JPH0975733A - Oxide catalyst material for removing nitrogen oxide and method for removing nitrogen oxide - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To adsorb sulfur oxides in exhaust gas on the surface of a catalyst metal, and to cause poisoning deterioration by sulfur to cause NO _x and C _x H.
_It hinders the adsorption of _y and O ₂ and reduces the ability to decompose and remove harmful substances. SOLUTION: A spinel-type composite oxide containing Ni and Ga as main metal elements mixed with CeO ₂ or Mn ₂ O ₃ is selected from transition metals, alkali metals, and noble metals, or each of them. At least one of them is added to form an oxide catalyst material for removing nitrogen oxides, and the oxide catalyst material is an oxidation catalyst in which sulfur oxide and high concentration oxygen are present and reducing gas such as hydrocarbon coexists. The exhaust gas containing nitrogen oxides is contacted in the atmosphere to reduce and decompose the 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. In particular, a diesel engine or the like having a low exhaust gas temperature, which is suitable for purification of exhaust gas containing sulfur oxides, is preferably used as an oxide catalyst material for removing nitrogen oxides, and a sulfur oxide is contained at a low temperature using the oxide catalyst material. The present invention relates to a method for removing nitrogen oxides in exhaust gas.

[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 and C contained in exhaust gas of automobiles, which are sources of movement of air pollution.
There is an urgent need to develop a method for decomposing and removing harmful substances such as O _x .

Conventionally, NO _x and C in exhaust gas of automobiles
As a method of decomposing and removing harmful substances such as O _x, a three-way catalyst that simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (C _x H _y ) and reduces nitrogen oxides (NO _x ). It has been commonly 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 only at a low oxygen concentration of about 0.5%, which is required to reduce fuel consumption from the viewpoint of energy saving. As a means, combustion is performed with an air-fuel mixture with excess oxygen, but there is a drawback that it does not function effectively in a high-concentration atmosphere where the oxygen concentration in the exhaust gas exceeds 1%.

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 the generation mechanisms of O and C _x H _y and NO _x have contradictory characteristics, combustion must be maintained in a limited state, and exhaust gas purification in a high oxygen concentration as described above is not possible. The current situation is that almost nothing 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]

However, sulfur (S) is contained in light oil used as a fuel for diesel engines.
The exhaust gas contains the sulfur (S)
SO ₂ produced by combustion of SO ₂ is contained, and the SO ₂ is further oxidized by the catalyst metal in an oxygen-excess atmosphere to form SO _2.
3 , which adsorbs NO _x , C _x H _y , and O ₂ necessary for decomposing and removing the harmful substances discharged from the diesel engine by adsorbing them on the surface of the catalyst metal, so that the so-called catalytic metal There is a problem in that poisoning deterioration due to sulfur is caused, and as a result, the ability to decompose and remove the harmful substance is reduced.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a high N concentration even in a high-velocity exhaust gas, such as a diesel engine, which has a high oxygen concentration containing water and contains sulfur oxides.
An object of the present invention is to provide a catalyst material which exhibits an O _x reduction decomposition action and can effectively purify NO _x in exhaust gas and which has excellent heat resistance, and a nitrogen oxide removing method using the same. .

[0010]

The present invention is directed to Ni and G
Cs, which is a transition metal or an alkali metal such as W, Mo, Cu, or Co, or Rh, is added to a carrier in which a spinel-type composite oxide containing a as a main metal element and CeO ₂ or Mn ₂ O ₃ are mixed. , One of the noble metals such as Ru, or the addition of each of the noble metals, the sulfur oxides such as SO ₂ and SO ₃ are easily separated from the catalyst surface, and poisoning deterioration due to sulfur can be prevented.
Even in an atmosphere containing sulfur oxides at high oxygen concentration, it is not easily poisoned by sulfur, has excellent so-called SO ₂ resistance, has high catalytic activity for a long period of time, and exhibits a high NO _x reduction decomposition action and is effectively exhausted. The inventors have found that NO _x in gas can be purified.

That is, the oxide catalyst material for removing nitrogen oxides of the present invention contains Ni and Ga as main metal elements and has a Ga / Ni atomic ratio n of 2.5 to 3.3. To a complex oxide having a spinel structure,
75 wt% CeO ₂ or 1-20 wt% Mn ₂ O
It is characterized in that 0.1 to 40% by weight of any one of transition metals such as W, Mo, Cu and Co or Cs which is an alkali metal is added to a carrier in which ₃ is mixed.

