JPH07124477A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst capable of efficiently converting NOx in exhaust gas into harmless gas even in the case where the concn. of oxygen in the exhaust gas is high and having high durability. CONSTITUTION:Copper is carried on a crystalline aluminosilicate contg. one or more kinds of elements selected from among Zn, Mn and B, and one or more kinds of elements (Me) selected from among B, P, Bi and Sb are further carried preferably by 0.01-6.0wt.% (expressed in terms of oxides) to obtain the objective catalyst for reduction and removal of NOx in exhaust gas in the presence of hydrocarbon in an oxidizing atmosphere. The molar ratio between Me and Cu is preferably regulated to 0<Me/Cu<=0.7.

Description

Detailed Description of the Invention [Industrial applications]

[0001] The present invention is an exhaust gas for decomposing nitrogen oxides discharged from a mobile internal combustion engine such as a gasoline automobile and a diesel automobile, a stationary internal combustion engine such as a cogeneration, various industrial furnaces such as a boiler, into a harmless gas. The present invention relates to a purification catalyst.

[0002]

BACKGROUND ART Exhaust gas from automobiles, stationary internal combustion engines and various industrial furnaces generally contains a large amount of nitrogen oxides (NO _X ) represented by NO and NO _2. ing. These NO _X are said to be the cause of photochemical smog. Regarding the method of reducing NO _X , when the amount of oxygen in the exhaust gas is small, as in gasoline automobiles, NO _X is reduced and removed with a reducing agent such as carbon monoxide or hydrocarbon, a so-called three-way catalyst system. Exhaust gas treatment has been established.

On the other hand, when a large amount of oxygen is contained in the exhaust gas such as a large stationary emission source such as a boiler, a selective NO _X reduction method in which ammonia is added from the outside to reduce the NO _X amount is operated. And has some effect. However, the former method is applicable only to the exhaust gas from a gasoline engine with an extremely low oxygen concentration, and the latter method uses ammonia, so it is not suitable for use in small stationary emission sources and mobile emission sources. It's difficult.

Therefore, as a reducing agent other than ammonia,
Various methods using hydrogen, carbon monoxide, various hydrocarbons, etc. have been studied, but most of them are non-selective contact that enables removal of nitrogen oxides only after oxygen in exhaust gas is completely consumed. It has a drawback that it is a reduction method.
Conventionally, the following method has been proposed as a novel selective catalytic reduction method (a method for selectively reducing and removing nitrogen oxides even in the presence of oxygen) capable of solving such a difficulty, but it is sufficient. No satisfactory results have been obtained.

For example, according to Japanese Patent Laid-Open No. 63-100919, a catalyst in which copper is supported on a porous carrier such as alumina, silica, or zeolite is used, and exhaust gas containing oxygen in the presence of hydrocarbons is used. A method of removing nitrogen oxides has been proposed. With this method, the denitration rate is 10 to 25%, and high denitration activity cannot be obtained. Further, the oxygen concentration in the exhaust gas of the example is 2.1%, and it is unknown whether the nitrogen oxide can be selectively reduced and denitrated similarly even when the oxygen concentration is higher. Furthermore, the durability is unknown. Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst that can purify nitrogen oxides into a harmless gas with high efficiency even if the oxygen concentration in the exhaust gas is high, and that has high durability.

[0006]

An exhaust gas purifying catalyst according to the present invention is a catalyst for reducing and removing nitrogen oxides (NO _x ) in exhaust gas in an oxidizing atmosphere in the presence of hydrocarbons, A crystalline aluminosilicate (catalyst support) containing one or more elemental components selected from Zn, Mn and B carries a Cu component (main catalyst), and is further selected from B, P, Bi and Sb. It is also characterized in that it is configured to carry one or more elemental components (promoters). The oxidizing atmosphere is H ₂ by completely oxidizing carbon monoxide contained in exhaust gas, hydrogen, hydrocarbons and reducing substances of hydrocarbons added as necessary in this treatment.
This is a state in which an amount of oxygen is contained in excess of the amount of oxygen required for conversion into O and CO ₂ .

