JP5899525B2 - Exhaust gas purification catalyst and catalyst body supporting the same - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst and a catalyst body supporting the exhaust gas purifying catalyst. More specifically, the present invention relates to an exhaust gas purification catalyst that has excellent exhaust gas purification activity and durability and does 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 (CeO ₂ ) -zirconia (ZrO ₂ ) composite oxide and a ceria (CeO ₂ ) -zirconia (ZrO ₂ ) composite oxide are dispersed at least partially in a solid solution. 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, the problem of the present invention is to contain platinum (Pt) as a catalyst component,
An object of the present invention is to provide an exhaust gas purifying catalyst that can oxidize carbon monoxide (CO) and hydrocarbons (HC), which are exhaust gas components, and efficiently reduce nitrogen oxides (NOx). Furthermore, an object of the present invention is to provide an exhaust gas purification catalyst having a purification start temperature as low as 300 ° C. or lower and a purification efficiency of each gas component contained in the exhaust gas of 99% or more.

  As a result of intensive studies in order to solve the above problems, the present inventor has added a specific amount of palladium to a catalyst precursor heated by adding a carbon material to an iron compound and a cerium compound. The present inventors have found that an exhaust gas catalyst having excellent high-temperature durability can be obtained. That is, the present invention is specifically composed of the following technical means.

(1) A method for producing an exhaust gas purifying catalyst , characterized in that a palladium compound is contained in a catalyst precursor obtained by heating a composition containing a carbon material, an iron compound, and a cerium compound.

(2) The catalyst precursor has a weight fraction of 1.0 to 70.0% by weight of carbon atoms in the carbon material, iron atoms in the iron compound, and cerium atoms in the cerium compound, respectively. It is 0-65.0% and 5.0-90.0%, The manufacturing method of the exhaust gas purification catalyst as described in (1) characterized by the above-mentioned.

(3) The weight fraction of palladium atoms in the palladium compound with respect to the exhaust gas purification catalyst is 0.035 to 0.30%, preferably 0.035 to 1.0%, more preferably 0.035 to The method for producing an exhaust gas purifying catalyst according to (1) or (2), wherein the content is 0.35%.

(4) The exhaust according to any one of (1) to (3), wherein the carbon material is manufactured by heat treatment in a gas atmosphere selected from water vapor, hydrogen gas, and nitrogen gas. A method for producing a gas purification catalyst.

(5) The method for producing an exhaust gas purifying catalyst according to any one of (1) to (4), wherein the carbon material is graphite.

(6) A method for producing a catalyst body , characterized in that an exhaust gas purification catalyst produced by the method for producing an exhaust gas purification catalyst described in any one of (1) to (5) is supported on a catalyst carrier.

  According to the present invention, carbon monoxide (CO) and hydrocarbons (HC) contained in exhaust gas can be efficiently oxidized, and nitrogen oxide (NOx) can be efficiently reduced. It is possible to provide an exhaust gas purifying catalyst that is excellent in durability at high temperature of not lower than ° C. and does not contain platinum (Pt) as a catalyst component.

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, a diagram illustrating NOx, CO, and conversion of HC _(C 3 _{H 6).} 2 is a diagram showing test results at 200 to 1000 ° C. of an exhaust gas purifying catalyst in Example 1. FIG. It is a figure which shows the test result (durability) for a long time in 200-1000 degreeC of the exhaust gas purification catalyst in Example 1. FIG. It is a figure which shows the test result (durability) for a long time in 200-1000 degreeC of the exhaust gas purification catalyst in Example 1. FIG. In Example 2, a diagram showing NOx, CO, and conversion of HC _(C 3 _{H 6).} It is a figure which shows the measurement result at the time of carrying out nitrogen gas treatment of the carbon material which comprises the exhaust gas purification catalyst in Example 3. FIG. It is a figure which shows the measurement result at the time of carrying out hydrogen gas processing of the carbon material which comprises the catalyst for exhaust gas purification in Example 4. FIG. It is a figure which shows the measurement result at the time of carrying out the steam process of the carbon material which comprises the catalyst for exhaust gas purification in Example 5. FIG. 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.} It is a figure which shows the conversion rate of NOx and CO in the comparative example 3. 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 _{6, NOx, CO, HC (} C 3 H 6), is a diagram illustrating the conversion of _{H 2.}

  Hereinafter, embodiments of the present invention will be described in detail.

