Analysis method for precious metal elements

Abstract

To provide a method for analyzing the trace amount of a noble metal element contained in a solid sample containing a water-soluble tungsten oxide.SOLUTION: Disclosed is a method for analyzing at least one noble metal element in a solid sample containing a water-soluble tungsten oxide, which includes steps (1) to (3): (1) a firing step of firing a solid sample containing the water-soluble tungsten oxide in an oxidizing atmosphere to obtain a fired solid sample in which the water-soluble tungsten oxide is a tungsten oxide fired body; (2) an extraction step of extracting the noble metal element from the fired solid sample into an acidic aqueous solution to obtain an extract; and (3) a quantification step of measuring the concentration of each of the noble metal elements contained in the extract.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing precious metal elements contained in a solid sample containing a water-soluble tungsten oxide. [Background technology]

[0002] It is well known that composites composed of tungsten oxide function as solid acids or oxidation catalysts. For example, a composite in which tungsten oxide is supported on zirconia functions as a solid superacid catalyst and promotes the isomerization reaction of alkanes at low temperatures (Non-Patent Document 1). Furthermore, a composite in which a heteropolyacid and / or its salt is supported on a support is known to function as a catalyst for the synthesis of esters from carboxylic acids and olefins (Patent Document 1). A composite in which tungsten oxide and zinc oxide are supported on tin oxide is known to be an effective oxidation catalyst for the epoxidation reaction of olefins using hydrogen peroxide as an oxidizing agent (Non-Patent Document 2).

[0003] In catalytic reactions, reactions can proceed due to low concentrations of precious metals on the order of ppm or ppb by mass contained in raw materials or laboratory equipment. For example, Non-Patent Document 3 reports that the Suzuki-Miyaura coupling reaction proceeds due to palladium on the order of ppb by mass contained in sodium carbonate. Non-Patent Document 4 reports that the Suzuki-Miyaura coupling reaction proceeds due to trace amounts of metal contained in used PTFE stir bars.

[0004] In order to prevent unexpected side reactions caused by trace amounts of precious metal contamination, it is important to analyze the precious metal components contained in catalysts with high precision. Commonly used methods for analyzing the precious metal components in catalysts include quantifying the metal components using XRF (X-ray fluorescence analysis) on pelletized catalysts, and quantifying the metal concentration in the extract obtained by extracting the catalyst with an acidic solution using ICP (inductively coupled plasma) mass spectrometry or ICP atomic emission spectrometry.

[0005] However, it is difficult to quantify trace amounts of precious metal components using XRF. Furthermore, when extracting a catalyst directly with an acidic solution and analyzing it using ICP, the detection of trace amounts of precious metal components is difficult due to space charge effects and polyatomic ion interference caused by the major catalyst components dissolved in the extract. In particular, when analyzing solid samples containing water-soluble tungsten oxide, tungsten can contaminate or clog the sample introduction system, reducing the stability of the instrument. Therefore, analysis must be performed using a sufficiently diluted solution, making it extremely difficult to analyze trace amounts of precious metal components in the sample. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 09-118647 [Non-patent literature]

[0007] [Non-Patent Document 1] Journal of the Chemical Society,Chemical Communications, p.1259-1260(1988). [Non-patent document 2] Angewandte Chemie International Edition, volume 50, p.12411-12413(2011). [Non-patent document 3] The Journal of Organic Chemistry, Vol. 70, pp. 161-168 (2005). [Non-patent document 4] ACS Catalysis, vol. 9, pp. 3070-3081 (2019). Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems, an object of the present invention is to provide a method for analyzing trace amounts of precious metal elements contained in a solid sample containing water-soluble tungsten oxide. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have found that by calcining a solid sample containing a water-soluble tungsten oxide in an oxidizing atmosphere and then extracting the resulting calcined solid sample with an acidic solution, and measuring the concentration of the precious metal in the extract, it is possible to analyze precious metal elements in a solid sample on the order of ppb by mass, and have completed the present invention.

