JP2827532B2 - Catalyst device for reducing diesel particulates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst device for reducing diesel particulates contained in exhaust gas of a diesel engine (hereinafter referred to as DE).

[0002]

2. Description of the Related Art Regarding gasoline engines, harmful substances in exhaust gas have been steadily reduced due to strict regulations on exhaust gas and advances in technology capable of coping with it. But DE
With regard to, the regulation and development of technology are behind in comparison with gasoline engines because of the peculiar circumstances that harmful components are mainly emitted as particulates, and there is a need for the development of an exhaust gas purification device that can reliably purify.

[0003] As a DE exhaust gas purifying apparatus which has been developed to date, a method using a trap (without a catalyst and with a catalyst) and an open type SOF decomposition catalyst are known. Of these, the method using a trap is
It traps diesel particulates and regulates emissions, and is particularly effective for exhaust gas with a high dry suit ratio. However, a regenerative processing device is required, and many practical problems remain, such as cracking of the catalyst structure during regeneration, clogging by ash, or a complicated system.

On the other hand, as an open type SOF decomposition catalyst, a catalyst in which an oxidation catalyst such as a platinum group metal is supported on a support layer of activated alumina or the like is used as in a gasoline engine, as shown in, for example, JP-A-1-171626. And CO
SOF in Diesel Particulate with HC and HC
(Soluble Organic Fraction) is purified by oxidative decomposition. This open-type SOF cracking catalyst has the drawback of low removal rate of dry suits, but the amount of dry suits can be reduced by improving the DE and the fuel itself, and has the great advantage of not requiring a regeneration unit. Therefore, further improvement of technology is expected in the future.

[0005]

However, the open type S
The OF decomposition catalyst can efficiently decompose SOF at a high temperature, but has a disadvantage that the function of the oxidation catalyst is low and the purification performance of the SOF deteriorates at a low temperature. Therefore, when the engine is started or idling, the temperature of the exhaust gas is low, and a phenomenon occurs in which undecomposed SOF becomes soot and accumulates in the honeycomb passage. Then, there is a problem that the catalyst is clogged by the deposited soot and the catalyst performance is reduced.

In the open type SOF decomposition catalyst, SO ₂ in the exhaust gas is also oxidized in a high temperature range, and
₃ is generated, and on the contrary, the amount of particulates increases. This is because SO ₂ is not measured as particulates, but SO ₃ is measured as particulates. In particular, in DE, oxygen gas is sufficiently present in the exhaust gas, and the oxidation reaction of SO ₂ is likely to occur.

[0007] Further, in the open type SOF decomposition catalyst, it is known that the oxidation catalyst is poisoned by a large amount of sulfur contained in the exhaust gas of DE, and the catalytic activity is reduced. That is, SO ₂ generated from the sulfur in the fuel reacts with the alumina in the catalyst supporting layer to form aluminum sulfate (Al ₂ (SO ₄ )).
₃ ) is formed, which covers the oxidation catalyst and reduces the catalytic activity. Therefore, in the field of exhaust gas treatment such as boilers, catalysts in which titania (TiO ₂ ) having excellent resistance to sulfur poisoning is used as a catalyst supporting layer and an oxidation catalyst such as Pt and V is supported have been developed and put to practical use. However, this type of catalyst is
There is no OF adsorption property, and SOF is directly discharged in a low temperature range.

[0008] The present invention has been made in view of such circumstances, and efficiently adsorbs SOF in a low-temperature region to improve SOF.
It is an object of the present invention to prevent the emission of SO ₃ , suppress the production of SO ₃ , and prevent the oxidation catalyst from being poisoned.

[0009]

According to the present invention, there is provided a catalytic device for reducing diesel particulates, comprising a first honeycomb body having a first coat layer made of a material selected from activated alumina and zeolite. A first catalyst disposed on the upstream side, TiO ₂ , SiO ₂ , ZrO ₂
And a second catalyst formed of a second honeycomb body having a second coat layer made of a material selected from CaO and an oxidation catalyst supported on the second coat layer and disposed in an exhaust passage downstream of the first catalyst. It is characterized by becoming.

[0010] The catalyst device of the present invention comprises a first catalyst disposed upstream of an exhaust passage and a second catalyst disposed downstream thereof. The first catalyst includes a honeycomb body as a catalyst carrier substrate and a first coat layer formed on the honeycomb body surface. As the honeycomb body, there can be used a ceramic carrier such as cordierite, a metal carrier, or the like having a number of conventionally known honeycomb-shaped passages. The number of passages is desirably 100 to 200 cells / in ² . In this way, the passage diameter becomes relatively large, and clogging can be prevented. Incidentally, as a conventional degree of clogging, clogging occurs in a range of 10 to 20 mm from the upstream end face in the case of a honeycomb body of 400 cells / in ² .

