Methane oxidation catalyst device

Abstract

The present invention provides a methane oxidation catalyst apparatus that can reduce the active metal content while maintaining the desired methane oxidation efficiency. [Solution] The methane oxidation catalyst device includes a methane oxidation catalyst for oxidizing methane contained in exhaust gas. At least a portion of the methane oxidation catalyst has an active metal that oxidizes the components to be oxidized, including methane, in the exhaust gas. Furthermore, the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

Description

[Technical Field]

[0001] This disclosure relates to a methane oxidation catalyst apparatus. [Background technology]

[0002] Harmful substances (such as hydrocarbons and nitrogen oxides) contained in exhaust gases emitted from internal combustion engines and other sources contribute to air pollution. Specifically, exhaust gases emitted from internal combustion engines powered by natural gas contain unburned methane, as some of the methane in the natural gas does not burn. To decompose (oxidize) this methane contained in exhaust gases, a technology is known that involves placing a methane oxidation catalyst in the exhaust passage through which the exhaust gas flows to oxidize the methane.

[0003] As such a methane oxidation catalyst, a methane oxidation catalyst has been proposed that consists of a catalyst support and palladium as an active metal supported on the catalyst support, with a palladium support amount of 4% by mass (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2018-510767 [Overview of the project] [Problems that the invention aims to solve]

[0005] On the other hand, platinum group metals such as palladium, which act as active metals, are expensive. Therefore, from the perspective of cost reduction, it is necessary to reduce the content of active metals while maintaining the oxidation efficiency of oxidizing methane contained in exhaust gas.

[0006] The present disclosure aims to provide a methane oxidation catalyst apparatus that can reduce the active metal content while maintaining a desired methane oxidation efficiency. [Means for solving the problem]

[0007] The present disclosure [1] includes a methane oxidation catalyst apparatus for oxidizing methane contained in exhaust gas, wherein at least a portion of the methane oxidation catalyst has an active metal that oxidizes components to be oxidized, including methane, in the exhaust gas, and the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

[0008] In such a methane oxidation catalyst system, a methane oxidation catalyst is provided that has an active metal that oxidizes the oxidizable components, including methane, in the exhaust gas, and the amount of active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0009] The reaction by which methane oxidation catalysts oxidize methane-containing components in exhaust gas is an exothermic reaction. Therefore, the temperature of the exhaust gas increases from the upstream to the downstream side in the direction of exhaust gas flow. Furthermore, with methane oxidation catalysts, the oxidation efficiency of methane-containing components is higher when the exhaust gas temperature is relatively high.

[0010] In other words, in a methane oxidation catalyst system, the temperature of the exhaust gas increases from the upstream to the downstream side in the direction of exhaust gas flow. Therefore, even if the amount of active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. To put it another way, the amount of active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0011] This disclosure [2] includes the methane oxidation catalyst apparatus described in [1] above, wherein all of the methane oxidation catalysts have the active metal.

[0012] In such methane oxidation catalyst systems, all methane oxidation catalysts contain active metals. Therefore, methane oxidation efficiency can be further improved.

[0013] The present disclosure [3] includes the methane oxidation catalyst device according to the above [1], wherein the methane oxidation catalyst device comprises a plurality of the methane oxidation catalysts, the methane oxidation catalyst disposed on the upstream side in the flow direction of the exhaust gas has the active metal, and the methane oxidation catalyst disposed on the downstream side in the flow direction of the exhaust gas does not have the active metal.

[0014] In such a methane oxidation catalyst device, the methane oxidation catalyst disposed on the upstream side in the flow direction of the exhaust gas has the active metal, and the methane oxidation catalyst disposed on the downstream side in the flow direction of the exhaust gas does not have the active metal. Therefore, on the upstream side in the flow direction of the exhaust gas, heat is generated when oxidizing the components to be oxidized including methane, and the temperature of the exhaust gas rises. Then, on the downstream side in the flow direction of the exhaust gas, since the exhaust gas having a relatively high temperature is supplied, even the methane oxidation catalyst having no active metal can maintain a desired methane oxidation efficiency. As a result, the content of the active metal can be further reduced.

