JP4457897B2 - Inspection and analysis method of double oxide powder for catalyst - Google Patents

Description

    The present invention relates to a method for inspection and analysis of a double oxide powder for a catalyst.

    An oxygen storage material is added to an exhaust gas purification catalyst for an engine. For example, in a three-way catalyst, an oxygen storage material is added to expand an air-fuel ratio region where HC (hydrocarbon), CO, and NOx (nitrogen oxide) can be simultaneously purified.

    As an oxygen storage material, ceria has been known for a long time, and recently, in order to improve its heat resistance, a double oxide containing Zr in addition to Ce (also referred to as a composite oxide), in addition to Ce, other than Ce. Double oxides containing rare earth elements are also known. In such an oxygen storage material, the crystal structure is distorted when Ce is changed from trivalent to tetravalent, and oxygen is taken in by this distortion. Therefore, the crystal structure affects the quality of the oxygen storage characteristics.

    However, even if the oxygen storage material is prepared in the same process and is determined to have the same crystal structure by X-ray diffraction analysis, the reason is not clear, but the oxygen storage capacity is not necessarily the same. That is, for example, the oxygen storage capacity varies among lots, which may affect the catalyst performance, and the structural analysis by X-ray diffraction cannot accurately determine the quality of the oxygen storage capacity.

On the other hand, Patent Document 1 describes that the composite oxide powder for catalyst is selected by Raman spectroscopic analysis. It is intended the ratio of about 450cm peak intensity existing in the vicinity of ^-1 of the Raman spectrum (I ₄₅₀₎ and about 300cm peak intensity existing in the vicinity of _{^{-1 (I 300) (I 300}} / I 450) is less than a predetermined value By sorting, the variation in characteristics is reduced.
JP 2004-237168 A

    However, according to the results of experiments and research that the inventor has conducted in the past, even if a double oxide having the same peak intensity ratio as described above is actually used as a catalyst, the exhaust gas purification performance is relatively low. There could be a big difference.

    Accordingly, the present invention provides a method for inspecting and analyzing catalytic double oxides, which is useful for knowing in advance what kind of exhaust gas purification characteristics will be obtained when double oxides are actually used as catalysts. Let it be an issue.

    The present invention has found that the change in the peak intensity ratio obtained by Raman spectroscopic analysis with respect to such a problem is related to the catalyst performance when the double oxide is used as a catalyst. The crystal structure characteristics of the double oxide were examined based on the change in the peak intensity ratio with temperature.

The invention according to claim 1 is a method for inspecting and analyzing catalyst double oxide powder containing Zr,
By Raman spectroscopic analysis, the ratio I ₁ / I ₂ of the peak intensity I ₁ in the first wave number region and the peak intensity I _{2 in} the second wave number region of the Raman shift related to oxygen atoms contained in the above-mentioned double oxide powder is Obtained at multiple temperatures in a reducing atmosphere,
The degree to which the peak intensity ratio I ₁ / I ₂ changes depending on the temperature is determined,
The crystal structure characteristics of the double oxide powder in which oxygen atoms are involved are examined based on the degree of change in the peak intensity ratio I ₁ / I ₂ .

    That is, the catalyst has a temperature exhibiting activity, and the activation temperature is generally higher than room temperature. For example, an exhaust gas purifying catalyst normally exhibits activity at a temperature of 250 ° C. or higher, and may become high temperatures of 600 ° C. and 700 ° C. when exposed to exhaust gas. Such a temperature change affects the crystal structure of the double oxide used in the catalyst, and the structure change affects the performance of the catalyst.

The relationship between the change in crystal structure and the Raman shift characteristic is schematically shown in FIG. Of the two Raman shift characteristics in the figure, the upper side is a characteristic exhibited by the double oxide at a high temperature, and the lower side is a characteristic exhibited by the same double oxide at a low temperature. As described above, the Raman shift characteristics at the low temperature and the high temperature are different. Therefore, the peak intensity I ₁ in the first wave number region and the peak intensity I _{2 in} the second wave number region related to the oxygen atoms contained in the complex oxide are different. And the ratio I ₁ / I ₂ also depends on the temperature.

The difference in the peak intensity ratio I ₁ / I ₂ is due to the difference in the position occupied by oxygen atoms in the double oxide crystal shown on the right side of FIG. In this case, the broken-line circle indicates the ideal position of the oxygen atom, and the solid-line circle indicates the position actually occupied by the oxygen atom. When the peak intensity ratio I ₁ / I ₂ is large, the oxygen atom has a large positional shift, and when the peak intensity ratio I ₁ / I ₂ is small, the oxygen atom has a small positional shift.

