WO2014034524A1

WO2014034524A1 - Exhaust gas purifying catalyst

Info

Publication number: WO2014034524A1
Application number: PCT/JP2013/072437
Authority: WO
Inventors: 中原　祐之輔; 央記法師人; 誠治森内; 博昭奥村; 文和木俣; 豊史津田; 清藏宮田; 亀山　秀雄; ユ郭
Original assignee: 三井金属鉱業株式会社; スズキ株式会社
Priority date: 2012-08-27
Filing date: 2013-08-22
Publication date: 2014-03-06
Also published as: DE112013004202B4; DE112013004202T5; CN104302392A; JP2014042880A; JP5921387B2

Abstract

The present invention relates to an exhaust gas purifying catalyst that contains C-Fe-Ce, and provides a novel catalyst for exhaust gases, which is able to exhibit stable purification performance even if the flow rate of an exhaust gas changes, while having durability in terms of wide temperature changes. Proposed is an exhaust gas purifying catalyst which has a configuration wherein a mixture containing carbon (C), iron (Fe) and cerium (Ce) is supported by an inorganic porous powdery carrier, and which is characterized in that the content of the mixture relative to the inorganic porous powdery carrier is 10-300% by mass.

Description

Exhaust gas purification catalyst

The present invention relates to an exhaust gas purification catalyst that can be used to purify exhaust gas discharged from an internal combustion engine.

The exhaust gas from gasoline fueled vehicles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The hydrocarbon (HC) is oxidized to be converted to water and carbon dioxide, the carbon monoxide (CO) is oxidized to be converted to carbon dioxide, and the nitrogen oxide (NOx) is reduced to be converted to nitrogen It is necessary to purify each harmful component with a catalyst.
As a catalyst for treating such exhaust gas (hereinafter referred to as "exhaust gas purification catalyst"), a three-way catalyst (Three way catalysts: TWC) capable of oxidizing and reducing CO, HC and NOx is used. . The three-way catalyst is generally mounted in the form of a converter between the engine and the muffler of the exhaust pipe.

As such a three-way catalyst, a refractory oxide porous body having a high specific surface area, for example, an alumina porous body having a high specific surface area, such as platinum (Pt), palladium (Pd), rhodium (Rh), etc. It is known to carry a noble metal and to carry it on a substrate, for example a monolithic substrate made of a refractory ceramic or metal honeycomb structure, or on refractory particles. There is.

In this type of three-way catalyst, precious metals oxidize hydrocarbons in exhaust gas to convert them into carbon dioxide and water, oxidize carbon monoxide to convert them into carbon dioxide, and reduce nitrogen oxides to nitrogen It is preferable to keep the ratio of fuel to air (air-fuel ratio) constant (at the theoretical air-fuel ratio) in order to effectively generate catalytic action for both reactions simultaneously.
In an internal combustion engine such as a car, the air-fuel ratio changes largely according to the operating conditions such as acceleration, deceleration, low-speed traveling, high-speed traveling, etc. / F) is controlled constant. However, just by controlling the air-fuel ratio (A / F) in this way, the catalyst can not sufficiently exhibit the purification catalyst performance, so the function of controlling the air-fuel ratio (A / F) also in the catalyst layer itself is Desired. Then, the catalyst which added the co-catalyst to the precious metal which is a catalyst active component is used for the purpose of preventing the fall of the purification performance of the catalyst which arises due to change of an air fuel ratio with the chemical action of catalyst itself.

As such a cocatalyst, there is known a cocatalyst (referred to as “OSC material”) having an oxygen storage capacity (OSC: Oxygen Storage Capacity) which releases oxygen in a reducing atmosphere and absorbs oxygen in an oxidizing atmosphere. For example, ceria (cerium oxide, CeO ₂ ), ceria-zirconia composite oxide, etc. are known as OSC materials having an oxygen storage ability.