<Exhaust gas purification catalyst>
The exhaust gas purifying catalyst of the present invention is characterized in that a palladium precursor is contained in a catalyst precursor obtained by heating a composition containing a carbon material, an iron compound, and a cerium compound. is there. Hereinafter, each component constituting the exhaust gas purification catalyst will be described.

(Carbon material)
As the carbon material that can be used in the exhaust gas purifying catalyst of the present invention, the carbon in the carbon material is catalytically active 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. If it can exhibit, it will not be restrict | limited in particular. Examples of the carbon material include graphite, furnace black, channel black, acetylene black, thermal black, nano diamond, fullerene, carbon nanotube, graphene, and the like.

  Moreover, what was produced | generated by heating the precursor of a carbon material as said carbon material can also be used as a carbon material. The precursor of the 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. , Polyamide resin, polyimide resin, furan resin, chelate resin, polyacrylonitrile, cellulose, carboxymethyl cellulose, positive sulfone, lignin, pitch, protein and other thermosetting resins, 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 exhaust gas purifying 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. It is what you have.

  Furthermore, as the carbon material used for the exhaust gas purifying catalyst of the present invention, the precursor of the above carbon material is used in an inert gas atmosphere such as nitrogen, argon, helium, or hydrogen, water vapor, carbon dioxide gas, ammonia. In addition, a heat-treated product at 500 to 1500 ° C. in a reactive gas atmosphere such as air can be used. This is because heat treatment with the inert gas or the active gas can increase the surface area of the carbon material to obtain 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. Carbon material. Furthermore, the carbon material is finely divided in advance with a pulverizer such as a ball mill or a jet mill, and coarse particles are removed using a sieve having different openings to make uniform fine particles, thereby increasing the surface area of the carbon material and exhaust gas. The catalytic activity when used as a purification catalyst can be improved.

Furthermore, the 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 for the exhaust gas purifying catalyst of the present invention.

(Iron compounds)
Iron compounds that can be used in exhaust gas purifying catalysts include iron oxides, hydroxides, halides, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, organic acid salts, carbonization Examples thereof include iron and iron complexes such as iron ferrocyanide, and at least one iron compound selected from the group of iron phthalocyanine.

  Moreover, at least one part of the said iron compound can be substituted by at least 1 type of 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 Acid salts, ferrocyanides and the like can be used.

(Cerium compound)
The cerium compounds that can be used in exhaust gas purification catalysts include cerium oxides, hydroxides, halides, complexes, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, and organic acid salts. Etc. can be used.

  Further, at least a part of the cerium compound can be substituted with at least one kind of zirconium (Zr) -based compound or lanthanum-based compound. Zirconium-based and lanthanum-based compounds include zirconium and lanthanum oxides, hydroxides, halides, complexes, nitrates, nitrites, carbonates, acetates, sulfides, sulfates, sulfites, and organic acid salts. One or more kinds of zirconium compounds and lanthanum compounds selected from among them can be used.

(Catalyst precursor)
The catalyst precursor of the exhaust gas purifying catalyst of the present invention is obtained by heat-treating the composition containing the above carbon material, iron compound and cerium compound, and contains carbon atoms, iron atoms and cerium atoms.

  The conditions for heat-treating the composition containing the carbon material, iron compound and cerium compound are not particularly limited as long as the heating conditions can improve the durability of the exhaust gas purification catalyst. . For example, the temperature used as the exhaust gas treatment catalyst is preferably 300 to 800 ° C. When the heating temperature is 300 ° C. or higher, the durability of the exhaust gas purifying catalyst is improved, and when it is 600 ° C. or lower, it is preferable because the operating temperature is when the catalyst is used.

  The time for the heat treatment is not particularly limited, but is preferably 1.0 to 3.0 hours. If it is 1.0 hour or longer, durability is obtained as a sufficient catalyst, and it is preferable that the time is 3.0 hours or shorter, because the time for catalyst preparation becomes short.

