JP3276193B2 - Exhaust treatment catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitrogen oxide (hereinafter referred to as NO
x), carbon monoxide (CO) and hydrocarbons (hereinafter, referred to as x).
(Abbreviated as HC).

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles and the like, a three-way catalyst (NOx,
Purification is generally performed using a catalyst (composition: Pt, Rh / Al ₂ O ₃ system) called a catalyst that simultaneously removes three substances of CO and HC, but in a very narrow range around the stoichiometric air-fuel ratio. Only NOx is purified. 2. Description of the Related Art In recent years, as global environmental problems have increased, there has been a strong demand for lower fuel consumption of automobiles, and a lean burn engine that burns at a stoichiometric air-fuel ratio or more has attracted attention as a key technology. However, taking into account the running performance and acceleration of the vehicle, the engine only in the lean region has many disadvantages, and it is actually necessary to perform combustion in both the vicinity of the stoichiometric air-fuel ratio (stoichio) and the lean region. Recently, regarding the purification of NOx in a lean region, a crystalline silicate catalyst containing cobalt or copper has been spotlighted as a catalyst having high performance.

[0003]

Although these catalysts have sufficient performance in the early stage of the reaction, there are problems in durability, and various catalysts for improving the crystalline silicate have been used to improve the durability. Is being considered. For example, in order to prevent desorption of aluminum, which is a main constituent element of crystalline silicate, and to attain stability of cobalt or copper, a group VIII element or a rare earth element ( Japanese Unexamined Patent Publication No.
JP-A-165816) and a method using a novel silicate to which an alkaline earth metal (Japanese Patent Application No. 3-319195) is further added has been proposed. In addition, in order to prevent the intrusion of steam that promotes the desorption of aluminum, the application of crystalline silicate with improved steam resistance by growing a crystal of hydrophobic silicalite on the surface layer of crystalline silicate is also being studied. (Japanese Patent Application No. 3-192829).

However, by using these catalysts, the durability in a lean atmosphere has been greatly improved. However, when accelerating at a high speed of 100 km / h,
The gas temperature may instantly reach around 700 ° C,
The gas composition at this time is a rich atmosphere in which a reducing agent such as hydrogen is excessively present. Under these conditions, the deterioration of the catalyst cannot be prevented even when the above-mentioned improved crystalline silicate is applied. Therefore, improvement of the durability of the catalyst in a high-temperature rich atmosphere is a major problem in practical use of these catalysts. .

[0005] In view of the above technical level, the present invention prevents catalyst deterioration even in a rich atmosphere in which a reducing agent is excessively present,
Another object of the present invention is to provide a catalyst capable of efficiently treating exhaust gas even in a lean atmosphere or a rich atmosphere.

[0006]

In order to overcome the disadvantages of the conventional Cu / crystalline silicate catalyst, the present inventors have found that the state of the active metal does not change even in a high-temperature reducing atmosphere and the lean metal atmosphere does not change. As a result of intensive studies on metals having sufficient activity, it was found that rhodium (Rh) is a preferable metal. This rhodium metal was found to have high activity in a lean atmosphere even on the crystalline silicate used in the present invention, and to have denitration activity, CO and HC removal activity in the same temperature range as the Cu / crystalline silicate catalyst. . Furthermore, it was also found that by adding rhodium to copper, reduction of copper was suppressed and durability as Cu / crystalline silicate was improved.

