JPH08229401A - Oxide catalyst material for removing nitrogen oxide and removal of nitrogen oxide - Google Patents

Abstract

PURPOSE: To purify NOx in exhaust gas within a wide temp. range without generating N2 O by using a catalyst prepared by supporting a specific amt. of palladium and at least one kind of platinum, rhodium and osmium on a carrier prepared by mixing multiple oxide having a spinnel type structure containing nickel and gallium as main metal elements and alumina. CONSTITUTION: A multiple oxide powder having a spinnel type crystal structure containing nickel and gallium as main metal elements and an Al2 O3 powder are mixed to be heated to predetermined temp. to form a carrier. Palladium and at least one kind of platinum, rhodium and osmium are supported on 100 pts.wt. of the support in the sum total of 0.05-0.4 pt.wt. to obtain an oxide catalyst. In this case, 50wt.% or more of palladium is added as a main component and it is most pref. to support 0.07-0.2 pt.wt. of palladium and at least one kind of platinum, rhodium and osmium on 100 pts.wt. of the carrier.

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 using the same, and more particularly to exhaust gas. The present invention relates to a catalyst for nitrogen oxide reduction and removal in diesel engines and the like having a low temperature, and a method for removing nitrogen oxide in exhaust gas at low temperature using the catalyst.

[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, harmful substances such as NO _x and CO _{x in} exhaust gas of automobiles, which are sources of migration of air pollution, are decomposed. There is an urgent need to develop a method for removal.

Conventionally, NO _x , C in the exhaust gas of automobiles
Decomposing harmful substances O _X such as a method of removing, using an oxidation of carbon monoxide (CO) and hydrocarbons (C _X H _X), nitrogen oxide three-way catalyst to perform reduction at the same time the (NO _X) The method has been adopted.

As a three-way catalyst used in such a method, a refractory material such as cordierite coated with γ-alumina (Al ₂ O ₃ ) is used, and palladium (Pd) or platinum (Pd) is used.
t) and those carrying a noble metal such as rhodium (Rh) have been used.

However, although the three-way catalyst can efficiently purify the exhaust gas only at a low oxygen concentration of about 0.5%, the three-way catalyst has a high oxygen concentration of more than 1%. It has the drawback of not working effectively in the region.

Therefore, normally, the oxygen concentration in the exhaust gas is measured, and the air-fuel ratio is controlled so that CO, C _X H _X , and NO _X can be processed at a high purification rate, and the air-fuel ratio is in a range close to the theoretical equivalent value. However, the CO and C _X H _X , and N
Since O _X generation mechanisms have contradictory properties, it is necessary to support combustion in a state where limited exhaust gas purification at a high oxygen concentration in than it is at present, not hardly.

Further, since energy saving and resource saving have recently been demanded, in a gasoline engine, research and development of a lean combustion system have been carried out in order to achieve low fuel consumption. Has a disadvantage that the noble metal of the catalyst cannot be purified by exhaust gas due to oxygen poisoning.

Also in the diesel engine, in the present combustion system, the exhaust gas is not purified at all because the oxygen concentration in the exhaust gas is high.

On the other hand, it occurs at a high temperature of about 1000 ° C. or higher,
As a method of effectively purifying NO _X , the concentration of which increases as the combustion temperature increases, there is a selective catalytic reduction method using ammonia in addition to the above method. Although effective for purifying NO _{x in} high exhaust gas, applying this method to a mobile combustion device such as an automobile has a problem in safety.

[0010] Therefore, as to solve the above problems, a method of the hydrophobic zeolite carrying the metal removing NO _X while in contact with the hydrocarbon as a catalyst, is proposed in JP-A 4-349938 Patent Publication There is.

