A method for electrochemically synthesizing platinum nitrate

Abstract

The application discloses a method for electrochemically synthesizing platinum nitrate, and belongs to the technical field of precious metal chemical industry and electrochemical synthesis. The method discards the traditional fixed platinum anode, adopts a chemically inert electrode, and directly suspends platinum powder in a composite electrolyte composed of nitric acid, high-concentration sodium / potassium nitrate supporting electrolyte and sulfamic acid complexing agent. Under strong mechanical stirring, the electrode is subjected to electrolysis by applying a composite waveform current of pulse current or direct current superimposed on alternating current with specific parameters, so that the platinum powder is efficiently oxidized and dissolved through dynamic collision. After the electrolyte is subjected to heat filtration, the electrolyte is concentrated under low-temperature and reduced pressure until a crystal film appears, and then the electrolyte is subjected to cooling crystallization, washing and drying, so that a high-purity platinum nitrate product is obtained. The method solves the problem of anode passivation, significantly improves the current efficiency and reaction rate, is green and environment-friendly, has high product purity, and is easy to realize continuous production.

Description

Technical Field

[0001] This invention specifically relates to a green and efficient electrochemical synthesis method for platinum nitrate, belonging to the fields of precious metal chemical engineering and electrochemical synthesis technology. Background Technology

[0002] Platinum nitrate is an important platinum group chemical, widely used as a precursor for platinum catalysts in automotive exhaust catalysts, electronic materials, and electroplating. Traditional methods for synthesizing platinum nitrate primarily involve dissolving metallic platinum in aqua regia, followed by multiple evaporations to remove the nitrate. This method severely pollutes the environment, as the aqua regia dissolution process generates chlorine gas (Cl2) and nitrogen oxides (NOx). X It contains toxic and harmful gases such as chloride ions, and it is difficult to completely remove chloride ions from the product, which affects its application in certain chlorine-sensitive catalytic reactions.

[0003] Chinese patent application No. 201910100935.X, published on April 12, 2019, discloses a method for preparing platinum nitrate solution. This method first prepares a platinum hydroxyl intermediate to prepare platinum nitrate. The steps are cumbersome and introduce a large amount of sodium ions during the formation of platinum hydroxyl, resulting in incomplete washing and residual chlorine and sodium. Chinese patent application No. 202210985478.9, published on November 22, 2022, discloses another method for preparing platinum nitrate solution. This method dissolves metallic platinum in aqua regia, then evaporates it multiple times to remove nitrate, adds silver nitrate solution to precipitate chloride ions, and finally separates it from the platinum nitrate solution. This method suffers from the inability to precisely control the amount of silver nitrate added, leading to the presence of Ag in the solution. + The introduction of this issue.

[0004] Electrochemical synthesis, as a green alternative, directly uses platinum as the anode and dissolves it in nitric acid electrolyte. However, existing electrochemical methods suffer from inherent drawbacks such as low current efficiency, slow dissolution rate, and easy anode passivation. The root cause lies in the excessively thick ion diffusion layer on the anode surface under traditional DC electrolysis, which easily forms a dense oxide passivation film, hindering the continuous reaction. This results in high energy consumption, long production cycles, and difficulty in industrial application. Therefore, developing a highly efficient synthesis method that can effectively overcome passivation and enhance mass transfer is urgently needed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electrochemical method that can effectively prevent anodic passivation, greatly improve mass transfer efficiency and current efficiency, thereby achieving efficient and energy-saving synthesis of platinum nitrate, in order to overcome the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for electrochemically synthesizing platinum nitrate, characterized by comprising the following steps: S1. Chemically inert electrodes are used as the anode and cathode and placed in the electrolytic cell; S2. Add platinum powder and a composite electrolyte solution to the electrolytic cell described in step S1. The composite electrolyte solution contains nitric acid, a supporting electrolyte, and a complexing agent. S3. Under mechanical stirring, a pulsed current or a composite waveform current of DC superimposed AC is applied between the anode and cathode described in step S1 to perform electrolysis, and the electrolyte temperature is controlled so that the platinum powder dissolves and generates a solution containing platinum ions. S4. The solution obtained in step S3 is subjected to hot filtration, concentrated under reduced pressure until a crystal film appears or the solution becomes viscous, then cooled for crystallization, solid-liquid separation, washing and drying to obtain solid platinum nitrate product.

