JP2000074858A - Method for quantitating palladium palladium catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for analyzing quantitatively a palladium quantity in a palladium catalyst upto relatively high concentration range (about 10 wt.%) quickly and highly precisely. SOLUTION: In this method, correlation between a palladium concentration (wt.%) and fluorescent X-ray intensity is prelimiarily measured by fluorescent X-ray measurement using a solid body as a standard sample prepared mixing.pulveriziong.pressure-molding powder of a base material (for example, lithium tetraborate), a prescribed standard amount of palladium oxide powder and a binder under a prescribed condition, a solid body prepared by mixing.pulverizing.pressure-molding a powder sample of a palladium catalyst as a measuring object, the powder of the base material and the binder under the prescribed condition is measured by fluorescent X-ray measurement, and palladium in the powder sample of the palladium catalyst of the measuring object is determined quantitatively based on a measured result of the correlation between the palladium concentration (wt.%) and the fluorescent X-ray intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a catalyst metal contained in a selective combustion layer material of a thin film element type semiconductor gas sensor, and particularly to aluminum oxide (Al ₂ O ₃ : alumina).
The present invention relates to a method for quantitatively analyzing palladium (Pd) supported on a substrate.

[0002]

2. Description of the Related Art A gas sensor has a function of recognizing a specific gas component and a function of converting the recognized signal into an electrical signal or the like. The measurement object is a general combustible gas such as city gas or carbon monoxide. Toxic gases and so on. Typical materials for a semiconductor gas sensor include tin oxide, zinc oxide, titanium oxide, and the like. The signal conversion method utilizes a change in electron conduction caused by gas adsorption and reaction on a semiconductor surface. In particular, the surface control type sensor as described above is generally used for measuring combustible gas.

Further, in order to improve gas sensing characteristics, a material in which a trace amount of noble metal is dispersed and supported on a sensor material has been developed, a high-performance gas alarm which detects various types of gases with good sensitivity, and a small and power-saving gas alarm. The development of a battery-driven thin-film gas sensor is being actively pursued. In this case, it is important to increase the methane sensitivity and ensure gas selectivity as a material for the selective combustion layer of the thin film gas sensor, and development and application of an aluminum oxide-supported palladium catalyst and the like are being studied as adapting to this.

A palladium catalyst supported on aluminum oxide is
Aluminum oxide powder is impregnated with a predetermined amount of an aqueous solution of palladium chloride, then dried, and an aluminum oxide-based additive (alumina solu- tion, etc.) is added, mixed, pulverized, and heat-treated.
Aluminum oxide is used as a carrier for the palladium catalyst, and the supported palladium is a catalyst mainly composed of palladium oxide. The palladium catalyst in the gas sensor is located on the outermost surface of the sensor unit, and is applied in a thin film by a coating method, a spin coating method, or the like to form a selective combustion layer.

The development of gas sensors requires quantitative evaluation of gas sensitivity characteristics and sensor material composition. In particular, the analysis of the amount of palladium in the palladium catalyst is important, and a method for accurate and rapid quantification is required. . A general method for determining palladium is described, for example, in “Analytical Chemistry Handbook, Fourth Revised Edition (1991)”, edited by the Japan Society for Analytical Chemistry. Here, the pretreatment method of dissolving palladium in aqua regia when the sample is in the form of a metal, the separation of coexisting substances, and the subsequent quantitative analysis methods include gravimetric method, potentiometric titration method, spectrophotometric method, Atomic absorption methods and the like are described.

[0006]

However, a generalized analytical method including a pretreatment method for an analytical sample mainly composed of palladium oxide has not been established yet. Further, palladium (Pd) in the analysis sample forms palladium oxide (PdO) because the material has undergone heat treatment, and is insoluble in aqua regia. Therefore, the above method cannot be applied as a sample pretreatment.

As a countermeasure for this, a method of applying a method of reducing a material containing palladium oxide by hydrogen is considered. In this case, there is a problem that a new processing facility is required, and it is difficult to determine the degree of hydrogen reduction. Further, as a pretreatment method of the analysis sample, sodium potassium carbonate (NaKCO
An alkali melting method such as ₃ ) can be considered. In this case, since the reducing action is partial, there is a problem that the mixed state of the metal palladium and the palladium oxide is caused, and the entire palladium cannot be recovered.

