Hydrocarbon trap, exhaust air purification device and hybrid vehicle

Abstract

To provide a hydrocarbon trap capable of improving adsorption rate in a predetermined temperature region of hydrocarbon contained in exhaust air.SOLUTION: A hydrocarbon trap 12 is used for adsorbing hydrocarbons contained in the exhaust of a direct-injection gasoline engine 1. The hydrocarbon trap 12 has a hydrocarbon adsorbent supported on the surface of the pores of a porous substrate. The hydrocarbon adsorbent includes a first zeolite, capable of adsorbing olefins contained in the exhaust, and a second zeolite, capable of adsorbing paraffins and aromatic compounds contained in the exhaust. The first zeolite adsorbs olefins in a first temperature range and desorbs olefins in a second temperature range, which is higher than the first temperature range. The second zeolite desorbs paraffins and aromatic compounds in the first temperature range and adsorbs paraffins and aromatic compounds in the second temperature range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrocarbon trap, an exhaust purification device and a hybrid vehicle. [Background technology]

[0002] Efforts to mitigate or reduce the impact of climate change have been ongoing, and research and development into exhaust purification devices has been conducted to achieve this. Exhaust purification devices are installed in the exhaust passage of an internal combustion engine and are equipped with a three-way catalyst. However, for example, during a cold start of the internal combustion engine, the three-way catalyst does not reach its activation temperature. Therefore, exhaust purification devices are equipped with hydrocarbon traps to adsorb hydrocarbons contained in the exhaust. The hydrocarbon trap is, for example, made of a honeycomb substrate with a hydrocarbon adsorbent supported thereon.

[0003] Patent Document 1 describes an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a three-way catalyst and a hydrocarbon adsorbent that adsorbs hydrocarbons contained in the exhaust gas from the internal combustion engine. Here, the hydrocarbon adsorbent includes a first zeolite layer made of a first zeolite having a silica-to-alumina ratio of 5 to 45, and a second zeolite layer made of a second zeolite having a silica-to-alumina ratio of 10 to 100. The first zeolite is an FAU-type zeolite or a BEA-type zeolite that has been ion-exchanged with Cu ions or Cr ions, and the second zeolite is an MFI-type zeolite, an FAU-type zeolite, a BEA-type zeolite, or a YFI-type zeolite that has been ion-exchanged with Cs ions, Rb ions, or K ions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-35716 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is desired to improve the adsorption rate of hydrocarbons contained in exhaust gas within a predetermined temperature range.

[0006] An object of the present invention is to provide a hydrocarbon trap that can improve the adsorption rate of hydrocarbons contained in exhaust gas within a predetermined temperature range. [Means for solving the problem]

[0007] (1) A hydrocarbon trap used to adsorb hydrocarbons contained in the exhaust gas of an internal combustion engine, the hydrocarbon trap comprising: a porous substrate having a hydrocarbon adsorbent supported on the surface of the pores thereof; the hydrocarbon adsorbent comprising a first zeolite capable of adsorbing olefins contained in the exhaust gas; and a second zeolite capable of adsorbing paraffins and aromatic compounds contained in the exhaust gas; the first zeolite adsorbs the olefins in a first temperature range and desorbs the olefins in a second temperature range that is higher than the first temperature range; and the second zeolite desorbs the paraffins and aromatic compounds in the first temperature range and adsorbs the paraffins and aromatic compounds in the second temperature range.

[0008] (2) The hydrocarbon trap according to (1), wherein a layer containing the first zeolite and the second zeolite is formed on the surface of the pores of the porous substrate, or a layer containing the first zeolite and a layer containing the second zeolite are stacked on the surface of the pores of the porous substrate.

[0009] (3) The hydrocarbon trap according to (2), wherein a layer containing the first zeolite and a layer containing the second zeolite are sequentially laminated on the surfaces of the pores of the porous substrate.

[0010] (4) A hydrocarbon trap according to any one of (1) to (3), wherein the ratio of the second zeolite to the first zeolite corresponds to the ratio of the paraffins and aromatic compounds to the olefins.

