JP2007222842A - CATALYST FOR CLARIFYING EMITTED NOx, AND ITS CARRIER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst which efficiently clarifies emitted diesel-based NOx, which is heretofore difficult to clarify, in a low-temperature range, and also provide a carrier thereof. <P>SOLUTION: Alumina or zirconia into which a specific functional group is incorporated is used as a carrier for carrying a catalyst for clarification of emitted NOx. In order to increase the activity at a low temperature of the catalyst, a meso porous material into which a specific functional group is incorporated is used as the carrier, the meso porous material having a high specific surface area. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust NOx purification catalyst and a carrier for supporting the catalyst. By using the catalyst of the present invention, the low-temperature activity of the automobile exhaust NOx purification catalyst can be dramatically improved.

  The three-way catalyst, which is the mainstream of exhaust gas purification catalysts for gasoline automobiles, uses a monolith molded body made of cordierite (mineral name) as a catalyst support, and several hundred nm as a catalyst on the inner wall of the gas flow path of the molded body It has a structure in which activated alumina (= γ-alumina) particles having a size of several μm to several tens of μm containing platinum-palladium-rhodium particles having a size of ˜several μm are applied. The activated alumina particles are agglomerates of fine particles of several tens nm to several hundreds nm, and the catalyst particles are adsorbed in the gaps between the fine particles. However, as will be described below, activated alumina has few pores and little spatial expansion, which is not advantageous for a gas phase catalytic reaction in which the contact area with the catalyst is a key.

On the other hand, synthetic zeolites with micropores and mesoporous materials with mesopores are mainly used as catalyst carriers for chemical synthesis, but they have a very large specific surface area and spread through a network. Since it is a porous material having a (pore channel), it is very advantageous for gas phase catalytic reactions.
In general, industrial catalysts are often used in a state where they are supported on a porous material. According to IUPAC (International Pure and Applied Chemical Association), the pores of the porous material are classified into micropores with a pore diameter of 2 nm or less, mesopores with 2 to 50 nm, and macropores with 50 nm or more. 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 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 activated alumina particles as the adsorbent is 110 to 340 m ² / g. The specific surface area of the catalyst is about ²⁰ to 40 m ² / g when estimated from the particle size. On the other hand, as described above, mesoporous materials having a specific surface area of 1000 m ² / g or more are known as industrial materials, and catalyst particles can be produced with a particle size of several nanometers due to the recent development of catalyst preparation methods. Yes. The catalyst particles of several nm alone have a specific surface area of about 1000 m ² / g. Therefore, although the conventional activated alumina particles have a specific surface area that is large enough to support the catalyst particles, it is difficult to say that they are sufficient to maximize the catalytic effect.

  From the above, it is conceivable to use a mesoporous material having a high specific surface area as a carrier for automobile catalysts, but the dramatic catalytic effect as expected even when using mesoporous alumina instead of conventional activated alumina Is not obtained. This is solved by simply replacing the exhaust NOx purification reaction of the automobile catalyst with a material having a high specific surface area because it is a very complicated reaction between the substrates (NOx, reducing agent, and oxygen) on the surface of the supported catalyst. It implies that it is not a simple problem that can be done. The reason why synthetic zeolite is not used as a carrier for automobile three-way catalysts is that aluminum, which is a component of synthetic zeolite, is eluted by high-temperature NOx and water vapor contained in the exhaust gas, and the pore structure of the carrier is destroyed. is there.

  In addition, the three-way catalyst is effective for purifying exhaust gas of gasoline vehicles, but there is also a problem that it is not used for purifying exhaust NOx of diesel vehicles that run on light oil fuel. This is due to the difference in qualitative and exhaust gas temperatures between exhaust gas from gasoline vehicles and diesel vehicles. The oxygen concentration of exhaust gas from gasoline vehicles is 1% or less, but since the air-fuel ratio of light oil is several times higher than the air-fuel ratio 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. The exhaust gas temperature of gasoline vehicles is usually 300 to 600 ° C., but the temperature of diesel exhaust gas is 120 to 200 ° C. during transient running and 200 to 400 ° C. during steady running. The reason why the above three-way catalyst cannot be used as a diesel exhaust gas purification catalyst is mainly due to the oxidative degradation of the catalyst due to the relatively high concentration of oxygen in the exhaust gas. There is also a problem that the catalytic activity for NOx in the region is remarkably low. Catalyst development for purifying NOx in the low temperature range of 120 to 200 ° C that diesel vehicles emit during transitional travel (approximately 80% of the exhausted NOx is exhausted during transitional travel) is also in the field of catalytic chemistry It is unsolved, and no practical catalyst for treating diesel exhaust gas is known at present.

