JPH0985094A - Oxide catalyst material for removing nitrogen oxides and removal of nitrogen oxides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxide catalyst material having a high NOx reduction decomposition effect over an extensive range upto a low temperature zone, in the presence of steam and under an oxygen-rich concentration atmosphere, even if the W/F value is high, and for cleaning an exhaust gas or a noxious substance containing NOx from various types of internal combustion engines for saving energy and natural resources or preventing the global temperatures from rising. SOLUTION: CeO2 in an amount of 5-75wt.% bearing 0.01-5.0wt.% of at least one kind element selected from Pt, Pd, Rh, Ru and Ir is added to a spinel type crystalline composite oxide containing Ni and Ga as main metal elements, as an oxide catalyst material for removing nitrogen oxides. In addition, the nitrogen oxides are decomposed by reduction and removed by bringing the oxide catalyst material into contact with an exhaust gas containing the nitrogen oxides in an oxidation atmosphere in which a highly concentrated oxygen and a reducible gas of hydrocarbons are present.

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 using the same, and more particularly to exhaust gas. The present invention relates to an oxide catalyst material for removing nitrogen oxides suitable for purifying automobile exhaust gas such as diesel engine having a low temperature, and a method for removing nitrogen oxides in exhaust gas at low temperature using the oxide catalyst material. .

[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, the above-mentioned proposed copper ion-exchanged zeolite, metal silicate, alumina catalyst, etc. are all inferior in heat resistance, so that performance deterioration due to structural destruction during long-term operation or SV resistance.
(Space velocity) property is poor, and SV value is 200,000 / hr.
Under the conditions of the actual engine exhaust gas exhibiting the above high speed, there is a problem that the NO reduction resolution is remarkably 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 The present invention relates to an exhaust gas having a high oxygen concentration containing water, such as a diesel engine and various automobile engines, having an SV value of 2000.
00 / hr. A catalyst material that exhibits a high NOx reducing decomposition action in a low temperature range around 300 ° C. even at the above high speed and can effectively purify NOx in exhaust gas, and a nitrogen oxide removing method using the same. It is provided.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a spinel type crystalline composite oxide containing Ni and Ga as main metal elements is added to Pt and P.
The catalytic material added with CeO ₂ carrying at least one selected from noble metals such as d, Rh, Ru and Ir has a high catalytic activity for a long time even in a high oxygen concentration atmosphere,
Moreover, the inventors have found that NOx in exhaust gas can be effectively purified by exhibiting a high NOx reducing decomposition action even at a low temperature of 300 ° C.

That is, the oxide catalyst material for removing nitrogen oxides of the present invention is a composite oxide containing Ni and Ga as main metal elements and having a spinel structure, and is 0.01 to
5.0% by weight of CeO ₂ carrying at least one selected from noble metals such as Pt, Pd, Rh, Ru and Ir is added.
It is a catalyst material formed by adding about 75% by weight.

In particular, it is an oxide catalyst material in which 10 to 50% by weight of CeO ₂ carrying 0.05 to 1.0% by weight of at least one selected from the above noble metals is added to a spinel type composite oxide. More preferably, in particular, CeO ₂ carrying 0.05 to 0.5% by weight of at least one selected from the above noble metals is added to the spinel type composite oxide in an amount of 20 to
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. To the complex oxide whose crystal phase is a spinel structure, and 0.01 to 5.0% by weight of Pt,
It is characterized in that a catalyst material formed by adding 5 to 75% by weight of CeO ₂ carrying at least one kind selected from noble metals such as Pd, Rh, Ru and Ir is brought into contact with exhaust gas containing nitrogen oxides. It is a thing.

Among them, CeO ₂ carrying 0.05 to 1.0% by weight of at least one selected from the above noble metals as the oxide catalyst is added to the spinel type composite oxide in an amount of 10 to 10.
It is more preferable to use 50% by weight of an oxide catalyst material, and in particular, CeO ₂ carrying 0.05 to 0.5% by weight of at least one selected from the above noble metals is added to the spinel type composite oxide in an amount of 20 to 40% by weight. It is most preferable to use the oxide catalyst material added in%.

