JP2786933B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to hydrocarbons (HC) and carbon monoxide (C), which are harmful components contained in exhaust gas from internal combustion engines such as automobiles.
O) and relates to nitrogen oxides (NO _X) at the same time the exhaust gas purifying catalyst for removing, has excellent durability be especially under conditions such as a high-temperature oxidizing atmosphere, and the harmful components On the other hand, the present invention relates to an exhaust gas purifying catalyst having high purification performance at low temperatures.

(Prior Art) Conventionally, purification catalyst of an exhaust gas discharged from an internal combustion engine such as an automobile has been proposed, is now CO, three-way catalyst for simultaneously removing HC and NO _X is becoming mainstream I have.

As the above three-way catalyst, those in which a noble metal such as platinum, palladium, rhodium or the like is used as an active component, which is supported on alumina or the like, and those in which cerium oxide (hereinafter referred to as ceria) is added as a promoter component are generally used. Ceria, a cocatalyst component, changes the electronic state of the noble metal, an active component, by releasing or taking in oxygen (usually referred to as oxygen straightening capability) in automobile exhaust gas whose reaction atmosphere fluctuates on the oxidation / reduction side. , CO, HC oxidation reaction and
The reduction reaction of the NO _X in which greatly facilitated. However, it is widely known that when ceria is used at a high temperature, the co-catalyst function decreases with a decrease in surface area.

To improve the heat resistance of ceria, see JP-A-2-43951.
Japanese Patent Application Laid-Open No. H11-157, discloses a technique using ceria stabilized by zirconia, but does not have sufficient heat resistance when exposed to high-temperature exhaust gas during high-speed running.

Japanese Patent Application Laid-Open No. 1-281144 discloses a heat-resistant ceria.However, on the manufacturing method, zirconium, cerium and a salt solution of each of the rare earth elements are immersed in a monolithic carrier coated with alumina in advance, and dried and calcined to carry. This is completely different from the stabilized ceria of the present invention in terms of catalyst production.

When ceria is impregnated and supported on this alumina, it is difficult to reduce the surface area of ceria at a high temperature, and a catalyst having heat resistance cannot be obtained.

(Problems to be Solved by the Invention) The present invention provides an exhaust gas purifying catalyst and a method for producing the same, and particularly, a harmful component which has durability in a high-temperature oxidizing atmosphere and is contained in exhaust gas. An object of the present invention is to provide an exhaust gas purifying catalyst having high purification performance at a low temperature and a method for producing the same.

(Means for Solving the Problems) The present inventors have conducted intensive studies in order to solve the above problems, and as a result, cerium oxide stabilized by a specific oxide,
A catalyst obtained by coating a catalyst composition containing activated alumina and a platinum group metal on a monolithic carrier was found, and the present invention was completed.

Namely, (1) stabilized cerium oxide containing (a) zirconia, (b) at least one of yttrium and calcium, and (c) at least one of rare earth elements (excluding yttrium and cerium) (I), activated alumina (II), and at least one platinum group metal (III) selected from the group consisting of rhodium, platinum and palladium. ) Is 10 to 50% by weight as ceria, 0.1 to 15% by weight of at least one oxide (b) of yttrium and calcium, and oxidation of at least one or more of the rare earth elements (excluding yttrium and cerium) The product (c) is obtained by coating a catalyst composition containing 0.1 to 15% by weight on a monolith carrier having a honeycomb structure. Gas purifying catalyst.

(2) The catalyst according to (1), wherein the stabilized cerium oxide (I) is contained in the catalyst composition in an amount of 5 to 80% by weight.

(3) The catalyst according to (1), wherein the rare earth element contained in the stabilized cerium oxide (I) is at least one of neodymium and lanthanum.

(4) At least one platinum group metal (III) selected from the group consisting of platinum and palladium is activated alumina (I
The catalyst according to claim 1, which is supported on I) and / or stabilized cerium oxide (I).

(5) Activated alumina (II) contains 0.02 to
Claims (2) wherein at least 2% by weight of rhodium and at least one selected from the group consisting of 0 to 10% by weight of platinum and palladium per catalyst composition (total of platinum and palladium excluding 0% by weight) are supported. The catalyst according to 1).

