JPH0724324A - Catalyst for treating exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst purifying exhaust gas containing nitrogen oxide, carbon monoxide and hydrocarbon. CONSTITUTION:A catalyst for treating exhaust gas is composed of crystalline silicate having an X-ray diffraction pattern and having a chemical formula represented by aR2O[bIr2O3.cMeO3].y-SiO2 (wherein R is an alkali metal ion and/or a hydrogen ion, M is at least one element ion selected from a group cosisting of group VIII elements, a rare earth element, titanium, vanadium, chromium, niobium, antimony, gallium and aluminum, a>=0, b>0, c>=0, b+c=1 and y>11) containing oxides in a mol ratio in a dehydrated state.

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 use CO and HC in the exhaust gas to purify it using a noble metal catalyst with alumina as a carrier. NOx is purified only in an extremely narrow range. 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 the elimination of aluminum, which is the main constituent element of crystalline silicate, and to stabilize cobalt or copper, the
Group VIII elements and rare earth elements (Japanese Patent Application No. 3-165816), and alkaline earth metals (Japanese Patent Application No. 3-31919).
No. 5) has been proposed to use a novel silicate. 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, it is usually 1
When accelerating at a high speed of 00 km / h, the gas temperature may instantly reach around 700 ° C., and the gas composition at this time is a rich atmosphere in which a reducing agent such as hydrogen 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,
If the developed crystalline silicate can be used with a metal other than a base metal having a denitration activity in a lean atmosphere, the durability is sufficiently ensured, and it is considered that the practical use will be greatly advanced. So far, the inventors have found that the catalyst in which the platinum group element, particularly iridium, is supported on the crystalline silicate developed by the present invention has stable activity with almost no decrease in activity even in a high temperature rich atmosphere of 700 ° C. or higher. Found and proposed (Japanese Patent Application No. 5-26369)
issue).

[0006]

Means for Solving the Problems As a result of diligent analysis of the active sites of this crystalline silicate carrying iridium, the present inventors have found that iridium arranged in the crystalline lattice of the crystalline silicate effectively acts. It was Therefore, in order to further enhance the functionality of this catalyst, it was found that when synthesizing a crystalline silicate, by adding an iridium element to grow a crystal, it has higher performance and durability than ever before. Has been completed.

That is, the present invention provides X shown in Table 1 below.
It has a line diffraction pattern and is expressed as a molar ratio of oxides in the dehydrated state: aR ₂ O. [bIr ₂ O ₃ .cMe O ₃ ] .ySiO ₂ (wherein R is an alkali metal ion and / or Hydrogen ion, M is at least one element ion selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, gallium and aluminum, a ≧ 0, b> 0, c ≧ 0, b + c = 1, y>
An exhaust gas treatment catalyst, which is a crystalline silicate having the chemical formula 11).

[0008]

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

[0009]

By using the crystalline silicate used in the present invention in which iridium is arranged in the crystal lattice, NOx, CO, HC
A purifying reaction formula for purifying exhaust gas containing oxygen in excess of oxygen is as follows.

[0010]

[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 catalyst of the present invention has a high denitration activity in the above formula in the range of 250 to 500 ° C. Even in the vicinity of the stoichiometric air-fuel ratio where O ₂ is small, the catalyst of the present invention undergoes the denitration reaction in a wide temperature range due to the following reactions (5) and (6).

[Chemical 2]

It has been found that the catalyst of the present invention has durability even when exposed to a high temperature lean or rich atmosphere of 700 ° C. or higher for a long time, and the reaction rate constants of k _{1 to} k ₆ are hardly changed. There is.

The catalyst of the present invention is usually synthesized by a hydrothermal synthesis method using an autoclave, and the activity is sufficiently exhibited when the SiO ₂ / Ir ₂ O ₃ ratio in the crystalline silicate after synthesis is 5,000 or less. , And preferably has a high activity at a SiO ₂ / Ir ₂ O ₃ ratio of 1,000 or less. Hereinafter, the present invention will be described in detail with reference to Examples.

