JPH081006A - Exhaust gas purification catalyst and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a catalyst for purifying exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons, and a method for producing the same. [Structure] Crystalline silicate having specific X-ray diffraction pattern and chemical formula, γ-alumina, θ-alumina, zirconia, titania, titania-zirconia composite oxide,
Silica / alumina composite oxide, alumina / titania composite oxide, sulfate group-containing zirconia, sulfate group-containing zirconia / titania, Y-type zeolite, X-type zeolite, ZSM
-5 type zeolite, mordenite, silicalite, and at least one carrier, and a crystallite diameter of 30
A catalyst for purifying exhaust gas, which is characterized in that Å to 30 μm of iridium metal is supported.

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 and a method for producing the same.

[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.
However, although the above catalyst has sufficient performance in the early stage of the reaction, it has a problem in durability.

Therefore, as a result of investigations for overcoming the above-mentioned problems of the catalyst, the present inventors found that a catalyst having an iridium element supported on a carrier has a denitration performance in a lean atmosphere and is durable. However, it has been found that the catalyst hardly deteriorates (Japanese Patent Application No. 5-22838).
2, Japanese Patent Application No. 6-7667). However, in the above catalysts, even if the composition was the same, a difference in denitration performance was observed, and it was not always possible to obtain high denitration performance in a lean state.

[0004]

In view of the above technical level, the present invention is to provide a denitration catalyst using iridium as an active metal, which has high denitration performance and excellent durability, and a method for producing the same.

[0005]

Means for Solving the Problems As a result of extensive studies on the cause of the above difference in performance, the present inventors have found that the active metal, iridium, is in a crystalline state. The iridium element supported on the carrier exists in the state of metal or oxide, but the element having high denitration activity is the case of being supported in the state of metal. In particular, the crystallite diameter of iridium metal is Ir (1) by X-ray diffraction method (X-ray source: Cu kα ₁ ).
11) From the diffraction intensity of the plane, it was found that it is necessary to have a size of 30 Å or more by Sherrer's formula. This Sherrer's formula is described in "X-ray Diffraction Principles" by Kariti, published by Agne Co., Ltd., p. This Sherrer's formula is D (crystallite diameter) = K. λ / β · cos θ [K: constant (= 0.9), λ: wavelength of X-ray source (1.5405Å in the case of Cu), β: half width of diffraction peak (radian), θ: diffraction angle] Is used to identify the average crystallite size of the crystalline material. Further, when the high-performance catalyst was observed with a transmission electron microscope, it was found that the particle size of iridium supported on the carrier was 30 Å or more on average.

Further, as a unique phenomenon, it was found that the high performance iridium-supported catalyst has a reduction initiation temperature by H ₂ of 250 ° C. or lower. The reduction reaction formula of the iridium-supported catalyst is represented as follows. IrO ₂ (Iridium supported catalyst) + 2H ₂ → Ir +
2H ₂ O The fact that this reduction reaction occurs at 250 ° C. or lower indicates that oxygen on the iridium-supported catalyst is easily reduced by hydrogen. The reduction start temperature of an inactive catalyst or general IrO ₂ is 250 ° C. or higher. That is, although the state of the highly active iridium-supported catalyst is not clear, there is active oxygen which is extremely highly reactive in the iridium particles which are catalytically active metals from the above phenomenon, and the oxygen reacts with the hydrocarbon or nitrogen oxide. Therefore, it is considered to have high denitration activity.

