JP2003170043A - Exhaust gas treatment catalyst and production method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ventilation type exhaust gas treatment catalyst with improved exhaust gas treatment capability and excellent durability without increasing the pressure loss of an exhaust gas. <P>SOLUTION: The exhaust gas treatment catalyst is a ventilation type exhaust gas treatment catalyst composed of a catalyst carrier and catalytic components deposited on a honeycomb substrate in a manner that at least 90% by mass of the catalyst carrier and the catalytic components respectively are deposited in pores of the cell walls of the honeycomb substrate. Preferably, the honeycomb substrate has a porosity of the cell walls in a range from 40 to 75% and D50 pore diameter in a range from 10 to 50 μm and the pores of the cell walls of the honeycomb substrate are practically nonpenetrating holes. Such an exhaust gas treatment catalyst can be produced by preparing a slurry of particles having D90 particle diameter smaller than the D50 pore diameter of the cell walls of the honeycomb substrate and washing-coating the honeycomb substrate with the slurry. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow-type exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst for efficiently purifying exhaust gas discharged from an internal combustion engine such as an automobile engine with a low pressure loss. Regarding catalysts.

[0002]

2. Description of the Related Art Exhaust gas emitted from an internal combustion engine such as an automobile engine contains carbon monoxide (CO), hydrocarbon (H
C), nitrogen oxides (NO _x ), etc., and these harmful substances are generally platinum (Pt), rhodium (Rh), palladium.
It is purified by an exhaust gas purification catalyst containing a noble metal such as (Pd) as a catalyst component. Such exhaust gas purification catalyst
Usually, a honeycomb substrate made of cordierite or the like having a large number of cells is coated with a catalyst carrier such as γ-alumina, and the above catalyst components are further carried.

However, in order to protect the environment, various improvements have been made on the purification performance of such exhaust gas purification catalysts. As one of the measures for this improvement, it has been attempted to increase the cell density of the honeycomb substrate and thereby increase the contact efficiency of the catalyst component with the exhaust gas.

[0004]

However, the cell density of the honeycomb substrate has already been considerably increased, and increasing the number of cells further increases the proportion of the cell wall cross section in the cross section of the exhaust gas passage. Will be increased. Therefore, increasing the cell density further increases the pressure loss of the exhaust gas flowing through the exhaust gas purification catalyst,
This leads to deterioration of fuel efficiency. Further, the exhaust gas purifying catalyst needs to endure mechanical action such as vibration for a long period of time.

By the way, the applicant of the present invention has previously disclosed that the Japanese Patent Laid-Open No. 9-
Japanese Patent No. 94434 discloses a wall-flow type in which every other cell is plugged and exhaust gas flows through a cell wall of an open hole for the purpose of purifying particulates and the like contained in exhaust gas of a diesel engine. An exhaust gas purification filter is proposed. However, this publication makes no particular mention of purification performance, pressure loss, and durability of the flow-type exhaust gas purification catalyst.

Therefore, according to the present invention, in a flow-type exhaust gas purifying catalyst, the pressure loss of the exhaust gas flowing through the exhaust gas purifying catalyst is not increased, and the contact efficiency of the catalyst component with the exhaust gas is increased to improve the exhaust gas. An object of the present invention is to provide an exhaust gas purifying catalyst that has improved gas purification performance and excellent durability.

[0007]

The above object is an exhaust gas purifying catalyst in which a catalyst carrier and a catalyst component are supported on a honeycomb substrate, wherein the catalyst carrier and the catalyst component are each at least 90% by mass. Are disposed in the pores of the cell wall of the honeycomb substrate, which is achieved by the flow-through type exhaust gas purifying catalyst.

That is, the exhaust gas purifying catalyst of the present invention comprises a honeycomb base material having a large number of cells as a basic constituent material, and both ends of the cells are opened so that exhaust gas flows, and the honeycomb base material In the pores of the cell wall, at least 9 parts each of a catalyst carrier such as γ-alumina and a catalyst component such as platinum are contained.
This is an exhaust gas purifying catalyst in which 0 mass% is arranged.

FIG. 1 shows a model of the exhaust gas purifying catalyst of the present invention. By arranging the catalyst carrier and the catalyst components in the pores of the cell wall, the flow path of the exhaust gas is narrowed. Without doing so, the catalyst carrier and the catalyst component are arranged and fixed on the honeycomb substrate. FIG. 2 is a model view of a conventional exhaust gas purifying catalyst, in which a catalyst carrier and a catalyst component are arranged on a cell wall and an exhaust gas passage is narrowed, so that the exhaust gas pressure loss is reduced. Will be increased.

