JPH05138026A - Catalyst for purifying exhaust gas of diesel engine - Google Patents

Abstract

PURPOSE:To purify HC, CO and SOF and to reduce the discharge amount of a diesel particulate and that of sulfate. CONSTITUTION:A catalyst for purifying the exhaust gas of a diesel engine consists of a carrier base material 1, the metal oxide layer 2 formed to the surface of the carrier base material and composed of oxide 20 of at least one kind of a metal selected from Cu, Mn, Ni, Fe and Co and the catalyst metal 21 supported on the metal oxide layer 2.

Description

Detailed Description of the Invention

[0001]

The present invention relates to H contained in exhaust gas from a diesel engine (hereinafter referred to as DE).
The present invention relates to a catalyst that can purify C, CO and SOF (Soluble Organic Fraction), reduce the emission amount of diesel particulates, and reduce the emission amount of sulfate.

[0002]

2. Description of the Related Art With respect to gasoline engines, toxic substances in exhaust gas have been steadily reduced due to strict regulations on exhaust gas and advances in technology capable of coping with the regulations. But DE
With regard to the above, due to the peculiar circumstances in which harmful components are mainly discharged as particulates, the regulations and the development of technology are behind that of the gasoline engine, and the development of an exhaust gas purification device that can surely purify is desired.

As a DE exhaust gas purifying apparatus that has been developed so far, there are roughly known methods using a trap (without a catalyst and with a catalyst) and an open type SOF decomposition catalyst. Of these, the method that uses a trap is
Diesel particulates are trapped to control emissions, which is especially effective for exhaust gas with a high proportion of dry suits. However, a regeneration treatment device is required, and many problems remain for practical use, such as cracking of the catalyst carrier during regeneration, blockage due to ash, or complicated system.

On the other hand, as the open type SOF decomposition catalyst, as disclosed in, for example, Japanese Patent Application Laid-Open No. 1-171626, a catalyst carrying an oxidation catalyst such as a platinum group metal is used as in a gasoline engine, and it is used together with CO and HC in diesel. SOF in particulates is oxidatively decomposed and purified. This open type SOF decomposition catalyst has the drawback that the removal rate of dry suit is low, but the amount of dry suit can be reduced by improving the DE and the fuel itself, and there is a great merit that a regeneration treatment device is not required. Therefore, further improvement in technology is expected in the future.

[0005]

Open type S
Emission of diesel particulates in OF decomposition catalyst
It was difficult to reduce the amount. Ie open
The activated alumina layer formed on the type SOF decomposition catalyst is
SO₂Has the property of adsorbing. Therefore, the elimination of DE
SO contained in gas₂Is adsorbed on the activated alumina layer
When the temperature of the catalyst rises, the SO₂
Are oxidized by the catalytic action of the catalytic metal. Or exhaust
SO in gas₂Are directly oxidized. Therefore SO₂Is
SO₃The amount of particulates increases because it is discharged as
There is a problem of doing. This is SO ₂Is a particulate
SO is not measured as₃Is particulate
This is because it is measured as. Exhaust especially in DE
Sufficient oxygen gas in the gas, SO₂The oxidation reaction of
It is easy to get rid of. And SO₃Exists in exhaust gas in large quantities
Reacts readily with water vapor to form sulfate.

Therefore, Japanese Patent Publication No. 32-32934 discloses a method of adding a third component such as vanadium as an SO ₃ suppressing component. However, vanadium and the like have the drawback of reducing the activity of the catalytic metal to HC, CO and SOF. In addition, JP-A-1-17162
No. 6 discloses a method using a coating material other than alumina, such as titania and zirconia. However, with these coating materials, the oxidation activity is likely to decrease due to the sintering of the catalyst metal at high temperature. Enough SO ₃
Is difficult to control.

Furthermore, the higher the oxidation activity of the catalytic metal, the more S
Since the emission amount of O ₃ is also increased, the oxidation activity of the catalyst metal is also reduced, but in this case, the purification performance of HC, CO and SOF is also reduced. That is, HC, C
It has heretofore been difficult to achieve both purification of O and SOF and reduction of SO ₃ emission. The present invention has been made in view of the above circumstances, and an object thereof is to purify HC, CO, and SOF, and to reduce the emission amount of diesel particulates and also the emission amount of sulfates.