JP-A-5-254827 Japanese National Patent Publication No. 5-503499 Japanese National Patent Publication No. 6-509374

  In view of the above circumstances, an object of the present invention is to provide a catalyst for dramatically improving the purification performance of an exhaust NOx purification catalyst for automobiles. Specifically, for example, it is to provide a lean burn exhaust NOx purification catalyst that can effectively perform diesel exhaust NOx purification in a low temperature range of 120 to 200 ° C., which has been difficult in the past.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the acid-treated oxide support is very effective for low-temperature activation of the catalyst. The present invention has been completed based on the above.
That is, this invention is invention of following (1)-(3).
(1) 1000cm ^-1 ~1250cm ^-1 to the carrier of the exhaust NOx purifying catalyst, characterized in that it is composed of at least one of alumina or zirconia with IR absorption bands.
(2) 1000 cm ^-1 alumina having an absorption band of IR to ～1250Cm ^-1 or zirconia, characterized in that it is a mesoporous material having a specific surface area of pore size and 100~1400m ² / g of 1~50nm claims Item 2. A catalyst carrier for exhaust NOx purification according to Item 1.
(3) The catalyst carrier having a platinum-containing catalyst supported on the carrier of the exhaust NOx purification catalyst described in (1) or (2) above is a structure in which the catalyst carrier is attached to the inner wall of the gas flow path of the monolith molded body. Monolith catalyst for purifying exhaust NOx.

  The catalyst supported on the carrier of the present invention can perform lean burn exhaust NOx treatment, which could not be achieved in the past, extremely efficiently, for example, even in a low temperature range of 120 to 200 ° C. For example, a conventional platinum catalyst supported on activated alumina has a purification rate of about 20% of nitric oxide in an atmosphere with an oxygen concentration of 14% or less at 200 ° C. or less, but the mesoporous alumina of the present invention was used as a carrier. The platinum catalyst can purify nitric oxide by 50% to 100% at a temperature of 160 to 200 ° C.

Hereinafter, the present invention will be described in detail.
One feature of the present invention is the use of alumina or zirconia with IR absorption band at 1000cm ^-1 ~1250cm ^-1 as a carrier of a catalyst for NOx purification. The trigger of the present invention was to discover that there is a difference in the low-temperature activity of the catalyst between the platinum catalyst supported on silica and the platinum catalyst supported on activated alumina. Conventionally, activated alumina (γ-alumina) has been mainly used as a carrier for automobile catalysts. Activated alumina produced by high-temperature firing is an amphoteric oxide having a specific surface area of usually 110 to 340 m ² / g, and is known to have a strong adsorption power for adsorbing catalytic metal ions. On the other hand, silica, which is an acidic oxide, has a specific surface area comparable to that of activated alumina, but has a weaker adsorption power for catalytic metal ions than activated alumina. This reason is considered to be caused by a special functional group present on the silica surface. However, the present inventors have found that an appropriate adsorptive power possessed by silica with respect to catalytic metal ions, that is, a special functional group greatly contributes to the improvement of the low-temperature activity of the catalyst. It has been found that this principle can be applied to oxides other than silica by introducing special functional groups on the surface of the oxide. Examples of such oxides include Group IIIb oxides such as alumina, Group IVa oxides such as zirconia, Group IIIa oxides such as yttria, lanthanum oxide, ceria, samarium oxide, and gadolinium oxide, and Group Va oxides such as Niobia. , Group VIa oxides such as molybdenum oxide and tungsten oxide, Group IIa oxides such as magnesia, calcia, and barium oxide, and composite oxides thereof. Of these, alumina, zirconia, and composite oxides thereof having a special functional group introduced are particularly preferable. The presence of the special functional group in the present invention the carrier can be observed by broad plurality of absorption bands at 1000cm ^-1 ~1250cm ^-1 region in the infrared absorption spectrum. The attribution of the newly introduced special functional group is an IR absorption band that does not exist in the original alumina and zirconia, and the absorption band overlaps with the absorption band of silica, so that M—O ⁻ ion (M = metal) and Though possible, the attribution is not clear at present. The introduction of the special functional group into the carrier is usually performed by boiling in an aqueous solution in which ordinary acids such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphoric anhydride, polyphosphoric acid, heteropolyacid, etc. are dissolved, After impregnating, a baking treatment at 200 to 800 ° C., a gas phase treatment at 200 to 800 ° C. with a mixed gas of acidic gas such as chlorine, nitrogen dioxide and sulfurous acid and water vapor, and the like can be performed.

