JPH0550338B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a cordierite ceramic honeycomb structured catalyst body. More specifically, the present invention relates to a method for producing a cordierite ceramic honeycomb structured catalyst body that does not require wash coating with γ-alumina or the like in the catalyst supporting step and has low expansion and excellent thermal shock resistance. Note that wash coating refers to coating the surface of a carrier material with a high specific surface area material in order to obtain the specific surface area necessary for catalytic activity. (Prior Art) Cordierite ceramic honeycomb structures have low expansion, excellent thermal shock resistance, and high heat resistance, so they are widely used as catalyst carriers for automobiles. In order to use a cordierite ceramic honeycomb structure as a catalyst carrier, as disclosed in Japanese Patent Publication No. 56-27295, the surfaces of the partition walls constituting the honeycomb structure are usually wash-coated with γ-alumina or the like. The adsorption surface area of catalyst components should be 5 to 50 m ² /
A method is used in which the catalyst is supported on the catalyst by immersing it in a solution containing a catalyst component. At this time, γ-alumina and catalyst components may be supported simultaneously. The reason why a wash coat is required with γ-alumina etc. is that the specific surface area of ceramic honeycomb structures such as cordierite is generally extremely small, 1 m ² /g or less, and if used as a catalyst carrier as is, the catalytic activity is low, and the high temperature This is because sintering of the catalyst noble metal occurs quickly in the atmosphere, resulting in extremely low activity. One of the drawbacks of cordierite honeycomb structures that are wash-coated with γ-alumina etc. is that γ-
Depending on the amount of coating with alumina, the specific surface area required for the catalyst carrier can be obtained, but the weight increases, and since the surface is coated with γ-alumina, which has high thermal expansion, the low expansion properties of cordierite are impaired, resulting in a large width. Deterioration of thermal shock resistance occurs, and expensive γ-alumina etc. are used and immersion supported.
It requires a lot of man-hours such as the baking process, which increases the cost. On the other hand, JP-A-49-129704 and U.S. Patent No.
As disclosed in Publication No. 3958058, a cordierite honeycomb is immersed in a 1 to 5N strong acid aqueous solution such as HNO ₃ , HCl, and H ₂ SO ₄ to partially dissolve MgO,
It is known that elution of the Al ₂ O ₃ component significantly reduces thermal expansion and improves thermal shock resistance. In this case, there are disadvantages such as a decrease in strength corresponding to a decrease in weight, and a rise in coefficient of thermal expansion (CTE) to the same level as before acid treatment due to long-term heat treatment at 1000°C or higher. (Problems to be Solved by the Invention) The objects of the present invention are as follows. (1) Improving the thermal shock resistance of cordierite honeycomb structure catalysts (2) Providing a new honeycomb catalyst manufacturing process that eliminates the need for expensive γ-alumina and the labor-intensive γ-alumina coating process (3) γ - To provide a process for obtaining a cordierite honeycomb structured catalyst body having a thermal stability comparable to that of an alumina-coated catalyst body. (Means for Solving the Problems) The present invention has been made to solve the above problems, and consists of acid-treating a cordierite ceramic honeycomb structure, then heat-treating it at 600°C to 1000°C, and then removing the catalyst components. A method for producing a cordierite ceramic honeycomb structured catalyst body characterized in that it supports a cordierite ceramic honeycomb structured catalyst body. The present invention also provides a method for producing a cordierite ceramic honeycomb structure catalyst body, which is characterized in that the cordierite ceramic honeycomb structure is treated with an acid, and then a catalyst component is supported and then heat treated at 600°C to 1000°C. In the present invention, a cordierite ceramic honeycomb structure is treated with an acid, and then a catalyst component is supported.
The purpose can also be achieved by heat treatment at 600°C to 1000°C. The cordierite ceramic honeycomb structure catalyst obtained by the production method of the present invention has a specific surface area of 5.
m ² /g or more, the compressive strength of the honeycomb structure catalyst in the flow path direction is 100 Kg/cm ² or more, and the thermal expansion coefficient at 40°C to 800°C is 1.0 × 10 ^-6 /°C or less. do. The supported catalyst of the present invention uses an oxidation catalyst, a three-way catalyst, or an industrial deodorizing catalyst for purifying automobile exhaust gas. (Function) The present inventors have noticed that the acid treatment of a cordierite honeycomb structure not only reduces thermal expansion but also significantly increases the specific surface area. This increase in specific surface area is considered to correspond to the high silicic acid components left behind by the selective elution of MgO and Al ₂ O ₃ . There are no restrictions on the type of acid used as acid treatment conditions to obtain the high specific surface area required for catalyst support.
Mineral acids such as HCl, H ₂ SO ₄ and HNO ₃ are preferred in terms of cost and effectiveness. The relationship between treatment time and specific surface area is positive, and from the viewpoint of efficiency, a concentration of 1 to 5N and a temperature of 50 to 100℃
It is preferable to process at a temperature of about 100 ml. 1N
Treatment with HNO ₃ , HCl, H ₂ SO ₄ at 90° C. for 3 hours reaches a level of 20 m ² /g, which is preferred as a catalyst support. The acid treatment method generally involves immersion in a circulating high-temperature acidic aqueous solution, but there are no particular limitations as long as the method is efficient. The cordierite honeycomb ceramic used in the present invention is preferably a conventional low expansion cordierite honeycomb structure coated with γ-alumina. That is, Japanese Patent Application Laid-open No. 53-82822,
A monolithic honeycomb structure with a wall thickness of 100 μm to 500 μm and a cell count of 30 to 600 cells per square inch, similar to that disclosed in JP-A-50-75611, with a porosity of approximately 20 to 50%. , 40℃ to 800℃
