JP2000350933A - Exhaust gas purifying catalyst and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To burn an alumina without turning the same into α and obtain a catalyst of superior hydrocarbon purifying performance by carrying a precious metal on alumina powder heat treated under specified conditions. SOLUTION: A catalyst used suitably for purifying exhaust gas exhausted out of two-wheel auto-vehicles, four-wheel auto-vehicles, and the like, particularly purifying the exhaust gas out of a two-stroke engine is prepared by carrying a precious metal on alumina powder heat treated at 1000 deg.C or higher for within one hour. The alumina powder to be used is preferably the largest size powder in the range of fine pore diameter of 50-500 angstrom pore diameter, and the alumina powder is preferably prepared by using a continuous modification oven. As the precious metal to be used, at least one or more kinds selected from platinum, rhodium and palladium is used. The alumina can be burnt without turning the same into α by using the above catalyst of superior hydrocarbon purifying performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and a method for producing the same, and more particularly, to purifying exhaust gas discharged from a motorcycle, a motorcycle, a special automatic machine, and more particularly to a two-stroke. The present invention relates to a catalyst suitably used for purifying exhaust gas from an engine and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a three-way catalyst in which a noble metal is supported on alumina is known as an exhaust gas purifying catalyst for a four-stroke engine used in automobiles and the like. JP-A-58-
Japanese Patent No. 30333 discloses a technique for improving durability and adhesion by subjecting alumina powder used in an alumina slurry to heat treatment at 1000 ° C. or higher to obtain α-alumina. In Japanese Patent Application Laid-Open No. Hei 8-206498, in a catalyst for purifying NOx in an oxygen-excess atmosphere (lean), alumina powder is heat-treated at 700 to 1000 ° C. for 1 hour or more to obtain the largest pore distribution at 30 to 130 °. The NOx purification rate is improved by using alumina.

[0003] However, the exhaust gas of a two-stroke engine used in a motorcycle or the like is different from the exhaust gas of a four-stroke engine, and particularly contains a large amount of hydrocarbon components. Therefore, α-alumina is used as described in JP-A-58-30333, or alumina having the largest pore distribution at 30 to 130 ° is used as described in JP-A-8-206498. For example, it was difficult to sufficiently purify. This is because the pores of alumina as disclosed in the above document are not optimal for purifying hydrocarbon components, and provide insufficient performance especially for exhaust gas purification for a two-stroke engine. Did not.

[0004]

Normally, when activated alumina is heat-treated at a temperature of 1000 ° C. or more, it becomes α-alumina. Will decrease. In view of the above-mentioned problems of the prior art, the present inventors have intensively studied to develop a method for producing a catalyst that does not become α-alumina and has excellent purification performance of hydrocarbons and the like. As a result, the present inventors set the heating temperature near the phase transition temperature of α-alumina (about 11
(00 ° C.) for a short time of about several minutes to prepare alumina having pores having a high peak around 200 ° in the pore distribution. Was found to be resolved. The present invention has been completed from such a viewpoint.

[0005]

That is, the present invention provides:
An object of the present invention is to provide a method for producing an exhaust gas purifying catalyst, wherein a noble metal is supported on alumina powder which has been subjected to a heat treatment at 000 ° C. or more and within 1 hour. Here, as the alumina powder, the largest powder having a pore volume of 50 to 500 ° in the range of pore diameter is used, and the powder having a pore diameter of 10 ° or less and a pore volume of 0.05 cc / g or less is used. Is preferred. Preferably, the alumina powder is prepared using a continuous shift furnace.

Further, the present invention provides a catalyst produced by the above method, wherein the heat-treated alumina is an alumina component other than α-alumina. is there. It is preferable that these catalysts carry at least one or more selected from the group consisting of platinum, rhodium and palladium as the noble metal. Further, the present invention relates to 10
Another object of the present invention is to provide an alumina slurry for an exhaust gas purifying catalyst, characterized in that the main component (50% by weight or more) is alumina powder which has been heat-treated at a temperature of 00 ° C. or more and within 1 hour.