[0007] Optionally, the chemically inert electrode in step S1 is selected from one or more of titanium electrodes and graphite electrodes.

[0008] Optionally, in step S2, the composite electrolyte is nitric acid with a concentration of 1-3 mol / L; the supporting electrolyte is sodium nitrate or potassium nitrate, with a concentration of 3-5 mol / L sodium nitrate solution or 2-3.5 mol / L potassium nitrate solution; and the complexing agent is aminosulfonic acid with a concentration of 0.4-0.8 mol / L.

[0009] Optionally, in step S3, the power supply method is either pulse power supply or composite waveform power supply with superimposed DC and AC components. The peak current density of the pulse power supply is 150-600 mA / cm², the frequency is 50-500 Hz, and the duty cycle is 10%-25%. The composite waveform power supply is based on a DC current density of 20-60 mA / cm², with an AC waveform superimposed on it, having a frequency of 5-30 Hz and an amplitude of 15%-25% of the DC component.

[0010] Optionally, in step S3, the mechanical stirring speed is 800~1500 rpm, and the electrolyte temperature is controlled at 50~70℃.

[0011] Optionally, in step S4, the low-temperature rotary evaporation temperature is 40~60℃; washing is performed using pre-cooled dilute nitric acid or a mixture of dilute nitric acid and alcohol; drying is carried out at 40~60℃ and an absolute pressure below 20 kPa.

[0012] The beneficial effects of the present invention include, but are not limited to: 1. This invention uses pulse power supply or a composite waveform power supply with superimposed DC and AC components, combined with mechanical stirring of platinum powder, to change the traditional method of using platinum sheet as anode, reducing the possibility of platinum sheet passivation and greatly improving the electrolysis efficiency of platinum powder.

[0013] 2. This invention, by supporting the addition of potassium nitrate / sodium nitrate electrolytes, improves the conductivity of the electrolyte, reduces cell voltage, significantly saves energy, and reduces ineffective heating caused by solution resistance, resulting in more precise temperature control. Simultaneously, as a "reaction promoter," it provides a high concentration of nitrate ions and stabilizes the acidic environment, facilitating the dissolution of newly formed Pt. 4+ Preliminary electrostatic stabilization is performed to detach it from the metal surface and initiate dissolution.

[0014] 3. The addition of the complexing agent aminosulfonic acid in this invention, during the electrolysis process in step S3, reacts with the generated [Pt(NO3)6]. 2- The platinum-aminosulfonic acid complex, through its sulfonic acid group, coordinates with Pt(IV) to form a stable platinum-aminosulfonic acid complex soluble in nitric acid medium, carrying it deep into the solution and preventing Pt(IV) from accumulating near the electrode and hydrolyzing into PtO2, thus preventing anode passivation. During the rotary evaporation process in step S4, the concentration of all components increases as the solvent evaporates. Platinum nitrate, due to its low solubility, crystallizes out first. The crystallization process continuously removes Pt(IV) from the solution, further disrupting the coordination balance in the solution. To compensate, the platinum-aminosulfonic acid complex continuously dissociates Pt(IV) to participate in the formation of platinum nitrate crystals, while aminosulfonic acid, due to its high water solubility, remains in the mother liquor, achieving automatic separation from the product.

[0015] 4. The process of this invention is completely chlorine-free, fundamentally avoiding the introduction of chloride ions. The resulting platinum nitrate product has high purity and a chloride ion content of less than 50 ppm, making it particularly suitable for high-end catalytic fields that are sensitive to chloride.