[0011]

However, a catalyst using the above-mentioned metal-supporting hydrophobic zeolite as a catalyst has poor water resistance. For example, when water is contained in exhaust gas such as a diesel engine, water vapor NO _X by existence
There is a problem that the purification rate of
When the exhaust gas temperature is as low as 350 ° C. or lower, the catalyst has low NO reduction activity, and its use is limited.
Furthermore, there is a problem that N ₂ O, which is a cause of global warming, is generated as a by-product gas, and not only heat resistance is excellent, but also water resistance is excellent, and it is widely used in a low temperature range of 350 ° C. or lower. A catalyst material that exhibits NO reduction activity and does not generate N ₂ O has been desired.

[0012]

SUMMARY OF THE INVENTION The present invention does not require a highly toxic reducing agent such as ammonia, and provides a relatively low-temperature exhaust gas having a high oxygen concentration containing water, such as a diesel engine, with a high flow velocity of the exhaust gas. Even so, the present invention provides a useful catalyst material capable of effectively purifying NO _x in exhaust gas in a wide temperature range without producing N ₂ O, and a nitrogen oxide removing method using the same. .

[0013]

The present invention has been made in view of the above problems, and provides a composite oxide having a spinel structure as a crystal phase containing nickel (Ni) and gallium (Ga) as main metal elements. Alumina (Al ₂ O ₃ )
Noble metal palladium (Pd)
Similarly, an oxide catalyst material supporting at least one of platinum (Pt), rhodium (Rh), and osmium (Os) exhibits excellent catalytic activity over a wide temperature range even at high oxygen concentration in the presence of water vapor. It has been found to have a long term.

That is, the oxide catalyst material for removing nitrogen oxides of the present invention contains a composite oxide powder containing nickel (Ni) and gallium (Ga) as main metal elements and having a crystal phase having a spinel type structure. Palladium (Pd), platinum (Pt), rhodium (Rh), and osmium (Os) were added to a support in which Al ₂ O ₃ powder was mixed, and at least one of them was added in a total amount of 0. 05-
It is characterized by carrying 0.4 parts by weight.

In particular, at least one of palladium (Pd), platinum (Pt), rhodium (Rh), and osmium (Os) is added in a total amount of 0.07 to 0.3 parts by weight per 100 parts by weight of the carrier. It is preferable that the oxide catalyst material is partially supported, and in particular, contains 50% by weight or more of the palladium (Pd) as a main component, and among the main component and platinum (Pt), rhodium (Rh), and osmium (Os). It is most preferable that at least one kind is supported in a total amount of 0.07 to 0.2 parts by weight with respect to 100 parts by weight of the carrier.

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 carrier prepared by mixing Al ₂ O ₃ with a complex oxide whose crystal phase is a spinel structure,
Palladium (Pd), platinum (Pt), rhodium (R
h), an oxide catalyst material formed by supporting at least one of osmium (Os) in a total amount of 0.05 to 0.4 parts by weight with respect to 100 parts by weight of the support, and an exhaust gas containing nitrogen oxides. It is characterized in that they are brought into contact with each other.

Among them, as the oxide catalyst material, palladium (Pd), platinum (Pt) and rhodium (R) are used.
It is desirable to use at least one of h) and osmium (Os) which is carried in a total amount of 0.07 to 0.3 parts by weight with respect to 100 parts by weight of the carrier, and further, palladium (Pd) as the main component is used. Of 50% by weight or more, and the main component and at least one of platinum (Pt), rhodium (Rh), and osmium (Os) in total of 0.07 to 0.2 parts by weight relative to 100 parts by weight of the carrier. It is most preferable to use a partially supported one.

In the present invention, as the oxide catalyst material for removing nitrogen oxides, palladium (Pd), which is a noble metal, and platinum (Pt) and rhodium (R) are also used for the carrier.
h) and osmium (Os), when at least one of them is less than 0.05 parts by weight in total with respect to 100 parts by weight of the carrier, NO in a low temperature range of 350 ° C. or lower
On the contrary, when the amount exceeds 0.4 parts by weight, only the simple oxidation reaction of the reducing agent proceeds and the NO reduction reaction does not appear.