The CTE is 1.5×10 ^-6 /°C or less. It is preferable that the cordierite material has as large an amount of cordierite crystals as possible and has a small glass component, that is, a cordierite crystal amount of 90% or more, because it will have a high specific surface area when treated with an acid. However, in the case of industrial catalysts for which the coefficient of thermal expansion is not a particular problem, the present invention can also be applied to composite materials based on cordierite such as cordierite-mullite, cordierite-alumina, and cordierite-zirconia. On the other hand, the high specific surface area generally obtained by this acid treatment has the disadvantage that it rapidly decreases when heated above 600° C., as shown in the unheated product in FIG. FIG. 1 is a characteristic diagram showing the relationship between heating temperature and specific surface area, and shows the case where each temperature was maintained for 1 hour. In order to control the decrease in specific surface area due to heating above 600℃ and the increase in CTE due to long-term isothermal heating above 1000℃, the present inventors investigated various heat treatment conditions and stabilized the specific surface area and stabilized CTE. succeeded in improving the sex. Curves C and D in Figure 1
represents the specific surface area of the material treated with acid according to the present invention. In the present invention, heat treatment is achieved by holding at 600°C to 1000°C, more preferably 650°C to 900°C, for 0.5 to 10 hours. The temperature increase schedule is not particularly limited, and is 10° C./hour to 200° C./hour, but the faster the cooling schedule, the more preferable it is, and the rapid cooling treatment is desirable to the extent that it does not damage the product. The reason why heat treatment is limited to 600℃ or higher is because heat treatment below 600℃ leads to a decrease in specific surface area during actual use, resulting in a decrease in catalytic activity, whereas heat treatment at temperatures above 1000℃ causes a significant decrease in specific surface area. This is because, although high-temperature stability of the specific surface area can be obtained, problems arise in the catalytic activity. The reason why a faster cooling schedule is preferable is not well understood at present, but it is thought to be because local ultrafine crystallization of the high silicic acid component phase is promoted. The furnace used for heat treatment is not particularly limited, and electric furnaces, gas furnaces, large continuous furnaces, etc. can be used. For long-term isothermal aging at temperatures above 1000°C, short-term heat treatment at 600°C to 1000°C partially transforms the amorphous high silicic acid phase into a metastable crystalline phase other than cristobalite, which is harmful to thermal expansion. Although there is a slight increase in thermal expansion, the rate of increase is greatly improved. Furthermore, by carrying out heat treatment, dimensional stability during isothermal long-term aging is also improved. For example, when supporting noble metals such as Pt, Pd, and Rh as a catalyst for automobile exhaust gas, the catalyst supporting process is
Precious metal catalyst components such as chloroplatinic acid aqueous solution, and
Acid treatment of slurry containing rare earth oxides such as _CeO2 ,
A process can be used in which the heat-treated cordierite honeycomb structure is immersed, excess solution is removed with air, etc., and then dried or baked at a temperature of 600° C. or less. Catalysts used in the present invention include three-way catalysts based on noble metals such as Pt, Pd, and Rh, oxidation catalysts, deodorizing catalysts,
Base metal catalysts such as Mn, Fe, Cu, etc. can be supported using a similar supporting method. Further, in the present invention, a catalyst component can be supported on the surface of the cordierite honeycomb in a high specific surface area state after acid treatment, and then a heat treatment step at 600°C to 1000°C can be performed. However, in this case, it is preferable to carry out the heat treatment at a relatively low temperature of 900° C. or lower since there is a loss of the supported catalyst such as volatilization of precious metals such as Pt. Regarding the characteristics of the honeycomb catalyst obtained in the present invention, acid treatment provides a cordierite honeycomb structure with a high specific surface area and low expansion, but the drawback is a decrease in mechanical strength. In the case of commercial catalysts, in order to maintain the pressure resistance of 100 kg/cm ² (flow path direction) or more required when canning the catalyst container, for example, 1.5N, 90℃,
It is desirable to limit the HNO ₃ treatment to 8 hours or less. Since the cordierite ceramic honeycomb structured catalyst body of the present invention does not support γ-alumina, it is possible to produce a catalyst body with extremely low expansion according to the manufacturing method of the present invention. For example, 40℃ for cordierite honeycomb structure
Coefficient of thermal expansion (CTE) from to 800℃ is 0.6×
Even if the supporting method is improved by supporting high thermal expansion γ-alumina even at the 10 ^-6 /℃ level, the temperature is 1.5×10 ^-6 /℃.
Although it has been difficult to obtain a CTE as low as below ℃,
In the present invention, low expansion due to acid treatment also contributes to the catalyst body.
CTE of 1.0×10 ^-6 /℃ or less is now possible. In the present invention, the specific surface area is at least 5 m ² /g because it has a significant relationship with the activity of the supported catalyst.
Acid treatment to preferably 10 m ² /g or more,
It is necessary to control the heat treatment conditions. (Example) Example 1 Number of cells per square inch with cell wall thickness of 150 μm
400, square cell shape diameter 4.16 inches x length 4
FIGS. 2 and 3 show the measurement results of the specific surface area and compressive strength of inch cylindrical cordierite honeycomb structures treated under the respective acid treatment conditions. The compressive strength was measured using a sample of 1 inch in diameter x 1 inch in length, and the specific surface area was measured by the BET method (N ₂ adsorption). FIGS. 2 and 3 are characteristic diagrams showing the relationship between processing time, specific surface area, and compressive strength. Example 2 Number of cells per square inch with cell wall thickness of 150 μm
400, square cell shape diameter 4.16 inches x length 4
An inch cylindrical cordierite honeycomb structure was acid-treated by immersing it in a 2N, HNO ₃ aqueous solution at 90° C. for 3 hours, and then heat-treated under the heat treatment conditions shown in Table 1. The specific surface area after heat treatment, the coefficient of thermal expansion (CTE) from 40°C to 800°C, and the specific surface area and CTE after isothermal aging at 800°C for 100 hours were measured. The results are shown in Table 1. The specific surface area after acid treatment is 40
m ² /g, CTE ^{0.5×10 −6} /°C (40°C to 800°C). Further, FIG. 1 shows the change in specific surface area during heating for the samples C and D according to the present invention and those for non-heat treatment.