By the way, since the price of precious metals is so high that most of the price of catalyst is precious metals, development of new catalytically active components to replace precious metals is being carried out.
For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2005-296735) discloses a catalyst in which iron oxide is supported on a carrier containing a ceria-zirconia composite oxide.
Further, Patent Document 2 (Japanese Patent Laid-Open No. 2004-160433) includes a catalyst comprising a complex oxide of iron and at least one metal selected from the group consisting of ceria, zirconia, aluminum, titanium and manganese. It is disclosed.
Patent Document 3 (Japanese Unexamined Patent Publication No. 2008-18322) discloses a catalyst having a structure in which iron oxide is dispersed in a ceria-zirconia composite oxide and at least partially in solid solution.

Further, Patent Document 4 (Japanese Unexamined Patent Publication No. 2012-50980) discloses an exhaust gas purification catalyst consisting of carbon (C) -iron (Fe) -cerium (Ce).

JP 2005-296735 A JP 2004-160433 A JP, 2008-18322, A JP, 2012-50980, A

In addition to durability against severe temperature changes, catalysts for automobiles are required to have performance capable of exhibiting stable purification performance even when the flow velocity of exhaust gas changes. When the heat treatment is performed for a long time at a high temperature of 900 to 1,000 ° C. in the atmosphere to guarantee the durability of the exhaust gas purification catalyst, the exhaust gas catalyst tends to reduce the surface area and the catalyst activity by sintering. There is. In particular, C-Fe-Ce catalyst, which has high catalytic activity, has a problem that sintering tendency is strong.

Therefore, an object of the present invention is to provide a new exhaust gas purification catalyst containing C-Fe-Ce, which has not only durability against severe temperature change, but also new performance capable of exhibiting stable purification performance even when the flow velocity of exhaust gas changes. To provide an exhaust gas catalyst.

In order to achieve the above object, the present invention is characterized in that a mixture containing carbon (C), iron (Fe) and cerium (Ce) is supported on an inorganic porous powdery carrier. Proposes an exhaust gas purification catalyst.

The exhaust gas purification catalyst proposed by the present invention has a mixture containing carbon (C), iron (Fe) and cerium (Ce) supported on an inorganic porous powdery support, and has a temperature of 900 to 1,000.degree. Even when exposed to high temperatures, sintering is suppressed, and as a result, it is possible to exhibit stable purification performance at a high level even if the durability is high and the flow velocity of the exhaust gas changes.
The reason why sintering is suppressed even when exposed to high temperature as described above is that many fine pores are present on the surface of the inorganic porous powdery carrier, and carbon in the state of entering into each of the pores It can be considered that sintering is suppressed as a result of preventing contact with the adjacent mixture because there is a mixture containing (C), iron (Fe) and cerium (Ce). In addition, a mixture containing carbon (C), iron (Fe) and cerium (Ce) is dispersed on the inorganic porous powdery support, the reaction effective area is increased, and the purification performance is stable even if the flow rate of the exhaust gas changes. It can be considered that the

It is the schematic of the apparatus which measures model gas concentration used by the performance test of the catalyst of an Example. It is the schematic of the reaction tube in the apparatus of FIG. It is the figure which showed the measured value of T50 in an Example as a triangular composition isoactivity diagram which makes carbon + iron, cerium, and an alumina the top.

Next, an embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

<Exhaust gas purification catalyst>
In an exhaust gas purification catalyst (referred to as "the present catalyst") as an example of an embodiment of the present invention, a mixture containing carbon (C), iron (Fe) and cerium (Ce) is supported on an inorganic porous powdery carrier An exhaust gas purification catalyst having a configuration as described above.

Here, as said mixture containing carbon (C), iron (Fe) and cerium (Ce), a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide can be mentioned.
At this time, iron carbide (Fe ₃ C), iron oxide and cerium oxide each act as active sites showing an oxidation / reduction action. Among them, Fe ₃ C exhibits high activity as an active site exhibiting an oxidation / reduction action. However, on the other hand, when Fe ₃ C is used alone, for example, when it is subjected to durability treatment at 900 ° C. to 1,000 ° C., most of it is oxidized to form oxides such as Fe ₂ O ₃ because of its low heat resistance. It is usual that the activity will be greatly reduced. However, as a result of supporting the present catalyst as a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide on an inorganic porous powdery support, it has high catalytic activity even after such durability treatment Can be demonstrated.

