JPH02293050A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst having a high rate of removal of NOx and superior durability by supporting zeolite contg. the double oxide of different transition metals or the double oxide of a transition metal and an alkaline earth metal in the pores. CONSTITUTION:The double oxide of different transition metals such as a rare earth metal having atomic number 21 or 39 and other transition metal selected among transition metals having atomic numbers 21 to 30, 39 to 48, 57 to 80 and 89 or the double oxide of an alkaline earth metal having atomic number 4, 12, 20 and a transition metal is used. Zeolite contg. the double oxide in the pores is supported on a refractory carrier such as cordierite. The resulting catalyst has a high rate of removal of NOx on the lean side and superior durability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust purification catalyst used in vehicles such as automobiles, and more particularly, to a catalyst for purifying NOx in exhaust gas at a high rate even in an oxygen-rich atmosphere where the air-fuel ratio is on the lean side. It is related to a catalyst that can purify wastewater. [Conventional technology] Carbon monoxide (Co) and hydrocarbon 2 (HC) l! are used as catalysts for automobile exhaust purification. [? , g, nitrogen oxides (N
Catalysts that simultaneously reduce O x ) are widely used. Basically, such catalysts are made by coating a refractory support such as cordierite with γ-alumina slurry, firing it, and then applying P.
d, metals such as PtRh or mixtures thereof are supported. By the way, the purification characteristics of the above-mentioned catalyst are greatly influenced by the air-fuel ratio setting of the engine. 4. In a lean mixture, that is, on the lean side where the air-fuel ratio is high, the amount of oxygen (0 units) increases even after combustion, and the oxidizing action becomes active and the reducing action becomes inactive. Conversely, on the rich side where the air-fuel ratio is low, oxidation is inactive and reduction is active. The stoichiometric air-fuel ratio that balances this oxidation and reduction (A/F = 14.6)
The catalyst works most effectively in the vicinity. In automobiles equipped with exhaust purification devices that use such catalysts, feedback control is performed to detect the oxygen concentration in the exhaust system and maintain the air-fuel mixture near the stoichiometric air-fuel ratio. On the other hand, there is a demand for lower fuel ratios in automobiles, and it is known that this can be achieved by burning a mixture with excess oxygen as much as possible during normal driving. However, if this is done, the air-fuel ratio will be on the lean side, resulting in an oxygen-rich atmosphere, and although HC and Co among the harmful components in the exhaust can be removed by oxidation, NOx
It is said that it is difficult to reduce and remove 04 because contact with active metals is hindered by 04 adsorbed on the catalyst bed. In order to improve these drawbacks, the present applicant filed a patent application filed in 1983.
In No. 291258, we proposed an exhaust purification catalyst characterized by a zeolite ion-exchanged with a transition metal supported on a refractory carrier. The above transition metals include Cu, Go, CrNi, Fe
, Mn are preferred, and Cu is particularly preferred. As is well known, zeolite has the general formula; xM /neAu. , O sysio.
A crystalline aluminosilicate represented by I. The tunnel structure (pore diameter) in the crystal structure varies depending on the differences in M (n-valent metal), x, and y, and many types are available on the market. Also, a part of Sil+ is ARl-1! Because of the substitution, there is a lack of positive charge, and to compensate for the lack, N a'',
It has the ability to exchange cations such as K'-. Furthermore, zeolites are also known as molecular sieves and have pores with A unit sizes that match the size of molecules. Therefore, HC is selectively taken into the pores, where it is adsorbed to the ugliness. In addition, since there are active sites of transition metals introduced by ion exchange in the pores, No is adsorbed there and active CO generated from HC or HC is absorbed.
This causes a reaction. Therefore, NOx can be removed efficiently even on the lean side. The applicant also stated in Japanese Patent Application No. 63-140281,
We have proposed a catalyst for converting exhaust gas into nitride, which is characterized by having a catalyst layer made of zeolite in which copper is supported by ion exchange and precious metals are supported on a refractory carrier. The catalyst marked with does not only produce NOx but also HC and C on the lean side.
The purification property of O is also high. As precious metals, PL, Pd,
Examples include Rh. [Problems to be Solved by the Invention] However, when a transition metal such as copper is supported by ion exchange, there is a risk that copper will adhere not only to the inside of the zeolite pores but also to the surface of the zeolite particles. It tends to aggregate due to the heat load during use, and this is a major cause of decreased activity and durability. The present invention is intended to solve the problems in the prior art described above. The purpose of rJI's 7J4l is to provide a highly durable exhaust purification catalyst with a high NOx conversion rate on the lean side. In addition to the above, the second object of the present invention is to provide an exhaust gas purification catalyst that can further increase the purification rate of HC and CO and can be used not only as a lean NOx catalyst but also as a three-way catalyst. It is to be. [Means for Solving the Problems] That is, the exhaust purification catalyst of the present invention is a zeolite having in its pores a composite oxide of different types of transition metals or a composite oxide of a transition metal and an alkaline earth metal. is supported on a refractory carrier. The term transition metal has the broadest meaning commonly used.
That is, atomic number 2 1 (S c) ~ 3 0 (
Up to Z n:), 39 (Y) to 48 (Cd), 57
(La) to 80 (Hg), and 89 (Ac
) includes the above elements. Preferred examples of composite oxides of different types of transition metals include rare earth metals (atomic number 21 (Sc),
39 (Y). 57 (La) to 71 (LLI)) and other transition metals. Other composite oxides used in the present invention include transition metals and alkaline earth metals [atomic numbers 4 (Be), 12 (Mg). 2
0 (Ca). 38 (Sr), 56 (Ba). 88
(Ra)). One type of composite oxide may be used, or two or more types of composite oxide may be used in combination. The crystal type of the composite oxide is preferably ilmenite type, perovskite type, BiNi0.3 type, Subinel type, and similar types thereof, and particularly preferred is berovskite type.

