JPH09313941A - Oxide catalyst material for removing nitrogen oxide and removal of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide catalyst material having high NOx reductive decomposition action within a range up to a low temp. range even if the value of a catalyst amt. (W/F) of the flow velocity of reactive gas is high in the presence of steam or under a high oxygen concn. range and purifying exhaust gas of an internal combustion engine of every kind conversed in energy and resources and preventing global warming or NOx -containing harmful substance. SOLUTION: A nitrogen oxide removing oxide catalyst is produced by adding 5-75wt.% of CeO2 having 0.1-20wt.% of Ga supported thereon to a spinnel type crystalline composite oxide containing Ni and Ga as main metal elements and brought into contact with exhaust gas containing a nitrogen oxide in an oxidizing atmosphere containing a sulfur oxide, highly conc. oxygen and a hydrocarbon being reducing gas to reductively decompose and remove a nitrogen oxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 sulfur oxides by using the same. Which has a low exhaust gas temperature and is suitable for purifying exhaust gas of automobiles such as diesel engines containing sulfur oxides and suitable for removing nitrogen oxides, and sulfur at low temperature using the oxide catalyst material. The present invention relates to a method for removing nitrogen oxides in exhaust gas containing oxides.

[0002]

2. Description of the Related Art In recent years, air pollution caused by various pollutants has become a major social problem, and among them, NOx and C contained in exhaust gas of automobiles, which are sources of migration of air pollution.
There is an urgent need to develop a method for decomposing and removing harmful substances such as Ox.

Conventionally, NOx in exhaust gas of automobiles,
As a method for decomposing and removing toxic substances such as COx, a three-way catalyst that simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (Cx Hy) and reduces nitrogen oxides (NOx) has been widely used. .

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 drawbacks, the oxygen concentration in the exhaust gas is measured, and CO, Cx Hy and NOx are constantly measured.
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 the generation mechanisms of O, Cx Hy, and NOx have contradictory characteristics, it is necessary to maintain combustion in a limited state, and exhaust gas purification in high oxygen concentration as described above is almost complete. The current situation is that there are none.

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 carrying a metal, a metal silicate, an alumina catalyst, etc. have been proposed (see JP-A-4-349938).

[0008]

However, light oil used as fuel for diesel engines contains sulfur oxides, and the exhaust gas thereof contains the sulfur (S).
SO ₂ generated by the combustion of the SO ₂ is contained, and the SO ₂ is further oxidized by the catalyst metal in an oxygen excess atmosphere,
₃ , which impedes the adsorption of NOx, Cx Hy, and O ₂ necessary for decomposing and removing the harmful substances discharged from the diesel engine by adsorbing on the surface of the catalytic metal, and so-called catalyst metal sulfur coating. There is a problem that poisoning is caused, and as a result, the ability to decompose and remove harmful substances is reduced.

On the other hand, as an automobile exhaust gas purifying catalyst, since the heat resistance is excellent and the actual automobile exhaust gas temperature is 200 to 350 ° C., the operating temperature range where the NOx removal rate shows the maximum is conventional. Even lower temperature 300 ~
There is a demand for a catalyst material that can be used near 350 ° C, and there is a problem that effective NOx purification is difficult as it is.

[0010]

An object of the present invention is to provide an exhaust gas having a high oxygen concentration containing water and containing sulfur oxide, which is used in various automobile engines such as a diesel engine, at a high flow rate of the exhaust gas. Even in the low temperature range around 300 ° C, the NOx reduction decomposition effect is high, and N in exhaust gas is effectively
The present invention provides a catalyst material capable of purifying Ox and a method for removing nitrogen oxides using the same.

[0011]

Means for Solving the Problems The present invention has been made in view of the above problems, and GaO-supported CeO ₂ was added to a spinel type crystalline complex oxide containing Ni and Ga as main metal elements. The catalyst material has a high catalytic activity for a long period of time even in an atmosphere containing a high oxygen concentration and sulfur oxides, and exhibits a high NOx reductive decomposition action even at a low temperature of 300 ° C. to effectively purify NOx in exhaust gas. I found that I could do it.

That is, the oxide catalyst material for removing nitrogen oxides according to the present invention is a crystalline composite oxide having a spinel type structure containing Ni and Ga as main metal elements.
This is a catalyst material obtained by adding CeO ₂ carrying 0.1 to 20% by weight of a to the spinel type crystalline composite oxide in an amount of 5 to 75% by weight.