Further, in the conventional exhaust gas purifying catalyst, as shown in FIG. 2, the catalyst carrier is thickly coated at the corners of the cell, and the exhaust gas does not substantially flow at the corners. Not only does this lead to an increase in pressure loss, but the catalyst carrier and catalyst components are wasted, and the heat capacity of the exhaust gas purifying catalyst is unnecessarily increased.

In a preferred embodiment, the cell wall of the honeycomb base material which constitutes the exhaust gas purifying catalyst of the present invention is 40 to
It has a porosity of 75% and a D50 pore size of 10 to 50 μm. When the porosity and the D50 pore diameter of the honeycomb substrate are within these ranges, the honeycomb substrate can favorably support the catalyst carrier and the catalyst component, and at the same time, can provide the catalyst component with high contact efficiency with exhaust gas.

Further, in a preferred embodiment, the pores of the cell wall of the honeycomb substrate are substantially non-penetrating pores. By placing the catalyst carrier and the catalyst component in the pores of the cell wall of the honeycomb substrate, the catalyst carrier and the catalyst component are held by the cell walls surrounding them, and in addition, the pores are non-through holes. Therefore, it is considered that the catalyst carrier and the catalyst components and the cell wall are partially prevented from falling off due to mechanical action such as vibration, and high durability can be exhibited.

Such an exhaust gas purifying catalyst of the present invention is
As shown in Examples described later, it has been proved that the pressure loss of exhaust gas is small and the exhaust gas purification performance is excellent. This low pressure loss is because the flow path of the exhaust gas is not narrowed, and the excellent exhaust gas purification performance is
It is considered that this is because the contact efficiency of the catalyst component with the exhaust gas is improved.

That is, in the exhaust gas purifying catalyst of the present invention, the catalyst component is carried in the state of being present in the cell wall and being buried in the cell wall, but the pores of the cell wall are curved. Therefore, it is considered that the supporting area is increased and the residence time of the exhaust gas is increased due to the pore volume, so that high contact efficiency with the exhaust gas can be provided as a whole.

Further, the exhaust gas purifying catalyst of the present invention has an advantage in that the waste of the catalyst carrier and the catalyst component at the corner of the cell in the above-mentioned conventional technique is eliminated. Furthermore, the unnecessary increase in heat capacity resulting from this waste is also eliminated. Therefore, the early warm-up property is improved, and it can be suitably used also as a start-up catalyst arranged near the engine exhaust port.

The shape of the cells of the honeycomb substrate may be a regular quadrangle, or may be the hexagonal shape shown in FIG. 3 or another polygonal shape. Since the present invention supports the catalyst carrier and the catalyst component on the cell wall, the polygonal shape increases the circumferential length of the cross section of the cell wall, which leads to an increase in the supported amount of the catalyst carrier and the catalyst component. is there.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention comprises:
A catalyst carrier and a catalyst component are supported on a honeycomb substrate, and each of the catalyst carrier and the catalyst component is at least 90% by mass.
Are arranged in the pores of the cell walls of the honeycomb substrate.

As the honeycomb substrate, cordierite,
A material made of a heat-resistant ceramic material such as alumina, zirconia, or silicon carbide can be preferably used. The honeycomb base material used has a large number of cells having open ends, and the cell density of the honeycomb base material is not particularly limited in the present invention, and is about 200 cells / square inch. High density, 1000 cells /
High densities such as square inches or more can be used.

Examples of the catalyst carrier include oxides such as alumina, zirconia and ceria, as well as zirconia-ceria, alumina-ceria-zirconia and ceria-zirconia.
Those composed of composite oxides such as yttria and zirconia-calcia can be preferably used.

The catalyst component is 3A to 7A in the periodic table.
Group, group 8 including noble metals, group 1B, and transition metals including f-block elements can be preferably used, and manganese (M
n), iron (Fe), cobalt (Co), nickel (Ni), copper
(Cu), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), lanthanum (La), cerium (Ce), praseodymium. (Pr), Neodymium (Nd),
And noble metals such as platinum (Pt), gold (Au), palladium (Pd), ruthenium (Ru), and rhodium (Rh) are exemplified, and preferably manganese, iron, cobalt, nickel, copper, platinum, gold, palladium. And at least one transition metal selected from ruthenium, and rhodium.

[0021] Preferably, the cell wall of the above-mentioned honeycomb substrate has a porosity of 40 to 75% and a D50 pore diameter of 10 to 50 µm. Here, the term "porosity of cell wall" in the present invention means a porosity measured by a mercury porosimetry using a mercury porosimeter, and the term "D50 pore diameter of cell wall" means this mercury. It means a pore size having a cumulative volume of 50% in the pore size distribution measured according to the method using a porosimeter.