On the other hand, for analysis of a trace amount of catalytic metal in which a carrier is tin oxide and platinum or palladium is carried on the carrier, a method in which a powder sample is pressure-formed using a solid organic material as a pedestal and measured by X-ray fluorescence analysis Has been proposed by the present inventor (see JP-A-2-145949). However, this method has a problem that the linearity and reproducibility of the correlation between the palladium concentration (wt%) and the fluorescent X-ray intensity cannot be obtained at a high palladium concentration, and is limited to about 1.2 wt%. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to prepare an analytical sample by an appropriate method so that a high palladium concentration (10 wt%) can be obtained. A method that enables rapid and accurate quantitative analysis of the amount of palladium of a palladium catalyst supported on aluminum oxide, etc., by a simple preparation method that enables quantification by fluorescent X-ray analysis up to the extent) and does not dissolve or melt with acids or alkalis. Is to provide.

[0010]

Means for Solving the Problems To solve the above-mentioned problems, according to the invention of claim 1, in a method for determining palladium in a palladium catalyst for a gas sensor comprising palladium supported on a carrier powder such as aluminum oxide, A solid body obtained by mixing, pulverizing, and pressing a powder as a base material, a predetermined standard amount of palladium oxide powder, and a binder under predetermined conditions is used as a standard sample, and the palladium concentration (wt%) and the fluorescence X The correlation with the line intensity is calibrated in advance by X-ray fluorescence measurement, and the powder sample of the palladium catalyst to be measured,
X-ray fluorescence measurement of a solid obtained by mixing, pulverizing, and press-molding the powder as the base material and the binder under predetermined conditions, and a calibration result of a correlation between the palladium concentration (wt%) and the X-ray fluorescence intensity Based on the above, palladium in the palladium catalyst powder sample to be measured is determined.

A powder having a high palladium concentration (about 10% by weight) is prepared by mixing a powder as a suitable base material with a target sample and mixing, pulverizing and pressing under predetermined conditions to prepare a solid sample. Up to) can be quantified by fluorescent X-ray analysis.

According to the second aspect of the present invention, lithium tetraborate is used as a preferable substrate. Lithium tetraborate
The absorption of fluorescent X-rays is small, and there is no interference such as the proximity line of palladium. This enables quantification in a wide concentration range. According to the invention of claim 3, stearic acid is used as a binder, and an aluminum ring is used as a sample holding frame for pressure-forming a solid body. This facilitates the adjustment of the sample.

According to the present invention, the background is corrected in the X-ray fluorescence measurement. This enables stable measurement and high-precision analysis.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

[Preparation of measurement sample and standard sample] FIG.
3 is a flowchart showing a solid sample preparation procedure for quantitative analysis of Pd in a palladium catalyst powder sample according to an example of the present invention.

[0016] Pd in the analysis sample is contained in the aluminum oxide powder supported thereon, and accurately weighs 0.1 g as a powder sample. 5 g of lithium tetraborate (Li ₂ B ₄ O ₇ ) as a base material and 0.5 g of stearic acid as a binder are weighed and collected in order to form a solid by pressure molding.

Next, a solid sample as a standard sample is prepared. As a standard sample, powder of palladium oxide reagent was used.
Change the amount to be weighed in the range of 0.001 to 0.01 g, and
Five points corresponding to 1 to 10 wt% with respect to 0.1 g are weighed and collected. Next, 5 g of lithium tetraborate as a base material and 0.5 g of stearic acid as a binder are weighed and collected in the same manner as in the sample preparation. In each case, a beaker with a capacity of 50 ml is used as a container for temporary storage after weighing. The collected powder sample is mixed and pulverized using an agate mortar. Usually, palladium catalyst powder is produced at the tens of grams level. The amount used as a material for this gas sensor is a trace amount of milligram level or less, and a small amount of 1 gram or less is used for composition analysis of the material. Therefore, in order to make a powder sample into a solid sample, a base material that holds and increases a small amount of powder of the analysis sample is required.

Lithium tetraborate (Li) used as a substrate_TwoB
_FourO₇) Powder has relatively low hygroscopicity,
Compounds that are composed of light elements
Low absorption of fluorescent X-rays
Is used as a base material because there is no close X-ray and it does not interfere
Suitable for use as a bulking agent. The amount used here is solid
An appropriate amount that satisfies the form of the finished product of the body was examined and set to 5 g.
Stearic acid (CH_Three(CH _Two)₁₆COOH] is waxy and repellent
Water-based and can be handled in powder form, suitable as a binder
ing. The binder is equivalent to 10 wt% of the total amount of the sample including the base material
Optimum amount of binder to solidify by pressure molding
It was decided after considering the conversion.

The particle size of each powder material and the sample for preparing the analysis sample is adjusted to 100 μm or less. In this case, the particle size can be adjusted to a certain level by sieving the sieve with a sieve opening of 90 μm. The smaller the particle size, the better the pressure moldability. Further, the larger the specific surface area, the more suitable for the fluorescent X-ray intensity measurement.

