JPH07204510A - Catalyst to purify exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst having excellent durability and low temp. activity to remove nitrogen oxides from oxygen-rich exhaust gas by constituting the catalyst of copper and solid acid produced by adding tungsten to zirconia and specifying the amts. of tungsten and zirconia of the compsn. CONSTITUTION:This catalyst to purify exhaust gas is used to remove nitrogen oxides and hydrocarbons from oxygen-rich exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons. The catalyst consists of copper and solid acid prepared by adding tungsten to zirconia, and the compsn. of the catalyst is 0.2-5.0mol% tungsten, 0.2-5.0mol% copper and 90-99.6mol% zirconia. Nitrogen oxides in oxygen-rich exhaust gas are removed by bringing the oxygen-rich exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons into contact with the catalyst for purification of exhaust gas. The oxygen-rich exhaust gas to be purified is, for example, exhaust gas from an inner combustion engine such as of an automobile, especially in a large air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to nitrogen oxides in exhaust gas discharged from an internal combustion engine such as an automobile engine,
The present invention relates to an exhaust gas purifying catalyst that removes carbon monoxide and hydrocarbons, and more particularly to a catalyst that purifies combustion exhaust gas containing excess oxygen.

[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 removed by a three-way catalyst having Pt, Rh, Pd, etc. supported on a carrier. ing. However, such a three-way catalyst has a drawback that nitrogen oxides in exhaust cannot be reduced and removed when oxygen is present in excess. In other words, it is difficult to purify nitrogen oxides in the exhaust gas of diesel engines that contain a large amount of oxygen, and in recent years, gasoline engines have also been burned under conditions of lean gasoline concentration for the purpose of reducing fuel consumption and reducing carbon dioxide emissions. A lean burn engine has been developed, but since this exhaust gas is in an oxygen excess atmosphere, nitrogen oxides cannot be purified with a three-way catalyst.

As a purifying catalyst in an oxygen excess atmosphere, a crystalline aluminosilicate catalyst in which copper is ion-exchanged has been attracting attention as a promising catalyst, but it has a problem in durability.

A solid acid catalyst such as zirconia is also effective as a purifying catalyst in an oxygen excess atmosphere and has excellent durability, but there is a problem that the temperature range showing high activity is a high temperature around 500 ° C.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art, and to remove nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-rich exhaust gas. The present invention provides a catalyst which is excellent in durability and has activity in a low temperature range.

[0006]

Means for Solving the Problems As a result of studies by the present inventors, when copper is further added to a solid acid obtained by adding tungsten to zirconia, excess oxygen exhaust containing nitrogen oxides, carbon monoxide and hydrocarbons is exhausted. As a catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons from gas, it has been found that it has excellent durability and has activity in a low temperature range.

That is, the present invention comprises a solid acid obtained by adding tungsten to zirconia and copper, the composition of which is 0.2 to 5.0 mol% of tungsten and 0.2 to 5.0 m of copper.
nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-rich exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, characterized in that the ol% and zirconia are in the range of 90 to 99.6 mol%. The present invention relates to an exhaust gas purifying catalyst for removing.

The present invention will be described in detail below.

Of the added metal oxide, the amount of tungsten added must be 0.2 to 5.0 mol%. At this time, the acid strength function Ho of the solid acid obtained by adding tungsten to zirconia by the Hammett indicator is −8.2 ≦ Ho ≦ +
3.3. When the added amount is less than 0.2 mol% and the acid strength is Ho> +3.3, only hydrocarbon combustion occurs and the decomposition activity of nitrogen oxides decreases, and the added amount is 5 mo.
When it exceeds 1% and the acid strength is -8.2> Ho, the decomposition of hydrocarbons does not proceed well and the decomposition activity of nitrogen oxides also decreases. Also, the amount of copper added must be 0.2 to 5.0 mol%. When the amount added exceeds 5 mol%, only hydrocarbon combustion occurs and the decomposition activity of nitrogen oxides decreases, and when the amount added is less than 0.2 mol%, hydrocarbon decomposition does not proceed well and nitrogen oxides do not progress. The decomposition activity of is also reduced.

The state of the metal oxide added in the present invention may be either solid solution or supported. There is no particular limitation on the surface area, and a larger surface area is desirable.

