Heat storage material and exhaust gas purification catalyst

Abstract

To provide a heat storage material which is capable of suppressing or preventing detachment of a shell layer covering the surface of core particles upon agitation of a slurry containing the heat storage material, and to provide an exhaust gas purification catalyst using the same.SOLUTION: A heat storage material includes core particles composed of a phase-change heat storage material and a shell layer including α-alumina that covers the surfaces of the core particles. As observed by X-ray diffraction, the α-alumina has a ratio of the half width of the 104 plane to that of the 012 plane of 1.125 or more and 1.363 or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a heat storage material and an exhaust gas purification catalyst, and more specifically to a heat storage material capable of suppressing or preventing peeling of a shell layer during a manufacturing process of an exhaust gas purification catalyst, and an exhaust gas purification catalyst using the same. [Background technology]

[0002] Patent Document 1 discloses a latent heat storage microcapsule with excellent heat storage density and thermal conductivity, which can ensure the repeated use strength of the capsule by making the shell thicker and does not cause a change in the composition of the phase change material even during the manufacturing process, and is stable during the heat storage cycle and usable at relatively high temperatures. This latent heat storage microcapsule is a latent heat storage microcapsule in which the surface of a core particle made of a latent heat storage material is covered with an oxide film. The oxide film is a three-layer oxide film consisting of a first oxide film directly covering the surface of the core particle, a second oxide film covering the first oxide film, and a third oxide film covering the second oxide film. The first oxide film is a dense oxide film made of oxides of the composition elements of the core particle, the second oxide film is a porous oxide film made of oxides of the composition elements of the core particle, and the third oxide film is a porous oxide film made of oxides of the composition elements of the core particle, which has a structure different from that of the second oxide film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 200021 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the inventors prepared a slurry containing the microcapsules in a manufacturing process for an exhaust gas purification catalyst for automobiles using latent heat storage microcapsules as disclosed in Patent Document 1, they encountered a problem in that when they stirred the slurry to uniformly disperse the microcapsules in the slurry, the oxide coating covering the surface of the core particles was peeled off.

[0005] The present invention has been made in consideration of the problems associated with such conventional technology, and aims to provide a heat storage material and an exhaust gas purification catalyst using the same that can suppress or prevent peeling of the shell layer, which corresponds to the oxide coating covering the surface of the core particle, when stirring a slurry containing the heat storage material, which corresponds to a microcapsule. [Means for solving the problem]

[0006] As a result of extensive investigations to achieve the above object, the present inventors have found that the above object can be achieved by adjusting the ratio of the half-width of the 104 plane to the half-width of the 012 plane in α-alumina observed by X-ray diffraction within a predetermined range, and have thus completed the present invention.

[0007] That is, the heat storage material of the present invention comprises a core particle made of a phase-change type heat storage material and a shell layer containing α-alumina that coats the surface of the core particle. The ratio of the half-width of the 104 plane to the half-width of the 012 plane in α-alumina observed by X-ray diffraction is 1.125 or more and 1.363 or less.

[0008] The exhaust gas purifying catalyst of the present invention comprises a monolithic support and a catalyst coating layer formed in an exhaust gas flow passage of the monolithic support. The catalyst coating layer includes a heat storage material. The heat storage material comprises a core particle made of a phase-change type heat storage material and a shell layer containing α-alumina that coats the surface of the core particle. The ratio of the half-width of the 104 plane to the half-width of the 012 plane in α-alumina observed by X-ray diffraction is 1.125 or more and 1.363 or less. Effect of the Invention

[0009] According to the present invention, the ratio of the 104 face half-width to the 012 face half-width in α-alumina observed by X-ray diffraction is set within the above-mentioned range, so that it is possible to provide a heat storage material and an exhaust gas purification catalyst using the same that can suppress or prevent peeling of the shell layer covering the surface of the core particle when stirring a slurry containing the heat storage material. [Brief description of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram illustrating an embodiment of an exhaust gas purification catalyst according to the present invention. [Diagram 2] 2 is a cross-sectional view showing a schematic diagram of a heat storage material contained in the catalyst coating layer shown in FIG. 1. [Diagram 3] 1 is a graph showing the relationship between the half-value width of the 012 plane and the half-value width of the 104 plane of α-alumina observed by X-ray diffraction in each example of the heat storage material. [Figure 4] FIG. 2 is an explanatory diagram showing an outline of a method for measuring the amount of hydrogen generated. [Diagram 5] 1 is a graph showing the relationship between the stirring time and the amount of hydrogen generated in each example of heat storage material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The heat storage material and the exhaust gas purification catalyst of the present invention will be described in detail below with reference to the drawings. Note that the dimensional ratios of the drawings cited below are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0012] The upper view of Fig. 1 is an external view showing an embodiment of the exhaust gas purification catalyst of the present invention, and the lower view of Fig. 1 is a partially enlarged view of a part surrounded by line A shown in the upper view of Fig. 1. Also, Fig. 2 is a cross-sectional view showing a heat storage material included in the catalyst coat layer shown in Fig. 1.

