JP2008215253A - NOx EMISSION CONTROL METHOD AND NOx EMISSION CONTROL DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently purify NOx emission in a low temperature area. <P>SOLUTION: This NOx emission control method and control device are characterized by supplying reducer to an NOx emission control catalyst and purifying NOx in exhaust gas by the NOx emission control catalyst. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust NOx purification method and an exhaust NOx purification device for purifying NOx contained in exhaust gas from an automobile.

  Conventionally, NOx, carbon monoxide, and hydrocarbons contained in exhaust gas from gasoline vehicles have been purified by a three-way catalyst composed of a platinum group element (see Patent Document 1). The three-way catalyst usually uses a cordierite monolith molded body as the catalyst support, and the activated alumina particles having a size of several μm to several tens of μm are applied to the inner wall of the gas flow path of the molded body. In this structure, platinum-palladium-rhodium particles having a size of several tens of nanometers to several hundreds of nanometers are supported. The purification method with a three-way catalyst is included in the exhaust gas by controlling the air-fuel ratio, which is the air: fuel weight mixing ratio, close to the theoretical air-fuel ratio (= 14.7) (this combustion is called rich burn). Since the oxygen concentration can be maintained at 1% or less, carbon monoxide and hydrocarbons contained in the exhaust gas can be used as a reducing agent for NOx. However, when the oxygen concentration in the exhaust gas exceeds several percent, the catalyst There is a problem that oxidation deterioration occurs.

  In addition, a so-called urea SCR method using a transition metal compound or a platinum group element as a catalyst and urea water as a reducing agent has been studied for exhaust gas treatment of large diesel vehicles such as trucks and buses that run on light oil fuel (patents). Reference 2). This method has the advantage of being able to efficiently purify NOx from a relatively low temperature region near 100 ° C. to a relatively high temperature region near 600 ° C., but it requires the mounting of expensive urea water as a reducing agent. There is a problem that most of the low temperature exhaust NOx below about 200 ° C. is discharged as ammonium nitrate, which causes water environmental pollution.

On the other hand, a three-way catalyst cannot be used for exhaust NOx treatment of small diesel vehicles such as diesel passenger cars. Because the air-fuel ratio is more than several times that of gasoline (combustion of diesel fuel is called lean burn), the oxygen concentration in diesel exhaust gas is usually over 5% and contains almost no reducing substances. Because it is not. For the same reason, it is difficult to purify the exhaust gas from lean burn gasoline vehicles with a three-way catalyst. A so-called NOx occlusion reduction catalyst in which a NOx occlusion agent is added to a platinum group catalyst as a catalyst has been studied for the exhaust NOx treatment of small diesel vehicles (see Patent Document 3). In this method, lean burn and rich burn cycle combustion is performed, lean burn exhaust NOx is absorbed by the NOx storage agent, absorbed NOx is released in a rich burn atmosphere, and the released NOx is released from the carbon monoxide and hydrogen in the rich burn exhaust gas. Based on the idea of reducing with hydrocarbons and other reducing substances. The purification method using the NOx occlusion reduction catalyst can purify NOx from about 250 ° C. to about 600 ° C. even in a high-concentration oxygen atmosphere in which a three-way catalyst used for exhaust gas treatment of gasoline passenger cars cannot be used. Although there is an advantage, there is a problem that NOx purification at about 200 ° C. or lower is very difficult and a problem that the NOx storage agent is remarkably deteriorated by moisture in the exhaust gas and a small amount of SOx. In addition, there is a problem that most of NOx purification in the vicinity of the intermediate temperature from 250 ° C. to 300 ° C. stops at the stage of dinitrogen monoxide (N ₂ O) having a very large warming potential.

As a method using a reducing agent other than urea water, a hydrocarbon SCR method using an automobile fuel (hydrocarbons such as ethylene and propylene contained in a small amount in the fuel) as a reducing agent has been studied. Although a high purification rate can be obtained for the rich burn exhaust NOx, this method is not always preferable because it has a problem of reducing fuel consumption. Moreover, although the method of using methanol as a reducing agent is proposed (refer nonpatent literature 1), there exists a problem that reaction start temperature is 300 degreeC or more. Furthermore, recently, after reforming the fuel with the reforming catalyst,
A method of treating exhaust NOx by introducing it into exhaust gas and treating the exhaust NOx with an exhaust gas purifying catalyst has been proposed (see Patent Document 4 and Non-Patent Document 2), but there is a problem that the reaction start temperature is 300 ° C. or higher. Further, the zeolite-supported catalyst that has been studied for purifying exhaust NOx such as diesel exhaust gas has a problem that the activity is remarkably lowered by moisture and oxygen under hydrothermal conditions.
By the way, in Japan, the temperature of exhaust gas discharged from diesel passenger cars is approximately 120 ° C. to 200 ° C. during transient travel and approximately 200 ° C. to 400 ° C. during stable travel, but about 80% of the NOx discharged is transient travel. Sometimes discharged.

From the above, the catalyst required for the exhaust NOx treatment of diesel passenger cars is desired to be a catalyst having high activity with respect to the lean burn exhaust NOx in the low temperature range of 120 ° C. to 200 ° C. At present, no effective NOx purification method has been found for lean burn NOx below 250 ° C. Moreover, the problem that most of NOx purification in the low temperature to medium temperature region stops at the stage of dinitrogen monoxide (N ₂ O) having a very large warming coefficient has not been solved.

In general, industrial catalysts are often used in a state where they are supported on a porous material. The pores of the porous material are classified into micropores with a pore diameter of 2 nm or less, mesopores of 2 to 50 nm, and macropores of 50 nm or more according to IUPAC (International Pure and Applied Chemical Association). Yes. No single porous material other than activated carbon has a wide distribution ranging from the micro to meso range.
In recent years, silica, alumina, and silica-alumina-based mesoporous molecular sieves have been developed in which pores having a pore size of several nm are regularly arranged and the specific surface area has a very large value of 400 to 1100 m ² / g. These are disclosed in, for example, Patent Documents 1, 2, and 3, and are named crystalline mesoporous molecular sieves because the pore arrangement of pores is similar to the atomic arrangement of crystalline substances. .

Since the catalytic reaction is a surface reaction, the larger the specific surface area of the catalyst, the higher the catalytic activity. Further, the carrier for supporting the catalyst is more likely to exhibit the catalytic activity as the specific surface area is larger. From this point of view, when looking at a three-way catalyst for automobiles, the monolith molded body as a support has a mesh-shaped cross section and is provided with gas flow paths partitioned by thin walls parallel to each other in the axial direction. It is a molded body, the specific surface area is about 0.2 m ² / g, the specific surface area of alumina particles as a support is 110 to 340 m ² / g, and the specific surface area of the catalyst is about ²⁰ to 40 m ² / g from the particle size. Presumed to be. Therefore, the surface area of the catalyst is 10 ^{2 of that of the} conventional three-way catalyst by supporting the nano-sized catalyst particles that are one to two orders of magnitude smaller than the particle diameter of the conventional catalyst particles in the pores of the mesoporous material. since 10 becomes ⁴ times larger, which is believed to enhance the catalytic activity for automotive exhaust by applying monolith forming body, this idea, for example, disclosed in Patent Document 5 to 10. However, it has been difficult to effectively remove low-temperature exhaust NOx around 120 ° C. to 200 ° C. discharged by diesel passenger cars and the like.