As the one or more elemental components selected from Zn, Mn and B, a soluble salt can be used when synthesizing the crystalline aluminosilicate. For example, the nitrate of the element,
They are halogen compounds, carbonates, and organic acid salts. The content of these elemental components is preferably 0.05 to 1.5, more preferably 0.125 to 1.0 in terms of the molar ratio (Me / Al) of the element (Me) to Al in the catalyst carrier. There is no particular structural limitation on the crystalline aluminosilicate, but a pentasil-type crystalline aluminosilicate is preferable. The pentasil-type crystalline aluminosilicate is a zeolite, and its constituent basic unit is a 5-membered oxygen ring.

For example, ferrilite, mordenite,
ZSM-5, ZSM-11, etc. correspond. Zeolites other than the pentasil-type crystalline aluminosilicate have relatively low hydrothermal resistance, so the durability is low even if they carry Cu component and one or more elemental components selected from B, P, Bi and Sb. There is a risk of becoming. Among such pentasil-type crystalline aluminosilicates, those having SiO ₂ / Al ₂ O ₃ (molar ratio) of 10 or more are preferable.

When the SiO ₂ / Al ₂ O ₃ content is less than 10, since the hydrothermal resistance is relatively low, the Cu component and one or more elemental components selected from B, P, Bi and Sb are supported. However, there is a risk that durability will be reduced. Among the above pentasil-type crystalline aluminosilicates, those having an MFI structure or a MEL structure are preferable. This MFI structure is ZSM-5
To ZSM-5, and other structures such as ZSM-8, ZSM-11, zeta 1, zeta 3, Nu-4, Nu-5, TZ-1, TPZ-1. Is applicable. Further, the MEL structure means ZSM-
Refers to a structure similar to 11.

As the Cu component, for example, when it is supported by an ion exchange method or an impregnation method, a soluble salt can be used. Examples of such substances include nitrates, halogen compounds, carbonates, organic acid salts, and copper ammine complexes. Further, when the Cu component is supported on the catalyst carrier by the physical mixing method, an oxide or a hydroxide can be used in addition to the soluble salt. The content of this Cu component is preferably 0.25 to 1.25 in terms of the molar ratio of Cu to Al in the catalyst carrier (Cu / Al), and more preferably
It is 0.5 to 1.0.

As the one or more elemental components selected from B, P, Bi and Sb, soluble salts can be used when these cocatalysts are supported by the ion exchange method or the impregnation method. In the case of Bi, Sb, the soluble salts include nitrates, halogen compounds, carbonates, organic acid salts and the like. In case of B and P,
Inorganic acid salts, alkali metal salts, ammonium salts and the like.
For B and P, these salts can be used for supporting on a catalyst carrier by a vapor deposition method. When the catalyst carrier is loaded with these components by a physical mixing method,
In addition to the above soluble salts, oxides and hydroxides can be used.

The content of these co-catalysts is preferably 0.01 to 6.0 wt% in terms of oxide, based on the whole catalyst,
More preferably, it is 0.01 to 4.0 wt%. Further, the molar ratio (Me / Cu) of these elements (Me) and Cu is 0 <Me / Cu ≦ 0.7.
And more preferably 0 <Me / Cu ≦ 0.3
And most preferably 0 <Me / Cu ≦ 0.2. Thus, by setting the content of the co-catalyst to 0.01 wt% or more, the effect of improving the purifying activity and durability according to the present invention becomes remarkable, while the content of the co-catalyst does not exceed 6.0 wt%. Alternatively, when the molar ratio (Me / Cu) of the element (Me) and Cu does not exceed 0.7, high purification activity and durability according to the present invention can be obtained. The catalyst may have any shape, for example, pellet, plate, column, or lattice. Further, a catalyst may be coated on a lattice-shaped carrier such as cordierite, mullite or alumina, and a base material such as wire mesh.