Also, preferably, the pores existing in the cell wall of the honeycomb substrate are substantially non-through holes. Here, the term “substantially non-through holes” in the present invention refers to pores observed in a cross section of a cell wall in a direction perpendicular to a flow direction of exhaust gas, and has a number average of at least 70%, and more preferably, At least 90% means not penetrating both walls of the cell wall. Whether or not the pores of the cell wall are through-holes can be evaluated by observing the cross section of the cell wall, as shown in Examples described later.

The honeycomb substrate and the exhaust gas purifying catalyst of the present invention using the honeycomb substrate can be manufactured, for example, as follows. The honeycomb substrate can be obtained by extruding a ceramic raw material mixture using a honeycomb mold, and then performing drying and firing. Here, for example, if a burnable material having a controlled particle size is blended in a predetermined amount in the raw material mixture, the porosity of the cell wall and the D50 pore size of the resulting honeycomb substrate are within the target range. It is possible to control.

Examples of the burnable material include graphite particles, carbon black, carbon fiber chops, and the like, which have a particle diameter or length adjusted to a desired range, but are relatively easy. It is available.

Further, the honeycomb substrate in which the pores of the cell walls are substantially non-through holes is preferably graphite particles or carbon black having a relatively narrow particle size distribution, and these burnable materials are used in the composition. It can be obtained by preparing a raw material mixture by adding a dispersant as necessary so as not to agglomerate, and then performing the above-mentioned extrusion molding and drying / firing. Further, by using a carbon fiber chop shorter than the cell wall thickness, it is possible to obtain a honeycomb substrate having a non-through hole that extends one-dimensionally in the same manner.

On the honeycomb substrate thus obtained,
A catalyst carrier and a catalyst component are supported. The loading of these can be performed, for example, as follows. A slurry is prepared using the above-mentioned powder of alumina, zirconia, ceria-zirconia, etc., and the honeycomb substrate is immersed in this slurry to impregnate the honeycomb substrate with the slurry. Alternatively,
The honeycomb substrate is forcibly impregnated with the slurry by dipping the honeycomb substrate in the slurry to reduce the pressure of the slurry or by applying mechanical vibration such as ultrasonic waves to the honeycomb substrate.

Next, the honeycomb substrate impregnated with this slurry is dried and fired to coat a catalyst carrier, and then, for example, nitrates, chlorides, etc. of the above various catalyst components are used,
The catalyst component is supported by evaporation dryness method, precipitation method, adsorption method, ion exchange method, reduction precipitation method, or the like.

Here, a slurry is prepared in which the catalyst carrier in the slurry has a D90 particle size smaller than the D50 pore size of the cell wall of the honeycomb substrate, and then the slurry is wash-coated on the honeycomb substrate, and then the catalyst component is prepared. According to the method of supporting the catalyst on the catalyst carrier, the exhaust gas purifying catalyst of the present invention in which at least 90% of each of the catalyst carrier and the catalyst component is arranged in the pores of the cell wall of the honeycomb substrate is relatively easy. Can be obtained.

"D90 particle size" of the slurry of this catalyst carrier
Means the particle size of 90% cumulative mass of the catalyst carrier in the prepared slurry. Here, the method for measuring the particle size in the slurry includes a dynamic light scattering method, a light diffraction scattering method, a gas chromatography method, a sedimentation method and the like, and the "D90 particle size" in the present invention is the light diffraction scattering. The value measured by the method.

The D90 particle size of the catalyst carrier in the slurry can be reduced to a desired level by milling the slurry, the strength and the addition of a dispersant.
Hereinafter, the present invention will be described more specifically with reference to Examples.

[0031]

Example 1 350 parts by weight of kaolin, 300 parts by weight of talc, and 100 parts by weight of alumina were used as oxide raw materials, and 300 parts by weight of water, 30 parts by weight of methyl cellulose as a binder, and pore-forming material were used. Material has D50 particle size of 10 μm
10 parts by mass of the graphite particles of No. 1 were added, and these were kneaded with a kneader for 2 hours to prepare a raw material mixture for the honeycomb substrate.

This compound was extruded and fired for 20 hours at 1450 ° C. in an air atmosphere to obtain a diameter of 80 mm × length of 95.
mm, cell density 300 cells / inch 2, cell wall thickness 2
A honeycomb substrate having a cordierite composition of 00 μm was obtained.
The porosity of the obtained honeycomb substrate was measured by a mercury porosimeter (Autopore 9420 manufactured by Micromeritic Co., Ltd.) according to the mercury porosimetry.
2%, D50 pore diameter was 20 μm.