The present invention has been completed based on the above findings. (1) The present invention has the X-ray diffraction pattern shown in Table A, which will be described in detail in the text, and has an oxide in a dehydrated state. Expressed by the molar ratio of (1 ± 0.8) R ₂ O. [aM ₂ O ₃ .bM'O
.CAl ₂ O ₃ ] .ySiO ₂ (wherein R is an alkali metal ion and / or hydrogen ion, M is a Group VIII element,
At least one element ion selected from the group consisting of rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium, M ′ is an alkaline earth metal ion of magnesium, calcium, strontium or barium, a> 0, 20> b ≧ 0, a + c = 1, 3000>
y> 11) a crystalline silicate having the chemical formula: γ-
Alumina, θ-alumina, zirconia, titania, titania / zirconia composite oxide, silica / alumina composite oxide, alumina / titania composite oxide, sulfate-containing zirconia, sulfate-containing zirconia / titania, Y-type zeolite, X-type zeolite An exhaust gas-purifying catalyst, characterized in that at least one carrier selected from the group consisting of ZSM-5 type zeolite, mordenite and silicalite is loaded with iridium metal having a crystallite diameter of 30Å to 30 μm. (2) The exhaust gas-purifying catalyst according to (1) above, wherein the H ₂ -reduction start temperature of the iridium-supported catalyst is 250 ° C. or lower. (3) The catalyst having iridium metal supported on the carrier according to the above (1) is exposed to a stoichio atmosphere gas or a rich atmosphere gas at 150 to 900 ° C., which is the above (1) or (2). Exhaust gas purification catalyst manufacturing method. (4) For exhaust gas purification according to (1) or (2) above, wherein the catalyst having iridium supported on the carrier according to (1) above is exposed to a gas containing steam at 150 to 900 ° C. Method for producing catalyst. Is.

[0008]

[Table 1]

[0009]

[Function] Usually, a catalyst using iridium having an average crystallite diameter of 30Å to 30 μm as an active metal produces NOx, CO,
The purification reaction formula for purifying the exhaust gas containing HC is as follows.

[0010]

Embedded image * 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 iridium-supported catalyst is 2 in a lean atmosphere.
It has high denitration performance at 50 ° C to 600 ° C. Furthermore, the catalyst of the present invention can remove NOx even in a stoichiometric atmosphere.
It is known to have CO combustion and HC combustion performance. Further, the catalyst of the present invention can be exposed to a high temperature lean or rich atmosphere of 700 ° C. or higher for a long time, and the above k ₁ , k ₂ , k
The reaction rate constants of ₃ and k ₄ hardly changed, and it was found that the catalyst had durability. By exposing the catalyst supporting iridium to a stoichiometric atmosphere gas or a rich atmosphere gas at 150 to 900 ° C., the crystallite diameter of Ir can be increased and converted to a highly active metal having a crystallite diameter of 30Å to 30 μm.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

Example 1 Preparation of Catalyst 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,
Aluminum sulfate: 718.9 g, ferric chloride: 110 g, calcium acetate: 47.2 g, sodium chloride: 262 g, 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 were supplied at a constant ratio to form a precipitate, which was sufficiently stirred to pH = 8.
Get a zero slurry. 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 carried out, and further 500
The crystalline silicate 1 is obtained by baking at 3 ° C. for 3 hours. This crystalline silicate 1 has a molar ratio of oxides (the water of crystallization is omitted).
It is represented by the following composition formula and its crystal structure is determined by X-ray diffraction as shown in Table A above.
Is displayed in. 0.5Na ₂ O ・ 0.5H ₂ O ・ [0.8Al ₂ O ₃・
0.2Fe ₂ O ₃ · 0.25CaO] · 25SiO _{2 The} above crystalline silicate 1 was added with 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 g of the above H-type crystalline silicate 1, alumina sol as a binder: 3 g, silica sol:
55g (SiO _2: 20%) and water: 200 g was added, to thereby prepare a slurry for wash-coating performs stirred thoroughly. Next, the monolith substrate for cordierite (lattice of 400 cells) was dipped in the slurry and taken out, and then excess slurry was blown 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
The above honeycomb coated article 1 was immersed in H ₂ O: 2.88 g / 100 cc: H ₂ O) and impregnated for 1 hour, and the liquid adhering to the wall of the substrate was wiped off and dried at 200 ° C. Next 50
Purging treatment was performed at 0 ° C. in a nitrogen atmosphere for 12 hours, and as activation treatment, nitrogen gas containing 10% steam was supplied at 700 ° C. for 10 hours to obtain a honeycomb catalyst 1.

