JPH0470944B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a catalyst suitable for a complete oxidation reaction at a high temperature exceeding 500°C (hereinafter referred to as a high-temperature oxidation reaction),
In particular, the present invention relates to a complete oxidation catalyst (hereinafter simply referred to as catalyst or oxidation catalyst) that has excellent heat resistance and can maintain stable characteristics. (Conventional structure and its problems) In general, a catalyst supporting a noble metal such as platinum is made by dispersing and supporting a noble metal such as platinum as extremely fine particles on an inorganic support such as γ-alumina, which has a large specific surface area. It is. Such catalysts are relatively thermally stable and are therefore often used in high-temperature oxidation reactions. However, in a reaction that generates a large amount of reaction heat or in a use where the catalyst is exposed to a high temperature atmosphere for a long period of time, both the support and the noble metal catalyst undergo thermal deterioration. For this reason, catalytic ability is usually rapidly lost. Many proposals have been made to improve this thermal deterioration. Most of these improvements were made in terms of material quality, such as adding and mixing higher melting point substances to improve the thermal resistance of the carrier. (Object of the invention) The present invention was made in view of the above circumstances, and
The object of the present invention is to provide a catalyst body in which durability deterioration of catalytic performance during high-temperature reactions is significantly reduced. (Structure of the Invention) The oxidation catalyst of the present invention is a catalyst in which a carrier layer made of zirconia or titania and alumina is formed on the surface of a molded base material, and platinum is dispersedly supported on this carrier layer. At least 15% by weight of the total zirconia or titania contains particles with a particle size of 0.05 to 0.5μ, and
At least 30% by weight (hereinafter wt
%) or more, and the pore distribution of the catalyst has a pore range of 0.01 to 1.0μ, and further has a pore volume of 0.01 to 0.1μ and a pore volume of 0.1 to 1.0μ. Both pore volumes are 5% by volume of the total pore volume (hereinafter vol
%), and this configuration can significantly reduce the durability deterioration of the catalytic ability in high-temperature reactions. (Explanation of Examples) Example 1 Leached silica cloth with increased silica component ratio by dealkalization (hereinafter referred to as silica cloth)
was heated in advance at 1200°C for 1 minute in an electric furnace in an atmospheric atmosphere. The surface area of this cloth was 0.1 m ² /g. This silica cloth is 1wt of silica (SiO ₂ )
%. It was immersed in an aqueous silica sol solution, dried (120°C), and then fired (550°C). On the other hand, the particle size
70 parts of zirconia (ZrO ₂ ) particles with a particle size of 1.0 to 10.0μ, 30 parts of zirconia (ZrO ₂ ) particles with a particle size of 0.05 to 0.5μ, and 85 parts of alumina xerogel were mixed with 35 parts of acetic acid and 1000 parts of ion-exchanged water. , stirring was continued until each solute in the solution was sufficiently homogeneous to prepare an immersion liquid.
The silica-supported silica cloth was immersed in this mixture, dried (120°C), and then fired (550°C). The cloth carrier thus prepared had 1wt% silica on the surface of the silica cloth, and a 26wt% zirconia and alumina layer thereon. The supporting ratio of silica, alumina, and zirconia was 4:44:52 (%). In addition, the surface area after carrier preparation was 32 m ² /g,
Pore volume distribution is 38vol% below 0.01μ, 0.01~0.1μ
is 8vol%, 0.1 to 1.0μ is 13vol%, and 1.0μ or more is 41vol
It was %. The above-mentioned carrier was immersed in a chloroplatinic acid aqueous solution, dried (120°C), and then calcined and decomposed in an air atmosphere at 750°C. The catalyst body had 0.5 wt% platinum. The surface area is 34m ² /g, and the pore volume distribution is
0.01μ or less is 33vol%, 0.01~0.1μ is 6vol%, 0.1~
1.0μ was 15vol%, and 1.0μ or more was 46vol%. Here, the specific surface area was measured by the BET method using nitrogen gas, and the pore volume distribution was measured by the mercury intrusion method. Based on the above examples, by changing the formulation composition of alumina and zirconia precursors, Table 1
Catalysts 1-8 were prepared as shown. and,
Regarding these catalysts, the specific surface area and pore volume distribution measurement results after catalyst preparation and the specific surface area and pore volume distribution after heating catalysts 1 to 8 at 950°C for 100 hours in an electric furnace air atmosphere. Table 3 shows the measurement results.
Shown below. Catalysts 1, 7, and 8 used only one type of zirconia (in terms of particle size distribution) as a carrier precursor, and were prepared as comparative examples for the present invention.

