JP5303867B2 - Manufacturing method of exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to a novel method for producing an exhaust gas purification catalyst and an exhaust gas purification catalyst, and more particularly to a novel method for producing an exhaust gas purification catalyst and an exhaust gas purification catalyst with improved purification performance.

Conventionally, carbon monoxide (CO), nitrogen oxides (NO _x ), and unburned hydrocarbons (HC) contained in exhaust gas discharged from an internal combustion engine such as an automobile gasoline engine gin are converted into carbon dioxide, nitrogen, and water. Various supported catalysts in which a noble metal catalyst is supported on an oxide carrier are known as three-way catalysts for purifying exhaust gas by conversion.
Platinum (Pt) and rhodium (Rh) are known as catalyst metals of these supported catalysts, and SiO ₂ , alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) and the like are known as supports.

These supported catalysts have been conventionally prepared by an impregnation method or a coprecipitation method. Since Rh is in an oxide state (Rh ₂ O ₃ ), its activity is lower than that in a metal state.
In addition, these exhaust gas purifying supported catalysts cannot avoid sintering of the catalyst metal due to the high temperature exhaust gas, so that the total catalytic activity is lowered, and there is a problem of rare noble metal catalyst resources, and improvement in purification performance is required. .
For this reason, attempts have been made to combine different kinds of catalysts or to add other metal oxides to the support in order to improve the catalytic activity, the heat resistance of the supported catalyst and the sintering of the catalyst (Patent Documents 1 to 3). ).

JP-A-10-216514 Japanese Patent Laid-Open No. 2002-282692 JP 2006-26556 A

JP-A-10-216514 discloses an exhaust gas obtained by mixing a first catalyst powder supporting Rh on a support containing alumina and zirconia and a second catalyst powder supporting Pt on the support. It is described that the purification catalyst is excellent in catalytic activity and durability. However, the specifically disclosed carrier is mainly composed of Al ₂ O ₃ which is an acidic carrier, and there is a limit to the sintering suppression effect. Further, there is no description about the interaction of _Al 2 _{O 3} and ZrO _2.

In the above-mentioned Japanese Patent Application Laid-Open No. 2002-282692, La ₂ O ₃ or the like is formed on a lower catalyst layer in which Pt is supported on an oxide carrier obtained from Al ₂ O ₃ powder, a composite oxide of CeO ₂ and ZrO ₂ and alumina sol. It is described that an exhaust gas purifying catalyst comprising a two-layer supported catalyst in which an upper catalyst layer is formed by supporting Rh on a ZrO ₂ support to which an additive containing a lanthanoid element is added exhibits heat resistance and high activity. . However, the production process of the catalyst is complicated in order to produce a uniform supported catalyst. Further, there is no description about the interaction of _Al 2 _{O 3} and ZrO _2.

In the above Japanese Patent Application Laid-Open No. 2006-26556, Rh and a catalyst supporting Al, Ce, La or an alkaline earth metal on a support made of SiO ₂ and a catalyst supporting Rh on ZrO ₂ are mixed. It is described that the exhaust gas purifying catalyst suppresses sintering. However, the main component of the carrier is limited to a SiO ₂ sintering inhibiting effect is acidic carrier. Moreover, there is no description about the interaction between SiO ₂ and ZrO ₂ .

As a result of research aimed at improving the activity of a supported catalyst for exhaust gas purification, the present inventors have found that the acid point and base point of the support are related to the sintering and catalyst activity of the catalyst. As a result of continuing, this invention was completed.
Accordingly, an object of the present invention is to provide a method for producing an exhaust gas purifying catalyst having good catalytic activity and improved purifying performance.

This invention heats a mixture of a hydroxide of a basic carrier material and an aluminum salt or Al ₂ O ₃ and a solvent in which the ratio of Al ₂ O ₃ to the exhaust gas purification catalyst is 10 to 30% by mass. After drying to remove the solvent, firing to produce a carrier,
The present invention relates to a method for producing an exhaust gas purifying catalyst, characterized in that Rh is supported as a noble metal to be supported on the obtained carrier at a ratio of 0.025 to 0.5% by mass with respect to the carrier .

