Hydrocarbon adsorption device

Abstract

The present invention provides a hydrocarbon adsorption device (10) that allows a fluid to flow therethrough and adsorbs hydrocarbons in the above-mentioned fluid. The hydrocarbon adsorption device (10) has a first hydrocarbon adsorption section (20) containing zeolite and a second hydrocarbon adsorption section (30) containing zeolite, which is provided on the downstream side of the first hydrocarbon adsorption section (20) in the flow direction of the above-mentioned fluid. The pore diameter (P1) of the zeolite contained in the first hydrocarbon adsorption section (20) is smaller than the pore diameter (P2) of the zeolite contained in the second hydrocarbon adsorption section (30) (i.e., P1 < P2).

Description

Technical Field

[0001] The present invention relates to a hydrocarbon adsorption device. In particular, it relates to a hydrocarbon adsorption device that allows exhaust gas to flow through and adsorbs hydrocarbons in the exhaust gas.

[0002] The present invention claims priority based on Japanese Patent Application No. 2020-178212 filed on October 23, 2020, and incorporates the entire content of this application by reference into this specification. Background Art

[0003] Exhaust gas discharged from an internal combustion engine of a vehicle or the like contains hydrocarbons (HCs), such as chain saturated hydrocarbons (alkane-based hydrocarbons) such as methane, ethane, and propane, chain unsaturated hydrocarbons (olefin-based hydrocarbons) such as ethylene, propylene, and butene, and cyclic hydrocarbons (aromatic hydrocarbons) such as benzene, toluene, and xylene. In order to remove these various HCs from the exhaust gas, currently, a method of bringing the exhaust gas into contact with a catalyst metal (for example, an oxidation catalyst, a three-way catalyst) is widely used (see, for example, Patent Documents 1 to 6).

[0004] However, for example, when starting an internal combustion engine or the like, when the internal combustion engine is in a cold state and the temperature of the exhaust gas is low and does not reach the temperature at which the catalyst metal is activated, HCs cannot be sufficiently purified. In addition, since a mixture with a high fuel concentration is supplied to the internal combustion engine, the concentration of HCs contained in the exhaust gas becomes higher than that during normal operation. Therefore, for example, Patent Document 1 discloses an exhaust gas purification catalyst having a substrate, an HC adsorption layer formed on the surface of the substrate and containing an HC adsorption material, and a catalyst layer formed on the surface of the HC adsorption layer and containing a catalyst metal. In the exhaust gas purification catalyst of Patent Document 1, during the cold state of the internal combustion engine, HCs contained in the exhaust gas are temporarily adsorbed on the HC adsorption layer. The HCs adsorbed on the HC adsorption layer are desorbed from the HC adsorption layer when the exhaust gas reaches a specified temperature (desorption temperature) or higher, and are decomposed and removed by the catalyst metal.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-210371

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-007260

[0009] Patent Document 3: International Publication No. 2005 / 092482

[0010] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-089881

[0011] Patent Document 5: Japanese Unexamined Patent Application Publication No. 2013-119845

[0012] Patent Document 6: Japanese Patent Application Laid-Open No. 2015-173993 Summary of the Invention

[0013] However, as described above, the types of HC discharged from the internal combustion engine are various. According to the research of the inventors of the present invention, when competitive adsorption of various HC species occurs in the HC adsorption layer, the HC species with strong adsorption force (for example, HC species with small molecular size and unsaturated bonds) are preferentially adsorbed, and the HC species with weak adsorption force (for example, HC species with large molecular size and no unsaturated bonds) are relatively difficult to be adsorbed. Therefore, in the existing exhaust gas purification catalysts, specific HC species are mainly adsorbed by the HC adsorption layer, and the unadsorbed HC species are directly discharged, resulting in deteriorated emissions. For the increasingly strict exhaust restrictions year by year, further reduction of the emissions of HC species is required.

[0014] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a novel hydrocarbon adsorption device capable of effectively adsorbing hydrocarbons.

[0015] By using the present invention, a hydrocarbon adsorption device that allows a fluid to flow through and adsorbs hydrocarbons in the fluid can be provided. Such a hydrocarbon adsorption device includes: a first hydrocarbon adsorption section containing zeolite and a second hydrocarbon adsorption section containing zeolite provided on the downstream side in the flow direction of the fluid relative to the first hydrocarbon adsorption section. The pore diameter P1 of the zeolite contained in the first hydrocarbon adsorption section is smaller than the pore diameter P2 of the zeolite contained in the second hydrocarbon adsorption section.

[0016] In the above configuration, the fluid comes into contact with the first hydrocarbon adsorption section before coming into contact with the second hydrocarbon adsorption section. The first hydrocarbon adsorption section contains zeolite with a smaller pore diameter compared to the second hydrocarbon adsorption section. Among the various HC species contained in the fluid, the HC species with a small molecular size are adsorbed by the first hydrocarbon adsorption section. The second hydrocarbon adsorption section is disposed on the downstream side of the first hydrocarbon adsorption section. The second hydrocarbon adsorption section contains zeolite with a larger pore diameter compared to the first hydrocarbon adsorption section. The HC species with a large molecular size are adsorbed by the second hydrocarbon adsorption section. Thus, by utilizing the inherent pores of the zeolite, for each molecular size of the HC species, the HC species are adsorbed onto different hydrocarbon adsorption sections, thereby reducing the competitive adsorption of the HC species and effectively adsorbing the HC. As a result, the HC can be appropriately removed from the fluid.

[0017] It should be noted that in this specification, "narrow pore diameter" refers to the largest narrow pore diameter shown for each framework type in the database "Atlas of Zeolite Framework Types (<Internet>https: / / www.sciencedirect.com / book / 9780444530646 / atlas-of-zeolite-framework-types?via=ihub=)" of the International Zeolite Association. In other words, it refers to the major axis. In the case of having two sets of pore channels, it refers to the largest major axis among them. Additionally, in the case of containing two or more types of zeolites, it refers to the weighted average based on mass of the largest narrow pore diameter (major axis) of each framework type. It should be noted that in this database, the radius r(O 2- ) is assumed to be

[0018] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the difference (P2 - P1) between the above-mentioned P1 and the above-mentioned P2 is above below. Thereby, competitive adsorption of HC species can be better reduced, and the technical effects disclosed herein can be exerted at a high level.

[0019] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the above-mentioned P1 is above below. Thereby, adsorption of olefinic hydrocarbons with small molecular sizes (e.g., those with a small number of carbon atoms, as an example, lower ones with 4 or fewer carbon atoms) can be promoted.

