JP2006081957A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a novel mesoporous catalyst capable of efficiently performing cleaning treatment of a diesel exhaust NOx in which treatment is difficult conventionally; and a monolithic catalyst coated with the catalyst. <P>SOLUTION: A hardly soluble mesoporous material having a fine pore of an average diameter of 2-50 nm and a specific surface area of 100-1,400 m<SP>2</SP>/g is carried with a nano-particle comprising a platinum particle having an average particle diameter of 1-20 nm and/or an iridium particle as a main catalyst at 0.01-20 mass%. The catalyst (mesoporous catalyst) can efficiently clean/treat NOx at 150-300°C in a lean burn atmosphere (usually an atmosphere of oxygen concentration of 5% or more) in which treatment is difficult conventionally. The monolithic catalyst in which a molded body is coated with the mesoporous catalyst is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a mesoporous catalyst having a high specific surface area and a monolith catalyst in which this catalyst is applied to the inner wall of a gas flow path of a monolith molded body. By using the monolith catalyst, NO _x contained in lean burn automobile exhaust gas can be efficiently produced. It can be purified.

The three-way catalyst, which is the mainstream of automobile exhaust gas purification catalyst, uses a cordierite monolith molded body as a catalyst support, and has a size of several hundred nm to several μm as a catalyst on the inner wall of the gas flow path of the molded body. It has a structure in which activated alumina particles having a size of several μm to several tens of μm containing platinum-palladium-rhodium particles are applied. The activated alumina particles are aggregates of fine particles of several tens of nm to several hundreds of nm, and the catalyst particles are adsorbed in the gaps between the fine particles. The pore-type pores have little spatial spread (planar), and the basic structure is the penetration-type pore structure (called pore channel) that spreads in a network form in synthetic zeolite and mesoporous materials used in the present invention. Different. That is, the conventional catalyst particles are not in a state where the catalyst particles are trapped in the three-dimensional pores. Since a catalyst supported on a molecular sieve such as a synthetic zeolite is generally called a pore-supported catalyst, in order to distinguish it from the conventional three-way catalyst type, we will adsorb it below. This is referred to as a mold supported catalyst. The three-way catalyst is very effective for the exhaust gas treatment of gasoline vehicles, but has little effect on the exhaust gas treatment of diesel vehicles running on light oil fuel. In particular, the catalyst development for purifying exhaust NO _x of 150 to 300 ° C. discharged during a transient traveling is outstanding in the field of catalytic chemistry. And even now, no practical catalyst for diesel vehicle exhaust gas treatment is known. The main reason for this is that the three-way catalyst causes a significant decrease in activity in a relatively high concentration oxygen atmosphere in diesel exhaust gas. The oxygen concentration of gasoline vehicle exhaust gas is 1% or less, but since the air-fuel ratio of light oil is more than several times that of gasoline, the oxygen concentration contained in diesel exhaust gas is usually 5% or more. In the case of a gasoline vehicle, co-existing oxygen is controlled to 1% or less by burning near the stoichiometric air-fuel ratio indicating the theoretical weight mixing ratio of air and fuel. This combustion is called rich burn. The combustion of diesel fuel is called lean burn because the intake amount is excessively larger than the theoretical value and the fuel supply amount is relatively small. This is because the activity of the three-way catalyst is almost deactivated when the oxygen concentration becomes 5% under these combustion conditions.

In general, industrial catalysts are often used in a state where they are supported on a porous material. According to IUPAC, the pores of the porous material are classified into micropores having a pore diameter of 2 nm or less, mesopores of 2 to 50 nm, and macropores of 50 nm or more. 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 mesoporous molecular sieves having a pore peak at a position of several nm and a very large specific surface area of 400 to 1100 m ² / g have been developed. These are disclosed in, for example, Patent Documents 1, 2, and 3.

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 the three-way catalyst for automobiles, the specific surface area of the monolith molded body as the support is about 0.2 m ² / g, and the specific surface area of the alumina particles as the adsorbent is 110 to 340 m ² / g. . The specific surface area of the catalyst is estimated to be about ²⁰ to 40 m ² / g from the particle size. Therefore, a nano-sized catalyst supported on a mesoporous material having a high specific surface area (hereinafter referred to as a nano-catalyst having a nano-sized catalyst and a nano-catalyst supported on the pores of the mesoporous material. The surface area of the nano catalyst is 10 ² to 10 ⁴ times that of the three-way catalyst.) An effective mesoporous catalyst for purifying lean burn exhaust gas based on such an idea is not known.

JP-A-5-254827 Special table hei 5-503499 published Special table hei 6-509374 publication

In view of the above circumstances, an object of the present invention is to provide a novel catalyst that performs the NOx purification treatment contained in the lean burn exhaust gas, which could not be achieved conventionally, very efficiently even in a low temperature region. More specifically, in order to purify conventionally difficult a diesel exhaust NO _x efficiently, novel mesoporous catalyst and the catalyst at a relatively high concentration oxygen atmosphere in a lean burn active against exhaust NO _x It is to provide a monolith catalyst coated with.

