DE112013004202B4 - Exhaust gas purification catalyst - Google Patents

Abstract

An exhaust gas purifying catalyst comprising a structure having a mixture containing carbon (C), iron (Fe) and cerium (Ce) loaded on an inorganic porous powdery carrier, wherein the content of C is from 0.04 to 0.86 % By weight, the content of Fe are 3.20 to 63.15% by weight and the content of Ce are 2.59 to 50.00% by weight with respect to the total amount of C, Fe and Ce, respectively.

Description

Technical area

The present invention relates to an exhaust gas purifying catalyst useful in purifying exhaust gas emitted from an internal combustion engine.

background

The exhaust gas of an automobile that uses gasoline as a fuel contains harmful components such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ). It is necessary to purify each of these harmful components using a catalytic converter in such a way that the hydrocarbons (HC) are converted to water and carbon dioxide by oxidation, the carbon monoxide (CO) is converted to carbon dioxide by oxidation and the nitrogen oxides (NO _x ) by reduction be converted into nitrogen.

As such a catalyst for treating exhaust gas (hereinafter referred to as an “exhaust gas purifying catalyst”), a three-way catalyst (TWC) capable of oxidizing CO and HC and _{reducing NO x has been} used. The three-way catalytic converter is generally mounted in the form of a converter in an intermediate position between the engine and the muffler of the exhaust pipe.

As such a three-way catalyst, a three-way catalyst is known, which by loading a noble metal such as platinum (Pt), palladium (Pd) or rhodium (Rh) on a heat-resistant, porous oxide body with a high specific surface such as a porous alumina body with a high specific surface area, and its subsequent loading on a substrate such as a heat-resistant ceramic substrate or a monolithic substrate with a metal honeycomb structure or on a heat-resistant particle.

The noble metal in this type of three-way catalyst has a function by which the hydrocarbons in the exhaust gas are converted into water and carbon dioxide by oxidation; carbon monoxide in the exhaust gas is converted into carbon dioxide by oxidation; in the meantime, the nitrogen oxides in the exhaust gas are converted into nitrogen by reduction. It is preferred that the fuel to air ratio (air-to-fuel ratio) be held constant (at the theoretical air-to-fuel ratio) in order to effectively promote catalysis for both reactions at the same time.

The air-fuel ratio of internal combustion engines of an automobile and the like changes drastically depending on the driving conditions such as acceleration, deceleration, driving at low speed and driving at high speed, and thus the fluctuating air-fuel ratio ( A / F) constantly controlled by the operating conditions of the engine using an oxygen sensor (zirconium oxide). However, it is not possible for the catalyst to exert sufficient purifying catalytic performance only by controlling the air-fuel ratio (A / F) as described above, and thus the catalyst layer itself should also have the effect of reducing the air-fuel ratio. Control ratio (A / F). Therefore, a catalyst is used in which a promoter is added to a noble metal of the catalytic component for the purpose of preventing a deterioration 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 one such promoter, a promoter (referred to as an "OSC material") is known which has the oxygen storage capacity (OSC) to release oxygen in a reducing atmosphere and to absorb oxygen in an oxidizing atmosphere. For example, cerium oxide (cerium oxide CeO ₂ ) or cerium oxide-zirconium oxide composite oxides are known as OSC material with this oxygen storage capacity.

However, the price of the noble metals is so high that it is said that the price of the catalyst is largely due to the noble metals, and thus development of a new catalyst component to replace the noble metals has been carried out.

For example, in Patent Document 1 ( JP 2005-296735 A ) discloses a catalyst in which iron oxide is loaded onto a carrier containing a ceria-zirconia composite oxide.

In addition, Patent Document 2 ( JP 2004-160433 A ) discloses a catalyst composed of a composite oxide of at least one kind of metal selected from the group consisting of ceria, zirconia, aluminum, titanium and manganese, and iron.

In Patent Document 3 ( JP 2008-18322 A ) discloses a catalyst having a structure in which iron oxide is dispersed in a Ceroixd-zirconium oxide composite oxide and is at least partially in a solid solution state.

Furthermore, an exhaust gas purifying catalyst composed of carbon (C) -iron (Fe) -ceria (Ce) is disclosed in Patent Document 4 ( JP 2012-50980 A ) disclosed.

The publication "Studies on Exhaust Gas Purifying Catalysts Using Cerium / lon / Carbon-based Material" by Oda H. et al, in "Advances in the 43rd annual autumn meeting of the SCEJ" from August 13, 2011 discloses an exhaust gas purification catalyst made from a material Cerium-iron-carbon system. This is obtained by impregnating a carrier made of anodized aluminum with a solution of cerium (Ce) and iron (Fe) and subsequent reaction at a temperature of 525 ° C. for 2 hours under a CO atmosphere. This document thus also discloses an exhaust gas purifying catalyst composed of carbon (C) -iron (Fe) -cer (Ce).

In the publication U.S. 4,252,687 A general methods of making a catalyst are described.

In the publication DE 10 2011 103 370 A an exhaust gas purifying catalyst is disclosed. This consists of a CeZr mixed oxide powder doped with a catalytic metal, in which the catalytic metal is solids dissolved in CeZr-based mixed oxide, and a second component consisting of at least one component selected from the group consisting of: i) activated aluminum oxide powder; ii) Zr-based oxide backed alumina powder in which Zr-based oxide is supported on activated alumina particles; iii) CeZr-based mixed oxide powder in which the catalytic metal is not dissolved in solids and iv) CeZr-based mixed oxide powder in which the catalytic metal is not dissolved in solids.