[0020] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the above-mentioned P2 is above below. Thereby, adsorption of aromatic hydrocarbons with large molecular sizes (e.g., those with a large number of carbon atoms or a large-volume structure), such as m-xylene and o-xylene, can be promoted.

[0021] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the silica-to-alumina ratio of the zeolite contained in the above-mentioned first hydrocarbon adsorption section is less than the silica-to-alumina ratio of the zeolite contained in the above-mentioned second hydrocarbon adsorption section. According to the research of the inventors of the present invention, among HC species with small molecular sizes (e.g., lower ones with 4 or fewer carbon atoms), there are many with unsaturated bonds and much stronger adsorption forces. By making the silica-to-alumina ratio of the zeolite contained in the first hydrocarbon adsorption section smaller, adsorption of HC species with strong adsorption forces can be promoted.

[0022] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption section is 10 or more and 30 or less. Thereby, lower HC compounds can be suitably adsorbed. The durability of the first hydrocarbon adsorption section can also be improved.

[0023] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the zeolite contained in the first hydrocarbon adsorption section contains at least one framework type of CHA and FER. Thereby, the desorption temperature of HC compounds can be increased, and HC compounds can be suitably retained until the fluid is sufficiently heated.

[0024] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the zeolite contained in the second hydrocarbon adsorption section contains at least one framework type of MFI and FAU. Thereby, the desorption temperature of HC compounds can be increased, and HC compounds can be suitably retained until the fluid is sufficiently heated.

[0025] In a preferred embodiment of the hydrocarbon adsorption device disclosed herein, the fluid is a gas (e.g., exhaust gas). Thereby, HC compounds contained in the gas (e.g., exhaust gas) can be suitably adsorbed, and the emission of HC compounds can be reduced.

[0026] According to the present invention, an exhaust gas purification system can also be provided, which is disposed in the exhaust path of an internal combustion engine and purifies hydrocarbon compounds in the exhaust gas discharged from the internal combustion engine. Such an exhaust gas purification system has the above-described hydrocarbon adsorption device and a catalyst metal section containing a catalyst metal.

[0027] With the above configuration, for example, when the internal combustion engine is in a cold state, HC compounds can be suitably adsorbed. The desorption temperature of HC compounds can also be increased, and after the internal combustion engine is sufficiently heated, HC compounds can be suitably desorbed. Therefore, the emission of HC compounds can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram showing an exhaust gas purification system according to an embodiment.

[0029] Figure 2 It is a cross-sectional view schematically showing a partition wall portion between the first hydrocarbon adsorption section and the second hydrocarbon adsorption section.

[0030] Figure 3 It is a temperature rising diagram during the adsorption and desorption evaluation of HC compounds.

[0031] Figure 4 It is a graph showing the relationship between the desorbed THC and the temperature in Test Example 1.

[0032] Figure 5 It is a graph showing the relationship between the difference in the THC desorption peak temperature and the pore diameter in Test Example 1.

[0033] Figure 6 It is a graph showing the relationship between the desorbed THC and temperature in Test Example 2.

[0034] Figure 7 It is a graph showing the relationship between the difference between the THC desorption peak temperature and the pore diameter in Test Example 2.

[0035] Figure 8 It is a schematic cross-sectional view of the partition wall portion of the hydrocarbon adsorption device related to other embodiments.

[0036] Figure 9 It is a schematic cross-sectional view of the partition wall portion of the hydrocarbon adsorption device related to other embodiments.

[0037] Figure 10 It is a schematic cross-sectional view of the partition wall portion of the exhaust gas purification catalyst body with a hydrocarbon adsorption portion used in Test Example 3.

[0038] Figure 11 It is a graph showing the performance evaluation test results of two types (Example 11 and Comparative Example 11) of exhaust gas purification catalyst bodies with a hydrocarbon adsorption portion used in Test Example 3. The horizontal axis represents time (seconds), and the vertical axis represents the HC purification rate (%). Detailed Embodiments

[0039] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that, regarding matters other than those specifically mentioned in this specification and necessary for implementing the present invention, they can be understood as design matters of those skilled in the art based on the prior art in this field. The present invention can be implemented based on the content disclosed in this specification and the common technical knowledge in this field. In addition, in the following drawings, sometimes the same reference numerals are assigned to components and parts that achieve the same function, and repeated explanations are omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in each figure do not necessarily reflect the actual dimensional relationships. Also, in this specification, the expression of "A to B" (A and B are arbitrary values) representing a range includes the meaning of A or more and B or less, as well as the meanings of "preferably greater than A" and "preferably less than B".

[0040] "Exhaust Gas Purification System"

[0041] Figure 1 It is a schematic diagram of the exhaust gas purification system 1. The exhaust gas purification system 1 includes an internal combustion engine (engine) 2, an exhaust gas purification device 3, and an engine control unit (ECU) 7. The exhaust gas purification system 1 is configured to purify HC contained in the exhaust gas discharged from the internal combustion engine 2 by using the exhaust gas purification device 3. It should be noted that Figure 1The arrow indicates the flow direction of the exhaust gas. Additionally, in the following description, along the flow direction of the exhaust gas, the side closer to the internal combustion engine 2 is referred to as the upstream side, and the side farther from the internal combustion engine 2 is referred to as the downstream side.

[0042] The internal combustion engine 2 is configured mainly as a gasoline engine of a gasoline vehicle here. However, the internal combustion engine 2 can also be an engine other than gasoline, such as a diesel engine and an engine mounted on a hybrid vehicle. The internal combustion engine 2 has a combustion chamber (not shown). The combustion chamber is connected to a fuel tank (not shown). Among them, gasoline is stored in the fuel tank. However, the fuel stored in the fuel tank can also be diesel fuel (gas oil), etc. In the combustion chamber, the fuel supplied from the fuel tank is mixed with oxygen and burned. Thereby, the combustion energy is converted into mechanical energy. The combustion chamber communicates with an exhaust port 2a. The exhaust port 2a communicates with an exhaust gas purification device 3. The burned fuel gas becomes exhaust gas and is discharged to the exhaust gas purification device 3. "Exhaust gas" is an example of a fluid, more specifically a gas. The exhaust gas contains various HC species with different molecular sizes. For example, it can contain HC species with a relatively small size of about and HC species with a large size of about 5.5 to or so.