【table】

【table】

【table】

[Table] *marks cannot be detected and Example 2 A honeycomb-shaped base material made of cordierite was mixed with the zirconia particles with a particle size of 0.5 to 5μ used in Example 1 and the zirconia particles with a particle size of 0.05 to 0.5μ. ,
Furthermore, alumina and xerogel are mixed with ion-exchanged water, thoroughly stirred, and then immersed in a slurry liquid whose viscosity has been adjusted to an appropriate level by adjusting the pH. After removing it by spraying, it was dried (120°C) and then fired (550°C). The honeycomb carrier thus prepared was immersed in a chloroplatinic acid aqueous solution, dried (120°C), and then calcined and decomposed in an air atmosphere at 750°C. The catalyst body had 0.5 wt% platinum.
Here, catalysts 9 to 12 were prepared by changing the blending ratio of the carrier precursor. Its contents are shown in Table 1. Catalysts 11 and 12 are comparative examples. Example 3 Catalysts 13 to 15 were prepared in the same manner as in Example using 0.05 to 0.5 μ particles and 1.0 to 10.0 μ particles of rutile titania as carrier precursors. The contents are shown in Table 2. Catalyst 15 is a comparative example. Table 3 shows the measurement results of surface area and pore volume distribution for catalysts 9 to 15 of Examples 2 and 3 after preparation and after heating at 950° C. for 100 hours. Next, in order to examine the effects of the present invention, the characteristics of each catalyst were compared by measuring the gas temperature at the inlet of the catalyst when 10% CO was converted. Here, the measurement conditions are SV=4×10 ⁴ h ^-1 , CO200 _PPM ,
AIR balanced. The results are shown in Table 3 after preparation (before heating) and after heating in an electric furnace air atmosphere at 950°C for 100H. In Table 3, the CO activity before heating is from catalyst 1 to
There is no particularly noticeable difference between the 15. The difference is at most 8℃
is the measurement error range. On the other hand, the CO activity after heating was 258°C to 398°C, as high as 140°C, indicating the superiority of the catalyst in terms of activity. Among Catalysts 1 to 15, Catalysts 1, 7, 8, 11, 12, and 15 prepared as comparative examples all have a temperature of 350°C or higher, while the others have a temperature of 300°C or lower. Among them, catalyst 12 has the highest temperature at 398°C. As shown in Table 1, this catalyst 12 does not contain zirconia as a carrier structure, only alumina, and its precursor xerogel was heated at 550°C.
The material is γ-alumina only. For this reason, it is thought that heating at 950°C for 100 hours caused a structural transition of some alumina, resulting in a significant surface reduction as measured in the surface area in Table 3. On the other hand, Catalysts 1, 7, 8, and 11, which were also prepared as comparative examples, used either zirconia with a higher or lower viscosity as a carrier precursor, and as a result, after the preparation In the pore volume distribution (before heating), 0.01 to 1.0μ
The distribution is highly skewed between the two. When this is heated, most of the pores smaller than 0.1μ disappear, and it is thought that the surface area is formed by pores larger than 0.1μ or a simple structured surface (macroscopic outer surface). As a result of measuring the surface area of the supported platinum, it was found that it had decreased to the point where it could hardly be measured, and the disappearance of the pores was the cause that significantly promoted the condensation of the platinum particles supported therein, more than the decrease in the surface area. It is thought that it has become. For these,
By adjusting the particle size of fine particles of refractory material (zirconia and titania), which are the constituent elements of the present invention, and mixing them with alumina, the pore volume distribution as a carrier can be adjusted, especially from 0.01 to 1.0μ. The catalyst prepared by controlling the distribution between
Since it has pores down to 0.1μ and has a measurable platinum surface area, it is thought that it exhibits the CO activity shown in Table 3 as a result. The effect of the present invention is less affected by the material of the refractory material, and the effect is more pronounced by the shape (particle size). , Ceria, Lantern, Magnesia,
Calcia or the like may be used as long as it can obtain the particle size distribution of this example. Although silica cloth and cordierite honeycomb have been described as base materials, the effects of the present invention can generally be expected with any material and shape of the support as long as it is a carrier coated with alumina on the surface of the base material. (Effects of the Invention) As described above, according to the oxidation catalyst according to the present invention, durability deterioration of catalytic ability in high-temperature reactions can be significantly reduced. It is particularly effective in catalysts using carriers in which carrier materials are supported or coated on honeycomb-shaped or cross-shaped molded substrates.

Claims (1)

[Scope of Claims] 1. A catalyst in which a carrier layer made of zirconia or titania and alumina is formed on the surface of a molded base material, and platinum is dispersed and supported on this carrier layer, wherein the particle size of the zirconia or titania is 0.05 to 0.05. A complete oxidation catalyst characterized by containing at least 15% by weight of all zirconia or titania particles having a diameter in the range of 0.5μ, and at least 30% by weight or more of particles having a particle size in the range of 1.0 to 10.0μ. Medium. 2 The pore distribution of the catalyst has a pore range of 0.01 to 1.0 μ, and a pore volume of 0.01 to 0.1 μ and a pore range of 0.1 to 1.0 μ.
2. The complete oxidation catalyst according to claim 1, wherein the pore volumes of 1.0 μ together account for 5% by volume or more of the total pore volume.