JPH04197444A - Catalyst for exhaust gas purification and its production - Google Patents

Abstract

PURPOSE:To obtain a catalyst for exhaust gas purification for gas exhausted at reduced engine exhaust pressure by enabling an alumina layer to be junctioned to a metal honeycomb carrier under dispersion reaction and further the alumina layer to carry a precious metal. CONSTITUTION:An alumina layer with a thickness of 2 to 20mum is junctioned to a metal honeycomb carrier of an Al alloy of 20wt.% and 5wt.% Cr in a non-oxidation atmosphere using dispersion reaction technique such as heating. Then a precious metal such as Pt or Rh is allowed to be carried by the alumina layer. This design enables the alumina layer to be made thinner than a wash coat layer. Subsequently, it is possible to enlarge the open area of the metal honeycomb carrier and reduce the exhaust pressure of an exhaust gas significantly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a catalyst body for exhaust gas purification that has a carrier in the shape of a metal honeycomb and that reduces the exhaust pressure of an engine.

(Prior art and its problems) Conventionally, noble metals were supported on metal honeycomb carriers by: 1. Wash-coating γ-alumina (Al2O3) directly on the metal honeycomb carrier, or 2. After generating Al2O3 on the surface by heating with
The method used is to wash coat and then support the metal. As shown in (2), when directly wash-coating a metal honeycomb carrier, it is difficult to form a strong bond between the metal honeycomb carrier and the wash-coated γ-A1203, so the thick coated γ-AlvOs may peel off. In the case of ■, when the metal honeycomb carrier is oxidized in advance, the AlzOs generated on the carrier surface by the oxidation treatment and the γ-Altos wash-coated thereon are different from each other in terms of Altos. Although they are identical, the peel resistance of washcoated γ-AnzOs is insufficient because there is no chemical bond between them.

Furthermore, JP-A-56-96726 discloses that the metal carrier foil contains 15-25% by weight of Cr, 3-6% by weight of A1, optionally 0.3-1.0% by weight of Y, and the balance is Fe. 87 in air when the ferritic stainless steel alloy is
When heated at a suitable temperature between 0 and 970°C, Autos whiskers are formed on the processed surface of the metal foil, which firmly bond the coating layer to the foil when the γ-AlzOs is washcoated. It is said that it is useful for

However, the role of Al2O5 whiskers on metal foil is γ-
The whisker simply becomes entangled with the AlzOs coating layer and prevents the coating layer from peeling off.

Therefore, with this technology, γ-
It is not possible to suppress peeling of the AI20s coating layer.

In addition, as mentioned above, wash coated γ-Aj
7 is O, and the coating layer is as thick as 50 μm.

Therefore, the presence of the coating layer reduces the open area of the honeycomb carrier and causes an increase in exhaust pressure of the engine. However, the opening area of metal carriers is considerably smaller than that of ceramic carriers.

In other words, the ceramic carrier can significantly reduce engine exhaust pressure compared to the ceramic honeycomb carrier. However, γ-AI! If the tOs wash coat layer can be eliminated, the opening area can be further increased,
This makes it possible to further reduce engine exhaust pressure.

(Object of the Invention) In order to solve the problems of the prior art described above, the present invention aims to provide an exhaust gas purifying catalyst body that eliminates the γ-Af20s layer wash-coated on a metal honeycomb carrier and reduces engine exhaust pressure. It is something to do.

(Description of the first invention) In the first invention, a metal honeycomb carrier and a joint portion formed thereon are bonded together by a diffusion reaction. 2~20μ
The present invention relates to an exhaust gas purifying catalyst body characterized by comprising an alumina layer of m and a noble metal supported on the alumina layer.

