JPH0438454B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a catalyst body that purifies harmful components in exhaust gas. Configuration of conventional examples and their problems Perovskite-type composite oxide is used as a catalyst component to simultaneously purify CO and _NO Supported catalysts have been proposed. This catalyst has the advantages of activity comparable to precious metals, excellent heat resistance, and low cost; however, the method for producing a supported catalyst body is to impregnate and support it with a solution in which the catalyst components are uniformly dispersed. A common method is to apply and support the material on a carrier via a binder such as cement. However, in the former case, the first
As shown in the figure, the dissolving solvent component 1 has the disadvantage that the surface of the carrier cannot be used effectively because it is supported in a concentrated manner in the pores 3 of the carrier 2. Due to the presence of catalyst component 4, the catalyst component 1 is buried or non-uniformly dispersed, resulting in a disadvantage that effective catalytic action cannot be obtained. Furthermore, catalyst components may fall off during long-term use,
Alternatively, it may be deactivated by reacting with the binder. Purpose of the Invention In view of the above-mentioned problems with supported catalysts, it is an object of the present invention to provide an excellent catalyst body that can effectively utilize the surface of the carrier, can be strongly supported, and can withstand long-term harsh use. That is. Structure of the Invention The catalyst of the present invention is a supported catalyst comprising a carrier and a perovskite complex oxide catalyst (hereinafter referred to as catalyst component) supported on the surface of the carrier by thermal spraying. Suitable carrier materials include honeycomb molded bodies made of ceramics such as alumina, cordierite and mullite, heat-resistant and corrosion-resistant wire meshes made of stainless steel, cloth made of ceramic fibers such as alumina and silica, and the like. Description of Examples FIG. 3 shows a cross section of a surface portion common to the supported catalyst bodies shown in Examples. The catalyst component 1 is uniformly supported on the surface of the carrier, and the surface utilization efficiency is very high. Table 1 shows the activity of the supported catalyst of the present invention together with conventional examples. La _0.1 for catalyst component
Sr _0.9 Co _0.2 Fe _0.8 O ₃ was used, and an alumina honeycomb molded body (110 mmφ×10 mmt, 3×3 mm cells, 500 cells) was used as the carrier. A desolvent component was deposited on the surface of this carrier to a thickness of about 100 μm by hydrogen flame spraying (Example 1). Conventional examples include a method in which the same catalyst component is mixed with alumina cement at a weight ratio of 3:2 and coated on the surface of a carrier to a thickness of about 300 μm (Conventional Example 1), and an aqueous solution in which the catalyst component is dispersed is also applied. Two examples were used in which the same carrier was supported by vacuum impregnation (Conventional Example 2). This catalyst body was attached to the top of the combustion tube of a commercially available portabun oil stove, and the concentration and NO _x (=NO+NO ₂ ) concentration in the exhaust gas before and after passing through the catalyst body were measured. The exhaust gas temperature was approximately 600°C.