Preparation of Catalysts 2 to 15 In the method for synthesizing the crystalline silicate 1 in the preparation of the above-mentioned honeycomb catalyst 1, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, chloride Crystalline silicate 2 is repeated by repeating the same operation as in crystalline silicate 1 except that titanium, 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 were prepared. The crystal structure of these crystalline silicates is shown in Table A above by X-ray diffraction, and its composition is expressed by the molar ratio of oxides (dehydrated form) of 0.5Na ₂ O · 0.5H. ₂ O ・ (0.2M ₂ O
₃・ 0.8Al ₂ O ₃・ 0.25CaO) ・ 25SiO
₂ Where M is Co, Ru, Rh, La, Ce,
Ti, V, Cr, Sb, Ga and Nb.

Further, in the method of synthesizing the crystalline silicate 1, magnesium acetate, strontium acetate, and barium acetate are used as C instead of calcium acetate in terms of oxides.
The same operations as in the crystalline silicate 1 were repeated except that the same number of moles as that of aO was added to the crystalline silicates 13 to 1.
5 was prepared. The crystal structure of these crystalline silicates is shown in Table A above by X-ray diffraction, and its composition is 0.5 in terms of the oxide molar ratio (dehydrated form).
Na ₂ O ・ 0.5H ₂ O ・ (0.2Fe ₂ O ₃・ 0.8
Is an _{Al 2 O 3 · 0.25MeO) ·} 25SiO 2.
Here, Me is Mg, Sr, or Ba.

Using the above crystalline silicates 2 to 15, the H type crystalline silicate 2 is prepared in the same manner as the honeycomb catalyst 1.
.About.15 were obtained, and the silicate was further coated on the cordierite monolith substrate by the same steps as in the preparation of the honeycomb catalyst 1 to obtain honeycomb coated products 2 to 15. Next, the honeycomb catalyst was immersed in an aqueous solution of iridium chloride and subjected to an activation treatment in the same manner as the honeycomb catalyst 1 to obtain honeycomb catalysts 2 to 15. The properties of the above honeycomb catalysts 1 to 15 and I by X-ray diffraction method
The crystallite diameters of r are summarized in Table B below.

Further, the reduction characteristics of these honeycomb catalysts 1 to 15 with H ₂ were measured as follows. The catalyst coating component of the honeycomb catalyst 1 is sampled and the inner diameter is 5 m.
Fill a quartz tube of mφ with 20 mg. First, in order to remove impurities (H ₂ O, CO _2, etc.) adsorbed on the catalyst, a pretreatment is performed with a pure He gas at 500 ° C. for 1 hour at a gas amount of 30 cc / min. After purging, the temperature is lowered to 50 ° C. under He flow. He purge gas is H ₂ : 0.5
% / He, and supplied to the catalyst layer at 30 cc / min. The temperature of the catalyst was raised at 10 ° C./min, and the H ₂ concentration decreased by the reaction with the catalyst and the H ₂ O concentration produced by the reaction were measured by a mass spectrometer. Honeycomb catalyst 2
15 was measured in the same manner, and the reduction start temperature by H ₂ is also shown in Table B.

[0019]

[Table 2]

Further, instead of the crystalline silicate of the honeycomb catalyst 1, γ-Al ₂ O ₃ , θ-Al ₂ O ₃ , Z
rO ₂ , TiO ₂ , TiO ₂ · ZrO ₂ , SiO ₂ · A
l ₂ O ₃ , Al ₂ O ₃ TiO ₂ , SO ₄ / ZrO ₂ ,
SO ₄ / ZrO ₂ · TiO ₂ , Y-type zeolite, X-type zeolite, ZSM-5 type zeolite, mordenite and silicalite were used to carry iridium in the same manner as in catalyst 1 and after activation treatment, Honeycomb catalyst 16 ~
I got 29. Table C shows the compositions of these catalysts 16 to 29, the crystallite size of Ir, and the reduction start temperature by H ₂ .