Particularly, Ce carrying 1 to 10% by weight of Ga is used.
O ₂ is added to the spinel type crystalline complex oxide in an amount of 10 to 5
It is more preferable to use an oxide catalyst material added with 0% by weight, and especially CeO loaded with 2 to 5% by weight of Ga.
₂ to 20 to 40 based on the spinel type crystalline complex oxide
Most preferred is an oxide catalyst material added in weight percent.

Further, the method for removing nitrogen oxides of the present invention contains nickel (Ni) and gallium (Ga) as main metal elements in an oxidizing atmosphere in which a high concentration of oxygen and a carbon-containing gas having a reducing property are present. To a composite oxide whose crystal phase has a spinel type structure, added with CeO ₂ carrying 0.1 to 20% by weight of Ga in an amount of 5 to 75% by weight based on the spinel type crystalline composite oxide. And an exhaust gas containing nitrogen oxides are brought into contact with each other.

Among them, CeO ₂ loaded with 1 to 10% by weight of Ga is added to the spinel type crystalline complex oxide in an amount of 10%.
It is more preferable to use an oxide catalyst material added with ˜50% by weight, especially CeO ₂ loaded with 2 to 5% by weight of Ga.
It is most preferable to use an oxide catalyst material obtained by adding 20 to 40% by weight to the spinel type crystalline composite oxide.

In the present invention, as the oxide catalyst material for removing nitrogen oxides, firstly, Ga supported on CeO ₂ is less than 0.
When it is less than 1% by weight, it does not contribute to the improvement of the catalytic activity in the vicinity of 300 ° C. On the contrary, when it exceeds 20% by weight, the catalytic activity in the low temperature range is lowered, so that the loading of Ga The amount is specified to be 0.1 to 20% by weight, particularly 1 to 10% by weight is preferable from the viewpoint that the activity reduction due to sulfur oxide is small, and 2 to 5 from the viewpoint that the maximum value of NO removal rate is high. Weight percent indicates the most desirable trend.

Moreover, Ce carrying the predetermined amount of Ga
When the amount of O ₂ is less than 5% by weight, even if the amount of loaded Ga is a predetermined amount, the effect of improving the catalytic activity does not appear at around 300 ° C. On the contrary, when it exceeds 75% by weight. Even if it is the same as the above, the catalyst activity will decrease, so that the amount is specified to be 5 to 75% by weight, and particularly 10 to 50% by weight is preferable in terms of the activation temperature range, and the maximum NO removal rate is further increased. From the viewpoint of value, 20 to 40% by weight is most desirable.

When the spinel type crystalline complex oxide is brought into contact with exhaust gas containing NOx, even if the oxygen concentration in the exhaust gas is as high as 3% or more, It has excellent NOx reduction performance over a wide temperature range even in an atmosphere containing water vapor and sulfur oxides.

Further, in the exhaust gas atmosphere, hydrocarbons such as C ₂ H ₄ , C ₃ H ₆ and C ₃ H ₈ as a reducing agent, CH
Sulfur oxides can be obtained by mixing an alcohol such as ₃ OH and C ₂ H ₅ OH, a carbon-containing gas having a reducing property such as CO and the like and bringing the composite oxide into contact with a catalyst material to which CeO ₂ is added. Can effectively prevent poisoning by NOx
The reduction performance is even higher.

The composite oxide contains Ni and Ga as main metal elements, and the Ga / Ni atomic ratio n is
A spinel crystalline composite oxide consisting of the ratio of _{2.5~3.3, NiGa n O 4 + z} ( where, n = 2.5 to
It is represented by the general formula of 3.5), and (O _{4 + z} ) in the above formula is an oxygen amount necessary for stable existence as a complex oxide, and the oxygen amount is n 0.2 depending on the value
It changes from time to time within the following range.

The composite oxide used in the present invention comprises:
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.

[0022]

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 of the present invention is a spinel type crystalline complex oxide containing Ni and Ga as metal elements. Is added with 5 to 75% by weight of CeO ₂ supporting 0.1 to 20% by weight of Ga, and when the catalyst material is brought into contact with exhaust gas containing sulfur oxide, Ga is SO ₂ Since the adsorption capacity is small, it is difficult to generate highly poisoned SO ₃ , and the SO ₂ adsorbed on the catalyst surface is easily desorbed from the Ga to prevent poisoning.