[0010] That is, the present invention relates to the following [1] to [9]. [1] 1. A method for analyzing at least one precious metal element in a solid sample containing at least one water-soluble tungsten oxide, comprising: (1) a calcination step of calcining the solid sample containing the water-soluble tungsten oxide in an oxidizing atmosphere to obtain a calcined solid sample in which the water-soluble tungsten oxide is converted into a calcined tungsten oxide body; (2) an extraction step of extracting the precious metal element from the fired solid sample into an acidic aqueous solution to obtain an extract; and (3) a quantitative step of measuring the concentration of each of the precious metal elements contained in the extract; A method for analyzing precious metal elements including: [2] The method for analyzing a precious metal element according to [1], wherein the water-soluble tungsten oxide is silicotungstic acid or phosphotungstic acid. [3] The method for analyzing a precious metal element according to [2], wherein the solid sample is a mixture of tungstosilicic acid or tungstophosphoric acid and silica. [4] The method for analyzing a precious metal element according to any one of [1] to [3], wherein the precious metal element is at least one selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, and gold. [5] The method for analyzing a precious metal element according to any one of [1] to [3], wherein the precious metal element is at least one selected from the group consisting of palladium and platinum. [6] The method for analyzing precious metal elements according to any one of [1] to [5], wherein the concentration of each of the precious metal elements is in the range of 1 to 1000 ppb by mass. [7] The method for analyzing a precious metal element according to any one of [1] to [6], wherein the firing temperature in the firing step is 700 to 1000°C. [8] The method for analyzing a precious metal element according to any one of [1] to [7], wherein the acidic aqueous solution in the extraction step is an aqueous solution of at least one selected from the group consisting of hydrogen chloride and nitric acid. [9] The method for analyzing a precious metal element according to any one of [1] to [8], wherein the concentration is measured in the quantitative determination step by ICP mass spectrometry or ICP atomic emission spectrometry. [Effects of the Invention]

[0011] According to the present invention, trace amounts of precious metal elements contained in a solid sample containing a water-soluble tungsten oxide can be analyzed with high sensitivity. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments and can be applied in various ways within the spirit and scope of the present invention.

[0013] <Analysis method for precious metal elements> A method for analyzing a noble metal element in one embodiment is a method for analyzing at least one noble metal element in a solid sample containing at least one water-soluble tungsten oxide, and includes the following steps (1) to (3). (1) A calcination step in which a solid sample containing water-soluble tungsten oxide is calcined in an oxidizing atmosphere to obtain a calcined solid sample in which the water-soluble tungsten oxide is converted into a calcined tungsten oxide body. (2) An extraction step in which precious metal elements are extracted from the fired solid sample into an acidic aqueous solution to obtain an extract. (3) A quantitative step of measuring the concentration of each precious metal element contained in the extract.

[0014] [Solid sample] The analysis target of the analytical method of one embodiment is a solid sample containing one or more water-soluble tungsten oxides.

[0015] Water-soluble tungsten oxides refer to a group of compounds containing tungsten and oxygen that have a solubility in water of 10 g / 100 mL or more at room temperature (23°C).

[0016] Specific examples of water-soluble tungsten oxides include sodium tungstate, potassium tungstate, ammonium metatungstate, tungstosilicic acid, lithium tungstosilicic acid, sodium tungstosilicic acid, potassium tungstosilicic acid, phosphotungstic acid, lithium tungstosilicic acid, sodium tungstosilicic acid, and potassium tungstosilicic acid. In one embodiment, tungstosilicic acid or tungstosilicic acid is particularly useful as an analyte.

[0017] The form of the solid sample containing water-soluble tungsten oxide is not particularly limited, and may be, for example, water-soluble tungsten oxide itself, a physical mixture containing water-soluble tungsten oxide, or water-soluble tungsten oxide supported on a carrier or the like.

[0018] The method for preparing a solid sample containing water-soluble tungsten oxide is not particularly limited, and any method may be used, such as physically mixing water-soluble tungsten oxide with other raw materials, or adhering or depositing water-soluble tungsten oxide on other raw materials by impregnation or ion exchange, followed by drying.

[0019] The content of the water-soluble tungsten oxide in the solid sample is not particularly limited, but is preferably 10 to 80 mass %, more preferably 20 to 70 mass %, and even more preferably 30 to 60 mass %.

[0020] Specific examples of the other component of the solid sample include silica, alumina, titania, zirconia, silica-alumina, zeolite, and activated carbon. The other component of the solid sample is preferably silica. That is, in one embodiment, the solid sample is preferably a mixture of tungstosilicic acid or tungstophosphoric acid and silica. The other component of the solid sample can be used as a support for the water-soluble tungsten oxide.

[0021] [Precious metal elements] Examples of the noble metal element to be analyzed by the analytical method of one embodiment include ruthenium, rhodium, palladium, iridium, osmium, rhenium, platinum, gold, and silver. Preferably, the noble metal element is at least one selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, and gold, and more preferably, at least one selected from the group consisting of palladium and platinum.