[0014]

【Example】

(Example 1) Water glass No. 1 (SiO ₂ : 30%): 56
16 g is dissolved in water: 5429 g, and this solution is referred to as solution A. On the other hand, water: 4175 g was mixed with iridium chloride (H _{2
IrCl 6 ··· as Ir: 10%} ) aqueous solution: 1715
g, sodium chloride: 262 g, concentrated hydrochloric acid: 2020 g, and this solution is referred to as solution B. Solution A and solution B are supplied at a constant ratio to generate a precipitate, and the mixture is sufficiently stirred to adjust pH =
You get a slurry of 8.0. This slurry was charged into a 20 liter autoclave, 500 g of tetrapropylammonium bromide was further added, and hydrothermal synthesis was carried out at 160 ° C. for 72 hours. After the synthesis, washing with water and drying were conducted, and further 5
The crystalline silicate 1 is obtained by baking at 00 ° C. for 3 hours. 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 shown in Table 1 by X-ray diffraction. 0.5 NaO ₂ .0.
5H ₂ O ・ Ir ₂ O ₃・ 80SiO ₂

Next, to 100 parts of the above crystalline silicate 1, alumina sol: 3 parts, silica sol: 55 parts (SiO ₂ : 20%) and water: 200 parts were added as a binder, and the mixture was sufficiently stirred to wash slurry for washcoat. And
Next, the monolith substrate for cordierite (lattice of 400 cells) was immersed in the slurry, taken out, and then excess slurry was blown off and dried at 200 ° C. Base material 1
200 g per liter is supported, and this coated product is used as a honeycomb catalyst 1.

Example 2 In the solution B of Example 1, salt was added.
Cobaltide, ruthenium chloride, rhodium chloride, lanthanum chloride
Tan, cerium chloride, titanium chloride, vanadium chloride, salt
Chromium chloride, antimony chloride, gallium chloride, niobium chloride
And aluminum chloride in terms of oxide respectively Ir₂O₃When
Same as crystalline silicate 1 except that the same number of moles was added
Repeat the above procedure to prepare crystalline silicates 2-13
did. The crystal structures of these crystalline silicates are X-ray diffraction
Is shown in Table 1 above, and its composition is an oxide.
Expressed as a molar ratio (in dehydrated form) of 0.5 Na₂
O ・ 0.5H₂O (Ir₂O ₃・ M₂O₃) ・ 80Si
O₂Is. Where M is Co, Ru, Rh, La, C
e, Ti, V, Cr, Sb, Ga, Nb and Al
It These crystalline silicates 2 to 13 were used as catalysts in Example 1.
Coating a cordierite substrate by the same method as the medium preparation method
Then, honeycomb catalysts 2 to 13 were obtained.

(Example 3) Iridium chloride (H ₂ IrCl ₆ ... As I) added to the solution B in Example 1
r: 10%) aqueous solution 82 g, 343 g, 857, respectively.
g, 3430 g, and the crystalline silicates 14 to 17 were synthesized by the same operation as in Example 1, and further the honeycomb catalyst 1
4 to 17 were obtained. Table 2 shows the compositions of the catalysts 1 to 17 of the present invention.

[0018]

[Table 2]

(Experimental Example 1) The samples prepared in Examples 1 to 3
An activity evaluation test of Nicham catalysts 1 to 17 was carried out. Active evaluation
Valuation 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
× 15 mm × 60 mm (144 cells) Desorption of the catalyst in the initial state at reaction temperatures of 350 and 450 ° C
The glass ratio is shown in Table 3.

(Experimental Example 2) The honeycomb catalysts 1 to 17 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 ) Experimental example 1 was prepared using catalysts 1 to 17 treated under the above-mentioned forced deterioration condition
The activity evaluation test was carried out under the activity evaluation conditions of. Table 3 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 3, it was confirmed that the catalysts 1 to 17 of the present invention maintain high catalyst activity even in a high temperature reducing atmosphere.

[0021]

[Table 3]

[0022]

As described above, the exhaust gas purifying catalyst according to the present invention can be a durable and stable catalyst, and can be used for lean burn engine exhaust gas of gasoline vehicles and diesel engine exhaust gas purifying catalyst. Can be used as

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 53/36 104 A (72) Inventor Akira Serizawa 1-1 1-1 Atsunoura-cho, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries Nagasaki Shipyard Co., Ltd.

Claims (1)

[Claims] 1. An aR ₂ O. [bIr ₂ O ₃ .cMe O ₃ ] which has an X-ray diffraction pattern shown in Table 1 described in detail herein and is expressed as a molar ratio of oxides in a dehydrated state. 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, gallium and aluminum. More than one kind of elemental ion, a ≧ 0, b> 0, c ≧ 0, b + c = 1, y>
An exhaust gas treatment catalyst, which is a crystalline silicate having the chemical formula 11).