JP2010201334A - Oxidation catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide oxidation catalysts which can display excellent oxidation performance. <P>SOLUTION: An oxidation catalyst 1 includes at least a first catalyst 10 containing iron, cerium and lanthanum and a second catalyst 20 (excluding the first catalyst) containing iron and cerium. The ratio [M<SB>2</SB>/(M<SB>1</SB>+M<SB>2</SB>)] of the mass (M<SB>2</SB>) of the second catalyst 20 to the total mass (M<SB>1</SB>+M<SB>2</SB>) of the first catalyst 10 and the second catalyst 20, is not less than 0.4 and less than 1.0. Another oxidation catalyst 1 includes at least the first catalyst 10 containing iron, cerium and lanthanum and the second catalyst 20 (excluding the first catalyst) containing iron and cerium. The ratio [M<SB>2</SB>/(M<SB>1</SB>+M<SB>2</SB>)] of the mass (M<SB>2</SB>) of the second catalyst 20 to the total mass (M<SB>1</SB>+M<SB>2</SB>) of the first catalyst 10 and the second catalyst 20, is not less than 0.4 and less than 0.8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oxidation catalyst. More specifically, the present invention relates to an oxidation catalyst comprising a first catalyst containing iron, cerium and lanthanum and a second catalyst containing iron and cerium in a predetermined ratio.

  Conventionally, the problem relating to the use of iron as a catalyst metal has been solved, and as an exhaust gas purification catalyst having a good oxygen storage capacity (OSC), the ceria-zirconia composite oxide and dispersed therein are at least partially dissolved. An exhaust gas purifying catalyst containing iron oxide is disclosed (see Patent Document 1).

JP 2008-18322 A

  However, the exhaust gas purification catalyst described in Patent Document 1 has a problem that the oxidation performance is not sufficient.

  The present invention has been made in view of such problems of the prior art. And the place made into the objective is to provide the oxidation catalyst which can express the outstanding oxidation performance.

The present inventor has intensively studied to achieve the above object.
As a result, by including a first catalyst containing iron, cerium and lanthanum and a second catalyst containing iron and cerium (excluding the first catalyst) at least in a predetermined ratio, The inventors have found that the above object can be achieved and have completed the present invention.

That is, the oxidation catalyst of the present invention includes at least a first catalyst containing iron, cerium, and lanthanum, and a second catalyst containing iron and cerium (excluding the first catalyst). The ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the second catalyst is 0.4 or more and less than 1.0. Features.

  According to the present invention, the first catalyst containing iron, cerium, and lanthanum and the second catalyst containing iron and cerium (excluding the first catalyst) are included at least in a predetermined ratio. An oxidation catalyst capable of exhibiting excellent oxidation performance in a lean atmosphere can be provided.

It is explanatory drawing which shows the schematic structure of the oxidation catalyst which concerns on 1st Embodiment. It is explanatory drawing which shows schematic structure of the oxidation catalyst which concerns on 2nd Embodiment. It is explanatory drawing which shows schematic structure of the oxidation catalyst which concerns on 3rd Embodiment. It is explanatory drawing which shows schematic structure of the oxidation catalyst which concerns on 4th Embodiment. It is explanatory drawing which shows the schematic structure of the oxidation catalyst which concerns on 5th Embodiment. It is explanatory drawing which shows schematic structure of the oxidation catalyst which concerns on 6th Embodiment. (A) And (b) is a graph which shows CO conversion rate of the oxidation catalyst of each example in 500 degreeC and 400 degreeC in lean atmosphere.

  Hereinafter, the oxidation catalyst according to the embodiment of the present invention will be described in detail.

The oxidation catalyst according to the embodiment of the present invention exhibits excellent oxidation performance, particularly in a lean atmosphere, and includes a first catalyst containing iron (Fe), cerium (Ce), and lanthanum (La), and iron (Fe ) And a second catalyst (excluding the first catalyst) containing cerium (Ce). Further, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It is what is.