Therefore, in the oxide catalyst material for removing nitrogen oxides, the carrier is palladium (Pd) and platinum (Pd).
t), rhodium (Rh), and osmium (Os), the total amount of at least one kind is limited to a total amount of 0.05 to 0.4 parts by weight based on 100 parts by weight of the carrier, and a catalyst. From the viewpoint of activity, it is desirable to support a total of 0.07 to 0.3 parts by weight, and particularly palladium (Pd) as a main component from the viewpoint of catalytic activity in a wide temperature range.
Of 50% by weight or more, and the total amount of the main components is 0.0
Most preferred is 7 to 0.2 parts by weight.

The composite oxide contains nickel (Ni) and gallium (Ga) as main metal elements and has a spinel type crystal phase represented by NiGa ₂ O ₄ as a general formula. The correlation between Ni and Ga of the composite oxide is preferably 1.4 or more, and most preferably 1.5 or more, from the viewpoint of catalytic activity, in terms of the count ratio of Ga to Ni by fluorescent X-ray analysis.

Further, it is considered appropriate that the Al ₂ O ₃ has a high specific surface area, and 60 m ² is practically used.
/ G or more is desirable, and although the change in catalyst activity due to the Al ₂ O ₃ mixed amount is small, the mixed amount is 20 to 70.
Weight percent is preferred and 25-60 weight percent is most desirable.

Further, on the carrier in which Al ₂ O ₃ is mixed with the complex oxide, palladium (Pd) which is a noble metal, platinum (Pt), rhodium (Rh) and osmium (O) are also used.
In the case of contacting an exhaust gas containing nitrogen oxide with an oxide catalyst material supporting 0.05 to 0.4 parts by weight in total of 100 parts by weight of the carrier, the exhaust gas containing C ₂ H ₄ and C as reducing agents in the atmosphere
Hydrocarbons such as ₃ H ₆ and C ₃ H ₈ , CH ₃ OH, C ₂ H ₅
When an alcohol such as OH or a reducing carbon gas such as CO is contained and brought into contact with the catalyst material, NO
_X- reducing property becomes higher.

[0023]

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 is N
Palladium (Pd), platinum (Pt), a mixed oxide containing i and Ga as main metal elements and having a crystal phase having a spinel structure and Al ₂ O ₃ were mixed,
At least one of rhodium (Rh) and osmium (Os) is added in a total amount of 0.05 based on 100 parts by weight of the carrier.
Since about 0.4 part by weight was supported, Al ₂ O ₃ in the carrier oxidizes NO in a high temperature range exceeding 350 ° C.
The composite oxide, which promotes the production of O ₂ and has a higher reduction activity for NO ₂ than NO, exhibits high characteristics due to the reductive decomposition action of NO _X.

On the other hand, in the low temperature range of 350 ° C. or lower, NO reduction activity is exhibited in a wide temperature range due to the catalytic action of the two or more kinds of the noble metals carried.

Further, generally in noble metal-supported catalysts, N
In the oxide catalyst material of the present invention, N ₂ O produced as a by-product of the O reduction reaction increases the selectivity of the reaction from NO to N ₂ due to the interaction between the carrier and the noble metal.
It is considered that the N ₂ O formation reaction does not occur.

[0026]

EXAMPLES 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.

The oxide catalyst material for removing nitrogen oxides of the present invention is obtained by weighing a predetermined amount of raw material powder containing Ni and Ga,
After sufficiently stirring and mixing, Al ₂ O ₃ powder was added, and heat treatment was performed at a temperature of 500 to 1600 ° C. for 5 to 30 hours in an oxidizing atmosphere to form a composite of spinel-type crystals containing Ni and Ga as main metal elements. A mixed powder of oxide and Al ₂ O ₃ is obtained.

Then, using the mixed powder as a carrier, an aqueous solution containing a predetermined amount of a noble metal is added and the mixture is evaporated to dryness, and the mixture is heated in a helium (He) gas at a temperature of 400 to 600 ° C. for 3 to 3 times.
After heat treatment for 5 hours, the oxide catalyst material of the present invention is obtained.

