JPH0549937A - Exhaust gas purifying catalyst - Google Patents

Abstract

PURPOSE:To provide a catalyst composed of Co3O4-containing zeolite having a particle diameter of 5000Angstrom or less and having high exhaust gas purifying activity even when the temp. of exhaust gas is low. CONSTITUTION:Zeolite containing Co3O4 having a particle diameter of 5000Angstrom or less as a catalytically active seed. The objective zeolite catalyst is produced, for example, by a method wherein zeolite and cobalt acetate are added to one or more kinds of monohydric alcohols such as ethyl alcohol, n-propyl alcohol or n-butyl alcohol and the resulting mixture is heated for several hr at 30-95 deg.C under stirring and subsequently washed with monohydric alcohol to be dried to obtain cobalt acetate hydroxide-containing zeolite which is, in turn, baked while gas with oxygen concn. of 0-below 22vol.% is passed through said zeolite at SV of 4000hr<-1> to obtain Co3O4-containing zeolite having a particle diameter of 5000Angstrom or less. This zeolite catalyst shows high purifying activity even when the temp. of exhaust gas is low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for purifying exhaust gas emitted from an internal combustion engine of an automobile, a boiler of a factory, etc., and more specifically to a zeolite-based exhaust gas purification containing Co ₃ O _4. It relates to a catalyst.

[0002]

2. Description of the Related Art In recent years, various methods for purifying harmful components in exhaust gas discharged from internal combustion engines of industrial plants and automobiles have been studied. Conventionally, there is a method of removing harmful components in exhaust gas by contacting them with a catalyst. For example, there is a method called a catalytic reduction method. This method uses ammonia,
A reducing agent such as hydrogen or carbon monoxide is required, and a special device for recovering or decomposing the unreacted reducing agent is required. On the other hand, the catalytic cracking method does not require a special reducing agent and can remove harmful components in exhaust gas, especially nitrogen oxides, by simply passing the exhaust gas through the catalyst layer. This is the preferred method. As a catalyst used in this process, a crystalline aluminosilicate catalyst containing copper ions and having a SiO ₂ / Al ₂ O ₃ molar ratio of 20 to 100 (JP-A-60-125250).
Issue gazette).

Further, in a gasoline engine, it has become necessary to perform lean combustion for the purpose of reducing fuel consumption and reducing carbon dioxide emissions. However, since the exhaust gas of this lean burning gasoline engine is in an oxygen excess atmosphere, Conventional three-way catalysts can not be used, as a method of removing harmful components,
A method of using a hydrophobic zeolite as a catalyst has been proposed (JP-A-63-283727).

[0004]

However, the transition metal and / or transition metal ion-containing crystalline aluminosilicate exhaust gas purifying catalyst has a problem that the activity is remarkably low when the operating temperature is low.

[0005]

As a result of various studies, the inventors of the present invention have found that they contain highly dispersed Co ₃ O ₄ in order to improve the purification activity of exhaust gas having a low temperature, which is the above-mentioned conventional problem. We have found that the use of zeolite as an exhaust gas purification catalyst has a high exhaust gas purification activity even when the exhaust gas temperature is low, and completed the present invention.

That is, the present invention proposes an exhaust gas purifying catalyst having a low temperature activity, which is composed of zeolite containing Co ₃ O ₄ having a particle size of 5000 angstroms or less.

The present invention will be described in detail below.

The type of zeolite containing Co ₃ O ₄ having a particle size of 5000 angstroms or less according to the present invention is not particularly limited, and examples thereof include mordenite, ferrierite, Y-type zeolite, ZSM-5 and ZSM-11. Among them, ZSM-5 is preferable among them.

There is no particular limitation on the SiO ₂ / Al ₂ O ₃ molar ratio of zeolite, but when the exhaust gas temperature is in a wide range from low temperature to high temperature, the durability is low when the SiO ₂ / Al ₂ O ₃ molar ratio is small. SiO can cause problems with
It is preferable to use a zeolite having a ₂ / Al ₂ O ₃ molar ratio of 20 or more.