[0011] (5) The hydrocarbon trap according to any one of (1) to (4), wherein the first zeolite is a silver ion-exchanged zeolite and the second zeolite is a copper ion-exchanged zeolite.

[0012] (6) The hydrocarbon trap according to any one of (1) to (5), wherein the first zeolite has a pore size of less than 4 Å, and the second zeolite has a pore size of 4 Å or more.

[0013] (7) The hydrocarbon trap according to (6), wherein the first zeolite is a CHA-type zeolite and the second zeolite is an FAU-type zeolite.

[0014] (8) The hydrocarbon trap according to any one of (1) to (7), wherein the hydrocarbon adsorbent further comprises a third zeolite capable of adsorbing paraffins and aromatic compounds contained in the exhaust gas, the third zeolite adsorbing the paraffins and aromatic compounds in the first temperature range and desorbing the paraffins and aromatic compounds in the second temperature range, and a first region comprising the first zeolite and the second zeolite and a third region comprising the third zeolite are arranged on the surface of the pores of the porous substrate without overlapping with each other.

[0015] (9) The hydrocarbon trap according to (8), wherein the third zeolite is a cesium-exchanged zeolite.

[0016] (10) The hydrocarbon trap according to (8) or (9), wherein the third zeolite has a pore size of 4 Å or more.

[0017] (11) The hydrocarbon trap according to (10), wherein the third zeolite is a YFI-type zeolite.

[0018] (12) An exhaust purification device provided in an exhaust passage of an internal combustion engine, the exhaust purification device comprising the hydrocarbon trap according to any one of (1) to (11) and a three-way catalyst, the three-way catalyst and the hydrocarbon trap being arranged in this order from the upstream side of the exhaust passage.

[0019] (13) The exhaust purification device according to (12), further comprising a heating unit that electrically heats the hydrocarbon trap.

[0020] (14) A hybrid vehicle equipped with the exhaust purification device according to (12) or (13). [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a hydrocarbon trap that is capable of improving the adsorption rate of hydrocarbons contained in exhaust gas within a predetermined temperature range. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram showing an example of an exhaust gas purification device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view showing the surface structure of the hole of the hydrocarbon trap of FIG. [Figure 3A] 1 is a graph showing the temperature characteristics of the adsorption rate of silver ion-exchanged CHA-type zeolite and copper ion-exchanged FAU-type zeolite. [Figure 3B] 1 is a graph showing the temperature characteristics of the adsorption rate of silver ion-exchanged CHA-type zeolite and copper ion-exchanged FAU-type zeolite. [Figure 4] 2 is a cross-sectional view showing a modified example of the surface structure of the hole of the hydrocarbon trap of FIG. 1. FIG. [Figure 5] 1 is a graph showing the temperature characteristics of the adsorption rate of cesium ion-exchanged YFI-type zeolite. [Figure 6] 1 is a graph showing temperature characteristics 1 of the adsorption rates of the hydrocarbon traps of Examples 1 to 3. [Figure 7] 10 is a graph showing temperature characteristics 1 and 2 of the adsorption rate of the hydrocarbon trap of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] FIG. 1 shows an example of an exhaust gas purification device according to this embodiment.

[0025] The exhaust purification device 10 is provided in an exhaust pipe 2 of a direct injection gasoline engine 1, which serves as an exhaust passage for the internal combustion engine, and includes a three-way catalyst 11 and a hydrocarbon trap 12. In this case, the three-way catalyst 11 and the hydrocarbon trap 12 are arranged in this order from the upstream side of the exhaust pipe 2. Here, the hydrocarbon trap 12 is used to adsorb hydrocarbons contained in the exhaust gas, and a hydrocarbon adsorbent is supported on the surface of the pores of a porous substrate.

[0026] The three-way catalyst 11 is not particularly limited as long as it can convert hydrocarbons contained in the exhaust gas into H2O and CO2, CO into CO2, and NOx into N2. The three-way catalyst 11 is, for example, a honeycomb substrate supported with a precious metal catalyst and an oxygen storage material. Examples of the precious metal catalyst include Pt, Pd, and Rh. Examples of the oxygen storage material include CeO2 and CeZr composite oxides. Examples of materials that make up the honeycomb substrate include cordierite, mullite, and silicon carbide. The three-way catalyst 11 is manufactured, for example, by dip-coating a honeycomb substrate with a slurry containing the precious metal catalyst and the oxygen storage material, followed by firing.