The present inventors have made intensive studies to achieve the above object, in a catalyst a specific noble metal supported on a mesoporous material having a specific pore distribution and high specific surface area lean burn exhaust NO _x treatment It has been found that the present invention is very effective, and based on this finding, the present invention has been completed. The present invention has a pore ratio of ^{2 to} 50 nm in diameter and a ratio of 100 to 1400 m ² / g. A lean catalyst comprising 0.01 to 20% by mass of nanoparticles composed of platinum particles and / or iridium particles having an average particle diameter of 1 to 20 nm as a main catalyst in a sparingly soluble mesoporous material having a surface area burn discharge _the NO _x purification for mesoporous catalyst, and is intended to provide a monolithic catalyst the mesoporous catalyst is applied to the gas passage inner wall of the monolith formed body.
That is, the present invention provides the following 1. To 7. Relates to the invention.

1． Nano consisting of platinum particles and / or iridium particles having an average particle size of 1 to 20 nm as a main catalyst in a hardly soluble mesoporous material having pores with a diameter of 2 to 50 nm and a specific surface area of 100 to 1400 m ² / g. lean burn exhaust _the NO _x purification for mesoporous catalyst, wherein the particle is 0.01 to 20 wt% carrying catalyst was.
2. The sparingly soluble mesoporous material is silica, alumina, zirconia, titania, silica-alumina, and composite materials thereof having substantially ² to 20 nm pores and a specific surface area of 100 to 1200 m ² / g as the main catalyst The average particle diameter of nanoparticles composed of platinum particles and / or iridium particles is 1 to 10 nm, and the supported amount of nanoparticles is 0.1 to 10% by mass. Lean burn exhaust _the NO _x purification for mesoporous catalyst according.
3. A mesoporous material in which the sparingly soluble mesoporous material contains 1 to 20 mol% of at least one element selected from the group 3A element, group 3B element, group 4A element, group 5A element and group 6A element in the periodic table 1. The material as described above. And 2. Lean burn exhaust _the NO _x purification for mesoporous catalyst according.
4). 1 above. To 3. Lean burn exhaust _the NO _x purification for monolithic catalyst for the mesoporous catalyst, characterized in that applied to the gas flow passage inner wall of the monolith formed body.
5. The coating amount of the mesoporous catalyst in the monolith catalyst is 3 to 30% by mass of the monolith catalyst, the supported amount of platinum and / or iridium in the mesoporous catalyst is 0.1 to 10% by mass, and platinum and / or iridium converted per monolith catalyst. The above-mentioned item 4, wherein the carrying amount is 0.03 to 3% by mass. Lean burn exhaust _the NO _x purification for monolithic catalyst according.
6). 4. And 5. Lean-burn with discharge _the NO _x purification for monolithic catalyst, exhaust NOx purifying catalyst for small diesel performing rich burn and the lean burn alternately.
7). 4. And 5. Lean-burn with discharge _the NO _x purification for monolithic catalyst, exhaust NOx purifying catalyst for a large diesel for mounting a urea supply system.

Mesoporous catalysts of the present invention can be carried out very efficiently even lean burn exhaust _the NO _x purification process which could not be conventionally achieved in a low temperature region. For example, a three-way catalyst can hardly purify nitric oxide in an atmosphere having an oxygen concentration of 14%, but the platinum catalyst supported on the mesoporous borosilicate of the present invention has 80% of nitric oxide coexisting in an atmosphere having an oxygen concentration of 14%. % Or more can be purified at 150-300 ° C.

Hereinafter, the present invention will be described in detail.
One feature of the present invention is to use a mesoporous material as a carrier of the NO _x purifying catalyst. The reason is that the mesoporous material has penetrating pores, so that the catalyst is strongly captured, the effect of gas diffusion through the pore channels can be expected, and the preferred particle size of the catalytically active species by controlling the pore distribution. This is because the range can be maintained, and by supporting the catalyst in the pores, the reaggregation of the catalyst particles can be suppressed and the catalyst can be uniformly and highly dispersed. As will be described below, since the particle diameter of the catalyst particles exhibiting high activity with respect to NO _x is nano-sized, the pore diameter of the mesoporous material that is the carrier must be approximately the same as that of the catalyst particles. Normally, the particle size of the catalyst supported in the pores of the mesoporous material is approximately the same as the pore size. Therefore, by controlling the pore size of the mesoporous material, the nano catalyst having a preferable particle size can be made uniform. Can be distributed and carried.