Although not particularly limited, the ratio of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst [M ₂ / (M ₁ + M ₂ )]. Is preferably 0.4 or more and less than 0.8, and more preferably 0.6 or more and less than 0.8.
In the above preferable range, for example, excellent oxidation performance can be exhibited even at 400 ° C. in a lean atmosphere (A / F> 14.6). Moreover, when it is the above-mentioned more preferable range, the outstanding oxidation performance can be exhibited also in 400 degreeC and 500 degreeC, for example in a lean atmosphere.

Furthermore, although not particularly limited, for example, it is desirable that the first catalyst and the second catalyst have different oxidation performance with respect to the oxygen partial pressure.
Specifically, for example, in a rich atmosphere to a lean atmosphere, even if the first catalyst increases the oxygen partial pressure, the oxidation performance does not change so much, and when the second catalyst increases the oxygen partial pressure, the oxidation performance improves. It is desirable to be a thing. In other words, in a rich atmosphere to a lean atmosphere, it is desirable that the first catalyst has a rate-determining oxygen desorption reaction in the catalytic reaction, and the second catalyst has a rate-determining oxygen absorption reaction in the catalytic reaction. .
More specifically, for example, the first catalyst and the second catalyst have a relatively high oxidation performance in the rich atmosphere (A / F <14.6), and the lean atmosphere ( In A / F> 14.6), it is desirable to satisfy the relationship that the oxidation performance of the second catalyst is relatively high.
At present, it is presumed that by combining the first catalyst and the second catalyst exhibiting such a tendency of oxidation performance, the oxidation-reduction cycle is accelerated and the oxidation performance is further improved. It is not necessarily limited to such a combination of the first catalyst and the second catalyst.

Such a difference in oxidation performance can be determined, for example, by measuring the CO conversion rate with respect to the oxygen partial pressure in various atmospheres from a rich atmosphere to a lean atmosphere.
In addition, the first catalyst made of Fe—Ce oxide and the second catalyst made of Fe—Ce—La oxide have different oxidation performance against oxygen partial pressure, and the oxidation of the first catalyst is performed in a rich atmosphere. The performance is relatively high, and the relationship that the oxidation performance of the second catalyst is relatively high in a lean atmosphere is satisfied. Further, in the rich atmosphere to the lean atmosphere, even if the first catalyst increases the oxygen partial pressure, the oxidation performance does not change much, and when the second catalyst increases the oxygen partial pressure, the oxidation performance improves.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is an explanatory diagram showing a schematic configuration of an oxidation catalyst according to the first embodiment. As shown in the figure, the oxidation catalyst of the first embodiment is composed of particles 11b containing iron and cerium on which particles 11a containing lanthanum are supported, as the first catalyst containing iron, cerium and lanthanum. The first catalyst particles 10 and the second catalyst particles 20 composed of particles 21 containing iron and cerium are contained as the second catalyst (excluding the first catalyst) containing iron and cerium.
Note that the iron and cerium-containing particles 11b on which lanthanum-containing particles are supported, and the iron and cerium-containing particles 21 on which lanthanum-containing particles are not supported are a scanning electron microscope (SEM), It can be discriminated as different depending on a photograph or processed image obtained by an electronic probe microanalyzer (EPMA). Further, the location of lanthanum in the particles 11 can be identified as different by qualitative analysis using a transmission electron microscope (TEM) or an energy dispersive X-ray spectrometer (EDX).
Further, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It has become.

Here, examples of the particles containing lanthanum include lanthanum (La) oxide particles. The average particle size of the lanthanum-containing particles is preferably 10 nm to 2 μm from the viewpoint of improving the oxidation performance.
The average particle diameter was measured and calculated directly from photographs and processed images in an arbitrary observation region such as SEM and EPMA because it was observed that particles containing lanthanum were dispersed almost uniformly. Things can be applied.

