JP2004237168A - Exhaust gas purification catalyst carrier, exhaust gas purification catalyst, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To selectively produce an exhaust gas purification catalyst carrier comprising a ceria-zirconia multiple oxide or a catalyst and a catalyst product which is excellent in initial characteristics and durability and in which the dispersion of characteristics is reduced. <P>SOLUTION: In a method for producing the exhaust gas purification catalyst carrier, the ceria-zirconia catalyst carrier whose X-ray diffraction pattern obtained by X-ray diffraction measurement shows the structure of a cubic system crystal is selected by judging whether a peak exists in the vicinity of about 300 cm<SP>-1</SP>of a Raman spectrum or not and produced, and the catalyst is produced by making the selected carrier support a noble metal selected from Pt, Pd, Rh, etc. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying catalyst used in an exhaust system from an automobile engine, a carrier, and a method for producing the same.
[0002]
[Prior art]
The exhaust gas purifying catalyst (three-way catalyst) includes, for example, a carrier substrate made of a heat-resistant ceramic such as cordierite, a catalyst carrier layer made of activated alumina or the like formed on the carrier substrate, and a catalyst carrier layer made of this material. And a supported catalytic metal such as Pt. The three-way catalyst, the hydrocarbons in the exhaust gas of an internal combustion engine (HC) and carbon monoxide (CO) was oxidized and purified, nitrogen oxides (NO _X) is reduced and purified.
[0003]
However, since the oxygen concentration in the exhaust gas fluctuates greatly depending on the operating conditions of the internal combustion engine, the purification activity of oxidation and reduction may become unstable in the three-way catalyst. Therefore, ceria (CeO ₂ ) is added to the catalyst supporting layer. Ceria has an oxygen storage capacity (hereinafter referred to as OSC) for storing oxygen in an oxidizing atmosphere and releasing oxygen in a reducing atmosphere, so that a stable purification activity can be obtained even if the oxygen concentration in the exhaust gas fluctuates. .
[0004]
Also, it is said that a three-way catalyst containing a catalyst metal and ceria is likely to reduce OSC due to ceria crystal growth when used at a high temperature of 800 ° C. or higher. Therefore, means for adding zirconia (ZrO ₂ ) to ceria has been developed in order to suppress the crystal growth of ceria and maintain a high OSC (JP-A-63-116741, JP-A-3-131343). . JP-A-63-116741 discloses that at least a part of ceria and zirconia is formed into a composite oxide or a solid solution. By adding zirconia in this manner, heat resistance is improved, and a decrease in OSC due to use at high temperatures is suppressed.
[0005]
As a method for producing such a ceria-zirconia catalyst carrier, the following production method has been disclosed.
[0006]
JP-A-3-131343 discloses an oxide powder containing cerium and zirconium produced from an aqueous solution containing ions of cerium and zirconium by a precipitation reaction (coprecipitation method) and an alumina containing or not containing a noble metal. A production method is disclosed in which an aqueous slurry is prepared using a powder and applied to a monolithic carrier to produce a catalyst. According to this manufacturing method, cerium and zirconium have a strong interaction in the catalyst coating layer that cannot be obtained by simply mixing the respective oxide powders, and the OSC inherent in cerium oxide and its heat resistance Is improved.
[0007]
JP-A-6-226094 discloses a method for producing a composition based on a composite oxide of cerium, zirconium and, if necessary, yttrium and having a specific surface area of at least 80 m ² / g. , An aqueous mixture containing soluble compounds of zirconium and, optionally, yttrium, in proportions consistent with the stoichiometry of the desired product, and then heating the mixture to obtain the reaction thus obtained. A method is disclosed for producing a composition that collects the product and, finally, calcines the recovered reaction product.
[0008]
Japanese Patent Application Laid-Open No. Hei 8-215569 discloses a technique using a Ce-Zr composite oxide prepared from a metal alkoxide. The Ce-Zr composite oxide prepared from a metal alkoxide by a sol-gel method is a solid solution in which Ce and Zr are compounded at the atomic or molecular level as compared with the Ce-Zr composite oxide prepared from a nitrate. Therefore, heat resistance is improved, and a high OSC is secured from the initial stage to after use at a high temperature.
[0009]
The ceria-zirconia-based catalyst carriers produced by such various methods have different characteristics due to the difference in the production method. The determination of the superiority of the different characteristics is based on the fact that the composite oxide of cerium and zirconium has a CeO ₂ type cubic crystal as identified by X-ray diffraction in JP-A-6-226094. This has been done by associating the analytical results with the properties of the catalyst.
