JPH09215921A - Nox decomposition catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a NOX decomposition catalyst which demonstrates a good reduction effect even at low temperatures by selecting elements which constitute a compound having brownmillerite like structure expressed by a specified formula as a catalyst component. SOLUTION: A NOX decomposition catalyst for purifying exhaust gas by reducing NOX in the gas contains a catalyst component having brownmillerite like structure expressed by a general formula of A3- XBXC4- YDYOZ. The A site, B site, C site, and D site of the catalyst component contain at least one element selected from a group of elements which are indicated below, and in the formula, X, Y, and Z are in ranges indicated below: A is Mg, Ca, Sr, and Ba; B is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Zr, Mo, Sn, Hf, Al, Ga, Ge, Tc, Ag, In, Sb, and lathanides; C is lanthanides; D is Y, lanthanides, and 0<X<=1.5, 0<Y<=2.0, 7<=Z.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, NO capable of purifying exhaust gas by reducing NO _X contained in the exhaust gas.
_X decomposition catalyst.

[0002]

2. Description of the Related Art Conventionally, catalysts for catalytic reduction and direct decomposition are known as NO _X decomposition catalysts. In gasoline engines, platinum, rhodium are used as catalysts, and HC, CO, H in exhaust gas are used as reducing agents. Three-way catalysts using ₂ are known. However, although a three-way catalyst is one in which a noble metal is supported on alumina, zeolite, or a carrier thereof, the NO _x reduction rate is low in a lean burn region with excess oxygen, that is, a lean burn region or a diesel engine, and the three-way catalyst is low. Was not effective in purifying the exhaust gas emitted from diesel engines. That is, in a diesel engine,
Since it is burned at an excess air ratio, O ₂ is present in the exhaust gas and a large amount of nitrogen oxide NO _x is discharged. In contrast, in the gasoline engine is burned in stoichiometric, the exhaust gas does not exist remainder O _2, since NO is decomposed by reduction catalyst provided in flow after the engine, of the NO _X problem Absent. Conventionally, from diesel engines nitrogen oxides N
In order to suppress the discharge of O _X to the outside, various NO
An exhaust gas purifying device incorporating an x decomposition catalyst is known. However, the exhaust gas of a diesel engine is O ₂
However, there is a drawback that the catalyst does not function because it is contained in a large amount.

Therefore, for the purification of NO _{X in} the diesel engine and the lean burn region, that is, the lean burn region as described above, a perovskite catalyst has been developed, but the reduction rate of NO _X is low. There was a problem (for example, Japanese Patent Laid-Open Nos. 6-100319 and 6-315).
634). Further, the exhaust gas purifying catalyst disclosed in Japanese Patent Application Laid-Open No. 63-77543 includes a catalyst carrier,
It comprises a perovskite-type composite oxide composed of an oxide of an alkaline earth metal, lanthanum oxide and cerium oxide supported on the surface of the catalyst carrier, and a noble metal catalyst component. Further, the exhaust gas purifying catalyst disclosed in JP-A-63-77543 has Pd as a catalyst component on a catalyst carrier having a layer containing a perovskite complex oxide and an O ₂ storage rare earth oxide on the surface. Alternatively, Pd and another noble metal are supported.

[0004]

Various catalysts have been studied in view of the above-mentioned circumstances, but as a catalyst for reducing NO _x , a brown mira which does not require a reducing agent and undergoes direct reductive decomposition. There are compounds having a light-like structure, for example, compounds of Ba ₃ Y ₄ O ₉ and BaLa ₂ O ₄ . However, catalysts composed of such compounds are
When the temperature becomes lower, it has the property that its reduction ratio decreases, but to have a proper activation temperature for the reduction action of NO _X.

[0005]

The main object of the present invention is to provide N in exhaust gas discharged from a diesel engine.
The O _X is intended to purify by reduction, as a catalyst component,
An element constituting a compound having a brownmillerite-like structure represented by the general formula of A _{3 -X} B _X C _{4 -Y} D _Y O _Z is selected, the element is synthesized by a wet method, and a catalyst component, that is, It is an object of the present invention to provide a NO _X decomposition catalyst that secures an appropriate reducing ability by changing the selection of constituent elements and the firing temperature.

