JPH07171401A - Catalyst for treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purification of exhaust gas contg. NOx, CO and hydrocarbon. CONSTITUTION:Iridium is carried on a crystalline silicate having an X-ray diffraction pattern represented by the chemical formula (1+ or -0.4)R2O.[aBi2O3.bLa2 O3.cCe2O3.dM2O3].ySiO2 when the silicate is expressed in terms of the molar ratio among oxides in a dehydrated state. In the formula, R is ions of Na and/or H, M is ions of one or more kinds of group VIII: metals or an ion of Ti, V, Cr, Nb, Sb or Al, a+b+c+d=1, a>=0, b>=0, c>=0, d>=0, a+b+c>0 and y>=12. The objective catalyst for treatment of exhaust gas is obtd.

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)
A catalyst for treating exhaust gas containing C).

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles, it is general to purify NOx in an extremely narrow range near the stoichiometric air-fuel ratio by utilizing CO and HC in the exhaust gas. 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, the gas temperature instantly rises to a high temperature when accelerated, and the gas composition at this time is reduced by hydrogen or the like. It is a rich atmosphere in which the agent is present in excess. 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 high temperature in a rich atmosphere, 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.

[0006]

The inventors of the present invention have conducted extensive studies to overcome the drawbacks of conventional catalysts, and as a result, a crystalline silicate catalyst carrying an iridium element has denitration performance in a lean atmosphere. And, it was found that the catalyst hardly deteriorates even in a high temperature atmosphere,
The present invention has been completed based on this finding.

That is, the present invention has an X-ray diffraction pattern shown in Table A below and represents (1 ± 0.4) R ₂ O. [aBi as the molar ratio of oxides in the dehydrated state. ₂ O ₃ / bLa ₂ O _{3
· CCe 2 O 3 · dM 2} O 3 ] · ySiO ₂ (in the above formula, R: Na and / or H ions, M: 1 or more Group VIII metal ions, titanium, vanadium,
An ion selected from the group consisting of chromium, niobium, antimony and aluminum, a + b + c + d = 1, a ≧ 0,
b ≧ 0, c ≧ 0, d ≧ 0, a + b + c> 0, y ≧ 12)
An exhaust gas treatment catalyst, characterized in that iridium is supported on a crystalline silicate having the following chemical formula.

[0008]

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

The above-mentioned crystalline silicate is disclosed in JP-B-62-43.
No. 27, Japanese Patent Publication No. 2-49245, the present inventors have already specified, and it is possible to synthesize a crystalline silicate having a regulated porosity, and further various reactions such as a conversion reaction of methanol. It has the characteristics of high activity and long life.

[0010]

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

[0011]

[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 catalyst supporting iridium has a high denitration performance at 250 to 500 ° C.
Even if the catalyst is exposed to a high temperature lean atmosphere of 700 ° C. or higher or a rich atmosphere for a long time, the above k ₁ , k ₂ , k ₃ and k ₄
It has been found that the reaction rate constant of is almost unchanged and the catalyst has durability. On the crystalline silicate used in the present invention, the dispersibility of the iridium element is uniformly maintained under any condition, and no phenomenon such as sintering is observed.

The catalyst of the present invention may be obtained by immersing the above-mentioned crystalline silicate in an aqueous solution of a metal salt of an iridium element and carrying it by an ion exchange method or an impregnation method. The iridium element to be carried exhibits a sufficient activity at 0.002 wt% or more, and preferably has a high activity at 0.02 wt% or more. Hereinafter, the present invention will be described in detail with reference to Examples.

[0014]

【Example】

Example 1 Synthesis of Crystalline Silicate 1 Water glass No. 1 (SiO ₂ : 30%): 5616 g of water:
It is dissolved in 5429 g, and this solution is referred to as solution A. on the other hand,
Bismuth chloride: 157.6 g, sodium chloride: 262 g, and concentrated hydrochloric acid: 2020 g are dissolved in water: 4175 g, and this solution is referred to as solution B. Solution A and solution B are supplied at a constant ratio to form a precipitate, which is sufficiently stirred to obtain a slurry having a pH 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, followed by washing with water and drying.
The crystalline silicate 1 is obtained by firing for a time. 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 (Bi ₂ O ₃ ) ・ 56S
iO _{2 The} above crystalline silicate 1 was added with a 4N NH ₄ Cl aqueous solution 40
NH ₄ ion exchange was carried out by stirring at ℃ for 3 hours. After washing after ion exchange and drying at 100 ° C for 24 hours, 4
H-type crystalline silicate 1 was obtained by baking at 00 ° C. for 3 hours.

Catalysis Next, to 100 parts of the above H-type crystalline silicate 1, alumina sol as a binder: 3 parts, silica sol:
55 parts (SiO ₂ : 20%) and 200 parts of water were added and sufficiently stirred to obtain a washcoat slurry. 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. The coated amount is 200 g per liter of the substrate, and this coated product is referred to as honeycomb coated product 1. Next, iridium chloride (IrCl ₄ · H
₂ O: 2.88 g / H ₂ O: 200 cc) was dipped in the above honeycomb coated article 1 and impregnated for 1 hour, and then the liquid adhering to the wall of the substrate was wiped off and dried at 200 ° C. Then 50
Purge treatment was performed at 0 ° C. in a nitrogen atmosphere for 12 hours to obtain a honeycomb catalyst 1. The properties of this honeycomb catalyst 1 are shown in Table B below.
Shown in.

