JPS63116742A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the lowering in purifying capacity at high temp., by supporting a catalystic metal by a supporting layer consisting of oxides of cerium, zirconium and lanthanum partially being a composite oxide or a solid solution. CONSTITUTION:A catalyst supporting layer containing cerium oxide, zirconium oxide and lanthanum oxide partially present at least as a composite oxide or a solid solution is formed to a carrier base material having a honeycomb form composed of activated alumina. A noble metal such as Pt, Rh, Pd, Ir, Ru or Os or a base metal such as Cr, Ni, V, Cu, Co or Mn is supported by said catalyst supporting layer to form a catalyst for purifying exhaust gas. This catalyst is excellent in oxygen storage capacity at high temp. and the detachment of the catalyst supporting layer from the carrier base material is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to the treatment of CO (-M carbonized carbon i>, HC (hydrocarbon), NOX ( This article relates to an exhaust gas purifying catalyst that removes and purifies nitrogen oxidation (85).

[Prior Art] Conventional catalysts for purifying exhaust gas from automobiles are generally known to consist of a catalyst support layer and a catalyst metal supported on the catalyst support layer. And for the purpose of efficient purification,
Various exhaust gas purifying catalysts have been developed.

For example, Japanese Patent Publication No. 59-41775, Japanese Patent Publication No. 59-906
No. 95 and Japanese Patent Publication No. 58-20307 disclose techniques using cerium.

In these exhaust gas purification catalysts, cerium exists as an oxide, releases or takes in oxygen (M storage capacity) through the reaction shown in equation (1), and regulates the oxidation reaction of CO and HC and the reduction reaction of NOX. This aims to improve purification efficiency.

Ce0ze-raCeOt-:t+hand02- (1) By the way, it is known that the reaction of the above formula (1) occurs on the surface of the cerium oxide particles. However, in the conventional exhaust gas purifying catalyst described above, when used at a high temperature of 800° C. or higher, the cerium oxide may grow grains and the surface area may decrease. Therefore, there was a problem in that the purification performance deteriorated due to a decrease in oxygen storage capacity.

In addition, with the goal of stabilizing activated alumina,
-7537, JP-A-48-18180, JP-A-61
-3531, USP30030201USP3951
No. 860, USP 4,170,573, etc., disclose a technique of simultaneously using cerium and other rare earths or transition metals. For example, in Japanese Patent Publication No. 60-7537, using cerium and lanthanum at the same time, a composite oxide C as shown in formula (2) was prepared.
e +-x-L ax Ot--7-(2)(0,3
≦Me≦0.5) is disclosed.

This exhaust gas purification catalyst has lattice defects with oxygen vacancies formed in the talcite-type structure of the composite oxide, thereby making the oxygen storage ability of cerium diluted durable. However, in this exhaust gas purification catalyst, lanthanum generates 1aAffiO3 at high temperatures and shrinks in volume. As a result, internal stress is generated in the alumina catalyst support layer, the bonding strength between the alumina catalyst support layer and the carrier base material is reduced, and the alumina catalyst support layer is shaved off.

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and aims to suppress the grain growth of cerium oxide under high temperatures while maintaining the purification performance, thereby reducing the deterioration of the purification performance. prevent and LaAλ
The present invention provides an exhaust gas purifying catalyst that prevents the generation of 03.

[Means for Solving the Problems] The exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst comprising a catalyst support layer and a catalytic metal supported on the catalyst support layer. It is characterized in that it contains cerium oxide, zirconium oxide, and lanthanum oxide, and at least a part of the cerium oxide, zirconium oxide, and lanthanum oxide exists as a composite oxide or a solid solution.

The catalyst supporting layer supports a catalytic metal, and for example, activated alumina, zirconia, titanium oxide, etc., which have a large specific surface area, can be used. Generally γ-alumina,
θ-alumina or the like is used. In addition, the catalyst support layer is
It may be used as it is, or a carrier base material may be used and a catalyst supporting layer may be formed on the surface of the carrier base material.

Note that the carrier base material may be the same as conventional carrier base materials, such as a honeycomb-shaped monolith carrier base material or a pellet-shaped carrier base material. Further, as the material of the carrier base material, known materials such as ceramics such as cordierite, mullai l-, alumina, magnesia, and spinel, or heat-resistant metals such as ferritic steel can be used.

The catalyst metal supported on the catalyst support layer is platinum (Pt
), rhodium (Rh), palladium (Pd), iridium (Ir), ruthenium (RU), osmium (Os>
precious metals such as chromium (Cr), nickel (N
+>, base metals such as vanadium (V), copper (Cu), cobalt (co), manganese (Mn), and the like as in the past can be used.