Alternatively, it is a catalyst material obtained by adding 0.01 to 10% by weight of any one of noble metals such as Rh and Ru to the carrier.

Alternatively, W, Mo, Cu,
A catalyst material comprising 0.1 to 40% by weight of any one of transition metals such as Co and Cs which is an alkali metal, and 0.01 to 10% by weight of any one of noble metals such as Rh and Ru. is there.

Furthermore, the method for removing nitrogen oxides of the present invention contains Ni and 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, and Ga / Ni atoms are contained. A composite oxide having a spinel structure in which the crystal phase having a ratio n of 2.5 to 3.3 has 5 to 7
5 wt% CeO ₂ or 1-20 wt% Mn ₂ O ₃
In a carrier mixed with C., one kind of Cs which is a transition metal such as W, Mo, Cu and Co or Cs which is an alkali metal is added.
It is characterized in that the catalyst material added by 1 to 40% by weight is brought into contact with exhaust gas containing nitrogen oxides.

Alternatively, a catalyst material obtained by adding 0.01 to 10% by weight of any one of noble metals such as Rh and Ru to the carrier is brought into contact with exhaust gas containing nitrogen oxides. To do.

Alternatively, W, Mo, Cu,
A catalyst material comprising 0.1 to 40% by weight of any one of transition metals such as Co and Cs which is an alkali metal, and 0.01 to 10% by weight of any one of noble metals such as Rh and Ru. It is characterized by being brought into contact with exhaust gas containing nitrogen oxides.

As the oxide catalyst material for removing nitrogen oxides of the present invention, the spinel type composite oxide contains Ni and Ga as main metal elements, and the atomic ratio n represented by Ga / Ni is 2.5. 3.3 a spinel composite oxide comprising a ratio of the general formula NiGa _n O _{4 + Z} (where, n
= 2.5 to 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 0.2 depending on the value of n
It changes from time to time within the following range.

The spinel type complex oxide is Ga
When the value of the atomic ratio n represented by / Ni deviates from the range of 2.5 to 3.3, the catalytic activity decreases, so that the range is specified, and 2.8 to 3.0 is the most desirable. .

On the other hand, CeO ₂ mixed with the composite oxide
Is less than 5% by weight, there is no effect of improving the catalytic activity at low temperatures, and conversely, if it exceeds 75% by weight, the characteristics of CeO ₂ itself, which has no NO reducing ability, become strong, and the catalytic activity decreases. The mixing amount is limited to 5 to 75% by weight, preferably 10 to 50% by weight, particularly 10 to 40% by weight.
Is most desirable.

Also, Mn ₂ O ₃ mixed in the same manner as described above,
If the mixing amount is less than 1% by weight, there is no effect of improving the catalyst activity at low temperature, and if it exceeds 20% by weight, the complete oxidizing activity of the reducing agent becomes too strong and the NO reducing activity decreases, so the mixing amount is Limited to 1 to 20% by weight, 1 to 10
Better wt%, especially 2-10 wt% is best.

Next, W, Mo, added to the support,
Cs which is a transition metal such as Cu or Co or an alkali metal
If the addition amount is less than 0.1% by weight, the effect of SO ₂ resistance is not exerted, and conversely, if it exceeds 40% by weight, the reducing agent combustion activity becomes too high and the NO reduction activity decreases, so ．
It is limited to 1 to 40% by weight.

The composite oxides Ni--Ga and CeO ₂
Alternatively, since the mixture of Mn ₂ O ₃ shows NO reduction activity, the amount of the transition metal or alkali metal added is 0.1 to 30% by weight from the viewpoint of keeping the activity high.
Is more preferable, and 0.1 to 20% by weight is the most preferable.

On the other hand, the noble metals such as Rh and Ru added in the same manner as described above have an S resistance of less than 0.01% by weight.
There is no effect of O ₂ property, and if it exceeds 10% by weight, the combustion activity of the reducing agent becomes too high, and S due to the oxidation of SO ₂
The production of O ₃ rapidly increases, the SO ₃ easily reacts with H ₂ O to change to H ₂ SO ₄ which is more likely to generate poisoning, and the poisoning by sulfur sharply increases.

Therefore, the above-mentioned addition amount is limited to 0.01 to 10% by weight, and from the viewpoint of the amount of SO ₃ produced and the ability to desorb SO ₂ , 0.01 to 5% by weight is desirable, and further 0.1. 01
~ 3% by weight is more preferred.

