Exhaust gas purification system

Abstract

This invention provides an exhaust gas purification device that can achieve excellent exhaust gas purification performance even when the engine operating time is short, by easily raising the temperature of the exhaust gas purification catalyst. [Solution] If a heat transfer material located in one of several regions of an exhaust gas purification device is designated as the upstream heat transfer material, and a heat transfer material located in another region downstream of that region in the flow direction is designated as the downstream heat transfer material, then the cubic inorganic compound in the upstream heat transfer material and the cubic inorganic compound in the downstream heat transfer material have different crystal structures. When the ratio W440 / W400 of the full width at half maximum (FWHM) of the 440-plane peak W440 and the FWHM of the 400-plane peak W400 of the crystal of the cubic inorganic compound is calculated by X-ray diffraction intensity measurement, if the ratio W440 / W400 of the cubic inorganic compound in the downstream heat transfer material is A, and the ratio W440 / W400 of the cubic inorganic compound in the upstream heat transfer material is B, then the ratio A / B is greater than 1.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device.

Background Art

[0002] Automobiles are equipped with an exhaust gas purification device for purifying exhaust gas. This exhaust gas purification device includes an exhaust gas purification catalyst that is a catalyst for a purification reaction to purify exhaust gas, and a heat storage material that supplies heat to the exhaust gas purification catalyst to suppress a temperature drop of the exhaust gas purification catalyst. When exhaust gas flows through the exhaust gas purification device, the heat of the exhaust gas is transferred to the exhaust gas purification catalyst and the exhaust gas purification catalyst becomes high temperature. Therefore, the catalytic activity of the exhaust gas purification catalyst increases, the purification reaction proceeds, and the exhaust gas is purified.

[0003] However, the exhaust gas purification catalyst disposed in the downstream region in the flow direction of the exhaust gas in the exhaust gas purification device requires a relatively long time until its temperature becomes sufficiently high compared to the exhaust gas purification catalyst disposed in the upstream region. Therefore, a certain amount of time is required until the temperatures of the exhaust gas purification catalysts in all regions become sufficiently high. Therefore, a certain engine operation time was required until the catalytic activities of the exhaust gas purification catalysts in all regions became sufficiently high and the exhaust gas was sufficiently purified. When the temperature of the exhaust gas purification catalyst is low, the catalytic activity becomes low, and thus there is a possibility that the purification reaction of the exhaust gas does not proceed sufficiently.

[0004] Patent Document 1 discloses a technique for improving the warm-up performance of an exhaust gas purification catalyst by providing a gradient in the concentration of a noble metal in the exhaust gas purification catalyst. That is, by making the concentration of the noble metal in the exhaust gas purification catalyst disposed in the downstream region lower than the concentration of the noble metal in the exhaust gas purification catalyst disposed in the upstream region in the flow direction of the exhaust gas, the rate of increase in the temperature of the exhaust gas purification catalyst disposed in the downstream region is increased.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-140846 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the technology disclosed in Patent Document 1, there was a risk that the temperature of the exhaust gas purification catalyst located in the downstream region would not reach a sufficiently high temperature when the engine operating time was short. The present invention aims to provide an exhaust gas purification device that can easily raise the temperature of the exhaust gas purification catalyst and exhibit excellent exhaust gas purification performance even when the engine operating time is short. [Means for solving the problem]

[0007] An exhaust gas purification device according to one aspect of the present invention is an exhaust gas purification device installed in an exhaust gas flow path to purify the exhaust gas flowing through the flow path, wherein the exhaust gas purification device is divided into a plurality of regions along the direction of exhaust gas flow, and each of these plurality of regions is provided with an exhaust gas purification catalyst, which is a catalyst for a purification reaction that purifies the exhaust gas, a heat storage material that supplies heat to the exhaust gas purification catalyst to suppress the temperature drop of the exhaust gas purification catalyst, and a heat transfer material that absorbs heat from the exhaust gas and sends it to the heat storage material and the exhaust gas purification catalyst, wherein the heat transfer material has a cubic inorganic compound, and the heat transfer material provided in one of the plurality of regions is designated as the upstream heat transfer material, If we define a heat transfer material located in a different region downstream of a given region in the flow direction as the downstream heat transfer material, then the cubic inorganic compound present in the upstream heat transfer material and the cubic inorganic compound present in the downstream heat transfer material have different crystal structures. When calculating the ratio W440 / W400 of the full width at half maximum (FMAX) of the 440-plane peak W440 and the FMAX of the 400-plane peak W400 of the crystal of the cubic inorganic compound by X-ray diffraction intensity measurement, if we let the ratio W440 / W400 of the cubic inorganic compound present in the downstream heat transfer material be A and the ratio W440 / W400 of the cubic inorganic compound present in the upstream heat transfer material be B, then the ratio A / B is greater than 1. [Effects of the Invention]

[0008] According to the present invention, even when the engine operating time is short, the temperature of the exhaust gas purification catalyst tends to rise, and excellent exhaust gas purification performance can be achieved. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view of an exhaust gas purification device according to one embodiment of the present invention. [Figure 2] Figure 1 is a magnified view of a portion of the exhaust gas purification device. [Modes for carrying out the invention]

[0010] One embodiment of the present invention is described below. This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention.

[0011] The exhaust gas purification device according to this embodiment is installed in the flow path of exhaust gas and purifies the exhaust gas flowing through the flow path. This exhaust gas purification device is divided into multiple regions along the direction of exhaust gas flow. Each of these multiple regions is provided with an exhaust gas purification catalyst, which is a catalyst for the purification reaction that purifies the exhaust gas; a heat storage material that supplies heat to the exhaust gas purification catalyst to suppress the temperature drop of the exhaust gas purification catalyst; and a heat transfer material that absorbs heat from the exhaust gas and sends it to the heat storage material and the exhaust gas purification catalyst. This heat transfer material has a cubic inorganic compound.

[0012] If we define the heat transfer material located in one of the aforementioned multiple regions (excluding the region located furthest downstream in the flow direction) as the upstream heat transfer material, and the heat transfer material located in another region further downstream in the flow direction than that region as the downstream heat transfer material, then the cubic inorganic compound of the upstream heat transfer material and the cubic inorganic compound of the downstream heat transfer material have different crystal structures.