[0013] 1, an exhaust gas purification catalyst 1 of this embodiment includes a monolithic support 10 and a catalyst coating layer 20 formed on an exhaust gas flow path 10a of the monolithic support 10. Here, as the monolithic support 10, it is preferable to use a monolithic support or a honeycomb support made of a heat-resistant material such as ceramics, such as cordierite, or metal, such as ferritic stainless steel.

[0014] The catalyst coating layer 20 includes a heat storage material 30 as shown in FIG. 2. The heat storage material 30 includes a core particle 31 made of a phase-change type heat storage material and a shell layer 33 containing α-alumina that covers the surface 31a of the core particle 31. Here, the catalyst coating layer 20 may include, for example, a heat storage material and a conventionally known catalyst component that exhibits an exhaust gas purification effect in the same layer, or may include these in separate layers. Therefore, the catalyst coating layer 20 may have a structure consisting of one layer, or may have a laminated structure consisting of multiple layers.

[0015] Furthermore, the ratio of the half width of the 104 plane to the half width of the 012 plane in α-alumina observed by X-ray diffraction is 1.125 or more and 1.363 or less.

[0016] Moreover, the ratio of the half width of the 104 plane to the half width of the 012 plane is preferably 1.250 or more and 1.363 or less.

[0017] Furthermore, the half width of the 012 plane is preferably 0.04° or less.

[0018] Furthermore, the phase-change type heat storage material is preferably a metal or a metal oxide.

[0019] Furthermore, the phase-change type heat storage material is preferably an Al-Si alloy or an Al-Zn alloy.

[0020] Next, the advantages of this embodiment will be described. In this embodiment, in a heat storage material 30 including a core particle 31 made of a phase-change type heat storage material and a shell layer 33 containing α-alumina covering the surface 31a, the ratio of the half width of the 104 plane to the half width of the 012 plane in α-alumina observed by X-ray diffraction is 1.125 to 1.363. This makes it possible to suppress or prevent the shell layer covering the surface of the core particle from peeling off during stirring of the slurry containing the heat storage material. In other words, it is believed that a heat storage material and an exhaust gas purification catalyst using the same with improved impact resistance during the stirring operation of the slurry in the manufacturing process of the exhaust gas purification catalyst can be provided.

[0021] Here, the shell layer may contain Ba, La, Zr, Ce, Nd, Si, Fe, Co, Ni or a mixture of these elements in addition to α-alumina, and the inclusion of these elements tends to further stabilize the α-Al2O3 crystal. It is preferable that the shell layer contains these elements at a ratio of 0.01 to 10 mass %. Furthermore, it is more preferable that the shell layer contains these elements at a ratio of 0.01 to 0.5 mass %, and even more preferable that the shell layer contains these elements at a ratio of 0.01 to 2 mass %. On the other hand, the content of α-alumina is 90% by mass or more, preferably 95% by mass or more, and further preferably 98% by mass or more.

[0022] Furthermore, in heat storage materials in which peeling of the shell layer is suppressed or prevented (for example, core particles: Al-Si (phase-change heat storage material), shell layer: α-alumina), the phase-change heat storage material is not exposed, so that the phase-change heat storage material is unlikely to come into contact with moisture in the exhaust gas and react, such as 2Al+6H2O→2Al(OH)3+3H2, and hydroxides and hydrogen are not produced. Therefore, the phase-change heat storage material can exhibit excellent heat storage and heat release functions without losing reversibility.

[0023] At present, we believe that the above-mentioned effects have been achieved for the following reasons.

[0024] The crystal structure of α-alumina is a close-packed hexagonal lattice structure, and the thermodynamically most stable crystal structure is a plate-like structure with a well-developed <0001> plane.

[0025] When α-alumina is observed by X-ray diffraction in heat storage materials such as those in Examples 1, 2, and Comparative Example 1 described later in detail, diffraction peaks are observed in the 012, 104, 110, and 113 planes, but no diffraction peak is observed in the 001 plane.

[0026] Of the planes on which these diffraction peaks were observed, attention was focused on the 012 plane, which is a plane relatively close to the direction of the 001 plane, and the 104 plane, which is a plane relatively close to the direction of the 001 plane and perpendicular to it.

[0027] For α-alumina to have a stable crystal structure, it is considered preferable that the crystals grow in the direction of the 001 plane and the 012 plane, which is a plane that is relatively closer to that direction than the 104 plane, and the crystallites become larger (the half-width becomes smaller). On the other hand, it is considered preferable that the crystals do not grow in the direction of the 104 plane, which is a plane that is relatively closer to the 001 plane and the 104 plane, which is a plane that is relatively closer to the perpendicular direction than the 012 plane, and the crystallites become smaller (the half-width becomes larger).

