JPH0490852A - Waste gas cleaning catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst with which waste gas is cleaned efficiently while suppressing H2S generation by carrying catalytic active substances consisting of metal oxide elements, noble metals, and alumina-stabilized ceria (cerium dioxide) in three-dimensional structure. CONSTITUTION:Catalytic active substances consisting of oxides of metals such as iron, cobalt, strontium, etc., noble metals such as platinum, rhodium, etc., and alumina-stabilized ceria are carried in a three-dimensional structure, e.g. ceramic honeycomb carrier, etc. A catalyst obtain in this way decomposes HC, CO, NOx efficiently while suppressing H2S generation without using nickel. Since nickel is not used, problem such as possibility to cause cancer is avoided.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a catalyst for purifying exhaust gas, and more specifically, to effectively purify exhaust gas from internal combustion engines such as automobiles while suppressing the generation of hydrogen sulfide. Concerning catalysts for purification.

(Prior Art) Many catalysts for purifying exhaust gas emitted from internal combustion engines such as automobiles have been proposed and put into practical use. Initially hydrocarbons (HC) and -carbon oxides (cO)
An oxidation catalyst that removes HC and Co has been put into practical use, but due to stricter regulations and the uniqueness of the source, three-way catalysts that simultaneously decompose and remove nitrogen oxides (NOx) in addition to HC and Co are now mainstream. It has become. This three-way catalyst simultaneously performs the oxidation reaction of HC and Co and the reduction reaction of NOx.

However, the fuel gasoline contains a trace amount of sulfur compounds, and these sulfur compounds are discharged from the internal combustion engine as sulfur oxides (S OX).

s in the exhaust gas if this exhaust gas is in the reduction zone.

X is reduced to hydrogen sulfide (H2S) by the reducing action of the three-way catalyst and is discharged.

As a measure to suppress the reduction of SOx to H2S, a catalyst in which the generation of H2S is suppressed by adding nickel is proposed in European Patent No. 244117. However, in recent years,
The use of nickel is being restricted due to suspicions that nickel carbonyl is a carcinogen.

In addition, a catalyst to which alkali metals were added was published in Japanese Unexamined Patent Application Publication No. 54-13
No. 3488, No. 55-15643, No. 56-1029
Although disclosed in each publication No. 40, these catalysts
Since the purpose is not to suppress the generation of S, its suppressive effect is not sufficient.

Therefore, there is currently a demand for an exhaust gas purifying catalyst that can suppress the generation of H2S and efficiently decompose and remove HC, CO, and NOx without using nickel.

By the way, as a method for supporting a precious metal on a three-dimensional structure such as a honeycomb structure having an integral structure, activated alumina is supported on the structure in advance, and then this three-dimensional structure is immersed in a noble metal solution. The three-dimensional structure can be supported by chemical adsorption or physical adsorption, or by pre-impregnating activated alumina with a noble metal solution, drying and firing, and wet-pulverizing the resulting powder into a slurry. A method of supporting the compound as a carbon dioxide is generally used.

However, it is known that catalysts obtained by these methods are in a state where SOX contained in exhaust gas is very likely to be reduced to H2S.

(Issues to be Solved by the Invention!) The purpose of the present invention is to provide a catalyst that purifies exhaust gas by efficiently decomposing and removing HC, CO, and NOx while suppressing the generation of H2S without using nickel as a catalyst component. The goal is to provide the following.

(Means for Solving the Problems) According to the research of the present inventors, alumina-stabilized ceria is used, and this is mixed with an oxide of at least one metal selected from iron, cobalt, strontium, magnesium, and manganese. It was found that the above object could be achieved by using it in combination with the above, and based on this knowledge, the present invention was completed.

That is, the present invention provides: (a) an oxide of at least one metal selected from the group consisting of iron, cobalt, strontium, magnesium, and manganese; (b) platinum;
The present invention relates to a catalyst for exhaust gas purification, characterized in that a three-dimensional structure supports at least one noble metal selected from the group consisting of rhodium and palladium, and (c) a catalytically active substance consisting of alumina-stabilized ceria.

