Method for measuring platinum group metal content in vehicle catalyst

Abstract

The invention relates to the technical field of metal element determination, in particular to a method for determining the content of platinum group metal in a vehicle catalyst. The method comprises the following steps: acquiring a uniform sample of a vehicle catalyst sample; adding an alkaline flux into the sample, heating, and completely reacting to form a uniform frit; performing water dissolution and acidification treatment on the frit to form an acidified solution; adding an oxidizing agent into the acidified solution to oxidize the platinum group metal to a stable high valence state; adding a tellurium solution, heating, adding a stannous chloride solution, and continuously heating until a black precipitate is generated; standing and aging the precipitate, filtering, and washing with hydrochloric acid and deionized water in sequence to remove impurity ions; heating and dissolving the washed precipitate with aqua regia; and determining the content of the platinum group metal in the dissolved solution after metering the volume of the dissolved solution. According to the method, efficient and complete decomposition of the sample can be achieved, and meanwhile multiple key platinum group metal elements such as platinum, palladium, rhodium, ruthenium and iridium can be accurately determined.

Description

Technical Field

[0001] This application relates to the field of metal element determination technology, and more specifically, to a method for determining the platinum group metal content in automotive catalysts. Background Technology

[0002] Platinum group metals (PGMs) possess unique catalytic activity, selectivity, and stability, making them key active components in automotive catalysts. Their content and proportion directly determine catalytic purification efficiency and overall vehicle emissions performance. Therefore, accurately determining the PGM content is of great significance for catalyst development, process optimization, and product quality control.

[0003] Currently, the determination of platinum group metal content in automotive catalysts mainly relies on standard HJ 509-2009, "Determination of Platinum, Palladium, and Rhodium in Automotive Ceramic Catalytic Converters: Inductively Coupled Platinum Atomic Emission Spectrometry and Inductively Coupled Plasma Mass Spectrometry." This method uses a mixed acid system of hydrofluoric acid, hydrochloric acid, perchloric acid, and nitric acid for digestion. However, this method has the following limitations in application: Firstly, it often fails to completely dissolve catalyst samples supported by sparingly soluble materials such as silicon carbide, and hydrofluoric acid easily reacts with the matrix metal to form sparingly soluble fluoride precipitates, which encapsulate precious metal particles, leading to insufficient extraction and lower measurement results. Secondly, this method only targets platinum, palladium, and rhodium, and cannot cover key platinum group metals such as ruthenium and iridium, which are already used in new catalysts.

[0004] With the diversified development of catalyst technology, analytical methods capable of simultaneously and accurately determining the content of multiple platinum group metals, including platinum, palladium, rhodium, ruthenium, and iridium, and overcoming the shortcomings of existing pretreatment methods, have become an urgent need in the industry to support the research and development and precise control of next-generation catalysts. Therefore, this application is submitted. Summary of the Invention

[0005] This application aims to address the technical problems of incomplete sample pretreatment, susceptibility to matrix interference, and narrow applicability in existing determination methods. It provides a simple, accurate, and reliable method for the simultaneous determination of multiple platinum group metals (PMMs) in automotive catalysts. This method achieves efficient and complete sample decomposition, avoids the encapsulation of PMMs by sparingly soluble fluoride precipitates, and can simultaneously and accurately determine multiple key PMM elements such as platinum, palladium, rhodium, ruthenium, and iridium. This provides a reliable analytical tool for the development and quality control of next-generation catalysts.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application provides a method for determining the platinum group metal content in automotive catalysts, including: Obtain a uniform sample of the automotive catalyst; An alkaline flux was added to the sample and heated until the reaction was complete, forming a uniform melt. The molten metal is subjected to water dissolution and acidification treatment to form an acidified solution; An oxidizing agent is added to the acidified solution to oxidize the platinum group metals to a stable high valence state; Add tellurium solution and heat, then add stannous chloride solution and continue heating until a black precipitate forms; After the precipitate is allowed to stand and age, it is filtered and washed with hydrochloric acid and deionized water in turn to remove impurity ions. Dissolve the precipitate after washing by heating it with aqua regia. After the solution was brought to a constant volume, the content of platinum group metals was determined by inductively coupled plasma mass spectrometry or inductively coupled plasma atomic emission spectrometry.

