JPS63205143A - Preparation of combustion catalyst - Google Patents

Abstract

PURPOSE:To reduce a necessary amount of a catalyst component, by mixing a carbon fiber having a specific length and diameter with an inorg. material powder having a high specific surface area to form a slurry and adhering said slurry to an inorg. honeycomb carrier to bake the same. CONSTITUTION:5-50vol.% of a carbon fiber or combustible fiber having a length of 10-5,000mum and a diameter of 1-500mum is mixed with an inorg. material powder having a high specific surface area to prepare a slurry. This slurry is supported by an inorg. honeycomb carrier to be dried and a catalyst component is further supported by said carrier and the whole is subsequently baked to prepare a combustion catalyst. As the inorg. substance constituting the inorg. honeycomb molded body, there are cordierite, alumina or the like and, as the inorg. material powder having a high specific surface area, there are gamma-alumina, beta-alumina, silica, composite oxide of BaO.Al2O3 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a combustion catalyst, and particularly to a method for manufacturing a combustion catalyst suitable for reducing the required amount of catalyst components.

[Conventional technology]

Catalysts using honeycomb carriers have a large specific surface area per unit of contact and have low pressure loss for fluids passing through the catalyst, so they are widely used in automobile exhaust gas treatment catalysts, chemical reaction equipment, catalytic combustion equipment, etc. There is. Here, the term "honeycomb" refers not only to the shape of a honeycomb, but also to generically refers to other polygonal shapes other than hexagonal shapes and other similar shapes.

One method of supporting a catalyst on a honeycomb carrier is to prepare the carrier itself from a material with a high specific surface area and to support the catalyst components on it. However, the usage conditions of the catalyst, such as the requirements for strength and thermal shock resistance, When this is high, a method is used in which a carrier with high strength or a carrier with a low coefficient of thermal expansion is used, and a material having a high specific surface area is coated on the surface of the carrier to support the catalyst component (wash coating method). Patents related to this include, for example, JP-A-56-51245 and JP-A-58-51245.
No. 193740, JP-A-59-44101, JP-A-5
No. 9-15042 is known.

Generally, noble metals such as platinum and palladium, as well as powders of metals and alloys that have been cleaved through special treatment, are used as catalyst components supported on catalyst carriers. Efforts are being made to reduce the required amount by increasing the dispersibility of the components and increasing their activity.

[Means for solving problems]

By the way, in the catalyst used for the combustion reaction of combustible gas, which is the object of the present invention, only the catalyst components present in the thin part of the surface that comes into contact with the combustible gas of the high specific surface area layer coated on the surface of the carrier. Catalytic components that are involved in the reaction and exist deep within are hardly utilized effectively.

Therefore, if the catalyst component present in the deep layer of the high specific surface area layer that is coated on the carrier surface and supports the catalyst component can be effectively utilized, the amount of the catalyst component can be reduced and the manufacturing cost can be reduced. However, in the conventional wash coating method, this point has not been sufficiently studied, and a large amount of catalyst components are required to obtain a predetermined catalytic performance, resulting in a high production cost of the catalyst.

An object of the present invention is to provide a method for molding a combustion catalyst that effectively utilizes catalyst components supported deep in a high specific surface area layer and reduces the amount of catalyst components required for catalyst production. be.

[Failure to solve the problem]

The above purpose is to coat a high specific surface area layer on the surface of a carrier by coating an inorganic material powder with a high specific surface area with a slurry in which 5 to 50 vol% of organic fibers or carbon fibers having specific dimensions are mixed, and then firing the slurry. This is achieved by incinerating the fibers in a high specific surface area. That is, the present invention provides a combustion catalyst molding method in which a combustion catalyst component is supported on a carrier in which the surface of an inorganic honeycomb molded body is coated with an inorganic material powder having a high specific surface area. The inorganic material powder with a high specific surface area has a fiber length of 10
~5000μm, fJll fiber diameter 1~500μrn carbon fiber or combustible fiber 5~50■oI! % to form a slurry, which is then deposited on an inorganic honeycomb carrier and fired, which is then used as the catalyst carrier.

[Effect]

The fibers mixed in the high specific surface area layer coated on the surface of the carrier are burned out by the sintering process to form fine continuous elongated cavities in the layer. As a result, the catalyst component present in the deep part of the high specific surface area layer is brought into contact with the combustion gas and effectively utilized for the reaction, so that the amount of catalyst component required to obtain a predetermined catalytic performance is reduced.

The inorganic honeycomb molded body used in the present invention is obtained by molding alumina, cordierite, aluminum titanate, or the like into a honeycomb shape by a known method as a raw material.

In addition, examples of inorganic material powder with a high specific surface area include γ-alumina,
Examples include complex oxides such as β-alumina, silica, and BaO.A/203.

In the present invention, examples of the combustion catalyst supported on the inorganic material powder or carrier having a high specific surface area include known combustion catalysts such as palladium, platinum, and cobalt.

In the present invention, carbon fibers or combustible fibers are used as the fibers mixed with the inorganic material powder having a high specific surface area, but any fiber can be used as long as it can be incinerated in the firing process after coating.

