JP2023035716A - Exhaust gas cleaning apparatus, and exhaust gas cleaning method - Google Patents

Abstract

To provide an exhaust gas cleaning apparatus equipped with a hydrocarbon HC adsorbent capable of suppressing desorption of adsorbed HC and giving a higher HC adsorption factor than conventional ones and an exhaust gas cleaning method using the apparatus.SOLUTION: An exhaust gas cleaning apparatus 2 is equipped with a three-way catalyst 4 and a HC adsorbent 60. The HC adsorbent 60 includes a first zeolite layer 61 made of first zeolite having a silica-alumina ratio of 5-45 and a second zeolite layer 62 made of second zeolite having a silica-alumina ratio of 10-100. The first zeolite is FAU-type zeolite or BEA-type zeolite ion-exchanged with a Cu ion or a Cr ion. The second zeolite is MFI-type zeolite, FAU-type zeolite, BEA-type zeolite, or YFI-type zeolite ion-exchanged with a Cs ion, a Rb ion, or a K ion. An exhaust gas cleaning method uses the exhaust gas cleaning apparatus 2.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purification device provided with a hydrocarbon (hereinafter referred to as HC) adsorbent and an exhaust gas purification method using the same.

2. Description of the Related Art Conventionally, in an exhaust purification device provided in an exhaust passage of an internal combustion engine, a three-way catalyst (hereinafter referred to as TWC) is not sufficiently activated, for example, when the internal combustion engine is cold-started. Therefore, an exhaust purification device is provided with an HC adsorbent for the purpose of adsorbing HC in the exhaust gas. Zeolite is generally used as the HC adsorbent and is used in combination with TWC.

For example, a technique of oxidizing and purifying HC adsorbed by an HC adsorbent has been disclosed (see, for example, Patent Document 1). In this technology, an HC adsorbent made of zeolite and a TWC mainly composed of platinum-rhodium catalyst components are provided in the front stage of the catalyst, and an HC adsorbent made of zeolite, an oxygen supply agent made of cerium oxide, It is said that HC in the exhaust can be efficiently purified by providing a TWC mainly composed of palladium in the rear stage of the catalyst.

JP-A-9-85056

As in Patent Document 1, it is common practice to combine an HC adsorbent and a TWC in order to oxidize and purify the adsorbed HC when it is desorbed. However, since low-temperature activity of the TWC is required in order to oxidize and purify desorbed HC with certainty, a large amount of precious metal is required, resulting in an increase in cost. In addition, if the desorption of HC occurs suddenly, oxygen becomes insufficient and HC cannot be purified by oxidation, so an oxygen supply agent is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an exhaust gas purification device equipped with an HC adsorbent capable of suppressing desorption of adsorbed HC and obtaining a higher HC adsorption rate than conventional ones, and an exhaust gas purification method using the same. Hereinafter, in the present invention, "-" includes the upper and lower values.

(1) The present invention is provided in an exhaust passage (for example, an exhaust pipe 3, which will be described later) of an internal combustion engine (for example, an engine 1, which will be described later), and adsorbs hydrocarbons contained in a three-way catalyst and the exhaust gas of the internal combustion engine. and a hydrocarbon adsorbent (for example, an HC adsorbent 60 to be described later) (for example, an exhaust gas purification device 2 to be described later), wherein the hydrocarbon adsorbent has a Keiban ratio of 5 to 45. A first zeolite layer made of a certain first zeolite (for example, a first zeolite layer 61 described later) and a second zeolite layer made of a second zeolite having a Keiban ratio of 10 to 100 (for example, a second zeolite layer 62 described later ), wherein the first zeolite is FAU-type zeolite or BEA-type zeolite ion-exchanged with Cu ions or Cr ions, and the second zeolite is ion-exchanged with Cs ions, Rb ions, or K ions MFI-type zeolite, FAU-type zeolite, BEA-type zeolite, or YFI-type zeolite.

(2) In the exhaust purification device of (1), the first zeolite may be ion-exchanged with Cu ions, and the ion exchange ratio of Cu to Al may be 30% to 70%.

(3) In the exhaust purification device of (1) or (2), the second zeolite may be ion-exchanged with Cs ions, and the ion exchange ratio of Cs to Al may be 80% to 120%.

(4) In the exhaust purification device of any one of (1) to (3), the hydrocarbon adsorbent may be arranged downstream of the three-way catalyst provided in the exhaust passage.

(5) The present invention also provides an exhaust purification method using the exhaust purification device of any one of (1) to (4).

