JPH01127044A - Catalyst for clarifying exhaust gas - Google Patents

Abstract

PURPOSE:To improve clarification capacities for NOx, CO, etc., in an lean-burn atmosphere, by forming a catalyst, wherein a carrier is first coated with a catalyst layer composed of catalyst components for oxidation reaction and further coated with a catalyst layer composed of copper and zeolite. CONSTITUTION:A catalyst for clarifying hydrocarbons, carbon monoxide and nitrogen oxides in an exhaust gas out of an internal combustion engine is formed by arranging the first catalyst layer composed of catalyst components effective for oxidation reaction on a carrier made of a porous sintered body such as cordierite, alumina, silica-alumina, spodumene, etc., and further arranging the second catalyst layer composed of copper and zeolite upon the first catalyst layer. The first and second catalyst layers are preferably composed of a catalyst of noble metal supported on alumina and that of copper supported on zeolite by ion-exchange reaction, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a three-way catalyst for purifying exhaust gas for removing harmful components from the exhaust gas of an internal combustion engine.

[Prior art]

In recent years, exhaust purifying catalysts for internal combustion engines, particularly automobile internal combustion engines, are required to have extremely high performance in terms of durability, purification performance, and the like. Monolithic catalysts, granular catalysts, and the like are used as this exhaust purification catalyst.

As the catalyst component, one or more noble metals such as platinum (PL), rhodium (Rh), and palladium (Pd) are used, and these are often supported on a carrier. By sending the exhaust gas to a catalytic converter filled with these catalysts, the harmful substances in the exhaust gas, such as hydrocarbons (HC), -oxidants (CO), and nitrogen oxides (NOx), are oxidized or reduced. and purify it. The main harmful substances in the exhaust are the above-mentioned HC, CO, and NO.
x, and a catalyst that can purify these three components at once is called a three-way catalyst.

Conventionally, automotive catalysts aimed at improving catalytic properties as three-way catalysts have been proposed. For example, USP 4.128, 5
The catalyst described in No. 06 is in the form of pellets, and catalyst components are separated and supported in layers on a carrier. And Pt(!:Rh) is used as a catalyst component.

In addition, the catalyst described in Japanese Patent Publication No. 57-20013 has a 2N layer of sintered alumina or zirconia containing catalyst components on a heat-resistant ceramic carrier, and Pt-Rh in the upper layer and Pt-Rh in the lower layer. is an oxidation catalyst supporting Pd or Pd-PL.

[Problems to be solved]

However, with conventional three-way catalysts, when the oxygen concentration in the exhaust gas becomes higher than the theoretical value (the minimum oxygen concentration necessary to completely oxidize unburned components in the exhaust gas),・This method (referred to as "burn") has the disadvantage that it cannot reduce and remove NOx in the exhaust gas.

The present invention has been made to solve the problems of the prior art described above, and is efficient even in a lean burn atmosphere.
The present invention aims to provide a three-way catalyst that can purify NOx, Co, and HC.

[Means for solving problems]

The present invention provides a catalyst for purifying hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas of an internal combustion engine, which comprises providing a first catalyst layer made of a catalyst component effective for an oxidation reaction on a carrier,
Furthermore, a second catalyst layer made of copper and zeolite is formed on the first catalyst layer.
An exhaust purification catalyst characterized by being provided with a catalyst layer.

The catalyst according to the present invention has a first catalyst layer made of a catalyst component effective for oxidation reactions and a second catalyst layer made of copper (Cu) and zeolite. Then, one catalyst layer is placed on the carrier.
The catalyst layer is further provided with a second catalyst layer thereon.

Therefore, the catalyst components used in the first catalyst layer are as follows:
Examples include noble metals such as Pt, Pd and Rh, rare earth oxides such as ceria (CeOz) and lanthanum oxide (LazO3), and zirconium oxide.

One or more of these may be used.

Further, Cu as a catalyst component used in the second catalyst layer may be in the form of metal Cu or copper oxide (CIJO). Zeolite used with Cu is also called zeolite, has a chemical composition similar to feldspars or semi-feldspars, and has the general formula WmZn0zn-s H2O [where W is Na, C
a, Ba or SL, Z is Si+AA (Si:A
e>1), s is not constant]. The second catalyst layer is prepared by mixing zeolite and Cu, or by supporting Cu on zeolite by ion exchange. As shown in the Examples, this ion exchange support is carried out by immersing the zeolite layer in an aqueous copper solution such as copper acetate or copper nitrate and drying it. As a result, elements such as Na or alkali in the zeolite undergo ion exchange with Cu. Further, the ion exchange rate at this time is preferably 50 to 100%. 5
This is because if it is less than 0%, it is difficult to obtain the effects of the present invention.

Here, the ion exchange rate of Cu refers to the amount of -valent Cu exchanged with elements such as Na or alkali in the zeolite.