Zeolite is Na type, K
Although it is possible to start from a mold, NH can be prepared by using an aqueous solution of a water-soluble ammonium salt such as ammonium nitrate or ammonium chloride.
Type ₄ or ion-exchanged to type H with a mineral acid such as hydrochloric acid may be used.

In the present invention, the catalytically active species has a particle size of 5
It is essential to contain Co ₃ O ₄ of 000 Å or less. It is preferably 1000 angstroms or less. When the particle size is larger than 5000 angstrom, sufficient exhaust gas purification activity is not exhibited at low temperature. Co ₃ O ₄ can be confirmed by a conventional method such as XRD, and the particle size can be confirmed by an electron microscope or the like.

The content of Co ₃ O ₄ is 0.5 wt% to 3
0 wt% (dry base), preferably 3 to 10 wt%
Is. When the content of Co ₃ O ₄ is less than 0.5 wt%, the harmful components in the exhaust gas cannot be sufficiently removed. On the other hand, when it is more than 30 wt%, the effect is small as compared with the content of Co ₃ O ₄ and it is not economical.

There is no particular limitation on the method for preparing the zeolite containing Co ₃ O ₄ having a particle size of 5000 angstroms or less, and one example thereof is a method via a zeolite containing cobalt acetate hydroxide. That is, zeolite and cobalt acetate are added to one or more monohydric alcohols such as ethyl alcohol, n-propyl alcohol and n-butyl alcohol, and the mixture is heated and stirred at a temperature of 30 to 95 ° C. for several hours, and then the above 1 It is washed with a divalent alcohol and dried to obtain a cobalt acetate hydroxide (chemical formula: C ₁₀ H ₁₆ Co ₃ O ₁₁ ) -containing zeolite. Oxygen concentration of the obtained cobalt acetate hydroxide-containing zeolite was higher than 0 and was 22 vol%.
Less than, preferably 1 to 15 vol% gas SV4
00Hr ^-1 or more, preferably distributed 600Hr ^-1 or more, the firing temperature two hundred and fifty to nine hundred fifty ° C., preferably from 300 to 6
It is possible to prepare a Co ₃ O ₄ -containing zeolite having a particle size of 5000 angstroms or less by firing at 00 ° C. Generates C when SV is less than 400 hr ^-1
The state of o ₃ O ₄ is not stabilized. Here, SV is a value obtained by dividing the flow gas flow rate F (cc / hr) by the volume V of the agent to be fired. When the oxygen concentration of the gas to be circulated is zero, the cobalt compound does not become Co ₃ O ₄ . 22v
When it is ol% or more, C having a small particle size is present on the zeolite crystal surface.
o ₃ O ₄ is not generated. As a result, it is considered that the interaction between Co ₃ O ₄ and zeolite is weakened. When the firing temperature is less than 250 ° C. is Kobarutoasete - DOO hydroxamate site is not a _Co 3 _{O 4.} When the temperature is higher than 950 ° C., the generated Co ₃ O ₄ becomes CoO.

Another method is to use a cobalt-oxalate-containing zeolite. Zeolite and a soluble cobalt salt are added to one or more monohydric alcohols such as ethyl alcohol, n-propyl alcohol and n-butyl alcohol, and the monohydric alcohol-soluble oxalate is added while stirring at a temperature of 20 to 50 ° C. Was added, and after heating and stirring for several hours, the above monohydric alcohol was washed and dried,
A cobalt oxalate-containing zeolite is obtained. The obtained cobalt oxalate-containing zeolite is treated with a gas having an oxygen concentration of more than 0 and less than 22 vol%, preferably ¹ to 15 vol%, SV 400 hr ⁻¹ or more, preferably 600 h.
Zeolite containing Co ₃ O ₄ having a particle diameter of 5000 angstroms or less can be prepared by circulating the mixture at r ⁻¹ or more and firing at a firing temperature of 300 to 950 ° C., preferably 350 to 450 ° C. When the SV is less than 400 hr ^-1, the state of Co ₃ O ₄ produced is not stabilized. When the oxygen concentration of the gas to be circulated is zero, the cobalt compound does not become Co ₃ O ₄ . When it is 22 vol% or more, small particle size Co ₃ O ₄ is not formed on the surface of the zeolite crystal. As a result, it is considered that the interaction between Co ₃ O ₄ and zeolite is weakened. When the firing temperature is lower than 300 ° C., cobalt oxalate does not become Co ₃ O ₄ .
When the temperature is higher than 950 ° C., the generated Co ₃ O ₄ becomes CoO.

