according to claim 9, characterized in that, The drying temperature is 40~60℃.

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