JP3129346B2 - Exhaust gas treatment catalyst and exhaust gas treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to nitrogen oxides (hereinafter referred to as NO
x), a catalyst for purifying exhaust gas containing carbon monoxide and hydrocarbons (hereinafter abbreviated as HC), and a method for treating the exhaust gas.

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles, etc.
Called three-way catalyst using CO and HC in the fuel
Catalyst (Composition: Pt, Rh / Al_TwoO_ThreeSystem)
Generally, but extremely narrow around the stoichiometric air-fuel ratio.
NOx is purified only in the range. In recent years, global environmental problems
Demand for low fuel consumption of automobiles is growing
A lean burn engine that burns at an air-fuel ratio or higher
It is attracting attention as a knology. However, the running of the car
Taking into account the performance and acceleration, only the lean region engine
The air-fuel ratio is actually stoichiometric (stoichio)
It is necessary to cause combustion in both the vicinity and the lean region.
Recently, regarding the purification of NOx in the lean region, copper was contained.
Crystalline silicate catalysts as a catalyst with high performance
It is receiving light. On the other hand, in the stoichio area,
Pt, Rh / Al_TwoO _ThreeSystem three-way catalyst is high
Because of its activity, it can exhaust both lean and stoichiometric areas.
If the above conditions are met, the combination of the above two catalysts
A law has been proposed. When combined, Cu / crystalline
The silicate and the three-way catalyst are arranged in parallel or in series.
No. 62-296423, Japanese Patent Application No. 02-41196
5) In parallel, switch according to gas composition and gas temperature
The method of controlling the gas flow path with a valve is adopted,
Many difficulties are required for control. On the other hand, Cu /
Crystalline silicate (first stage) and three-way catalyst (second stage) in series
When applied, exhaust gas changes from lean to stoichiometric
That the denitration reaction of the three-way catalyst does not work during the transition period
A match has occurred.

[0003]

When a Cu / crystalline silicate catalyst and a three-way catalyst are combined, the series connection is technically more practical. When the three-way catalyst is disposed in series, CO, which is a reducing agent for the denitration reaction of the three-way catalyst, is consumed in the Cu / crystalline silicate catalyst at the preceding stage during the transition period from lean to stoichiometric because the three-way catalyst does not work. It is mentioned that the denitration reaction does not sufficiently occur even if it enters the region.

The present invention has been made in view of the above-mentioned state of the art, and provides a Cu / crystalline silicate capable of suppressing the combustion activity of CO to solve the above-mentioned problems of the prior art.

[0005]

The present invention provides (1 ) an X-ray diffraction pattern shown in Table 1, which is expressed as a molar ratio of oxide in a dehydrated state (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 at least one or more selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium) M ′ is an alkaline earth metal ion of magnesium , calcium, strontium, barium, a ≧ 0, 2
0>b> 0 , a + c = 1,3000>y> 11) A crystalline silicate having a chemical formula of copper and further a Vb group,
An exhaust gas treatment catalyst comprising at least one metal of the group VIb element.

(2) The crystalline silicate according to the above (1) is obtained by using a crystalline silicate synthesized in advance as a mother crystal, and having an outer surface of the mother crystal having the same crystal structure as the mother crystal.
The exhaust gas treatment catalyst according to the above (1), wherein the catalyst is a layered composite crystalline silicate obtained by growing a crystalline silicate consisting of O and O.

(3) In treating an exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, the exhaust gas treating catalyst according to the above (1) or (2) is disposed at a preceding stage,
A method for treating exhaust gas, comprising arranging an oxidation catalyst in a subsequent stage and passing the exhaust gas through the catalyst. It is.

[0008]

In the exhaust gas treatment catalyst of the present invention, the elements of the Vb group and the VIb group coexisting with copper are phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), Selenium (Se) and tellurium (Te).
The addition of these elements is important for the Cu / crystalline silicate catalyst C
It effectively acts to suppress the combustion activity of O, and when combined in series with a three-way catalyst, has a sufficient denitration effect even when the gas composition changes from lean to stoichiometric.

