JP6153841B2 - Diesel particulate collection filter catalyst - Google Patents

Description

  The present invention relates to a diesel particulate filter (DPF) catalyst and an exhaust gas purification system.

  Exhaust gas discharged from an internal combustion engine such as an engine contains harmful substances such as particulate matter (PM), hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx). . Since these substances cause air pollution, it is necessary to purify the exhaust gas.

  In particular, exhaust gas discharged from a diesel engine contains a large amount of PM, and DPF is used to collect this. Since the collected PM accumulates in the DPF, there is a problem that the pressure loss increases and the output decreases due to an increase in the amount of PM deposited.

  Therefore, in order to remove the accumulated PM, the DPF is subjected to high temperature conditions, and regeneration of the DPF that burns PM is performed. However, since a high temperature of 600 ° C. or higher is required to burn PM, platinum group metals supported on a carrier are used in the DPF in order to burn PM at a lower temperature (for example, patents). Reference 1).

JP 2008-207082 A

Sulfur components contained in diesel fuel are attached to the DPF used for collecting PM. If a large amount of sulfur component adheres when regenerating the DPF, a large amount of sulfur component is released at a time, and white smoke is generated. As a method for suppressing the generation of white smoke, control of an exhaust gas purification system is generally performed, but this method causes a problem of causing deterioration in fuel consumption.
Therefore, an object of the present invention is to provide a new technique for suppressing the generation of white smoke.

As a result of intensive studies by the present inventors, the sulfur component causing white smoke is attached to the carrier in the DPF, and it is possible to reduce the adhesion amount of the sulfur component by adjusting the specific surface area and amount of the carrier. I found it.
That is, the present invention includes the following.

[1] A DPF catalyst comprising a DPF base material and a catalyst layer disposed on the DPF base material,
The catalyst layer includes a support and a catalyst metal supported on the support,
The total surface area of the carrier per volume of the DPF substrate, which is the product of the specific surface area (m ² / g) of the carrier and the amount of the carrier per volume of the DPF substrate (g / L) m ² / L) is 5~450m ² / L, the DPF catalyst.
[2] The DPF catalyst according to [1], wherein the support has a specific surface area of 1 to 50 m ² / g.
[3] The DPF catalyst according to [1] or [2], wherein the amount of the support per volume of the DPF substrate is 5 to 15 g / L.

[4] The DPF catalyst according to any one of [1] to [3] and a diesel oxidation catalyst,
The exhaust gas purification system, wherein the diesel oxidation catalyst is installed upstream of the DPF catalyst in the exhaust gas flow direction.

[5] A DPF catalyst comprising a DPF substrate, a first catalyst layer disposed on the DPF substrate, and a second catalyst layer disposed on the first catalyst layer,
The first catalyst layer includes a first carrier and a first catalyst metal supported on the first carrier;
The second catalyst layer includes a second carrier and a second catalyst metal supported on the second carrier;
The first catalytic metal is a metal having a function of promoting combustion of particulate matter;
The second catalytic metal is a metal having a function of oxidizing nitric oxide;
The product of the specific surface area (m ² / g) of the first carrier and the amount (g / L) of the first carrier per volume of the DPF substrate, per volume of the DPF substrate. The total surface area of the first support (m ² / L); the specific surface area of the second support (m ² / g); and the amount of the second support per volume of the DPF substrate (g / is the product of L), the second total surface area of the support per volume of the DPF substrate ^(m 2 / L); the sum of a 5~450m ² / L, the DPF catalyst.

  According to the present invention, the generation of white smoke during regeneration of the DPF catalyst can be suppressed.

An example of a DPF base material is shown. An example of the exhaust gas purification system containing a DPF catalyst and DOC is shown. The relationship between the total surface area of the support | carrier per volume of a DPF base material and the adhesion amount of sulfur, and the relationship between the adhesion amount of sulfur and generation | occurrence | production of white smoke are shown.

Hereinafter, the present invention will be described in detail.
The present invention relates to a DPF catalyst including a DPF base material and a catalyst layer disposed on the DPF base material. In the DPF catalyst according to the present invention, the catalyst layer includes a support and a catalyst metal supported on the support, and the total surface area (m ² / L) of the support per volume of the DPF base material is 5 -450 m < ² > / L. Here, the “total surface area of the carrier per volume of the DPF substrate” is the product of the specific surface area (m ² / g) of the carrier and the amount of carrier (g / L) per volume of the DPF substrate. is there.