The present invention will be explained in detail below.

The alumina-stabilized ceria used as the catalyst component (c) in the present invention means cerium oxide stabilized by alumina, which is obtained by firing a cerium compound in the presence of an aluminum compound. Specifically, a water-insoluble cerium compound is mixed with a water-soluble aluminum compound and/or a water-insoluble cerium compound.
Or impregnated with alumina hydrate, usually 100 to 30
It is obtained by drying at 0'C and then firing at 300-700'C in air.

The above-mentioned water-insoluble cerium compound includes cenium oxide,
Examples include cerium hydroxide and cerium carbonate. Among these, cerium carbonate is particularly preferably used. This water-insoluble cerium compound is usually used in the form of fine powder, and its particle size is 0.1 to 10011 m.

In addition, the water-soluble aluminum compounds and alumina hydrates include aluminum nitrate, aluminum chloride,
Examples include fEM aluminum, gibbsite, bayerite, boehmite, alumina gel, and alumina sol. Among these, aluminum nitrate is particularly preferably used.

There is no particular restriction on the ratio of the water-insoluble cerium compound to the water-soluble aluminum compound and/or aluminum hydrate, and an effective alumina-stabilized ceria can be obtained by appropriately determining the ratio, but cerium (ce>
As the atomic ratio of and aluminum (82), C, e/A
It is preferable that P=1/1 to 20/1, especially Ce/
It is preferable that older brother A=2/1 to 10/1.

The alumina-stabilized ceria obtained as described above has a higher oxygen storage capacity than ordinary cerium oxide because it has more lattice defects in its structure, and also promotes the activation of steam involved in the water gas shift reaction. The storage effect and water gas shift reaction promotion effect are improved, and as a result, the decomposition and removal performance of HClC0 and NOx is dramatically improved compared to the conventional catalyst using cerium oxide.
It is thought that the window width will also be expanded.

As starting materials for the metal oxide component (a), sulfates, nitrates, carbonates, acetates, chlorides, and other W salts of iron, cobalt, strontium, tin, magnesium, and manganese are used (A There are no particular restrictions on the usage form of the metal oxide component (a), but after impregnating the alumina-stabilized ceria with the at least one metal salt, the metal oxide component (a) is heated at 100 to 300°C. It is preferable to dry it at 100° C. and then to sinter it in air at 300 to 700° C., and use it as supported on alumina-stabilized ceria.

As the metal oxide component (a), in addition to combinations such as iron oxide-magnesium oxide, iron oxide-cobalt oxide, and iron oxide-strontium oxide, magnesium oxide, strontium oxide, etc. are preferably used.

As the noble metal component (b), at least one selected from the group consisting of platinum, rhodium, and palladium is used, and as the rhodium source, rhodium nitrate, rhodium chloride, rhodium sulfate, rhodium sulfide complex salt, rhodium ammine complex salt, etc. is preferably used. In addition, platinum sources and palladium sources include chloroplatinic acid, platinum nitrate,
Dinitrodiammine platinum, platinum sulfide complex salt, platinum tetramine chloride, palladium nitrate, palladium chloride, palladium sulfide complex salt, palladium tetramine chloride, and the like are preferably used.

When the catalytically active substance used in the present invention consists of the metal oxide component (a), noble metal component (b) and alumina-stabilized ceria component (c), the amount of these components supported on the three-dimensional structure is 0.5 each per liter of original structure
~log, about 0.01 to 5 g and 10 to 150 g.

The catalytically active material constituting the exhaust gas purifying catalyst of the present invention is
In addition to the above components (a), (b) and (c), (
cl) May contain a refractory inorganic oxide.

Activated alumina is usually used as the refractory non-molecular oxide component (d). As this activated alumina, one having a specific surface area of 50 to 180 m27g is preferably used. There are no particular restrictions on the crystal structure of activated alumina, and γ
, δ, θ, χ, and η can be used. In addition, at least one rare earth element such as lanthanum, cerium, and neodymium or an alkaline earth metal element such as calcium and barium is added in an amount of 0.1 to 3
Activated alumina loaded at 0% by weight can also be used.