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
An alcohol such as ₃ OH or C ₂ H ₅ OH, a carbon-containing gas having a reducing property such as CO, or the like is mixed, and the transition metal or the noble metal or the like is added to the mixture of the complex oxide and CeO ₂ or Mn ₂ O _3. When the catalyst material added is brought into contact, poisoning by sulfur can be effectively prevented, and the NO _x reducing property is further enhanced.

[0026]

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 Ni
And a spinel-type composite oxide containing Ga as a metal element and CeO ₂ or Mn ₂ O ₃ on a support,
When a metal such as a transition metal, an alkali metal, or a noble metal is added, and the catalyst material added with the transition metal or the alkali metal is brought into contact with exhaust gas containing sulfur oxide, the transition metal is oxidized by SO ₂ . Due to its small characteristics, it is difficult to generate highly toxic SO _3, and because the SO ₂ adsorption power is small, SO ₂ adsorbed on the catalyst surface easily separates from the transition metal to prevent poisoning. .

When a metal such as a noble metal is added in the same manner as described above, even if the amount of addition is small, SO ₂ adsorbed on the catalyst surface moves to the added metal, so-called spillover is promoted, and SO ₂ Desorption is likely to proceed and, moreover, water in the reaction gas is less susceptible to SO ₂ desorption inhibition.

Further, the transition metal or alkali metal having a high SO ₂ desorbing ability and the precious metal having a high SO ₂ spillover ability from the catalyst surface to the added metal are added together, and a catalyst material containing sulfur oxide is exhausted. When brought into contact with gas, it acts to further enhance the ability to remove SO ₂ from the catalyst surface.

On the other hand, although CeO ₂ or Mn ₂ O ₃ itself mixed as a support does not show NO _x reduction resolution, CeO ₂ or Mn ₂ O ₃ oxidizes NO to NO ₂
To promote the formation of by high reduction activity to NO ₂ than NO Ni-Ga-based oxide catalyst, than in the case of Ni-Ga catalyst alone improves _the NO _x reduction decomposition activity at lower temperature region.

Further, the complex oxide and CeO ₂ or M
By supporting the noble metal in a mixture with n ₂ O ₃ , 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.

[0031]

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 in detail below.

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. In the composite oxide material of the present invention, the raw material powder containing Ni and Ga is weighed so that the atomic ratio n of Ga / Ni is 2.5 to 3.3, sufficiently stirred and mixed, and then oxidized. In a sex atmosphere, 5
By performing heat treatment at a temperature of 00 to 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 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.

In addition to the above, the composite oxide material can 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. It is not limited to.

In any of the above-mentioned manufacturing methods, when the heat treatment temperature is lower than 500 ° C., the crystallization becomes insufficient, and conversely, when the heat treatment temperature exceeds 1600 ° C., densification occurs, so that oxidation at a temperature of 500 to 1600 ° C. 5 in the atmosphere
It is carried out for 30 hours, but heat treatment at a particularly low temperature is effective for increasing the specific surface area of the powder, and in practice, it is desirable to set the specific surface area to be 35 m ² / g or more.

The above-mentioned composite oxide powder when mixed with CeO ₂ or Mn ₂ O ₃ has a high specific surface area from the viewpoint of ensuring the contact area with exhaust gas and effectively decomposing and removing nitrogen oxides. Having a specific surface area of 3
It is preferably 0 to 100 m ² / g, and particularly preferably 40 to 80 m ² / g.

Next, a predetermined amount of CeO ₂ or Mn ₂ O ₃ powder is added to and mixed with a composite oxide powder containing a spinel type crystal containing Ni and Ga as a main crystal phase to prepare a carrier.

The method of adding CeO ₂ or Mn ₂ O _{3 to} the composite oxide powder is CeO ₂ or Mn.
There is a method of pulverizing and mixing the ₂ O ₃ powder and the complex oxide powder with a ball mill or a mortar, and the present invention is not limited to these methods.

Next, a predetermined amount of W, Mo,
Cs which is a transition metal such as Cu or Co or an alkali metal
Or any one of noble metals such as Rh and Ru, or any one of the transition metals or alkali metals, and an aqueous solution containing any one of the noble metals are added to evaporate to dryness, and then, Heat treatment is carried out in a helium (He) gas stream at a temperature of 400 to 600 ° C. for 3 to 5 hours to obtain an oxide catalyst material for removing nitrogen oxides carrying the above-mentioned elements.