[0043] The exhaust gas purification device 3 has an exhaust gas path 4 communicating with the internal combustion engine 2, an oxygen sensor 8, a hydrocarbon adsorption device 10, and a catalyst metal part 40. The exhaust gas path 4 is an exhaust gas flow path through which the exhaust gas flows. Among them, the exhaust gas path 4 has an exhaust manifold 5 and an exhaust pipe 6. The upstream end of the exhaust manifold 5 is connected to the exhaust port 2a of the internal combustion engine 2. The downstream end of the exhaust manifold 5 is connected to the exhaust pipe 6. In the middle of the exhaust pipe 6, the hydrocarbon adsorption device 10 and the catalyst metal part 40 are arranged in sequence from the upstream side. However, the arrangement of the hydrocarbon adsorption device 10 and the catalyst metal part 40 can be changed arbitrarily. Additionally, the number of the hydrocarbon adsorption device 10 and the catalyst metal part 40 is not particularly limited, and multiple can be provided respectively.

[0044] The hydrocarbon adsorption device 10 is configured to adsorb HC components in the exhaust gas when the internal combustion engine 2 is in a cold state, for example, at a low temperature of less than about 170°C, and to remove the HC components when the exhaust gas reaches a specified temperature (for example, about 170°C) or higher. The hydrocarbon adsorption device 10 includes a first hydrocarbon adsorption section 20 and a second hydrocarbon adsorption section 30. Among them, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 are arranged in series. It should be noted that the configurations of the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 will be described in detail later. An oxygen sensor 8 is provided between the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 in the exhaust gas flow direction. Considering that during the desorption of HC components, the exhaust gas becomes a weak rich atmosphere due to temperature rise. By arranging the oxygen sensor 8 between the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30, it is easy to control the atmosphere of the exhaust gas to the stoichiometric air-fuel ratio (theoretical ratio). As a result, the purification rate of HC components can be better improved.

[0045] The catalyst metal section 40 is configured to decompose and remove HC components in the exhaust gas when the exhaust gas reaches a specified temperature or higher. The catalyst metal section 40 must contain a catalyst metal that decomposes HC components in the exhaust gas. As the catalyst metal, there is no particular limitation, and one or more kinds of currently known various metal species that are used in this application and function as oxidation catalysts and three-way catalysts can be used. As a specific example, noble metals can be cited, namely, platinum group, rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), silver (Ag), gold (Au). In addition, instead of noble metals, or in addition to using noble metals, base metals such as alkali metals, alkaline earth metals, and transition metals can be used. For example, metal species such as iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) can be used. Substances alloyed from two or more of these metals can also be used. HC components are oxidized by the catalyst metal and converted (purified) into water, carbon dioxide, etc.

[0046] The catalyst metal section 40 may also contain optional components. As an example of the optional components, inorganic oxides, OSC materials with oxygen storage capacity (Oxygen Storage Capacity: OSC), NOx adsorption materials with NOx storage capacity, stabilizing materials, etc. can be cited. As the inorganic oxide, for example, alumina, Al-containing oxides such as oxides containing alumina can be cited. As the OSC material, for example, cerium dioxide, cerium dioxide (CeO 2 ) - zirconia (ZrO 2 ) composite oxides (CZ composite oxides) and other Ce-containing oxides can be cited. As the NOx adsorption material, for example, alkaline earth elements such as calcium (Ca), barium (Ba), and strontium (Sr) can be cited. As the stabilizing material, for example, rare earth elements such as yttrium (Y), lanthanum (La), and neodymium (Nd) can be cited.

[0047] It should be noted that, on the upstream side of the hydrocarbon adsorption device 10, for example, the following can also be arranged: a three-way catalyst that simultaneously purifies HC, CO, and NOx contained in the exhaust gas; a gasoline particulate filter (GPF: Gasoline Particulate Filter) that removes particulate matter (PM: Particulate matter) contained in the exhaust gas; a diesel particulate filter (DPF: Diesel Particulate Filter) that removes PM contained in the exhaust gas; a diesel oxidation catalyst (DOC: Diesel Oxidation Catalyst) that purifies HC and CO contained in the exhaust gas; a NOx storage-reduction (NSR: NOx Storage-Reduction) catalyst that stores NOx during normal operation (lean conditions) and purifies NOx when a large amount of fuel is injected (rich atmosphere), etc. In particular, a three-way catalyst can be provided on the upstream side of the hydrocarbon adsorption device 10. Thereby, the amount of CO and / or NOx flowing into the hydrocarbon adsorption device 10 can be reduced, and the amount of HC that the hydrocarbon adsorption device 10 can adsorb can be increased.

[0048] The ECU 7 is configured to control the internal combustion engine 2 and the exhaust gas purification device 3. The ECU 7 is electrically connected to the internal combustion engine 2 and sensors (such as an oxygen sensor 8, a temperature sensor not shown, a pressure sensor, etc.) provided at various parts of the exhaust gas purification device 3. It should be noted that the configuration of the ECU 7 can be the same as that of the prior art and is not particularly limited. The ECU 7 is, for example, a processor or an integrated circuit. The ECU 7 has an input port (not shown) and an output port (not shown). The ECU 7 receives information such as the operating state of the vehicle, the amount, temperature, and pressure of the exhaust gas discharged from the internal combustion engine 2, for example. The ECU 7 receives the information detected by the sensors (such as the amount of oxygen measured by the oxygen sensor 8) via the input port. The ECU 7 sends a control signal via the output port based on the received information, for example. The ECU 7 controls the operation of the internal combustion engine 2, such as fuel injection control, ignition control, and intake air amount adjustment control. The ECU 7 controls the driving and stopping of the exhaust gas purification device 3 based on the operating state of the internal combustion engine 2, the amount of exhaust gas discharged from the internal combustion engine 2, etc., for example.

[0049] "Hydrocarbon Adsorption Device"

[0050] The hydrocarbon adsorption device 10 sequentially includes a first hydrocarbon adsorption section 20 and a second hydrocarbon adsorption section 30 from the upstream side. Among them, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 are independent of each other. However, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 can also be integrally formed. Among them, the outer shapes of the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 are respectively cylindrical shapes. However, the outer shape of the hydrocarbon adsorption device 10 is not particularly limited and can be, for example, an elliptical cylinder shape, a polygonal cylinder shape, a tubular shape, a foam shape, a granular shape, a fibrous shape, etc.

[0051] Figure 2 It is a partial cross-sectional view of the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 after being partially enlarged. It should be noted that Figure 2 the arrow in Figure 2 indicates the flow direction of the exhaust gas. In

[0052] As the substrates 21 and 31, there is no particular limitation, and various raw materials and forms of substrates currently used in this application can be used respectively. The substrates 21 and 31 can be, for example, ceramic carriers made of ceramics such as silicon carbide (SiC), cordierite, and aluminum titanate, or metal carriers made of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, etc. The substrates 21 and 31 can also be an electrically heated catalytic converter (EHC: Electrically Heated Converter) or a plasma-type catalytic converter.