The carbon fiber used in the present invention is not particularly limited as long as it has the above-mentioned predetermined dimensions, and may be made by heat-treating fibers made from rayon, polyacrylonitrile, pitch, etc., or by vapor phase method. It also includes fibrous materials.

Examples of combustible fibers include polyolefin synthetic fibers such as polyethylene and polypropylene, acrylic synthetic fibers, and polyamide synthetic fibers.

The above-mentioned carbon fibers or combustible fibers are coated onto a honeycomb with an inorganic material powder slurry containing them, and then burned by a firing process to form fine and elongated cavities inside the carrier.

In the present invention, the inorganic material powder having a high specific surface area, the additives of the coating slurry, and the blending ratio thereof are appropriately determined depending on the usage conditions of the catalyst, the required specifications, and the coating construction conditions.

〔Example〕

FIG. 1 shows the shape and dimensions of a honeycomb carrier used in a combustion catalyst manufactured in an example of the present invention. The material is cordierite, the cell is 1.411-square, and the cell wall thickness is 0.4 mm. FIG. 2 is a process chart showing the method for manufacturing the honeycomb catalyst of this example.

B a 0 ·6 A l! with an average particle size of about 1 μm is used as an inorganic material powder with a high specific surface area to coat the surface of the carrier. z O
3, and the fiber to be mixed with this has a diameter of about 1 μm and a length of 30. crm carbon fiber was used.

Ba0.6A1203 powder adjusted to the above particle size and carbon fiber were placed in a mixing tank at a volume ratio of 80:20, and mixed with a stirrer while adding water to prepare a slurry. In addition to the above-mentioned two components, an organic binder was added to the slurry to adjust the viscosity of the slurry and to prevent the rii layer from peeling off during drying, and an inorganic binder was added to strengthen the adhesion of the coating layer after firing. An antifoaming agent was added because foaming of the slurry would significantly impede the coating process. In a slurry with fibers added in this way, the fibers are poorly dispersed and become small lumps, which reduces the fluidity of the slurry and makes coating impossible. Therefore, in this example, the slurry was mixed for 30 minutes using a stirrer. Thereafter, the mixture was dispersed in an ultrasonic cleaner for 5 minutes and passed through a 150 mesh sieve to remove the fiber lumps. In addition, Q,'l wt% of sodium alginate was added as a dispersant to facilitate the dispersion of carbon fibers.

Table 1 shows the weight composition of the slurry used for coating.

Table 1 In this example, the honeycomb carrier shown in FIG. 1 was repeatedly coated with 3U using the above slurry to obtain a carrier with a coating amount of about 22 wt%.

This was fired at 1200° C. for 2 hours to burn off the fibers, and Ba0.6 A I1203 was baked onto the carrier to produce a carrier.

The honeycomb carrier produced in this way was immersed in a 2.8 wt% palladium nitrate solution and dried at room temperature.
It was calcined at 0° C. for 2 hours to support the catalyst component.

Figure 3 shows Ba0.6A7!203 as an inorganic material powder.
FIG. 3 is a diagram showing the results of comparing the increase rate of the contact area with outside air of honeycomb carriers coated with coating slurries with different mixing ratios using carbon fibers and carbon fibers, with the rate of increase in the contact area with the outside air set to 1 when no fibers are added. In this case, the amount of Ba0.6Aε203 coated was about 15 wt% of the weight of the carrier, and the average thickness of the coated high specific surface layer was about 30 μm.

As the amount of combustible fibers added to the high specific surface area inorganic material powder increases, the area of the part that comes into contact with flammable gas in the high specific surface area layer after the fibers are incinerated increases, but the fluidity of the coating slurry decreases. This makes it difficult to coat the honeycomb carrier, and the high specific surface area layer also becomes weak, making it easy to peel off.

In other words, as shown in the figure, when the mixing ratio of carbon fibers is increased, the contact area increases, and the 20voj of this example
! % mixing ratio is about 2.7 times that of no fiber added. However, at a fiber mixing ratio of 5 vo/% or less, the ratio of holes created by firing the fibers opening on the surface of the high specific surface area layer is small, so the effect of adding fiber is small and the contact area with the outside air is different from the case without additives. Therefore, in order to obtain the effect of increasing the contact area by adding fiber, at least 5■0! It was found that a mixing amount of fibers of % or more is required.

The contact area increased as the amount of fibers mixed increased, but the viscosity of the coating slurry increased as shown in Figure 4, resulting in a mixing ratio of 45vo7! % or more, it becomes difficult to coat the honeycomb carrier, and even if it is coated, it will peel off after drying.
It was easy. Furthermore, since the 8-year-old particles are entangled to form small lumps, the slurry tends to adhere unevenly to the carrier, and when the catalyzed catalyst is subjected to a combustion test, combustion unevenness is significant. Even if a honeycomb carrier with 51-square cells is used, which is easy to coat, the mixing ratio must be set to 5 to ensure uniform coating.
It was necessary to keep it below QvoJ%.

From the above, the mixing ratio of combustible fiber to inorganic material powder is 5vo
7! % or more and 50 voJ% or less was found to be appropriate.

