JPH0788378A - Exhaust gas purifying catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purifying exhaust gas contg. NOx, CO and hydrocarbon. CONSTITUTION:Indium and one or more kinds of rare earth elements are allowed to coexist with a crystalline silicate having an X-ray diffraction pattern shown by table A and a chemical formula (1+ or -0.8)R2O.[aM2O3.bM'O.cAl2 O3]-.ySiO2 (expressed in terms of the molar ratio among oxides in a dehydrate state) to obtain the objective exhaust gas purifying catalyst. In the formula, R is an alkali metal ion and/or an H ion, M is ions of one or more kinds of elements selected among group VIII elements, rare earth elements, Ti, V, Cr, Nb, Sb and Ga, M' is an alkaline earth metal ion of Mg, Ca, Sr or Ba, a>0, 20>b>=0. a+c=1 and 3,000>y>11.

Description

Detailed Description of the Invention

[0001]

The present invention relates to nitrogen oxides (hereinafter referred to as NO
abbreviated as x), carbon monoxide (CO), hydrocarbon (hereinafter, H)
The present invention relates to a catalyst for purifying exhaust gas containing C).

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles and the like, it is common to utilize CO and HC in the exhaust gas to purify it using a noble metal catalyst, but within an extremely narrow range near the theoretical air-fuel ratio. Only NOx is purified. In recent years, the demand for low fuel consumption of automobiles has been strongly demanded due to the increase of global environmental problems, and a lean burn engine that burns at a ratio higher than the theoretical air-fuel ratio has been attracting attention as a key technology. However, considering the driving and acceleration characteristics of the automobile, there are many problems with the engine only in the lean region, and it is necessary to actually perform combustion both in the vicinity of the stoichiometric air-fuel ratio (Stoichio) and in the lean region. Recently, regarding purification of NOx in the lean region, a crystalline silicate catalyst containing cobalt or copper has been highlighted as a catalyst having high performance.

These catalysts have sufficient performance in the initial stage of the reaction, but have problems in durability,
Up to now, various crystalline silicates have been studied for improvement in order to improve durability. For example, in order to prevent desorption of aluminum, which is a main constituent element of crystalline silicate, and to stabilize cobalt or copper, a Group VIII element or a rare earth element in the crystal lattice (Japanese Patent Laid-Open No. 3-165816). , And alkaline earth metals (Japanese Patent Application No. 3-3191)
A method using a novel silicate added with 95) has been proposed. In addition, in order to prevent the invasion of steam that promotes the desorption of aluminum, the application of a crystalline silicate in which the hydrophobic silicalite is crystal-grown on the surface layer of the crystalline silicate to improve the steam resistance is being studied. (Japanese Patent Application No. 3-192829).

However, although the durability in a lean atmosphere is dramatically improved by using these catalysts, the gas temperature instantly rises to high temperature when accelerated, and the gas composition at this time is hydrogen or the like. A rich atmosphere in which the reducing agent is excessively present. Under these conditions, even if the improved crystalline silicate is applied, deterioration of the catalyst cannot be prevented. Therefore, improvement of durability of the catalyst in a high temperature rich atmosphere is a major problem in practical application of these catalysts. .

[0005]

The above problems are unavoidable as long as copper or cobalt is used as the active metal. That is, at a high temperature of 700 ° C. or higher, all base metal elements cause sintering and aggregate. for that reason,
It is considered that if the developed crystalline silicate can be used with a metal other than the base metal having denitration activity in a lean atmosphere, the durability will be sufficiently ensured and a great progress will be made toward practical application.

[0006]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies to overcome the disadvantages of conventional catalysts. As a result, a crystalline silicate catalyst carrying iridium has a denitration performance in a lean atmosphere. Moreover, it has been found that the catalyst hardly deteriorates even in a high temperature atmosphere under rich conditions. Further, as a result of earnest research, the present inventors have made at least one metal selected from rare earth elements coexist in addition to iridium in order to improve the denitration performance of the catalyst under high oxygen concentration. They found that the catalyst is effective, and completed the present invention.