JP-A-5-254827 Special table hei 5-503499 published Special table hei 6-509374 publication WO2005 / 103461 US Pat. No. 5,143,707 JP-A-8-257407 JP 2001-9275 A JP 2002-210369 A JP 2002-320850 A JP 2003-135963 A Applied Catalysis B: Environmental 17 (1998) 115-129. Applied Catalysis B: Environmental 17 (1998) 333-345.

  In view of the above circumstances, an object of the present invention is to efficiently purify exhaust NOx in a low temperature region.

The present invention for solving the above problems is as follows.
(1) A method for purifying NOx exhausted from an automobile by supplying a reducing agent to the exhaust NOx purification catalyst. (2) Reforming the reducing agent with a reforming catalyst. After that, the exhaust NOx purification method according to (1), wherein the exhaust NOx purification catalyst portion is filled with the exhaust NOx purification catalyst portion and the NOx purification catalyst portion filled with the exhaust NOx purification catalyst portion. An exhaust NOx purification device comprising a reducing agent supply unit for supplying a reducing agent (4) A reducing agent reforming unit for modifying the reducing agent (3) It is related with the exhaust-NOx purification apparatus of description.

  The exhaust NOx purification method of the present invention can perform lean burn exhaust NOx treatment, which could not be achieved conventionally, very efficiently even in a low temperature region. For example, although a three-way catalyst can hardly purify nitrogen monoxide in an atmosphere having an oxygen concentration of 14%, the reformed gas derived from ethanol reformed by the reforming catalyst according to the present invention is supplied to the exhaust gas purifying catalyst. Thus, 60% or more of NOx in an atmosphere having an oxygen concentration of 14% can be purified at 180 ° C. to 400 ° C. In addition, 60% or more of the exhausted NOx is reduced to the nitrogen stage. Furthermore, by supplying alcohol as a reducing agent, 90% or more of the exhausted NOx is reduced to the nitrogen stage.

Hereinafter, embodiments in which the present invention can be used will be described.
[Exhaust NOx purification catalyst]
As the exhaust NOx purification catalyst in the present invention, an exhaust NOx oxidation-reduction catalyst or a NOx adsorption-reduction catalyst containing a NOx adsorbent and a NOx oxidation-reduction catalyst can be used.
The role of the NOx adsorbent in the present invention is to adsorb NOx (mainly NO ₂ ) in a lean burn atmosphere with little reducing substance and desorb the adsorbed NOx in a lean burn atmosphere rich in reducing substance.
The role of the NOx oxidation-reduction catalyst is to oxidize NO to NO ₂ in a lean burn atmosphere with a small amount of reducing substances and to reduce NOx in a lean burn atmosphere rich in reducing substances.

Here, it can be explained that the role of the NOx adsorbent can be achieved based on the following NOx purification mechanism. In a lean burn atmosphere with little reducing substance, the NO ₂ concentration is high due to NO oxidation by the NOx redox catalyst, while in a lean burn atmosphere rich in reducing substances, NO _{2 is} reduced by NOx reduction with the NOx redox catalyst. The NOx adsorbent in a low concentration state adsorbs NO _{2 in a} lean burn atmosphere with a low reducing substance, and desorbs the adsorbed NO ₂ in a lean burn atmosphere rich in reducing substances.

The adsorption and desorption properties of the NOx adsorbent depend on the concentration of the adsorbent, but not on the temperature, like the properties of the adsorbent such as activated carbon. Therefore, the adsorption of NO ₂ begins at about room temperature in the NO ₂ concentration is high atmosphere, NO ₂ concentration desorption of NO ₂ occurs even at around room temperature in the lower atmosphere.
Therefore, the exhaust gas temperature at which the purification method of the present invention is effective substantially depends on the activation temperature of the NOx redox catalyst, the lower limit temperature is about 160 ° C., and the upper limit temperature is about 750 in which the influence of the sintering of the catalyst appears. ° C. Further, the NOx adsorbent also adsorbs a small amount of SOx contained in the exhaust gas, but since it is easily desorbed in a lean burn atmosphere rich in reducing substances, there is almost no catalyst poisoning by SOx.

  The conventional three-way catalyst can purify NOx from about 160 ° C. to 600 ° C. to almost 100% if the reducing substance is about 10 times the NOx molar concentration in an atmosphere having an oxygen concentration lower than 1%. However, when the oxygen concentration is high such as several percent or more, the NOx purification rate decreases drastically as the temperature increases in a high temperature region of 250 ° C. or higher even if the reducing substance is abundant. This cannot be fully explained because the three-way catalyst is poisoned by oxygen. Probably, it is considered that the complete combustion reaction of the reducing substance on the catalyst is significantly faster than the NOx reduction reaction when the temperature exceeds 250 ° C. Since this problem is the combustion of the reducing agent, the above-described phenomenon occurs as the reducing agent is more susceptible to the oxidation reaction by oxygen, and such a phenomenon is unlikely to occur when the reducing agent is less susceptible to oxidation. The NOx oxidation-reduction catalyst in the present invention is somewhat improved in such an unfavorable catalytic reaction as compared with the conventional three-way catalyst, but is essentially unchanged.

Therefore, when hydrocarbon, carbon monoxide, hydrogen or the like that is susceptible to an oxidation reaction is used as the reducing agent in the exhaust NOx purification catalyst in the present invention, the supply of the reducing agent to the lean burn exhaust gas is performed by chemical reaction with oxygen. It is preferable that the amount is greater than the stoichiometric ratio.
When an alcohol that is relatively less susceptible to oxidation is used as the reducing agent, it is preferable to supply about 10 times the molar concentration of NOx regardless of the oxygen concentration.
When ammonia which is not easily oxidized is used as a reducing agent, it is preferable to supply the same concentration as the molar concentration of NOx regardless of the oxygen concentration.
Further, when the exhaust NOx purification catalyst in the present invention is used, the reducing agent is supplied to the lean burn exhaust gas entering the NOx adsorption reduction catalyst in a constant cycle, but the reducing agent supply cycle is the adsorption of NOx adsorbent. It is designed individually depending on performance. Usually, it can be performed in a cycle of supplying a few seconds every minute.

[NOx adsorbent]
Examples of the NOx adsorbent in the present invention include carbon nitride compounds, boron carbonitride compounds, boron nitride, silicon carbonitride, boron carbide, nitrides, carbides, borides, activated carbons, metals and alloys, and zeolites. Among these, carbon nitride compounds, boron carbonitride compounds, nitrides, group 13 element metals or alloys thereof, and zeolite are preferred adsorbents.

(Carbon nitride compound)
As the carbon nitride compound, a carbon nitride having a planar structure in which the 1,3,5 positions of the triazine ring are bonded with NH groups, and a carbon nitride having a planar structure in which the 1,5,9 positions of the tristriazine ring are bonded with NH groups are used. Ride can be mentioned.
(Boron carbonitride compound)
Examples of the boron carbonitride compound include carbon boron nitride having a structure similar to graphite.
Since the nitrogen atom which comprises a carbon nitride compound and a boron carbonitride compound has a lone pair, it is thought that this is a NOx adsorption site.