[0027] The exhaust purification device 10 may further include a heating unit that electrically heats the hydrocarbon trap 12. This makes it possible to heat the hydrocarbon trap 12 at a predetermined timing and oxidize the hydrocarbons adsorbed in the hydrocarbon trap 12.

[0028] The heating unit is not particularly limited as long as it is capable of electrically heating the hydrocarbon trap 12, and examples thereof include a resistance heating unit.

[0029] FIG. 2 shows the surface structure of the pores of the hydrocarbon trap 12.

[0030] The hydrocarbon trap 12 includes a honeycomb substrate as a porous substrate. A first layer 22 containing a first zeolite and a second layer 23 containing a second zeolite are sequentially laminated on the surface of the partition walls 21 of the honeycomb substrate. The partition walls 21 of the honeycomb substrate define the cells of the honeycomb substrate. The first zeolite is capable of adsorbing olefins contained in the exhaust gas, and the second zeolite is capable of adsorbing paraffins and aromatic compounds contained in the exhaust gas. The first zeolite adsorbs olefins in a first temperature range and desorbs olefins in a second temperature range higher than the first temperature range. Meanwhile, the second zeolite desorbs paraffins and aromatic compounds in the first temperature range and adsorbs paraffins and aromatic compounds in the second temperature range. This improves the adsorption rate of hydrocarbons contained in the exhaust gas across a predetermined temperature range, including the first and second temperature ranges. As a result, rapid desorption of hydrocarbons contained in the exhaust gas is suppressed. Here, zeolite generally has a temperature range in which it adsorbs hydrocarbons and a temperature range in which it desorbs hydrocarbons within a temperature range below the activation temperature of the three-way catalyst 11. Therefore, rapid desorption of hydrocarbons is suppressed during cold start of the direct injection gasoline engine 1, and as a result, hydrocarbon emissions are suppressed. In this case, the exhaust purification device 10 equipped with the hydrocarbon trap 12 is particularly effective when installed in a hybrid vehicle in which the direct injection gasoline engine 1 is started and stopped frequently. Note that the hydrocarbon trap 12 may have catalytic ability to oxidize adsorbed olefins to CO2 and HO.

[0031] At this time, the second layer 23, which is more likely to be exposed to exhaust gas, reaches the second temperature range earlier than the first layer 22, and therefore the adsorption rate of hydrocarbons contained in the exhaust gas in a predetermined temperature range including the first temperature range and the second temperature range is further improved.

[0032] The hydrocarbon trap 12 is manufactured, for example, as follows. First, a honeycomb substrate is immersed in a first slurry containing a first zeolite, a binder, and a solvent, and then fired to form a first layer 22 on the surfaces of the partition walls 21 of the honeycomb substrate. Next, the honeycomb substrate, with the first layer 22 formed on the surfaces of the partition walls 21, is immersed in a second slurry containing a second zeolite, a binder, and a solvent, and then fired to form a second layer 23 on the surfaces of the first layer 22. The binder is not particularly limited, but an example of such a binder is silica sol. The solvent is not particularly limited, but an example of such a binder is water.

[0033] The first zeolite is not particularly limited as long as it is capable of adsorbing olefins in a first temperature range and desorbing olefins in a second temperature range higher than the first temperature range, and examples thereof include silver ion-exchanged zeolite. The second zeolite is not particularly limited as long as it is capable of desorbing paraffins and aromatic compounds in the first temperature range and adsorbing paraffins and aromatic compounds in the second temperature range, and examples thereof include copper ion-exchanged zeolite.

[0034] In this case, the copper ion-exchanged zeolite contained in the second layer 23, which is easily exposed to exhaust gas, improves its adsorption performance for paraffins and aromatic compounds contained in the exhaust gas at high temperatures when the exhaust gas contains HO. This is presumably because the copper ions constituting the copper ion-exchanged zeolite are coated with HO at low temperatures.