Further, the transition metal can be added by physically mixing the oxide of the transition metal other than the evaporation dryness method.

[0041]

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, Ni
And Ga are weighed so that the metal ratio is 1: 3, and these reagents are dissolved in distilled water and neutralized with ammonia water with stirring. At this time, the formed precipitate is filtered, washed, and frozen. 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
m ² / g of spinel type complex oxide powder was obtained.

Then, the spinel type complex oxide powder was added to CeO ₂ having a specific surface area of 80 m ² / g or 15 m ² / g.
The above Mn ₂ O ₃ powder was added and mixed at a ratio shown in Tables 1 to 4 to prepare a carrier.

An aqueous solution containing each of the metals shown in Tables 1 to 4 and having various contents was added to the obtained support, and after evaporating to dryness, the mixture was heated at a temperature of 500 ° C. in a He gas stream. A mixed powder supporting each metal was obtained by heat treatment for 3 hours.

Thereafter, the mixed powder is added at 200 kg / cm.
Mold press molding with a pressing force of ² and further compressing by cold isostatic pressing, then crushing and sieving the molded product, 500
A sample for evaluation was prepared by adjusting the particle size to more than 700 μm and below μm.

Comparative samples were prepared by mixing the above CeO ₂ or Mn ₂ O ₃ but not supporting the metal element at all, and a sample containing only the spinel type composite oxide catalyst.

The powder of the sample for evaluation thus obtained was used to identify the crystal phase by X-ray diffraction measurement (XRD), and it was confirmed that the crystal phase consisted of spinel crystal and Mn ₂ O ₃ crystal phase.

Next, NO is 100 as simulated exhaust gas.
0 ppm, O ₂ 10%, H ₂ O 10%, C ₃ H ₆ as a reducing agent, 666 ppm, SO ₂ 50 ppm, the balance of He is used as the reaction gas, and the reaction gas is in contact with the catalyst material. As W / F is 0.03 g · sec /
The reaction gas was set to cc, the reaction gas was flowed through the catalyst layer filled with the evaluation sample, and N ₂ produced by the reduction of NO was measured by gas chromatography through the catalyst layer in the temperature range of 200 to 600 ° C. The conversion rate of NO was determined from the amount of N ₂ produced, and the highest value was regarded as the highest activity, and those higher than the highest activity of the comparative example were evaluated as good.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

As is clear from the results of Tables 1 to 4,
The maximum activity of each of the sample numbers 1 and 2 which are comparative examples is 16
% And 10%, and all of the sample numbers outside the scope of the claims of the present invention are less than that, which is poor in practicality, while all of the sample numbers of the present invention have the highest activity of the comparative example. It can be seen that the NO reduction activity is exceeded, showing sufficient NO reduction activity.

In addition, all of the evaluation samples of the present invention did not show a great change in the above-mentioned characteristics even after being reacted with the reaction gas at a temperature of 350 ° C. for 100 hours continuously. It was

Further, the evaluation sample was attached to an exhaust pipe of a 4-cylinder diesel engine bench test apparatus, and a durability test was carried out in which the diesel engine was operated for 100 hours at the maximum rotation speed and full load. When the NO reduction activity of the sample for evaluation was evaluated in the same manner as described above, it was confirmed that the NO removal rate was hardly decreased in any of them, and it was proved that both the water resistance and the heat resistance were excellent. .

In the examples of the present invention, transition metals such as W, Mo, Cu and Co are used as the metal added to the carrier.
In addition, the noble metals Rh and Ru have been described in detail as an example, but other transition metals such as Ti, Fe and Ni, and noble metals such as P
It has been confirmed that d, Ir, and Pt also have the same effects as described above.

[0057]

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, not only in the atmosphere containing sulfur oxides but also in the presence of water vapor, Even if the oxygen concentration in the exhaust gas is 3% or more in a high oxygen concentration atmosphere, and even if the gas flow rate is high, it has excellent NO _x reduction performance and is contained in the exhaust gas. The NO _{x generated} can be effectively reduced and removed.

