JPH10180105A - Oxide catalyst material for removing nitrogen oxide and method for removing nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst material which has a high NO reduction- decomposition function in exhaust gas containing alkanes of poor reactivity in the presence of water vapor and in a high oxygen concentration atmosphere and purifies exhaust gas from various internal combustion engines for saving energy and resources and for preventing the global warming and a method for removing nitrogen oxides using the catalyst material. SOLUTION: A catalyst material is prepared by adding 0.5-20.0wt.% of chromium oxide (Ce2 O3 ) to a spinel-type crystalline complex oxide containing Ni and Ga as main metal elements. The catalyst material is contacted with exhaust gas containing nitrogen oxides in an oxidizing atmosphere of a high oxygen concentration containing a hydrocarbon has of alkanes to reduction-remove the nitrogen oxides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel oxide catalyst material capable of reducing and removing nitrogen oxides and a method for removing nitrogen oxides in exhaust gas containing hydrocarbons using the same. In particular, an exhaust gas temperature is low, and an oxide catalyst material for removing nitrogen oxides suitable for purifying automobile exhaust gas such as a diesel engine containing alkane hydrocarbons, and a low temperature using the oxide catalyst material. The present invention relates to a method for removing nitrogen oxides in exhaust gas containing alkane hydrocarbons.

[0002]

2. Description of the Related Art In recent years, contamination of the atmosphere by various pollutants has become a major social problem, and among them, NO _x , C contained in exhaust gas of automobiles, which is a moving source of air pollution.
There is an urgent need to develop a method for decomposing and removing harmful substances such as O _x .

[0003] Conventionally, NO _{x in} exhaust gas of automobiles,
As a method for decomposing and removing harmful substances such as CO _x, a three-way catalyst for simultaneously oxidizing carbon monoxide (CO) and hydrocarbons (C _x H _y ) and reducing nitrogen oxides (NO _x ) is commonly used. It has been.

Examples of the three-way catalyst used in such a method include cordierite in which a noble metal such as palladium (Pd), platinum (Pt), and rhodium (Rh) is coated with γ-alumina (Al ₂ O ₃ ). Supported on a refractory carrier.

However, the three-way catalyst can efficiently purify the exhaust gas at a low oxygen concentration of about 0.5%, but has a high oxygen concentration in the exhaust gas exceeding 1%. There is a disadvantage that it does not work effectively in a concentration atmosphere.

On the other hand, in order to avoid the above-mentioned drawback, the oxygen concentration in the exhaust gas is measured, and CO, C _x H _y , NO _x
Is controlled so as to have an air-fuel ratio in a range close to a stoichiometric equivalent value that can be processed at a high purification rate.
Since O and C _x H _y and NO _x generation mechanisms have contradictory characteristics, combustion in a limited state must be maintained, and exhaust gas purification in a high oxygen concentration as described above. At present, little has been done.

Therefore, even in the presence of such a high concentration of oxygen, NO
_{As a} catalyst capable of efficiently removing _x , a copper ion-exchanged zeolite such as a hydrophobic zeolite supporting a metal, a metal silicate, an alumina catalyst, and the like have been proposed (see JP-A-4-349938).

[0008]

[SUMMARY OF THE INVENTION However, in the exhaust gas such as automobile engine, with the hydrocarbon of the NO _x high reactivity to reduction alkenes, carbonization of relatively low reactivity of alkanes There is a problem that hydrogen is present, and this gas does not effectively act as a reducing agent for the nitrogen oxide reduction removal reaction.

[0009]

An object of the present invention is to provide a useful catalyst material capable of purifying NO _{x in} exhaust gas containing alkanes having a high oxygen concentration containing water, such as diesel engines and various automobile engines. And a method for removing nitrogen oxides using the same.

[0010]

Means for Solving the Problems The present invention has been made in view of the above problems, the spinel crystalline composite oxide containing Ni and Ga as the main metal element, Cr ₂ O ₃
Has been found to be effective for a nitrogen oxide reduction removal reaction using alkanes as a reducing agent.

That is, the oxide catalyst material for removing nitrogen oxides according to the present invention is a spinel-type crystalline composite oxide containing Ni and Ga as main metal elements, containing 0.5% of Cr ₂ O ₃ .
It is a catalyst material obtained by adding about 20.0% by weight.

Further, the method for removing nitrogen oxides according to the present invention provides a method for removing a carbon-containing gas having a high concentration of oxygen and a reducing property, particularly propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), and ethane (C ₂ H
₆ ) In an oxidizing atmosphere where alkanes such as
And a catalyst material formed by adding Cr ₂ O ₃ to an exhaust gas containing nitrogen oxides, and a spinel-type crystalline composite oxide containing Ga and Ga as a metal element.

On the other hand, Cr ₂ O added to the composite oxide
_If the amount of ₃ is less than 0.5% by weight, the effect of improving the catalytic activity will not be exhibited, and if it exceeds 20.0% by weight, the catalytic activity will be reduced. 0% by weight
From the point of the catalyst activation temperature range.
0% by weight is preferable, and from the viewpoint of the maximum activity value of the NO removal rate, 3.0 to 7.0% by weight is most preferable.