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

Further, since it is considered that the raw material powder improves the reductive decomposition property of NO _x by solid-dissolving Ga metal in NiGa ₂ O ₄ having a stoichiometric spinel structure, the metal of Ga with respect to Ni is It is desirable to mix them so that the element ratio is 2.1 or more.

Further, the above-mentioned composite oxide can be synthesized by a solid-phase reaction with oxides or other metal salts other than the above, or by a sol-gel method of metal alkoxide, etc., and is not limited to these production methods. It is not something that will be done.

The temperature of the heat treatment of the mixed powder is 50
If the temperature is lower than 0 ℃, the crystallization will be insufficient, and conversely 1600 ℃.
If it exceeds, it will be densified, so it is 500-1600 ℃
At a temperature of 5 to 30 hours in an oxidizing atmosphere, but heat treatment at a particularly low temperature is effective for increasing the specific surface area of the powder, and practically the specific surface area is 60 m ² / g or more. It is desirable to set

Next, in evaluating the present invention, Ni (NO ₃ ) ₂ .6H ₂ O and Ga (NO ₃ ) _{3 were used} as starting materials.
-Using a reagent of 9H ₂ O, weighed so that the metal element ratio of Ni and Ga was 1: 3, dissolved these reagents in distilled water, and neutralized with ammonia water while stirring.
50 parts by weight of Al ₂ O ₃ powder was added to 100 parts by weight of the resulting precipitate, and the mixture was sufficiently stirred and mixed by an ultrasonic emulsification disperser, and then freeze-dried.

Next, the dry powder was heat-treated in the air at a temperature of 700 ° C. for 30 hours, and then an aqueous solution containing each noble metal in an amount shown in Table 1 was added to the powder and evaporated to dryness. In a helium (He) stream, heat treatment was performed at a temperature of 500 ° C. for 3 hours.

After that, the powder carrying the noble metal is molded by a die press, CIP-molded, the molded body is crushed and sieved, and the particles are sized to exceed 500 μm and 700 μm or less to obtain a sample for evaluation. Prepared.

Comparative examples were those in which no noble metal was supported on the carrier, and those in which the carrier was zeolite and the noble metal was supported.

[0037]

[Table 1]

The count ratio of Ga to Ni determined by fluorescent X-ray analysis of the thus obtained evaluation sample was 1.
It was 93.

The 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 γ-Al ₂ O ₃ phase.

Next, NO of 1000 ppm and O ₂ of 1
0%, H ₂ O 10%, C ₂ H ₄ 100 as reducing agent
A reaction gas containing water vapor of 0 ppm and the rest being He is used as a condition for contacting the reaction gas with the catalyst material.
/ F was set to 0.03 g · sec / cc, the sample for evaluation was flown through the catalyst layer, and N ₂ produced by the reduction of NO in the temperature range of 250 to 600 ° C. was measured by a gas chromatograph. The NO conversion rate at each temperature was determined from the amount of production of ₂ , and those having a NO reduction activity above a certain level in a low temperature range of 350 ° C. or lower within the measurement temperature range were evaluated as good.

Further, the presence or absence of N ₂ O production was measured by the same gas chromatograph as above.

[0042]

[Table 2]

As is clear from Table 2, the sample No. 1, which does not support the noble metal, which is a comparative example, shows no NO reduction activity at a temperature of 350 ° C. or lower, and the sample No. 34 of the zeolite carrier has a temperature of 350. Although it shows NO reduction activity at a temperature of ℃ or less, the production of N ₂ O has been confirmed, and the material numbers 9, 21, and 27, which are outside the scope of the present invention, are 3
At a temperature of 50 ° C. or lower, NO reduction activity is low as a whole, which is not practical.

