JP2004105787A - Manufacturing method for catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a high active catalyst for cleaning exhaust gas in which a porous carrier is uniformly carried with a catalyst component. <P>SOLUTION: In the manufacturing method for a catalyst for cleaning exhaust gas, after the base material is carried with the catalyst component, it is dried and calcined. A pH adjusting agent is added to acidic sol containing the catalyst component to adjust the pH to a pH area where the sol becomes unstable. Thereafter, it is impregnated to the porous carrier in the state that urine or a urine derivative coexists and is heated in the state that drying is restricted. The impregnated catalyst component-containing sol is subjected to gelation and is dried and calcined. <P>COPYRIGHT: (C)2004,JPO

Description

【００２４】
表１から、触媒体寸法が５０ｍｍと短いために、実用時のガス流れ方向と平行方向での担持量に大きな差は見られなかったが、垂直方向の分布は比較例で担持量が大きく変化し、表面の担持量が多くなっていることが分かる。これに対し、各実施例では表面から中心部まで触媒成分が均一に担持されていることが分かる。
【００２５】
なお、垂直方向の担持量の分布は、

として、平行方向の担持量の分布は、

として求めたものである。
【００２６】
【発明の効果】
本願の請求項１に記載の発明によれば、触媒活性成分および／または触媒担体成分が均一に担持され、安定した高活性の排ガス浄化用触媒が得られる。
本願の請求項２に記載の発明によれば、上記発明の効果に加え、より触媒活性に優れた排ガス浄化用触媒が得られる。
【００２７】
本願の請求項３に記載の発明によれば、上記発明の効果に加え、水分移動の影響を極力排除して触媒成分の担持量がより均一な触媒が得られる。
本願の請求項４に記載の発明によれば、上記発明の効果に加え、触媒活性がより高い排ガス浄化用触媒が得られる。
【図面の簡単な説明】
【図１】触媒成分の濃度分布測定位置を示す説明図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst including a catalyst-supporting particulate removal filter in which a catalyst component is supported on a porous carrier, and which is discharged from an internal combustion engine such as a diesel engine. The present invention relates to a method for producing an exhaust gas purifying catalyst capable of efficiently removing fine particles in exhaust gas to be discharged.
[0002]
[Prior art]
As a method for producing an exhaust gas purifying catalyst, a method of applying a catalyst component to a metal or inorganic fiber base material and a method of extruding the catalyst component into a honeycomb shape by a molding machine are widely known. In addition, for a honeycomb catalyst, a production method is known in which a porous carrier such as cordierite is preliminarily molded, and then a catalyst component is supported. Is widely used as a catalyst component.
[0003]
However, in the above catalyst production method, as the volume of the catalyst increases, the rate of increase in the internal temperature during drying decreases, and since the catalyst dries from the surface, the water inside the catalyst moves to the surface during drying, and this water content increases. Since the catalyst component also moves to the surface with the transfer of the catalyst, there has been a problem that the amount of the catalyst component carried becomes uneven at the central portion and the surface layer portion of the catalyst. Further, when the internal temperature is increased while restricting the drying, the dripping of the water increases, and it is difficult to eliminate the unevenness in the amount of the catalyst component carried.
[0004]
If the carried amount of the catalyst component becomes uneven, the catalytic activity is reduced in the portion where the carried amount is small, and it becomes impossible to obtain sufficient catalytic performance as a whole. Therefore, in order to solve such a problem, it is conceivable to increase the supported amount of the catalyst component as a whole. However, this would increase the required amount of the catalyst component and increase the cost.
[0005]
Therefore, it is desired to develop a technique for uniformly supporting a catalyst active component or a catalyst carrier component (hereinafter, also simply referred to as a catalyst component) on a catalyst substrate. When drying the substrate impregnated with the catalyst component, heat input is required. A technique has been proposed in which the rate of water generation is limited by limiting the rate, thereby ensuring uniform dispersibility of the catalyst component (for example, see Patent Document 1). In addition, as a related technique, a solution containing a hydrolyzable liquid or soluble compound is adjusted to pH, and then an aqueous acidic catalyst is added to polymerize the obtained gel. The obtained gel is slowly dried and calcined. There is a method for producing a fixed mixed metal oxide (for example, see Patent Document 2).
[Patent Document 1] Japanese Patent Application Laid-Open No. Hei 9-117668 [Patent Document 2] Japanese Patent Application Laid-Open No. 11-500995 [0006]
[Problems to be solved by the invention]
However, even in the above-mentioned prior art, the catalyst component cannot be sufficiently uniformly supported on the porous carrier as the catalyst base material, and an improvement thereof has been desired.
An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a highly active exhaust gas purifying catalyst in which a catalytically active component or a catalyst carrier component is uniformly supported on a porous carrier. .
