JPH08318163A - Catalyst for removal of nox in exhaust gas - Google Patents

Abstract

PURPOSE: To produce a catalyst for purification of exhaust gas capable of efficiently converting NOx into harmless gas even in the case of a high concn. of oxygen in exhaust gas discharged from the internal-combustion engine of an automobile, etc., and having high durability. CONSTITUTION: A Cu component and an Mo component and/or a W component, are deposited on a catalyst carrier contg. a pentasil type crystalline aluminosilicate so that the molar ratio of Mo to Cu, W to Cu or (Mo+W) to Cu is regulated to 0.003-0.40 to obtain the objective catalyst for removal of NOx in exhaust gas in the presence of hydrocarbon in an atmosphere contg. excess oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for efficiently removing nitrogen oxides in exhaust gas discharged from internal combustion engines such as automobile engines, various combustors, nitric acid manufacturing plants and the like.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas from an internal combustion engine, palladium (P
A three-way catalyst carrying a noble metal component such as d), platinum (Pt), and rhodium (Rh) is used. This is effective only when operating the internal combustion engine under conditions near the stoichiometric air-fuel ratio (stoichiometric ratio), and when operating the internal combustion engine under lean conditions with high oxygen content and better fuel economy, it is sufficient. NOx removal performance cannot be obtained. It is known that a catalyst composed of a metal ion-exchanged zeolite is effective for removing NOx under such lean conditions. {Iwamoto, Small Discussion "Catalyst Technology for Nitrogen Oxide Reduction" Preliminary Report Shu, p71 (1990); W. Held, A. Konin
g, T. Richter and L. Puppe, SAE Paper 900496 (1
990)}. In particular, a Cu-zeolite catalyst in which Cu is supported on zeolite by an ion exchange method has a high gas space velocity (GHS
V), shows excellent performance in a relatively high temperature range. However, when this catalyst is exposed to high temperatures of 600 ° C. or higher, the NOx removal performance deteriorates with time,
It cannot withstand long-term use. In addition, the temperature range for maintaining high activity is not sufficient, and therefore it has not yet been put to practical use.

The main cause of activity deterioration when the above catalyst is exposed to high temperatures is C at the ion exchange site in zeolite.
It is considered that this is because u (active ingredient) moves out of the site due to heat and causes sintering. Therefore, methods for stabilizing Cu with various additives have been vigorously studied and proposed. However, it is hard to say that all of them have been sufficiently satisfactory.

For example, according to Japanese Unexamined Patent Publication No. 3-135437, a catalyst having excellent NOx removing ability and durability by supporting Cu and one or more kinds of metals selected from 10 kinds of valence variable metals on zeolite. Is supposed to be obtained. With this catalyst, there are as many as 10 effective valence variable metals, but the difference in the effects of these metals, that is, superiority or inferiority, is unknown. Moreover, in the case of any of the metals, the preferable content range is 0.01 to 3% by weight with respect to the zeolite, and the range is wide, and the unique optimum content of each of the 10 kinds is unknown. Further, the amount of the specific metal to be coexisted is considered to depend on the amount of supported copper, but although there is a description of the preferable amount of copper in this catalyst, the optimum amount of the valence variable metal with respect to the amount of copper [specific metal / Copper (molar ratio)] is unknown.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to efficiently purify nitrogen oxides into harmless gas even if oxygen in exhaust gas discharged from an internal combustion engine of an automobile has a high concentration. Moreover, it is to provide an exhaust gas purifying catalyst having high durability.

[0006]

The exhaust gas-purifying catalyst of the present invention is a catalyst for reducing and removing nitrogen oxides (NOx) in exhaust gas in the presence of hydrocarbons in an oxidizing atmosphere, and is a pentasil-type crystal. A catalyst carrier containing a water-soluble aluminosilicate is configured to carry a copper (Cu) component and a molybdenum (Mo) component and / or a tungsten (W) component, and Mo /
Cu (molar ratio), W / Cu (molar ratio) or (Mo +
W) / Cu (molar ratio) is 0.003 or more and 0.40 or less.

