Preparation method of high-purity platinum nitrate

Abstract

This invention relates to the field of platinum nitrate preparation technology, and more particularly to a method for preparing high-purity platinum nitrate. The method comprises the following steps: Step A, adding aqua regia to platinum powder to completely dissolve the powder and prepare a chloroplatinic acid solution; Step B, adding excess sodium hydroxide under stirring and heating to prepare a sodium hydroxyplatinate mixture; Step C, titrating the sodium hydroxyplatinate mixture with nitric acid under stirring in an ice-water bath, maintaining the temperature below 50°C during titration. This method for preparing high-purity platinum nitrate is characterized by its simplicity, absence of complex reactions, and the resulting platinum nitrate being chloride-free, highly pure, and having a high yield and preparation efficiency. It solves the technical problems of existing platinum precursor chloroplatinic acid containing a large amount of chloride ions, which easily affects catalytic effects, and the low preparation efficiency of existing platinum nitrate preparation methods.

Description

Technical Field

[0001] This invention relates to the field of platinum nitrate preparation technology, and in particular to a method for preparing high-purity platinum nitrate. Background Technology

[0002] Commonly used platinum precursors for three-way catalysts include chloroplatinic acid, platinum nitrate, and di(ethanolamine) hexahydroxyplatinic acid. Chloroplatinic acid was initially chosen as the mainstream precursor due to its ease of preparation and low cost. However, chloroplatinic acid contains a large number of chloride ions. If chloride ions cannot be completely removed during the preparation of the precursor, it will inhibit the catalytic performance and affect the lifespan of the catalyst. It will also corrode the metal support, leading to problems such as easy rusting. Therefore, more manufacturers have begun to develop new chloride-free platinum precursors.

[0003] Currently, sodium hydroxyplatinate is prepared by adding excess sodium hydroxide to sodium chloroplatinate, then neutralizing it with acetic acid to prepare hydroxyplatinic acid, and finally dissolving it with ethanolamine to obtain hexahydroxyplatinic acid di(ethanolamine), with a yield of 96%. However, this does not demonstrate that this precursor has better catalytic activity than similar precursors. Nevertheless, compared to chloroplatinic acid, hexahydroxyplatinic acid di(ethanolamine) does have the advantage of being free of chlorine and alkaline earth metal residues. Performance evaluations have also been conducted on two platinum precursors, chloroplatinic acid and platinum nitrate. Experimental results show that the catalyst prepared from platinum nitrate exhibits significantly better performance than the catalyst prepared from chloroplatinic acid.

[0004] How to prepare high-purity platinum nitrate more efficiently is also a problem that needs to be solved. Currently, some research teams have recovered platinum from waste catalysts. Starting with platinum, they first prepare potassium chloroplatinate, then reduce potassium chloroplatinate to potassium chloroargonplatinate. By adjusting the pH, platinum hydroxide precipitate is generated. The precipitate is reacted with nitric acid to prepare platinum nitrate solution with a yield of 94.52%. However, the preparation process is cumbersome and complicated, involving multiple reactions. It requires high control of the reaction process and is not suitable for continuous production, resulting in low preparation efficiency. Summary of the Invention

[0005] In response to the problems raised in the background art, the purpose of this invention is to propose a method for preparing high-purity platinum nitrate, which is characterized by a simple process, no complex reactions, and the obtained platinum nitrate is free of chloride ions, has high purity, high yield, and high preparation efficiency. This solves the technical problems of existing platinum precursor chloroplatinic acid containing a large number of chloride ions that easily affect the catalytic effect and the low preparation efficiency of existing platinum nitrate preparation methods.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing high-purity platinum nitrate includes the following steps: Step A: Add aqua regia to platinum powder to completely dissolve the platinum powder and prepare chloroplatinic acid solution; Step B: Add excess sodium hydroxide while stirring, and heat to prepare a sodium hydroxyplatinate mixture; Step C: Titrate the sodium hydroxyplatinate mixture with nitric acid under stirring in an ice-water bath. Keep the temperature below 50°C during the titration. The titration endpoint is pH=5. Separate the precipitate and liquid. Wash the precipitate with an ice-water solution of nitric acid at pH=5 until no chloride ions are present to obtain solid hydroxyplatinic acid. Step D: Add ammonium acetate to the hydroxyplatinic acid solid, then add nitric acid solution to dissolve the hydroxyplatinic acid solid and obtain platinum nitrate solution.

