JPH10235193A - Catalyst for diesel exhaust gas purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adsorb efficiently HC and SOF in a low temperature zone, prevent the discharge of HC and SOF and control further the formation of sulfate by mixing acidic carrier powder on which a catalyst metal is carried with basic carrier powder of more basic than the acidic carrier powder. SOLUTION: Mixed powder formed by mixing acidic carrier 20 powder on which a catalyst metal such as platinum, palladium or silver, or iron or copper and with basic carrier 21 powder more basic than the acidic carrier 20 powder can be applied for coating a honeycomb type or a pellet type shaped carrier base 1. As for the acidic carrier 20, a carrier of low adsorptivity of SO2 in exhaust gas is discharged out, and at least one kind selected out of SiO2 -TiO2 , ZrO2 -SiO2 and SiO2 is used desirably. As the base carrier 21, any carrier of more basic, even slightly more, than the acidic carrier 20 can be used, and a carrier of high adsorptivity of SOF and SO2 is desirably used, and at least one kind selected out of Al2 O3 , ZrO2 and TiO2 is desirably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention oxidizes and purifies HC (hydrocarbon) and SOF (Soluble Organic Fraction) contained in exhaust gas of a diesel engine (hereinafter referred to as DE) and reduces the amount of diesel particulate emissions. To a diesel exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art With respect to gasoline engines, harmful components in exhaust gas have been steadily reduced due to strict regulations on exhaust gas and advances in technology capable of responding to the strict regulations. However, with regard to DE, due to the unique circumstances that harmful components are mainly emitted as particulates, regulations and development of technology are delayed compared to gasoline engines, and the development of an exhaust gas purification catalyst that can reliably purify harmful components is expected. It is rare.

[0003] As a DE exhaust gas purifying apparatus which has been developed to date, a method using a trap (without a catalyst and with a catalyst) and an open type SOF decomposition catalyst are known. Of these, the method using a trap is
It captures diesel particulates and regulates their emissions, and is especially effective for exhaust gas with a high dry suit ratio. However, the method using a trap requires a reprocessing device to incinerate the captured diesel particulates, which causes many practical problems such as cracking of the catalyst structure during regeneration, blockage by ash, or complicated systems. Is leaving.

On the other hand, as an open type SOF decomposition catalyst, a catalyst in which a catalytic metal such as a platinum group metal is supported on a supporting layer of activated alumina or the like as in a gasoline engine is used, as shown in, for example, JP-A-1-171626. And CO
SOF is oxidized and decomposed together with HC and purified. This open-type SOF cracking catalyst has the drawback of low removal rate of dry suits, but the amount of dry suits can be reduced by improving the DE and the fuel itself, and has the great advantage of not requiring a regeneration unit. Therefore, further improvement of technology is expected in the future.

[0005] However, the open type SOF decomposition catalyst can efficiently decompose SOF at a high temperature, but has a drawback that at low temperature conditions, the catalytic action of the catalyst metal is low and the purification performance of the SOF is reduced. Further, in the open-type SOF decomposition catalyst, there is a problem that SO ₂ in the exhaust gas is also oxidized in a high temperature region to generate SO ₃ or SO ₄ , which becomes sulfate and conversely increases the amount of particulates. This is because SO ₂ is not measured as particulate,
This is because sulfate is measured as particulates. In particular, in DE, a large amount of oxygen gas is present in the exhaust gas, and the oxidation reaction of SO ₂ is likely to occur.

On the other hand, in the field of exhaust gas treatment such as boilers, titania (TiO ₂ ) excellent in sulfur poisoning resistance is used for a catalyst support layer, and a catalyst in which a catalyst metal such as Pt and V is supported has been developed. Has been provided. However, this type of catalyst has no SOF adsorption property, and HC and S
OF is directly discharged. In view of this, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 4-267282 that a catalyst having a highly adsorptive coat layer such as activated alumina or zeolite and having no catalyst metal is arranged on the upstream side of the exhaust gas flow, and titania, silica, etc. A catalyst device has been proposed in which an exhaust gas purifying catalyst in which a catalyst metal is supported on a carrier having a coating layer with low adsorption property is disposed downstream.