[0007] Compared with the prior art, the beneficial effects of this application are as follows: 1. By using specific alkaline fluxes and proportions for high-temperature melting, various acid-resistant automotive catalyst carriers can be efficiently and completely decomposed, allowing all platinum group metals to be completely transferred into the solution, overcoming the problems of incomplete decomposition and low recovery rate that may exist in traditional acid digestion methods.

[0008] 2. Selecting specific weak oxidants to oxidize ruthenium and iridium to stable high valence states: Ru(VI), Ru(VII), Ir(IV) not only improves the co-precipitation recovery rate of ruthenium and iridium, but also effectively inhibits the formation and volatilization of RuO4, thus avoiding the loss of ruthenium.

[0009] 3. The tellurium coprecipitation method is adopted, which uses the nascent elemental tellurium colloid generated by the reduction of stannous chloride as a carrier and trapping agent to efficiently adsorb and encapsulate the simultaneously reduced platinum group metal elements, thereby achieving simultaneous enrichment of multiple platinum group metals, effectively separating matrix interferences such as alkali metals and alkaline earth metals, and reducing matrix effects in subsequent detection. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 This is a flowchart illustrating a method for determining the platinum group metal content in automotive catalysts, as provided in an embodiment of this application. Detailed Implementation

[0012] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of this application, including various details to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0013] Figure 1 This is a flowchart illustrating a method for determining the platinum group metals (PGMs) content in an automotive catalyst, as provided in this embodiment. This embodiment is applicable to scenarios where the PGMs content in an automotive catalyst (containing platinum, palladium, rhodium, ruthenium, and iridium) is determined. Figure 1 As shown, this embodiment provides a method for determining the platinum group metal content in automotive catalysts, including the following steps: S110. Obtain a uniform sample of the automotive catalyst.

[0014] The automotive catalyst sample was dried at 200℃~600℃ for 2h~5h (h means hour), cooled, ground, mixed, and passed through a 200-mesh sieve to obtain a uniform sample.

[0015] S120. Add alkaline flux to the sample and heat it until the reaction is complete, forming a uniform melt.

[0016] Weigh 0.1g to 1g of the sample and place it in an alkali-resistant zirconia or corundum crucible. Add an alkaline flux, which may include any of the following: sodium peroxide, a mixture of sodium hydroxide and sodium nitrite, or a mixture of potassium hydroxide and potassium nitrite. The amount of sodium peroxide added is 3 to 10 times the sample mass. In the mixture of sodium hydroxide and sodium nitrite, the amount of sodium nitrite added is 10 to 30 times the sample mass, and the amount of sodium hydroxide added is 3 to 10 times the sample mass. In the mixture of potassium hydroxide and potassium nitrite, the amount of potassium nitrite added is 10 to 30 times the sample mass, and the amount of potassium hydroxide added is 3 to 10 times the sample mass.

[0017] Place the crucible in a muffle furnace and melt it at 400℃~800℃ for 10min~60min until the reaction is complete and a uniform melt is formed.

[0018] In this step, a specific alkaline flux and ratio are used for high-temperature melting. Compared with the traditional mixed acid digestion method, this method can not only efficiently decompose catalyst samples supported by acid-resistant materials such as silicon carbide and cordierite, but also completely release the platinum group metals encapsulated inside or on the surface of the support, overcoming the defect of incomplete dissolution leading to low measurement results in acid dissolution methods; it also avoids the use of strong acids such as hydrofluoric acid, preventing the formation of insoluble fluoride precipitates that could physically encapsulate and co-precipitate the platinum group metals; alkaline melting can convert the platinum group metals in the sample into soluble salts, laying the foundation for subsequent quantitative enrichment and determination, and significantly improving the applicability and accuracy of the method.

[0019] S130. The molten block is dissolved in water and acidified to form an acidified solution.

[0020] After cooling the molten metal, transfer it to a beaker, add 50 mL of water, and heat and stir until completely dissolved; then add 20 mL to 60 mL of hydrochloric acid for acidification.

[0021] S140. Add an oxidizing agent to the acidified solution to oxidize the platinum group metals to a stable high valence state.

[0022] The oxidant is a sodium chlorate solution or hydrogen peroxide with a concentration of 300 g / L; the amount of sodium chlorate solution added is 15 mL to 30 mL, and the amount of hydrogen peroxide added is 6 mL to 12 mL.