According to the present invention, it is possible to provide an exhaust gas purification device equipped with an HC adsorbent that can suppress the desorption of adsorbed HC and has a higher HC adsorption rate than conventional ones, and an exhaust gas purification method using the same. Therefore, by using the HC adsorbent and the TWC together for oxidizing and purifying the desorbed HC, it is not necessary to increase the amount of noble metal in the TWC, and the oxygen supply agent is not required, thereby reducing the cost.

1 is a diagram showing an exhaust purification device provided with an HC adsorbent according to one embodiment of the present invention; FIG. It is a figure which shows the structure of the HC trap which concerns on the said embodiment. FIG. 4 is a diagram showing the characteristics of the HC adsorbent according to the embodiment; It is a figure which shows the electronic arrangement of various metal elements. It is a figure which shows a zeolite frame|skeleton. 4 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 1. FIG. FIG. 10 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 2; FIG. 10 is a diagram showing the configuration of an HC adsorbent in an HC trap according to Example 3; FIG. 3 is a diagram showing the relationship between temperature and HC adsorption rate in the HC traps according to Examples 1-3. FIG. 4 is a diagram showing HC adsorption amounts, desorption amounts, and their differences in HC traps according to Examples 1 to 3; FIG. 4 is a graph showing the relationship between temperature and HC adsorption rate in HC traps according to Examples 1 and 4 and Comparative Examples 1 and 2; FIG. 4 is a diagram showing HC adsorption amounts, desorption amounts, and their differences in HC traps according to Examples 1 and 4 and Comparative Examples 1 and 2; FIG. 10 is a diagram showing the structure of an HC adsorbent in an HC trap according to Example 5; FIG. 10 is a diagram showing the structure of an HC adsorbent in an HC trap according to Example 6; FIG. 10 is a diagram showing the structure of an HC adsorbent in an HC trap according to Example 7; FIG. 10 is a graph showing the relationship between temperature and HC adsorption rate in HC traps according to Examples 5-7. FIG. 10 is a diagram showing HC adsorption amounts, desorption amounts, and their differences in HC traps according to Examples 5 to 7;

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an exhaust purification system 2 of an internal combustion engine (hereinafter referred to as "engine") 1 according to this embodiment.
The engine 1 is a direct injection gasoline engine. As shown in FIG. 1, the exhaust purification device 2 according to this embodiment includes a TWC 4, a GPF 5, and an HC trap 6, which are provided in order from the upstream side of an exhaust pipe 3 through which exhaust gas flows.

The TWC 4 purifies the exhaust gas by oxidizing or reducing HC to _H2O and _CO2 , CO to _CO2 , and NOx to _N2, respectively. As the TWC 4, for example, a carrier made of an oxide such as alumina, silica, zirconia, titania, ceria, or zeolite on which a noble metal such as Pd or Rh is supported as a catalytic metal is used. This TWC4 is usually carried on a honeycomb support.

TWC4 also includes an OSC material with OSC capabilities. As the OSC material, in addition to CeO ₂ , a composite oxide of CeO ₂ and ZrO ₂ (hereinafter referred to as “CeZr composite oxide”) or the like is used. Among them, the CeZr composite oxide is preferably used because of its high durability. The catalyst metal may be supported on these OSC materials.

The method for preparing TWC4 is not particularly limited, and it is prepared by a conventionally known slurry method or the like. For example, after preparing a slurry containing the above-mentioned oxides, noble metals, OSC materials, etc., the prepared slurry is coated on a cordierite honeycomb substrate and fired.

GPF5 traps and cleans particulate matter in the exhaust. Specifically, the GPF 5 includes a filter base material and an exhaust purification catalyst supported on partition walls of the filter base material. As the exhaust purification catalyst, a TWC is used in this embodiment, and the same as the TWC4 described above is used. The filter base material has, for example, a cylindrical shape elongated in the axial direction, and is made of a porous material such as cordierite, mullite, or silicon carbide (SiC). The filter base material is provided with a plurality of cells extending from the inflow side end surface to the outflow side end surface, and these cells are partitioned by partition walls. The filter base material is a so-called wall-flow type filter, and the cells are alternately plugged on the inflow side end surface and the outflow side end surface. The GPF 5 having such a configuration traps particulate matter by accumulating particulate matter on the surface of the partition wall when the exhaust gas passes through fine pores in the partition wall.

Particulate matter includes particulate matter such as soot (carbon soot), fuel or oil residue (SOF), and ash, which is oil ash. In recent years, emission regulations for these particulate matter have been tightened. The number of discharged small particulate matter with a particle diameter of 2.5 μm or less is being regulated (PN regulation). On the other hand, GPF5 can correspond to these PM regulation and PN regulation. Also, TWC may be used instead of GPF.

