JP3251009B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to hydrocarbons (HC), carbon monoxide (C) discharged from internal combustion engines of automobiles, oil stoves or factories, etc.
The present invention relates to a catalyst for efficiently removing O) and nitrogen oxides (NO _x ) at a low temperature of 250 ° C. or lower and a method for producing the same.

(Prior Art) In recent years, maintenance of the natural environment has been given particular importance, and regulations on exhaust gas from automobiles and the like tend to be strengthened. As part of the tightening of regulations, there is a problem of purifying NO _x , HC and CO from exhaust gas at the start of operation (cold start) of a vehicle.
The temperature of the catalyst layer at the time of cold start is as low as 300 ° C or less until it is heated by the exhaust heat (about 2 minutes). The catalyst layer is made of a conventional noble metal such as platinum (Pt) or rhodium (Rh). The three-way catalyst for automobile exhaust, which consists of rare earth oxides such as ceria (CeO ₂ ) as a catalyst and a carrier such as alumina (Al ₂ O ₃ ), has a high purification temperature of 300 ° C or higher. At present, the harmful components, particularly HC, discharged until the catalyst layer is heated to 300 ° C. or more are not sufficiently purified. Therefore, at the time of a cold start, a catalyst converter having a built-in heater for heating to a temperature at which the catalyst exhibits activity, and a method of trapping the harmful component by an adsorption trapper using zeolite or the like until the activity of the catalyst occurs, Gold (Au) / iron oxide (Fe ₂ O) having the ability to oxidize CO from -70 ° C
₃ ) A method using a catalyst has been considered. However, they have cost and technical problems, that is, the capacity of the heater battery, that is, extra power is required for heating the heater, and the conventional battery is insufficient and needs a large capacity battery. Becomes Then, it is necessary to provide a very large adsorption trapper in order to adsorb all the HC discharged at the time of cold start. Then
A very poor HC purification ability is a major problem.

Also, in oil stoves, etc.,
There is a similar problem with the removal of harmful gases such as.

(Object of the Invention) The present invention solves the above-mentioned disadvantages of the prior art by using a 250 ° C.
In the following low temperature range, NO _x in the exhaust gas discharged from an internal combustion engine of an automobile, HC, CO in particular to provide a catalyst and a manufacturing method thereof for efficiently removable new exhaust gas purifying HC Aim.

(Description of the First Invention) The first invention comprises at least one oxide of cobalt, nickel, iron, chromium, and manganese and at least one of platinum, rhodium, and palladium. Purification function of hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gas of internal combustion engines at a temperature of 250 ° C. or less at a temperature of 250 ° C. or lower by forming a solid solution at an interface where at least one of the platinum, rhodium and palladium contacts at least This is an exhaust gas purifying catalyst characterized by being configured to produce

According to this catalyst, HC, C
O, can be efficiently purify NO _x. In particular, it enabled the purification of HC, which could hardly be purified with the conventional catalyst.

Although the action of the present catalyst is not clear, it is considered as follows.

The conventional three-way catalyst is a harmful component in exhaust gas, C
O, HC and NO _x are adsorbed on the noble metal and removed by the following reaction.

CO + O ₂ → CO ₂ ··· NO _x + H ₂ → N ₂ + H ₂ O ··· NO _x + CO → CO ₂ + N ₂ ··· HC + O ₂ → H ₂ O + CO ₂ ··· Rare earth oxides such as CeO ₂ which is a co-catalyst In addition to improving the thermal stability of the carrier and ensuring high dispersion of precious metals, CeO ₂ converts O ₂ to precious metals in a reducing atmosphere at 400 ° C or higher, that is, even if oxygen (O ₂ ) is insufficient in exhaust gas. It has the function of advancing the oxidation of CO and HC by the so-called O ₂ storage capacity to be supplied. However, in low-temperature 250 ° C. or less occurs in preference adsorption to the noble metal of CO, O _2, adsorption of the HC and the like is prevented HC, removal of NOx is not almost performed, also O ₂ supply CeO ₂ At a low temperature of 250 ° C. or less, it was hardly performed, and purification of HC and the like based on the O ₂ storage capacity of CeO ₂ was impossible.