[0007] According to this catalyst device, the upstream side catalyst is H
C and SOF are adsorbed at a low temperature and SO ₂ are adsorbed. However, since the upstream side catalyst has no catalytic metal,
The oxidation of ₂ is prevented. In the downstream catalyst, HC and SOF released from the upstream catalyst at a high temperature are oxidized and purified by the catalyst metal. On the other hand, S
O _{2 is} also released, but the downstream catalyst has low adsorptivity,
Oxidation by adsorption of O ₂ is suppressed, and formation of sulfate is prevented.

[0008] The catalyst device disclosed in the above publication is certainly effective under steady-state conditions. However, when a large amount of SO ₂ adsorbed and accumulated in the upstream catalyst is released at a high temperature and flows into the downstream catalyst at a low temperature, not a small amount of SO ₂ which comes into contact with the catalyst metal of the downstream catalyst is present, and the sulfate is present. There was a problem that was discharged as.

Japanese Patent Application No. 7-320313 (not disclosed at the time of filing of the present application) discloses a catalyst for purifying diesel exhaust gas in which the carrier is divided into two layers and the upper layer does not carry the catalytic metal but only the lower layer carries the catalytic metal. Is disclosed. With such a configuration, HC, SOF and S
O ₂ is adsorbed and accumulated. Since the upper layer has no catalytic metal, HC, SOF and SO ₂ accumulate without being oxidized. HC and SOF become liquid phases, penetrate by capillary action, are adsorbed to the lower layer, and are oxidized and purified. However, SO ₂ is in a gaseous phase even at a low temperature, and is hardly adsorbed compared to HC and SOF, and is difficult to move to the lower layer. Therefore, emission of particulates in a low temperature range is suppressed.

When the temperature of the exhaust gas becomes high, the flow rate of the high-temperature exhaust gas is large, so that HC and SOF adsorbed in the upper layer
And SO ₂ is insufficient time to diffuse to the oxide point of the lower layer is present catalyst metal, HC, SOF and SO ₂ is directly discharged without being excessively oxidized. Therefore, since almost no sulfate is generated, the amount of particulates emitted from the high-temperature exhaust gas itself is small.

[0011]

However, even in a catalyst in which a catalytic metal is supported only in the lower layer as described above, SO ₂
Is inevitable to penetrate to some extent from the upper layer to the lower layer, and the problem that sulfate is generated in the lower layer is inevitable. In addition, since no catalytic metal was exposed, there was a problem that the oxidizing ability of HC and SOF was low.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to efficiently adsorb HC and SOF in a low temperature range to prevent the emission of HC and SOF and to further suppress the production of sulfate. Aim.

[0013]

According to the first aspect of the present invention, there is provided a diesel exhaust gas purifying catalyst comprising: an acidic carrier powder having a catalytic metal supported on at least a part thereof; And a basic carrier powder. The feature of the catalyst for purifying diesel exhaust gas according to claim 2 is that, in the catalyst for purifying diesel exhaust gas according to claim 1, the acidic carrier powder is TiO ₂ —S
iO ₂ , at least one selected from ZrO ₂ —SiO ₂ and SiO ₂ , wherein the basic carrier powder is Al ₂ O ₃ ,
It is at least one selected from ZrO ₂ and TiO ₂ .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
The catalytic metal is supported only on the acidic carrier powder. In other words, even when the amount of the catalyst metal carried by the exhaust gas purifying catalyst as a whole is the same as that of the conventional catalyst, the catalyst metal is supported on the acidic carrier powder at a higher density than before. Thereby, the oxidation start temperature of the SOF decreases, and the purification activity in a low temperature range improves. In the low temperature region of the exhaust gas, SOF and SO ₂ are adsorbed on the carrier, but since SO ₂ is an acidic substance,
It is hardly adsorbed on the acidic carrier powder and preferentially adsorbed on the basic carrier powder. Therefore, SO ₂ is less likely to be adsorbed in the vicinity of the catalytic metal, so that the oxidation of SO ₂ in a high temperature range is suppressed and the production of sulfate is suppressed. Also SO
F tends to be adsorbed on the basic carrier in a low temperature range. In a high temperature range, the adsorbed SOF is in a gaseous state and easily moves, and the probability of contact with the catalyst metal supported at high density on the acidic carrier powder adjacent to the basic carrier powder is increased. It is oxidized and purified by metal. Therefore, the purification rate of SOF is improved in all temperature ranges.