Next, a solid sample is prepared by pressure molding. FIG. 2 shows a configuration at the time of pressure molding for preparing a solid sample according to an embodiment of the present invention. An aluminum ring 5 having a diameter of 40 mm, a thickness of 1 mm, and a height of 5 mm is used for protecting the sample, and the sample is filled with the powder and pressed. Before the filling of the powder sample, the organic thin film 3 is inserted between the pressure forming pedestals 22 and 23 and the sample formed of the aluminum ring 5. Pressurization is performed with a hydraulic press to a total pressure of 15 t. This pressing force was determined by examining the pressing force such that the sample was solidified and sufficient mechanical strength for handling was obtained. The organic thin film 3 is a mylar film (material;
(Polyester, about 5 μm thick). Accordingly, contamination of the analysis surface of the solid sample 4 can be prevented, and the solid sample 4 can be easily separated from the pedestals 22 and 23, so that a good solid sample having a smooth analysis surface can be obtained. In this way, a solid body of about 40φ and a height of about 3 mm is obtained, and the preparation of the analysis sample and the standard sample is completed.

By measuring the fluorescent X-ray intensity of this solid sample, quantitative analysis of Pd can be performed.

[Pd Fluorescence X-Ray Measurement] Next, a method of measuring Pd by X-ray fluorescence analysis will be described below. FIG.
1 is a configuration diagram of an optical system of an X-ray fluorescence analyzer for quantitative analysis of Pd in a solid sample according to an embodiment of the present invention. When primary X-rays from an X-ray tube are irradiated on a substance, fluorescent X-rays of secondary X-rays are generated. X-ray spectroscopy conditions are Bragg's equation
2d sin θ = nλ (d: plane spacing of the dispersive crystal, θ: incident angle of the X-ray to the dispersive crystal, λ: wavelength of the incident X-ray, n: diffraction order).

In this case, a solid sample is set at the sample setting position, and the element (Pd) can be quantitatively analyzed from the wavelength of the fluorescent X-ray generated from the sample. FIG. 4 shows a spectrum of PdKα rays including the analysis conditions and a background correction position of continuous X-rays regarding the fluorescent X-ray intensity measurement for quantitative analysis of Pd in a solid sample according to the embodiment of the present invention. It is an example of a spectrum.

In the fluorescent X-ray spectrum of FIG.
The characteristic X-ray at the dKα (16.75 deg) position indicates the intensity at which continuous X-rays are included as a background. Generally, the intensity of a continuous X-ray appears between samples due to differences in constituent elements of the sample and the surface state of the sample. In the quantitative analysis of Pd, the background was corrected to obtain the relationship between only the intensity of the PdKα characteristic X-ray and the Pd concentration in the sample. At this time, the correction was performed by obtaining the intensity of 和 of the sum of the background BG1 (16.2 deg) and BG2 (17.5 deg), and subtracting this from the intensity at the position of PdKα (16.75 deg).

[Preparation of Calibration Curve] Next, preparation of a calibration curve will be described.

The measured values of the intensity of the fluorescent X-rays and the Pd in the sample
From the relationship with the concentration (% by weight), the calibration curve constant is determined by the least squares method. 5 and 6 show the background (B
G) Calibration curves before and after correction are shown. The empirical formula at that time is as follows. Calibration curve before BG correction Pd = 0.0003746Y-12.95 Correlation coefficient 0.
992 Calibration curve after BG correction Pd = 0.0004141Y-1.21 Correlation coefficient 0.
999 Here, Y is the characteristic X-ray intensity (cps) of PdKα (16.75 deg).

It can be seen that the correlation coefficient between the characteristic X-ray intensity and the Pd concentration before the BG correction is 0.992, and the correlation coefficient after the BG correction is improved to 0.999. In addition, the linearity of the calibration curve is good, which is useful for improving the analysis accuracy. In this method, the calibration curve after the background (BG) correction of FIG. 6 is used. At this time, the applicable range of the quantitative analysis of the Pd concentration is 0.1 to 12 wt%. Since the carried amount of the palladium catalyst is often on the order of several percent, its application to actual samples is sufficient.

[Study of Pd Analysis Accuracy] Using the solid sample prepared by the sample preparation method shown in FIG.
Table 1 shows the result of measuring the fluorescent X-ray intensity of d and repeatedly measuring the Pd concentration based on the calibration curve shown in FIG.

(Measurement conditions) Analytical element: Pd, spectral crystal: LiF, X-ray tube target: Cr, X-ray tube voltage: 50 KV, X-ray tube current: 5
0 mA, Pd Peak 2θ: 16.75 deg (wavelength: 0.5869 °), pack coolant 2θ: BG1 = 16.2, BG2 = 17.5 deg

[0030]

[Table 1] From Table 1, the repeat analysis accuracy of Pd in the solid sample is
It can be seen that the coefficient of variation is good at 0.7% or less.