[0008]

The catalyst for purifying exhaust gas of DE of the present invention which solves the above-mentioned problems is formed from a carrier base material and Cu, Mn, Ni, Fe and Co formed on the surface of the carrier base material. It is characterized by comprising a metal oxide layer composed of an oxide of at least one selected metal, and a catalyst metal supported on the metal oxide layer. In addition, a carrier substrate, a coat layer formed on the surface of the carrier substrate from at least one material selected from alumina, titania and silica, and Cu, Mn, Ni, Fe and Co contained in the coat layer. A metal oxide powder composed of an oxide of at least one metal selected from the following, and a catalyst metal supported on the metal oxide powder,
It is also possible to have a configuration of.

The carrier base material is the same as the carrier base material of the exhaust gas purifying catalyst used in the conventional gasoline engine, and a monolith carrier base material, a foam filter, a honeycomb filter, a pellet or the like is used. The material is selected from ceramics such as cordierite, or metal. The most important feature of the present invention is that Cu, Mn, Ni, which has a catalytic metal supported on the surface of a carrier substrate or at least one coat layer selected from alumina, titania, and silica,
It has at least one metal oxide selected from Fe and Co.

The metal oxide contained in the metal oxide layer or the coating layer may be an oxide of one kind of metal selected from Cu, Mn, Ni, Fe and Co, or a plurality of metals selected from these. The oxide may be mixed. The catalyst metal supported on the metal oxide layer is SO
It contributes to the oxidation reaction of F, HC and CO, and P
One or more kinds of conventional materials such as t, Rh, and Pd can be used. The supported amount of the catalyst metal is preferably about 0.05 to 2 g per liter of the carrier substrate volume.

In the purifying catalyst of the present invention, SO ₂ is selectively chemisorbed by the metal oxide, so that the oxidizing action of SO ₂ by the catalytic metal is hard to work. Therefore, since the production of SO ₃ is suppressed, the emission amount of diesel particulates is reduced.

[0012]

In the exhaust purification catalyst of DE of the present invention, the metal oxide and the catalyst metal are present on the outermost surface.
SO ₂ in the exhaust gas is selectively adsorbed on the metal oxide before undergoing the oxidation reaction by the catalytic metal. Therefore SO
_The probability that ₂ is adsorbed by the catalyst metal is reduced, the oxidation reaction of SO ₂ is prevented, and the emission of SO ₃ is prevented. Further, even if the temperature of SO ₂ becomes high and the movement of SO ₂ is activated to generate SO ₂ which is not adsorbed on the metal oxide, all of the catalyst metal is supported on the metal oxide.
O ₂ is less likely to come into contact with the catalytic metal. Therefore, SO ₃ emission is prevented even at high temperatures.

On the other hand, the catalytic metal oxidizes and purifies HC, CO and SOF, regardless of the adsorption of SO ₂ . Therefore, unlike the conventional case, it is not necessary to reduce the oxidation activity of the catalyst metal in order to suppress the oxidation reaction of SO ₂ , and the catalyst metal can be configured to have high oxidation activity. The purification performance of SOF can be improved.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples. The manufacturing method will be described instead of the detailed description of the configuration. (Embodiment 1) FIG. 1 is a schematic view of a main portion of an exhaust gas purification catalyst of this embodiment. This catalyst comprises a cordierite honeycomb-shaped carrier substrate 1 and Pt21 coated on the surface of the carrier substrate 1.
And a metal oxide layer 2 made of CuO powder.