The HC trap 6 has an HC adsorbent 60 . The HC trap 6 has the property of adsorbing HC contained in the exhaust. For example, when the engine 1 is cold-started, the HC trap 6 adsorbs HC in the exhaust gas when the TWC 4 is not sufficiently activated and does not function. In the HC trap 6, the HC adsorbent 60 itself has a self-cleaning function capable of oxidizing and cleaning HC. However, the present invention is not limited to this, and if the HC adsorbent 60 does not have a self-cleaning function or the self-cleaning function is insufficient, the HC adsorbent 60 and TWC coating are used together.

The HC trap 6 is configured by supporting an HC adsorbent 60, which will be described in detail later, on a base material made of a porous material such as cordierite, mullite, silicon carbide (SiC), or the like. As the substrate, a honeycomb substrate having a honeycomb structure is usually used.

The method for preparing the HC trap 6 is not particularly limited, and it is prepared by a conventionally known slurry method or the like. For example, after preparing a slurry containing the HC adsorbent 60, which will be described in detail later, a cordierite honeycomb base material is coated with the prepared slurry and fired.

Next, the HC adsorbent 60 will be described in detail.
FIG. 2 is a diagram showing the configuration of the HC trap. As shown in FIG. 2, the HC adsorbent 60 of the HC trap is carried on the partition walls that partition and form each cell of the honeycomb substrate 6a. The HC adsorbent 60 is carried not only on the surfaces of the partition walls but also on the inner surfaces of the pores within the partition walls.

The HC adsorbent 60 has a first zeolite layer 61 and a second zeolite layer 62 as essential components. HC adsorbent 60 may further comprise a third zeolite layer 63 . The HC adsorbent 60 shown as an example in FIG. 2 includes a first zeolite layer 61, a second zeolite layer 62, and a third zeolite layer 63 which are laminated in order from the honeycomb substrate 6a side. However, the stacking order of these layers is not limited.

The first zeolite layer 61 is composed of the first zeolite, and the second zeolite layer 62 is composed of the second zeolite. In the present embodiment, the first zeolite has the property of desorbing HC in a relatively low temperature range and adsorbing HC in a relatively high temperature range, and the second zeolite is , while having the property of desorbing HC in a high temperature range, it is preferable to adsorb HC in a low temperature range. Here, the low temperature range is, for example, the range from 75° C. to 150° C., and the high temperature range is the range from 150° C. to 250° C., for example. By combining the first zeolite and the second zeolite having such properties, the desorption of adsorbed HC can be more reliably suppressed, and a higher HC adsorption rate than conventionally obtained can be obtained more reliably.

The first zeolite layer 61 is made of first zeolite having a Keiban ratio of 5-45. The first zeolite having a Keiban ratio of 5 to 45 has an HC adsorption action at around 200.degree. Therefore, by combining the first zeolite layer 61 and a second zeolite layer 62 described later, desorption of adsorbed HC can be suppressed, and an HC adsorbent having a higher HC adsorption rate than conventional HC adsorbents can be obtained. A more preferable Keiban ratio of the first zeolite is 6-20. Further, the amount of Al element in the first zeolite is preferably 1.7-29.8% by mass, more preferably 4.1-29.8% by mass, still more preferably 7.8-22. It is 0% by mass.

The first zeolite is preferably zeolite with a pore size of 0.5 nm or more. Specifically, as the first zeolite, FAU-type zeolite or BEA-type zeolite is preferably used from the viewpoint of improving heat resistance.

The first zeolite is ion-exchanged with a metal element in which one electron in the outermost shell is arranged on the s orbital and all or half of the d orbitals in the inner shell inside one of the outermost shells are filled with electrons. It is preferably a metal ion-exchanged zeolite. Higher HC adsorption performance is obtained at around 200° C. by using the above metal elements as the ion-exchange species of zeolite.

More specifically, zeolite ion-exchanged with Cu ions or Cr ions is preferably used as the first zeolite. Higher HC adsorption performance is obtained at around 200° C. by using the above metal elements as the ion-exchange species of zeolite. In addition, the zeolite ion-exchanged with these Cu ions (hereinafter referred to as "Cu ion-exchanged zeolite") and the zeolite ion-exchanged with Cr ions (hereinafter referred to as "Cr ion-exchanged zeolite") have good HC adsorption performance. This is because it has a so-called self-purification function capable of oxidizing and purifying HC. In this case, when a Cu ion-exchanged zeolite or a Cr ion-exchanged zeolite is used as the first zeolite, it is not necessary to arrange the TWC after the HC trap 6 . Among them, Cu ion-exchanged zeolite is particularly preferably used as the first zeolite.

