JPS62282642A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the sintering of Pd in a high-temp. reducing atmosphere and to prevent the deterioration of the catalyst by depositing Pd on the catalyst as the perovskite type composite oxide or its equivalent in the catalyst contg. at least Pd. CONSTITUTION:A monolithic carrier base material with an alumina coat layer is dipped in an aq. soln. of neodymium nitrate, palladium nitrate, cerium nitrate, etc., dried, and baked to form the perovskite type composite oxide of Pd on the alumina coat layer. The material, is then dipped in an aq. soln. of dinitrodiammine platinum, and then dried to obtain the catalyst. The highly active catalyst for purifying the exhaust gas from an internal combustion engine exhibiting sufficiently the characteristic of Pd, having the oxidation-reduction action of the perovskite type composite oxide, and wherein the interaction between Pd and Pt is reduced can be obtained in this way. Besides, the perovskite type structure is expressed by the general formula ABO3 (A is Nd, La, Ca, etc., and B is Pd, etc.), and a perovskite-like structure, etc., such as an ilumenite structure can exemplified as the equivalent.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an exhaust gas purification catalyst that purifies exhaust gas discharged from an internal combustion engine.

[Conventional technology]

Conventionally, Co contained in automobile exhaust gas, )IC1
Catalysts carrying noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) singly or in combination are widely used as effective components for simultaneously removing harmful components such as NOx. However, since catalysts such as PL and Rh are expensive, the use of Pd, which is more affordable, has been promoted in recent years.

For example, in Japanese Patent Application Laid-open No. 58-146441, Pd
A catalyst that has both the characteristics of a Pt-Rh-based catalyst and the characteristics of a Pt-Rh-based catalyst has two separate layers: a Pd-containing alumina layer and a Pt-Rh or Rh-containing alumina layer on a honeycomb-shaped catalyst carrier. A catalyst for purifying exhaust gas formed as a layer is disclosed.

JP-A No. 59-162948 discloses that a perovskite-type composite oxide and a rare earth 14 fa with 02 storage properties are coated on the surface.
The catalyst carrier provided with the layer containing Pd or Pd
An exhaust gas purifying catalyst is disclosed in which catalyst components include 1 and other precious metals.

JP-A-60-241933 discloses a carrier having an activated alumina layer containing ceria on the surface of a monolith carrier base material and an activated alumina layer containing a perovskite type composite oxide of ceria and a-Rh on this layer. , discloses an exhaust gas purifying catalyst on which platinum is supported.

[Problem that the invention seeks to solve]

However, Pd has the disadvantage that it is sintered in a reducing atmosphere at high temperatures and its activity is significantly degraded. In addition, Pd is
It is known that when coexisting with pt or Rh, they form an alloy and lose their catalytic action [Reference Journal Ca
57185 (197B)).

In the exhaust gas purification catalyst disclosed in JP-A-58-146441, even though the alumina layer of the Pd-based catalyst and the alumina layer of the Pt-Rh-based catalyst are separate layers, a reaction occurs between the Pd and pt-Rh between the two layers. However, since alloying cannot be completely prevented,
It cannot be said that the above problems have been fully solved yet.

The catalyst for exhaust gas purification disclosed in JP-A-59-162948 forms a catalyst layer containing Pd on the surface of the catalyst carrier even though the surface of the catalyst carrier is made of perovskite-type composite oxide. alloying with the metal occurs, and alloying within the catalyst layer cannot be satisfactorily resolved.

The exhaust gas purifying catalyst disclosed in JP-A No. 60-241933 does not contain Pd, and the carrier is formed of a perovskite-type composite oxide, and the PT of the catalyst itself is not a perovskite-type composite oxide. It cannot form the basis of the present invention described later.

The present invention prevents deterioration of the catalyst by preventing sintering of Pd in a catalyst containing at least Pd in a high-temperature reducing atmosphere, and also reduces the interaction between Pd and pt or Rh to improve the purification performance of the catalyst. The purpose of the present invention is to provide a highly active exhaust gas purification catalyst that maintains the following properties.

[Means for solving problems]

The exhaust gas purification catalyst of the present invention that meets this objective is an exhaust gas purification catalyst containing at least Pd as a catalyst component, in which the Pd is supported as a perovskite-type composite oxide or an equivalent to the composite oxide. consists of things.