Next, as a carrier for supporting the first catalyst layer.

Cordierite, alumina, silica/alumina.

Porous sintered bodies such as spodumene are available. Also.

The shape of the carrier may be arbitrary, such as a single grain or a honeycomb shape, but an integral carrier such as a honeycomb shape is preferable in order to improve contact with exhaust gas and improve the purification rate. Further, the carrier is, for example, on the surface of a cordierite carrier which is a -type carrier.

Furthermore, a porous body of alumina or the like can be formed by depositing and firing a powder of alumina or the like.

Further, it is preferable that the amount of the first catalyst layer supported on the carrier is 0.1 to Log with respect to the carrier 11. If the amount supported is less than 0.1 g, it is difficult to obtain the effects of the present invention. Even if it exceeds 10 g, it is difficult to obtain an effect commensurate with the amount supported.

Next, as a method for providing a second catalyst layer on the first catalyst layer, for example, firstly, a porous layer of zeolite powder is coated on the carrier on which the first catalyst layer is formed, and then a porous layer of zeolite powder is coated. This is carried out by immersing Cu in an aqueous copper solution such as copper acetate to support Cu by ion exchange. However, 18
The amount of the second catalyst layer supported on the carrier 12 is 0. It is preferable to set it as 1-20g. 0.1g
In less than.

It is difficult to obtain the effects of the present invention, and even if it exceeds 20 g, it is difficult to obtain the effects commensurate with that.

Note that the exhaust purification catalyst according to the present invention has a molecular weight of 200 to 800.
Preferably, it is used at ℃. Also.

The space velocity of the exhaust gas introduced into the catalyst layer is GH3V1.
It is preferable to set it as 10,000-120,000/hour.

Furthermore, as will be described later, when a catalyst according to the present invention is used, NOx in the exhaust gas is mainly purified by reacting with HC. This HC may be one that remains in the exhaust gas, but
If the amount of HC is insufficient to cause the above reaction, it is better to add HC from the outside into the exhaust gas.

It is better to have more HC than is necessary for the above reaction.

The above reaction is further promoted.

[Action and effect]

In the present invention, a first catalyst layer is provided on the carrier.

Furthermore, since a second catalyst layer is provided on top of the catalyst to form a catalyst, it can be used in a lean burn atmosphere, that is, an oxygen-excess atmosphere, which was previously thought to be difficult.

Efficient < can purify NOx and also reduce CO, H
C can also be efficiently purified. Therefore, an excellent three-way catalyst can be used.

The reason why the catalyst of the present invention exhibits such excellent effects is not clear, but it is thought to be as follows.

That is, when exhaust gas comes into contact with the catalyst, first the N in the gas is
Ox is caused by the second catalyst layer consisting of Cu and zeolite,
Similarly, it selectively reacts with HC in the gas. The reaction at this time is considered to be a linear equation.

aHc+bNOx-+cH2'O+dCOz Therefore, this purifies NOx into harmless substances.

Also, the remaining HC that did not react with the NOx.

and CO react with oxygen in the exhaust gas by the first catalyst layer of one catalyst to become H, O, and Co□ and are purified into harmless substances.

As described above, in the catalyst of the present invention, the second catalyst layer selectively purifies NOx, and the first catalyst layer purifies HC and Co, so it is highly efficient even in an oxygen-rich atmosphere. can purify HC and Co.

[Example] First Example Alumina was coated on an integral support made of cordierite to form a support, Pd was supported as a first catalyst layer, and Cu was further applied thereon as a second catalyst layer. - A catalyst according to the present invention was prepared by supporting zeolite.

Next, the purification activity of the catalyst was evaluated using engine exhaust gas. Similar activity evaluations were also performed on comparative catalysts.

Preparation of the catalyst of the present invention (Nα1.Nα2); Alumina 100
A washcoat slurry was produced by ball milling 14 parts of aluminum nitrate and 14 parts of an aqueous aluminum nitrate solution with water and nitric acid.

A cordierite monolithic carrier having a volume of 1.3 L and containing approximately 400 channels per inch of cross-sectional area was then immersed in the washcoat slurry.

Subsequently, the excess liquid was blown away with compressed air, the integrated product was dried to remove free water, and then calcined at 700°C for 1 hour to coat the integrated support with alumina with a thickness of about 25 μm. .

Subsequently, the carrier was immersed in a nitric acid aqueous solution of dinitrodiammine palladium at a concentration of 0.009 mol/L,
After drying, bake at 200°C for 1 hour.

1.5 g/L of palladium (P
d) was supported.

Next, 100 parts of zeolite and 80 parts of silica sol are ball-milled together with water and nitric acid to form a washcoat slurry, and the Pd-supported material is immersed in the slurry to a thickness of approximately 25 μm in the same manner as in the case of alumina.
Coated with m zeolite.