The method of preparing the catalyst according to the present invention is as follows.
A crystalline aluminosilicate containing one or more elemental components selected from n and B is synthesized. At this time, these elemental components may be added at any time from the preparation of the gel to the start of crystallization. The crystallization agent (seed crystal) used when synthesizing this catalyst carrier is not particularly limited, but mordenite is preferably used, and particularly has a lattice plane spacing (d value) shown in Table 1 below in powder X-ray diffraction. When mordenite is used as a crystallization agent, a crystalline aluminosilicate having high hydrothermal resistance can be synthesized.

[0014]

[Table 1]

Next, the obtained crystalline aluminosilicate was added to
A catalyst according to the present invention is prepared by supporting a Cu component and one or more elemental components selected from B, P, Bi and Sb. There is no particular limitation on the supporting method, for example, an ion exchange method,
An impregnation method, a vapor deposition method, a physical mixing method or the like can be used. A method for purifying an exhaust gas using an exhaust gas purifying catalyst according to the present invention is a method in which an exhaust gas is brought into contact with a catalyst in the presence of a hydrocarbon having a THC concentration / NO _X concentration of 0.5 to 200 in an oxidizing atmosphere, Nitrogen oxides are reduced and removed to N ₂ and H ₂ O. The T
The HC (total hydrocarbon) concentration is the concentration when hydrocarbons are converted into methane.

The specific reaction conditions are 0.5 to 200, preferably 1 to 100, in terms of the concentration of hydrocarbon expressed as THC concentration / NO _X concentration. For example, NO _X concentration is 100p
For pm, the THC concentration is 50-20,000 ppm. When the abundance of hydrocarbons is lower than the lower limit, the denitration performance does not appear, and when it is higher than the upper limit, the denitration rate increases, but the economic efficiency of the entire system decreases and the combustion heat of hydrocarbons increases. It is not preferable because of abnormal heat generation of the catalyst layer.

The above-mentioned hydrocarbon may be a hydrocarbon that remains in the exhaust gas, but when it is insufficient than the amount necessary to cause the denitration reaction, or when the exhaust gas does not contain any hydrocarbons. Is preferably externally added with hydrocarbon. The kind of hydrocarbon added for this purpose is not particularly limited, and examples thereof include methane, LPG, gasoline, light oil, kerosene, and heavy oil A. About the catalyst reaction temperature, 200-8
The temperature is 00 ° C, preferably 300 to 600 ° C. Usually, the higher the temperature, the higher the denitrification rate, but if the temperature exceeds 800 ° C, the catalyst deteriorates, which is not preferable, and if it is lower than 200 ° C, the denitrification rate becomes low.

For Gas Space Velocity (GHSV), it is usually 2,000
It is 0 to 200,000 h ^-1 , preferably 5,000 to 100,000 h ^-1 .
When GHSV is slower than 2,000h ^-1 , the denitration rate is high,
When the amount of catalyst used increases and when it is faster than 200,000 h ^-1 , the denitration rate becomes low. The exhaust gas targeted by the purification catalyst of the present invention is an exhaust gas containing NO _X and oxygen, for example, a lean burn (lean burn) type gasoline automobile, a mobile internal combustion engine such as a diesel automobile, a stationary type such as a cogeneration system. Exhaust gas emitted from an internal combustion engine, a boiler, various industrial furnaces, etc. may be mentioned.

[0019]

【Example】 Example 1 First, aluminum sulfate 13.5g, sulfuric acid (97%) 10.0g,
A solution consisting of 2.10 g of zinc acetate dihydrate and 330 g of water (solution
I), water glass (SiO₂: 28.4%, Na₂O: 9.5%) 21
Solution consisting of 1g and 200g of water (Solution II) and sodium chloride
A solution consisting of 39.5 g of thorium and 92 g of water (Solution III)
Prepared). Next, solution I and II are simultaneously added to solution III.
The mixture was gradually added dropwise. Add sulfuric acid (50
%) 2 g and then mordenite [Si
O₂/ Al₂O₃= 20 (molar ratio)] 0.5 g was added.

