JPH0796139A - Method for purifying waste gas - Google Patents

Abstract

PURPOSE:To effectively remove the NOx in a waste gas by bringing a zirconia having a specified BET specific surface and contg. kind of compd. selected from Cr, Co. Ni and Cu into contact with the oxygen-excess waste gas contg. hydrocarbons. CONSTITUTION:A zirconia having >=2m<2>/g BET specific surface and contg. >=1 kind of compd. selected from Cr, Co, Ni and Cu is brought into contact with an oxygen-excess waste gas contg. hydrocarbons. The waste gas purification catalyst is formed, for example, by mixing the material obtained by filtering the zirconium hydroxide obtained by neutralizing an aq. zirconium salt soln. with alkali or the hydrated zirconia obtained by hydrolyzing the aq. zirconium salt soln., and then washing it with water, with >=1 kind of aq. metallic salt soln. selected from Cr, Co, Ni and Cu, drying and then calcining the mixture. This catalyst is capable of highly efficiently purging NOx in the waste gas at a low temp. of about 200-500 deg.C in the presence of steam and is excellent in durability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an exhaust gas in excess of oxygen containing nitrogen oxides discharged from a boiler, an automobile gasoline engine, etc. The present invention relates to a method for purifying exhaust gas capable of removing substances.

[0002]

2. Description of the Related Art Nitrogen oxides, carbon monoxide and hydrocarbons, which are harmful substances in exhaust gas discharged from an internal combustion engine, are
For example, it is removed by a three-way catalyst in which Pt, Rh, Pd, etc. are supported on a carrier. However, the exhaust gas of a diesel engine does not have an effective catalyst component because it is in an oxygen excess atmosphere, and exhaust gas purification by a catalyst has not been performed. In addition, in recent gasoline engines, it has become necessary to perform lean combustion for the purpose of reducing fuel consumption and reducing carbon dioxide in exhaust gas. However, since the exhaust gas of this lean burn gasoline engine is in an oxygen excess atmosphere, the conventional three-way catalyst as described above cannot be used, and a method for removing harmful components has not been put to practical use. Therefore, it has been desired to develop a denitration catalyst that can efficiently purify nitrogen oxides in an oxygen excess atmosphere.

Conventionally, as a method of purifying exhaust gas using zirconia, one or more of palladium and rhodium are formed on zirconia having a BET specific surface area of 50 to 200 m ² / g and an average primary particle diameter of 50 to 200 angstrom. A catalyst for purifying exhaust gas from a diesel engine, which is composed of a catalyst component in which a noble metal is dispersed and supported (JP-A-4-200637). General formula AXB _1-xy B′O _z (A = Ca, Sr, Ba,
B = Zr, Hf, Ti, B ′ = Fe, Co, Ni, C
u, x = 0.05~0.5, y = 0.01~0.3) consisting fluorite or perovskite-type composite oxide having oxygen defects represented by NO _X decomposition catalyst (JP-4-
118050) Purification of exhaust gas containing nitrogen oxides by contacting exhaust gas containing metal oxides and nitrogen oxides treated with a compound having a sulfate group in the presence of hydrocarbons in an oxidizing atmosphere containing excess oxygen A method (Japanese Patent Laid-Open No. 4-90825) and the like are known.

[0004]

The exhaust gas purifying catalyst has a BET specific surface area of 50 to 200 m ² / g,
Zirconia having an average particle size of primary particles of 50 to 200 angstroms is impregnated with noble metals of palladium and rhodium and dried to obtain a catalyst component. When the catalyst component is contacted with a gas containing nitrogen oxides in the presence of hydrocarbon, Usually N ₂ O
Therefore, it is not suitable as an exhaust gas purifying catalyst. NO _x decomposition catalyst of is zirconia sol with Ca, S
A salt of r, Ba, Fe, Co, Ni, Cu is mixed and fired to obtain a fluorite-type, perovskite-type composite oxide. This catalyst component does not use a reducing agent such as hydrocarbon,
Although nitrogen oxides can be directly decomposed into nitrogen at a temperature of 800 ° C., the decomposition activity of nitrogen oxides becomes extremely low at a temperature of 200 to 500 ° C., which is not practical as an exhaust gas purifying catalyst. The exhaust gas purifying catalyst of is a zirconia carrying sulfuric acid treatment of zirconia and supporting sulfate, but the catalyst component obtained by this method has a low purification rate of nitrogen oxides when the space velocity is increased when contacting with the exhaust gas. When it coexists with water vapor, the reducing activity is lost and it becomes impractical as an exhaust gas purifying catalyst. In any case, the above exhaust gas purification catalyst has a low purification rate of nitrogen oxides and has poor heat resistance.

