JPH11104491A - Oxidation catalyst for co and nitrogen oxides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To oxidize a lower oxide such as nitrogen monoxide and carbon monoxide efficiently by using an oxidation catalyst containing one kind of mixed powder of active manganese dioxide carrying copper, active zeolite having specified properties, and/or active alumina as an effective component. SOLUTION: An oxide catalyst contains at least one kind of mixed powder selected from active manganese dioxide carrying copper, active zeolite having properties of 0.2 g/ml or above in apparent density, 50 m<2> /g or above in BET specific surface area, 10 g/100 g or above (25 deg.C) in water absorption at relative humidity 50%, and active alumina as an effective component. The active manganese dioxide is porous manganese dioxide having a large specific surface area obtained at least by the wet oxidation decomposition of a manganese salt. The active zeolite is that activated by burning. As the active alumina, alumina of structure close to spinel structure of ρ, χ, γ, η, and δ is indicated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CO and NOx oxidation catalyst excellent in the ability to oxidize harmful low-grade oxides such as carbon monoxide and nitrogen monoxide contained in exhaust gas at low temperatures.

[0002]

2. Description of the Related Art Recently, exhaust gases discharged from internal combustion engines such as automobiles, boilers, and industrial plants contain harmful oxides such as harmful nitrogen monoxide and carbon monoxide. The removal of harmful components from flue gas has been studied from various aspects.

Conventionally, various purification methods using an oxidation catalyst have been proposed for purifying these harmful substances contained in exhaust gas. For example, a method using an oxidation catalyst composed of manganese dioxide and iron oxide (JP-A-49-45894) and a method using an oxidation catalyst composed of manganese dioxide and lead oxide (JP-A-50-62859) are proposed. Have been.

On the other hand, with respect to carbon monoxide, a method using an oxidation catalyst in which nickel and copper are supported on a carrier having a spinel structure (Japanese Patent Application Laid-Open No. 52-27085), a method using manganese, cobalt or chromium oxide as a catalyst component. A method using one or more oxides of titanium and iron
No. 12768), a method using an oxidation catalyst in which at least one of iron, manganese, and cerium is supported on an alumina carrier in combination with palladium (Japanese Patent Application Laid-Open No. 62-14944).
A method has been proposed in which a mixture of manganese dioxide and another metal oxide is supported on the surface of a granular thermoplastic resin (JP-A-63-178849).

A method has also been proposed in which these harmful lower oxides are collectively oxidized to render them harmless. For example, a method using a catalyst in which a zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of not less than a specific value contains cobalt, an alkaline earth metal, and Pt and / or Mn (Japanese Patent Laid-Open No.
-219146 discloses), a method using a molar ratio of SiO ₂ / Al ₂ O ₃ is obtained by incorporating cobalt and rare earth metals and Pt and / or Mn in the zeolite is specified above catalyst (JP-A-4-219149) , SiO ₂ / A
a method of using a catalyst in which manganese, an alkaline earth metal and Pt and / or Mn are contained in a zeolite having a molar ratio of l ₂ O ₃ of not less than a specific value (JP-A-4-21950); Of at least one of activated alumina and cerium oxide to form a monolithic catalyst having a catalyst component supporting layer containing at least one of potassium, cesium, strontium and barium, and at least one of cobalt and manganese. (JP-A No. 7-16466), a method using a catalyst in which a copper-anodolite layer formed by adding copper to expanded illusionite on a refractory carrier is used (Japanese Patent Laid-Open No. 8-166). 19
No. 2053) has been proposed.

[0006]

However, the method using these oxidation catalysts has a drawback that, although a considerable catalytic activity can be expected in a high temperature range, the catalytic activity is significantly reduced in a low temperature range of 100 ° C. or less. is there.

In view of the above problems, the present inventors have made intensive studies on oxidation catalysts capable of oxidizing harmful low-grade oxides such as nitrogen monoxide and carbon monoxide in exhaust gas at a relatively low temperature range. As a result of the stacking, a mixed powder of activated manganese dioxide carrying copper, a specific apparent density, a specific surface area, and an activated zeolite and / or activated alumina having a superior water adsorption capacity, in a relatively low temperature range, The present inventors have found that it is possible to efficiently oxidize lower oxides of nitrogen monoxide and carbon monoxide, and have completed the present invention.

That is, the present invention provides a CO and NOx oxidation catalyst capable of efficiently oxidizing lower oxides such as nitrogen monoxide and carbon monoxide even in a low temperature range of 100 ° C. or lower. Aim.