[0010]
However, even in the case of ceria-zirconia-based catalyst carriers considered to be the same in X-ray diffraction, large variations occur in the initial characteristics of the catalyst using these carriers and the characteristics after use at high temperatures, It has been difficult to produce catalyst products with uniform properties.
[0011]
[Patent Document 1] JP-A-63-116741
[Patent Document 2] Japanese Patent Application Laid-Open No. 03-131343
[Patent Document 3] JP-A-06-226094
[Patent Document 4] JP-A-08-215569
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and it is an object of the present invention to selectively manufacture an exhaust gas purifying catalyst carrier or a catalyst comprising a ceria-zirconia-based composite oxide to reduce the variation in the characteristics of a catalyst product.
[0016]
[Means for Solving the Problems]
The first manufacturing method of the exhaust gas-purifying catalyst carrier of the present invention is characterized by a composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, X-ray diffraction measurement and Raman Performing a measurement, including a sorting step of sorting, from the complex oxide powder, a complex oxide powder having an X-ray diffraction pattern showing a cubic structure and having no peak near about 300 cm ^{-1 in} a Raman spectrum. It is in.
[0017]
The feature of the second manufacturing method of the exhaust gas purifying catalyst carrier of the present invention is that a composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and a Raman measurement is performed on the composite oxide powder, It is intended to include a selection step of selecting a composite oxide powder having a peak at about 450 cm ^{-1 in the} Raman spectrum and having no peak at about 300 cm ^-1 from the composite oxide powder.
[0018]
The feature of the third manufacturing method of the exhaust gas purifying catalyst carrier of the present invention is that a composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and a Raman measurement is performed on the composite oxide powder, From the composite oxide powder, the ratio (I ₃₀₀ / I ₄₅₀ ) of the peak intensity (I ₄₅₀ ) of the peak near about 450 cm ⁻¹ and the peak intensity (I ₃₀₀ ) near about 300 cm ⁻¹ in the Raman spectrum. ) Includes a sorting step of sorting a composite oxide powder having a predetermined value or less.
[0019]
The fourth manufacturing method of the exhaust gas purifying catalyst carrier of the present invention is characterized by a composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, an X-ray diffraction measurement and Raman Performing a measurement, including a sorting step of sorting, from the complex oxide powder, a complex oxide powder having an X-ray diffraction pattern showing a cubic structure and having a peak near about 300 cm ^{-1 in} a Raman spectrum. It is in.
[0020]
The feature of the fifth manufacturing method of the exhaust gas purifying catalyst carrier of the present invention is that a composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and a Raman measurement is performed on the composite oxide powder, from the composite oxide powder is to include a selection step of peak exists in the vicinity of about 450 cm ^-1 of the Raman spectrum, selecting a composite oxide powder peak is present at around 300 cm ^-1.
[0021]
The first exhaust gas purifying catalyst carrier of the present invention is an exhaust gas purifying catalyst carrier comprising a composite oxide containing cerium and zirconium, which is produced by the above-described first to third production methods of the exhaust gas purifying catalyst carrier of the present invention. It is.
[0022]
A second exhaust gas purifying catalyst carrier of the present invention is an exhaust gas purifying catalyst comprising a composite oxide containing cerium and zirconium, which is produced by the fourth or fifth method for producing the exhaust gas purifying catalyst carrier of the present invention. Carrier.
[0023]
The feature of the first exhaust gas purifying catalyst carrier of the present invention resides in that the first exhaust gas purifying catalyst carrier of the present invention includes the noble metal.
[0024]
The feature of the second exhaust gas purifying catalyst carrier of the present invention resides in that the second exhaust gas purifying catalyst carrier of the present invention contains the noble metal.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
From the results of previous studies by the present inventors, it has been found that a ceria-zirconia-based catalyst carrier having a fluorite-type crystal structure is advantageous in terms of catalytic performance. As shown in FIG. 8, the fluorite-type crystal structure has a typical cubic crystal structure found in an inorganic compound whose composition is represented by AB ₂ (A: metal element, B: nonmetal element). As a kind, A atom occupies each lattice point of the face-centered cubic lattice (hereinafter, referred to as A atom position), and B atom is located at the center of a small cube obtained by dividing the unit cell into eight (hereinafter, referred to as B atom position). The crystal structure that is located. Further, as a result of further research, the present inventor found that the relationship between the structure of the ceria-zirconia-based catalyst carrier and the catalytic characteristics using this carrier was as follows: the initial characteristics of the exhaust gas purifying catalyst using the ceria-zirconia-based catalyst carrier and Characteristics after use at high temperatures (hereinafter referred to as durability characteristics) are greatly affected by the oxygen structure of the ceria-zirconia-based catalyst carrier, which is difficult to analyze by the conventional X-ray diffraction method. In the case where oxygen is located only at the B atom position of the fluorite-type crystal structure and the case where oxygen is also located at a position slightly displaced from the B atom position (hereinafter, referred to as a B atom shift position), the initial state of the catalyst is determined. It has been found that the characteristics and the durability characteristics change greatly. That is, a catalyst using a ceria-zirconia catalyst carrier in which oxygen is located only at the B atom position is more durable than a catalyst using oxygen at a B atom shift position slightly deviated from that position. Excellent, conversely, a catalyst using a ceria-zirconia-based catalyst carrier including one in which oxygen is also located at a B atom shift position has better initial characteristics than a catalyst using only a B atom position. And completed the present invention.