Subsequently, this material was immersed in a 0.02 mol/L copper acetate aqueous solution for 24 hours to carry Cu by ion exchange. The ion exchange rate of Cu at that time was 89%. Further, the amount of Cu supported was 20 g/L relative to the carrier IL.

As a result, by using Pd as the first catalyst layer and Cu-zeolite as the second catalyst layer, the Cu-I non-exchange rate was 89%.
The catalyst layer 1 according to the present invention was prepared.

Further, the concentration of the copper acetate aqueous solution was 0.01 m.

Catalyst Nα2 according to the present invention was prepared under the same conditions as above except that the Cu ion exchange rate was 60% and was the same as the above-mentioned NG and 1 catalyst.

Preparation of comparative catalysts (C1, C2, C3); the above Nα
A catalyst in which only Pd was supported as a catalyst component was prepared in the same manner as in Catalyst-1 except that zeolite and Cu were not supported in Catalyst 1.

That is, this catalyst was obtained by coating alumina on the cordierite integrated carrier, and further supporting 1.5 g/L of Pd thereon in the same manner as above. This catalyst is designated as kcl.

Next, a comparison catalyst NaC2 was prepared by performing the steps of coating alumina and supporting Pd, and supporting zeolite and Cu in the preparation of the Nα engineered catalyst described above, but under the same conditions except for the same steps. Contrary to the Nα1 catalyst according to the present invention, the kc2 catalyst has a catalyst layer made of zeolite and Cu on the cordierite integrated support, and a catalyst layer made of alumina and Pd on top of that. It was formed.

In addition, in the same manner as in the case of the above-described catalyst No. 1, a support was prepared by first coating the surface of a cordierite integral support with alumina having a thickness of about 50 II m. Next, the carrier was immersed in an aqueous solution of 2.5 mo1/L of cerium nitrate, dried and then calcined in air at 600°C for 3 hours, and 0.3 mo I/L of cerium oxide (Cent) was added onto the carrier. carried it. Furthermore.

This material is rhodium chloride 0. The carrier was immersed in an aqueous solution with an OQ of 2 mol/L, dried, and then calcined at 200°C for 1 hour to support 0.3 g/L of rhodium (Rh) on the carrier. Furthermore, this material was immersed in an acidic nitric acid aqueous solution of dinitrodiammine platinum at a concentration of 0.005 mol/L, and after drying, 2
After baking at 00° C. for 1 hour, 1.5 g/L of platinum (pt) was supported on the above carrier. As a result, Pt Pd Cent
Catalyst N [lC3 was prepared.

Evaluation of purification activity: The five types of catalysts described above were installed in the exhaust system of a 6L engine with exhaust It, and the catalytic activity was examined. During this time, the temperature of the exhaust gas at the inlet of the catalyst layer was changed to 400°C and 500°C, and the purification rate was measured for each. In addition, the engine air-fuel ratio (A/F
) under oxygen excess (i.e.

Lean Burn) was set at 18. Further, the space velocity GH3V of the exhaust gas was approximately 60,000/hour. The measurement results are shown in Table 1.

As is clear from Table 1, the exhaust gas purification catalyst according to the present invention exhibits extremely high purification activity even in the presence of excess oxygen. Namely, 1. Both of the catalysts N (kl and 2) of the present invention have a high purification rate of 95 to 98% for HC and Co, and a high purification rate of 35 to 45% for NOx at 400°C.
%, and at 500°C, it shows a purification rate of 62-70%.

What should be noted in particular is that the catalyst of the present invention exhibits an extremely high purification rate for NOx compared to the comparative catalysts NllCl-C3.

As described above, it can be seen that the exhaust purification catalyst of the present invention is an excellent three-way catalyst.

Second Example A catalyst according to the present invention was prepared in the same manner as the catalyst 1 above, except that Pt Rh Cent was supported as the first catalyst layer and Cu-zeolite was supported as the second catalyst layer, and the purification activity was evaluated. Ta.

Preparation of the catalyst of the present invention (3.4): 100 parts of stabilized alumina and 14 parts of aluminum nitrate aqueous solution
A washcoat slurry was produced by ball milling the sample with water and nitric acid. And there is a cross-sectional area of 1 inch! Volume 35 containing approximately 400 channels per
A monolithic support of cc cordierite was soaked. Then, like the Nα1 catalyst, it was calcined at 700″C for 1 hour, and alumina with a thickness of about 25 μm was coated on the integrated carrier.

Note that the above stabilized alumina was produced as follows. That is, an aqueous solution of lanthanum nitrate was added to alumina powder with a surface area of 160 rrr/g.

Impregnation was carried out at a ratio such that the lanthanum content was 1.3 mo1% with respect to alumina. after that.