  The catalyst precursor is obtained by heat-treating a composition containing the carbon material, iron compound, and cerium compound, and therefore oxidizes carbon monoxide (CO) and hydrocarbon (HC) to form nitrogen. It is possible to purify the exhaust gas by reducing oxide (NOx), the purification start temperature as the exhaust gas purification catalyst is as low as 300 ° C., and the purification efficiency is as high as about 99%, and the exhaust gas purification catalyst And so on.

Although the reason why the catalytic activity as the exhaust gas purifying catalyst is increased by using the catalyst precursor is not clear, the transfer of electrons accompanying the oxidation-reduction reaction causes the iron atom to have a divalent valence ( FeO) and trivalent (Fe ₂ O ₃ ), and the cerium atom can change the valence to trivalent (Ce ₂ O ₃ ) and tetravalent (CeO ₂ ), so in an oxidizing atmosphere it becomes high valence. In a reducing atmosphere, oxygen is adsorbed and desorbed due to a low valence, and the oxidation-reduction reaction is promoted. If a carbon material having a lower catalytic activity than iron and cerium atoms is added thereto, the three-component catalyst is more active than a catalyst comprising iron and cerium, so that the carbon atoms in the carbon material are iron atoms and cerium. It is thought to have some interaction with the transfer of atoms' electrons.

  The catalyst precursor is obtained by heating a composition containing a carbon material, an iron compound, and a cerium compound, and the constituent weight of the carbon atom in the carbon material, the iron atom in the iron compound, and the cerium atom in the cerium compound. The fractions are 1.0 to 70.0%, 5.0 to 65.0%, and 5.0 to 90.0%, respectively. When the constituent atomic fraction of the carbon atom in the carbon material, the iron atom in the iron compound, and the cerium atom in the cerium compound is less than the lower limit or exceeds the upper limit, Since the activity decreases, it is not preferable because the amount of the catalyst component used needs to be increased.

(Palladium compound)
The exhaust gas purifying catalyst of the present invention is a quaternary redox catalyst containing a palladium precursor in addition to a catalyst precursor obtained by heating a composition containing a carbon material, an iron compound and a cerium compound.

The exhaust gas purifying catalyst contains a palladium compound as a fourth component in the catalyst precursor, so that it is possible to purify exhaust gas by oxidizing CO and HC and reducing NOx. Low purification start temperature and high purification efficiency. Moreover, harmful substances such as ammonia, hydrogen sulfide (H ₂ S), formaldehyde, volatile organic compounds (VOCs) such as benzene, toluene, xylene, dichloromethane, and environmental load substances. It functions as an exhaust gas purification catalyst that can be used for detoxification by oxidation or reduction, or for the production of chemicals such as acids and alcohols. Furthermore, the exhaust gas purifying catalyst is excellent in high temperature durability because the catalyst precursor is treated at a high temperature.

  Palladium compounds that can be used in exhaust gas purification catalysts include palladium chloride, hydroxide, halide, nitrate, nitrite, carbonate, acetate, sulfide, sulfate, sulfite, organic acid salt, citric acid. Examples thereof include iron complexes such as acid salts, palladium carbide and palladium ferrocyanide, and palladium compounds such as palladium phthalocyanine. Among the palladium compounds, palladium chloride, palladium nitrate, palladium acetate, and palladium citrate are preferable.

  Further, at least a part of the palladium compound can be replaced with at least one kind of compound of nickel compound, copper compound, and 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 Acid salts, ferrocyanides and the like can be used.

<Catalyst body for exhaust gas purification>
The exhaust gas purifying catalyst of the present invention can be made into a catalyst body by being supported on a catalyst carrier. By carrying the exhaust gas purifying catalyst on a catalyst carrier having a large surface area and durability at high temperatures, purification activity and durability at high temperatures can be improved.