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted extensive studies on a method of impregnating and supporting a catalyst component on a porous carrier, and a method of drying and calcining the obtained impregnated body. Although the stable pH range differs depending on the type of sol, gelation and precipitation tend to occur if the sol is outside the stable pH range. After being adjusted so that the porous carrier is impregnated with urea or a urea derivative in the presence of the urea derivative, and supported, and then gelled and precipitated, the influence of moisture transfer by drying is small, and the catalyst component is reduced. Heating is effective to uniformly support the porous carrier and (2) promote gelation and precipitation of the acidic sol, but by heating in a state where drying is restricted, It found that liquid dripping like with increasing carrier unevenness and vapor pressure due to 燥速 is too fast is prevented, in which have reached the present invention.
[0008]
That is, the invention claimed in the present application is as follows.
(1) In a method for producing an exhaust gas purifying catalyst in which a catalyst active component and / or a catalyst carrier component is supported on a substrate, and then dried and calcined, the acidic sol containing the catalyst active component and / or the catalyst carrier component is preferably After adding a pH adjuster to adjust the acidic sol to a pH range in which the acid sol becomes unstable, or impregnating the porous carrier in the presence of urea or a urea derivative, heating with limiting drying, A method for producing an exhaust gas purifying catalyst, comprising: gelling a sol containing a catalyst active component and / or a catalyst carrier component impregnated in a porous carrier, followed by drying and calcining.
[0009]
(2) The method for producing an exhaust gas purifying catalyst according to the above (1), wherein a solution containing an alkaline earth metal element or a rare earth element is used as the pH adjuster.
(3) The heating in a state where the drying is restricted is performed by covering a side surface of the porous carrier impregnated with the catalytically active component and / or the catalytic carrier component, which is parallel to a gas flow direction in practical use, with a heat-resistant rubber, Alternatively, the method for producing an exhaust gas purifying catalyst according to the above (1) or (2), wherein the whole is covered with a vinyl sheet and brought into contact with heated air.
(4) A method for producing an exhaust gas purifying catalyst, characterized by further impregnating the exhaust gas purifying catalyst produced by any one of the above methods (1) to (3) with a catalytically active component, followed by drying and calcining.
[0010]
In the present invention, examples of the catalytically active component include Pt, Pd, Rh and the like, and examples of the catalyst carrier component include Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO _{2 and the} like. As the porous carrier, for example, porous cordierite, paper honeycomb or the like is suitably used.
[0011]
In the present invention, the stable pH range and unstable pH range of an acidic sol containing a catalyst component differ depending on the type of sol. For example, the stable pH range of an acidic sol obtained by mixing alumina sol and cerium sol at a weight ratio of 2: 1 is, for example, The pH is 3-4.5, and the unstable pH region is, for example, pH = 5 or more.
[0012]
In the present invention, as the pH adjusting agent added to the acidic sol containing the catalyst component, a solution containing an alkaline earth metal element or a rare earth element is suitably used, and the alkaline earth metal element or the rare earth element is used as a catalyst component. More preferably, it functions. Further, as the pH adjuster, for example, an alkaline aqueous solution that is decomposed by baking such as ammonia water can be used.
[0013]
In the present invention, instead of adjusting the pH of the acidic sol containing the catalyst component, the acidic sol may be impregnated into a porous carrier in the presence of urea or a urea derivative, and then heated. In this case, when the acidic sol-impregnated porous carrier is heated above the thermal decomposition temperature of urea or a urea derivative, ammonia is generated by thermal decomposition, whereby the acidic sol can be neutralized to an unstable pH range. . For example, when urea is used, the following thermal decomposition reaction proceeds when the acidic sol-impregnated porous carrier is heated to about 90 ° C. or higher.
[0014]
That is, on the acidic side, as shown in the following formula (1), ammonia is generated, absorbed by water, and subjected to a neutralization reaction.
_{(NH 2) 2 CO + 3H} 2 O → 2NH 4 + + CO 2 + 2OH - ·· (1)
On the other hand, on the alkaline side, oxonium ions are generated, absorbed by water and subjected to a neutralization reaction as shown in the following formula (2).
_{(NH 2) 2 CO + 4H} 2 O → 2NH 3 + CO 3 2- + 2H 3 O + ··· (2)
At this time, the concentration distribution of urea in the sol is uniform, the gelation of the solution proceeds uniformly and vigorously, and the fluidity is lost, so that the catalyst component is uniformly supported without being affected by the movement of moisture during drying. Become like
[0015]