Further, the spinel-type crystalline composite oxide is brought into contact with an exhaust gas containing NO _x so that even if the concentration of oxygen contained in the exhaust gas is as high as 3% or more, it is further increased. It has excellent NO _x reduction performance even in the presence of steam of low reactivity alkane even in the presence of steam.

The composite oxide contains Ni and Ga as main metal elements, and has an atomic ratio n of Ga / Ni of 2.
It is a spinel-type crystalline composite oxide having a ratio of 5 to 3.3, and NiGa _n O _{4 + z} (where n = 2.5 to 3.
5) and represented by the general formula (O)
_{4 + z} ) is the amount of oxygen necessary for stable existence as a composite oxide, and the amount of oxygen changes as needed in the range of 0.2 or less depending on the value of n.

The composite oxide used in the present invention is:
If the value of the atomic ratio n of Ga / Ni deviates from the range of 2.5 to 3.3, the catalytic activity is reduced. Therefore, the catalytic activity is specified in the above range.
3.0 is most desirable.

[0017]

According to the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention, the oxide catalyst material comprises N
Since Cr ₂ O ₃ is added to a spinel-type crystalline composite oxide containing i and Ga as metal elements in an amount of 0.5 to 20.0% by weight, Cr ₂ O ₃ itself has a NO _x reduction resolution. Although not shown, the added Cr ₂ O ₃ promotes participation of the alkanes in the NO reduction reaction, and the same NO _x reduction and decomposition characteristics as when the alkenes are used as the reducing agent are obtained.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention will be described below in detail with reference to examples.

First, an example of the method for producing the oxide catalyst material for removing nitrogen oxides of the present invention will be described in detail.

The composite oxide of the present invention is obtained by mixing a raw material powder containing Ni and Ga with an atomic ratio n of Ga / Ni of 2.5 to 2.5.
After being weighed to 3.3 and sufficiently stirred and mixed, it is subjected to a heat treatment at a temperature of 500 to 1600 ° C. for 5 to 30 hours in an oxidizing atmosphere, so that Ni and Ga are used as metal elements.
A composite oxide powder having a spinel-type crystal containing as a main crystal phase is obtained.

Examples of the raw material powder include oxides of Ni and Ga and carbonates thereof that form oxides by heat treatment.
Nitrate, acetate and the like can be used.

The composite oxide can be synthesized by a solid-phase reaction method using an oxide or another metal salt or a sol-gel method such as a metal alkoxide. It is not something to be done.

In any of the above-mentioned manufacturing methods, in any of the heat treatments, if the heat treatment temperature is lower than 500 ° C., the crystallization becomes insufficient, and if the heat treatment temperature exceeds 1600 ° C., the crystallization becomes insufficient. In an oxidizing atmosphere, 5
Heat treatment at a low temperature is effective for increasing the specific surface area of the powder, and practically, it is desirable to set the specific surface area to 35 m ² / g or more.

The above-mentioned composite oxide powder when Cr ₂ O _{3 is} added has a high specific surface area from the viewpoint of securing a contact area with exhaust gas and effectively decomposing and removing nitrogen oxides. It is desirable that the specific surface area is 30 to 120 m
² / g, particularly preferably from 40 to 90 m ² / g.

As the raw material powder of Cr ₂ O ₃ , carbonates, nitrates, acetates and the like which form oxides by heat treatment can be used.
Heat treatment at a temperature of ８００800 ° C. for 1 to 5 hours gives a Cr ₂ O ₃ raw material powder.

The method of adding Cr ₂ O ₃ is as follows.
There is a method of pulverizing and mixing the Cr ₂ O ₃ powder and the composite oxide powder with a ball mill or a mortar, but the present invention is not limited to these mixing methods at all.

[0027]

Next, the present invention was evaluated as described in detail below. First, Ni (NO ₃₎ as the starting material ₂ · 6H
₂ O, and Ga (NO ₃₎ with reagents ₂ · 9H ₂ O,
Weigh so that the metal ratio of Ni and Ga becomes 1: 3, dissolve these reagents in distilled water, neutralize with ammonia water while stirring, and then filter and wash the generated precipitate. Lyophilized.

The dry powder thus obtained is heat-treated in the atmosphere at a temperature of 700 ° C. for 30 hours and has a specific surface area of 40 to
A spinel-type crystalline composite oxide powder of 50 m ² / g was obtained.

Next, Cr ₂ O ₃ powder was added to and mixed with the spinel-type crystalline composite oxide at the ratio shown in Table 1, and the mixed powder was molded by a die press. The sample was crushed, sieved, and sized to exceed 500 μm and 700 μm or less to prepare a sample for evaluation. Incidentally, a comparative example that does not adding Cr ₂ O _3.