Therefore, the pore size and pore distribution of the mesoporous material are important design factors, and the specific surface area is the next design factor. The pore diameter of the mesoporous material for supporting the nanocatalyst is substantially in the range of 2 to 50 nm, preferably in the range of 2 to 20 nm. The term “substantially” used herein means that the pore volume occupied by pores in the range of 2 to 50 nm is 60% or more of the total pore volume. Even if the pore diameter is less than 2 nm, the nanocatalyst can be supported, but it is not so preferable because the influence of contamination by impurities and the like is large. If it exceeds 50 nm, the dispersed and supported nanocatalyst tends to grow into giant particles by sintering under hydrothermal high temperature conditions, etc., which is not preferable. The specific surface area should be as high as possible unless there are special circumstances. The specific surface area of mesoporous materials that may be used in the present invention is 100~1400m ² / g, preferably 100~1200m ² / g, and more preferably from 400~1200m ² / g. When the specific surface area is less than 100 m ² / g, the supported amount of the catalyst becomes small, so the catalytic performance of the supported catalyst is not so great. If the specific surface area exceeds 1400 m ² / g, there is a problem in material strength, which is not preferable.

As the mesoporous material used in the present invention, a hardly soluble mesoporous material is used from the viewpoint of durability against high-temperature water vapor contained in the exhaust gas. The poor solubility of the material has no practical problem if the weight of the substance extracted when the sample is placed in hot water at 150 ° C. for 1 hour is 0.01% or less. Examples of hardly soluble mesoporous materials include mesoporous silica, alumina, titania, zirconia, yttria, ceria, niobia, silica-alumina, and composite materials thereof. Among these, silica, alumina, titania, zirconia, silica -Alumina and their composites are preferred because of their relatively high mechanical properties. Surprisingly, mesoporous materials that combine at least one element selected from Group 3A elements, Group 3B elements, Group 4A elements, Group 5A elements, and Group 6A elements with a mesoporous material give low-temperature activity to the catalyst. This is particularly preferable. For group 3A elements, scandium, yttrium, and cerium are preferred, for group 3B elements, boron is preferred, for group 4A elements, titanium and zirconium are preferred, for group 5A, niobium and tantalum are preferred, for group 6A, chromium, molybdenum, and tungsten are preferred. . Although the unexpected low temperature activation mechanism that the starting temperature of the catalytic reaction by the mesoporous catalyst is lowered by about 50 to 100 ° C. due to the mesoporous material combined with these elements is still unclear, the NO _x concentration effect in the vicinity of the catalyst is still unclear. It seems to be related. The amount of these elements introduced is preferably 1 to 20 mol% with respect to the main metal constituting the mesoporous material.

The main catalyst used in the present invention is a catalyst containing platinum and / or iridium noble metal nanoparticles. Conventionally, the three-way catalyst has been known as automobile exhaust gas treatment catalyst containing platinum, the catalyst is known to have little effect on diesel exhaust _the NO _x purification process. The reason is that palladium and rhodium, which are constituent elements other than platinum, undergo surface oxidation by a low concentration of oxygen. Since the three-way catalyst is composed of platinum-palladium-rhodium, it is easily deactivated when subjected to surface oxidation. The reason for using platinum and / or iridium in the present invention, these noble metals are high catalytic ability to oxidize to nitrogen dioxide by the principal component of the nitric oxide coexistence oxygen is the exhaust NO _x, chemically even during hot oxygen atmosphere It is because it is stable. Among precious metals, platinum is active at a relatively low temperature, and iridium is active at a relatively high temperature. Therefore, a catalytic reaction in a wide temperature range can be expected with these mixed catalysts. Nitrogen dioxide produced by the catalytic reaction is easily converted into nitrogen and water by reducing substances such as lower olefins having 1 to 6 carbon atoms and lower paraffin (a small amount in fuel) or ammonia urea (which can be mounted on trucks). Disassembled.

Since the surface area of the catalyst particles is inversely proportional to the square of the particle diameter, the smaller the catalyst particles, the higher the catalytic activity. For example, the surface area of the catalyst particles of 1nm is 10 ⁴ times greater than that of 0.1 [mu] m. In addition, catalyst particles atomized into nano-sizes have a large number of high-order crystal planes such as edges, corners, and steps that exhibit activity, so that not only catalytic activity is significantly improved but also catalytic activity is exhibited in bulk. It is known that even an inert metal such as this may exhibit unexpected catalytic activity. Therefore, finer catalyst particles are preferable from the viewpoint of catalytic ability, but on the other hand, there are also undesirable properties such as surface oxidation and side reactions due to atomization, so there is an optimum range for the particle size of the fine particles. . It has been found that the average particle diameter of the catalyst particles exhibiting an effective activity for the target NO _x decomposition and purification treatment in the present invention is in the range of 1 to 20 nm, particularly in the range of 1 to 10 nm.