(6) stabilized cerium containing (a) zirconia, (b) at least one of yttrium and calcium, and (c) at least one of rare earth elements (excluding yttrium and cerium) A honeycomb support having a monolith structure, comprising a catalyst composition containing an oxide (I), activated alumina (II), and at least one platinum group metal (III) selected from the group consisting of rhodium, platinum and palladium. In the production of an exhaust gas purifying catalyst coated with cerium oxide, the stabilized cerium oxide (I) is added to zirconium oxide and / or its hydroxide by at least one selected from yttrium salts and calcium salts. Impregnated with a solution of a salt, at least one salt of a rare earth element (excluding yttrium and cerium) and a cerium salt The method of manufacturing the exhaust gas purifying catalyst is obtained by calcination.

 Hereinafter, the present invention will be described in more detail.

As the zirconia source of zirconia according to the present invention, zirconium oxide or zirconium hydroxide is used.

The surface area of zirconium oxide is not particularly limited as long as it is not sintered such as from 0 to several m ² / g, but 50 m ² / g
Those having the above are preferred.

The calcium and / or yttrium source is not particularly limited as long as it is water-soluble, and for example, nitric acid, sulfuric acid, acetate, chloride and the like are used.

At least one oxide of yttrium and calcium is a stabilized cerium oxide (I)
It is preferably used in an amount of 0.1 to 15% by weight, more preferably 0.1 to 10% by weight.

(C) rare earth elements (excluding yttrium and cerium) used are lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium ( T
b) oxides of dysprosedimate (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb), and at least one selected from these elements is used. Furthermore, when at least one of neodymium and / or lanthanum is included among the above rare earth elements, the high-temperature heat resistance is further improved as compared with the case where another rare earth element is added. These rare earth elements are not particularly limited as long as they are water-soluble, and nitric acid, sulfuric acid, acetate, chloride and the like are used.

These rare earth elements are used by being appropriately contained in the stabilized cerium oxide (I), and preferably 0.1 to 1
5% by weight, more preferably 0.1 to 10% by weight can be used.

As the activated alumina (II), commonly used aluminas such as γ-alumina, θ-alumina and δ-alumina are used.

Rhodium can be supported at 0.02 to 2% by weight, preferably 0.1 to 1.0% by weight, based on the catalyst composition.

Platinum and palladium each range from 0 to 10 per catalyst composition.
% By weight (however, except that the total of platinum and palladium is 0% by weight).

At least one platinum group metal (III) selected from the group consisting of platinum and palladium can be supported on activated alumina (II) and / or stabilized cerium oxide (I).

Rhodium can be supported on either activated alumina (II) and / or stabilized cerium oxide (I), but is preferably supported only on activated alumina (II).

In producing the above catalyst, any production method can be appropriately selected as long as it satisfies the catalyst constitution according to the present invention.
A preferred procedure example of the method for producing stabilized cerium oxide (I), which is a feature of the present invention, is described as follows. Stabilized cerium oxide is composed of zirconium oxide and / or a hydroxide thereof containing cerium salt, yttrium salt and calcium. Impregnated with at least one salt selected from salts, and at least one salt selected from the rare earth elements (excluding yttrium and cerium);
It is obtained by calcining at a temperature of 700700 ° C., preferably 400-600 ° C. As another method, a zirconium oxide or hydroxide is impregnated with a cerium salt and at least one salt selected from yttrium salts and calcium salts, dried and calcined. It can also be obtained by impregnating at least one or more salts selected from rare earth elements (excluding yttria and ceria), drying and baking the same as above. Each salt solution used above is not particularly limited as long as it is water-soluble, and examples thereof include nitric acid, sulfuric acid, acetate, and chloride.

Next, preferred examples of the production method according to the present invention will be described.
Activated alumina was impregnated with a mixture of a predetermined dinitrodiammineplatinic acid aqueous solution of nitric acid and an aqueous solution of rhodium nitrate, dried and calcined at 400 ° C. in air to obtain platinum and rhodium-supported alumina powder.