[0022] The concentration of each precious metal element in the solid sample containing water-soluble tungsten oxide is preferably in the range of 1 to 1000 mass ppb, more preferably in the range of 2 to 500 mass ppb, and even more preferably in the range of 5 to 250 mass ppb. If the concentration of each precious metal element is less than 1 mass ppb, the concentration in the extract may be below the detection limit of the analysis.

[0023] [(1) Firing process] (1) The calcination step is a step of calcining a solid sample containing a water-soluble tungsten oxide in an oxidizing atmosphere to obtain a calcined solid sample in which the water-soluble tungsten oxide is converted into a calcined tungsten oxide body.

[0024] The oxidizing atmosphere is not particularly limited as long as it contains oxygen gas, but air is preferred from the viewpoint of cost.

[0025] (1) In the calcination step, there is an appropriate calcination temperature range from the viewpoint of calcining the water-soluble tungsten oxide in an oxidizing atmosphere to form a calcined tungsten oxide. The calcination temperature is preferably 700 to 1000°C, and more preferably 800 to 950°C. If the calcination temperature is less than 700°C, the conversion of the water-soluble tungsten oxide to a calcined tungsten oxide may not proceed sufficiently. If the calcination temperature is higher than 1000°C, the precious metal to be analyzed may sublimate.

[0026] There is no particular limitation on the time for the calcination treatment, and it can be determined appropriately depending on the amount of the solid sample, etc.

[0027] [(2) Extraction process] (2) The extraction step is a step of extracting precious metal elements from a fired solid sample containing a fired tungsten oxide body into an acidic aqueous solution to obtain an extract. After extraction, the extract containing the precious metal elements is subjected to solid-liquid separation by filtration or the like.

[0028] The type of acidic aqueous solution used for extracting the precious metal elements is not particularly limited, but for example, at least one aqueous solution selected from the group consisting of hydrogen chloride and nitric acid can be used. A mixed aqueous solution of hydrochloric acid and nitric acid (for example, aqua regia) can also be used.

[0029] There are no particular limitations on the temperature or time of extraction, and the extraction conditions may be determined after estimating the composition of the solid sample and the amount of precious metal elements.

[0030] [(3) Measurement process] (3) The measuring step is a step of measuring the concentration of each of the precious metal elements contained in the extract. The measuring method is not particularly limited, but for example, ICP mass spectrometry or ICP atomic emission spectrometry can be used. [Example]

[0031] The present invention will be further described with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0032] [Bulk density measurement of silica support] The silica carrier was added to a tared glass measuring cylinder in several portions, and the measuring cylinder containing the carrier was tapped each time until the carrier reached the measuring volume of the measuring cylinder. The weight of the measuring cylinder containing the carrier was then measured, and the bulk density of the carrier was determined from the tared weight and volume of the measuring cylinder.

[0033] [ICP mass spectrometry] The concentration of precious metal elements was quantified using the calibration curve method using an Agilent Technologies 7700. Palladium was measured in helium mode and quantified using m / z = 105.

[0034] [XRF analysis] The concentration of precious metal elements was quantified using a Rigaku ZSX Primus II. The analytical sample was pressurized at 20 MPa for 1 minute and formed into a disk with a diameter of 3 cm before measurement.

[0035] [Preparation of solid sample A] Commercially available Keggin-type tungstosilicic acid 24-hydrate (H4SiW 12 O 40 120 g of palladium nitrate (Pd(NO3)2; Nippon Inorganic Chemical Industry Co., Ltd.) and 0.003 mg of palladium nitrate (Pd(NO3)2; Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved in 75.8 g (75.8 mL) of purified water to prepare 108 mL of aqueous solution. The resulting aqueous solution was added to 0.3 L (134 g) of commercially available silica support (spherical, diameter: approximately 5 mm, bulk density: 451 g / L) and mixed well to impregnate the support, obtaining an impregnated material. The resulting impregnated material was transferred to a porcelain dish, air-dried for 1 hour, and then dried for 5 hours in a dryer adjusted to 130 °C to obtain solid sample A.

[0036] [Example 1] (Firing process) After crushing solid sample A in an agate mortar, 2 g of the powder was placed in an alumina crucible with a lid. The mixture was then fired in a muffle furnace at 900°C for 3 hours under air flow.