[0021]

[Table 3]

Example 2 The honeycomb coated article 1 of Example 1 was impregnated with iridium chloride, dried, and then 50
After performing a purging process at 0 ° C. for 12 hours in the same manner as in Example 1, a nitrogen gas containing 1% of hydrogen corresponding to a rich atmosphere gas is supplied for 10 hours at 700 ° C. as an activation process to supply the honeycomb catalyst 30. Got In addition, after performing a purging process at 500 ° C. for 12 hours in the same manner as described above, an activation process was performed at 650 ° C., which was hydrogen equivalent to a rich atmosphere gas:
Nitrogen gas containing 1% and H ₂ O: 10% was supplied for 10 hours to obtain a honeycomb catalyst 31.

Further, the same procedure as above was performed at 500 ° C. for 1 hour.
After performing the purging process for 2 hours, the activation process is performed at 750
The honeycomb catalyst 32 was obtained by exposing it to the exhaust gas from stoichiometric operation for 2 hours in an actual vehicle (gasoline vehicle) at ℃. Analysis of exhaust gas from stoichio operation showed NO: 2000pp
m, CO: 4000 ppm, THC: 2000 ppm,
O ₂ : 0.4%, H ₂ O: 10%, CO ₂ : 10%,
Remaining: N ₂ . Ir of the above honeycomb catalysts 30 to 32
The reduction start temperature by crystallite diameter and H ₂ are shown together in Table C.

(Comparative Example) Honeycomb coated article 1 of Example 1
Impregnated with iridium chloride and dried, then 500 ℃
The honeycomb catalyst 33 was obtained by firing for 12 hours in the air. The crystallite size of Ir and the reduction start temperature by H ₂ of this honeycomb catalyst are also shown in Table C as well.

FIG. 1 shows X-ray diffraction patterns of the honeycomb catalyst 1 of Example 1 and the honeycomb catalyst 33 of Comparative Example. FIG.
1A is an X-ray diffraction pattern of the honeycomb catalyst 1, and FIG. 1B is an X-ray diffraction pattern of the honeycomb catalyst (comparative example) 33. From Figure 1,
Although the Ir crystallite size of the honeycomb catalyst 1 was determined to be 100Å, the Ir crystallite size of the honeycomb catalyst 33 could not be identified, and was estimated to be 30Å or less. Further, FIG. 2 shows transmission electron micrographs of the Ir metallographic structures of the honeycomb catalyst 1 and the honeycomb catalyst 33. FIG. 2A shows a honeycomb catalyst 1
2B is the same photograph of the honeycomb catalyst 33. From FIG. 2, the Ir crystallite diameter of the honeycomb catalyst 1 is about 100 to
It was confirmed to be 200Å, but the honeycomb catalyst 33
Of Ir had a crystallite diameter of 30 Å or less.
Furthermore, FIG. 3 also shows the honeycomb catalyst 1 and the honeycomb catalyst 33.
3 is a chart showing a reduction pattern of H ₂ with H ₂ . That, of H ₂ fed 0.5% inclusive He gas, is a table showing a result of with observed changes in the concentration of H ₂ the _{(H 2 + 1 / 2O 2} → H 2 O) to raise the temperature. In FIG. 3, M / S means mass number. That is, hydrogen (H ₂ ) = 2, water (H ₂ O)
= 18, each concentration change was observed over time.

