JPS62277150A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain the title catalyst having high durability and purifying property by depositing a perovskite(-like) composite oxide of at least platinum and a lanthanoide element or an alkaline-earth metal on a catalyst carrier. CONSTITUTION:The perovskite-like composite oxide expressed by the general formula ABO3 (A is a lanthanoide element or an element selected from alkaline- earth metals, and B is platinum or a mixture of platinum and a transition metal) or the perovskite-like composite oxide shown by K2NiF4, etc., is deposited on the catalyst carrier to obtain the catalyst for purifying exhaust gas. In this case, the catalyst carrier layer is firstly formed on the surface of the carrier base material, and then the composite oxide is deposited on the carrier layer. Consequently, the platinum is capable of sufficiently exhibiting its SV (space velocity) characteristic.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a catalyst for purifying exhaust gas of internal combustion engines, such as automobiles. By supporting it on a catalyst carrier,
J: In addition to exhibiting an excellent purification effect, it also prevents thermal deterioration and alloying of platinum, thereby promoting an exhaust gas purification catalyst with high durability and purification performance.

[Prior Art] Generally, a catalyst for purifying automobile exhaust gas is composed of a catalyst carrier and a catalyst component supported on the catalyst carrier. Precious metals such as platinum, palladium, and rhodium are used alone or in combination as catalyst components.

However, these precious metals, especially rhodium, are not abundant in resources and are also expensive. Furthermore, although palladium has superior heat resistance compared to platinum, it is significantly inferior in poison resistance to lead in gasoline and phosphorus in lubricating oil. For this reason, CO (-carbon oxide) in exhaust gas,
As a three-way catalyst for the purpose of oxidizing HC (hydrocarbons) and reducing NOx (nitrogen oxides), platinum is an essential component since it has more resources than rhodium.

However, since platinum is oxidized and sintered in a high-temperature oxygen atmosphere, its activation as a catalyst component is significantly reduced. Furthermore, when platinum and palladium coexist, they form an alloy with a low melting point and are deactivated.

One way to prevent the thermal deterioration of catalyst components that occurs at high temperatures in conventional monolithic exhaust gas purification catalysts is to mix rhodium-supported lanthanide oxide powder and platinum-supported alumina powder. A method for producing a monolithic catalyst is known in which a slurry is formed, a carrier base material is immersed in the slurry, the slurry is applied thereto, and the monolithic catalyst is dried and fired (Japanese Patent Laid-Open No. 19037/1983).

This is an attempt to prevent the formation of Rh2Q3, which is a cause of thermal deterioration, by supporting rhodium on lanthanide oxide, which affects oxygen storage capacity, and furthermore, to prevent the formation of a solid solution of rhodium and alumina. .

[Problem to be Solved by the Invention 1] However, the effects of the above-mentioned conventional exhaust gas purification catalysts on exhaust gas purification are still not sufficient.

The present invention aims not only to simply prevent thermal deterioration of catalyst components as described above, but also to provide an exhaust gas purifying catalyst that has superior purification performance.

[Means for Solving the Problems] The exhaust gas purifying catalyst of the present invention comprises a catalyst carrier and a catalyst component supported on the catalyst carrier, and the catalyst component is a perovskite containing at least a lanthanide element or an alkaline earth metal. It is characterized by being a type composite oxide or a similar composite oxide.

The catalyst carrier can be formed from a catalyst carrier base material and a support layer formed on the surface of the base material. This catalyst carrier base material may be the same as conventional catalyst carrier base materials, such as a honeycomb-shaped monolith carrier base material or a pellet-shaped carrier base material. In addition, the material of the carrier base material is cordierite, Murai 1
~, alumina, magnesia, spinel or heat resistant,
'i2 Notification and other known forms can be used.

The catalyst supporting layer is formed on the surface of the catalyst carrier base material and supports the catalyst component, and can be made of conventional materials such as activated alumina, zirconia, titanium oxide, etc., which have a large specific surface area.

Further, the perovskite type composite oxide constituting the catalyst component can be represented by the general formula ABO3.

Here, A is an element selected from lanthanide elements or alkaline earth metals, and B is platinum alone or a mixture of platinum and a transition metal. Further, the catalyst component may be a complex oxide having a structure similar to so-called perovskite type, such as ilmenite type, BaNi*Os type, KxNiFa type, etc.

Incidentally, after first forming a catalyst supporting layer on the surface of the 10-body substrate,
When the composite oxide is supported on the surface of the support layer, it is possible to enjoy the effect that platinum can be placed in a state where the SV (space velocity) characteristics can be fully volatilized.

In the present invention, whether a catalyst component other than platinum is supported on the catalyst support layer can be arbitrarily selected depending on the purpose. These catalyst components include rhodium (Rh),
Metallic metals such as palladium (Pd), iridium (Ir), ruthenium (RUB, osmium (Os)), or chromium (Cr), nickel (N + ), vanadium (
V), copper (CIJ), cobalt (CO), manganese (M
The same base metals as conventional ones such as base metals such as n) can be used.