[0013] Furthermore, when the ratio W440 / W400 of the full width at half maximum (FMAX) of the 440-plane peak W440 and the 400-plane peak W400 of the crystal of the cubic inorganic compound is calculated by X-ray diffraction intensity measurement, if the ratio W440 / W400 of the cubic inorganic compound in the downstream heat transfer material is A, and the ratio W440 / W400 of the cubic inorganic compound in the upstream heat transfer material is B, then the ratio A / B is greater than 1.

[0014] A ratio A / B greater than 1 means that the cubic inorganic compound in the downstream heat transfer material is more crystallinity than the cubic inorganic compound in the upstream heat transfer material. Since crystals with higher crystallinity have higher thermal conductivity, the downstream heat transfer material has higher thermal conductivity than the upstream heat transfer material. Therefore, the heat from the exhaust gas is less easily absorbed by the upstream heat transfer material and more easily absorbed by the downstream heat transfer material. Compared to the case where the crystallinity of the cubic inorganic compound in the upstream heat transfer material and the cubic inorganic compound in the downstream heat transfer material are the same (when the same type of cubic inorganic compound is used in both the upstream and downstream heat transfer materials), the rate at which the temperature of the exhaust gas purification catalyst located in the other region rises becomes faster. Thus, in this embodiment, even when the engine operating time is short, the temperature of the exhaust gas purification catalyst in all regions tends to rise, so excellent exhaust gas purification performance can be achieved.

[0015] The aforementioned multiple regions may consist of two regions or three or more regions. If the multiple regions consist of two regions, the upstream region becomes "Region 1," and the downstream region becomes "Another Region." If the multiple regions consist of three regions, the most upstream region becomes "Region 1," and at least one of the central region and the most downstream region becomes "Another Region," or at least one of the most upstream region and the central region becomes "Region 1," and the most downstream region becomes "Another Region." In other words, it is sufficient that the above conditions are met in at least two of the three regions. If the multiple regions consist of four or more regions, the same applies as in the case of three regions.

[0016] The exhaust gas purification device according to this embodiment may have two types (i.e., crystallinity) of cubic inorganic compounds. In other words, if the plurality of regions is two regions, the exhaust gas purification device according to this embodiment may have two types of cubic inorganic compounds. A first type of cubic inorganic compound is placed in "one region," and a second type of cubic inorganic compound is placed in "the other region."

[0017] If the plurality of regions is three, the exhaust gas purification device according to this embodiment may contain two or three types of cubic inorganic compounds (i.e., the crystallinity of the cubic inorganic compounds in the three regions may all be different). If the plurality of regions is four or more, the exhaust gas purification device according to this embodiment may contain two, three, or four or more types of cubic inorganic compounds. Furthermore, since it is sufficient for the downstream heat transfer material to have higher thermal conductivity than the upstream heat transfer material, the objective of the present invention can be achieved even if the downstream heat transfer material contains a cubic inorganic compound and the upstream heat transfer material does not.

[0018] Here, an example of an exhaust gas purification device according to this embodiment will be described in detail. The exhaust gas purification device shown in Figures 1 and 2 is equipped with a tubular honeycomb structure. More specifically, this honeycomb structure is formed by arranging multiple cells 10, which are divided into rectangular prism shapes by partition walls 20 extending in the axial direction (left-right direction in Figure 1) of the tubular honeycomb structure, in a grid pattern in the vertical and horizontal directions.

[0019] The shape of cell 10 is not limited to a rectangular prism; other shapes are acceptable as long as they can form a honeycomb structure. For example, triangular or hexagonal prisms are also acceptable. Furthermore, even in the case of a rectangular prism, the cross-sectional shape of cell 10 is not limited to a square as shown in the enlarged view of Figure 2; it may also be a rectangle, parallelogram, rhombus, or other shape.

[0020] Also, the type of material constituting the partition wall 20 is not particularly limited, and metals and ceramics can be used. The type of ceramic is not particularly limited, and examples include silicon carbide, silicon nitride, silicon dioxide, aluminum oxide, zirconium oxide, and titanium oxide.

[0021] The tubular honeycomb structure is divided into two regions 1A and 1B along the axial direction. In each of the two regions 1A and 1B, an exhaust gas purification catalyst that is a catalyst for the purification reaction of exhaust gas, a heat storage material that supplies heat to the exhaust gas purification catalyst to suppress a temperature drop of the exhaust gas purification catalyst, and a heat transfer material that absorbs heat from the exhaust gas and sends it to the heat storage material and the exhaust gas purification catalyst are arranged.

[0022] Specifically, the exhaust gas purification catalyst, the heat storage material, and the heat transfer material are arranged on the inner surface (the surface of the partition wall 20) of each cell 10 in both of the two regions 1A and 1B. Specifically, as shown in the enlarged view of FIG. 2, the inner surface of the cell 10 is covered with a heat storage layer 30 having a heat storage material and a heat transfer material, and the inner surface of the heat storage layer 30 is covered with a catalyst layer 40 having an exhaust gas purification catalyst. That is, the heat storage layer 30 and the catalyst layer 40 are laminated. And inside the catalyst layer 40, there is a tubular cavity extending in the axial direction, and this cavity forms a flow path 50 through which exhaust gas flows.

[0023] That is, in the exhaust gas purification device according to the present embodiment, each of the plurality of regions 1A and 1B has a laminate in which a catalyst layer 40 having an exhaust gas purification catalyst and a heat storage layer 30 having a heat storage material and a heat transfer material are laminated. The catalyst layer 40 is arranged facing the flow path 50, and the heat storage layer 30 is arranged on the side opposite to the side facing the flow path 50 among both surfaces of the catalyst layer 40.

[0024] In the exhaust gas purification device shown in FIG. 1, the exhaust gas flows from the left side to the right side in FIG. 1. That is, the exhaust gas flows through the flow path 50 of the exhaust gas purification device shown in FIG. 1 from the left side to the right side. Therefore, the region 1A becomes the upstream region in the flow direction of the exhaust gas, and the region 1B becomes the downstream region in the flow direction of the exhaust gas.