(Experimental Example 1) An activity evaluation test (Run) was carried out using the honeycomb catalysts 1 to 33 prepared in Examples and Comparative Examples.
1-33) were carried out. The activity evaluation conditions are as follows. 〇 (gas composition) NO: 500ppm, CO: 1000ppm, C
_{2 H 4: 1500ppm, O 2} : 8%, CO 2: 10
%, H ₂ O: 10%, balance: N ₂ 〇 Gas amount: 405 Nl / min, GHSV: 30,000
0h ⁻¹ ○ Catalyst shape: 15 mm × 15 mm × 60 mm (144 cells) 135 cc arranged ○ Reaction temperature: 350,450 ° C. The denitration rate of the catalyst in the initial state is shown in Table D below.

(Experimental Example 2) Run No. A forced heating test was performed on the catalysts arranged in 1 to 33 in a rich atmosphere (reducing atmosphere). The forced heating test is as follows. 〇 (Gas condition) H ₂ : 5%, H ₂ O: 10%, balance: N ₂ GHSV: 5000 h ⁻¹ , temperature: 500 ° C., gas supply time: 100 hours Catalyst shape: 15 mm × 15 mm × 60 mm (144 cells )

Run N treated under the above-mentioned forced heating conditions
o. An activity evaluation test was performed on the catalysts 1 to 33 under the activity evaluation conditions of Experimental Example 1. Table D also shows the denitration rate of the catalyst after the forced heating test at reaction temperatures of 350 and 450 ° C. From Table D, it was confirmed that the honeycomb catalysts 1 to 32 of the present invention had high activity even at the initial stage and after the heat treatment, as compared with the catalyst having no small iridium crystallite size (honeycomb catalyst 33) without activation treatment.

[0029]

[Table 4]

[0030]

[Table 5]

[0031]

EFFECTS OF THE INVENTION The catalyst having an iridium metal of 30Å to 30 μm of the present invention can denitrate extremely efficiently by using hydrocarbon as a reducing agent, and acts extremely advantageously for purification of exhaust gas for lean burn engine and diesel engine. To do.

[Brief description of drawings]

FIG. 1 is a chart showing X-ray diffraction patterns of a catalyst of the present invention (honeycomb catalyst 1) and a comparative catalyst (honeycomb catalyst 33).

FIG. 2 is a transmission electron micrograph of the Ir metallographic structures of the catalyst of the present invention (honeycomb catalyst 1) and the comparative catalyst (honeycomb catalyst 33).

FIG. 3 is a chart showing reduction patterns of the catalyst of the present invention (honeycomb catalyst 1) and a comparative catalyst (honeycomb catalyst 33) with H ₂ .

Claims (4)

[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 ± 0.8) 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 VIII
Group I element, rare earth element, at least one element ion selected from the group consisting of titanium, vanadium, chromium, niobium, antimony and gallium, M'is an alkaline earth metal ion of magnesium, calcium, strontium, barium, a > 0, 20> b ≧ 0, a + c = 1,
3000>y> 11) crystalline silicate, γ-alumina, θ-alumina, zirconia, titania, titania-zirconia composite oxide, silica-alumina composite oxide, alumina-titania composite oxide, containing sulfate radical Zirconia, sulfate containing zirconia / titania,
At least one carrier selected from the group consisting of Y-type zeolite, X-type zeolite, ZSM-5 type zeolite, mordenite and silicalite, and having a crystallite diameter of 30Å to 30 μm.
A catalyst for purifying exhaust gas, which is obtained by carrying the iridium metal. _{2. The} reduction initiating temperature of H _{2 for} an iridium-supported catalyst is 250 ° C. or lower.
Exhaust gas purifying catalyst described. 3. The exhaust gas purifying method according to claim 1 or 2, wherein the catalyst prepared by supporting the iridium metal on the carrier according to claim 1 is exposed to a stoichio atmosphere gas or a rich atmosphere gas at 150 to 900 ° C. For producing catalyst for automobile. 4. The catalyst for purifying exhaust gas according to claim 1, wherein the catalyst having iridium supported on the carrier according to claim 1 is exposed to a gas containing steam at 150 to 900 ° C. Production method.