[0007] To further clarify, in step B, adding excess sodium hydroxide under stirring means adding sodium hydroxide at a rate of more than 5 times the molar amount of platinum under stirring.

[0008] To further explain, in step A, after adding aqua regia to the platinum powder, the mixture is heated at 150°C until the platinum powder is completely dissolved.

[0009] To further explain, after heating until the platinum powder is completely dissolved, there is also a step of removing the acid. The temperature is raised to 260°C, hydrochloric acid is added to remove the acid, and after dilution, a chloroplatinic acid solution is obtained.

[0010] To further clarify, in the step of adding hydrochloric acid to remove acid, the hydrochloric acid is obtained by mixing 1 volume of hydrochloric acid with 5 volumes of pure water.

[0011] To further clarify, the heating temperature in step B is 300°C.

[0012] To further clarify, the nitric acid in step C is nitric acid obtained by mixing 1 volume of nitric acid with 2 volumes of pure water.

[0013] To further clarify, in step C, the temperature of the nitric acid ice solution with pH=5 is 3°C.

[0014] To further clarify, in step D, the mass ratio of the amount of ammonium acetate added to the amount of platinum powder added in step A is 1:20.

[0015] To further clarify, the ratio of the amount of nitric acid solution added in step D to the amount of platinum powder added in step A is: 2-10 ml of nitric acid solution for every 1 g of platinum powder.

[0016] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: 1. A method for preparing platinum nitrate involves using platinum powder as a raw material. The platinum powder is dissolved in aqua regia to prepare a chloroplatinic acid solution. An excess of sodium hydroxide is then dissolved in the chloroplatinic acid solution to prepare a sodium hydroxyplatinate mixture. The pH is adjusted by titrating the sodium hydroxyplatinate with nitric acid to prepare hydroxyplatinic acid. Chloride ions are removed from the hydroxyplatinic acid precipitate through filtration and washing. Finally, the solid hydroxyplatinic acid is dissolved in nitric acid to prepare a platinum nitrate solution. The resulting platinum nitrate is chloride-free and of high purity. This method is simple, involves no complex reactions, and currently achieves a yield greater than 96%.

[0017] 2. During the preparation process, by directly adding excess sodium hydroxide to the chloroplatinic acid solution, a sodium hydroxyplatinate mixture can be prepared more quickly, and the excess hydroxide and sodium ions can inhibit the hydrolysis of sodium hydroxyplatinate, resulting in a higher conversion rate.

[0018] 3. By lowering the temperature during the titration of the sodium hydroxyplatinate mixture, the formation of byproducts such as platinum oxide from the resulting hydroxyplatinic acid can be prevented from dehydrating at high temperatures. Simultaneously, lowering the system temperature after titration reduces the solubility of hydroxyplatinic acid. During the filtration and separation of the precipitate and liquid, washing with a pH 5 nitric acid ice solution further reduces the solubility of hydroxyplatinic acid at low temperatures, minimizing platinum loss during washing.

[0019] 4. Since the filtered hydroxyplatinic acid solid is in the form of a filter cake, a small amount of ammonium acetate can be added to the filtered hydroxyplatinic acid solid. Ammonium acetate acts as a co-solvent to make the filter cake into a paste, which helps the filter cake to dissolve quickly after the addition of nitric acid. The filter cake (hydroxyplatinic acid solid) can be completely dissolved in almost 10 minutes to obtain a red transparent platinum nitrate solution. The reaction time is short and the preparation efficiency is high. Attached Figure Description

[0020] Figure 1 This is a technical roadmap diagram illustrating a method for preparing high-purity platinum nitrate according to an embodiment of the present invention. Detailed Implementation

[0021] A method for preparing high-purity platinum nitrate includes the following steps: Step A: Add aqua regia to platinum powder to completely dissolve the platinum powder and prepare chloroplatinic acid solution; Step B: Add excess sodium hydroxide while stirring, and heat to prepare a sodium hydroxyplatinate mixture; Step C: Titrate the sodium hydroxyplatinate mixture with nitric acid under stirring in an ice-water bath. Keep the temperature below 50°C during the titration. The titration endpoint is pH=5. Separate the precipitate and liquid. Wash the precipitate with an ice-water solution of nitric acid at pH=5 until no chloride ions are present to obtain solid hydroxyplatinic acid. Step D: Add ammonium acetate to the hydroxyplatinic acid solid, then add nitric acid solution to dissolve the hydroxyplatinic acid solid and obtain platinum nitrate solution.