The present invention has a general formula of A _{3 -X} B _X C
_4-Y D _Y O _Z A-site, B-site, C-site and D-site of the catalyst component having a brown-milarite-like structure include at least one element selected from the group of elements shown below, The present invention relates to a NO _X decomposition catalyst, wherein X, Y and Z in the above formula are in the following ranges. However, A: Mg, Ca, Sr, Ba B: Ti, V, Cr, Mn, Fe, Co, Ni, C
u, Nb, Zr, Mo, Sn, Hf, Al, Ga, G
e, Tc, Ag, In, Sb, lanthanoid C: lanthanoid D: Y, lanthanoid 0 <X ≦ 1.5, 0 <Y ≦ 2.0, 7 ≦ Z

Further, the NO _x decomposition catalyst has an ionization potential of the B site ion of the B site from divalent to trivalent of 24 eV or less.

In this NO _x decomposition catalyst, the A site of the catalyst component is Ba, the B site is Hf,
Ce, Zr, Fe, Co, Ni, Cu containing at least one or more elements, the C site is Y, and the D site is at least one or more elements in the La, Ce element group. It contains elements.

The NO _x decomposition catalyst has a specific surface area of 1 m ² / gr or more.

Further, since this NO _X decomposition catalyst is constructed as described above, the compound having a brownmillerite-like structure undergoes phase transition upon heating and is present in exhaust gas due to disordered oxygen defects. Donating electrons by reducing NO _x , or by converting the valences of the constituent elements,
Since NOx can be reduced by elimination, NO of the compound
Catalytic activity of _X in the reducing action can be ensured adsorption activity is high NO _X reduction ratio, thereby reducing the abundance of the NO _X in the exhaust gas.

[0011]

Embodiments of the NO _x decomposition catalyst according to the present invention will be described below. This NO _X decomposition catalyst is used, for example, for NO of exhaust gas exhausted from a diesel engine.
It is applied to an exhaust gas purification device that reduces and purifies _X. Generally, a diesel engine reciprocates in a cylinder head fixed to a cylinder block with a gasket interposed therebetween, an intake / exhaust port formed in the cylinder head, a cylinder liner provided in the cylinder block, and a cylinder bore formed in the cylinder liner. It has a piston. The exhaust port is connected to the exhaust pipe, and the exhaust pipe is provided with an exhaust gas purification device. This NO _X decomposition catalyst is used by being incorporated in the above-mentioned exhaust gas purifying apparatus, and is used in the exhaust gas from the diesel engine.
Reducing the NO _X so as to reduce the O _X, it is used to convert the N _2.

The NO _x decomposition catalyst according to the present invention has a general formula of A _{3 -X} B _X C _4-Y D _Y O _Z having a brown-millarite-like structure as a catalyst component.
The C site and D site contain at least one or more elements from the group of elements shown below, and X, Y and Z are in the following ranges. That is, A site is Mg, Ca, S
It contains at least one element of the element group of r and Ba. B site is Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Nb, Zr, Mo, S
n, Hf, Al, Ga, Ge, Tc, Ag, In, S
b, it contains at least one element of the lanthanide element group. The C site contains at least one element of the lanthanoid element group. Further, the D site contains at least one element from the element group of Y and lanthanoid. Further, X is in the range of 0 <X ≦ 1.5,
Y is in the range of 0 <Y ≦ 2.0, and Z is 7 ≦
It is the range of Z. This is a numerical value that keeps the structure electrically neutral.

Further, in this NO _X decomposition catalyst, the ionization potential of the B site ion of the B site from divalent to trivalent is 24 eV or less. This NO _X decomposition catalyst
Its specific surface area is 1 m ² / gr or more. In this NO _x decomposition catalyst, in particular, the A site of the catalyst component is B
a and B sites are Hf, Ce, Zr, Fe, Co, Ni,
At least one element selected from the group consisting of Cu and C
It is preferable that the site contains La and that the D site contains at least one element selected from the group of elements Y and Ce.