In order to use the catalyst according to the present invention for removing harmful components in exhaust gas, it may be in powder form,
It is formed into a cylindrical shape, spherical shape, Raschig ring shape, and honeycomb shape. Alternatively, a monolith catalyst coated on a ceramic or metal honeycomb structure is preferable. In that case, natural clays (eg kaolin,
Halloysite, montmorillonite etc.) and / or inorganic oxides (eg alumina, silica, magnesia, titania, zirconia, hafnia, aluminum phosphate, silica-alumina, silica-zirconia, silica-magnesia etc. binary gels, silica-magnesia-alumina Ternary gel etc.) and the like can also be used.

The production of zeolite containing Co ₃ O ₄ having a particle size of 5000 Å or less is
It can also be carried out after forming the zeolite.

The zeolite catalyst containing Co ₃ O ₄ having a particle diameter of 5000 angstroms or less as described above is used as an exhaust gas purification catalyst. At this time, the origin of the exhaust gas is not particularly limited, and for example, a gas containing nitrogen oxide, carbon monoxide, hydrocarbon, oxygen, nitrogen, etc. may be brought into contact with the catalyst. The temperature at that time is about 200 to 950.
The temperature and the space velocity SV may be in the range of 200 to 200,000 hr ⁻¹ . Here, SV is the flow gas flow rate F
It is a value obtained by dividing (cc / hr) by the volume V of the agent to be calcined.

[0018]

According to the present invention, when a zeolite catalyst containing Co ₃ O ₄ having a particle size of 5000 angstroms or less is used as an exhaust gas purification catalyst, it exhibits high purification activity even when the exhaust gas temperature is low. The effect was obtained.

[0019]

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 (Synthesis of Zeolite and Preparation of Exhaust Gas Purifying Catalyst) ZS according to Example 1 of JP-A-2-265622.
M-5 was synthesized. As a result of chemical analysis, the composition had the following composition expressed as a molar ratio of oxides on an anhydrous basis.

0.99Na ₂ O · Al ₂ O ₃ · 39.5SiO ₂ Zeolite was added to a 2 mol / l ammonium chloride aqueous solution weighed so that the number of ammonium molecules was 10 times the number of Al atoms in the zeolite, and the solution was added. The mixture was stirred at a temperature of 60 ° C for 2 hours. After solid-liquid separation, it was thoroughly washed with water and dried at 100 ° C. for 10 hours to obtain a base material NZ-1.

1.47 g of cobalt acetate tetrahydrate was dissolved in 100 ml of ethyl alcohol, and then 10 g (anhydrous basis) of NZ-1 thus obtained was added and the liquid temperature was adjusted to 70.
The temperature was maintained at 0 ° C. and the mixture was stirred for 2 hours. After solid-liquid separation, it was dried at 100 ° C. for 10 hours to obtain a cobalt acetate hydroxide-containing zeolite. The powder X-ray diffraction pattern is shown in FIG.