[0015] The present disclosure [4] includes the methane oxidation catalyst device according to any one of the above [1] to [3], wherein the content of the active metal per unit area of the methane oxidation catalyst gradually decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

[0016] In such a methane oxidation catalyst device, the content of the active metal per unit area of the methane oxidation catalyst gradually decreases from the upstream side to the downstream side in the flow direction of the exhaust gas. Therefore, it is possible to easily manufacture a methane oxidation catalyst device that maintains a desired methane oxidation efficiency and can reduce the content of the active metal.

[0017] The present disclosure [5] includes the methane oxidation catalyst device according to any one of the above [1] to [4], which comprises a plurality of methane oxidation catalyst units along the flow direction of the exhaust gas, wherein each of the plurality of methane oxidation catalyst units has the methane oxidation catalyst, and the content of the active metal per unit area of the methane oxidation catalyst included in the methane oxidation catalyst unit is substantially uniform in the flow direction of the exhaust gas.

[0018] In such a methane oxidation catalyst device, a plurality of methane oxidation catalyst units are provided along the flow direction of exhaust gas, each of the plurality of methane oxidation catalyst units has a methane oxidation catalyst, and in the flow direction of exhaust gas, the content of active metal per unit area of the methane oxidation catalyst included in each methane oxidation catalyst unit is substantially uniform. Therefore, each of the plurality of methane oxidation catalyst units can be easily manufactured, and as a result, the methane oxidation catalyst device can be easily manufactured.

[0019] The present disclosure [6] includes the methane oxidation catalyst device according to the above [5], wherein among the methane oxidation catalyst units adjacent to each other in the exhaust gas flow direction, the content of the active metal per unit area of the methane oxidation catalyst included in the methane oxidation catalyst unit disposed on the upstream side in the exhaust gas flow direction is larger than the content of the active metal per unit area of the methane oxidation catalyst included in the methane oxidation catalyst unit disposed on the downstream side in the exhaust gas flow direction.

[0020] In such a methane oxidation catalyst device, among the methane oxidation catalyst units adjacent to each other in the exhaust gas flow direction, the content of active metal per unit area of the methane oxidation catalyst included in the methane oxidation catalyst unit disposed on the upstream side in the exhaust gas flow direction is larger than the content of active metal per unit area of the methane oxidation catalyst included in the methane oxidation catalyst unit disposed on the downstream side in the exhaust gas flow direction. Therefore, the content of active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0021] The present disclosure [7] includes the methane oxidation catalyst device according to the above [5] or [6], wherein the methane oxidation catalyst has a base material, the active metal is supported on the base material, and the methane oxidation catalyst unit comprises a plurality of the methane oxidation catalysts stacked in layers.

[0022] In such a methane oxidation catalyst device, the methane oxidation catalyst has a base material, the active metal is supported on the base material, and the methane oxidation catalyst unit comprises a plurality of stacked methane oxidation catalysts. Therefore, the methane oxidation catalyst device can be easily manufactured. Effects of the Invention

[0023] The methane oxidation catalyst apparatus of this disclosure comprises a methane oxidation catalyst having an active metal that oxidizes oxidizable components including methane in the exhaust gas, wherein the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0024] The reaction by which methane oxidation catalysts oxidize methane-containing components in exhaust gas is an exothermic reaction. Therefore, the temperature of the exhaust gas increases from the upstream to the downstream side in the direction of exhaust gas flow. Furthermore, with methane oxidation catalysts, the oxidation efficiency of methane-containing components is higher when the exhaust gas temperature is relatively high.

[0025] In other words, in a methane oxidation catalyst system, the temperature of the exhaust gas increases from the upstream to the downstream side in the direction of exhaust gas flow. Therefore, even if the amount of active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. To put it another way, the amount of active metal can be reduced while maintaining the desired methane oxidation efficiency. [Brief explanation of the drawing]