The first coat layer is formed from one or both of activated alumina and zeolite. The first coat layer has excellent SOF adsorption performance and adsorbs SOF in a low temperature range such as at idling to prevent discharge. Second
The catalyst includes a honeycomb body as a catalyst carrier base material, a second coat layer formed on the surface of the honeycomb body, and an oxidation catalyst supported on the second coat layer. The honeycomb body can be configured in the same manner as the first catalyst, and a conventionally known honeycomb-shaped body having a large number of passages such as a ceramic carrier such as cordierite and a metal carrier can be used. The number of passages is preferably 300 to 400 cells / in ^2, which is larger than that of the first catalyst. In this case, the surface area is increased, and the oxidation catalyst performance is sufficiently exhibited.

The second coat layer is made of TiO ₂ , SiO ₂ , Z
It is composed of one or more of rO ₂ and CaO. Since this second coat layer does not adsorb SO ₂ , SO ₂
Oxidation reaction of ₂ hardly occurs, and the amount of particulates is reduced. An oxidation catalyst is supported on the second coat layer. As this oxidation catalyst, a noble metal catalyst similar to the conventional one such as Pt, Rh, and Pd can be used.
In some cases, a base metal can be used together.

The amount of the first coat layer and the second coat layer attached to the honeycomb body is not particularly limited, and can be about 20 to 200 g per liter of the honeycomb body as in the conventional case. The amount of the oxidation catalyst carried by the second coat layer is about 0.05 to 2 g per liter of the honeycomb body as in the conventional case. It is conceivable to use a ceramic foam in which a coat layer of activated alumina, zeolite, or the like is formed, or a pellet of activated alumina or zeolite as the first catalyst, but this is not preferable because the pressure loss increases.

[0014]

In the catalytic device of the present invention, the exhaust gas of the diesel engine first passes through the first catalyst. Here, since the first catalyst has the first coat layer made of activated alumina or zeolite, it exhibits high SOF adsorption performance, and SOF is adsorbed even at low temperatures during idling or start-up, and SOF emission is suppressed. You. Furthermore, although SO ₂ is also adsorbed by the first catalyst, no poisoning occurs because the first catalyst has no oxidation catalyst. Therefore, the first catalyst also serves as a poison trap.

On the other hand, the second catalyst, which carries an oxidation catalyst, oxidizes and decomposes the SOF at a high temperature of about 300 ° C. or higher. At a high temperature, the SOF adsorbed on the first coat layer becomes a vapor and is desorbed from the first coat layer, and is oxidized and decomposed by the second catalyst. Since the second coating layer is hardly adsorbing ability of SO _2, SO ₂ is discharged as such hardly oxidized, the discharge amount of particulates is reduced. Further, since SO ₂ is not adsorbed by the second catalyst, poisoning of the oxidation catalyst hardly occurs.

The number of honeycomb passages of the first catalyst is set to
If the diameter is smaller than that of the catalyst and the diameter of the honeycomb passage is increased, the honeycomb passage is prevented from being blocked by the adsorbed SOF even under severe conditions such as idling for a long time, and the catalyst due to clogging is prevented. Performance degradation is prevented.

[0017]

Thus, according to the catalyst device of the present invention,
At the time of idling or starting, the first catalyst suppresses the emission of SOF, and at a high temperature, the second catalyst oxidizes and decomposes the SOF. Since SO ₂ is not adsorbed to the second coat layer,
Even at high temperatures, the formation of SO ₃ is prevented, and the amount of diesel particulate emissions is reduced. Therefore, the SOF is suppressed from the low temperature range to the high temperature range while suppressing the generation of SO _3.
Can be reliably suppressed. Further, at a low temperature, the SOF is adsorbed by the first catalyst, so that clogging of the second catalyst is prevented and deterioration of the catalyst performance is prevented.

[0018]

The present invention will be specifically described below with reference to examples. FIG.
FIG. 1 shows a schematic view of the catalyst device of this embodiment. This catalyst device includes a first catalyst A and a second catalyst B, and is held in a container 100 via a sealing material 101 in a line on the same axis. Then, the first catalyst A is located on the upstream side of the exhaust passage, and after the exhaust gas passes through the first catalyst A, the second catalyst B
It is configured to pass through.

