JPS60206447A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance purification efficiency, by using a catalyst formed by adhering a slurry, which is prepared by compounding a cerium-containing activated alumina powder and a cerium oxide powder in an alumina sol, to the surface of a monolithic carrier base material before supporting a noble metal component. CONSTITUTION:Activated alumina supporting cerium oxide in an amount of 1- 5% by wt. of alumina as a cerium metal is obtained. A cerium oxide powder with a specific surface area of 50m<2>/g or more is compounded in said activated alumina powder along with water to obtain an aqueous slurry which is, in turn, compounded and slurried in an alumina sol. The resulting slurry is adhered to the surface of a monolithic carrier base material and a noble metal component such as platinum, rhodium or palladium is subsequently supported by said carrier base material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) This invention relates to nitrogen oxides (NOx) and hydrocarbons (I(O) The present invention relates to an exhaust gas purifying catalyst that simultaneously and efficiently reduces carbon oxide (CO).

(Prior art) After adhering activated alumina powder containing cerium to the surface of a monolithic carrier base material, a catalyst supporting platinum, rhodium, palladium, etc., either alone or in combination, is prepared, for example, by No. 116779,
This method has been proposed in Publication No. 54-159391.

However, although such conventional exhaust gas purification catalysts support a large amount of expensive precious metals such as platinum, rhodium, and palladium, which are catalyst components, a large amount of cerium is supported on activated alumina. Since the noble metal was supported after the catalyst was supported, the dispersion state of the noble metal in the obtained catalyst deteriorated, resulting in a problem that the activity, particularly in the low temperature range, decreased.

(Disclosure of the Invention) The present invention has been made by focusing on such conventional problems, and is made by combining activated alumina powder containing cerium in advance and cerium oxide powder having a specific surface area of 50 or more into an alumina sol. After the slurry obtained by mixing and adhering to the surface of the monolith carrier base material, platinum, rhodium,
By supporting at least one noble metal component selected from the group consisting of palladium, the oxygen (0,) storage effect of ceria is increased in order to prevent deterioration of the dispersion state of the precious metal and at the same time improve exhaust gas purification performance. The purpose of the present invention is to provide a catalyst for exhaust gas purification that has a reduced amount of precious metals.

In general, activated alumina such as γ-alumina and δ-alumina transforms into stable inactive alumina called α-alumina at high temperatures, and has a specific surface area of only 1 to 2. Therefore, if an activated alumina carrier is used as it is as a catalyst carrier and a noble metal such as platinum or rhodium is supported on it to form a catalyst, the supported noble metal will sinter and lose its activity when exposed to high temperatures. Lose it.

However, when cerium oxide is supported on activated alumina as in the case of the catalyst of the present invention, the heat resistance of activated alumina is significantly improved, and it becomes difficult to convert into α-alumina even when used at high temperatures. The amount of cerium oxide supported on activated alumina is 1 to 5% by weight relative to alumina in terms of cerium metal.If it is less than 1 weight US, the effect of improving the heat resistance of activated alumina will be small, and if it exceeds 5 weight US Although heat resistance is improved, the specific surface area of activated alumina is relatively reduced, which is not preferable.

In this invention, in order to fully take these effects into consideration and further increase the storage effect of cerium oxide, activated alumina powder containing cerium oxide in advance has a specific surface area of 50111"/l; Cerium oxide (hereinafter referred to as high specific surface area ceria)
After the slurry obtained by blending the powder is adhered to the surface of the monolithic carrier base material, the noble metal component is supported. This noble metal component is supported by a commonly used method.

The high specific surface area ceria used here is, for example, among various cerium salts, cerium nitrate, cerium acetate (specific surface area obtained by baking rum at 650°C for 1 hour in an air atmosphere, or 7 g or more). ceria obtained from cerous nitrate is 50.8 m'/gl:・s
Ceria obtained from cerium acetate is e o, o m2/
It has a specific surface area of Lg. Ceria obtained by firing other cerium salts under the same conditions has a low yield of 17.9 J/g for ceria obtained from cerium carbonate, and 19.6 ML''/9 for ceria obtained from cerium oxalate. Ceria, which only has a specific surface area of less than 50 m, has a specific surface area of 64 m. Compared to the case of using commercially available ceria with a specific surface area of about 64 m, the performance cannot be improved to meet the inventors' requirements. , the specific surface area is 50 m”
Use 7g or more of ceria.

As a result, the catalyst has ceria, which has a specific surface area almost equal to that of activated alumina, and its exhaust gas purification performance does not deteriorate even if the amount of precious metal supported is reduced, and it also has excellent durability when used for purifying automobile exhaust gas. was also sufficient. In particular, the 02 storage capacity of the high specific surface 7 rear has a large effect on the purification performance, and even when the combustion range of the internal combustion engine of the automobile is on the rich side (fuel excess side),
Celia's 0. As a result of the increased storage effect, stable and high purification performance is exhibited.