[0053] The substrates 21 and 31 have, for example, a honeycomb structure having a plurality of small chambers (voids) serving as exhaust gas flow paths regularly arranged in the cylinder axis direction X and partition walls (ribs) partitioning the plurality of small chambers. Among them, the substrates 21 and 31 are so-called straight flow structures in which the upstream end and the downstream end of each small chamber are open. However, it can also be various structures currently known in the art, such as a wall flow structure in which the end of one small chamber is open and the end of the other small chamber is closed. Although not particularly limited, the length (average length) of the substrates 21 and 31 in the cylinder axis direction X is approximately 10 to 200 mm, and can be, for example, 20 to 100 mm. In addition, the volume including the substrates 21 and 31 (the apparent volume (bulk volume) including the volume of the substrates themselves (pure volume) and the volume of the internal small chambers) is approximately 0.1 to 10 L, and can be, for example, 0.5 to 5 L.

[0054] Among them, the first hydrocarbon adsorption layer 22 is provided on the substrate 21. Specifically, it is provided on the surface of the partition wall of the substrate 21. Among them, the second hydrocarbon adsorption layer 32 is provided on the substrate 31. Specifically, it is provided on the surface of the partition wall of the substrate 31. The first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 are respectively arranged along the cylinder axis direction X. The first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 can be continuously arranged or intermittently arranged respectively.

[0055] The first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 must respectively contain zeolite. The zeolite has a fine pore diameter matching the molecular size of HC species. The following micropores. In the present embodiment, the fine pore diameter P1 of the zeolite contained in the first hydrocarbon adsorption layer 22 is smaller than the fine pore diameter P2 of the zeolite contained in the second hydrocarbon adsorption layer 32. That is, P1 < P2. The first hydrocarbon adsorption layer 22 is configured to selectively adsorb HC species with small molecular sizes due to the shape selectivity of the inherent fine pores of the zeolite. The second hydrocarbon adsorption layer 32 is configured to selectively adsorb HC species with relatively larger molecular sizes than the HC species adsorbed by the first hydrocarbon adsorption layer 22 due to the shape selectivity of the inherent fine pores of the zeolite. In this way, according to the molecular size, the HC species are adsorbed on their respective hydrocarbon adsorption parts, thereby reducing the competitive adsorption of the HC species and effectively adsorbing HC classes.

[0056] As the zeolite, one or two or more kinds of various zeolites currently known to be usable in this application can be used. The zeolites contained in the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 can be natural zeolites produced as natural mineral resources or synthetic zeolites synthesized artificially. The zeolites contained in the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 can be appropriately selected, for example, from the framework types recorded by the three capital letter structure codes in the database of the International Zeolite Association.

[0057] As an example, ACO, AEI, AEN, AFX, AFT, AFN, ANA, APC, APD, ATT, BEA, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, FER, FAU (β type), GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, MOR, MFI (ZSM-5 type), NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON and various framework types can be listed. The zeolite can be, for example, an ion-exchanged zeolite in which part or all of the hydrogen is exchanged with ions such as copper. These zeolites themselves are already commercially available. As an example, some framework type zeolites are shown in Table 1.

[0058] [Table 1]

[0059] Table 1

[0060]

[0061] Source: Atlas of Zeolite Framework Types (database of the International Zeolite Association)

[0062] Although not particularly limited, in several preferred embodiments, the first hydrocarbon adsorption layer 22 contains zeolite of at least one framework type selected from CHA and FER. Among them, H-CHA zeolite that has not been ion-exchanged is preferred. Thereby, desorption of the adsorbed HC can be more favorably suppressed, and the HC can be suitably retained in the first hydrocarbon adsorption layer 22 until the exhaust gas is sufficiently heated (for example, to 200°C or higher).

[0063] Although not particularly limited, in several preferred embodiments, the second hydrocarbon adsorption layer 32 contains zeolite of at least one framework type selected from MFI and FAU. MFI has three-dimensional pores and excellent adsorption performance. FAU has excellent adsorption and retention performance for a wide range of HC species. Therefore, the technical effects disclosed herein can be exhibited at a high level.

[0064] Although not particularly limited, in several preferred embodiments, the pore diameter P1 of the zeolite contained in the first hydrocarbon adsorption layer 22 is approximately or more, preferably or more, for example or more, approximately or less, preferably or less, for example or less. Thereby, adsorption of lower olefinic hydrocarbons having a small molecular size such as hydrocarbons having 4 or less carbon atoms (especially 3 carbon atoms) can be promoted. In the case where the fuel is gasoline, such a configuration is particularly preferred.

[0065] Although not particularly limited, in several preferred embodiments, the pore diameter P2 of the zeolite contained in the second hydrocarbon adsorption layer 32 is approximately or more, preferably or more, for example or more, or more, approximately or less, preferably or less, for example As described below, it is thus possible to promote the adsorption of aromatic hydrocarbons having a large molecular size, such as m-xylene and o-xylene, for example, higher ones having 5 to 10 carbon atoms or a large-sized structure. In addition, the ratio of the major axis to the minor axis (minor axis / major axis) of the zeolite contained in the second hydrocarbon adsorption layer 32 as described in the above-mentioned "Atlas of Zeolite Framework Types" may be 0.98 or less, for example, 0.9 ≤ (minor axis / major axis) ≤ 0.95. Thus, even for HC species with weak adsorption force, desorption at cold temperatures can be better suppressed, and the retention performance can be improved.

[0066] Although not particularly limited, in several preferred embodiments, the difference (P2 - P1) between the pore diameter P1 of the zeolite contained in the first hydrocarbon adsorption layer 22 and the pore diameter P2 of the zeolite contained in the second hydrocarbon adsorption layer 32 is approximately or more, preferably or more, approximately or less, preferably or less. Thus, competitive adsorption of HC species can be better reduced, and HC species with a wide range of molecular sizes, such as those with a size of about 2 to 12 carbon atoms, can be widely adsorbed. Therefore, the technical effects disclosed herein can be achieved at a high level.

[0067] Although not particularly limited, in several preferred embodiments, the first hydrocarbon adsorption layer 22 contains a zeolite having 8 and / or 10 ring atoms, particularly a zeolite having 8 ring atoms. In addition, in several preferred embodiments, the second hydrocarbon adsorption layer 32 contains a zeolite having 10 or 12 ring atoms. The number of ring atoms of the zeolite contained in the second hydrocarbon adsorption layer 32 may be the same as or greater than the number of ring atoms of the zeolite contained in the first hydrocarbon adsorption layer 22.