  The sulfur component contained in diesel fuel is more likely to adhere to the support as the specific surface area of the support increases. In addition, the sulfur component is more easily attached as the amount of the carrier increases. Therefore, by reducing the specific surface area of the carrier and reducing the amount of the carrier, the total surface area of the carrier per volume of the DPF substrate is adjusted within a certain range, so that the DPF catalyst can be used during PM collection. The amount of the sulfur component adhering to can be reduced. As a result, it is possible to suppress large-scale release of sulfur components during regeneration of the DPF catalyst and avoid the generation of white smoke.

  As the DPF base material contained in the DPF catalyst according to the present invention, it is not necessary to use a special one, and a filter base material generally used for the purpose of collecting PM can be used. For example, a wall flow type monolith honeycomb substrate can be used as the DPF substrate (for example, FIG. 1). The material of the base material is not particularly limited, and examples thereof include base materials such as ceramic, silicon carbide, and metal.

  A catalyst layer is disposed on the DPF substrate. Here, when the DPF substrate is a wall flow type monolith honeycomb substrate, the catalyst layer is disposed on the surface of the pores formed inside the cell walls constituting the plurality of cells in the substrate. It is preferable. Moreover, the catalyst layer may be arrange | positioned on the surface of a cell wall.

The catalyst layer contains a support and a catalyst metal. The specific surface area (m ² / g) of the support has a great influence on the amount of sulfur component deposited, and therefore it is preferable to adjust it within a certain range. The smaller the specific surface area of the carrier, the more difficult it is for the sulfur component to adhere, so the specific surface area of the carrier is preferably, for example, 1-50 m ² / g, more preferably 1-30 m ² / g, It is especially preferable to set it as 15 m < ² > / g. By setting the specific surface area of the support in such a range, it is possible to reduce the adhesion of the sulfur component and to disperse and carry the catalyst metal. Thereby, the sintering of the catalyst metal can be suppressed and the catalyst activity can be prevented from being lowered.

  The “specific surface area of the carrier” in the present specification is measured by a laser diffraction / scattering particle size distribution measuring apparatus (LA-920, manufactured by Horiba, Ltd.).

  Further, the amount of the carrier per volume of the DPF substrate (g / L) is also preferably adjusted within a certain range because it greatly affects the amount of sulfur component deposited. The smaller the amount of the carrier per volume of the DPF substrate, the less the sulfur component adheres. Therefore, for example, the amount of the carrier is preferably 5 to 15 g / L, and more preferably 5 to 10 g / L. preferable. The “volume of the DPF substrate” means the volume of the substrate including voids inside the substrate (for example, cells, pores inside the cell wall, etc.).

As described above, the amount of the sulfur component adhering to the DPF catalyst depends on the specific surface area (m ² / g) of the carrier and the amount of the carrier per volume of the DPF substrate (g / L). Therefore, the amount of sulfur component adhering to the DPF catalyst is reduced by adjusting the total surface area (m ² / L) of the support per volume of the DPF substrate, which is the product of these factors, within a certain range. can do. Therefore, the total surface area of the support per volume of the DPF substrate is 5 to 450 m ² / L, preferably 5 to 250 m ² / L.

  The type of the carrier is not particularly limited because it does not significantly affect the amount of the sulfur component deposited. Therefore, the carrier may be any material that can withstand the regeneration of the DPF catalyst under high temperature conditions. Examples of such a carrier include heat-resistant particles, particularly heat-resistant metal particles. Specific examples include alumina, titania, silica, ceria, zirconia, cerium-zirconium composite oxide, zeolite, and the like.

  Since the type of catalyst metal supported on the carrier does not significantly affect the amount of sulfur component deposited, the type of catalyst metal is not particularly limited. The catalyst metal to be supported can be appropriately selected according to the intended use. For example, when promoting PM combustion, platinum, palladium, vanadium, gold, silver, iron, or the like can be used as the catalyst metal.

  The amount of the catalytic metal is not particularly limited, but is preferably 0.1 to 2 g, preferably 0.3 to 1 g per volume (1 L) of the DPF base material in order to sufficiently promote the combustion of PM. It is more preferable.

  The catalyst layer may further contain an optional component as long as the effect of the present invention is not adversely affected.

<Exhaust gas purification system>
The present invention further relates to an exhaust gas purification system including the DPF catalyst and a diesel oxidation catalyst (DOC). As shown in FIG. 2, in the exhaust gas purification system according to the present invention, the DOC 2 is installed upstream of the DPF catalyst 3 in the exhaust gas flow direction inside the exhaust pipe 1.

The DOC has a function of oxidizing unburned gas in the exhaust gas. Unburned gas mainly contains HC, CO, and NO. DOC oxidizes HC to H ₂ O and CO ₂ , CO to CO ₂ and NO to NO ₂ . Since NO ₂ has a very strong oxidizing power, combustion of PM deposited on the DPF catalyst installed on the downstream side can be promoted.