  The catalyst of the present invention is a supported catalyst supported on pores of a mesoporous material. The supported amount of platinum and / or iridium as the main catalyst is 0.01 to 20% by mass, preferably 0.1 to 10% by mass. If there is no quantitative problem, the supported amount is usually several percent. Use. The molar ratio of platinum and iridium in the mixed catalyst is arbitrary. Usually, if it is equimolar, high activity can be achieved from low temperature to high temperature. When priority is given to low-temperature activity, the ratio of platinum should be increased, and when priority is given to high-temperature activity, the ratio of iridium should be increased. The supported amount of catalyst of the mesoporous material can be 20% by mass or more, but if the supported amount is excessive, the catalyst in the deep part of the pores that hardly contributes to the reaction is not good. Moreover, if it is less than 0.01 mass%, activity is not enough.

  By adding a co-catalytic component having a different function to the platinum and / or iridium catalyst which is the main catalyst of the present invention, the catalyst performance can be improved by the synergy effect. Examples of such components include chromium, manganese, iron, cobalt, nickel, copper, zinc, barium, scandium, yttrium, titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, lanthanum, cerium, barium, and these. Can be mentioned. Among these, chromium, iron, cobalt, nickel, which is a passivating film, copper with a relatively high adsorptive power of reducing agents, barium oxide with NOx storage, cerium oxide and trioxide with moderate oxidizing power Manganese, copper-zinc, iron-chromium, molybdenum oxide and the like effective for preventing SOx poisoning are preferable. The amount of this component added is usually from about the same mass to about 100 times the main catalyst, but may be 100 times or more as required.

  The method for synthesizing the mesoporous material of the present invention is not particularly limited, and a desired material can be produced using a conventional method. For example, it can be produced according to a conventional method using a surfactant as a template for mesopores (for example, Patent Documents 1, 2, and 3). In this method, a metal alkoxide is usually used as the precursor of the mesoporous material. Surfactants include micelle-forming surfactants used to make conventional mesopore molecular sieves, such as long-chain quaternary ammonium salts, long-chain alkylamine N-oxides, long-chain sulfonates, Any of polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester and the like 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 molar ratio of the precursor / surfactant is 1 to 30, preferably Is 1 to 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 0.2-0.6.

The reaction temperature is in the range of 20 to 180 ° C, preferably 20 to 100 ° C. The reaction time ranges from 5 to 100 hours, preferably from 10 to 50 hours. The reaction product is usually separated by filtration, washed thoroughly with water, dried, and then extracted with an organic solvent such as alcohol and then thermally decomposed at a high temperature of 500 to 1000 ° C. It can be completely removed to obtain a mesoporous material.
For mesoporous materials composed of 3A group elements, 3B group elements, 4A group elements, 5A group elements, and 6A group elements, add appropriate amounts of alkoxides, acetylacetonates, etc. of these elements to the precursors of the mesoporous materials. It can be manufactured by a method similar to the method for manufacturing the mesoporous material.

The mesoporous catalyst of 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 the 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 platinum catalyst materials 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. Examples of the iridium catalyst raw material include H ₂ IrCl ₄ , (NH ₄ ) ₂ IrCl ₄ , H ₂ IrCl ₆ , (NH ₄ ) ₂ IrCl ₆ , IrCl ₄ , iridium acetylacetonate, and the like. .

  As a raw material of the co-catalytic component added to the main catalyst as necessary, for example, water-soluble salts such as chloride, nitrate, sulfate, carbonate and acetate can be used. The co-supported catalyst of platinum and iridium can be produced in the same manner by mixing the respective catalyst raw materials. A catalyst obtained by adding a promoter component to platinum and / or iridium can also be produced in the same manner by mixing the raw material with the main catalyst raw material. As the reducing agent, 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 monolith molded body of the present invention is a molded body in which a cross section of the molded body is mesh-shaped and provided with gas flow paths partitioned by thin walls in parallel to the axial direction. Although the external shape of a molded object is not specifically limited, Usually, it is a cylindrical shape. The monolith catalyst of the present invention means a catalyst in which a mesoporous catalyst is applied to the inner wall of a gas flow path of a monolith molded body. The coating amount of the mesoporous catalyst is preferably 3 to 30% by mass. Application exceeding 30% is not preferable because gas diffusion to the catalyst existing inside the carrier is slow. Moreover, if it is 3% or less, the catalyst performance is not sufficient. The adhesion amount corresponding to the coating amount of the catalyst on the monolith molded body is preferably 0.03 to 3% by mass of the molded body.

  The monolith catalyst of this invention can be manufactured according to the manufacturing method of the monolith molded object which adhered the three-way catalyst for motor vehicles. For example, after preparing a mixture of mesoporous catalyst and colloidal silica as binder, usually in a mass ratio of 1: (0.01-0.2), and preparing a slurry of usually 10-50% by mass by water dispersion. The monolith molded body is immersed in the slurry, and the slurry is attached to the inner wall of the gas flow path of the monolith molded body. After drying, heat treatment is performed at 500 to 1000 ° C. for several hours in an inert atmosphere such as nitrogen, helium, and argon. Can be manufactured by. As a binder other than colloidal silica, methyl cellulose, acrylic resin, polyethylene glycol, or the like can be used as appropriate. As another method, it can also be produced by a method in which a mesoporous material is applied to a monolith molded article, and thereafter a catalyst raw material is impregnated in the mesoporous material, followed by reduction treatment and heat treatment. The thickness of the mesoporous catalyst layer applied to the molded body is usually preferably 1 μm to 100 μm, and particularly preferably 10 μm to 50 μm. If it exceeds 100 μm, the diffusion of the reaction gas becomes slow, which is not good. If it is less than 1 μm, the catalyst performance deteriorates quickly, which is not good.