On the other hand, although CeO ₂ itself does not exhibit NOx reduction decomposition ability, the added CeO ₂ oxidizes NO to promote the production of NO ₂ , and Ni-Ga, which has a higher reduction activity for NO ₂ than NO, is higher. Ni-G
The NOx reductive decomposition activity is improved in the low temperature range as compared with the case where the catalyst a is used alone.

Further, by supporting the above-mentioned Ga, the amount of adsorbed oxygen increases, the oxidation of NO to NO ₂ is further promoted, and the catalytic activity in the low temperature range is improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the oxide catalyst material for removing nitrogen oxides and the method for removing nitrogen oxides of the present invention will be described in detail based on 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 converting a raw material powder containing Ni and Ga into G
After weighing so that the atomic ratio n of a / Ni is 2.5 to 3.3 and thoroughly stirring and mixing, 500 to 500 in an oxidizing atmosphere.
By performing heat treatment at a temperature of 1600 ° C. for 5 to 30 hours, it is possible to obtain a composite oxide powder containing a spinel type crystal containing Ni and Ga as metal elements as a main crystal phase.

As the raw material powder, for example, oxides of Ni and Ga, and their carbonates, nitrates, acetates and the like which generate oxides by heat treatment can be used.

In addition to the above, the composite oxide can also be synthesized by a solid-phase reaction method using an oxide or another metal salt, a sol-gel method using a metal alkoxide or the like, and is not limited to these production methods. It is not something that will be done.

In any of the above-mentioned manufacturing methods, when the heat treatment temperature is lower than 500 ° C., crystallization becomes insufficient, and when the heat treatment temperature exceeds 1600 ° C., densification occurs. 5 in the atmosphere
Although the heat treatment is performed for 30 hours, heat treatment at a particularly low temperature is effective in 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 complex oxide powder at the time of adding CeO ₂ preferably has a high specific surface area from the viewpoint of ensuring a contact area with exhaust gas and effectively decomposing and removing nitrogen oxides. , Its specific surface area is 30 to 120 m ² /
It is preferably g, particularly 40 to 90 m ² / g.

Then, an aqueous solution containing Ga as the above-mentioned CeO ₂ was added and evaporated to dryness.
The heat treatment is performed at a temperature of 700 ° C. for 1 to 5 hours to obtain the GaO-supported CeO _{2 of} the present invention.

Then, the CeO ₂ loaded with Ga is replaced with N
An oxide catalyst material is produced by adding a spinel type crystal containing i and Ga to a composite oxide powder having a main crystal phase.

As a method of adding the CeO ₂ loaded with Ga, there is a method of pulverizing and mixing the CeO ₂ powder and the complex oxide powder in a ball mill or a mortar. In the present invention, any of these mixing methods can be used. It is not limited.

[0034]

Next, the present invention was evaluated as described in detail below.

First, as a starting material, Ni (NO ₃ ) ₂ ·
6H ₂ O, and Ga (NO ₃₎ with reagents ₂ · 9H ₂ O, metal ratio of Ni and Ga were weighed to be 1: 3,
These reagents were dissolved in distilled water and neutralized with aqueous ammonia while stirring. At this time, the formed precipitate was filtered, washed and freeze-dried.

The dry powder thus obtained was dried in air at 700
Heat treatment at a temperature of 30 ° C. for 30 hours to have a specific surface area of 40 to 50
A spinel-type crystalline composite oxide powder of m ² / g was obtained.

Next, CeO ₂ having a specific surface area of 70 m ² / g.
After adding an aqueous solution containing Ga in the amount shown in Table 1 and evaporating to dryness, the mixture was heated to 500 in a helium (He) gas atmosphere.
By heat-treating at a temperature of ° C for 3 hours, GaO-supported CeO ₂ was obtained.

Then, the spinel type crystalline complex oxide
With respect to the above-mentioned Ga-loaded CeO _TwoThe powder is shown in Table 1.
After adding and mixing in a ratio, the mixed powder is pressed by a die press.
After molding and further compression by cold isostatic pressing,
Shaped material is crushed and sieved to exceed 500 μm, 700 μm
The particles were sized below to prepare an evaluation sample.

The catalytic activity of the CeO ₂ -added spinel type crystalline complex oxide catalyst which does not support Ga and the spinel type crystalline complex oxide catalyst alone was used as a comparative example.

A crystal phase was identified by X-ray diffraction measurement (XRD) using each powder of the evaluation sample thus obtained, and it was confirmed that the crystal phase consisted of spinel crystal and CeO ₂ crystal phase.