[0028] From this viewpoint, it is considered necessary that the ratio of the 104 plane half width to the 012 plane half width in α-alumina in the heat storage material is calculated to be greater than or equal to a certain value. In detail, from the ratio of the 104 plane half width to the 012 plane half width in α-alumina calculated in the heat storage materials of Comparative Example 1, Example 1, and Example 2 described later and the evaluation results, the lower limit of the ratio of the 104 plane half width to the 012 plane half width in α-alumina can be set to 1.125 (see FIG. 3).

[0029] It is believed that the numerical value when α-alumina becomes single crystallized corresponds to the upper limit of the ratio of the 104 face half-width to the 012 face half-width in α-alumina. For example, from the d (lattice distance) of the 012 face of single crystal α-alumina in the document disclosed at https: / / www.globalsino.com / EM / page2591.html being 3.479 and the d (lattice distance) of the 104 face being 2.552, the upper limit of the ratio of the 104 face half-width to the 012 face half-width in α-alumina can be determined to be 1.363 by calculating the reciprocal ratio (see FIG. 3).

[0030] When the ratio of the 104 half-width to the 012 half-width in α-alumina is less than 1.125, it is believed that crystals do not grow much in the direction of the thermodynamically stable 001 plane and in the direction of the 012 plane, which is a plane close to that direction, and therefore excellent impact resistance cannot be obtained. On the other hand, when the ratio of the 104 half-width to the 012 half-width in α-alumina is greater than 1.363, it is believed that crystals grow in the direction of the thermodynamically stable 001 plane, but it is believed that a shell layer covering the core particle is difficult to form over the entire surface of the core particle.

[0031] However, it goes without saying that even if the above-mentioned effects are obtained for reasons other than those mentioned above, they are still included in the scope of the present invention.

[0032] Furthermore, according to a preferred embodiment of the present invention, the ratio of the half-width of the 104 plane to the half-width of the 012 plane is 1.250 or more. This makes it easier for crystals to grow in the thermodynamically stable 001 plane direction of α-alumina and in the 012 plane direction which is close to that direction, thereby providing better impact resistance.

[0033] Furthermore, according to a preferred embodiment of the present invention, the half-width of the 012 plane is 0.04° or less, and the small half-width leads to a large crystallite size, which increases the bonding strength in the direction of the 012 plane of α-alumina, thereby providing better impact resistance.

[0034] Furthermore, according to a preferred embodiment of the present invention, since the phase-change heat storage material is a metal or a metal oxide, the above-mentioned core-shell structure can be easily produced by the boehmite treatment. Preferred examples of the metal include aluminum alloys such as Al-Si alloys and Al-Zn alloys, and preferred examples of the metal oxide include alkaline earth metal hydroxides such as magnesium hydroxide (Mg(OH)2) and calcium hydroxide (Ca(OH)2).

[0035] Furthermore, according to a preferred embodiment of the present invention, the phase-change type heat storage material is an Al-Si alloy or an Al-Zn alloy, and since Al or Zn is an amphoteric metal, the above-mentioned core-shell structure can be subjected to boehmite treatment to produce metal oxides (Al(OH)3, Zn(OH)2), which can then be fired to produce an oxide coating. EXAMPLES

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0037] Example 1 3L of pure water was poured into a 5L stainless steel cup and stirred with a blade stirrer. Next, the pure water was heated to 60°C, and after the temperature of the pure water reached 60°C, 150g of Al-12Si alloy (manufactured by Hikari Materials Industry Co., Ltd., shape: spherical, particle size: 38μm or less) was poured in, and 150g of boehmite 1 (manufactured by Sasol, crystallite size: about 10nm) was further poured in, and after stirring for 3 hours, it was cooled and subjected to suction filtration. Thereafter, the residue was dried overnight at room temperature, further dried at 60°C, and crushed with a blender. Thereafter, the crushed residue was fired in air at 1050°C for 24 hours to obtain the heat storage material of this example. Using an X-ray diffraction device, the diffraction angle of α-alumina of the obtained heat storage material was identified and the half-width was obtained. The obtained results are shown in FIG. 3.

[0038] Example 2 The same operation as in Example 1 was repeated except that the boehmite 1 in Example 1 was replaced with boehmite 2 (manufactured by Sasol, crystallite diameter: about 30 nm), to obtain a heat storage material of this example. The half-width was determined in the same manner as in Example 1. The obtained results are shown in FIG.

[0039] Comparative Example 1 The same operation as in Example 1 was repeated except that the boehmite 1 in Example 1 was replaced with boehmite 3 (manufactured by Sasol, product name: DISPERAL), to obtain a heat storage material of this example. The half-width was determined in the same manner as in Example 1. The obtained results are shown in FIG.