<Exhaust gas treatment with exhaust gas purification catalyst>
The exhaust gas purifying catalyst of the present invention functions both as a so-called oxidation catalyst and a reduction catalyst. The exhaust gas purifying catalyst can oxidize carbon monoxide (CO) into carbon dioxide (CO ₂ ) in an oxidizing atmosphere. The conversion rate to CO ₂ is improved. When the temperature is 250 ° C. or higher, the conversion rate is further improved. When the temperature is 300 ° C. or higher, the conversion rate is almost 100%, and carbon monoxide (CO) can be purified almost completely. . Ammonia, sulfur oxide (SOx), and hydrogen sulfide (H ₂ S) can also be converted to nitrogen (N ₂ ), sulfuric acid, water, and the like, respectively.

Further, the exhaust gas purifying catalyst of the present invention can oxidize hydrocarbons such as propane and butane more efficiently to water and CO ₂ when the oxidation temperature is 200 ° C. or higher. Becomes a 250 ° C. or higher to improve the conversion of water and CO _2. When the temperature is 300 ° C. or higher, the conversion rate is almost 100%, and the hydrocarbons in the exhaust gas can be purified almost completely.

  The use temperature of the exhaust gas purifying catalyst of the present invention is preferably 200 ° C. or higher and 800 ° C. or lower. If it is 200 ° C. or higher, the activity as an oxidation catalyst is improved, and carbon monoxide (CO) or carbonization is performed. The oxidation ability of hydrogen (HC) is significantly improved. Moreover, the activity as a reduction catalyst improves that it is 200 degreeC or more, and the capability to reduce | restore nitrogen oxide (NOx) comes to be remarkably excellent.

  In addition, it is not preferable that the use temperature of the exhaust gas purifying catalyst exceeds 800 ° C., because catalyst deterioration due to aggregation of catalyst components exposed for a long time is observed.

  The exhaust gas purifying catalyst of the present invention may be used in an environment up to about 800 ° C. in an engine direct type, but it is instantaneous, and even in an under floor type, it is always used at a temperature of about 300 to 400 ° C. Therefore, the function can be sufficiently exhibited. Since the composition range in which the reduction catalyst function can be exhibited tends to be narrower than the composition range in which the function as an oxidation catalyst is exhibited, it is desirable to use a catalyst having a composition range capable of exhibiting a function as a reduction catalyst. Further, since carbon materials are usually oxidized at such high temperatures and have low heat resistance, they have not been used as exhaust gas purification catalysts.

However, by forming a compound of carbon, iron, cerium, and oxygen, it is surprisingly difficult to oxidize even at a high temperature of about 800 ° C. and heat resistance is improved. it can. Furthermore, by including palladium as the fourth component, the purification activity as a catalyst and the high temperature durability are also excellent.

  The exhaust gas purifying catalyst of the present invention functions as a reduction catalyst and reduces nitrogen oxides (NOx) in a reducing atmosphere. It can also be used as an industrial reduction catalyst such as reducing acid to aldehyde and alcohol. The temperature for reducing nitrogen oxide (NOx) is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, and further preferably 400 ° C. or higher.

  Furthermore, the exhaust gas purifying catalyst in the present embodiment can reduce nitrogen oxide (NOx) that is difficult to purify as compared with carbon monoxide (CO) or hydrocarbon (HC). As an exhaust gas purifying catalyst, nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) contained in the exhaust gas can be purified.

The automobile exhaust gas treated by the exhaust gas purifying catalyst of the present invention is carbon monoxide (CO) to carbon dioxide (CO ₂ ) and hydrocarbon (HC) to water and carbon dioxide (CO ₂ ) in an oxidizing atmosphere. Oxidized and nitrogen oxide (NOx) is reduced to nitrogen in a reducing atmosphere, but the region where oxidation and reduction react with a good balance is limited to the vicinity of the theoretical air-fuel ratio. Therefore, in order for the exhaust gas purification catalyst to function as a three-way catalyst, it is desirable that the composition of the automobile exhaust gas be controlled in the vicinity of the stoichiometric air-fuel ratio.