[0035] Copper ion-exchanged zeolite has catalytic ability to oxidize adsorbed olefins to CO2 and HO at temperatures of 300°C or higher. The catalytic ability of copper ion-exchanged zeolite may be improved by supporting a noble metal catalyst on the copper ion-exchanged zeolite.

[0036] The pore size of the first zeolite is preferably less than 4 Å. When the pore size of the first zeolite is less than 4 Å, the adsorption performance of olefins contained in exhaust gas is improved. The pore size of the first zeolite is, for example, 3 Å or more. The pore size of the second zeolite is preferably 4 Å or more. When the pore size of the second zeolite is 4 Å or more, the adsorption performance of paraffins and aromatic compounds contained in exhaust gas is improved. The pore size of the second zeolite is, for example, less than 13 Å.

[0037] Examples of silver ion-exchanged zeolites having a pore size of 3 Å or more and less than 4 Å include, but are not limited to, CHA-type zeolites, and examples of copper ion-exchanged zeolites having a pore size of 4 Å or more and less than 13 Å include, but are not limited to, FAU-type zeolites.

[0038] The silica-aluminum ratio of the silver ion-exchanged CHA-type zeolite is preferably 15 or more and 45 or less, more preferably 15 or more and 35 or less, and even more preferably 21 or more and 27 or less. The ion exchange amount (Ag / Al) of the silver ion-exchanged CHA-type zeolite is preferably 0.3 or more and 0.9 or less, more preferably 0.3 or more and 0.8 or less, and even more preferably 0.4 or more and 0.6 or less.

[0039] The silica-aluminum ratio of the copper ion-exchanged FAU zeolite is preferably 5 or more and 45 or less, more preferably 10 or more and 20 or less, and even more preferably 13 or more and 29 or less. The ion-exchange amount (Cu / 2Al) of the copper ion-exchanged FAU zeolite is preferably 0.3 or more and 0.6 or less, and more preferably 0.35 or more and 0.45 or less.

[0040] The mass ratio of the copper ion-exchanged FAU-type zeolite to the silver ion-exchanged CHA-type zeolite is preferably 1 or more and 7 or less, more preferably 2 or more and 5 or less, and even more preferably 2.5 or more and 3.5 or less.

[0041] In this case, the ratio of the second zeolite to the first zeolite preferably corresponds to the ratio of the paraffins and aromatic compounds contained in the exhaust gas to the olefins contained in the exhaust gas. For example, when the ratio of the carbon equivalent concentrations [ppmC] of the paraffins and aromatic compounds contained in the exhaust gas to the olefins contained in the exhaust gas is 72 / 28, the mass ratio of the copper ion-exchanged FAU-type zeolite to the silver ion-exchanged CHA-type zeolite is set to 3.

[0042] The washcoat amount of the hydrocarbon adsorbent in the hydrocarbon trap 12 is preferably 120 g / L or more and 240 g / L or less, and more preferably 180 g / L or more and 220 g / L or less.

[0043] Figures 3A and 3B show the temperature characteristics of the adsorption rate of silver ion-exchanged CHA-type zeolite and copper ion-exchanged FAU-type zeolite, respectively. In Figure 3, a positive adsorption rate indicates that hydrocarbons are being adsorbed, and a negative adsorption rate indicates that hydrocarbons are being desorbed. The areas enclosed by the straight line representing the 0% adsorption rate and the curves representing the positive and negative adsorption rates represent the adsorption and desorption amounts, respectively.

[0044] 3A and 3B show that silver ion-exchanged CHA-type zeolite adsorbs olefins in the first temperature range (50°C or higher and 200°C or lower) and desorbs olefins in the second temperature range (more than 200°C and 400°C or lower). Also, copper ion-exchanged FAU-type zeolite desorbs paraffins and aromatic compounds in the first temperature range (120°C or higher and 180°C or lower) and adsorbs paraffins and aromatic compounds in the second temperature range (more than 180°C and 300°C or lower).