In the present catalyst, the content of the mixture relative to the inorganic porous powdery carrier (100% by mass) is preferably 10.0 to 300% by mass, and more preferably at least 20.0% by mass or at most 180% by mass Are particularly preferable, and among them, it is particularly preferable that the content is 30% by mass or more or 120% by mass or less.
In the present catalyst, if the content of the mixture with respect to the inorganic porous powdery support is 300% by mass or less, the composite carbonated particles can be prevented from being in intimate contact with each other, and when exposed to high temperatures. Since the sintering can be prevented, it is possible to suppress the decrease of the purification rate due to the reduction of the effective area. On the other hand, if it is 10.0 mass% or more, the number of catalyst particles can be maintained, and the purification rate can be maintained by the presence of effective active sites.

Further, the mass ratio of C, Fe, and Ce atoms (C: Fe: Ce) contained in the mixture is 0.01 to 1.4 with respect to the total amount (100 mass%) of C, Fe, and Ce. It is preferable that the content is 0.1% to 98.9% by mass: 0.1% to 98.9% by mass.

From this point of view, the content of carbon (C) is preferably 0.01 to 1.4% by mass, particularly 0.3% by mass, with respect to the total amount (100% by mass) of C, Fe and Ce. It is more preferable that the content is above or 1.3 mass% or less.
The content of iron (Fe) is preferably 0.1 to 98.9% by mass with respect to the total amount (100% by mass) of C, Fe and Ce, and in particular, 7.8% by mass or more or 98. The content is particularly preferably 7% by mass or less, and more preferably 26.7% by mass or more or 90.8% by mass or less.
The content of cerium (Ce) is preferably 0.1 to 98.9% by mass with respect to the total amount (100% by mass) of C, Fe and Ce, and more preferably 0.1% by mass or more or 92. The content is particularly preferably 1% by mass or less, and more preferably 7.9% by mass or more or 73.0% by mass or less.

The mixture may further contain Co. Heat resistance can be improved by containing Co.
The content of Co is preferably more than 0.1% by mass and less than 15% by mass, and more preferably 5% by mass or more or 10% by mass or less based on the total amount (100% by mass) of C, Fe and Ce Is preferred.

(Inorganic porous powdery carrier)
Examples of the inorganic porous powdery carrier include a compound selected from the group consisting of silica, alumina and a titania compound, or an inorganic porous powdery carrier consisting of an OSC material such as ceria-zirconia complex oxide. .
More specifically, there can be mentioned, for example, porous powder comprising a compound selected from alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia and alumina-ceria.

As the alumina, alumina having a specific surface area of more than 50 m ² / g, such as γ, δ, θ, α alumina can be used. Among them, it is preferable to use γ or θ alumina. In addition, about alumina, in order to raise heat resistance, a trace amount of lanthanum (La) can also be included.

As an OSC material, a cerium compound, a zirconium compound, ceria-zirconia complex oxide etc. can be mentioned, for example.

(Other ingredients)
The present catalyst may have a constitution in which a noble metal is supported on an inorganic porous powdery carrier in addition to the above mixture.
The amount of the noble metal supported is preferably 0.01% by mass or more, and more preferably 0.41% by mass or more, based on the mass (100% by mass) of the catalyst powder to be supported.

Under the present circumstances, palladium (Pd), platinum (Pt), rhodium (Rh) can be mentioned as a precious metal. Among these, palladium (Pd) and platinum (Pt) are remarkably preferable.

(Manufacturing method)
Next, an example of a method for producing the present catalyst will be described. However, it is not limited to such a manufacturing method.