[0009] Generally, the reaction formula for purifying exhaust gas containing NOx, CO and HC using Cu / crystalline silicate is as follows.

Embedded image * 1) C ₃ H ₆ is shown as a representative example of hydrocarbon (HC). * 2) CH ₂ O is shown as a representative 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. Element Cu
/ By adding to the crystalline silicate catalyst, the reaction rate constants of k ₁ , k ₂ and k ₃ hardly change,
lowering the reaction rate constant k _4. The reason why elements of the Vb and VIb groups effectively work to suppress the combustion activity of CO is as follows.
All of these elements have an unshared electron pair, and it is considered that the formation of a stable coordination bond with the catalyst inhibits the adsorption of CO and suppresses the combustion activity of CO.

The crystalline silicate used in the present invention has an X-ray diffraction pattern shown in Table 1 below, and is expressed as a molar ratio of oxide (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 at least one or more selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium) M ′ is an alkaline earth metal ion of magnesium , calcium, strontium, barium, a ≧ 0, 2
0>b> 0 , a + c = 1, 3000>y> 11).

[0012]

[Table 2]

A layered composite obtained by using a crystalline silicate previously synthesized from the above-mentioned crystalline silicate as a mother crystal, and growing a crystalline silicate made of Si and O having the same crystal structure as the mother crystal on the outer surface of the mother crystal. Crystalline silicate may be used. Due to the hydrophobic action of the crystalline silicate composed of Si and O (referred to as silicalite) grown on the outer surface of the layered composite crystalline silicate, only H ₂ O hardly penetrates into the interior of the crystalline silicate, and the It has the effect of lowering the concentration of H ₂ O around the reaction active site, and has the effect of suppressing the demetallation effect. for that reason,
Even in a high-temperature steam atmosphere, deterioration of the catalyst is suppressed.

The catalyst comprises copper and Vb on the above crystalline silicate.
Immersion in an aqueous solution of a Group IIIb or Group VIb salt to support metal ions by an ion exchange method, or by immersion in an aqueous solution of a metal salt such as chloride, nitrate or sulfate. Furthermore, a method is also possible in which after the copper is supported, the oxides and chlorides of the Vb group and the VIb group are supported on the supply in a gaseous state.

[0015]

【Example】

(Example 1) 〇 (Synthesis of mother crystal A) Water glass No. 1 (SiO ₂ : 30)
%) 5616 g was dissolved in 5429 g of water, and this solution was designated as solution A. On the other hand, aluminum sulfate 7 was added to 4175 g of water.
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 rate to form a precipitate, and the mixture is sufficiently stirred to obtain a pH.
= 8.0 slurry is obtained. This slurry was charged into a 20-liter autoclave, and 500 g of tetrapropylammonium bromide was further added. Hydrothermal synthesis was performed at 160 ° C. for 72 hours. After the synthesis, the resultant was washed with water and dried. Obtain silicate 1. This crystalline silicate is represented by the following composition formula in terms of the molar ratio of the oxide (omitting the water of crystallization), and the crystal structure is shown in Table 1 by X-ray diffraction. 0.5NaO ₂・
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, and 4590 g of colloidal silica (SiO ₂ : 20%) was further added, followed by sufficient stirring to obtain 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 the solution a is being stirred, the solution b is gradually added dropwise to form a precipitate to obtain a slurry. The slurry is placed in an autoclave, and a solution of 568 g of tetrapropylammonium bromide dissolved in 2106 g of water is added to the autoclave. 160 ° C in this autoclave,
Hydrothermal synthesis is performed for 72 hours (stirring at 200 rpm), and after stirring, washing and drying, baking is performed at 500 ° C. for 3 hours to obtain a layered composite crystalline silicate 1.

The layered composite crystalline silicate 1 was stirred at 40 ° C. in a 4N aqueous NH ₄ Cl solution for 3 hours to carry out NH ₄ ion exchange. Washing after ion exchange, 100 ° C, 24
After drying for an hour, it was fired at 400 ° C. for 3 hours to obtain an H-type layered composite crystalline silicate 1.