The amount of high specific surface area ceria powder to be mixed with activated alumina powder is 5 to 50% by weight based on the alumina layer attached to the monolithic carrier base material in terms of metal, and if it exceeds 50% by weight, there is a weight increase effect. If the amount is less than 5% by weight, the effect of adding ceria with a high specific surface area is insufficient compared to the performance required by the inventor.

(Examples of the Invention) The present invention will be explained using the following Examples, Comparative Examples, and Test Examples.

Example 1 Gamma alumina as main component and TΦ congratulatory carrier (particle size 2-41
31) was impregnated in an aqueous cerium nitrate solution, dried, and then calcined at 600°C for 1 hour in an air atmosphere to obtain a carrier containing 1% by weight of cerium oxide based on alumina in terms of metal.

Next, alumina sol (sol obtained by adding 10% by weight HNO3 to a 10% by weight suspension of boehmite alumina) 2478.09, 1419 g of active alumina granular support containing cerium, high ratio obtained from ceric nitrate Ceria powder with a surface area of 108.2 mm was placed in a ball mill pot and ground for 6 hours, and the resulting slurry was adhered to a monolithic carrier substrate (1,71400 cells), dried, and then baked at 650°C for 2 hours. . The amount of adhesion layer deposited at this time was set at 840 g/piece. Furthermore, this carrier contains 0.779 g of platinum and 0.13 g of rhodium per carrier.
After supporting so that
Catalyst 1 was obtained.

Example 2 The same procedure as in Example 1 was carried out except that a granular carrier containing gamma alumina as the main component was impregnated in a cerium nitrate water bath solution, dried, and calcined to obtain a carrier containing 3% by weight of cerium oxide based on alumina in terms of metal. Catalyst 2 was obtained.

Example 8 Catalyst 8 was obtained in the same manner as in Example 1, except that 903 g of activated alumina granular carrier containing cerium and 619 g of high specific surface area ceria powder were used.

- Example 4 Catalyst 4 was obtained in the same manner as in Example 1 except that 491 g of activated alumina granular support containing cerium and 1082 g of high specific surface area ceria powder were used.

Example 5 Catalyst 5 was obtained in the same manner as in Example 2, except that the activated alumina granular carrier containing cerium was changed to 10079 g and the high specific surface area ceria powder was changed to 516 g.

Example 6 Catalyst 6 was obtained in the same manner as in Example 2, except that the active alumina granular carrier containing cerium 4919 and the high specific surface area ceria powder 1032 were used.

Example? In Example], a granular carrier mainly composed of gamma alumina was impregnated with an aqueous cerium nitrate solution, dried, and calcined to obtain a carrier containing 5 wt % of ceria with a high specific surface area in terms of metal compared to alumina. Catalyst 7 was obtained.

Example 8 Catalyst 8 was obtained in the same manner as in Example 7, except that the activated alumina granular carrier 1007 containing cerium was replaced with 516 g of high specific surface area powder.

Example 9 Catalyst 9 was obtained in the same manner as in Example 7 except that 491 g of activated alumina granular carrier containing cerium and 1082 g of high specific surface area ceria powder were used.

Comparative Example 1 Alumina A/2568.09, activated alumina granular carrier 1487. (1, '11400 cell) was mixed into a ball mill and pulverized for 6 hours.
and baked at 650° C. for 2 hours.

The amount of adhesion at this time was set at 840 gl.

Further, this carrier was immersed in an acidic solution of platinum and rhodium in hydrochloric acid to support 1.997 parts of platinum and 1 part of 19 g of rhodium, and then calcined at 600°C for 2 hours to make catalyst A.
I got it.

Comparative example 2 Alumina sol 25639, cerium 5% by weight in terms of metal
Catalyst B was obtained in the same manner as in Comparative Example 1 except that activated alumina granular carrier 14879 containing 14879 was used. However, the amount of platinum deposited was set at 1.99/piece and the amount of rhodium was set at 0.19/piece.

Comparative Example 8 Catalyst C was obtained in the same manner except that 2478 g of alumina sol, 9889 g of high specific surface area ceria powder (specific surface area 50 m2/g), and 466 g of activated alumina granular carrier were used. However, the amount of noble metal supported was set to 1.9 g of platinum and 0.199 g of rhodium per catalyst.

Comparative Meeting Catalyst paste was obtained in the same manner as in Example 1, except that 2568 g of alumina sol, 1167.2 g of active A) Y Mina granular carrier containing 0.5% by weight of cerium in terms of metal, and 69.89 g of high specific surface area ceria powder were used. Ta. However, the amount of precious metal supported is catalyst 1
Per unit was set at 0.7729 for platinum and 0.12869 for rhodium.