List of citations

Patent document

• Patent Document 1: JP 2005-296735 A
• Patent Document 2: JP 2004-160433 A
• Patent Document 3: JP 2008-18322 A
• Patent Document 4: JP 2012-50980 A
• Patent Document 5: U.S. 4,252,687 A
• Patent Document 6: DE 10 2011 103 370 A

Non-patent document: Oda H. et al., "Studies on Exhaust Gas Purifying Catalysts Using Cerium / lon / Carbon-based Material" Progress of the 43rd Annual Fall SCEJ, August 13, 2011

Disclosure of the invention

Object to be achieved by the invention

A catalytic converter for a motor vehicle should have a performance which is capable of exhibiting stable cleaning performance despite a change in the flow rate of the exhaust gas, in addition to durability against a large change in temperature. There is a tendency that the surface area of the exhaust gas purifying catalyst is decreased by sintering and hence the catalytic activity is decreased when the exhaust gas purifying catalyst is heat-treated at a high temperature of 900 to 1000 ° C in air for a long time to ensure its durability. In particular, there is a problem of strong tendency to sinter in a C-Fe-Ce catalyst which has a high catalytic activity.

Accordingly, the object of the invention relates to an exhaust gas purifying catalyst which contains C-Fe-Ce, and is to provide a novel catalyst for exhaust gas having a performance capable of stably purifying performance despite a change in the flow rate of the exhaust gas, in addition to showing durability against a sharp change in temperature.

Means of solving the task

In order to achieve the above object, the invention provides an exhaust gas purifying catalyst having a structure in which a mixture containing carbon (C), iron (Fe) and cerium (Ce) is loaded on an inorganic porous powdery carrier, wherein the content of C from 0.04 to 0.86% by weight, the content of Fe 3.20 to 63.15% by weight and the content of Ce from 2.59 to 50.00% by weight, in each case in With respect to the total amount of C, Fe and Ce is.

Effect of the invention

The exhaust gas purifying catalyst proposed by the invention is obtained by loading a mixture containing carbon (C), iron (Fe) and cerium (Ce) on an inorganic porous powdery carrier and thereby sintering thereof, even if the exhaust gas purifying catalyst is one high temperature of 900 to 1000 ° C is suppressed. As a result, the exhaust gas purifying catalyst proposed by the invention has high durability and can exert stable purifying performance at a high level in spite of a change in the flow rate of the exhaust gas.

As a reason why the sintering is suppressed even when the exhaust gas purifying catalyst is exposed to a high temperature as described above, it can be considered that there are a large number of fine pores on the surface of the inorganic porous powdery carrier and that the mixture containing carbon (C), iron (Fe) and cerium (Ce) is in a state that it has penetrated into each of these pores, and thus contact with an adjacent mixture is inhibited, as a result of which sintering is inhibited is prevented. In addition, it can be presumed that the mixture containing carbon (C), iron (Fe) and cerium (Ce) is dispersed in the inorganic porous powdery carrier and thus the effective reaction area is increased, as a result, stable cleaning performance despite a Change in the flow rate of the exhaust gas can be exerted.

Figure list

• 1 Fig. 13 is a schematic diagram of an apparatus for measuring the concentration of a model gas used in the performance test of a catalyst of Examples;
• 2 FIG. 13 is a schematic diagram of a reaction tube in the apparatus of FIG 1 ; and
• 3 Fig. 13 is a diagram illustrating the measured values of T50 in the examples as a ternary composition-isoactivity diagram with carbon + iron, cerium and alumina as the vertices.

Mode (s) for carrying out the invention

Next, embodiments for carrying out the invention will be described. However, the invention is not limited to the embodiments described below.

Exhaust gas purification catalyst

The exhaust gas purifying catalyst as an example of the embodiments of the invention (referred to as “the present catalyst”) is an exhaust gas purifying catalyst having a structure in which a mixture containing carbon (C), iron (Fe) and cerium (Ce) is deposited on an inorganic porous , powdery carrier is loaded, the content of C from 0.04 to 0.86 wt .-%, the content of Fe 3.20 to 63.15 wt .-% and the content of Ce 2.59 to 50, 00% by weight each with respect to the total amount of C, Fe and Ce.

As the above mixture containing carbon (C), iron (Fe) and cerium (Ce), a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide can be exemplified here.

At this time, each of iron carbide (Fe ₃ C), iron oxide and cerium oxide serves as an active site which exerts an oxidizing and reducing effect. Among them, Fe ₃ C exerts high activity as an active site which exerts an oxidizing and reducing effect. On the other hand, however, a simple substance of Fe ₃ C has low heat resistance and therefore most will Fe ₃ C is oxidized to an oxide such as Fe ₂ O ₃ when subjected to a durability treatment at 900 to 1000 ° C, and its activity generally deteriorates markedly as a result. However, the present catalyst is obtained by _{loading a mixture containing iron carbide (Fe 3} C), iron oxide and cerium oxide on an inorganic porous powdery carrier, and as a result, it can exhibit high catalytic activity even after such durability treatment.

In the present catalyst, the content of the mixture with respect to the inorganic porous powdery carrier (100% by weight) is preferably from 10.0 to 300% by weight, among which it is particularly preferably 20.0% by weight. % or more or 180% by weight or less, and among these, it is particularly preferably 30% by weight or more or 120% by weight or less.

In the present catalyst, it is possible to prevent the composite carbonate particles from being in close contact with each other and to prevent sintering upon exposure to a high temperature when the content of the mixture is relative to the inorganic, porous, powdery Carrier is 300% by weight or less. It follows that it is possible to suppress a decrease in the rate of performance due to a decrease in the effective area. On the other hand, when the content is 10.0% by weight or more, it is possible to maintain the number of the catalyst particles and maintain the performance rate by the presence of the effective active site.