The perovskite type composite oxide is represented by the general formula ABO3. The perovskite-type composite oxide used in the present invention contains Nd −, La, and Ce% in the A-site ion.
Rare earth elements such as P, Sn, Eu or Mg, C
Alkaline earth metals such as a, Sr, and Ba can be used alone or in combination. As the B site ion, Pd alone may be used, Pd and Ce may be used, or a transition metal may be doped.

In the present invention, equivalents of perovskite complex oxides include ilmenite type, BaNiOz type, K□N
So-called perovskite-like structures, such as the tFa type, are similar to humans, and I have a million-type bridge.

[Effect]

In the above catalyst, Pd, Ce (B site ion), and Nd (A site ion) are allowed to form a perovskite-type composite oxide once in a waiting state. Due to this,
Sintering of Pd in a reducing atmosphere is prevented, and Pd, Ce, and Nd
By distributing perovskite type composite oxide on the surface of the coating layer, the characteristics of Pd can be fully exhibited, and the perovskite type composite oxide itself has redox action Nd (Pd”°, , Ce”°25 -zxce"o,
5-zJ, zx) Os-J +II N! ↑=
Nd(Pd”e, sce”zJce”a, 5-zJ)O
*-J+xoztNd(Pd"a, sCe"z5
*H+Ce ”o, 5-is-zx)Oz-5-
x + XCO2↑−X O.

Nd(Pd"6.5Ce'°!5 Ce"o, 5-z5
) (h4 and oxygen storage effect Nd (Pd ``o, sCe''zJ +z*Ce'°
o, s-*J-z++) (h-J-x■ □×02: Nd(Pd"°o, sce"zs Ce'°
o, 5-zJ) Off4□×O1: Nd(Pd"o, scego°zJ-zxce"
o, s-zJ, tx) Os-1i+y can also be exhibited.

〔Example〕

Next, the present invention will be explained in further detail using the following examples.

Example 1 A slurry was prepared by adding 300 g of ion-exchanged water and 1000 g of alumina powder to 00 g of alumina silica with an alumina content of 10 w (%). After blowing off the slurry inside the cell with an air stream and drying at 150°C for 1 hour,
It was baked at 0°C for 2 hours. This operation was repeated twice to form an alumina coat layer. Next, neodymium nitrate, palladium nitrate, and cerium nitrate are mixed in a molar ratio of 2=1:l, and ion-exchanged water is added to form an aqueous solution. The monolith carrier base material on which the alumina coat layer was formed was immersed in this aqueous solution, pulled up, blown off excess water, dried at 150°C for 1 hour, and then fired at 700°C for 2 hours to form a Pd perovskite. A type composite oxide was formed on the alumina coat layer. Next, it was immersed in a dinitrodiammine platinum aqueous solution for 1 hour, then taken out, the excess water was blown off, and the mixture was heated at 150°C for 1 hour.
After drying for several hours, an exhaust gas purifying catalyst 1 as shown in FIG. 1 was obtained. In addition, at this time, Pt, Pd, Nd,
The Ce and La contents were as shown in Table 1 (shown later).

In FIG. 1, 1 is a catalyst for exhaust gas purification, and 2 is a base material for a monolith carrier (not shown), which is usually made of cordierite.
The alumina coat layer supporting the catalyst l formed thereon is shown. The alumina coat layer 2 contains P as a catalyst component.
d perovskite-type composite oxide or an equivalent to the composite oxide (in this figure, Pd perovskite-type composite oxide 3)
) and Pt4! It is carried.

In Example 1, Pd is supported as the perovskite-type composite oxide 3 or an equivalent to the composite oxide, so sintering of Pd that occurs in a reducing atmosphere at high temperatures is avoided and the activity of Pd is increased. At the same time, the durability of the catalyst is improved.

In Example 1, as shown in FIG. 1, both Pd and Pt4 are supported on the alumina coat layer of the carrier formed on the monolithic carrier base material (not shown), but Pd is a perovskite-type composite oxide. Since the compound 3 or the compound oxide is equivalent to the compound oxide (perovskite compound oxide 3 in the figure), there is no interaction between Pd and Pt4, and the purification performance is maintained.

