JP2012050980A - Catalyst, oxidation catalyst, reduction catalyst, and exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas, which does not contain platinum (Pt) as a catalyst component, oxidizes carbon monoxide (CO) and a hydrocarbon (HC) which are an exhaust gas component, and further can efficiently reduce nitrogen oxide (NOx).SOLUTION: A composition containing a carbon atom, an iron atom, and a cerium atom is heated, thereby the catalyst is obtained. The catalyst does not contain platinum (Pt) as a catalyst component, oxidizes carbon monoxide (CO) and a hydrocarbon (HC) which are an exhaust gas component, and further can efficiently reduce nitrogen oxide (NOx).

Description

  The present invention relates to a catalyst, an oxidation catalyst, a reduction catalyst, and an exhaust gas purification catalyst. More specifically, the present invention relates to a catalyst, an oxidation catalyst, a reduction catalyst, and an exhaust gas purification catalyst that are extremely excellent in exhaust gas purification activity and high-temperature durability and do not contain platinum (Pt) as a catalyst component.

In order to purify the exhaust gas discharged from the internal combustion engine, a three-way catalyst in which a catalyst component such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported on a carrier is mainly used. Also, odorous harmful substances such as ammonia, hydrogen sulfide (H ₂ S), formaldehyde, volatile organic compounds (VOCs) such as benzene, toluene, xylene and dichloromethane, and platinum (Pt) for oxidizing or reducing environmentally hazardous substances. The platinum catalyst which uses as a catalyst component is used (refer patent documents 1-4).

  However, among the above catalyst components, in particular, platinum (Pt) is very expensive, its reserves are small, and it is unevenly distributed on the earth, so there is a possibility that a stable supply will not be made over the long term in the future. There is. Therefore, there is a need for an exhaust gas purifying catalyst containing a catalyst component that can be stably supplied over a long period of time instead of platinum (Pt).

  For example, Patent Document 1 includes metal M element (Fe) and metal X element (Ce, Zr, Al, Ti, Mg), and releases oxygen by forming a complex oxide of M and X in a reducing atmosphere. In addition, the composite oxide is oxidized in an oxidizing atmosphere to form M oxide and X oxide, thereby providing an OSC ability to occlude oxygen. A catalyst is disclosed.

Patent Document 2 discloses that a ceria (Ce) -zirconia (ZrO ₂ ) composite oxide and the ceria (Ce) -zirconia (ZrO ₂ ) composite oxide are dispersed and at least partially dissolved. An exhaust gas purifying catalyst using a composite oxide containing iron oxide as a catalyst component is disclosed. Further, Patent Document 3 discloses a finely divided metal oxide, metal phthalocyanine as a catalyst for an adsorbent deodorant capable of effectively adsorbing and deodorizing composite harmful odorous substances such as ammonia, hydrogen sulfide, formaldehyde, and toluene. In addition, a catalyst containing titanium oxide, platinum, gold, or copper oxide as a catalyst component is disclosed. In Patent Document 4, as a catalyst for oxidizing gaseous or vapor hydrocarbons (VOCs) and selectively reducing nitrogen oxides (NOx), a rare-earth element and a heavy metal cobalt are formed on a support by a multi-stage crystallization process. Alternatively, a catalyst component in which a crystal layer of a catalytically active substance with manganese is formed is disclosed.

  However, the exhaust gas purification catalysts disclosed in Patent Documents 1 to 4 have a high catalyst activation temperature, and are satisfactory in terms of purification activity (catalytic efficiency) of each gas component contained in the exhaust gas. It wasn't possible.

  In addition, this patent applicant presents the following patent documents as prior art.

JP 2004-160433 A JP 2008-18322 A JP 2003-70887 A JP 2008-86987 A

  Therefore, an object of the present invention is to oxidize carbon monoxide (CO) and hydrocarbon (HC), which are exhaust gas components, without containing platinum (Pt) as a catalyst component, and further convert nitrogen oxide (NOx). An exhaust gas purification catalyst that can be efficiently reduced is provided.