In the present invention, such a drawback of the conventional method is solved that the purification rate of nitrogen oxides is high, that is, the selective reduction property is extremely high even at a low exhaust gas temperature of 200 to 500 ° C. in a steam atmosphere, and It is an object of the present invention to provide a method for purifying exhaust gas that has high heat resistance and excellent durability.

[0006]

Means for Solving the Problems The present inventors have focused on zirconia having high heat resistance and a partial oxidation action of a transition metal on a hydrocarbon (reducing species), and have a zirconia containing a transition metal and a reduction activity. According to a detailed examination of the relationship, the BET specific surface area is 2 m ² / g or more, and
Zirconia containing one or more compounds selected from Cr, Co, Ni and Cu is used in a steam atmosphere at 200
The inventors have found that the purification rate of nitrogen oxides is high even at a low exhaust gas temperature of ˜500 ° C. and the durability is excellent, and the present invention has been achieved.

That is, the present invention has a BET specific surface area of 2
m ² / g or more and Cr, Co, Ni and C
It is a gist to purify nitrogen oxides in exhaust gas by bringing zirconia containing one or more compounds selected from u into contact with exhaust gas in excess of oxygen containing hydrocarbon. Hereinafter, the present invention will be described in more detail.

In the present specification, the "BET specific surface area" relating to zirconia means that measured using nitrogen as an adsorbed molecule.

The exhaust gas purifying catalyst used in the present invention is C
It is necessary to be zirconia containing one or more compounds selected from r, Co, Ni and Cu. If the zirconia does not contain Cr, Co, Ni and Cu compounds, the reducing activity is exhibited at the exhaust gas temperature around 550 ° C., but the reducing activity is almost lost at a low temperature of 200 to 500 ° C. This is because it becomes unsuitable as an exhaust gas purification catalyst used in. The content of the compound of the metal is preferably 0.05 to 10% by weight, and more preferably 0.1 to 5% by weight, as the weight ratio of the metal to zirconia.

The BET specific surface area of the above exhaust gas purifying catalyst must be 2 m ² / g or more. When the BET specific surface area is smaller than 2 m ² / g, the catalytic component has few active sites, and when it is brought into contact with exhaust gas under a condition of high space velocity, the reducing activity is mostly reduced because the active site is few. This is because it will not be suitable as an exhaust gas purifying catalyst used in the present invention. Preferred B
The ET specific surface area is 15 to ²⁰⁰ m ² / g, and more preferably 20 to 100 m ² / g. Further, the above-mentioned catalyst component is not limited in the form when it is brought into contact with the exhaust gas, and can be used, for example, in the form of powder, granules, pellets, etc., but in addition to these, it is mixed with a binder such as an inorganic substance. It can also be molded and used. Furthermore, the exhaust gas purifying catalyst used in the present invention may be used as a wash coat on a honeycomb-shaped substrate made of cordierite or a metal.