In the catalyst body according to the present invention, Af2O formed on the surface of the carrier
The thickness of the i-layer can be reduced to less than 20 μm (because it is possible to reduce the thickness of the conventional γ
-AI! The thickness is 1/1 compared to the zOs wash coat layer.
It is possible to make the metal honeycomb carrier as thin as 2 or less, thereby increasing the opening area of the metal honeycomb carrier and significantly reducing the exhaust gas exhaust pressure compared to the conventional metal honeycomb carrier. In addition, metal honeycomb carrier and A 1220 s
It is strongly bonded to the layer by a chemical reaction, and is simply γ-
The peeling resistance of the AlzOs layer was significantly improved compared to the conventional carrier which was merely wash-coated with AlzOs.

(Description of other inventions of the first invention) In the first invention, the metal honeycomb carrier is an iron-based alloy,
For example, Fe-20% by weight Cr-5% by weight A1 alloy is used. Since the carrier is molded into a corrugated shape, it must be made of a material with good workability. Usually used in foil form. The thickness is preferably about 30 to 100 μm. 30
If it is thinner than μm, the strength of the metal honeycomb carrier will not be sufficient, making it difficult to handle. Moreover, if it is thicker than 100 μm, the opening area of the honeycomb carrier will be small (i.e., the effect of reducing the exhaust gas pressure will be small), and the advantage of using a metal honeycomb carrier and the effect of applying the present invention will be reduced.

The thickness of the AlzOs layer used is 2 to 20 μm.

It is significantly thinner than conventional washcoat layers.

If it is thicker than 20 μm, the opening area of the metal honeycomb carrier will be small, and the effect of reducing the exhaust gas pressure of exhaust gas will be small. Conversely, if it is thinner than 2 μm, it will be difficult to support precious metals.

The carrier and AI! The junction with the zOs layer is bonded by a diffusion reaction. The diffusion reaction treatment is performed by heating in a non-oxidizing atmosphere as described below.

Further, as the noble metal that is the catalyst metal, Pt, Rh, Pd, etc., which are commonly used in catalysts, are used. Precious metals are usually Pt and R
h or Pt, or a combination of Rh and Pd.

In the case of Pt/Rh catalyst, the supporting ratio of Pt and Rh is 1.0 to 2.0 g/A for Pt and 0.10 to 0 for Rh.
．． Carrying 5g/12. Preferably, Pt is 1.2 to 1.
6 g/β, and Rh is supported at 0.16 to 0.4 g/l. P
In the case of t/Pd/Rh catalyst, P 10.2 to 1. og
/i! , PdO12~1.2g/l, Rh 0.05~
0.4g, # loaded. Preferably pt is 0.3 to 0.
7g/l, Pd 0.3-1. Og/A, Rh 0.0
7-0.3g/I! to carry.

In the Pt/Rh catalyst, the amount of Pt is 1.0 to 2.0 g.
The reason why the amount of /CRh is set to 0.1 to 0.5/l is that Pt
The amount is 1.0#, the Rh amount is 0.1g/jl! This is because the exhaust gas emission cannot satisfy the regulation value in the following manner. Further, even if the amount of Pt is 2.0 g/l and the amount of Rh is 0.5 g/A or more, there is no commensurate effect. The reason for the limitation is the same for the Pt/Pd/Rh catalyst.

In addition, Ce may be contained in the A(22Ch layer) in the form of Cen2. When CaO2 is contained, its oxygen storage ability is utilized to reduce NO, HC at near the stoichiometric air-fuel ratio.
, the range of CO purification activity can be expanded.

The content is preferably 0.13 to 0.53 mol/β.

If it is less than 2.5%, the aforementioned oxygen storage ability by Ce cannot be exhibited. On the other hand, no effect can be expected even if the amount exceeds 10%.

(Description of the second invention) The second invention comprises a step of forming an aluminum layer on the surface of an iron-based alloy thin plate by vapor deposition, a step of forming the iron-based metal thin plate into a honeycomb-shaped carrier, and a step of forming the iron-based metal thin plate into a honeycomb-shaped carrier. a diffusion treatment step in which the Nicum carrier and the aluminum layer are bonded by diffusion by heating in a non-oxidizing atmosphere, and a diffusion treatment step in which the Nicum carrier subjected to the diffusion treatment is heated in an oxidizing atmosphere to oxidize the aluminum The present invention relates to a method for producing a catalyst body for exhaust gas purification, which comprises an oxidation step in which the honeycomb carrier is converted into alumina, and a step in which a noble metal is supported on the honeycomb carrier.