[0016] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments in order to more clearly explain the advantages of the present invention. The embodiments described are merely exemplary and do not constitute any limitation on the scope of the present invention.

[0018] Example 1 a. Take two pieces with an effective area of ​​64 cm² 2 High-purity graphite electrodes are placed parallel to each other in the electrolytic cell as the anode and cathode.

[0019] b. Preparation of the composite electrolyte solution: Measure deionized water and add concentrated nitric acid to prepare a 2 mol / L HNO3 solution; add sodium nitrate while stirring to a concentration of 4.0 mol / L; finally add aminosulfonic acid to a concentration of 0.5 mol / L. The total volume is 1.0 L.

[0020] c. Add the electrolyte to the tank and place it in a constant temperature water bath at 60℃. Turn on the magnetic stirrer at 1000 rpm. Add 10.00g of platinum powder. Connect the pulse power supply and set the parameters: peak current density 300 mA / cm². 2 (Corresponding current 19.2A), frequency 100 Hz, duty cycle 15%, electrolysis begins.

[0021] d. After 7 hours of electrolysis, the platinum powder was essentially dissolved. The reaction was stopped, and the solution was hot-filtered at 60°C. The filtrate was then concentrated to approximately 200 mL by rotary evaporation under reduced pressure at 55°C and approximately 11 kPa (a large amount of crystal film appeared). The solution was then transferred to 4°C and allowed to crystallize for 12 hours. After filtration, the crystals were rapidly washed twice with 20 mL of pre-cooled 0.5 mol / L nitric acid-ethanol mixture (1:1, v / v). The wet crystals were then vacuum-dried at 45°C and 10 kPa for 6 hours. 27.3 g of orange-yellow platinum nitrate crystals were obtained, with a yield of 96.0%.

[0022] Product Analysis: Platinum content ~34.9% (ICP-OES), sulfate ion content <100 ppm, chloride ion (Cl... - Content <50ppm (ion chromatography).

[0023] Example 2 a. Take a piece with an effective area of ​​64 cm 2 A titanium electrode is used as the anode, and a graphite electrode of equal area is used as the cathode, both placed in the electrolytic cell.

[0024] b. Prepare a compound electrolyte solution: 3 mol / L nitric acid, 3.5 mol / L potassium nitrate, 0.8 mol / L aminosulfonic acid, total volume 1.0L.

[0025] c. Maintain a temperature of 70℃ and mechanically stir at 1500 rpm. Add 10.00g of platinum powder. Connect the power supply and apply a composite waveform current: DC current density 60 mA / cm². 2 (Corresponding current 3.84A), superimposed with a sinusoidal AC wave with a frequency of 30 Hz and an amplitude of 25% DC component.

[0026] d. After 6 hours of electrolysis, the platinum powder was completely dissolved. Post-processing was then performed as in Example 1.

[0027] e. 27.15g of platinum nitrate product was obtained, with a yield of 95.4%.

[0028] Product analysis: Sulfate ion content <120 ppm, chloride ion (Cl-) content <50 ppm (ion chromatography).

[0029] Example 3 a. Same as the device in Example 1.

[0030] b. Preparation of the composite electrolyte solution: Measure deionized water and add concentrated nitric acid to prepare a 1 mol / L HNO3 solution; add sodium nitrate while stirring to a concentration of 3.0 mol / L; finally add sulfamic acid to a concentration of 0.4 mol / L. The total volume is 1.0 L.

[0031] c. Add the electrolyte to the tank and place it in a constant temperature water bath at 50℃. Turn on the magnetic stirrer at 800 rpm. Add 10.00g of platinum powder. Connect the pulse power supply and set the parameters: peak current density 150 mA / cm². 2 (Corresponding current 9.6A), frequency 50Hz, duty cycle 10%, electrolysis begins.