In addition, the mass ratio of the C atom to the Fe atom to the Ce atom (C: Fe: Ce), which are contained in the mixture, is preferably 0.01 to 1.4% by weight: 0.1 to 98, 9% by weight: 0.1 to 98.9% by weight based on the total amount of C, Fe and Ce (100% by weight).

The content of iron (Fe) with respect to the total amount of C, Fe and Ce (100% by weight) is preferably 7.8% by weight or more, and particularly preferably 26.7% by weight or more.

The content of cerium (Ce) is preferably 7.9% by weight or more with respect to the total amount of C, Fe and Ce (100% by weight).

In addition, the mixture can also contain cobalt (Co). It is possible to improve the heat resistance by containing cobalt.

The content of cobalt is preferably higher than 0.1% by weight and less than 15% by weight with respect to the total amount of C, Fe and Ce (100% by weight), and among these, it is particularly preferred that it is 5% by weight or more or 10% by weight or less.

Inorganic, porous, powdery carrier

Examples of the inorganic porous powdery carrier may include an inorganic porous powdery carrier formed from a compound selected from the group consisting of a silica compound, an alumina compound and a titania compound, or an OSC -Material such as a ceria-zirconia composite oxide.

In particular, it is possible to take a porous powder formed from a compound selected from alumina, silica, silica-alumina, an alumino-silicate, alumina-zirconia, alumina-chromia and alumina-ceria as an example.

Aluminum oxide with a specific surface area of more than 50 m ² / g, for example γ, δ, θ or α aluminum oxide, can preferably be used as aluminum oxide. Among these, γ alumina or θ alumina are preferably used. At the same time, a trace amount of lanthanum (La) may be contained in the alumina to increase the heat resistance.

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

Other components

The present catalyst may be a catalyst having a structure in which, in addition to the mixture, a noble metal is loaded on an inorganic porous powdery carrier.

The loaded amount of the noble metal is preferably 0.01% by weight or more with respect to the mass of the loaded catalyst powder (100% by weight), and among these, it is particularly preferably 0.41% by weight or more.

At this time, examples of noble metals may include palladium (Pd), platinum (Pt), and rhodium (Rh). Among them, palladium (Pd) or platinum (Pt) are particularly preferred.

production method

Next, the method for producing the present catalyst will be described.

The present catalyst is prepared as follows. An inorganic porous powdery carrier is added to a solution of an iron compound and a cerium compound, and the iron compound and the cerium compound are attached to the inorganic porous powdery carrier. Thereafter, the result thus obtained is heated and calcined in the air to load iron oxide and cerium oxide on the inorganic porous powdery carrier, and then the result thus obtained is in an atmosphere of a reactive carbonaceous gas such as carbon monoxide (CO) - Gas heated.

At this time, examples of the method of attaching an iron compound and a cerium compound to an inorganic porous powdery carrier may include a method in which an inorganic porous powdery carrier is added to a solution of an iron compound and a cerium compound. Thereafter, a basic substance such as ammonia water or sodium carbonate is added dropwise with stirring to give a pH of 10 to 11, whereby a composite hydroxide of Fe and Ce or a composite carbonate salt is precipitated. The precipitate is washed with water and dried. However, the method is not limited to such a method. In addition, it is also possible to employ a method in which heating is carried out in an inert gas atmosphere in the presence of a carbon-containing substance, in addition to a method in which heating is carried out in a reactive carbon-containing gas atmosphere.

As described above, since the Fe compound and the Ce compound are attached to the inorganic porous powdery carrier in a solution state, Fe and Ce can penetrate into the fine pores, and thus it is possible for a catalyst to be clearly preferred State of dispersion is obtained.

In addition, it is not only possible to load the mixture of iron oxide and ceria on the inorganic porous powdery carrier in a uniformly dispersed state, but also to uniformly disperse carbon (C) as iron carbide when heating in an atmosphere of a reactive carbonaceous Gas such as CO gas is performed, in other words, CO treatment is performed by the gas phase method.

Present catalyst structure

It is possible to manufacture an exhaust gas purifying catalyst structure (referred to as “present catalyst structure”) by forming a catalyst layer containing the present catalyst on a substrate.

It is possible to prepare a catalyst structure, for example, by forming a catalyst layer on the surface of a substrate having a honeycomb (monolithic) structure, wash-coating or the like of a catalyst composition containing the present catalyst.

Substrate

In the present catalyst structure, examples of the material of the substrate may include a refractory material such as ceramics or a metal material.

Examples of the material of the ceramic substrate may include a refractory ceramic such as cordierite, cordierite-alpha-alumina, silicon nitride, zircon mullite, spodumene, alumina-silica-magnesia, zirconium silicate, sillimanite, magnesium silicate, zirconium, petalite, alpha-alumina and an alumino-silicate .

Examples of the material of the metallic substrate can include a refractory metal such as stainless steel or other suitable iron-based corrosion-resistant alloys.

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

As a honeycomb material, for example, a cordierite material such as ceramics is widely used in general. In addition, it is also possible to use a honeycomb formed from a metal material such as ferritic stainless steel.

In the case of using a substrate having a honeycomb shape, it is possible to use, for example, a monolithic substrate having a large number of parallel and fine gas flow passages, namely channels, inside the substrate so that the fluid flows through the inside of the substrate. At this time, it is also possible to form a catalyst layer by coating with a catalyst composition on the surface of the inner walls of each of the channels of the monolithic substrate by wash coating or the like.

Catalyst composition

The catalyst composition for forming a catalyst layer of the present catalyst structure may further contain, if necessary, a stabilizer or other component from above in addition to the present catalyst.

For example, it is possible to add a stabilizer for the purpose of suppressing the reduction of palladium oxide (PdO _x ) in metallic palladium in a propellant-rich atmosphere.