In this embodiment, the first catalyst A and the second catalyst B were used in combination of various compositions. Less than,
The description of each manufacturing method is replaced with the description of each configuration. (First Catalyst A ₁ ) A columnar cordierite-based honeycomb carrier having a diameter of 90 mm, a length of 60 mm, a cell number of 200 cells / in ² , and a cell wall thickness of 0.3 mm was prepared, and γ-alumina powder, alumina sol, aluminum nitrate, It was immersed in a slurry composed of distilled water. After pulling up and removing excess slurry, the slurry was dried at 120 ° C. for 3 hours, and calcined at 600 ° C. for 2 hours to form a first coat layer made of activated alumina.
To obtain a catalyst A _1. The attached amount of the first coat layer was 150 g per liter of the honeycomb carrier. (First Catalyst A ₂ ) On the same honeycomb carrier as the first catalyst A ₁ , a first coat layer also made of zeolite was formed using a slurry made of zeolite powder (H-type mordenite), silica sol, and distilled water. . The attached amount of the first coat layer was about 150 g per liter of the honeycomb carrier. (First catalyst A ₃ ) Same as the first catalyst A ₁ except that a columnar cordierite-based honeycomb carrier having a diameter of 90 mm, a length of 60 mm, a cell number of 100 cells / in ² , and a cell wall thickness of 0.43 mm was used. And 1 per liter of honeycomb carrier
First having a first coating layer of 50 g of activated alumina
To obtain a catalyst A _3. (Second Catalyst B ₁ ) A columnar cordierite-based honeycomb carrier having a diameter of 90 mm, a length of 60 mm, and a cell count of 400 cells / in ² was prepared and immersed in a slurry composed of TiO ₂ powder, TiO ₂ sol, and distilled water. After pulling up to remove excess slurry, the slurry was dried at 120 ° C. for 3 hours, and then dried at 600 ° C. for 2 hours.
By firing for a time, a second coat layer made of TiO ₂ was formed. The attached amount of the second coat layer was 150 g per liter of the honeycomb carrier.

Next, the honeycomb carrier having the second coat layer was immersed in an aqueous solution of dinitrodiammine platinum, pulled up and blown off excess water droplets, dried and fired to carry 1.5 g of Pt per liter of carrier. . (Second Catalyst B ₂ ) Pt, Pd, and Rh were similarly supported on a honeycomb carrier having a second coat layer similar to that of the second catalyst B ₂ using chloroplatinic acid, palladium chloride, and rhodium chloride aqueous solution. The ratio of each oxidation catalyst is 0.6 g of Pt, 0.6 g of Pd, and 0.3 g of Rh per liter of the carrier. (Second catalyst B ₃ ) A columnar cordierite-based honeycomb carrier having a diameter of 90 mm, a length of 60 mm, and a cell number of 300 cells / in ² was prepared, and a slurry composed of SiO ₂ powder, SiO ₂ sol, and distilled water was used. About 15 per liter of carrier
A second coat layer of 0 g of SiO ₂ was formed. Then, using an aqueous solution of palladium chloride, 1.5 g of Pd was supported per liter of the carrier. (Second Catalyst B ₄ ) The same honeycomb carrier as the second catalyst B ₃ was prepared, and a slurry composed of ZrO ₂ powder, ZrO ₂ sol, and distilled water was used to prepare 150 g of Z per 1 liter of the carrier.
A second coat layer of rO ₂ was formed. Then, using an aqueous rhodium chloride solution, 1.0 g per liter of carrier
Of Rh was supported. (Comparative catalyst C ₁ ) A columnar cordierite-based honeycomb support having a diameter of 90 mm, a length of 120 mm, and a cell number of 400 cells / in ² was prepared, and a slurry composed of γ-alumina powder, alumina sol, and aluminum nitrate distilled water was used. About 150 g of an activated alumina supporting layer was formed per liter of the carrier. Then, using an aqueous solution of dinitrodiammine platinum, 1.5 g of Pt was supported per liter of the carrier. (Comparative catalyst C ₂ ) An activated alumina supporting layer was similarly formed on the same honeycomb carrier as the comparative catalyst C ₁ , and the second catalyst B
₂ similarly to the carrier per liter of Pt: 0.6 g, P
d: 0.6 g and Rh: 0.3 g were supported. (Comparative catalyst C ₃ ) A slurry composed of SiO ₂ powder, SiO ₂ sol and distilled water was used on the same honeycomb carrier as the comparative catalyst C ₁ to obtain about 150 g of Si per liter of the carrier.
A coat layer made of O ₂ was formed. Then, using an aqueous palladium chloride solution, 1.5 g of P
d.