  Examples of particles containing iron and cerium on which such lanthanum-containing particles are carried include iron (Fe) -cerium (Ce) oxide particles. Moreover, it is preferable from a viewpoint of the improvement of oxidation performance that the average particle diameter of the particle | grains containing iron and cerium is 10 nm-2 micrometers. Furthermore, the average particle diameter of the particles containing iron and cerium is preferably 10 nm to 500 nm from the viewpoint of improving the oxidation performance.

  Furthermore, the metal atomic ratio of iron and cerium in the particles containing iron and cerium is preferably Fe: Ce = 1: 0.05 to 1: 1.0 from the viewpoint of improving oxidation performance. Furthermore, the metal atomic ratio of iron and cerium to lanthanum in particles containing iron, cerium and lanthanum is Fe + Ce: La = 1: 0.05 to 1: 1 from the viewpoint of improving the oxidation performance. preferable.

(Second Embodiment)
FIG. 2 is an explanatory diagram showing a schematic configuration of the oxidation catalyst according to the second embodiment. Moreover, about the thing equivalent to what was demonstrated in 1st Embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.
As shown in the figure, the oxidation catalyst according to the second embodiment includes, as the first catalyst containing iron, cerium, and lanthanum, first catalyst particles 10 composed of particles 13 containing iron, cerium, and lanthanum, and iron. And a second catalyst particle 20 composed of particles 21 containing iron and cerium as the second catalyst containing cerium (excluding the first catalyst).
In addition, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It has become.

  Here, examples of the particles containing iron, cerium, and lanthanum include iron (Fe) -cerium (Ce) -lanthanum (La) oxide particles. Further, as the iron (Fe) -cerium (Ce) -lanthanum (La) oxide particles, for example, an oxide in which at least a part of lanthanum (La) is dissolved in iron (Fe) -cerium (Ce) oxide. Particles can be mentioned. Moreover, it is preferable from a viewpoint of the improvement of oxidation performance that the average particle diameter of the particle | grains containing iron, cerium, and lanthanum is 10 nm-2 micrometers.

  The metal atomic ratio of iron and cerium to lanthanum in particles containing iron, cerium, and lanthanum is preferably Fe + Ce: La = 1: 0.05 to 1: 1 from the viewpoint of improving oxidation performance. .

(Third embodiment)
FIG. 3 is an explanatory diagram showing a schematic configuration of the oxidation catalyst according to the third embodiment. Moreover, about the thing equivalent to what was demonstrated in 1st or 2nd embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.
As shown in the figure, the oxidation catalyst of the third embodiment is a first catalyst containing iron, cerium, and lanthanum, and particles 11b containing iron and cerium on which particles 11a containing lanthanum are supported and iron. First catalyst particle 10 comprising particles 13 containing cerium and lanthanum, and second catalyst comprising particles 21 containing iron and cerium as a second catalyst containing iron and cerium (excluding the first catalyst). The particles 20 are contained.
In addition, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It has become.

  The manufacturing method of the oxidation catalyst which concerns on the 1st-3rd embodiment mentioned above is demonstrated concretely.

The first catalyst and the second catalyst can be prepared, for example, by a precipitation method. Specifically, first, a precipitant is added while stirring an aqueous solution of a metal salt such as iron (Fe), cerium (Ce), or lanthanum (La) to generate a precipitate. Conversely, an aqueous solution of a metal salt may be added to an aqueous solution of a precipitant to generate a precipitate. As the metal salt, nitrates, sulfates, carbonates and the like of the above metals can be used. Moreover, as a precipitant, sodium carbonate aqueous solution, sodium hydroxide aqueous solution, and ammonia aqueous solution can be used, By this, the precipitate which consists of hydroxides can be obtained. Next, in order to remove unnecessary components, the precipitate is washed with distilled water and filtered. Thereafter, the washed precipitate is dried and fired. Furthermore, if necessary, the first catalyst and the second catalyst after calcination are pulverized to make the average particle diameter 1 nm to 2 μm. For the pulverization, a ball mill or a bead mill can be used.
The average particle size is, for example, a dynamic light scattering type particle size distribution measuring apparatus (manufactured by Horiba, Ltd., LB-550) that executes a dynamic light scattering method, or a particle size distribution analyzer (stock) It can be measured using a company HORIBA, Ltd., LA-920 type. The average particle diameter and the above-described average particle diameter can be substantially matched as the size tendency. That is, if the average particle size at the time of production is reduced, the average particle size in the product is also reduced.