The catalytically active substances used in the present invention include a metal oxide component (a), a noble metal component (b), an alumina-stabilized ceria component (c), and a refractory state a! When consisting of the oxide component (d), the amount of these components supported on the three-dimensional structure is 0.5 to 10 g and 0.01 to 5 g, respectively, per liter of the three-dimensional structure.
g, about 10 to 150 g and about 30 to 150 g.

Note that the volume of the three-dimensional structure, which serves as a reference for the amount of each component supported, means the apparent volume of the three-dimensional structure.

The three-dimensional structure used in the present invention may be made of any fire-resistant material, and its shape may be particle-like, monolith-like, plate-like, rod-like, or fibrous. good.

In particular, a three-dimensional structure having an integral structure is preferably used.

A specific example of a three-dimensional structure having such an integral structure is what is generally called a ceramic honeycomb carrier. In particular, honeycomb carriers made of cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, titanium aluminum, betalite, subodumene, aluminosilicate, magnesium silicate, etc. are preferred, and among them, honeycomb carriers made of cordierite are preferred. It is suitable for internal combustion engines.

In addition, an integral structure made of an oxidation-resistant, heat-resistant metal such as stainless steel or a Fe-Cr-AR gold alloy can also be used.

The monolith carrier as described above can be manufactured by extrusion molding, a method of rolling and compacting a sheet-like element, or the like. There are no particular restrictions on the shape of the gas passage port (cell shape);
It may be hexagonal, quadrilateral, triangular or corrugated.

A cell density (number of cells/unit cross-sectional area) of 150 to 600 cells/square inch can be used sufficiently and good results can be obtained.

(Effects of the Invention) The exhaust gas purifying catalyst of the present invention comprises a metal oxide component (a),
Noble metal component (b), and alumina stabilized ceria component (
c), and if necessary, a refractory inorganic oxide component (d)
A three-dimensional structure supports a catalytically active substance consisting of HC, Co and NO while suppressing the generation of H2S.
The exhaust gas can be efficiently purified by efficiently decomposing and removing x, and furthermore, since nickel is not used, the problem of carcinogenesis can be avoided.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 150ml of an aqueous solution containing 41.2g of aluminum nitrate
Alumina-stabilized ceria (ce/AM =5/1 (atomic ratio))
(hereinafter sometimes simply referred to as "ceria") powder was prepared.

30.36g of ferric nitrate and 8.17g of strontium nitrate
An aqueous solution prepared by dissolving 500 g in 60 m2 of fishing rod was thoroughly mixed with 100 g of the above alumina stabilized serif, dried at 130°C for 10 hours, and then calcined at 500"C for 1 hour to obtain iron oxide-strontium oxide supported ceria powder. I got it.

Next, a nitric acid aqueous solution of dinitrodiammine platinum containing 1.5 g of platinum (Pt) and a rhodium nitrate aqueous solution containing 0.3 g of rhodium (Rh) were mixed, and the resulting mixture was mixed with the above iron oxide-strontium oxide. After mixing with supported ceria powder and sufficiently drying, it was fired in air at 400° C. for 2 hours to obtain iron oxide-strontium oxide supported ceria powder containing Pi-Rh.

This powder was wet-milled to prepare an aqueous slurry. Commercially available cordierite monolith carrier (manufactured by Nippon Insulator Co., Ltd.,
A cylindrical carrier with an outer diameter of 33 mm and a length of 76 mm having approximately 400 gas flow cells per square inch of cross section) approximately 6
5 m2 was crushed in the above aqueous slurry, pulled up, and the excess slurry was blown out with compressed air to remove clogging.
Next, the catalyst (A) was prepared by drying at 130° C. for 3 hours.

In this catalyst (A), Pt per liter of three-dimensional structure
75 g of O, 0.15 g of Rh, 50 g of alumina stabilized serif, 3 g of iron oxide, and 2 g of strontium oxide were supported.