A crystal phase was identified by X-ray diffraction measurement (XRD) using each powder of the evaluation sample thus obtained. In each of the evaluation samples according to the present invention, the crystal phases were spinel crystal and Cr ₂ O _3. It was confirmed that it consisted of a crystalline phase. As a typical X-ray diffraction measurement result of the oxide catalyst material for removing nitrogen oxides of the present invention, an X-ray diffraction chart of an evaluation sample of Sample No. 6 shown in Table 1 is shown in FIG.

Next, as the simulated exhaust gas, NO was 1000
ppm, O ₂ is 10%, and propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), ethane (C
_A reaction gas consisting of 666 ppm of any one of ₂ H ₆ ) and the balance of He was used as a condition for contacting the reaction gas with the catalyst material, and a space velocity (SV) of 40000 / hr. And flowed through the catalyst layer filled with the evaluation sample,
N ₂ generated through the catalyst layer in a temperature range of ５550 ° C.
The gas was measured with a gas chromatograph.

The NO reduction ability of the catalyst is determined to be twice the value of the N ₂ concentration (ppm) at the outlet of the catalyst layer, and to the NO reduction at the inlet side of the catalyst layer.
The percentage divided by the concentration (ppm) was taken as the NO removal rate (%), and the NO removal rate at each temperature was determined.

From the results, a sample having an NO reduction activity at 400 ° C. of less than 20% was evaluated as poor, a sample of 20% or more and less than 30% was evaluated as good, and a sample of 30% or more was evaluated as excellent.

[0034]

[Table 1]

As is clear from the table, low-reactivity C ₃ H ₈ , C ₄ H ₁₀ , and C ₂ H ₆ alkanes are used as a reducing agent using only the Ni—Ga spinel type crystalline composite oxide as a catalyst. In Sample Nos. 1, 12, and 20 of the comparative examples used, the NO removal rate at a temperature of 400 ° C. was very low as 7.7% or less, and Sample Nos. Also at 11, 19 and 27, N at a temperature of 400 ° C.
The O removal rate is 19.2% or less.

On the other hand, in the present invention, the NO removal rate at a temperature of 400 ° C. is a maximum of 37.0%, and even when a low-reactivity alkane is used as a reducing agent, Cr ₂ O ₃ is converted to an alkane. It can be seen that the reactivity was improved and participation in the NO reduction reaction was promoted.

[0037]

As described in detail above, according to the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention, the oxide catalyst material contains nickel (Ni) and gallium (Ga). Chromium oxide (Cr ₂ O ₃ ) is added to a spinel-type crystalline composite oxide containing 0.5 to
An oxide catalyst material for removing nitrogen oxides, which is added in an amount of 20.0% by weight. The oxide catalyst material has a high concentration of oxygen and an alkane hydrocarbon gas having a reducing property in an oxidizing atmosphere. effectively reduced from contacting the exhaust gas containing oxide catalyst material and nitrogen oxides, even in an atmosphere that exists water vapor, has excellent _the NO _x reduction performance, the NO _x contained in the exhaust gas Can be removed.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart showing a typical X-ray diffraction measurement result of the oxide catalyst material for removing nitrogen oxides of the present invention.

Claims (6)

[Claims] 1. A spinel-type crystalline composite oxide containing nickel (Ni) and gallium (Ga) as main metal elements, and chromium oxide (Cr ₂ O ₃ ) with respect to the spinel-type crystalline composite oxide. An oxide catalyst material for removing nitrogen oxides, characterized by being added in an amount of 0.5 to 20.0% by weight. 2. A nitrogen oxide according to claim 1, wherein said chromium oxide (Cr ₂ O ₃ ) is added in an amount of 1.0 to 10.0% by weight based on a spinel-type crystalline composite oxide. Oxide catalyst material for material removal. 3. The nitrogen oxide according to claim 1, wherein said chromium oxide (Cr ₂ O ₃ ) is added in an amount of 3.0 to 7.0% by weight based on the spinel-type crystalline composite oxide. Oxide catalyst material for material removal. 4. A spinel-type crystalline composite oxide containing nickel (Ni) and gallium (Ga) as main metal elements in a oxidizing atmosphere in which a carbon-containing gas having oxygen and a reducing property is present. An oxide catalyst material for removing nitrogen oxide, which is obtained by adding 0.5 to 20.0% by weight of (Cr ₂ O ₃ ) to the spinel-type crystalline composite oxide, and an exhaust gas containing nitrogen oxide. A method for removing nitrogen oxides, comprising contacting. 5. An oxide catalyst material for removing nitrogen oxides, wherein said chromium oxide (Cr ₂ O ₃ ) is added in an amount of 1.0 to 10.0% by weight based on a spinel-type crystalline composite oxide; 5. The method for removing nitrogen oxides according to claim 4, wherein the exhaust gas contains an oxide. 6. An oxide catalyst material for removing nitrogen oxides, wherein said chromium oxide (Cr ₂ O ₃ ) is added in an amount of 3.0 to 7.0% by weight based on a spinel-type crystalline composite oxide; 5. The method for removing nitrogen oxides according to claim 4, wherein the exhaust gas contains an oxide.