The exhaust gas purifying catalyst of the present invention is obtained by coating a mixed powder obtained by mixing an acidic carrier powder carrying a catalytic metal and a basic carrier powder onto a honeycomb-type or pellet-type carrier substrate. Can be used. As such a carrier substrate, a monolith carrier substrate made of a heat-resistant inorganic substance such as cordierite or a metal carrier substrate made of metal is used. In some cases, it may be used after being formed into a carrier substrate shape from the mixed powder.

The difference between the acidity and the basicity of the acidic carrier and the basic carrier is relative. If the acid carrier is slightly more basic than the acidic carrier, it can be used as a basic carrier. If it is slightly acidic, it can be used as an acidic carrier. The degree of acidity / basicity is
It can be classified based on the acidity measurement using a Hammett indicator or the like and the electronegativity value of the carrier.

However, as an acidic carrier, SO in the exhaust gas is used.
₂ having a low adsorptivity is preferable, and SiO ₂ —Ti
It is desirable to use at least one selected from O ₂ , ZrO ₂ —SiO ₂ , and SiO ₂ . One of these may be used alone, or a plurality of them may be used in combination. The basic carrier, may be used if even slightly basic than the acidic carrier, SOF and SO ₂
It is desirable that the material has a high adsorptivity of Al ₂ O ₃ , ZrO ₂
It is desirable to use at least one selected from TiO ₂ and TiO ₂ . One of these may be used alone, or a plurality of them may be used in combination.

The catalytic metals supported on the acidic carrier powder include platinum (Pt), palladium (Pd), rhodium (R
h), noble metals such as silver (Ag), and base metals such as iron (Fe), nickel (Ni), chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), and cerium (Ce) Is also used, and is selected according to the intended oxidizing power. The supported amount of the catalytic metal is set to 0.1 for the noble metal per 1 liter of the catalyst volume as a whole of the exhaust gas purifying catalyst.
About 1 to 1.5 g / L, 0.05 to 0.5 g for base metal
About mol / L is appropriate. If only the acidic carrier powder is used, it is appropriate that the noble metal is about 2 to 30 g / L and the base metal is about 1 to 10 mol / L. If the supported amount is smaller than this range, the oxidizing power of HC and SOF becomes insufficient, and if the supported amount is larger than this range, the effect is saturated and a problem in terms of cost may occur.

The mixing ratio between the acidic carrier powder and the basic carrier powder is preferably such that the basic carrier powder is in the range of 1 to 30% by weight of the whole. 1 basic carrier powder
If it is less than 10% by weight, it becomes difficult to adsorb SOF.
The purification rate of F decreases. Further, when the basic support powder is more than 30 wt%, the amount of adsorption of SO ₂ increases the production of sulfates in the high temperature region becomes excessive. A particularly desirable range is a range of 5 to 20% by weight of the basic carrier powder, and it is recommended to be around 10% by weight.

In some cases, a sol-like binder is used to fix the acidic carrier powder and the basic carrier powder to the carrier substrate, and this binder becomes a powder having the same components as the acidic or basic carrier powder after firing. . Therefore, the mixing ratio between the acidic carrier powder and the basic carrier powder is calculated by including either one according to the binder component and the degree of acidity / basicity.

When the binder powder is an acidic powder, the catalyst metal is originally supported on the acidic powder for the purpose of supporting the catalyst metal, and is not supported on the binder powder. This is no problem in use. That is, it is sufficient if at least it is not supported on the basic carrier powder. When the binder powder is an acidic powder, a part of the acidic carrier powder (binder powder) in which the catalytic metal is not supported is generated.
Therefore, in claim 1, the expression "at least a part of the catalyst metal is supported" is used.

