JP6216234B2 - Exhaust gas purification catalyst - Google Patents

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. .

  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 engine operating conditions 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, a catalyst containing carbon (C) -iron (Fe) -cerium (Ce) (referred to as “C—Fe—Ce catalyst”) has a problem of strong sintering tendency because of its particularly high catalytic activity. It was.

  Accordingly, an object of the present invention is to provide a new exhaust gas catalyst having durability against a drastic temperature change, with respect to an exhaust gas purification catalyst containing C, Fe and Ce.

  In order to achieve the above object, the present invention provides carbon (C), iron (Fe), cerium (Ce), copper (Cu), nickel (Ni), zinc (Zn) and manganese (Mn). We propose an exhaust gas purification catalyst having a structure in which a noble metal is further supported on catalyst particles having a structure in which a mixture containing one or two or more additive elements is supported on an inorganic porous carrier.

  In the present invention, in addition to carbon (C), iron (Fe) and cerium (Ce), one or more of copper (Cu), nickel (Ni), zinc (Zn) and manganese (Mn) may be used. As a result, it was confirmed that sintering was suppressed even when exposed to a high temperature of 900 ° C. when catalyst particles formed by supporting a mixture containing additive elements on an inorganic porous carrier were further supported with a noble metal. High durability against severe temperature changes, and stable purification performance can be demonstrated at a high level.

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 relationship between the temperature and the conversion rate of NOx about the catalyst powder obtained in Example 1 and Comparative Example 1 before the durability treatment (Fresh) and after the durability treatment (Aging). It is the figure which showed the relationship between temperature and the conversion rate of CO about the catalyst powder obtained in Example 1 and the comparative example 1 about each of the catalyst powder before a durable process (Fresh) and a durable process (Aging). It is a figure which shows the result of the performance test of the catalyst powder about the catalyst powder obtained in Example 2, and is the figure which showed the relationship between the mass ratio of Mn / Fe, and T50 or T90 of CO. It is a figure which shows the result of the performance test of the catalyst powder about the catalyst powder obtained in Example 2, and is the figure which showed the relationship between the mass ratio of Mn / Fe and T50 or T90 of NOx. It is a figure which shows the result of the performance test of the catalyst powder about the catalyst powder obtained in Example 1, 3, 4 and 5, and is the figure which showed the relationship between temperature and the conversion rate of CO for every element. It is a figure which shows the result of the performance test of the catalyst powder about the catalyst powder obtained in Example 1, 3, 4 and 5, and is the figure which showed the relationship between temperature and the conversion rate of NOx for every element.

  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 includes, in addition to carbon (C), iron (Fe), and cerium (Ce), copper (Cu), nickel (Ni). In addition, catalyst particles having a configuration in which a mixture containing one or more additive elements (referred to as “M element”) of zinc (Zn) and manganese (Mn) is supported on an inorganic porous carrier, Furthermore, an exhaust gas purification catalyst having a structure in which a noble metal is supported is proposed.

Here, as the mixture containing carbon (C), iron (Fe), cerium (Ce), and M element, iron carbide (Fe ₃ C), iron oxide, cerium oxide, and oxide of M element And a mixture containing
At this time, iron carbide (Fe ₃ C), iron oxide, cerium oxide, and oxide of M element each act as an active point showing 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, this catalyst is a mixture containing iron carbide (Fe ₃ C), iron oxide, cerium oxide and M element oxide, and is supported on an inorganic porous carrier. However, it has become possible to demonstrate high catalytic activity.

In the present catalyst, the content of the mixture with respect to the inorganic porous 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. Particularly preferred 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 support is 300% by mass or less, the composite carbonate particles can be prevented from being in close contact with each other, and sintering when exposed to a high temperature is possible. Therefore, the reduction in the purification rate due to the decrease in the 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: M) of C, Fe, Ce, and M element contained in the said mixture is with respect to the total amount (100 mass%) of C, Fe, Ce, and M element. 0.01 to 1.4% by mass: 0.1 to 90.8% by mass: 0.1 to 98.8% by mass: 0.01 to 84.6% by mass is preferable.