[0025] The catalyst layer 40 in region 1A and the catalyst layer 40 in region 1B may have the same configuration. For example, the catalyst layer 40 may have platinum and rhodium. In addition, the catalyst layer 40 may have a composite oxide of metals (for example, a composite oxide of cerium and zirconium, or a composite oxide of zirconium and lanthanum) along with precious metals such as platinum and rhodium.

[0026] On the other hand, the heat storage layer 30 in region 1A and the heat storage layer 30 in region 1B have different crystallinity of the cubic inorganic compound of the heat transfer material. That is, if the ratio W440 / W400 of the cubic inorganic compound of the heat transfer material (downstream heat transfer material) in the heat storage layer 30 of region 1B is A, and the ratio W440 / W400 of the cubic inorganic compound of the heat transfer material (upstream heat transfer material) in the heat storage layer 30 of region 1A is B, then the ratio A / B is greater than 1. Note that the heat storage material in the heat storage layer 30 of region 1A and the heat storage material in the heat storage layer 30 of region 1B may be the same type of heat storage material or different types of heat storage material.

[0027] In this configuration, the heat transfer material in region 1B has higher thermal conductivity than the heat transfer material in region 1A. Therefore, the heat from the exhaust gas flowing through the flow path 50 of the exhaust gas purification device is more easily absorbed by the heat transfer material in region 1B than by the heat transfer material in region 1A. As a result, the rate at which the temperature of the exhaust gas purification catalyst located in region 1B rises is faster compared to the case where the thermal conductivity of the heat transfer materials in region 1A and region 1B are the same.

[0028] To elaborate, if the thermal conductivity of the heat transfer material in region 1A and the heat transfer material in region 1B are the same, then regardless of the difference in thermal conductivity, much of the heat from the exhaust gas will be absorbed by the heat transfer material in the upstream region 1A, and less heat will be absorbed by the heat transfer material in the downstream region 1B. As a result, the rate at which the temperature of the exhaust gas purification catalyst located in region 1B rises will be slower, so if the engine operating time is short, the temperature of the entire exhaust gas purification catalyst (exhaust gas purification catalyst in all regions) will not rise easily.

[0029] In contrast, if the heat transfer material in region 1B has higher thermal conductivity than the heat transfer material in region 1A, then only a small amount of heat from the exhaust gas flowing through the exhaust gas purification device's flow path 50 will be absorbed by the heat transfer material in the upstream region 1A, while most of it will be absorbed by the heat transfer material in the downstream region 1B. As a result, the rate at which the temperature of the exhaust gas purification catalyst located in region 1B rises will increase.

[0030] Of course, if the heat transfer material in region 1A has higher thermal conductivity than the heat transfer material in region 1B, then much of the heat from the exhaust gas will be absorbed by the heat transfer material in the upstream region 1A, and the rate at which the temperature of the exhaust gas purification catalyst in region 1B rises will be slower. Therefore, the result will be the same as when the heat transfer materials in region 1A and region 1B have the same thermal conductivity.

[0031] Thus, in the exhaust gas purification device according to this embodiment, the temperature of the exhaust gas purification catalyst located in the downstream region 1B rises rapidly. As a result, the temperature of the exhaust gas purification catalyst tends to rise in all regions, so excellent exhaust gas purification performance can be achieved even when the engine operating time is short.

[0032] The applications of the exhaust gas purification device according to this embodiment are not particularly limited, but for example, it can be used to purify exhaust gases emitted from automobiles, factories, etc. Although automobiles are equipped with exhaust gas purification devices, the exhaust gas purification device according to this embodiment can be used as such a device. Furthermore, the exhaust gas purification device according to this embodiment can be used not only for automobile exhaust gases but also as a catalyst for purifying exhaust gases from internal combustion engines.

[0033] The exhaust gas purification device according to this embodiment will be described in more detail below. (1) Regarding heat transfer materials The heat transfer material contains a cubic inorganic compound. The heat transfer material may consist solely of the cubic inorganic compound, or it may consist of the cubic inorganic compound and other components.

[0034] Cubic inorganic compounds are crystalline inorganic compounds, and their crystal system is cubic. While there are no particular limitations on the types of cubic inorganic compounds, examples include γ-alumina and composite oxides. Examples of composite oxides include cerium-zirconium composite oxide (ceria-zirconia), cerium-aluminum composite oxide (ceria-alumina), zirconium-aluminum composite oxide (zirconia-alumina), lanthanum-aluminum composite oxide, and lanthanum-cerium composite oxide.

[0035] As mentioned above, the ratio W440 / W400 of the full width at half maximum (FMAX) of the 440-plane peak W440 to the FMAX of the 400-plane peak W400 of the cubic inorganic compound crystal is calculated by measuring the X-ray diffraction intensity. The 400-plane has a unidirectional heat transfer direction, while the 440-plane has bidirectional heat transfer directions. Therefore, the ratio W440 / W400 can represent the high thermal conductivity of the cubic inorganic compound.

[0036] In the exhaust gas purification device according to this embodiment, if the ratio W440 / W400 of the cubic inorganic compound in the downstream heat transfer material is A, and the ratio W440 / W400 of the cubic inorganic compound in the upstream heat transfer material is B, then the ratio A / B is greater than 1. When the ratio A / B is greater than 1, the cubic inorganic compound in the downstream heat transfer material is more crystalline than the cubic inorganic compound in the upstream heat transfer material, and therefore has higher thermal conductivity.

[0037] The ratio A / B must be greater than 1, preferably 1.07 or higher, more preferably 1.10 or higher, and even more preferably 1.19 or higher. A larger ratio A / B results in a faster rate of temperature rise for the exhaust gas purification catalyst located in the downstream region, so the temperature of the exhaust gas purification catalyst tends to rise in all regions, even when the engine operating time is short.

