JP5178164B2 - Exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst containing silver.

Patent Documents 1 to 4 describe exhaust gas purifying catalysts containing silver. The exhaust gas purifying catalyst containing silver is excellent in the purifying performance of exhaust gas discharged from the combustion engine, particularly nitrogen oxide (NO _x ).

However, the present inventors have found the following facts when inventing the present invention. That is, many of the exhaust gas purifying catalysts containing silver have a narrow temperature range in which excellent performance is exhibited. The exhaust gas-purifying catalyst containing silver is likely to be poisoned by sulfur even if it can exhibit excellent performance in a relatively wide temperature range. Since exhaust gas emitted by diesel engines contains sulfur at a relatively high concentration, exhaust gas purification catalysts containing silver have excellent performance for a long time when used to purify exhaust gas emitted by diesel engines. It may not be sustainable.
JP 10-337443 A JP 2001-9275 A Japanese Patent Laid-Open No. 2003-80081 JP-A-9-117638

An object of the present invention is to provide a technique that is advantageous for widening the temperature range in which an exhaust gas purifying catalyst containing silver exhibits excellent NO _x purification performance and making it difficult to cause poisoning by sulfur. is there.

According to one aspect of the present invention, a base material, and a catalyst layer supported by the base material and containing silver-supported zeolite, silver-supported alumina, and titania , the catalyst layer includes silver-supported zeolite and titania. There is provided an exhaust gas purifying catalyst characterized by including a multilayer structure of a first layer containing a second layer containing a silver-carrying alumina and titania .

According to the present invention, together with a wider temperature range to exhibit _the NO _x purification performance including silver exhaust gas purifying catalyst is good, advantageous technique is provided to hardly occurs poisoning due to the sulfur.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a structure that can be employed in the exhaust gas purifying catalyst shown in FIG.

  The exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 is an open flow type monolith catalyst used for purifying exhaust gas discharged from, for example, a diesel engine. The exhaust gas-purifying catalyst 1 includes a substrate 2 such as a monolith honeycomb substrate. The substrate 2 is typically made of ceramics such as cordierite.

  A catalyst layer 3 is formed on the partition walls of the substrate 2. The catalyst layer 3 contains silver-supported zeolite, silver-supported alumina, and titania. In the example shown in FIG. 2, silver-supported zeolite, silver-supported alumina, and titania are mixed substantially uniformly, and the catalyst layer 3 has a single layer structure.

  The silver-supported zeolite is, for example, a silver ion exchange zeolite. Silver ion-exchanged zeolite can be obtained, for example, by substituting at least a part of cations such as ammonium ions ion-bonded to aluminum with silver ions.

  In this silver-supported zeolite, the molar ratio of silica to alumina is, for example, in the range of 20 to 50. When this molar ratio is small, the stability of the zeolite may be insufficient. When this molar ratio is large, it is difficult to support a sufficient amount of silver on the zeolite.

The silver supported amount of the silver supported zeolite is, for example, in the range of 1% by mass to 10% by mass, and typically in the range of 3% by mass to 8% by mass. When the amount of silver supported is small, a sufficient NO _x purification effect cannot be obtained. When the amount of silver carried is large, poisoning due to sulfur is likely to occur, and there is almost no performance improvement accompanying an increase in the amount of silver carried.

Silver-carrying alumina is obtained by, for example, carrying silver fine particles on the surface of alumina particles. The silver carrying amount of the silver carrying alumina is, for example, in the range of 1 to 10% by mass, and typically in the range of 3 to 8% by mass. When the amount of silver supported is small, a sufficient NO _x purification effect cannot be obtained. When the amount of silver carried is large, poisoning due to sulfur is likely to occur, and there is almost no performance improvement accompanying an increase in the amount of silver carried.

The mass ratio of the silver-carrying zeolite to the silver-carrying alumina is, for example, in the range of 1/3 to 3, and typically in the range of 2/3 to 3/2. When this mass ratio is small, the NO _x purification performance in a low temperature region may be insufficient. If this mass ratio is large, the NO _x purification performance at high temperatures may be insufficient.

The mass ratio of titania relative to the sum of silver zeolite and silver alumina is, for example, in the range of 1/10 to 1/4. When this mass ratio is small, the effect of suppressing poisoning by sulfur is small. When this mass ratio is large, the silver content decreases, and a sufficient NO _x purification effect may not be obtained.

The coating amount of the catalyst layer 3 per liter of the substrate 2 is, for example, in the range of 100 g / L to 250 g / L, and typically in the range of 150 g / L to 200 g / L. When the coating amount is small, it is difficult to achieve high NO _x purification performance. Increasing the coating amount increases the heat capacity of the exhaust gas-purifying catalyst 1.