Next, a catalyst carrier and a catalyst component were loaded on this honeycomb substrate as follows. 50 parts by mass of γ-alumina (specific surface area: about 150 m ² / g, D50 particle size: 20
μm) and 50 parts by mass of ceria-zirconia (specific surface area: about 100 m ² / g, CeO ₂ / ZrO ₂ = 1/1 molar ratio), and 200 parts by mass of ion-exchanged water, and the mixture is mixed with a ball mill at 5
Milled for 0 hours.

The D50 particle diameter of this mixed powder was 2 μm, and the D90
The particle size was 15 μm. Alumina sol (A-200 manufactured by Nissan Chemical Industries, Ltd.) was added to this mixed powder in an amount such that the solid content of the alumina sol was 3% based on the total mass of the mixed powder, and ion-exchanged water was further added to obtain 25% solid content. A catalyst carrier slurry was obtained. The D50 particle diameter and the D90 particle diameter were measured by a light diffraction scattering method (LA-920 manufactured by Oliver).

Next, the above honeycomb substrate was immersed in this catalyst carrier slurry, and then excess slurry was blown off by high-pressure air and fired in an air atmosphere at 400 ° C. for 1 hour to wash coat the catalyst carrier. As a result, the honeycomb substrate was coated with 80 g of catalyst carrier (160 g of catalyst carrier / 1 liter of carrier).

Next, the catalyst carrier on the honeycomb substrate was impregnated with a solution of platinum dinitrodiammine Pt (NH ₃ ) ₂ (NO ₂ ) ₂ and rhodium nitrate Rh (NO ₃ ) ₃ and dried, and then 400 ° C.
Was fired for 1 hour in the air atmosphere to carry 1.5 g of Pt and 0.3 g of Rh per liter of the honeycomb substrate. Through the above steps, the catalyst carrier γ-alumina and ceria-zirconia and the catalyst components Pt and Ph are formed on the honeycomb substrate.
Thus, an exhaust gas purifying catalyst of the present invention carrying the above was obtained.

Examples 2 to 6 and Comparative Example 1 In the preparation of the blend in Example 1, a blend whose summary is shown in Table 1 was prepared in the same manner as in Example 1 except that the blending amount of graphite particles was changed. And then in the same manner as in Example 1,
A honeycomb substrate was prepared, and γ-alumina and ceria-zirconia as catalyst carriers and Pt and Ph as catalyst components were carried on the honeycomb substrate to obtain exhaust gas purifying catalysts of Examples and Comparative Examples whose summary is shown in Table 1. It was

Examples 7 to 12 and Comparative Example 2 In the preparation of the compound in Example 1, the compound whose summary is shown in Table 2 was prepared in the same manner as in Example 1 except that graphite particles having different particle sizes were compounded. A honeycomb base material was prepared and then processed in the same manner as in Example 1, and the catalyst support γ-
Alumina and ceria-zirconia and catalyst components Pt and P
By carrying h, the exhaust gas purifying catalysts of Examples and Comparative Examples whose summary is shown in Table 2 were obtained.

Reference Example 3 In the preparation of the catalyst carrier slurry of γ-alumina and ceria-zirconia in Example 1, 50 using a ball mill was used.
Instead of time crushing, crushing for 5 hours was carried out, and the procedure of Example 1 was repeated except that the catalyst carrier was coated with the slurry of the mixed powder having D90 particle size of 35 μm. An exhaust gas purification catalyst was obtained.

-Measurement of supported amounts of catalyst component and catalyst carrier- "Supported amount in pores" of catalyst carrier and catalyst component shown in Tables 1 and 2.
Cuts each exhaust gas purification catalyst, scrapes off the catalyst carrier located outside the cell wall, and measures the mass of the catalyst carrier and ICP emission analysis of the contained catalyst component to determine the catalyst carrier outside the pores of the cell wall. It is a value calculated by obtaining the mass of the catalyst component and subtracting this amount from the amount initially loaded.

-Observation of Structure in Honeycomb Substrate-The catalyst for purifying exhaust gas of Example 4 was impregnated with epoxy resin and cured, and then cut at a right angle to the flow direction of exhaust gas. Scanning electron microscope images of this cross section are shown in FIGS.
It can be seen from FIGS. 4 to 5 that most of the catalyst carrier is arranged in the pores of the cell wall, and that the pores of the honeycomb substrate are all non-penetrating pores that do not penetrate the cell wall. I understand.

