JPS5952530A - Catalyst - Google Patents

Abstract

PURPOSE:To obtain a highly efficient catalyst, by a method wherein a porous carrier layer having a heat resistant noble metal catalyst supported is formed on the surface of an inorg. base material and a non-porous carrier layer having a heat resistant noble metal catalyst supported is formed on the surface of said porous carrier layer. CONSTITUTION:A first carrier layer is formed on the surface of a non-porous inorg. base material such as a silica fiber increased in silica purity, a metal fiber or the like. The first carrier layer comprises porous silica, porous gamma- alumina or a mixture thereof and formed by impregnating the same with palladium, platinum or a mixture thereof to be supported. In the next step, zirconia, titania, gamma-alumina or a mixture of two or more thereof having palladium, platinum or a mixture thereof to be supported preliminarily adhered thereto is adhered to the surface of the first layer to form a second carrier layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a catalyst for purifying exhaust gas residues.

Conventional configuration and its problems In combustors that burn petroleum-based fuels, hydrocarbons are unburned or incompletely burned components.

- Carbon oxide, etc. are included in the exhaust gas and emitted into the atmosphere. Although the amount of this depends on the quality of the burner in the combustor □'', it is impossible to completely eliminate these components with current combustion burners. When kigayu is emitted into the outdoor atmosphere, the level of air pollution from these components is extremely small compared to other sources of pollution, with the exception of some large combustion furnaces. For indoor exhaust type combustors, such as those seen in gas stoves, indoor air pollution becomes a serious problem.

Therefore, in order to purify the unburned and incompletely burned components discharged from the combustor, a complete oxidation catalyst is installed in the exhaust system of the combustor to purify the exhaust gas. Several types of catalysts have been proposed for this purpose. Many of these differ mainly in their external shapes, and as catalysts themselves, noble metal catalysts have been widely used because of their oxidation properties and stability at relatively high temperatures. However, with the current product trend of making combustors smaller and smaller, this type of catalyst is being installed closer and closer to the burner, and as a result, a catalyst that can withstand higher temperatures is required. Ru. Furthermore, the effects of poisoning by so-called catalyst poisons such as sulfur contained in fuel and metal particles scattered from metal parts that make up the burner are significant. I! It has been desired to take measures to shorten the life of the II medium. Conventionally, since increasing the amount of catalyst supported on the surface of a carrier is effective in purifying combustion exhaust gas, many proposals have been made to improve catalysts mainly in this respect. Among them, catalysts using inorganic fiber as a carrier are typical of this type. On the other hand, from the perspective of the catalyst life mentioned above, catalysts supported on the external surface of the Jυ body are particularly susceptible to thermal and poisoning by tissue poisons.

To improve this point, the metal salt can be adsorbed into the pores of the porous carrier by utilizing its selective adsorption properties, and the concentration of the catalyst metal can be increased from the surface of the carrier to the deeper part of the carrier to avoid exposure to catalyst poison. In addition, a dual-supporting method has been proposed in which a catalytic metal with low poisoning resistance is selectively adsorbed inside, and another catalytic metal with strong poisoning resistance is supported at a high concentration on the surface.

Although these methods all have certain effects, since they utilize selective adsorption, they are greatly influenced by the adsorption capacity of the carrier for these metal salts, and in order to achieve more effective loading, there are restrictions on the material of the carrier. The support layer needs to have a thickness of several tens to 100 microns or more, so that the outer surface cannot be used for catalytic reactions in high-temperature, high-speed diffusion-limited stages, such as complete oxidation reactions in combustion exhaust gas. The catalyst metal supported internally does not contribute to the reaction, and especially when the catalyst metal is a noble metal such as platinum, the amount of reaction per amount of supported metal is extremely small, resulting in a catalyst with low efficiency. There was an unavoidable problem.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a catalyst which has excellent thermal resistance and resistance to catalyst poisons, and which can purify exhaust gases and gases with high reaction efficiency.

Structure of the Invention In the catalyst of the present invention, a porous first carrier layer supporting a heat-resistant noble metal catalyst is formed on the surface of an inorganic base material. On the surface of the carrier layer, a heat-resistant, non-porous granular second carrier layer is formed which supports a metal-based catalyst that is resistant to catalyst poisons.

As the mW-free base material, non-porous materials such as silica fibers whose silica purity has been increased by acid treatment and metal fibers can be used. Alternatively, it can be used in the form of a fabric or net.

The first carrier layer is a layer made of porous silica, γ-alumina, or a mixture thereof, and after this layer is impregnated and supported with palladium, platinum, or a mixture thereof, platinum is preliminarily applied to the surface of the layer.