The greatest feature of the present invention is that the catalyst support layer contains cerium oxide, zirconium oxide, and lanthanum oxide, and at least a portion of the cerium oxide, zirconium oxide, and lanthanum oxide exists as a composite oxide or a solid solution. It's where you are.

Cerium oxide, as a single oxide, tends to grow grains, and according to research by the present inventors, when heated at 1000°C, grains grow to a diameter of 0.1
It is known that grains grow up to 1 degree μmP. Even if an attempt is made to purify CO by the reaction of equation (3) after heating at 1000°C, the reaction rate becomes almost zero, and l! It has also been found that the i-search storage capacity is significantly reduced.

C○1CeO2→ヱCO2+Ce○2−c −(3) Therefore, as a result of intensive research, the present inventors found that in a heat-treated product in which ceryllum oxide, zirconium oxide, and lanthanum oxide coexist, the The present invention was completed by discovering that it has excellent oxygen storage ability and prevents the catalyst support layer from falling off the carrier base material.

The composite oxide or solid solution referred to in the present invention is composed of at least a portion of cerium oxide, zirconium oxide, and lanthanum oxide. For example, a composite oxide or solid solution of cerium oxide and lanthanum oxide, a composite oxide or solid solution of zirconium oxide and lanthanum oxide, a composite oxide or solid solution of cerium oxide, zirconium oxide, and lanthanum oxide, each alone or as a composite mixture. can do. Each oxide may be contained alone together with these composite oxides or solid solutions.

The present inventors added lanthanum nitrate alone, a mixture of lanthanum nitrate and cerium nitrate, a mixture of lanthanum nitrate and zirconium oxynitrate, and a mixture of lanthanum nitrate, cerium nitrate, and zirconium oxynitrate to the θ-alumina powder as aqueous solutions. It was impregnated and heat treated in air at varying temperatures for 5 hours. Thereafter, LaA1O3 was identified for each by X-ray diffraction method. The result is the first
As shown in the figure. In FIG. 1, the vertical axis shows the xg;+ diffraction intensity ratio of LaA1O3 based on θ-alumina, and the horizontal axis shows the heat treatment temperature.

As shown in Figure 1, LaAffio3 is produced from about 800 to 900°C in lanthanum alone and in a lanthanum-cerium mixed system, but in a lanthanum-cerium-zirconium mixed system, even when heated to 1100°C, 1aAJ! It can be seen that 03 is hardly generated.

Therefore, it is desirable to use a lanthanum-cerium-zirconium mixed oxide or solid solution.

To form a composite oxide or solid solution containing at least a portion of cerium oxide, zirconium oxide, and lanthanum oxide in the catalyst support layer, an aqueous solution of cerium salt, zirconium salt, and lanthanum salt is added to the catalyst simultaneously or separately. This can be done by impregnating the support layer and firing at a temperature of 600° C. or higher. In addition, an oxide of at least one of cerium, zirconium, and lanthanum is used, and after mixing with activated alumina powder during formation of the catalyst support layer, 8oO
It can also be carried out by firing at a temperature of .degree. C. or higher.

If the temperature is lower than these values, it is difficult to form a compound oxide or a solid solution, grain growth of cerium oxide is likely to occur, and LaAffi○3 is likely to be formed.

Note that the cerium oxide, zirconium oxide, and lanthanum oxide may be contained inside the catalyst support layer, or may be supported on the surface of the catalyst support layer. In particular, if it is present on the supporting layer:& surface, it will have an extremely excellent purification performance and can reliably prevent the formation of LaAlO3.

In addition, the ratio of cerium, zirconium, and lanthanum is not particularly limited, but cerium oxide, zirconium oxide, and lanthanum oxide have a ratio of 5 to 100 zirconium atoms and 5 to 5 lanthanum atoms per 100 cerium atoms. It is preferable to configure the atomic ratio to be 150 atoms.

In the above atomic ratio, if the number of zirconium atoms is less than 5 atoms, grain growth tends to occur in cerium oxide, and L
aAlO3 becomes easier to generate. Also, when the number of zirconium atoms exceeds 100 atoms, the number of cerium atoms decreases relatively, and based on formula (1), the oxygen storage capacity becomes insufficient and the purification performance decreases.When the number of lanthanum atoms decreases below 5 atoms, Oxygen storage capacity is reduced due to lattice defects with oxygen vacancies in the crystal structure of the composite oxide, and alumina grain growth is likely to occur.Also, when the number exceeds 150 atoms, the number of cerium atoms becomes relatively small, and the equation (1) The oxygen storage capacity based on the

[Operations and Effects of the Invention] In the exhaust gas purifying catalyst of the present invention, the catalyst supporting layer contains cerium oxide, zirconium oxide, and lanthanum oxide, and at least one of cerium oxide, zirconium oxide, and lanthanum oxide. part exists as a composite oxide or a solid solution.