Monolith catalyst of the present invention, an automobile, in particular by mounting the diesel automobile can car purifying very effectively in a wide temperature range of 150 to 700 ° C. The lean burn exhaust NO _x to be discharged. Although the processing of the exhaust NO _x is required reducing agent, in the case of small vehicles, such as passenger cars, lower olefins and lower paraffins with carbon atoms of 1 contained a small amount in light oil which is fuel 6 is a reducing agent Therefore, the fuel may be supplied onto the catalyst directly or through the reformer. Since the oxygen concentration is low at the time of rich burn and the oxygen concentration is high at the time of lean burn, when the monolith catalyst of the present invention is used for exhaust gas purification treatment of a small diesel that can perform rich burn and lean burn alternately, 150 to Exhaust NOx can be purified efficiently over a wide temperature range of 700 ° C. Also, in the case of large vehicles such as trucks, it is usually possible to use a system that thermally decomposes urea water to generate ammonia as a reducing agent and supplies it onto the catalyst. It can also be used as an exhaust NOx purification catalyst.

The present invention will be specifically described below with reference to examples.
The powder X-ray diffraction patterns in the examples were measured with a RINT2000 type X-ray diffraction apparatus manufactured by Rigaku Corporation. The average particle diameter of the catalyst was determined by direct observation using a transmission electron microscope, and it was confirmed that the average particle diameter of the catalyst coincided with the value calculated by substituting the half width of the main peak of the powder X-ray diffraction pattern into the Scherrer equation. 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 synthesized mesoporous materials have peaks at specific pore diameter positions in an exponentially increasing distribution. This peak is called a pore peak for convenience. Thermal analysis for investigating the crystallinity of the material and the residual surfactant was measured with a DTA-50 type thermal analyzer manufactured by Shimadzu Corporation at a heating rate of 20 ° C. min ⁻¹ . Helium-diluted nitric oxide, oxygen, and reducing gas (ethylene or ammonia) were used as model gases for automobile exhaust NOx. The content of NOx contained in the treated gas was quantitatively analyzed according to the following zinc-reduced naphthylethylenediamine method (JISK 0104) to determine the treatment rate of nitric oxide. [Operation method] Collect the reaction gas in the Tedlar bag. Insert a gas tight syringe into the Tedlar bag containing the reaction gas and collect 20 ml of the reaction gas. The inside of the eggplant flask having a capacity of 100 ml with a three-way cock is evacuated, and the reaction gas in the gas tight syringe is introduced in its entirety. Add 20 ml of 0.1N ammonia water to the eggplant flask and leave for 1 hour. Add 1 ml of a solution of 1 g of sulfanilamide in a 10% aqueous hydrochloric acid solution, stir for about 30 seconds and let stand for 3 minutes. To this, 1 ml of a solution obtained by dissolving 0.1 g of N- (1-naphthyl) ethylenediamine dihydrochloride in 100 ml of distilled water is added, stirred for about 30 seconds, and allowed to stand for 20 minutes. This solution is put into a quartz cell (cell length: 10 mm), and the absorbance at 540 nm is measured. The reaction rate of nitric oxide was determined by the following formula (1).

"Comparative example 1" synthesis of comparative sample
An aqueous solution prepared by dissolving 0.215 g of PtCl ₄ · 5H ₂ O, 0.106 g of PdCl ₂ · 2H ₂ O and 0.162 g of Rh (NO ₃ ) ₃ · 2H ₂ O in 20 ml of distilled water is placed in an evaporating dish. 10 g of γ-alumina (fine particles with a particle size of 2 to 3 μm) was added to the solution, evaporated to dryness in a steam bath, and then vacuum dried at 100 ° C. for 3 hours. This sample was placed 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 precious metal content of about 2% by weight. This was used in a comparative experiment as a noble metal catalyst simulating a three-way catalyst.

Example 1 Synthesis of platinum / mesoporous silica 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 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 crystalline mesoporous silica material. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.2 nm, the specific surface area is 933 m ² / g, the pore volume is 1.35 cm ³ / g, and the pores are 2 to 50 nm. The volume was 1.34 cm ³ / g. An aqueous solution in which 0.267 g of H ₂ PtCl ₆ · 6H ₂ O is dissolved in 20 g of distilled water is placed in an evaporating dish, 5 g of the above mesoporous silica material is added thereto, evaporated to dryness in a steam bath, and then placed in a vacuum dryer. Vacuum drying was performed at 3 ° 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 mesoporous catalyst having a platinum content of about 2 mass%. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.