The Cu ion-exchanged zeolite and Cr ion-exchanged zeolite preferably have an ion exchange ratio of Cu or Cr with respect to Al of 100% or less. The higher the metal ion exchange rate of Cu or Cr, the higher the HC adsorption rate, but the lower the heat resistance. In the case of Cu ion-exchanged zeolite, the ion exchange ratio of Cu to Al is preferably 30% to 70%. According to this Cu ion-exchanged zeolite, an HC adsorbent having both high HC adsorption performance and high heat resistance can be obtained. The ion exchange rate shown here is the molar ratio of Metal/Al, where Metal indicates the number of moles of metal and Al indicates the number of moles of aluminum.

The second zeolite layer 62 is made of a second zeolite having a Keiban ratio of 10-100. According to the second zeolite having a Keiban ratio of 10 to 100, excellent HC desorption performance can be obtained in the high temperature range of around 200° C. where the first zeolite exhibits HC adsorption performance. Therefore, by combining the second zeolite layer 62 and the above-described first zeolite layer 61, desorption of adsorbed HC can be suppressed, and an HC adsorbent having a higher HC adsorption rate than conventional ones can be obtained. A more preferable Keiban ratio of the second zeolite is 20-40. Also, the amount of Al element in the second zeolite is preferably 0.8 to 14.5% by mass, more preferably 1.7 to 14.5% by mass, still more preferably 4.1 to 7.5% by mass. 8% by mass.

The second zeolite is preferably zeolite with a pore size of 0.5 nm or more. Specifically, as the second zeolite, MFI-type zeolite, FAU-type zeolite, BEA-type zeolite, or YFI-type zeolite is preferably used from the viewpoint of heat resistance.

The second zeolite is a metal ion-exchanged with a metal element in which one electron in the outermost shell is arranged on the s orbital and all the p orbitals in the inner shell inside one of the outermost shells are filled with electrons. It is preferably an ion-exchanged zeolite. According to the second zeolite using the above metal element as the ion-exchange species of the zeolite, excellent HC desorption performance can be obtained in the high temperature range around 200° C. where the above-mentioned first zeolite exhibits HC adsorption performance. be done.

More specifically, the second zeolite includes zeolite ion-exchanged with Cs ions (hereinafter referred to as "Cs ion-exchanged zeolite") and zeolite ion-exchanged with Rb ions (hereinafter referred to as "Ru ion-exchanged zeolite"). ) or zeolite ion-exchanged with K ions (hereinafter referred to as "K ion-exchanged zeolite") is preferably used. This improves the HC adsorption performance. Among them, Cs ion-exchanged zeolite is particularly preferably used as the second zeolite.

The second zeolite preferably has an ion exchange rate of 10% to 120% with respect to Al. The higher the ion exchange rate of the metal, the higher the HC adsorption rate. When Cs ion-exchanged zeolite, Rb ion-exchanged zeolite and K ion-exchanged zeolite are used, the ion exchange ratio of Cs, Rb or K to Al is preferably 50% to 120%. In particular, the Cs ion-exchanged zeolite preferably has an ion exchange ratio of Cs to Al of 80% to 120%. Cs is expensive, but if the ion exchange rate of Cs with respect to Al is within this range, a high HC adsorption rate can be obtained while suppressing costs.

The third zeolite layer 63 is composed of third zeolite. As described above, the third zeolite layer 63 may have any configuration, but it is preferable to include the third zeolite layer 63 in this embodiment. As the third zeolite layer 63, BEA type zeolite with a high silicon ratio is preferably used. BEA-type zeolites with high Kaban ratios exhibit hydrophobicity. The HC adsorbent 60 is hydrophilic and strongly affected by the moisture contained in the exhaust gas, whereas the BEA zeolite is a zeolite having a pore diameter most suitable for the HC molecular diameter in the exhaust gas. Therefore, by using BEA type zeolite with a high Keiban ratio, which is hydrophobic, the physical adsorption performance of HC can be improved, and although the high temperature desorption performance of HC is not exhibited, the low temperature adsorption performance of HC is improved.

FIG. 3 is a diagram showing the characteristics of the HC adsorbent 60. As shown in FIG. In FIG. 3, the horizontal axis represents temperature (° C.) and the vertical axis represents HC adsorption rate (%). FIG. 3 shows that HC is adsorbed on the upper side of the straight line with an adsorption rate of 0%, and HC is desorbed on the lower side. The area (integral value) surrounded by the straight line with the adsorption rate of 0% and each curve represents the amount of adsorption and the amount of desorption.