[0038] (2) Exhaust gas purification catalyst In the exhaust gas purification device according to this embodiment, the type of exhaust gas purification catalyst is not particularly limited, but examples include catalytic activity (oxidation catalytic activity) for oxidation reactions that oxidize hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas to convert them into water (H2O) and carbon dioxide (CO2), and nitrogen oxides (NO2). X Examples of catalysts include those having catalytic activity (reductive catalytic activity) for a reduction reaction that reduces ) to nitrogen gas (N2).

[0039] In the exhaust gas purification device according to this embodiment, the exhaust gas purification catalyst may contain a precious metal. The type of precious metal is not particularly limited, and examples of precious metals include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). Among these precious metals, rhodium is preferred, as it results in a higher NOx conversion rate.

[0040] In the exhaust gas purification device according to this embodiment, the precious metal contained in the exhaust gas purification catalyst may or may not be supported on a carrier. The method for supporting the precious metal on a carrier is not particularly limited, but for example, the precious metal can be supported on a carrier by mixing the precious metal and the carrier and sintering them.

[0041] (3) Regarding heat storage materials In the exhaust gas purification device according to this embodiment, the type of heat storage material is not particularly limited, but for example, it may be a heat storage material comprising heat storage particles having a core containing a phase-change type heat storage metal capable of heat storage and heat release using a solid-liquid phase change, and a shell consisting of a coating containing a metal oxide that covers the core.

[0042] (4) Phase change type heat storage metals The type of phase-change heat storage material is not particularly limited as long as it is capable of heat storage and heat release using solid-liquid phase change, but elemental metals or alloys are suitable as phase-change heat storage materials. Specific examples of elemental metals include aluminum (Al), zinc (Zn), magnesium (Mg), lead (Pb), tin (Sn), and indium (In). Specific examples of alloys include aluminum alloys, zinc alloys, magnesium alloys, tin alloys, and indium alloys.

[0043] Aluminum alloys are alloys that contain at least one of silicon (Si), magnesium, copper (Cu), zinc, etc. as alloying components, with aluminum being the most abundant component. Zinc alloys are alloys that contain at least one of aluminum, copper, magnesium, etc. as alloying components, with zinc being the most abundant component. Magnesium alloys are alloys that contain at least one of aluminum, zinc, etc. as alloying components, with magnesium being the most abundant component.

[0044] While the alloy composition ratio of these alloys is not particularly limited, it is preferable that the alloy composition ratio has a eutectic point. Alloys with a eutectic point do not undergo changes in their crystalline structure even when repeatedly subjected to phase changes (repeated melting and solidification), so their performance as a heat storage material does not deteriorate easily.

[0045] There are no particular limitations on the types of aluminum alloys, but examples include the 4000 series aluminum alloy (aluminum-silicon alloy) which contains silicon as an alloying component, the 5000 series aluminum alloy which contains magnesium as an alloying component, the 6000 series aluminum alloy which contains silicon and magnesium as alloying components, and the 7000 series aluminum alloy which contains zinc and magnesium as alloying components.

[0046] The alloy composition ratio of the aluminum-silicon alloy is not particularly limited, but it is preferably 60 to 99 atomic percent of aluminum and 1 to 40 atomic percent of silicon. For example, an aluminum-silicon alloy with 88 atomic percent aluminum and 12 atomic percent silicon is preferred because it is an alloy that has a eutectic point.

[0047] The types of zinc alloys are not particularly limited, but examples include zinc alloys containing aluminum. This zinc alloy may be an alloy consisting of zinc and aluminum, or an alloy containing other components, as long as zinc is the most abundant component. The types of zinc and aluminum alloys are not particularly limited, but examples include zinc alloys in which the zinc content is 83% to 98% by mass and the aluminum content is 2% to 17% by mass. If the zinc alloy further contains components other than zinc and aluminum, the types of these other components are not particularly limited, but examples include magnesium, tin, indium, and lead.

[0048] The melting points of the metal elements and alloys used as phase-change heat storage materials are not particularly limited, but are preferably 300°C to 600°C, and more preferably 350°C to 400°C. The melting point of an aluminum-silicon alloy with an alloy composition ratio of 88 atomic% aluminum and 12 atomic% silicon is 573°C.

[0049] (5) About the core The core of the heat storage particles contains a phase-change type heat storage metal. The core of the heat storage particles may be formed solely of the phase-change type heat storage metal, or it may be formed of the phase-change type heat storage metal and other components. The core may contain one type of phase-change type heat storage metal, or two or more types.

[0050] (6) About the shell The shell consists of a coating containing a metal oxide. Since metal oxides are difficult to oxidize further, the shell can suppress the oxidation of the core, which would otherwise degrade its performance as a heat storage material. This coating may be formed solely of metal oxides, or it may also contain other components besides metal oxides.

[0051] The type of metal oxide is not particularly limited, but examples include at least one of aluminum oxide (Al2O3) and zinc oxide (ZnO). If the coating further contains other components besides metal oxides, the type of other components is not particularly limited, but examples include phosphorus pentoxide (P2O5), silicon dioxide (SiO2), and titanium dioxide (TiO2).

[0052] In a heat storage particle, the shell is formed on the surface of the core and covers the core surface, but the heat storage particle may have parts other than the core and shell. For example, it may have an intermediate layer between the core and the shell, or an outer layer outside the shell. The number of intermediate layers and outer layers in the heat storage particle may be one layer or multiple layers for each layer.

[0053] (7) Regarding heat storage particles The diameter of the heat storage particles is not particularly limited, but smaller is preferable. For example, the diameter of the heat storage particles is preferably 50 μm or less, and more preferably 30 μm or less. The smaller the diameter of the heat storage particles, the faster the melting and solidification rates of the heat storage particles become, so it is possible to store and release heat by the heat storage material in a short time (i.e., the heat storage rate and heat release rate tend to be fast). Furthermore, there may be one type of heat storage particle, or two or more types. In other words, a mixture of multiple types of heat storage particles, each differing in at least one of the phase-change type heat storage metal and diameter, may be used as a heat storage material.