Although the mechanism is not yet clear, grain growth of cerium oxide is suppressed by its presence as a composite oxide or solid solution. Since the structure of the composite oxide crystal has lattice defects with oxygen vacancies, oxygen movement within the crystal is very easy and the oxygen storage capacity is very high. Furthermore, since these composite oxides are difficult to grow grains, their purification performance remains high even when used at high temperatures.

Furthermore, the formation of LaAλ03 is prevented, and a suitable amount of lanthanum atoms penetrate into the alumina particles, thereby suppressing alumina grain growth.

That is, according to the exhaust gas purifying catalyst of the present invention, since oxygen movement within the crystal structure is easy, the oxygen storage capacity is high and the catalyst performance is excellent. Since grain growth of cerium oxide is suppressed when used at high temperatures, the surface area of cerium oxide itself can maintain a sufficiently large value. Therefore, there is no problem such as a decrease in the oxygen storage capacity of cerium oxide, and the purification performance can be maintained at a high level over a long period of time.

Further, since volumetric shrinkage due to the formation of LaAio3 is prevented, internal stress is prevented from being generated in the catalyst support layer, and it is possible to prevent the catalyst support layer from falling sharply from the carrier base material.

[Example] This will be explained in detail below using examples.

(Example 1, Comparative Example 1) 00 g of alumina silua with an alumina content of 10 wt%,
1000 g of alumina powder and 300 g of distilled water were mixed and stirred to prepare a slurry.

A honeycomb-shaped monolithic catalyst carrier base material made of cordierite was immersed in this slurry for 1 minute, then pulled out, the slurry inside the cell was blown away by an air stream, and the base material was heated at 150"C for 1 minute.
After drying for an hour, it was baked at 7°C for 2 hours. This operation 2
This was repeated several times to form a catalyst support layer made of activated alumina.

Next, nitrate (ce (NO3) 3)
is 0°05mol/λ, zirconium oxynitrate (Zr
O(No3)2) was 0.15mol/1 and lanthanum nitrate (La(NO3)3) was O,Q5m.

The long monolithic carrier material on which the catalyst supporting layer was formed was immersed in a mixed aqueous solution containing 1/λ for 1 minute, then pulled up, the excess water was blown off, and after drying at 200°C for 3 hours, it was heated to 600"C.
It was baked for 5 hours. As a result, a monolith carrier base material (A) having a catalyst support layer containing cerium oxide, zirconium oxide, and lanthanum oxide was obtained.

In addition, a monolithic carrier base material containing cerium oxide, zirconium oxide, and lanthanum oxide at the values shown in Table 1 was prepared in the same manner except that mixed aqueous solutions with different concentrations of cerium nitrate, oxy61'lJM zirconium, and lanthanum nitrate were used. (B-E) is 19. In addition, the monolith carrier base material (F) was immersed in the same manner except that it was immersed only in an aqueous solution containing 0.3 mol/ffi of cerium nitrate, and 0.3 m of cerium nitrate was immersed without using an aqueous solution of zirconium oxynitrate.
A monolith carrier base material (G) was obtained in the same manner except that it was immersed in a mixed aqueous solution containing 0.2 mol/1 of lanthanum nitrate and lanthanum nitrate.

Next, catalyst metals shown in Table 1 were supported on each of these monolith carrier base materials (A-G). In order to support the catalytic metal, the carrier base material is immersed in distilled water to absorb sufficient water, then pulled out and the excess moisture is blown off.For platinum, it is immersed in an aqueous solution containing dinitrodiammine platinum for 1 hour.
Rhodium is similarly immersed in an aqueous solution containing rhodium chloride,
Palladium was similarly immersed in an aqueous solution containing palladium chloride, pulled up, blown off excess moisture, and dried at 200°C for 1 hour to obtain platinum < Pt).
, rhodium (Rh) and palladium (Pd) were supported to form a catalyst, and the exhaust gas purifying catalyst of Examples 1a to 1e and Comparative Examples 1a and 1b shown in Table 1 was prepared as No. 19.

(For each exhaust gas purification catalyst, 3
Attached to the exhaust system of a λ inline 6-cylinder engine, the air-fuel ratio (Δ/
A 200-hour durability test was conducted under the conditions of F) of 14.6 and an inlet gas temperature of 850°C. Then, for each catalyst in the durability test, using the same engine as in the durability test,
= 1'1.6, 1-tc under the condition of large gas temperature 400℃
The purification rate of XCo and NOx was measured.

In addition, for each exhaust gas purification catalyst, a gas burner was used to bring the large gas temperature to 1000°C.
A time durability test was conducted. Then, the degree of shedding of the catalyst support layer was determined from the difference in dosage before and after the durability test.