Next, the stabilized cerium oxide obtained by the above method and platinum and rhodium-supported activated alumina are mixed. The mixing ratio at this time is such that the stabilized ceria is in the range of 5 to 80% by weight of the whole catalyst composition, preferably 5 to 80% by weight.
An excellent catalyst for purifying exhaust gas of an internal combustion engine can be obtained by being contained in an amount of about 50% by weight and coexisting with a platinum group metal.

The mixing is performed by wet pulverization or the like, and the slurry is formed.

A monolithic carrier having a honeycomb structure was immersed in the obtained slurry, pulled up, and then the excess slurry was blown and shaken, followed by drying to obtain a completed catalyst.

(Examples) Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it is contrary to the gist of the present invention.

Example 1 of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 50g, yttrium nitrate _{(Y (NO 3) 3 ·} 6H 2 O) 3.4g and neodymium nitrate (N
d a _{(NO 3) 3 · 6H 2} O) 5.2g was dissolved in water 100 ml, specific surface area 9
50 g of zirconia having 7 m ² / g (manufactured by Daiichi Element Co., Ltd.) is impregnated and mixed, dried sufficiently, and baked at 500 ° C. for 1 hour.
A stabilized ceria powder was obtained. Next, 146 g of activated alumina having a specific surface area of 150 m ² / g was impregnated with a mixture of a nitric acid aqueous solution of dinitrodiammineplatinum containing 1.095 g of platinum and an aqueous solution of rhodium nitrate containing 0.219 g of rhodium, and after sufficiently drying, was dried in air.
By baking at 0 ° C. for 2 hours, an alumina powder containing platinum and rhodium was obtained.

Next, 73 g of the obtained platinum group-containing alumina and stabilized ceria powder were wet-ground with a ball mill together with water and nitric acid to obtain an aqueous slurry. The obtained slurry was coated on a cordierite monolithic carrier (33 mmφ × 110 mmol),
After drying at 30 ° C. for 3 hours, a completed catalyst was obtained. The slurry coverage of the finished catalyst was 150 g /.

Example 2 A completed catalyst was obtained in the same manner as in Example 1 except that yttrium nitrate was changed to 2.9 g of calcium nitrate (Ca (NO ₃ ) ₂ ).

 The supported amount of the catalyst is shown in Table 1.

Example 3 In Example 1, it carried out similarly to Example 1 except having changed yttrium nitrate 3.4g to 0.25g.

 The supported amount of the catalyst is shown in Table 1.

Example 4 In Example 1, it carried out similarly to Example 1 except having changed yttrium nitrate 3.4g into 20.3g. The supported amount of the catalyst is shown in Table 1.

Example 5 In Example 1, it carried out similarly to Example 1 except having changed neodymium nitrate 5.2g to 0.19g. The supported amount of the catalyst is shown in Table 1.

Example 6 The procedure of Example 1 was repeated, except that neodymium nitrate (5.2 g) was replaced with 20.5 g. The supported amount of the catalyst is shown in Table 1.

Example 7 73 g of the stabilized ceria powder obtained in Example 1 was impregnated with an aqueous nitric acid solution of dinitrodiammineplatinum containing 0.438 g of platinum, dried sufficiently, and calcined at 400 ° C. for 2 hours in air to stabilize the platinum content. Got ceria.

A finished catalyst was obtained in the same manner as in Example 1 except that platinum and rhodium-containing alumina powder were changed from Example 1 to 1.057 g of platinum to 0.657 g. The supported amount of the catalyst is shown in Table 1.

Examples 8 to 18 In Example 1, neodymium nitrate was replaced by lanthanum,
Finished catalysts (Examples 8 to 18) in the same manner as in Example 1 except that praseodymium, samarium, europium, gadolinium, terbium, dysprosedim, hofium, erbium, thorium and ytterbium are used as the respective nitrates.
I got

The rare earth addition amount is the same amount of nitrate as the equivalent of neodymium nitrate oxide in Example 1. The supported amount of the catalyst is shown in Table 1.

Example 19 In Example 1, 5.2 g of neodymium nitrate was replaced with neodymium nitrate.
A completed catalyst was obtained in the same manner as in Example 1, except that 3.9 g and 0.95 g of lanthanum nitrate were used. The supported amount of the catalyst is shown in Table 1.