Examples of this type of stabilizer may include an alkaline earth metal or an alkali metal. Among them, it is possible to select one kind or two or more kinds of metals selected from the group consisting of magnesium, barium, calcium and strontium, and preferably strontium and barium. Among them, barium is preferred from the viewpoint that it has the highest temperature for the reduction of PdO _x , that is, it is hardly reduced.

In addition, the catalyst composition can contain a known additive component such as a binder component.

As the binder component, it is possible to use an inorganic binder such as an aqueous solution such as alumina sol, silica sol or zirconia sol. These can be converted to the form of an inorganic oxide when calcined.

production method

As an example of manufacturing the present catalyst structure, it is possible to use a method in which the present catalyst is added to water, mixed and stirred by a ball mill or the like to obtain a slurry, and a substrate such as a ceramic Honeycomb body or the like is immersed in this slurry, then the result thereof is taken out and calcined, whereby a catalyst layer is formed on the surface of the substrate or the like, exemplified.

However, the method for producing the present catalyst is not limited to the above example, and any known method can be used.

Explanation of terms

According to the present description, the term “X to Y” (X and Y are any numbers) includes the meaning “preferably more than X” or “preferably less than Y” and the meaning “X or more and Y or less” unless otherwise specified a.

In addition, the term “X or more” (X is any number) or “Y or less” (Y is any number) also includes the intent of “preferably more than X” or “preferably less than Y”.

Examples

In the following, the invention will be described in more detail with reference to the following examples and comparative examples.

Examples 1 to 28 and Comparative Examples 1 to 10

Ferrous nitrate (nonahydrate) and cerium (III) nitrate (hexahydrate) were dissolved in pure water, and then alumina powder (m001) or an OSC material (ceria-zirconia composite oxide) was added while stirring, whereby a mixed solution was prepared.

At this time, the masses of iron (II) nitrate (nonahydrate), cerium (III) nitrate (hexahydrate), aluminum oxide powder and OSC material were adjusted so that the mass of the iron atom contained in the iron (II) nitrate ( Nonahydrate), the mass of the cerium atom contained in the cerium (III) nitrate (hexahydrate), the mass of the aluminum oxide and the mass of the OSC material gave the composition shown in Table 1.

Next, ammonia-water was added dropwise to the mixed solution until the pH thereof became 10 to 11, and the result was stirred for 3 hours at a stirrer rotating speed of 600 rpm. Thereafter, the solution was filtered and the precipitate was washed 2 to 3 times with water and then dried in a dryer at 120 ° C.

Subsequently, the precipitate thus obtained was calcined at 500 ° C for 3 hours in an air atmosphere, then the result was ground using a mortar and heated at 525 ° C for 4 hours in a CO gas atmosphere to thereby produce a C- Fe-Ce / aluminum oxide catalyst or a C-Fe-Ce / OSC material catalyst with a structure in which a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide was loaded onto aluminum oxide or an OSC material, to obtain.

Quantification procedure for each component

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 mixing amounts for each of them, and therefore their quantification was not particularly carried out.

On the other hand, it was found that the amount of carbon was measured by a carbon and sulfur analyzer (manufactured by Horiba, Ltd.) and multiplying the amount of mixture by the coefficient of C amount (19%) after heat treatment at 500 ° C or higher and 1000 ° C or less can be determined. Furthermore, the amount of carbon may decrease by a pyrogenic reaction in some cases, and thus the amount of carbon after the durability treatment was measured at 1000 ° C for 5 hours, but no change in the amount of carbon was observed before and after the durability treatment because the heating was at 500 ° C or higher in the examples above. Table 1 C (wt%) Fe (wt%) Ce (wt%) m001 (wt%) OSC material (% by weight) Examples 1 to 4 0.25 18.25 18.55 62.94 Example 5 0.09 6.49 42.06 51.35 Example 6 0.09 6.49 42.06 51.35 Example 7 0.14 9.99 24.97 64.91 Example 8 0.24 17.80 13.60 68.36 Example 9 0.34 24.92 24.92 49.83 Example 10 0.41 29.88 9.96 59.76 Example 11 0.22 16.16 9.08 74.54 Example 12 0.22 16.36 32.33 51.09 Example 13 0.39 28.89 24.40 46.32 Example 14 0.40 29.48 2.59 67.53 Example 15 0.53 38.69 9.65 51.13 Example 16 0.13 9.19 25.07 65.62 Example 17 0.16 11.98 9.98 77.87 Example 18 * 0.68 49.66 0.00 49.66 Example 19 0.52 38.50 24.87 36.11 Example 20 0.04 3.20 37.38 59.37 Example 21 * 0.25 18.35 0.00 81.40 Example 22 * 0.75 54.79 0.00 44.47 Example 23 * 0.00 0.00 50.00 50.00 Example 24 0.63 45.91 26.23 27.23 Example 25 0.10 7.49 4.00 88.41 Example 26 * 0.86 63.15 0.00 35.99 Example 27 * 0.00 0.00 49.30 50.70 Example 28 * 0.00 0.00 16.40 83.60 Comparative Examples 1 to 4 0.99 17.72 81.29 Comparative example 5 0.00 0.00 30.00 70.00 Comparative example 6 0.00 0.00 100.00 0.00 Comparative example 7 0.00 0.00 0.00 100.00 Comparative example 8 0.68 49.66 49.66 0.00 Comparative example 9 1.34 98.66 0.00 0.00
* These examples are comparative examples not according to the invention

Shelf life test method

The exhaust gas purifying catalyst was treated under the durability conditions shown in Table 2 to examine durability. Table 2 Shelf life conditions temperature 1000 ° C Time 5 hours Gas condition Air (10 s) ⇔ A / F13.5 (20 s) A / F 13.5 texture C ₃ H ₆ 3333 ppmC O ₂ 0.105% H ₂ O 10% Hey rest

Procedure for the performance test of the catalyst

The performance test of the catalyst was carried out using a model gas shown in Table 3. Table 3 Composition of the model gas O ₂ 1.0% NO 0.1% CO 1.0% C ₃ H ₆ 0.1% H ₂ 0.2% CO ₂ 8.0% H ₂ O 10.0% HE Base Air-fuel ratio A / F 14.63 (theoretical air-fuel ratio)

• 1 Fig. 13 is a schematic diagram illustrating an apparatus for measuring the concentration of the model gas containing NO _x , CO or H ₂ and C ₃ H ₃ as HC.
• 2 Fig. 13 is a schematic diagram illustrating the reaction tube which is a part of the apparatus for measuring from above.