Thus, the fact that the peak intensity ratio I ₁ / I ₂ changes greatly between low temperature and high temperature means that the crystal structure of the double oxide is easily distorted. If it is an occlusion material, the oxygen occlusion ability is increased and the exhaust gas purification performance is improved.

Therefore, the present invention obtains the degree to which the peak intensity ratio I ₁ / I ₂ changes depending on the temperature, and examines the crystal structure characteristics of the double oxide powder based on the degree of change. is there. In addition, since the Raman spectroscopic analysis is performed in a reducing atmosphere, it is advantageous in accurately capturing the Raman shift characteristics related to the behavior of oxygen atoms when the temperature changes.

    Therefore, according to the present invention, it is possible to evaluate in advance the catalyst performance when the double oxide powder is used as a catalyst, and if the double oxide is selected based on the inspection result and used in the catalyst, A catalyst with stable quality can be prepared.

As the degree of change, the rate of change from the peak intensity ratio (I ₁ / I ₂ ) _{T1 at} the first temperature to the peak intensity ratio (I ₁ / I ₂ ) _T2 at the second temperature different from the first temperature, peak intensity ratio (I ₁ / I ₂₎ peak intensity ratio _T1 (I ₁ / I _{2) T2} ratio of (I ₁ / I _{2) T2} / (I ₁ / I _{2) T1,} or the peak intensity ratio (I ₁ / I ₂ ) Any amount of change from _T1 to peak intensity ratio (I ₁ / I ₂ ) _T2 (difference between both peak intensity ratios) may be employed.

The invention according to claim 2 is the invention according to claim 1,
The complex oxide powder is a Zr complex oxide having a cubic structure containing 50 mol% or more of Zr,
One of the first wave number region and the second wave number region is a wave number region near 470 cm ⁻¹ , and the other is a wave number region near 630 cm ⁻¹ .

That is, in the case of a Zr-rich double oxide, the Raman shift peaks associated with the oxygen atoms appear around 470 cm ⁻¹ and 630 cm ⁻¹ . Therefore, by setting the first wave number region and the second wave number region as described above, the crystal structure characteristics of the double oxide powder are accurately inspected based on the degree of change of the peak intensity ratio I ₁ / I ₂ with temperature. be able to.

The invention according to claim 3 is the invention according to claim 1,
The double oxide powder is a Ce-Zr double oxide having a cubic structure containing 50 mol% or more of Ce,
One of the first wavenumber range and the second wavenumber range is the wave number range near 300 cm ^-1, the other is being a wavenumber range near 470 cm ^-1.

That is, in the case of Zr rich composite oxide, the peak of the Raman shift the oxygen atoms associated appears in the vicinity of 300 cm ^-1 and near 470 cm ^-1. Therefore, by setting the first wave number region and the second wave number region as described above, the crystal structure characteristics of the double oxide powder are accurately inspected based on the degree of change of the peak intensity ratio I ₁ / I ₂ with temperature. be able to.

As described above, according to the present invention, by Raman spectroscopy, the peak intensity I ₁ in the first wavenumber region and the peak in the second wavenumber region of the Raman shift related to oxygen atoms contained in the complex oxide powder containing Zr. The ratio I ₁ / I ₂ to the intensity I ₂ is obtained at a plurality of temperatures in a reducing atmosphere, the degree to which this peak intensity ratio I ₁ / I ₂ changes depending on the temperature is obtained, and based on this degree of change Since the crystal structure characteristics involving oxygen atoms of the double oxide powder are inspected, the catalyst performance when the double oxide powder is used as a catalyst can be evaluated in advance. Thus, if a double oxide is selected and used as a catalyst, a catalyst with stable quality can be prepared.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Preparation of double oxide>
As a sample to which the method according to the present invention is applied, two types of double oxide powders having different compositions as shown in Table 1, that is, a plurality of lots of each powder of Zr rich double oxide and Ce rich double oxide were prepared. .

上記２種類の複酸化物粉末は材料組成が異なるだけで調製法は同じであり、それは次の通りである。オキシ硝酸ジルコニウム、硝酸第一セリウム、硝酸ネオジム(III)含水、硝酸ロジウム溶液の所定量を混合し、水を加えて室温で約１時間撹拌した。この混合溶液を８０℃まで加熱昇温させた後、これに撹拌しながら２８％アンモニア水を所定量加えて混合した。アンモニア水の混合により白濁した溶液を一昼夜放置し、生成したゲルを遠心分離器にかけて十分に水洗した。この水洗したゲルを約１５０℃の温度で乾燥させた後、４００℃の温度に５時間保持し、次いで５００℃の温度に２時間保持するという条件で焼成した。

The above two types of double oxide powders are different in material composition and the preparation method is the same, which is as follows. Predetermined amounts of zirconium oxynitrate, cerium nitrate, water containing neodymium (III) nitrate, and rhodium nitrate solution were mixed, water was added, and the mixture was stirred at room temperature for about 1 hour. This mixed solution was heated up to 80 ° C., and then a predetermined amount of 28% ammonia water was added and mixed with stirring. The solution clouded by mixing with aqueous ammonia was left for a whole day and night, and the resulting gel was sufficiently washed with a centrifuge. The water-washed gel was dried at a temperature of about 150 ° C. and then calcined under the condition that it was held at a temperature of 400 ° C. for 5 hours and then held at a temperature of 500 ° C. for 2 hours.