As a means to solve the above problems, as a result of intensive studies on the activity improvement of iron and cerium-based catalysts, by adding carbon to iron compounds and cerium compounds and heating them, it has an oxidation catalyst function and a reduction catalyst function, and exhaust gas purification It has been found that a highly active catalyst can be obtained as a catalyst, and the present invention has been completed. That is, the present invention is specifically composed of the following technical means.
(1) A catalyst comprising a composition containing a carbon atom (carbon material), an iron atom (iron compound), and a cerium atom (cerium compound).
(2) The mass fraction of carbon atoms, iron atoms, and atoms in the composition is 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. The catalyst according to (1), wherein
(3) The composition is heat-treated at 100 ° C. to 800 ° C. in a gas atmosphere selected from nitrogen, argon, helium, hydrogen, water vapor, carbon dioxide, ammonia, and air ( The catalyst according to 1) or (2).
(4) The catalyst according to any one of (1) to (3), wherein the catalyst is an exhaust gas purification catalyst. (5) The constituent mass fractions of carbon atom, iron atom, and cerium atom are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. An oxidation catalyst characterized by.
(6) The oxidation catalyst according to (5), which can promote oxidation reaction of malodorous harmful substances, volatile organic compounds, environmentally hazardous substances, and chemicals at a temperature of 200 ° C. or higher and 800 ° C. or lower.
(7) The constituent mass fractions of carbon atom, iron atom, and cerium atom are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. An oxidation catalyst characterized by.
(8) The reduction catalyst according to (7), wherein the reduction reaction of malodorous harmful substances, volatile organic compounds, environmentally hazardous substances, and chemicals can be promoted at a temperature of 200 ° C. or higher and 800 ° C. or lower.

  The catalyst of this invention consists of a composition containing a carbon material, an iron compound, and a cerium compound. This catalyst is preferably heat-treated at 100 ° C. to 800 ° C. in order to further improve the activity. The catalyst of the present invention is a redox catalyst containing a carbon atom, an iron atom, and a cerium atom. Since the catalyst of the present invention has the above-described configuration, it is possible to purify exhaust gas that oxidizes CO and HC and reduces NOx, and has a low purification start temperature and high purification efficiency.

Since the catalyst of the present invention has the above-described configuration, it is possible to purify the exhaust gas that oxidizes CO and HC and reduces NOx, has a low purification start temperature and high purification efficiency, and further, ammonia, hydrogen sulfide. Hazardous substances such as (H ₂ S), formaldehyde, volatile organic compounds (VOCs) such as benzene, toluene, xylene, and dichloromethane, detoxification by oxidation or reduction of environmentally hazardous substances, or production of chemicals such as acids and alcohols It functions as an oxidation catalyst, a reduction catalyst, an exhaust gas purification catalyst, and the like.

Although the reason why the catalytic activity of the catalyst of the present invention is high is not clear, the transfer of electrons accompanying the oxidation-reduction reaction causes the iron atom to be divalent (FeO) and trivalent (Fe ₂ O ₃ ), and cerium. The atoms can change the valence between trivalent (Ce ₂ O ₃ ) and tetravalent (CeO ₂ ), so that they have a high valence in an oxidizing atmosphere and a low valence in a reducing atmosphere, thereby absorbing oxygen. It is thought that it desorbs and promotes the redox reaction. When carbon having a lower catalytic activity than iron and cerium is added thereto, the three-component catalyst becomes more active than a catalyst made of iron and cerium, so that the carbon atom is an electron of the above iron atom or cerium atom. This is thought to be due to some interaction with the exchange.

  The use temperature of the catalyst of the present invention is 200 ° C. or higher and preferably 800 ° C. or lower. When the temperature is lower than 200 ° C., the activity of the oxidation catalyst is improved, and the oxidation ability of CO and HC is remarkably improved. Similarly, the activity of the reduction scheme is improved, and the ability to reduce NOx is remarkably improved. On the other hand, when the use temperature exceeds 800 ° C., catalyst deterioration due to aggregation of catalyst components exposed for a long time is observed.

  When the catalyst of the present invention (oxidation / reduction catalyst) is used as an exhaust gas purification catalyst, on the one hand, it may reach about 800 ° C. when used in an engine direct type, but it is instantaneous and not always, Then, when it is used in an underfloor mold, it is always at a temperature of about 550 ° C., so that its function can be sufficiently exhibited. Since the composition range that can exhibit the reduction catalyst function tends to be narrower than the composition range that exhibits the oxidation catalyst function, it is desirable to use a catalyst having a composition range that can exhibit the reduction catalyst function when used as an exhaust gas purification catalyst. .