[0032] d. After 8.5 hours of electrolysis, the platinum powder was completely dissolved. The post-treatment process was the same as in Example 1.

[0033] e. 26.8g of platinum nitrate product was obtained, with a yield of 94.2%.

[0034] Product Analysis: Sulfate ion content <80 ppm, chloride ion (Cl...) - Content <50ppm (ion chromatography).

[0035] Example 4 a. The device is the same as in Example 1.

[0036] b. Preparation of the composite electrolyte solution: Measure deionized water and add concentrated nitric acid to prepare a 2 mol / L HNO3 solution; add sodium nitrate while stirring to a concentration of 5.0 mol / L; finally add aminosulfonic acid to a concentration of 0.6 mol / L. The total volume is 1.0 L.

[0037] c. Maintain a temperature of 65℃ and stir at 1200 rpm. Add 10.0g of platinum powder. Apply a pulsed current: peak current density 600mA / cm². 2 (Corresponding current 38.4A), frequency 500 Hz, duty cycle 25%, electrolysis begins.

[0038] d. After 3.5 hours of electrolysis, the platinum powder was completely dissolved. The post-treatment process was the same as in Example 1.

[0039] e. 26.51g of platinum nitrate product was obtained, with a yield of 93.0%.

[0040] Product Analysis: Sulfate ion content <150 ppm, chloride ion (Cl...) - Content <50ppm (ion chromatography).

[0041] Example 5 a. Take a piece with an effective area of ​​64 cm 2A titanium electrode is used as the anode, and a graphite electrode of equal area is used as the cathode, both placed in the electrolytic cell.

[0042] b. Prepare a compound electrolyte solution: nitric acid concentration 2 mol / L, sodium nitrate concentration 4.0 mol / L, and aminosulfonic acid concentration 0.5 mol / L. Total volume 1.0L.

[0043] c. Maintain a temperature of 60℃ and mechanically stir at 1000 rpm. Add 10.00g of platinum powder. Connect the power supply and apply a composite waveform current: DC current density 30 mA / cm². 2 (Corresponding current 1.92A), superimposed with a sinusoidal AC wave with a frequency of 10 Hz and an amplitude of 20% of the DC component.

[0044] d. After electrolysis for 12 hours, the platinum powder was completely dissolved. Post-processing was then performed as in Example 1.

[0045] e. 26.4g of platinum nitrate product was obtained, with a yield of approximately 92.6%.

[0046] Product analysis: Sulfate ion content <150 ppm, chloride ion content <50 ppm Comparative Example 1 a. Take a 10.00g platinum sheet (area ~64 cm²) 2 ) serves as the anode, and graphite as the cathode.

[0047] b. The electrolyte is the same as in Example 1.

[0048] c. Maintain a temperature of 60℃ and stir. Apply a direct current with a current density of 30 mA / cm². 2 (Corresponding current 1.92A). After electrolysis began, the cell voltage steadily increased from 5V, exceeding 20V after 2 hours, resulting in severe anode passivation. After 7.5 hours, the platinum sheet only lost 1.0g, making it impossible to obtain a usable product.

[0049] Comparative Example 2 a. Same as the device in Example 1.

[0050] b. Prepare an electrolyte that does not contain aminosulfonic acid, but otherwise the same as in Example 1.

[0051] c. Same pulse parameters and operation as in Example 1. Approximately 30 minutes after the start of electrolysis, a large amount of brownish-red precipitate is produced in the solution, the reaction stops, and it cannot continue.

[0052] Comparative Example 3 a. Same as the device in Example 1.

[0053] b. Prepare an electrolyte containing only nitric acid (2.0 M) and aminosulfonic acid (0.5 M).

[0054] c. Same pulse parameters as in Example 1. After power-on, the tank voltage >18V, causing severe overheating and forcing a shutdown.

[0055] Comparative Example 4 a. Same apparatus and raw materials as in Example 1.