The exhaust gas purification catalyst can be used mainly for purification of automobile exhaust gas, but is not limited to this, and nitrogen oxide (NOx) and carbon monoxide (CO) contained in other gases. ), Hydrocarbon (HC) can also be purified. For example, it is suitable for use as an oxidation catalyst that removes a small amount of carbon monoxide (CO) contained in hydrogen obtained by reforming natural gas or the like as fuel for a fuel cell, and supplies gas to the fuel electrode of the fuel cell Carbon monoxide (CO) in hydrogen by disposing the present oxidation catalyst in a carbon monoxide (CO) removal device for the use, or mixing this oxidation catalyst with the fuel electrode catalyst of the fuel cell and using it in the fuel electrode portion Can be oxidized to carbon dioxide (CO ₂ ) to prevent poisoning of the electrode catalyst.

To measure the rate at which nitrogen oxides (NOx), carbon monoxide (CO), or hydrocarbons (HC) are oxidized or reduced by the exhaust gas purification catalyst and converted to CO ₂ , nitrogen, etc. For example, automobile exhaust gas can be used directly. However, since it is difficult to control the concentration of nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) contained in the exhaust gas, a model gas can also be used. The model gas preferably has a composition similar to, for example, actual exhaust gas of a gasoline vehicle.

FIG. 1 shows a schematic diagram of an apparatus for measuring the concentration of a model gas containing C ₃ H ₆ 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 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, for example, NOx, NO, NO ₂ , CO, SO _{2 and the} like can be quantitatively analyzed by, for example, a NOx analyzer.

  The reaction tube 6 is made of quartz. As shown in FIG. 2, the exhaust gas purifying catalyst 10 is preferably filled in the central portion 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 purification 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 cerium compound needs to be used based on the atomic fraction (constituent weight fraction) of the iron atom and cerium atom contained in the heated catalyst. However, even if at least one of these compounds is an insoluble compound, it should be used by dispersing it in water as fine particles having an average particle size of about 0.1 to 1.0 μm and evenly adhering to the surface of the carbon material. You can also.

  While stirring the obtained solution or dispersion with a propeller-type stirrer or the like, carbon 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 material with the iron compound and the cerium compound and disperse the aggregated carbon, the carbon material can be mixed using a dispersing machine such as a ball mill, a sand mill, or a homomixer.

  The mixed liquid can be dried by removing the solvent with a dryer at 100 to 150 ° C., put into a heating furnace after drying, and heated at 200 to 1500 ° 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.

  In this way, by flowing an inert gas during heating, the volatile components and pyrolysis products contained in the carbon atoms, iron compound and cerium compound in the carbon material can be discharged out of the heating furnace as they are. Further, a gas containing the same component as the exhaust gas can be introduced. Furthermore, the catalyst precursor can be activated by flowing a reactive gas such as carbon dioxide, water vapor, or hydrogen.

  When using a carbon precursor as a carbon material to be 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, by heating, It is also possible to produce the catalyst precursor with a single heating.

  A palladium solution in which a palladium compound is dissolved is added to the catalyst precursor thus prepared and stirred. The palladium component is dispersed and supported on the catalyst precursor by stirring, and this is dried at a low temperature and calcined in the air, whereby an exhaust gas purification catalyst can be produced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples at all.

<Example 1>
(Manufacture of exhaust gas purification catalyst)
The exhaust gas purifying catalyst used in this example was prepared as follows. The carbon material used in this example is powdered commercial graphite (Wako Pure Chemical Industries, Ltd.). The iron compound containing iron is iron (III) nitrate (9 hydrate) (Kishida Chemical Co., Ltd.). The cerium compound containing cerium is cerium (III) nitrate (hexahydrate) (Kokusan Chemical Co., Ltd.). The nickel compound containing nickel is nickel nitrate (II) (hexahydrate) (Kishida Chemical Co., Ltd.).

  In a beaker containing 50 ml of pure water at room temperature, 12.43 g of iron (III) nitrate nonahydrate (Kishida Chemical Co., Ltd.) and 24.22 g of cerium (III) nitrate hexahydrate (Kokusan Chemical Co., Ltd.) Was stirred with a stirrer and completely dissolved. While stirring this solution, 0.5 g of graphite (Wako Pure Chemical Industries, Ltd.) was added as a carbon material and stirred for 10 minutes, and then 28 wt% so that the pH value of this mixed solution was 10.0. Adjust with ammonia water.