Cobalt in the present invention, nickel, iron, chromium, or an oxide of manganese is different from the CeO ₂
Cobalt, nickel, iron, chromium,
O ₂ occluded by any metal of manganese itself
The spit allowed promoting the reaction of CO were preferentially adsorbed on platinum and rhodium and palladium, CO can be changed to CO _2, can be adsorbed on the order O _2, HC, platinum and rhodium and palladium also NO _x So that
Than it allows to purify the HC and NO _x.

In addition, since the above-mentioned reactions (1) to (4) are performed, the temperature of the catalyst itself increases due to the heat of the reaction, and the catalytic activity is also enhanced.

(Description of Other Inventions of First Invention) In the first invention, the oxide of any one of cobalt, nickel, iron, chromium, and manganese is Co.
Examples include ₃ O ₄ , NiO, Fe ₂ O ₃ , Cr ₂ O ₃ , Nn ₂ O _3, etc., but these are only examples. One or more of these are used. Any of these metal oxides has a size of 2000 ° or less and a specific surface area of 0.2 to ²⁰⁰ m ² / g. If it exceeds this range, good purification activity cannot be exhibited. Desirably 100Å
Below, 50m ² / g~200m ² / g is good.

One or more of Rh, Pt, and Pd are used as the noble metal. The amount is 0.05 to 10 at% based on the metal oxide. 0.05at%
If the content is less than the above, the purification activity is not exhibited. Conversely, if the content is more than 10 at%, the amount of the noble metal is too large and agglomerates with each other to lower the activity. Desirably, the content is 1 to 1.2 at%. The particle size of the noble metal is 500 ° or less.

The metal oxide and the noble metal are uniformly mixed and used. As described above, in order to oxidize CO adsorbed on the surface of the noble metal by O ₂ exhaled from the metal oxide and efficiently remove CO from the noble metal surface, the noble metal and the metal oxide are present in close contact It is necessary. In addition, the interface where these two substances come into contact with each other exhibits better purification characteristics when they are in solid solution.

The catalyst according to the present invention is produced by the following method.

A conventionally known method, a method of impregnating an aqueous solution of any of the above-described noble metal salts with a solution obtained by thermally decomposing the metal nitrate, organic metal salt or metal chloride, hydrolyzing the various metal salts, After the obtained hydroxide is calcined, any one of the method of supporting any of the above-mentioned noble metals and the method of co-precipitating from a mixed solution comprising the above-mentioned metal salt and any of the above-mentioned noble metal salts is used. May be used.

More specifically, the method of the present invention comprises the steps of drying a mixture of the precipitate of the above-mentioned metal compound and the precipitate of any of the above-mentioned noble metal compounds to form a powder, and heating the powder in air. This is a manufacturing method of firing.

Alternatively, a manufacturing method in which a powder of any one of the above-mentioned compounds of a metal is impregnated with an aqueous solution of any one of the above-mentioned compounds of a noble metal, and then the powder is heated in air to be fired.

The shape and production of the catalyst composed of the metal oxide and the noble metal are not limited, such as powder, pellet, and honeycomb. In addition, a binder such as alumina sol, silica sol, zirconia sol, titania sol, etc. is added to a powdered catalyst to form a predetermined shape, or water is added, and a slurry is formed on a refractory substrate such as alumina having a honeycomb shape in the form of a honeycomb. It may be applied.

Example A catalyst according to the present invention was manufactured, and the purification activity of NO _x , CO, and HC was evaluated for the catalyst using a model gas having a stoichiometric air-fuel ratio. Similar activity evaluation was also performed for the comparative catalyst.