[Example 1] In Example 1, 1.5 mol of barium acetate and 1.6 mol of yttrium nitrate were weighed and dissolved in water. While stirring this solution, adjust the pH with aqueous ammonia, for example, adjust to weak alkali,
Furthermore, the solution was stirred until it became uniform. Next, the obtained solution was heated on a hot stirrer (hot plate) to remove water. Then, the obtained precursor (precursor) was pulverized to prepare a powder. This powder was heated at 600 ° C. in the atmosphere to remove nitrate radicals and acetate radicals from the powder. Next, the powder from which the nitrate radical and the acetate radical were removed was pulverized again, and the obtained powder was fired at 900 ° C. in an Ar atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

Example 2 In Example 2, instead of firing the powder of Example 1 at 900 ° C. in an Ar atmosphere, the firing temperature was variously changed within the range of 500 ° C. to 1400 ° C. When the above powder was fired, as in Example 1,
A complex oxide with a brown-milarite-like structure could be obtained.

[Example 3] In Example 3, 1.47 mol of barium acetate, 0.024 mol of cerium nitrate, and 1.6 mol of yttrium nitrate were weighed and dissolved in water. While stirring this solution, the pH was adjusted with aqueous ammonia, for example, a weak alkali, and further stirred until the solution became uniform. Next, the obtained solution was heated on a hot stirrer to remove water. Therefore, the obtained precursor was pulverized to prepare a powder. This powder was heated at 600 ° C. in the atmosphere to remove nitrate radicals and acetate radicals from the powder. Next, the powder from which the nitrate radical and the acetate radical were removed was pulverized again, and the obtained powder was fired at 950 ° C. in an Ar atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

[Example 4] In Example 4, 1.6 mol of yttrium nitrate, and barium acetate and cerium nitrate were weighed variously as shown in Table 1 and dissolved in water. Powder was obtained from this solution by the same process as in Example 3. When each of these powders was subjected to X-ray diffraction,
It was confirmed that each of these powders was a complex oxide having a brown-milarite-like structure.

[Table 1]

[Example 5] In Example 5, 1.47 mol of barium acetate, 0.024 mol of hafnium nitrate, and 1.6 mol of yttrium nitrate were weighed and dissolved in water. While stirring this solution, pH with ammonia water
Was adjusted, for example, adjusted to weak alkali, and further stirred until the solution became uniform. Next, the obtained solution was heated on a hot stirrer to remove water. Therefore, the obtained precursor was pulverized to prepare a powder. This powder was heated at 600 ° C. in the atmosphere to remove nitrate radicals and acetate radicals from the powder. Next, the powder from which the nitrate radical and the acetate radical were removed was pulverized again, and the obtained powder was fired at 950 ° C. in an Ar atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

Example 6 In Example 6, 1.6 mol of yttrium nitrate, and barium acetate and hafnium nitrate were variously weighed as shown in Table 2 and dissolved in water. Powder was obtained from this solution by the same steps as in Example 5. When each of these powders was subjected to X-ray diffraction,
It was confirmed that each of these powders was a complex oxide having a brown-milarite-like structure.

[Table 2]

[Embodiment 7] In Embodiment 7, metal salts of various nitric acids are used in place of the hafnium nitrate used in Embodiments 5 and 6, and the manufacturing process is similar to that of Embodiments 5 and 5. A powder was obtained through the same steps as those in Example 6. As the metal constituting the metal salt, the following can be selected, and the mixing ratio at that time was compounded in the same manner as in Examples 5 and 6. These metals include Ti, V, Cr, Mn, Fe, C
Although it can be selected from o, Ni, Cu, Nb, Zr, Mo, and Sn, in Example 7, Sn was particularly selected. When the powder was subjected to X-ray diffraction, the powder was
It was confirmed that each was a complex oxide having a brown-milarite-like structure.

[Example 8] In Example 8, 1.2 mol of strontium acetate and 1.6 mol of yttrium nitrate were weighed and dissolved in water. While stirring this solution, the pH was adjusted with aqueous ammonia, for example, a weak alkali, and further stirred until the solution became uniform. Next, the obtained solution is heated on a hot stirrer,
The water was removed. Therefore, the obtained precursor was pulverized to prepare a powder. Heating this powder at 600 ° C in air,
Nitrate and acetate were removed from the powder. Then, the powder from which nitrate radical and acetate radical were removed was pulverized again, and the obtained powder was
Firing was performed at 900 ° C. in an r atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

[Example 9] In Example 9, powder was produced by the same steps as in Example 8 except that 1.6 mol of yttrium nitrate and calcium acetate were selected as raw materials. When the powder was subjected to X-ray diffraction, it could be confirmed that the powder was a complex oxide having a brown-milarite-like structure.