(Nitride)
As nitrides, silicon nitride, silicon nitride oxide (= silicon oxynitride), aluminum nitride, transition metal nitride (titanium nitride, titanium nitride oxide, vanadium nitride, zirconium nitride, chromium nitride, tungsten nitride, molybdenum nitride, nitride) Examples thereof include nitrides of rare earth elements such as iron, manganese nitride, cobalt nitride, nickel nitride), scandium nitride, hafnium nitride, niobium nitride, tantalum nitride, and cerium nitride. Preferably, a transition metal nitride is used. More preferably, titanium nitride oxide is used. The transition metal nitride is considered to easily adsorb NOx because the bond electron density is biased toward nitrogen atoms.

(Group 13 element metal or alloy thereof)
Examples of the metal or alloy include metals of Group 13 elements in the periodic table or alloys thereof.
Preferably, metal indium or an indium alloy is used. Indium is an element with an outermost shell electron deficiency, so it is considered that NOx is easily adsorbed (zeolite).
Zeolite is a general term for natural zeolite and synthetic zeolite (zeolite A, zeolite X, zeolite Y, zeolite L, mordenite, ZSM-5, and other compounds having zeolite-like properties and structures. And cation exchange zeolite).

In addition, those in which a cation is introduced into these compounds by a coordination bond or an ionic bond are preferable because they are excellent in NOx adsorption.
That the NOx adsorbent has the property of adsorbing NOx is demonstrated by measuring the mass increase of the material in the presence of NOx. Also, it is NOx adsorption and not NOx absorption because the infrared absorption spectrum of the adsorbed material shows NOx characteristic group frequency but not nitrate ion or nitrite ion characteristic group frequency. Proven. Further, the NOx adsorbent in the present invention may be used as it is, or may be used by being supported on a porous material.

[NOx adsorption reduction catalyst]
The NOx adsorption-reduction catalyst in the present invention is usually used as a so-called mixed catalyst in which a NOx adsorbent and a NOx oxidation-reduction catalyst are mixed. The mixing ratio of the NOx adsorbent and the NOx redox catalyst can be arbitrarily set according to the NOx removal conditions.
[Reducing agent reforming catalyst] and [NOx redox catalyst]
The reducing agent reforming catalyst and the exhaust NOx redox catalyst in the present invention are preferably mesoporous catalysts in which a catalytically active component is supported on a mesoporous material. The mesoporous material used as the support for the mesoporous catalyst has a high specific surface area and a pore size of nano-size, so that the specific surface area of the catalyst supported thereon can be dramatically increased, and the catalyst is supported in the pores. Thus, there are excellent effects such as suppressing reaggregation of the catalyst particles and achieving uniform and high dispersion of the catalyst. The higher the specific surface area of the mesoporous material, the better, unless there are special circumstances.

The specific surface area of mesoporous materials that may be used in the present invention is 100~4000m ² / g, preferably 200~3000m ² / g, and more preferably from 400~2000m ² / g. When the specific surface area is less than 100 m ² / g, the supported amount of the catalyst is reduced. Therefore, it is preferably 100 m ² / g or more in order to bring out the catalyst performance of the supported catalyst. On the other hand, in terms of material strength, the specific surface area is preferably 4000 m ² / g or less. The specific surface area of the mesoporous material is a value measured by the BET nitrogen adsorption method using nitrogen as an adsorption / desorption gas.

  Examples of such mesoporous materials include silica, alumina, titania, zirconia, magnesia, calcia, ceria, niobia, activated carbon, porous graphite, etc., silica, alumina, titania, zirconia, magnesia, calcia, ceria, Activated carbon and composite materials thereof are preferable, and silica, alumina, magnesia, activated carbon, and composite materials thereof are more preferable. In some cases, an existing zeolitic material that is a microporous molecular sieve material may be used. In some cases, a catalyst form in which a NOx redox catalyst is supported on a porous NOx adsorbent may be used, or the NOx redox catalyst may be microencapsulated with a porous NOx adsorbent.

  Furthermore, in the present invention, the mesoporous material is preferably basic. The basicity is preferably 10 to 14 as an index of pH. Since the mesoporous material used in the present invention is not water-soluble, in order to know the pH, a mesoporous material is dispersed in a colloidal form in a neutral liquid and a pH indicator that changes color at a specific pH is added. The pH is measured from the color change. pH indicators include those in basic regions such as phenolphthalein, α-naphtholbenzoin, thymolphthalein, alizarin yellow, diazo violet, salicyl yellow, tropeoline, alizarin blue S, nitramine, trinitrobenzene, trinitrobenzoic acid, etc. Indicators that change color sensitively at pH can be used. The basic modification of weakly acidic to weakly basic materials such as silica, alumina, titania, zirconia, ceria, and activated carbon usually absorbs an aqueous solution in which an alkali element or alkaline earth compound is dissolved in a mesoporous material. Then, it is performed by heating and baking at 200 ° C. to 1000 ° C.

  Further, most of the pores of the mesoporous material in the present invention have a pore diameter (diameter display) in the range of 1 to 50 nm, preferably in the range of 2 to 20 nm, more preferably in the range of 2 to 10 nm. . The majority of the pores referred to here means that the pore volume occupied by pores of 1 to 50 nm is 60% or more of the total pore volume. The catalyst can be supported even if the pore diameter is less than 1 nm, but 1 nm or more is preferable in consideration of the influence of contamination due to the flow of the reducing agent and impurities. If it exceeds 50 nm, the dispersion-supported catalyst tends to grow into giant particles by sintering (= sintering) under hydrothermal high temperature conditions and the like. The pore diameter of the mesoporous material is a value measured by a nitrogen adsorption method using nitrogen as an adsorption / desorption gas, and is represented by a pore distribution (differential distribution display) in the range of 1 to 200 nm obtained by the BJH method. It is.

Next, as the catalytically active component used in the present invention, a transition metal oxide catalyst and a platinum group catalyst are preferable. Examples of the transition element of the transition metal oxide catalyst include elements of Group 3 to Group 11 in the periodic table. Among these, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, tungsten , Rhenium, and iron, cobalt, and tungsten are most preferable.
The platinum group element of the platinum group catalyst is a generic name of six elements of ruthenium, rhodium, palladium, osmium, iridium, and platinum. Among these, rhodium, palladium, iridium, and platinum are preferable, and platinum is the most preferable. preferable.

The platinum-based catalyst is high in the ability of platinum, which is the main component of the catalyst, to oxidize NO, which is the main component of exhaust NOx, into NO _2, and has a high ability to reduce NO ₂ into N ₂ O and nitrogen using a reducing agent, It is chemically stable even in a high-concentration oxygen atmosphere, and platinum is relatively active at a relatively low temperature among the platinum group elements.
Further, by adding a promoter component having a different function to a platinum-based catalyst, the catalyst performance can be improved by a synergistic effect. Examples of such components include Group 1 to Group 3 elements, among which alkali metal or alkaline earth metal oxides, hydroxides, carbonates, and bicarbonates. When alcohol is used as the reducing agent, it is preferable because it has an effect of promoting the alcohol reforming reaction. The added mass of these promoter components is usually about 0.01 to 100 times that of platinum, but may be 100 times or more as required.

  Since the particle size of the catalyst supported in the pores of the mesoporous material of the present invention is approximately the same as or smaller than the pore size, the pore diameter range is also the particle size range of the catalyst exhibiting high activity. Match. In general, catalyst particles atomized to nano size have a large number of high-order crystal planes such as edges, corners, and steps showing activity, so that not only catalytic activity is significantly improved but also catalytic activity in the bulk. It is known that even an inert metal such as this may exhibit unexpected catalytic activity. Therefore, the smaller the catalyst, the better from the viewpoint of catalytic ability. However, on the other hand, undesirable properties such as surface oxidation and side reaction due to atomization also appear, so there is an optimum range for the particle size of the fine particles.