[Analysis of Palladium Catalyst of Actual Sample] Table 2 shows the results of applying the above-established method to the analysis of Pd of the palladium catalyst powder of the actual sample. The catalyst of the sample was prepared such that the amount of Pd supported on the aluminum oxide carrier was within a range of 1 to 7.5 wt%.
It is a powder sample that is manufactured by changing the kind, and is crushed after a heat treatment step and dried to remove adsorbed moisture.

[0032]

[Table 2] According to Table 2, the sample of the palladium catalyst powder supported on aluminum oxide, despite its small amount of 0.1 g, was capable of quantitative analysis of Pd at a level of several% by the above-mentioned sample preparation method and the measurement method of Pd. It can be seen that the evaluation can be quickly and accurately performed. In the above description, the case where aluminum oxide is used as the carrier has been described. However, even when other carrier materials are used, within the scope of the technical idea of the present invention, it is preferable to adjust a suitable solid body and obtain a fluorescent X-ray. Determination of palladium by measurement is possible.

[0033]

According to the first aspect of the present invention, in a method for quantifying palladium in a palladium catalyst for a gas sensor in which palladium is carried on a carrier powder such as aluminum oxide, the method comprises the steps of: The amount of palladium oxide powder and the binder were mixed, crushed and pressed under predetermined conditions, and a solid sample was used as a standard sample. The correlation between the palladium concentration (wt%) and the fluorescent X-ray intensity was determined using the fluorescent X-ray The solid body, which has been calibrated in advance by measurement and the powder sample of the palladium catalyst to be measured, the powder to be the base material, and the binder are mixed, pulverized, and pressed under predetermined conditions to obtain a fluorescent X
3. The method according to claim 2, wherein the palladium in the palladium catalyst powder sample to be measured is quantified based on a calibration result of a correlation between the palladium concentration (wt%) and the fluorescent X-ray intensity. For example, by using lithium tetraborate as a suitable substrate, it is possible to quantitatively determine the concentration of palladium in a wide concentration range by a fluorescent X-ray analysis up to a high palladium concentration (about 10 wt%).

According to the third aspect of the present invention, the preparation of the sample is facilitated by using stearic acid as the binder and the aluminum ring as the sample holding frame for pressure-forming the solid. Further, according to the invention of claim 4, in the fluorescent X-ray measurement, the background is corrected by the above-described method, so that stable measurement and high-precision analysis can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure for preparing a solid analytical sample according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of each member used for pressure molding of a solid analytical sample according to an embodiment of the present invention.

FIG. 3 is an X-ray fluorescence analyzer according to an embodiment of the present invention.
It is a block diagram of an optical system.

FIG. 4 is a spectrum diagram showing an example of a PdKα fluorescent X-ray spectrum and background correction according to the embodiment of the present invention.

FIG. 5 is a diagram showing a calibration before continuous X-ray intensity correction of a background according to the embodiment of the present invention.

FIG. 6 is a diagram showing a calibration after continuous X-ray intensity correction of a background according to the embodiment of the present invention.

[Explanation of symbols]

 3. Organic thin film 4. Solid sample 5. Sample holding frame (aluminum ring)

Claims (4)

[Claims] 1. A method for determining palladium in a palladium catalyst for a gas sensor in which palladium is carried on a carrier powder such as aluminum oxide, comprising: a base material powder; a predetermined standard amount of palladium oxide powder; Is mixed, crushed, and pressed under predetermined conditions, and the solid body is used as a standard sample, and the palladium concentration (wt.
%) And the X-ray fluorescence intensity are calibrated in advance by X-ray fluorescence measurement, and the powder sample of the palladium catalyst to be measured, the powder to be the base material, and the binder are mixed under predetermined conditions. -Fluorescent X-ray measurement of the pulverized and pressure-molded solid body is performed, and palladium in the palladium catalyst powder sample to be measured is determined based on the calibration result of the correlation between the palladium concentration (wt%) and the fluorescent X-ray intensity. A method for quantifying palladium in a palladium catalyst. 2. The method for determining palladium in a palladium catalyst according to claim 1, wherein the powder used as the base material is lithium tetraborate. 3. The method according to claim 1, wherein the binder is stearic acid, and an aluminum ring is used as a sample holding frame for pressure molding of the solid body. Method. 4. The method according to claim 1, wherein the characteristic X-ray wavelength PdKα0.5869Å is used for the fluorescent X-ray measurement.
From the value of the fluorescent X-ray intensity at the dKα 0.5869 ° position, the average value of the fluorescent X-ray intensity at the positions before and after the value is subtracted,
A method for quantifying palladium in a palladium catalyst, comprising performing background correction of continuous X-rays.