  Thereafter, the mixture is stirred for 3.0 hours or more at a rotation speed of 600 rpm. Then, after filtering the said mixed solution and wash | cleaning precipitation 2-3 times with water, the precipitation was hold | maintained at 120 degreeC, the water | moisture content was evaporated, and it was set as the powder (40-50 mesh) with the mortar.

  The powder was placed in a beaker containing 30 ml of water, and 0.1 g of palladium (II) nitrate dihydrate (Kishida Chemical Co., Ltd.) was added as a palladium compound, followed by stirring for 2.0 hours. It was kept at 0 ° C., the water was evaporated, and powdered in a mortar (40-50 mesh). The obtained powder was calcined in the air at 500 ° C. for 1.0 hour to obtain an exhaust gas purification catalyst of Example 1.

(Exhaust gas purification activity test method)
The exhaust gas purification activity test was conducted by flowing a mixed model gas of 1000 ppm of nitrogen monoxide (NO), 1.0% of oxygen (O ₂ ) and 1000 ppm of propylene (C ₃ H ₆ ) shown in Table 1. The exhaust gas purifying catalyst powder produced above is diluted into four layers with quartz sand, and this powder is placed in a quartz reaction tube (see FIG. 2: inner diameter 6.0 mm), and the mixed model gas is introduced into the space. It was circulated at a temperature of 200 to 800 ° C. or 1000 ° C. at a rate of 90,000 ml / (g · h).

The analysis of the reaction gas and model gas is carried out using FID, TCD gas chromatograph (product name “GC-14B” manufactured by Shimadzu Corporation), nitrogen oxide (NOx) measuring instrument (product name “PG-235” gas analyzer). , Manufactured by HORIBA, Ltd.). In the FID, propylene (C ₃ H ₆ ) is measured, and in TCD, dinitrogen monoxide (N ₂ O), carbon monoxide (CO), carbon dioxide (CO ₂ ), and oxygen (O ₂ ) are measured. In the NOx measuring device, nitrogen oxide (NOx) and carbon monoxide (CO) were measured. Table 2 shows the gas chromatographic analysis conditions.

(Exhaust gas purification activity test)
The exhaust gas purification catalyst produced above is filled in 0.1 g in the center of a quartz reaction tube having an inner diameter of 6.0 mm, and 0.5 g of quartz sand is packed on each side of the catalyst layer in order to make the gas distribution uniform. It was. Thereafter, a model gas was introduced into the quartz reaction tube, and the conversion rates of NOx, CO, and hydrocarbon (C ₃ H ₆ ) were measured. The measurement results are shown in FIG.

  The exhaust gas purifying catalyst used in Example 1 is a C-Fe-Ce catalyst precursor (constituting weight fractions of carbon atoms, iron atoms, and cerium atoms of 5.0% and 17.0%, respectively). And 78.0%), and the constituent weight fraction of palladium atoms in the palladium compound is designed to be 0.35% with respect to the entire exhaust gas purifying catalyst.

  In the exhaust gas purification test of Example 1, model gas containing NOx, CO, and HC was used. Table 1 shows the components of the model gas and the reaction conditions. Note that the reaction system was controlled to a theoretical air-fuel ratio atmosphere (A / F = 14.63).

In Example 1, the exhaust gas purification catalyst prepared above was collected after reacting with the model gas for 1 hour at each temperature of 100 ° C. in the range of 200 ° C. to 1000 ° C., and NOx, CO The conversion of HC (C ₃ H ₆ ) was calculated. FIG. 4 shows the measurement results of NOx, CO, and hydrocarbon (C ₃ H ₆ ).

As shown in FIG. 4, in the case of the exhaust gas purification catalyst used in Example 1, CO was oxidized at 300 ° C., and a conversion rate of 97% was obtained. At 400 ° C., CO was completely purified, and C ₃ H ₆ also had a conversion rate of about 100%. Although the reduction temperature of NOx is higher than that of CO and HC, about 100% of NOx was reduced at 400 ° C., and harmful three components in exhaust gas were reduced and purified at 500 ° C.