For example, an inorganic porous powdery carrier is added to a solution of an iron compound and a cerium compound, and after the iron compound and the cerium compound are attached to the inorganic porous powdery carrier, the inorganic porous powdery carrier is heated and calcined in the air to obtain the inorganic compound. The present catalyst can be produced by supporting iron oxide and cerium oxide on a porous powdery carrier and then heating in a reactive carbon-containing gas atmosphere such as carbon monoxide (CO) gas.

Under the present circumstances, as a method of making an iron compound and a cerium compound adhere to an inorganic porous powdery carrier, for example, after adding an inorganic porous powdery carrier to the solution of an iron compound and a cerium compound, ammonia water and carbonic acid are stirred, A complex hydroxide of Fe and Ce or a complex carbonate is precipitated by adding an alkaline substance such as sodium dropwise to adjust the pH to 10-11. The method of washing the precipitate with water and drying can be mentioned. However, it is not limited to such a method.
In addition to the method of heating in a reactive carbon-containing gas atmosphere, it is also possible to employ a method in which a carbon-containing substance is coexistent and heating is performed in an inert gas atmosphere.

As described above, since the Fe compound and the Ce compound are deposited in the solution state on the inorganic porous powdery carrier, the Fe and Ce can enter into the fine pores, and the catalyst is very well dispersed. You can get
In addition, heating is performed in a reactive carbon-containing gas atmosphere such as CO gas, in other words, when CO treatment is performed by a vapor phase method, a mixture of iron oxide and cerium oxide is uniformly dispersed in the inorganic porous powdery carrier Not only can it be supported in a state, but it is also possible to disperse carbon (C) as iron carbide uniformly.

<Catalyst structure>
An exhaust gas purification catalyst structure (referred to as "the present catalyst structure") can be produced by forming a catalyst layer containing the present catalyst on a base material.

For example, a catalyst layer can be formed by wash-coating a catalyst composition containing the present catalyst on the surface of a substrate exhibiting a honeycomb (monolith) structure, to form a catalyst structure.

(Base material)
In the catalyst structure, examples of the material of the base include refractory materials such as ceramics and metal materials.
The material of the ceramic base material is refractory ceramic material such as cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicate, Zircon, petalite, alpha alumina and aluminosilicates can be mentioned.
The material of the metallic substrate can include refractory metals, such as stainless steel or other suitable corrosion resistant alloys based on iron.

The shape of the substrate may be honeycomb, pellet, or spherical.

As the honeycomb material, in general, cordierite materials such as ceramics are often used. In addition, a honeycomb made of a metal material such as ferritic stainless steel can also be used.
When a honeycomb-shaped substrate is used, for example, a monolithic substrate having a large number of fine gas flow passages parallel to the inside of the substrate, ie, channels, can be used so that the fluid can flow inside the substrate. At this time, the catalyst composition can be coated on the inner wall surface of each channel of the monolithic substrate by wash coating or the like to form a catalyst layer.

(Catalyst composition)
As a catalyst composition for forming the catalyst layer of the present catalyst structure, in addition to the above-mentioned present catalyst, if necessary, a stabilizer and other components may be contained.

For example, a stabilizer can be blended for the purpose of suppressing the reduction of palladium oxide (PdOx) to metal under a fuel-rich atmosphere.
Examples of this type of stabilizer include alkaline earth metals and alkali metals. Among them, it is possible to select one or more of metals selected from the group consisting of magnesium, barium, calcium and strontium, preferably strontium and barium. Among them, barium is preferable from the viewpoint that the temperature at which PdO x is reduced is the highest, that is, it is difficult to be reduced.

Moreover, you may contain well-known addition components, such as a binder component.
As the binder component, an inorganic binder, for example, a water-soluble solution such as alumina sol, silica sol, or zirconia sol can be used. These can take the form of inorganic oxides when fired.

(Manufacturing method)
As an example for producing the present catalyst structure, the present catalyst is added to water, mixed, stirred by a ball mill or the like to form a slurry, and a substrate such as a ceramic honeycomb body is immersed in the slurry, The method of pulling up, baking, and forming a catalyst layer in the base-material surface etc. can be mentioned.
However, as a method for producing the present catalyst, any known method can be adopted, and the present invention is not limited to the above example.