The oxidizing atmosphere is H ₂ O obtained by completely oxidizing carbon monoxide, hydrogen, hydrocarbons contained in exhaust gas and reducing substances of hydrocarbons added as necessary in the present treatment.
And an oxygen-excess atmosphere containing oxygen in excess of the amount of oxygen required for conversion into CO ₂ . As the copper component, for example, when it is supported by an ion exchange method or an impregnation method, or when it is a method of incorporating a copper component when synthesizing zeolite, a soluble salt can be used. Examples of such substances include nitrates, halogen compounds, carbonates, organic acid salts, and copper ammine complexes. Further, by the physical mixing method, in the case of containing a copper component in the catalyst, in addition to the soluble salt, an oxide,
Hydroxides can also be used.

The content of this copper component with respect to the entire catalyst is 2.0 to 10.0% by weight in terms of Cu. Examples of the molybdenum component include ammonium salt, potassium salt, calcium salt, sodium salt and lithium salt of molybdic acid. In addition, examples thereof include organic molybdenum such as molybdenum hexacarbonyl, and heteropolyacid such as molybdophosphoric acid, but not limited thereto.

Examples of the tungsten component include ammonium salts, potassium salts, calcium salts, sodium salts and lithium salts of tungstic acid. In addition, organic tungsten such as tungsten hexacarbonyl and heteropolyacid such as tungstophosphoric acid can be used, but the invention is not limited thereto. Such molybdenum and tungsten components are impregnated, liquid phase reaction method, vapor deposition method,
It may be supported by a reaction such as an ion exchange method, or may be contained when the zeolite is synthesized.

The content of molybdenum and / or tungsten is 0.1 to 3.0% by weight. The content is 0.
If it is less than 1% by weight, high purification activity and durability due to the inclusion of the molybdenum component and the tungsten component of the present invention cannot be obtained, and if it exceeds 3.0% by weight, the exhaust gas purification performance is deteriorated, and the durability Is not seen. The molar ratio Mo / Cu (molar ratio), W / Cu (molar ratio) or (Mo + W) / Cu (molar ratio) of molybdenum component, tungsten component and copper component is 0.003 or more and 0.4.
Set to 0 or less. If it is less than 0.003, there is no effect,
If it is more than 0.40, the exhaust gas purification performance is deteriorated and the durability is not improved.

The pentasil-type crystalline aluminosilicate
Is a zeolite, for example, ferrierite, mol
Denite, ZSM-5, ZSM-11, etc. correspond. Bae
With zeolites other than ntasil-type crystalline aluminosilicate
Has relatively low hydrothermal resistance, so molybdenum and tongue
There is a possibility that the durability of the catalyst after supporting the stainless steel may be reduced. this
Among such pentasil-type crystalline aluminosilicates, S
iO₂/ Al₂O ₃When the (molar ratio) is less than 20
In this case, since the hydrothermal resistance is relatively low, molybdenum and tongue
There is a risk that the heat resistance after supporting the stainless steel will be low. But 8
When it is larger than 0, the Cu ion exchange sites decrease,
Since the amount of active Cu decreases, 20 to 80 is preferable.
New

Of the above pentasil-type crystalline aluminosilicates, those having an MFI structure are preferable. This MFI structure refers to a structure that is the same as or similar to ZSM-5, and other than ZSM-5, for example, ZSM-8, Z
SM-11, Zeta 1, Zeta 3 Nu-4, Nu-5,
The structures such as TZ-1 and TPZ-1 are applicable.

The catalyst of the present invention is used by molding it into any shape, for example, pellet, plate, column, or grid.
Usually, it is preferably used in a honeycomb shape, and usually, various carrier base materials formed in a honeycomb shape, for example, a carrier base material such as cordierite, mullite or alumina are coated with a catalyst powder and used. In this case, the catalyst powder obtained as described above is mixed with a binder such as alumina sol, water is further added, and the slurry is applied to the honeycomb material. As the honeycomb material, generally, a cordierite material is often used, but the material is not limited to this, and a honeycomb carrier made of a metal material can be used. Furthermore, the catalyst powder itself is formed into a honeycomb shape. May be. By making the shape of the catalyst honeycomb, it is possible to increase the contact area with the catalyst exhaust gas and suppress the pressure loss. Furthermore, since it is an integrated type, it is hardly worn by vibration, and is extremely advantageous as a catalyst for purifying automobile exhaust gas.