[0054] These heat storage particles can be manufactured, for example, by the following method. First, metal particles are subjected to a passivation treatment to passivate their surface, forming a coating containing metal oxides on the surface of the metal particles. The metal oxides contained in this coating include oxides of phase-change type heat storage metals. The temperature during the passivation treatment is preferably above the temperature at which the phase-change heat storage metal becomes passivated. For example, if the phase-change heat storage metal is a zinc alloy containing aluminum, the temperature may be 60°C to 100°C.

[0055] Next, the metal particles, on which a metal oxide-containing film has been formed on their surface by passivation treatment, are subjected to a firing treatment in an oxygen-containing atmosphere. Examples of oxygen-containing atmospheres include oxygen gas and air. The firing temperature is not particularly limited, but for example, it may be between 500°C and 800°C.

[0056] Next, we will explain in more detail how to use the exhaust gas purification device according to this embodiment, using the case of purifying automobile exhaust gas as an example. The exhaust gas purification device according to this embodiment is installed near the exhaust pipe of the exhaust gas. When the engine of a car is operated, high-temperature exhaust gas flows through the exhaust gas passage. The heat from the exhaust gas is transferred to the heat storage material and the exhaust gas purification catalyst via the heat transfer material, causing the temperature of the exhaust gas purification catalyst to rise and the temperature of the heat storage material to rise as well. At this time, the heat storage particles melt and the heat storage material stores heat. As the exhaust gas purification catalyst becomes hot, its catalytic activity increases, the purification reaction proceeds, and the exhaust gas is purified.

[0057] Next, when the car engine is stopped, the temperature of the exhaust gas purification catalyst and heat storage material decreases, but the heat storage material releases heat as the heat storage particles solidify. This heat release suppresses the temperature drop of the exhaust gas purification catalyst, and the temperature of the exhaust gas purification catalyst can be maintained at the temperature at which the catalyst is activated without using electrical energy. [Examples]

[0058] The present invention will be described in more detail below with reference to examples and comparative examples. [Example 1] 150g of aluminum zinc alloy powder (Zn-5Al) manufactured by Hikari Material Industry Co., Ltd., 150g of boehmite manufactured by Sasol, and 3L of water were placed in a 5L stainless steel container and stirred for 3 hours while maintaining a temperature of 60°C.

[0059] Zinc alloy Zn-5Al is an alloy composed of zinc and aluminum, with a zinc content of 95% by mass and an aluminum content of 5% by mass. The melting point of zinc alloy Zn-5Al is 381°C. The particle size of the aluminum-zinc alloy powder is 38 μm or less. The boehmite crystals are needle-shaped, and the crystallite size is 30 nm.

[0060] While stirring was continued, heating was stopped and the mixture of aluminum zinc alloy powder, boehmite, and water was cooled until its temperature fell below 40°C. This mixture was then filtered, and the solid was collected on filter paper. The collected solid was dried together with the filter paper. Drying was carried out in two stages: the first stage was dried at room temperature for 24 hours, and the second stage was dried at 60°C for 24 hours.

[0061] Next, the dried solid material was placed in a muffle furnace and heated from room temperature to 300°C over 4 hours in an oxygen gas atmosphere. Then, it was calcined by holding it at 300°C for 2 hours to obtain a mixture of heat storage particles and γ-alumina (hereinafter referred to as "mixture X"). In other words, this mixture is a mixture of heat storage material and heat transfer material.

[0062] X-ray diffraction intensity measurements were performed on mixture X, and from the resulting chart, the full width at half maximum (FMAX) W440 of the 440-plane peak and the FMAX W400 of the 400-plane peak of the γ-alumina crystal were obtained, and their ratio W440 / W400 was calculated. The full width at half maximum (FMAX) of the peak at the 440-plane of the γ-alumina crystal, W440, was 1.50°, and the FMAX of the peak at the 400-plane of the γ-alumina crystal, W400, was 1.53°. Therefore, the ratio W440 / W400, calculated by dividing FMAX W440 by FMAX W400, was 0.98.

[0063] The measurement conditions for X-ray diffraction intensity are as follows: Equipment name: Rigaku Corporation SmartLab 9kW X-ray diffractometer Voltage, Current: 45kV, 200mA X-ray wavelength:CuKα1 Optical system: Focusing method, Johansson monochromator + 1D detector (D / teX) Pretreatment: The material was measured after being ground in an agate mortar. Identification and analysis software: PDXL2 manufactured by Rigaku Corporation

[0064] Next, a mixture of heat-retaining particles and γ-alumina (hereinafter referred to as "mixture Y") was prepared in the same manner as mixture X, except that the boehmite crystals used were spherical with a crystallite size of 10 nm and the firing temperature was 500°C. When the X-ray diffraction intensity was measured in the same manner as for mixture X, the full width at half maximum (FMAX) W440 of the 440-plane peak of the γ-alumina crystal was 1.26°, and the FMAX W400 of the 400-plane peak of the γ-alumina crystal was 1.08°, so the ratio W440 / W400 was 1.17.

[0065] Next, a test specimen of Example 1 was prepared using mixture X and mixture Y. This test specimen has the same configuration as the exhaust gas purification device shown in Figure 1, except that it does not have a catalyst layer. That is, this test specimen has a tubular honeycomb structure in which multiple cells, each partitioned into a rectangular prism shape by axially extending partitions, are arranged vertically and horizontally in a grid pattern to form a honeycomb structure.

[0066] The method for producing the test specimen of Example 1 is described below. Mixture X, boehmite, and water were mixed to obtain slurry X. This slurry X was then applied to the inner surface of the cells (the surface of the partitions) of a cordierite honeycomb structure to form a heat storage layer. This honeycomb structure is tubular with a diameter of 36 mm and a length of 60 mm, and has 600 cells per square inch. The thickness of the partitions of this honeycomb structure is 4 / 1000 inch (approximately 102 μm).

[0067] When applying slurry X, a predetermined amount of slurry X was applied to form a heat storage layer to prevent clogging of the inside of the cells. More specifically, the predetermined amount of slurry X was applied by repeatedly applying a small amount of slurry X, drying it, and then applying another small amount of slurry X and drying it. After firing at 400°C for 1 hour, the honeycomb structure was cut in the axial center to a length of 30 mm to obtain a honeycomb structure X. This honeycomb structure X contains 70 g of heat storage material per liter of honeycomb structure volume.