[Table] Example 3 For the heat-treated products A to H of Example 2, Pd catalyst was supported at a rate of 2 g per honeycomb structure volume, and the conversion rate of C ₃ H ₈ gas was determined under the conditions shown in Table 2. And the thermal shock resistance was measured by taking it out in an electric furnace. The measurement results are also shown in Table 2. On the other hand, J is the same Pd as the unheated product of Example 2.
These samples supported a catalyst and were subjected to the same heat treatment conditions as B and C, respectively.

[Table] 1. Effects of the invention) (1) Due to the increase in specific surface area, the wash coating (γ-alumina support) process, which is a catalyst carrier support process, becomes unnecessary, and the work process can be significantly shortened. (2) The coefficient of thermal expansion is greatly reduced, and since gamma alumina coating is not required, the weight of the catalyst body is reduced, and thermal shock resistance is greatly improved. (3) Thermal stability, which was a drawback of acid-treated cordierite, is improved.

[Brief explanation of the drawing]

Figure 1 shows the thermal stability of specific surface area, Figure 2 shows the relationship between acid treatment time and specific surface area, and Figure 3 shows the relationship between acid treatment time and specific surface area.
The figure is a diagram showing the relationship between acid treatment time and compressive strength.

Claims (1)

[Scope of Claims] 1. A method for producing a cordierite ceramic honeycomb structured catalyst body, which comprises treating the cordierite ceramic honeycomb structure with an acid, followed by heat treatment at 600°C to 1000°C, and then supporting a catalyst component. 2. The cordierite ceramic honeycomb structure catalyst has a specific surface area of 5 m ² /g or more, a compressive strength in the flow path direction of the honeycomb structure catalyst of 100 Kg/cm ² or more, and a thermal expansion coefficient of 1.0 at 40°C to 800°C. ×
10 ^-6 /°C or less, the method for producing a cordierite ceramic honeycomb structure catalyst according to claim 1. 3. The method for producing a cordierite ceramic honeycomb structured catalyst body according to claim 1 or 2, wherein the supported catalyst is an oxidation catalyst, a three-way catalyst, or an industrial deodorizing catalyst for purifying automobile exhaust gas. 4 The cordierite ceramic honeycomb structure was treated with acid, and then the catalyst component was supported at 600°C.
A method for producing a cordierite ceramic honeycomb structured catalyst body characterized by heat treatment at ~1000°C. 5 The cordierite ceramic honeycomb structure catalyst has a specific surface area of 5 m ² /g or more, a compressive strength in the flow path direction of the honeycomb structure catalyst of 100 Kg/cm ² or more, and a thermal expansion coefficient of 1.0 at 40°C to 800°C. ×
10 ^-6 /°C or less, the method for producing a cordierite ceramic honeycomb structured catalyst body according to claim 4. 6. The method for producing a cordierite ceramic honeycomb structured catalyst body according to claim 3 or 4, wherein the supported catalyst is an oxidation catalyst, a three-way catalyst, or an industrial deodorizing catalyst for purifying automobile exhaust gas.