JPH0557191A - Catalyst for purifying exhaust gas of diesel engine - Google Patents

Abstract

PURPOSE:To purify HC, CO and SOF, to reduce not only the discharge amount of a diesel particulate but also the discharge amount of sulfate and to prevent the poisoning of a catalytic metal. CONSTITUTION:A catalyst consists of a carrier base material 1, the activated alumina layer 2 formed to the surface of the carrier base material, the catalytic metal 3 supported on the activated alumina layer 2 and the coating layer 4 formed to the surface of the activated alumina layer 2 and composed of at least one component selected from alumina, titania and silica and oxide of at least one kind of a metal selected from Mn, Co, Sn, Fe, Ca, Ni, Ce, Zr, Mg and Cu is added to the coating layer 4.

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 progress in technology capable of coping with the regulations. But DE
With respect 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 a gasoline engine, and it is desired to develop an exhaust gas purification device that can surely purify.

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 in 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
With the OF decomposition catalyst, it was difficult to reduce the emission amount of diesel particulates. That is, the activated alumina layer formed on the open type SOF decomposition catalyst is
It has the property of adsorbing SO ₂ and SO ₃ . Therefore, SO ₂ contained in the exhaust gas of DE is adsorbed on the activated alumina layer, and when the temperature of the catalyst becomes higher, the adsorbed SO ₂ is oxidized by the catalytic action of the catalytic metal and is discharged as SO ₃ , or directly. Oxidizes SO _{2 in} exhaust gas,
There is a problem that the amount of particulates increases. This is because SO ₂ is not measured as particulates,
This is because SO ₃ is measured as particulates. Particularly in DE, oxygen gas is sufficiently present in the exhaust gas, and the SO ₂ oxidation reaction easily occurs. Also, the higher the catalytic activity of the catalytic metal, the greater the amount of SO ₃ emitted,
It has been difficult to satisfy both purification of C, CO and SOF and regulation of the emission amount of SO ₃ . SO ₃ easily reacts with water vapor present in a large amount in the exhaust gas to form sulfate.

Further, it is known that the catalytic metal is poisoned by a large amount of sulfur contained in DE exhaust gas and its catalytic activity is lowered. That is, S derived from sulfur in the fuel
O ₂ reacts with the activated alumina layer to react with aluminum sulfate (A
l ₂ (SO 4) ₃ ) is formed, which covers the catalytic metal and reduces the catalytic activity. Therefore, in the field of exhaust gas treatment such as boilers, titania (T
A catalyst supporting an oxidation catalyst such as Pt or V using iO ₂ ) as a catalyst supporting layer has been developed and put into practical use. However, in a catalyst using TiO ₂ , when exposed to a high temperature atmosphere, sintering of TiO ₂ particles occurs, and a phase change from anatase type to rutile type occurs. As a result, the surface area is reduced, and grain growth of the oxidation catalyst occurs, resulting in a decrease in oxidation performance. That is, the durability at the time of high temperature use was not sufficient. Also TiO ₂
In comparison with activated alumina, it is difficult to carry the catalyst metal in a highly dispersed state, and there is also a problem that the oxidation activity is inferior.

The present invention has been made in view of the above circumstances, and purifies HC, CO and SOF, and
It is an object to reduce the emission amount of diesel particulates, reduce the emission amount of sulfates, and prevent poisoning of catalytic metals.

[0008]

The exhaust gas purifying catalyst for DE according to the present invention, which solves the above problems, has a carrier base material, an activated alumina layer formed on the surface of the carrier base material, and an activated alumina layer. It comprises a catalyst metal and at least one coat layer selected from alumina, titania and silica formed on the surface of the activated alumina layer, and the coat layer contains Mn, Co and S.
It is characterized in that it contains an oxide of at least one metal selected from n, Fe, Ca, Ni, Ce, Zr, Mg and Cu.

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. An active alumina layer made of γ-alumina is formed on at least the surface of the carrier substrate that comes into contact with exhaust gas. The thickness of the activated alumina layer is not particularly limited, and 1
About 0 to 70 μm is sufficient.

The catalyst metal supported on the activated alumina layer contributes to the oxidation reaction of SOF, HC, and CO, and one or more kinds of conventional metals such as Pt, Rh, and Pd may be used. it can. The supported amount of the catalytic metal is 0.05 to 2 g per liter of the carrier substrate volume.
A degree is preferable. The greatest feature of the present invention is that Mn, Co, Sn, Fe, Ca, Ni, Ce,
It has at least one coat layer selected from alumina, titania, and silica containing an oxide of at least one metal selected from Zr, Mg, and Cu.