[0068] Furthermore, the boehmite mixed with mixture X was used as an adhesive to bond the heat storage layer to the partition walls of the honeycomb structure. Therefore, although boehmite is converted to γ-alumina by firing, the crystallinity of this γ-alumina is not particularly limited; it can be highly crystalline or low-crystalline γ-alumina.

[0069] Next, a honeycomb structure Y was obtained in exactly the same manner as described above, except that mixture Y was used instead of mixture X. Then, one axial end of honeycomb structure X and one axial end of honeycomb structure Y were connected so that honeycomb structure X and honeycomb structure Y were aligned in a straight line, and a tubular test specimen was obtained. In this test specimen, each cell of honeycomb structure X and each cell of honeycomb structure Y are in communication, so gas introduced into the opening at the other axial end of honeycomb structure X is introduced into honeycomb structure Y through the cells of honeycomb structure X and is discharged from the opening at the other axial end of honeycomb structure Y through the cells of honeycomb structure Y.

[0070] The thermal conductivity of the heat storage layer was tested using the manufactured test specimen. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Example 1 from the other axial end of honeycomb structure X. After 280 seconds of flowing 600°C air, the temperature of the heat storage layer of honeycomb structure X and the heat storage layer of honeycomb structure Y were measured using thermocouples. As a result, the temperature of the heat storage layer of honeycomb structure X was approximately 500°C, which was higher than the temperature of the heat storage layer of honeycomb structure Y, and the temperature difference between the two honeycomb structures was 3°C.

[0071] The ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the downstream heat transfer material) in the heat storage layer of honeycomb structure Y is 1.17, and the ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the upstream heat transfer material) in the heat storage layer of honeycomb structure X is 0.98, so the ratio A / B is 1.19.

[0072] Therefore, from the above test results, it can be seen that the cubic inorganic compound in the downstream heat transfer material is more crystalline than the cubic inorganic compound in the upstream heat transfer material, and that the downstream heat transfer material has higher thermal conductivity than the upstream heat transfer material. As a result, the temperature of the downstream heat transfer material rises faster, and it can be heated to a high temperature in a time as short as that of the upstream heat transfer material. Therefore, the temperature of the entire exhaust gas purification catalyst can be raised to a high temperature in a short time.

[0073] [Example 2] A mixture of heat storage particles and γ-alumina (hereinafter referred to as "mixture Z") was prepared in the same manner as mixture X, except that the boehmite crystals used were spherical and had a crystallite size of 30 nm. When the X-ray diffraction intensity was measured in the same manner as for mixture X, the full width at half maximum (FMAX) W440 of the 440-plane peak of the γ-alumina crystal was 1.08°, and the FMAX W400 of the 400-plane peak of the γ-alumina crystal was 0.99°, so the ratio W440 / W400 was 1.09.

[0074] Next, a honeycomb structure Z was obtained in exactly the same manner as described above, except that mixture Z was used instead of mixture X. A honeycomb structure Y was also manufactured in the same manner as in Example 1. Then, one axial end of honeycomb structure Z and one axial end of honeycomb structure Y were connected so that honeycomb structure Z and honeycomb structure Y were in a straight line, and a tubular test specimen was obtained. In this test specimen of Example 2, each cell of honeycomb structure Z and each cell of honeycomb structure Y are in communication, so the gas introduced into the opening at the other axial end of honeycomb structure Z is introduced into honeycomb structure Y through the cells of honeycomb structure Z and is discharged from the opening at the other axial end of honeycomb structure Y through the cells of honeycomb structure Y.

[0075] The thermal conductivity of the heat storage layer was tested using the test specimen of Example 2 that was manufactured. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Example 2 from the other axial end of the honeycomb structure Z. After the 600°C air had flowed for 280 seconds, the temperature of the heat storage layer of honeycomb structure Z and the heat storage layer of honeycomb structure Y were measured using thermocouples. As a result, the temperature of the heat storage layer of honeycomb structure Z was approximately 500°C, which was higher than the temperature of the heat storage layer of honeycomb structure Y, and the temperature difference between the two honeycomb structures was 8°C.

[0076] The ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the downstream heat transfer material) in the heat storage layer of honeycomb structure Y is 1.17, and the ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the upstream heat transfer material) in the heat storage layer of honeycomb structure Z is 1.09, so the ratio A / B is 1.07.

[0077] Therefore, from the above test results, it can be seen that the cubic inorganic compound in the downstream heat transfer material is more crystalline than the cubic inorganic compound in the upstream heat transfer material, and that the downstream heat transfer material has higher thermal conductivity than the upstream heat transfer material. As a result, the temperature of the downstream heat transfer material rises faster, and it can be heated to a high temperature in a time as short as that of the upstream heat transfer material. Therefore, the temperature of the entire exhaust gas purification catalyst can be raised to a high temperature in a short time.

[0078] [Example 3] A honeycomb structure X was manufactured in the same manner as in Example 1, and a honeycomb structure Z was manufactured in the same manner as in Example 2. Then, one axial end of honeycomb structure X and one axial end of honeycomb structure Z were connected so that honeycomb structure X and honeycomb structure Z were aligned in a straight line, and a tubular test specimen was obtained. In this test specimen of Example 3, each cell of honeycomb structure X and each cell of honeycomb structure Z are in communication, so gas introduced into the opening at the other axial end of honeycomb structure X passes through the cells of honeycomb structure X and is introduced into honeycomb structure Z, and is discharged from the opening at the other axial end of honeycomb structure Z through the cells of honeycomb structure Z.

[0079] The thermal conductivity of the heat storage layer was tested using the test specimen of Example 3 that was manufactured. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Example 3 from the other axial end of honeycomb structure X. After the 600°C air had flowed for 280 seconds, the temperature of the heat storage layer of honeycomb structure X and the heat storage layer of honeycomb structure Z were measured using thermocouples. As a result, the temperature of the heat storage layer of honeycomb structure X was approximately 500°C, which was higher than the temperature of the heat storage layer of honeycomb structure Z, and the temperature difference between the two honeycomb structures was 6°C.

