JPS6322186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a monolithic catalyst for exhaust gas purification. In recent years, monolithic catalysts have been increasingly used instead of pellet catalysts as catalysts for purifying exhaust gas emitted from internal combustion engines such as automobiles.
The monolithic catalyst carrier, which is the base of this monolithic catalyst, has a large surface area to improve purification performance.
For example, 15 to 100 square, triangular, hexagonal, etc. pores are formed per cm through which exhaust gas passes.
A catalyst such as platinum or palladium is supported on the walls forming the pores.

[Conventional technology]

A conventional monolithic catalyst for exhaust gas purification has a configuration in which a catalyst such as platinum or palladium is uniformly supported on the wall surface forming the pores from the gas inlet to the gas outlet.

[Problem that the invention seeks to solve]

Under actual usage conditions of monolithic catalysts for exhaust gas purification, catalyst poisons such as lead (Pb) in fuel and phosphorus (P) in oil tend to adhere to the pores on the gas inlet side. When deposited in this manner, a reaction as shown in the following formula occurs, for example, through the catalyst layer. As a result, lead sulfate (PbSO ₄ ),
Lead compounds such as lead oxide (PbO) can grow large and block the minute pores, causing clogging and reducing purification performance.

PbX ₂ +H ₂ O→PbO+2HX SO ₂ +1/20 ₂ →SO ₃ PbO+SO ₃ →PbSO _4In order to suppress clogging, it is possible to enlarge the pores, but this would reduce the surface area of the monolithic catalyst carrier. , the purification performance decreases.

[Means for solving problems]

The present invention has been made in view of the problems of the prior art described above. The present invention focuses on the fact that lead compounds are easily generated on the gas inlet side in a monolithic catalyst for exhaust gas purification, and the surface of the catalyst layer on the gas inlet side where lead compounds are easily generated is covered with a coating layer. It is something.

That is, the monolithic catalyst for exhaust gas purification of the present invention comprises a monolithic catalyst carrier having a porous catalyst support layer that defines pores having a gas inlet at one end and a gas outlet at the other end, and a monolithic catalyst carrier that defines the pores. In a monolithic catalyst for exhaust gas purification comprising a catalyst layer supported on the catalyst support layer, the catalyst layer supported on the gas inlet side of the pores is
It is characterized in that it is covered with a porous coating layer that is formed of the same material as the catalyst support layer of the monolithic catalyst carrier and allows gas to pass therethrough.

The monolithic catalyst carrier that is a component of the present invention is
It has the function of supporting a catalyst and the function of maintaining its external shape so that it can be installed in the exhaust system of automobiles, etc.
The carrier can be formed in a conventional manner.
That is, it generally has a honeycomb structure (honeycomb shape) and has an exhaust gas inflow side end face and an exhaust gas outflow side end face,
A large number of pores (usually 15 to
100 pieces/cm2), and its outer shape is usually columnar. As the material of the carrier, cordierite, which has strong thermal shock resistance, is used as in the past, but other materials such as mullite, alumina, magnesia, spinel, etc. can also be used.

The catalyst layer, which is a component of the present invention, can be formed in a conventional manner. In other words, it has the function of converting hydrocarbons, carbon monoxide, and nitrogen oxides in exhaust gas into water, carbon dioxide, and nitrogen, and generally converts from platinum, palladium, iridium, ruthenium, rhodium, osmium, chromium, nickel, vanadium, etc. It has been made. The catalyst layer is usually formed by coating the pore wall surfaces of a monolithic catalyst carrier with a porous catalyst support layer such as an activated alumina layer, and impregnating the porous catalyst support layer with a catalyst.

By the way, as described above, lead in fuel, phosphorus in oil, etc. tend to adhere to the catalyst layer supported on the gas inlet side of the pores. In this regard, in the present invention, the catalyst layer supported on the gas inlet side of the pores is covered with a coating layer, which is a characteristic feature of the present invention. Therefore, the catalyst layer is not exposed in the area covered with the coating layer. As a result, the catalyst poison adheres to the coating layer and does not adhere to the catalyst layer covered with the coating layer. The internal structure, material, length, thickness, etc. of the coating layer are variously selected depending on the required purification rate. The coating layer is porous enough to allow exhaust gas to pass through, but not to allow catalyst poisons (lead in fuel, phosphorus in oil) to pass through. By making the exhaust gas porous in this way, the exhaust gas passes through the coating layer and reaches the catalyst layer covered with the coating layer, where it is purified. Therefore, the coating layer is preferably formed of an aggregate of ceramic powder. In this case, the coating layer is made of the same material as the catalyst support layer, for example, activated alumina. For example, the carrier is immersed in alumina slurry to adhere the alumina slurry to the walls of the pores, and the alumina slurry is then fired and solidified by applying hot air, and the fired and solidified portion can be used as the coating layer. The coating layer is 1/10 the length of the monolithic catalyst carrier.
The length is preferably about 1/4 to 1/4. This is because if the length of the coating layer is made too long, the number of catalyst layers covered by the coating layer becomes too large, which reduces the exhaust gas purifying power of the monolith catalyst as a whole. The coating layer is preferably in the form of a thin film with a thickness of about 30 to 100 microns.