  In this invention, the basic carrier means A. L. Allred and E.M. G. Elements having an electronegativity (Cotton Wilkinson Gauss Fundamental Inorganic Chemistry Book 2nd edition p59) using the Rochow approximation (J. Inorg. Nucl. Chem., 1958, 5264) of less than 1.23 and greater than 1.01 An oxide support of

  In this invention, the acidic carrier means A. L. Allred and E.M. G. Electronegativity using the Rochow approximation (J. Inorg. Nucl. Chem., 1958, 5264) (Cotton Wilkinson Gauss Fundamental Inorganic Chemistry Book 2nd edition, p59) refers to an oxide support of an element having 1.23 or more. . In the case of a complex oxide, the average value of the electronegativity calculated from the surface composition of the complex oxide measured by X-ray photoelectron spectroscopy (XPS) is shown.

  Furthermore, in the present invention, 2θ (deg) has a peak at 60.2 ° by X-ray diffraction analysis, and that it contains a metal composite oxide composed of at least alumina and zirconia, the composition of alumina and zirconia changes. Means that a metal complex oxide having a clear peak at a constant position where 2θ (deg) is 60.2 ° in X-ray diffraction analysis is included.

According to the present invention, it is possible to manufacture an exhaust gas purifying catalyst that suppresses sintering of the catalyst, exhibits good catalytic activity, and has improved purifying ability, by a simple method.
In addition, according to the present invention, it is possible to obtain an exhaust gas purifying catalyst that suppresses sintering of the catalyst, exhibits good catalytic activity, and has improved purifying ability.

A preferred embodiment of the present invention will be described below.
1) The said manufacturing method which carries | supports Rh on the said support | carrier.
2) a basic carrier component is ZrO _2, acidic support component is _Al 2 _{O 3,} wherein the process is 10-30% by weight ratio of _Al 2 _{O 3} is for the entire exhaust gas purifying catalyst.

In the present invention, it is necessary to prepare a carrier by mixing a hydroxide of a basic carrier material and a salt of an acidic carrier material or an acidic carrier and baking them.
Even if the hydroxide of the basic carrier raw material is used alone, there is an effect as compared with the case where the basic carrier is used as it is, but the salt of the acidic carrier raw material or the acidic carrier is used alone. In this case, the catalytic activity is low, which is not preferable.

The hydroxide of the basic carrier raw material is not particularly limited as long as it is a hydroxide that provides a basic carrier for an exhaust gas purification catalyst, and zirconium hydroxide can be preferably used.
The basic carrier material is not particularly limited as long as it can provide a basic carrier for an exhaust gas purification catalyst and can be a hydroxide, zirconium oxynitrate, zirconium oxychloride, zirconium oxyhydroxide, zirconium sulfate, Examples thereof include zirconium acetate, ammonium zirconium carbonate, zirconium stearate, and zirconium octylate.

Examples of the salt of the acidic carrier raw material or the acidic carrier include Al (NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , Al (SCN) ₃ , Al (C ₂ H ₃ O ₂ ) ₃ , Al ₂ O ₃ , Examples thereof include SiO ₂ , preferably Al (NO ₂ ) ₃ , Al ₂ (SO ₄ ) ₃ , Al (SCN) ₃ , Al (C ₂ H ₃ O ₂ ) ₃ , and Al ₂ O ₃ .

The above-mentioned salt or acidic carrier of the acidic carrier raw material is preferably used alone, but Ce, La and alkaline earth metals (Mg, Ca, Sr, Ba, Ra, Be, etc.) may be added.
These Ce, La and alkaline earth metals can be added by impregnation method, ion exchange method, adsorption method, reduction precipitation method and the like with a metal salt such as nitrate.

In the present invention, first, the hydroxide of the basic carrier raw material and the salt of the acidic carrier raw material or the acidic carrier are mixed.
The ratio of the basic carrier component to the acidic carrier is the ratio of the basic carrier as the main component, that is, the ratio of the mass percentage of the acidic carrier component to the whole catalyst [(acidic carrier component / whole catalyst) × 100%]. , Less than 100% by mass, particularly 50% by mass or less, 5% by mass or more, and preferably 10 to 30% by mass.
In particular, it is preferable that the basic carrier component is ZrO ₂ , the acidic carrier component is Al ₂ O ₃ , and the ratio of Al ₂ O _{3 to} the entire catalyst is 10 to 30% by mass.

  The hydroxide of the basic carrier raw material is obtained by uniformly mixing the starting raw material of the basic carrier and ammonia, and then obtaining a solid mixture, preferably by filtration or centrifugal separation. Can be obtained by heating and drying at 100 to 200 ° C. for several hours to about 1 day and then crushing if necessary.