As in 1 Illustrated is the device for measuring which is provided by a standard gas cylinder 1 , a mass flow controller 2 , a water tank 3 , a water pump 4th , a vaporizer 5 , a reaction tube 6th , a cooler 8th , a gas analyzer 9 and the like is operated as follows. First, each model gas is taken from the standard gas cylinder 1 generated, the gases are mixed by the mass flow controller 2 , Water coming from the water pump 4th is introduced is through the vaporizer 5 evaporated and the respective gases are through the evaporator 5 brought together and into the reaction tube 6th introduced. Then the reaction tube 6th containing the model gas by an electric heating furnace 7th heated.

Each of the model gases is passed through a catalyst 10 in the reaction tube 6th oxidized or reduced. The gas is after the reaction of removing the water vapor in the cooler 8th and then the composition thereof is subjected to by the gas analyzer 9 analyzed.

The gas analyzer 9 is capable of quantitative analysis of O ₂ , CO, N ₂ O, CO ₂ , HC (C ₃ H ₆ ), H ₂ or the like by gas chromatography. NO _x , NO, NO ₂ , CO or the like can be quantitatively _{analyzed by a NO x} analyzer.

The purification performance of the catalyst was determined as the conversion rate of each gas by the following formula for calculation using the measuring device above. $$\begin{array}{l}{\text{Implementation rate NO}}_{\text{x}}=\{(\text{molar flow rate of NO}+{\text{molar flow rate of NO}}_2\text{at the}\\ \text{entry})-\left(\text{molar flow rate of NO}+{\text{molar flow rate of NO}}_2\text{at the exit}\right)\}/\\ \left(\text{molar flow rate of NO}+{\text{molar flow rate of NO}}_2\text{at the entrance}\right)\times 100\%\end{array}$$

The present catalyst is produced by heat treatment in a CO gas atmosphere, and thereby amorphous C is fixed on the surface, and as a result, in some cases, an amount of C is measured as a mixing ratio which is larger than the stoichiometric carbon ratio of Fe ₃ C. Therefore, it is desirable to examine the catalyst which is subjected to the durability treatment in order to compare the stable catalytic performance.

Accordingly, the conversion rate of NO _x and the temperature (T50) at which the conversion rate of NO _{x became} 50% were measured after the durability treatment at 1000 ° C for 5 hours, if necessary.

Investigation of the effect of the dispersion of the C-Fe-Ce catalyst on aluminum oxide powder

Table 4 shows the results of measurement of the temperature (T50) at which the conversion rate of NO _{x of} the catalyst obtained by dispersing C-Fe-Ce on the alumina powder becomes 50%. Table 4 C (wt.%) Fe (wt%) Ce (wt%) m001 (wt.%) T50 (NO _x ) SV value (ml / ming) Shelf life conditions example 1 0.25 18.25 18.55 62.94 682 500 Available Example 2 0.25 18.25 18.55 62.94 348 500 Absent Example 3 0.25 18.25 18.55 62.94 1000 3000 available Example 4 0.25 18.25 18.55 62.94 510 3000 Absent Comparative example 1 0.99 17.72 81.29 930 500 available Comparative example 2 0.99 17.72 81.29 470 500 absent Comparative example 3 0.99 17.72 81.29 1367 3000 available Comparative example 4 0.99 17.72 81.29 694 3000 absent

It was confirmed that the catalyst dispersed on the alumina powder has a low T50 even after the durability treatment. The reason for this is believed to be that sintering is suppressed by the dispersion of the catalyst on the alumina.

In addition, the results obtained by varying the SV value are also shown in Table 4. It was confirmed that the catalyst dispersed on the alumina has a low T50 even after a high SV value and its activity is high.

Investigation of the effect of the dispersion of the C-Fe-Ce catalyst on OSC material

Table 5 shows the results of measurement of the temperature (T50) at which the conversion rate of NO _{x of} the catalyst obtained by dispersing C-Fe-Ce on an OSC material becomes 50%. Table 5 C (wt.%) Fe (wt%) Ce (wt%) m001 (wt.%) OSC material (except Ce) T50 (NO _x ) SV value (ml / ming) Shelf life conditions Comparative example 1 0.99 17.72 81.29 1300 ° C or higher 500 available Example 5 0.09 6.49 42.06 51.35 800 500 available Example 6 0.09 6.49 42.06 51.35 784 500 available

From the results of Table 5, it was confirmed that the catalyst obtained by dispersing C-Fe-Ce on an OSC material had a lower T50 than the catalyst obtained by dispersing C-Fe-Ce on the Alumina powder and an apparently lower T50 than the catalyst which is not obtained by dispersion on a carrier.

Investigation of the compositional range which exerts beneficial T50

The ratio of the catalyst after the durability treatment at 1000 ° C for 5 hours is shown in Table 6.