As shown in FIG. 3, the Cu ion-exchanged FAU-type zeolite (CuFAU; loading amount per honeycomb substrate 6a: 145 g/L (hereinafter the same)), which is an example of the first zeolite, itself has a relative Absorbs HC in a relatively high temperature range (higher than about 150°C to about 250°C) while desorbing HC in a low temperature range (about 75°C or higher and about 150°C or lower). is found to have In addition, Cs ion-exchanged MFI zeolite (CsMFI; 55 g/L), which is an example of the second zeolite, itself adsorbs HC in a relatively low temperature range (about 75 ° C. or higher and about 150 ° C. or lower). On the other hand, it has the property of desorbing HC in a relatively high temperature range (higher than about 150° C. and about 250° C. or lower).

On the other hand, the HC adsorbent 60 is a combination of a first zeolite layer 61 made of the first zeolite and a second zeolite layer 62 made of the second zeolite, and is heated to the temperature shown in FIG. The corresponding HC adsorption properties are shown. That is, the HC adsorbent 60 uses a combination of two zeolites having different HC desorption temperature ranges and different HC adsorption temperature ranges so that the HC adsorption amount is larger than the HC desorption amount. HC desorption can be suppressed, and a higher HC adsorption rate than before can be obtained.

As described above, a Cu ion-exchanged zeolite such as CuFAU has an HC oxidation function, that is, a so-called HC self-cleaning function. Therefore, the Cu ion-exchanged zeolite can oxidize and purify HC adsorbed without desorption into CO ₂ and H ₂ O at 300° C. or higher. In addition, it is possible to assist the oxidation function of Cu by impregnating and supporting a trace amount of precious metal in zeolite.

FIG. 4 is a diagram showing the electronic arrangement of various metal elements. The present applicant has found that the electron configuration of various metal elements in zeolite has a correlation with the HC adsorption/desorption performance. Specifically, elements with one electron in the outermost shell and electrons buried in the orbits of the inner shell tend to have excellent HC adsorption performance. In particular, Cu and Ag having an s-orbital as the outermost shell and a d-orbital as the innermost shell have a high HC desorption temperature. Cr and Mo are metastable elements in which half of the electrons in orbitals in front of the outermost shell are buried, and Cr in particular exhibits high-temperature desorption of HC. Alkali metals have one outermost electron, but the inner shell is a p-orbital. Others with one outermost electron and an inner s-orbital include B, Al, Ga, and In. However, none of them show high-temperature desorption performance. Therefore, an element with one electron in the outermost shell and filled with electrons in the d-orbital and p-orbital in the inner shell exhibits high-temperature desorption.

Therefore, as described above, as the first zeolite, one electron in the outermost shell is arranged on the s orbital, and all or half of the d orbitals in the inner shell inside one of the outermost shells are filled with electrons. It is preferable to use a metal ion-exchanged zeolite ion-exchanged with a metal element. In addition, as the second zeolite, one electron in the outermost shell is arranged on the s orbital, and all the p orbitals in the inner shell inside one of the outermost shells are ion-exchanged with a metal element filled with electrons. It is preferred to use a metal ion-exchanged zeolite.

Here, zeolite will be described in more detail.
Zeolites are crystalline aluminosilicates with high surface areas and regular pore sizes. Zeolite is an oxide crystal mainly composed of Si, Al, and O, and has excellent HC adsorption performance. Zeolites composed mostly of _SiO2 have a physical HC adsorption performance determined by the pore size and the intermolecular attractive force with HC. Also, since Si is tetravalent and Al is trivalent, this creates sites where elements can exchange ions. The chemical adsorption/desorption behavior of HC changes depending on the type of ion-exchange element. Chemisorption exhibits a higher adsorptive power than physical adsorption, and HC can be retained at high temperatures. Therefore, the higher the amount of Al, the higher the adsorptive power, but on the contrary, the more unstable the state, the lower the heat resistance. Moreover, the heat resistance differs depending on the ion-exchange species, and the heat resistance also differs depending on the zeolite species. Elements that are not ion-exchanged adversely affect heat resistance, so the ion exchange rate is set as described above.

FIG. 5 is a diagram showing a zeolite framework. Any metal M can be ion-exchanged to the ion-exchange sites generated by Al in the zeolite framework. Unsaturated HCs having double bonds such as aromatics and olefins are polar HCs, and when chemically adsorbed to ion-exchanged metals M, strong HC adsorption power is exhibited.

On the other hand, Al in the zeolite framework is desorbed by heat, resulting in structural destruction. Therefore, when the amount of Al is large, heat resistance is lowered due to dealumination. That is, heat resistance and HC adsorption performance (improved desorption temperature) are contradictory characteristics. In this regard, it can be said that the HC adsorbent 60 according to the present embodiment is selected from zeolite species that provide a good balance between heat resistance and HC adsorption performance.