Next, this mixture was placed in an autoclave having a volume of 1 liter and left for 20 hours while stirring at 170 ° C. and 300 rpm under self-pressure. After cooling, the mixture was filtered and the precipitate was washed thoroughly with excess pure water. After this, 120
ZSM-5 containing Zn by drying at ℃ for 20 hours
A crystalline aluminosilicate having a structure (MFI structure) was synthesized. Next, this crystalline aluminosilicate was placed in a muffle furnace and fired at 500 ° C. for 4 hours. The crystalline aluminosilicate thus obtained had a SiO ₂ / Al ₂ O ₃ (molar ratio) of 3
8, Zn / Al (molar ratio) was 0.24.

Next, a catalyst in which the B component and the Cu component were supported on the crystalline aluminosilicate was prepared by using an aqueous solution of boric acid and an aqueous solution of copper acetate. The amounts of the B component and the Cu component supported in this catalyst were B ₂ O ₃ : 0.3 wt% and CuO:
It was 4.6 wt% and the molar ratio of B to Cu (B / Cu) was 0.15. Next, this catalyst was evaluated for initial activity and activity after steaming (hydrothermal) treatment as described below.

That is, regarding the evaluation of the initial activity, first,
After filling 2 cc of this catalyst into a stainless steel reaction tube, a model gas was used as a processing gas, and GHSV = 80,000 h in the reaction tube.
^-Introduced in ^-1 . The composition of this model gas is NO _X : 500ppm,
O ₂ : 4.5%, LPG: 833ppm (THC concentration is about 2500pp
m). Next, the gas from the outlet of this reaction tube was introduced into a chemiluminescence analyzer to measure the NO _X concentration. The NO _X removal rate (%) of the model gas after the catalytic reaction was calculated by comparing the NO _X concentration of the model gas before and after introducing the reaction tube. When this model gas was introduced, the temperature of the reaction tube was 300 ° C.
Was kept at. The measurement results are shown in Table 2 below.

Regarding the evaluation of the activity after the steaming treatment, first, as the steaming treatment, the catalyst prepared in this example was treated with 10% water, 4.5% oxygen, GHSV = 80,000 h ^-1 ,
The temperature was maintained at 650 ° C. for 4 hours. After cooling, similarly to the case of the evaluation of the initial activity, after filling the stainless reaction tube, the model gas was introduced into the reaction tube as a processing gas, and then the NO _X removal rate was calculated in the same manner as above. . When this model gas was introduced, the temperature of the reaction tube was 350 ° C.
Was kept at. The measurement results are shown in Table 2 below.

Example 2 As in Example 1, manganese acetate tetrahydrate was used in place of zinc acetate dihydrate, and Mn-containing crystalline aluminosilicate having a ZSM-5 structure was used as in Example 1. The salt was synthesized.
The obtained crystalline aluminosilicate had an SiO ₂ / Al ₂ O ₃ (molar ratio) of 36 and an Mn / Al (molar ratio) of 0.38. Next, a catalyst in which the B component and the Cu component were supported on the crystalline aluminosilicate was prepared by using an aqueous boric acid solution and an aqueous copper acetate solution. The supported amounts of B component and Cu component in this catalyst are B ₂ O ₃ : 0.3 wt% and CuO: 4.9 wt% respectively in terms of oxide, and B and C.
The molar ratio of u (B / Cu) was 0.14. For this catalyst, the initial activity and the activity after the steaming treatment were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 3 First, a solution of 6.6 g of aluminum sulfate, 3.4 g of boron oxide, 17.6 g of sulfuric acid (98%) and 250 g of water (referred to as solution I), water glass (SiO ₂ 28.4%, Na ₂ O 9.5). %) 211 g,
A solution consisting of 200 g of water (referred to as solution II) and a solution consisting of 79.0 g of sodium chloride and 122 g of water (referred to as solution III)
Prepared. After this, solutions I and II were simultaneously dropped into solution III and mixed.