The zeolite used to form the composite oxide in the pores is a siliceous exchanger, such as an aluminosilicate or one in which aluminum is replaced with a rare earth metal or an alkaline earth metal. good. The following: 5t table shows the names of the main zeolites and their properties.

Table 1 Super cage inlet and network structure of main zeolites Among the zeolites in Table 1, ZSM-5 is particularly preferred.
-5 compared to other zeolites, S i O 2
/An;: 03 is large and acid strength is high; it is a 10-membered oxygen ring; it has very little crystal water, is hydrophobic, and has few weak acid sites. For example, ZSM-5 has the following characteristics: tea. G.T. Kokota
ilo), zs. El, o-}n (S.L. Lagata
n) and D. Koichi, Ch. Olson CD. H. O
Ison) “Structure of Synthetic Zeolite ZSM-5)”. Nature
re) Volume 272, March 30, 1978, page 437, in order to form a composite oxide within the pores of zeolite, a transition metal is supported on zeolite by an ion exchange method, and then Process under specified conditions. The ion exchange method may be a conventional method using an aqueous solution. As an aqueous solution, compounds of the desired metal such as inorganic acid salts such as urate, halides, i.
salt, and as a ligand, e.g. Co, H0NH3
, NO, etc. can be used. Then, after ion exchange, alkali treatment is performed, for example, at 300 to 800°C with an oxygen partial pressure of 0.1 to 50 atm.
Bake for 100 hours. Although various organic or inorganic alkaline solutions can be used for alkali treatment, it is preferable to use aqueous ammonia solution. Examples of the refractory carrier used in the catalyst of the present invention include ceramic carriers such as cordierite, metal carriers, and the like.
The amount of zeolite applied to the refractory carrier, the size and shape of the refractory carrier, and other properties are selected depending on the characteristics required of the catalyst. [Function] The catalyst of the present invention utilizes the oxygen atoms in the lattice of the zeolite structure in the pores (about 5 to 10A in diameter) of the zeolite to form a composite oxide (with a unit cell size of about 3.5 to 48A). ) is formed, so NOXE by zeolite catalyst
It has both I element action and HC and GO oxidation action due to the complex oxide. Furthermore, since the catalyst has the above-mentioned structure, the heat resistance of the zeolite structure is improved and the catalyst has excellent durability. [Examples] The present invention will be explained in more detail with the following Examples and Comparative Examples. Note that the present invention is not limited to the following examples. Examples 1 to 5 The following components: ) Silica sol (30 wt% Si02) 1i) (rs Na20/R20,) compound (R is a rare earth metal) 111) Pure water ■) Tetraprobylammonium hydroxide (TPA
OH) aqueous solution (lmol/c) was finally eosto2
φR203●1.5 NaO-2.9TPAOH●5
Mix to a composition ratio of 50 tizo and stir at room temperature for about 10 minutes. After that, in the autoclave,
After reacting at 160°C for 10 hours, washing with water, and drying, approximately 500
Bake at ℃. 50 parts of the zeolite powder synthesized above, 35 parts of silicazo/lz (20 wt% Sin,), and 15 parts of pure water are mixed and stirred to obtain a slurry. Next, this slurry was coated on a cordierite monolith test bead with a diameter of 30 mm and a length of 50 mm (
Coating amount = 120gl), this was heated at 500℃ for 3
Bake for an hour. Next. Ion exchange was performed using a 0.02M transition metal (M) aqueous solution, and 2 to 3 g of transition metal was added to the test bead.
I will take care of it. Thereafter, this is treated with an alkali (e.g. 0.
(soaked in 5N ammonia aqueous solution) and further oxygen partial pressure 0
．． By firing at 500°C for 2 hours under 2 ATM to form a composite oxide, the exhaust purification catalyst l shown in the figure was prepared.
I got it. Table 2 shows Examples 1 to 3 in which rare earth metals and transition metals were changed.
Each of the catalysts No. 5 (No. 1 to 5) is shown below. Comparative Example 1 Sodium aluminate (1.5N a
30/A120 3) Catalyst No. 2 shown in Table 2 was prepared in the same manner as in Examples 1 to 5, except that an aqueous solution was used. I got 6. Comparative Example 2 Examples 1 to 5 except that ion exchange with transition metal was not performed.
Catalyst No. shown in Table 2 was prepared in the same manner as in the method of I got a 7.