[0037] (extraction process) 0.1 g of the calcined sample was placed in a quartz beaker, followed by the addition of 3 mL of ultrapure water, 1 mL of 68% by weight aqueous nitric acid solution (HNO3; Tama Chemicals Co., Ltd., TAMAPURE-AA-100), and 1 mL of 30% by weight hydrochloric acid (HCl; Tama Chemicals Co., Ltd., TAMAPURE-AA-100). The contents were heated for 2 hours on a hot plate set at 100°C, with shaking each time. After the contents were cooled, 5 mL of ultrapure water was added. The solution was then filtered through a 0.45 μm disposable filter and collected in a polypropylene container. The quartz beaker was washed with 10 mL of ultrapure water, and the washings were filtered through a 0.45 μm disposable filter, and the filtrate was collected in a polypropylene container. This washing process was performed three times in total.

[0038] (Quantitative process) The filtrate collected in a polypropylene container was adjusted to a constant volume of 50 mL, and the palladium concentration in the solution was quantified by ICP mass spectrometry. The palladium concentration in solid sample A was calculated from the palladium concentration analysis value and the weight of solid sample A used. Two analyses were performed, and the results and average values ​​are shown in Table 1. Example 1 demonstrates that noble metal elements on the order of several ppb by mass can be detected with good reproducibility.

[0039] [Comparative Example 1] An attempt was made to quantify the palladium concentration by carrying out the same procedure as in Example 1, except that the calcination step was omitted and the extract was further diluted 50 times to adjust the concentration of tungsten, the main component in the solution, to a concentration suitable for analytical procedures, but palladium could not be detected. The specific operating procedure is as follows.

[0040] (extraction) Solid sample A was crushed in an agate mortar, and 0.1 g of the powder was placed in a quartz beaker. 3 mL of ultrapure water, 1 mL of 68% by weight aqueous nitric acid solution (HNO3; Tama Chemicals Co., Ltd., TAMAPURE-AA-100), and 1 mL of 30% by weight hydrochloric acid (HCl; Tama Chemicals Co., Ltd., TAMAPURE-AA-100) were then added. The contents were heated on a hot plate set to 100°C for 2 hours, with shaking each time. After cooling, 5 mL of ultrapure water was added. The solution was filtered through a 0.45 μm disposable filter and collected in a polypropylene container. The quartz beaker was washed with 10 mL of ultrapure water, and the washings were filtered through a 0.45 μm disposable filter. The filtrate was collected in a polypropylene container. This washing process was performed three times.

[0041] (Quantitative) The filtrate collected in a polypropylene container was diluted to a constant volume of 50 mL and further diluted 50 times with ultrapure water to prepare a measurement sample, and the palladium concentration in the solution was quantified by ICP mass spectrometry. The palladium concentration in solid sample A was calculated from the palladium concentration analysis value and the weight of the charged solid sample A. Two analyses were performed, but palladium was not detected in either case.

[0042] Comparative Example 2 Approximately 4 g of solid sample A was packed into a polyvinyl chloride ring with an inner diameter of 3 cm and pressed at 20 MPa for 2 minutes to produce a disk. XRF analysis was performed twice using the resulting disk, but palladium was not detected in either case.

[0043] [Table 1]

Claims

1. 1. A method for analyzing at least one precious metal element in a solid sample containing at least one water-soluble tungsten oxide, comprising: (1) a calcination step of calcining the solid sample containing the water-soluble tungsten oxide in an oxidizing atmosphere to obtain a calcined solid sample in which the water-soluble tungsten oxide is converted into a calcined tungsten oxide body; (2) an extraction step of extracting the precious metal element from the fired solid sample into an acidic aqueous solution to obtain an extract; and (3) A quantitative step of measuring the concentration of each of the precious metal elements contained in the extract. Including, the concentration of each of the noble metal elements is in the range of 1 to 1000 ppb by mass, The method for analyzing precious metal elements, wherein the firing temperature in the firing step is 900 to 1000°C.

2. 2. The method for analyzing a precious metal element according to claim 1, wherein the water-soluble tungsten oxide is silicotungstic acid or phosphotungstic acid.

3. 3. The method for analyzing precious metal elements according to claim 2, wherein the solid sample is a mixture of tungstosilicic acid or tungstophosphoric acid and silica.

4. 4. The method for analyzing a precious metal element according to claim 1, wherein the precious metal element is at least one selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, and gold.

5. 4. The method for analyzing a precious metal element according to claim 1, wherein the precious metal element is at least one selected from the group consisting of palladium and platinum.

6. 6. The method for analyzing a precious metal element according to claim 1, wherein the acidic aqueous solution in the extraction step is an aqueous solution of at least one selected from the group consisting of hydrogen chloride and nitric acid.

7. The method for analyzing a precious metal element according to any one of claims 1 to 6, wherein the concentration measurement method in the quantification step is ICP mass spectrometry or ICP optical emission spectrometry.

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