Furthermore, the alumina or zirconia having a special functional group of the present invention is preferably a mesoporous material. The reason is that mesoporous materials have penetrating pores, so that the capture of the catalyst is strong, the effect of gas diffusion through the pore channels can be expected, and the preferred particles of the catalytically active species by controlling the pore distribution. This is because there are excellent effects such as that the diameter range can be maintained and that the catalyst is supported in the pores, thereby preventing reaggregation of the catalyst particles and achieving uniform and high dispersion of the catalyst. As will be described below, since the particle size of the catalyst particles exhibiting high activity with respect to NOx is nano-sized, the pore size 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. The pore diameter of the mesoporous material that is the carrier of the present invention is in the range of 1 to 50 nm, preferably in the range of 2 to 20 nm. Even if the pore diameter is less than 1 nm, the nanocatalyst can be supported, but considering the influence of contamination due to impurities etc., 1 nm or more is preferable. If it exceeds 50 nm, the nanocatalyst dispersed and supported tends to grow into giant particles by sintering under hydrothermal high temperature conditions and the like. Here, the pore diameter in the present invention refers to the value of the pore diameter (indicated by the diameter) that gives the maximum value in the pore distribution measured by the pore distribution measurement method using the BJH method. The specific surface area should be as high as possible unless there are special circumstances. The specific surface area of the mesoporous material of the present invention is 100 to 1400 m ² / g, preferably 200 to 1200 m ² / g, more preferably 400 to 1200 m ² / g. The specific surface area is preferably 100 m ² / g or more from the viewpoint of the amount of catalyst supported, while the specific surface area is preferably 1400 m ² / g or less from the viewpoint of material strength. Here, the specific surface area in the present invention is a surface area per 1 g of a substance obtained from a BET adsorption isotherm using physical adsorption of nitrogen.

  The method for synthesizing the mesoporous material used in the present invention is not particularly limited, and a desired material can be produced using a conventional method. For example, in accordance with a conventional method using a surfactant as a template for mesopores (for example, the above-mentioned Japanese Patent Application Laid-Open Nos. 5-2554827, 5-503499, and 6-509374) Can be manufactured. 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 among these, hydrophilic solvents such as water, methanol, ethanol, and propanol are 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, a compound having a metal coordination ability such as acetylacetone, tetramethylenediamine, ethylenediaminetetraacetic acid, pyridine, picoline and the like is preferable. The composition of the reaction system consisting of the precursor, surfactant, solvent and stabilizer is 0.01 to 0.60, preferably 0.02 to 0.50, and the precursor / surfactant molar ratio is 1 to 30 with respect to the composition of the precursor. The molar ratio of solvent / surfactant is 1-1000, preferably 5-500, and the molar ratio of stabilizer / main agent 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. As described above, the method of introducing a special functional group into the obtained mesoporous material is usually boiled in an aqueous acid solution, impregnated with an aqueous acid solution into a carrier, and calcined at 200 to 800 ° C., It can be carried out by gas phase treatment at 200 to 800 ° C. with a mixed gas of acidic gas such as chlorine, nitrogen dioxide, sulfurous acid and water vapor.