[Effect 1] In the present invention, platinum is used as a catalyst component which is characterized by No reducibility and is essential for a three-way catalyst. I am carrying it.

For example, platinum is lanthanum (La), strontium (
perovskite type composite oxide (L, a+-x
srxPtoi-j) (Q≦x≦1) By configuring the ToshiT catalyst component, sintering of platinum due to oxidation in an oxygen atmosphere can be prevented. Furthermore, since platinum exists as a perovskite-type composite oxide, it is possible to prevent thermal deterioration of platinum (deactivation due to alloying with palladium). Furthermore, the porosity of the composite oxide improves the purification performance as an exhaust gas purification catalyst.

It is believed that the purification of NOx and CO from the catalyst component according to the present invention is based on the following reaction formula.

(1) しα）λSV'V, Agu, 6p, ■4ox-4mu [αχ leg ■knee j"/(JtW○・-needle・"±"Nz'
F → [. 0 S4λ2 only ξ-60, -纏+] (2) to the formula S, HA blindness -
s-4-1 Gomi CCh T By distributing platinum as a perovskite-type composite oxide on the surface of the alumina coat layer, the characteristics of platinum can be fully exhibited, and the redox action unique to the perovskite-type structure (see (1) above) can be fully exhibited. ,,(2
) formula) and the oxygen storage effect (formula (3) above) can be exhibited.

[Example] The present invention will be explained below based on specific examples.

(First Example) (a) Alumina Silua 00 with alumina content of 10 wt%
9, alumina powder 1000Q, and distilled water 300 (l) were mixed and stirred to prepare a slurry.

(b) A honeycomb-shaped monolithic catalyst carrier base material made of cordierite was immersed in this slurry for 1 minute, then pulled up, and the slurry inside the cells was blown away with an air flow.
After drying at 0°C for 1 hour, it was fired at 700°C for 2 hours. This operation was repeated twice to form a support layer made of activated alumina.

(c) Next, lanthanum nitrate (La (NO3) s ),
Strontium nitrate (Sr (NO3)z), Tet7
2I'' platinic acid (Pt (NOx) ao) with the desired composition (here x = 1/2, i.e. L a + hS r
+, 6PtOq-a) and added distilled water to prepare an aqueous solution.

(d) The base material for the monolithic carrier on which the catalyst support layer has been formed is immersed in this aqueous solution for 1 minute, then pulled out to blow off excess water, dried at 150°C for 1 hour, and then baked at 7Q○°C for 2 hours. As a result, platinum was supported on the catalyst support layer in the form of a perovskite complex oxide structure.

(e) Next, this was immersed in a palladium chloride aqueous solution for 1 hour, then pulled out, excess water was blown off, and dried at 150''C for 1 hour.

In this way, a catalyst (I) in which a platinum complex oxide and palladium were supported in a mixed state was obtained.

(Second Example) (a) Preparation of slurry, (b) Formation of support layer, (c) Preparation of aqueous solution 51, (d) Support of catalyst component
It was carried out in the same manner as in the example.

Next, 00g of alumina silua with alumina content of 1Qwt%
, 1000 g of alumina powder, and 3009 g of ion-exchanged water were mixed and stirred to prepare a slurry. In this slurry,
The monolith carrier base material, on which platinum has already been formed as a perovskite-type composite oxide in an alumina coat layer, was immersed for 1 minute, then pulled out, the slurry inside the cell was blown off with an air flow, dried at 150°C for 1 hour, and then heated at 700°C for 2 hours. Baked for an hour. After that, it was immersed in a palladium chloride aqueous solution for 1 hour, then pulled out, and the excess water was blown off with an air flow.
It was dried at 0°C for 1 hour.

In this way, a catalyst (If) was obtained in which the platinum composite oxide support layer and the palladium support layer were supported in a separated state.

(Third Example) (a) Prepare lanthanum nitrate, 6 nM strondium, and tetranitroplatinic acid to a desired composition (here, X-1/2, that is, L a +/, S r%P t Ch-s), Distilled water was added to make an aqueous solution. This aqueous solution was evaporated to dryness and calcined at 700° C. for 2 hours to form a platinum composite oxide. This composite oxide was confirmed to have a perovskite structure by XSa diffraction measurement.

(b) Next, this composite oxide is powdered, and the target platinum amount of the composite oxide, 00 g of alumina silica with an alumina content of 10 wt%, 10 oOq of alumina powder, and 30 g of distilled water are added.
A slurry was prepared by mixing 0 (l) and stirring.

(c) Add the monolith carrier base material to this slurry for 1 minute.
The cell was pulled up and the excess slurry inside the cell was blown off with an air stream, dried at 150°C for 1 hour, and then fired at 700°C for 2 hours.