[0009]

The oxidation catalyst for CO and NOx to be provided by the present invention is composed of activated manganese dioxide carrying copper and BE having an apparent density of 0.2 g / ml or more.
T specific surface area of 50 m ² / g or more and relative humidity of 50%
The composition is characterized in that a mixed powder with active zeolite and / or active alumina having a property of adsorbing water of 10 g / 100 g (25 ° C.) or more is used as an active ingredient.

An activated manganese dioxide supporting the copper,
The composition ratio of activated zeolite and / or activated alumina is preferably in the range of 1: 2 to 3: 1 as a weight ratio.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The oxidation catalyst for CO and NOx according to the present invention comprises activated manganese dioxide carrying copper, an amount of water adsorbed at an apparent density of 0.2 g / ml or more, a BET specific surface area of 50 m ² / g or more, and a relative humidity of 50%. Is 10 g / 100 g (25
The mixed powder with at least one selected from the group consisting of activated zeolite and activated alumina having the above-mentioned properties is used as an active ingredient.

In the present invention, active manganese dioxide is
A porous manganese dioxide having a large specific surface area obtained by at least wet oxidative decomposition of a manganese salt indicates γ for a battery.
-The material is different from the high-density type such as manganese dioxide having a large specific surface area. Therefore, when represented by the general formula MnOy, in many cases, 1.8 <y <2.0.
And MnO ₂ is not necessarily obtained. The composition of the activated manganese dioxide has a nitrogen adsorption specific surface area (BET) of 50 m ² / g or more, preferably 200 m ² / g or more.
Those having a size of up to 1000 m ² / g are preferably used.

In the present invention, the above-mentioned activated manganese dioxide having copper supported thereon is preferably used. The supported amount of copper is in the range of 0.9 to 9.0, preferably 1.5 to 7.5 in terms of Mn / Cu molar ratio.

Copper may be copper alone or a copper compound, and examples of the copper compound include oxides.

The method of supporting copper on activated manganese dioxide is an impregnation method in which active manganese dioxide is impregnated with an aqueous solution of cupric salt and dried to carry the solution. Active manganese dioxide is added to the aqueous solution of cupric salt and stirred. A coprecipitation method in which an alkali aqueous solution is added to the mixture, and a heat treatment is carried out to support the mixture, and a co-precipitation method in which an alkali solution containing an oxidizing agent and a permanganate is added to a mixed solution of a soluble salt of manganese and copper and coprecipitated. For example, a method described in JP-A-5-12981 may be used.

The oxidation catalyst of the present invention comprises, as other components of the active manganese dioxide, an apparent density of 0.2 g / ml or more, preferably 0.3 to ² g / ml, and a BET specific surface area of 50 m ² / g or more. , Preferably 200 to 1000 m ²
/ G, the amount of water adsorbed at 50% relative humidity is 10 g /
100 g (25 ° C.) or more, preferably 15 g / 100 g
It is an important requirement to use activated zeolite and / or activated alumina having the above properties.

Here, the activated zeolite means that the zeolite is calcined at 200 ° C. or more, preferably at 400 ° C.
This shows that the water in the zeolite crystal was activated until it was substantially absent.

Examples of the active zeolite include alkali metal A zeolite such as sodium A zeolite and potassium A zeolite, alkaline earth metal A zeolite such as calcium A zeolite, sodium P zeolite, and the like.
Alkaline metal P-type zeolite such as potassium P-type zeolite, alkaline earth metal P such as calcium P-type zeolite
Zeolite, sodium Y zeolite, potassium Y
Alkali metal Y zeolite such as zeolite, alkaline earth metal Y zeolite such as calcium Y zeolite, alkali metal X zeolite such as sodium X zeolite and potassium X zeolite, alkaline earth such as calcium X zeolite Metal X-type zeolite and the like can be mentioned.

As the activated alumina, alumina having a structure close to the spinel structure of ρ, χ, γ, η, and δ is cited due to the difference in crystal structure. These active zeolites and activated alumina are used alone or in combination of two or more.

Activated zeolite and activated alumina are components for making the oxidation reaction of activated manganese dioxide more efficient. That is, it selectively adsorbs moisture in the exhaust gas, generates heat, and efficiently stores the heat resulting from the heat generation to enhance the reaction activity of the active manganese dioxide.

The reason why the apparent density is limited to 0.2 g / ml or more is that if the apparent density is less than 0.2 g / ml, heat is easily released, and the catalytic activity of active manganese dioxide tends to be inferior. . In the present invention, the apparent density is determined by the following equation by a static method based on the method described in JIS-K-5101.