In addition, Table 6 also shows the results of measurement of the temperature (T50) at which the conversion rate of NO _x becomes 50% by the above catalytic performance determination method. Table 6 C (wt.%) Fe (wt%) Ce (wt%) m00 1 (wt.%) C / (C + Fe + Ce) Fe / (C + Fe + Ce) Ce / (C + Fe + Ce) (C + Fe + Ce) / m00 1 T50 (NO _x ) SV value (ml / min g) Durability conditions example 1 0.25 18.25 18, 55 62.9 4 0.67% 49.2 6% 50.0 7% 58.8 7% 682 500 Available Example 7 0.14 9.99 24, 97 64.9 1 0.39% 28.4 6% 71.1 5% 54.0 6% 724 500 Available Example 8 0.24 17.80 13, 60 68.3 6 0.77% 56.2 5% 42.9 8% 46.2 8% 727 500 Available Example 9 0.34 24.92 24, 92 49.8 3 0.68% 49.6 6% 49.6 6% 100.6% 740 500 available Example 10 0.41 29.88 9.9 6 59.7 6 1.01% 74.2 4% 24.7 5% 67.3 5% 746 500 available Example 11 0.22 16.16 9.0 8 74.5 4 0.86% 63.4 8% 35.6 6% 34.1 6% 750 500 available Example 12 0.22 16.36 32, 33 51.0 9 0.46% 33.4 5% 66.0 9% 95.7 5% 750 500 available Example 13 0.39 28.89 24, 40 46.3 2 0.73% 53.8 1% 45.4 6% 115.9% 750 500 available Example 14 0.40 29.48 2.5 9 67.5 3 1.24% 90.7 9% 7.97% 48.0 9% 750 500 available Example 15 0.53 38.69 9.6 5 51.1 3 1.08% 79.1 8% 19.7 4% 95.5 8% 750 500 available Example 16 0.13 9.19 25, 07 65.6 2 0.36% 26.7 2% 72.9 1% 52.4 0% 750 500 available Example 17 0.16 11.98 9.9 8 77.8 7 0.74% 54.1 4% 45.1 2% 28.4 1% 760 500 available Example 18 * 0.68 49.66 0.0 0 49.6 6 1.34% 98.6 6% 0.00% 101.36% 769 500 available Example 19 0.25 38.50 24, 87 36.1 1 0.82% 60.2 5% 38.9 2% 176, 93% 800 500 available Example 5 0.09 6.49 42, 06 51.3 5 0.18% 13.3 5% 86.4 7% 94.7 2% 800 500 available Example 20 0.04 3.20 37, 38 59.3 7 0.11% 7.87% 92.0 2% 68.4 2% 800 500 available Example 21 * 0.25 18.35 0.0 0 81.4 0 1.34% 98.6 6% 0.00% 22.8 6% 800 500 available Example 22 * 0.75 54.79 0.0 0 44.4 7 1.34% 98.6 6% 0.00% 124, 89% 800 500 available Example 23 * 0.00 0.00 50.00 50.0 0 0.00% 0.00% 100.00% 100.00% 826 500 available Example 24 0.63 45.91 26, 23 27.2 3 0.86% 63.0 9% 36.0 5% 267, 26% 850 500 available Example 25 0.10 7.49 4.0 0 88.4 1 0.88% 64.6 4% 34.4 8% 13.1 1% 850 500 available Example 26 * 0.86 63.15 0.0 0 35.9 9 1.34% 98.6 6% 0.0% 177, 87% 850 500 available Example 27 * 0.00 0.00 49, 30 50.7 0 0.00% 0.00% 100.00% 97.2 4% 850 500 available Example 28 * 0.00 0.00 16, 40 83.6 0 0.00% 0.00% 100.00% 19.6 2% 850 500 available Comparative example 5 0.00 0.00 30.00 70.0 0 0.00% 0.00% 100.00% 42.8 6% 869 500 available Comparative example 6 0.00 0.00 10 0.0 0 0.00 0.00% 0.00% 100.00% - 944 500 available Comparative example 7 0.00 0.00 0.0 0 100.00 - - - 0.00% 949 500 available Comparative example 8 0.68 49.66 49, 66 0.00 0.68% 49.6 6% 49.6 6% - 1005 500 available Comparative example 9 1.34 98.66 0.0 0 0.00 1.34% 98.6 6% 0.00% - 1103 500 available Comparative example 10 0.00 0.00 75.00 25.0 0 0.00% 0.00% 100.00% 300.00% 1233 500 available * These examples are comparative examples not according to the invention

A ternary composition-isoactivity diagram with carbon + iron, cerium and aluminum oxide as vertices was created from the measured values of the T50 in Table 6 using the graphics software OriginPro7.5 available from LightStone Corp. and the compositions in which the T50 was 725 ° C, 750 ° C, 775 ° C, 800 ° C, 850 ° C, 900 ° C and 950 ° C were merged by a line (isoactivity temperature line). The triangle diagram thus obtained is in 3 illustrated.

As a result, the ratio of the catalyst component (C + Fe + Ce) with respect to the alumina (100% by weight) is preferably from 12.3 to 268%, among which it is preferably 21.4 to 177% by weight. and among them, it is particularly preferred from 34.4 to 116% by weight. In addition, the optimum composition having the lowest T50 was that of (carbon + iron), cerium and alumina were 18.50 wt%, 18.55 wt% and 62.94 wt%, respectively.

From the above result, it can be assumed that the content of the mixture with respect to the inorganic, porous, powdery carrier (100% by weight) is preferably 10.0 to 300% by weight, below this particularly preferably 20.0% by weight. -% or more or 180% by weight or less and, among this, very particularly preferably 30.0% by weight or more or 120% by weight or less.