{(Catalysis) Next, 3 parts of alumina sol and 55 parts of silica sol (SiO ₂ : 20) were used as binders for the above 100 parts of the H-type layered composite crystalline silicate 1.
%), And sufficiently stirred to obtain a wash coat slurry. Next, a cordierite monolith substrate (400 cell grid) is immersed in the slurry,
After being taken out, excess slurry was blown off and dried at 200 ° C. The coating amount is 200 g per 1 liter of the base material.

Next, cuprous chloride and a phosphoric acid solution (Cu
_{Cl: 26.8g, H 3 PO 4} : 21.5g / 200c
After the honeycomb coated article 1 was immersed in cHCl) and impregnated for 1 hour, the liquid adhering to the substrate wall was wiped off and dried at 200 ° C. Next, a purging treatment was performed at 500 ° C. in a nitrogen atmosphere for 12 hours to obtain a honeycomb catalyst 1.

(Example 2) In the method for synthesizing the mother crystal 1 of Example 1, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride, Mother crystals 2 to 12 were prepared by repeating the same operation as for mother crystal 1 except that antimony chloride, gallium chloride and niobium chloride were each added in the same mole number as Fe ₂ O _{3 in} terms of oxide. The crystal structures of these mother crystals are shown in Table 1 by X-ray diffraction, and their compositions are expressed as a molar ratio of oxide (dehydrated form) of 0.5.
Na ₂ O · 0.5H ₂ O · (0.2M ₂ O ₃ · 0.8A
l ₂ O ₃ .0.25 CaO) .25 SiO ₂ . Where M is Co, Ru, Rh, La, Ce, Ti, V, C
r, Sb, Ga, is a N b.

Further, a mother crystal 13 was obtained in the same manner as that of the mother crystal 1, except that nothing was added instead of ferric chloride and calcium acetate.

These mother crystals 2 to 13 are finely pulverized, and in the same manner as in the synthesis of the layered composite crystalline silicate 1 of Example 1, the mother crystals 2 to 13 are used in place of the mother crystal 1 and an autoclave is used. As a result, the layered composite crystalline silicates 2 to 13 were obtained.

Using the layered composite crystalline silicates 2 to 13 described above, H-type layered composite crystalline silicates 2 to 13 are obtained in the same manner as in Example 1, and the silicate is further prepared in the same manner as in the preparation of the catalyst of Example 1. In the step of, a cordierite monolith substrate is coated to obtain honeycomb coated products 2 to 13, and then immersed in a cuprous chloride and phosphoric acid / hydrochloric acid solution. ~ 13 (Honeycomb catalyst 1
3 is a reference example) .

Further, only the mother crystal 1 is made of H as in the first embodiment.
And then coated on a honeycomb substrate to obtain a honeycomb article 1
4 was obtained. The coated product 14 was immersed in a cuprous chloride / phosphate solution in the same manner as in Example 1 to obtain a honeycomb catalyst 14.

(Example 3) In the method for synthesizing the mother crystal 1 of Example 1, magnesium acetate was used instead of calcium acetate.
Mother crystals 15 to 17 were prepared by repeating the same operation as for mother crystal 1 except that strontium acetate and barium acetate were each added in the same mole number as CaO in terms of oxide. The crystal structures of these mother crystals are shown in Table 1 by X-ray diffraction, and the composition is represented by a molar ratio of oxide (dehydrated form) of 0.5Na ₂ O · 0.5H ₂ O ・
(0.2Fe ₂ O ₃ · 0.8Al ₂ O ₃ · 0.25Me
O) · 25SiO ₂ . Where Me is Mg, Sr,
Ba. These mother crystals 15 to 17 were pulverized and hydrothermally synthesized 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 15 to 17. . Further, honeycomb catalysts 15 to 17 were obtained from the above silicates 15 to 17 in the same manner as in Example 1.