[0022]

The present invention will be specifically described below with reference to examples and comparative examples. (Embodiment 1) FIG. 1 is an enlarged sectional view of a main part of an exhaust gas purifying catalyst according to an embodiment of the present invention. This exhaust gas purifying catalyst is
It comprises a honeycomb-shaped carrier substrate (1) made of cordierite and a coating layer (2) formed on the surface of the carrier substrate (1). The carrier substrate (1) is a honeycomb carrier having a diameter of 147 × 95 mm, a length of 150 mm, a cell number of 400 cells / in2, a cell wall thickness of 0.15 mm, and a capacity of 1.7 liter.

The coating layer (2) is formed as an acidic carrier powder.
TiO_Two-SiO_TwoPowder (20) and a basic carrier powder
Al_TwoO_ThreePowder (21);
_Two-SiO_TwoPt (22) supported on powder (20)
I have. Hereinafter, a method for producing the exhaust gas purifying catalyst will be described.
Then, the detailed description of the configuration will be replaced. First, titanium isop
Loxide and tetraethyl orthosilicate are mixed at a molar ratio of T
i: Si = 1: 9 mixed and alkoxide method
TiO_Two-SiO _TwoA powder was prepared.

Next, tet containing 0.7 g as Pt
Laminine platinum hydroxide solution with TiO _Two-SiO_TwoPowder 1
24 g, impregnated for 1 hour, filtered after
After drying for 1 hour, heat treatment at 500 ° C for 1 hour_Two−
SiO_TwoPt was supported on the powder. And carried Pt
TiO_Two-SiO_TwoTotal amount of powder and Al_TwoO_Three12g powder
And SiO_Two85 g of silica sol containing 40% by weight of
The slurry was prepared by mixing and stirring with 230 g.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. (Example 2) A tetraammine platinum hydroxide solution containing 0.78 g of Pt was prepared in the same manner as in Example 1 by using T
111 g of iO ₂ —SiO ₂ powder was impregnated, filtered after stirring for 1 hour, dried at 120 ° C. for 1 hour, and then heat-treated at 500 ° C. for 1 hour to support Pt on the TiO ₂ —SiO ₂ powder.

Next, TiO ₂ —SiO ₂ carrying Pt
A slurry was prepared by mixing and stirring the total amount of powder, 25 g of ZrO ₂ powder, 85 g of silica sol containing 40% by weight of SiO ₂ , and 230 g of water. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry, and then pulled up to blow off excess slurry.
After drying at 200C for 2 hours, baking was performed at 500C for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier.

Example 3 232 g of a TiO ₂ —SiO ₂ powder prepared in the same manner as in Example 1 was impregnated with a tetraammine platinum hydroxide solution containing 1.5 g of Pt, stirred for 1 hour, and filtered. 5 hours after drying at 120 ° C for 1 hour
Heat treatment was performed at 00 ° C. for 1 hour to carry Pt on the TiO ₂ —SiO ₂ powder.

Next, TiO ₂ —SiO ₂ carrying Pt
The total amount of powder, 46 g of TiO ₂ powder, 155 g of silica sol containing 40% by weight of SiO ₂ , and 460 g of water were mixed.
The slurry was prepared by stirring. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry and then pulled up to blow off excess slurry.
After drying at 0 ° C. for 2 hours, baking was performed at 500 ° C. for 1 hour. This operation was repeated to form a coat layer of 340 g ± 5 g on the surface of the honeycomb carrier.

Example 4 90 g of SiO ₂ powder and 1 g of water
Alumina sol 5 containing 50 g and 20% by weight of Al ₂ O ₃
After stirring and evaporating to dryness, 2 g at 500 ° C.
After sintering for an hour, a SiO ₂ —Al ₂ O ₃ powder was prepared. Next, TiO ₂ carrying Pt prepared in the same manner as in Example 1
And -SiO ₂ powder 54 g, and the SiO ₂ -Al ₂ O ₃ powder 11g, silica sol 5 comprising SiO ₂ 40 wt%
2.5 g and 110 g of water were mixed and stirred to prepare a slurry.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a coat layer of 85 g ± 5 g on the surface of the honeycomb carrier. (Example 5) 20 g of TiO ₂ powder and 5 of Al ₂ O ₃ powder
0 g, 150 g of water, and 200 g of a titania sol containing 15% by weight of TiO ₂ were mixed, stirred, evaporated and dried, and then calcined at 500 ° C. for 2 hours to prepare a TiO ₂ —Al ₂ O ₃ powder.