In the present invention, the porous carrier impregnated with the acidic sol is heated to promote the gelation and precipitation of the acidic sol, but the drying is restricted in order to increase the drying speed and prevent dripping due to the heating. It is heated in the state. Heating in a state where drying is restricted means, for example, when the catalyst is applied to actual exhaust gas (hereinafter referred to as “practical use”), the side of the catalyst body which is parallel to the gas flow direction is heated with heat-resistant rubber. And a method in which the object to be heated is heated while being covered with a vinyl sheet. As a result, it is possible to eliminate unevenness in loading of the catalyst component caused by unevenness in drying, and to prevent loss of the catalyst body due to handling during manufacture. At this time, it is preferable that the catalyst component-impregnated porous support is brought into contact with heated air while being turned upside down. Further, the whole may be uniformly heated by a microwave or the like.
[0016]
In the present invention, impregnation of the porous carrier with the catalyst component is performed, for example, by immersing the porous carrier in a catalyst component-containing sol.
In the present invention, the prepared catalyst for purifying exhaust gas may be further impregnated with a catalytically active component and supported thereon, if necessary, to obtain a more active catalyst.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in detail with reference to examples.
Example 1
An impregnating solution was prepared by adding 3.5% by weight of urea to an aqueous solution in which alumina sol (Nissan Chemical Co., Alumina Sol 200) and cerium sol (Taki Chemical Co., Ltd., Niedral) were mixed at a weight ratio of 2: 1. A particulate filter (manufactured by Hitachi Metals, porous cordierite) is immersed and impregnated, drained by centrifugation, placed in a plastic bag and sealed to limit drying, and placed for 10 to 30 minutes After curing at 100 ° C. for 8 hours, the product was taken out of a plastic bag, dried at 150 ° C. for 6 hours, and calcined at 500 ° C. for 2 hours to obtain a catalyst. The obtained catalyst was impregnated with dinitrodiammineplatinum nitrate and supported, cured under the same conditions as above, dried at 150 ° C. for 6 hours, and calcined at 550 ° C. for 2 hours to obtain an oxidation catalyst for exhaust gas purification. .
[0018]
FIG. 1 shows a cross-sectional view of the obtained catalyst body cut in half along the gas flow direction. The catalyst composition at points A to D in FIG. 1 was measured by X-ray fluorescence analysis to determine the supported amount. The supported amounts of the catalyst carrier components at points A to D were 47 (g / L) and 43 ( g / L), 60 (g / L) and 54 (g / L). The supported amounts of the catalytically active components at points A to D are 1.0 (g / L), 1.0 (g / L), 1.1 (g / L), and 1.0 (g / L), respectively. )Met.
[0019]
Example 2
A catalyst was prepared and analyzed in the same manner as in Example 1 except that a small amount of aqueous ammonia was added instead of urea in Example 1 and an impregnating solution adjusted to pH = 4.5 was used. As a result, the supported amounts of the catalyst carrier components at points A to D in FIG. 1 were 39 (g / L), 36 (g / L), 88 (g / L), and 86 (g / L), respectively. . The supported amounts of the catalytically active components at points A to D are 0.8 (g / L), 0.7 (g / L), 1.4 (g / L), and 1.3 (g / L), respectively. )Met.
[0020]
Comparative Example 1
Except that urea or ammonia water was not added in Examples 1 and 2, catalysts were prepared under the same conditions as in each of the above Examples, and the same analysis was performed. As a result, the loading of the catalyst carrier components at points A to D in FIG. The amounts were 27 (g / L), 22 (g / L), 140 (g / L) and 134 (g / L), respectively. The supported amounts of the catalytically active components at points A to D are 0.6 (g / L), 0.6 (g / L), 4.4 (g / L), and 4.8 (g / L), respectively. )Met.
[0021]
Example 3
Instead of being put in a plastic bag in Example 1, the side parallel to the gas flow direction in practical use is covered with silicon rubber, and dried by contacting with air heated to 100 ° C. for 3 hours. After that, the catalyst was prepared by drying and calcining under the same conditions as in Example 1 above, and the same analysis was performed. As a result, the supported amount of the carrier component at points A to D in FIG. g / L), 46 (g / L), 73 (g / L) and 82 (g / L). The supported amounts of the catalytically active components at points A to D are 0.9 (g / L), 1.0 (g / L), 1.1 (g / L), and 1.4 (g / L), respectively. )Met.
[0022]
Comparative Example 2
A catalyst was prepared under the same conditions as in Example 3 except that the coating with the silicone rubber in Example 3 was not performed, and the same analysis was performed. As a result, the amount of the supported catalyst carrier component at points A to D in FIG. 20 (g / L), 28 (g / L), 172 (g / L) and 165 (g / L), respectively. The supported amounts of the catalytically active components at points A to D are 0.3 (g / L), 0.3 (g / L), 6.4 (g / L), and 5.8 (g / L), respectively. )Met.
[0023]
Table 1 summarizes the analysis results in Examples 1 to 3 and Comparative Examples 1 and 2, and the loading ratio in the direction parallel or perpendicular to the gas flow direction.
[Table 1]