In addition, from the results described above and the results of tests carried out, it can be assumed that the content of carbon (C) is preferably 0.01 to 1.4% by weight with respect to the total amount of Is C, Fe and Ce (100 wt%), and among them, it is particularly preferably from 0.3 to 1.3 wt%. It can be presumed that the content of iron (Fe) is preferably 0.1 to 98.9% by weight with respect to the total amount of C, Fe and Ce (100% by weight), particularly preferably 7 among them .8 to 98.7% by weight, and among these is most preferably 26.7 to 90.8% by weight. It can be considered that the content of cerium (Ce) is preferably 0.1 to 98.9% by weight with respect to the total amount of C, Fe and Ce (100% by weight), among which it is particularly preferably 0 , 1 to 92.1% by weight and, among this, very particularly preferably 7.9% by weight to 73.0% by weight.

Examples 29 to 31: Investigation of the effect of adding noble metal

The catalysts were prepared in the same manner as in Examples 1 to 28 except that the mass of the iron atom, the mass of the cerium atom and the mass of the alumina were changed to the proportions shown in Table 7. Thereafter, the catalyst powder thus obtained was added to a Pd nitrate solution taken so as to have the loaded amount of noble metal shown in Table 7, stirred for 3 hours at a rotation speed of 600 rpm and then dried in a dryer at 120 ° C. Subsequently, the result was calcined at 600 ° C for 3 hours in the air atmosphere, whereby a noble metal-laden powdery catalyst (Examples 29 to 31) with a structure in which a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide on aluminum oxide has been loaded.

Table 7 shows the results of measurement of the temperature (T50) at which the conversion rate of NO _{x of} the catalyst obtained by loading Pd into the mixture of Example 1 becomes 50%.

The T50 of NO _x decreases with an increase in the loaded amount of Pd, and it was thus confirmed that Pd contributes well to the improvement of the performance of an exhaust catalyst.

Furthermore, this loaded amount of Pd is about a fraction of the amount normally loaded on an exhaust gas purifying catalyst, and thus this fact may contribute to a decrease in the amount of use of expensive Pd at the same time.

In consideration of this point of view, it is considered that the loaded amount of a noble metal is preferably 0.01 wt% or more with respect to the loading catalyst powder (100 wt%), and among these, it is particularly preferably 0.41 wt%. % or more. Table 7 Pd (wt.%) C (wt.%) Fe (wt%) Ce (wt%) m001 (wt.%) T50 (NOx) SV value (ml / ming) Shelf life conditions example 1 0 0.25 18.25 18.55 62.94 682 500 available Example 29 0.073 0.25 18.24 18.54 62.90 393 500 available Example 30 0.41 0.25 18.18 18.48 62.68 348 500 available Example 31 0.66 0.25 18.13 18.43 62.53 329 500 available

Examples 32 to 34: Investigation of the effect of the addition of Co

Ferrous nitrate (nonahydrate), cerium (III) nitrate (hexahydrate) and cobalt nitrate were dissolved in pure water, and then an alumina powder (m001) was added thereto while stirring, thereby preparing a mixed solution. The masses of iron (II) nitrate (nonahydrate), cerium (III) nitrate (hexahydrate), cobalt nitrate and aluminum powder used were adjusted so that the mass of the iron atom contained in the iron (II) nitrate (nonahydrate), the The mass of the cerium atom contained in the cerium (III) nitrate (hexahydrate), the mass of the cobalt atom contained in the cobalt nitrate, and the mass of the alumina became the ratio shown in Table 8.

Next, an aqueous solution of sodium carbonate was added dropwise to the mixed solution until its pH became from 10 to 11, and the result was stirred for 3 hours at a stirrer rotating speed of 600 rpm. Thereafter, the solution was filtered and the precipitate was washed 2 to 3 times with water and then dried in a dryer at 120 ° C. Subsequently, the precipitate thus obtained was calcined at 500 ° C for 3 hours in the air atmosphere, and the result was ground using a mortar and heated at 525 ° C for 4 hours in a CO gas atmosphere, thereby giving the C-Fe-Ce-Co / Alumina catalyst having a structure in which a mixture containing iron carbide (Fe ₃ C), iron oxide and ceria loaded on alumina was obtained.

The ratio of C, Fe, Ce, Co, alumina and T50 of NO _x is shown in Table 8. Table 8 Co (wt%) C (wt.%) Fe (wt%) Ce (wt%) m001 (wt.%) T50 (NOx) SV value (ml / ming) Shelf life conditions example 1 0 0.25 18.25 18.55 62.94 682 500 Available Example 32 5 0.24 17.34 17.63 59.80 504 500 Available Example 33 10 0.22 16.43 16.70 56.65 541 500 Available Example 34 15th 0.21 15.52 15.77 53.50 780 500 Available

The T50 of NO _x decreases with an increase in the amount of Co added, but increases when the amount of CO added exceeds a certain amount. From this result, it was confirmed that Co contributes to the improvement of the performance of an exhaust catalyst.

Taking this point of view into consideration, it is assumed that the content of Co is preferably more than 0.1% by weight and less than 15% by weight with respect to the catalyst material (100% by weight), and below this, it is particularly preferably 5 to 10 wt%.

Example 35: Effect of Co and Pt addition

Ferrous nitrate (nonahydrate), cerium (III) nitrate (hexahydrate) and cobalt nitrate were dissolved in pure water, and then an alumina powder (m001) was added thereto while stirring, thereby preparing a mixed solution. The masses of iron (II) nitrate (nonahydrate), cerium (III) nitrate (hexahydrate), cobalt nitrate and aluminum powder used were adjusted so that the mass of the iron atom contained in the iron (II) nitrate (nonahydrate), the The mass of the cerium atom contained in the cerium (III) nitrate (hexahydrate), the mass of the cobalt atom contained in the cobalt nitrate) and the mass of the alumina became the ratio shown in Table 9.