  In the present invention, the hydroxide of the basic carrier raw material is put in a solvent, for example, water if necessary, and mixed with the salt of the acidic carrier raw material or the acidic carrier, and if necessary, any shape, for example, a pellet shape Alternatively, it is formed into a honeycomb shape and is preferably heated and dried at a temperature of about 100 ° C. or more, particularly about 100 to 200 ° C. for several hours to about 1 day, and then preferably 200 ° C. or more, particularly about 200 to 300 ° C. The carrier can be obtained by baking at a temperature of about 10 minutes to overnight, and preferably at 400 ° C. or higher, particularly 400 to 1000 ° C. for about 10 minutes to 10 hours.

The supported catalyst in the present invention may be any supported catalyst obtained by supporting a catalyst metal on the carrier in an arbitrary shape, preferably a pellet-shaped or honeycomb-shaped molded body, or by supporting the catalyst metal on a carrier. It can manufacture by shape | molding to the molded object of the shape of.
For example, rhodium oxides such as rhodium oxide Rh ₂ O ₃ , rhodium nitrate Rh (NO ₃ ) ₃ , rhodium chloride RhCl ₃ .4H ₂ O, dinitrodiammine platinum Pt (NH ₃ ) ₂ (NO ₂ ) ₂ , dichlorotetraammine platinum Pt (NH ₃ ) ₄ Cl ₂ .nH ₂ O (n = 1), hexachloroplatinic acid hexahydrate H ₂ [PtCl ₆ ] .6H ₂ 0, platinum oxide PtO ₂ , platinum compounds such as organic platinum as catalyst components The catalyst metal such as Rh and Pt can be supported by a catalyst supporting method such as an evaporation coagulation method, an impregnation method, an ion exchange method, an adsorption method, a reduction precipitation method, and preferably an impregnation method.
The amount of the catalyst metal supported is preferably about 0.025 to 1% by mass, particularly about 0.025 to 0.5% by mass, based on the carrier.

  The exhaust gas purifying catalyst of the present invention comprises, for example, the basic carrier raw material hydroxide and the salt of the acidic carrier raw material or the acidic carrier mixed with a solvent, for example, water, if necessary, in any shape, preferably It may be formed by supporting the catalyst metal on a pellet-shaped or honeycomb-shaped support, or after supporting the catalyst metal on the support and crushing it to form a supported catalyst, It can be manufactured by forming into a honeycomb shape.

Further, the exhaust gas purifying catalyst of the present invention, for example, cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2) The support substrate of a honeycomb shape formed from _{MgO · Al 2 O 3 · SiO} 2 composite oxide such as The coating layer made of the above support is formed by any method, for example, impregnation, coating, etc., and then the catalyst metal is supported on the coating layer made of the support by any method, or on the honeycomb-shaped support substrate in advance. It can also be produced by laminating the prepared supported catalyst composed of the carrier and the catalyst metal by any method.

  As a method for supporting the catalyst metal component on the support, preferably, the catalyst metal component slurry is applied and sprayed on the molded support, preferably the catalyst metal component slurry is zone-coated, Or impregnate the molded carrier into the catalyst metal component slurry, or mix the carrier and the catalyst metal component slurry, knead while evaporating water to form a catalyst metal paste, and extrude it with an extrusion molding machine etc. And a method of impregnating the support with a catalytic metal component.

  In the present invention, preferably, after drying by heating at a temperature of about 100 ° C. or more, particularly about 100 to 200 ° C. for several hours to about 1 day or night, at 400 ° C. or more, particularly 400 to 800 ° C. for about 30 minutes to 5 hours The exhaust gas purification catalyst of the present invention can be produced by calcining for a period of time and reducing the catalyst metal component if necessary.

Hereinafter, according to the above description, which is a preferred embodiment of the present invention, zirconium hydroxide and an aluminum salt are mixed and calcined to prepare a carrier, and the resulting carrier is impregnated with a catalytic metal component. A specific example will be described with reference to FIGS. 4 to 6 which are X-ray diffraction diagrams (XRD).
In these figures, FIG. 4 shows that Al ₂ O ₃ / total catalyst is 10 mass%, FIG. 5 shows that Al ₂ O ₃ / total catalyst is 20 mass%, and FIG. 6 shows that Al ₂ O ₃ / total catalyst is 30 mass%. The supported catalyst is shown.

4 to 6, the X-ray diffraction analysis has a peak at 60.2 ° where 2θ (deg) is constant although the intensity is different.
Therefore, these supports are considered to contain the same metal complex oxide composed of Al, Zr and O.
This composite oxide is represented by Al _0.16 Zr _0.84 O _1.96 as a composition formula.