[0022] This invention utilizes platinum powder as a raw material. A chloroplatinic acid solution is prepared by dissolving the platinum powder in aqua regia. An excess of sodium hydroxide is dissolved in the chloroplatinic acid solution to prepare a sodium hydroxyplatinate mixture. The pH is adjusted by titrating the sodium hydroxyplatinate with nitric acid to prepare hydroxyplatinic acid. Chloride ions are removed from the hydroxyplatinic acid precipitate by filtration and washing. Finally, the solid hydroxyplatinic acid is dissolved in nitric acid to prepare a platinum nitrate solution. The resulting platinum nitrate is chloride-free and of high purity. This method is simple, involves no complex reactions, and currently achieves a yield greater than 96%.

[0023] In addition, by directly adding excess sodium hydroxide to the chloroplatinic acid solution during the preparation process, a sodium hydroxyplatinate mixture can be prepared more quickly, and the excess hydroxide and sodium ions can inhibit the hydrolysis of sodium hydroxyplatinate, resulting in a higher conversion rate.

[0024] By lowering the temperature during the titration of the sodium hydroxyplatinate mixture, the formation of byproducts such as platinum oxide from the resulting hydroxyplatinic acid can be prevented from dehydrating at high temperatures. Simultaneously, lowering the system temperature after titration reduces the solubility of hydroxyplatinic acid. During the filtration and separation of the precipitate and liquid, washing with a pH 5 nitric acid-ice solution further reduces the solubility of hydroxyplatinic acid at low temperatures, minimizing platinum loss during washing.

[0025] Since the filtered hydroxyplatinic acid solid is in the form of a filter cake, a small amount of ammonium acetate can be added to the filtered hydroxyplatinic acid solid. Ammonium acetate acts as a co-solvent to make the filter cake into a paste, which helps the filter cake to dissolve quickly after the addition of nitric acid. The filter cake (hydroxyplatinic acid solid) can be completely dissolved in almost 10 minutes to obtain a red and transparent platinum nitrate solution. The reaction time is short and the preparation efficiency is high.

[0026] The method for preparing high-purity platinum nitrate is simple, involves no complex reactions, and produces high-purity platinum nitrate free of chloride ions. It also boasts high yield and high preparation efficiency, solving the technical problems of existing platinum precursor chloroplatinic acid containing a large number of chloride ions that easily affect catalytic effects and the low preparation efficiency of existing platinum nitrate preparation methods.

[0027] To further clarify, in step B, adding excess sodium hydroxide under stirring means adding sodium hydroxide at a rate of more than 5 times the molar amount of platinum under stirring.

[0028] By directly adding excess sodium hydroxide to the chloroplatinic acid solution, a sodium hydroxyplatinate mixture can be prepared more quickly, and the excess hydroxide and sodium ions can inhibit the hydrolysis of sodium hydroxyplatinate, resulting in a higher conversion rate.

[0029] Specifically, in step A, aqua regia is a liquid obtained by mixing nitric acid and hydrochloric acid in a volume ratio of 1:3, and 6 mL to 20 mL of aqua regia is used to dissolve 1 g of platinum powder.

[0030] To further explain, in step A, after adding aqua regia to the platinum powder, the mixture is heated at 150°C until the platinum powder is completely dissolved.

[0031] To further explain, after heating until the platinum powder is completely dissolved, there is also a step of removing the acid. The temperature is raised to 260°C, hydrochloric acid is added to remove the acid, and after dilution, a chloroplatinic acid solution is obtained.

[0032] To further clarify, in the step of adding hydrochloric acid to remove acid, the hydrochloric acid is obtained by mixing 1 volume of hydrochloric acid with 5 volumes of pure water.

[0033] To further clarify, the heating temperature in step B is 300°C.

[0034] To further clarify, the nitric acid in step C is nitric acid obtained by mixing 1 volume of nitric acid with 2 volumes of pure water.