[0024]
From Table 1, there was no significant difference in the supported amount in the direction parallel to the gas flow direction in practical use because the catalyst body size was as short as 50 mm, but the distribution in the vertical direction was significantly different in the comparative example. It can be seen that the amount of supported on the surface increased. In contrast, in each of the examples, it can be seen that the catalyst component is uniformly supported from the surface to the center.
[0025]
The distribution of the amount of loading in the vertical direction is

As a distribution of the carried amount in the parallel direction,

It was obtained as.
[0026]
【The invention's effect】
According to the first aspect of the present invention, the catalyst active component and / or the catalyst carrier component are uniformly supported, and a stable and highly active exhaust gas purifying catalyst can be obtained.
According to the invention described in claim 2 of the present application, in addition to the effects of the above invention, an exhaust gas purifying catalyst having more excellent catalytic activity can be obtained.
[0027]
According to the invention described in claim 3 of the present application, in addition to the effects of the above invention, a catalyst having a more uniform loading amount of the catalyst component can be obtained by minimizing the influence of water movement.
According to the invention described in claim 4 of the present application, in addition to the effects of the above invention, an exhaust gas purifying catalyst having higher catalytic activity can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a concentration distribution measurement position of a catalyst component.

Claims (4)

In a method for producing an exhaust gas purifying catalyst in which a catalyst active component and / or a catalyst carrier component is supported on a substrate, and then dried and calcined, the acidic sol containing the catalyst active component and / or the catalyst carrier component is subjected to a pH adjuster. Is added to adjust the pH range so that the acidic sol becomes unstable, or impregnated in a porous carrier in the presence of urea or a urea derivative, and heated in a state in which drying is restricted, thereby heating the porous carrier. A method for producing an exhaust gas purifying catalyst, comprising: gelling a sol containing a catalytically active component and / or a catalyst carrier component impregnated in a gel, followed by drying and calcining. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein a solution containing an alkaline earth metal element or a rare earth element is used as the pH adjuster. The heating in a state where the drying is restricted is performed by covering a side surface of the porous carrier impregnated with the catalyst active component and / or the catalyst carrier component, which is parallel to a gas flow direction in practical use, with a heat-resistant rubber, or covering the entire surface. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the catalyst is brought into contact with heated air while being covered with a vinyl sheet. A method for producing an exhaust gas purifying catalyst, characterized by further impregnating the exhaust gas purifying catalyst produced by the method according to claim 1 with a catalytically active component, followed by drying and calcining.

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