Comparative example 3 Activated alumina 100? ! &, alumina sol (10wt%
SiO. , ), 30 minutes of pure water, and 15 parts of a nitric aluminum aqueous solution (40 wt%) were mixed and stirred to obtain a washcoat slurry. This was wash coated on the same test beads as in Examples 1 to 5 (coat i:
120g/l) and baked at 700℃ for 1 hour. Separately, dinitrodiammine platinum [Pt (M}I 3
)． , (NO2), :] aqueous solution and rhodium chloride [Rh
C sentence, ] aqueous solution Pt/Rh=1.5/0.3
g/cat to give an appearance, and prepare a liquid-bearing solution. The fired test beads were immersed in the precious metal supporting solution for 1 hour to support the precious metals, then pulled out, the excess liquid was blown off with an air stream, and the beads were fired at 250°C for 1 hour, platinum and rhodium were added to each test piece. Catalyst No. 8 was obtained by supporting 1.5 g and 0.3 g. Comparative Example 4 45 parts of zeolite, silica sol (20wt%S i 0
2) Mix 35 parts of LaCo03 powder, 5 parts of LaCo03 powder, and 15 parts of pure water and stir to obtain a wash coat slurry. Using this, in the same manner as in Comparative Example 3, catalyst No. 9
I got it. Catalyst No. Nos. 1 to 9 were heat treated at aOO°C in air for 5 hours, and then their purification performance was measured under the following conditions. Evaluation conditions = Inlet gas temperature 400℃, sv = eoo
oo h-,'A/F=22 The results are shown in Table 2 below. Table 2: Purification performance of various catalysts 1) It can be seen that the overall purification rate is very superior compared to rare earth monosilicate type zeolite ~9. When examined in more detail, catalyst No. 1 to 5 and catalyst No.
．． Comparing with catalyst No. 8, catalyst No. 1 to 5 are catalyst Nos. 8
The NOx purification rate was significantly higher, which indicates the effectiveness of zeolite as a support layer for catalyst components. Also, catalyst No. 1 to 5 are catalyst Nos. The overall purification rate, especially of NOx, is higher than that of Nos. 6 and 7, which is considered to be rare. Also, catalyst No. 1 to 5 are catalyst Nos. 9, the purification rate is higher overall, especially for NOx. This shows that simply combining a complex oxide with zeolite is not effective, and that it is important that the complex oxide is formed within the zeolite pores. By having this structure, the catalyst of the present invention can reduce NOx and reduce HC and CO.
The oxidation action of the catalyst is promoted, and it has a flexible property that exhibits excellent performance not only in lean atmospheres but also in areas where three-way catalysts have traditionally been used. In Table 2, catalyst No. The reason for the difference in the purification rates of No. 1 to No. 5 is due to the stability of the formed composite oxide and the degree of strain exerted on the zeolite structure.
That is, preferable rare class 7 metals (R) and transition metals (M)
The combination is the following formula I: [where r3 represents the ionic radius of the R atom, rNl is M
represents the ionic radius of the atom, r. ．． ) represents the ionic radius of the oxygen atom] is 0.8 to 1.0.
A good combination of degrees. In this case (7), it is thought that a perovskite-type complex oxide is generated. In addition to Examples 1 to 5, composite oxides such as S r T t O 3 and SrCeO3La were added to the pores of the zeolite.
Fe03, SmFe03, SrLa03, BaCe03
, BaFe03. LaRh03, C a C e O
:I, SrRu03, NdCoO3, NdFe03, S
Similar effects were obtained with catalysts such as mIn03. (Effects of the Invention) As described above, the exhaust purification catalyst of the present invention has a composite oxide in the pores of the zeolite, so it has both the NOxil source action of the zeolite catalyst and the HC and Co oxidation action of the composite oxide. It has overall high exhaust purification properties in a lean atmosphere.In addition, unlike conventional zeolite-type exhaust purification catalysts, the transition metals supported by ion exchange do not aggregate due to heat load, etc. In addition, the catalyst of the present invention can be used not only as a lean NOx catalyst but also as a three-way catalyst.Furthermore, in the catalyst of the present invention, transition metals and alkaline earth By changing the type of metal or using a combination of two or more types, various modifications can be made, and various exhaust purification catalysts can be obtained in accordance with the requirements using the same method.

[Brief explanation of the drawing]

The figure is a perspective view of an example of the exhaust purification catalyst of the present invention. In the figure, i. ．． ．． ．． ．． ．． Exhaust Purification Catalyst Patent Applicant Toyota Motor Corporation 11th Air Purification Employee! ! i act 1 no

Claims (1)

[Claims] An exhaust purification catalyst comprising a zeolite having in its pores a composite oxide of different types of transition metals or a composite oxide of a transition metal and an alkaline earth metal supported on a refractory carrier. .