[0026]
The reason why the difference in the oxygen structure causes the difference in the initial characteristics and durability characteristics of the catalyst is not always clear, but in the case where oxygen is also located at the position where the B atom is displaced, the oxygen of the carrier is catalyzed by the dislocation of oxygen. It is thought that the initial characteristics of the catalyst are improved because the catalyst becomes involved. Conversely, the case where oxygen is located only at the B atom position is considered to have excellent durability characteristics because the structure is stable and stable.
[0027]
Evaluation of a conventionally used catalyst carrier is performed by the X-ray diffraction method as described above. The X-ray diffraction method is a method of irradiating a substance with X-rays and analyzing a diffraction pattern of X-rays mainly scattered by electrons constituting atoms. Therefore, in X-ray diffraction, it is possible to determine whether cerium or zirconium of the ceria-zirconia catalyst support is located at the position of the A atom of the fluorite-type crystal structure and whether or not it forms a cubic crystal. With respect to oxygen having a small number of constituent electrons and low X-ray scattering ability, it is difficult to determine whether oxygen is also located at a B atom shift position in the fluorite-type crystal structure.
[0028]
Therefore, in the present invention, the catalyst carrier is selected based on a spectrum obtained by performing Raman measurement. In the Raman analysis, since the analysis is performed using Raman scattered light scattered by the lattice vibration of the crystal, information reflecting the oxygen structure of the substance can be obtained.
[0029]
In the Raman measurement, the oxygen structure in which the oxygen of the ceria-zirconia catalyst support is located at the B atom position is a peak near about 450 cm ^{-1 in the} Raman spectrum, and the oxygen of the ceria-zirconia catalyst support is shifted to the B atom position. Appears as a peak near about 300 cm ^{-1 in the} Raman spectrum.
[0030]
Therefore, the ceria-zirconia-based catalyst support whose X-ray diffraction pattern obtained by the X-ray diffraction measurement shows a cubic structure composed of the A atom position of the fluorite-type crystal structure was converted to a Raman spectrum corresponding to the B atom position of about 300 cm ⁻ By determining whether there is a peak near ¹ or not and producing a catalyst, and carrying a noble metal such as Pt, Pd and Rh on the selected carrier to produce a catalyst, the Raman spectrum is about 300 cm. ^{When a} peak having a peak near ^-1 is selected, a catalyst product having excellent initial characteristics and a small variation in characteristics can be produced, and a peak exists at about 300 cm- ^{1 in the} Raman spectrum. When those which are not used are selected, it is possible to produce a catalyst product having excellent durability characteristics and little variation in characteristics.
[0031]
In addition, the ceria-zirconia-based catalyst support has a peak at about 450 cm ^{-1 in the} Raman spectrum corresponding to the A atom position and about 300 cm ^-1 in the B atom position in the fluorite-type crystal structure. A catalyst may be produced by carrying out sorting and producing a noble metal such as Pt, Pd and Rh on the selected carrier. Also in this case, when a product having a peak near about 300 cm ^{-1 in the} Raman spectrum is selected, a catalyst product having excellent initial characteristics and small variation in characteristics can be produced. In the case where those having no peak at about 300 cm ^-1 are selected, it is possible to produce a catalyst product having excellent durability characteristics and little characteristic variation.