(2) Next, it was immersed in a palladium chloride aqueous solution for 1 hour, pulled out, excess moisture was blown off, and dried at 150° C. for 1 hour.

In this way, a catalyst (lI[) in which a platinum complex oxide and palladium were supported in a mixed state was obtained.

(Fourth Example) (a) Formation of a composite oxide, (b) preparation of a slurry, and (c) support of a platinum composite oxide were carried out in the same manner as in the third example.

Next, 00g of alumina silua with alumina content of 10wt%
, 1000a of alumina powder, and 300g of 1lfl water were mixed and stirred to prepare a slurry. To this slurry, a monolith carrier base material made of activated alumina on which platinum has already been supported in the form of a velor sky 1~ type composite oxide structure is added.
After soaking for a minute, lift the cell, blow off the slurry inside the cell with an air stream, dry at 150℃ for 1 hour, and then dry at 700℃ for 2 hours.
Baked for an hour. Next, this was immersed in an aqueous palladium chloride solution for 1 hour, then taken out, excess moisture was blown off with an air stream, and dried at 150° C. for 1 hour.

In this way, a catalyst (TV) was obtained in which the platinum composite oxide support layer and the palladium support layer were supported in a separated state.

(Comparative Example 1) (a) Alumina Silua 00 with alumina content of 10 wt%
C], alumina powder 10009, 300 g of distilled water, and further lanthanum oxide and strontium carbonate were mixed and stirred to prepare a slurry.

(0) A base material for a monolithic carrier was immersed in this slurry for 1 minute, then pulled out, dried for 1 hour, and then fired at 700° C. for 2 hours to form an alumina coat layer containing la and 3r.

(c) Next, this is dinitrodiammine platinum [Pt(NH
3) 2 (Not ) did.

(d) Next, after being immersed in a palladium chloride aqueous solution for 1 hour,
It was dried at 150°C for 1 hour.

In this way, a catalyst (v) supporting platinum and palladium in a mixed state was obtained.

(Comparative Example 2) The same methods as in Comparative Example 1 were used to (a) form a slurry, (b) form a support layer, and (c) support a catalyst.

Next, 00g of alumina silua with alumina content of 10wt%
, mixed 1000g of alumina powder and 3009g of distilled water,
The slurry was stirred to vAvJ. A base material for a monolithic carrier having a support layer made of alumina containing La, Sr, and Pt in a molar ratio of 1:1:2, respectively, was immersed in this slurry for 1 minute, and then pulled out and air-flowed. The slurry in the cell was blown away and heated at 150°C.
After drying for an hour, it was fired at 700°C for 2 hours. Next, this was immersed in a palladium chloride aqueous solution for 1 hour and heated to 150°C for 1 hour.
Dry for an hour.

In this way, a catalyst (VI) in which a platinum support layer and a palladium support layer were supported in a separated state was obtained.

(Comparative Example 3) 00 g of alumina silua with an alumina content of 10 wt%, 1000 g of alumina powder, and 300 Q of distilled water.

Furthermore, perovskite type composite oxide L as a co-catalyst
A slurry was prepared by stirring ao, qs ro, and 3 COO3.

The base material for a monolithic carrier was immersed in this slurry for 1 minute, then pulled out, dried for 1 hour, and then fired at 700'C for 2 hours to form an alumina coat layer containing Lao, 7Sro, and 3CoO3.

Next, this was dinitrodiamine platinum [Pt(N+-13
)2 After 1 hour immersion in (NO2)zl aqueous solution, 15
It was dried at 0° C. for 1 hour to support pt.

Next, after immersing in a palladium chloride aqueous solution for 10 hours,
It was dried at 0° C. for 1 hour to support Pd.

In this way, perovskite type composite oxide Lao7
A catalyst (VI) containing Sro, ICOO3 and supporting Pt and Pd in a mixed state was obtained.

Table 1 Four types of catalysts containing 1 g in Examples 1 to 4 and Comparative Example 1.
Table 11 shows the component contents of the three types of catalysts obtained from 2.3.

(Durability Test! A) A durability test was conducted on these six types of catalysts using the following method to evaluate their purification performance.

The durability test was conducted by installing a catalyst in the exhaust system of a 6-cylinder 2800cc engine, and setting the air-fuel ratio (Δ/F) to 16.0. S
V is 60.000)-1r-', catalyst bed temperature is 800°C,
It was carried out for 200 hours.

In order to accelerate deterioration due to poisoning, 3O-CC engine oil was dripped into the engine intake system per hour, and gasoline containing 0.05 CI/liter of lead was used as fuel.

Regarding purification performance, CO2%, C3Ha20oppm
, CC3H5800pl), 022%, 00210%,
H2O 10% the rest is NZ, 5V = 56750Hr -
' was passed through the catalyst, and the purification rate of CO1HC was measured.