The amount of silver supported per liter of the substrate 2 is, for example, in the range of 1 g / L to 20 g / L, and typically in the range of 1 g / L to 10 g / L. When the amount of silver supported is small, it is difficult to achieve high NO _x purification performance. When the amount of silver supported is large, the silver content decreases and a sufficient NO _x purification effect may not be obtained.

As described above, the exhaust gas-purifying catalyst 1 uses silver-supported zeolite and silver-supported alumina. Silver-supported zeolite is superior in NO _x purification performance in a low temperature range as compared with silver-supported alumina. Silver-supported alumina is superior in NO _x purification performance and heat resistance in a high temperature range as compared with silver-supported zeolite. And titania plays the role which suppresses the poisoning by sulfur. Therefore, the exhaust gas-purifying catalyst 1 has a wide temperature range that exhibits excellent NO _x purification performance, and is not easily poisoned by sulfur.

Further, when the exhaust gas-purifying catalyst 1 is used, typically, a special reduction process such as a rich spike is unnecessary. Therefore, according to the exhaust gas-purifying catalyst 1, more excellent fuel efficiency can be achieved as compared with the storage reduction system. Furthermore, when using the exhaust gas-purifying catalyst 1, typically, unlike urea addition type _the NO _x reduction system, the cost for the additive and spare system does not occur. Therefore, the exhaust gas-purifying catalyst 1 is extremely useful for purifying exhaust gas discharged from a diesel engine.

Various modifications can be made to the exhaust gas-purifying catalyst 1.
FIG. 3 is a cross-sectional view schematically showing another example of a structure that can be employed in the exhaust gas purifying catalyst shown in FIG. FIG. 4 is a cross-sectional view schematically showing still another example of a structure that can be employed in the exhaust gas-purifying catalyst shown in FIG.

  In the exhaust gas-purifying catalyst 1 shown in FIGS. 3 and 4, the catalyst layer 3 has a multilayer structure including a first layer 3a and a second layer 3b. In the exhaust gas-purifying catalyst 1 shown in FIG. 3, the first layer 3a is interposed between the base material 2 and the second layer 3b. In the exhaust gas-purifying catalyst 1 shown in FIG. 4, the second layer 3b is interposed between the base material 2 and the first layer 3a.

  The first layer 3a contains silver-supported zeolite and titania. The silver-supporting zeolite and titania are mixed substantially uniformly, and the first layer 3a has a single layer structure.

The second layer 3b contains silver-carrying alumina and titania. Silver-carrying alumina and titania are mixed substantially uniformly, and the second layer 3b has a single-layer structure.
As described above, the catalyst layer 3 may have a multilayer structure.

  The catalyst layer 3 may further contain materials other than silver-supported zeolite, silver-supported alumina and titania. For example, the catalyst layer 3 may further include a noble metal such as platinum, palladium and rhodium, or an oxygen storage material such as cerium oxide.

  The above-described technique can be applied to other than the open flow type monolith catalyst. For example, the above-described technique can be applied to other types of catalysts such as a wall flow type monolith catalyst and a pellet catalyst.

  Examples of the present invention will be described below.

<Manufacture of catalyst C1>
In this example, the exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 2 was produced by the following method.
First, 8.5 g of silver nitrate was dissolved in 100 g of pure water. Ammonia water was added to adjust the pH value to 8 to 10, and 100 g of zeolite was added to this solution. Here, a zeolite having a molar ratio of silica to alumina of 40 was used. After stirring for about 1 hour, the zeolite was sequentially subjected to drying and heat treatment at 500 ° C. to obtain a silver-supported zeolite. Hereinafter, this silver-supported zeolite is referred to as silver-supported zeolite Z1.

  Next, 8.5 g of silver nitrate was dissolved in 200 g of pure water. 100 g of γ-alumina powder was added to this solution. After stirring for about 1 hour, the alumina powder was sequentially subjected to drying and heat treatment at 500 ° C. to obtain silver-supported alumina. Hereinafter, this silver-supported alumina is referred to as silver-supported alumina A1.

  Next, 100 g of silver-supported zeolite Z1, 100 g of silver-supported alumina A1, 40 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. Here, a silica sol having a solid content of 30% by mass was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S1.

  Thereafter, the catalyst layer 3 was formed by repeating the coating of the slurry S1 on the monolith honeycomb substrate 2 made of cordierite and the heat treatment of the substrate 2. Here, as the substrate 2, an open flow type monolith honeycomb substrate having a length of 50 mm, a diameter of 30 mm, a volume of 35 cc, and 400 cells per square inch was used. .

  As described above, an exhaust gas-purifying catalyst 1 was obtained in which the washcoat amount of the catalyst layer 3 per 1 L of the volume of the substrate 2 was 200 g and the silver loading amount was 6.8 g. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as catalyst C1.