The thickness of this coat layer is preferably about 5 to 100 μm. If the thickness is less than 5 μm, SO ₂ is likely to come into contact with the activated alumina layer, and the effect of the present invention is difficult to obtain. Again 1
If it is thicker than 00 μm, the contact between the exhaust gas and the catalytic metal may be hindered, and the purification performance of HC, CO, etc. may deteriorate. The content of the metal oxide contained in this coat layer is appropriately in the range of 0.05 to 3 mol. If it is less than this, the adsorption performance of SO ₂ is lowered, and if it is more than this, the adsorption performance is increased, but conversely the oxidation activity is lowered, which is not preferable.

In the purification catalyst of the present invention, SO ₂ is selectively adsorbed on this coat layer. And the adsorbed SO ₂
Is prevented from coming into contact with the catalyst metal, so that SO ₂ is prevented from being oxidized. Therefore, since the production of SO ₃ is suppressed, the emission amount of diesel particulates is reduced. Furthermore, since SO ₂ is adsorbed on the coat layer and prevented from contacting with the activated alumina layer, poisoning of the catalyst metal by aluminum sulfate is prevented.

[0013]

The DE exhaust purification catalyst of the present invention has at least one coating layer selected from alumina, titania and silica on the surface of the activated alumina layer, and the coating layer contains Mn, Co and Sn. , Fe, Ca, Ni, C
It contains an oxide of at least one metal selected from e, Zr, Mg and Cu. SO ₂ in the exhaust gas is selectively adsorbed by the coating layer by this metal oxide, so that contact with the catalytic metal carried on the activated alumina layer is prevented. Therefore, the oxidation reaction of SO ₂ is prevented and the emission of SO ₃ is prevented.

Further, since the contact between SO ₂ and the activated alumina layer is prevented, poisoning of the metal catalyst due to the formation of aluminum sulfate can be prevented, and the oxidation catalytic action of the metal catalyst is not hindered. Therefore, the purification performance of HC, CO and SOF can be maintained high. Further, since the catalytic metal is supported on the activated alumina layer as in the conventional case, its high dispersion supporting property is not impaired.

[0015]

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 the main part of the catalyst of this embodiment. Commercially available cylindrical cordierite honeycomb carrier substrate 1
(Diameter 30 mm, length 50 mm) was prepared, dipped in a slurry consisting of γ-alumina powder, aluminum nitrate, alumina sol and distilled water, pulled up to blow off excess slurry, and dried at 120 ° C. for 2 hours to 700 The activated alumina layer 2 was formed by firing at 2 ° C. for 2 hours. The activated alumina layer 2 is formed in an amount of about 120 g per liter of the carrier substrate 1.