The catalyst of the present invention is prepared by allowing a pentasil-type crystalline aluminosilicate to support copper, molybdenum and / or tungsten components by, for example, an ion exchange method, an impregnation method, a physical mixing method, or a vapor phase vapor deposition method. can do. The ion exchange method is, for example, immersing zeolite powder in an aqueous solution of copper nitrate for several tens of hours, filtering the aqueous solution, washing the zeolite powder, and then 400 to 600 ° C.
It can be performed by firing for several hours. At this time, ammonia water is added dropwise to the copper nitrate aqueous solution to obtain an appropriate p
Adjusting to H improves the ion exchange rate.

The impregnation method can be carried out, for example, by immersing the zeolite powder in an aqueous solution of copper nitrate for 0.5 to 3 hours, drying the aqueous solution at 100 ° C. or higher, and then calcining at 400 to 600 ° C. The physical mixing method can be performed, for example, by mixing the zeolite powder and the CuCl ₂ powder using a mulcher and firing the mixture at 400 to 600 ° C. The vapor deposition method is, for example, CuCl
It can be carried out by sending the vapor obtained by heating ₂ to high temperature into the zeolite layer kept at high temperature.

[0016]

The exhaust gas purifying method using the exhaust gas purifying catalyst of the present invention is conducted by bringing the exhaust gas into contact with the catalyst in the presence of a hydrocarbon having a THC concentration / NOx concentration of 0.5 to 200 in an oxidizing atmosphere, The nitrided oxide therein is reduced and removed into N ₂ and H ₂ O. The THC concentration is a concentration when hydrocarbon is converted into methane. The specific reaction condition is 0.5 to 200, preferably 1 to 100, when the THC concentration / NOx concentration is expressed with respect to the hydrocarbon concentration. For example, if the NOx concentration is 100 ppm, TH
The C concentration is 50 to 20000 ppm.

When the amount of hydrocarbons present 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 economical efficiency of the entire system decreases and the hydrocarbons decrease. It is not preferable because of abnormal heat generation of the catalyst layer due to the heat of combustion. The hydrocarbon may be a hydrocarbon that remains in the exhaust gas, but if it is insufficient than the amount necessary to cause the denitration reaction, or if the exhaust gas does not contain any hydrocarbons, the external It is advisable to add hydrocarbons from

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. Exhaust gas symmetrical with the purifying catalyst of the present invention is an exhaust gas containing NOx and oxygen,
Examples thereof include exhaust gas emitted from lean-burn (lean burn) type gasoline automobiles, mobile internal combustion engines such as diesel automobiles, stationary internal combustion engines such as cogeneration, boilers, various industrial furnaces, and the like.

[0019]

The present invention will be described with reference to the following examples, comparative examples and test examples. Example 1 First, 337.5 g of aluminum sulfate and sulfuric acid (97%)
A solution consisting of 362.5 g and 8250 g of water (referred to as solution I), water glass (SiO ₂ 28.4%, Na ₂ O 9.
5%) 5275 g and water 5000 g (solution II
And sodium chloride 987.5 g, water 2300
A solution of g (referred to as solution III) was prepared.

Next, the solutions I and II were simultaneously added to the solution III.
The mixture was added dropwise. The reaction mixture was p.
After adjusting to H9.5, mordenite [S
iO ₂/ Al₂O₃= 20 (molar ratio)] 12.5 g
Added Next, this reaction product is put into an autoclave of 25 liter capacity.
Put in crepe, self pressure 170 ℃, 300rpm
It was left for 20 hours with stirring. After cooling, the reaction mixture
The mixture was filtered, and the precipitate was thoroughly washed with excess pure water. This
Then, by drying at 120 ℃ for 20 hours, ZS
Aluminosilicate Zeora with M-5 structure (MFI structure)
Ito was synthesized.