When tungsten is added in the preparation of the catalyst of the present invention, it is necessary to add it to amorphous zirconia. This is because when added to crystalline zirconia, no effect is exhibited. There is no particular limitation on the addition of copper. The preparation method is not particularly limited, and various methods can be used. For example, zirconium hydroxide can be incorporated with a metal oxide by a method such as impregnating and supporting, or ion exchange. It can also be obtained from an aqueous solution containing a zirconium salt and a salt of an added metal species by a coprecipitation method or the like, or by an alkoxide method using an organic metal salt or the like. Alternatively, the catalyst can be obtained by impregnating and supporting copper in the zirconium containing tungsten by a method such as impregnating and supporting, or ion exchange.

The impregnation, loading and ion exchange of the additive are carried out by mixing zirconium hydroxide with the solution containing the added metal salt, stirring, filtering, drying and firing. Zirconium hydroxide may be a commercially available product or may be obtained from a solution containing a zirconium salt by a precipitation method or the like. If the temperature is too high, WO ₃ aggregates and precipitates and the effect of addition is not exhibited, so the firing temperature is preferably 850 ° C. or lower. As the raw material of the metal salt, hydroxide, nitrate, sulfate, chloride, various organic acid salts and the like can be used.

These methods exemplify the method for preparing the exhaust gas purifying catalyst according to the present invention, and the catalyst according to the present invention may be prepared by a method other than the above.

The exhaust gas purifying catalyst of the present invention can be used alone or in the form of a mixture with a binder such as clay mineral. Examples of the binder used for molding include viscous minerals such as kaolin, attapulkite, montmorillonite, bentonite, allophane, and sepiolite. Furthermore, it is also possible to wash coat the present catalyst on a honeycomb-shaped substrate made of cordierite or metal.

The exhaust gas purifying catalyst of the present invention is used for removing nitrogen oxides from exhaust gas in excess of oxygen. Removal of nitrogen oxides in the oxygen excess exhaust gas can be performed by bringing the exhaust gas purification catalyst of the present invention into contact with the oxygen excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. Exhaust gas in excess of oxygen targeted by the present invention means exhaust gas containing oxygen in excess of the amount of oxygen required to completely oxidize carbon monoxide, hydrocarbons and hydrogen contained in the exhaust gas. Examples of such exhaust gas include exhaust gas discharged from an internal combustion engine such as an automobile, particularly exhaust gas in a state where the air-fuel ratio is large. The use conditions of the catalyst are not particularly limited, but the temperature range is preferably 200 ° C to 850 ° C. Also S
It may be a 1000h ^-1 ~500000h ^-1 for V.

[0016]

The exhaust gas purifying catalyst of the present invention is excellent in the purifying ability of nitrogen oxides, carbon monoxide and hydrocarbons in an oxygen excess atmosphere, and therefore the exhaust gas of a diesel engine and lean burn engine in which oxygen is excessive. It is possible to purify nitrogen oxides, carbon monoxide, and hydrocarbons contained in the exhaust gas in a relatively low temperature range.

[0017]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 <Catalyst 1> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was added dropwise to 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ° C., 10 g of this hydroxide was added to Cu (NO ₃ ) ₂ .3H ₂ O: 0.15 g.
And WO ₃ (0.15 g) were dissolved in ammonia water, mixed with a solution whose pH was adjusted to 9.0, stirred, and then filtered to 1
Dry at 00 ° C and calcine at 800 ° C for 2 hours to obtain catalyst composition C
uO: 1 mol%, WO ₃ : 1 mol%, ZrO ₂ : 98
A mol% catalyst was prepared. The acid strength function Ho by the Hammett indicator of the catalyst was +1.5.

Example 2 <Catalyst 2> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was dropped into 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying the precipitate at 100 ° C., 10 g of this hydroxide was added to Cu (NO ₃ ) ₂ .3H ₂ O: 0.08 g
And WO ₃ (0.15 g) were dissolved in ammonia water, mixed with a solution whose pH was adjusted to 9.0, stirred, and then filtered to 1
Dry at 00 ° C and calcine at 800 ° C for 2 hours to obtain catalyst composition C
uO: 0.5 mol%, WO ₃ : 1 mol%, ZrO ₂ :
A 98.5 mol% catalyst was prepared. The acid strength function Ho by the Hammett indicator of the catalyst was +1.5.