Each of the first catalyst and the second catalyst is
The catalyst devices of Examples 1 to 7 were combined as shown in Table 1 and held in a container 100 as shown in FIG. The first catalyst is located upstream and the second catalyst is located downstream. Further, each of the comparative catalysts was independently held in the container 100 as shown in FIG.

[0022]

[Table 1]

[0023]

[Table 2] (Test Example 1) The catalyst devices of Example 1 and Comparative Example 1 were installed in an exhaust system of a passenger car equipped with a swirl chamber type DE with a displacement of 2400 cc. After idling (30 seconds) → 60 km / h (60 seconds) 10 times on the chassis dynamo, idling (60 seconds)
→ The vehicle traveled in a pattern of 100 km / h (120 seconds), and the particulate reduction rate at every 5000 km travel was measured in a new 10 mode pattern. The results are shown in FIG. Note that the particulate reduction rate is represented by the following equation.

Particulate reduction rate (%) = (upstream-side particulate amount−downstream-side particulate amount) ──────────────────────── ───── × 100 (particulate amount on the upstream side) From FIG. 3, it can be seen that the catalyst device of Example 1 shows more stable purification performance than Comparative Example 1. In this test, since the exhaust gas temperature rose up to 380 ° C,
No clogging occurred in either device. (Test Example 2) The catalyst devices of Example 2 and Comparative Example 2 were installed in an exhaust system of a truck equipped with a direct injection DE with a displacement of 3000 cc, respectively, and continuously operated in an idling state to measure a back pressure. FIG. 4 shows the results.

As apparent from FIG. 4, the back pressure of the catalyst device of Example 2 hardly changes even after 60 hours. That is, it is clear that no clogging has occurred. On the other hand, in the catalyst device of Comparative Example 2, it can be seen that the back pressure sharply increases after 12 hours and the clogging increases synergistically. (Test Example 3) The catalyst devices of Examples 3 to 7 and Comparative Examples 1 to 3 were run in the same pattern as in Test Example 1, and the reduction rate of particulates at the start of running and after running 15,000 km was measured. It was measured with the new 10 mode pattern. Table 3 shows the results.

[0026]

[Table 3] From Table 3, the values of Examples 4 and 7 are lower than those of the catalyst devices of the other examples, but this is due to the fact that the number of cells of the first catalyst is as small as 100 cells / in ² . However, as compared with the comparative example, as in the other examples, it shows a high value even after traveling 15,000 km.

On the other hand, Comparative Examples 1 and 2, which have an activated alumina supporting layer having a high SOF adsorption capacity, show a high value at the initial stage, but decrease extremely after traveling 15,000 km, and almost reduce particulates. I cannot purify. This is the soot accumulation and S
This is due to poisoning due to the adsorption of OF. However, Examples 3, 4, and 7 having a similar activated alumina coat layer
It shows a high value even after running. This is apparently due to the effect of separating the active alumina coat layer and the oxidation catalyst.

Further, Comparative Example 3 shows a low value even at the initial stage because the carrier layer does not have the SOF adsorption ability, and the soot is deposited after traveling, and the value becomes even lower. That is, according to the catalyst device for reducing diesel particulates of the present embodiment, clogging is prevented and SOF can be efficiently oxidatively decomposed even when the device is operated for a long time in an idling state.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a catalyst device of the present invention.

FIG. 2 is a schematic configuration explanatory view of a catalyst device of a comparative example.

FIG. 3 is a graph showing a change in a particulate reduction rate depending on a traveling distance.

FIG. 4 is a graph showing a change in back pressure with operating time.

[Explanation of symbols]

A: First catalyst B: Second catalyst 100: Container 1
01: Sealing material

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B01J 23/58 B01D 53/36 104A

Claims (1)

(57) [Claims] 1. A first catalyst comprising a first honeycomb body having a first coat layer made of a material selected from activated alumina and zeolite and disposed on an upstream side of an exhaust passage, TiO ₂ , S
a second honeycomb body having a second coat layer made of a material selected from iO ₂ , ZrO ₂ and CaO, and an oxidation catalyst supported on the second coat layer, disposed in the exhaust passage downstream of the first catalyst; And a second catalyst to be used.