Example 2 A catalyst was prepared using the same commercially available cordierite monolith support as used in Example 1 as the three-dimensional structure. This monolithic support has a cross section of about 40
Has 0 gas flow cells, outer diameter 33mm, length 7
It was 6 mm cylindrical and had a volume of about 65 m.

A nitric acid aqueous solution of dinitrodiammine platinum containing 1.5 g of platinum (Pt) and a rhodium nitrate aqueous solution containing 0.3 g of rhodium (Rh) were mixed, and the resulting mixture had a specific surface area of 100 mj! /g of activated alumina, thoroughly dried, and then calcined in air at 400°C for 2 hours to obtain P.
Alumina powder containing t-Rh was prepared.

Next, an aqueous solution of 41.2 g of aluminum nitrate dissolved in 150 mV of water and cerium carbonate powder (1 t containing ce: Ce
(47% by weight as O2) and 201 g of
After drying at 0°C for 10 hours, baking at 500°C for 1 hour,
An alumina-stabilized ceria (ce/AJ2=5/1 (atomic)) powder was prepared.

100 g of this ceria powder was thoroughly mixed with an aqueous solution of 30.36 g of ferric nitrate and 8.17 g of strontium nitrate dissolved in 60 mR of fishing rod, dried at 130"C for 10 hours, and then baked at 500 °C for 1 hour. Thus, ceria powder supporting iron oxide-strontium oxide was prepared.

The Pt-Rh-containing alumina powder and the iron oxide-strontium oxide-supporting ceria powder obtained as described above were wet-pulverized to prepare an aqueous slurry. After immersing the monolithic carrier in this aqueous slurry for 30 seconds, pulling it out,
The excess slurry was blown away with compressed air to remove clogging, and then dried at 130°C for 3 hours to obtain a catalyst (B).

In this catalyst (B), Pt per liter of three-dimensional structure
0.75 g, RhO, 15 g, 100 g of alumina, 50 g of alumina stabilized serif, 3 g of iron oxide, and 2 g of strontium oxide were supported.

Example 3 Catalyst (c) was obtained in the same manner as in Example 2, except that 13.30 g of cobalt acetate was used instead of strontium nitrate.

In this catalyst (c), Pt per liter of three-dimensional structure
0.75 g of Rh, 0.15 g of Rh, 100 g of alumina, 50 g of alumina stabilized serif, 3 g of iron oxide, and 2 g of cobalt oxide were supported.

Example 4 In Example 2, the amount of ferric nitrate used was 40.48g.
and 1 liter of magnesium nitrate instead of strontium nitrate. Catalyst (D) was obtained in the same manner as in Example 2 except that 72 g was used.

In this catalyst (D), Pt per liter of three-dimensional structure
0.75 g, Rh 0.15 g - 100 g of alumina, 50 g of alumina stabilized serif, 4 g of pig iron oxide and 1 g of magnesium oxide were supported.

Example 5 A catalyst (E) was obtained in the same manner as in Example 2, except that 23.26 g of tin chloride was used instead of ferric nitrate and strontium nitrate.

In this catalyst (E), PL per liter of three-dimensional structure
75 g of O, 0.15 g of Rh, 100 g of alumina, 50 g of alumina stabilized serif, and 5 g of tin oxide were supported.

Example 6 A catalyst (F) was obtained in the same manner as in Example 2, except that 63.63 g of magnesium nitrate was used instead of ferric nitrate and strontium nitrate.

In this catalyst (F), Pt per liter of three-dimensional structure
0.75g, Rh0.15g, Alumina 100g,
Alumina stabilized serif 50g and magnesium oxide 5
g was supported.

Example 7 In Example 6, the amount of magnesium nitrate used was 1 liter.
The catalyst (G
) was obtained.

In this catalyst (G), Pt per liter of three-dimensional structure
0.75 g of Rh, 0.15 g of Rh, 100 g of alumina, 50 g of alumina stabilized serif, and 1 g of magnesium oxide were supported.

Example 8 A catalyst (H) was obtained in the same manner as in Example 6 except that 32.37 g of manganese nitrate was used instead of magnesium nitrate.