Comparative Example 1 <Comparative Catalyst 1> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was dropped into 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ℃, 800 ℃
The mixture was calcined for 2 hours to prepare a catalyst having a catalyst composition of ZrO ₂ : 100 mol%. The acid strength function Ho by the Hammett indicator of the catalyst was +6.8.

Comparative Example 2 <Comparative Catalyst 2> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was dropped into 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ° C., 10 g of this hydroxide was added to Cu (NO ₃ ) ₂ .3H ₂ O: 0.15 g.
Was dissolved, mixed with a solution whose pH was adjusted to 9.0, stirred, filtered, dried at 100 ° C., and calcined at 800 ° C. for 2 hours to obtain a catalyst composition CuO: 1 mol%, ZrO ₂ : 99 m.
An ol% catalyst was prepared. The acid strength function Ho by the Hammett indicator of the catalyst was +6.8.

Comparative Example 3 <Comparative Catalyst 3> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was added dropwise to 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ° C., 10 g of this hydroxide was mixed with 0.37 g of WO ₃ dissolved in ammonia water and mixed with a solution whose pH was adjusted to 9.0.
Filter, dry at 100 ° C, calcine at 800 ° C for 2 hours,
Catalyst composition WO ₃ : 2.5 mol%, ZrO ₂ : 97.5 m
An ol% catalyst was prepared. The acid strength function Ho by the Hammett indicator of the catalyst was +1.5.

Comparative Example 4 <Comparative Catalyst 4> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was added dropwise to 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ° C., 10 g of this hydroxide was added to Cu (NO ₃ ) ₂ .3H ₂ O: 0.16 g
And WO ₃ (1.11 g) were dissolved in ammonia water, mixed with a solution whose pH was adjusted to 9.0, stirred and then filtered to 1
Dry at 00 ° C and calcine at 800 ° C for 2 hours to obtain catalyst composition C
uO: 1 mol%, WO ₃ : 7 mol%, ZrO ₂ : 92
A mol% catalyst was prepared. The acid strength function Ho of the catalyst is −
It was 13.75.

Comparative Example 5 <Comparative Catalyst 5> 200 ml of a 1 mol / liter ZrOCl ₂ aqueous solution was added dropwise to 500 ml of a 6N ammonia aqueous solution to obtain a hydroxide precipitate. After drying this precipitate at 100 ° C., 10 g of this hydroxide was added to Cu (NO ₃ ) ₂ .3H ₂ O: 1.15 g.
And WO _3: the 0.16g was dissolved in aqueous ammonia, mixing the solution adjusted to pH 9.0, stirred and filtered 1
Dry at 00 ° C and calcine at 800 ° C for 2 hours to obtain catalyst composition C
uO: 7 mol%, WO ₃ : 1 mol%, ZrO ₂ : 92
A mol% catalyst was prepared. The acid strength function Ho by the Hammett indicator of the catalyst was +1.5.

Example 3 The catalysts obtained in Examples 1 and 2 were press-molded, then crushed and sized to 12 to 20 mesh, and the gas having the composition shown in Table 1 was used by a normal pressure fixed bed flow reactor. SV = 2500
The NO purification rate was measured at h ^-1 . The results are shown in Table 2.

[0026]

[Table 1]

The NO purification rate is expressed by the following equation.

NO purification rate (%) = (NOin-NOou
t) / NOin × 100 NOin: Fixed bed reaction tube inlet NO concentration NOout: Fixed bed reaction tube outlet NO concentration

[0029]

[Table 1]

Comparative Example 4 Purification rates of the catalysts obtained in Comparative Examples 1 to 5 were measured under the same conditions as in Example 3. The results are shown in Table 3.

[0031]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01D 53/36 104 A

Claims (1)

[Claims] 1. A solid acid obtained by adding tungsten to zirconia and copper, the composition of which is about 0.2 to 20% tungsten.
5.0 mol%, 0.2 to 5.0 mol% of copper, 90 to 99.6 mol% of zirconia in the range of excess oxygen containing nitrogen oxides, carbon monoxide and hydrocarbons. An exhaust gas purification catalyst that removes nitrogen oxides, carbon monoxide, and hydrocarbons from gas.