[0035] To further clarify, in step C, the temperature of the nitric acid ice solution with pH=5 is 3°C.

[0036] To further clarify, in step D, the mass ratio of the amount of ammonium acetate added to the amount of platinum powder added in step A is 1:20.

[0037] To further clarify, the ratio of the amount of nitric acid solution added in step D to the amount of platinum powder added in step A is: 2-10 ml of nitric acid solution for every 1 g of platinum powder.

[0038] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0039] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0040] Example 1 Step A: Take 2g of platinum powder in a beaker, add 10ml of nitric acid and 30ml of hydrochloric acid, heat on a hot plate at 150℃ until completely dissolved, raise the temperature to 260℃, evaporate to about 5ml, add 20mL of hydrochloric acid to remove the acid, repeat 3-5 times, dilute the solution to 50mL with 1+5 hydrochloric acid to prepare chloroplatinic acid solution. Step B: Add 20g of sodium hydroxide solid to the chloroplatinic acid solution prepared in step A under stirring. After the addition is complete and the reaction is no longer vigorous, transfer it to a hot plate at 300°C and heat it under stirring until the solution turns yellow-green and a large amount of yellow precipitate is formed. Remove it and cool it to prepare a sodium hydroxyplatinate mixture. Step C: Titrate the sodium hydroxyplatinate mixture obtained in Step B with 1+2 nitric acid in an ice-water bath, keeping the solution temperature below 50°C and stirring continuously. Titrate until pH=5. After complete titration, cool the mixture in ice water and let it stand for 1 hour to form a white hydroxyplatinic acid precipitate. Collect the precipitate using a G3 glass frit. Wash the precipitate with an ice-water solution of nitric acid at 3°C ​​and pH=5 until the filtrate is free of chloride ions (specifically, during washing, take the washing liquid and add silver nitrate solution to detect chloride ions; if a white precipitate is formed, chloride ions are present; if no white precipitate is formed, chloride ions are absent; the same applies to the following examples). Obtain solid hydroxyplatinic acid. Step D: Transfer the sintered sand core to a clean vacuum filtration flask, add 0.1g of ammonium acetate to the hydroxyplatinic acid precipitate, add 20mL of concentrated nitric acid, the precipitate dissolves rapidly to form a platinum nitrate solution, after the precipitate is completely dissolved, start the air compressor to filter the obtained platinum nitrate solution, use nitric acid to wash the sintered sand core until the filtrate has no obvious color, transfer the obtained platinum nitrate to a 100ml volumetric flask, and make up to volume, yield 93.3%.

[0041] Example 2 Step A: Take 20g of platinum powder in a beaker, add 50mL of nitric acid and 150mL of hydrochloric acid, heat on a hot plate at 150℃ until completely dissolved, raise the temperature to 260℃, evaporate to about 50mL, add 40mL of hydrochloric acid to remove the acid, repeat 3-5 times, dilute the solution to 100mL with 1+5 hydrochloric acid to prepare chloroplatinic acid solution. Step B: Add 100g of sodium hydroxide solid to the chloroplatinic acid solution prepared in step A while stirring. After the addition is complete and the reaction is no longer vigorous, transfer it to a hot plate at 300°C and heat it while stirring until it boils until the solution turns orange-yellow and a large amount of yellow precipitate is formed. Remove it and cool it to prepare a sodium hydroxyplatinate mixture. Step C: Titrate the sodium hydroxyplatinate mixture obtained in step B with 1+2 nitric acid in an ice-water bath, keeping the solution temperature below 50°C and stirring continuously. Titrate until pH=5. After complete titration, cool the mixture in ice water and let it stand for 1 hour to form a white hydroxyplatinic acid precipitate. Collect the hydroxyplatinic acid precipitate using a G3 glass frit. Wash the precipitate with nitric acid solution at 3°C ​​and pH=5 until the filtrate is free of chloride ions to obtain solid hydroxyplatinic acid. Step D: Transfer the sintered sand core to a clean vacuum filtration flask, add 1g of ammonium acetate to the hydroxyplatinic acid precipitate, add 100mL of concentrated nitric acid, the precipitate dissolves rapidly to form a platinum nitrate solution, after the precipitate has completely dissolved, start the air compressor to filter the obtained platinum nitrate solution, use nitric acid to wash the sintered sand core until the filtrate has no obvious color, transfer the obtained platinum nitrate to a 200ml volumetric flask, and make up to volume, yield 90.2%.