[0022]

## EQU1 ## Apparent density (g / ml) = F / V (where F: mass (g) of the processed sample in the receiver, V;
Indicates the capacity (ml) of the receiver. )

The amount of adsorbed water is determined by measuring the weight W ₂ (g) after heating and exhausting the sample at 400 ° C. for 1 hour in advance and then introducing water vapor adjusted to a relative humidity of 50% at 25 ° C. to adsorb the water. The measured weight W ₁ (g) was measured, and the weight difference [W ₁ (g) −W ₂ (g)] at that time was used to determine the amount of water adsorbed per 100 g of the sample by the formula [W ₁ (g) −W ₂ (g )] ÷ [W ₁ (g)
/ 100 (g)].

The reason why the amount of water adsorbed at 50% relative humidity is limited to 10 g / 100 g (25 ° C.) is that if the amount of water adsorbed at 50% relative humidity is smaller than 10 g / 100 g, the generated heat of adsorption is efficiently reduced. This is because the reaction activity of the active manganese dioxide tends to be low because it cannot be used.

The reason for limiting the specific surface area to 50 m ² / g or more is that if the specific surface area is less than 50 m ² / g, the water adsorbing ability is inferior, which is not preferable.

Usually, these activated zeolites and activated aluminas are known as carriers of activated manganese dioxide, but in the present invention, these porous inorganic powders are not used as carriers. That is, the method of using as a support, the active manganese dioxide is dispersed on the surface of the active zeolite and the active alumina, held on the surface of the porous inorganic powder, to increase the contact area of the active manganese dioxide to the oxidized gas. Is what you do. On the other hand, the oxidation catalyst for CO and NOx according to the present invention is composed of a mixed powder of activated manganese dioxide, activated zeolite having the above properties and activated alumina, and activated zeolite and activated alumina selectively remove water in exhaust gas. The manganese dioxide absorbs heat and generates heat, and the heat generated by the heat is efficiently stored to increase the reaction activity of the active manganese dioxide. These physical property differences can be confirmed by observation analysis using an electron microscope.

The weight ratio of MnO ₂ to activated zeolite and / or activated alumina can be varied according to the respective physical properties, and in many cases is 1: 2 to 3: 1, preferably 1: 1 to 2 : 1 range. The reason is:
If the ratio is outside the range of 2-3: 1, the oxidizing performance of the active manganese dioxide against the exhaust gas tends to rapidly decrease.

In the method for producing a CO and NOx oxidation catalyst of the present invention, the above two components are blended in a desired ratio, then kneaded with a desired binder, molded and dried to obtain a desired catalyst for oxidation of exhaust gas. It can be used for applications.

Examples of the binder include clay, cement, silica sol, alumina sol, sodium silicate, and a water-soluble polymer. In the present invention, in addition to the above two components, other components such as zeolite and copper oxide supporting copper ions may be blended as required.

Other zeolites supporting copper ions are those in which copper ions are replaced and supported by zeolite cations by utilizing ion exchange of zeolites. Zeolite A, zeolite L, Zeolite X, zeolite Y, zeolite P, clinoptilolite, mordenite and the like can be mentioned, but zeolite A is most preferably used in terms of performance and cost. The copper ion is usually Cu ²⁺ , but may be a complex ion. The supported amount of copper ions is
Although not particularly limited, it is desirable that the amount is at least 30% or more based on the amount of cation exchange of the zeolite.

Examples of the copper oxide include copper oxide, cuprous oxide, copper hydroxide, and basic copper oxide.

The exhaust gas targeted by the present invention is discharged from a nitric acid production plant, a metal surface treatment plant, a plant having a metal melting process, etc., a road tunnel, a road with a shelter, a deep underground space, a road intersection, and the like. Low-grade oxides such as CO and NO emitted from ventilation equipment, air or fuel equipment used at home.

The concentration of lower oxides such as CO and NO in the exhaust gas applicable to the oxidation catalyst of the present invention varies depending on the source of the exhaust gas.
0 ppm, preferably about 10 to 500 ppm.

It should be noted that NOx in the present invention means that x is 1
/ 2 to 5/2, for example, N 2_TwoO,
NO, N _TwoO_Three, N _TwoO_Four, N _TwoO_FiveAnd the like.

The set temperature of the oxidation catalyst according to the present invention is usually 30 to 100 ° C., preferably 60 to 100 ° C. The contact time varies depending on the composition of the catalyst used, but is usually 0.036 to 3.6 seconds, preferably 0.072 to 0.3.
It can be as short as 72 seconds. The oxide oxidatively decomposed under the above conditions may be adsorbed on an adsorbent such as activated carbon or zeolite, or may be dissolved in an aqueous alkaline solution.