[0026] [Figure 1] Figure 1 shows a perspective view of one embodiment of the methane oxidation catalyst apparatus of the present disclosure. [Figure 2] Figure 2 shows a perspective view of the methane oxidation catalyst unit included in the methane oxidation catalyst apparatus shown in Figure 1. [Figure 3] Figure 3 shows the methane oxidation catalyst contained in the methane oxidation catalyst unit shown in Figure 2. [Figure 4] Figure 4 is a schematic graph showing the relationship between the active metal content per unit area of ​​the methane oxidation catalyst and the distance from the upstream side in the direction of exhaust gas flow, in one embodiment of a methane oxidation catalyst device. [Figure 5]Figure 5 is a schematic graph showing the relationship between the active metal content per unit area of ​​the methane oxidation catalyst and the distance from the upstream side in the exhaust gas flow direction in one embodiment of the methane oxidation catalyst, in the first modified example of the methane oxidation catalyst apparatus. [Figure 6] Figure 6 is a schematic graph showing the relationship between the active metal content per unit area of ​​the methane oxidation catalyst and the distance from the upstream side in the exhaust gas flow direction in one embodiment of the methane oxidation catalyst, in a second modified example of the methane oxidation catalyst device. [Modes for carrying out the invention]

[0027] 1. One embodiment of a methane oxidation catalyst apparatus An embodiment of the methane oxidation catalyst apparatus 1 of this disclosure will be described with reference to Figures 1 to 3.

[0028] The methane oxidation catalyst device 1 is installed in the exhaust passage through which methane-containing exhaust gas flows and is used to decompose (oxidize) the methane contained in the exhaust gas. Specifically, the methane oxidation catalyst device 1 can be used for methane-containing exhaust gas discharged from LNG-fueled ships. It can also be used for methane-containing exhaust gas generated in processes such as gas-phase reactions in chemical plants.

[0029] As shown in Figure 1, the methane oxidation catalyst apparatus 1 of this embodiment comprises a plurality of methane oxidation catalyst units 2 arranged along the direction of exhaust gas flow.

[0030] Furthermore, as shown in Figure 2, the methane oxidation catalyst unit 2 includes a methane oxidation catalyst 10.

[0031] 1.1. Methane Oxidation Catalyst The methane oxidation catalyst 10 is not particularly limited as long as it can oxidize the oxidizable components, including methane, in the exhaust gas. However, at least a portion of the methane oxidation catalyst 10 has an active metal 11 that oxidizes the oxidizable components, including methane, in the exhaust gas. All of the methane oxidation catalysts 10 in this embodiment have an active metal 11. Examples of oxidizable components include methane, carbon monoxide, and hydrocarbons (excluding methane).

[0032] As shown in Figure 3, the methane oxidation catalyst 10 further comprises, for example, a substrate 12, and the active metal 11 is supported on the substrate 12. The active metal 11 may be supported on the substrate 12 alone, or together with particulate components described later. Furthermore, the methane oxidation catalyst 10 may contain additives as needed.

[0033] The content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 is, for example, 0.5 g / m². 2 ~50g / m 2 Preferably, 1 g / m 2 ~25g / m 2 The content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 is the content of the active metal 11 per unit area on the surface in contact with the methane oxidation catalyst 10 and the exhaust gas. In other words, it is the content of the active metal 11 per unit area on the surface of the methane oxidation catalyst 10 that extends in the surface direction (the direction of exhaust gas flow and the width direction) (the same applies hereinafter).

[0034] The content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 is, for example, 0.5 g / m². 2 Preferably, 1 g / m 2 In addition, for example, 50g / m 2 Preferably, 25 g / m 2 The following applies:

[0035] The content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 described above is the content of the active metal 11 per unit area of ​​each individual methane oxidation catalyst 10 used in the methane oxidation catalyst device 1. In this embodiment, the content of the active metal 11 per unit area of ​​each methane oxidation catalyst 10 is substantially uniform in the direction of exhaust gas flow.

[0036] (1)Active metal The active metal 11 is supported on the substrate 12, for example. Specifically, the active metal 11 is supported on the substrate 12 together with the particulate components described later.

[0037] The active metal 11 contains platinum group metals and / or oxides of platinum group metals. Preferably, it contains platinum group metals and / or oxides of platinum group metals as its main component. More preferably, it consists of platinum group metals and / or oxides of platinum group metals. In other words, the active metal 11 preferably does not contain other metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals.