In this catalyst (H), Pt per liter of three-dimensional structure
0.75g, Rho, 1!5g, Alumina 100g
, 50 g of alumina stabilized serif and 4 g of manganese oxide
was carried.

Example 9 Catalyst (1) was obtained in the same manner as in Example 6, except that 20.42 g of strontium nitrate was used instead of magnesium nitrate.

In this catalyst (1), PL per liter of three-dimensional structure
O, 75g, Rh0.15g, alumina 100g, alumina stabilized serif 50g and strontium oxide 5g
was carried.

Comparative Example 1 A catalyst (J) was obtained in the same manner as in Example 2, except that ferric nitrate and strontium nitrate were not used.

In this catalyst (J), Pt per liter of three-dimensional structure
0.75 g, Rh 0.15 g, alumina 100 g and alumina stabilized serif 50 g were supported.

Comparative Example 2 In Example 2, instead of mixing ferric nitrate and strontium nitrate with alumina-stabilized ceria and firing to form iron oxide-strontium carbide-supported ceria, iron oxide and strontium oxide were simply mixed with alumina-stabilized ceria. A catalyst (K) was obtained in the same manner as in Example 2 except for mixing.

In this catalyst (K), Pt per liter of three-dimensional structure
0.75g, Rh0.15g, alumina 100g, alumina stabilized serif 50g1. 3 g of iron oxide and 2 g of strontium oxide were supported.

Comparative Example 3 A catalyst (L) was obtained in the same manner as in Example 2 except that tin oxide was used instead of manganese nitrate.

In this catalyst (L), PL per liter of three-dimensional structure
75 g of O, 0.15 g of Rh, 100 g of alumina, 50 g of alumina stabilized serif, and 5 g of tin oxide were supported.

Comparative Example 4 A nitric acid aqueous solution of dinitrodiammine platinum containing 1.5 g of platinum and a rhodium nitrate aqueous solution containing 0.3 g of rhodium were mixed, and this aqueous solution was mixed with 200 g of activated alumina having a specific surface area of 100 m''/g, and then sufficiently After drying, it was fired in air at 400°C for 2 hours to prepare a Pt-Rh-containing alumina powder.

This powder was wet-pulverized with 100 g of serif, 6 g of iron oxide, and 4 g of strontium oxide to prepare an aqueous slurry.
The same monolithic carrier used in Example 1 was immersed for 30 seconds, then pulled out and the excess slurry was blown out with compressed air to remove clogging, and then dried at 130°C for 3 hours to obtain catalyst (M). Ta.

In this catalyst (M), Pt per liter of three-dimensional structure
75 g of O, 0.15 g of Rh, 100 g of alumina, 50 g of serif, 3 g of M pig iron, and 2 g of strontium oxide were supported.

Example 10 Catalyst (A) prepared in Examples 1 to 9 and Comparative Examples 1 to 4
-(M) were tested for the amount of H2S generated and catalyst performance. The amount of H2S generated and catalyst performance were measured by the following method.

(H2S Generation Amount Test) A commercially available electronically controlled 4-cylinder 2000cc engine was used, and a catalyst was installed at a position approximately 1.5 m behind the engine manifold. The fuel used was gasoline to which thiophene was added so that the sulfur content in the gasoline was 0.029% by weight.

First, after operating for 15 minutes under the following operating condition (1), the system was switched to the following operating condition (2), and at the same time, exhaust gas was introduced into the gas absorption bottle at a rate of 1 liter per minute for 5 minutes to absorb H2S.

The absorption amount of H2S was measured by J I 5-KO108 methylene blue spectrophotometry.

Operating conditions 1) Rotation speed: 2000±20 (rpm) Boost pressure:
340±34 (mmHg) A/F (air/fuel)
:15.6±0.1Catalyst entrance temperature:550±10 (℃
) Circular rotation conditions (2) Rotation speed: 1000±20 (rpm) Boost pressure = 5
10±50 (mmHg) A/F: 13.6
±0.1 Catalyst inlet temperature: (Catalyst performance test) The following two tests were conducted to evaluate catalyst performance. In addition, prior to the test, the catalyst sample was left in an electric furnace at a temperature of 900° C. for 20 hours in an atmosphere containing 1% W, 10% water vapor, and nitrogen balance for durability treatment.