  The first catalyst and the second catalyst can be prepared by utilizing high frequency induction heating. High frequency induction heating is a phenomenon in which when the metal is inserted into a coil connected to an AC power source, the metal itself generates heat despite the coil and the metal being separated. That is, this is a phenomenon in which a high-density eddy current is generated near the surface of the metal that is the object to be heated by an alternating current, and the object to be heated generates heat due to its Joule heat. The metal oxide is evaporated by high-frequency induction heating of the metal in oxygen gas. Then, the metal oxide can be obtained by reacting the evaporated metal with oxygen gas. Moreover, you may grind | pulverize the obtained metal oxide with a bead mill etc. as needed. High frequency induction heating can be performed using a commercially available high frequency induction heating apparatus.

  Thus, the first catalyst and the second catalyst can be prepared by utilizing a precipitation method or high-frequency induction heating. However, the present invention is not limited to these production methods, and any method can be used as long as the first catalyst and the second catalyst can be obtained. For example, the first catalyst can be obtained by further impregnating a dried product, which is an example of the precursor of the second catalyst, with an aqueous solution of a metal salt of lanthanum (La), drying, and calcining. Furthermore, you may grind | pulverize the obtained 1st catalyst with a bead mill etc. as needed.

In addition, the first to third embodiments can be made by the following methods, for example.
The first catalyst in the first embodiment can be obtained by impregnating the second catalyst with an aqueous solution of a metal salt of lanthanum (La) and calcining at a low temperature. Thereafter, the oxidation catalyst according to the first embodiment can be manufactured by mixing the first catalyst and the second catalyst.
Furthermore, the first catalyst in the second embodiment can be obtained by impregnating the second catalyst with an aqueous solution of a metal salt of lanthanum (La), calcining at a high temperature, and compositing. Moreover, it can also obtain by the coprecipitation method by three components mentioned above. Then, the oxidation catalyst which concerns on 2nd Embodiment can be manufactured by mixing a 1st catalyst and a 2nd catalyst.
Furthermore, the oxidation catalyst of the third embodiment can be manufactured by mixing the first catalyst in the first embodiment, the first catalyst in the second embodiment, and the second catalyst.

(Fourth embodiment)
FIG. 4 is an explanatory diagram showing a schematic configuration of the oxidation catalyst according to the fourth embodiment. Moreover, about the thing equivalent to what was demonstrated in 1st-3rd embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.
As shown in the figure, the oxidation catalyst of the fourth embodiment is composed of iron and cerium-containing particles 11b on which lanthanum-containing particles 11a are supported as the first catalyst containing iron, cerium and lanthanum. As the first catalyst particle 10, the second catalyst containing iron and cerium (excluding the first catalyst), the second catalyst particle 20 composed of particles 21 containing iron and cerium, and the inorganic base material particle 30 It contains.
The inorganic base particles 30 surround or fix the first catalyst particles 10 and the second catalyst particles 20.
In addition, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It has become.

  Here, as an inorganic base material, the inorganic oxide containing aluminum (Al), zirconium (Zr), titanium (Ti), silicon (Si), or tungsten (W) can be mentioned, for example. By setting it as such a structure, the said 1st catalyst and 2nd catalyst can function more effectively as an active point. Examples of such an inorganic substrate include those containing oxides such as aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, and tungsten oxide. Further, alumina, zirconia, titania, silica or tungsten oxide may be mixed and used as the inorganic base material. Further, an oxide in which two or more kinds of the inorganic oxides are dissolved may be used.