Example 1 A solution obtained by dissolving 54 g of cobalt nitrate and 0.433 g of palladium nitrate in ion-exchanged water 2 (atomic ratio Pd: Co = 1: 100) at room temperature at a speed of about 0.6 m / sec from a separating funnel was obtained. 50 g of sodium carbonate is dropped into an alkaline aqueous solution dissolved in ion-exchanged water 2 and stirred. After leaving this solution for one hour, it is filtered, washed, and dried under reduced pressure. Then, the obtained powder was fired in air at 350 ° C. for 3 hours. About 2 to 3
The resultant was compacted into a die having a diameter of mm to obtain Example Catalyst No. 1 composed of Pd and Co ₃ O ₄ .

Example 2 In the method of Example 1, dinitrodiamino Pt was used instead of palladium nitrate (the atomic ratio of Pt to Co was 1: 100).
Catalyst No. 2 consisting of Pt and Co ₃ O _{4 under the} same conditions except that ammonium carbonate was used as the alkaline aqueous solution
I got

Example 3 An aqueous solution of cobalt nitrate (50 g /) was dropped into an aqueous solution of sodium carbonate (50 g /) and stirred to precipitate cobalt hydroxide, followed by filtration, washing, drying under reduced pressure, and drying in air under a pressure of 350 g. Pd nitric acid aqueous solution is added to the powder obtained by firing at
It was impregnated at a content of 1 at% and then fired at 350 ° C. in air. This calcined material is compacted into a die of 2-3 mm,
Example catalyst No. 3 consisting of d and Co ₃ O ₄ was obtained.

Except for using dinitrodiamino Pt instead of Pd nitrate to give Example catalyst No.4 of Pt and Co ₃ O ₄ Metropolitan under the same conditions in the method of Example 4 Example 3.

Example 5 Co nitrate was calcined in air at 600 ° C. for 5 hours and thermally decomposed to obtain Co ₃ O ₄ . This Co ₃ O ₄ powder was impregnated so as to have a Pd nitrate content of 3.5 at%, and then fired in air at 350 ° C. for 3 hours. The calcined product was compacted into a die having a size of 2 to 3 mm to obtain Example Catalyst No. 5 composed of Pd and Co ₃ O ₄ .

Example 6 Example catalyst No. 6 consisting of Pt and Co ₃ O ₄ was obtained under the same conditions as in Example 5 except that dinitrodiamino Pt was used instead of Pd nitrate.

Example 7 Example catalyst No. 7 consisting of Pd and NiO was obtained under the same conditions as in Example 5 except that Ni nitrate was used instead of Co nitrate.

Example 8 Example catalyst No. 8 comprising Pd and Fe ₂ O ₃ was obtained under the same conditions as in Example 5 except that ferric nitrate was used instead of Co nitrate.

Example 9 In the method of Example 1, 18 g of nickel nitrate was added in addition to 54 g of cobalt nitrate and 0.433 g of palladium nitrate, and the amount of sodium carbonate was 70 g. Except for this, Example Catalyst No. 9 consisting of Pd, NiO, and Co ₃ O ₄ was obtained under the same conditions.

Comparative Example 1 γ-Al ₂ O ₃ having a specific surface area of about 220 m ² / g La (La 0.03 mol / 12
0g) Ce nitrate so as to contain 0.3 mol as CeO _{2 in} 120 g of powder
And baked in the air at 650 ° C for 3 hours, then using an aqueous dinitrodiamino Pt solution to contain 1.5 g as Pt amount,
It was impregnated and calcined in the atmosphere at 250 ° C. for 3 hours. Thereafter, impregnation was performed using an aqueous solution of Rh nitrate so as to contain 0.3 g as an amount of Rh.
It was dried in air at 0 ° C. overnight. This was compacted into a die having a size of about 2 to 3 mm to obtain Comparative Catalyst No. C1. This comparative example catalyst is a Pt-Rh-based three-way catalyst usually used for an automobile exhaust catalyst.

Comparative Example 2 A comparative example catalyst No. C2 consisting of only Co ₃ O ₄ was obtained in the same manner as in Example 1 except that palladium nitrate was not added and the other conditions were the same.