The present invention has been completed based on the above findings and includes the following constitutions (1) to (4).
You. (1) In a dehydrated state, expressed as a molar ratio of oxide, (1 ± 0.6) R ₂ O. [aM ₂ O ₃ .bAl ₂ O ₃ .cMeO] .ySiO ₂ (in the above formula, R Is an alkali metal ion and / or a hydrogen ion, M is at least one element selected from the group consisting of a group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony, and gallium; Me is an alkaline earth element; a> 0, b> 0, c> 0 , a + b = 1, y / c> 1
An exhaust treatment catalyst comprising copper and rhodium supported on a crystalline silicate having a chemical formula of 2, y> 12) and having an X-ray diffraction pattern shown in Table A below . (2) A layered composite crystal in which a crystalline silicate is a previously synthesized crystalline silicate as a mother crystal, and a crystalline silicate made of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. The exhaust treatment catalyst according to the above (1 ), wherein the exhaust treatment catalyst is a functional silicate. (3) Cobalt is further added to the exhaust treatment catalyst of the above (1).
An exhaust treatment catalyst comprising one or more metals selected from the group consisting of nickel, iron, aluminum, zirconium and tin. (4) The exhaust treatment catalyst of the above (1) further comprises cobalt,
An exhaust treatment catalyst comprising one or more metals selected from the group consisting of nickel, iron, aluminum, zirconium and tin .

[0008]

Normally, NO is produced using Cu / crystalline silicate.
The purification reaction formula for purifying the exhaust gas containing x, CO, and HC is as follows.

[0009]

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. Cu / crystalline silicate Only in the high-temperature reducing atmosphere, the above k ₁ , k ₂ , k ₃ , k ₄
Although the reaction rate constant gradually decreases, the addition of Rh to Cu has an effect of hardly changing the reaction rate constant.

The crystalline silicate used in the present invention has an X-ray diffraction pattern shown in Table A below, and expressed as a molar ratio of oxide (1 ± 0.
6) R ₂ O · _{[aM 2 O 3 · bAl 2 O} 3 · cMeO ]
• ySiO ₂ (wherein, R is an alkali metal ion and / or a 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) Me is an alkaline earth element of magnesium, calcium, strontium, barium, a ≧ 0, b ≧ 0, c
≧ 0, a + b = 1, y / c> 12, y> 12).

[0012]

[Table 2]

Further, in the present invention, a crystalline silicate previously synthesized from the above crystalline silicate is used as a mother crystal, and the outer surface of the mother crystal has the same crystal structure as that of the mother crystal.
A layered composite crystalline silicate obtained by growing a crystalline silicate composed of i and O 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. Therefore, deterioration of the catalyst is suppressed even in a high-temperature steam atmosphere.

The catalyst of the present invention is obtained by adding Cu to the above crystalline silicate.
And Rh are immersed in an aqueous solution of each metal salt to carry metal ions by an ion exchange method, or chloride, nitrate,
There is a method in which a metal salt such as a sulfate is supported by an impregnation method. Furthermore, a method is also possible in which after Cu and Rh are supported, oxides and chlorides of the above metals are supplied in a gaseous state and supported.

In addition, in addition to the active metal, cobalt (C
o), nickel (Ni), iron (Fe), aluminum (Al), zirconium (Zr), and tin (Sn) have been found to improve the durability of the catalyst.

C in the exhaust treatment catalyst of the present invention
The supported amount of u and Rh is generally Cu: 0.2 to metal conversion.
20 wt%, Rh: 0.01 to 10 wt%, C
The supported amounts of o, Ni, Fe, Al, Zr, and Sn are 0.1 to 20 wt% in terms of metal.

[0017]

【Example】

(Example 1) Water glass No. 1 (SiO ₂ : 30%): 56
16 g was dissolved in 5429 g of water, and this solution was designated as solution A. On the other hand, water: 4175 g and aluminum sulfate: 71
8.9 g, ferric chloride: 110 g, calcium acetate: 4
7.2 g, sodium chloride: 262 g, concentrated hydrochloric acid: 202
0 g is dissolved, and this solution is referred to as solution B. The solution A and the solution B are supplied at a constant rate to form a precipitate, and the mixture is sufficiently stirred to obtain a slurry having a pH of 8.0. 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. The crystalline silicate 1 is represented by the following composition formula in terms of the molar ratio of the oxide (omitting the crystallization water), and the crystal structure is represented by X-ray diffraction in Table A above. 0.5NaO ₂
・ 0.5H ₂ O ・ [0.8Al ₂ O ₃・ 0.2Fe ₂ O
₃ · 0.25CaO] · 25SiO ₂

The above crystalline silicate 1 is made of 4N NH ₄ C
The aqueous solution was stirred at 40 ° C. for 3 hours to carry out NH ₄ ion exchange. After washing after ion exchange and drying at 100 ° C. for 24 hours, it was calcined at 400 ° C. for 3 hours to obtain H-type crystalline silicate 1.