Although the oxidation mechanism of the oxidation catalyst for CO and NOx of the present invention is not clear, the strong oxidation of copper-supported activated manganese dioxide and the selective adsorption of water from activated zeolite and / or activated alumina are considered. It generates heat and uses the heat as a heat source to effectively promote the oxidizing action of the active manganese dioxide carrying copper, and relatively reduces low-grade oxides such as CO and NO in the exhaust gas. It is considered that oxidation occurs efficiently even at low temperatures.

[0037]

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

Examples 1-2 Cu adjusted by the method described in JP-A-5-12981
Nitrogen adsorption specific surface area containing 21.2% by weight of O (BE
T) To 100 parts by weight of activated manganese dioxide of 268 m ² / g, an activated alumina having the properties shown in Table 1 was added in the amount shown in Table 1, then 5 parts by weight of bentonite was added and kneaded. Dry and pellet (3m diameter
m, 4-8 mm long columnar shape).

Examples 3 and 4 Cu prepared by the method described in JP-A-5-12981
Nitrogen adsorption specific surface area containing 21.2% by weight of O (BT)
E) To 100 parts by weight of activated manganese dioxide of 268 m ² / g, sodium A-type zeolite having the properties shown in Table 1 (zeolite A) was added in the amount shown in Table 1, and then 5 parts by weight of bentonite was added and kneaded. After extrusion molding, the pellets were dried to obtain pellets.

Comparative Example 1 Cu prepared by the method described in JP-A-5-12981
Nitrogen adsorption specific surface area containing 22.8% by weight of O (BE
T) 5 parts by weight of bentonite was added to 100 parts by weight of 268 m ² / g active manganese dioxide, kneaded, extruded, and dried to obtain pellets.

[0041]

[Table 1]

<CO Gas Oxidation Test> A column having a diameter of 25 mm and a length of 30 mm was filled with the samples obtained in Examples 1 to 5 and Comparative Example 1 by 126 mm. Next, the high-concentration standard gas was diluted with an atmosphere adjusted to a humidity of 50% to obtain 30 ppm CO2.
It was gaseous and flowed into the column. Column inlet,
The CO concentration at the outlet was measured to determine the oxidation rate of the CO gas, and the results are shown in FIG.

Table 2 summarizes the measurement conditions.

[0044]

[Table 2]

<NO gas oxidation test> The NO gas oxidation test was evaluated by the following two methods. NO gas oxidation test-1 A column having a diameter of 25 mm and a length of 30 mm was filled with 126 mm of each sample obtained in Examples 1 to 5 and Comparative Example 1. Next, the high-concentration standard gas was diluted with air adjusted to a humidity of 50% to obtain 30 ppm NO gas, which was introduced into the column. The NO concentration at the inlet and outlet of the column was measured to determine the NO gas oxidation rate, and the results are shown in FIG. Table 3 summarizes the measurement conditions.

[0046]

[Table 3]

NO Gas Oxidation Test-2 Each of the samples obtained in Examples 1 to 5 and Comparative Example 1 was filled with 126 mm into a column having a diameter of 25 mm and a length of 30 mm around which a ribbon heater was wound, and then maintained at 100 ° C. Then
The high-concentration standard gas was diluted with air adjusted to a humidity of 50% to obtain a 30 ppm NO gas, which was introduced into a column maintained at 100 ° C. The NO concentration at the inlet and outlet of the column was measured to determine the oxidation rate of NO gas. The result is shown in FIG. Table 4 summarizes the measurement conditions.

[0048]

[Table 4]

[0049]

As described above, according to the oxidation catalyst for CO and NOx of the present invention, even at a low temperature range of 100 ° C. or lower, harmful lower oxides such as nitrogen monoxide and carbon monoxide can be efficiently produced. Since it can be oxidized well, its utility as a decomposer for nitric oxide and carbon monoxide is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of a CO gas oxidation test in an example of the present invention.

FIG. 2 is an NO gas oxidation test in an example of the present invention-1.
FIG. 5 is a view showing the results of a NO gas oxidation test by using FIG.

FIG. 3 is a NO gas oxidation test in an example of the present invention-2.
FIG. 5 is a view showing the results of a NO gas oxidation test by using FIG.

Claims (2)

[Claims] 1. An active manganese dioxide supporting copper, having an apparent density of 0.2 g / ml or more and a BET specific surface area of 50 g / ml.
The active ingredient is a mixed powder with active zeolite and / or active alumina having a property of not less than m ² / g and a water adsorption amount at a relative humidity of 50% of not less than 10 g / 100 g (25 ° C.). CO and NOx oxidation catalyst. 2. The oxidation catalyst for CO and NOx according to claim 1, wherein the composition ratio of the activated manganese dioxide supporting copper and the activated zeolite and / or activated alumina is 1: 2 to 3: 1 as a weight ratio. .