  Since the composition range that can exhibit the reduction catalyst function tends to be narrower than the composition range that exhibits the oxidation catalyst function, it is desirable to use a catalyst having a composition range that can exhibit the reduction catalyst function when used as an exhaust gas purification catalyst. . Also, since carbon is oxidized at such a high temperature, it has not been used as having low heat resistance.

  Until now, the carbon material is oxidized at such a high temperature, so that the heat resistance is low, and it has not been used as a catalyst for exhaust gas purification. However, by constructing a carbon material, an iron compound, a cerium compound, and an oxygen compound, it is surprisingly difficult to oxidize and heat resistance is improved. As a result, it has been found that the exhaust gas purifying catalyst of the present invention can be sufficiently used not only for an underfloor type engine but also for a direct type engine.

  According to the catalyst of the present invention, a catalyst containing no platinum (Pt) as a catalyst component can be provided. Furthermore, carbon monoxide (CO) and stretched hydrogen (HC) can be efficiently oxidized. In addition, nitrogen compounds (NOx) can be reduced efficiently. In addition, malodorous harmful substances, volatile organic compounds, environmentally hazardous substances, and chemicals can be efficiently oxidized.

It is the schematic of the apparatus which measures the density | concentration of NOx, CO, and HC to be purified. It is the schematic of the reaction tube in the apparatus of FIG. In Example _{1, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} It is a figure which shows the long-term test result in 600 degreeC in Example 11. FIG. It is a figure which shows the long-term test result in 800 degreeC in Example 11. FIG. FIG. 7 is an active temperature diagram of the triangular composition etc. showing the T50 of NOx in the catalysts of the compositions corresponding to the other plots in Examples 1 to 10 and the triangular composition diagram, and the catalysts of the compositions of Comparative Examples 1 to 7 below. . FIG. 7 is an active temperature diagram of triangular composition and the like showing T50 of HC in Examples 1 to 10 and catalysts having compositions corresponding to other plots in the triangular composition diagram, and catalysts having compositions of Comparative Examples 1 to 7 below. . FIG. 7 is an active temperature diagram of a triangular composition, etc. showing a T50 of CO in Examples 1 to 10 and catalysts having compositions corresponding to other plots in the triangular composition diagram, and catalysts having compositions of Comparative Examples 1 to 7 below. . In Comparative Example _{1, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} In Comparative Example _{2, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} In Comparative Example _{3, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} In Comparative Example _{4, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} In Comparative Example _{5, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.} In Comparative Example _{8, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.}

  Hereinafter, embodiments of the present invention (hereinafter referred to as “this embodiment” as appropriate) will be described.

<Catalyst>
The catalyst of this embodiment consists of a composition containing a carbon material, an iron compound, and a cerium compound. Hereinafter, each component constituting the exhaust gas purification catalyst will be described.

(Carbon material)
As the carbon material that can be used for the catalyst of the present embodiment, the carbon in the carbon material exhibits catalytic activity without reducing the catalytic activity of the iron atom in the iron compound as the catalyst component and the cerium atom in the cerium compound. As long as it can be used, there is no particular limitation. Examples of such a carbon material include at least one kind of carbon selected from graphite, furnace black, channel black, acetylene black, thermal black, nano diamond, fullerene, carbon nanotube, and graphene.

  Further, as a carbon material that can be used in the present embodiment, carbon generated by heating a precursor of the carbon material can be used as the carbon material. The precursor of the above-described carbon material is not particularly limited as long as it can be carbonized by a treatment such as thermosetting. For example, phenol resin, phenol formaldehyde resin, epoxy resin, melamine resin, urea resin, Thermosetting resins such as polyamide resin, polyimide resin, furan resin, chelate resin, polyacrylonitrile, cellulose, carboxymethylcellulose, positive sulfone, lignin, pitch, protein, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, polymethacrylic acid, Thermoplastic resins such as polyvinyl chloride, polyvinylidene chloride, polyfurfuryl alcohol, polycarboxymethyl methacrylate, and ionomer resin can be used.

  Moreover, as precursors of carbon materials, pyrrole compounds such as polypyrrole, phthalocyanine complexes, imide compounds such as polyimide and polycarbodiimide, amide compounds such as polyamide, imidazole compounds such as polyimidazole, humic acid, polyaniline, ε-caprolactam, Substances containing carbon such as organic compounds such as polyvinyl pyridine, biomass, wood, and coal can be used. That is, the catalyst of the present invention has great technical significance in that not only organic chemical industrial products made from petroleum and the like, but also natural recycled resources such as waste materials can be used as the raw material. .