[0032]
In addition, the peak intensity (I ₄₅₀ ) of the peak near about 450 cm ⁻¹ and the peak intensity (I ₃₀₀ ) of the peak near about 300 cm ⁻¹ in the Raman spectrum obtained by Raman measurement of the ceria-zirconia catalyst support are shown. By comparing the ratio (I ₃₀₀ / I ₄₅₀ ) with a predetermined value, and producing a catalyst by supporting a noble metal such as Pt, Pd, and Rh on the selected carrier. The characteristic can be set within a characteristic variation range corresponding to a predetermined value. Here, as shown in FIG. 9, the peak intensity is the intensity of the peak apex using the baseline connecting the end points at both ends of the peak as the intensity reference (the intensity is 0 on the baseline). The value can be set to any value according to the degree to which the variation in catalyst performance is allowed, but it is preferable to set the value to 0.01 or less.
[0033]
In the present invention, after the noble metal is supported on the ceria-zirconia-based catalyst carrier, X-ray diffraction measurement or Raman measurement is performed as described above to confirm the presence or absence of a peak and to compare the peak intensity ratio with a predetermined value. , The catalyst may be selectively manufactured. Further, the ceria-zirconia-based catalyst carrier in the present invention is a composite oxide containing cerium and zirconium, and the composite oxide is a concept including a solid solution.
[0034]
【Example】
_{Ce (NH 4) 2 (NO} 3) 2 and _{10.83g, ZrO (NO 3) 2} · 2H 2 O and 2.26g, Pr _{(NO 3)} water 3 · 6H ₂ O for about a 1.11 g 50 cc Was dissolved. Although this solution showed free acidity, it was neutralized by adding 28% aqueous NH ₃ while checking with a pH meter to neutralize the acidity. This was placed in a pressure vessel and heated at 150 ° C. for 2 hours. Thereafter, 28% aqueous NH _{3 was} further added to adjust the pH to about 8.5. The hydroxide precipitated in this process was subjected to suction filtration, dried at 120 ° C. overnight, and calcined at 500 ° C. for 2 hours to prepare a Ce—Zr—Pr composite oxide carrier. Pt is supported on this Ce-Zr-Pr composite oxide carrier using a platinum dinitrodiammine chemical solution so that Pt becomes 1 wt%, and subjected to a drying and baking step at 120 ° C. × 2 hours and 500 ° C. × 2 hours. Thus, a catalyst powder was obtained. This preparation was performed six times to produce six lots of catalyst powder.
[0035]
FIG. 1 shows the results of X-ray diffraction analysis of this catalyst. In FIG. 1, it was confirmed that the peaks other than Pt were diffraction peaks of the Ce—Zr—Pr composite oxide (cubic system). Also, the Ce-Zr-Pr composite oxide (cubic) and precision measurement and the measurement results of the lattice constants a, ZrO ₂ cubic, located between the lattice constant of CeO ₂ cubic, approximately, the ZrO ₂ On the other hand, it was confirmed that Ce and Pr were dissolved in the same amount as the charged amount.
[0036]
This catalyst was analyzed by dispersion Raman (laser light: 532.20 nm). The results are shown in FIGS. The X-ray diffraction measurement results were the same for all catalysts, but there was some variation in Raman analysis, and of the 6 lots, 2 lots had a peak at about 300 cm ^{-1 as} shown in FIG. The other four lots showed a type (type 2) spectrum having no peak at about 300 cm ^{−1 as} shown in FIG. 3. Since the Raman spectrum of the Ce-Zr-Pr composite oxide carrier before supporting Pt alone was the same as that after supporting Pt, the structural difference of the carrier itself appeared at about 300 cm ^-1. Was confirmed.
[0037]
Here, two lots showing the type 1 spectrum were used as the catalyst A, and four lots showing the type 2 spectrum were used as the catalyst B.
[0038]
Catalyst A and catalyst B were each pelletized, subjected to a temperature rise evaluation with a stoichiometric model gas, and the CO 50% purification temperature, which is the temperature when the CO purification rate reached 50%, is shown in FIG. . Thus, regarding the initial characteristics, it can be seen that the catalyst A having a peak at about 300 cm ^-1 has excellent low-temperature activity.
[0039]
Next, the catalyst A and catalyst B respectively 3 cc, while switching 2% _{N 2} model gas consisting of a gas containing CO and model gas consisting of 5% _{N 2} gas containing _{O 2} for every minute, flow rate 20L RL endurance (Rich-Lean endurance) of treating at 1000 ° C. for 3 hours at a flow rate of 1 hour / minute, and again obtaining the CO 50% purification temperature is shown in FIG. Thus, after RL durability, catalyst B exhibited better low-temperature activity.
[0040]
From FIGS. 4 and 5, by selecting the catalyst A and the catalyst B, it is possible to obtain the catalyst A having excellent initial characteristics and reduced characteristic variation, and has excellent durability characteristics and characteristic variation. It is clear that catalyst B with reduced amount can be obtained.