Example 2 A perovskite-type composite oxide of Pd was formed in the aluna coat layer by the same operation as in Example 1. Next, add alumina to 00g of alumina powder at a rate of 10-(%).
Add 000g 1. 300 g of ion-exchanged water was added and stirred to form a slurry. A cordierite award monolith carrier substrate with a Pd complex oxide formed as an alumina coat layer was immersed in this slurry for 1 minute, then pulled out, the slurry inside the cell was blown away by an air stream, and then dried at 150°C for 1 hour. It was baked at 700°C for 2 hours. Thereafter, it was immersed in a dinitrodiammine platinum aqueous solution for 1 hour, pulled up and blown off with an air flow to remove excess moisture, and dried at 150° C. for 1 hour to obtain an exhaust gas purifying catalyst 5 as shown in FIG. 2.

In Example 2, a perovskite-type composite oxide of Pd or a substance equivalent to the perovskite-type composite oxide (in this figure, a perovskite-type composite oxide of Pd 7 ) is carried,
A layer of Pt6 is formed on the alumina coat layer as a separate layer. Specifically, as shown in FIG. 2, the catalyst layer consists of a Pd perovskite-type composite oxide 7 as a lower layer.
It consists of an alumina coat layer 8 carrying Pt and an upper layer 719 made of Pt6.

In Example 2, Pd is formed into a perovskite type composite oxide. Moreover, since the perovskite-type composite oxides 7 of Pt6 and Pd are formed as separate N8.9, the interaction between Pt6 and Pd becomes more intense than in Example 1, and the purification performance is improved. .Other operations are the same as in Example 1.

Example 3 Neodymium nitrate, palladium nitrate, cerium nitrate in 2:
They were mixed at a molar ratio of 1:1, and ion-exchanged water was added to form an aqueous solution. This aqueous solution was evaporated to dryness and fired at 700° C. for 2 hours to form a Pd composite oxide. The Pd complex oxide was confirmed to have a perovskite structure by X-ray diffraction measurement. This perovskite-type composite oxide of Pd is powdered, and the composite oxide has an amount of Pd sufficient to develop the catalytic effect as an exhaust gas purification catalyst, 1000 g of alumina powder, 00 g of alumina silua with an alumina content of 10 wt%, and W distilled water. 300 g was added and stirred thoroughly to prepare a slurry.

The base material for a monolithic carrier was immersed in this slurry for 1 minute and then pulled out, the excess slurry inside the cells was blown off with an air stream, and the material was dried at 150°C for 1 hour and then fired at 700°C for 2 hours. Next, it was immersed in a dinitrodiammine platinum aqueous solution for 1 hour, pulled out, blown off the excess moisture, and dried at 150°C for 1 hour to obtain the exhaust gas purification catalyst lO shown in Figure 36. The structure of the exhaust gas purifying catalyst 10 of Example 3 shown and the structure of the exhaust gas purifying catalyst 1 of Example 1 shown in FIG. 1 have the same or similar appearance in the final product. However, the catalyst 1 of Example 1 was prepared by impregnating Pd ions, Ce ions, and Nd ions in the pre-formed alumina coat layer, taking it out and calcining it in the alumina coat layer.
In contrast to the perovskite-type composite oxide 3 of Example 3 formed in the alumina coat layer 2, the exhaust gas purifying catalyst 10 of Example 3 has a Pd perovskite-type composite oxide 11 prepared in advance, and then Alumina and Pt13 are mixed and supported on the alumina coat layer 12.

In the exhaust gas purification catalyst 10 of Example 3, Pd is a perovskite-type composite oxide or an equivalent to a cough composite oxide (in this figure, a perovskite-type composite oxide of Pd 11).
Therefore, Pd is added to the same alumina coat layer 12.
Even if Pd and ptt3 coexist, the interaction between Pd and PT4 disappears, and the purification performance is maintained.

Moreover, in Example 3, unlike in Example 1, in which Pd is made into a perovskite-type composite oxide in the catalyst preparation process, Pd is made into a perovskite-type composite oxide in advance and then coated with alumina. Since it is supported on the layer, the conversion into a perovskite-type composite oxide is more complete than in Example 1, and a good exhaust gas purification catalyst in which interaction between Pd and pt is less likely to occur can be obtained.