The second carrier layer is formed by adhering zirconia, titania, a-alumina particles, or two or more thereof, on which rhodium or a mixture thereof is adhered and supported. The heat-resistant particles such as zirconia, titania, and a-alumina constituting the second carrier layer preferably have a particle size of 0.1 μm or less.

The first carrier layer impregnated and supported on the inorganic base material has a thickness of about 1 μm at most since the inorganic base material itself is a non-porous fiber, and therefore the catalyst impregnated in this carrier layer has a thickness of about 1 μm at most. The depth of metal impregnation is at most 1 μm or less, and the heat-resistant granular second carrier layer, such as zirconia, attached to this surface has a particle size of about 0.1 μm and is non-porous. The catalyst metal attached to the particle surface is 1
It is in the form of fine particles of less than 00 shaku. Therefore, all of the supported catalyst metal is present in the region most suitable for the outer surface reaction in the diffusion-controlled complete oxidation reaction, and the reaction amount per unit weight of catalyst metal is naturally large. This allows for efficient catalytic reactions. In addition, by placing a catalyst metal on the outer surface that is more resistant to catalyst poisons contained in the reaction gas, the life of the catalyst can be extended. By impregnating a porous carrier with catalyst metal and supporting a catalyst metal with low heat resistance on a carrier with high heat resistance, the overall heat resistance is increased. This makes it possible to obtain a catalyst with high activity and a large amount of reaction per unit weight of catalytic metal.

Description of Examples Example 1: Silica cloth made of alkali-free glass fibers with increased silica purity by acid treatment was woven into a woven fabric.
Annealed material for less than 1 hour at a high temperature of 1300°C to 1300°C is used as a base material, and this is immersed in a suspension of boehmite/alumina gel dispersed in a ratio of 15 parts to 100 parts of ion-exchanged water. After drying at 120°C for several hours, it was fired in the air at 500°C to 700°C for 1 to 3 hours to form a T-alumina coating layer on the surface of the silica cloth. The amount of alumina supported is 15% by weight based on the weight of the cloth of the base material, and scanning electron microscopy reveals that this layer thickness is 0.5 to 1.5μ compared to the diameter of the silica filaments forming the silica cloth, which is approximately 9μ. there were. Next, this alumina-supporting cloth was immersed in an aqueous palladium chloride solution, dried at 120°C for 30 minutes to 1 hour, and then burned in the air at 600°C to 700°C for 1 to 2 hours to support palladium.

The amount of palladium supported was 0.06% by weight based on the weight of the carrier. On the other hand, zirconium oxide 2 with an average particle size of 0.5μ
0 part suspended in 100 parts of ion-exchanged water, 1 part of zirconium nitrate and 0.5 part of chloroplatinic acid were mixed. After drying at 120℃ for 1 hour, drying at 600℃ to 700℃ for 2 hours.
20 parts of the product fired in the atmosphere for 1 hour, 5 parts of boehmite alumina gel and 3 parts of aluminum nitrate.
The palladium-supported cloth was immersed in a mixture of 100 parts of ion-exchanged water and 100 parts of ion-exchanged water.
After drying at 20° C. for 1 hour, it was fired at 600° C. to 70° C. for 2 hours in the air.

Specifically, as shown in the drawing, a cloth catalyst in which a first carrier layer 2 of γ-alumina supporting palladium and a second carrier layer 3 of zirconia particles supporting platinum are formed in this order on a silica cloth 1. I got it.

Analysis of this catalyst revealed that it contained 19% by weight of alumina, 5% by weight of zirconia, 0.06% by weight of palladium, and 0.01% by weight of platinum based on the weight of the silica cloth of the base material.

Example 2: A cross catalyst was obtained in the same manner as in Example 1, except that platinum was supported in place of palladium in Example 1, and rhodium was supported in place of platinum. Analysis of this material reveals that it is 21% by weight of alumina.

Zirconia 6% by weight, platinum 0.08% by weight, rhodium 0
．． 01% by weight.

Example 3: In Example 1, after palladium was supported on γ-alumina, titania powder was used instead of zirconia powder to support platinum, and then Example 1
In the same manner as above, platinum-supported titania fine particles were adhered and supported on a Bawadium-supported γ-alumina layer to obtain a cross catalyst.

Analysis of this catalyst revealed that 18% by weight of alumina, 7% by weight of titania, 0.05% of palladium, and 0.0% of platinum.
A pair of 1% by weight.゛Example 4: In place of zirconia in Example 2, a-
A catalyst was obtained in the same manner as in Example 2 except that fine alumina particles were supported. Analysis of this material shows 20% by weight of alumina and 6% by weight of α-alumina.