In order to obtain the exhaust gas purifying catalyst used in the present invention, the BET specific surface area is 2 m ² / g or more, and it is selected from Cr, Co, Ni and Cu.
If zirconia containing more than one compound can be prepared,
What is obtained by any method may be used, and as a preparation method thereof, for example, a) zirconium hydroxide obtained by neutralizing an aqueous solution of zirconium salt with alkali, or hydration obtained by hydrolysis of an aqueous solution of zirconium salt is used. Zirconia filtered and washed with water and selected from Cr, Co, Ni and Cu 1
Method of mixing with at least one kind of metal salt aqueous solution and drying and then baking b) Method of mixing and drying zirconia having a BET specific surface area of 2 m ² / g and the above metal salt aqueous solution c) Zirconium salt and the above metal salt A method of neutralizing an aqueous solution consisting of, with an alkali, filtering and washing the washed product with water d) Hydrolyzing an aqueous zirconium salt solution to obtain a hydrated zirconia-containing solution, and adding the above metal salt thereto A method in which the mixture is mixed, filtered and washed with water e) e) Zirconium hydroxide or hydrated zirconia of the above a) is mixed with an aqueous ammine complex salt solution of the above metal to obtain a suspension, and the pH of the suspension is obtained. Is adjusted to 9 or more, and then the filtered product is baked. F) A suspension is obtained by mixing zirconia having a BET specific surface area of 2 m ² / g or more and an aqueous solution of an ammine complex salt of the above metal.
A method in which the pH of the suspension is adjusted to 9 or more and then the filtered product is dried can be mentioned. Hereinafter, the method for preparing the exhaust gas purifying catalyst according to the present invention will be described in more detail.

When the catalyst component is obtained by the method a),
A suspension containing zirconium hydroxide produced by mixing an aqueous zirconium salt solution with an alkali or a suspension obtained by mixing hydrated zirconia produced by hydrolysis of an aqueous zirconium salt solution with an alkali has a pH of 8 or more.
It is preferable to adjust so as to obtain, and to filter and wash with water.
If the pH is lower than 8, the coagulability of zirconium hydroxide or hydrated zirconia in the suspension is lowered, resulting in poor filterability, and it takes a long time for filtration and washing with water, and productivity is lowered. Is. The pH of the more preferable suspension is 9-14. Zirconium hydroxide or hydrated zirconia thus obtained and Cr, Co, N
There is no limitation on the drying method for mixing with an aqueous solution containing one or more metal salts selected from i and Cu and drying, and for example, a method of heating the suspension before drying to concentrate and dry it; A method of heating the suspension while rotating to concentrate and dry it; a method of spray drying the suspension;
Examples include a method of adding an organic solvent to the suspension and spray drying. Particularly, when the suspension is spray-dried, it becomes a dry powder in which metal salts of Cr, Co, Ni and Cu are uniformly mixed, and when it is calcined, the uniformity of Cr, Co, Ni and Cu of the catalyst component obtained is obtained. Of the catalyst, the catalyst performance is further improved. In addition, when an organic solvent is added and spray-dried, the sintering of the catalyst component is eased during firing, which makes it easier to handle during molding, and is effective when the catalyst component is processed into various molded bodies for use. Target. When the dry powder thus obtained is calcined, it becomes the exhaust gas purifying catalyst used in the present invention.

When the catalyst component is obtained by the method b), it is necessary to use zirconia having a BET specific surface area of 2 m ² / g or more. When the BET specific surface area is less than 2 m ² / g, the BET specific surface area of the catalyst component obtained by mixing with one or more metals selected from Cr, Co, Ni and Cu and drying the mixture is less than 2 m ² / g. This is because it becomes smaller and, as described above, it becomes unsuitable as an exhaust gas purifying catalyst. There is no limitation on the method of drying the suspension containing zirconia and the metal salt as in the case of a).