<Manufacture of catalyst C2>
In this example, the exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 3 was produced by the following method.
First, 200 g of silver-supported zeolite Z1, 40 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the titania powder and the silica sol, the same ones used in the production of the catalyst C1 were used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S2.

  Next, the first layer 3a was formed by repeating the coating of the slurry S2 on the monolith honeycomb substrate 2 and the heat treatment of the substrate 2. Here, the same substrate 2 as that used in the production of the catalyst C1 was used.

  Next, 200 g of silver-supported alumina A1, 40 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the titania powder and the silica sol, the same ones used in the production of the catalyst C1 were used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S3.

  Next, the second layer 3b was formed by repeating the coating of the slurry S3 on the monolith honeycomb substrate 2 and the heat treatment of the substrate 2.

  As described above, an exhaust gas-purifying catalyst 1 in which the washcoat amount of each of the first layer 3a and the second layer 3b per 1 L of the base material 2 was 100 g and the silver loading amount was 6.8 g was obtained. . Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as catalyst C2.

<Manufacture of catalyst C3>
In this example, the exhaust gas-purifying catalyst 1 shown in FIGS. 1 and 4 was produced by the following method.
First, the second layer 3b was formed by repeating the coating of the slurry S3 on the monolith honeycomb substrate 2 and the heat treatment of the substrate 2. Here, the same substrate 2 as that used in the production of the catalyst C1 was used.

  Next, the first layer 3a was formed by repeating the coating of the slurry S2 on the monolith honeycomb substrate 2 and the heat treatment of the substrate 2.

  As described above, an exhaust gas-purifying catalyst 1 in which the washcoat amount of each of the first layer 3a and the second layer 3b per 1 L of the base material 2 was 100 g and the silver loading amount was 6.8 g was obtained. . Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as catalyst C3.

<Manufacture of catalyst C4>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 150 g of silver-supported zeolite Z1, 50 g of silver-supported alumina A1, 100 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the titania powder and the silica sol, the same ones used in the production of the catalyst C1 were used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S4.

  Next, the catalyst layer was formed by repeating the coating of the slurry S4 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C4.

<Manufacture of catalyst C5>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 50 g of silver-supported zeolite Z1, 150 g of silver-supported alumina A1, 100 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the titania powder and the silica sol, the same ones used in the production of the catalyst C1 were used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S5.

  Next, the catalyst layer was formed by repeating the coating of the slurry S5 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C5.

<Manufacture of catalyst C6>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 200 g of silver-supported zeolite Z1, 100 g of pure water, and 200 g of silica sol were mixed. As the silica sol, the same one used in the production of the catalyst C1 was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S6.

  Next, the catalyst layer was formed by repeating the coating of the slurry S6 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C6.

<Manufacture of catalyst C7>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 200 g of silver-supported alumina A1, 100 g of pure water, and 200 g of silica sol were mixed. As the silica sol, the same one used in the production of the catalyst C1 was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S7.

  Next, the catalyst layer was formed by repeating the coating of the slurry S7 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C7.

<Manufacture of catalyst C8>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 50 g of silver-supported zeolite Z1, 150 g of silver-supported alumina A1, 100 g of pure water, and 200 g of silica sol were mixed. As the silica sol, the same one used in the production of the catalyst C1 was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S8.

  Next, the catalyst layer was formed by repeating the coating of the slurry S8 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a catalyst layer washcoat amount of 173 g and a silver carrying amount of 6.8 g per 1 L of the base material volume was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C8.

<Manufacture of catalyst C9>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 160 g of silver-supported zeolite Z1, 40 g of silver-supported alumina A1, 100 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the silica sol, the same one used in the production of the catalyst C1 was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S9.

  Next, the catalyst layer was formed by repeating the coating of the slurry S9 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C9.

<Manufacture of catalyst C10>
In this example, an exhaust gas purification catalyst was produced by the following method.
First, 40 g of silver-supported zeolite Z1, 160 g of silver-supported alumina A1, 100 g of titania powder, 100 g of pure water, and 200 g of silica sol were mixed. As the silica sol, the same one used in the production of the catalyst C1 was used. While stirring this liquid mixture, the particle | grains which it contains were grind | pulverized, and the slurry was obtained. Hereinafter, this slurry is referred to as slurry S10.

  Next, the catalyst layer was formed by repeating the coating of the slurry S10 on the monolith honeycomb substrate and the heat treatment of the substrate. Here, the same substrate as that used in the production of the catalyst C1 was used.

  As described above, an exhaust gas purifying catalyst having a wash coat amount of 200 g per 1 L of the base material and a silver loading of 6.8 g was obtained. Hereinafter, the exhaust gas-purifying catalyst is referred to as catalyst C10.