Next, the catalysts supported on the carrier of the present invention are mostly known catalysts for the purpose of NOx purification treatment and catalysts under research. For automobiles, a conventional three-way catalyst for gasoline cars or a catalyst mainly composed of platinum can be used. However, as a catalyst for diesel cars, a platinum-containing catalyst is preferable. Moreover, a copper-type or iron-type catalyst is preferable for the factory exhaust NOx treatment.
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 effective activity for the target NOx decomposition purification treatment in the present invention is in the range of 1 to 20 nm, and particularly in the range of 1 to 10 nm. The supported amount of the platinum-containing catalyst supported on the support of the present invention is 0.01 to 20% by mass, preferably 0.1 to 10% by mass, but is usually several% by mass if there is no quantitative problem. . The supported amount of the catalyst can be 20% by mass or more. However, if the supported amount is excessive, the catalyst in the deep pores that hardly contribute to the reaction increases, so 20% by mass or less is preferable. Moreover, 0.01 mass% or more is preferable in order to obtain sufficient catalytic activity. By adding a co-catalytic component having a different function to the platinum catalyst, the catalytic 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, palladium, Examples thereof include rhodium, iridium, rhenium and their compounds. 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 Preference is given to manganese, tungsten oxide which is an acidic oxide having an oxidizing power, copper-zinc, iron-chromium, molybdenum oxide effective for preventing SOx poisoning, iron, tungsten, rhodium, iridium, rhenium, etc. having an anti-sintering effect . The amount of this component added is usually about 1/100 to 100 times the mass of the platinum catalyst, but may be 100 times or more as required.

  When the catalyst of the present invention is used as a catalyst for purifying NOx for automobiles, the carrier of the present invention is usually attached to the inner wall of the gas flow path of the monolith molded body that is a support for the automobile catalyst, and then the catalyst is supported on this. In the form (for convenience, this is referred to as a monolith catalyst). The monolith molded body as used herein refers to a molded body in which the cross section of the molded body is mesh-shaped and provided with gas flow paths partitioned by thin walls parallel to each other in the axial direction. Although the external shape of a molded object is not specifically limited, Usually, it is a cylindrical shape. The monolith catalyst is usually produced by a method in which a support material is previously attached to the inner wall of the gas flow path of the monolith molded body, and then the catalyst is supported. And a method of attaching to the inner wall of the flow path. Further, the adhesion of the carrier material to the inner wall of the gas flow path of the monolith molded body is a conventional method in which the mixed slurry of the carrier material and the binder is applied to the inner wall of the gas flow path of the monolith molded body, dried and fired, The carrier material precursor can be deposited on the inner wall of the gas channel by a chemical vapor deposition (CVD) method or the like, followed by drying and firing. In the former conventional method, it can be manufactured according to a method for manufacturing a monolith molded article to which a three-way catalyst for automobiles is attached. For example, a mixture of the present invention carrier and alumina sol or colloidal silica as a binder is usually mixed at a mass ratio of 1: (0.01 to 0.2), and this is dispersed in water to prepare a slurry of usually 10 to 50% by mass. After the adjustment, the monolith molded body is immersed in the slurry to adhere the slurry to the inner wall of the gas flow path of the monolith molded body, and after drying, for several hours at 500 to 1000 ° C. under an inert atmosphere of nitrogen, helium, argon, etc. A monolith molded body coated with a carrier is produced by heat treatment. As the binder other than the above, methylcellulose, acrylic resin, polyethylene glycol, and the like can be used as appropriate. In the latter method, a surface active agent and a condensing agent are attached in advance to the inner wall of the gas flow path of the monolith molded body, and a gas containing the carrier precursor is brought into contact therewith to thereby form a thin-film intermediate substance. The thin film carrier material is deposited by depositing, drying and baking. As the surfactant and the condensing agent, materials used in the production of mesoporous materials can be used. As the carrier precursor, metal alkoxides, halides, hydrides, organometallic compounds, and the like that are volatile or sublimable at room temperature and pressure can be used. 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 , Polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester and the like can be used. As the condensing agent, usual acidic substances such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, phosphoric anhydride, heteropolyacid, acetic acid and the like can be used. The reaction temperature and reaction time for forming a thin film are from several tens of seconds to several tens of hours in the range of minus temperature to several hundreds of degrees centigrade, and the firing temperature is usually from 500 ° C. to 1000 ° C. for several tens of minutes to several tens of hours. These conditions are preferably selected based on the chemical and physical properties of the support precursor.