A commercially available CuO powder (average particle size: 10 μm) was impregnated with an aqueous solution of platinum dinitrodiammine, and after each step of evaporation, firing and pulverization, a CuO powder 20 carrying about 2.5% by weight of platinum 21 was prepared. did. Then this powder 100
By weight, 75 parts by weight of distilled water and 25 parts by weight of alumina sol were mixed and thoroughly milled to prepare a slurry. A commercially available cylindrical cordierite honeycomb carrier substrate 1 (volume: 1.7 liter) was immersed in this slurry, and the excess slurry was blown off and then dried, and dried at 120 ° C. for 2 hours and then at 600 ° C. for 2 hours. After firing for a period of time, a metal oxide layer 2 made of Pt-CuO powder was formed. About 75 g of the metal oxide layer 2 was formed per liter of the carrier substrate 1. (Example 2) Commercially available Mn ₂ O ₃ powder (average particle diameter 10 μm
m) was impregnated with an aqueous solution of platinum dinitrodiammine, and each step of evaporation, firing, and pulverization was performed to prepare Mn ₂ O ₃ powder carrying about 2.5% by weight of platinum. Then, a slurry is prepared in the same manner as in Example 1, and Pt is similarly formed on the same carrier substrate surface.
A metal oxide layer made of —Mn ₂ O ₃ powder was formed. The metal oxide layer is about 75 g per liter volume of the carrier substrate.
Been formed. (Example 3) Commercially available CoO powder (average particle diameter 10 μm) was impregnated with an aqueous palladium nitrate solution, and after each step of evaporation, firing, and pulverization, CoO carrying about 2.5% by weight of Pd was carried out.
A powder was prepared. Then, it was slurried in the same manner as in Example 1, and a metal oxide layer made of Pd—CoO powder was similarly formed on the same carrier substrate surface. About 75 g of metal oxide layer was formed per liter of the volume of the carrier substrate. (Example 4) An aqueous sodium carbonate solution adjusted to pH 8 to 10 was prepared, and a mixed aqueous solution of cobalt nitrate and palladium nitrate was gradually added dropwise from above while stirring. Thereafter, the precipitate was filtered off, dried and calcined at 400 ° C. to obtain a Co oxide having Pd supported by about 2.5%. This Co oxide was confirmed to be Co ₃ O ₄ by the X-ray diffraction method.
It was confirmed that the composition was This Co oxide was pulverized into powder. Then, it was slurried in the same manner as in Example 1, and a metal oxide layer made of Pd—Co ₃ O ₄ powder was similarly formed on the same carrier substrate surface. About 75 g of metal oxide layer was formed per liter of the volume of the carrier substrate. Example 5 A commercially available NiO powder (average particle size 10 μm) was impregnated with an aqueous solution of platinum dinitrodiammine, and each step of evaporation, firing, and pulverization was performed to prepare a NiO powder carrying Pt at about 2.5 wt%. did. Then, it was slurried in the same manner as in Example 1, and a metal oxide layer made of Pt—NiO powder was similarly formed on the same carrier substrate surface. About 75 g of metal oxide layer was formed per liter of the volume of the carrier substrate. Example 6 Commercially available Fe ₂ O ₃ powder (average particle size 10 μm
m) was impregnated with an aqueous solution of platinum dinitrodiammine, and Fe ₂ O ₃ powder carrying about 2.5% by weight of Pt was prepared through the steps of evaporation, firing and pulverization. Then, a slurry is prepared in the same manner as in Example 1, and Pt is similarly formed on the same carrier substrate surface.
A metal oxide layer made of —Fe ₂ O ₃ powder was formed. The metal oxide layer is about 75 g per liter volume of the carrier substrate.
Been formed. Example 7 A schematic diagram of the catalyst of this example is shown in FIG. This catalyst comprises a carrier substrate 1, a coat layer 3 formed on the surface of the carrier substrate 1 and mainly composed of activated alumina 30, and a Fe ₂ O ₃ powder 4 containing Pt 40 contained in the coat layer 3. It is configured.

Commercially available Fe ₂ O ₃ powder (average particle size 10 μm
m) was impregnated with an aqueous solution of platinum dinitrodiammine, and Fe ₂ O ₃ powder 4 carrying about 5.0% by weight of Pt was prepared through the steps of evaporation, firing, and pulverization. Then this powder 1
00 parts by weight and activated alumina powder 1 having an average particle size of 10 μm
A slurry was prepared by mixing 00 parts by weight, 50 parts by weight of alumina sol, and 150 parts by weight of distilled water. Then, a coat layer 3 made of Pt—Fe ₂ O ₃ / alumina powder was similarly formed on the surface of the carrier substrate 1 similar to that in Example 1. The coating layer 3 was formed in an amount of about 75 g per liter of the carrier substrate 1. (Comparative Example 1) A schematic view of the catalyst of this Comparative Example is shown in FIG. This catalyst comprises a carrier substrate 1, an activated alumina layer 5 formed on the surface of the substrate 1, and a P supported on the activated alumina layer 5.
t50 and Fe ₂ O ₃ 51.

Activated alumina powder 10 having an average particle size of 10 μm
0 parts by weight, alumina sol 25 parts by weight, distilled water 75 parts by weight
Were mixed to prepare a slurry, and the same carrier substrate as in Example 1 was prepared.
Approximately 75 g per liter of the volume of the carrier substrate on the surface of the material 1
The activated alumina layer 5 was formed. Next, water absorption treatment of this carrier
Then, soak in an aqueous solution of platinum dinitrodiammine for 1 hour, and
Approximately 1 liter of carrier volume after drying at 50 ° C for 2 hours
1.8 g of Pt50 was carried. Next, iron nitrate is added to this carrier.
(Fe (NO₃)₃) Absorb aqueous solution at 250 ° C for 2
After drying for 1 hour, calcination at 500 ℃ for 1 hour and Fe₂O₃51
It was supported. Fe ₂O₃The carrying amount of 51 is 1 liter of carrier
It is about 24 g. (Comparative Example 2) A schematic view of the catalyst of this Comparative Example is shown in FIG. This
The catalyst of 1 is formed on the surface of the carrier substrate 1 and activated.
Coat layer 6 mainly composed of crystalline alumina, and contained in coat layer 6
Fe₂O₃Powder 7 and P carried on coat layer 6
and t60.