That is, the present invention (1) has the X-ray diffraction pattern shown in Table A, which will be described later in detail, and represents (1 ± 0.8) R ₂ O expressed by the molar ratio of oxides in the dehydrated state.・ [AM ₂ O ₃・ bM'O ・ c
Al ₂ O ₃ ] .ySiO ₂ (wherein R is an alkali metal ion and / or hydrogen ion, M is selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium. At least 1
More than one kind of elemental ion, M ′ is an alkaline earth metal ion of magnesium, calcium, strontium, barium, a> 0, 20> b ≧ 0, a + c = 1, 3000> y
An exhaust gas purifying catalyst characterized in that iridium and at least one metal selected from rare earth elements coexist in a crystalline silicate having a chemical formula of> 11). (2) A layered composite crystal in which a crystalline silicate is a pre-synthesized crystalline silicate as a mother crystal, and a crystalline silicate composed of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. The exhaust gas purifying catalyst according to (1) above, which is an organic silicate. Is.

[0008]

The purifying reaction formula for purifying exhaust gas containing NOx, CO, and HC using the crystalline silicate of the present invention carrying iridium is as follows.

[0009]

[Chemical 1] * 1) As an example of hydrocarbon (HC), C ₃ H ₆ is shown as a representative. * 2) CH ₂ O is shown as an example of the oxygen-containing hydrocarbon. In the above reaction formula, (1) means activation of HC, (2) means combustion of HC, (3) means denitration reaction, and (4) means combustion of CO.

The crystalline silicate of the present invention carrying iridium and one or more kinds of metals selected from rare earth elements also undergoes the denitration reaction due to the above reaction, but by adding the rare earth element, a high oxygen concentration can be obtained. Also in (3)
The NOx removal reaction can be further promoted.

The catalyst of the present invention, even when exposed to a high temperature lean or rich atmosphere of 700 ° C. or higher for a long time, has the above k ₁ ,
It has been found that the reaction rate constants of k ₂ , k ₃ and k ₄ hardly change and the catalyst has durability.

The crystalline silicates used in the present invention have the X-ray diffraction patterns shown in Table A below and are expressed in the dehydrated state in terms of oxide molar ratio (1 ± 0.
8) R ₂ O ・ [aM ₂ O ₃・ bM'O ・ cAl ₂ O ₃ ]
YSiO ₂ (In the above formula, R is an alkali metal ion and / or hydrogen ion, M is at least one selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium. Element ion of M, M'is alkaline earth metal ion of magnesium, calcium, strontium, barium, a> 0,2
0> b ≧ 0, a + c = 1, 3000>y> 11).

[0013]

[Table 1] VS: Very strong S: Strong M: Intermediate W: Weak X-ray source: Cu Kα

A layered composite in which a crystalline silicate synthesized in advance from the above crystalline silicate is used as a mother crystal, and a crystalline silicate composed of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. Crystalline silicates may be used. This layered composite crystalline silicate has a hydrophobic action of a crystalline silicate composed of Si and O (called silicalite) grown on the outer surface, so that only H ₂ O hardly permeates into the inside of the crystalline silicate. It has the effect of lowering the concentration of H ₂ O around the reaction active point and exerts the effect of suppressing the demetallizing action. for that reason,
Even in a high temperature steam atmosphere, the structure of crystalline silicate is maintained, and the carrier effect for iridium and rare earth elements is maintained, so there is almost no catalyst deterioration.

That is, unlike conventional silica carriers and the like, the dispersibility of iridium and rare earth elements is uniformly maintained under any condition on the crystalline silicate of the present invention, and phenomena such as sintering are recognized. Absent.