  Further, as the carbon material used in the catalyst of the present invention, the above-mentioned carbon compound precursor is used in an inert gas atmosphere such as nitrogen, argon, helium, or hydrogen, water vapor, carbon dioxide, ammonia, air, etc. Those heated at 500 ° C. to 1,500 ° C. in a reactive gas atmosphere can be used. This is because heating with the above-described inert gas or active gas can increase the surface area of the carbon material and provide an activated carbon material.

  These carbon materials are porous because some carbon and hydrogen, oxygen, and nitrogen are volatilized as water, carbon dioxide, carbon monoxide, nitrogen dioxide, nitrogen monoxide, etc. from the precursor of the carbon material by heat treatment. It is a quality carbon. Furthermore, carbon was finely divided by a pulverizer such as a ball mill or a jet mill in advance, and coarse particles were removed using a sieve having a different opening to make uniform fine particles, thereby increasing the surface area of carbon and using it as a catalyst. The activity of time can be improved.

Furthermore, the above-described carbon material can be made into a nanostructure of a carbon material by utilizing a segregation reaction of a metal acetylide compound. For example, Ag ₂ C ₂ nano dendritic monolith produced from silver nitrate and acetylene in an alkaline aqueous solution is packed in a polytetrafluoroethylene container, dehydrated in a stainless steel container, and heated to 200 ° C. for an instant. Then, a segregation reaction between silver and carbon occurs, and the enormous amount of heat of reaction causes the silver to become vapor, which inflates the carbon balloon and becomes silver nanoparticles that precipitate in the carbon. When these silver particles are dissolved with silver nitrate, a graphene sheet is formed and can be used as a carbon material used in the catalyst of the present invention.

(Iron compounds)
Examples of iron compounds that can be used in the catalyst of the present invention include iron oxides, hydroxides, halides, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, organic acid salts, and iron carbides. And an iron complex such as iron ferrocyanide, and at least one iron compound selected from the group of iron phthalocyanine.

  Moreover, at least a part of the iron compound described above can be replaced with at least one compound of a nickel compound, a copper compound, and a cobalt compound. Nickel compounds, copper compounds and cobalt compounds include nickel, copper and cobalt oxides, hydroxides, halides, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, organic At least one compound selected from the group of acid salts and ferrocyanides can be used.

(Cerium compound)
Examples of cerium compounds that can be used in the catalyst of the present invention include cerium oxides, hydroxides, halides, complexes, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, and organic acid salts. And at least one cerium compound selected from the group.

  Moreover, as a cerium compound which can be used by this invention, it can substitute by containing at least 1 type of compound of a zirconium (Zr) type | system | group and a lanthanum type compound. The lanthanum compound is selected from the group of lanthanum oxides, hydroxides, halides, complexes, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, and organic acid salts. Further, at least one kind of lanthanum compound or the like can be used.

  When the catalyst in this embodiment is used for exhaust gas purification, NOx that is difficult to purify as compared with CO and HC is reduced. The exhaust gas purification catalyst functions as a three-way catalyst that simultaneously purifies NOx, CO, and HC in an oxidation-reduction atmosphere in which oxygen and a reducing agent coexist.

As an exhaust gas containing NOx, CO, and HC, for example, an exhaust gas of an automobile is assumed. In automobile exhaust gas, CO is oxidized to CO ₂ in an oxidizing atmosphere, HC is oxidized to water and CO ₂ , and NOx is reduced to nitrogen in a reducing atmosphere, but the region where oxidation and reduction react in a well-balanced region is the stoichiometric air-fuel ratio. Limited to neighborhood. Therefore, in order for the catalyst of the present invention to function as a three-way catalyst for automobile exhaust gas purification, it is desirable that the composition of the automobile exhaust gas is controlled in the vicinity of the stoichiometric air-fuel ratio.