According to the manufacturing method of the second invention, a thin Af2Ch of 20 μm or less can be easily formed on the surface of a metal honeycomb carrier, so a catalyst body that can reduce the exhaust pressure of engine exhaust residue can be easily manufactured. In addition, after the A1 layer formed by vapor deposition is subjected to a diffusion treatment in a non-oxidizing atmosphere, the A1 layer is
I! by oxidizing A1. Since the tOs layer is formed, a catalyst body in which the metal honeycomb carrier and the A12Ch layer are firmly bonded can be obtained.

(Description of other inventions of the second invention) In the second invention, AA is deposited by vacuum evaporation. Vapor deposition is performed on both sides of the iron-based alloy thin plate.

Vacuum deposition is performed by a conventional method such as sputtering or electron beam deposition.

Next, a part of the thin plate on which the AJ7 was deposited was formed into a corrugated shape. The corrugated thin plate and the Al-deposited flat plate are stacked and wound up so that the flat plate is on the inside, and formed into a honeycomb shape to obtain a honeycomb carrier.

This honeycomb carrier is subjected to a diffusion treatment at a temperature between 300° C. and 650° C. in a vacuum or in a non-oxidizing gas flow such as H2.

The treatment time is about 2 hours at a low temperature of close to 300°C. However, the processing time can be shortened with temperature, and 65
At 0°C, the processing time may be about 30 minutes. Through this treatment, a portion of Af is diffused into the underlying iron-based alloy, and the 11th layer is bonded to the carrier, and the protrusion of the corrugated foil and the flat plate are also firmly bonded.

Next, this honeycomb carrier is heated to 1000°C or higher and 1200°C.
When heated in an oxidizing atmosphere at the following temperature for about 1 to 2 hours, the A1 layer is oxidized to become an Affi2CL layer.

AI generated in this way! The 203 layer is strongly bonded to the underlying iron-based alloy and will not peel off.

Next, a noble metal is supported on the metal honeycomb carrier produced in this manner. In the present invention, noble metal molecules or colloids are used so that noble metal particles are fine and uniformly supported.

Examples of noble metal molecules include metal carbonyl clusters. As a carbonyl cluster of Pt, (NE t 4
) [(P t 5(CO)s) n co (n=1~5
) etc. As a carbonyl cluster of Rh, Rh
Examples include a(Co)16 and Rh4(CO)1□.

These clusters are dissolved in a solvent such as tetrahydrofuran, and impregnated and supported on the honeycomb carrier. Thereafter, the honeycomb is heated in air at 500° C. for 1 hour to decompose carbonyl clusters and deposit and support noble metals.

Noble metal colloids can be prepared using polymers (e.g. N-
vinyl-2-pyrrolidone). This colloid solution is used to impregnate and support the colloid on the honeycomb carrier. After impregnating, heat at about 500℃ for 1 hour in a chemical atmosphere to decompose the polymer.
Precious metals are supported in the honeycomb.

Further, the noble metal may be supported in a three-way catalyst by a commonly used method of supporting the noble metal on the wash coat Anz03 layer.

In addition, to form an Altos layer containing Ce 02,
When depositing AI, Ce is simultaneously deposited, for example, by dual simultaneous vacuum deposition. AI! , Ce may be simultaneously vapor-deposited in the same manner as in the case where only Al is vapor-deposited.

(Example) First, a Fe-20% by weight Cr-5% by weight An iron-based alloy was cold rolled to produce a foil with a thickness of 50 μm. This foil was placed in a vacuum evaporation apparatus, and two-dimensional simultaneous evaporation was performed using A1 and Ce as evaporation sources to form evaporation layers on both sides of the foil. The thickness of the layers obtained is approximately IO μm, with several layers containing C
0.3 mol/l of E was supported.