[0023] This step uses a specific weak oxidizing agent to oxidize ruthenium and iridium to a stable high valence state, so that they can be uniformly reduced to elemental form during the subsequent reduction of stannous chloride and efficiently captured by nascent tellurium, thus improving the recovery rate of precious metals. At the same time, it also inhibits the formation of volatile substances RuO4, preventing ruthenium from being released at any time. The use of a weak oxidizing agent is mild and does not damage the stability of other platinum group metals in the solution, ensuring the simultaneous and quantitative enrichment of the five elements.

[0024] S150, add tellurium solution and heat, then add stannous chloride solution and continue heating until a black precipitate is formed.

[0025] After adding an oxidant to the acidified solution, add 10 mL to 20 mL of a 10 g / L tellurium solution, heat to a gentle boil (heat the solution to just boiling point), then add 5 mL to 10 mL of a 150 g / L stannous chloride solution, and continue heating until a black precipitate forms.

[0026] S160. After the precipitate has been allowed to stand and aged, it is filtered and washed with hydrochloric acid and deionized water in sequence to remove impurity ions.

[0027] S150-S160 employs tellurium coprecipitation to separate and enrich platinum group metals, effectively removing a large number of matrix ions such as alkali metals, alkaline earth metals, aluminum, and silicon. This significantly reduces matrix effects in subsequent ICP-MS (inductively coupled plasma mass spectrometry) measurements, improving accuracy. The precipitate is washed to obtain a high-purity concentrate with no loss of target elements, ensuring quantitative recovery for subsequent determinations.

[0028] S170. Dissolve the precipitate after washing by heating with aqua regia.

[0029] Dissolve the precipitate after washing by heating with 10 mL to 20 mL of aqua regia.

[0030] S180. After adjusting the volume of the solution, determine the content of platinum group metals by inductively coupled plasma mass spectrometry or inductively coupled plasma atomic emission spectrometry.

[0031] The platinum group elements that need to be measured simultaneously include: platinum, palladium, rhodium, ruthenium, and iridium.

[0032] To accurately calculate the platinum group metal content in the solution, the solution needs to be transferred to a volumetric flask, and then dilute acid or water is added precisely so that the lowest point of the liquid level is exactly aligned with the graduation mark on the volumetric flask, thus obtaining the accurate volume of the final solution (e.g., 100 ml).

[0033] Inductively coupled plasma mass spectrometry (ICP-MS) can detect extremely low concentrations of metals, with sensitivity typically reaching parts per trillion (ppt). Inductively coupled plasma atomic emission spectrometry (ICP-AES) also utilizes ICP (inductively coupled plasma) to excite samples at high temperatures, but it detects the intensity of the characteristic spectra emitted by atoms when they return to their ground state after excitation. Its sensitivity is slightly lower than ICP-MS, and it is typically used to determine trace to constant levels (ppb-ppm, or even percentage levels, i.e., parts per billion to parts per million to percentages). It has a wide dynamic range and good stability.

[0034] The embodiments of this application have the following technical effects: 1. By using specific alkaline fluxes and proportions for high-temperature melting, various acid-resistant automotive catalyst carriers can be efficiently and completely decomposed, allowing all platinum group metals to be completely transferred into the solution, overcoming the problems of incomplete decomposition and low recovery rate that may exist in traditional acid digestion methods.

[0035] 2. Selecting specific weak oxidants to oxidize ruthenium and iridium to stable high valence states: Ru(VI), Ru(VII), Ir(IV) not only improves the co-precipitation recovery rate of ruthenium and iridium, but also effectively inhibits the formation and volatilization of RuO4, thus avoiding the loss of ruthenium.

[0036] 3. The tellurium coprecipitation method is adopted, which uses the nascent elemental tellurium colloid generated by the reduction of stannous chloride as a carrier and trapping agent to efficiently adsorb and encapsulate the simultaneously reduced platinum group metal elements, thereby achieving simultaneous enrichment of multiple platinum group metals, effectively separating matrix interferences such as alkali metals and alkaline earth metals, and reducing matrix effects in subsequent detection.

[0037] The following examples illustrate in detail the process of determining the content of five platinum group metals in automotive catalysts.

[0038] Example 1 (using sodium peroxide flux and sodium chlorate oxidation) S1. Obtain a uniform sample of the automotive catalyst. Weigh 0.5000g and place it in an alkali-resistant zirconium oxide crucible or corundum crucible. Add 3.0g of sodium peroxide and place the crucible in a muffle furnace. Melt at 700℃ for 30 minutes to form a uniform molten block.

[0039] S2. After the molten metal is dissolved in water, 40 mL of concentrated hydrochloric acid is added for acidification. The resulting solution is clear and transparent with no visible insoluble matter.

[0040] S3. Then, add 20 mL of 300 g / L sodium chlorate solution to the acidified solution and gently boil for 5 minutes to oxidize it, keeping the solution clear.

[0041] S4. Add 15 mL of 10 g / L tellurium solution and 8 mL of 150 g / L stannous chloride solution sequentially for co-precipitation enrichment. After removing impurity ions and dissolving the precipitate in aqua regia, a clear test solution is obtained.

[0042] S5. Inductively coupled plasma mass spectrometry was used for determination.

[0043] Results: The recoveries of the five platinum group metals, platinum, palladium, rhodium, ruthenium and iridium, were 99.8%, 101.2%, 100.5%, 99.1% and 98.7%, respectively, with relative standard deviations of less than 2.0%.

[0044] Example 2 (using a mixed flux of sodium hydroxide and sodium nitrite and oxidation with hydrogen peroxide) S1. Obtain a uniform sample of the automotive catalyst. Weigh 0.2500g and place it in an alkali-resistant zirconium oxide or corundum crucible. Add 5.0g of sodium nitrite and 1.5g of sodium hydroxide. Place the crucible in a muffle furnace and melt it at 600℃ for 45 minutes to form a uniform melt.

[0045] S2. After the molten metal is dissolved in water and acidified, the solution becomes clear and transparent.

[0046] S3. Then, add 8 mL of 30% hydrogen peroxide to the acidified solution and oxidize by gentle boiling for 8 minutes, keeping the solution clear.

[0047] S4~S5, subsequent co-precipitation, removal of impurity ions, dissolution, and determination steps are the same as in Example 1.

[0048] Results: The recoveries of the five platinum group metals, platinum, palladium, rhodium, ruthenium and iridium, were 98.5%, 100.8%, 99.7%, 97.9% and 99.3%, respectively, with relative standard deviations of less than 2.5%.

[0049] To highlight the technical effects of the embodiments of this application and the necessity of some steps, three comparative examples are provided below: Comparative Example 1 (without tellurium coprecipitation enrichment) The same sample and pretreatment steps (S1~S3) as in Example 1 were used, but after acidification and oxidation, tellurium coprecipitation was not performed. The clarified oxidized solution obtained in S3 was directly diluted to volume and measured by inductively coupled plasma mass spectrometry.

[0050] Results: The recoveries of platinum, palladium, rhodium, ruthenium, and iridium exhibited drastic and irregular fluctuations. In different parallel experiments, the recoveries for the same element ranged from abnormally high (>150%) to abnormally low (<30%), with relative standard deviations exceeding 10%. This indicates that, without selective enrichment, the large number of coexisting ions in the sample matrix produced unpredictable and severe suppression or enhancement effects on inductively coupled plasma mass spectrometry (ICP-MS), leading to uncontrolled recoveries.

[0051] Comparative Example 2 (oxidation step omitted) The same sample and steps as in Example 1 were used, but step S3 was omitted, i.e., tellurium coprecipitation was performed directly after acidification in S2 (S4).

[0052] Results: The recovery rate of ruthenium decreased significantly to 75%-80%, with large fluctuations between parallel samples (relative standard deviation >8%); the recovery rate of iridium was 89%-93%. The recoveries of platinum, palladium, and rhodium remained above 96%. This indicates that the oxidation step is the core step to ensure the quantitative enrichment of all target platinum group metals, especially ruthenium and iridium.

[0053] Comparative Example 3 (using a strong oxidizing agent instead of a weak oxidizing agent) The process is basically the same as in Example 1, but in step S3, a sufficient amount of potassium permanganate solution is used instead of sodium chlorate solution for oxidation until the solution turns a persistent purple-red color and boils gently for several minutes.