The catalyst can be used mainly for purification of automobile exhaust gas, but is not limited to this, and can also purify NOx, CO, and HC contained in other gases. For example, a CO removal device for supplying gas to the fuel electrode of a fuel cell, suitable for use as an oxidation catalyst for removing a small amount of CO contained in hydrogen obtained by reforming natural gas or the like as fuel for a fuel cell The oxidation catalyst for purifying exhaust gas according to the present invention is disposed in the catalyst, or the oxidation catalyst is mixed with the fuel electrode catalyst of the fuel cell and used in the fuel electrode portion, so that CO in hydrogen is oxidized to CO ₂ , and the electrode catalyst Can also be prevented.

Incidentally, NOx NOx, CO, or hydrocarbons and measuring the ratio which is converted to be oxidized or reduced CO ₂ or nitrogen by the catalyst, for example, can also be used automobile exhaust gas directly included Since it is difficult to control the concentration of CO, HC, model gas can also be used. The model gas preferably has a composition similar to, for example, actual exhaust gas of a gasoline vehicle.

<Device for measuring the concentration of model gas>
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, the apparatus for measuring the concentration of the model gas is 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, and a gas analyzer 9. Etc.

  First, each model gas is generated from the standard 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 each gas is merged by the evaporator 5. Introduced into the reaction tube 6. 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 steamed in the cooler 8 and then analyzed in the gas analyzer 9. The gas analyzer 9 can perform quantitative analysis of O ₂ , H _2, CO, N ₂ O, CO ₂ , HC (C ₃ H ₆ ), H _2, etc. by gas chromatography, for example, NOx, NO, NO ₂ , CO, SO _{2 and the} like can be quantitatively analyzed with, for example, a NOx analyzer.

For the analysis of the above gas, specifically, gas chromatography (product name: GC-14B, such as O ₂ , H ₂ , CO, N ₂ O, CO ₂ , hydrocarbon (HC), etc. of Shimadzu Corporation) perform quantitative analysis, NOx analyzer (product name: PG-250) of HORIBA, Ltd in _{NO x, NO, NO 2,} CO, a quantitative analysis of such SO ₂ was conducted.

  The reaction tube 6 is made of quartz. As shown in FIG. 2, the exhaust gas purification catalyst 10 is preferably filled in the center thereof. Then, quartz sand 11 and quartz wool 12 can be packed on both sides of the catalyst 10 in order to distribute the model gas to a portion where the catalyst is present.

In the above measuring apparatus, the purification performance of the catalyst can be 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%
C ₃ H ₆ conversion = _(C 3 _{H 6} molar flow rate of the inlet of the _C 3 _{H 6} molar flow rate primary outlet) / (inlet of _C 3 _{H 6} molar flow rate) × 100%
CO conversion rate = (CO molar flow rate at the inlet 1 CO molar flow rate at the outlet) / (CO molar flow rate at the inlet) × 100%
H ₂ conversion = _{(H 2} molar flow rate of the inlet of the _{H 2} molar flow rate primary outlet) / (inlet of _{H 2} molar flow rate) × 100%

The above conversion rate indicates how much NOx, CO, H ₂ , and HC are oxidized or reduced by the catalyst, and the higher conversion rate indicates that the higher one is oxidized or reduced, 100% If present, it indicates that NOx, CO, and HC have been completely purified.

<Method for producing exhaust gas purification catalyst>
The method for producing the exhaust gas purifying catalyst of the present invention is not particularly limited, and examples thereof include a production method including the following steps. A solution or dispersion of at least one compound of iron compound and at least one compound of cerium compound is prepared. These compounds are preferably deposited from a solvent in order to uniformly adhere to the carbon surface as metal ions, and those having high solubility are used. The solvent is preferably water, but ethanol or a mixture of water and ethanol can also be used.

  The concentration of the compound in the solution is preferably 0.5 to 50.0 g / L. The amount of the iron compound and the cerium compound needs to be used based on the atomic fraction (constituent mass fraction) of iron atoms and cerium atoms contained in the catalyst after heating. However, even if at least one of these compounds is an insoluble compound, it can be used by dispersing it in water as fine particles having an average particle size of about 0.1 to 1 μm and uniformly adhering to the carbon surface.

  While stirring the obtained solution or dispersion with a propeller-type stirrer or the like, a carbon material is added to prepare a uniform mixed solution. The amount of carbon material to be added needs to be used based on the atomic fraction of carbon atoms contained in the exhaust gas purification catalyst after heating. Since carbon atoms in the carbon material tend to decrease during heating, it is necessary to consider the amount of decrease in advance. In order to uniformly mix the added carbon with the iron compound and the cerium compound and disperse the aggregated carbon, the carbon can be mixed using a dispersing machine such as a ball mill, a sand mill, or a homomixer.