After the water absorption treatment, the activated alumina layer 2 was loaded with platinum 3 by immersing it in an aqueous solution of platinum dinitrodiammine for 60 minutes and drying it at 250 ° C. for 2 hours. At this time, the amount of platinum 3 supported is 1 g per 1 liter of the carrier volume. Then, using a slurry prepared by adding manganese nitrate powder to the above slurry, the coating layer 4 was formed on the surface of the activated alumina layer 2 by dipping, drying and firing in the same manner as above. The coat layer 4 contains 0.1 mol / 100 of manganese oxide.
It is composed of alumina contained at a concentration of g and its thickness is 20
μm. (Example 2) As in Example 1, a carrier substrate 1 having an activated alumina layer 2 supporting platinum was used, and SiO ₂ powder and Si were used.
A coating layer 4 was similarly formed from a slurry composed of O ₂ sol, manganese nitrate powder and distilled water. This coat layer 4
Is made of SiO ₂ containing manganese oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Example 3) As in Example 1, a carrier substrate 1 having an active alumina layer 2 supporting platinum was used, and TiO ₂ powder and Ti were used.
A coating layer 4 was similarly formed from a slurry composed of O ₂ sol, manganese nitrate powder and distilled water. This coat layer 4
Is made of TiO ₂ containing manganese oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Example 4) The same as Example 1 except that the same amount of cobalt nitrate was used instead of manganese nitrate. Coat layer 4
Is made of alumina containing cobalt oxide at a concentration of 0.1 mol / 100 g, and its thickness is 20 μm. (Example 5) The same as Example 1 except that the same amount of tin chloride was used instead of manganese nitrate. The coat layer 4 is made of alumina containing tin oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Example 6) The same as Example 1 except that the same amount of iron nitrate was used instead of manganese nitrate. The coat layer 4 is made of alumina containing iron oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Example 7) The same as Example 1 except that the same amount of calcium nitrate was used instead of manganese nitrate. The coat layer 4 is made of alumina containing calcium oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Example 8) The same as Example 1 except that the same amount of nickel nitrate was used instead of manganese nitrate. Coat layer 4
Is made of alumina containing nickel oxide at a concentration of 0.1 mol / 100 g, and its thickness is 20 μm. (Example 9) The same as Example 1 except that the same amount of cerium nitrate was used instead of manganese nitrate. Coat layer 4
Is made of alumina containing cerium oxide at a concentration of 0.1 mol / 100 g, and its thickness is 20 μm. (Example 10) The same as Example 1 except that the same amount of zirconium nitrate was used instead of manganese nitrate. The coat layer 4 contains zirconium oxide in an amount of 0.1 mol / 100 g.
Made of alumina contained at a concentration of 20 μm and its thickness is 20 μm
m. (Example 11) The same as Example 1 except that the same amount of magnesium nitrate was used instead of manganese nitrate. The coating layer 4 contains 0.1 mol / 100 g of magnesium oxide.
Made of alumina contained at a concentration of 20 μm and its thickness is 20 μm
m. (Example 12) The amount of magnesium nitrate was set to 1 of Example 11.
Example 11 is the same as that of Example 11 except having set it as / 10. The coating layer 4 has 0.01 mol / 100 of magnesium oxide.
It is composed of alumina contained at a concentration of g and its thickness is 20
μm. (Example 13) The amount of magnesium nitrate was changed to 5 of Example 11.
Example 11 is the same as Example 11 except that it was used twice. The coat layer 4 is made of alumina containing magnesium oxide at a concentration of 0.5 mol / 100 g and has a thickness of 20 μm. (Example 14) The same as Example 1 except that the same amount of copper nitrate was used instead of manganese nitrate. This coat layer 4
Is composed of alumina containing copper oxide at a concentration of 0.1 mol / 100 g and has a thickness of 20 μm. (Comparative Example 1) As shown in FIG. 2, the same as Example 1 except that the coating layer 4 containing manganese oxide was not formed. (Comparative Example 2) Using the same carrier substrate as in Example 1, using TiO 2
_After immersing in a slurry consisting of ₂ powders, TiO ₂ sol and distilled water, pulling up and blowing off excess slurry, it is dried and calcined in the same manner as in Example 1 to obtain about 1 volume per liter.
A 00 g TiO ₂ layer was formed. This carrier was immersed in an aqueous solution of ammonium metavanadate, dried and calcined to carry 20 g of V ₂ O ₅ per liter of the carrier. Further, platinum was loaded in the same manner as in Example 1 to obtain a catalyst of Comparative Example 2. (Test Example 1) Each of the above catalysts was subjected to a displacement of 2400
Installed in the exhaust system of the cc swirl chamber type DE, and the exhaust temperature is 4
The purification rate of HC under the condition of 50 ° C. was measured. Also,
At the same time, the conversion rate of SO ₂ into SO ₃ was determined by the following equation using a non-dispersive infrared analyzer. The results are shown in Table 1.

[0017]

[0018]

[Table 1]

From Table 1, in the conventional catalyst of Comparative Example 1, H
Although the C purification rate is good, the conversion rate to SO ₃ is high, which is not preferable. Further, in the catalyst of Comparative Example 2, the conversion rate to SO ₃ is low, but the HC purification rate is low, which is not preferable. On the other hand, it can be seen that the catalysts of the Examples are all prevented from converting SO ₂ to SO ₃ except for Example 12. This is the coat layer 4
It is clear that the effect is due to the inclusion of a metal oxide in. That is, SO ₂ is chemically adsorbed by the metal oxide in the coating layer, so that it is not subjected to the catalytic action of platinum and S 2
Not converted to O ₃ . Furthermore, the activated alumina layer supporting platinum does not come into contact with SO ₂ and is not poisoned by platinum. As a result, HC, CO, SOF, etc. are efficiently purified.

Comparing the catalysts of Examples 11, 12 and 13, when the content of magnesium oxide in the coating layer 4 was 0.01 mol, conversion to SO ₃ occurred and 0.5
It can be seen that, in mol, conversion to SO ₃ does not occur, but conversely, the purification performance of HC is slightly deteriorated. Therefore, the optimum content of magnesium oxide is 0.01 to 0.5.
It is presumed to be between mol.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a catalyst according to an example of the present invention.

FIG. 2 is a schematic sectional view of a conventional catalyst of Comparative Example 1.

[Explanation of symbols]

1: Carrier substrate 2: Activated alumina layer 3: Platinum
4: coat layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location B01J 23/62 A 8017-4G 23/64 104 A 8017-4G 37/02 301 L 8516-4G

Claims (1)

[Claims] 1. A carrier base material, an activated alumina layer formed on the surface of the carrier base material, a catalytic metal supported on the activated alumina layer, and alumina formed on the surface of the activated alumina layer,
At least one coat layer selected from titania and silica, and the coat layer contains Mn, Co, Sn, Fe, Ca, Ni,
At least one selected from Ce, Zr, Mg, Cu
An exhaust gas purification catalyst for a diesel engine, characterized in that it contains oxides of various metals.