Next, 3 parts of alumina sol were used as a binder with respect to 100 parts of the H-type crystalline silicate 1 described above.
Silica sol: 55 parts (SiO ₂ : 20%) and water: 200
Then, the mixture was sufficiently stirred to obtain a slurry for washcoat. Next, a monolith base material for cordierite (a grid of 400 cells) was immersed in the above slurry, taken out, and then sprayed with excess slurry and dried at 200 ° C. The coating amount is 200 g per 1 liter of the base material.

Next, cupric chloride and an aqueous solution of rhodium chloride (CuCl ₂ .2H ₂ O: 23.0 g, RhCl ₃ .3)
_{H 2 O: 2g / 200ccH 2} O) after immersion impregnated 1 hour the honeycomb coating material 1 and dried at 200 ° C. wiping the adhered liquid walls of the substrate. Next, a purging treatment was performed at 500 ° C. in a nitrogen atmosphere for 12 hours, and the honeycomb catalyst 1
I got

Example 2 In the method for synthesizing the crystalline silicate 1 of Example 1, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, and chromium chloride were used. , antimony chloride, except for adding only the same number of moles as the Fe ₂ O ₃ in each oxide conversion gallium chloride and niobium chloride were prepared crystalline silicate 2 to 12 by repeating the same operation as the mother crystal 1. The crystal structures of these crystalline silicates are those shown in Table A above by X-ray diffraction,
Its composition is represented by the molar ratio of oxides (dehydrated form), 0.5 NaO ₂ .0.5H ₂ O. (0.2M ₂ O.
It is a _{0.8Al 2 O 3 · 0.25CaO) ·} 25SiO 2. Where M is Co, Ru, Rh, La, Ce, T
i, V, Cr, Sb, Ga, Nb.

Further, in the method for synthesizing crystalline silicate 1 of Example 1, except that magnesium acetate, strontium acetate, and barium acetate were added in the same molar amount as CaO in terms of oxide, respectively, instead of calcium acetate. By repeating the same operation as above, crystalline silicates 13 to 15 were prepared. The crystal structure of these mother crystals is X
It is shown in Table A by X-ray diffraction, and its composition is represented by a molar ratio of oxide (dehydrated form) of 0.5 N
_{a 2 O · 0.5H 2 O ·} (0.2Fe 2 O 3 · 0.8A
l ₂ O ₃ · 0.25MeO) · 25SiO ₂ . Here, Me is Mg, Sr, and Ba.

These crystalline silicates 2 to 15 were converted to H-type by the same method as in Example 1, and honeycomb catalysts 2 to 15 were obtained by the same method as in Example 1.

(Example 3) 1000 prepared in Example 1
g of the crystalline silicate 1 is pulverized and added to 2160 g of water, and further colloidal silica (SiO ₂ : 20
%): 4590 g was added, and the mixture was sufficiently stirred, and this solution was designated as 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 stirring the solution a, the solution b is gradually added dropwise to form a precipitate to obtain a slurry. This slurry was placed in an autoclave, and 568 g of tetrapropylammonium bromide was added to 21 parts of water.
The solution dissolved in 06 g is added to the autoclave. Hydrothermal synthesis is performed in this autoclave at 160 ° C. for 72 hours (stirring at 200 rpm). After stirring, washing and drying, baking is performed at 500 ° C. for 3 hours to obtain a layered composite crystalline silicate 1.

The prepared layered composite crystalline silicate 1 was converted to H-type in the same manner as in the example, and a honeycomb catalyst 16 was obtained in the same manner as in the example 1.