  The mixed solution can be dried by removing the solvent with a dryer at 100 ° C. to 150 ° C., put into a heating furnace after drying, and heated at 200 ° C. to 1,500 ° C. to prepare a catalyst. During heating, the heating furnace contains an inert gas such as nitrogen, argon or helium, or a model gas similar to the exhaust gas used to measure catalytic activity, and a reactive gas such as carbon dioxide, water vapor, or hydrogen. It is desirable to heat while inflowing.

  As described above, by introducing an inert gas during heating, volatile components and pyrolysis products contained in carbon atoms, iron compounds and cerium compounds in the carbon material can be discharged out of the heating furnace as they are. . Further, the same gas as the exhaust gas can be introduced. Furthermore, the catalyst can be activated by flowing a reactive gas such as carbon dioxide, water vapor, or hydrogen.

  When a carbon precursor is used as the carbon material used in the present invention, before carbonization, the carbon precursor is mixed with an iron compound and a cerium compound, and after homogenized and dried, 100 ° C to 800 ° C. It is also possible to produce an exhaust gas purifying catalyst by one heating.

  Hereinafter, in order to clarify the technical scope of the present invention, samples with varying contents of carbon material, iron compound, and cerium compound were prepared, and the exhaust gas purification performance of the sample was tested. EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples. Samples were prepared as follows.

<Example 1>
(Manufacture of exhaust gas purification catalyst)
In a beaker containing 50 mL of distilled water at room temperature, put 12.43 g of iron (II) nitrate (9 hydrate) (Kishida Chemical Co., Ltd.) and 24.22 g of cerium (III) nitrate (hexahydrate) The mixture was stirred with a stirrer and completely dissolved. While stirring, 0.5 g of graphite (Wako Pure Chemical Industries, Ltd.) was added to the solution and stirred for 10 minutes, and then 28% by mass of ammonia water was added until the pH value reached 10, and carbon-iron -A precipitate consisting of cerium was obtained. Furthermore, after stirring at a rotational speed of 600 rpm for 3 hours, the solution was filtered to separate precipitates, washed with water and dried at 120 ° C. to obtain a three-way catalyst. The composition of the catalyst was measured with an ICP emission analyzer (ICPE-9000, manufactured by Shimadzu Corporation). The catalyst composition also contains oxygen, but was excluded from the composition determination. The sample was ground in a mortar and passed through a 40 mesh screen.

  The obtained sample was filled in 0.1 g at the center of a quartz reaction tube having an inner diameter of 6 mm, and 0.5 g of quartz sand was packed on each side of the catalyst layer in order to make the gas distribution uniform. Place the quartz reaction tube in an electric heater, adjust the model gas containing NOx, HC and CO shown in Table 1 to a theoretical air-fuel ratio of 14.63, and let it flow at 150 mL / min. The reaction tube was heated to 800 ° C. at a temperature increase rate of 20 ° C./min. From 200 ° C. to 800 ° C., the temperature increase was stopped every 100 ° C., held for 1 hour, and the conversion rate was determined from the concentrations of the inflow gas (NOx, HC, CO) and the outflow gas. A graph of temperature and conversion is shown in FIG. The temperature (T50) at which the conversion was 50% was determined from FIG.

<Examples 2 to 10>
In Example 1, the amounts of iron (II) nitrate (9 hydrate), cerium (III) nitrate (hexahydrate) and graphite were measured according to No. 2 in Table 2. Except changing to the quantity shown in 2-10, operation similar to Experimental example 1 was performed and T50 of each gas of NOx, HC, and CO was calculated | required. The results are also shown in Table 2.

  The T50 measurement values of the catalysts having the compositions corresponding to the other plots in the triangular composition diagram of Examples 1 to 10 and FIG. 6 and the catalysts of the compositions of Comparative Examples 1 to 7 below were obtained from Lightstone Corporation, Origin Pro 7.5. Using graphing software, a composition in which the T50 of each gas has the same temperature was connected to a triangular composition isoactive diagram of carbon, iron, and cerium by a line (isoactive temperature line). The triangular composition diagram in the case of NOx is shown in FIG. 6, the case of HC in FIG. 7, and the case of CO in FIG. The NOx, HC, and CO gas T50 was highest for NOx, and CO was the lowest in the order of HC and CO.