[0040] (Impact resistance test) FIG. 4 is an explanatory diagram showing a method for measuring the amount of hydrogen generated using the heat storage material of each example in an operation simulating the slurry preparation process of an exhaust gas purification catalyst. Specifically, 6.5 g of heat storage material and 52 g of 0.1% HNO3 solution were prepared. Next, the 0.1% HNO3 solution was put into an Erlenmeyer flask and stirred with a magnetic stirrer. In addition, a fluororesin tube with a rubber stopper was connected to the Erlenmeyer flask, and preparations were made to collect hydrogen using a graduated cylinder by the water displacement method. Furthermore, the rubber stopper was removed from the Erlenmeyer flask, the heat storage material was put into the Erlenmeyer flask, and the flask was covered with a rubber stopper. The amount of hydrogen (H2) generated at each collection time was read, with the collection time being set to zero when the rubber stopper was put on the cover. The results obtained are shown in FIG. 5.

[0041] 5, in a comparison between Example 1, in which the ratio of the 104 plane half-width to the 012 plane half-width in α-alumina observed by X-ray diffraction within the scope of the present invention is 1.125 or more and 1.363 or less, and Comparative Example 1 outside the present invention, it is found that the amount of hydrogen generated in Example 1 after 8 hours of stirring is about 1 / 5 of the amount of hydrogen generated in Comparative Example 1 after 8 hours of stirring. This shows that the impact resistance of Example 1 is about 5 times higher than that of Comparative Example 1.

[0042] 5, in comparison between Example 1, in which the ratio of the 104 plane half-width to the 012 plane half-width in α-alumina observed by X-ray diffraction within the scope of the present invention is 1.125 to 1.363, and Example 2, in which the ratio is 1.250 to 1.363, the amount of hydrogen generated in Example 2 is even smaller than the amount of hydrogen generated in Example 1. This shows that the impact resistance of Example 2 is further improved compared to that of Example 1.

[0043] Although the present invention has been described above with reference to some embodiments and examples, the present invention is not limited to these, and various modifications are possible within the scope of the gist of the present invention.

[0044] In the present invention, in order to provide a heat storage material 30 capable of suppressing or preventing peeling of the shell layer 33 covering the surface 31a of the core particle 31 when stirring a slurry containing the heat storage material 30, and an exhaust gas purification catalyst 1 using the same, the gist of the present invention is that the ratio of the 104 face half-width to the 012 face half-width in α-alumina observed by X-ray diffraction method is within the above-mentioned range.

[0045] Therefore, in the above-mentioned embodiment, the exhaust gas purification catalyst 1 is described as having an integral structure type carrier 10, but the present invention is not limited to this. In the present invention, for example, the heat storage material may be supported on a high specific surface area substrate such as alumina.

[0046] Furthermore, for example, the above-mentioned components are not limited to the configurations shown in the above-mentioned embodiments and examples, and it is possible to change the details of the specifications and materials of the integrally structured carrier, catalyst coating layer, and heat storage material, and it is also possible to appropriately delete suitable components of one embodiment. [Explanation of symbols]

[0047] 1. Exhaust gas purification catalyst 10. Monolithic structure carrier 10a Exhaust gas flow path 20 Catalyst coating layer 30 Heat storage material 31 Core Particles 31a surface 33 Shell Layer

Claims

1. A heat storage material comprising a core particle made of a phase-change type heat storage material and a shell layer containing α-alumina covering the surface of the core particle, The ratio of the half width of the 104 plane to the half width of the 012 plane in the α-alumina observed by X-ray diffraction is 1.125 or more and 1.363 or less. A heat storage material characterized by:

2. 2. The heat storage material according to claim 1, wherein a ratio of the half-value width of the 104 plane to the half-value width of the 012 plane is 1.250 or more.

3. 3. The heat storage material according to claim 1, wherein the half width of the 012 plane is 0.04° or less.

4. 2. The heat storage material according to claim 1, wherein the phase-change type heat storage material is a metal or a metal oxide.

5. 2. The heat storage material according to claim 1, wherein the phase-change type heat storage material is an Al-Si alloy or an Al-Zn alloy.

6. An exhaust gas purification catalyst comprising an integral structure type carrier and a catalyst coating layer formed in an exhaust gas flow path of the integral structure type carrier, The catalyst coating layer includes a heat storage material, The heat storage material comprises a core particle made of a phase-change type heat storage material and a shell layer made of α-alumina coating the surface of the core particle, The ratio of the half width of the 104 plane to the half width of the 012 plane in the α-alumina observed by X-ray diffraction is 1.125 or more and 1.363 or less. An exhaust gas purification catalyst characterized by:

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