The HC adsorbent 60 having the above structure is prepared, for example, as follows.
The zeolite constituting the first zeolite layer 61, the second zeolite layer 62 or the third zeolite layer 63 is pulverized and mixed with silica sol as a binder and pure water for 12 hours in a ball mill. Next, a cordierite honeycomb substrate is immersed in the slurry thus obtained and then fired to form the first zeolite layer. The HC adsorbent 60 can then be prepared by similarly forming successively stacked zeolite layers.

According to the HC adsorbent 60 described above, by including the above-described first zeolite layer and second zeolite layer, desorption of adsorbed HC can be suppressed, and the HC adsorbent has a higher HC adsorption rate than conventional HC adsorbents. can provide In addition, in order to purify HC efficiently, it is necessary to oxidize and purify HC before it is desorbed. I dealt with both sides. However, in order to lower the HC purification temperature, it is necessary to increase the amount of noble metal in the catalyst, and oxygen is required for oxidation. Therefore, in Patent Document 1 described above, palladium, which is excellent in low-temperature activity, and cerium oxide, which can supply oxygen, are used, resulting in a high cost.

In contrast, in the present embodiment, desorption of HC is suppressed. Furthermore, it is made possible to self-purify HC. That is, since the zeolite itself has an oxidizing function and can be self-purified even without a noble metal catalyst layer, the noble metal catalyst layer is unnecessary (or a very small amount is added to the adsorbent layer), and the cost can be reduced. At the same time, since there is no catalyst layer that inhibits HC adsorption, the HC adsorption performance is further improved. Furthermore, since the HC adsorbent can be placed in the rear where it is difficult to warm up, the amount of HC adsorbed increases. Since it has weaker oxidation performance than noble metals and is placed in the last stage, the temperature rise is slow, so oxidation is possible with a small amount of oxygen by oxidizing gradually. In addition, since the catalytic function is weakened, another normal three-way catalyst is required between the three-way catalyst and the HC adsorbent, but the amount of precious metal is generally small in the rear three-way catalyst ( 1 to 2 g/L), the cost is lower than that of purifying adsorbed HC by combining an adsorbent and a three-way catalyst.

The present invention is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present invention.

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[Example 1]
FIG. 6 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 1. FIG. As shown in FIG. 6, as Example 1, CsMFI (50) constituting the second zeolite layer 62 and BEA type zeolite having a Keiban ratio of 1555 constituting the third zeolite layer 63 were used in order from the honeycomb substrate side. An HC adsorbent was prepared by laminating CuFAU (174) (hereinafter referred to as BEA) (7) and forming the first zeolite layer 61 .

Specifically, first, 100 parts by weight of CsMFI powder, 50 parts by weight of silica sol as a binder, and 110 parts by weight of pure water were pulverized and mixed in a ball mill for 12 hours. A 1 inch diameter, 60 mm long, 400 cells, 3.5 mil cordierite honeycomb substrate was immersed in the resulting slurry. After that, 50 g/L of CsMFI was supported on the honeycomb substrate by firing.

Next, 100 parts by weight of BEA powder, 50 parts by weight of silica sol as a binder, and 110 parts by weight of pure water were pulverized and mixed in a ball mill for 12 hours. The honeycomb base material supporting CsMFI was immersed in the slurry thus obtained. After that, 7 g/L of BEA was further supported on the honeycomb substrate by firing.

Next, 100 parts by weight of CuFAU powder, 50 parts by weight of silica sol as a binder, and 110 parts by weight of pure water were pulverized and mixed in a ball mill for 12 hours. The honeycomb substrate supporting CsMFI and BEA described above was immersed in the slurry thus obtained. After that, 174 g/L of CuFAU was further supported on the honeycomb substrate by firing. As described above, an HC adsorbent was obtained.

As the CuFAU used in Example 1, a Cu ion-exchanged FAU-type zeolite having a Kaban ratio of 10, a pore size of 0.9 nm, and an ion exchange ratio of Cu to Al of 50% was used. As the CsMFI used in Example 1, a Cs ion-exchanged MFI type zeolite having a Keiban ratio of 40, a pore size of 0.58 nm, and an ion exchange ratio of Cs to Al of 100% was used.

[evaluation]
The evaluation was carried out under the following conditions (the same applies to each example and each comparative example described later).