[0042] Example 3 Step A: Take 1000g of platinum powder in a beaker, add 1000mL of nitric acid and 3000mL of hydrochloric acid, heat on a hot plate at 150℃ until completely dissolved, raise the temperature to 260℃, evaporate to about 3000mL, add 200mL of hydrochloric acid to remove the acid, repeat 3-5 times, dilute the solution to 5000mL to obtain chloroplatinic acid solution; Step B: Add 5000g of sodium hydroxide solid to the chloroplatinic acid solution prepared in step A under stirring. After the addition is complete and the reaction is no longer vigorous, transfer it to a hot plate at 300°C and heat it under stirring until the solution turns orange-red and a large amount of yellow precipitate is formed. Remove it and cool it to prepare a sodium hydroxyplatinate mixture. Step C: Titrate the sodium hydroxyplatinate mixture obtained in step B with 1+2 nitric acid in an ice-water bath, keeping the solution temperature below 50°C and stirring continuously. Titrate until pH=5. After complete titration, cool the mixture in ice water and let it stand for 1 hour to form a white hydroxyplatinic acid precipitate. Collect the hydroxyplatinic acid precipitate using a G3 glass frit. Wash the precipitate with nitric acid solution at 3°C ​​and pH=5 until the filtrate is free of chloride ions to obtain solid hydroxyplatinic acid. Step D: Transfer the sintered sand core to a clean vacuum filtration flask, add 50g of ammonium acetate to the hydroxyplatinic acid precipitate, and add 2000mL of concentrated nitric acid. The precipitate dissolves rapidly to form a platinum nitrate solution. After the precipitate is completely dissolved, start the air compressor to filter the obtained platinum nitrate solution. Use nitric acid to wash the sintered sand core until the filtrate has no obvious color. Transfer the obtained platinum nitrate to a 5000ml volumetric flask and make up to volume. The yield is 96.4%.

[0043] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing high-purity platinum nitrate, characterized in that, Includes the following steps: Step A: Add aqua regia to platinum powder to completely dissolve the platinum powder and prepare chloroplatinic acid solution; Step B: Add excess sodium hydroxide while stirring, and heat to prepare a sodium hydroxyplatinate mixture; Step C: Titrate the sodium hydroxyplatinate mixture with nitric acid under stirring in an ice-water bath. Keep the temperature below 50°C during the titration. The titration endpoint is pH=5. Separate the precipitate and liquid. Wash the precipitate with an ice-water solution of nitric acid at pH=5 until no chloride ions are present to obtain solid hydroxyplatinic acid. Step D: Add ammonium acetate to the hydroxyplatinic acid solid, then add nitric acid solution to dissolve the hydroxyplatinic acid solid and obtain platinum nitrate solution.

2. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, In step B, adding excess sodium hydroxide under stirring means adding sodium hydroxide at a rate of more than 5 times the molar amount of platinum under stirring.

3. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, In step A, after adding aqua regia to the platinum powder, the mixture is heated at 150°C until the platinum powder is completely dissolved.

4. The method for preparing high-purity platinum nitrate according to claim 3, characterized in that, After heating until the platinum powder is completely dissolved, the process also includes an acid removal step, where the temperature is raised to 260°C, hydrochloric acid is added to remove the acid, and after dilution, a chloroplatinic acid solution is obtained.

5. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, In the step of adding hydrochloric acid to remove acid, the hydrochloric acid is obtained by mixing 1 volume of hydrochloric acid with 5 volumes of pure water.

6. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, The heating temperature in step B is 300°C.

7. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, The nitric acid in step C is obtained by mixing 1 volume of nitric acid with 2 volumes of pure water.

8. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, In step C, the temperature of the nitric acid ice solution with pH=5 is 3°C.

9. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, In step D, the mass ratio of the amount of ammonium acetate added to the amount of platinum powder added in step A is 1:

20.

10. The method for preparing high-purity platinum nitrate according to claim 1, characterized in that, The ratio of the amount of nitric acid solution added in step D to the amount of platinum powder added in step A is: 2-10 ml of nitric acid solution for every 1 g of platinum powder.

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