JPH09141103A - Oxide catalyst material for removing nitrogen oxide and removal of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent such a phenomenon that SO2 formed by the combustion of fuel for a diesel engine is further oxidized to become SO3 and this SO3 is absorbed on the surface of a catalyst metal to prohibit the adsorption of NOx or CxHy and O2 and the catalytic metal generates the poisoning deterioration caused by sulfur to lower the decomposing and removing capacity of harmful substances in exhaust gas of a car. SOLUTION: CeO2 wherein 0.1-20wt.% of Sn is supported on spinnel type crystalline composite oxide containing Ni and Ga as main metal elements is added to spinnel type composite oxide in an amt. of 5-7wt.% to obtain an oxide catalyst material for removing nitrogen oxides. This oxide catalyst material is brought into contact with exhaust gas containing nitrogen oxides in an oxidizing atmosphere in which sulfur oxide, highly conc. oxygen and hydrocarbons being reductive gas are present to reduce, decompose and remove nitrogen oxides.

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 of decomposing and removing harmful substances such as COx, a three-way catalyst that simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (CxHy) 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, CxHy 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, CxHy, and NOx have contradictory characteristics, it is necessary to maintain combustion in a limited state, and exhaust gas purification in the high oxygen concentration as described above is hardly achieved. is the current situation.

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 or the like has been proposed (see Japanese Patent Laid-Open No. 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 adsorbs NOx, CxHy, and O ₂ necessary for decomposing and removing the harmful substances exhausted from the diesel engine by adsorbing on the surface of the catalyst metal, so-called poisoning of the catalyst metal by sulfur. There is a problem that deterioration 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 is the maximum is the conventional one. Even lower temperature 300 ~
A catalyst material that can be used even at around 350 ° C. is required, and there is a problem that effective NOx purification is difficult as it is.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas having a high oxygen concentration containing water and containing sulfur oxides, such as diesel engines and various automobile engines, with a high flow velocity of the exhaust gas. Also shows a high NOx reduction decomposition action in the low temperature range around 300 ° C., and effectively reduces N in exhaust gas.
The present invention provides a catalyst material capable of purifying Ox and a nitrogen oxide removing method using the same.

[0011]

Means for Solving the Problems The present invention has been made in view of the above problems, and CeO ₂ supporting Sn was added to a spinel type crystalline composite oxide containing Ni and Ga as main metal elements. The catalyst material has a high catalytic activity for a long time even in an atmosphere containing a high oxygen concentration and sulfur oxides, and exhibits a high NOx reduction 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 of the present invention is a composite oxide having a spinel type structure containing Ni and Ga as main metal elements, and Sn.
It is a catalyst material obtained by adding 5 to 75% by weight of CeO ₂ supported by 1 to 20% by weight.

In particular, Ce carrying 1 to 10% by weight of Sn is used.
It is more preferable to use an oxide catalyst material in which O ₂ is added to the spinel-type composite oxide in an amount of 10 to 50 wt%, and particularly, CeO ₂ carrying 2 to 5 wt% of Sn is added to the spinel-type composite oxide in an amount of 20 to 20 wt%. Most preferred is an oxide catalyst material added at 40% by weight.

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. The catalyst material formed by adding 5 to 75% by weight of CeO ₂ supporting 0.1 to 20% by weight of Sn to a composite oxide whose crystal phase is a spinel structure is contacted with exhaust gas containing nitrogen oxides. It is characterized by that.

Above all, Sn is used as the oxide catalyst.
It is more preferable to use a material obtained by adding 10 to 50% by weight of CeO ₂ supported on the spinel type composite oxide, and in particular, CeO 2 supporting 2 to 5% by weight of Sn.
It is most preferable to use a material obtained by adding 20 to 40% by weight of ₂ to the spinel type composite oxide.

In the present invention, when the amount of Sn supported on CeO ₂ is less than 0.1% by weight as the oxide catalyst material for removing nitrogen oxides, it does not contribute to the improvement of the catalytic activity at around 300 ° C. On the other hand, when the content exceeds 20% by weight, the catalytic activity in the low temperature range decreases, so that the supported amount of Sn is 0.
It is specified to be 1 to 20% by weight, particularly preferably 1 to 10% by weight from the viewpoint that the activity decrease due to sulfur oxide is small, and 2 from the viewpoint that the maximum value of NO removal rate is high.
~ 5% by weight shows the most desirable tendency.

Further, when the amount of CeO ₂ loaded with Sn is less than 5%, the catalytic activity improving effect at around 300 ° C. does not appear even if the loaded amount of Sn loaded is a predetermined amount. On the contrary, if the amount exceeds 75% by weight, the catalytic activity will be reduced even if it is similar to the above, so the amount is 5 to 75%.
% By weight, and particularly 10 to 10 in terms of the activation temperature range.
50% by weight is preferable, and 20 to 40% by weight is the most desirable from the viewpoint of the maximum value of NO removal rate.