In addition, it is possible to make the thickness of the catalyst layer in the portion covered with the coating layer as thin as the thickness of the coating layer, and to make the surface of the coating layer and the surface of the catalyst layer not covered with the coating layer coplanar. preferable. In this way, it is not necessary to unnecessarily increase the thickness of the layer attached to the wall surface of the pore, and therefore, it is possible to suppress an increase in pressure loss when the exhaust gas passes through the pore.

[Function and effect of the invention]

As described above, according to the monolithic catalyst for exhaust gas purification of the present invention, the catalyst layer on the gas inlet side is covered with the coating layer. This prevents catalyst poisons such as lead and phosphorus from adhering to the catalyst layer on the gas inlet side.

Therefore, clogging is less likely to occur even on the gas inlet side, where clogging has conventionally been apt to occur, and the supported catalyst layer can be used for a long period of time. As a result, the exhaust gas purification performance is improved compared to the conventional method, and high purification performance can be maintained for a long period of time.

〔Example〕

1 and 2 schematically show a first embodiment of the present invention. The monolith catalyst of this example is
The main components are a monolithic catalyst support 1, a catalyst layer 2, and a coating layer 3. Monolithic catalyst carrier 1
is made of cordierite in a columnar shape so as to form a honeycomb structure, and has a large number of pores 4 extending in the axial direction. Pore 4
are formed in large numbers in order to increase the surface layer and improve purification performance. One end of the pore 4 serves as a gas inlet 5, and the other end serves as a gas outlet 6.

The catalyst layer 2 is supported on the wall surface 7 forming the pores 4 . As shown in FIG. 1, the catalyst layer 2 includes a first catalyst layer 2a having a thickness of 30 to 100μ, and the first catalyst layer 2a.
The second catalyst layer 2b is formed on the upper surface of the catalyst layer a and has a thickness of 30 to 150 μm. First catalyst layer 2a
is formed attached to the wall surface 7 over the entire length L1 of the monolithic catalyst carrier 1. Also, the second catalyst layer 2
b is formed on the first catalyst layer 2a except for 1/4 of the total length L1 (i.e., length L2) of the monolithic catalyst carrier 1 from the gas inlet 5 side as shown in FIG. There is.

The coating layer 3 is the first catalyst layer 2a on the gas inlet 5 side.
It covers. This has a length of 1/4 of the total length L1 of the monolithic catalyst carrier 1, that is, a length L2, and is formed from the gas inlet 5 side. Note that the shaded area in FIG. 2 indicates the area where the covering layer 3 is formed. Covering layer 3
is formed of a porous material, that is, an aggregate of alumina particles that are the same material as the catalyst support layer that is a component of the catalyst layer 2. Therefore, the covering layer 3 is porous and allows exhaust gas to pass therethrough. Note that the thickness of the coating layer 3 was 30 to 100 μm.

In manufacturing the monolithic catalyst of this example, alumina is coated in a thin film over the entire length L1 on the wall surface 7 of the pores 4 of the monolithic catalyst carrier 1, thereby forming the first catalyst supporting layer. . Next, remove the length L2 from the gas inlet 5 side,
The surface of the first catalyst support layer is similarly coated with alumina in the form of a thin film, thereby forming a second catalyst support layer. After forming the first catalyst support layer and the second catalyst support layer as described above, palladium chloride, dinitrodiamine platinum, rhodium chloride (palladium 0.5g/L, platinum 0.5g/L, rhodium
The monolithic catalyst carrier 1 was immersed in an aqueous solution containing 0.1g/L) for 60 minutes, and then the monolithic catalyst carrier 1
was taken out from the aqueous solution and dried and solidified. and,
As a result, a catalyst was supported on the first catalyst support layer and the second catalyst support layer, thereby making the first catalyst support layer the first catalyst layer 2a and the second catalyst support layer the second catalyst layer 2b.

Next, as shown in FIG. 1, alumina was coated in a thin film on the gas inlet 5 side of the first catalyst layer 2a, which is the part where the second catalyst layer 2b is not formed. A coating layer 3 was obtained by suitably drying and solidifying alumina. The coating layer 3 is made of activated alumina powder with a particle size of 1 to 100μ.
It was formed from a slurry of 1000g of water, 450g of water, and 700g of alumina sol mixed and stirred.

In the monolithic catalyst of this example, the gas inlet 5
The side first catalyst layer 2a is covered with a covering layer 3. Therefore, adhesion of catalyst poisonous substances such as lead and phosphorus to the catalyst on the gas inlet 5 side is suppressed compared to the case where there is no coating layer 3. Therefore, unlike the prior art, it is possible to suppress the growth of lead sulfate, lead oxide, etc. via the catalyst layer, and therefore it is possible to suppress clogging of the fine pores 4.