Next, this zeolite was 550 in an air stream.
It was calcined at ℃ for 6 hours. SiO ₂ / Al ₂ O ₃ (molar ratio) of the aluminosilicate zeolite thus obtained
Was 32. Next, 100 ml of an aqueous solution containing 0.1 M of copper nitrate and 0.01 M of ammonium molybdate was added to 100 g of this aluminosilicate zeolite, followed by ion exchange, filtration, and drying at 120 ° C. for 12 hours, at 600 ° C. Aluminosilicate zeolite catalyst powder supporting copper and molybdenum was synthesized by firing for 1 hour. The copper content in this catalyst was 2.5% by weight, the molybdenum content was 0.2% by weight, and the Mo / Cu ratio was 0.1.
It was 053. This was designated as catalyst powder-A. 2250 g of this catalyst-A powder was added to 1 sol of silica sol (solid content 20%).
250 g and 1500 g of water were put into a ball mill pot and pulverized for 4 hours to obtain a slurry. This slurry was treated with a cordierite honeycomb (diameter: 9.4 cm, height: 10) having about 300 flow paths per square inch cross section.
cm, capacity 0.7 L), 120 in a hot air dryer
After drying for 1 hour at 400 ° C., baking for 1 hour at 400 ° C.
Catalyst 1 of was obtained. The coating amount of catalyst powder at this time is 170 g
Was / L.

Examples 2 to 4 In each of the examples, as shown in Table 1, the loading concentrations of copper and molybdenum were changed, and a catalyst powder was prepared in the same manner as in Example 1 and carried out. A catalyst was coated on a cordierite honeycomb carrier in the same manner as in Example 1.
The copper content in the catalyst powder according to Example 2 was 6.0% by weight, the molybdenum content was 0.6% by weight, and the Mo / Cu ratio was 0.066. At this time, the Cu concentration during ion exchange is 0.2 M, and ammonium molybdate is 0.03 M.
Met. The copper content in the catalyst powder according to Example 3 is
9.5 wt%, molybdenum content 0.7 wt%, Mo
The / Cu ratio was 0.049. At this time, the Cu concentration at the time of ion exchange was 0.3M, and the ammonium molybdate was 0.03M. In the catalyst according to Example 4, the copper content was 5.0% by weight, the molybdenum content was 2.5% by weight,
The Mo / Cu ratio was 0.238. At this time, the Cu concentration at the time of ion exchange was 0.2M, and the ammonium molybdate was 0.1M.

Examples 5 to 7 Examples were carried out except that ammonium tungstate was used instead of ammonium molybdate, and the loading amounts of copper and tungsten and the charge concentration during ion exchange were as follows. A catalyst was prepared as in Example 1. The copper content in the catalyst powder according to Example 5 was 6.0% by weight, the tungsten content was 0.2% by weight, and the W / Cu ratio was 0.0.
It was 12. At this time, the Cu concentration at the time of ion exchange was 0.2M, and the ammonium mobdenate was 0.005M. The copper content in the catalyst powder according to Example 6 was 2.5% by weight, the tungsten content was 0.6% by weight, and the W / Cu ratio was 0.083. Cu at the time of ion exchange at this time
Concentration is 0.1M, ammonium molybdate is 0.01
It was 5M. The copper content in the catalyst powder according to Example 7 was 6.0% by weight, the tungsten content was 0.7% by weight, and W
The / Cu ratio was 0.040. At this time, the Cu concentration during ion exchange was 0.2 M, and the ammonium molybdate was 0.015 M.

Example 8 A catalyst was prepared in the same manner as in Example 1 except that ammonium tungstate was added in addition to ammonium molybdate so that the contents of copper, molybdenum and tungsten and the charge concentration during ion exchange were as follows. Prepared. The copper content in the catalyst powder is 9.5% by weight, the molybdenum content is 0.2% by weight, the tungsten content is 0.2% by weight, (Mo + W).
The / Cu ratio was 0.021. At this time, the Cu concentration during ion exchange is 0.3 M, ammonium molybdate is 0.01 M, and ammonium tungstate is 0.02 M.
Met.