In obtaining the catalyst component by the method c), an aqueous solution of zirconium salt and one or more kinds of metal salts selected from Cr, Co, Ni and Cu is neutralized with an alkali, filtered and washed with water. Then, zirconium hydroxide containing the metal is obtained, and the zirconium hydroxide may be filtered, washed with water, dried and calcined. Further, in the case of the method d), the zirconium salt aqueous solution is hydrolyzed to hydrate. A zirconia sol-containing liquid is obtained, and one or more metal salts selected from Cr, Co, Ni and Cu are added thereto, and the hydrated zirconia containing the metal obtained by neutralizing with an alkali is filtered, washed with water, If dried and calcined, the exhaust gas purifying catalyst used in the present invention can be obtained. C) and d) above
When both are neutralized with alkali, while stirring a solution of zirconium salt or hydrated zirconia of 1 mol / l or less, 1 mol / l of an alkaline aqueous solution of 2 mol / l or less is stirred.
If added at a rate of (l · h) or less, Cr, Co, N
Zirconium hydroxide or hydrated zirconia containing i, Cu uniformly containing a metal compound is obtained, and when it is filtered, washed with water and calcined, it becomes zirconia uniformly containing the metal, and is more excellent in reducing activity. It becomes a thing. When the pH of the suspension obtained by neutralization with an alkali becomes lower than 8, the filterability becomes poor and the productivity becomes low as described in a) above.

When the catalyst component is obtained by the above method e), the zirconium hydroxide or hydrated zirconia obtained in the above a) and an aqueous solution of one or more ammine complex salts selected from Cr, Co, Ni and Cu are used. It is advisable to mix them to obtain a suspension, adjust the pH of the suspension to 9 or higher, and carry the metal on zirconium hydroxide or hydrated zirconia. When the pH of the suspension is lower than 9, ion exchange between the protons of the surface OH groups of zirconium hydroxide or hydrated zirconia and the ammine complex of the metal does not occur easily, and zirconium hydroxide obtained by filtration is obtained. This is because hydrated zirconia is less likely to contain the compound of the metal, and the exhaust gas purifying catalyst used in the present invention is difficult to obtain. The pH of the preferred suspension is 10.5-14,
More preferably, it is 11-12. The pH of the above suspension can be adjusted by adding aqueous ammonia. The reaction time required for ion exchange is 1 to 30 hours when the temperature of the suspension is in the range of 10 to 50 ° C., and the optimum concentration of the ammine complex salt is the concentration of the ammine complex salt (mo
When expressed as a ratio of the slurry concentration (g / l) of 1 / l) / zirconia, it is 10 ⁻⁶ to 10 ⁻³ mol / g. In addition, when the above zirconium hydroxide or hydrated zirconia is suspended in an aqueous ammonia solution having a pH of 9 or more, and the ammine complex salt aqueous solution is mixed with the suspension, the ion exchange property between the proton of the surface hydroxyl group and the ammine complex is obtained. Since it becomes high, it is effective to uniformly contain the metal.
The exhaust gas purification catalyst used in the present invention is obtained by filtering, drying and calcining the suspension thus obtained.

When the catalyst component is obtained by the method f), zirconia having a BET specific surface area of 2 m ² / g or more is used, and one or more aqueous ammine complex salt solution selected from Cr, Co, Ni and Cu is used. Must be mixed.
When the BET specific surface area becomes smaller than 2 m ² / g, the BET specific surface area of the catalyst component obtained by mixing with an aqueous ammine complex salt solution of the metal and filtering becomes smaller than 2 m ² / g. This is because it becomes unsuitable as an exhaust gas purification catalyst used in. The pH of the suspension obtained by mixing zirconia and an aqueous solution of an ammine complex salt of the metal may be adjusted to 9 or higher so that the metal is supported on the zirconia. This is because when the pH is lower than 9, it becomes difficult to obtain the exhaust gas purifying catalyst of the present invention as described in e) above. More preferable suspension pH is 10.5 to
14 and preferably 11 to 12. The pH adjustment of the suspension, the reaction time at the time of ion exchange, the reaction temperature and the concentration of the ammine complex salt may be set in the same manner as in the above e), and the ion exchange property is enhanced to make the metal uniform in zirconia. In order to support the same on p.
You may suspend zirconia in the ammonia aqueous solution whose H is 9 or more, and mix an ammine complex salt aqueous solution with the suspension.