The catalyst of the present invention can be produced by a method of immersing the above-mentioned crystalline silicate in an aqueous solution of iridium and a metal salt of a rare earth element and carrying it by an ion exchange method or an impregnation method. The supported iridium has a sufficient activity at 0.002 wt% or more, and preferably has a high activity at 0.02 wt% or more. Rare earth elements that coexist are lanthanum (La), cerium (Ce), praseodymium (P).
r), neodymium (Nd), samarium (Sm) and the like, and high activity can be achieved by adding 0.002 wt% or more of one or more rare earth elements. Hereinafter, the present invention will be described in detail with reference to Examples of the present invention.

[0017]

【Example】

(Example 1) ○ (Synthesis of mother crystal 1) Water glass No. 1 (SiO ₂ : 30)
%) 5616 g is dissolved in 5429 g of water, and this solution is referred to as solution A. On the other hand, 4175 g of water and 7 parts of aluminum sulfate
18.9 g, ferric chloride 110 g, calcium acetate 4
7.2 g, sodium chloride 262 g, concentrated hydrochloric acid 2020 g
Is dissolved, and this solution is referred to as solution B. Solution A and solution B are supplied at a constant ratio to form a precipitate, and the mixture is sufficiently stirred to adjust the pH.
= 8.0 is obtained. This slurry was charged into a 20 liter autoclave, 500 g of tetrapropylammonium bromide was further added, hydrothermal synthesis was carried out at 160 ° C. for 72 hours, washed with water after the synthesis, dried, and further calcined at 500 ° C. for 3 hours to crystallize. Obtain sex silicate 1. This crystalline silicate 1 is represented by the following composition formula in terms of the molar ratio of oxides (excluding the water of crystallization), and the crystal structure is represented by the above-mentioned Table A by X-ray diffraction. 0.5Na ₂ O
・ 0.5H ₂ O ・ [0.8Al ₂ O ₃・ 0.2Fe ₂ O
₃・ 0.25CaO] ・ 25SiO ₂

〇 (Synthesis of layered composite crystalline silicate 1)
Finely pulverized mother crystal 1 (crystalline silicate 1) 100
0 g was added to 2160 g of water, 4590 g of colloidal silica (SiO ₂ : 20%) was further added, and the mixture was sufficiently stirred to give a solution a. On the other hand, 105.8 g of sodium hydroxide is dissolved in 2008 g of water to obtain a solution b.
While stirring the solution a, the solution b is gradually added dropwise to form a precipitate, thereby obtaining a slurry. This slurry was placed in an autoclave and tetrapropylammonium bromide 56 was added.
A solution prepared by dissolving 8 g in 2106 g of water is added to the autoclave. 160 ℃, 72 in this autoclave
Hydrothermal synthesis is carried out (stirring at 200 rpm) for an hour, and after stirring, washing, drying, and firing at 500 ° C. for 3 hours, layered composite crystalline silicate 1 is obtained.

The layered composite crystalline silicate 1 was subjected to NH ₄ ion exchange by stirring in a 4N NH ₄ Cl aqueous solution at 40 ° C. for 3 hours. Washed after ion exchange at 100 ℃, 24
After drying for an hour, it was baked at 400 ° C. for 3 hours to obtain an H-type layered composite crystalline silicate 1.

(Catalyst) Next, to 100 parts of the above H-type layered composite crystalline silicate 1, 3 parts of alumina sol as a binder and 55 parts of silica sol (SiO ₂ : 2)
(0%) and 200 parts of water were added, and the mixture was sufficiently stirred to obtain a washcoat slurry. Next, the monolith substrate for cordierite (lattice of 400 cells) was dipped in the slurry, taken out, and then excess slurry was blown off and dried at 200 ° C. Coating amount is 200g per liter of substrate
It is carried, and this coated product is referred to as a honeycomb coated product 1.