  FIG. 5 shows long-term test results of the exhaust gas purifying catalyst used in Example 1 at 200 to 1000 ° C. As a result, conversion of 80 to 100% was achieved for NOx, CO, and C3H6. It was confirmed that this catalyst has an extremely high exhaust gas purification activity by three.

FIG. 6 shows long-term test results (durability) of the exhaust gas purification catalyst used in Example 1 at 200 to 1000 ° C. As shown in FIG. 6, at 400 ° C., initial activity was obtained in which NOx, CO, and C ₃ H ₆ were almost completely purified on the catalyst of the present invention. However, after 12 hours, a NOx conversion of about 91% could be maintained and there was no degradation until 25 hours. The activities of CO, C ₃ H ₆ and H ₂ were maintained at the initial activity and could be maintained for up to 25 hours. It was confirmed that the catalyst has high durability even at a high temperature of 1000 ° C.

Furthermore, in Example 1, T50 and T90 of the noxious gas three components (NOx, CO, C ₃ H ₆ ) in the model gas were examined. Here, T50 is a temperature at which a purification rate of 50% of harmful gas components is obtained. Similarly, T90 is a temperature at which a purification rate of 90% of harmful gas components is obtained. The results are shown in Table 3. As a reference example, T50 and T90 of a catalyst not containing palladium and a conventional platinum catalyst were also measured as exhaust gas purification catalyst components, and the results are also shown in Table 3.

  According to Table 3, the exhaust gas purifying catalyst of Example 1 containing a palladium component in a catalyst precursor obtained by heat-treating a composition containing a carbon material, an iron compound, and a cerium compound is equivalent to the palladium component of Reference Example 1. Compared with the exhaust gas purifying catalyst not contained and the platinum-cerium catalyst of Reference Example 2, both T50 and T90 showed good values. That is, the exhaust gas purifying catalyst of Example 1 is superior in the purifying activity of nitrogen oxides, carbon monoxide, and hydrocarbons than the exhaust gas purifying catalyst of the reference example.

<Example 2>
Exhaust gas purification tests were performed in the same manner as in Example 1 except that the constituent weight fraction of palladium atoms contained in the exhaust gas purification catalyst was 0.035%. The results are shown in FIG.

<Examples 3 to 5>
Except for the carbon materials constituting the exhaust gas purifying catalyst at 1000 ° C. for 3.0 hours, nitrogen gas treatment (Example 3), hydrogen treatment (Example 4) and steam treatment (Example 5), respectively. In the same manner as in No. 1, the model gas was processed, and T50 and T90 were measured. The measurement results of the above examples are shown in FIGS. 8 to 10, and the measurement results of T50 and T90 are shown in Tables 5 to 7, respectively.

  In Table 5, the former stage refers to the measurement result when the exhaust gas treatment temperature is raised from 200 ° C. to 1000 ° C., and the latter stage is the temperature lowered from 1000 ° C. to 200 ° C. The measurement result when it is performed.

  According to FIGS. 8 to 10 and Tables 5 to 7, the exhaust gas purifying catalyst in which a palladium compound is added to a catalyst precursor obtained by heating a composition containing a carbon material, an iron compound, and a cerium compound is T50 and T90. In all cases, good values were shown. Further, it has been found that the presence of various gases in the heat treatment of the carbon material constituting the exhaust gas purification catalyst can control the above-mentioned pre-stage and post-stage characteristics of the catalyst. That is, it can be understood that the performance of the exhaust gas purifying catalyst can be changed by appropriately adjusting various conditions such as gas and temperature in the heat treatment.

<Comparative Example 1>
The reaction gas was allowed to flow without putting the catalyst in the reaction tube, and the NO _x , CO, hydrocarbon (C ₃ H ₆ ), and hydrogen conversion rates were measured in the same manner as in Example 1. The result is shown in FIG.

As shown in FIG. 11, when no catalyst was added, the NOx and CO conversions at 200 to 800 ° C. were almost zero. The conversion rate of C ₃ H ₆ 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>
A commercially available graphite as a carbon material was put into a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The result is shown in FIG.