The relationship between the purification rate of Co and HC obtained as a result of the measurement and the temperature is shown in FIG. 1 and FIG. 2, respectively.

According to this, catalysts V, V
[RF, t, has purification performance of CO and HC at around 280-300°C. In addition, in catalyst ① obtained from Comparative Example 3, since it retains Velorsky 1~ type composite oxide as a co-catalyst, compared to ① and ①,
It has a certain degree of purification performance even in the temperature range of 0°C to 300°C. However, compared to these, Examples 1 to 4
The catalyst material obtained in Example 2 shows sufficiently high CO purification rates and HC purification rates of approximately 50% or more even at temperatures around 220 to 250°C.

Thus, compared to Comparative Examples 1.2 and 3, the catalysts prepared in Examples 1 to 4, which retain platinum as a perovskite complex oxide structure, exhibit purification performance in a lower temperature range than conventional catalysts. This was recognized.

In addition, by making platinum into a composite oxide with 3r and l-a, sintering due to oxidation in an oxygen atmosphere, which is the biggest cause of deterioration of platinum, can be eliminated. It was also possible to prevent deactivation, and it was possible to obtain an exhaust gas purification catalyst that had better purification performance and was highly durable.

In the example, "In order to prevent deactivation due to alloying of C1 platinum and Pd, catalysts ■ and ■ were separated from platinum and P (j), but there was a large difference in purification performance compared to catalysts ■ and ■. It is assumed that this is because alloying with Pd did not proceed because it was supported as a platinum perovskite type composite oxide.

Furthermore, by supporting platinum on Velor Sky 1 as a composite oxide, the porosity of the composite oxide itself was added, and a highly active catalyst was obtained.

Since the atomic arrangement of the perovskite structure (cubic close-packed) and the atomic arrangement of activated alumina used in the alumina support layer are the same, activated alumina changes from inert α-alumina (hexagonal close-packed). The transition of was suppressed, and a catalyst with excellent heat resistance could be obtained.

In the examples, perovskite type composite oxide (ABO3)
As Δ site ions, la and 3r were used, but in addition, rare earth metals such as yttrium (Y) and cerium (Ce), magnesium (MCI), calcium (Ca),
Alkaline earth metals such as barium (Ba) can be used alone or in combination. On the other hand, although platinum was used as the B site ion, the redox effect and oxygen storage ability of the catalyst can be further enhanced by substituting it with Ce or a transition metal. Therefore, it exhibits a buffering effect against minute changes in the oxygen temperature in exhaust gas, and is thought to greatly contribute to expanding the window width when used as a three-way catalyst.

In addition, the supported state of the catalyst is not limited to perovskite structure, but also ilmenite structure, BaNiO3 structure, K Z
Good results were also obtained with the so-called perovskite-like structure and bluffsite-type structure of the N iF 4 type.

[Effects of the Invention] As described above, in the exhaust gas purifying catalyst of the present invention, platinum is supported on the catalyst carrier as a perovskite type or a complex oxide having a similar structure.

For this reason, the so-called oxygen storage ability of perovskite-type composite oxides prevents the formation of a solid solution of platinum and alumina, improving the durability as an exhaust gas purification catalyst, and the redox action of perovskite-type composite oxides prevents the formation of a solid solution of platinum and alumina. , it becomes possible to further improve the purification performance.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the purification rate of the exhaust gas purifying catalyst with respect to Ce, and FIG. 2 is a diagram showing the purification rate of the exhaust gas purifying catalyst with respect to HC.

Claims (3)

[Claims] (1) In an exhaust gas purification catalyst consisting of a catalyst carrier and a catalyst component supported on the catalyst carrier, the catalyst component is at least a perovskite-type composite oxide of platinum and a lanthanide element or an alkaline earth metal, or a similar composite oxide thereof. A catalyst for exhaust gas purification characterized by being a material. (2) The catalyst carrier is composed of a carrier base material and a support layer formed on the surface of the carrier base material, and the perovskite-type composite oxide is produced and supported by an aqueous solution of a compound containing a lanthanide element or an alkaline earth metal and platinum. 2. The catalyst for exhaust gas purification according to claim 1, which is produced and supported by adhering an aqueous solution of a compound containing the compound to the support layer and firing it. (3) The catalyst carrier is composed of a carrier base material and a support layer formed on the surface of the carrier base material, and the perovskite type composite oxide is supported by a compound containing a lanthanide element or an alkaline earth metal and platinum. Form a perovskite-type composite oxide or a similar composite oxide by evaporating the aqueous solution containing the perovskite-type composite oxide or its similar composite oxide, and mixing this with a slurry of the substance forming the support layer,
The exhaust gas purifying catalyst according to claim 1, which is supported simultaneously with the formation of the support layer.