On the other hand, a tetraammine platinum hydroxide solution containing 1.5 g as Pt was impregnated into 58 g of TiO ₂ —SiO ₂ powder prepared in the same manner as in Example 1, filtered for 1 hour, stirred at 120 ° C. 1 hour at 500 ℃
After heat treatment for a period of time, Pt was supported on the TiO ₂ —SiO ₂ powder. Next, the total amount of the TiO ₂ —SiO ₂ powder supporting Pt, 6 g of the TiO ₂ —Al ₂ O ₃ powder,
55 g of silica sol containing 40% by weight of O ₂ and 110 g of water
Was mixed and stirred to prepare a slurry.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a coating layer of 86 g ± 5 g on the surface of the honeycomb carrier. Example 6 Zirconium butoxide and tetraethyl orthosilicate were mixed at a molar ratio of Zr: Si = 1: 9, and a ZrO ₂ —SiO ₂ powder was prepared by an alkoxide method.

Next, tet containing 0.7 g as Pt
Laammine platinum hydroxide solution with ZrO _Two-SiO_TwoPowder 1
32 g, impregnated for 1 hour, filtered after stirring at 120 ° C.
After drying for 1 hour, heat-treating at 500 ° C for 1 hour, ZrO_Two−
SiO_TwoPt was supported on the powder. And carried Pt
ZrO_Two-SiO_TwoTotal amount of powder and Al_TwoO_Three13g powder
And SiO_Two62.5 g of silica sol containing 40% by weight of
And 230 g of water are mixed and stirred to prepare a slurry.
Was.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. (Example 7) A tetraammine platinum hydroxide solution containing 2.4 g as Pt was prepared in the same manner as in Example 6.
116 g of rO ₂ —SiO ₂ powder was impregnated, filtered after stirring for 1 hour, dried at 120 ° C. for 1 hour, and heat-treated at 500 ° C. for 1 hour to carry Pt on the ZrO ₂ —SiO ₂ powder.

Next, ZrO ₂ —SiO ₂ carrying Pt
A slurry was prepared by mixing and stirring the total amount of powder, 23 g of ZrO ₂ powder, 77.5 g of silica sol containing 40% by weight of SiO ₂ , and 230 g of water. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry and then pulled up to blow off excess slurry.
After drying at 20 ° C. for 2 hours, baking was performed at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier.

Example 8 275 g of a ZrO ₂ —SiO ₂ powder prepared in the same manner as in Example 6 was impregnated with a tetraammine platinum hydroxide solution containing 0.7 g of Pt, stirred for 1 hour, and filtered. 5 hours after drying at 120 ° C for 1 hour
Heat treatment was performed at 00 ° C. for 1 hour to carry Pt on the ZrO ₂ —SiO ₂ powder.

Next, ZrO ₂ —SiO ₂ carrying Pt
Total amount of powder and SiO ₂ -A prepared as in Example 4
14 g of l ₂ O ₃ powder, 128 g of silica sol containing 40% by weight of SiO ₂ , and 215 g of water were mixed and stirred to prepare a slurry. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a coat layer of 340 g ± 5 g on the surface of the honeycomb carrier.

Example 9 117 g of ZrO ₂ —SiO ₂ powder prepared in the same manner as in Example 6 was impregnated with a tetraammine platinum hydroxide solution containing 0.23 g as Pt, and the mixture was stirred for 1 hour and filtered. 5 hours after drying at 120 ° C for 1 hour
Heat treatment was performed at 00 ° C. for 1 hour to carry Pt on the ZrO ₂ —SiO ₂ powder.

Next, ZrO ₂ —SiO ₂ carrying Pt
The total amount of powder and TiO ₂ -A prepared as in Example 5
12 g of l ₂ O ₃ powder, 108 g of silica sol containing 40% by weight of SiO ₂ , and 215 g of water were mixed and stirred to prepare a slurry. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a coat layer of 172 g ± 5 g on the surface of the honeycomb carrier.