  The catalyst of the present invention is compressed and crushed as necessary, and used as a catalyst having a desired shape, for example, a pellet-shaped or honeycomb-shaped catalyst having a diameter of 1 to 2 mm, as an exhaust gas purification catalyst having a good purification ability. Can do.

Although the carrier in the present invention include _Al 0.16 _{Zr 0.84} O _1.96, the _Al 0.16 _{Zr 0.84} O _Al content of _1.96 3.87 wt%, Zr content The rate is 68.62% by mass, and the O content is 27.51% by mass.
The Al content of Al ₂ O ₃ = 10 mass% and ZrO ₂ = 89.75 mass% is 5.29 mass%, and the Zr content is 66.44 mass.
Assuming that all Zr is Al _0.16 Zr _0.84 O _1.96 , the excess Al content is 1.55% by mass.
The Al content of Al ₂ O ₃ = 20 mass% and ZrO ₂ = 79.75 mass% is 10.58 mass%, and the Zr content is 59.04 mass%.
Assuming that all Zr is Al _0.16 Zr _0.84 O _1.96 , the excess Al content is 7.26% by mass.
The Al content of Al ₂ O ₃ = 30% by mass and ZrO ₂ = 69.75% by mass is 15.88% by mass, and the Zr content is 51.64% by mass.
Assuming that all Zr is Al _0.16 Zr _0.84 O _1.96 , the excess Al content is 12.97% by mass.

Examples of the present invention will be described below.
In each of the following examples, the performance of the exhaust gas purification catalyst was evaluated by the measurement method described below.
1. Measurement of acid amount of supported catalyst By ammonia temperature programmed desorption (TPD), the acid amount was measured from NH ₃ desorption amount using ammonia as an adsorption gas, and the intensity distribution of acid points of the sample was evaluated. The device used was TPD-MASS. The NH ₃ desorption amount may be displayed by omitting the unit. In this case, the unit means a relative value when the value when Al ₂ O ₃ is 10 mass% is 2007.97.

2. Measurement of reduction temperature of supported catalyst The reduction temperature of the catalyst (Rh ₂ O ₃ ) was measured by using temperature-reduction TPR (Temperature Programmed Reduction / Reaction) using H ₂ as the reducing gas. The lower the reduction temperature, the easier the noble metal catalyst is reduced and the higher the activity. The device used was TPD-MASS.
3. Purification characteristic test The obtained catalyst (shape: pellet) was set in an exhaust gas purification performance apparatus, and each of C ₃ H ₆ , NO _x , and CO under the conditions of a space velocity of 400000 h ⁻¹ with the gas composition shown in Table 1 below. % Purification temperature was measured and the catalytic activity was evaluated. The rich gas λ (excess air ratio = air / fuel ratio / theoretical air / fuel ratio) = 0.46, and the lean gas λ = 2.32. The lower the 50% purification temperature, the higher the catalytic activity.

4). Measurement of CO adsorption amount Using a constant volume type adsorption amount measurement device, the amount of CO adsorption on the metal surface was measured by a conventional method, and the particle size of the catalyst Rh was determined from the following conversion formula. The apparatus used a CO pulse.
Conversion formula: 1860.465116 × C / (V × a ² × d / adsorption ratio) (Å) = 3.887123746 / V (Å)
C: Rh loading concentration = 0.25 (%)
V: CO adsorption amount per gram of catalyst a: Lh lattice constant (Å) = 3.8030
Adsorption ratio: molar ratio of CO adsorbed on Rh1 mole = 1.5
d: Rh specific gravity (g / cc) = 12.41
5. Measurement of the base amount of the supported catalyst Using the temperature programmed desorption method TPD (Temperature Programmed reduction), the base amount is measured from the desorbed CO ₂ amount of the sample using CO ₂ as the adsorption gas, and the intensity distribution of the base points is evaluated. did. The device used was TPD-MASS. When the unit is omitted and displayed for the CO ₂ desorption amount, the unit means a relative value when the value of Rh / ZrO ₂ prepared by the coprecipitation method is 5 × 10 ⁻⁹ .
6). X-ray diffraction (XRD) measurement XRD measurement conditions Apparatus: manufactured by RINT2500 Measurement method: Continuous Start angle: 3 degrees End angle: 85 degrees Sampling width: 0.02 degrees Scanning speed: 5.0 degrees / min
Voltage ... 50kV
Current: 300mA

Example 1
Ammonia was added to zirconium oxynitrate and stirred overnight, then separated and washed with a centrifuge to obtain a solid content, and the solid content was crushed at 120 ° C. After pulverization, the resulting zirconium hydroxide was mixed with water and aluminum nitrate at a ratio of Al ₂ O ₃ / total catalyst of 10% by mass, and then mixed and dried at 120 ° C. overnight. Next, it was calcined at 250 ° C. for 1 hour, crushed, and calcined at 800 ° C. for 3 hours to obtain a carrier.
This support was impregnated with rhodium nitrate, dried at 120 ° C. overnight, and calcined at 500 ° C. for 2 hours to obtain a supported catalyst having a supported amount of 0.25% by mass (Rh / support).
The exhaust gas purification catalyst which is this supported catalyst was evaluated. The results are summarized in Table 2, FIG. 1, FIG. 2 and FIG.