[0068] Although not particularly limited, in several preferred embodiments, the silica-to-alumina ratio of each of the zeolites contained in the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 is approximately 5 or more, preferably 10 or more, for example, 13 or more, approximately 3000 or less, preferably 2000 or less, for example, 1500 or less. HC species have the property of being easily adsorbed onto Al among Si and Al, which are the main components of zeolite. Therefore, by setting the silica-to-alumina ratio below a specified value, the adsorption performance and retention performance of the hydrocarbon adsorption device 10 for HC species can be improved. In addition, by setting the silica-to-alumina ratio above a specified value, the crystalline structure can be stably maintained even when the hydrocarbon adsorption device 10 is exposed to high temperatures due to exhaust gas, and the adsorption performance of HC species can be exhibited. It should be noted that in this specification, the "silica-to-alumina ratio" refers to the molar ratio of the silica component to the alumina component in the zeolite (SiO 2 / Al2 O 3 ).

[0069] Although not particularly limited, in some preferred embodiments, the silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption layer 22 is smaller than the silica-alumina ratio of the zeolite contained in the second hydrocarbon adsorption layer 32. According to the research of the inventors of the present invention, HCs with small molecular sizes (in other words, low-order HCs with a small number of carbon atoms) have more unsaturated bonds and stronger adsorption power. By reducing the silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption layer 22, the adsorption of low-order HCs with strong adsorption power can be promoted.

[0070] For the reasons described above, the silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption layer 22 is approximately 100 or less, preferably 30 or less, and for example, 23 or less. In addition, the silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption layer 22 is approximately 5 or more, preferably 10 or more, and for example, 13 or more. As a result, the adsorption of zeolite and HC becomes too strong, and desorption becomes difficult, thereby being able to suppress the effective adsorption amount from slowly decreasing. As a result, excellent adsorption performance can be maintained for a long time. In addition, in some preferred embodiments, the silica-alumina ratio of the zeolite contained in the second hydrocarbon adsorption layer 32 is approximately 50 or more, preferably 100 or more, 300 or more, and for example, 500 or more, and approximately 3000 or less, preferably 2000 or less, and for example, 1500 or less. As a result, it is possible to have both the adsorption performance of HC and the durability performance at a high level.

[0071] Zeolite may contain at least one of transition metal elements such as manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and silver (Ag), alkaline earth elements such as calcium (Ca), barium (Ba), and strontium (Sr), alkali metal elements such as sodium (Na), and potassium (K), and precious metal elements such as platinum group (PGM). This can improve the HC retention performance and further increase the desorption temperature.

[0072] The first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 may contain any component other than zeolite. As an example of the arbitrary component, the catalyst metals exemplified as the components contained in the catalyst metal portion 40, such as platinum group such as Rh, Pd, and Pt, may be cited. In addition, as another example of the arbitrary component, the inorganic oxides exemplified as the components that may be contained in the catalyst metal portion 40, such as aluminum oxide, aluminum oxide-containing oxides, and other Al-containing oxides may be cited. Thus, even when the hydrocarbon adsorption device 10 is exposed to high temperatures due to exhaust gas, excellent adsorption performance can be maintained for a long period of time.

[0073] Although not particularly limited, the content (solid component amount) of zeolite in the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 is approximately 50 to 300 g / L, typically 90 to 200 g / L, and can be, for example, 100 to 150 g / L, respectively, per 1 L volume of the substrates 21 and 31. Since the adsorption amount of HC species is proportional to the amount of zeolite, by making the content above a specified value, a sufficient adsorption amount can be ensured and the adsorption performance can be improved. By making the content below the specified value, the heat capacity of the hydrocarbon adsorption device 10 can be suppressed and the heating effect can be improved. The peel resistance and durability of the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 can also be improved.

[0074] It should be noted that the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 can be manufactured by the following methods, respectively. For example, for the first hydrocarbon adsorption section 20, first, a substrate 21 and a slurry for forming the first hydrocarbon adsorption layer 22 are prepared. Regarding the slurry, zeolite is contained as an essential raw material component, and can be prepared by being dispersed in a dispersion medium together with any other components, such as binders, various additives, etc. As the binder, for example, aluminum sol, silica sol, etc. can be used. As the dispersion medium, for example, water, aqueous solvents can be used. After flowing this slurry into the substrate 21 by a currently known method, such as an impregnation method, a wash coating method, etc., the substrate 21 is fired at a specified temperature and time, thereby the first hydrocarbon adsorption layer 22 can be formed. In addition, for the second hydrocarbon adsorption section 30, it can also be formed by the same method.

[0075] As described above, in the technology disclosed herein, focusing on the molecular size of HC species, the first hydrocarbon adsorption section 20 containing zeolite with a relatively small pore diameter is arranged on the upstream side, and the second hydrocarbon adsorption section 30 containing zeolite with a relatively large pore diameter is arranged on the downstream side. Moreover, the first hydrocarbon adsorption layer 22 located on the upstream side selectively adsorbs HC species with a relatively small molecular size, and the second hydrocarbon adsorption layer 32 located on the downstream side selectively adsorbs HC species with a relatively large molecular size. In this way, using the inherent pores of zeolite, HC species are distinguished according to molecular size, and the HC species with a small molecular size are selectively adsorbed on the first hydrocarbon adsorption section 20, thereby enabling the desorption temperature of HC species in the second hydrocarbon adsorption section 30 to be increased. As a result, for example, when the internal combustion engine is in a cold state, the emission of HC species can be reduced.

[0076] "Use of the Hydrocarbon Adsorption Device"

[0077] The hydrocarbon adsorption device 10 can be used in applications for adsorbing HC contained in various fluids (such as gases, liquids, and miscible fluids). For example, it can be applied to purify the exhaust gas discharged from internal combustion engines of ships, tankers, jet skis, personal watercraft, outboard motors, etc. marine products, lawn mowers, chainsaws, trimmers, etc. gardening products, golf carts, all-terrain vehicles, etc. leisure products, combined heat and power systems, etc. power generation equipment, waste incinerators, etc., represented by vehicles such as cars, trucks, motorcycles, and bicycles with prime movers. Among them, it can be suitably used for vehicles such as cars.

[0078] Hereinafter, test examples of the present invention will be described, but the present invention is not intended to be limited to the examples shown in the following test examples.

[0079] 〔Test Example 1〕

[0080] (Example 1)

[0081] First, prepare 2 cylindrical honeycomb substrates (Φ30 mm × 25 mm, number of cells: 300 cpsi (cells per square inch), made of cordierite).