Comparative Example 5 Catalyst E was obtained in the same manner as in Example 1, except that 256.9 g of alumina sol, 81.9 g of activated alumina granular carrier containing 10% by weight of cerium as metal, and 14059 high specific surface area ceria powder were used. The amount of noble metal supported per catalyst was set to 0.772% of platinum and 0.12867% of rhodium.

Example 10 A catalyst IO was obtained in the same manner as in Example 1, except that ceria obtained from cerium acetate and having a specific surface area of 80 mg/g was used.

Example 11 In Example 1, the monolith carrier base material was 400 cells, 1
．． Catalyst 11 was obtained in the same manner except that the number of cells was changed from 7 to 800 and 0.91. However, the total amount of the adhesion layer of activated alumina containing cerium and high specific surface area rear alumina sol is 1 s o 9A, and the amount of noble metals supported is 0.95359 platinum and 0.1589 rhodium per piece.
It was set to g.

Example 12 In Example 1, the monolithic carrier substrate was prepared using a 40° cell 1.
Catalyst 12 was obtained in the same manner except that the number of cells was changed from 7 to 800 cells to 0.7. However, the amount of adhesion layer is 140g/,
y. The amount of noble metals supported was set at 0.7865 g of platinum and 0.0787 g of rhodium per piece.

Example 18 In Example 1, the monolithic carrier substrate was prepared with 400 cells 1,
Catalyst 12 was obtained in the same manner except that 400 cells were changed from 7 t to 1.321 t. However, the amount of adhesion layer is 2 e
49hz precious metal bearing child has platinum 0.59939 per piece,
It was set at 0,0999 rhodium.

Comparative Example 6 1419 g of activated alumina granular carrier containing 1% by weight of cerium oxide based on alumina, and alumina sol 2
478g, the specific surface area obtained from cerium carbonate is 17
, 9 WP/g of Serif 108.2 was put into a ball mill pot and pulverized for 6 hours, and the resulting slurry was milled into a monolithic carrier base material (1,77, '400 ce/L/
), and after drying, it was baked at 650°C for 2 hours.

The adhesion amount at this time was set to a 4 o 9/piece. Furthermore, □ was loaded with 0.77 g of platinum and 0.18 g of rhodium per i, followed by firing (6
00°C for 2 hours) to obtain catalyst F.

Comparative Example 7 Catalyst G was obtained in the same manner as in Comparative Example 6, except that commercially available ceria having a specific surface area of 644 was used.

The amount of precious metal supported per catalyst is 0.779 platinum,
Rhodium was set at 0.139.

Comparative Example 8 In Comparative Example 1, the monolithic carrier base material was 400 cells 1.
Catalyst F was obtained in the same manner except that 71 was changed to 3007N0.97. The amount of slurry deposited in this case was 1807/piece after firing. However, the amount of noble metals supported was set to 0.9'5859 g of platinum and 0.1589 g of rhodium per piece.

Comparative Example 9 In this example, an example of the catalyst disclosed in JP-A-52-116779 is shown.

Activated alumina granular carrier 14379 containing 2,568 g of silica and 8% by weight of cerium (metal equivalent) was mixed in a ball mill, and after pulverizing for 6 hours, it adhered to a coating carrier base material (400 cells, 1.77), and was heated at 650°C for 2 hours. Baked for an hour. The adhesion amount at this time was set at 3409/piece. Further, this coated carrier was immersed in a mixed water bath solution of chloroplatinic acid and rhodium chloride, and reduced in a flow of H/N.The amount of precious metals supported at this time was 1.9 l/kg of platinum and 0.9 l/kg of rhodium.
It was set at 19 g/kg. Thereafter, it was calcined at 600°C for 2 hours to obtain a catalyst.

Comparative Example 10 In this example, an example of the catalyst disclosed in JP-A-54-159891 is shown. Alumina sol 25689, activated alumina granular carrier 14
After mixing 87 g into a ball mill and grinding for 6 hours, coated carrier base material (40° cell, 1..7 j)
It was then baked at 650'C for 2 hours. The adhesion amount at this time was set at 840 l/kg.

In the next step, 289 cerium in terms of cerium metal was deposited using an Oe (No. 8) 8 aqueous solution. After this, 12°
It was dried for 8 hours at 600'C in air and calcined for 2 hours at 600'C.

Further, it was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride to support the platinum and rhodium in amounts of 1.99 g of platinum and 0.19 g of rhodium, and then calcined to obtain catalyst J.

Example 14 In Example 1, the amount of adhesion on the palladium was set to 0.779/
A catalyst 14 was obtained in the same manner except that rhodium was supported at 0.18 g/kg.

Example 15 In Example 5, the amount of palladium deposited was 0.77 g/
Catalyst 15 was obtained in the same manner except that it was supported on rhodium o, ta9/ke.