Furthermore, the coating layer 3 of this example is porous enough to allow gas to pass through, but not lead or the like. Therefore, the exhaust gas passing through the coating layer 3 is purified by the first catalyst layer 2a covered by the coating layer 3, and therefore, in this example, while suppressing clogging of the pores 4, the exhaust gas is purified as required. Purification rate can be ensured.

Further, in this example, as shown in FIG. 1, the thickness of the first catalyst layer 2a is made thinner by the thickness of the coating layer 3, and the coating layer 3 is formed on the first catalyst layer 2a.
Therefore, the surface 3a of the coating layer 3 and the second catalyst layer 2
It can be made substantially flush with the surface 2e of b. With such a configuration, there is no need to unnecessarily increase the thickness of the layer formed on the wall surface 7 of the pore 4, and therefore, it is possible to suppress an increase in pressure loss when exhaust gas passes through compared to the conventional method. obtain. That is, in the example shown in FIGS. 1 and 2, clogging of the pores 4 can be suppressed with almost the same pressure loss as in the case of the prior art.

In the second embodiment, after coating the wall surface 7 with the first catalyst supporting layer and drying and baking the carrier 1,
The catalyst component is supported on the first catalyst supporting layer by immersing it in a solution in which the catalyst component is dissolved, thereby forming the first catalyst layer 2a.

Next, a second catalyst support layer is formed by coating over the entire length, and the carrier 1 is immersed in a solution containing a catalyst component, thereby supporting the catalyst component on the second catalyst support layer. At this time, the portion that will become the coating layer 3 is prevented from being immersed in the solution, and the catalyst component is not supported on the coating layer 3.

Further, the catalyst components of the first catalyst layer 2a and the second catalyst layer 2b may not be the same, and may have different composition ratios and component elements. In other words, the first catalyst layer 2a is
The second catalyst layer 2a may be changed as appropriate, such as supporting mainly Pd and the second catalyst layer 2a supporting mainly Pt and Rh.

FIG. 3 schematically shows a third embodiment of the present invention. In this example, the second catalyst layer 2b is not formed. The coating layer 3 in this example is formed from an aggregate of alumina particles and is porous, as in the above-mentioned example. In this example, pressure loss during passage of exhaust gas tends to be disadvantageous in general, but by making the thickness of catalyst layer 2 as thin as possible, increase in pressure loss can be suppressed.

FIG. 4 schematically shows a fourth embodiment of the present invention. In this example, the boundary between the coating layer 30 and the catalyst layer 20 is tapered as shown in FIG. In this case, the wall surface 7 forming the pores 4 of the monolithic catalyst carrier 1 is coated with a catalyst supporting layer such as alumina. After that, the required amount of the catalyst support layer on the gas inlet 5 side is removed by suction from the gas inlet 5 side, or
A required amount of the catalyst support layer on the gas inlet 5 side is blown away by force-feeding gas from the side. Next, the monolithic catalyst carrier 1 is immersed in a solution containing a catalyst component such as platinum or rhodium to cause the catalyst component to be supported on the catalyst support layer, thereby forming the catalyst support layer into a catalyst layer 20. As shown in FIG. 4, this catalyst layer 20 has a tapered shape that becomes thinner toward the gas inlet 5 side due to the above-described suction process and pressure feeding process. Next, the gas inlet 5 side was coated with alumina in the form of a thin film, and this was appropriately dried and solidified to form the coating layer 30.

[Brief explanation of the drawing]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a partial cross-sectional view of the main part of the monolithic catalyst carrier, and FIG. 2 is a monolithic catalyst carrier in which the parts on which the coating layer is formed are shown with diagonal lines. FIG. FIG. 3 shows a third embodiment of the present invention, and is a partial cross-sectional view of a main part of a monolithic catalyst carrier. FIG. 4 shows a fourth embodiment of the present invention, and is a partial cross-sectional view of a main part of a monolithic catalyst carrier. It is. In the figure, 1 is a monolithic catalyst carrier, 2 is a catalyst layer, and 3 is a monolithic catalyst carrier.
4 indicates a coating layer, 4 indicates a pore, and 5 indicates a gas inlet.

Claims (1)

[Scope of Claims] 1. A monolithic catalyst carrier having a porous catalyst support layer that defines pores having a gas inlet at one end and a gas outlet at the other end, and a catalyst supported on the catalyst support layer that defines the pores. In a monolithic catalyst for exhaust gas purification, the catalyst layer supported on the gas inlet side of the pores is
A monolithic catalyst for exhaust gas purification, characterized in that it is covered with a porous coating layer formed of the same material as the catalyst supporting layer of the monolithic catalyst carrier and through which exhaust gas passes. 2. The monolithic catalyst for exhaust gas purification according to claim 1, wherein the surface of the coating layer is substantially the same as the surface of the catalyst layer not covered with the coating layer.