In the present invention, as the oxide catalyst material for removing nitrogen oxides, first, Pt and P supported on CeO ₂ are used.
When at least one kind of noble metals such as d, Rh, Ru and Ir is less than 0.01% by weight, it does not contribute to the improvement of the catalytic activity in the vicinity of 300 ° C, and conversely exceeds 5.0% by weight. Since the catalytic activity in the low temperature range is reduced,
It is specified to be 01 to 5.0% by weight, particularly preferably 0.05 to 1.0% by weight from the viewpoint that the activation temperature range is wide, and 0.1% from the viewpoint that the maximum value of NO removal rate is high.
05-0.5 wt% shows the most desirable tendency.

Moreover, when the amount of CeO ₂ supporting at least one kind of the above-mentioned predetermined amount of the precious metal is less than 5%, even if the amount of the above-mentioned element carried is the predetermined amount, the catalytic activity at around 300 ° C. On the contrary, if it exceeds 75% by weight, the catalytic activity is lowered even if it is more than 75% by weight. Therefore, the amount is specified to be 5 to 75% by weight. From the point, 10 to 50% by weight is preferable,
Further, from the viewpoint of the maximum value of NO removal rate, 20 to 40% by weight is most desirable.

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 as high as 3% or more, and in addition, in an atmosphere where water vapor is present, a wide temperature range can be obtained. It has excellent NOx reduction performance.

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
_When an alcohol such as ₃ OH or C ₂ H ₅ OH or a carbon-containing gas having a reducing property such as CO is mixed and brought into contact with the catalyst material obtained by adding the composite oxide and CeO ₂ ,
Ox reduction performance is further enhanced.

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. On Pt, Pd, Rh, Ru, Ir
0.01 to at least one selected from precious metals such as
Since CeO ₂ supported by 5.0 wt% was added in an amount of 5 to 75 wt%, CeO ₂ itself does not exhibit NOx reduction decomposition ability, but the added CeO ₂ oxidizes NO to NO ₂
With the Ni-Ga-based oxide catalyst that promotes the production of NOx and has a higher reduction activity for NO ₂ than NO, the NOx reduction decomposition activity is improved in a lower temperature range than when the Ni-Ga catalyst alone is used.

Further, by supporting the noble metal, the amount of adsorbed oxygen is increased, the oxidation of NO to NO ₂ is further promoted, and the catalytic activity in the low temperature range is improved.

[0024]

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 or the like which produce oxides by heat treatment can be used.

In addition to the above, the complex 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., the 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 the 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, using CeO ₂ as a carrier, an aqueous solution containing at least one selected from the noble metal elements of Pt, Pd, Rh, Ru and Ir in the predetermined amount is added and evaporated to dryness, and helium (He) is added. 400 to 6 in gas atmosphere
CeO ₂ carrying the noble metal of the present invention is obtained by heat treatment at a temperature of 00 ° C. for 3 to 5 hours.

Then, CeO ₂ carrying the precious metal is
A spinel type crystal containing Ni and Ga is added to a composite oxide powder having a main crystal phase to prepare an oxide catalyst material.

As a method for adding the CeO ₂ carrying the noble metal, there is a method in which the CeO ₂ powder and the complex oxide powder are pulverized and mixed in a ball mill or a mortar. In the present invention, any of these mixing methods can be used. It is not limited.

[0033]

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 each of the noble metals as the supported elements in the amounts shown in Tables 1 to 3 and evaporating to dryness, helium (H
e) Heat treatment was performed in a gas atmosphere at a temperature of 500 ° C. for 3 hours to obtain CeO ₂ carrying each noble metal.

After that, CeO ₂ powders carrying the above-mentioned noble metals on the above spinel-type composite oxides are shown in Tables 1 to 3.
After adding and mixing in the proportions shown in Table 1, the mixed powder was molded by a die press and further compressed by a cold isostatic pressing method, and then the molded product was crushed and sieved to exceed 500 μm, 70
An evaluation sample was prepared by adjusting the particle size to 0 μm or less.