(Example 10) 0.7 g as Pt was contained.
The tetraammine platinum hydroxide solution_TwoPowder 12
4 g, impregnated for 1 hour and filtered at 120 ° C.
After drying for an hour, heat-treat at 500 ° C for 1 hour to obtain SiO 2_TwoPowder
Supported Pt. Next, Pt-supported SiO_TwoPowder
Total amount and Al_TwoO_Three12 g of powder and SiO _TwoIs 40 weight
% 85% silica sol and 230g water
Thus, a slurry was prepared.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. (Example 11) Pt tetraammine platinum water salt solution containing 0.78g impregnated with SiO ₂ powder 116g as, filtered after stirring for 1 hour, then heat-treated for 1 hour at 500 ° C. After 1 hour drying at 120 ° C. Pt was supported on SiO ₂ powder.

Next, a total amount of Pt-supported SiO ₂ powder, 23 g of ZrO ₂ powder, 100 g of silica sol containing 40% by weight of SiO ₂ , and 230 g of water were mixed and stirred to prepare a slurry. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the slurry, pulled up, and blown off excess slurry.
After drying for one hour, it was baked at 500 ° C. for one hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier.

(Example 12) The total amount of Pt-supported SiO ₂ powder prepared in the same manner as in Example 11, 60 g of TiO ₂ powder, and silica sol containing 40% by weight of SiO ₂ 77.
5 g and 230 g of water were mixed and stirred to prepare a slurry. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and dried at 50 ° C.
It was baked at 0 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier.

Example 13 The total amount of Pt-supported SiO ₂ powder prepared in the same manner as in Example 11, 12 g of the SiO ₂ —Al ₂ O ₃ powder prepared in the same manner as in Example 4,
108 g of silica sol containing 40% by weight of iO ₂ and 21 parts of water
5 g was mixed and stirred to prepare a slurry.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. (Example 14) The total amount of Pt-supported SiO ₂ powder prepared as in Example 11, 12 g of TiO ₂ —Al ₂ O ₃ powder prepared as in Example 5, and 40% of SiO ₂
A slurry was prepared by mixing and stirring 108 g of silica sol containing weight% and 215 g of water.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. Comparative Example 1 60 g of Al ₂ O ₃ powder and ₂ g of Al ₂ O ₃
120 g of alumina sol containing 0% by weight and 130 g of water were mixed and stirred to prepare a slurry.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours and fired at 500 ° C. for 1 hour. This operation was repeated to form a 75 g ± 5 g first coat layer on the surface of the honeycomb carrier. Next, 60 g of TiO2 powder is impregnated with a tetraammine platinum hydroxide solution containing 0.5 g of Pt,
After stirring for 1 hour, filter and dry at 120 ° C for 1 hour.
For 1 hour to carry Pt on the TiO ₂ powder.

Next, the total amount of the TiO ₂ powder carrying Pt and 160 g of a titania sol containing 15% by weight of TiO ₂ were prepared.
And 130 g of water were mixed and stirred to prepare a slurry. Then, the honeycomb carrier on which the first coat layer was formed was immersed in the slurry, pulled up, blown off excess slurry, dried at 120 ° C. for 2 hours, and baked at 500 ° C. for 1 hour. This operation was repeated, and 84 g ±
2.5 g of the second coat layer was formed.

(Comparative Example 2) 0.7 g as Pt is contained
A tetraammine platinum hydroxide solution was prepared in the same manner as in Example 1.
TiO made_Two-SiO_Two127 g of powder is impregnated,
After stirring for 1 hour, filter and dry at 120 ° C. for 1 hour.
Heat treated at ℃ for 1 hour_Two-SiO _TwoPt on powder
Was carried.

TiO ₂ —SiO ₂ supporting Pt
Silica sol 10 containing the total amount of powder and 40% by weight of SiO ₂
8 g and 215 g of water were mixed and stirred to prepare a slurry. A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and dried at 50 ° C.
It was baked at 0 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier.