A catalyst was prepared in the same manner as in Example 1 except that ammonium phosphomolybdate was used instead of ammonium molybdate, and the supported amounts of copper and molybdenum and the charged concentration during ion exchange were as shown in Table 1. . The copper content in the catalyst was 5.0% by weight, the molybdenum content was 0.3% by weight, and the Mo / Cu ratio was 0.040. At this time, the Cu concentration at the time of ion exchange was 0.2M, and the ammonium phosphomolybdate was 0.01M.

Example 10 Ammonium phosphotungstate was used instead of ammonium molybdate, and the supported amounts of copper and tungsten and the charge concentration at the time of ion exchange were set as follows.
A catalyst was prepared in the same manner as in Example 1. Copper content in the catalyst is 5.0% by weight, tungsten content is 0.3% by weight, W
The / Cu ratio was 0.021. At this time, the Cu concentration at the time of ion exchange was 0.2M, and the ammonium phosphotungstate was 0.01M.

Comparative Examples 1 to 4 In each Comparative Example, a catalyst was prepared in the same manner as in Example 1 except that the loading amounts of copper and molybdenum and the charged concentration at the time of ion exchange were changed as follows. The copper content in the catalyst powder according to Comparative Example 1 was 16.5% by weight, the molybdenum content was 0.05% by weight, and the Mo / Cu ratio was 0.002.
At this time, the Cu concentration at the time of ion exchange was 0.5M, and the ammonium molybdate was 0.002M. Comparative Example 2
The copper content in the catalyst powder according to Example 1 is 6.0% by weight, the molybdenum content is 4.1% by weight, and the Mo / Cu ratio is 0.45.
Met. At this time, the Cu concentration during ion exchange is 0.2.
M and ammonium molybdate were 0.2M. The copper content in the catalyst powder according to Comparative Example 3 was 1.0% by weight, the molybdenum content was 0.1% by weight, and the Mo / Cu ratio was 0.0.
It was 66. At this time, the Cu concentration at the time of ion exchange is 0.05M, and the ammonium molybdate is 0.005M.
Met. The copper content of the catalyst powder according to Comparative Example 4 was 1
2.0 wt%, molybdenum content is 1.0 wt%, M
The o / Cu ratio was 0.55. At this time, the Cu concentration at the time of ion exchange was 0.4M, and the ammonium molybdate was 0.03M.

Comparative Examples 5-6 In each comparative example, S of aluminosilicate zeolite was used.
iO₂/ Al₂O₃(Molar ratio), bearing copper and molybdenum
Change the holding amount and ion exchange concentration to
A catalyst was prepared in the same manner as in Example 1. Catalyst powder according to Comparative Example 5
SiO of the end aluminosilicate zeolite₂/ Al₂
O₃(Molar ratio) is 10, copper content is 8.5% by weight, molybdenum
Buden content is 1.8% by weight, Mo / Cu ratio is 0.14
Met. At this time, the Cu concentration during ion exchange is 0.2.
M and ammonium molybdate were 0.03M.
Aluminosilicate Zeola in catalyst powder according to Comparative Example 6
Ito's SiO₂/ Al ₂O₃(Molar ratio) is 100, including copper
Content is 4.0% by weight, molybdenum content is 0.7%
%, Mo / Cu ratio was 0.12. Io at this time
The Cu concentration at the time of exchange is 0.2M, ammonium molybdate
Um was 0.03M.

Comparative Example 7 A catalyst was prepared in the same manner as in Example 1 except that ammonium tungstate was added in addition to ammonium molybdate, and the contents of copper, molybdenum and tungsten and the charge concentration at the time of ion exchange were set as follows. did. The copper content in the catalyst powder is 1.5% by weight, the molybdenum content is 1.5% by weight, and the tungsten content is 2.0% by weight (Mo + W).
The / Cu ratio was 1.12. At this time, the Cu concentration during ion exchange is 0.05 M, ammonium molybdate is 0.03 M, and ammonium tungstate is 0.03 M.
Met.