The average particle diameter of the catalyst exhibiting effective activity for the target NOx purification treatment in the present invention is in the range of 1 to 50 nm, preferably in the range of 1 to 20 nm, and particularly preferably in the range of 1 to 10 nm.
When the platinum-based catalyst is supported on the mesoporous material, the supported amount of platinum is 0.01 to 20% by mass, preferably 0.1 to 10% by mass. It is used in a loading amount of 1 to several mass%. The supported amount can be 20% by mass or more, but if the supported amount is excessive, the catalyst in the deep pores that hardly contributes to the reaction increases, so 20% by mass or less is preferable. Since activity is not enough if it is less than 0.01 mass%, 0.01 mass% or more is preferable.

  The mesoporous material used in the present invention can be produced by applying a sol-gel method using a surfactant micelle as a template, which is a conventional method. In the case of mesoporous silica, the precursor of the mesoporous material is usually tetramethoxysilane, tetraethoxysilane, tetra-i-propoxysilane, tetra-n-propoxysilane, tetra-i-butoxysilane, tetra-n-butoxysilane. An alkoxide such as tetra-sec-butoxysilane or tetra-t-butoxysilane is used. Mesoporous alumina, titania, zirconia, magnesia, calcia, ceria and niobia can also be usually produced using an alkoxide. Examples of micelle-forming surfactants include long-chain alkylamines, long-chain quaternary ammonium salts, long-chain alkylamine N-oxides, long-chain sulfonates, polyethylene glycol alkyl ethers, polyethylene glycol fatty acid esters, etc. Any of these may be used. As the solvent, one or more of water, alcohols, and diols are usually used, and an aqueous solvent is preferable. When a small amount of a compound having a coordination ability to metal is added to the reaction system, the stability of the reaction system can be remarkably enhanced.

  As such a stabilizer, compounds having metal coordination ability such as acetylacetone, tetramethylenediamine, ethylenediaminetetraacetic acid, pyridine, and picoline are preferable. The composition of the reaction system comprising the precursor, surfactant, solvent and stabilizer is such that the molar ratio of the precursor is 0.01 to 0.60, preferably 0.02 to 0.50, and the precursor / surfactant The molar ratio is 1-30, preferably 1-10, the solvent / surfactant molar ratio is 1-1000, preferably 5-500, and the stabilizer / main agent molar ratio is 0.01-1.0, preferably Is 0.2 to 0.6. The reaction temperature is in the range of 20 to 180 ° C, preferably 20 to 100 ° C. The reaction time is 5 to 100 hours, preferably 10 to 50 hours. The reaction product is usually separated by filtration, sufficiently washed with water, dried, and then thermally decomposed and removed from the template by high-temperature baking at 500 to 1000 ° C. to obtain a mesoporous material. If necessary, the surfactant can be extracted with alcohol or the like before firing.

  The mesoporous catalyst used in the present invention can be produced, for example, by an ion exchange method or an impregnation method. These two methods are different in that the catalyst is deposited on the support, although the ion exchange method uses the ion exchange capacity of the support surface and the impregnation method uses the capillary action of the support. The general process is almost the same. That is, it can be produced by immersing a strongly basic mesoporous material in an aqueous solution of the catalyst raw material, followed by filtration, drying, washing with water as necessary, and reduction treatment with a reducing agent.

Examples of the platinum catalyst material include H ₂ PtCl ₄ , (NH ₄ ) ₂ PtCl ₄ , H ₂ PtCl ₆ , (NH ₄ ) ₂ PtCl ₆ , Pt (NH ₃ ) ₄ (NO ₃ ) ₂ , Pt (NH ₃ ) ₄ (OH) ₂ , PtCl ₄ , platinum acetylacetonate, and the like can be used. A catalyst to which a co-catalytic component is added as necessary is manufactured in the same manner by mixing water-soluble salts such as nitrate, sulfate, carbonate, and acetate of the co-catalytic component with the platinum catalyst raw material. Can do. As the reducing agent for the catalytically active component, hydrogen, an aqueous hydrazine solution, formalin, or the like can be used. The reduction may be performed under normal conditions known for each reducing agent. For example, hydrogen reduction can be performed by placing a sample in a hydrogen gas stream diluted with an inert gas such as helium and treating the sample at 300 to 500 ° C. for several hours. After reduction, if necessary, heat treatment may be performed at 500 to 1000 ° C. for several hours under an inert gas stream.

  The mesoporous catalyst used in the present invention is usually used by adhering to a monolith molded article that is used as a support for automobile catalysts. A monolith molded body is a molded body in which the molded body has a mesh-like cross section and is provided with gas flow paths partitioned by thin walls parallel to each other in the axial direction. A catalyst is attached to the monolith molded body. Such a catalyst is hereinafter referred to as a monolith catalyst. Although the external shape of a molded object is not specifically limited, Usually, it is a cylindrical shape. The adhesion amount of the catalyst when the NOx adsorption reduction catalyst is adhered to the gas flow path inner wall of the monolith molded body is preferably 3 to 30% by mass. It is preferably less than 30% from the viewpoint of gas diffusion to the catalyst existing inside the support. Moreover, 3% or more is preferable in order to draw out sufficient catalyst performance. The adhesion amount corresponding to the coating amount of the catalyst on the monolith molded body is preferably 0.03 to 3 mass% of the molded body.

  Said monolith catalyst can be manufactured according to the manufacturing method of the monolith molded object which adhered the three-way catalyst for motor vehicles. For example, a mixture in which a NOx adsorption reduction catalyst and colloidal silica as a binder are usually mixed at a mass ratio of 1: (0.01 to 0.2) is prepared, and this is usually 10 to 50% by mass by water dispersion. After the slurry is adjusted, the monolith molded body is dipped in the slurry to adhere the slurry to the inner wall of the gas flow path of the monolith molded body, and after drying, 500 to 1000 ° C. in an inert atmosphere such as nitrogen, helium, argon, etc. Can be produced by heat treatment for several hours. As a binder other than colloidal silica, methyl cellulose, acrylic resin, polyethylene glycol, or the like can be used as appropriate. Alternatively, it can also be produced by a method in which a mesoporous material is applied to a monolith molded body, and then a catalyst raw material is impregnated in the mesoporous material, followed by reduction treatment and heat treatment. In the method of attaching the slurry, the thickness of the NOx adsorption / reduction catalyst layer to be attached to the monolith molded body is usually preferably 1 μm to 100 μm, particularly preferably in the range of 10 μm to 50 μm. If it exceeds 100 μm, the diffusion of the reaction gas becomes slow, so that it is preferably 100 μm or less. In order to suppress deterioration of catalyst performance, 1 μm or more is preferable.

[Reducing agent]
As the reducing agent in the present invention, reducing substances such as carbon monoxide, hydrogen, hydrocarbons, steam, hydrocarbon-derived reformed gas, alcohol and alcohol-derived reformed gas can be used. Among these, it is preferable to use a reformed gas derived from alcohol. The alcohol-derived reformed gas is used as the reducing agent because the alcohol-derived reformed gas exhibits high activity against exhaust NOx in the oxidizing atmosphere, unlike the lower olefin that functions as a reducing agent in the hydrocarbon SCR method. This is because a feature has been found. Further, it has been found that the reduction proceeds to the nitrogen stage even in the low to medium temperature range from about 200 ° C. or lower to about 300 ° C.