Example 4 Honeycomb coated article 1 coated with H-type layered composite crystalline silicate 1 obtained in Example 1
Using cuprous chloride and arsenic acid {CuCl: 26.8
g, arsenic acid solution: 180 g (containing 60% of H ₃ AsO ₄ ) / H
Cl 200cc｝, cuprous chloride and antimony chloride (C
uCl: 26.8 g, SbCl ₃ : 22.5 g / HCl
200cc), cuprous chloride and bismuth chloride (CuC
1: 26.8 g, BiCl ₃ : 22 g / HCl 200
cc), cuprous chloride and sulfuric acid (CuCl: 26.8 g, H
₂ SO ₄ : 7.8 g / HCl 200 cc), cuprous chloride and selenium tetrachloride (CuCl: 26.8 g, SeC)
l ₄ : 18 g / HCl 200 cc), cuprous chloride and tellurium tetrachloride (CuCl: 26.8 g, TeCl ₄ : 24)
g / HCl 200 cc) to obtain honeycomb catalysts 18 to 23 in the same manner as in the catalysis of Example 1.

Example 5 Using the layered composite crystalline silicate 1 of Example 1, 0.04M copper acetate and 0.04M copper acetate were used.
Ion exchange was performed by immersing in a bismuth chloride aqueous solution at 30 ° C. and stirring. After washing and drying, a powder catalyst a was obtained.

Next, a honeycomb catalyst 24 was obtained by coating the above-mentioned powder catalyst a on a monolith substrate in the same manner as in the catalysis of Example 1.

(Comparative Example) A cuprous chloride / hydrochloric acid solution (CuCl: 26.8 g / H) was applied to the honeycomb coat 1 obtained in Example 1.
Cl 200 cc), and thereafter, a honeycomb catalyst 25 was obtained in the same manner as in Example 1.

The constitutions of the above-mentioned catalysts of the present invention, the catalysts of the reference example and the catalysts of the comparative examples are summarized in Tables 2 and 3 below.

[0031]

[Table 3]

[0032]

[Table 4]

(Experimental Example 1) Activity evaluation tests of the honeycomb catalysts 1 to 25 prepared in Examples 1, 2, 3, and 4 and Comparative Example were performed. The activity evaluation conditions are as follows. ○ (gas composition) NO: 400 ppm, CO: 1000 ppm, C
₂ H ₄ : 1000 ppm, C ₃ H ₆ : 340 ppm, O
_{2: 8%, CO 2:} 10%, H 2 O: 10%, remaining:
N ₂ , GHSV: 30000 h ⁻¹ , catalyst shape: 15 mm
× 15 mm × 60 mm (144 cells) Tables 4 and 5 show the denitration rate and CO conversion rate of the catalyst in the initial state at a reaction temperature of 350 and 450 ° C. From these results, it can be seen that all of the honeycomb catalysts 1 to 25 have a high NOx conversion rate, but the CO conversion rates of the honeycomb catalysts 1 to 12 and 14 to 24 of the present invention are all low.

[0034]

[Table 5]

[0035]

[Table 6]

(Experimental Example 2) The above honeycomb catalysts 1 to 24 were used as the first catalyst layer, and Pt-Rh-CeO was used as the second catalyst layer.
An experiment was conducted in which ₂ / Al ₂ O ₃ catalysts were connected in series as shown in FIG. 1 and the exhaust gas flowed from the first catalyst layer to the second catalyst layer.

The Pt-Rh-C used for the second catalyst layer
The eO ₂ / Al ₂ O ₃ catalyst is usually called a three-way catalyst, and the preparation method is as follows. First, specific surface area 2
For 100 parts of 00 m ² / g alumina, 3 parts of alumina sol and 55 parts of silica sol (SiO ₂ :
20%) and 200 parts of water, and sufficiently stirred to obtain a slurry for washcoat. Next, a cordierite monolith substrate (400 cell grids) was immersed in the slurry, taken out, dried, and fired at 700 ° C. for 1 hour.
The coating amount was 100 g per liter of the base material, and a coated material 26 was obtained. Next, the coated material 26 is immersed in an aqueous solution of cerium nitrate 2.5 mol / liter, dried, and dried.
The mixture was fired at 0 ° C. for 3 hours in the air, and cerium oxide (CeO ₂ ) 0.3 mol / liter (coat base material) was supported on the coated product. Further, this is treated with rhodium chloride 0.0
200 ° C after immersion in an aqueous solution of 02 mol / L and drying
For 1 hour, and 0.3 g / l of rhodium (Rh) (coated base material) was supported on the coated material. Furthermore,
This was immersed in an aqueous solution of dinitrodiamineplatinum at a concentration of 0.005 mol / liter in a nitric acid solution, dried, and dried.
Baking at 0 ° C for 1 hour, platinum (Pt)
1.5 g / liter (coated substrate). The obtained catalyst is referred to as a honeycomb catalyst 26.