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, Ce and M elements. More preferably, it is 3 mass% or more or 1.3 mass% or less.
The content of iron (Fe) is preferably 0.1 to 90.8% by mass with respect to the total amount (100% by mass) of C, Fe, Ce and M elements, and more preferably 7.8% by mass or more. Alternatively, it is particularly preferably 90.8% 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 98.8% by mass with respect to the total amount (100% by mass) of C, Fe, Ce and M elements, and more preferably 0.1% by mass or more. Alternatively, it is particularly preferably 92.1% by mass or less, and more preferably 7.9% by mass or more or 73.0% by mass or less.

  It is particularly preferable that the total mass of the additive elements M contained in the mixture is 0.1 to 5.5 times the mass of the iron element contained in the mixture. It is more preferable that the mass is 4.0 times the mass, and especially the mass is 1.0 times or more or 1.25 times the mass.

(Inorganic porous carrier)
Examples of the inorganic porous carrier include a compound selected from the group consisting of silica, alumina, and a titania compound, or an inorganic porous 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.

(Precious metal component)
The amount of noble metal supported in the catalyst is preferably 0.01% by mass or more, more preferably 0.41% by mass or more, based on the mass of the catalyst (100% by mass).

  Examples of the noble metal include palladium (Pd), platinum (Pt), and rhodium (Rh), and one or more of these can be used in combination. 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 carrier is added to a solution of an iron compound and a cerium compound, and an iron compound, a cerium compound, and an M element compound are attached to the inorganic porous carrier, and then heated and fired in the atmosphere to thereby form the inorganic porous carrier. After supporting the oxide of iron oxide, cerium oxide, and M element on the porous carrier, it is pulverized as necessary, heated and fired in an air atmosphere, and pulverized as necessary, so that C, Fe, Ce And the intermediate particle powder provided with the structure by which the additional element M is carry | supported by the inorganic porous support | carrier can be obtained. Next, the intermediate particle powder thus obtained is heated in a carbon monoxide atmosphere to perform CO treatment and carbonization treatment. If necessary, the catalyst can be produced by pulverization, addition of a noble metal salt to the intermediate particles, adhesion of the noble metal salt to the intermediate particles, and heating in the atmosphere.
If manufactured in this way, the Fe compound, Ce compound, and M element compound are deposited in a solution state on the inorganic porous carrier, so that the Fe, Ce, and M element can enter into the fine pores. A catalyst with a very good dispersion state can be obtained.

  At this time, as a method of attaching the iron compound, cerium compound and M element compound to the inorganic porous carrier, for example, after adding the inorganic porous carrier to a solution of iron compound, cerium compound and M element compound, stirring, An aqueous sodium carbonate solution is added to adjust the pH to 10 to 11, thereby precipitating a composite hydroxide or composite carbonate of Fe, Ce, and M elements. Examples thereof include a method of washing the precipitate with water and drying. However, it is not limited to this method.

  As for the heating and firing conditions in the air atmosphere, if the temperature is too low, it may not be oxidized, and if the temperature is too high, the particle size may increase. Further, if the firing time is too short, the oxidation may not proceed. From this point of view, heating may be performed so that the product temperature is maintained at 400 to 800 ° C. for 2 to 10 hours in an air atmosphere. Of these, heating is particularly preferably 500 ° C. or more and 700 ° C. or less, and particularly preferably 550 ° C. or more and 650 ° C. or less. Especially, heating is preferably 2 hours or more or 7 hours or less, and more preferably 3 hours or more or 6 hours or less.