  As shown in FIG. 12, in the 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>
As a comparative example, a catalyst made of carbon and iron without using cerium was placed in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The constituent weight fractions of carbon atoms and iron atoms are 50% and 50%, respectively. The result is shown in FIG.

  As shown in FIG. 13, in the case of a catalyst composed of carbon and iron, the NOx conversion was almost zero at 400 ° C. or lower. 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>
As a comparative example, a catalyst composed of carbon and cerium without using Fe was placed in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The constituent weight fractions of carbon atom and cerium atom are 50% and 50%, respectively. The result is shown in FIG.

As shown in FIG. 14, in the case of a catalyst composed of carbon and cerium, the NOx conversion rate was almost zero at 400 ° C. or lower. 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 to 500 ° C. to completely purify CO. C ₃ H ₆ had a conversion of 36% at 400 ° C. and 87% at 500 ° C.

<Comparative Example 5>
As a comparative example, a carbon material was not used and a catalyst composed of iron and cerium was placed in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. The constituent weight fractions of iron atom and cerium atom are 25% and 75%, respectively. The result is shown in FIG.

As shown in FIG. 15, the catalyst composed of iron and cerium had a NOx conversion of almost zero at a temperature of 400 ° C. or lower. As the temperature increased, the NOx conversion rate gradually improved, but even at 800 ° C., there was only a 77% conversion rate. C ₃ H ₆ was oxidized from 300 ° C. 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.

<Comparative Example 6>
As a comparative example, as a catalyst made of Pt without using a carbon material, a commercially available Pt-cerium oxide catalyst for purifying exhaust gas was put in a reaction tube, a reaction gas was flowed, and measurement was performed in the same manner as described above. Note that the supported amount of Pt is 1.0 wt%. The result is shown in FIG.

As shown in FIG. 16, in the case of the Pt-based catalyst, the conversion of NOx, C ₃ H ₆ , and CO was almost zero at 250 ° C. or lower. Although the conversion rate was considerably low even at 300 ° C., the three components of NOx, C ₃ H ₆ , and CO were almost completely purified at a conversion rate of about 100% above 500 ° C.

  Table 8 summarizes the T50 temperatures of the activities described in the above examples and comparative examples. From this table, it can be seen that the C-Fe-Ce-based catalyst of the example shows a lower T50 value of harmful three components contained in the exhaust gas than the catalyst of the other comparative examples. It can be said that the activity is the most excellent.

  According to the present invention, carbon monoxide (CO) is supported by supporting a palladium compound on a catalyst precursor constituted by heating a composition containing a carbon material, an iron compound, and a cerium compound without using Pt. In addition, it is possible to provide an exhaust gas purifying catalyst that can oxidize and purify hydrocarbons (HC) and reduce and purify nitrogen oxides (NOx).

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 Exhaust Gas Purification Catalyst 11 Quartz Sand 12 Quartz Wool 13 Thermocouple

Claims (6)

A method for producing an exhaust gas purifying catalyst , wherein a catalyst precursor obtained by heating a composition containing a carbon material, an iron compound, and a cerium compound is contained in a palladium compound. In the catalyst precursor, the weight fractions of carbon atoms in the carbon material, iron atoms in the iron compound, and cerium atoms in the cerium compound are 1.0 to 70.0% and 5.0 to 65, respectively. The method for producing an exhaust gas purifying catalyst according to claim 1, characterized by being 0.0% and 5.0-90.0%. The method for producing an exhaust gas purification catalyst according to claim 1 or 2, wherein a weight fraction of palladium atoms in the palladium compound with respect to the exhaust gas purification catalyst is 0.035 to 0.35%. . The method for producing an exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the carbon material is produced by heat treatment in a gas atmosphere selected from water vapor, hydrogen gas, and nitrogen gas. . The method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the carbon material is graphite. A method for producing a catalyst body , wherein the exhaust gas purification catalyst produced by the method for producing an exhaust gas purification catalyst according to any one of claims 1 to 5 is supported on a catalyst carrier.

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