Next, the catalyst is supported on the monolith molded body usually 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, the monolith molded body coated with the carrier of the present invention is immersed in an aqueous solution of a catalyst raw material, filtered, dried, washed with water as necessary, and reduced 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. As a raw material for the promoter component added to the platinum catalyst as necessary, for example, water-soluble salts such as chloride, nitrate, sulfate, carbonate and acetate can be used. 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. As another method, a catalyst may be supported on the carrier of the present invention in advance and applied to a monolith molded body. The coating amount of the catalyst per monolith molded body is preferably 0.01 to 10% by mass. When the coating exceeds 10%, gas diffusion to the catalyst existing inside the carrier is slow, so 10% or less is preferable. In order to obtain sufficient catalyst performance, 0.01% or more is preferable. The thickness of the catalyst layer applied to the molded body is usually preferably 1 μm to 100 μm, and particularly preferably 10 μm to 50 μm. In order to obtain a sufficient diffusion rate of the reaction gas, it is preferably 100 μm or less, and preferably 1 μm or more from the viewpoint of preventing deterioration of catalyst performance.

  When the monolith catalyst is mounted on an automobile, particularly a diesel automobile, the lean burn exhaust NOx discharged by the automobile can be extremely effectively purified in a wide temperature range of 150 to 700 ° C. Although a reducing agent is required for the treatment of exhaust NOx, in the case of small cars such as passenger cars, lower olefins and lower paraffins having 1 to 6 carbon atoms contained in a small amount of light oil as fuel become reducing agents. The fuel may be supplied directly or through the reformer onto the catalyst. 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. For factory exhaust NOx, it can also be used as a purification catalyst using ammonia as a reducing agent.

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 synthesized mesoporous materials have peaks at specific pore diameter positions in an exponentially increasing distribution. The pore diameter at this time is the pore diameter. The surface hydroxyl group was measured using an infrared absorption spectrum measuring apparatus (JASCO FT-IR460). The thermal analysis for examining the residual surfactant of the material was measured with a DTA-50 type thermal analyzer manufactured by Shimadzu Corporation at a temperature rising 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 treatment rate of nitric oxide was calculated according to the following equation (1) by measuring NOx contained in the treated gas with a reduced pressure chemiluminescence NOx analyzer (manufactured by Nippon Thermo Co., Ltd .: model 42C).

Comparative Example 1 Synthesis of [Pt-Pd-Rh / γ-alumina] catalyst 10 g of γ-alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m ² / g, pore diameter 6.2 nm) is 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 were dissolved in 20 g of an aqueous solution, evaporated to dryness, and then vacuum dried at 120 ° C. for 3 hours. . The 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 platinum content of about 2% by mass. This was used in a comparative experiment as a noble metal catalyst simulating a three-way catalyst.

Comparative Example 2 Synthesis of Comparative Sample [Platinum / γ-Alumina] Catalyst γ-Alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m ² / g, pore diameter 6.2 nm) is 0.267 g of PtCl ₄ .5H ₂ O The solution was put into 10 g of an aqueous solution in which the solution was dissolved, evaporated to dryness, and then vacuum dried at 120 ° C. for 3 hours. The 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 platinum content of about 2% by mass.

Comparative 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 mesoporous alumina. 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 380 m ² / g, the pore volume is 0.32 cm ³ / g, and the pores are 2 to 50 nm. The volume was 0.32 cm ³ / g. Next, 5 g of the sample was placed in 10 g of an aqueous solution in which 0.267 g of PtCl ₄ .5H ₂ O was dissolved, evaporated to dryness, and then vacuum dried at 120 ° 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 platinum content of about 2% by mass.

Comparative Example 4 Synthesis of [Platinum / Zirconia] Catalyst An aqueous solution in which 5 g of zirconia (manufactured by Daiichi Rare Element Co., Ltd .: specific surface area 128 m ² / g, pore diameter 7 nm) is dissolved in 0.267 g of PtCl ₄ .5H ₂ O After putting into 10 g and evaporating to dryness, vacuum drying was performed at 120 ° 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 platinum content of about 2% by mass.