  As described above, as a method of supporting the noble metal on the intermediate particles, the intermediate particle powder is added to an aqueous solution of a salt of a noble metal such as a chloroplatinic acid aqueous solution and stirred, and the product temperature is 400 to 800 ° C. in an air atmosphere. And may be heated to maintain 2 to 8 hours. Of these, heating is particularly preferably 500 ° C. or more and 700 ° C. or less, and particularly preferably 550 ° C. or more and 650 ° C. or less. Especially, heating is preferably 2 hours or more or 6 hours or less, and more preferably 3 hours or more or 5 hours or less.

Moreover, what is necessary is just to make it heat above said carbon treatment in reactive carbon containing gas atmosphere, such as CO gas. Regarding heating conditions at that time, if the temperature is too high, carbonization proceeds and reduction proceeds, and if the treatment time is too long, carbon is deposited. From this viewpoint, the product temperature may be maintained at 300 to 600 ° C. for 1 to 8 hours. Of these, heating is preferably 400 ° C. or more or 550 ° C. or less, and particularly preferably 475 ° C. or more and 525 ° C. or less, and particularly preferably 3 hours or more or 7 hours or less, and particularly preferably 4 hours or more or 6 hours or less.
Thus, when the CO treatment is performed by the vapor phase method, a mixture of iron oxide, cerium oxide, and M element oxide can be supported in a state of being uniformly dispersed in the inorganic porous carrier, as well as iron carbide. Carbon (C) 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.

<Example 1>
After iron (II) nitrate (9 hydrate), cerium nitrate (III) (hexahydrate) and manganese nitrate are dissolved in pure water, alumina powder (m001) is added while stirring to prepare a mixed solution. did.
At this time, the mass of iron (II) nitrate (9 hydrate), cerium (III) nitrate (hexahydrate), manganese nitrate and alumina powder used was iron nitrate (II) (9 hydrate). The mass of iron atoms contained is 2 wt%, the mass of cerium atoms contained in cerium (III) nitrate (hexahydrate) is 18 wt%, the mass of manganese atoms contained in manganese nitrate is 2 wt%, The mass was adjusted to 78 wt%.

  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 mixture was pulverized using a mortar to obtain an intermediate powder.

Next, the intermediate powder obtained as described above was pulverized using a mortar and heated at 525 ° C. for 6 hours in a CO gas atmosphere. In addition to the chloroplatinic acid aqueous solution, the mixture was stirred for 3 hours at a rotation speed of 600 rpm and then dried in a dryer at 120 ° C. to obtain catalyst powder (0.35 Pt / 2Fe3C-2Mn-18Ce / Al ₂ O ₃ ).

<Example 2>
In Example 1, the catalyst powder was the same as in Example 1 except that the amount of manganese nitrate was changed and the mass of manganese atoms contained in manganese nitrate was changed in the range of 0.5 to 10 wt%. It manufactures, to obtain a catalyst powder 0.35Pt / 2Fe3C-0.5~10Mn-18Ce / Al 2 O 3).

<Example 3>
In Example 1, except that nickel nitrate was dissolved in pure water instead of manganese nitrate, a catalyst powder was produced in the same manner as in Example 1 to obtain catalyst powder (0.35 Pt / 2Fe3C-2Ni-18Ce / Al ₂ O ₃ ) was obtained.

<Example 4>
In Example 1, except that zinc nitrate was dissolved in pure water instead of manganese nitrate, a catalyst powder was produced in the same manner as in Example 1 to obtain a catalyst powder (0.35 Pt / 2Fe3C-2Zn-18Ce / Al ₂ O ₃ ) was obtained.

<Example 5>
In Example 1, except that copper nitrate was dissolved in pure water instead of manganese nitrate, a catalyst powder was produced in the same manner as in Example 1 to obtain a catalyst powder (0.35 Pt / 2Fe3C-2Cu-18Ce / Al ₂ O ₃ ) was obtained.

<Comparative Example 1>
In Example 1, except that manganese nitrate was not dissolved in pure water, a catalyst powder was produced in the same manner as in Example 1, and a catalyst powder (0.35 Pt / 2Fe3C-18Ce / Al ₂ O ₃ )) was used. Obtained.