Example 2 Synthesis of Iridium / Mesoporous Silica Catalyst An aqueous solution of 0.175 g of H ₂ IrCl ₄ dissolved in 20 g of distilled water is placed in an evaporating dish, to which 5 g of the mesoporous silica material of Example 1 is added, and evaporated in a steam bath. After solidifying, it was put in a vacuum dryer and vacuum dried at 100 ° C. for 3 hours. This sample was placed 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 mesoporous catalyst having an iridium content of about 2 mass%. The average particle size of the iridium particles supported on the mesoporous catalyst was about 3.0 nm.

Example 3 Synthesis of platinum / mesoporous alumina 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, 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 contained dodecylamine to obtain a crystalline mesoporous alumina material. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.2 nm, the specific surface area is 870 m ² / g, the pore volume is 1.32 cm ³ / g, and pores of 2 to 50 nm are occupied The volume was 1.28 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 4 Synthesis of platinum / mesoporous zirconia catalyst
In a 1 liter beaker, add 210 g of distilled water, 114 g of ethanol and 32.7 g of 1-hexadecyltrimethylamine bromide, and slowly add dropwise a mixed solution of 140.1 g of 70% zirconium tetrapropoxide, 150 g of ethanol and 12 g of acetylacetone. did. The mixture was stirred at room temperature for 2 hours and then allowed to stand at 80 ° C. for 48 hours. This was transferred to a stainless steel autoclave and stirred at 160 ° C. for 24 hours to obtain a reaction mixture. The reaction mixture was filtered, washed with water, dried at 80 ° C., and the template was extracted and removed with an ethanol solution of 0.1 N hydrochloric acid. Next, after performing hot air drying at 110 ° C. for 1 hour, the contained template was completely removed by baking in air at 550 ° C. for 5 hours. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.5 nm, the specific surface area is 155 m ² / g, the pore volume is 0.48 cm ³ / g, and the volume occupied by 2 to 50 nm pores Was 0.42 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 5 Synthesis of platinum / mesoporous titania catalyst
In a 1 liter beaker, 210 g of distilled water, 114 g of ethanol, and 32.7 g of 1-hexadecyltrimethylamine bromide were added and dissolved. Under stirring, a mixed solution of 140 g of tetraisopropoxytitanium, 150 g of ethanol, and 12 g of acetylacetone was slowly added dropwise. The mixture was stirred at room temperature for 2 hours and then allowed to stand at 80 ° C. for 48 hours. This was transferred to a stainless steel autoclave and stirred at 160 ° C. for 24 hours to obtain a reaction mixture. The reaction mixture was filtered and washed with water, and the template was extracted and removed with a 0.1 N hydrochloric acid acidic ethanol solution. After drying with hot air at 100 ° C. for 5 hours, the contained template was completely removed by baking in air at 550 ° C. for 5 hours to obtain a mesoporous titania material. As a result of measuring the specific surface area and pore distribution by the nitrogen adsorption / desorption method, there is a pore peak at a position of about 5.2 nm, the specific surface area is 350 m ² / g, the pore volume is 0.56 cm ³ / g, 2 to 50 nm The volume occupied by the pores was 0.50 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 6 Synthesis of platinum / mesoporous silica alumina 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 24 g of aluminum isopropoxide were added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 100 ° C for 5 hours, and then in air at 550 ° C for 5 hours. The mesoporous silica alumina material was obtained by decomposing and removing the contained dodecylamine by firing. The Si / Al molar ratio was about 5. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 2.1 nm, the specific surface area is 1065 m ² / g, the pore volume is 0.73 cm ³ / g, and the pores are 2 to 50 nm. The volume was 0.51 cm ³ / g. Using 5 g of the synthesized mesoporous silica alumina, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

[Example 7] Synthesis of platinum-copper / mesoporous silica alumina catalyst An aqueous solution in which 0.023 g of H ₂ PtCl ₆ · 6H ₂ O and 2.85 g of cupric acetate were dissolved in 10 g of distilled water was placed in an evaporating dish. After adding 10 g of the mesoporous silica alumina material of Example 4 and evaporating to dryness in a steam bath, it was placed in a vacuum dryer and vacuum dried at 100 ° C. for 3 hours. This sample is placed in a quartz tube and reduced for 3 hours at 500 ° C in a helium-diluted hydrogen gas (10v / v%) stream. This mesoporous material has a platinum content of about 0.1% by weight and a copper content of about 10% by weight. A catalyst was synthesized.