(Comparative Example 3) 0.7 g as Pt
Dinitrodiammine platinum nitrate solution_TwoO _ThreePowder
After stirring for 1 hour, the mixture was filtered at 120 ° C.
And heat-treated at 500 ° C for 1 hour,_TwoO
_ThreePt was supported on the powder. Next, Pt-loaded Al_Two
O_ThreeTotal amount of powder and Al_TwoO_ThreeContaining 20% by weight of
Mix and stir 215 g of sol and 130 g of water to make a slurry.
Was prepared.

A cordierite honeycomb carrier having a capacity of 1.7 liters was prepared, immersed in the above slurry, pulled up and blow off excess slurry, dried at 120 ° C. for 2 hours, and fired at 500 ° C. for 1 hour. This operation was repeated to form a 170 g ± 5 g coat layer on the surface of the honeycomb carrier. (Evaluation test) Each of the above exhaust gas purifying catalysts was
Attached to the exhaust system of a 4.2-liter direct-injection turbocharged diesel engine.
Under a constant condition of ° C., fine particle components were collected from a part of the incoming gas and the outgoing gas using a dilution tunnel. Then, SOF in the incoming gas and SOF in the outgoing gas were extracted and quantified with dichloromethane, and the SOF purification rate was calculated from the difference between the values and shown in Table 1.

At a rotation speed of 2160 rpm and a steady condition of 400 ° C., a fine particle component was collected from a part of the incoming gas and the outgoing gas using a dilution tunnel. Then, the sulfate in the incoming gas and the sulfate in the outgoing gas were extracted and quantified by ion chromatography, and the amount of sulfate produced was calculated from the difference between the values.

[0054]

[Table 1]

Comparative Example 2 was an acid carrier powder carrying Pt
It is composed of Therefore SO _TwoNo adsorption
Therefore, sulfate production is extremely suppressed.
However, since the SOF adsorption is also inhibited, the SOF purification rate is high.
It's getting lower. Comparative Example 3 carried Pt.
It is composed of a basic carrier powder. So SO_Twoof
So much adsorption occurs and adsorbed SO_TwoIs acid by nearby Pt
The production of sulfate has increased due to the conversion.

In Comparative Example 1, the lower layer was coated with a basic carrier powder not carrying Pt, and the upper layer was coated with an acidic carrier powder carrying Pt. Therefore, although the adsorption of SO ₂ to the upper layer is suppressed, the probability of contact with Pt is increased, and the amount of sulfate generated is increased. Further, since the adsorption of SOF hardly occurs, the SOF purification rate is low.

However, in the exhaust gas purifying catalyst of each embodiment,
Since it is composed of an acidic carrier powder carrying Pt and a basic carrier powder not carrying Pt, the adsorption of SOF is promoted while suppressing the adsorption of SO ₂ , thereby preventing the formation of sulfate. SOF is efficiently purified.

[0058]

In other words, according to the catalyst for purifying diesel exhaust gas of the present invention, SO ₂ adsorbed and accumulated at a low temperature does not easily become sulfate at a high temperature. In addition, SOF is easily adsorbed on the basic carrier powder, and the adsorbed SOF is smoothly oxidized by Pt carried on the adjacent acidic carrier powder at high density. Therefore, the amount of discharged particulate can be reduced from a low temperature to a high temperature.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a main part of an exhaust gas purifying catalyst according to one embodiment of the present invention.

[Explanation of symbols]

1: carrier substrate 2: coat layer
22: Pt 20: TiO ₂ —SiO ₂ powder (acidic carrier powder) 21: Al ₂ O ₃ powder (basic carrier powder)

Claims (2)

[Claims] 1. A diesel exhaust gas purifying catalyst comprising a mixture of an acidic carrier powder having at least a part of a catalytic metal supported thereon and a basic carrier powder more basic than the acidic carrier powder. 2. The method according to claim 1, wherein the acidic carrier powder is TiO._Two-Si
O_Two, ZrO_Two-SiO _TwoAnd SiO_TwoSmall
At least one kind, wherein the basic carrier powder is Al
_TwoO_Three, ZrO_TwoAnd TiO_TwoAt least selected from
The diesel according to claim 1, wherein the diesel is a kind.
Exhaust gas purification catalyst.