Activated alumina powder 10 having an average particle size of 10 μm
0 parts by weight, commercially available Fe ₂ O ₃ powder 7 (average particle size 10 μ
m) 100 parts by weight, 50 parts by weight of alumina sol, 1 distilled water
A slurry was prepared by mixing 50 parts by weight, and a mixed coating layer 6 of about 75 g per liter of the volume of the carrier substrate was formed on the surface of the carrier substrate 1 as in Example 1. Next, this carrier was subjected to water absorption treatment, immersed in an aqueous solution of platinum dinitrodiammine for 1 hour, and dried at 250 ° C. for 2 hours to carry about 1.8 g of Pt60 per liter of carrier volume. Comparative Example 3 Activated alumina powder 10 having an average particle size of 10 μm
0 parts by weight, commercially available CoO powder (average particle size 10 μm) 10
A slurry was prepared by mixing 0 part by weight, 50 parts by weight of alumina sol, and 150 parts by weight of distilled water to form a mixed coating layer on the surface of the carrier substrate in the same manner as in Example 1 and having a weight of about 75 g per liter of the carrier substrate. did. Next, after water absorption treatment of this carrier,
Immerse in an aqueous solution of palladium nitrate for 1 hour and dry at 250 ° C. for 2 hours to obtain about 1.8 g of Pd per liter of carrier volume
Was carried. (Test Example) Each of the above catalysts was subjected to a displacement of 2400c.
Installed in the exhaust system of the swirl chamber type DE of c, the inlet gas temperature is 40
Sulfate production and HC at 0 ° C and 500 ° C
The purification rate was measured. The catalyst inlet gas temperature at this time was adjusted by adjusting the torque while keeping DE constant at 2400 rpm. The amount of sulfate produced was determined by collecting a certain amount of gas entering and leaving the catalyst, capturing particulates in the exhaust gas with a glass filter coated with Teflon, and analyzing by hot water extraction and ion chromatography. The results are shown in Table 1.

[0019]

[Table 1] (Evaluation) From Table 1, in the catalyst of the comparative example, the inlet gas temperature is 400
Although the amount of sulfate produced was small under the condition of ° C, the amount of sulfate produced was remarkably increased when the inlet gas temperature reached 500 ° C. On the other hand, in the catalyst of the example, 50
It can be seen that the formation of sulfate is considerably suppressed even at 0 ° C. Regarding the HC purification rate, the examples and the comparative examples show almost the same performance.

That is, in the catalyst of the comparative example, the catalyst metal is supported mainly on the activated alumina in a highly dispersed state, and other C
While the metal oxide such as uO exists independently of the catalyst metal, in the catalyst of the example, the catalyst metal is supported on the metal oxide such as CuO. Therefore, in the catalysts of Examples, the interaction between the metal oxide and the catalyst metal was enhanced, and the formation of sulfate was prevented even at high temperature.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a catalyst of Example 1 of the present invention.

FIG. 2 is a schematic sectional view of a catalyst of Example 7 of the present invention.

FIG. 3 is a schematic sectional view of a catalyst of Comparative Example 1.

FIG. 4 is a schematic sectional view of a catalyst of Comparative Example 2.

[Explanation of symbols]

1: Support substrate 2: Metal oxide layer
3: coat layer 4: Fe ₂ O ₃ powder

Claims (2)

[Claims] 1. A support base material, and a metal oxide layer formed on the surface of the support base material and comprising an oxide of at least one metal selected from Cu, Mn, Ni, Fe and Co. A catalyst for exhaust emission purification of a diesel engine, comprising a catalyst metal supported on a metal oxide layer. 2. A carrier substrate and at least one selected from alumina, titania, and silica.
Coating layer formed on the surface of the carrier substrate from various materials, and Cu, Mn, Ni, Fe and Co contained in the coating layer.
An exhaust gas purification catalyst for a diesel engine, comprising a metal oxide powder composed of an oxide of at least one metal selected from among the above, and a catalyst metal supported on the metal oxide powder.