Comparative Example 11 Catalyst K was obtained in the same manner as in Comparative Example 1, except that the amount of palladium deposited was 1.9 g/piece and the amount of rhodium was 0.19974 g/piece.

Test Example 1 Catalysts 1-15 obtained from Examples 1 to 15, Comparative Examples 1 to 11
The catalyst ANK obtained from I was subjected to durability under the following conditions.
Table 1 shows a comparison of the purification rates of O mode selection.

Durability test conditions Catalyst Monolithic noble metal catalyst Exhaust gas catalyst outlet temperature 750°C (85'0°C Example 10) Comparative example 6 Space velocity Approximately 70,000 Hr-1 (approximately 100,000 Hf1 Example 10
) Comparative Example 6 Durability time 100 hours Engine displacement 2200 CC Durability middle low emission Co' 0.4-0.6%0
20.5±0.1 Chi No. 2500ppm He 1000 ppm 00, 14.9±0.1% 10 mode evaluation vehicle Sedrik Displacement 2000cc (Product name manufactured by Nissan Motor Co., Ltd.) ■ What is 0X-50? , indicates that the amount of cerium added to alumina is 1% by weight, and the amount of cerium in the mixed ceria is 5% by weight.

Test Example 2 Catalysts 1 to 15 obtained from Examples 1 to 15, Comparative Example 1 Neal
Catalyst A-K obtained from Example 1 was thermally degraded in advance under the following conditions, and two characteristics were evaluated using a laboratory evaluation device, and the He and No conversion rates are shown in FIGS. 1 to 8.

Thermal deterioration test temperature x time 750'C
Model gas flow 1k 27.517m1n Space velocity SV
27500Hr-1 Catalyst entry log gas temperature 400'C Each gas concentration determined by 00. , H, O are constant Figure 1 compares catalyst A and catalysts 1 and 2.3, Figure 2 compares catalyst C and catalysts 4 and 5.6, Figure 8 &J catalyst B and catalyst? , 8.9, Figure 4 is a comparison between catalyst E and catalyst 1, Figure 5 is a comparison between catalyst H and catalysts 11 and 12゜18, and Figure 6 is a comparison between catalyst H and catalysts 11 and 12゜18.
The figure shows a comparison between catalysts 1.4 and 15, Figure 7 shows a comparison between catalysts I and J and catalyst 5, and Figure 8 shows a comparison between catalysts F, G and catalyst IO.
A comparison of each is shown below.

From Figures 1 to 8, the catalyst of the present invention has excellent two properties, and in particular, a high conversion rate of HO can be obtained in the oxygen-deficient region of two values of 0.4 and 0.7, so that the catalyst has a specific surface area of 50rI/9 or more. 0.0 of cerium oxide. Improvement in storage efficiency was confirmed.

(Effect of the invention) .

As explained above, in the catalyst of the present invention, a slurry obtained by blending ceria with a high specific surface area into activated alumina powder containing cerium in advance is deposited on the surface of a monolithic carrier substrate, and then a noble metal component is supported. As is clear from Table 1, the purification rate was significantly improved despite the reduction in precious metals.
In particular, the higher the ratio of ceria with a high specific surface area to be mixed, the better the 02 storage effect of the ceria, the higher the NO purification rate, and the more stable and high purification performance can be obtained.

[Brief explanation of drawings]

Figures 1 to 8 show the NO of the catalysts of Examples and Comparative Examples, respectively.
, are curves showing the relationship between He conversion rate and binary values. Figure 1 is a comparison between catalyst A and catalysts 1 and 2.8, and Figure 2 is a comparison between catalyst O and catalyst 4.
, 5.6, Figure 8 is a comparison between catalyst B and catalysts 7 and 8.9, Figure 4 is a comparison between catalyst B, E and catalyst 1, and Figure 5 is a comparison between catalyst H and catalyst 11.1218. , FIG. 6 shows a comparison between the catalyst and the catalyst 14 and 15, FIG. 7 shows a comparison between the catalyst J and the catalyst 6, and FIG. 8 shows a comparison between the catalysts F and G and the catalyst 10. Fig. 1 04 0.7 f, 0 /, 2 Z 舊 Fig. 3 2 Monk 2 o, a o, 'y /, Of2 73 0.4 0.7 f, 0 12

Claims (1)

[Claims] L A slurry obtained by blending activated alumina powder containing cerium in advance and cerium oxide powder with a specific surface area of 50 m2/g or more into alumina sol is attached to the surface of a monolithic carrier base material, and then platinum is added to the surface of the monolith carrier base material. An exhaust gas purifying catalyst that efficiently reduces hydrocarbons, carbon oxides, and nitrogen oxides in the exhaust gas of an internal combustion engine, the catalyst supporting one or more noble metal components selected from the group consisting of , rhodium, and palladium.