Next, an aqueous solution of sodium carbonate was added dropwise to the mixed solution until its pH became from 10 to 11, and the result was stirred for 3 hours at a stirrer rotating speed of 600 rpm. Thereafter, the solution was filtered and the precipitate was washed 2 to 3 times with water and then dried in a dryer at 120 ° C. Subsequently, the precipitate thus obtained was calcined at 500 ° C. for 3 hours in the air atmosphere, and the result was introduced into an aqueous solution of chloroplatinic acid and stirred for 3 hours, thereby loading platinum (Pt) became. The loaded amount of Pt is shown in Table 9. Thereafter, the result was further dried in a dryer at 120 ° C., calcined at 500 ° C. for 3 hours in the air atmosphere, and then ground using a mortar. Thereafter, the result was heated at 525 ° C. for 4 hours in a CO gas atmosphere, thereby obtaining a Pt / C-Fe-Ce-Co / alumina catalyst having a structure in which Pt on a catalyst obtained by loading a mixture containing iron carbide (Fe ₃ C), iron oxide and cerium oxide on aluminum oxide.

Example 36: Effect of adding Co and Pd

A Pd / C-Fe-Ce-Co / alumina catalyst was obtained in the same manner as in Example 35 except that an acetone solution of palladium acetate was used in place of the aqueous solution of chloroplatinic acid and palladium (Pd) was loaded by vacuum drying in Example 35 became. The loaded amount of Pd is shown in Table 9. Table 9 Pt Pd C. Fe Co Ce m001 T50 SV value Shelf life conditions (Wt%) (Wt%) (Wt%) (Wt%) (Wt%) (Wt%) (Wt%) (NOx) (ml / min ^. g) Example 35 ° 0.35 0 0.38 2.0 2.0 18.0 77.62 402 3000 available Example 36 ° 0 0.35 0.38 2.0 2.0 18.0 77.62 383 3000 available * These examples are comparative examples not according to the invention

The T50 of NO _x exerted a low value even in a case where the SV value was even 3000 mL / min g, and it was confirmed that the C-Fe-Ce-Co / alumina catalyst containing Pt or Pd was loaded exhibited favorable performance even in a case where Pt or Pd was loaded in only a small amount, which is about a fraction of the amount normally loaded on an exhaust gas purifying catalyst.

List of reference symbols

1

Standard gas cylinder

2

Mass flow controller

3

Water tank

4th

water pump

5

Evaporator

6th

Reaction tube

7th

electric heater

8th

cooler

9

Gas analyzer

10

catalyst

11

Quartz sand

12th

Quartz wool and

13th

Thermal coupling

Claims (11)

An exhaust gas purifying catalyst comprising a structure having a mixture containing carbon (C), iron (Fe) and cerium (Ce) loaded on an inorganic porous powdery carrier, wherein the content of C is from 0.04 to 0.86 % By weight, the content of Fe are 3.20 to 63.15% by weight and the content of Ce are 2.59 to 50.00% by weight with respect to the total amount of C, Fe and Ce, respectively. Emission control catalytic converter after Claim 1 wherein the mixture is a mixture _{including iron carbide (Fe 3} C), iron oxide and cerium oxide. Exhaust gas purification catalyst according to one of the Claims 1 or 2 , wherein the content of the mixture with respect to 100 wt .-% of the inorganic, porous, powdery carrier is 10.0 to 300 wt .-% and the mass ratio of the C atom to the Fe atom to the Ce atom, which in the Mixture are contained, 0.01 to 1.4 wt .-%: 0.1 to 98.9 wt .-%: 0.1 to 98.9 wt .-% in relation to 100 wt .-% of the total amount C, Fe and Ce. Exhaust gas purification catalyst according to one of the Claims 1 until 3 wherein the mixture further contains cobalt (Co). Emission control catalytic converter after Claim 4 wherein the Co includes from 5 to 10% by weight with respect to the total amount of C, Fe and Ce. Exhaust gas purification catalyst according to one of the Claims 1 until 5 wherein the inorganic porous powdery carrier is an inorganic porous powdery carrier containing a ceria-zirconia composite oxide. Exhaust gas purification catalyst according to one of the Claims 1 until 6th wherein a noble metal is further loaded on the exhaust gas purifying catalyst. Emission control catalytic converter after Claim 7 wherein the noble metal is platinum (Pt) or palladium (Pd). An exhaust gas purifying catalyst structure comprising a substrate and a catalyst layer which the exhaust gas purifying catalyst according to any one of Claims 1 until 8th includes. Process for the production of an exhaust gas purification catalyst according to Claim 1 comprising: dissolving an iron compound and a cerium compound in a solution; the addition of an inorganic, porous, powdery carrier thereto and the attachment of the iron compound and the cerium compound on the inorganic, porous, powdery carrier, then the loading of iron oxide and cerium oxide onto the inorganic, porous, powdery carrier with heating and calcination of the result in the Air and then; heating the result in a reactive carbon-containing gas atmosphere to obtain an exhaust gas purifying catalyst having a mixture containing carbon (C), iron (Fe) and cerium (Ce) loaded on an inorganic porous powdery carrier. Process for the production of an exhaust gas purification catalyst according to Claim 10 comprising: dissolving an iron compound, a cerium compound and a cobalt compound in a solution; the addition of an inorganic, porous, powdery carrier to it and the attachment of the iron compound, the cerium compound and the cobalt compound on the inorganic, porous, powdery carrier, then the loading of iron oxide and cerium oxide on the inorganic, porous, powdery carrier with heating and calcination of the Result in the air and then; heating the result in a reactive carbon-containing gas atmosphere to produce an exhaust gas purification catalyst with a mixture containing carbon (C), iron (Fe), cerium (Ce) and cobalt (Co) loaded on an inorganic, porous, powdery carrier , to obtain.

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