On the other hand, in the present invention, all 350
It can be seen that a sufficient NO reduction activity is exhibited in a wide temperature range including a temperature of 0 ° C. or lower, and N ₂ O does not exist.

Using the above-mentioned sample for evaluation, it was set in the exhaust pipe of a four-cylinder diesel engine bench test apparatus, and the diesel engine was operated under the conditions of maximum rotation speed and full load.
A durability test of running for 0 hours was carried out, and the NO reduction activity of the evaluation sample after the test was evaluated in the same manner as described above.
It was confirmed that the NO conversion rate was 20% or more in the temperature range of 50 to 450 ° C., N ₂ O was not detected, and the heat resistance and water resistance were excellent.

[0046]

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 Ni and Ga as main metal elements. Al ₂ O for spinel type complex oxide
₃ to carrier obtained by mixing total, and palladium (Pd), platinum (Pt), of the rhodium (Rh), osmium (Os), at least one with respect to the carrier 100 parts by weight from 0.05 to 0. 4 parts by weight are carried, and 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 a high concentration of oxygen and a carbon-containing gas having a reducing property are present, steam is generated. Not only in the existing atmosphere but also in a high oxygen concentration atmosphere in which the oxygen concentration in the exhaust gas is 3% or more, and in addition, even if the gas flow rate is high, a wide range in a low temperature range of 350 ° C or less Excellent NO
_{It has X} reduction performance and does not generate N ₂ O at all,
Exhaust gas from various internal combustion engines such as diesel engine and lean burn engine, which can be effectively reduced and removed of NO _X contained in exhaust gas and is developed with the goal of energy saving, resource saving and prevention of global warming. Begin,
It is extremely useful for purifying various harmful substances containing NO _x .

Claims (6)

[Claims] 1. A support in which a composite oxide having a spinel structure containing nickel (Ni) and gallium (Ga) as main metal elements and alumina (Al ₂ O ₃ ) are mixed, and palladium (Pd) is added to the support. Platinum (Pt), Rhodium (R
h), and at least one of osmium (Os) is supported in a total amount of 0.05 to 0.4 parts by weight with respect to 100 parts by weight of the support, and an oxide catalyst material for removing nitrogen oxides. 2. Palladium (Pd) and platinum (Pd)
At least one of t), rhodium (Rh), and osmium (Os) is supported in a total amount of 0.07 to 0.3 parts by weight with respect to 100 parts by weight of the support, and nitrogen is contained. Oxide catalyst material for oxide removal. 3. Palladium (Pd) as a main component, and at least one of the main component and platinum (Pt), rhodium (Rh), and osmium (Os) is added in a total amount of 0 based on 100 parts by weight of the carrier. 0.07 to 0.2 part by weight is supported, and the oxide catalyst material for removing nitrogen oxides according to claim 1 or 2, 4. A composite oxide having a spinel structure and nickel containing 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. (Al ₂ O ₃ ) is mixed in the carrier, and at least one of palladium (Pd), platinum (Pt), rhodium (Rh), and osmium (Os) is added to the carrier in a total amount of 0. .05
A method for removing nitrogen oxides, characterized in that 0.4 parts by weight of an oxide catalyst material is brought into contact with exhaust gas containing nitrogen oxides. 5. Palladium (Pd) and platinum (Pd)
t), rhodium (Rh), and osmium (Os), at least one of which is 0.0 in total with respect to 100 parts by weight of the carrier.
5. The method for removing nitrogen oxides according to claim 4, wherein the oxide catalyst material supported by 7 to 0.3 parts by weight is brought into contact with exhaust gas containing nitrogen oxides. 6. Palladium (Pd) as a main component, and at least one of the main component and platinum (Pt), rhodium (Rh), and osmium (Os) is added to 100 parts by weight of the support in total. The method for removing nitrogen oxides according to claim 4 or 5, wherein the oxide catalyst material supported by 0.07 to 0.2 parts by weight is brought into contact with exhaust gas containing nitrogen oxides.