[0056] b. The electrolyte is the same as in Example 1.

[0057] c. Use a DC power supply with a current density of 30 mA / cm². 2 (Corresponding current 1.92A). After 7.5 hours of electrolysis, the solution became turbid. Following the same post-treatment, 18.0 g of impure solid was obtained, with a yield of approximately 63.3%. Product analysis: sulfate ion content >600 ppm; dull color.

[0058] Table 1. Comparison of key data between the examples and comparative examples As can be seen from the comparison data in the table above, this invention successfully solved the core problem of anodic passivation in the electrochemical synthesis of platinum nitrate by applying inert electrodes, suspended platinum powder, specific waveform power supply, high conductivity supporting electrolyte, and complexation protection. It has achieved efficient, stable, and high-purity green synthesis and has significant industrial application value. The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the invention shall still fall within the protection scope of the present invention.

Claims

1. A method for the electrochemical synthesis of platinum nitrate, characterized in that, Includes the following steps: S1. Chemically inert electrodes are used as the anode and cathode and placed in the electrolytic cell; S2. Add platinum powder and a composite electrolyte solution to the electrolytic cell described in step S1. The composite electrolyte solution contains nitric acid, a supporting electrolyte, and a complexing agent. S3. Under mechanical stirring, a pulsed current or a composite waveform current of DC superimposed AC is applied between the anode and cathode described in step S1 to perform electrolysis, and the electrolyte temperature is controlled so that the platinum powder dissolves and generates a solution containing platinum ions. S4. The solution obtained in step S3 is subjected to hot filtration, concentrated under reduced pressure until a crystal film appears or the solution becomes viscous, then cooled for crystallization, solid-liquid separation, washing and drying to obtain solid platinum nitrate product.

2. The method for electrochemical synthesis of platinum nitrate according to claim 1, characterized in that, The chemically inert electrode is selected from one or more of titanium electrodes and graphite electrodes.

3. The method for electrochemical synthesis of platinum nitrate according to claim 1, characterized in that, The concentration of nitric acid in the composite electrolyte solution is 1.0 ~ 3.0 mol / L; the supporting electrolyte is selected from one or more of sodium nitrate or potassium nitrate; when the supporting electrolyte is sodium nitrate, its concentration is 3.0 ~ 5.0 mol / L; when the supporting electrolyte is potassium nitrate, its concentration is 2.0 ~ 3.5 mol / L; the complexing agent is selected from aminosulfonic acid, and its concentration is 0.4 ~ 0.8 mol / L.

4. The method for electrochemical synthesis of platinum nitrate according to claim 1, characterized in that, In step S3, the peak current density of the pulse current is 150 ~ 600 mA / cm², the frequency is 50 ~ 500 Hz, and the duty cycle is 10% ~ 25%. The composite waveform current is based on a DC current density of 20 ~ 60 mA / cm², with an AC waveform having a frequency of 5 ~ 30 Hz and an amplitude of 15% ~ 25% of the DC component superimposed on it.

5. The method for electrochemical synthesis of platinum nitrate according to claim 1, characterized in that, The mechanical stirring speed in step S3 is 800-1500 rpm, and the electrolyte temperature is controlled at 50-70℃.

6. The method for electrochemical synthesis of platinum nitrate according to claim 1, characterized in that, In step S4, the temperature of the vacuum concentration is 40-60℃ and the absolute pressure is 5-20 kPa; the washing uses pre-cooled dilute nitric acid or a mixture of dilute nitric acid and alcohol; the drying is carried out at 40-60℃ and an absolute pressure below 20 kPa.

7. A platinum nitrate product, characterized in that, Prepared by the method according to any one of claims 1 to 6, the product contains sulfate ions (SO4). 2- The content of chloride ions (Cl) is less than 200 ppm, and the chloride ion content is less than 200 ppm. - The content is less than 50 ppm.

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