  Among them, zirconia, titania, silica, and tungsten oxide hardly form a complex oxide (solid solution) with the first catalyst and the second catalyst. Therefore, for example, the first catalyst and the second catalyst can be supported in a state dispersed in the oxide. Specifically, as shown in FIG. 4, the first catalyst particles 10 and the second catalyst particles 20 are included in a partition separated by inorganic base particles 30 such as zirconia, titania, syria, and tungsten oxide. It is preferable. As described above, in the oxidation catalyst, the first catalyst particles 10 and the second catalyst particles are included in the compartments separated by the inorganic base material particles 30, thereby exceeding the compartments separated by the inorganic base material particles 30. It can prevent that the particle | grains of the 1st catalyst particle 10 and the 2nd catalyst particle 20 contact directly, and it enlarges. Therefore, it is possible to suppress the reduction in the surface area of the first catalyst particles 10 and the second catalyst particles 20 and maintain the oxidation performance even in a high temperature state.

  Although not shown, when the inorganic base material is a porous body, the entire first catalyst particles and second catalyst particles may be surrounded. However, when the inorganic base material is not a porous body, when the entire particle is surrounded, the contact ratio between the first catalyst particle and the second catalyst particle and the exhaust gas may be reduced. Therefore, as shown in FIG. 4, it is preferable to partially surround the first catalyst particles 10 and the second catalyst particles so that the adjacent first catalyst particles and the second catalyst particles do not directly contact each other. .

(Fifth embodiment)
FIG. 5 is an explanatory diagram showing a schematic configuration of the oxidation catalyst according to the fifth embodiment. Moreover, about the thing equivalent to what was demonstrated in the 1st-4th embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.
As shown in the figure, the oxidation catalyst of the fifth embodiment is a first catalyst particle 10 composed of particles 13 containing iron, cerium and lanthanum, as the first catalyst containing iron, cerium and lanthanum, As the second catalyst containing cerium and lanthanum (excluding the first catalyst), the second catalyst particles 20 composed of particles 21 containing iron and cerium and the inorganic base particles 30 are contained.
The inorganic base particles 30 surround or fix the first catalyst particles 10 and the second catalyst particles 20.
Incidentally, the second catalyst mass with respect to the first catalyst and the total mass of the second catalyst _{(M 1 + M 2) (} M 2) the ratio of _{[M 2 / (M 1 +} M 2)] is 0.4 or more and less than 1.0 It has become.

(Sixth embodiment)
FIG. 6 is an explanatory diagram showing a schematic configuration of an oxidation catalyst according to a sixth embodiment. Moreover, about the thing equivalent to what was demonstrated in 1st-5th embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.
As shown in the figure, the oxidation catalyst of the sixth embodiment is a first catalyst containing iron, cerium, and lanthanum, and particles 11b containing iron and cerium on which particles 11a containing lanthanum are supported and iron. First catalyst particle 10 comprising particles 13 containing cerium and lanthanum, and second catalyst comprising particles 21 containing iron and cerium as a second catalyst containing iron and cerium (excluding the first catalyst). The particles 20 and the inorganic base particles 30 are contained.
The inorganic base particles 30 surround or fix the first catalyst particles 10 and the second catalyst particles 20.
In addition, the ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and less than 1.0. It has become.

  Next, the manufacturing method of the oxidation catalyst which concerns on the 4th-6th embodiment mentioned above is demonstrated concretely.

  First, the first catalyst particles and the second catalyst particles prepared as described above are dispersed in a solvent to prepare a slurry. For example, water can be used as the solvent. Next, a slurry in which the inorganic base material precursor is dispersed in a solvent is prepared separately. As the precursor, alumina sol can be used when the inorganic base material is alumina, zirconia sol when zirconia is used, titania sol when titania is used, and silica sol when silica is used. Next, the slurry containing the first catalyst and the second catalyst in the form of fine particles and the slurry of the precursor are mixed and stirred at a high speed, so that the first catalyst and the second catalyst are used as the inorganic substrate precursor. Surrounds the fine particles. Then, an oxidation catalyst can be obtained by drying and baking the slurry containing the first catalyst particles and the second catalyst particles surrounded by the precursor.