(Aging condition)
Temperature/time: fresh, 850°C x 10 hours Atmosphere: Rich (80 seconds)/Air (20 seconds)
Rich: _C3H6 = 1.0%, _O2 = 2.5%, _H2O = 10%, _N2 = balance flow rate: 500 cc _/ min (φ1 inch)

(Evaluation conditions)
Pretreatment: Air atmosphere 700°C x 10 minutes Gas composition: NO = ₅₀₀ ppm, _C3H6 = 240 ppmC, _isoC5H12 = 120 ppmC, toluene = 840 _ppmC , _H2 = 0.17%, CO = 0.5%, O2 = 0.49%, _CO2 = 14%, _H2O = 10%, _N2 = balance, heating rate: 20°C/min Measurement temperature: 50-500°C
Gas volume: 25 L/min Catalyst size: φ25.4 mm x 60 mm (30 cc)
SV: equivalent to 50,000h ^-1

As a specific operating procedure, first, the prepared HC adsorbent was subjected to aging treatment at 850° C. for 10 hours (aging treatment under the above aging conditions). Next, after cooling the HC adsorbent after the aging treatment to room temperature (25° C.), it was reheated in an air atmosphere at 700° C. for 10 minutes as a pretreatment. Next, after cooling to room temperature (25° C.), while raising the temperature from 50° C. to 500° C. at a rate of 20° C./min, 25 L/min of simulated exhaust gas composed of the above gas composition was applied to the HC adsorbent. It was circulated and the performance was evaluated. The size of the test piece was φ25.4×60 mm, and the performance was evaluated by measuring the gas composition after flowing the HC adsorbent.

[Example 2]
FIG. 7 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 2. FIG. As shown in FIG. 7, in Example 2, CuFAU (131) forming the first zeolite layer 61, CsMFI (49) forming the second zeolite layer 62, and the third zeolite layer were arranged in this order from the honeycomb substrate side. An HC adsorbent was prepared by laminating BEA (13) constituting 63. The materials and preparation method used were the same as in Example 1.

[Example 3]
FIG. 8 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 3. FIG. As shown in FIG. 8, in Example 3, CuFAU (117) forming the first zeolite layer 61, CsMFI (29) forming the second zeolite layer 62, and the third zeolite layer were arranged in order from the honeycomb substrate side. An HC adsorbent was prepared by laminating BEA (4) comprising 63. The materials and preparation method used were the same as in Example 1.

FIG. 9 is a graph showing the relationship between temperature and HC adsorption rate in the HC traps according to Examples 1-3. FIG. 10 is a diagram showing the HC adsorption amount, the desorption amount, and their difference in the HC traps according to Examples 1-3. As shown in FIGS. 9 and 10, in all of the HC adsorbents according to Examples 1 to 3, it was confirmed that the HC adsorption amount was larger than the HC desorption amount, indicating that a high HC adsorption rate was obtained. confirmed.

Note that the temperature range of the adsorbent in which the amount of desorbed HC is to be reliably reduced in the actual equipment is up to 150°C. This is because when the temperature of the adsorbent exceeds 150°C, the TWC arranged upstream is activated and becomes capable of purifying HC, so the amount of HC flowing into the HC adsorbent becomes almost zero. is. However, even if the temperature exceeds 150°C, HC will be released if the adsorbed HC is desorbed. . For example, a Cu ion-exchanged zeolite such as CuFAU has a self-cleaning function when the temperature exceeds about 300°C. Therefore, if it is adsorbed up to about 300°C, it can self-clean HC, so it can be said that there is no problem.

[Example 4]
As Example 4, an HC adsorbent was prepared in the same manner as in Example 1, except that the amount of CuFAU supported was changed to 200 g/L. The materials and preparation method used were the same as in Example 1.

[Comparative Example 1]
As Comparative Example 1, an HC adsorbent was prepared by laminating BEA (15) forming the third zeolite layer 63 and CsMFI (135) forming the second zeolite layer 62 in this order from the honeycomb substrate side. The materials and preparation method used were the same as in Example 1.

[Comparative Example 2]
As Comparative Example 2, an HC adsorbent was prepared by supporting 100 g/L of CuFAU constituting the first zeolite layer 61 on a honeycomb substrate. The materials and preparation method used were the same as in Example 1.

FIG. 11 is a diagram showing the relationship between temperature and HC adsorption rate in the HC traps according to Examples 1 and 4 and Comparative Examples 1 and 2. FIG. Also, FIG. 12 is a diagram showing the amount of hydrogen adsorbed, the amount of hydrogen desorbed, and the difference between them in the HC traps according to Examples 1 and 4 and Comparative Examples 1 and 2. As shown in FIG. As shown in FIGS. 11 and 12, in each comparative example, the amount of HC desorbed was greater than the amount of HC adsorbed, or the amount of HC adsorbed was only slightly greater than the amount of desorbed, and a high HC adsorption rate was not obtained. Confirmed not. On the other hand, in both the HC adsorbents of Examples 1 and 4, it was confirmed that the HC adsorption amount was much larger than the HC desorption amount, and it was confirmed that a high HC adsorption rate was obtained. In particular, it was confirmed that Example 4, in which the amount of CuFAU supported was greater than Example 1, provided a higher HC adsorption rate.