[0082] Next, a first hydrocarbon adsorption layer is formed on one honeycomb substrate to produce a first adsorption catalyst body. Specifically, first, a powder of zeolite (H-CH A, silica-alumina ratio: 13) with a framework type of CHA and aluminosol as an inorganic binder are mixed so that the mass ratio of solid components becomes 12:1. Pure water is added to this mixture so that the zeolite becomes 35% by mass of the whole, and after stirring, it is pulverized and sized using a ball mill. Then, the viscosity is adjusted with a thickener to prepare a slurry. This slurry is wash-coated so that the content of zeolite becomes 135 g / L relative to the volume (1 L) of the honeycomb substrate. Then, it is heated and dried using a dryer, and after removing the moisture, it is fired at 500 °C in the air for 1 hour. Thus, a first adsorption catalyst body having a first hydrocarbon adsorption layer composed of CHA-type zeolite formed on the substrate is produced.

[0083] Next, a second hydrocarbon adsorption layer is formed on the other honeycomb substrate to produce a second adsorption catalyst body. Specifically, zeolite (silica-alumina ratio: 1500) with a framework type of MFI is used, and it is mixed so that the mass ratio of the solid components of the zeolite powder to the inorganic binder is 10:1, and the content of zeolite is 116 g / L relative to the volume (1 L) of the honeycomb substrate. Except for this, in the same manner as the above first hydrocarbon adsorption layer, a second adsorption catalyst body having a second hydrocarbon adsorption layer composed of MFI-type zeolite formed on the substrate is produced.

[0084] Then, the first adsorption catalyst body is arranged on the upstream side, and the second adsorption catalyst body is arranged in series on the downstream side to fabricate an adsorption device.

[0085] (Example 2)

[0086] In Example 2, a CHA-type zeolite ion-exchanged with Cu ions (Cu-CHa, Cu loading: 3.6 mass%) was used. Otherwise, the same operations as in Example 1 were performed to fabricate the first adsorption catalyst body. Regarding the second adsorption catalyst body, the same second adsorption catalyst body as in Example 1 was prepared to fabricate an adsorption device.

[0087] (Example 3)

[0088] In Example 3, a zeolite with a framework type of FER (silica-to-alumina ratio: 18) was used, and the powder of the zeolite and the solid component mass ratio of the inorganic binder were mixed in a ratio of 10:1. The content of the zeolite was 116 g / L with respect to the volume of the honeycomb substrate (1 L). Otherwise, the same operations as in Example 1 were performed to fabricate the first adsorption catalyst body. Regarding the second adsorption catalyst body, the same second adsorption catalyst body as in Example 1 was prepared to fabricate an adsorption device.

[0089] (Comparative Example 1)

[0090] In Comparative Example 1, the arrangement of the adsorption catalyst bodies in Example 1 was changed, that is, the second adsorption catalyst body was arranged on the upstream side, and the first adsorption catalyst body was arranged in series on the downstream side to fabricate an adsorption device.

[0091] (Comparative Example 2)

[0092] In Comparative Example 2, two second adsorption catalyst bodies of Example 1 were prepared. Then, the same two adsorption catalyst bodies were arranged in series to fabricate an adsorption device.

[0093] [HC Class Adsorption and Desorption Evaluation]

[0094] The adsorption devices related to each example were set in an evaluation device to evaluate the desorption temperature of HC classes. Specifically, first, the adsorption device was fired at 500 °C for 5 minutes for pre-treatment to remove HC classes remaining in the pores. Then, as shown in the Figure 3 temperature rise diagram, after the adsorption device was cooled to 100 °C, mixed HC (decane (C 10 H 22 ): 600 ppmC, propylene (C 3 H 6): 600 ppmC) was circulated in the adsorption device for 5 minutes, maintained for 3 minutes, and then the temperature was raised to 500°C at a heating rate of 20°C / min to evaluate the desorption temperature of HC adsorbed by the adsorption device. The relationship between the concentration of desorbed HC (desorbed THC; Total HC) and temperature is shown in Figure 4 In addition, Table 2 shows the THC desorption peak temperature of each example.

[0095] [Table 2]

[0096] Table 2

[0097]

[0098] Figure 5 It is a graph showing the relationship between the THC desorption peak temperature ΔT (relative value relative to Comparative Example 1) and the difference in pore diameter (P2-P1). Figure 5 As shown, in Examples 1 to 3 where the pore diameter P1 of the zeolite contained in the adsorption catalyst body on the upstream side is smaller than the pore diameter 2 of the zeolite contained in the adsorption catalyst body on the downstream side, in other words, 0<(P2-P1), the THC desorption peak temperature is shifted to the high temperature side compared with Comparative Example 1 where (P2-P1)<0 and Comparative Example 2 where (P2-P1)=0. This is considered to be because by selectively adsorbing HC species with a small molecular size on the adsorption catalyst body on the upstream side, the competitive adsorption of HC species can be reduced, and the desorption temperature of HC species in the adsorption catalyst body on the downstream side can be increased. As described above, it can be seen that by P1<P2, the desorption temperature of HC species can be increased. In addition, from the comparison between Examples 1 and 2, it can be seen that the zeolite contained in the adsorption catalyst body on the upstream side is preferably an H-CHA type that has not been ion-exchanged.

[0099] [Test Example 2]

[0100] (Example 4)

[0101] In Example 4, a second adsorption catalyst body was prepared in the same manner as in Example 1 except that a zeolite of FAU framework type (ratio of silica to alumina: 500) was used and the zeolite powder and the inorganic binder were mixed in a solid content mass ratio of 10:1 and the zeolite content was 116 g / L relative to the volume (1 L) of the honeycomb substrate. As for the first adsorption catalyst body, the same first adsorption catalyst body as in Example 2 was prepared to produce an adsorption device.

[0102] (Example 5)

[0103] In Example 5, an adsorption device was produced in the same manner as in Example 4, except that the same first adsorption catalyst body as in Example 3 was prepared as the first adsorption catalyst body.

[0104] (Comparative Example 3)

[0105] In Comparative Example 3, the configuration of the adsorption catalyst bodies in Example 4 was changed, that is, the second adsorption catalyst body was disposed on the upstream side, and the first adsorption catalyst body was disposed in series on the downstream side to fabricate an adsorption device.

[0106] (Comparative Example 4)

[0107] In Comparative Example 4, the configuration of the adsorption catalyst bodies in Example 5 was changed, that is, the second adsorption catalyst body was disposed on the upstream side, and the first adsorption catalyst body was disposed in series on the downstream side to fabricate an adsorption device.

[0108] Then, in the same manner as in Test Example 1, the desorption temperature of HC was evaluated. The relationship between the concentration of the desorbed HC (desorbed THC; Total HC) and the temperature is shown in Figure 6 . In addition, the THC desorption peak temperature of each example is shown in Table 3.