Next, iridium chloride and cerium chloride aqueous solution (IrCl ₄ · H ₂ O: 2.88 g + CeCl ₃ : 1)
The honeycomb coated product was dipped in 0 g / 200 cc, H ₂ O) and impregnated for 1 hour, and then the liquid adhering to the wall of the substrate was wiped off and dried at 200 ° C. Next, a purging process was performed at 500 ° C. in a nitrogen atmosphere for 12 hours to obtain a honeycomb catalyst 1.

(Example 2) In the synthesis method of the mother crystal 1 of Example 1, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride,
Mother crystal 2 is repeated by repeating the same operation as mother crystal 1 except that titanium chloride, vanadium chloride, chromium chloride, antimony chloride, gallium chloride and niobium chloride are added in the same mole number as Fe ₂ O _{3 in} terms of oxide. 12 was prepared. The crystal structure of these mother crystals is shown in Table A above by X-ray diffraction, and its composition is expressed by the molar ratio of oxides (dehydrated form) of (1 ± 0.8) R ₂ O.・ (0.2M
₂ O ₃ / 0.8Al ₂ O ₃ / 0.25CaO) / 25S
iO ₂ . Where R is Na and H, M is Co, R
u, Rh, La, Ce, Ti, V, Cr, Sb, Ga,
Nb. The structures of these mother crystals are shown in Table B below.

These mother crystals 2 to 12 were finely pulverized, and the mother crystals 2 to 12 were used in place of the mother crystal 1 in the same manner as in the synthesis of the layered composite crystalline silicate 1 of Example 1, and an autoclave was prepared. As a result of hydrothermal synthesis using the same, layered composite crystalline silicates 2 to 12 were obtained.

The same operation as in the mother crystal 1 except that magnesium acetate, strontium acetate, and barium acetate were added instead of calcium acetate in the same manner as CaO in the method of synthesizing the mother crystal 1 of Example 1. Were repeated to prepare mother crystals 13 to 15. The crystal structure of these mother crystals is shown in Table A above by X-ray diffraction, and its composition is expressed by the molar ratio of oxides (dehydrated form) of 0.5NaO ₂ .0.5H ₂ O.・ (0.2Fe _{2
O 3 · 0.8Al 2 O 3 ·} 0.25MeO) · 25Si
It is O ₂ . Here, Me is Mg, Sr, or Ba. These mother crystals 13 to 15 were finely pulverized, and hydrothermal synthesis was carried out using an autoclave in the same manner as in the synthesis of the layered composite crystalline silicate 1 of Example 1 to obtain layered composite crystalline silicates 13 to 15. It was

Using the above layered composite crystalline silicates 2 to 15, H type layered composite crystalline silicates 2 to 15 were obtained in the same manner as in Example 1, and this silicate was further prepared in the same manner as in the preparation of the catalyst of Example 1. In the step, the cordierite monolith substrate was coated to obtain honeycomb coated products 2 to 15.
Next, it was immersed in an aqueous solution of iridium chloride and cerium chloride and treated in the same manner as in Example 1 to obtain honeycomb catalysts 2 to 15.

Example 3 Mother crystal 1 obtained in Examples 1 and 2
To H-type crystalline silicates 16 to 30 are obtained in the same manner as in Example 1 using Nos. 15 to 15, and the silicate is further subjected to the same steps as in the preparation of the catalyst of Example 1 for the honeycomb-coated product and the honeycomb catalyst 16-. I got 30.

Example 4 Cordierite monolith substrates were coated with the mother crystals 1 to 15 (those not layered and ion-exchanged) shown in Examples 1 and 2 to form honeycomb-coated products 31 to 31. 45 was obtained, and this was immersed in an aqueous solution of iridium chloride and cerium chloride in the same manner as in Example 1 to obtain honeycomb catalysts 31 to 45.