<Explanation of the phrase>
In the present specification, when expressing as “X to Y” (where X and Y are arbitrary numbers), “preferably more than X” or “preferably Y” with the meaning of “X or more and Y or less” unless otherwise stated. Also includes the meaning of "smaller".
Also, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), “greater than X is preferable” or “preferably less than Y” It also includes the intention.

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

Examples 1 to 28 and Comparative Examples 1 to 10
After dissolving iron nitrate (II) (9 hydrate) and cerium nitrate (III) (hexahydrate) in pure water, alumina powder (m 001) or OSC material (ceria-zirconia complex oxide) while stirring Was added to make a mixed solution.
Under the present circumstances, the mass of iron nitrate (II) (9 hydrate), cerium nitrate (III) (hexahydrate), alumina powder and OSC material used is iron nitrate (II) (9 hydrate) The mass of iron atoms contained, the mass of cerium atoms contained in cerium (III) nitrate (hexahydrate), the mass of alumina, and the OSC material were adjusted to have the compositions shown in Table 1.

Next, ammonia water was dropped into the mixed solution until the pH reached 10-11, and the mixture was stirred for 3 hours at a rotation speed of 600 rpm of a stirrer. The solution was then filtered, the precipitate washed with water 2-3 times and then the precipitate was dried in a dryer at 120 ° C. Then, after calcining at 500 ° C. for 3 hours in the air atmosphere, it is pulverized using a mortar and heated at 525 ° C. for 4 hours in CO gas atmosphere to obtain iron carbide (Fe ₃ C), iron oxide and cerium oxide A C-Fe-Ce / alumina catalyst or a C-Fe-Ce / OSC material catalyst was obtained, having a configuration in which the mixture containing the catalyst is supported on alumina or OSC material.

(Method of quantifying each component)
Since the mass of iron atom, the mass of cerium atom, the mass of alumina, and the OSC material mass are respectively the same as the compounding amounts, quantification was not performed.
On the other hand, it was found that the amount of carbon can be measured by a carbon / sulfur analyzer (manufactured by Horiba, Ltd.) and can be determined by the C amount coefficient (19%) after heat treatment at a compounding amount × 500 ° C. or more and 1000 ° C. or less . Furthermore, since the amount of carbon may decrease due to a high heat reaction, when the amount of carbon after performing the durability treatment at 1,000 ° C. for 5 hours was measured, heating of 500 ° C. or more was performed in the above example. As a result, no change in carbon content was observed before and after the above-mentioned durability treatment.

(Durability test method)
The exhaust gas purification catalyst was treated under the endurance conditions shown in Table 2, and the durability was evaluated.

(Test method of catalyst performance)
Catalyst performance tests were conducted using the model gases shown in Table 3.

FIG. 1 is a schematic view of an apparatus for measuring the concentration of a model gas containing NOx, CO, H ₂ , and C ₃ H ₃ as HC. Moreover, the schematic of the reaction tube which is a part of said measuring apparatus is shown in FIG.
As shown in FIG. 1, the measuring apparatus comprising a standard gas cylinder 1, a mass flow controller 2, a water tank 3, a water pump 4, an evaporator 5, a reaction tube 6, a cooler 8, a gas analyzer 9, etc. Each model gas is generated from the gas cylinder 1, mixed by the mass flow controller 2, the water introduced from the water pump 4 is vaporized by the evaporator 5, and the gases are combined by the evaporator 5 to the reaction pipe 6 Introduce. Then, the reaction tube 6 containing the model gas is heated by the electric heating furnace 7.
Each model gas is oxidized or reduced by the catalyst 10 in the reaction tube 6. The gas after reaction is analyzed for composition by the gas analyzer 9 after water vapor is removed in the cooler 8.
The gas analyzer 9 can perform quantitative analysis of O ₂ , CO, N ₂ O, CO ₂ , HC (C ₃ H ₆ ), H _{2 and the} like by gas chromatography, and NOx, NO, NO ₂ , CO and the like can be quantitatively analyzed by the NOx analyzer.

The purification performance of the catalyst was evaluated as the conversion of each gas by the following calculation formula using the above-mentioned measuring apparatus.
NOx conversion rate = {(inlet NO molar flow rate 10 NO ₂ molar flow rate)-(outlet NO molar flow rate 10 NO ₂ molar flow rate) / (inlet NO molar flow rate 10 NO ₂ molar flow rate) x 100%

Since the present catalyst is produced by heat treatment in a CO gas atmosphere as a compounding ratio, amorphous C adheres to the surface, so a C amount larger than the stoichiometric carbon ratio of Fe ₃ C is measured. There is a thing. Therefore, in order to compare stable catalyst performance, it is desirable to evaluate the catalyst subjected to the durability treatment.
Therefore, after performing an endurance treatment at 1,000 ° C. for 5 hours as necessary, the temperature (T50) at which the conversion rate of NOx and the conversion rate of NOx become 50% was measured.

(Study on the effect of dispersing C-Fe-Ce catalyst on alumina powder)
The results of measuring the temperature (T50) at which the conversion of NOx of the catalyst obtained by dispersing C-Fe-Ce on alumina powder is 50% are shown in Table 4.

The catalyst dispersed on alumina powder was found to have a low T50 even after durability treatment. It is considered that this is because sintering was suppressed by dispersing on alumina.
The results of changing the SV value are also shown in Table 4. The catalyst dispersed on alumina was found to have low T50 and high activity even under high SV.

(Study on the effect of dispersing C-Fe-Ce catalyst on OSC material)
Table 5 shows the results of measurement of the temperature (T50) at which the conversion of NOx of the catalyst in which C-Fe-Ce is dispersed on the OSC material becomes 50%.

From the results in Table 5, it is found that the catalyst in which C-Fe-Ce is dispersed on the OSC material has T50 lower than that of the catalyst in which C-Fe-Ce is dispersed on alumina powder, and the catalyst not dispersed in the carrier. It was clearly found that T50 is low.

(Examination of composition range showing good T50)
The ratio of the catalyst after the endurance treatment at 1,000 ° C. for 5 hours is shown in Table 6.
Moreover, the result of having measured the temperature (T50) used as the conversion ratio of NOx becoming 50% by the evaluation method of the catalyst performance mentioned above is match | combined with Table 6 and shown.

Using T50 measurement values of Table 6, OriginPro 7.5 graph creation software of Lightstone Co., Ltd. is used to create a triangle composition isoactivity diagram with carbon + iron, cerium, alumina as the apex, T50 725 ° C, 750 The compositions which become ° C, 775 ° C, 800 ° C, 850 ° C, 900 ° C and 950 ° C were connected by a line (isoactivity temperature line). The triangular diagram is shown in FIG.
As a result, the ratio of the catalyst component (C + Fe + Ce) to alumina (100% by mass) is preferably 12.3 to 268% by mass, more preferably 21.4 to 177% by mass, and particularly preferably 34.4 to 116% by mass Is preferred. In addition, the optimum compositions for minimizing T50 were (carbon + iron), cerium and alumina 18.50 mass%, 18.55 mass%, and 62.94 mass%, respectively.
From these results, the content of the mixture relative to the inorganic porous powdery carrier (100% by mass) is preferably 10.0 to 300% by mass, and more preferably at least 20.0% by mass or at most 180% by mass. It is considered particularly preferable that there be 30% by mass or more or 120% by mass or less.

Moreover, based on the above results and the test results conducted so far, the content of carbon (C) is 0.01 to 1.4 mass% with respect to the total amount (100 mass%) of C, Fe and Ce It can be considered that is preferably 0.3 to 1.3 among them. The content of iron (Fe) is preferably 0.1 to 98.9% by mass, more preferably 7.8 to 98.7% by mass, with respect to the total amount (100% by mass) of C, Fe and Ce. It is particularly preferable that the ratio is 26.7 to 90.8% by mass. The content of cerium (Ce) is preferably 0.1 to 98.9% by mass, more preferably 0.1 to 92.1% by mass, based on the total amount (100% by mass) of C, Fe and Ce. It is particularly preferable that it is particularly preferable that 7.9 to 73.0% by mass is more preferable.

<Examples 29 to 31: Examination of precious metal addition effect>
A catalyst was produced in the same manner as in Examples 1 to 28 except that the mass of iron atom, the mass of cerium atom, and the mass of alumina were changed to the ratios shown in Table 7. Then, the obtained catalyst powder was added to a Pd nitrate solution measured to have the amount of the supported noble metal shown in Table 7, stirred at a rotational speed of 600 rpm for 3 hours, and then dried in a dryer at 120 ° C. Next, the noble metal-supported powder catalyst has a configuration in which the mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide is supported on alumina by calcining at 600 ° C. for 3 hours in the air atmosphere (Example 29) I got ~ 31).

The results of measuring the temperature (T50) at which the conversion of NOx of the catalyst supporting Pd on the composition of Example 1 is 50% are shown in Table 7.
It was found that T50 of NOx decreased as the loading amount of Pd increased, and Pd greatly contributed to the improvement of the performance of the exhaust gas catalyst.
Further, the amount of Pd supported is about a fraction of the amount usually supported on the exhaust gas purification catalyst, which can also contribute to the reduction of the amount of expensive Pd used.
In consideration of such a viewpoint, the supported amount of the noble metal is preferably 0.01% by mass or more with respect to the supported catalyst powder (100% by mass), and more preferably 0.41% by mass or more. It is considered preferable.

Examples 32 to 34: Examination of Co Addition Effect
After dissolving iron nitrate (II) (9 hydrate), cerium nitrate (III) (hexahydrate) and cobalt nitrate in pure water, add alumina powder (m 001) while stirring to prepare a mixed solution did. The mass of iron (II) nitrate (9 hydrate), cerium (III) nitrate (6 hydrate), cobalt nitrate and alumina powder to be used is contained in iron (II) nitrate (9 hydrate) The ratio of mass of iron atom, mass of cerium atom contained in cerium (III) nitrate (hexahydrate), mass of cobalt atom contained in cobalt nitrate, and mass of alumina are shown in Table 8 Adjusted to

Next, an aqueous solution of sodium carbonate was dropped to the mixed solution until the pH reached 10-11, and the mixture was stirred for 3 hours at a rotation speed of 600 rpm of a stirrer. The solution was then filtered, the precipitate washed with water 2-3 times and then the precipitate was dried in a dryer at 120 ° C. Then, after calcining at 500 ° C. for 3 hours in the atmospheric atmosphere, and then pulverizing using a mortar, heating at 525 ° C. for 4 hours in CO gas atmosphere, iron carbide (Fe ₃ C), iron oxide and cerium oxide A C—Fe—Ce—Co / alumina catalyst was obtained, comprising a structure in which a mixture containing C. is supported on alumina.

The ratios of C, Fe, Ce, Co, alumina, and T50 of NOx are shown in Table 8.

The T50 of NOx decreases as the addition amount of Co increases, and increases above a certain amount. From this result, it is found that Co contributes to the improvement of the performance of the exhaust gas catalyst.
In view of such a viewpoint, the content of Co is preferably more than 0.1% by mass and less than 15% by mass with respect to the catalyst material (100% by mass), and particularly preferably 5 to 10% by mass. Is considered to be more preferable.

Example 35 Effects of Co and Pt Addition
After dissolving iron nitrate (II) (9 hydrate), cerium nitrate (III) (hexahydrate) and cobalt nitrate in pure water, add alumina powder (m 001) while stirring to prepare a mixed solution did. The mass of iron (II) nitrate (9 hydrate), cerium (III) nitrate (6 hydrate) and cobalt nitrate and alumina powder to be used is contained in iron (II) nitrate (9 hydrate) The mass of iron atom, the mass of cerium atom contained in cerium (III) nitrate (hexahydrate), the mass of cobalt atom contained in cobalt nitrate, and the mass of alumina become the ratios shown in Table 9 Adjusted to

Next, an aqueous solution of sodium carbonate was dropped to the mixed solution until the pH reached 10-11, and the mixture was stirred for 3 hours at a rotation speed of 600 rpm of a stirrer. The solution was then filtered, the precipitate washed with water 2-3 times and then the precipitate was dried in a dryer at 120 ° C. Next, after calcining at 500 ° C. for 3 hours in the air atmosphere, it was put into an aqueous solution of chloroplatinic acid and stirred for 3 hours to load platinum (Pt). The loading amount is shown in Table 9. Furthermore, it was dried in a dryer at 120 ° C., calcined at 500 ° C. for 3 hours in an air atmosphere, and then crushed using a mortar. Thereafter, heating is performed at 525 ° C. for 4 hours in a CO gas atmosphere, and Pt / C in a configuration in which Pt is supported on a catalyst in which a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide is supported on alumina. -Fe-Ce-Co / alumina catalyst was obtained.

Example 36 Effects of Co and Pd Addition
In Example 35, Pd / C-Fe is used in the same manner as Example 35 except that an acetone solution of palladium acetate is used instead of an aqueous solution of chloroplatinic acid and palladium (Pd) is supported by vacuum drying. A Ce-Co / alumina catalyst is obtained. The amount of supported Pd is shown in Table 9.

The T50 of NOx shows a low value even when the SV value is as high as 3,000 mL / min · g, and in C-Fe-Ce-Co / alumina catalysts supporting Pt or Pd, Pt or Pd is usually an exhaust gas purification It has been found that even when only a fraction of the amount supported by the catalyst is supported, good performance is exhibited.

1: Standard gas cylinder, 2: Mass flow controller, 3: Water tank, 4: Water pump, 5. Evaporator, 6. Reaction tube, 7. Electric heating furnace, 8 ... cooler, 9 ... gas analysis device, 10 ... catalyst, 11 ... quartz sand, 12 ... quartz wool, 13 ... thermocouple

Claims

An exhaust gas purification catalyst comprising a configuration in which a mixture containing carbon (C), iron (Fe) and cerium (Ce) is supported on an inorganic porous powdery carrier.
The mixture, iron carbide (Fe 3 C), according to claim 1, wherein the exhaust gas purifying catalyst which is a mixture comprising iron oxide and cerium oxide.
The content ratio of the mixture to the inorganic porous powdery carrier (100% by mass) is 10.0 to 300% by mass, and the mass ratio of C to Fe to Ce atom contained in the mixture (C: Fe: Ce) is 0.01 to 1 with respect to the total amount of C, Fe and Ce (100% by mass).
The exhaust gas purification catalyst according to claim 1 or 2, characterized in that 4% by mass: 0.1 to 98.9% by mass: 0.1 to 98.9% by mass.
The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the mixture further contains cobalt (Co).
The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the inorganic porous powdery carrier is an inorganic porous powdery carrier containing alumina or a ceria-zirconia composite oxide.
The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein a noble metal is further carried on the exhaust gas purification catalyst.
The exhaust gas purification catalyst according to claim 6, wherein the noble metal is platinum (Pt) or palladium (Pd).
An exhaust gas purification catalyst structure comprising a base material and a catalyst layer containing the exhaust gas purification catalyst according to any one of claims 1 to 7.
An iron compound and a cerium compound are dissolved in a solution, an inorganic porous powdery carrier is added, and the iron compound and the cerium compound are attached to the inorganic porous powdery carrier, and then the inorganic compound is heated and calcined in the air to obtain the inorganic compound. After supporting iron oxide and cerium oxide on a porous powdery carrier, the mixture is heated under a reactive carbon-containing gas atmosphere, and a mixture containing carbon (C), iron (Fe) and cerium (Ce) is inorganic porous. What is claimed is: 1. A method for producing an exhaust gas purification catalyst, comprising the steps of: obtaining an exhaust gas purification catalyst supported on a high-quality powdery carrier.