Comparative Example 1 containing 0.07% by weight of palladium and 0.02% by weight of platinum: The surface of the same silica cloth used in the example was coated with γ-alumina by a conventional method, and then immersed in a chloroplatinic acid solution. Then, it was dried and calcined to obtain a platinum-supported catalyst. Analysis of this catalyst revealed that γ
- Alumina is 18% by weight relative to the base material cloth
The platinum content was 0.05% by weight.

Comparative Example 2: Sintered alumina pellet (3 mm diameter.

length 5 tnm)? : A γ-alumina layer was formed on the surface of the pellet by immersing it in boehmite alumina sol, drying and calcination, and then impregnated with dichloroplatinic acid by the immersion method, and supporting platinum by drying and calcination. Analysis of this material revealed that the supported amount of γ-alumina was 17% by weight and the amount of platinum supported was 0.1% by weight based on the pellet weight of the base material.

For each of the catalysts obtained in Examples 1-4 and Comparative Examples 1-2, 1100 pp of CO was added to these catalysts.

A model gas containing 50 ppm of C3H6, 30 ppm of C6H14, 17 g of oxygen, and the remaining amount of nitrogen gas has a space velocity of 5 x 10 h and a linear velocity of 2. The rate of decrease in the concentration of each component was examined by passing the sample under OCR conditions of 7 seconds. In the test, the reaction gas temperature was set at 600 to 700°C, and the reduction rate of each component was investigated during the initial gas passage and after continuing the reaction for 500 hours.

The results are shown in Table 1.

Table 1 On the other hand, using a kerosene-burning burner with a calorific value of 3000 kcal/hour, each catalyst obtained in Examples 1 to 4 and Comparative Examples 1 to 2 was adjusted to a space velocity such that the entire amount of exhaust gas from the burner passed through. 3 x 10 h CO and total hydrocarbon concentration (THC) after passing through the catalyst + 7)
The purification rate was investigated. The test was conducted immediately after the start of use (Freno: L)
The initial purification rate and the purification rate after 1000 hours of continuous combustion were investigated, and the temperature of the catalyst layer was set at 600 to 800°C. The results are shown in Table 2.

Table 2 From these test results, it can be seen that the catalysts obtained in Examples 1 to 4 all have superior exhaust gas purification performance compared to those of Comparative Examples 1 and 2. In particular, the 10 shown in Table 2
There is a large difference in the characteristics between the example and the comparative example after 00 hours of continuous combustion, and the resistance to other components other than the incomplete combustion components that are emitted during combustion, especially to catalyst poisons such as heavy metal fine powder and SOX. This is thought to be due to the difference in the degree of Qualitatively, analysis of the catalyst after use revealed that iron, manganese, sulfur, etc. other than catalyst components were present in the comparative example.
This is because it was confirmed more markedly than that of No. 4.

In addition, in these examples, the case where silica cloth was used as the base material was explained, but almost the same results were obtained when other inorganic fibers such as alumina fibers and silica alumina fibers were used. Furthermore, the first carrier layer is formed of a porous carrier and the second carrier layer is formed of a non-porous carrier, but the porous carrier has a bed specific surface area of 30 to 30.
150n? /f and as a non-porous support 10 n
V? It is necessary that the following is true. In addition, the pore distribution is preferably 50 to 500λ for a porous carrier, and 50 to 500λ for a non-porous carrier.
It is preferable that it is above 0^. Previous: E Example 1~
The specific surface area of the first carrier layer of No. 4 (all γ-alumina) is 70 to 100 n? /l, and after the second carrier layer was attached, the specific surface area was 40 to 70 m
It was e/s'. With only this second carrier fine powder, 0
．． 1~8tt? /f.

Effects of the Invention The catalyst of the present invention has excellent thermal resistance and resistance to catalyst poison, and has the effect that exhaust gas can be purified with high efficiency due to its high reaction efficiency.

[Brief explanation of the drawing]

The drawing is a sectional view showing an embodiment of the present invention. 1... Silica cloth (inorganic base material), 2... First carrier layer, 3... Second carrier layer 2 2 159-

Claims (3)

[Claims] (1) A porous first carrier layer formed on the surface of an inorganic base material and supporting a heat-resistant noble metal catalyst, and a noble metal catalyst resistant to catalyst poisons formed on the surface of this first carrier layer. and a heat-resistant, non-polymerized granular second support layer. (2) The first carrier layer is a γ-alumina layer, and the second carrier layer is zirconia particles, titania particles, or a-alumina particles attached to the surface of the first carrier. The catalyst described in (1). (3) Claim 4, wherein the heat-resistant noble metal catalyst is platinum, palladium, or a mixture thereof, and the noble metal catalyst resistant to catalyst poison is platinum, rhodium, or a mixture thereof. Said no#&
The catalyst according to claim 1, wherein the silica substrate is a silica fiber with high silica purity.