Figure 5 shows the effect of fiber length on the viscosity of the slurry by preparing coating slurry using carbon fibers with a diameter of 3 μm and different lengths under the preparation conditions shown in Table 1. If the length of the fiber exceeds 1000 μm, the viscosity becomes high, making it difficult to coat the honeycomb. Even if a carrier with a cell size of 5u square is used, the cell size is 5000μ
If the thickness exceeds m, coating becomes impossible.

Furthermore, Figure 6 shows the results of investigating the contact area of the honeycomb carrier coated with the above slurry with the outside air.If the fiber length is 10 μm or less, the fiber length is too short and the ratio is too high. The pores are insufficiently connected by the combustible fibers in the deep part of the surface layer, and the contact area due to the addition of fibers does not increase much. On the other hand, even if the length is increased to 5000 μm or more, the branching of the pores is reduced, so the contact area does not increase despite the addition.

Therefore, the length of the combustible fibers added to the slurry is 10~
A range of 5000 μm was found to be suitable.

Figure 7 shows that carbon fibers of length 30 μm and different diameters were coated on a honeycomb carrier under the slurry cleavage conditions shown in Table 1 in order to examine the effect of fiber diameter on the activity of the combustion catalyst. The ignition temperature of propane gas is increased by supporting it.

Carbon particles were used instead of fibers under conditions where the diameter and length of the fibers were similar, but the pores formed in the high specific surface area layer had poor connectivity compared to when fibers were used, and at the same mixing amount, flammable gas The contact area becomes smaller and the ignition temperature becomes higher. On the other hand, if the fiber diameter is significantly smaller than the particle diameter of BaO 6AJ203 particles, the diameter of the burned residue of the fiber is small, so the combustion reaction proceeds near the opening, and the catalyst in the deep layer is not utilized, so the fiber is There is no significant difference from the case without additives.

Therefore, it is preferable that the diameter-to-length ratio of the fiber is 0.7 or less, and the minimum diameter is larger than 60% of the average particle diameter of the inorganic material with a high specific surface area coated on the honeycomb.
In particular, it is preferable that the ratio of the fiber diameter to length is within the range of 0.1 to 0.4.

Figure 8 shows the effect of the mixing amount of carbon fiber on the activity of the combustion catalyst. The effect of the mixing amount of carbon fiber on the activity of the combustion catalyst was investigated. The following shows the results of measuring the ignition temperature of propane gas.

The fiber mixing ratio is 5voI! % or more, the catalyst components deep in the high specific surface area layer are also effectively utilized.
The overall activity of the catalyst is improved and the ignition temperature is lowered. At a mixing rate of 2Qvoi 2% produced in this example, the temperature is approximately 150°C.
However, a combustion catalyst without fiber added produced under the same conditions could not achieve the same performance unless approximately 2.8 times more catalyst components were added. No further improvement in activity was observed in this example even when the amount was 2QvoA% or more.From these results, in the catalyst production method of the present invention, by mixing a predetermined amount of the fiber component into the slurry, the amount of the catalyst component can be reduced to approximately It can be seen that it can be reduced by 60%.

〔Effect of the invention〕

According to the present invention, the catalyst components present in the deep layer of the high specific surface area layer coated on the surface of the honeycomb carrier are also effectively utilized for the combustion reaction, so that the catalyst components necessary for the combustion catalyst to exhibit the predetermined performance are effectively utilized for the combustion reaction. The amount of catalyst components can be reduced by 40 to 70 wt%.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the dimensions and shape of a honeycomb carrier used in an embodiment of the method for manufacturing a combustion catalyst of the present invention, and FIG. 2 is a molding process of a combustion catalyst in an embodiment of the present invention. Figure 3 is a diagram showing the influence of the mixing ratio of carbon fibers on the surface of the combustion catalyst that is in contact with the outside air, and Figure 4 is a diagram showing the effects of the viscosity of the coating slurry in the example of the present invention. FIG. 5 is a diagram showing the effect of fiber length on the viscosity of the coating slurry in an example of the present invention. FIG. Figure 7 is a diagram showing the influence of the length of carbon fiber on the area of the combustion catalyst surface in contact with the outside air. The figure is a diagram showing the influence of the carbon fiber mixing ratio on the combustion performance of the combustion catalyst of the example of the present invention. Agent Patent Attorney Takeshi Kawakita Mixing ratio of long carbon fiber (vo!O7・) Figure 5 Fiber length pm) Figure 6 Fiber length Im) Figure 7 Fiber diameter/fiber length

Claims (1)

[Claims] (1) In a method for producing a combustion catalyst in which a combustion catalyst component is supported on a carrier in which the surface of an inorganic honeycomb molded body is coated with an inorganic material powder having a high specific surface area, the catalyst component is supported as necessary. Surface area of inorganic material powder to fiber length 1
A slurry is formed by mixing 5 to 50 vol% of carbon fibers or combustible fibers with a fiber diameter of 0 to 5,000 μm and a fiber diameter of 1 to 500 μm, and then this is deposited on an inorganic honeycomb carrier and fired, and the catalyst carrier is used as the catalyst carrier. A method for producing a combustion catalyst.