Example 10 In Example 10, powder was produced by the same process as in Example 8 except that 1.6 mol of yttrium nitrate and magnesium acetate were selected as raw materials. When the powder was subjected to X-ray diffraction, it could be confirmed that the powder was a complex oxide having a brown-milarite-like structure.

[Example 11] In Example 11, 1.2 mol of barium acetate, 1.57 mol of yttrium nitrate, and 0.03 mol of lanthanum nitrate were weighed and dissolved in water. While stirring this solution, pH with ammonia water
Was adjusted, for example, adjusted to weak alkali, and further stirred until the solution became uniform. Next, the obtained solution was heated on a hot stirrer to remove water. Therefore, the obtained precursor was pulverized to prepare a powder. This powder was heated at 600 ° C. in the atmosphere to remove nitrate radicals and acetate radicals from the powder. Next, the powder from which the nitrate radical and the acetate radical were removed was pulverized again, and the obtained powder was fired at 900 ° C. in an Ar atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

[Example 12] In Example 12, 1.5 mol of barium acetate, and yttrium nitrate and lanthanum nitrate were weighed variously as shown in Table 3 and dissolved in water. Powder was obtained from this solution by the same steps as in Example 11. When each of these powders was subjected to X-ray diffraction, it could be confirmed that each of these powders was a complex oxide having a brown-milarite-like structure.

[Table 3]

[Example 13] In Example 13, 1.2 mol of barium acetate, 1.57 mol of yttrium nitrate, and 0.03 mol of cerium nitrate were weighed and dissolved in water. While stirring this solution, pH with ammonia water
Was adjusted, for example, adjusted to weak alkali, and further stirred until the solution became uniform. Next, the obtained solution was heated on a hot stirrer to remove water. Therefore, the obtained precursor was pulverized to prepare a powder. This powder was heated at 600 ° C. in the atmosphere to remove nitrate radicals and acetate radicals from the powder. Next, the powder from which the nitrate radical and the acetate radical were removed was pulverized again, and the obtained powder was fired at 900 ° C. in an Ar atmosphere. When X-ray diffraction was performed on the powder obtained by each of the above steps, it was confirmed that the powder was a complex oxide having a Brownmillerite-like structure.

Example 14 In Example 14, 1.5 mol of barium acetate, and yttrium nitrate and cerium nitrate were weighed variously as shown in Table 4 and dissolved in water. A powder was obtained from this solution by the same steps as in Example 13. When each of these powders was subjected to X-ray diffraction, it could be confirmed that each of these powders was a complex oxide having a brown-milarite-like structure.

[Table 4]

Regarding the NO _X decomposition catalyst according to the present invention,
The composite oxide having a brownmillerite-like structure obtained in the above respective Examples were subjected to evaluation test of the NO _X degradation test under the following conditions. The NO of the reaction gas is 800 ppm / N ₂ , the temperature of the reaction gas is 500 ° C., and the space velocity SV of the reaction gas is 1 × 10 ⁵ / h.

Regarding the NO _X decomposition catalyst according to the present invention,
FIG. 1 shows the difference between the samples in which the component ratios of the A-site ions and the B-site ions were changed, taking Example 3 and Example 4 as examples. Figure 1 shows B as the A site ion.
(Ba + C in Ce as a and B site ion
3 is a graph showing the correlation between the ratio of Ce to e) and the reduction rate of NO _x . In FIG. 1, the abscissa plots the ratio of B site ions to the total of A site ions and B site ions, and the ordinate plots the NO _x reduction rate (%). As can be seen from FIG.
It can be seen that the catalyst in which the ratio of Ce to (Ba + Ce) is 0% to 50% has a high NO _x reduction rate, that is, NO _x decomposition ability.