  As a method of supplying the reducing agent, a method of supplying fuel (a fuel containing reducing hydrocarbons) to a lean burn exhaust gas by a common rail ejector (sprayer), a fuel is reformed through a reforming catalyst. A method of supplying the exhaust gas of lean burn later, a method of supplying hydrogen, carbon monoxide, hydrocarbon, alcohol, etc. directly as the reducing agent to the exhaust gas of lean burn can be used. Alcohol has recently attracted attention as an alternative fuel for gasoline. However, since it is a substance that is also used as a raw material for reducing substances such as aldehyde, carbon monoxide, and hydrogen, it can also be used as a reducing agent for NOx. According to the study by the present inventors, when an appropriate reforming catalyst for alcohol is used, it exhibits high activity against exhaust NOx in an oxidizing atmosphere, unlike a lower olefin that functions as a reducing agent in the hydrocarbon SCR method. It has been found. It has also been found that the reduction proceeds to the nitrogen stage even in the low to medium temperature range from about 200 ° C. or lower to about 300 ° C.

  As the alcohol as the reducing agent, lower alcohols such as methanol, ethanol, propanol and butanol and alcohols having 5 or more carbon atoms are effective. Among these, methanol, ethanol, propanol and butanol are excellent in reducibility. Among them, ethanol is preferable, and ethanol is more preferable because of its low flammability and low oral toxicity. The above alcohol is also effective as a hydrous alcohol. Hydrous alcohol can cause a steam reforming reaction of alcohol. The water content is preferably such that it does not affect the reforming temperature of the alcohol, and is usually within about 10%.

When alcohol-derived reformed gas is used as the reducing agent, the amount of alcohol supplied through the reforming catalyst is somewhat affected by the oxygen concentration in the exhaust gas, but the oxygen concentration is within a range of 20% or less. The number of moles is not particularly limited as long as it is from the same number of moles as NOx to several tens of moles. Moreover, you may mix a small amount of air with alcohol as an oxidizing agent.
The amount of air is not particularly limited as long as it is an amount that causes partial oxidation of alcohol, but is usually about several moles or less. The reforming temperature of the alcohol is set to an appropriate temperature depending on the type of alcohol and the type of reforming catalyst. In the present invention, it is usually carried out in the range of 100 ° C to 500 ° C. The reforming catalyst can be heated by a method such as exhaust heat recovery or direct heating.

[Purification method and purification apparatus]
Next, the exhaust NOx purification method and the purification apparatus in the present invention will be described. FIG. 1 is a schematic view of an exhaust gas purifying apparatus according to the present invention.
The exhaust gas purification apparatus according to the present invention includes an exhaust NOx purification catalyst unit 7 and a reducing agent supply unit 1, and the exhaust NOx purification catalyst unit 7 is provided in the exhaust gas flow path 5.
In the present invention, exhaust gas is purified by supplying a reducing agent from the reducing agent supply unit 1 to the exhaust NOx purification catalyst unit 7 provided in the exhaust gas flow path 5.

Further, the exhaust NOx purification catalyst section 7 can have a heating section 6 for heating the catalyst as necessary. The heating unit 6 can be provided for heating from the outside so that the catalyst unit becomes active when the exhaust gas temperature is 160 ° C. or lower, which is the lower limit of the purification catalyst in the present invention.
Further, the reducing agent supply unit 1 includes a reducing agent storage unit 2 for storing the reducing agent, a reducing agent reforming unit 3 for modifying the reducing agent as necessary, and a reducing agent as an NOx adsorption reduction catalyst unit. It is comprised from the ejector 4 for supplying to.

The reducing agent reforming unit 3 is a device for reforming a reducing material as necessary when using an alternative fuel such as fuel or alcohol as a reducing agent.
The exhaust NOx purification method and apparatus of the present invention is extremely effective in the low temperature region of 160 ° C. to 600 ° C. when NOx in the lean burn exhaust gas discharged by the automobile is mounted on automobiles, particularly diesel automobiles and lean burn gasoline automobiles. Can be removed. It can also be used as a method for purifying exhaust NOx for large vehicles such as trucks.

The present invention will be specifically described below with reference to examples.
The specific surface area and pore distribution were measured with a Sorpmatic 1800 type apparatus manufactured by Carlo Elba using nitrogen as a desorption gas. The specific surface area was determined by the BET method. The pore distribution was measured in the range of 1 to 200 nm and indicated by a differential distribution obtained by the BJH method. Many of the produced mesoporous materials peaked at specific pore diameter positions in an exponentially increasing distribution. The pore diameter that gives this peak is the pore diameter.
As a model gas for automobile exhaust NOx, a mixed gas of helium diluted nitric oxide and oxygen was used. The reduced pressure chemiluminescence NOx analyzer (Nippon Thermo Co. preparation: Model 42i-HL and 46C-H) (total of NO and NO ₂₎ NOx contained in the gas before and after treatment by the _N 2 O (NOx The NOx purification rate and the nitrogen selectivity were calculated by Equation (1) and Equation (2), respectively.

“Production Example 1” Synthesis of a catalyst similar to a three-way catalyst as a catalyst for exhaust gas purification 20 ml of 0.215 g of PtCl4 · 5H2O, 0.106 g of PdCl2 · 2H2O, and 0.162 g of Rh (NO3) 3 · 2H2O An aqueous solution dissolved in distilled water is placed in an evaporating dish, and 10 g of activated alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m 2 / g, fine particles with a pore diameter of 6.2 nm and a particle diameter of 2 to 3 μm) is added to the steam bath. After evaporating to dryness, it was put in a vacuum dryer and vacuum dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream to synthesize a catalyst having a noble metal content of about 2% by weight. This was used in a comparative experiment as a noble metal catalyst simulating a three-way catalyst.

“Production Example 2” Production of carbon nitride compound as NOx adsorbent 100 g of melamine and 100 g of zinc chloride were mixed, placed in a magnetic dish, and heated at 650 ° C. for 1 h in an electric furnace. The solid matter taken out after cooling to room temperature was pulverized, placed in concentrated hydrochloric acid and boiled for 1 hour. After allowing to cool to room temperature, vacuum filtration, washing with water, washing with 0.1N sodium hydroxide, washing with water, and vacuum drying at 200 ° C. were performed to produce a carbon nitride compound. Elemental analysis, IR measurement, X-ray diffraction measurement, mass spectrometry, and the like identified the carbon nitride compound having a planar structure in which the 1,3,5 position of the triazine ring was bonded with an NH group.

“Production Example 3” Production of boron carbonitride compound as NOx adsorbent 100g of fine powder of polyacrylonitrile (manufactured by Asahi Kasei Corporation: PAN homopolymer) is heated to about 70 ° C, and boron trichloride gas is circulated through it for 1 hour. After the reaction, the mixture was heated at 500 ° C. for 1 hour under a nitrogen stream, and then heated at 1000 ° C. for 2 hours under a nitrogen stream to remove volatile substances. Boron carbonitride was produced by pulverizing the solid matter taken out after cooling to room temperature and placing it in an electric furnace and firing at 1500 ° C. for 10 hours in a nitrogen stream. Elemental analysis, IR measurement, X-ray diffraction measurement, X-ray photoelectron spectroscopic spectrum measurement, etc. identified carbon boron nitride BC3N having a graphite-like structure.