Comparative Example 5 Synthesis of [Platinum / Activated Alumina / Monolith] Catalyst 10 g of 10 g of γ-alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m ² / g, fine particles with a pore diameter of 6.2 nm, particle diameter of 2 to 3 μm) Add to 100 g of an alumina sol aqueous solution and stir. A mini-molded body (21 cells, diameter 8 mm × length 9 mm) cut from a commercially available cordierite monolith molded body (manufactured by NGK, 400 cells / in ² , diameter 118 mm × length 50 mm, weight 243 g), 5 pieces (0.15 g in weight) were placed and allowed to stand for 10 minutes, and then the molded body was taken out and heated at 300 ° C. for 1 hour. This operation was repeated 5 times and then calcined in air at 500 ° C. for 3 hours. The coating amount of γ-alumina was about 10% by mass of the mini-molded body, and the thickness of the coating layer was about 100 μm. Next, this molded body was immersed in 10 g of an aqueous solution in which 0.0267 g of PtCl ₄ .5H ₂ O was dissolved for 1 hour, and then the molded body was taken out and vacuum dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and heat-treated at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream to synthesize a monolith catalyst having a platinum content of about 2% by mass.

Example 1 Synthesis of [platinum / special functional group-introduced γ-alumina] catalyst 10 g of γ-alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m ² / g, pore diameter 6.2 nm) 1% sulfuric acid and 1 nitric acid It was put into 1000 g of an aqueous solution containing 5% by mass, boiled for 3 hours, filtered, washed with water, and vacuum dried at 200 ° C. for 3 hours. As a result of measuring the infrared absorption spectrum, .gamma.-alumina new absorption band in 1158cm ^-1 and 1077 cm ^-1 in addition to absorption bands were observed (as shown in Table 1). Next, 5 g of the sample was placed in 10 g of an aqueous solution in which 0.267 g of PtCl ₄ .5H ₂ O was dissolved, evaporated to dryness, and then vacuum dried at 120 ° 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 platinum content of about 2% by mass.

Example 2 Synthesis of [platinum / special functional group-introduced 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 mesoporous alumina. 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 380 m ² / g, the pore volume is 0.32 cm ³ / g, and the pores are 2 to 50 nm. The volume was 0.32 cm ³ / g. Next, 10 g of the obtained mesoporous alumina was added to 1000 g of an aqueous solution containing 0.1% by mass of sulfuric acid and 0.1% by mass of nitric acid, followed by boiling treatment for 3 hours, filtration, washing with water, and vacuum drying at 200 ° C. for 3 hours. As a result of measuring the infrared absorption spectrum, a new absorption band in 1158cm ^-1 and 1077 cm ^-1 in addition to the absorption band of the mesoporous alumina was observed (as shown in Table 1). Next, a catalyst having a platinum content of about 2% by mass was synthesized by the same method as in Example 1 using the obtained sample.

Example 3 Synthesis of [platinum / special functional group-introduced zirconia] catalyst 10 g of zirconia (manufactured by Daiichi Rare Element Co., Ltd .: specific surface area 128 m ² / g, pore diameter 7 nm) 1% by mass of sulfuric acid and 1% by mass of nitric acid It was put into 1000 g of the aqueous solution contained, and boiled for 1 hour, filtered, washed with water, and vacuum dried at 200 ° C. for 3 hours. As a result of measuring the infrared absorption spectrum, 1211cm ^-1 in addition to the absorption bands of zirconia, a new absorption band was observed in 1114Cm ^-1 and 1047cm ^-1 (according to Table 1). Next, a catalyst having a platinum content of about 2% by mass was synthesized by the same method as in Example 1 using the obtained sample.

Example 4 Synthesis of [Platinum / Special Functional Group-Introduced Mesoporous Alumina / Monolith] Catalyst 10 g of the special functional group-introduced mesoporous alumina prepared in Example 2 is added to 100 g of an aqueous 10 mass% alumina sol solution and stirred. A mini-molded body (21 cells, diameter 8 mm × length 9 mm) cut from a commercially available cordierite monolith molded body (manufactured by NGK, 400 cells / in ² , diameter 118 mm × length 50 mm, weight 243 g), 5 pieces (0.15 g in weight) were placed and allowed to stand for 10 minutes, and then the molded body was taken out and heated at 300 ° C. for 1 hour. This operation was repeated 5 times and then calcined in air at 500 ° C. for 3 hours. The coating amount of the special functional group-introduced mesoporous alumina was about 10% by mass of the mini-molded body, and the thickness of the coating layer was about 100 μm (described in Table 1). Next, this molded body was immersed in 10 g of an aqueous solution in which 0.0267 g of PtCl ₄ .5H ₂ O was dissolved for 1 hour, and then the molded body was taken out and vacuum dried at 120 ° C. for 3 hours. This sample was put in a quartz tube and heat-treated at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream to synthesize a monolith catalyst having a platinum content of about 2% by mass.