  For each gas, the catalyst composition is a single component (the apex of the triangle composition isoactivity diagram: carbon, iron, cerium) and two components (the sides of the trigonometric composition activity diagram: carbon-iron, carbon-cerium, iron-cerium) ), T50 tends to be lower in the case of 3 components. From the activity diagram of three triangular compositions, the composition range of the catalyst of the present invention is as follows: carbon: 1 to 70% by mass, iron: 5 to 65% by mass, cerium 5 to 90% by mass (calculating oxygen atoms Not rate). Among them, in particular, a catalyst having a composition mass fraction of carbon, iron, and cerium of 5.0%, 17.0%, and 78.0%, respectively, has the lowest T50 and high purification performance. was gotten.

  As shown in FIG. 3, in the catalyst of Example 1, CO was oxidized at 300 ° C., and a conversion rate of 94% was obtained. At 400 ° C., CO was completely purified, and HC was about 92% conversion. Although the reduction temperature of NOx is higher than that of CO and HC, about 34% of NOx was reduced at 400 ° C., and harmful three components were oxidized and reduced and purified at 500 ° C. The T50s of NOx, CO, and HC were as shown in Table 2, and were 425 ° C, 251 ° C, and 290 ° C, respectively.

<Example 11>
FIG. 4 shows the long-term test results (durability) at 600 ° C. with the catalyst amount of Example 1 being 0.3 g. As a result, it was confirmed that the conversion rate of about 100% was maintained for 20 hours for all of NOx, CO, and C ₃ H _{6 and} that this catalyst had high durability at 600 ° C.

FIG. 5 shows long-term test results (durability) at 800 ° C. with the catalyst amount of the catalyst of Example 1 being 0.3 g. As shown in the figure, the initial activity was obtained by completely purifying NOx, CO, and C ₃ H ₆ on this catalyst at 800 ° C., but the NOx conversion rate decreased by about 7% with the test time. However, after about 10 hours, the NOx conversion of about 93% could be maintained, and there was no deterioration until 50 hours. The activities of CO, C ₃ H ₆ , and H ₂ could be maintained up to 50 hours while maintaining the initial activity. It was confirmed that this catalyst has high durability even at a high temperature of 800 ° C.

(Comparative Example 1) (without catalyst)
The reaction gas was allowed to flow without putting the catalyst into the reaction tube, and the conversion rates of NO _x , CO, and HC were measured. The results are shown in FIG.

  As shown in FIG. 9, when no catalyst was added, the NOx and CO conversions at 200 to 800 ° C. were almost zero. The conversion rate of HC gradually improved at 500 ° C. or higher, but it was only 64% even at 800 ° C. It was confirmed that the gas could not be purified unless a catalyst was added.

(Comparative Example 2) (Graphite)
A commercially available graphite as a carbon raw material was put into a reaction tube, a reaction gas was allowed to flow, and measurement was performed in the same manner as described above. The results are shown in FIG. 10 and Table 2.

  As shown in FIG. 10, in the case of commercially available graphite, even if the temperature was increased to 800 ° C., the conversion rate of NOx and CO was not improved, and the catalytic effect was not obtained.

(Comparative Example 3) (Carbon-Iron)
In Example 1, a catalyst in which the atomic ratio of carbon to iron was 50% and 50% without using cerium was prepared. 0.1 g of the catalyst was put in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The results are shown in FIG.

  As shown in FIG. 11, in the case of a catalyst composed of carbon and iron, the NOx conversion was almost zero at 400 or less. Even at 500 ° C., it was only 52%. NOx was completely purified at 800 ° C. At 400 ° C., the CO conversion was 69%. The temperature was raised to 500 ° C. to completely purify CO.

(Comparative Example 4) (Carbon-cerium)
As a comparative example, a catalyst composed of carbon and cerium without using Fe was placed in a reaction tube, and a reaction gas was allowed to flow, and measurement was performed in the same manner as described above. The constituent mass fractions of carbon atom and cerium atom are 50% and 50%, respectively. The results are shown in FIG.