[0080] The ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the downstream heat transfer material) in the heat storage layer of honeycomb structure Z is 1.09, and the ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the upstream heat transfer material) in the heat storage layer of honeycomb structure X is 0.98, so the ratio A / B is 1.11.

[0081] Therefore, from the above test results, it can be seen that the cubic inorganic compound in the downstream heat transfer material is more crystalline than the cubic inorganic compound in the upstream heat transfer material, and that the downstream heat transfer material has higher thermal conductivity than the upstream heat transfer material. As a result, the temperature of the downstream heat transfer material rises faster, and it can be heated to a high temperature in a time as short as that of the upstream heat transfer material. Therefore, the temperature of the entire exhaust gas purification catalyst can be raised to a high temperature in a short time.

[0082] [Comparative Example 1] Two honeycomb structures Y were manufactured in the same manner as in Example 1. The two honeycomb structures Y were then connected at one end in the axial direction, so that they were aligned in a straight line, and a tubular test specimen was obtained. In this comparative example 1 test specimen, since the cells of the two honeycomb structures Y are in communication with each other, the gas introduced into the opening at the other axial end of the first honeycomb structure Y passes through the cells of the first honeycomb structure Y and is introduced into the second honeycomb structure Y, and then passes through the cells of the second honeycomb structure Y and is discharged from the opening at the other axial end of the second honeycomb structure Y.

[0083] The thermal conductivity of the heat storage layer was tested using the test specimen of Comparative Example 1 that was manufactured. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Comparative Example 1 from the other axial end of the first honeycomb structure Y. After the 600°C air had flowed for 280 seconds, the temperature of the heat storage layers of the two honeycomb structures Y was measured using thermocouples. As a result, the temperature of the heat storage layer (upstream heat transfer material) of the first honeycomb structure Y was approximately 480°C, which was higher than the temperature of the heat storage layer (downstream heat transfer material) of the second honeycomb structure Y, and the temperature difference between the two honeycomb structures was 60.9°C.

[0084] Since the ratio of γ-alumina W440 / W400 in the heat storage layer of the honeycomb structure Y is 1.17, the ratio A / B is 1.00. Therefore, from the above test results, it can be seen that if the crystallinity of the cubic inorganic compound in the upstream heat transfer material is the same as that of the downstream heat transfer material, and the thermal conductivity of the upstream and downstream heat transfer materials is the same, the rate at which the temperature of the downstream heat transfer material rises will be low, and it will be difficult for the downstream heat transfer material to be heated to a high temperature in a short time. For this reason, it is difficult to raise the temperature of the entire exhaust gas purification catalyst to a high temperature in a short time.

[0085] [Comparative Example 2] Honeycomb structure X and honeycomb structure Y were manufactured in the same manner as in Example 1. Then, one axial end of honeycomb structure Y and one axial end of honeycomb structure X were connected so that honeycomb structure Y and honeycomb structure X were in a straight line, and a tubular test specimen was obtained. In this comparative example 2 test specimen, each cell of honeycomb structure X and each cell of honeycomb structure Y are in communication, so gas introduced into the opening at the other axial end of honeycomb structure Y is introduced into honeycomb structure X through the cells of honeycomb structure Y and is discharged from the opening at the other axial end of honeycomb structure X through the cells of honeycomb structure X.

[0086] The thermal conductivity of the heat storage layer was tested using the test specimen of Comparative Example 2 that was manufactured. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Comparative Example 2 from the other axial end of the honeycomb structure Y. After the 600°C air had flowed for 280 seconds, the temperature of the heat storage layer of honeycomb structure X and the heat storage layer of honeycomb structure Y were measured using thermocouples. As a result, the temperature of the heat storage layer of honeycomb structure Y was approximately 490°C, which was higher than the temperature of the heat storage layer of honeycomb structure X, and the temperature difference between the two honeycomb structures was 31.9°C.

[0087] The ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the downstream heat transfer material) in the heat storage layer of honeycomb structure X is 0.98, and the ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the upstream heat transfer material) in the heat storage layer of honeycomb structure Y is 1.17, so the ratio A / B is 0.84.

[0088] Therefore, from the above test results, it can be seen that the cubic inorganic compound in the downstream heat transfer material is less crystalline than the cubic inorganic compound in the upstream heat transfer material, and that the thermal conductivity of the downstream heat transfer material is lower than that of the upstream heat transfer material. As a result, the rate at which the temperature of the downstream heat transfer material rises is slower, and it is difficult for the downstream heat transfer material to be heated to a high temperature in a short time. Consequently, it is difficult to raise the temperature of the entire exhaust gas purification catalyst to a high temperature in a short time.

[0089] [Comparative Example 3] Two honeycomb structures X were manufactured in the same manner as in Example 1. Then, using the two honeycomb structures X, a test specimen of Comparative Example 3 was obtained in the same manner as in Comparative Example 1. Using the test specimen of Comparative Example 3 that was manufactured, the thermal conductivity of the heat storage layer was tested in the same manner as in Comparative Example 1. As a result, the temperature of the heat storage layer (upstream heat transfer material) of the first honeycomb structure X was approximately 490°C, which was higher than the temperature of the heat storage layer (downstream heat transfer material) of the second honeycomb structure X, and the temperature difference between the two honeycomb structures was 17.8°C.

[0090] Since the ratio W440 / W400 of γ-alumina in the heat storage layer of the honeycomb structure X is 0.98, the ratio A / B is 1.00. Therefore, from the above test results, it can be seen that if the crystallinity of the cubic inorganic compound in the upstream heat transfer material is the same as that of the downstream heat transfer material, and the thermal conductivity of the upstream and downstream heat transfer materials is the same, the rate at which the temperature of the downstream heat transfer material rises will be low, and it will be difficult for the downstream heat transfer material to be heated to a high temperature in a short time. For this reason, it is difficult to raise the temperature of the entire exhaust gas purification catalyst to a high temperature in a short time.