  As the DOC, it is not necessary to use a special one, and a DOC generally used in exhaust gas purification can be used. DOC contains the base material and the catalyst layer arrange | positioned on the said base material, for example.

  As a base material of DOC, it is not necessary to use a special thing, and the base material currently utilized in general DOC can be used. For example, a straight flow type monolith honeycomb substrate can be used as the DOC substrate. The material of the base material is not particularly limited, and examples thereof include base materials such as ceramic, silicon carbide, and metal.

  A catalyst layer is disposed on the DOC substrate. Here, when the DOC base material is a straight flow type monolith honeycomb base material, the catalyst layer is preferably disposed on the surface of the cell wall constituting a plurality of cells in the base material.

  The catalyst layer of the DOC includes a support and a catalyst metal supported on the support. Examples of the DOC carrier include heat-resistant particles, particularly heat-resistant metal particles. Specific examples include alumina, titania, silica, cerium-zirconium composite oxide, ceria, zirconia, and zeolite.

  Examples of the DOC catalyst metal include a metal having a function of oxidizing NO. Specific examples include platinum, palladium, rhodium, iridium, and ruthenium.

  The amount of the DOC catalyst metal is not particularly limited, but is preferably 0.5 to 7 g, preferably 1 to 4 g per volume (1 L) of the DOC base material in order to sufficiently oxidize NO. Is more preferable.

  The DPF catalyst according to the present invention may be integrated with DOC. In this case, a DOC catalyst layer is further arranged on the catalyst layer of the DPF catalyst. That is, the integrated DPF catalyst is disposed on the DPF base material, the catalyst layer of the DPF catalyst disposed on the DPF base material (also referred to as “first catalyst layer”), and the catalyst layer of the DPF catalyst. And a DOC catalyst layer (also referred to as “second catalyst layer”).

  The support and catalyst metal (also referred to as “first support” and “first catalyst metal”, respectively) included in the first catalyst layer, and the support and catalyst metal (respectively “second”, respectively) included in the second catalyst layer. Examples of “support” and “second catalyst metal”) are as described above. By integrating the DPF catalyst and the DOC, the space required for installing them can be reduced.

In an integrated DPF catalyst, the sum of the total surface area of the first support per volume of the DPF substrate and the total surface area of the second support per volume of the DPF substrate is used to reduce the amount of sulfur component deposited. Is 5 to 450 m ² / L, preferably 5 to 250 m ² / L.

Here, each specific surface area of the first carrier and the second carrier, preferably to 1 to 50 m ² / g, more preferably to 1-30 m ² / g, and 1~15m ² / g It is particularly preferable to do this.

  The total amount of the first carrier and the second carrier per volume of the DPF substrate is preferably 5 to 15 g / L, more preferably 5 to 10 g / L.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, the technical scope of this invention is not limited to this.

<Manufacture of DPF catalyst>
[Example 1]
50 g of commercially available Al ₂ O ₃ powder (specific surface area: 1 m ² / g) was dispersed in 500 ml of ion-exchanged water using ultrasonic waves for 10 minutes. A dinitroammineplatinum (Pt) nitric acid solution was added to the dispersion, and Pt was adsorbed on the Al ₂ O ₃ powder surface. This was dried at 150 ° C. to remove water, and then fired at 500 ° C. in the atmosphere. As a result, a Pt-supported carrier having Pt supported on the Al ₂ O ₃ powder surface was obtained.

  The Pt-supported carrier was suspended in ion-exchanged water and prepared using a ball mill so that the Dt of the Pt-supported carrier was 2 μm to obtain a coating slurry.

After dipping the DPF substrate in the coating slurry, it was pulled up and vacuumed to remove excess slurry. Then, it dried at 110 degreeC and baked at 450 degreeC for 120 minutes. As a result, a DPF catalyst having a catalyst layer formed on the DPF substrate was obtained.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 5 g / L.

[Example 2]
Example except that 50 g of commercially available Al ₂ O ₃ powder (specific surface area: 5 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced in the same manner as in Example 1.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 15 g / L.

[Example 3]
Similar to Example 1 except that 50 g of commercially available CeZr powder (specific surface area: 15 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced.
The amount of CeZr per volume of the DPF substrate was 15 g / L.

[Example 4]
Example 1 except that 50 g of commercially available TiO ₂ powder (specific surface area: 50 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. Similarly, a DPF catalyst was produced.
The amount of TiO ₂ per volume of the DPF substrate was 5 g / L.