[0045] In this embodiment, the hydrocarbon trap may have a hydrocarbon adsorbent supported on the surfaces of the pores of a porous substrate, and the hydrocarbon adsorbent may contain a first zeolite and a second zeolite. Therefore, the hydrocarbon trap may have, for example, a single-layer structure in which a layer containing the first zeolite and the second zeolite is formed on the surfaces of the pores of the porous substrate.

[0046] FIG. 4 shows a modified example of the structure of the surface of the hole of the hydrocarbon trap.

[0047] The hydrocarbon trap 12A has a first region 31, in which a first layer 22 containing a first zeolite and a second layer 23 containing a second zeolite are sequentially stacked, and a second region 32 containing a third zeolite, arranged without overlapping on the surface of a partition wall 21 of a honeycomb substrate. The third zeolite is capable of adsorbing paraffins and aromatic compounds contained in exhaust gas. The third zeolite adsorbs paraffins and aromatic compounds in a first temperature range and desorbs them in a second temperature range. This further improves the adsorption rate of hydrocarbons contained in exhaust gas in a predetermined temperature range including the first and second temperature ranges.

[0048] The hydrocarbon trap 12A is manufactured in the same manner as the hydrocarbon trap 12, except that a zone coating method is used. The arrangement of the first layer 22 and the second layer 23 on the surface of the partition wall 21 of the honeycomb substrate is not particularly limited.

[0049] The third zeolite is not particularly limited as long as it is capable of adsorbing paraffins and aromatic compounds in the first temperature range and desorbing the paraffins and aromatic compounds in the second temperature range, but examples thereof include cesium ion-exchanged zeolites.

[0050] The silica-aluminum ratio of the cesium ion-exchanged zeolite is preferably 15 or more and 100 or less, and more preferably 20 or more and 42 or less. The ion-exchange amount (Cs / Al) of the cesium ion-exchanged zeolite is preferably 0.7 or more and 1.0 or less, and more preferably 0.85 or more and 1.0 or less.

[0051] The pore diameter of the third zeolite is preferably 4 Å or more. When the pore diameter of the third zeolite is 4 Å or more, the adsorption performance of paraffins and aromatic compounds contained in exhaust gas is improved. The pore diameter of the third zeolite is, for example, less than 13 Å.

[0052] The cesium ion-exchanged zeolite having a pore size of 4 Å or more and less than 13 Å is not particularly limited, but an example thereof is YFI-type zeolite.

[0053] At this time, the first region 31, in which the first layer 22 and the second layer 23 are laminated in this order, and the second region 32, which contains the third zeolite, are arranged without overlapping on the surface of the partition wall 21 of the honeycomb substrate. This prevents cesium ions from migrating to the second layer 23 when the hydrocarbon trap 12A is in use, thereby improving the durability of the hydrocarbon trap 12A.

[0054] FIG. 5 shows the temperature characteristics of the adsorption rate of cesium ion-exchanged YFI-type zeolite.

[0055] From FIG. 5, it can be seen that cesium ion-exchanged YFI-type zeolite adsorbs paraffins and aromatic compounds in the first temperature range (50°C or higher and 160°C or lower) and desorbs paraffins and aromatic compounds in the second temperature range (more than 160°C and 350°C or lower).

[0056] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the present invention. For example, the exhaust purification device 10 may have an exhaust purification filter disposed between the three-way catalyst 11 and the hydrocarbon trap 12. [Example]

[0057] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0058] [Honeycomb base material] A cordierite honeycomb substrate with a diameter of 25.4 mm, a length of 60 mm, a volume of 30 cc, and 400 cells was used.

[0059] [First slurry] A first slurry was obtained by pulverizing 100 parts by mass of silver ion-exchanged CHA-type zeolite, 50 parts by mass of silica sol, and 110 parts by mass of pure water in a ball mill for 12 hours. The silver ion-exchanged CHA-type zeolite had a pore diameter of 3.8 Å, a silica-alumina ratio of 25, and an ion-exchange capacity (Ag / Al) of 0.5.

[0060] [Second slurry] A second slurry was obtained by pulverizing 100 parts by mass of copper ion-exchanged FAU zeolite, 50 parts by mass of silica sol, and 110 parts by mass of pure water in a ball mill for 12 hours. The copper ion-exchanged FAU zeolite had a pore diameter of 7.4 Å, a silica-alumina ratio of 15, and an ion-exchange capacity (Cu / 2Al) of 0.4.