(Example 2) A crystal except that lanthanum chloride or cerium chloride was added instead of bismuth chloride in the same mole number as Bi ₂ O ₃ instead of bismuth chloride in the method of synthesizing the crystalline silicate 1 of Example 1. The same operations as those for the crystalline silicate 1 were repeated to obtain crystalline silicates 2 and 3. Also, in the crystalline silicate 1, the same operation as in the crystalline silicate 1 except that bismuth chloride and lanthanum chloride, lanthanum chloride and cerium chloride, and lanthanum chloride and aluminum chloride are added in an equimolar amount instead of bismuth chloride. Was repeated to obtain crystalline silicates 4, 5, and 6.

Using the above crystalline silicates 2 to 6, H type crystalline silicates 2 to 6 were obtained in the same manner as in Example 1, and the silicates were further processed in the same steps as in the preparation of the catalyst of Example 1. A cordierite monolith substrate was coated to obtain honeycomb coated products 2 to 6. Next, the honeycomb catalyst 2 was immersed in an aqueous solution of iridium chloride and treated in the same manner as in Example 1.
~ 6 was obtained. Properties of these honeycomb catalysts 2 to 6 are also shown in Table B below.

(Example 3) The crystalline silicates 1 to 6 used in Examples 1 and 2 in which the NH ₄ ion conversion operation shown in Example 1 was omitted were treated in the same manner as in Example 1 to prepare a honeycomb-coated product. And the honeycomb catalysts 7-12 were obtained.

(Example 4) In the method for synthesizing the crystalline silicate 1 of Example 1, bismuth chloride and ferric chloride, bismuth chloride and cobalt chloride, bismuth chloride and ruthenium chloride, bismuth chloride and rhodium chloride were used instead of bismuth chloride. , Bismuth chloride and titanium chloride, bismuth chloride and vanadium chloride, bismuth chloride and chromium chloride, bismuth chloride and antimony chloride, bismuth chloride and niobium chloride, bismuth chloride and gallium chloride, bismuth chloride and lanthanum chloride, cerium chloride and aluminum chloride, respectively. The same operations as in the crystalline silicate 1 were performed except that the equimolar number was added in terms of oxide to obtain crystalline silicates 13 to 23.

Using the above crystalline silicates 13 to 23, the H-type crystalline silicates 13 to 23 were produced in the same manner as in Example 1.
No. 23 was obtained, and this silicate was further coated on the cordierite monolith substrate by the same steps as in the preparation of the catalyst of Example 1 to obtain honeycomb coated products 13 to 23. Next, the honeycomb catalyst was immersed in an aqueous solution of iridium chloride and treated in the same manner as in Example 1 to obtain honeycomb catalysts 13 to 23. These honeycomb catalysts 13
The properties of Nos. 23 to 23 are shown in Table B below.

[0021]

[Table 2]

[0022]

[Table 3]

(Example 1) In Examples 1, 2, 3 and 4.
Conducted an activity evaluation test of the prepared honeycomb catalysts 1 to 23
It was The activity evaluation conditions are as follows. 〇 (gas composition) NO: 500ppm, CO: 1000ppm, C
₂H_Four: 1500ppm, O ₂: 8%, CO₂: 10
%, H₂O: 10%, balance: N₂, GHSV 30000
h^-1, Catalyst shape: 15 mm × 15 mm × 60 mm (14
4 cells) Desorption of catalyst in the initial state at reaction temperatures of 350 and 450 ° C
The glass ratio is shown in Table C below.

Experimental Example 2 The honeycomb catalysts 1 to 23 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 : 5%, H ₂ O: 10%, balance: N ₂ GHSV: 5000 h ⁻¹ , temperature: 750 ° C., gas supply time: 6 hours Catalyst shape: 15 mm × 15 mm × 60 mm (144 cells ) Experimental example 1 was prepared using catalysts 1 to 23 treated under the above-mentioned forced deterioration condition.
The activity evaluation test was carried out under the activity evaluation conditions of. The denitration rate of the catalyst after the forced deterioration test at reaction temperatures of 350 and 450 ° C. is also shown in Table C below. As shown in Table C, it was confirmed that the catalysts 1 to 23 of the present invention maintain high catalyst activity even in a high temperature reducing atmosphere.

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

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

Claims (1)

[Claims] 1. An X-ray diffraction pattern shown in Table A, which is described in detail in the present text, and expressed as a molar ratio of oxides in a dehydrated state is (1 ± 0.4) R ₂ O. [aBi ₂ O ₃ · bLa ₂ O _{3
· CCe 2 O 3 · dM 2} O 3 ] · ySiO ₂ (in the above formula, R: Na and / or H ions, M: 1 or more Group VIII metal ions, titanium, vanadium,
An ion selected from the group consisting of chromium, niobium, antimony and aluminum, a + b + c + d = 1, a ≧ 0,
b ≧ 0, c ≧ 0, d ≧ 0, a + b + c> 0, y ≧ 12)
An exhaust gas treatment catalyst, comprising iridium supported on a crystalline silicate having the following chemical formula.