The activity evaluation conditions are as follows. (Activity evaluation condition A) NO: 400 ppm, CO: 1000 ppm, C
_TwoH_Four: 1000 ppm, C _ThreeH₆: 340 ppm, O
_Two: 8%, CO_Two: 10%, H_TwoO: 10%, remaining: N _Two GHSV: 15000h^-1(Gas volume: 405 Nl
/ Min) Catalyst: First catalyst layer: 15 mm × 15 mm × 60 mm (1
44 cells) 2nd catalyst layer: 15 mm × 15 mm × 60 mm (144 cells)
）) (Activity evaluation condition B) NO: 2000 ppm, CO: 1000 ppm, C_TwoH
_Four: 1000 ppm, C_ThreeH₆: 340 ppm, O_Two:
0.6%, CO_Two: 10%, H_TwoO: 10%, remaining: N_Two GHSV: 15000h^-1(Gas volume: 405 Nl
/ Min) Catalyst: First catalyst layer: 15 mm × 15 mm × 60 mm (1
44 cells) 2nd catalyst layer: 15 mm × 15 mm × 60 mm (144 cells)
Le)

Tables 6 and 7 show the results of the conversion rates of NOx, CO and HC at 450 ° C. From this result, when the honeycomb catalysts 1 to 24 and the honeycomb catalyst 26 which is a three-way catalyst are combined in series, the activity evaluation condition A in the high O ₂ concentration region is obtained.
Activity evaluation condition B in low O ₂ concentration range even in (lean area)
It can be seen that all of the (stoichiometric region) have high denitration performance. On the other hand, the honeycomb catalyst 25 and the honeycomb catalyst 2
It can be seen that in the case of combining No. 6 in series, a high denitration rate cannot be obtained under the activity evaluation condition B.

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

According to the present invention, a Cu / crystalline silicate catalyst capable of suppressing the CO combustion activity is provided. By using the catalyst in combination with a conventional three-way catalyst, exhaust gas can be sufficiently purified in both a lean region and a stoichiometric region. Method is provided,
This is an extremely effective invention for exhaust gas from lean burn engines of gasoline vehicles and purification of exhaust gas from diesel engines.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an activity evaluation method in Experimental Example 2 of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-16239 (JP, A) JP-A-3-165816 (JP, A) JP-A-61-261211 (JP, A) JP-A-4-162 118030 (JP, A) JP-A-1-139145 (JP, A) JP-A-2-500822 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38 / 74

Claims (3)

(57) [Claims] 1. An X-ray diffraction pattern as shown in Table 1, which is expressed as a molar ratio of oxide (1 ± 0.8) R ₂ O · [aM ₂ O ₃ · bM ′ in a dehydrated state. O ・ cA
l 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. And at least one or more element ions, M 'is magnesium, calcium,
Alkaline earth metal ions of strontium and barium,
a ≧ 0, 20>b> 0 , a + c = 1, 3000>y> 1
1) An exhaust gas treatment catalyst comprising a crystalline silicate having a chemical formula represented by the formula (1), wherein copper and at least one metal of a Vb group or VIb group element are coexisted. [Table 1] 2. The crystalline silicate according to claim 1, wherein the crystalline silicate synthesized in advance is used as a mother crystal, and a crystalline silicate made of Si and O having the same crystal structure as the mother crystal on the outer surface of the mother crystal. 2. The exhaust gas treatment catalyst according to claim 1, wherein the catalyst is a layered composite crystalline silicate obtained by growing. 3. In treating an exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, an exhaust gas treatment catalyst according to claim 1 or 2 is disposed in a preceding stage, and an oxidation catalyst is disposed in a subsequent stage. A method for treating exhaust gas, comprising passing the exhaust gas through these catalysts.