“Production Example 4” Production of zeolite as NOx adsorbent 100 g of zeolite (manufactured by Tosoh Corporation: ZSM-5) was placed in 2 L of distilled water, 10 g of 10% by mass of barium nitrate aqueous solution was added thereto, and the mixture was stirred overnight at room temperature. did. Barium ion exchanged ZSM-5 was produced by vacuum filtration, washing with 100 mL of distilled water, and vacuum drying at 100 ° C.

[Production Example 5] Production of mesoporous transition metal nitride as NOx adsorbent 300 g of distilled water, 240 g of ethanol, 10 g of acetylacetone, and 30 g of dodecylamine were dissolved in a 1 liter beaker. Under stirring, 204 g of tetra-t-butoxy titanium was added dropwise and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove the contained dodecylamine to obtain a mesoporous titania material. As a result of small angle X-ray diffraction measurement of the mesoporous titania material, one broad diffraction peak was shown. Further, as a result of observation with a transmission electric microscope, a regular arrangement was not observed in the arrangement of the pores, and a disordered state was observed. From these results, it was confirmed that the produced mesoporous titania material was amorphous. Moreover, as a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.0 nm, the specific surface area is 400 m 2 / g, the pore volume is 1.21 cm 3 / g, and the pores are 2 to 50 nm. The volume was 1.20 cm3 / g. Next, 10 g of the above mesoporous titania material was put in a quartz tube, heated to 1000 ° C., and treated under an ammonia gas stream for 5 hours to obtain a mesoporous titanium oxynitride compound. The nitriding rate was about 20%.

“Production Example 6” Production of Indium Supported on Zeolite as NOx Adsorbent 10 g of zeolite (manufactured by Tosoh Corporation: ZSM-5) is placed in an evaporating dish, and 10 g of 10% by mass indium chloride aqueous solution is added to the steam bath. Evaporated to dryness. It put into the vacuum dryer and vacuum-dried at 100 degreeC-3 hours. This sample was put in a quartz tube and reduced at 300 ° C. for 3 hours under a helium-diluted hydrogen gas (10 v / v%) stream to synthesize zeolite-supported indium with an indium-supporting amount of about 5% by mass.

[Production Example 7] Production of platinum catalyst supported on mesoporous silica as NOx oxidation-reduction catalyst In a 1 liter beaker, 300 g of distilled water, 240 g of ethanol, and 30 g of dodecylamine were added and dissolved. While stirring, 125 g of tetraethoxysilane was added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried with warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove contained dodecylamine to obtain a mesoporous silica material. As a result of small angle X-ray diffraction measurement of the mesoporous silica material, one broad diffraction peak was shown. Further, as a result of observation with a transmission electric microscope, a regular arrangement was not observed in the arrangement of the pores, and a disordered state was observed. From these results, it was confirmed that the produced mesoporous silica material was amorphous. Moreover, as a result of pore distribution and specific surface area measurement, there was a pore peak at a position of about 3.2 nm, a specific surface area of 933 m ² / g, a pore volume of 1.35 cm ³ / g, and a pore of 1 to 50 nm. The volume occupied by was 1.34 cm ³ / g. An aqueous solution of chloroplatinic acid _{H 2} PtCl ₆ · 6H 2 O and 0.267g and rhodium nitrate _{Rh (NO 3) 3 · 2H} 2 O were dissolved 0.0016g in distilled water 20g were placed in an evaporating dish, to which the above mesoporous After adding 5 g of a silica material and evaporating to dryness in a steam bath, it was put in a vacuum dryer and vacuum dried at 100 ° C. for 3 hours. This sample was put into a quartz tube and reduced at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10 v / v%) stream, and a [Pt-Rh / mesoporous silica] catalyst having a platinum-rhodium loading of about 2% by mass was obtained. Synthesized. The average particle diameter of the platinum-rhodium particles supported on the mesoporous catalyst was about 3.0 nm.

"Production Example 7a" Synthesis of reforming catalyst for alcohol reforming In a 1 liter beaker, 300 g of distilled water, 240 g of ethanol, and 30 g of dodecylamine were added and dissolved. Under stirring, 125 g of tetraethoxysilane and 50 g of diethoxymagnesium were added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove contained dodecylamine to obtain a mesoporous silica / magnesia material. As a result of small-angle X-ray diffraction measurement of the mesoporous silica / magnesia material, it showed one broad diffraction peak. Further, as a result of observation with a transmission electric microscope, a regular arrangement was not observed in the arrangement of the pores, and a disordered state was observed. From these results, it was confirmed that the produced mesoporous silica / magnesia material was amorphous. Moreover, as a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.0 nm, a specific surface area of 650 m ² / g, a pore volume of 1.20 cm ³ / g, and a pore of 2 to 50 nm. The volume occupied by was 1.19 cm ³ / g. Next, 10 g of the above mesoporous silica / magnesia material is put into 100 mL of 0.3N cobalt nitrate aqueous solution, evaporated to dryness on a steam bath, put into a quartz tube, and heated at 500 ° C. under a helium diluted hydrogen gas (10 v / v%) stream. Was reduced for 3 hours to synthesize a mesoporous catalyst having a cobalt content of about 2% by mass. The average particle size of the cobalt particles supported on the mesoporous catalyst was about 3.0 nm.

[Production Example 7b] Synthesis of [Pt / basic mesoporous silica] catalyst as exhaust gas purification catalyst 10 g of the mesoporous silica material of Production Example 7a was placed in 100 mL of 0.1N aqueous sodium hydrogen carbonate solution, and evaporated to dryness on a steam bath. Then, it was placed in an electric furnace and heated at 500 ° C. for 4 hours. 0.1 g of a part of the obtained material was sampled, and 1 mL of distilled water was added thereto to prepare a colloidal dispersion. When two drops of 0.1% by weight of alizarin yellow aqueous solution were added thereto, the colloidal dispersion turned pale purple, and it was found that the pH was 10.1 to 12.1.
Next, put the aqueous solution 0.267g dissolved _{H 2} PtCl ₆ · 6H 2 O in distilled water 20g evaporation dish, to which the above-mentioned strongly basic mesoporous silica material 5g was added and evaporated to dryness on a steam bath Then, it put into the vacuum dryer and vacuum-dried at 100 degreeC for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours in a helium-diluted hydrogen gas (10 v / v%) stream to synthesize a strongly basic mesoporous catalyst having a platinum content of about 2% by mass. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.