-Measurement of Pressure Loss-Air was circulated at a flow rate of 7 m ³ / min through the exhaust gas purifying catalysts of Examples and Comparative Examples, and the differential pressure before and after the exhaust gas purifying catalyst was measured. The results are summarized in Tables 1 and 2. The results clearly show that the exhaust gas purifying catalyst of the example having a large amount of supported pores has a smaller pressure loss than the exhaust gas purifying catalyst of the comparative example having a small amount of supported pores.

-Evaluation of catalyst performance-For each of the exhaust gas purifying catalysts of Examples and Comparative Examples, a sample having a diameter of 30 mm and a length of 50 mm was cut out from each central portion, and C ₃ H ₆ was purified by the following model exhaust gas. The rate was evaluated. The result is 50% C ₃ H ₆ purification temperature
(T50) is shown collectively in Tables 1 and 2. 0.16% CO + 2400ppm C ₃ H ₆ + 1000ppm NO
+ 14.5% CO ₂ + 0.57% O ₂ + 10% H ₂ O (residual N ₂ )

From the results shown in Tables 1 and 2, the exhaust gas purifying catalyst of the example having a large amount of supported pores had a C ₃ H ₆ content higher than that of the exhaust gas purifying catalyst of the comparative example having a small amount of supported pores. It can be seen that the purification performance is high. The reason for this is considered to be that since the catalyst carrier is supported on the curved inner wall of the pores in the pores, the contact efficiency with the exhaust gas is higher than when the catalyst carrier is supported flat on the cell wall surface.

[0045]

INDUSTRIAL APPLICABILITY In a flow-type exhaust gas purifying catalyst,
It is possible to provide an exhaust gas purifying catalyst that improves the exhaust gas purifying performance by increasing the contact efficiency between the exhaust gas and the catalyst component without increasing the pressure loss of the exhaust gas and has excellent durability.

[0046]

[Table 1]

[0047]

[Table 2]

[Brief description of drawings]

FIG. 1 is a model view of an exhaust gas purifying catalyst of the present invention.

FIG. 2 is a model view of a conventional exhaust gas purifying catalyst.

FIG. 3 is a model view showing another embodiment of the exhaust gas purifying catalyst of the present invention.

FIG. 4 is a scanning electron micrograph showing the structure of a ceramic material in the exhaust gas purifying catalyst of the present invention.

5 is a scanning electron micrograph showing the structure of the ceramic material of FIG. 4 at high magnification.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/10 B01D 53/36 104A 3/28 301 ZAB 102B F term (reference) 3G091 AB01 BA01 GA06 GA16 GB06W GB07W GB17X 4D048 AA06 AA13 AA18 AB05 BA02Y BA03X BA08X BA10X BA12Y BA18Y BA19X BA28Y BA30X BA31Y BA32Y BA33X BA34Y BA35Y BA36Y BA38Y BA41Y BA42X BB02 BB17 4G069 AA03 AA08 BA01A BA01B BA05A BA05B BA13A BA13B BB02B BB04A BB06A BB06B BC09A BC16A BC16B BC31A BC33A BC40A BC43A BC43B BC51A BC51B BC62A BC65A BC66A BC67A BC68A BC69A BC70A BC71A BC71B BC72A BC75A BC75B CA03 CA09 EA19 EB05 EB12X EB12Y EC06X EC06Y EC17X EC17Y EC27 FA03 FB14 FB15 FB23 FB78

Claims (5)

[Claims] 1. An exhaust gas purifying catalyst in which a catalyst carrier and a catalyst component are carried on a honeycomb substrate, wherein at least 90% by mass of each of the catalyst carrier and the catalyst component is
A flow-type exhaust gas purifying catalyst, which is arranged in the pores of the cell wall of the honeycomb substrate. 2. The cell wall of the honeycomb substrate is 40 to 75%.
The exhaust gas purifying catalyst according to claim 1, having a porosity of 10 to 50 µm and a D50 pore diameter of 10 to 50 µm. 3. The exhaust gas purifying catalyst according to claim 1, wherein the pores in the cell wall of the honeycomb substrate are substantially non-penetrating pores. 4. The catalyst carrier is alumina, zirconia, ceria, zirconia-ceria, alumina-ceria-zirconia, ceria-zirconia-yttria, and zirconia-.
It is at least 1 sort (s) selected from the calcia.
The exhaust gas purifying catalyst according to any one of 3 to 3. 5. A slurry in which the catalyst carrier has a D90 particle size smaller than the D50 pore size of the cell wall of the honeycomb substrate is prepared, and then the slurry is wash-coated on the honeycomb substrate, and then the catalyst component is prepared. 5. The catalyst carrier is carried on the catalyst carrier.
Item 6. A method for producing an exhaust gas purifying catalyst according to item.