Example 20 73 g of the stabilized ceria powder obtained in Example 19 was impregnated with a nitric acid aqueous solution of dinitrodiammineplatinum containing 0.438 g of platinum, dried sufficiently, and calcined at 400 ° C. for 2 hours in air to obtain stabilized ceria containing platinum. I got

A finished catalyst was obtained in the same manner as in Example 1 using the platinum and rhodium-containing alumina powder obtained in Example 7. The supported amount of the catalyst is shown in Table 1.

Example 21 A completed catalyst was obtained in the same manner as in Example 1 except that the aqueous nitric acid solution of dinitrodiammineplatinum containing 1.095 g of platinum was changed to palladium nitrate containing 1.095 g of palladium. The supported amount of the catalyst is shown in Table 1.

Comparative Example 1 A completed catalyst was obtained in the same manner as in Example 1 except that neodymium nitrate was omitted. The supported amount of the catalyst is shown in Table 1.

Comparative Example 2 A completed catalyst was obtained in the same manner as in Example 1 except that yttrium nitrate and neodymium nitrate were omitted. The supported amount of the catalyst is shown in Table 1.

Comparative Example 3 A completed catalyst was obtained in the same manner as in Example 1, except that yttrium nitrate was omitted. The supported amount of the catalyst is shown in Table 1.

Comparative Example 4 In Example 1, ceria powder except for neodymium nitrate
After preparing 73 g, a completed catalyst was obtained in the same manner as in Example 7. The supported amount of the catalyst is shown in Table 1.

Comparative Example 5 146 g of activated alumina having a specific surface area of 150 m ² / g was wet-pulverized with water and nitric acid using a ball mill to obtain an aqueous slurry.
The obtained slurry was coated on a cordierite-based monolith carrier, dried at 130 ° C. for 3 hours, and calcined at 500 ° C. for 1 hour. Next, a mixed aqueous solution of zirconyl oxynitrate, cerium nitrate, yttrium nitrate and neodymium nitrate was prepared so as to have the same composition as the stabilized ceria powder obtained in Example 1, and the alumina-coated monolithic carrier was added to the aqueous solution. 1 minute after immersion, remove excess water and blow off at 130 ℃
After drying for one hour, it was baked at 500 ° C. for one hour. Next, on the monolithic carrier, platinum is a nitric acid aqueous solution of dinitrodiammine platinum,
Rhodium is immersed in a mixed aqueous solution of rhodium nitrate aqueous solution,
After chemisorption in a predetermined amount, it was pulled up to blow off excess water, dried at 130 ° C. for 3 hours, and calcined at 400 ° C. for 2 hours to obtain a finished catalyst. The supported amount of the catalyst is shown in Table 1.

Comparative Example 6 A completed catalyst was obtained in the same manner as in Example 1, except that 73 g of the stabilized ceria powder was replaced with 73 g of commercially available ceria (specific surface area: 100 m ² / g). The supported amount of the catalyst is shown in Table 1.

Comparative Example 7 Ceria powder in Example 21 except for neodymium nitrate
A completed catalyst was obtained in the same manner as in Example 21 except for using 73 g. The supported amount of the catalyst is shown in Table 1.

Example 22 Next, the catalysts of Examples 1 to 21 and Comparative Example 1
The catalyst activities of the catalysts of Comparative Example 7 to Comparative Example 7 after running under engine durability were examined.

A commercially available electronically controlled engine (8 cylinders, 4400 cc) was used, and a durability test was conducted by connecting a multi-converter filled with each catalyst to the exhaust system of the engine. The engine is operated in a mode operation of a steady operation of 60 seconds and a deceleration of 6 seconds (the fuel is cut at the time of deceleration, and the catalyst is exposed to severe conditions of a high-temperature oxidizing atmosphere). The catalyst was aged for 50 hours under the following conditions.

Evaluation of the catalyst performance after aging was performed using a commercially available electronically controlled engine (4-cylinder 1800 cc) and a multi-converter filled with each catalyst connected to the exhaust system of the engine. The three-way performance of the catalyst is 400 ° C at the catalyst inlet gas temperature.
The evaluation was performed under the conditions of space velocity of 90,000 hr- ¹ . At this time, a 1Hz sine wave type signal from an external oscillator is introduced into the engine control unit, and the air-fuel ratio (A / F) is ± 0.5A / F, 1
The average air-fuel ratio is continuously changed while oscillating at Hz, and the catalyst inlet and outlet gas compositions at this time are simultaneously analyzed to purify CO, HC and NO when the average air-fuel ratio is A / F = 15.1 to 14.1 The rate was determined.