The suspension thus obtained is filtered and dried to obtain the exhaust gas purifying catalyst used in the present invention. Further, after filtering the above suspension, further washing to remove the ammine complex salt adhering to zirconia,
The dispersibility of the metal present on the zirconia surface becomes high, and the catalyst performance becomes even more excellent. The aqueous solution used for washing is preferably distilled water or ammonia water, and may be washed until the color of the ammine complex in the filtrate becomes colorless and transparent. It is effective to use ammonia water having a pH of 9 or more at the time of washing because the ammine complex salt adhering to zirconia can be easily removed.

The dried powder obtained by the methods a), c), d), and e) can be converted into B by firing at a temperature of 1200 ° C. or lower.
A catalyst component having an ET specific surface area of 2 m ² / g or more can be obtained. A more preferable firing temperature is 300 to 1000 ° C, preferably 500 to 800 ° C. Further, if necessary, in order to improve the moldability of the catalyst components obtained in a) to f), pulverization treatment may be performed after firing.
Furthermore, when it is necessary to improve the durability at high temperature, one or more alkaline earth metals such as Be, Mg, Ca, Sr, and Ba may be used during the preparation of the above a) to f) and a catalyst component. May be added to.

The zirconia used in the above b) and f) may be obtained by any production method as long as the BET specific surface area can be obtained within the above range. As a method for producing zirconia, for example, an aqueous zirconium salt solution is neutralized with an alkali, and the resulting zirconium hydroxide is calcined; the aqueous zirconium salt solution is hydrolyzed, and the resulting hydrated zirconia is calcined; zirconium alkoxide. Water can be added to the alcohol solution to obtain hydrated zirconia, which can be calcined. Therefore, zirconia having a desired BET specific surface area can be obtained by controlling the firing temperature when firing the above-mentioned zirconium hydroxide or hydrated zirconia. In addition, the above a), c), d),
Examples of the zirconium salt used in e) include zirconium oxychloride, zirconyl nitrate, and zirconyl sulfate. As the alkali for neutralizing the zirconium salt aqueous solution, ammonia water, sodium hydroxide,
Potassium hydroxide can be mentioned, but in addition to these, a compound which shows basicity by decomposing like urea may be used. Cr, C used in the above a), b), c) and d)
Examples of metal salts of o, Ni and Cu include chlorides, nitrates, sulfates and acetates of the metals. Further, Cr, Co, N used in the above e) and f)
As the ammine complex salt of i and Cu, tetraammine copper,
Examples thereof include chlorides, nitrates and sulfates of hexaamminecobalt, hexaamminenickel and hexaamminechromium.

Regarding the catalyst components obtained by the above-mentioned preparation methods a) to f), considering the balance between the catalytic activity and the productivity, the preferred preparation methods are a), c), d), e),
f), more preferably e) and f), and a more preferable preparation method is f). The exhaust gas purifying catalyst thus prepared is contacted with an oxygen-excess exhaust gas containing nitrogen oxides and hydrocarbons to remove nitrogen oxides. It is essential that the exhaust gas used in the present invention contains nitrogen oxides and hydrocarbons and is in excess of oxygen, but it is also effective when it contains carbon monoxide, hydrogen, ammonia and the like. Exhaust gas in excess of oxygen means that oxygen is contained in excess of the amount required to completely oxidize carbon monoxide, hydrocarbons and hydrogen contained in the exhaust gas. For example, in the case of exhaust gas discharged from an internal combustion engine such as an automobile, the air-fuel ratio is large (lean region). The space velocity and temperature at the time of removing nitrogen oxides are not limited, but are 100 to 500000 h ⁻¹ , 200 to 800 ° C.
Is preferred.

[0021]

As described above, the exhaust gas purifying catalyst of the present invention has a high purification rate of nitrogen oxides and excellent durability in the presence of steam even at a low exhaust gas temperature of 200 to 500 ° C. .

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, the catalytic activity was evaluated by the following method.