Next, NO is 100 as simulated exhaust gas.
0 ppm, O ₂ is 10%, C ₃ H ₆ is 666 ppm, S
O ₂ is 50 ppm, the reaction gas balance being He, as a condition for the reaction gas and the catalyst material is in contact, a space velocity (SV) 20000 / hr. Was set, and the sample for evaluation was flown through the catalyst layer and the N ₂ gas produced by passing through the catalyst layer in the temperature range of 300 to 500 ° C. was measured by a gas chromatograph.

As for the NO reduction resolution of the catalyst, the value twice the N ₂ concentration (ppm) on the catalyst layer outlet side is the NO on the catalyst layer inlet side.
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, it was found that the measured temperature range was 40%.
Those showing a wide range of NO reduction activity in the low temperature range of 0 ° C or lower were evaluated as good.

[0044]

[Table 1]

As is clear from the table, the sample Nos. 1 and 24, which are comparative examples, have significantly low NO reduction activity at temperatures of 300 ° C. and 400 ° C. or lower, respectively, and are outside the scope of the claims of the present invention. , 11, 15, 23, 25,
It is understood that all of 32, 33, 41, 42 and 47 have low NO reduction activity in a predetermined temperature range and are not practical.

On the other hand, in the present invention, it is 300 to 450.
It can be seen that sufficient NO reduction activity is exhibited in a wide temperature range of ° C, and poisoning deterioration due to sulfur oxides is prevented.

Further, even after continuously reacting at a temperature of 350 ° C. for 100 hours in contact with the reaction gas, no significant change was observed in the above-mentioned various properties.

[0048]

As described above in detail, 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). For removing nitrogen oxides, characterized in that 5 to 75% by weight of CeO ₂ supporting 0.1 to 20% by weight of gallium (Ga) is added to a spinel type crystalline composite oxide containing as a main metal element. Is an oxide catalyst material,
Since the oxide catalyst material and the exhaust gas containing nitrogen oxide are brought into contact with each other in an oxidizing atmosphere in which sulfur oxide, a high concentration of oxygen and a carbon-containing gas having a reducing property are present, sulfur oxide and water vapor are present. Not only in the atmosphere but also in an atmosphere with a high oxygen concentration of 3% or more in the exhaust gas,
Moreover, even if the gas flow rate is high, excellent NOx
It has a reducing performance and can effectively reduce and remove NOx contained in the exhaust gas.

As a result, in purifying exhaust gases from various internal combustion engines such as diesel engines and lean burn engines, which are developed for the purpose of energy saving, resource saving and prevention of global warming, and various harmful substances containing NOx. It will be extremely useful.

Claims (6)

[Claims] 1. A cerium oxide (CeO ₂ ) in which 0.1 to 20% by weight of gallium (Ga) is supported on a spinel type crystalline composite oxide containing nickel (Ni) and gallium (Ga) as main metal elements. Is added to the spinel type crystalline complex oxide in an amount of 5 to 75% by weight. 2. The oxide catalyst for removing nitrogen oxides according to claim 1, wherein the cerium oxide (CeO ₂ ) is added in an amount of 10 to 50% by weight based on the spinel type crystalline composite oxide. material. 3. The oxide catalyst for removing nitrogen oxides according to claim 1, wherein the cerium oxide (CeO ₂ ) is added in an amount of 20 to 40% by weight with respect to the spinel type crystalline composite oxide. material. 4. Nickel (Ni) and gallium (G) in an oxidizing atmosphere in which a carbon-containing gas having a reducing property with oxygen is present.
0.1 to 20% by weight of gallium (Ga) in a spinel type crystalline composite oxide containing a) as a main metal element.
An oxide catalyst material for removing nitrogen oxides, which is obtained by adding 5 to 75% by weight of the supported cerium oxide (CeO ₂ ) to the spinel type crystalline complex oxide, and exhaust gas containing nitrogen oxides are contacted with each other. A method for removing nitrogen oxides, which comprises: 5. An oxide catalyst material for removing nitrogen oxides, comprising 10 to 50% by weight of cerium oxide (CeO ₂ ) added to a spinel type crystalline complex oxide, and an exhaust gas containing nitrogen oxides. 5. Contacting with
The method for removing nitrogen oxides described. 6. An oxide catalyst material for removing nitrogen oxides, comprising 20 to 40% by weight of cerium oxide (CeO ₂ ) added to a spinel type crystalline complex oxide, and exhaust gas containing nitrogen oxides. 5. Contacting with
The method for removing nitrogen oxides described.