(1) Three-dimensional characteristic test Using a 1800cc engine, space velocity 107000h
i', catalyst inlet temperature 40J)"C average A/F
C0 when changing from 15.1 to 14.1 per second
1HC and NO purification rates were measured.

When the purification rates of Co, HC, and NO and A/F are plotted on the vertical and horizontal axes, respectively, the point where the purification rate curves of CO and No intersect was defined as a crossover point. CO and N at this crossover point
o purification rate (%) and HC purification rate at this A/F value (
%) was measured.

(2) Light-off characteristic test The same engine as used in the above three-way characteristic test was used, and the A/F was set to 14.
6, the catalyst inlet temperature was varied from 200°C to 450°C, the purification rates of C01HC and No were determined, and the temperature at 50% purification rate was measured.
, ) (cTsa, and NOTss).

The results are shown in Table 1. (Leaving space below) Table 1 Proceedings (self-prompted) Date of 1990 / Deadline 1゜Indication of the incident 1990 Patent application No. 2 / Date 2, Name of invention Catalyst for exhaust gas purification Osaka Prefecture 4-1-1 Koraibashi, Chuo-ku, Osaka City Contents (1) In page 11, line 11 of the specification, "cordierite..." is corrected to "cordierite...".

(2) In the same page, page 15, line 5, "...activity with a specific surface area of 100 m/g" is corrected to "...activity with a specific surface area of 100 m/g".

(3) In the third line of page 20, "Iron oxide - carbide..." is corrected to "Iron oxide - Oxide...".

(4) On page 20, lines 13 to 14, "In Example 2, the catalyst was prepared in the same manner as in Example 2 except that tin oxide was used instead of manganese nitrate" was replaced with "In Example 8, A catalyst was prepared in the same manner as in Example 8 except that tin oxide was used instead of manganese nitrate.

(5) In the 4th line of page 21, "100m product" 7g of life..." was changed to "product 100■t/g..."
The life of...” is corrected.

(6) On the bottom line of page 22, Correct "Rotation condition (2)" to "Driving condition (2)".

(7) On page 23, lines 13 to 14, '00
0hr', catalyst inlet temperature 400''C, average A/
Change F from 15.1 to 14.1 per second” to “000h”
r-', catalyst inlet temperature 400°C amplitude ±1. OA/F,
Average A/F is 15.1 per 6 minutes under the condition of frequency IHz.
- Correct to 14,1.

Claims (6)

[Claims] (1) (a) At least one metal oxide selected from the group consisting of iron, cobalt, strontium, tin, magnesium and manganese; (b) At least one metal oxide selected from the group consisting of platinum, rhodium and palladium. A catalyst for purifying exhaust gas, characterized in that a three-dimensional structure supports a catalytically active substance comprising a noble metal and (c) alumina-stabilized ceria. (2) The catalyst for exhaust gas purification according to claim (1), wherein the alumina-stabilized ceria component (c) is obtained by calcining a cerium compound in the presence of an aluminum compound. (3) The exhaust gas purifying catalyst according to claim (1), wherein the metal oxide component (a) is supported on the alumina-stabilized ceria component (c). (4) The supported amounts of the metal oxide component (a), the noble metal component (b) and the alumina-stabilized ceria component (c) are 0.5 to 10 g, 0.01 to 5 g, and 10 to 10 g per liter of three-dimensional structure, respectively. The exhaust gas purifying catalyst according to claim 1, which weighs 150 g. (5) The catalyst for exhaust gas purification according to claim (1), wherein the catalytically active substance further contains (d) a refractory inorganic oxide. (6) Claim in which the refractory inorganic oxide is activated alumina (
5) The exhaust gas purifying catalyst described in 5). (7) The amount of the refractory inorganic oxide component (d) supported is 30 to 30 per liter of the three-dimensional structure.
The exhaust gas purifying catalyst according to claim 5, which weighs 150 g.