<Initial performance evaluation>
The first simulated gas was passed through each of the catalysts C1 to C7, C9, and C10, and the NO _x purification performance exhibited by each catalyst within the temperature range of 100 ° C. to 600 ° C. was examined.

  As the first simulated gas, a mixed gas composed of 1800 ppm of propylene, 300 ppm of nitric oxide, 10% of oxygen, and the remaining nitrogen was used. The flow rate of the first simulated gas was 20 L / min.

Further, as the NO _x purification performance, the purification rate calculated from the following equation was obtained.
Purification rate (%) = (inlet NO concentration−outlet NO _x concentration) / inlet NO concentration × 100
Here, “inlet NO concentration” indicates the carbon monoxide concentration at the inlet of the catalyst. "Exit concentration of NO _x" indicates the concentration of NO _x at the outlet of the catalyst.

5 and 6 are graphs showing examples of NO _x purification performance exhibited by the exhaust gas purification catalyst in the initial state. In the figure, the horizontal axis indicates the temperature, and the vertical axis indicates the purification rate.

As shown in FIGS. 5 and 6, the catalysts C1 to C5, C9 and C10, particularly the catalysts C1 to C5, showed superior NO _x purification performance in a wider temperature range than the catalysts C4 to C8. . Thus, exhibiting excellent NO _x purification performance over a wide temperature range under conditions of excessive oxygen means that it can be adapted to various regulatory modes, and in particular, diesel engines emit It is extremely advantageous for purifying exhaust gas.

<Performance evaluation after endurance>
First, in order to cause poisoning of the catalyst by sulfur, the second simulated gas was passed through each of the catalysts C1 to C3 and C6 to C8 for 5 hours under a temperature condition of 400 ° C. As the second simulated gas, a mixed gas composed of 200 ppm sulfur dioxide, 10% oxygen, and the balance nitrogen was used. The flow rate of the second simulated gas was 20 L / min.

Thereafter the durability test, each of the catalysts C1 to C3 and C6 to C8 in was circulated first simulation gas, each catalyst was examined _the NO _x purification performance shown in the temperature range of 100 ° C. to 600 ° C.. The flow rate of the first simulated gas was 20 L / min. Further, as the NO _x purification performance, the purification rate calculated from the above equation was obtained.

FIG. 7 is a graph showing an example of the NO _x purification performance of the exhaust gas purification catalyst after the durability test. In the figure, the horizontal axis indicates the temperature, and the vertical axis indicates the purification rate.

As shown in FIG. 7, the catalysts C1 to C3 showed superior NO _x purification performance in a wider temperature range than the catalysts C6 to C8. As is clear from a comparison between the data shown in the data and 7 shown in FIGS 5 and 6, the catalysts C1 to C3, compared to catalysts C6 to C8, reduction of the NO _x purification performance accompanying the endurance test Was suppressed.
The invention described in the original claims is appended below.
[1] An exhaust gas purifying catalyst comprising: a base material; and a catalyst layer supported by the base material and containing silver-supported zeolite, silver-supported alumina, and titania.
[2] The catalyst layer has a multilayer structure including a first layer containing silver supported zeolite and titania and a second layer containing silver supported alumina and titania. Item 2. The exhaust gas purifying catalyst according to Item 1.
[3] The exhaust gas purifying catalyst as described in [1], wherein the catalyst layer has a single layer structure.
[4] The exhaust gas purifying catalyst according to any one of [1] to [3], wherein a mass ratio of the silver-carrying zeolite to the silver-carrying alumina is in a range of 1: 3 to 3: 1.

1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a structure that can be employed in the exhaust gas purification catalyst shown in FIG. 1. Sectional drawing which shows schematically the other example of the structure employable as the exhaust gas purification catalyst shown in FIG. Sectional drawing which shows schematically the further another example of the structure employable as the exhaust gas purification catalyst shown in FIG. Graph exhaust gas purifying catalyst shows an example of the NO _x purification performance shown in the initial state. Graph exhaust gas purifying catalyst shows an example of the NO _x purification performance shown in the initial state. Graph showing an example of the NO _x purifying performance of the exhaust gas purifying catalyst is shown after the durability test.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification catalyst, 2 ... Base material, 3 ... Catalyst layer, 3a ... 1st layer, 3b ... 2nd layer.

Claims (2)

A substrate and a catalyst layer supported by the substrate and containing silver-supported zeolite, silver-supported alumina, and titania, and the catalyst layer includes a first layer containing silver-supported zeolite and titania; An exhaust gas purifying catalyst comprising a multilayer structure of a silver-supporting alumina and a second layer containing titania . 2. The exhaust gas purifying catalyst according to claim 1 , wherein a mass ratio of the silver-carrying zeolite and the silver-carrying alumina is in a range of 1: 3 to 3: 1.

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