[0061] [Third slurry] A third slurry was obtained by pulverizing 100 parts by mass of cesium ion-exchanged YFI zeolite, 50 parts by mass of silica sol, and 110 parts by mass of pure water in a ball mill for 12 hours. The cesium ion-exchanged YFI zeolite had a pore diameter of 6.2 Å, a silica-alumina ratio of 20, and an ion-exchange capacity (Cs / Al) of 1.0.

[0062] [Example 1] The honeycomb substrate was immersed in the first slurry and then fired to form a first layer on the surface of the partition walls of the honeycomb substrate. At this time, the washcoat amount of silver ion-exchanged CHA-type zeolite was 50 g / L. Next, the honeycomb substrate with the first layer formed on the surface of the partition walls was immersed in the second slurry and then fired to form a second layer on the surface of the first layer, thereby obtaining a hydrocarbon trap. At this time, the washcoat amount of copper ion-exchanged FAU-type zeolite was 150 g / L.

[0063] [Example 2] The honeycomb substrate was immersed in the first slurry and then fired to form a first layer on the surface of the partition walls of the honeycomb substrate. The amount of silver ion-exchanged CHA-type zeolite washcoated was 50 g / L. Next, the honeycomb substrate with the first layer formed on the surface of the partition walls was immersed in the third slurry and then fired to form a second layer on the surface of the partition walls of the honeycomb substrate. The amount of cesium ion-exchanged YFI-type zeolite washcoated was 50 g / L. Next, the honeycomb substrate with the second layer formed on the surface of the first layer was immersed in the second slurry and then fired to form a third layer on the surface of the second layer, thereby obtaining a hydrocarbon trap. The amount of copper ion-exchanged FAU-type zeolite washcoated was 100 g / L.

[0064] [Example 3] A hydrocarbon trap was obtained in the same manner as in Example 2, except that the lamination order of the first and second layers was reversed.

[0065] [Temperature characteristics of adsorption rate 1] The hydrocarbon trap was aged at 850°C for 10 hours while alternating between a rich atmosphere (80 seconds) and a lean atmosphere (20 seconds) under the following conditions, and then cooled to 25°C.

[0066] Rich atmosphere: C3H6 (1.0%), O2 (2.5%), H2O (10%), N2 (balance) Lean atmosphere: O2 (20%), H2O (10%), N2 (balance) Flow rate: 500cc / min (φ1 inch)

[0067] Next, the hydrocarbon trap was reheated in an air atmosphere at 700°C for 10 minutes and then cooled to 25°C. Next, under the following conditions, simulated exhaust gas was passed through the hydrocarbon trap, and the composition of the gas discharged from the hydrocarbon trap was measured to evaluate the temperature characteristics of the adsorption rate of the hydrocarbon trap.

[0068] Simulated exhaust: NO (500 ppm), propylene (348 ppmC), isopentane (108 ppmC), toluene (408 ppmC), isooctane (336 ppmC), H2 (0.17%), CO (0.5%), O2 (0.49%), CO2 (14%), H2O (10%), balance N2 Heating rate: 20°C / min Measurement temperature: 50~500℃ Flow rate: 25L / min Space velocity (SV): 50,000h -1

[0069] FIG. 6 shows the temperature characteristics 1 of the adsorption rate of the hydrocarbon traps of Examples 1 to 3.

[0070] It can be seen from FIG. 6 that the hydrocarbon traps of Examples 1 to 3 have high adsorption rates for hydrocarbons (propylene, isopentane, toluene, and isooctane) contained in the simulated exhaust gas in the temperature range of 300° C. or less.

[0071] [Temperature characteristics of adsorption rate 2] The temperature characteristics of the adsorption rate of the hydrocarbon trap were evaluated in the same manner as in [Temperature characteristics of adsorption rate 1], except that the composition of the simulated exhaust gas was changed as follows:

[0072] NO (500 ppm), propylene (348 ppmC), isopentane (108 ppmC), toluene (408 ppmC), isooctane (336 ppmC), H2 (0.17%), CO (0.5%), O2 (0.49%), CO2 (14%), N2 (balance)

[0073] FIG. 7 shows temperature characteristics 1 and 2 of the adsorption rate of the hydrocarbon trap of Example 2.