For example, a monolithic structure type oxidation catalyst having a catalyst layer containing an oxidation catalyst may be formed by coating a slurry containing the obtained oxidation catalyst on a monolithic structure type carrier. Further, the present invention is not limited to this. For example, a monolithic oxidation catalyst having a catalyst layer including an oxidation catalyst is formed by directly coating a monolithic carrier with a slurry which is an example of an oxidation catalyst precursor. Also good.
Here, as the monolithic structure type carrier, a monolithic carrier or a honeycomb carrier made of a heat-resistant material such as ceramics such as cordierite or metals such as ferritic stainless steel is used.

  Moreover, the slurry prepared by grind | pulverizing an inorganic base material with a bead mill instead of the said precursor can also be used. Specifically, zirconia, titania, silica, tungsten oxide or the like as an inorganic base material is pulverized to 500 nm or less, more specifically about 60 to 150 nm using a bead mill to prepare an inorganic base material slurry. To do. Then, the slurry of the inorganic base material and the slurry containing the first catalyst and the second catalyst in the form of fine particles are mixed and stirred at a high speed, whereby the first catalyst and the second catalyst are made of the inorganic base material fine particles. Surrounds the fine particles. Then, the oxidation catalyst can be obtained by drying and firing the slurry containing the first catalyst particles and the second catalyst particles surrounded by the fine particles of the inorganic base material.

  As the first catalyst particles surrounded by the inorganic base material, as shown in FIGS. 1 to 3, the particles 11 a containing lanthanum (La) are supported from the particles 11 b containing iron and cerium supported on the surface. The first catalyst particles 10 may be the first catalyst particles 10 composed of the particles 13 containing iron, cerium, and lanthanum, for example, solid solution particles containing iron, cerium, and lanthanum.

  By containing an inorganic base material as described above, the first catalyst and the second catalyst can function more effectively as active sites. For example, agglomeration of the first catalyst and the second catalyst, which can occur due to long-term use under high temperature conditions, can be suppressed. Accordingly, the first catalyst and the second catalyst can function more effectively as active sites even under long-term use under high temperature conditions. In particular, from the viewpoint of stability under high temperature conditions, it is preferable to apply zirconium oxide as the inorganic base material.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

Example 1
<Preparation of Fe-Ce oxide>
Iron nitrate and cerium nitrate were weighed so that Fe: Ce = 1: 1 (metal atomic ratio), poured into distilled water, stirred and dissolved. Next, a pH meter (manufactured by YOKOGAWA, MODEL PH81) was installed so that the pH of the obtained solution could be confirmed. Next, a sodium carbonate aqueous solution separately prepared was slowly dropped into the obtained solution to form a precipitate so that the pH was between 8.0 and 8.5. Thereafter, it was aged overnight. Subsequently, the precipitate obtained by aging was separated by suction filtration. Next, the precipitate obtained by filtration was washed with distilled water. In the cleaning, nitric acid was added to a container for receiving the distilled water after the cleaning, and the cleaning was repeated until the foaming of carbonic acid generated from nitric acid and sodium carbonate disappeared in the container.
Further, the precipitate obtained by washing was dried at 80 ° C. overnight. Thereafter, a part of the obtained dried product was calcined in a muffle furnace at 550 ° C. for 3 hours in the air and cooled to room temperature in the air to obtain an Fe—Ce oxide used in this example. The average particle diameter of the obtained Fe—Ce oxide was 10 μm.

<Preparation of Fe-Ce-La oxide>
The dried product obtained above was impregnated with an aqueous lanthanum nitrate solution and dried at 80 ° C. overnight. Thereafter, the obtained dried product was baked in a muffle furnace at 550 ° C. for 3 hours in the air and cooled to room temperature in the air to obtain an Fe—Ce—La oxide used in this example. The average particle diameter of the obtained Fe—Ce—La oxide was 8 μm.
At this time, the metal atomic ratio of iron, cerium, and lanthanum is Fe: Ce: La = 1: 1: 0.2 in the ratio of charged raw materials.