“Production Example 7c” Synthesis of [Pt / Mesoporous Alumina] Catalyst as Exhaust Gas Purifying Catalyst 300 g of distilled water, 240 g of ethanol, and 30 g of dodecylamine were placed in a 1 liter beaker and dissolved. Under stirring, 120 g of triisopropoxyaluminum was added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove the contained dodecylamine to obtain a mesoporous alumina material. As a result of small-angle X-ray diffraction measurement of the mesoporous alumina material, one broad diffraction peak was shown. Further, as a result of observation with a transmission electric microscope, a regular arrangement was not observed in the arrangement of the pores, and a disordered state was observed. From these results, it was confirmed that the produced mesoporous alumina material was amorphous. As a result of measuring the pore distribution and the specific surface area, there is a pore peak at a position of about 3.2 nm, a specific surface area of 460 m ² / g, a pore volume of 1.32 cm ³ / g, and pores of 1 to 50 nm. The occupied volume was 1.28 cm ³ / g. Next, 10 g of this material was placed in 100 mL of a 0.1N aluminum sulfate aqueous solution, evaporated to dryness on a steam bath, then placed in an electric furnace and heated at 500 ° C. for 4 hours. 0.1 g of a part of the obtained material was sampled, and 1 mL of distilled water was added thereto to prepare a colloidal dispersion. When two drops of 0.1% by weight of alizarin yellow aqueous solution were added thereto, the colloidal dispersion turned pale purple, and it was found that the pH was 10.1 to 12.1. Moreover, taken part of the obtained sample, the results of measuring the infrared absorption spectrum, attributed to the sulfate ion to the newly 1128cm around ^-1 and near 619Cm ^-1 in addition to the absorption bands of the active alumina as a raw material An absorption band was observed. Next, put the aqueous solution 0.267g dissolved _{H 2} PtCl ₆ · 6H 2 O in distilled water 20g evaporation dish, to which the above-mentioned strongly basic mesoporous alumina material 5g was added and evaporated to dryness on a steam bath Then, it put into the vacuum dryer and vacuum-dried at 100 degreeC for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours in a helium-diluted hydrogen gas (10 v / v%) stream to synthesize a strongly basic mesoporous catalyst having a platinum content of about 2% by mass. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.

[Production Example 7d] [Pt / basic mesoporous silica magnesia] as exhaust gas purification catalyst
Synthesis of catalyst In a 1 liter beaker, 300 g of distilled water, 240 g of ethanol, and 30 g of dodecylamine were added and dissolved. Under stirring, 125 g of tetraethoxysilane and 50 g of diethoxymagnesium were added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove contained dodecylamine to obtain a mesoporous silica / magnesia material. As a result of small-angle X-ray diffraction measurement of the mesoporous silica / magnesia material, it showed one broad diffraction peak. Further, as a result of observation with a transmission electric microscope, a regular arrangement was not observed in the arrangement of the pores, and a disordered state was observed. From these results, it was confirmed that the produced mesoporous silica / magnesia material was amorphous. Moreover, as a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.0 nm, a specific surface area of 650 m ² / g, a pore volume of 1.20 cm ³ / g, and pores of 2 to 50 nm. The occupied volume was 1.19 cm ³ / g. Next, 10 g of the above-mentioned mesoporous silica / magnesia material was put into 100 mL of a 0.1N sodium hydrogen carbonate aqueous solution, evaporated to dryness on a steam bath, and then placed in an electric furnace and heated at 500 ° C. for 4 hours. 0.1 g of a part of the obtained material was sampled, and 1 mL of distilled water was added thereto to prepare a colloidal dispersion. When two drops of 0.1% by weight of alizarin yellow aqueous solution were added thereto, the colloidal dispersion turned pale purple, and it was found that the pH was 10.1 to 12.1. Next, put the aqueous solution 0.267g dissolved _{H 2} PtCl ₆ · 6H 2 O in distilled water 20g evaporation dish, to which the above-mentioned strongly basic mesoporous silica magnesia material 5g added, evaporated to dryness on a steam bath After solidifying, it was put in a vacuum dryer and vacuum dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours in a helium-diluted hydrogen gas (10 v / v%) stream to synthesize a strongly basic mesoporous catalyst having a platinum content of about 2% by mass. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.

[Production Example 7e] Synthesis of [Pt / basic mesoporous activated carbon] catalyst as exhaust gas purification catalyst Commercial activated carbon (manufactured by Kansai Thermochemical Co., Ltd.) was used as mesoporous activated carbon. The activated carbon had a specific surface area of 3100 m ² / g, an average pore diameter of 2.0 nm, a pore volume of 1.62 cm ³ / g, and a volume occupied by 1-50 nm pores of 1.60 cm ³ / g. 10 g of this material was placed in 100 mL of a 0.1N aqueous sodium hydrogen carbonate solution, evaporated to dryness on a steam bath, then placed in an electric furnace and heated at 500 ° C. for 4 hours. 0.1 g of a part of the obtained material was sampled, and 1 mL of distilled water was added thereto to prepare a colloidal dispersion. When two drops of 0.1% by weight alizarin yellow aqueous solution were added thereto, the colloidal dispersion turned pale purple, so that the pH was 10
. It was found to be 1 to 12.1. Next, put the aqueous solution 0.267g dissolved _{H 2} PtCl ₆ · 6H 2 O in distilled water 20g evaporation dish, to which the above-mentioned strongly basic mesoporous activated carbon material 5g was added and evaporated to dryness on a steam bath Then, it put into the vacuum dryer and vacuum-dried at 100 degreeC for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours in a helium-diluted hydrogen gas (10 v / v%) stream to synthesize a strongly basic mesoporous catalyst having a platinum content of about 2% by mass. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.

[Production Example 7f] Synthesis of [Pt / basic mesoporous silica / monolith] catalyst as exhaust gas purifying catalyst 1 g of the catalyst of Production Example 7b and 0.1 g of colloidal silica are added to 10 ml of distilled water and stirred to prepare a slurry. did. Five mini-molded bodies (21 cells, diameter 8 mm × length 9 mm, weight 0.15 g) cut from a commercially available cordierite monolith molded body (400 cells / in ² , diameter 118 mm × length 50 mm, weight 243 g) After immersion, the sample was taken out and air-dried, and then heat-treated at 500 ° C. for 3 hours under a nitrogen stream. The adhesion amount of the mesoporous catalyst was about 10% by mass of the mini-molded product, and the supported amount of platinum per mini-molded product was about 0.2% by mass.

[Production Example 8] Production of mixed catalyst of carbon nitride compound and [Pt-Rh / mesoporous silica] catalyst 10 g of carbon nitride compound of Production Example 2 and 10 g of [Pt-Rh / mesoporous silica] catalyst of Production Example 7 were uniformly mixed. Thus, a NOx adsorption reduction catalyst was produced.
[Production Example 9] Production of mixed catalyst of boron carbonitride compound and [Pt-Rh / mesoporous silica] catalyst 10 g of boron carbonitride compound of Production Example 3 and 10 g of [Pt-Rh / mesoporous silica] catalyst of Production Example 7 The NOx adsorption reduction catalyst was produced by mixing with the above.
[Production Example 10] Production of mixed catalyst of zeolite and [Pt-Rh / mesoporous silica] catalyst 10 g of barium ion exchanged zeolite produced in Production Example 4 and 10 g of [Pt-Rh / mesoporous silica] catalyst of Production Example 7 By mixing, a NOx adsorption reduction catalyst was produced.

"Production Example 11" Production of mixed catalyst of mesoporous transition metal nitride and [Pt-Rh / mesoporous silica] catalyst 10 g of mesoporous transition metal nitride produced in Production Example 5 and [Pt-Rh / mesoporous silica] of Production Example 7 A NOx adsorption reduction catalyst was produced by uniformly mixing 10 g of the catalyst.
[Production Example 12] Production of mixed catalyst of indium supported on zeolite and [Pt-Rh / mesoporous silica] catalyst 10 g of zeolite-supported indium produced in Production Example 7 and 10 g of [Pt-Rh / mesoporous silica] catalyst of Production Example 6 Were mixed uniformly to produce a NOx adsorption reduction catalyst.