Each catalyst was press-molded, crushed and sized to a particle size width of 410 to 810 μm. 2 cc of the sized powder was filled in a fixed-pressure fixed-bed flow type reaction tube to simulate the exhaust gas of a lean burn engine (gas composition:
_{CO = 0.12vol%, C 3 H} 6 = 0.08vol%,
NO = 0.12 vol%, O ₂ = 4 vol%, CO ₂ = 1
₂ vol%, H ₂ O = 10 vol%, N ₂ = balance) while flowing at a space velocity of 20000 h ⁻¹ at 550 ° C.
After pretreatment for 0 minutes, the steady-state purification activity was measured at each temperature. The steady-state purification activity was the NO purification rate after holding at each temperature for 1 hour.

Example 1 1 liter of 0.4 mol / l zirconium oxychloride aqueous solution was boiled for 160 hours to obtain a hydrated zirconia sol having an average particle size of 0.1 μm. After adding 1.5 liters of 1N ammonia water to the hydrated zirconia sol-containing liquid,
It was filtered, washed with water and dried. The obtained dried powder of hydrated zirconia was calcined at a temperature of 600 ° C. for 5 hours to obtain a zirconia powder having a BET specific surface area of 51 m ² / g.

Then, 10 g of the above zirconia powder was mixed with 140 ml of 1.5N ammonia water to prepare a suspension containing zirconia. 0.07 mol /
An aqueous solution containing tetraamminecopper (II) was prepared by adding 150 ml of 1.5N ammonia water to 160 ml of 1-liter aqueous solution of copper acetate, which was added to the above suspension while stirring. The pH of the obtained suspension was 11.4, the slurry concentration of zirconia was 22 g / l, and the concentration of copper tetraammine was 0.025 mol / l. After maintaining this suspension at a temperature of 30 ° C. for 20 hours with stirring,
The mixture was filtered, washed with 1.5N aqueous ammonia until the color of the filtrate (blue) became colorless and transparent, and dried at a temperature of 110 ° C. to obtain a catalyst component.

When the activity of the above catalyst components was evaluated, it showed the highest activity at a temperature of 400 ° C., and the NO purification rate at that temperature was 12%.

Example 2 Except that a dry powder of hydrated zirconia was calcined at 800 ° C.
It carried out on the conditions similar to Example 1. The BET specific surface area of the obtained zirconia powder was 27 m ² / g. When the activity of the catalyst component was evaluated, it showed the highest activity at a temperature of 400 ° C., and the NO purification rate at that temperature was 8%.

Example 3 1 liter of a 0.4 mol / l zirconium oxychloride aqueous solution was boiled for 160 hours to obtain a hydrated zirconia sol having an average particle size of 0.1 μm. After adding 1.5 liters of 1N ammonia water to the hydrated zirconia sol-containing liquid,
It was filtered, washed with water and dried to obtain a dry powder of hydrated zirconia. Dry powder of this hydrated zirconia (zirconia conversion 10
g) was mixed with 140 ml of 1.5 N ammonia water to prepare a suspension containing hydrated zirconia. 0.
An aqueous solution containing tetraamminecopper (II) was prepared by adding 150 ml of 1.5 N ammonia water to 160 ml of a 07 mol / l copper acetate aqueous solution, which was added to the above suspension while stirring. The pH of the obtained suspension was 11.
1, the slurry concentration of hydrated zirconia (converted to zirconia) was 22 g / l, and the concentration of copper tetraammine was 0.0.
It was 25 mol / l. Stir this suspension 3
Hold at 0 ° C for 20 hours, then filter to 1.5
The filtrate was washed with N aqueous ammonia until the color (blue) of the filtrate became colorless and transparent, and dried at a temperature of 110 ° C. The dried powder was calcined at a temperature of 600 ° C. for 5 hours to obtain a catalyst component having a BET specific surface area of 45 m ² / g.

When the activity of the above catalyst component was evaluated, it showed the highest activity at a temperature of 450 ° C., and the NO purification rate at that temperature was 10%.