<Analysis by X-ray diffraction>
The result of the X-ray diffraction measurement of the Zr-rich double oxide powder (lots A to D) is shown in FIG. 2, and the result of the X-ray diffraction measurement of the Ce-rich double oxide powder (lots E to G) is shown in FIG. . As is clear from FIG. 2, the diffraction peaks of the Zr-rich double oxide powders of lots A to D all appear in the same manner. In this X-ray diffraction, the double oxide powders of lots A to D are cubic crystals. Although it can be seen that it has a structure, there is no difference in crystal structure between lots. This is the same for the Zr-rich double oxide powders of lots E to G shown in FIG. 3, and no difference in crystal structure between lots E to G is observed by X-ray diffraction.

<Raman spectroscopy>
Regarding the Zr-rich double oxide powder (lots A to D) and the Ce-rich double oxide powder (lots E to G), the former has a first temperature of 30 ° C. and a second temperature of 600 in a reducing atmosphere (hydrogen gas atmosphere). At each temperature, Raman spectroscopy analysis was performed at a first temperature of 30 ° C. and a second temperature of 100 ° C., respectively. The results are shown in FIG. 4 for the Zr-rich double oxide powder (lots A to D) and in FIG. 5 for the Ce-rich double oxide powder (lots E to G).

4 and 5, AG are lot symbols, temperature is analysis temperature, I ₁ is peak intensity in the first wave number region, and I ₂ is peak intensity in the second wave number region. The first wavenumber range is the wave number region around 470 cm ^-1 of the Zr-rich mixed oxide powder of FIG. 4 (Lot ^{A~D) (440cm -1 ~500cm -1)} , wavenumber range near the second wavenumber range is 630 cm ^-1 (600cm ^-1 ~660cm ^-1), the first wavenumber range is the wave number region around 300 cm ^-1 of Ce rich composite oxide powder of FIG. 5 (lot ^{E~G) (270cm -1 ~330cm -1)} , a second wavenumber range is the wave number range near ^{470cm -1 (440cm -1 ~500cm -1)} .

Peak intensity I ₁ of the first frequency range above the respective measured temperature of each lot, the peak intensity I ₂ of the second wavenumber range, the peak intensity ratio of the first temperature (I ₁ / I _{2) T1,} a second temperature Peak intensity ratio (I ₁ / I ₂ ) _T2 , peak intensity ratio (I ₁ / I ₂ ) _T1 to peak intensity ratio (I ₁ / I ₂ ) _T2 below change rate, and peak intensity ratio (I ₁ / I ₂ ) Ratio of peak intensity to _{T 1} (I ₁ / I ₂ ) _{T 2} ratio (I ₁ / I ₂ ) _{T 2} / (I ₁ / I ₂ ) _{T 1} is as shown in Table 2.

Rate of change = ((I ₁ / I ₂ ) _{T 1} − (I ₁ / I ₂ ) _{T 2} ) / (I ₁ / I ₂ ) _{T 1}
As shown in FIG. 1, the peak intensity I ₁ in the first frequency range is based on the baseline connecting the end points at both ends of the peak (zero intensity), and the peak intensity I ₂ in the _second frequency range is A baseline drawn horizontally from the end point on the high wavenumber side was used as a reference (zero intensity).

Ｚｒリッチ複酸化物粉末では低温側のピーク強度比（Ｉ₁／Ｉ₂）_T1から高温側のピーク強度比（Ｉ₁／Ｉ₂）_T2への変化率がプラスの値になり、Ｃｅリッチ複酸化物粉末ではマイナスの値になっているのは、前者は温度上昇と共に酸素原子の理想位置からのずれが小さくなり、後者は逆にそのずれが大きくなるためである。

Zr is the value of the rate of change plus low temperature side peak intensity ratio of from (I ₁ / I _{2) T1} peak intensity ratio of the high temperature side to the (I ₁ / I _{2) T2} is rich mixed oxide powder, Ce-rich double The reason why the oxide powder has a negative value is that, in the former, the deviation from the ideal position of the oxygen atom decreases as the temperature rises, and in the latter, the deviation increases.