[Example 5]
Example except that 50 g of commercially available Al ₂ O ₃ powder (specific surface area: 50 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced in the same manner as in Example 1.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 5 g / L.

[Example 6]
Example except that 50 g of commercially available Al ₂ O ₃ powder (specific surface area: 30 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced in the same manner as in Example 1.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 15 g / L.

[Comparative Example 1]
Example except that 50 g of commercially available Al ₂ O ₃ powder (specific surface area: 30 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced in the same manner as in Example 1.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 30 g / L.

[Comparative Example 2]
Example 1 except that 50 g of commercially available SiO ₂ powder (specific surface area: 30 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. Similarly, a DPF catalyst was produced.
The amount of SiO ₂ per volume of the DPF substrate was 50 g / L.

[Comparative Example 3]
Example except that 100 g of commercially available Al ₂ O ₃ powder (specific surface area: 30 m ² / g) was used instead of 50 g of Al ₂ O ₃ powder (specific surface area: 1 m ² / g) in Example 1. A DPF catalyst was produced in the same manner as in Example 1.
The amount of Al ₂ O ₃ per volume of the DPF substrate was 100 g / L.

  Table 1 shows the structures of the DPF catalysts produced in the examples and comparative examples.

<Evaluation of DPF catalyst>
(1) Sulfur adhesion test Engine exhaust gas distribution of DOC in which sulfur is adhered in order from the upstream side to the downstream side in the exhaust gas flow direction and the DPF catalyst produced in the examples and comparative examples until saturation. Attached to the device. Engine exhaust gas containing a specified amount of sulfur was passed through the apparatus so as to be 2.5 g / L in terms of sulfur. Thereafter, the DPF catalyst was decomposed, and the amount of sulfur deposited was measured using a sulfur analyzer. The results are shown in Table 2.

(2) White smoke generation test The DPF catalyst subjected to the sulfur adhesion test was installed downstream of the diesel internal combustion engine. After depositing PM on the DPF catalyst, the DPF catalyst was regenerated and white smoke was observed. The results are shown in Table 3.

  The evaluation results of the DPF catalyst are shown in FIG. As can be seen from FIG. 3, the amount of sulfur attached to the DPF catalyst can be reduced as the total surface area of the support per volume of the DPF substrate is reduced. Moreover, generation | occurrence | production of white smoke can be suppressed by reducing the quantity of sulfur adhering to a DPF catalyst.

1 .... exhaust pipe, 2 .... DOC, 3 .... DPF catalyst

Claims (6)

A DPF catalyst comprising a DPF substrate and a catalyst layer disposed on the DPF substrate,
The catalyst layer includes a support and a catalyst metal supported on the support,
The total surface area of the carrier per volume of the DPF substrate, which is the product of the specific surface area (m ² / g) of the carrier and the amount of the carrier per volume of the DPF substrate (g / L) m ² / L) is 5~450m ² / L, when the DPF catalyst (provided that the carrier, _CeO 2 -Pr composite oxide, _CeO 2 -Nd composite oxide, silicon carbide, or silicon oxide Except). Carrier, alumina, titania, ceria, zirconia, cerium - zirconium composite oxide, and is selected from the group consisting of zeolite, DPF catalyst according to claim 1. The DPF catalyst according to claim 1, wherein the support has a specific surface area of 1 to 50 m ² / g.   The DPF catalyst according to any one of claims 1 to 3, wherein the amount of the carrier per volume of the DPF substrate is 5 to 15 g / L. Including the DPF catalyst according to any one of claims 1 to 4 and a diesel oxidation catalyst,
The exhaust gas purification system, wherein the diesel oxidation catalyst is installed upstream of the DPF catalyst in the exhaust gas flow direction. A DPF catalyst comprising: a DPF substrate; a first catalyst layer disposed on the DPF substrate; and a second catalyst layer disposed on the first catalyst layer,
The first catalyst layer includes a first carrier and a first catalyst metal supported on the first carrier;
The second catalyst layer includes a second carrier and a second catalyst metal supported on the second carrier;
The first catalytic metal is a metal having a function of promoting combustion of particulate matter;
The second catalytic metal is a metal having a function of oxidizing nitric oxide;
The product of the specific surface area (m ² / g) of the first carrier and the amount (g / L) of the first carrier per volume of the DPF substrate, per volume of the DPF substrate. The total surface area of the first support (m ² / L); the specific surface area of the second support (m ² / g); and the amount of the second support per volume of the DPF substrate (g / is the product of L), the second total surface area of the support per volume of the DPF substrate ^(m 2 / L); the sum of a 5~450m ² / L, the DPF catalyst.

Images