<Quantitative method of each component>
Since the mass of the iron atom, the mass of the cerium atom, the mass of alumina, the mass of manganese, 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 900 ° C. for 5 hours was measured. The carbon content was not changed before and after the endurance treatment.

<Catalyst performance test>
The catalyst powders obtained in Example 1 and Comparative Example 1 were treated under the durability conditions shown in Table 1 below (Aging), and using the model gas shown in Table 2 below, before the durability treatment (Fresh) and the durability. With respect to the catalyst powder after the treatment (Aging), the performance test of the catalyst powder was conducted to measure the NOx conversion rate and the CO conversion rate at each temperature, and these results are shown in FIGS.

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 considered desirable to evaluate a catalyst that has been subjected to durability treatment.
Therefore, the catalyst powder obtained in Example 2 was treated under the durability conditions shown in Table 1 below, and then the performance test of the catalyst powder was performed using the model gas shown in Table 2 below. The temperature (T50) (T90) at which the CO conversion was 50% and 90% was measured, and the relationship between the mass ratio of Mn / Fe and T50 or T90 is shown in FIGS.

  The catalyst powders obtained in Examples 1, 3, 4 and 5 were treated under the durability conditions shown in Table 1 below, and then performance tests of the catalyst powder were performed using the model gas shown in Table 2 below. The conversion rate of NOx and the conversion rate of CO at each temperature were measured, and these results are shown in FIGS. Table 3 shows the NOx conversion rate of 50%, 90% temperature (T50, T90), CO conversion rate of 50%, and 90% temperature (T50, T90) for each element.

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%
CO conversion rate = (CO molar flow rate at the inlet) − (CO molar flow rate at the outlet) / (CO molar flow rate at the inlet) × 100%

(Discussion)
In addition to carbon (C), (Fe), and cerium (Ce), copper (Cu), nickel (Ni), zinc (Zn), and manganese (Mn ), A catalyst particle formed by supporting a mixture containing one or more additional elements on an inorganic porous carrier, and further supporting a noble metal thereon, suppresses sintering even when exposed to high temperatures. As a result, it was found that durability was high and stable purification performance could be exhibited at a high level.
The reason why sintering can be suppressed even when exposed to a high temperature in this manner is that there are many fine pores on the surface of the inorganic porous carrier, and carbon (C) , (Fe), cerium (Ce) and other additive elements are present, so that contact with the adjacent mixture is hindered, and as a result, sintering can be considered to be suppressed.

Further, from the viewpoint of durability, it is particularly preferable that the total mass of the M-added elements contained in the mixture is 0.1 to 5.5 times the mass of the iron element contained in the mixture. preferably, 0.1 times or more or 4.0 times or less among them, in particular 1.0 times or more, or 1.25 times or less in the of has been found to be more preferable.

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 (6)

Carbon (C), iron (Fe), cerium (Ce), copper (Cu), nickel (Ni), zinc (Zn) and manganese (Mn), one or more additive elements An exhaust gas purifying catalyst having a structure in which a noble metal is further supported on catalyst particles having a structure in which a mixture containing is supported on an inorganic porous carrier ,
The exhaust gas purifying catalyst , wherein the mixture includes iron carbide (Fe ₃ C), iron oxide, cerium oxide, and an oxide of the additive element.   The exhaust gas purification according to claim 1, wherein the total mass of the additive elements contained in the mixture is 0.1 to 5.5 times the mass of the iron element contained in the mixture. catalyst. The exhaust gas purification according to claim 1, wherein the total mass of the additive elements contained in the mixture is 1.0 to 5.5 times the mass of the iron element contained in the mixture. catalyst.   The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the inorganic porous carrier is an inorganic porous carrier containing alumina or a ceria-zirconia composite oxide.   The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the noble metal is at least one of platinum (Pt), palladium (Pd), and rhodium (Rh). 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 5.

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