Furthermore, the carrier base material after being heated at 100° C. for 100 hours was pulverized, and the particle size of cerium oxide was measured by Xa diffraction method. These results are also shown in Table 1.

(Example 2, Comparative Example 2) 1 g of γ-alumina granular carrier (manufactured by Yakitori Universal Co., Ltd.) with SET surface v4100 to 150 m2/(J and average pore diameter of 300 to 100 angstroms) was prepared with the following exceptions: a1 degree. were immersed in the same mixed aqueous solution as in Example 1 and Comparative Example 1, dried and fired in the same manner.Next, each granular carrier was ground to an average particle size of 7 μm using a vibration mill.Then, each of the obtained 1 part of 100mff powder, 30 parts by weight of an aqueous solution containing 40 wt% of aluminum !il'i acid, and 100 parts by weight of water were mixed and milled for 1 hour to prepare each slurry. A catalyst support layer is formed on the same honeycomb carrier as in Example 1 by the same method, and if necessary, the mixed aqueous solution is sprayed onto the catalyst support layer to impregnate it to adjust cerium, zirconium, and lanthanum. fM@1a~
10 and Comparative Examples 18 to 1b, the second
The exhaust gas purifying catalysts of Examples 2a to 2e and Comparative Examples 2a to 2b shown in the table are No. 19.

The obtained exhaust gas purifying catalyst was subjected to the same test as in Example 1, and the results are shown in Table 2.

(Example 3, Comparative Example 3) 1q of activated alumina powder obtained by crushing the granular carrier used in Example 2 above, zirconium oxide powder, lanthanum carbonate powder, and water were mixed in the mixing ratio shown in Table 3. The mixture was mixed to form a slurry, and a honeycomb carrier similar to that in Example 1 was immersed, dried, and fired in the same manner as in Example 1 to form a catalyst support layer containing zirconium oxide, lanthanum oxide, and a composite oxide or solid solution of both. After each carrier was impregnated with cerium nitrate aqueous solution at two concentrations, it was fired in the same manner as in Example 1 to support the catalyst metal, thereby obtaining the exhaust gas purifying catalysts of Examples 3a to 3b shown in Table 3. Ta. Note that in Comparative Example 3, only activated alumina powder was used in the slurry.

The obtained exhaust gas purifying catalyst was subjected to the same catalyst support layer shedding test as in Example 1, and the results are shown in Table 3.

<Example 4, Comparative Example 4> Except that cerium carbonate powder was used instead of zirconium oxide powder, zirconium oxychloride was used instead of cerium nitrate, and ferrite-based full bending material containing aluminum was used as the material of the honeycomb carrier. Exhaust gas purifying catalysts of Examples 48 to 4b and Comparative Examples 48 to 4b shown in Table 3 were obtained in the same manner as in Example 3 and Comparative Example 3.

(The thus obtained exhaust gas purifying catalyst was subjected to the same catalyst carrier shedding test as in Example 1, and the results are shown in Table 3.

(Evaluation) It is clear from each table that all Examples are superior in purification rate compared to Comparative Examples. It is clear that this is due to the effect that cerium oxide, zirconium oxide, and lanthanum oxide coexist at least in part as a composite oxide or solid solution in the exhaust gas purifying catalyst of the example.

In addition, in the exhaust gas purifying catalyst of the example, there is almost no particle growth of cerium oxide, and the particle size is 11 to 13 nm, which is significantly smaller than the 120 to 150 nm of the comparative example. This maintains a high oxygen storage capacity and contributes to improving the purification rate. The exhaust gas purifying catalyst of the example also showed extremely excellent results in the catalyst support layer shedding test, and has extremely excellent durability under high temperatures.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment temperature and X-ray diffraction intensity ratio indicating the amount of LaAlO3 produced. Patent applicant Toyota Motor Corporation Toyota Central Research Institute Co., Ltd. Representative Patent attorney Hiroshi Okawa Figure 1 (0C)

Claims (2)

[Claims] (1) In an exhaust gas purifying catalyst comprising a catalyst support layer and a catalyst metal supported on the catalyst support layer, the catalyst support layer contains cerium oxide, zirconium oxide, and lanthanum oxide; A catalyst for exhaust gas purification, characterized in that at least a portion of the cerium oxide, the zirconium oxide, and the lanthanum oxide exist as a composite oxide or a solid solution. (2) A patent in which cerium, zirconium, and lanthanum supported as oxides are configured such that the atomic ratio is 5 to 100 atoms of zirconium atoms and 5 to 150 atoms of lanthanum atoms to 100 atoms of cerium atoms. The exhaust gas purifying catalyst according to claim 1.