A plot of the CO, HC and NO purification rates versus the inlet air-fuel ratio obtained as described above is plotted to create a ternary durability curve, and the intersection of the CO and NO purification rate curves (called a crossover point). Of the catalyst and the HC purification rate at the A / F value at the intersection were determined as evaluation criteria for the three-way performance of the catalyst.

In addition, the purification performance of the catalyst at low temperatures is such that the air-fuel ratio is ± 0.5 A /
The average air-fuel ratio is set to A / F = 14.
The engine was operated with the temperature fixed to 6, and a heat exchanger was installed in front of the catalytic converter in the engine exhaust system to change the gas at the catalyst inlet and outlet when the catalyst inlet gas temperature was continuously changed from 200 ° C to 500 ° C. The composition was analyzed and evaluated by determining the purification rates of CO, HC and NO.

The purification rates of CO, HC, and NO versus the catalyst inlet gas temperature obtained as described above are plotted on a graph, and the catalyst inlet gas temperature (T ₅₀ ) at which the purification rate shows 50% is determined. It was a criterion for evaluating the purification performance.

Table 2 shows the results obtained by the above catalyst performance evaluation method. From Table 2, it is clear that the catalyst disclosed in the present invention has excellent durability with little deterioration even under severe conditions such as a high-temperature oxidizing atmosphere due to the stabilized cerium oxide. .

Continued on the front page. (72) Inventor Hideyuki Baba 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Pref. Inside the Catalyst Research Laboratory, Nippon Shokubai Chemical Industry Co., Ltd. (56) References JP-A-2-111442 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01J 23/00 B01D 53/36

Claims (6)

(57) [Claims] 1. A stabilized cerium containing (a) zirconia, (b) at least one of yttrium and calcium, and (c) at least one of rare earth elements (excluding yttrium and cerium). An oxide (I), activated alumina (II), and at least one platinum group metal (III) selected from the group consisting of rhodium, platinum, and palladium; ) Is 10 to 50% by weight as ceria, 0.1 to 15% by weight of at least one oxide (b) of yttrium and calcium, and at least one or more of the rare earth elements (excluding yttrium and cerium) Exhaust gas obtained by coating a catalyst composition containing 0.1 to 15% by weight of the oxide (c) on a monolithic carrier having a honeycomb structure. Purification catalyst. 2. The catalyst according to claim 1, wherein the stabilized cerium oxide (I) is contained in the catalyst composition in an amount of 5 to 80% by weight. 3. The catalyst according to claim 1, wherein the rare earth element contained in the stabilized cerium oxide (I) is at least one of neodymium and lanthanum. 4. A method according to claim 1, wherein at least one platinum group metal selected from the group consisting of platinum and radium is supported on activated alumina (II) and / or stabilized cerium oxide (I). The catalyst as described. 5. A method according to claim 1, wherein the activated alumina (II) is added in an amount of 0.
02 to 2% by weight of rhodium and 0 to 10% by weight of the catalyst composition and at least one selected from the group consisting of platinum and palladium (total of platinum and palladium excluding 0% by weight). Item (1). 6. (a) zirconia, (b) at least one of yttrium and calcium, and (c) a rare earth element (excluding yttrium and cerium)
Cerium oxide (I), activated alumina (II), and at least one platinum group metal (III) selected from the group consisting of rhodium, platinum and palladium, containing at least one of the following: In producing an exhaust gas purifying catalyst obtained by coating a catalyst carrier having a monolith structure with a catalyst composition containing the following, the stabilized cerium oxide (I) is converted into a zirconium oxide and / or a hydroxide thereof. At least one salt selected from yttrium salts and calcium salts, at least one salt of a rare earth element (excluding yttrium and cerium), and a solution of a cerium salt impregnated and calcined for exhaust gas purification Method for producing catalyst.