Comparative Example 3 γ-Al ₂ O ₃ pellet carrier having a specific surface area of about 140 m ² / g (2 to 3 m
mφ) in an aqueous solution of palladium nitrate, impregnated so that the Pd content is 0.14 wt% with respect to the weight of γ-Al ₂ O ₃ , and
℃, dried for 5 hours and calcined in air at 600 ° C for 3 hours. This calcined product was compacted into a die having a size of about 2 to 3 mm to obtain Comparative Example Catalyst No. C3 composed of Pd and Al ₂ O ₃ .

Comparative Example 4 Pt was obtained under the same conditions as in Comparative Example 3 except that dinitrodiamino Pt was used instead of palladium nitrate.
Comparative Example Catalyst No. C4 consisting of and Al ₂ O ₃ was obtained.

Evaluation of catalytic activity Using the catalysts of Example Nos. 1 to 9 and Comparative Example Nos. C1 to C4 in the form of dice, each of the catalysts at 50 ° C. to 600 ° C. in a model gas having a stoichiometric air-fuel ratio shown in Table 1 was used. Ingredients (NO, CO, H
The temperature raising purification characteristics of C) were measured. Of these results, Example Catalyst No. 1 is shown in FIG. 1 and Comparative Example Catalyst No. C1 (conventional three-way catalyst for automobile exhaust) is shown in FIG.

Example catalyst No. 1 can remove 100% of CO, HC and NO at 200 ° C. However, Comparative Example Catalyst No.
Even at ℃, the purification rate is only about 40 to 80% lower.

Table 2 summarizes the measurement results of the above catalysts at 50% purification rates of NO, CO, and HC.

Example catalyst No. 1 was compared with comparative example catalyst No. C1 and the like (No. 1).
(Comparison between FIG. 2 and FIG. 2 and comparison in Table 2).

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the purification rate and the temperature for Example Catalyst No. 1 and FIG. 2 for Comparative Example Catalyst No. C1.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Yokota 41, Chukumi Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central R & D Laboratories Co., Ltd. Examiner, Eiko Shigeta, Automobile Co., Ltd. (56) References JP-A 1-224047 (JP, A) JP-A 63-178847 (JP, A) JP-A 62-152540 (JP, A) JP 62-176544 (JP, A) JP-A-63-185453 (JP, A) JP-A-58-189035 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00 -37/36 B01D 53/86

Claims (4)

(57) [Claims] An oxide of at least one of cobalt, nickel, iron, chromium and manganese and at least one of platinum, rhodium and palladium, wherein at least one of said oxides and said platinum and rhodium; Solid solution at the interface where at least one of the palladium contacts
An exhaust gas purifying catalyst characterized in that it has a function of purifying hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gas of an internal combustion engine or the like at a temperature of 250 ° C or less. 2. An oxide comprising at least one oxide of any of cobalt, nickel, iron, chromium and manganese and at least one of platinum, rhodium and palladium, and said platinum, rhodium and palladium to said oxide. The amount of at least one is 0.05 to 1.2 at%, and at least one of the oxides and the platinum, rhodium, and at least one of palladium form a solid solution at an interface where they are in contact with each other and at a temperature of 250 ° C. An exhaust gas purifying catalyst characterized by having a function of purifying hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gas. 3. A method for producing an exhaust gas purifying catalyst comprising at least one of oxides selected from the group consisting of cobalt, nickel, iron, chromium and manganese and at least one of platinum, rhodium and palladium. A mixture of the precipitate of any of the compounds iron, chromium and manganese and the precipitate of at least one compound of platinum, rhodium and palladium is dried to form a powder, and the powder is heated in air to form a powder. A method for producing an exhaust gas purifying catalyst, characterized by firing. 4. A method for producing an exhaust gas purifying catalyst comprising at least one oxide selected from the group consisting of cobalt, nickel, iron, chromium and manganese, and at least one of platinum, rhodium and palladium. , Iron, chromium, powder of any one of the compounds of manganese, impregnated with an aqueous solution of at least one compound of the platinum, rhodium and palladium, the powder is heated in air and fired. A method for producing an exhaust gas purifying catalyst.