Next, the mordenite was added to the mixture in an amount of 0.
After adding 5 g, the mixture was put into the autoclave and left for 20 hours while stirring at 170 ° C. and 300 rpm under self-pressure. After cooling, the mixture was filtered and the precipitate was washed thoroughly with excess pure water. After that, by drying at 120 ° C. for 20 hours, a crystalline aluminosilicate having a ZSM-5 structure containing B was synthesized. Next, this crystalline aluminosilicate was placed in a muffle furnace and fired at 500 ° C. for 4 hours.

The crystalline aluminosilicate thus obtained had an SiO ₂ / Al ₂ O ₃ (molar ratio) of 85 and a Zn / Al (molar ratio) of 0.95. Next, using B boric acid aqueous solution and copper acetate aqueous solution to this crystalline aluminosilicate, the B component and Cu
A catalyst supporting the components was prepared. The supported amounts of B component and Cu component in this catalyst were calculated as oxides of B ₂ O ₃ : 0.3 wt.
%, CuO: 4.0 wt%, and the molar ratio of B to Cu (B / Cu) is 0.1
Was 7. Similar to Example 1, the initial activity and the activity after the steaming treatment of this catalyst and the catalysts of Examples 4 to 9 below were evaluated. The results are shown in Table 2.

Example 4 A catalyst carrying a P component and a Cu component was prepared by using an aqueous solution of diphosphorus pentoxide and an aqueous solution of copper acetate in the crystalline aluminosilicate synthesized in Example 3. P in this catalyst
The supported amount of each component and Cu component is P
₂ O ₅ : 0.6 wt%, CuO: 4.8 wt%, and the molar ratio of P and Cu (P /
Cu) was 0.14.

Example 5 A catalyst carrying a Bi component and a Cu component was prepared by using an aqueous solution of bismuth acetate and an aqueous solution of copper acetate in the crystalline aluminosilicate synthesized in Example 3. Bi in this catalyst
The amounts of supported components and Cu components are Bi ₂ O
₃ : 1.8wt%, CuO: 4.1wt%, and the molar ratio of Bi and Cu (Bi / C
u) was 0.15.

Example 6 A catalyst carrying Sb and Cu components was prepared by using an aqueous solution of antimony nitrate and an aqueous solution of copper acetate in the crystalline aluminosilicate synthesized in Example 3. In this catalyst
The supported amounts of Sb component and Cu component are Sb in terms of oxide, respectively.
₂ O ₃ : 1.2 wt%, CuO: 4.2 wt%, and the molar ratio of Sb and Cu (Sb
/ Cu) was 0.16.

Example 7 In Example 4, a catalyst was prepared in which the amounts of P component and Cu component supported were changed as follows. That is, the loading amounts of the P component and the Cu component in the catalyst according to the present example are respectively P ₂ O ₅ : 4.0 wt%, CuO: 7.5 wt% in terms of oxide, and the molar ratio of P and Cu (P / Cu). Cu) was 0.60.

Example 8 In Example 5, a catalyst was prepared in which the supported amounts of Bi component and Cu component were changed as follows. That is, the amounts of the Bi component and the Cu component supported in the catalyst according to the present example were respectively Bi ₂ O ₃ : 6.6 wt% and CuO: 3.9 wt% in terms of oxides, and the molar ratio of Bi and Cu (Bi / Cu) was 0.58.

Example 9 In Example 6, a catalyst was prepared in which the supported amounts of Sb component and Cu component were changed as follows. That is, the supported amounts of the Sb component and the Cu component in the catalyst according to the present example are Sb ₂ O ₃ : 4.4 wt% and CuO: 4.1 wt% in terms of oxides, and the molar ratio of Sb and Cu (Sb / Cu) was 0.59.

Example 10 In Example 5, a catalyst was prepared in which the supported amounts of Bi component and Cu component were changed as follows. That is, the supported amounts of the Bi component and the Cu component in the catalyst according to the present example are respectively Bi ₂ O ₃ : 9.9 wt% and CuO: 3.9 wt% in terms of oxide, and the molar ratio of Bi and Cu (Bi / Cu) was 0.87.