(Example 4) The honeycomb-coated material 1 obtained in Example 1 was impregnated with cupric chloride and rhodium chloride, further mixed with cobalt chloride (CoCl ₂ .6H ₂ O: 26 g) and nickel chloride (NiCl ₂ ). 6H ₂ O: 26 g), ferric chloride (FeCl ₃ .6H ₂ O: 20 g), aluminum chloride (AlCl ₃ .6H ₂ O: 20 g), zirconium chloride (ZrCl ₄ : 20 g), stannic chloride ( SnC
l ₄ : 22 g) were added to each other to prepare a mixed impregnating liquid, and the honeycomb coated article 1 was impregnated in the same manner as in Example 1 to obtain honeycomb catalysts 17 to 22. Table B below shows the honeycomb catalyst list.
Put together.

(Experimental Example 1) Honey prepared in Examples 1-4
An activity evaluation test of the cam catalysts (1 to 22) was performed. Activity
The evaluation conditions are as follows. 〇 (Gas composition) NO: 400ppm, CO: 1000p
pm, C_TwoH_Four: 1000 ppm, C _ThreeH₆: 340p
pm, O_Two: 8%, CO_Two: 10%, H_TwoO: 10%,
Remaining: N _Two, GHSV 30000h^-1, Catalyst shape: 15
mm × 15 mm × 60 mm (144 cells) Removal of catalyst in initial state at reaction temperature of 350 and 450 ° C.
Table C shows the nitrate rate.

(Experimental Example 2) A forced deterioration test was performed on the honeycomb catalysts 1 to 22 in a rich atmosphere (reducing atmosphere). The forced deterioration test is as follows. 〇 (gas composition) H ₂ : 3%, H ₂ O: 10%, balance: N ₂ GHSV: 5000 h ⁻¹ , temperature: 700 ° C., gas supply time: 6 hours Catalyst shape: 15 mm × 15 mm × 60 mm (144 cells) )

Catalysts 1 and 2 treated under the above forced deterioration conditions
2 was subjected to an activity evaluation test under the activity evaluation conditions of Experimental Example 1. Table C also shows the denitration ratio of the catalyst after the forced deterioration test at reaction temperatures of 350 and 450 ° C. As shown in Table C, it was confirmed that the catalysts 1 to 22 of the present invention maintained a high activity even in a reducing atmosphere.

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

As shown in the examples and experimental examples, the catalyst of the present invention has a stable activity even in a high-temperature reducing atmosphere.
It was found that the catalyst had durability and was of high industrial value.

Continuation of the front page (56) References JP-A-5-31369 (JP, A) JP-A-5-15783 (JP, A) JP-A-3-229620 (JP, A) JP-A-3-229638 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/94

Claims (4)

(57) [Claims] In the dehydrated state, expressed as a molar ratio of oxide, (1 ± 0.6) R ₂ O. [aM ₂ O ₃ .bAl ₂ O ₃ .cMeO] .ySiO ₂ (in the above formula, , R is an alkali metal ion and / or hydrogen ion, M is at least one element selected from the group consisting of a group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony, and gallium, and Me is an alkaline earth element. Element, a> 0, b> 0, c> 0 , a + b = 1, y / c> 1
2, y> 12) has a chemical formula represented by either One Table A X
An exhaust treatment catalyst comprising copper and rhodium supported on a crystalline silicate having a line diffraction pattern. [Table 1] 2. A layered structure in which a 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 is grown on an outer surface of the mother crystal. The exhaust treatment catalyst according to claim 1, wherein the catalyst is a composite crystalline silicate. 3. The exhaust treatment according to claim 1, further comprising one or more metals selected from the group consisting of cobalt, nickel, iron, aluminum, zirconium and tin. catalyst. 4. The exhaust treatment according to claim 2, further comprising one or more metals selected from the group consisting of cobalt, nickel, iron, aluminum, zirconium and tin. catalyst.