The spinel type composite oxide is NO
By contacting with the exhaust gas containing x, even if the oxygen concentration contained in the exhaust gas is a high concentration of 3% or more, and in addition, in an atmosphere in which water vapor and sulfur oxides are present, It has excellent NOx reduction performance in a wide temperature range.

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 composite oxide consisting of the ratio of _{2.5~3.3, NiGa n O 4 + z} ( where, n = 2.5 to 3.5)
Wherein (O _{4 + z} ) in the above formula
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 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. In addition, since CeO ₂ supporting 1 to 20% by weight of Sn was added to the spinel type crystalline composite oxide in an amount of 5 to 75% by weight, the catalyst material was added to the exhaust gas containing sulfur oxide. When contacted, Sn is S
Since the oxidizing ability of O ₂ is small, it is difficult to generate SO ₃ which is highly toxic, and because the adsorption power is small, SO ₂ adsorbed on the catalyst surface is easily desorbed from the Sn to prevent poisoning. To work.

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

Furthermore, by supporting the transition metal, 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, a composite oxide powder containing a spinel type crystal containing Ni and Ga as a metal element as a main crystal phase can be obtained.

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.

Next, an aqueous solution containing CeO ₂ as a carrier and containing a predetermined amount of Sn was added and evaporated to dryness.
The CeO ₂ carrying Sn of the present invention is obtained by heat treatment at a temperature of 00 to 700 ° C. for 1 to 5 hours.

Then, CeO ₂ loaded with Sn is replaced with N
A predetermined amount is added to a composite oxide powder containing i and Ga as the main crystal phase of a spinel type crystal to prepare an oxide catalyst material.

As a method of adding the CeO ₂ supporting Sn, 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.
In addition, S, which is a supporting element, is provided so as to have the respective supporting amounts shown in Table 1.
After adding an aqueous solution containing n and evaporating to dryness, heat treatment was performed in a helium (He) gas atmosphere at a temperature of 500 ° C. for 3 hours to obtain SnO-supported CeO ₂ .

Thereafter, the CeO ₂ powder supporting Sn on the spinel type composite oxide was added and mixed at a ratio shown in Table 1, the mixed powder was molded by a die press, and further cold isostatic pressure was applied. After being compressed by a molding method, the molded product was disintegrated, sieved, and sized to exceed 500 μm and 700 μm or less to prepare an evaluation sample.

It should be noted that CeO which does not support the transition metal at all
The catalytic activity of the _2- added spinel-type mixed oxide catalyst and the spinel-type mixed oxide catalyst alone was set 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, H ₂ O is 10%, and the balance is He, and the space velocity (SV) is 100,000 / hr. And flowed in the catalyst layer filled with the evaluation sample,
The N ₂ gas produced by passing through the catalyst layer in the temperature range of 500 ° C. was measured by gas chromatography.

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 can be seen from the table, the sample Nos. 1 and 24, which are comparative examples, have extremely low NO reduction activity at temperatures of 350 ° C. and 400 ° C. or less, 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.

The evaluation samples of the present invention all have SV values of 300,000 / hr. Until the oxygen concentration is 15
%, There is no significant decrease in the above properties, while 350 ° C
Even after 100 hours of continuous contact with the reaction gas for reaction at the above temperature, no significant change was observed in the above-mentioned various properties.

Further, the evaluation sample was attached to the exhaust pipe of a four-cylinder diesel engine bench test apparatus, and a durability test was conducted in which the diesel engine was operated for 100 hours under conditions of maximum rotation speed and full load. The NO reduction activity of the sample for evaluation was evaluated in the same manner as described above, but it was confirmed that the NO removal rate was hardly reduced, and poisoning deterioration due to sulfur contained in the diesel engine fuel could be effectively prevented. It was also proved to be excellent in water resistance and heat resistance.

[0049]

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). CeO ₂ supporting 0.1 to 20 wt% of Sn is added to the spinel type crystalline complex oxide contained as a main metal element, and added to the spinel type crystalline complex oxide in an amount of 5 to 75% by weight. Contacting the exhaust gas containing the oxide catalyst material and nitrogen oxides in an oxidizing atmosphere in which a sulfur-containing oxide and a carbon-containing gas having a reducing property with a high concentration of oxygen are present. From
Not only in an atmosphere in which sulfur oxides and water vapor are present, but also in an atmosphere with a high oxygen concentration of 3% or more in the exhaust gas, and even when the gas flow rate is high, it is excellent. NOx contained in exhaust gas with NOx reduction performance
Can be effectively reduced and removed.

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidemi Matsumoto Inventor Hidemi 1-4 Yamashita-cho, Kokubun-shi, Kagoshima Kyocera Corporation General Research Institute

Claims (6)

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