[0091] [Comparative Example 4] Two honeycomb structures Z were manufactured in the same manner as in Example 2. Then, using the two honeycomb structures Z, a test specimen of Comparative Example 4 was obtained in the same manner as in Comparative Example 1. Using the test specimen of Comparative Example 4 that was manufactured, the thermal conductivity of the heat storage layer was tested in the same manner as in Comparative Example 1. As a result, the temperature of the heat storage layer (upstream heat transfer material) of the second honeycomb structure Z was higher than that of the first honeycomb structure Z, and the temperature difference was 21.3°C.

[0092] Since the ratio W440 / W400 of γ-alumina in the heat storage layer of the honeycomb structure Z is 1.09, the ratio A / B is 1.00. Therefore, from the above test results, it can be seen that if the crystallinity of the cubic inorganic compound in the upstream heat transfer material is the same as that of the downstream heat transfer material, and the thermal conductivity of the upstream and downstream heat transfer materials is the same, the rate at which the temperature of the downstream heat transfer material rises will be low, and it will be difficult for the downstream heat transfer material to be heated to a high temperature in a short time. For this reason, it is difficult to raise the temperature of the entire exhaust gas purification catalyst to a high temperature in a short time.

[0093] [Comparative Example 5] A honeycomb structure Y was manufactured in the same manner as in Example 1, and a honeycomb structure Z was manufactured in the same manner as in Example 2. Then, one axial end of honeycomb structure Y and one axial end of honeycomb structure Z were connected so that honeycomb structure Y and honeycomb structure Z were in a straight line, and a tubular test specimen was obtained. In this comparative example 5 test specimen, each cell of honeycomb structure Y and each cell of honeycomb structure Z are in communication, so gas introduced into the opening at the other axial end of honeycomb structure Y passes through the cells of honeycomb structure Y and is introduced into honeycomb structure Z, and is discharged from the opening at the other axial end of honeycomb structure Z through the cells of honeycomb structure Z.

[0094] The thermal conductivity of the heat storage layer was tested using the test specimen of Comparative Example 5 that was manufactured. Using a hot air generator, air at a temperature of 600°C and a flow rate of 2.2 m / s was introduced into the test specimen of Comparative Example 5 from the other axial end of the honeycomb structure Y. After the 600°C air had flowed for 280 seconds, the temperature of the heat storage layer of honeycomb structure Y and the heat storage layer of honeycomb structure Z were measured using thermocouples. As a result, the temperature of the heat storage layer of honeycomb structure Y was higher than that of honeycomb structure Z, and the temperature difference was 33.8°C.

[0095] The ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the downstream heat transfer material) in the heat storage layer of honeycomb structure Z is 1.09, and the ratio W440 / W400 of γ-alumina (cubic inorganic compound present in the upstream heat transfer material) in the heat storage layer of honeycomb structure Y is 1.17, so the ratio A / B is 0.93.

[0096] Therefore, from the above test results, it can be seen that the cubic inorganic compound in the downstream heat transfer material is less crystalline than the cubic inorganic compound in the upstream heat transfer material, and that the thermal conductivity of the downstream heat transfer material is lower than that of the upstream heat transfer material. As a result, the rate at which the temperature of the downstream heat transfer material rises is slower, and it is difficult for the downstream heat transfer material to be heated to a high temperature in a short time. Consequently, it is difficult to raise the temperature of the entire exhaust gas purification catalyst to a high temperature in a short time. [Explanation of Symbols]

[0097] 1A...area 1B...area 30...heat storage layer 40...Catalyst layer 50...flow channel

Claims

1. An exhaust gas purification device installed in an exhaust gas flow path, which purifies the exhaust gas flowing through the flow path, The exhaust gas purification device is divided into a plurality of regions along the direction of the exhaust gas flow, and each of these plurality of regions is provided with an exhaust gas purification catalyst, which is a catalyst for the purification reaction that purifies the exhaust gas; a heat storage material that supplies heat to the exhaust gas purification catalyst to suppress the temperature drop of the exhaust gas purification catalyst; and a heat transfer material that absorbs heat from the exhaust gas and sends it to the heat storage material and the exhaust gas purification catalyst, wherein the heat transfer material has a cubic inorganic compound. If the heat transfer material located in one of the aforementioned multiple regions is designated as the upstream heat transfer material, and the heat transfer material located in another region downstream of the said region in the flow direction is designated as the downstream heat transfer material, then the cubic inorganic compound in the upstream heat transfer material and the cubic inorganic compound in the downstream heat transfer material have different crystal structures. An exhaust gas purification device in which, when the ratio W440 / W400 of the full width at half maximum (FWHM) of the 440-plane peak W440 and the FWHM of the 400-plane peak W400 of the crystal of the cubic inorganic compound is calculated by X-ray diffraction intensity measurement, if the ratio W440 / W400 of the cubic inorganic compound in the downstream heat transfer material is A, and the ratio W440 / W400 of the cubic inorganic compound in the upstream heat transfer material is B, then the ratio A / B is greater than 1.

2. The exhaust gas purification device according to claim 1, wherein the cubic inorganic compound is γ-alumina.

3. The exhaust gas purification device according to claim 1 or claim 2, wherein the ratio A / B is 1.07 or more.

4. The exhaust gas purification device according to claim 1 or claim 2, wherein the ratio A / B is 1.10 or more.

5. The exhaust gas purification device according to claim 1 or claim 2, wherein the ratio A / B is 1.19 or greater.

6. The exhaust gas purification device according to claim 1 or claim 2, wherein the heat storage material comprises heat storage particles having a core containing a phase-change type heat storage metal capable of heat storage and heat release using a solid-liquid phase change, and a shell consisting of a coating containing a metal oxide that covers the core.

7. The exhaust gas purification device according to claim 1 or claim 2, wherein each of the plurality of regions has a laminate in which a catalyst layer having the exhaust gas purification catalyst and a heat storage layer having the heat storage material and the heat transfer material are laminated, the catalyst layer is arranged facing the flow path, and the heat storage layer is arranged on the side of the catalyst layer opposite to the side facing the flow path.

8. The exhaust gas purification device according to claim 1 or claim 2, wherein the exhaust gas purification catalyst contains a precious metal.

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