<Exhaust gas purification performance>
About the mixed oxide powder of each of the above lots A to G, a slurry is prepared by mixing a predetermined amount of activated alumina, a binder and water, and a honeycomb carrier made of cordierite is dipped in this and pulled up. After the slurry was blown off, each test catalyst was obtained by performing calcination that was held at a temperature of 500 ° C. for 2 hours. These test catalysts were aged by holding them at a temperature of 1000 ° C. for 24 hours in an air atmosphere.

Then, each test catalyst is attached to the model gas flow reactor, and the model gas temperature flowing into the catalyst is gradually increased from 100 ° C. to 500 ° C., and the NOx purification rate when the catalyst inlet gas temperature is 400 ° C. Was measured. The model gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h ⁻¹ , and the heating rate is 30 ° C./min.

    The results are shown in FIG. 6 for the Zr-rich double oxide powder (lots A to D) and in FIG. 7 for the Ce-rich double oxide powder (lots E to G). A to G in the figure are lot symbols.

According to Table 2 above, the Zr-rich double oxide powders of lots A to D have substantially the same peak intensity ratio at 30 ° C., but their NO purification rates are relatively large as shown in FIG. There is a difference. This also applies to the Ce-rich double oxide powder shown in FIG. On the other hand, looking at the relationship between the change rate of the peak intensity ratio and the NOx purification rate, both the Zr-rich double oxide powder and the Ce-rich double oxide powder have a NOx purification rate that increases as the change rate of the peak intensity ratio increases. It shows a tendency to increase. Further, in terms of the ratio of the peak intensity ratio in Table 2, it can be said that the NOx purification rate increases as the deviation from the ratio 1 (no change in the peak intensity ratio) increases. That is, the NOx purification rate becomes higher as the degree to which the peak intensity ratio I ₁ / I ₂ changes depending on the temperature is larger. The difference in the NOx purification rate between the lots is that the double oxide powder works as an oxygen storage material for the catalyst, so whether or not the oxygen atoms in each lot are likely to be displaced, in other words, whether the crystals are easily distorted. It is recognized that this is due to the difference in oxygen storage capacity.

    As described above, according to the inspection analysis method according to the present invention, it is possible to analyze the crystal structure characteristics in which oxygen atoms of the double oxide powder are involved. It can be seen that the performance can be accurately evaluated in advance, and therefore a catalyst with stable quality can be prepared by selecting the double oxide powder based on the inspection result and using it as the catalyst.

    The present invention can be applied to a double oxide containing a rare earth element other than Zr and Ce (for example, Pr) in addition to the above-mentioned double oxide powder containing Ce and Zr.

It is explanatory drawing which shows the relationship between the Raman shift characteristic at the time of low temperature and high temperature of double oxide powder, and the shift | offset | difference of oxygen position in the crystal | crystallization. It is an X-ray diffraction chart of the Zr rich double oxide powder of lots A to D. FIG. 3 is an X-ray diffraction chart of Ce-rich double oxide powders of lots E to G. It is a Raman shift characteristic view at the time of low temperature and high temperature of the Zr rich double oxide powder of lots A to D. It is a Raman shift characteristic view at the time of low temperature and high temperature of the Ce rich double oxide powder of lots E to G. It is a graph which shows the relationship between the change rate of the peak intensity ratio of Zr rich complex oxide powder, and a NOx purification rate. It is a graph which shows the relationship between the change rate of the peak intensity ratio of Ce rich complex oxide powder, and a NOx purification rate.

Explanation of symbols

    None

Claims (3)

A method for inspecting and analyzing a double oxide powder for a catalyst containing Zr,
By Raman spectroscopic analysis, the ratio I ₁ / I ₂ of the peak intensity I ₁ in the first wave number region and the peak intensity I _{2 in} the second wave number region of the Raman shift related to oxygen atoms contained in the above-mentioned double oxide powder is Obtained at multiple temperatures in a reducing atmosphere,
The degree to which the peak intensity ratio I ₁ / I ₂ changes depending on the temperature is determined,
A method for inspecting and analyzing a catalyst double oxide, comprising: examining a crystal structure characteristic involving oxygen atoms of the double oxide powder based on a degree of change in the peak intensity ratio I ₁ / I ₂ . In claim 1,
The complex oxide powder is a Zr complex oxide having a cubic structure containing 50 mol% or more of Zr,
One of the first wave number region and the second wave number region is a wave number region near 470 cm ⁻¹ , and the other is a wave number region near 630 cm ^−1. Method. In claim 1,
The double oxide powder is a Ce-Zr double oxide having a cubic structure containing 50 mol% or more of Ce,
Above one of the first wavenumber range and the second wavenumber range and the wave number range near 300 cm ^-1, the other test analysis of catalyst for double oxide powder which is a wave number range near 470 cm ^-1 Method.

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