[0074] From FIG. 7, it can be seen that the hydrocarbon trap of Example 2 improves the adsorption rate of hydrocarbons (propylene, isopentane, toluene, and isooctane) contained in the simulated exhaust in the temperature range of 200°C or higher when the simulated exhaust contains H2O. [Explanation of symbols]

[0075] 1 Direct injection gasoline engine 2 exhaust pipes 10 Exhaust gas purification device 11 Three-way catalyst 12, 12A Hydrocarbon Trap 21 Honeycomb substrate partition wall 22 First layer 23 Second layer 31 First area 32 Second area

Claims

1. 1. A hydrocarbon trap for use in adsorbing hydrocarbons contained in the exhaust gas of an internal combustion engine, comprising: a hydrocarbon adsorbent is supported on the surfaces of the pores of the porous substrate; the hydrocarbon adsorbent includes a first zeolite capable of adsorbing olefins contained in the exhaust gas, and a second zeolite capable of adsorbing paraffins and aromatic compounds contained in the exhaust gas; the first zeolite adsorbs the olefin in a first temperature range and desorbs the olefin in a second temperature range that is higher than the first temperature range; The second zeolite is a hydrocarbon trap that desorbs the paraffins and aromatic compounds in the first temperature range and adsorbs the paraffins and aromatic compounds in the second temperature range.

2. 2. The hydrocarbon trap according to claim 1, wherein a layer containing the first zeolite and the second zeolite is formed on the surfaces of the pores of the porous substrate, or a layer containing the first zeolite and a layer containing the second zeolite are laminated on the surfaces of the pores of the porous substrate.

3. 3. The hydrocarbon trap according to claim 2, wherein a layer containing the first zeolite and a layer containing the second zeolite are sequentially laminated on the surfaces of the pores of the porous substrate.

4. 4. A hydrocarbon trap according to any one of claims 1 to 3, wherein the ratio of the second zeolite to the first zeolite corresponds to the ratio of the paraffins and aromatics to the olefins.

5. the first zeolite is a silver ion-exchanged zeolite; 4. A hydrocarbon trap according to any one of claims 1 to 3, wherein the second zeolite is a copper ion-exchanged zeolite.

6. The first zeolite has a pore size of less than 4 Å, 4. A hydrocarbon trap according to any one of claims 1 to 3, wherein the second zeolite has a pore size of 4 Å or greater.

7. The first zeolite is a CHA-type zeolite, 7. The hydrocarbon trap of claim 6 wherein the second zeolite is a FAU-type zeolite.

8. the hydrocarbon adsorbent further comprises a third zeolite capable of adsorbing paraffins and aromatic compounds contained in the exhaust gas; the third zeolite adsorbs the paraffins and aromatic compounds in the first temperature range and desorbs the paraffins and aromatic compounds in the second temperature range; 4. The hydrocarbon trap according to claim 1, wherein a first region containing the first zeolite and the second zeolite and a third region containing the third zeolite are arranged on the surface of the pores of the porous substrate without overlapping with each other.

9. 9. The hydrocarbon trap of claim 8 wherein the third zeolite is a cesium-exchanged zeolite.

10. 9. The hydrocarbon trap of claim 8, wherein the third zeolite has a pore size of 4 Å or greater.

11. 11. The hydrocarbon trap of claim 10, wherein the third zeolite is a YFI-type zeolite.

12. An exhaust purification device provided in an exhaust passage of an internal combustion engine, A hydrocarbon trap according to claim 1 and a three-way catalyst, an exhaust purification device in which the three-way catalyst and the hydrocarbon trap are arranged in this order from the upstream side of the exhaust passage;

13. The exhaust purification device according to claim 12, further comprising a heating unit that electrically heats the hydrocarbon trap.

14. A hybrid vehicle comprising the exhaust purification device according to claim 12 or 13.

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