Example 2
A supported catalyst was obtained in the same manner as in Example 1 except that aluminum nitrate was added at a ratio of 20% by mass of Al ₂ O ₃ / total catalyst.
The exhaust gas purification catalyst which is this supported catalyst was evaluated. The results are collectively shown in Table 2 and Table 3, FIG. 1, FIG. 2 and FIG.

Example 3
A supported catalyst was obtained in the same manner as in Example 1 except that aluminum nitrate was added at a ratio of Al ₂ O ₃ / total catalyst of 30% by mass.
The exhaust gas purification catalyst which is this supported catalyst was evaluated. The results are summarized in Table 2, FIG. 1, FIG. 2 and FIG.

Comparative Example 1
A supported catalyst was obtained in the same manner as in Example 1 except that no aluminum nitrate was added.
This supported catalyst was evaluated. The results are summarized in Table 2, Table 3, FIG. 1, FIG. 2 and FIG.

Comparative Examples 2-4
According to the following method, which is a known coprecipitation method, aluminum nitrate is added as alumina in a proportion of 10, 20, or 30% by mass, and a supported catalyst with a supported amount of 0.25% by mass (Rh / carrier) is added. Obtained.
Procedure of coprecipitation method: Ammonia was dropped into zirconium oxynitrate so that the pH was about 8, and the mixture was stirred overnight, dried at 120 ° C. for one day, and calcined at 500 ° C. for 2 hours.
These supported catalysts were evaluated. The results are collectively shown in Table 2 and Table 3, FIG. 1, FIG. 2 and FIG.

Moreover, when the amount of bases was measured from the amount of desorbed CO ₂ for the supported catalysts obtained in Examples 1 to 3 and Comparative Example 1, 20 × 10 ^{−9 to} 35 × 10 ⁻⁹ in Examples 1 to 3 and 12 × 10 in Comparative Example 1. ^-9 .

From the above, when Examples 1 to 3 and Comparative Examples 1 to 4 are compared, the exhaust gas purifying catalyst which is a supported catalyst according to the present invention has both the acid point and base point amount of Al ₂ O ₃ and ZrO ₂ alone. As a result, precious metal (Rh) becomes easily reducible and becomes metallized and becomes highly active, and the base point suppresses sintering of the precious metal (Rh), so that high activity and low sintering are achieved. An exhaust gas purifying catalyst having a high purifying ability and having a combination was obtained.

FIG. 1 shows the change in the acid amount of the supported catalyst by measuring the NH ₃ desorption amount when the addition amount of Al ₂ O ₃ is changed. FIG. 2 shows changes in the reduction temperature of Rh ₂ O ₃ supported on the supported catalyst when the amount of Al ₂ O ₃ added is changed. FIG. 3 shows changes in the 50% purification temperature of the supported catalyst and the particle diameter of Rh when the amount of Al ₂ O ₃ added is changed. FIG. 4 shows an X-ray diffraction pattern of the supported catalyst obtained in Example 1. FIG. 5 shows an X-ray diffraction pattern of the supported catalyst obtained in Example 2. FIG. 6 shows an X-ray diffraction pattern of the supported catalyst obtained in Example 3. FIG. 7 shows an X-ray diffraction pattern of the supported catalyst obtained in Comparative Example 1.

Claims (2)

A mixture of a hydroxide of the basic carrier material and an aluminum salt or Al ₂ O ₃ and a solvent in which the ratio of Al ₂ O _{3 to} the entire exhaust gas purification catalyst is 10 to 30% by mass is dried by heating. After removing the baked to produce a carrier,
A method for producing an exhaust gas purifying catalyst, characterized in that Rh is supported as a noble metal to be supported on the obtained carrier at a ratio of 0.025 to 0.5 mass% with respect to the carrier .   The production method according to claim 1, wherein the hydroxide of the basic carrier material is zirconium hydroxide.

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