The foil on which AI and Ce were simultaneously deposited in this manner was molded into a corrugated shape. Further, another foil deposited under the same conditions was left as a flat plate. A flat foil was layered on the corrugated foil and tightly wound up so that the flat foil was on the inside to form a honeycomb structure. The volume of the honeycomb carrier is 1.31, the cell density is 400 Cellh/sq, 1 nch, and the cell wall thickness is 50 μm. The thickness of the layer obtained is approximately IO
μm, and several layers contained 0.3 mol/l of Ce.

Next, the honeycomb structure was heat-treated in vacuum at 500° C. for 1 hour. Through this treatment, iron-based alloy foil and Af-Ce
Mutual diffusion occurs between the vapor deposited layers, adhesion occurs at the contact portion with the iron-based alloy foil, and the honeycomb structure is firmly integrated. At this point, the ends of the honeycomb structure are partially welded to fix the honeycomb structure.

The honeycomb structure thus obtained was heated in the air at 1100° C. for 1 hour. By this heating, the Af-Ce alloy layer deposited on the iron-based alloy foil is completely oxidized, and Al2O5 and Ce
It becomes a mixed layer of O2. This mixed layer is strongly bonded to the underlying iron-based alloy layer and does not peel off from the underlying layer.

Next, Pt/Rh noble metal was supported on the surface of the honeycomb structure. The supported amount of Pt and Rh is 1.5g/lR of pt.
h was set to 0.3 g/l. The loading of Pt and Rh is P
t and Rh carbonyl cluster (NE t
4) [(P t 5(Co)s) n co(n=1~5
) and Rh s(CO)+2 were dissolved in tetracitrofuran, a solvent, and the solution was flowed from one end of the honeycomb structure to the other to form a catalyst body (example catalyst) in which Pt and Rh were uniformly supported. Na1) was obtained.

Next, as a comparison catalyst, γ-Af20s was wash-coated on a metal honeycomb carrier similar to that used in the example catalyst, and Pt/Rh precious metal was impregnated and supported thereon in the same amount as the example catalyst (comparative example catalyst NlIC1 ) was obtained. The thickness of the washcoat layer was 50 μm.

The exhaust gas flow resistances of the catalyst bodies of the example catalyst bt and the comparative example catalyst NnC1 were determined and compared at the same volume and cell density. Distribution resistance was measured using the following method. The metal honeycomb carrier was installed in the same cylindrical holder that is used in automobiles so that exhaust gas passes only through the honeycomb, and pipes were connected to flanges at both ends of the holder. Air was flowed into the honeycomb from one pipe at a flow rate of 4 rrl'/min. At this time, thin tubes were attached to both pipes, and the pressure difference at both ends was measured using a manometer to determine the flow resistance of the honeycomb.

At a flow rate of 4 rrr/min, the comparative example catalyst stage CI
The flow resistance was 75 mmAq, but the example catalyst stage 1
is 68 mmAq, which indicates that the catalyst body of this example can reduce the flow resistance.

Claims (2)

[Claims] (1) For exhaust gas purification, comprising a metal honeycomb carrier, a 2-20 μm alumina layer formed on the carrier and bonded by a diffusion reaction, and a noble metal supported on the alumina layer. Catalyst body. (2) forming an aluminum layer on the surface of an iron-based alloy thin plate by vapor deposition; forming the iron-based alloy thin plate into a honeycomb-shaped carrier; and heating the honeycomb carrier in a non-oxidizing atmosphere to form a honeycomb. a diffusion treatment step of bonding the carrier and the aluminum layer by diffusion; an oxidation step of heating the honeycomb carrier subjected to the diffusion treatment in an oxidizing atmosphere to oxidize the aluminum into alumina; and supporting a noble metal on the honeycomb carrier. A method for producing a catalyst body for exhaust gas purification, comprising the steps of: