JP2014042880A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new catalyst for purifying an exhaust gas, which contains C-Fe-Ce, has durability against intense temperature change and also can show stable purification performance even though a flow rate of the exhaust gas changes.SOLUTION: The catalyst for purifying the exhaust gas has a structure in which a mixture containing carbon (C), iron (Fe) and cerium (Ce) is carried on an inorganic porous powdery carrier. A content of the mixture with respect to the inorganic porous powdery carrier is 10-300 mass%.

Description

  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 of automobiles using gasoline as fuel contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The hydrocarbon (HC) is oxidized and converted into water and carbon dioxide, the carbon monoxide (CO) is oxidized and converted into carbon dioxide, and the nitrogen oxide (NOx) is reduced and converted into 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 attached in the form of a converter at an intermediate position between the exhaust pipe engine and the muffler.

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

In this type of three-way catalyst, noble metals oxidize hydrocarbons in exhaust gas to convert them to carbon dioxide and water, oxidize carbon monoxide to convert to carbon dioxide, while reducing nitrogen oxides to nitrogen It is preferable to keep the ratio of fuel to air (air-fuel ratio) constant (to the stoichiometric air-fuel ratio) in order to effectively produce the catalytic action for both reactions at the same time.
In an internal combustion engine such as an automobile, the air-fuel ratio changes greatly depending on the operating conditions such as acceleration, deceleration, low-speed driving, and high-speed driving. Therefore, the air-fuel ratio (A) varies depending on the operating conditions of the engine using an oxygen sensor (zirconia). / F) is controlled to be constant. However, simply controlling the air-fuel ratio (A / F) in this way prevents the catalyst from fully exhibiting the purification catalyst performance, so that the catalyst layer itself also has the effect of controlling the air-fuel ratio (A / F). Desired. Therefore, a catalyst in which a promoter is added to a noble metal that is a catalytic active component is used for the purpose of preventing a reduction in the purification performance of the catalyst caused by a change in the air-fuel ratio by the chemical action of the catalyst itself.

As such a co-catalyst, a co-catalyst (referred to as an “OSC material”) having an oxygen storage capacity (OSC) that releases oxygen in a reducing atmosphere and absorbs oxygen in an oxidizing atmosphere is known. For example, ceria (cerium oxide, CeO ₂ ), ceria-zirconia composite oxide, and the like are known as OSC materials having oxygen storage ability.

By the way, since it is said that noble metal occupies most of the price of a catalyst, since the price of noble metal is high, development of the new catalytic active component which replaces noble metal is performed.
For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-296735) discloses a catalyst in which iron oxide is supported on a carrier containing a ceria-zirconia composite oxide.
Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-160433) discloses a catalyst made of 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 Patent Application Laid-Open 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 dissolved.

  Furthermore, Patent Document 4 (Japanese Patent Laid-Open No. 2012-50980) discloses an exhaust gas purification catalyst made of carbon (C) -iron (Fe) -cerium (Ce).

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

  Catalysts for automobiles are required to have the ability to exhibit stable purification performance even when the exhaust gas flow rate changes, in addition to durability against severe temperature changes. In order to guarantee the durability of the exhaust gas purification catalyst, when the heat treatment is performed at a high temperature of 900 to 1,000 ° C. for a long time in the atmosphere, the exhaust gas catalyst tends to have a reduced surface area due to sintering and a decrease in catalytic activity. There is. In particular, the C—Fe—Ce catalyst having a high catalytic activity has a problem of strong sintering tendency.

  Therefore, an object of the present invention relates to an exhaust gas purifying catalyst containing C-Fe-Ce, and has a new ability to exhibit a stable purifying performance even when the exhaust gas flow rate changes, in addition to durability against severe temperature changes. It is to provide a catalyst for exhaust gas.

  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 powder carrier. An exhaust gas purification catalyst is proposed.

The exhaust gas purifying catalyst proposed by the present invention has a mixture of carbon (C), iron (Fe), and cerium (Ce) supported on an inorganic porous powder carrier. Sintering is suppressed even when exposed to high temperatures. As a result, durability is high, and stable purification performance can be exhibited at a high level even when the flow rate of exhaust gas changes.
The reason for the suppression of sintering even when exposed to high temperatures is that there are many fine pores on the surface of the inorganic porous powder-like carrier, and carbon enters the pores. Since there is a mixture containing (C), iron (Fe), and cerium (Ce), it can be considered that sintering is suppressed as a result of hindering contact with the adjacent mixture. In addition, a mixture containing carbon (C), iron (Fe), and cerium (Ce) is dispersed on the inorganic porous powder carrier, the effective reaction area is increased, and the purification performance is stable even if the exhaust gas flow rate changes. Can be considered to have been able to demonstrate.

It is the schematic of the apparatus which measures the model gas concentration used in 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 an activity diagram of a triangular composition etc. which makes carbon + iron, cerium, and alumina apexes.

  Next, the form for implementing this invention is demonstrated. However, the present invention is not limited to the embodiment described below.

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

Here, examples of the mixture containing carbon (C), iron (Fe), and cerium (Ce) include a mixture containing iron carbide (Fe ₃ C), iron oxide, and cerium oxide.
At this time, iron carbide (Fe ₃ C), iron oxide, and cerium oxide each act as an active point that exhibits an oxidation / reduction action. Among these, Fe ₃ C shows high activity as an active site showing oxidation / reduction action. On the other hand, since the heat resistance of Fe ₃ C alone is low, for example, when durability treatment at 900 ° C. to 1,000 ° C. is performed, most of it is oxidized to an oxide such as Fe ₂ O ₃ , Usually the activity will be significantly reduced. However, the present catalyst is a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide. As a result of being supported on an inorganic porous powder carrier, the catalyst has high catalytic activity even after such durability treatment. Can be demonstrated.

In the present catalyst, the content of the mixture with respect to the inorganic porous powder carrier (100% by mass) is preferably 10.0 to 300% by mass, and more preferably 20.0% by mass or more or 180% by mass or less. Of these, it is particularly preferable that the content is 30% by mass or more and 120% by mass or less.
In the present catalyst, if the content of the mixture with respect to the inorganic porous powder carrier is 300% by mass or less, the composite carbonate particles can be prevented from being in close contact with each other, and when exposed to a high temperature. Since sintering can be prevented, a reduction in the purification rate due to a decrease in effective area can be suppressed. 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.

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

From this viewpoint, the content of carbon (C) is preferably 0.01 to 1.4% by mass with respect to the total amount (100% by mass) of C, Fe and Ce, and more preferably 0.3% by mass. More preferably, the content is 1.3% by 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 above all, 7.8% by mass or 98. It 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. 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. By containing Co, heat resistance can be improved.
The Co content is preferably more than 0.1% by mass and less than 15% by mass with respect to the total amount (100% by mass) of C, Fe and Ce, and more preferably 5% by mass or more or 10% by mass or less. Is preferred.

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

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

  Examples of the OSC material include a cerium compound, a zirconium compound, and a ceria / zirconia composite oxide.

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

  In this case, examples of the noble metal include palladium (Pd), platinum (Pt), and rhodium (Rh). Of these, palladium (Pd) and platinum (Pt) are significantly preferred.

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

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

At this time, as a method for attaching the iron compound and the cerium compound to the inorganic porous powder carrier, for example, the inorganic porous powder carrier is added to the solution of the iron compound and the cerium compound, and then stirred with ammonia water or carbonic acid. An alkaline substance such as sodium is dropped to adjust the pH to 10 to 11, thereby precipitating a composite hydroxide of Fe and Ce or a composite carbonate. A method of washing the precipitate with water and drying can be mentioned. However, it is not limited to this method.
In addition to the method of heating in a reactive carbon-containing gas atmosphere, it is also possible to employ a method of heating in an inert gas atmosphere in the presence of a carbon-containing material.

As described above, since the Fe compound and Ce compound are attached in a solution state on the inorganic porous powdery support, the catalyst can enter Fe and Ce into minute pores and has a very good dispersion state. Can be obtained.
In addition, when heated in a reactive carbon-containing gas atmosphere such as CO gas, in other words, when CO treatment was performed by a vapor phase method, a mixture of iron oxide and cerium oxide was uniformly dispersed in the inorganic porous powder carrier. In addition to being supported in a state, carbon (C) as iron carbide can be uniformly dispersed.

<This 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 substrate.

  For example, the catalyst structure can be formed by forming a catalyst layer on the surface of a substrate having a honeycomb-like (monolith) structure by, for example, wash-coating a catalyst composition containing the present catalyst.

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

  Examples of the shape of the substrate include a honeycomb shape, a pellet shape, and a spherical shape.

In general, a cordierite material such as ceramics is often used as the honeycomb material. 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 monolith type substrate having a large number of parallel and fine gas flow passages, that is, channels, can be used so that fluid flows through the substrate. At this time, the catalyst layer can be formed by coating the inner wall surface of each channel of the monolith substrate with the catalyst composition by wash coating or the like.

(Catalyst composition)
The catalyst composition for forming the catalyst layer of the present catalyst structure may further contain a stabilizer and other components as required in addition to the present catalyst.

For example, a stabilizer can be blended for the purpose of suppressing reduction of palladium oxide (PdOx) to metal in 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 metals selected from the group consisting of magnesium, barium, calcium and strontium, preferably strontium and barium. Among these, barium is preferable from the viewpoint that the temperature at which PdOx is reduced is highest, that is, it is difficult to reduce.

Moreover, you may contain well-known additive components, such as a binder component.
As the binder component, an inorganic binder, for example, an aqueous solution such as alumina sol, silica sol, or zirconia sol can be used. These can take the form of inorganic oxides upon firing.

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

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

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

<Examples 1 to 28, Comparative Examples 1 to 10>
After iron nitrate (II) (9 hydrate) and cerium nitrate (III) (hexahydrate) are dissolved in pure water, alumina powder (m001) or OSC material (ceria-zirconia composite oxide) is stirred with stirring. Was added to prepare a mixed solution.
At this time, the masses of iron nitrate (II) (9 hydrate), cerium nitrate (III) (hexahydrate), alumina powder and OSC material used were iron nitrate (II) (9 hydrate). The mass of iron atoms contained, the mass of cerium atoms contained in cerium nitrate (III) (hexahydrate), and the masses of alumina and OSC material were adjusted to the compositions shown in Table 1.

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

(Quantitative method of each component)
Since the mass of the iron atom, the mass of the cerium atom, the mass of alumina, and the mass of the OSC material were the same as the blending amount, no particular quantification was performed.
On the other hand, the carbon content can be measured by a carbon / sulfur analyzer (manufactured by Horiba Seisakusho), and it was found that the carbon content was obtained from the blending amount × 500 ° C. to 1000 ° C. after the heat treatment (19%). . Furthermore, since the amount of carbon may decrease due to a high-temperature reaction, the amount of carbon after the endurance treatment at 1,000 ° C. for 5 hours was measured. In the above example, heating was performed at 500 ° C. or more. Therefore, no change in carbon content was observed before and after the endurance treatment.

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

(Catalyst performance test method)
Using the model gas shown in Table 3, a catalyst performance test was conducted.

FIG. 1 shows a schematic diagram of an apparatus for measuring the concentration of a model gas containing C ₃ H ₃ as NOx, CO, H ₂ , or HC. Moreover, the schematic of the reaction tube which is a part of the said measuring apparatus is shown in FIG.
As shown in FIG. 1, a measuring apparatus including 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, the gas is mixed by the mass flow controller 2, the water introduced from the water pump 4 is vaporized by the evaporator 5, and the respective gases are merged by the evaporator 5, and are supplied to the reaction tube 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 the reaction is analyzed for composition by the gas analyzer 9 after the 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, etc. by gas chromatography, NOx, NO, NO ₂ , CO and the like can be quantitatively analyzed with a NOx analyzer.

Using the above measuring apparatus, the purification performance of the catalyst was evaluated as the conversion rate of each gas by the following calculation formula.
NOx conversion ratio = {(NO molar flow rate at the inlet + NO ₂ molar flow rate) − (NO molar flow rate at the outlet + NO ₂ molar flow rate)} / (NO molar flow rate at the inlet + NO ₂ molar flow rate) × 100%

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

(Examination of the effect of dispersing C-Fe-Ce catalyst on alumina powder)
Table 4 shows the results of measuring the temperature (T50) at which the NOx conversion rate of the catalyst in which C—Fe—Ce is dispersed on alumina powder becomes 50%.

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

(Examination of the effect of dispersing the C—Fe—Ce catalyst on the OSC material)
Table 5 shows the results of measuring the temperature (T50) at which the NOx conversion rate of the catalyst in which C—Fe—Ce is dispersed on the OSC material is 50%.

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

(Examination of composition range showing good T50)
Table 6 shows the ratio of the catalyst after the endurance treatment at 1,000 ° C. for 5 hours.
Table 6 also shows the results of measuring the temperature (T50) at which the conversion rate of NOx becomes 50% by the above-described method for evaluating catalyst performance.

Using the Origin Pro 7.5 graph creation software of Lightstone Co., Ltd., the T50 measurement value in Table 6 was created, and an activity diagram such as a triangular composition with carbon + iron, cerium, and alumina as the vertices was created. T50 was 725 ° C, 750 Compositions of 750 ° C., 775 ° C., 800 ° C., 850 ° C., 900 ° C., and 950 ° C. were connected by lines (isoactive temperature lines). 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 34.4 to 116% by mass. Is preferred. Moreover, the optimal composition with which T50 becomes the lowest was 18.50 mass%, 18.55 mass%, and 62.94 mass%, respectively (carbon + iron), cerium, and alumina.
From such results, the content of the mixture with respect to the inorganic porous powder carrier (100% by mass) is preferably 10.0 to 300% by mass, and more preferably 20.0% by mass or more or 180% by mass or less. It is particularly preferable that the content is 30% by mass or more or 120% by mass or less.

  Further, based on the above results and the test results that have been conducted so far, the content of carbon (C) is 0.01 to 1.4% by mass with respect to the total amount (100% by mass) of C, Fe and Ce. It is preferable that 0.3 to 1.3 is more preferable. 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 particularly 7.8 to 98.7% by mass. It is particularly preferable that 26.7 to 90.8% by mass is more preferable. 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 to 92.1% by mass. It is particularly preferable that 7.9 to 73.0% by mass is more preferable.

<Examples 29 to 31: Investigation of noble metal addition effect>
Catalysts were prepared in the same manner as in Examples 1 to 28 except that the masses of iron atoms, cerium atoms, and alumina were changed to the ratios shown in Table 7. Then, the obtained catalyst powder was added to a Pd nitrate solution weighed so as to have a supported noble metal amount 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, a noble metal-supported powder catalyst (Example 29) having a structure in which a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide is supported on alumina by firing at 600 ° C. for 3 hours in an air atmosphere. To 31).

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

<Examples 32 to 34: Examination of Co addition effect>
After iron (II) nitrate (9 hydrate), cerium nitrate (III) (hexahydrate) and cobalt nitrate are dissolved in pure water, alumina powder (m001) is added while stirring to prepare a mixed solution. did. The masses of iron (II) nitrate (9 hydrate), cerium nitrate (III) (hexahydrate), cobalt nitrate and alumina powder used are contained in iron (II) nitrate (9 hydrate). The mass of iron atoms, the mass of cerium atoms contained in cerium (III) nitrate (hexahydrate), the mass of cobalt atoms contained in cobalt nitrate, and the mass of alumina are in the ratios shown in Table 8. Adjusted.

Next, an aqueous sodium carbonate solution was dropped into the mixed solution until pH = 10 to 11, and the mixture was stirred for 3 hours at a rotation speed of a stirrer of 600 rpm. Thereafter, the solution was filtered, and the precipitate was washed with water 2-3 times, and then the precipitate was dried in a dryer at 120 ° C. Next, after baking at 500 ° C. for 3 hours in an air atmosphere, pulverization using a mortar, and heating for 4 hours at 525 ° C. in a CO gas atmosphere, iron carbide (Fe ₃ C), iron oxide and cerium oxide Thus, a C—Fe—Ce—Co / alumina catalyst having a constitution in which a mixture containing was supported on alumina was obtained.

  Table 8 shows the ratio of C, Fe, Ce, Co, and alumina, and T50 of NOx.

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

<Example 35: Effect of addition of Co and Pt>
After iron (II) nitrate (9 hydrate), cerium nitrate (III) (hexahydrate) and cobalt nitrate are dissolved in pure water, alumina powder (m001) is added while stirring to prepare a mixed solution. did. The mass of iron (II) nitrate (9 hydrate), cerium (III) nitrate (hexahydrate), cobalt nitrate and alumina powder used is contained in iron (II) nitrate (9 hydrate) The mass of iron atoms, the mass of cerium atoms contained in cerium (III) nitrate (hexahydrate), the mass of cobalt atoms contained in cobalt nitrate, and the mass of alumina are in the ratios shown in Table 9. Adjusted.

Next, an aqueous sodium carbonate solution was dropped into the mixed solution until pH = 10 to 11, and the mixture was stirred for 3 hours at a rotation speed of a stirrer of 600 rpm. Thereafter, the solution was filtered, and the precipitate was washed with water 2-3 times, and then the precipitate was dried in a dryer at 120 ° C. Subsequently, after baking for 3 hours at 500 ° C. in an air atmosphere, the solution was put into an aqueous solution of chloroplatinic acid and stirred for 3 hours to carry platinum (Pt). The supported 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 pulverized using a mortar. Thereafter, Pt / C having a structure 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 by heating at 525 ° C. for 4 hours in a CO gas atmosphere. -Fe-Ce-Co / alumina catalyst was obtained.

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

  NOx T50 shows a low value even when the SV value is as high as 3,000 mL / min · g, and Ct-Pe-Ce-Co / alumina catalyst loaded with Pt or Pd is usually treated with exhaust gas purification. It has been found that even when a small amount of about a fraction of the amount supported on the catalyst is supported, good performance is exhibited.

DESCRIPTION OF SYMBOLS 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 analyzer, 10 ... catalyst, 11 ... quartz sand, 12 ... quartz wool, 13 ... thermocouple

Claims (9)

  An exhaust gas purification catalyst comprising a structure in which a mixture containing carbon (C), iron (Fe), and cerium (Ce) is supported on an inorganic porous powder carrier. The exhaust gas purifying catalyst according to claim 1, wherein the mixture is a mixture containing iron carbide (Fe ₃ C), iron oxide, and cerium oxide.   The content of the mixture with respect to the inorganic porous powder carrier (100% by mass) is 10.0 to 300% by mass, and the mass ratio of C, Fe and Ce atoms contained in the mixture (C: Fe: Ce) is 0.01 to 1.4% by mass: 0.1 to 98.9% by mass: 0.1 to 98.9% by mass with respect to the total amount (100% by mass) of C, Fe and Ce. The exhaust gas purifying catalyst according to claim 1 or 2, wherein   The exhaust gas purifying 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 powder carrier is an inorganic porous powder carrier containing alumina or a ceria-zirconia composite oxide.   6. The exhaust gas purification catalyst according to claim 1, further comprising a noble metal supported on the exhaust gas purification catalyst.   The exhaust gas purifying 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 including the exhaust gas purification catalyst according to any one of claims 1 to 7.   An inorganic porous powder carrier is added by dissolving an iron compound and a cerium compound in a solution. After the iron compound and cerium compound are attached to the inorganic porous powder carrier, the inorganic compound is heated and fired in the atmosphere. After supporting iron oxide and cerium oxide on a porous powder carrier, the mixture containing carbon (C), iron (Fe), and cerium (Ce) is heated in a reactive carbon-containing gas atmosphere. A method for producing an exhaust gas purification catalyst, comprising obtaining an exhaust gas purification catalyst supported on a powdery carrier.

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