Example 4 After a perovskite-type composite oxide of Pd was generated in advance according to the procedure shown in Example 3, the perovskite-type composite oxide of Pd was contained in an alumina coat layer. Next, add alumina at a rate of 1 (ht%) to 00g of alumina,
1000 g of alumina powder and 300 g of ion-exchanged water were added and stirred to form a slurry. A monolithic body substrate containing a perovskite-type composite oxide of Pd in an alumina coat layer was immersed in this slurry for 1 minute, then pulled up and the slurry inside the cell was blown away by an air flow, and then dried at 150°C for 1 hour. It was baked at °C for 2 hours. Thereafter, it was immersed in a dinitrodiammine platinum aqueous solution for 1 hour, pulled up and blown off with an air flow to remove excess water, and dried at 150° C. for 1 hour to obtain an exhaust gas purifying catalyst 15 as shown in FIG. 4.

In Example 4, as shown in FIG. 4, an alumina coat layer 18 containing a perovskite-type composite oxide 17 of Pcl as a lower layer was formed on a monolithic base material (not shown);
An alumina coat layer 19 containing PTT6 is formed as an upper layer, and layers 18 and 19 are formed as separate layers.

In Example 4, Pd is formed into a perovskite-type composite oxide, and the Pd perovskite-type composite oxide 1
7 and Pt16 are each separate alumina coat layer X8.19
By forming Pt16 as Pt16, interaction between Pt16 and Pa becomes less likely to occur, and the purifying effect is further maintained. Furthermore, in Example 4, Pd is completely converted into a perovskite-type composite oxide in advance, and then the alumina coat layer 18
Compared to Examples 1 to 3, the most Pd
The interaction between Pt and Pt becomes less likely to occur.

Furthermore, in order to compare the above embodiment of the present invention with a conventional example, the following comparative example was prepared.

Comparative Example 1 700 g of alumina powder with an alumina content of 10-1%, 1000 g of alumina powder, 300 g of ion-exchanged water, and further neodymium oxide and cerium oxide were added in a molar ratio of 2=1, and the mixture was mixed and stirred to form a slurry. The base material for the monolithic body (monolith) is immersed in this slurry for 1 minute, then pulled up and the slurry inside the cell is blown away by an air flow, dried at 150°C for 1 hour, and then fired at 700°C for 2 hours to produce alumina containing Nd and Ce. A coat layer was formed. Then soaked in palladium chloride aqueous solution for 1 hour? Dry 1L at 150℃ for 1 hour to obtain Pd,
An alumina coat layer containing Nd, Ce in a molar ratio of 1:2+1 was formed. Next, it was immersed in a dinitrodiammine platinum aqueous solution for 1 hour and dried at 150°C for 1 hour.
An exhaust gas purifying catalyst 20 as shown in the figure was obtained. 21 is a mixture 22 of Nd and Ce and a mixture 23 of Pd and pt.
Pd does not form a perovskite-type composite oxide.

Comparative Example 2 According to the procedure shown in Comparative Example 1, Pd, Nd, and Ce were added to 1
: An alumina coat layer was formed containing alumina at a molar ratio of 2:1. Alumina Silua 00g with alumina content IQwt%
, 300 g of ion-exchanged water, and 1000 g of alumina powder were mixed and stirred to form a slurry. A base material for a monolithic carrier on which an alumina coat layer containing Pd and Nd5Ce at a molar ratio of 1:2:l was formed in the same manner as in Comparative Example 1 was immersed in this slurry for 1 minute, and then pulled up and the inside of the cell was removed by an air flow. After blowing off the slurry and drying it at 150℃ for 1 hour,
It was baked at ℃ for 2 hours. Next, dinitrodiammine platinum water i8? f1. The catalyst was immersed in water for 1 hour and dried at 150° C. for 1 hour to obtain an exhaust gas purifying catalyst 25 as shown in FIG. Reference numeral 26 indicates an alumina coat layer containing a compound of Pd, Nd, and Ce as a lower layer, and 27 indicates an alumina coat layer containing PT as an upper layer. Pd is not a perovskite type composite oxide. This example is from JP-A-58
．． This corresponds to the catalyst of No.-146441.

The above Examples 1 to 4 and Comparative Examples 1 and 2 are as follows.

These six types of catalysts were subjected to durability tests and their purification performance was evaluated using the following method. The durability test was conducted by installing a catalyst in the exhaust system of a 6-cylinder 2800cc engine, with an air-fuel ratio A/F #16.0 and a space velocity S, V = 60.0.
00'Ar-', catalyst bed temperature 800°C. To accelerate deterioration due to poisoning, drop 30cc of engine oil into the engine intake system per hour and use 0.05g of fuel.
/tt of lead-containing gasoline was used.