Next, the cobalt acetate-containing hydroxide-containing zeolite was passed through an air stream (SV6000h).
It was calcined at 500 ° C. for 1 hour under r ⁻¹ ) to obtain Co ₃ O ₄ -containing zeolite IA. As a result of chemical analysis, the cobalt content was 4.3 wt% in terms of Co ₃ O ₄ (anhydrous basis). The powder X-ray diffraction pattern of the obtained Co ₃ O ₄ -containing zeolite IA is shown in FIG. Co ₃ O ₄ specific peak (2
θ = 43.0, 36.4 and 22.1) were confirmed.

Co ₃ O was observed by scanning electron microscopy.
The particle size of No. ₄ was about 300 Å.

Example 2 (Preparation of Exhaust Gas Purifying Catalyst) The zeolite containing cobalt acetate containing hydroxite obtained in Example 1 was passed through 4% O ₂ /96% N ₂ (SV30).
000 hr ⁻¹ ) at 500 ° C. for 1 hour to form Co ₃
O ₄ containing zeolite IB was obtained. As a result of chemical analysis, the cobalt content is 4.3 w in terms of Co ₃ O ₄ (anhydrous basis).
It was t%. Obtained Co ₃ O ₄ -containing zeolite IB
The powder X-ray diffraction pattern of is shown in FIG. The peak peculiar to Co ₃ O ₄ (2θ = 43.0, 36.4 and 22.1) was confirmed.

It should be noted that Co ₃ O was observed by scanning electron microscopy.
The particle size of No. ₄ was about 250 Å.

Comparative Example 1 (Preparation of Comparative Catalyst) Commercially available Co was added to the catalyst base material NZ-1 obtained in Example 1 so as to have 4.3 wt% in terms of Co ₃ O ₄ (anhydrous basis).
₃ O ₄ was mixed to obtain Co ₃ O ₄ -containing zeolite II.

Co ₃ O was observed by scanning electron microscopy.
The particle size of No. ₄ was about 1 to 2 microns.

Comparative Example 2 (Preparation of comparative catalyst) 1.47 g of cobalt acetate tetrahydrate in 100 ml of pure water.
Was dissolved, and then NZ-1 obtained in Example 1; 10
g (anhydrous base) was added, and the mixture was kept at 110 ° C. in a thermostat for 16 hours and evaporated to dryness. Co-containing zeolite III was obtained. As a result of the chemical analysis, the cobalt content is Co ₃ O ₄
It was 4.3 wt% in terms of conversion (anhydrous basis).

Example 3 (Evaluation of activity of exhaust gas purifying catalyst) 0.65 g of the exhaust gas purifying catalysts Co ₃ O ₄ -containing zeolites IA and IB prepared in Examples 1 and 2; Under reaction gas flow of the following composition (600m
l / min. ) After pretreatment at 550 ° C. for 0.5 hour, 2
The temperature was lowered to 80 ° C., and the NO, CO, and C ₃ H ₆ purification rates were measured. The results are shown in Table 1.

Reaction gas composition NO 700 ppm O ₂ 4% CO 1000 ppm C ₃ H ₆ 400 ppm H ₂ O 3% N ₂ balance Comparative example 3 (activity evaluation of comparative exhaust gas purification catalyst) Comparative example prepared in Comparative example 1 and Comparative example 2 The exhaust gas purifying catalyst was evaluated in the same manner as in Example 3. N at 280 ° C
Table 1 shows the respective purification rates of O, CO, and C ₃ H ₆ .

[0032]

[Table 1]

[Brief description of drawings]

FIG. 1 is a powder X-ray diffraction pattern of the cobalt acetate-containing hydroxysite-containing zeolite obtained in Example 1.

FIG. 2 is a powder X-ray diffraction diagram of Co ₃ O ₄ -containing zeolite IA obtained in Example 1.

FIG. 3 is a powder X-ray diffraction diagram of Co ₃ O ₄ -containing zeolite IB obtained in Example 2.

Claims (1)

[Claims] 1. An exhaust gas purifying catalyst comprising zeolite containing Co ₃ O ₄ having a particle size of 5000 angstroms or less.