It should be noted that CeO ₂ which does not support the precious metal at all
The catalytic activity of only the added spinel-type composite oxide catalyst and the spinel-type composite oxide catalyst was set as a comparative example.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

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

Next, NO is 100 as simulated exhaust gas.
A space velocity (SV) of 200,000 is used as a condition that the reaction gas consisting of 0 ppm, O ₂ 10%, C ₃ H ₆ 666 ppm, and the balance He is in contact with the catalyst material.
/ Hr, flowed through the catalyst layer filled with the evaluation sample, and the N ₂ gas produced by passing through the catalyst layer in the temperature range of 300 to 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 set to 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.

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

As is clear from the table, the sample Nos. 1 and 47, 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. 10, 11, 19, 20,
28, 29, 37, 38, 46, 48, 56, 57, 6
It can be seen that all of Nos. 5, 66, 74, 75, 83, 84 and 92 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.

The evaluation samples of the present invention all had 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 an exhaust pipe of a 4-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 hardly decreased, and the water resistance,
It also proved to be excellent in heat resistance.

[0053]

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). 0.01 to at least one element selected from noble metals such as Pt, Pd, Rh, Ru and Ir is added to the spinel type crystalline complex oxide which is contained as a main metal element.
An oxide catalyst material for removing nitrogen oxides, characterized in that 5 to 75% by weight of CeO ₂ supported by 5.0% by weight is added, and a high concentration of oxygen and a carbon-containing gas having reducing properties are present. Since the oxide catalyst material and the exhaust gas containing nitrogen oxide are brought into contact with each other in an oxidizing atmosphere, not only in an atmosphere in which water vapor exists, but also in a high oxygen concentration atmosphere in which the oxygen concentration in the exhaust gas is 3% or more. In addition, even if the gas flow rate is high, it has excellent NOx reduction performance,
NOx contained in the exhaust gas can be effectively reduced and removed.

As a result, in purifying various harmful substances containing NOx, including exhaust gas 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. 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 spinel type crystalline composite oxide containing nickel (Ni) and gallium (Ga) as main metal elements, and platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), Oxide for removing nitrogen oxides, characterized by comprising adding 5 to 75% by weight of cerium oxide (CeO ₂ ) carrying 0.01 to 5.0% by weight of at least one selected from iridium (Ir). Catalyst material. 2. The cerium oxide (CeO ₂ ) is added in an amount of 10-5.
The oxide catalyst material for removing nitrogen oxides according to claim 1, wherein the oxide catalyst material is added in an amount of 0% by weight. 3. The cerium oxide (CeO ₂ ) 20 to 4
The oxide catalyst material for nitrogen oxide removal according to claim 1, wherein the oxide catalyst material is added in an amount of 0% by weight. 4. Nickel (Ni) and gallium (G) in an oxidizing atmosphere in which a carbon-containing gas having a reducing property with oxygen is present.
Platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (I) is added to the spinel type crystalline composite oxide containing a) as a main metal element.
an oxide catalyst material for removing nitrogen oxides, comprising 5 to 75% by weight of cerium oxide (CeO ₂ ) carrying 0.01 to 5.0% by weight of at least one selected from r); A method for removing nitrogen oxides, which comprises contacting with exhaust gas containing hydrogen. 5. The cerium oxide (CeO ₂ ) is added in an amount of 10-5.
5. The method for removing nitrogen oxides according to claim 4, wherein an oxide catalyst material for removing nitrogen oxides, which is added by 0% by weight, is brought into contact with exhaust gas containing nitrogen oxides. 6. The cerium oxide (CeO ₂ ) is added in an amount of ₂₀ to 4
5. The method for removing nitrogen oxides according to claim 4, wherein an oxide catalyst material for removing nitrogen oxides, which is added by 0% by weight, is brought into contact with exhaust gas containing nitrogen oxides.