Test Example The durability performance of the catalysts of the above Examples and Comparative Examples is shown in comparison with Tables 1 and 2 by a test of the rapid durability of the engine using actual exhaust gas and an activity evaluation using an exhaust gas simulation. .
FIG. 1a shows the catalyst 1 after the test sample of the catalyst was cut out, and FIG. 1b shows the cut catalyst sample 2. Activity evaluation conditions Evaluation device: atmospheric pressure fixed bed flow type reaction device Catalyst capacity: 0.05 L (diameter 3.5 cm, height 5 cm)
(0.7 L size catalyst (diameter 9.4 cm, height 10 c
m)) Gas space velocity: Approximately 35,000 h ^-1 Exhaust gas simulation gas composition: Total hydrocarbons = 3000 ppm (Cl
NO) Approx. 500 ppm CO = 2000 ppm O ₂ = 8.0% CO ₂ = 12% H ₂ O = 10.0% N ₂ = Remaining rapid endurance treatment conditions Catalyst inlet exhaust gas temperature: 630 ° C Engine: Nissan Motor ( Ltd. V type 8 cylinder 3000cc
Engine use Average air-fuel ratio (A / F): Approximately 15 (with fuel cut) Fuel: Unleaded regular gasoline Processing time: 30h

Tables 1 and 2 also show the NO removal performance of the catalysts of Examples and Comparative Examples at the catalyst inlet temperature of 375 ° C. The catalyst of the present invention maintains high NOx removal activity even after rapid durability treatment at a temperature of over 600 ° C, and is excellent in heat resistance and durability. Mo / Cu, W / C in catalyst
u or (Mo + W) / Cu (molar ratio) is 0.003 to
It can be seen that the effect appears in the range of 0.40.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

INDUSTRIAL APPLICABILITY The catalyst of the present invention is used for NOx in exhaust gas rich in oxygen such as lean burn engine exhaust gas.
Since it has high heat resistance and durability that can be efficiently purified, and can be used for a long time even at a temperature of 600 ° C. or higher, it is possible to provide an automobile with extremely low environmental pollution and good fuel consumption.

[Brief description of drawings]

FIG. 1 is a diagram showing how to cut out a catalyst used for activity evaluation.

[Explanation of symbols]

 1 Catalyst after cutting test sample of catalyst 2 Catalyst sample cut out

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Tadashi Kisen, 1280, Kamiizumi, Sodegaura, Chiba Prefecture, Idemitsu Kosan Co., Ltd. (72) Inventor Hiroshi Akama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Hiroyuki Kanasaka 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (5)

[Claims] 1. A catalyst for removing nitrogen oxides in exhaust gas in the presence of hydrocarbons in an oxygen excess atmosphere, comprising:
A catalyst carrier containing a pentasil-type crystalline aluminosilicate is a copper (Cu) component and a molybdenum (Mo) component and / or
Alternatively, it is configured to carry a tungsten (W) component, and M
o / Cu (molar ratio), W / Cu (molar ratio) or (Mo
+ W) / Cu (molar ratio) is 0.003 or more and 0.40 or less, a catalyst for purifying nitrogen oxides in exhaust gas. 2. The content of copper is 2.0% by weight or more and 10.0% by weight or less with respect to the crystalline aluminosilicate in a state where adsorbed water is removed. 1
Exhaust gas purifying catalyst described. 3. The content of molybdenum and / or tungsten is 0.1% by weight or more and 3.0% by weight or less with respect to the crystalline aluminosilicate in a state where adsorbed water is removed. The exhaust gas-purifying catalyst according to claim 1. 4. A crystalline aluminosilicate of the pentasil type.
The acid salt is SiO ₂/ Al₂O₃(Molar ratio) is 20 or more
Upper 80 or less, any one of claims 1 to 3, characterized in that
The exhaust gas purifying catalyst according to any one of the above items. 5. The pentasil-type crystalline aluminosilicate has an MFI structure.
The exhaust gas-purifying catalyst according to any one of 4 above.