Example 8: Synthesis of platinum / mesoporous borosilicate 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, 112 g of tetraethoxysilane and 5.4 g of trimethoxyborane were added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 100 ° C for 5 hours, and then in air at 550 ° C for 5 hours. By baking, the contained dodecylamine was decomposed and removed to obtain a mesoporous borosilicate material. The Si / B molar ratio was about 10. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 2.7 nm, a specific surface area of 1132 m ² / g, a pore volume of 0.92 cm ³ / g, and a volume occupied by pores of 2 to 50 nm Was 0.80 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 9 Synthesis of platinum-iridium / mesoporous borosilicate catalyst An aqueous solution prepared by dissolving 0.134 g of H ₂ PtCl ₆ .6H ₂ O and 0.125 g of H ₂ IrCl ₄ in 20 g of distilled water was placed in an evaporating dish. After adding 5 g of the mesoporous borosilicate material of Example 8 and evaporating to dryness in a steam bath, it was placed 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 mesoporous catalyst containing about 1% by mass of platinum and iridium.

Example 10: Synthesis of platinum / mesoporous titanosilicate 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, 124.8 g of tetraethoxysilane and an ethanol solution of tetraethoxytitanium (a solution of 9.1 g of tetraethoxytitanium in 5 g of ethanol) were added and stirred at room temperature for 22 hours. The product was filtered, washed with water, and washed at 100 ° C. Was dried in warm air 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 titanosilicate material. The Si / Ti molar ratio was about 10. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 2.6 nm, the specific surface area is 710 m ² / g, the pore volume is 0.60 cm ³ / g, and the volume occupied by the pores of 2 to 50 nm is It was 0.56 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 11: Synthesis of platinum / mesoporous stannous silicate 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, 99.6 g of tetraethoxysilane and an aqueous solution of ammonium tungstate (a solution of 17.87 g of ammonium tungstate pentahydrate in 40 g of distilled water) were added and stirred at room temperature for 22 hours, and the product was filtered and washed with water. Then, after drying in warm air at 100 ° C. for 5 hours, the dodecylamine contained was decomposed and removed by calcination at 550 ° C. in air for 5 hours to obtain a mesoporous silicate material. The Si / W molar ratio was about 10. 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 830 m ² / g, the pore volume is 0.65 cm ³ / g, the volume occupied by pores of 2 to 50 nm Was 0.60 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 12: Synthesis of platinum / mesoporous niobium silicate catalyst
In a 1 liter beaker, 150 g of distilled water, 120 g of ethanol, and 30 g of dodecylamine were added and dissolved. Under stirring, 62 g of tetraethoxysilane and an ethanol solution of pentaethoxyniobium (a solution of 9.5 g of pentaethoxyniobium in 5 g of ethanol) were added and stirred at room temperature for 22 hours. The product was filtered, washed with water and washed at 100 ° C. After drying in warm air for 5 hours, the dodecylamine contained was decomposed and removed by calcination in air at 550 ° C. for 5 hours to obtain a mesoporous niobium silicate material. The Si / Nb molar ratio was about 10. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 2.5 nm, the specific surface area is 757 m ² / g, the pore volume is 0.63 cm ³ / g, and the volume occupied by pores of 2 to 50 nm Was 0.60 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

Example 13: Synthesis of platinum / mesoporous cerium silicate 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, 124 g of tetraethoxysilane and an ethanol solution of tetraethoxycerium (a solution in which 19.05 g of tetraethoxycerium was dissolved in 20 g of ethanol) were added and stirred at room temperature for 22 hours, and then the product was filtered, washed with water, and washed at 100 ° C. After drying in warm air for 5 hours, the dodecylamine contained was decomposed and removed by baking in air at 550 ° C. for 5 hours to obtain a mesoporous cerium silicate material. The Si / Ce molar ratio was about 10. As a result of pore distribution and specific surface area measurement, there is a pore peak at a position of about 3.2 nm, the specific surface area is 850 m ² / g, the pore volume is 0.68 cm ³ / g, the volume occupied by pores of 2 to 50 nm Was 0.65 cm ³ / g. Using 5 g of this material, a mesoporous catalyst having a platinum content of about 2% by mass was synthesized in the same manner as in Example 1.

[Example 14] Synthesis of monolith catalyst 1 g of the catalyst of Example 1 and 0.1 g of colloidal silica were added to 10 ml of distilled water and stirred to prepare a slurry. To this, a mini-molded body (21 cells, diameter 8 mm x length 9 mm, weight 0.15 g) cut out from a commercially available cordierite monolith molded body (400 cells / in ² , diameter 118 mm x length 50 mm, weight 243 g) 5 samples were taken out, 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 weight of the mini-molded product, and the supported amount of platinum per mini-molded product was about 0.2% by mass.