“Comparative Examples 6 to 10” NOx treatment under lean burn conditions using ethylene as a reducing agent Each of the powdered catalyst samples of Comparative Examples 1 to 4 was charged in a continuous flow reaction tube made of quartz by 0.3 g. Two monoliths of 5 monolith catalysts were filled and treated with nitrogen monoxide adjusted in concentration with helium. 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 per minute, and the treatment temperature was 160 to 300 ° C. NOx contained in the treated gas was measured to determine the treatment rate of nitric oxide. The results are shown in Table 2.

“Examples 5 to 8” Lean burn NOx treatment using ethylene as a reducing agent Each of the powdery catalyst samples of Examples 1 to 3 was charged in a continuous flow reaction tube made of quartz in an amount of 0.3 g, and the monolith of Example 4 Two catalyst compacts were filled, 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 per minute, and the treatment temperature was 160 to 300 ° C. NOx contained in the treated gas was measured to determine the treatment rate of nitric oxide. The results are shown in Table 2. Table 2 shows that the platinum catalyst supported on the carrier of the present invention can efficiently purify NOx in the presence of high-concentration oxygen even in a low temperature region by using a hydrocarbon such as ethylene as a reducing agent. In particular, the platinum catalyst supported on the special functional group-introduced mesoporous alumina (catalysts of Examples 2 and 4) enabled efficient NOx purification at 160 to 200 ° C., which has never been achieved. Therefore, it turns out that it is suitable for the exhaust-NOx process of a small diesel vehicle.

[Example 9] Rich burn NOx treatment using ethylene as a reducing agent Nitric oxide was treated using 0.3 g of the mesoporous alumina-supported catalyst of Example 2. 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 adjustment gas was 100 ml per minute, and the treatment temperature was 200 to 600 ° C. NOx contained in the exhaust gas after the treatment was measured to determine the purification rate of nitric oxide. The results are shown in Table 3. From Table 3, it can be seen that the mesoporous alumina-supported catalyst using the carrier of the present invention can efficiently purify NOx under rich burn conditions from 250 ° C. to 600 ° C. using hydrocarbon as a reducing agent. Therefore, for example, if lean burn and rich burn are alternately performed, the catalyst supported on the carrier of the present invention can remove NOx in a wide temperature range. Therefore, a compact diesel vehicle capable of alternately performing lean burn and rich burn can be used. It can be seen that it is suitable for exhaust NOx treatment.

"Example 10" NOx treatment using ammonia as a reducing agent Nitric oxide was treated using 0.3 g of the mesoporous alumina supported catalyst of Example 2. 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 adjustment gas was 100 ml per minute, and the treatment temperature was 100 to 600 ° C. NOx contained in the exhaust gas after the treatment was measured to determine the purification rate of nitric oxide. The results are shown in Table 4. Table 4 shows that the mesoporous catalyst using the carrier of the present invention can efficiently purify NOx in the presence of high-concentration oxygen even when ammonia is used as a reducing agent. Therefore, it turns out that it is suitable for the exhaust-NOx purification process of the large-sized diesel vehicle carrying the urea supply system as an ammonia source.

  The carrier of the present invention is useful as a carrier for automobile exhaust NOx purification catalyst, particularly as a diesel exhaust NOx purification catalyst carrier.

Claims (3)

Carrier of the exhaust NOx purifying catalyst, characterized in that the 1000cm ^-1 ~1250cm ^-1 is configured from at least one of alumina or zirconia with IR absorption bands. To 1000cm ^-1 ~1250cm ^-1 alumina or zirconia with IR absorption bands, in claim 1, characterized in that the mesoporous material having a specific surface area of pore size and 100~1400m ² / g of 1~50nm A catalyst carrier for exhaust NOx purification as described. 3. A monolith for purifying exhaust NOx, characterized in that a catalyst support in which a platinum-containing catalyst is supported on the support of the catalyst for purifying exhaust NOx according to claim 1 or 2 is attached to an inner wall of a gas flow path of the monolith molded body. catalyst.