[0109] [Table 3]

[0110] Table 3

[0111]

[0112] Figure 7 is a graph showing the relationship between the THC desorption peak temperature ΔT (relative value with respect to Comparative Example 3) and the difference in pore diameter (P2 - P1). As shown in Table 3 and Figure 7 , similar to the case of Test Example 1, in Examples 4 and 5 where 0 < (P2 - P1), the THC desorption peak temperature shifted to the higher temperature side compared to Comparative Examples 3 and 4 where (P2 - P1) < 0.

[0113] As described above, several embodiments of the present invention have been described, but the above embodiments are merely examples. In addition, the present invention can be implemented in various ways. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the technical field. In the technology described in the claims, it includes various deformations and changes to the above-exemplified embodiments. For example, a part of the above embodiments can be replaced with other deformation methods, and other deformation methods can also be added to the above embodiments. In addition, if the technical feature is not described as an essential feature, it can also be appropriately deleted.

[0114] For example, in the hydrocarbon adsorption device 10 described above, the first hydrocarbon adsorption layer 22 of the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption layer 32 of the second hydrocarbon adsorption section 30 are each composed of zeolite. However, it is not limited thereto. The first hydrocarbon adsorption layer 22 and / or the second hydrocarbon adsorption layer 32 may contain, in addition to zeolite, a catalyst metal such as those exemplified as components contained in the catalyst metal section 40. For example, the first hydrocarbon adsorption layer 22 may contain Pd and / or Rh, and the second hydrocarbon adsorption layer 32 may contain Pt and / or Rh. In this case, the exhaust gas purification device 3 may not have the catalyst metal section 40.

[0115] For example, in the hydrocarbon adsorption device 10 described above, the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 are each supported on substrates 21 and 32, respectively, and the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 are independent of each other. However, it is not limited thereto. Figure 8 It is a partial cross-sectional view showing an enlarged partition wall portion of a hydrocarbon adsorption device 50 according to another embodiment. As Figure 8 shown, the hydrocarbon adsorption device 50 divides one substrate 51 into an upstream portion and a downstream portion, and the first hydrocarbon adsorption layer 52 and the second hydrocarbon adsorption layer 53 can be formed respectively.

[0116] In addition, Figure 9 It is a partial cross-sectional view showing an enlarged partition wall portion of a hydrocarbon adsorption device 60 according to another embodiment. As Figure 9 shown, the hydrocarbon adsorption device 60 may have a substrate 61, a second hydrocarbon adsorption layer 63 provided on the lower layer side and containing zeolite with a pore diameter P2, and a first hydrocarbon adsorption layer 62 provided on the upper layer side and containing zeolite with a pore diameter P1 (where P1 < P2).

[0117] For example, in the hydrocarbon adsorption device 10 described above, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 each have only the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32 on the substrates 21 and 31, respectively. However, it is not limited thereto. The first hydrocarbon adsorption section 20 and / or the second hydrocarbon adsorption section 30 may have one or more other layers in addition to the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32.

[0118] As a first modification, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 may each have an upper layer containing, for example, a porous inorganic oxide as an adsorption material for adsorbing substances other than HC on the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32. As the inorganic oxide, for example, alumina and Al-containing oxides such as oxides containing alumina, which are exemplified as components that can be contained in the catalyst metal section 40, can be cited.

[0119] As a second modification, regarding Test Example 3 described later, as Figure 10As shown, the first hydrocarbon adsorption section (upstream HC adsorption layer) 72 and the second hydrocarbon adsorption section (downstream HC adsorption layer) 73 may each have one or more catalyst metal sections (catalyst layers) 74, 75 formed in a layered manner on the upstream HC adsorption layer 72 and the downstream HC adsorption layer 73, respectively.

[0120] A catalyst metal section (catalyst layer) containing Pd and / or Rh, for example, may be provided above the first hydrocarbon adsorption section (upstream HC adsorption layer) 72, and a catalyst metal section (catalyst layer) containing Pt and / or Rh may be provided above the second hydrocarbon adsorption section (downstream HC adsorption layer) 73. A first catalyst metal layer containing an oxidation catalyst (e.g., at least one of Pd and Pt) and a second catalyst metal layer containing a reduction catalyst (e.g., Rh) may also be provided above the first hydrocarbon adsorption section (upstream HC adsorption layer) 72 and / or the second hydrocarbon adsorption section (downstream HC adsorption layer) 73.

[0121] As a third modification example, the first hydrocarbon adsorption section 20 and the second hydrocarbon adsorption section 30 may each have an upper layer containing an OSC material above the first hydrocarbon adsorption layer 22 and the second hydrocarbon adsorption layer 32, respectively. Examples of the OSC material include Ce-containing oxides such as cerium dioxide and CZ composite oxide, which can be exemplified as components that can be contained in the catalyst metal section 40.

[0122] [Test Example 3]

[0123] Next, as Test Example 3, an exhaust gas purification catalyst body with an HC adsorption section was fabricated, and an HC purification performance evaluation test was conducted using a gasoline engine bench.

[0124] (Example 11)

[0125] Specifically, first, a cylindrical cordierite honeycomb substrate with a diameter of about 106 mm, a length of about 75 mm, and a volume of about 0.7 liters (400 mesh: number of cells per square inch) was prepared.

[0126] An appropriate amount of the zeolite (Cu-CHa, Cu loading: 3.6% by mass) powder of the framework type ion-exchanged with Cu used in Example 1 above, silica sol as a binder, and ion-exchanged water were mixed to prepare a first slurry.

[0127] At the same time, an appropriate amount of the zeolite of the framework type MFI (silica-to-alumina ratio: 1500) powder used in Example 2 above, alumina sol as a binder, and ion-exchanged water were mixed to prepare a second slurry.

[0128] Next, the first slurry is introduced from the front side of the honeycomb substrate, and the second slurry is introduced from the rear side of the honeycomb substrate. As a result, a first HC adsorption layer (upstream HC adsorption layer) composed of the first slurry is coated on the wall surface in the range of 50% of the upstream side in the exhaust flow direction over the entire length of the honeycomb substrate. In addition, a second HC adsorption layer (downstream HC adsorption layer) composed of the second slurry is coated on the wall surface in the range of 50% of the downstream side in the exhaust flow direction over the entire length of the honeycomb substrate.

[0129] Then, after removing the remaining slurry, it is dried at 250 °C for 2 hours and then fired at 500 °C for about 2 hours. As Figure 10 shown, an upstream HC adsorption layer 72 and a downstream HC adsorption layer 73 are formed on the surface of the partition wall of the substrate 71 along the exhaust flow direction.