Regarding the NO _X decomposition catalyst according to the present invention,
FIG. 2 shows the reduction rate (%) due to the difference in the samples prepared by changing the components of the B site produced in Examples 3 to 7.
As can be seen from FIG. 2, a catalyst using as a raw material a small element having an ionization potential of B site ions from divalent to trivalent of 24 eV or less has a high NO _x reduction rate,
You can see that it has _X decomposition ability.

FIG. 3 shows the NO _X decomposition catalyst.
Shows the reduction rate (%) due to the difference between the samples prepared in Examples 11 to 12 in which the component ratios of La as the C site ion and Y as the D site ion were changed. As can be seen from FIG. 3, the catalyst having a ratio of Y to (La + Y) of 0% to 50% has a high NO _x reduction rate, that is, NO.
You can see that it has _X decomposition ability.

FIG. 4 shows the NO _X decomposition catalyst.
Shows the relationship between the specific surface area (m ² / gr) and the NO _x reduction rate (%). As you can see from Figure 4,
When the specific surface area of the catalyst is 0.5 m ² / gr or less, N
Although the reduction rate of O _x is as low as about 12%, it cannot be put to practical use, but the specific surface area of the catalyst is 1 m ² / gr.
In the above case, the reduction rate of NO _X becomes 30% or more,
It can be seen that it is effective in reducing NO _x . Also, this N
When the specific surface area of the catalyst prepared in Example 1 was measured by the BET method (gas adsorption method) for the O _X decomposition catalyst, the specific surface area of the catalyst particles was 1.17 m ² / gr. The specific surface area for this catalyst was 2 to 3 times that of the catalyst prepared by the usual solid phase method.

[0033]

As described above, the NO _x decomposition catalyst according to the present invention uses the ceramic particles having the brownmillerite-like structure as described above. , NO _x with high adsorption activity
A decomposition catalyst can be provided, NO _x contained in the exhaust gas is efficiently reduced, and NO _x is decomposed by a reducing action to decompose N ₂ and O ₂
It is varied to reduce the NO _X in the exhaust gas be in.

[Brief description of drawings]

FIG. 1 shows the relationship between the ratio of B site ion (Ce) to A site ion (Ba) and B site ion (Ce) to the total ion (Ce + Ba) and the reduction rate in the NO _X decomposition catalyst according to the present invention. It is a graph.

FIG. 2 is a graph showing the reduction rate with respect to the ionization potential of B site ions in the NO _X decomposition catalyst according to the present invention.

FIG. 3 shows the relationship between the reduction ratio and the ratio of D site ion (Y) to C site ion (La) and D site ion (Y) to the total ion (La + Y) in the NO _X decomposition catalyst according to the present invention. It is a graph.

FIG. 4 is a graph showing the relationship between the specific surface area and the reduction rate in the NO _X decomposition catalyst according to the present invention.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B01J 23/76 B01J 23/78 A 23/78 B01D 53/36 102H 102G

Claims (4)

[Claims] 1. The general formula is A _{3 -X} B _X C _4-Y D _Y O _Z
A site, B site, C site and D site of the catalyst component having a brown-milarite-like structure represented by at least one element selected from the group of elements shown below,
A NO _x decomposition catalyst, wherein X, Y and Z in the above formula are in the following ranges. A: Mg, Ca, Sr, Ba B: Ti, V, Cr, Mn, Fe, Co, Ni, C
u, Nb, Zr, Mo, Sn, Hf, Al, Ga, G
e, Tc, Ag, In, Sb, lanthanoid C: lanthanoid D: Y, lanthanoid 0 <X ≦ 1.5, 0 <Y ≦ 2.0, 7 ≦ Z 2. The NO _x decomposition catalyst according to claim 1, wherein the B site ion of the B site has an ionization potential from divalent to trivalent of 24 eV or less. 3. The A site of the catalyst component is Ba, and the B site is Hf, Ce, Zr, Fe, Co, N.
i, Cu containing at least one or more elements, the C site is Y, and the D site is La, C
The NO _x decomposition catalyst according to claim 1 or 2, which contains at least one element of the element group of e. 4. The NO according to claim 1, wherein the specific surface area is 1 m ² / gr or more.
_X decomposition catalyst.