<Preparation of oxidation catalyst>
The obtained Fe—Ce oxide and Fe—Ce—La oxide were weighed so that Fe—Ce oxide: Fe—Ce—La oxide = 0.75: 0.25 (mass ratio). The mixture was mixed in a mortar for 10 minutes to obtain an oxidation catalyst of this example. The average particle size of this mixture was 1.8 μm.

(Example 2)
In the preparation of the oxidation catalyst of Example 1, the Fe—Ce oxide and the Fe—Ce—La oxide obtained in Example 1 were changed to Fe—Ce oxide: Fe—Ce—La oxide = 0.5. : The same operation as in Example 1 was repeated except that the weight was adjusted to 0.5 (mass ratio) to obtain an oxidation catalyst of this example.

(Comparative Example 1)
In the preparation of the oxidation catalyst of Example 1, the Fe—Ce oxide and the Fe—Ce—La oxide obtained in Example 1 were mixed with Fe—Ce oxide: Fe—Ce—La oxide = 1: 0. The same operation as Example 1 was repeated except that it was weighed so as to have a (mass ratio) to obtain an oxidation catalyst of this example.

(Comparative Example 2)
In the preparation of the oxidation catalyst of Example 1, the Fe—Ce oxide and the Fe—Ce—La oxide obtained in Example 1 were used as Fe—Ce oxide: Fe—Ce—La oxide = 0: 1. The same operation as Example 1 was repeated except that it was weighed so as to have a (mass ratio) to obtain an oxidation catalyst of this example.

(Comparative Example 3)
In the preparation of the oxidation catalyst of Example 1, the Fe—Ce oxide and the Fe—Ce—La oxide obtained in Example 1 were used as Fe—Ce oxide: Fe—Ce—La oxide = 0.25. : The same operation as Example 1 was repeated except that it was weighed so that it might become 0.75 (mass ratio), and the oxidation catalyst of this example was obtained.
Table 1 shows a part of the specifications of the above examples.

[Performance evaluation]
0.1 g of the oxidation catalyst in each of the above examples was weighed and the following reaction test was performed.

(Reaction test)
A glass reaction tube was charged with 0.1 g of the oxidation catalyst of Example 1, and a reaction test was performed using a catalyst analyzer (BELCAT, manufactured by Nippon Bell Co., Ltd.) under the following conditions. A similar reaction test was performed on Example 2 and Comparative Examples 1 to 3.

Gas composition: CO; 0.5 _vol%, O 2; 0.5 vol%, the He; Balance Temperature: 500 ℃, 400 ℃
・ Gas flow rate: 50 cm ³ / min ・ Detection method: Q ・ mass

  And performance was evaluated by calculating CO conversion rate (%) by the following formula | equation (1). The obtained results are also shown in Table 1. Moreover, the obtained result is shown to Fig.7 (a) and (b).

As can be seen from Table 1 and FIG. 7, the oxidation catalysts of Examples 1 and 2 belonging to the scope of the present invention may have better oxidation performance than the oxidation catalysts of Comparative Examples 1 to 3 outside the present invention. I understand.
In particular, it can be seen that the oxidation catalyst of Example 1 is excellent in oxidation performance at 400 ° C. and 500 ° C. in a lean atmosphere.

1,1 ′ oxidation catalyst 10 first catalyst particle 20 second catalyst particle

Claims (3)

A first catalyst containing iron, cerium and lanthanum;
A second catalyst (excluding the first catalyst) containing iron and cerium, and
The ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more. An oxidation catalyst characterized by being less than 0. The ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.4 or more and 0.00. The oxidation catalyst according to claim 1, wherein the oxidation catalyst is less than 8. The ratio [M ₂ / (M ₁ + M ₂ )] of the mass (M ₂ ) of the second catalyst to the total mass (M ₁ + M ₂ ) of the first catalyst and the second catalyst is 0.6 or more and 0.00. The oxidation catalyst according to claim 1 or 2, wherein the oxidation catalyst is less than 8.

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