  As shown in FIG. 12, in the case of a catalyst composed of carbon and cerium, the NOx conversion was almost zero at 400 or less. Even at 500 ° C., it was only 15%. As the temperature increased, the NOx conversion rate gradually increased, and when it reached 700 ° C. or higher, NOx was completely purified. The CO conversion was 67 at 400 ° C. The temperature was raised at 500 ° C. to completely purify CO. HC had a conversion of 36 at 400 ° C. and was 87% at 500 ° C.

(Comparative Example 5) (Iron-cerium)
As a comparative example, a catalyst made of iron and cerium without using carbon was placed in a reaction tube, and a reaction gas was allowed to flow, and measurement was performed in the same manner as described above. The constituent mass fractions of iron atom and cerium atom are 25% and 75%, respectively. The results are shown in FIG.

As shown in FIG. 13, the catalyst composed of iron and cerium had a NOx conversion rate of almost zero at a temperature of 400 or less. As the temperature increased, the NOx conversion rate gradually improved, but even at 800 ° C., there was only a 77% conversion rate. HC was oxidized from 300 degrees and a conversion of 74% was obtained at 400 ° C. CO was oxidized from 300 ° C. to a conversion rate of 67%, and at 400 ° C., the CO was completely purified.
Put in

(Comparative Example 6)
As a comparative example, a catalyst made of only iron without using carbon and cerium was put in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The results are shown in Table 2.

  As shown in Table 2, the catalyst composed only of iron had a high T50 for any gas even when compared with the above-mentioned two-way catalyst.

(Comparative Example 7)
As a comparative example, a catalyst consisting only of cerium without using carbon and iron was placed in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The results are shown in Table 2.

  As shown in Table 2, the catalyst consisting only of cerium had a higher T50 for any gas than the catalyst consisting only of iron.

(Comparative Example 8) (Pt-cerium oxide)
As a comparative example, a commercial Pt-cerium oxide catalyst for exhaust gas purification was placed in a reaction tube as a catalyst made of Pt without using a carbon material, and a reaction gas was allowed to flow, and measurement was performed in the same manner as described above. The amount of Pt supported is 1.0 wt%. The results are shown in FIG.

  As shown in FIG. 14, in the case of the Pt-based catalyst, the conversion rates of NOx, HC, and CO were almost zero at 250 ° C. or lower. Although the conversion rate was considerably low even at 300 ° C., the three components of NOx, HC, and CO were almost completely purified at a conversion rate of about 100% above 500 ° C.

  Table 2 summarizes the temperatures of the active T50s described in the above examples and comparative examples. Also from this table, it can be seen that the C-Fe-Ce-based catalyst of the example shows a temperature at which the T50 value of harmful three components is lower than the catalyst of the other comparative examples, and the catalytic activity is most excellent. It can be said.

  According to the present invention, CO and HC are oxidized with a catalyst composed of a composition containing carbon atoms (carbon material), iron atoms (iron compound), and cerium atoms (cerium compound) without using Pt. Thus, it is possible to provide an oxidation catalyst, a reduction catalyst and an exhaust gas purification catalyst that can be purified by reducing NOx.

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 path, 8 ... cooler, 9 ... gas analyzer, 10 ... catalyst, 11 ... quartz sand, 12 ... quartz wool, 13 ... thermocouple

Claims (8)

A catalyst comprising a composition containing a carbon atom, an iron atom, and a cerium atom. The mass fractions of carbon atoms, iron atoms, and cerium atoms in the composition are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. The catalyst according to claim 1. 2. The composition according to claim 1, wherein the composition is heat-treated at 100 ° C. to 800 ° C. in a gas atmosphere selected from nitrogen, argon, helium, hydrogen, water vapor, carbon dioxide, ammonia, and air. 2. The catalyst according to 2. The catalyst according to any one of claims 1 to 3, wherein the catalyst is an exhaust gas purifying catalyst. The constituent mass fractions of carbon atoms, iron atoms, and cerium atoms are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. Oxidation catalyst. The oxidation catalyst according to claim 5, wherein the oxidation reaction of malodorous harmful substances, volatile organic compounds, environmentally hazardous substances, and chemicals can be promoted at a temperature of 200 ° C or higher and 800 ° C or lower. The constituent mass fractions of carbon atoms, iron atoms, and cerium atoms are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. Oxidation catalyst. The reduction catalyst according to claim 7, wherein the reduction reaction of malodorous harmful substances, volatile organic compounds, environmentally hazardous substances, and chemicals can be promoted at a temperature of 200 ° C or higher and 800 ° C or lower.