[0041]
FIGS. 6 and 7 show Raman spectra of Catalyst A and Catalyst B after RL durability. Although the catalyst B shown in FIG. 7 is not different from the initial stage, the peak near 450 cm ⁻¹ is weakened and the peak near 300 cm ⁻¹ is further increased in the catalyst A shown in FIG. However, no difference was observed between the X-ray diffraction patterns of the two. Since the peak near 300 cm ^-1 represents oxygen at a B atom shift position, the arrangement of metal atoms such as Ce-Zr is present at the A atom position in the catalyst A, but the oxygen position is shifted from the original B atom position. It is considered that those located at the B atom shift position have increased. This is presumably because oxygen vacancies were formed due to the change in valence of CeO ₂ , and the arrangement of oxygen was disturbed. If this disturbance is slight, the initial characteristics are presumed to work on the plus side. Further, since the structure of the catalyst B is stable, it is considered that the catalyst B has excellent durability characteristics.
[0042]
【The invention's effect】
According to the present invention, it is possible to obtain a catalyst product with reduced characteristic variation by selectively producing an exhaust gas purifying catalyst carrier or a catalyst comprising a ceria-zirconia-based composite oxide according to the initial characteristics or durability characteristics of the catalyst. Can be.
[Brief description of the drawings]
FIG. 1 is a diagram showing the results of X-ray diffraction analysis.
FIG. 2 is a diagram showing a Raman analysis result (type 1).
FIG. 3 is a diagram showing a Raman analysis result (type 2).
FIG. 4 is a graph showing an initial CO 50% purification temperature.
FIG. 5 is a graph showing a 50% CO purification temperature after RL durability.
FIG. 6 is a diagram showing a Raman analysis result of a catalyst A (type 1) after RL durability.
FIG. 7 is a diagram showing a Raman analysis result of catalyst B (type 2) after RL durability.
FIG. 8 shows a fluorite crystal structure. FIG. 9 shows an example of peak intensity.

Claims (9)

A composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and performing an X-ray diffraction measurement and a Raman measurement on the composite oxide powder. From the composite oxide powder, an X-ray diffraction pattern is obtained. A method for producing an exhaust gas purifying catalyst carrier, comprising a selecting step of selecting a composite oxide powder having a crystal structure and having no peak near about 300 cm ^{-1 in} a Raman spectrum. A composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and Raman measurement is performed on the composite oxide powder. From the composite oxide powder, a peak is observed at about 450 cm ^{−1 in} a Raman spectrum. A method for producing an exhaust gas purifying catalyst carrier, comprising a screening step of screening a composite oxide powder that is present and has no peak near about 300 cm ⁻¹ . A composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and performing a Raman measurement on the composite oxide powder to obtain a Raman spectrum peak at about 450 cm ⁻¹ from the composite oxide powder. And the ratio (I ₃₀₀ / I ₄₅₀ ) of the peak intensity (I ₄₅₀ ) of the peak at about 300 cm ^{−1 to} the peak intensity (I ₃₀₀ ) of about 300 cm ⁻¹ is not more than a predetermined value. A method for producing an exhaust gas purifying catalyst carrier, comprising: An exhaust gas purifying catalyst carrier comprising a composite oxide containing cerium and zirconium, produced by the method for producing an exhaust gas purifying catalyst carrier according to any one of claims 1 to 3. An exhaust gas purifying catalyst comprising the exhaust gas purifying catalyst carrier according to claim 4 and a noble metal. A composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and performing an X-ray diffraction measurement and a Raman measurement on the composite oxide powder. From the composite oxide powder, an X-ray diffraction pattern is obtained. A method for producing an exhaust gas purifying catalyst carrier, comprising a selecting step of selecting a composite oxide powder having a crystal structure and having a peak near about 300 cm ^{-1 in} a Raman spectrum. A composite oxide powder preparing step of preparing a composite oxide powder containing cerium and zirconium, and Raman measurement is performed on the composite oxide powder. From the composite oxide powder, a peak is observed at about 450 cm ^{−1 in} a Raman spectrum. A method for producing an exhaust gas purifying catalyst carrier, comprising a selecting step of selecting a composite oxide powder that is present and has a peak at about 300 cm ^-1 . An exhaust gas purifying catalyst carrier comprising a composite oxide containing cerium and zirconium, produced by the method for producing an exhaust gas purifying catalyst carrier according to claim 6 or 7. An exhaust gas purifying catalyst comprising the exhaust gas purifying catalyst carrier according to claim 8 and a noble metal.

Images