As a result, various harmful substances such as NO _{x in} the exhaust gas of future internal combustion engines developed with the goal of energy saving, resource saving and prevention of global warming, especially diesel engines in which sulfur oxides are produced. It will be extremely useful for purification.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/88 B01D 53/36 102B 23/89 102C B01J 23/82 A 23/84 311A (72) Inventor Hidemi Matsumoto 1-4 Yamashita Town, Kokubun City, Kagoshima Prefecture Kyocera Stock Company Research Institute

Claims (6)

[Claims] 1. Nickel (Ni) and gallium (Ga) are contained as main metal elements, and the Ga / Ni atomic ratio n is 2.
5 to 3.3 in the spinel type composite oxide composed of 5
75 wt% cerium oxide (CeO ₂₎ or 1
Csium (Cs) which is a transition metal such as tungsten (W), molybdenum (Mo), copper (Cu), cobalt (Co) or an alkali metal is added to a carrier containing 0% by weight of manganese oxide (Mn ₂ O ₃ ). ) Any one of 0.
An oxide catalyst material for removing nitrogen oxides, comprising 1 to 40% by weight. 2. Nickel (Ni) and gallium (Ga) are contained as main metal elements, and the Ga / Ni atomic ratio n is 2.
5 to 3.3 in the spinel type composite oxide composed of 5
75 wt% cerium oxide (CeO ₂₎ or 1
0.01 to 10% by weight of any one of noble metals such as rhodium (Rh) and ruthenium (Ru) is added to a carrier mixed with 0% by weight of manganese oxide (Mn ₂ O ₃ ). An oxide catalyst material for removing nitrogen oxides. 3. Nickel (Ni) and gallium (Ga) are contained as main metal elements, and the Ga / Ni atomic ratio n is 2.
5 to 3.3 in the spinel type composite oxide composed of 5
75 wt% cerium oxide (CeO ₂₎ or 1
Csium (Cs) which is a transition metal such as tungsten (W), molybdenum (Mo), copper (Cu), cobalt (Co) or an alkali metal is added to a carrier containing 0% by weight of manganese oxide (Mn ₂ O ₃ ). ) Any one of 0.
1-40% by weight, rhodium (Rh), ruthenium (R
0.01% to 10% by weight of any one of noble metals such as u)
An oxide catalyst material for removing nitrogen oxides, comprising: 4. Nickel (Ni) and gallium (G) in an oxidizing atmosphere in which a carbon-containing gas having a reducing property with oxygen is present.
a) as the main metal element and a Ga / Ni atomic ratio n of 2.5 to 3.3 in the spinel type composite oxide, 5 to 75% by weight of cerium oxide (CeO ₂ ) or 1 to Tungsten (W) and molybdenum (M) were mixed with a carrier containing 20% by weight of manganese oxide (Mn ₂ O ₃ ).
O), a transition metal such as copper (Cu) or cobalt (Co), or an oxide catalyst for removing nitrogen oxides, which is obtained by adding 0.1 to 40% by weight of any one of cesium (Cs) which is an alkali metal. A method for removing nitrogen oxides, which comprises contacting a material with an exhaust gas containing nitrogen oxides. 5. Nickel (Ni) and gallium (G) in an oxidizing atmosphere in which a carbon-containing gas having a reducing property with oxygen is present.
a) as the main metal element and a Ga / Ni atomic ratio n of 2.5 to 3.3 in the spinel type composite oxide, 5 to 75% by weight of cerium oxide (CeO ₂ ) or 1 to Rhodium (Rh) and ruthenium (Ru) were added to a carrier containing 20% by weight of manganese oxide (Mn ₂ O ₃ ).
Oxide removal for removing nitrogen oxides by adding 0.01 to 10% by weight of any one of the noble metals such as nitrogen oxides and exhaust gas containing nitrogen oxides. Method. 6. Nickel (Ni) and gallium (G) in an oxidizing atmosphere in the presence of a carbon-containing gas having a reducing property with oxygen.
a) as the main metal element and a Ga / Ni atomic ratio n of 2.5 to 3.3 in the spinel type composite oxide, 5 to 75% by weight of cerium oxide (CeO ₂ ) or 1 to Tungsten (W) and molybdenum (M) were mixed with a carrier containing 20% by weight of manganese oxide (Mn ₂ O ₃ ).
o), copper (Cu), cobalt (Co) and other transition metals, or cesium (Cs), which is an alkali metal, in an amount of 0.1 to 40% by weight, rhodium (Rh), ruthenium (Ru), etc. 0.01% of any one of
A method for removing nitrogen oxides, which comprises contacting an oxide catalyst material for removing nitrogen oxides containing 10% by weight with exhaust gas containing nitrogen oxides.