[0130] In this test example, the zeolite (Cu-CH A) content in the upstream HC adsorption layer 72 and the zeolite (MFI) content in the downstream HC adsorption layer 73 are each prepared in an amount of 58 g (58 g / L-cat) per 1 liter of the catalyst body.

[0131] Next, appropriate amounts of alumina powder, cerium zirconium composite oxide (CZ) powder, barium sulfate, dinitrodiammineplatinum nitrate solution, and ion-exchanged water as materials are mixed to prepare a Pt-containing slurry.

[0132] The Pt-containing slurry is introduced into the substrate 71 on which the upstream HC adsorption layer 72 and the downstream HC adsorption layer 73 are formed, and is coated over the entire length of the substrate 71.

[0133] Then, after removing the remaining slurry, it is dried at 250 °C for 2 hours and then fired at 500 °C for about 2 hours. As Figure 10 shown, a catalyst lower layer (Pt layer) 74 containing platinum as an oxidation catalyst metal is formed on the upstream HC adsorption layer 72 and the downstream HC adsorption layer 73.

[0134] In this embodiment, the content of each component contained in the catalyst lower layer (Pt layer) 74 is prepared in the following amounts.

[0135]

[0136] Next, appropriate amounts of alumina powder, cerium zirconium composite oxide (CZ) powder, rhodium nitrate solution, and ion-exchanged water as materials are mixed to prepare a Rh-containing slurry.

[0137] The Rh-containing slurry is introduced into the substrate 71 on which the upstream HC adsorption layer 72 and the downstream HC adsorption layer 73 and a catalyst lower layer (Pt layer) 74 are formed on their surfaces, and is coated over the entire length of the substrate 71.

[0138] Then, after removing the remaining slurry, it is dried at 250 °C for 2 hours and then fired at 500 °C for about 2 hours. As Figure 10 shown, a catalyst upper layer (Rh layer) 75 containing rhodium as a reduction catalyst metal is formed on a catalyst lower layer (Pt layer) 74.

[0139] In this embodiment, the catalyst upper layer (Rh layer) 75 is prepared with the contents of the respective components as follows.

[0140] Rh 0.4 g / L-cat

[0141] Aluminum oxide 34 g / L-cat

[0142] CZ 51 g / L-cat

[0143] Using the above series of processes, an exhaust gas purification catalyst body 70 with an HC adsorption part of Example 11 is fabricated.

[0144] (Comparative Example 11)

[0145] As Comparative Example 11 corresponding to the above Example 11, it is characterized in that: the downstream HC adsorption layer is formed using the above first slurry (zeolite species = Cu-CHA), and the upstream HC adsorption layer is formed using the above second slurry (zeolite species = MFI). Except for this, the materials and processes are the same as those of Example 11, and an exhaust gas purification catalyst body with an HC adsorption part of Comparative Example 11 is fabricated. That is, as shown in Table 4 below, Example 11 and Comparative Example 11 are characterized in that: the zeolite species constituting the upstream HC adsorption layer and the zeolite species constituting the downstream HC adsorption layer are opposite.

[0146] [Table 4]

[0147] Table 4

[0148]

[0149] The exhaust gas purification catalyst bodies with an HC adsorption part of Example 11 and Comparative Example 11 obtained above are respectively disposed in the exhaust path of an engine bench of a normal in-line 4-cylinder gasoline engine. The "inlet gas temperature" introduced into the exhaust gas purification catalyst body with an HC adsorption part via an exchanger is adjusted to 500 °C, and the exhaust gas from the above gasoline engine is introduced for 50 seconds. From the start of the introduction at this time until 50 seconds have elapsed, the HC purification rate of this test example is calculated based on the accumulation of the total HC concentration in the inlet gas introduced into the exhaust gas purification catalyst body with an HC adsorption part and the total HC concentration in the outlet gas discharged from the exhaust gas purification catalyst body with an HC adsorption part. The results are recorded in the corresponding column of Table 4 above. Figure 11It shows the change of the HC purification rate (%) from the start of exhaust gas introduction to 50 seconds in this test example. In this test example, since the catalyst body for purifying the test exhaust gas has an HC adsorption part (upstream HC adsorption layer and downstream HC adsorption layer), as shown in the figure, the adsorption - purification of the HC component in the exhaust gas appears in the transition region.

[0150] As shown in Table 4, regarding the HC purification rate, the catalyst body for purifying exhaust gas with an HC adsorption part in Example 11 is superior to the catalyst body for purifying exhaust gas with an HC adsorption part in Comparative Example 11. As described above, the structures of the lower catalyst layer (Pt layer) 74 and the upper catalyst layer (Rh layer) 75 formed on the HC adsorption part (upstream HC adsorption layer 72 and downstream HC adsorption layer 73) are the same. Therefore, the difference in the HC purification rate between Example 11 and Comparative Example 11 indicates that the catalyst body in Example 11, in which the zeolite contained in the upstream HC adsorption layer is Cu - CHA, can raise the HC desorption temperature and can appropriately retain HC until the catalyst body is fully heated.

Claims

1. A hydrocarbon adsorption device that allows a fluid to flow through and adsorbs hydrocarbons in the fluid, characterized in that it has: A first hydrocarbon adsorption section containing zeolite; and A second hydrocarbon adsorption section provided on the downstream side of the first hydrocarbon adsorption section with respect to the flow direction of the fluid and containing zeolite, The pore diameter P1 of the zeolite contained in the first hydrocarbon adsorption section is smaller than the pore diameter P2 of the zeolite contained in the second hydrocarbon adsorption section, The silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption section is smaller than the silica-alumina ratio of the zeolite contained in the second hydrocarbon adsorption section, and the silica-alumina ratio refers to the molar ratio of the silica component to the alumina component in the zeolite.

2. The hydrocarbon adsorption device according to claim 1, characterized in that: The difference between the said P1 and the said P2 (P2 - P1) is above below.

3. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The P1 is above below.

4. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The P2 is above below.

5. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The silica-alumina ratio of the zeolite contained in the first hydrocarbon adsorption section is 10 or more and 30 or less.

6. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The zeolite contained in the first hydrocarbon adsorption section contains at least one of the framework types CHA and FER.

7. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The zeolite contained in the second hydrocarbon adsorption section contains at least one of the framework types MFI and FAU.

8. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The fluid is a gas.

9. The hydrocarbon adsorption device according to claim 1 or 2, characterized in that: The fluid is exhaust gas.

10. An exhaust gas purification system arranged in the exhaust path of an internal combustion engine to purify hydrocarbons in the exhaust gas discharged from the internal combustion engine, characterized in that it has: The hydrocarbon adsorption device according to claim 1 or 2; and A catalyst metal section containing a catalyst metal.

Images