[0007] According to the production method of the present invention, it is possible to obtain a catalyst which can be calcined without converting α into alumina and which has excellent hydrocarbon purifying performance. Effective as a catalyst for expensive two-stroke engines. In addition, by preparing in consideration of the pore distribution and pore volume ratio of alumina, it is possible to further improve the purification performance of hydrocarbons and reduce the burial of noble metals into alumina pores and improve durability. Can be. Hereinafter, the present invention will be described in detail.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the accompanying drawings. In the production method of the present invention, first, in the heat treatment step, the activated alumina is subjected to 1000 ° C. or more, preferably 1000 ° C. to 1200 ° C.
° C, particularly preferably 1050 ° C to 1150 ° C, within one hour, preferably 1 minute to 30 minutes, particularly preferably 3 minutes.
Heat treatment for 10 minutes to 10 minutes. The heat-treated alumina obtained here is preferably an alumina component other than α-alumina. FIG. 1 is a chart showing the results of X-ray diffraction of each alumina powder when heat treatment was performed at 1100 ° C. for 3 hours and when heat treatment was performed at 1100 ° C. for 6 minutes. As can be seen from FIG.
In the case of the heat treatment according to the present invention, even if the heat treatment is performed at 1100 ° C. or more, the treatment time is extremely shortened,
The crystal structure of alumina does not reach the α-structure, and becomes a so-called amorphous state before crystallization. On the other hand, when the heat treatment is performed for a long time, a crystallized structure is formed, which is not preferable.

As the heat-treated alumina powder, it is preferable to use the powder having the largest pore volume in the range of pore diameter of 50 to 500 ° from the viewpoint of improving exhaust gas purification performance. FIG. 2 shows pore distribution curves when various heat treatments are performed. The alumina powder heat-treated at 1100 ° C. for 6 minutes has a distribution having many pores in the range of 50 to 500 °. FIG. 3 shows, as an example, the hydrocarbon (HC) purification performance when alumina having pores in the above-mentioned range according to the production method of the present invention is used. It can be seen that the hydrocarbon purification rate is excellent. . As described above, it is preferable to use alumina having many pores in the range of 50 to 500 °. This is probably because the molecular weight of hydrocarbons is larger than NOx and CO, and alumina having a pore distribution larger than 30 to 130 ° which is effective for NOx purification is effective for purification of hydrocarbons.

On the other hand, the heat-treated alumina powder has a pore volume of less than 10 °
It is preferable to use a powder of c / g or less from the viewpoint of improving the durability of the purification catalyst. From the purification performance in FIG. 3, it can be seen that the heat-treated alumina of Example is more durable than the untreated (fresh) alumina of Comparative Example 1. This is considered to be because the pores of 10 ° or less shown in FIG. 2 are reduced by the heat treatment, so that the noble metal supported in this portion is buried. Table 1 described below shows a pore volume of 10 ° or less, but in order to impart durability, the pore volume of 10 ° or less is preferably set to 0.05 cc / g or less.

Next, in the production method of the present invention, a noble metal is supported on the heat-treated alumina powder. That is, one or more kinds of noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) are supported on the above-mentioned heat-treated alumina powder. By dispersing and supporting these noble metals in pores effective for purifying hydrocarbons, active points effective for purifying action can be obtained. In particular, it is effective for purifying exhaust gas of a two-stroke engine. In addition, it is possible to prevent loading on pores of 10 ° or less, which is significantly reduced due to thermal deterioration, and the durability is improved.

The above heat treatment step in the present invention can be performed, for example, in a batch type electric furnace or a continuous type electric furnace, but by using the continuous shift furnace 1 shown in FIG. 4, the purification performance is further improved. Alumina powder can be obtained. In this continuous shift furnace 1, heat treatment is performed in a reducing atmosphere, so that pores of 10 ° or less are reduced and 50 to 50
The number of pores of 0 ° can be increased, and a catalyst excellent in hydrocarbon purification performance can be obtained. As shown in FIG. 4, a continuous shift furnace mainly includes a heating portion and a cooling portion, and the entire process is about 30 minutes. can get. The catalyst according to the present invention is particularly effective for purifying exhaust gas from a two-stroke engine containing a large amount of hydrocarbons, but is also suitably used for purifying exhaust gas from a four-stroke engine. Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0013]

EXAMPLES Example 1, Comparative Examples 1 to 5 [Preparation Step] First, activated alumina was fired at 1100 ° C. for 6 minutes in the continuous shift furnace shown in FIG. An alumina slurry was prepared using the obtained alumina, wash-coated on a punching pipe, dried, and fired at 500 ° C. Next, when the total amount of precious metals is 2.0 g / m ² , Pt
It was carried so that the / Rh ratio became 5/1.