Example 11 In Example 6, a catalyst was prepared in which the supported amounts of the Sb component and the Cu component were changed as follows. That is, the supported amounts of the Sb component and the Cu component in the catalyst according to the present example are Sb ₂ O ₃ : 6.6 wt% and CuO: 4.1 wt% respectively in terms of oxide, and the molar ratio of Sb and Cu (Sb / Cu) was 0.88.

Comparative Example 1 In Example 1, a crystalline aluminosilicate having a ZSM-5 structure was synthesized without using the solution I containing zinc acetate dihydrate. The crystalline aluminosilicate had a SiO ₂ / Al ₂ O ₃ (molar ratio) of 32. Next, a copper component-supported catalyst was prepared by using an aqueous solution of copper acetate in this crystalline aluminosilicate. The supported amount of the Cu component in this catalyst was CuO: 3.5 wt% in terms of oxide. For this catalyst, the initial activity and the activity after the steaming treatment were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0037]

[Table 2]

Discussion of Examples and Comparative Examples From Table 2, according to the catalysts of Examples 1 to 11, Zn, Mn, B
Since the crystalline aluminosilicate containing the selected elemental component is constituted by supporting the Cu component and further supporting the elemental component selected from B, P, Bi and Sb, the steaming is performed. It can be seen that after the treatment, even if the reaction temperature is a relatively low temperature of 350 ° C., the decrease in catalytic activity is not as great as that of the catalyst of Comparative Example. Therefore, the catalyst according to this example has high catalytic activity and excellent durability even after being used for a long time.

Then, according to the catalysts according to Examples 1 to 9, B, P, Bi, S supported on the crystalline aluminosilicate was used.
The supported amount of the elemental component selected from b is 0.01 in terms of oxide.
˜6.0 wt%, and the ratio of these elements (Me) to Cu is 0 <Me / Cu (molar ratio) ≦ 0.7, the catalytic activity after steaming treatment is related to Examples 10 and 11. It is higher than the catalyst. On the other hand, according to the catalyst of Comparative Example 1, even if the crystalline aluminosilicate does not contain any of Zn, Mn and B, and the crystalline aluminosilicate carries Cu, Since none of B, P, Bi, and Sb is supported, it can be seen that the decrease in catalytic activity after the steaming treatment is larger than that of the catalysts of Examples.

[0040]

EFFECTS OF THE INVENTION According to the exhaust gas purifying catalyst of the present invention, it is possible to purify nitrogen oxides into harmless gas with high efficiency even if the oxygen concentration in the exhaust gas is high, and the catalytic activity is high even at low temperature. It is durable and has a long life.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B01D 53/36 102 H (72) Inventor Yoshimi Kawashima 1280, Uezumizumi, Sodegaura-shi, Chiba Idemitsu Kosan Co., Ltd. In-house (72) Inventor Toshiaki Hayasaka 1280 Kamizumi, Sodegaura-shi, Chiba Idemitsu Kosan Co., Ltd. (72) Inventor Hiroshi Akama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Masuda Goji 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Hiroyuki Kanasaka 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (2)

[Claims] 1. A catalyst for reducing and removing nitrogen oxides (NO _x ) in exhaust gas in the presence of hydrocarbons in an oxidizing atmosphere, wherein at least one elemental component selected from Zn, Mn and B is added. An exhaust gas purifying catalyst, characterized in that the contained crystalline aluminosilicate carries a Cu component, and further carries at least one elemental component selected from B, P, Bi and Sb. 2. The amount of one or more elemental components selected from B, P, Bi, and Sb supported on the crystalline aluminosilicate is 0.01 to 6.0 wt% in terms of oxide, And the ratio of these elements (Me) and Cu is 0 <Me / Cu (molar ratio)
The exhaust gas-purifying catalyst according to claim 1, wherein ≦ 0.7.