After drying this and removing moisture, the temperature is 600°C.
It was fired in 0 air for 3 hours to make the alumina contain lanthanum. Furthermore, the alumina was heated at 870°C9 in air for 3
Stabilized alumina was prepared by calcining for hours. The stabilized alumina was made into powder with an average particle size of 10 μm using a vibration mill, and was used for the coating described above.

Using the stabilized alumina-coated carrier, Ptl was applied as the first catalyst layer on the surface of the carrier in the same manner as in the case of the comparative catalyst Nα3.

5g/L, Rh0.3g/L, Ce0.0.3mof/
I held L once.

Next, zeolite was coated on the first catalyst layer in the same manner as the first catalyst. continue.

This material was immersed in a 0.02 mol/L copper acetate aqueous solution for 24 hours, and this operation was repeated twice to carry Cu on the zeolite through ion exchange. Cu at that time
The ion exchange rate was 98%. Further, the amount of Cu supported was 25 g/L with respect to the carrier.

As a result, the catalyst Nα3 according to the present invention having an ion exchange rate of 98% was prepared using Pt-Rh-Ce0□ as the first catalyst layer and Cu-zeolite as the second catalyst layer.

Further, the same conditions as above were used except that the concentration of the aqueous copper acetate solution was O, O1 mol/L, and the same as the Nα3 catalyst was used except that the Cu ion exchange rate was 70%.

Eleven catalysts Nα4 according to the invention were manufactured.

Preparation of comparative catalysts (NIIC4, N11C5): First, catalyst No. having only Cu and zeolite as catalyst components,
C4 was prepared. The catalyst No. C4 is.

When preparing Catalyst No. 3 according to the present invention, the surface of the cordierite integrated support was coated with zeolite without forming the first catalyst layer.

Next, Cu was supported. The condition is the N
The same is true for the α3 catalyst.

Next, in the preparation of catalyst No. 3 above, the steps of coating stabilized alumina and supporting Pt Rh'Ce0z, and the steps of supporting zeolite and Cu were performed in reverse order, and a comparative catalyst kC5 was prepared under the same conditions as above. did. 21
Contrary to the NαC3 catalyst according to the present invention, the kC5 catalyst has a catalyst layer made of zeolite and Cu on the cordierite integrated support, and further has stabilized alumina and PL-Rh-CeO on the catalyst layer. , and a catalyst layer consisting of the following.

Purification activity evaluation: The above catalyst was filled into an experimental converter, an exhaust model gas was introduced into it, and the purification activity was measured.

This model gas is 0.3%C0, 0,1%H2゜3.2
%02 1600p pmca Hb (THC(
Total hydrocarbons): l, 1200 ppm
It consists of NOx, 10% Co, 10% HzO, and the balance N. Moreover, this gas is under oxygen excess.

This corresponds to engine exhaust with an air-fuel ratio (A/F) of 1B.

The gas was then heated to 400°C and introduced into the converter. The space velocity GH5v in the catalyst is 10
It was 10,000/hour. The results are shown in Table 2.

As is clear from Table 2, the catalyst of the present invention exhibits superior purification activity even in the presence of excess oxygen, compared to the comparative catalyst.

In particular, the α3,4 catalyst of the present invention exhibits a high purification rate for NOx. In comparison, N11C4 has only CU and zeolite as catalyst components.

Although it shows a slightly higher purification rate for NOx, )IC.

CO purification rate is low. In addition, the first catalyst layer and the second catalyst layer of the present invention
The N (LC5 catalyst), which corresponds to a catalyst layer formed in reverse, shows a high purification rate for HC and Co, but it
It shows only a low purification rate for x.

As described above, it can be seen that the exhaust purification catalyst of the present invention is an excellent three-way catalyst.

Claims (8)

[Claims] (1) A catalyst for purifying hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas of an internal combustion engine, in which a first catalyst layer made of a catalyst component effective for oxidation reaction is provided on a carrier, and A catalyst for exhaust purification, characterized in that a second catalyst layer made of copper and zeolite is provided on the first catalyst layer. (2) The exhaust purification catalyst according to claim 1, wherein the first catalyst layer is a catalyst in which noble metal is supported on alumina. (3) The exhaust purification catalyst according to claim 1, wherein the second catalyst layer is a catalyst in which copper is ion-exchanged supported on zeolite. (4) The exhaust purification catalyst according to claim 1, wherein the first catalyst layer is a catalyst in which a rare earth oxide is supported on alumina. (5) Claim 2, characterized in that the noble metal is one or more of platinum, palladium, and rhodium.
Exhaust purification catalyst described in section. (6) The exhaust purification catalyst according to claim 4, wherein the rare earth oxide is lanthanum oxide or cerium oxide. (7) The exhaust purification catalyst according to claim 3, wherein the ion exchange rate of copper is 50 to 100%. (8) The exhaust purification catalyst according to claim 1, wherein the carrier is an integral carrier.