Example 4 1 liter of a 0.4 mol / l zirconium oxychloride aqueous solution was boiled for 160 hours to obtain a hydrated zirconia sol having an average particle size of 0.1 μm. To this hydrated zirconia sol-containing liquid was added 1.5 liters of 1N ammonia water, followed by filtration, washing with water and drying to obtain a dried powder of hydrated zirconia. This hydrated zirconia dry powder (zirconia equivalent 1
4 g) was mixed with 140 ml of 1.5 N ammonia water to prepare a suspension containing hydrated zirconia. 1.
17 ml of 0.07 mol / l copper acetate aqueous solution was added to 290 ml of 5N aqueous ammonia to prepare an aqueous solution containing tetraamminecopper (II), which was added to the above suspension while stirring. The pH of the obtained suspension was 11.
2, the hydrated zirconia slurry concentration (converted to zirconia) was 31 g / l, and the tetraammine copper concentration was 0.0.
It was 027 mol / l. The suspension is maintained at a temperature of 30 ° C. for 20 hours with stirring, then filtered and
It was washed with 5N aqueous ammonia and dried at a temperature of 110 ° C. The dried powder was calcined at a temperature of 600 ° C. for 5 hours to obtain a catalyst component having a BET specific surface area of 50 m ² / g.

When the activity of the above catalyst components was evaluated, it showed the highest activity at a temperature of 450 ° C., and the NO purification rate at that temperature was 9%.

Example 5 1 liter of a 0.4 mol / l zirconium oxychloride aqueous solution was boiled for 160 hours to obtain a hydrated zirconia sol having an average particle size of 0.1 μm. After adding 1.5 liters of 1N ammonia water to the hydrated zirconia sol-containing liquid,
It was filtered, washed with water and dried. The obtained dried powder of hydrated zirconia was calcined at a temperature of 600 ° C. for 5 hours to obtain a zirconia powder having a BET specific surface area of 51 m ² / g.

Then, 10 g of the above zirconia powder was added to 140 ml of 1.5N ammonia water with stirring to prepare a suspension containing the zirconia powder.
0.029m containing 100ml of 1.5N ammonia water
ol / l hexaamminecobalt (III) 260m
1 was added to the above suspension with stirring. The pH of the obtained suspension was 11.3, the slurry concentration of zirconia was 25 g / l, and the concentration of hexaamminecobalt was 0.019 mol / l. The suspension was kept under stirring at a temperature of 30 ° C. for 20 hours, then filtered,
The filtrate was washed with 1.5 N ammonia water until the color of the filtrate (red-purple) became colorless and transparent, and dried at a temperature of 110 ° C. to obtain a catalyst component.

When the activity of the above catalyst component was evaluated, it showed the highest activity at a temperature of 450 ° C., and the NO purification rate at that temperature was 17%.

Example 6 Except that a dry powder of hydrated zirconia was calcined at 800 ° C.
It carried out on the conditions similar to Example 5. The BET specific surface area of the obtained zirconia powder was 27 m ² / g. When the activity of the catalyst component was evaluated, it showed the highest activity at a temperature of 450 ° C., and the NO purification rate at that temperature was 16%.

Comparative Example 1 Powder made of zirconia alone prepared in Example 1 (BE
When the catalyst activity was examined for a T specific surface area of 51 m ² / g), the NO purification rate was 3% or less at a temperature of 200 to 500 ° C.

Comparative Example 2 The same conditions as in Example 3 were carried out except that the baking was carried out at a temperature of 1300 ° C. The BET specific surface area of the obtained catalyst component is 1
It was m ² / g, and when its catalytic activity was evaluated, it showed almost no activity.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/72 ZAB A 8017-4G 23/74 ZAB A 8017-4G B01D 53/36 102 D

Claims (1)

[Claims] 1. A BET specific surface area of 2 m ² / g or more,
And it is characterized in that zirconia containing one or more compounds selected from Cr, Co, Ni and Cu is brought into contact with exhaust gas in excess of oxygen containing hydrocarbons to purify nitrogen oxides in the exhaust gas. Exhaust gas purification method.