Catalyst evaluation: GO2%, C3H5200ppm, C
l3800ppm, Oz2%, CO210%, 8.01
0% and the remaining N2 was passed through each catalyst at sv = 56750 'Ar-', and the purification rate of Co and IIc was measured. The measurement results are shown in FIGS. 7 and 8.

From FIG. 7 and FIG. 8, exhaust gas purifying catalysts a, b, c of Examples 1 to 4 in which Pd is supported as a perovskite-type composite oxide or an equivalent to the composite oxide,
d (a, b, , c, d are respectively Example 1.2.3.
4) are exhaust gas purification catalysts e of Comparative Examples 1 and 2 which are not made into perovskite-type composite oxides,
It can be seen that the catalyst exhibits higher activity than conventional catalysts at low temperatures compared to r, and high performance is obtained even at high temperatures, and that an improvement has been made in exhaust gas purification catalysts in which Pd and pt coexist.

The catalyst for exhaust gas purification with high activity and excellent durability was obtained by supporting Pd as a perovskite-type composite oxide with Nd and Ce or an equivalent to the composite oxide, thereby eliminating the causes of Pd deterioration. This is because the interaction between Pd and pt was eliminated, and the decrease in activity due to sintering of Pd in a reducing atmosphere at high temperatures was eliminated. moreover,
According to these examples, by supporting Pd as a perovskite-type composite oxide, the porosity of the perovskite-type composite oxide is added to the exhaust gas purifying catalyst, and the pore volume is increased, so that the support is Since a larger surface area can be obtained, a catalyst for purifying exhaust gas with higher performance can be obtained.

In the results of the durability tests shown in FIGS. 7 and 8, the exhaust gas purification catalysts a and b obtained in the first to fourth examples
, c, and d were not found because all of the exhaust gas purification catalysts a, b, c, and d of each example supported Pd as a perovskite-type composite oxide. This is presumably because the interaction between Pd and pt is eliminated and no influence is exerted between them.

Furthermore, the oxygen storage effect as described in the above action can be developed.

[Effects of the Invention] - Therefore, when using the exhaust gas purification catalyst of the present invention, by supporting Pd as a perovskite-type composite oxide and the composite oxide, the interaction between Pd and pt can be eliminated, and the interaction between Pd and pt can be eliminated. Performance degradation due to sintering in a high temperature reducing atmosphere can also be eliminated.

In addition, the redox effect and oxygen storage effect of the perovskite structure itself are added, making it possible to obtain a highly durable and highly active catalyst.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an exhaust gas purification catalyst according to Example 1 of the present invention, FIG. 2 is a configuration diagram of an exhaust gas purification catalyst according to Example 2 of the present invention, and FIG. 3 is a configuration diagram of an exhaust gas purification catalyst according to Example 2 of the present invention. FIG. 4 is a configuration diagram of an exhaust gas purification catalyst according to Example 3, FIG. 5 is a configuration diagram of an exhaust gas purification catalyst according to Example 4 of the present invention, and FIG. 5 is a configuration diagram of an exhaust gas purification catalyst according to FIGS. Figure 6 is a configuration diagram of an exhaust gas purification catalyst according to Comparative Example 1, which is different from Figure 5, and Figure 7 is a diagram showing the configuration of an exhaust gas purification catalyst according to Comparative Example 2. Characteristic diagram showing the CO activity of the exhaust gas purification catalysts of Example 4 and Comparative Example 1.2. Figure 8 shows the IIc activity of the exhaust gas purification catalysts of Examples 1 to 4 and Comparative Example 1.2. The characteristic diagram is . 1.5.10.15...tB output gas purification catalyst 3.7
．． 11.17... Perovskite type composite oxide of Pd Patent Applicant Toyota Motor Corporation Figure 3 1o Exhaust gas purification catalyst HHPd perovskite type composite oxide Figure 2 Figure 4 Figure 17 Perovskite type composite oxide of Pd Figure 5 Figure 6

Claims (1)

[Claims] (1) An exhaust gas purifying catalyst containing at least Pd as a catalyst component, characterized in that the Pd is supported as a perovskite type composite oxide or an equivalent to the composite oxide.