[Table] As is clear from the results, the activity of the Examples of the present invention is very high. In the example, the entire surface of the catalyst body is made up of catalyst components, and the reason for the high activity is that the number of effective active sites is much larger than in the conventional example. FIGS. 4 and 5 are examples of the case where it is supported on a stainless wire mesh. The same solvent components as above were used. The wire mesh used was a lath mesh made of SUS304 with openings of 10 mm in the major axis and 5 mm in the minor axis. The spraying of the solvent component was the same as described above, and this was designated as Example 2. Further, a sample in which a catalyst component was coated and supported in the same manner as Conventional Example 1 was used for comparison, and was designated as Conventional Example 3. This catalyst body was cut out into 30mmφ discs and placed in a stack of 5 sheets in a reaction tube to produce CO1500ppmNO _2.
A mixed gas of 40 ppm N ₂ was passed through the mixture, and the gas concentrations before and after passing through the catalyst were measured in the range of 300 to 900°C, and the rate of decrease in gas concentration was determined. In this example as well, both the CO oxidation rate and the NO ₂ reduction rate of Example 2 exceed the values of Conventional Example 3, and the difference in the supported state of the catalyst components is clearly evident. In addition, in the case of the wire mesh-supported type, the example of the present invention is superior in support strength, and when the supported wire mesh is bent, in the conventional catalyst body, the catalyst components around the bent part easily fall off together with the binder. In the case of the catalyst of the present invention, only cracks occur in the catalyst component layer at the bent portions. Next, the thermal stability and life of the catalyst will be described. The catalyst bodies of Example 1 and Conventional Example 1 using the alumina honeycomb molded carrier described above were installed at the top of the combustion tube of a portable gas stove, and burned for 30 minutes.
Repeat the extinguishing cycle 5,000 times, and
The CO concentration and NO _x concentration in the exhaust gas before and after passing through the catalyst were measured every 1000 times, and the reduction rate of each gas concentration was determined. The results are shown in FIGS. 6 and 7.
At the same time, the appearance of the catalyst body was observed to confirm the presence or absence of falling off of the catalyst layer, cracks, etc. From the activity data, it can be seen that not only the initial properties of the catalyst of the present invention are excellent, but also almost no decrease in activity is observed even after a long-term combustion test. On the other hand, the activity of conventional catalysts gradually decreases. When observing the appearance, no abnormality was observed in the catalyst body of the present invention, but in the conventional catalyst body, partial drop-off or lifting of the catalyst layer was observed, which is considered to be linked to a decrease in activity. As another example, we will describe the characteristics of a catalyst using alumina fiber cloth as a carrier. The carrier was made of a cloth with an opening of 2 mm x 2 mm made of threads made by twisting single fibers with a diameter of about 10 μm. The catalyst components and the method for supporting them were the same as in Example 1 and Conventional Diameter 1. These are referred to as Example 3 and Conventional Example 4, respectively. The activity was measured in the same manner as in the case of the honeycomb molded body described above. Two sheets of this catalyst body cut out to a diameter of 110 mm were placed on top of the combustion tube of a portable kerosene stove, and the concentration of components in the exhaust gas before and after passing through the catalyst body was measured. The results are shown in Table 2, and the superiority of the catalyst according to the present invention is clear.

[Table] Such a ceramic fiber carrier is itself flexible and has the characteristic that it can be formed into a relatively free shape. When thermal spraying is used, catalyst components can be supported with almost no loss of this property, but when a binder such as cement is used, flexibility is lost and the catalyst tends to fall off when bent forcibly, making it difficult to process freely. The degree is small. In the above examples, the case where X=0.8 was explained, but in the range of 0<X<1, similar effects were obtained when complex oxides having other compositions were used. Further, although the example deals with the case where Fe is used as Me, similar effects can be obtained when Mn, Cr, V, and Ti are used, or when they are used in combination. As a result of these various studies, it has become clear that the catalyst body produced by the thermal spraying method exhibits superior properties compared to the catalyst body produced by the conventional supporting method. Effects of the Invention As is clear from the examples above, by using thermal spraying, catalyst components can be easily supported on various carriers.
Moreover, since the surface of the carrier can be utilized as effectively as possible, a highly active catalyst can be obtained. Furthermore, because the adhesion strength to the carrier is extremely high, it has excellent thermal shock resistance, extends the life of the catalyst, and is relatively easy to post-process the catalyst body. .

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of the surface of an impregnated supported catalyst;
Figure 2 is a schematic cross-sectional view of the surface of a coated supported catalyst, Figure 3 is a schematic cross-sectional view of the surface of a spray supported catalyst, and Figure 4 is a schematic cross-sectional view of the surface of a spray supported catalyst.
Figure 5 is a graph showing the CO oxidation activity of the wire mesh supported catalyst, Figure 5 is the graph showing the NO ₂ reduction activity of the wire mesh supported catalyst, and Figure 6 is the life test (CO oxidation activity) of the honeycomb supported catalyst. Graph showing the results, FIG. 7 is a graph showing the results of the life test (NO _x reduction activity) of the honeycomb-supported catalyst.

Claims (1)

[Claims] 1 The general formula La _(1-x)/2 Sr _(1+x)/2 is formed by thermal spraying onto a carrier.
From a supported catalyst supporting a perovskite complex oxide represented by Co _1-x Me _x O ₃ (Me is at least one element selected from Fe, Mn, Cr, V, and Ti, O<X<1) A catalyst body for exhaust gas purification characterized by: 2. The catalyst body for exhaust gas purification according to claim 1, wherein the carrier is made of a ceramic molded body, a heat-resistant and corrosion-resistant wire mesh, or a ceramic fiber.