[Production Example 13] Synthesis of [zeolite-supported indium + Pt-Rh / mesoporous silica] catalyst supported on monolith 1 g of NOx adsorption-reduction catalyst of Production Example 12 and 0.1 g of colloidal silica were added to 10 ml of distilled water and stirred. The slurry was adjusted. Five mini-molded bodies (21 cells, diameter 8 mm × length 9 mm, weight 0.15 g) cut out from a commercially available cordierite monolith molded body (400 cells / in 2, diameter 118 mm × length 50 mm, weight 243 g) are immersed in this. The sample was taken out and air-dried, followed by heat treatment at 500 ° C. for 3 hours under a nitrogen stream. The adhesion amount of the mixed catalyst was about 10% by mass of the mini-molded body, and the supported amount of platinum per mini-molded body was about 0.2% by mass.

"Reforming ethanol with reforming catalyst"
The reforming catalyst sample of Production Example 7a was filled in 0.3 g in a quartz continuous flow reaction tube (reaction tube 1), and ethanol was reformed. The reaction tube 1 was heated to 300 ° C. by an external heater. Ethanol vapor whose concentration was adjusted with helium was supplied to the reaction tube 1. The molar concentration of ethanol was 1%. The feed gas flow rate was 100 ml per minute. As a result, the reforming rate (= reaction rate) of ethanol by the reforming catalyst is about 60%, and the gas components excluding unreacted ethanol after reforming are about 60% hydrogen and carbon monoxide. Was about 10% and carbon dioxide was about 30%.

“Examples 1 to 5” and “Comparative Example 1” Lean burn NOx treatment using a reformed gas of ethanol as a reducing agent 0.3 g of the reformed catalyst sample of Production Example 7a is charged into a quartz continuous flow reaction tube (Reaction tube 1). Quartz continuous flow reaction tubes were charged with 0.3 g of the exhaust gas purifying catalyst samples of Production Example 1 and Production Examples 7b to 7e (reaction tubes 2 to 6). Further, one mini-molded body carrying a catalyst, which is the monolith catalyst of Production Example 7f, was filled in a continuous flow reaction tube made of quartz (reaction tube 7). The reaction tube 1 and the reaction tube 2 are connected by a glass tube, and ethanol vapor adjusted in concentration with helium is supplied to the reaction tube 1, while nitric oxide, oxygen, and water vapor adjusted in concentration with helium are respectively supplied to the reaction tube 2. The reaction tube 2 was subjected to NOx treatment. The reaction tube 1 was heated to 300 ° C. by an external heater. The reaction tube 2 was adjusted to an arbitrary temperature of 100 ° C. to 500 ° C. by an external heater. The component molar concentration of the gas to be treated in the reaction tube 2 is ethanol 1% (however, as a supply to the reaction tube 1), nitric oxide 0.1%, oxygen 14%, water vapor 10%. The flow rate was 100 ml per minute. The exhaust gas was sampled, and the NOx treatment rate and selectivity were measured. Similarly, the reaction tubes 3 to 7 were also subjected to NOx treatment. As a result, as shown in Table 1, a high NOx purification rate of 60% or more was obtained from 180 ° C. to 400 ° C. Further, from the selectivity of NOx purification, it was found that 60% or more of the NOx purification was reduced to the nitrogen stage.

“Examples 6 to 11” and “Comparative Example 2” NOx treatment using propylene as a reducing agent The comparative catalyst of Production Example 1 and the NOx adsorption / reduction catalysts of Production Examples 8 to 12 were each placed in a quartz flow reaction tube. .3 g was charged. Also, five catalyst-supported mini-molded bodies, which are monolith catalysts of Production Example 13, were filled in a quartz continuous flow reaction tube. Each reaction tube was adjusted to an arbitrary temperature of 150 ° C. to 500 ° C. by an external heater. Next, a simulated lean burn gas with a low propylene concentration and a simulated lean burn gas with a high propylene concentration were alternately circulated in each reaction tube to perform NOx treatment. The simulated lean burn gas having a low propylene concentration was a gas containing 250 ppm of nitric oxide, 10% of oxygen, 10% of water vapor, 400 ppm of propylene adjusted in concentration with helium, and the flow rate was 100 mL per minute. The simulated lean burn gas with a high propylene concentration was a gas containing 250 ppm of nitric oxide, 10% oxygen, 10% water vapor, and 2% propylene with a helium concentration adjusted, and the flow rate was 100 mL per minute. The supply cycle of the lean burn simulated gas having a low propylene concentration and the lean burn simulated gas having a high propylene concentration was set to 60 seconds: 2 seconds. The exhaust gas was sampled, and the NOx purification rate and nitrogen selectivity were measured. The results are shown in Table 2.

“Example 12”, “Comparative Example 3” NOx treatment using ethanol as a reducing agent 0.3 g of the comparative catalyst of Production Example 1 and the NOx adsorption-reduction catalyst of Production Example 8 were filled in a quartz continuous flow reaction tube, respectively. did. Each reaction tube was adjusted to an arbitrary temperature of 150 ° C. to 500 ° C. by an external heater. Next, a simulated lean burn gas with a low ethanol concentration and a simulated lean burn gas with a high ethanol concentration were alternately circulated in each reaction tube to perform NOx treatment. The lean burn simulated gas having a low ethanol concentration was a gas containing 250 ppm of nitric oxide, 10% of oxygen, 10% of water vapor, and 400 ppm of ethanol adjusted in concentration with helium, and the flow rate was 100 mL per minute. The simulated lean burn gas with a high ethanol concentration was a gas containing 250 ppm of nitric oxide, 10% of oxygen, 10% of water vapor, and 4000 ppm of ethanol adjusted in concentration with helium, and the flow rate was 100 mL per minute. The supply cycle of the lean burn simulated gas having a low ethanol concentration and the lean burn simulated gas having a high ethanol concentration was set to 60 seconds: 2 seconds. The exhaust gas was sampled, and the NOx purification rate and nitrogen selectivity were measured. The results are shown in Table 3.

  As shown in Table 2, a high NOx purification rate of 60% or more was obtained from 180 ° C. to 500 ° C. Moreover, the selectivity of nitrogen was about 10% at 180 to 200 ° C and about 90% at 250 to 500 ° C.

As shown in Table 3, a high NOx purification rate of 60% or more was obtained from 180 ° C. to 500 ° C. Moreover, the selectivity of nitrogen was about 90% at 180 ° C. to 500 ° C.
From the above, it can be seen that the exhaust gas purification method of the present invention can efficiently purify NOx in the presence of high concentration oxygen even in a low temperature region.

  The exhaust gas purification method of the present invention is useful as a diesel exhaust NOx purification method.

Schematic which shows an example of the exhaust NOx purification apparatus in this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reducing agent supply part 2 Reducing agent storage part 3 Reducing agent reforming part 4 Ejector 5 Exhaust gas flow path 6 Heating part 7 Exhaust NOx purification catalyst part

Claims (4)

By supplying a reducing agent to the exhaust NOx purification catalyst,
An exhaust NOx purification method comprising purifying NOx discharged from an automobile.   2. The exhaust NOx purification method according to claim 1, wherein the reducing agent is supplied to an exhaust gas purification catalyst after being reformed by a reforming catalyst. An exhaust NOx purification device comprising: an exhaust NOx purification catalyst section filled with an exhaust NOx purification catalyst; and a reducing agent supply section for supplying a reducing agent to the NOx purification catalyst section.   The exhaust NOx purification device according to claim 3, further comprising a reducing agent reforming unit for reforming the reducing agent.

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