[0054] Results: The recovery rate of Ru was significantly low and unstable, ranging from 68% to 82%, while the recovery rates of the other four metals were less affected. This indicates that strong oxidants can lead to uncontrollable losses of ruthenium.

[0055] Examples 1-2 demonstrate that, within the scope of the technical solutions provided in this application, different combinations of alkaline fluxes and oxidants can achieve complete decomposition of automotive catalysts and efficient and accurate recovery of platinum group metals. Comparative Examples 1-3 show that: 1) without tellurium co-precipitation enrichment, complex matrices lead to test failure; 2) omitting the oxidation step results in a significant decrease in the recovery rates of ruthenium and iridium; 3) using inappropriate strong oxidants directly causes Ru volatilization loss.

[0056] This application aims to address the technical problems of incomplete sample pretreatment, susceptibility to matrix interference, and narrow applicability in existing methods, and provides a simple, accurate, and reliable method for the simultaneous determination of multiple platinum group metals in automotive catalysts. This method achieves efficient and complete sample decomposition, avoids the encapsulation of platinum group metals by sparingly soluble fluoride precipitates, and can simultaneously and accurately determine multiple key platinum group metal elements such as platinum, palladium, rhodium, ruthenium, and iridium, providing a reliable analytical tool for the research and quality control of next-generation catalysts.

[0057] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this application can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this application can be achieved, and this is not limited herein.

[0058] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for determining the platinum group metal content in automotive catalysts, characterized in that, include: Obtain a uniform sample of the automotive catalyst; An alkaline flux was added to the sample and heated until the reaction was complete, forming a uniform melt. The molten metal is subjected to water dissolution and acidification treatment to form an acidified solution; An oxidizing agent is added to the acidified solution to oxidize the platinum group metals to a stable high valence state; Add tellurium solution and heat, then add stannous chloride solution and continue heating until a black precipitate forms; After the precipitate is allowed to stand and age, it is filtered and washed with hydrochloric acid and deionized water in sequence to remove impurity ions. Dissolve the precipitate after washing by heating it with aqua regia. After the solution was brought to a constant volume, the content of platinum group metals was determined by inductively coupled plasma mass spectrometry or inductively coupled plasma atomic emission spectrometry.

2. The method according to claim 1, characterized in that, Obtaining a homogeneous sample of the automotive catalyst includes: The automotive catalyst sample was dried at 200℃~600℃ for 2h~5h, cooled, ground, mixed, and passed through a 200-mesh sieve to obtain a uniform sample.

3. The method according to claim 2, characterized in that, An alkaline flux is added to the sample and heated. After the reaction is complete, a homogeneous melt is formed, comprising: Place the sample in an alkali-resistant zirconia crucible or corundum crucible and add an alkaline flux. Place the crucible in a muffle furnace and melt it at 400℃~800℃ for 10min~60min until the reaction is complete and a uniform melt is formed.

4. The method according to claim 3, characterized in that, The alkaline flux includes any one of the following: sodium peroxide, a mixture of sodium hydroxide and sodium nitrite, or a mixture of potassium hydroxide and potassium nitrite.

5. The method according to claim 4, characterized in that, The molten metal is subjected to water dissolution and acidification treatment to form an acidified solution, comprising: After cooling the molten material, transfer it to a beaker, add 50 mL of water, and heat and stir until completely dissolved. Add 20mL to 60mL of hydrochloric acid for acidification.

6. The method according to claim 5, characterized in that, The oxidant is a sodium chlorate solution or hydrogen peroxide with a concentration of 300 g / L; wherein the amount of sodium chlorate solution added is 15 mL to 30 mL, and the amount of hydrogen peroxide added is 6 mL to 12 mL.

7. The method according to claim 6, characterized in that, Add tellurium solution and heat, then add stannous chloride solution and continue heating until a black precipitate forms, including: Add 10 mL to 20 mL of a 10 g / L tellurium solution, heat, then add 5 mL to 10 mL of a 150 g / L stannous chloride solution, and continue heating until a black precipitate forms.

8. The method according to claim 7, characterized in that, The precipitate after washing was dissolved in aqua regia by heating, including: Dissolve the precipitate after washing by heating with 10 mL to 20 mL of aqua regia.

9. The method according to claim 8, characterized in that, The platinum group metals include platinum, palladium, rhodium, ruthenium, and iridium.

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