(Example 5) Using the honeycomb coated article 1 coated with the layered composite crystalline silicate 1 obtained in Example 1, lanthanum chloride (L) was used instead of the cerium chloride aqueous solution.
aCl ₃ .7H ₂ O: 10 g / 200 cc, H ₂ O),
Praseodymium chloride _{(PrCl 3 · 7H 2 O:} 10g /
200 cc, H ₂ O), neodymium chloride (NdCl ₃ ·
6H ₂ O: 10 g / 200 cc, H ₂ O), samarium chloride (SmCl ₃ · 6H ₂ O: 10 g / 200 cc, H
₂ O), europium chloride (EuCl ₃ : 10 g / 20
(0 cc, H ₂ O) and then catalyzed by the same method as in Example 1 to obtain honeycomb catalysts 46 to 50.

(Comparative Example 1) A catalyst 51 in which only iridium was supported on α-Al ₂ O ₃ in Example 1 was obtained. Further, to obtain a honeycomb catalyst 52 was supported the same iridium and cerium as in Example 1 α-Al ₂ 0 ₃ carrier.

The constitutions of the example catalyst and the comparative catalyst of the present invention are shown in Table B above.

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

(Experimental Example 1) Examples 1, 2, 3, 4, 5 and
And the activity evaluation of the honeycomb catalysts 1 to 52 prepared in Comparative Example 1
Value test was conducted. The activity evaluation conditions are as follows. ○ (gas composition) NO: 400ppm, CO: 1000ppm, C
₂H_Four: 1000 ppm, C ₃H₆: 340ppm, O
₂: 8%, CO₂: 10%, H₂O: 10%, balance:
N ₂, GHSV 30000h^-1, Catalyst shape: 15mm
× 15mm × 60mm (144 cells)

The denitration rate of the catalyst in the initial state at reaction temperatures of 350 and 450 ° C. is shown in Table C below.

(Experimental Example 2) The honeycomb catalysts 1 to 52 were subjected to a forced deterioration test in a rich atmosphere (reducing atmosphere). The forced deterioration test is as follows. 〇 (gas _{composition) H 2: 3%, H} 2 O: 10%, remaining: N ₂ GHSV: 5000h ^-1, temperature: 700 ° C., gas supply time: 6 hours catalyst shape: 15mm × 15mm × 60mm (144 cells )

Catalysts 1-5 treated under the above-mentioned forced deterioration conditions
2 was subjected to an activity evaluation test under the activity evaluation conditions of Experimental Example 1. Table C also shows the denitration rate of the catalyst after the forced deterioration test at reaction temperatures of 350 and 450 ° C. As shown in Table C, it was confirmed that the catalysts 1 to 50 of the present invention maintain high catalyst activity even in a high temperature reducing atmosphere.

[0039]

[Table 6]

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

[Table 9]

[0043]

As described above, the exhaust gas purifying catalyst according to the present invention can be a stable catalyst with high durability, and can be used as a lean burn engine exhaust gas catalyst for a gasoline vehicle or a diesel engine exhaust gas purifying catalyst. It is available.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location B01J 29/04 ZAB 9343-4G B01D 53/36 104 A (72) Inventor Akira Serizawa 1 Akinoura-cho, Nagasaki-shi, Nagasaki Prefecture No. 1 Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard

Claims (2)

[Claims] 1. An X-ray diffraction pattern shown in Table A, which is described in detail in the present text, and expressed as the molar ratio of oxides in the dehydrated state is (1 ± 0.8) R ₂ O. [aM ₂ O ₃・ B
M'O.cAl ₂ O ₃ ] .ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is a Group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony and gallium. At least one elemental ion selected from the group, M ′ is magnesium,
Alkaline earth metal ions of calcium, strontium and barium, a> 0, 20> b ≧ 0, a + c = 1, 30
An exhaust gas purifying catalyst comprising a crystalline silicate having a chemical formula of 00>y> 11) and at least one metal selected from iridium and a rare earth element. 2. A layered composite in which a crystalline silicate synthesized in advance from a crystalline silicate is used as a mother crystal, and a crystalline silicate composed of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. The exhaust gas purifying catalyst according to claim 1, which is a crystalline silicate.