[Example 5]
FIG. 13 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 5. FIG. As shown in FIG. 13, in Example 5, CsMFI (36) constituting the second zeolite layer 62, BEA (4.5) constituting the third zeolite layer 63, and the first An HC adsorbent was prepared by laminating CuFAU (110) constituting the zeolite layer 61 . The materials and preparation method used were the same as in Example 1.

[Example 6]
FIG. 14 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 6. FIG. As shown in FIG. 14, as Example 6, CsYFI (35) constituting the second zeolite layer 62, BEA (3.5) constituting the third zeolite layer 63, and the first An HC adsorbent was prepared by laminating CuFAU (112) constituting the zeolite layer 61 . That is, in the HC adsorbent of Example 5, CsMFI constituting the second zeolite layer 62 was changed to CsYFI, and each supported amount was slightly changed. It should be noted that the same materials and preparation methods as in Example 1 were used for the configuration common to Example 5. As the CsYFI used in Example 6, a Cs ion-exchanged YFI zeolite having a Keiban ratio of 20, a pore size of 0.8 nm, and an ion exchange ratio of Cs to Al of 98% was used.

[Example 7]
FIG. 15 is a diagram showing the configuration of the HC adsorbent in the HC trap according to Example 7. FIG. As shown in FIG. 15, as Example 7, CsYFI (34) constituting the second zeolite layer 62 and CuFAU (111) constituting the first zeolite layer 61 were laminated in order from the honeycomb substrate side. An HC adsorbent was prepared. That is, in contrast to the HC adsorbent of Example 6, the third zeolite layer 63 was not formed, but a two-layer structure was formed, and the amount of each carried was slightly changed. The materials and preparation method used were the same as in Example 1.

FIG. 16 is a diagram showing the relationship between the temperature and the HC adsorption rate of the HC adsorbent in the HC traps according to Examples 5-7. FIG. 17 is a diagram showing the amount of HC adsorbed, the amount of desorbed HC in the HC adsorbent in the HC traps according to Examples 5 to 7, and the difference therebetween. As shown in FIGS. 16 and 17, in all of the HC adsorbents according to Examples 5 to 7, it was confirmed that the HC adsorption amount was larger than the HC desorption amount, and a high HC adsorption rate was obtained. was confirmed. In particular, it was confirmed that a higher HC adsorption rate was obtained in Example 6, in which CsMFI constituting the second zeolite layer 62 was changed to CsYFI in contrast to the HC adsorbent of Example 5. In contrast to the HC adsorbent of Example 6, in Example 7 in which the third zeolite layer 63 was not formed and the two-layer structure of the second zeolite layer 62 and the first zeolite layer 61 was used, the HC adsorbent was higher than that in Example 6. It was confirmed that the adsorption rate decreased, and the usefulness of the third zeolite 63 was confirmed.

1 engine (internal combustion engine)
2 exhaust purification device 3 exhaust pipe (exhaust passage)
4 TWC (three-way catalyst)
5 GPFs
6 HC trap 6a honeycomb substrate 60 HC adsorbent (hydrocarbon adsorbent)
61 first zeolite layer 62 second zeolite layer 63 third zeolite layer

Claims (5)

An exhaust purification device provided in an exhaust passage of an internal combustion engine, comprising a three-way catalyst and a hydrocarbon adsorbent for adsorbing hydrocarbons contained in the exhaust gas of the internal combustion engine,
The hydrocarbon adsorbent comprises a first zeolite layer made of a first zeolite having a Keiban ratio of 5 to 45 and a second zeolite layer made of a second zeolite having a Keiban ratio of 10 to 100,
The first zeolite is FAU-type zeolite or BEA-type zeolite ion-exchanged with Cu ions or Cr ions,
The second zeolite is an MFI zeolite, FAU zeolite, BEA zeolite, or YFI zeolite ion-exchanged with Cs ions, Rb ions, or K ions. 2. The exhaust purification device according to claim 1, wherein the first zeolite is ion-exchanged with Cu ions, and the ion exchange ratio of Cu to Al is 30% to 70%. 3. The exhaust purification device according to claim 1, wherein the second zeolite is ion-exchanged with Cs ions, and the ion exchange rate of Cs with respect to Al is 80% to 120%. 4. The exhaust purification device according to any one of claims 1 to 3, wherein said hydrocarbon adsorbent is arranged downstream of said three-way catalyst provided in said exhaust passage. An exhaust purification method using the exhaust purification device according to any one of claims 1 to 4.

Images