On the other hand, activated alumina was not treated (Comparative Example 1), 800 ° C., 20 hours (Comparative Example 2), 900 ° C., 2 hours.
After firing under the conditions of 0 hour (Comparative Example 3), 1000 ° C., 20 hours (Comparative Example 4), and 1100 ° C., 3 hours (Comparative Example 5), a catalyst was prepared in the same manner as in Example 1. The pore volume of 10 ° or less of the obtained catalyst was determined as shown in Table 1 below.
Shown in

[0015]

[Table 1]

[Evaluation] 1) Measurement of pore distribution The pore distribution was measured by a fully automatic gas adsorption amount measuring apparatus Autosorb-1 manufactured by Quantachrom. The measurement was performed by a constant volume method using physical adsorption of nitrogen gas at liquid nitrogen temperature.
The pretreatment was performed at 350 ° C. for 4 hours, using nitrogen as the adsorption gas and measuring at a temperature of 77 K which is the temperature of liquid nitrogen. 2) X-ray diffraction measurement X-ray diffraction measurement was performed using the X-ray diffractometer RU-200 manufactured by Rigaku Corporation.
X-rays were Cu K-α1, 40 kV, 100 mA. 3) Model gas measurement A stainless steel punching pipe coated with the catalyst was cut into a size of φ22 × 25, and evaluated under the conditions shown in Table 2 below. Here, THC indicates the concentration of all hydrocarbons, and the gas temperature before the catalyst indicates the gas temperature at the catalyst inlet.

[0017]

[Table 2]

FIG. 3 shows the evaluation results. FIG. 3 shows that the catalyst of the present invention is excellent in both hydrocarbon purification performance and durability.

[0019]

According to the production method of the present invention, it is possible to provide a catalyst which can be fired without converting alumina into α-form, and which has excellent hydrocarbon purification performance. In particular, it is effective as a catalyst for a two-stroke engine having a high hydrocarbon concentration in exhaust gas. In addition, by preparing in consideration of the pore distribution and pore volume ratio of alumina, it is possible to further improve the hydrocarbon purification performance and to reduce the burial of noble metals into alumina pores and improve durability. Can be.

In the production method of the present invention, by using a continuous shift furnace, alumina can be fired in a reducing atmosphere, and the pores of 50 to 500 ° are large and the pores of 10 ° or less are small. A catalyst with excellent purification performance can be provided. Further, the alumina slurry of the present invention has a small change in slurry viscosity with time, and a stable slurry is obtained,
Workability and productivity are improved.

[Brief description of the drawings]

FIG. 1 is a chart showing the results of X-ray diffraction of heat-treated alumina powder.

FIG. 2 shows pore distribution curves when various heat treatments are performed.

FIG. 3 is a diagram showing the purification rates of hydrocarbons (HC) in Examples and Comparative Examples.

FIG. 4 is a schematic configuration diagram showing an example of a continuous shift furnace;
(A) is an arrangement view viewed from above, and (b) is an arrangement view viewed from the side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Continuous transformation furnace 10 Thermocouple 11 1st cooling room 12 2nd cooling room 13 3rd cooling room 14 4th cooling room 15 Follower 16 Drive 17 Blower 18 Modification burner 19 Ultravision 20 Heating furnace 21 Exhaust duct 22 Exhaust fan a No treatment (fresh) b 800 ° C, 20 hours treatment c 900 ° C, 20 hours treatment d 1000 ° C, 20 hours treatment e 1100 ° C, 6 minutes treatment f 1100 ° C, 3 hours treatment

Continued on the front page (72) Inventor Ruri Higuchi 300 Takatsukacho, Hamamatsu-shi, Shizuoka Suzuki Co., Ltd. (72) Inventor Yukio Yamamoto 300 Takatsukacho, Hamamatsu-shi, Shizuoka Suzuki Co., Ltd. F-term (reference) 4D048 AA06 AA13 AA17 AA18 AB03 BA03X BA03Y BA30X BA30Y BA31X BA33X BA33Y BB01 BB05 CC39 CC52 4G069 AA03 AA08 BA01A BA01B BC71A BC71B BC72A BC75A BC75B CA03 CA09 DA05 EC11X EC12X EC14X EC15X EC22X EC22Y EC25 FB25

Claims (7)

[Claims] 1. A method for producing an exhaust gas purifying catalyst, wherein a noble metal is supported on alumina powder which has been subjected to heat treatment at 1000 ° C. or more for one hour or less. 2. The alumina powder having a pore volume of 5
2. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the largest powder in the range of the pore diameter of 0 to 500 [deg.] Is used. 3. The alumina powder having a pore volume of 1
The method for producing an exhaust gas purifying catalyst according to claim 1, wherein a powder having a pore diameter of 0 ° or less and 0.05 cc / g or less is used. 4. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein said alumina powder is prepared using a continuous shift furnace. 5. A catalyst produced by the method according to claim 1, wherein the heat-treated alumina is an alumina component other than α-alumina. . 6. A catalyst produced by the method according to claim 1, wherein at least one selected from the group consisting of platinum, rhodium and palladium is supported as the noble metal. An exhaust gas purification catalyst characterized by the above-mentioned. 7. An alumina slurry for an exhaust gas purifying catalyst, wherein an alumina powder subjected to heat treatment at 1000 ° C. or more for one hour or less is a main component.