[Example 15] NO _x treatment using ethylene as a reducing agent 0.3 g of the catalyst sample of the comparative example and the example was packed in a continuous flow reaction tube made of quartz, and nitrogen monoxide adjusted in concentration with helium was flow-treated. . The component molar concentrations of the gas to be treated were 0.1% nitric oxide, 14% oxygen, 10% water vapor, and 0.3% ethylene. The flow rate of the mixed gas introduced into the reaction tube was 100 ml / min, and the treatment temperature was 100 to 350 ° C. The exhaust gas was sampled every 50 ° C., and the purification rate of nitric oxide was determined. The results are shown in Table 1.
From Table 1, the mesoporous catalyst of the present invention, it can be seen that the NO _x in the hydrocarbon at a high concentration of oxygen presence using a reducing agent such as ethylene can efficiently purify even at a low temperature region. In particular, the platinum and platinum-iridium catalyst supported on the mesoporous borosilicate enabled efficient NO _x purification at 150 to 300 ° C., which was not used before. Therefore, it is understood that suitable waste NO _x treatment light duty diesel.

"Example 16"
Nitric oxide was treated with 0.3 g each of the catalyst of Example 8 and Example 14. The component molar concentration ratio of the gas to be treated was 0.1% nitric oxide, 1% oxygen, and 1% ethylene. The flow rate of the adjusting gas was 100 ml / min, and the processing temperature was 100 to 600 ° C. The NO _x contained in the exhaust gas after the treatment was determined purification treatment ratio of nitrogen monoxide was quantitatively analyzed. The results are shown in Table 2.
From Table 2, it can be seen that the mesoporous catalyst of the present invention can efficiently purify NO _x under rich burn conditions from a middle temperature region to a high temperature region using hydrocarbon as a reducing agent. Therefore, for example, if the lean burn and the rich burn are alternately performed, the catalyst of Example 5 can remove NOx in a wide temperature range. Therefore, the exhaust NOx of a small diesel vehicle capable of performing the lean burn and the rich burn alternately. It turns out that it is suitable for _x processing.

"Example 17" NO _x treatment Example 3 using ammonia as a reducing agent, examples 4, and Example 7 of the catalyst was treated with nitrogen monoxide using 0.3g respectively. The component molar concentration ratio of the gas to be treated was 0.1% nitric oxide, 14% oxygen, 10% water vapor, and 0.3% ammonia. The flow rate of the adjusting gas was 100 ml / min, and the processing temperature was 100 to 600 ° C. The NO _x contained in the exhaust gas after the treatment was determined purification treatment ratio of nitrogen monoxide was quantitatively analyzed. The results are shown in Table 3.
From Table 3, it can be seen that the mesoporous catalyst of the present invention can efficiently purify NO _x in the presence of high-concentration oxygen even when ammonia is used as a reducing agent. Therefore, it is understood that suitable for discharging _the NO _x purification process of a large diesel vehicles are equipped with urea supply system as ammonia source.

Mesoporous catalysts and monolithic catalyst of the present invention is useful as a diesel exhaust _the NO _x purification catalyst.

Claims (7)

Nano consisting of platinum particles and / or iridium particles having an average particle size of 1 to 20 nm as a main catalyst in a hardly soluble mesoporous material having pores with a diameter of 2 to 50 nm and a specific surface area of 100 to 1400 m ² / g. lean burn exhaust _the NO _x purification for mesoporous catalyst, wherein the particle is 0.01 to 20 wt% carrying catalyst was. The sparingly soluble mesoporous material is silica, alumina, zirconia, titania, silica-alumina, and composite materials thereof having substantially ² to 20 nm pores and a specific surface area of 100 to 1200 m ² / g as the main catalyst of platinum particles and / or an average particle size of the nanoparticles consisting of iridium particles 1 to 10 nm, lean burn exhaust NO _x according to claim 1 wherein the amount of supported nanoparticles, characterized in that from 0.1 to 10 wt% Purification mesoporous catalyst. The mesoporous material in which the sparingly soluble mesoporous material contains 1 to 20 mol% of at least one element selected from the group 3A element, group 3B element, group 4A element, group 5A element and group 6A element in the periodic table lean burn exhaust _the NO _x purification for mesoporous catalyst of claim 1 and second items, wherein it is a material. Lean burn exhaust _the NO _x purification for monolithic catalysts mesoporous catalyst of claims 1 3, characterized in that applied to the gas flow passage inner wall of the monolith formed body. The coating amount of the mesoporous catalyst in the monolith catalyst is 3 to 30% by mass of the monolith catalyst, the supported amount of platinum and / or iridium in the mesoporous catalyst is 0.1 to 10% by mass, and the platinum and / or iridium converted per monolith catalyst. claim 4 wherein the lean-burn exhaust _the NO _x purification for monolithic catalyst, wherein the carrying amount is 0.03 to 3 wt%. Claim 4 and with 5 of lean burn exhaust _the NO _x purification for monolithic catalyst, exhaust NOx purifying catalyst for small diesel performing rich burn and the lean burn alternately. Claim 4 and with 5 of lean burn exhaust _the NO _x purification for monolithic catalyst, exhaust NOx purifying catalyst for a large diesel for mounting a urea supply system.