[0038] Furthermore, when it is stated that the active metal 11 mainly consists of platinum group metals and / or oxides of platinum group metals, it means that if the active metal 11 contains other metals and other metal oxides in addition to platinum group metals and / or oxides of platinum group metals, the proportion of platinum group metals in the active metal 11 (= platinum group metal content / total amount of active metal 11 × 100) is greater than 50% by mass. In addition, even if the active metal 11 consists of platinum group metals and / or oxides of platinum group metals, the inclusion of unavoidable impurities is permissible. The proportion of unavoidable impurities in the active metal 11 is, for example, 1.0% by mass or less, preferably 0.5% by mass or less, and more preferably 0.1% by mass or less.

[0039] Examples of platinum group metals include palladium (Pd), platinum (Pt), iridium (Ir), rhodium (Rh), and ruthenium (Ru). Examples of platinum group metal oxides include palladium oxide, platinum oxide, iridium oxide, rhodium oxide, and ruthenium oxide. The active metal 11 may be used alone or in combination of two or more types.

[0040] The active metal 11 comprises platinum group metals and / or oxides of platinum group metals. More preferably, it comprises at least one selected from the group consisting of Pd, Pt, Ru, and their oxides. More preferably, it comprises at least one selected from the group consisting of Pd, Pt, and Ru. Even more preferably, it comprises Pd and Pt, or Pd and Ru (Pd-Pt composite support, Pd-Ru composite support).

[0041] The active metal 11 consists of a platinum group metal and / or an oxide of a platinum group metal. More preferably, it consists of at least one selected from the group consisting of Pd, Pt, Ru, and oxides thereof. Even more preferably, it consists of at least one selected from the group consisting of Pd, Pt, and Ru. Even more preferably, it consists of Pd and Pt, or Pd and Ru (Pd-Pt composite support, Pd-Ru composite support).

[0042] If the active metal 11 includes metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals, examples of other metals and other metal oxides include nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), and oxides thereof.

[0043] If the active metal 11 contains other metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals, the content of platinum group metals in the active metal 11 (= platinum group metal content / total amount of active metal 11 × 100) is, for example, more than 50% by mass, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0044] When the active metal contains Pd, the content ratio of Pd in the active metal (= Pd content / total amount of active metal × 100) is, from the viewpoint of ensuring catalytic activity, for example, 30 mass% or more, preferably 50 mass% or more, more preferably 70 mass% or more, and also, for example, less than 100 mass%, preferably 95 mass% or less, more preferably 90 mass% or less.

[0045] When the active metal contains Pt and / or Ru, the content ratio of Pt and Ru in the active metal (= Pt and Ru content / total amount of active metal × 100) is, for example, 1.0 mass% or more, preferably 5.0 mass% or more, more preferably 10 mass% or more, and also, for example, 60 mass% or less, preferably 40 mass% or less, more preferably 30 mass% or less.

[0046] (2) Particle component The particle component enhances the strength of the base material 12. That is, the strength of the methane oxidation catalyst 10 can be improved.

[0047] The particle component is supported on the base material 12 together with the active metal 11. The particle component may support the active metal 11, and in that case, the active metal 11 is supported on the base material 12 in a state of being supported by the particle component.

[0048] Examples of the particle component include metals and metal oxides other than platinum group metals and oxides of platinum group metals. Further, examples of the particle component also include semi-metal oxides. Examples of the particle component include zirconia, ceria, silica, alumina, titania, and zeolite.

[0049] The particle components may be used alone, or two or more kinds thereof may be used in combination. Further, the particle component may be a composite oxide containing zirconia, ceria, silica, alumina, titania, zeolite and the like. The particle component is preferably a composite oxide. Examples of the composite oxide include a ceria-zirconia composite oxide. Ceria-zirconia composite oxide (Ce X Zr1-X O2) is, for example, a solid solution of ceria (CeO2) and zirconia (ZrO2). Note that X is greater than 0 and less than 1.

[0050] The particulate components preferably include zirconia and / or ceria-zirconia composite oxides. The zirconia includes, for example, a monoclinic zirconia (m-ZrO2) phase and / or a tetragonal zirconia (t-ZrO2) phase. The ceria-zirconia composite oxide includes, for example, tetragonal ceria-zirconia (t-Ce X Zr 1-X Contains the O2 phase.

[0051] Furthermore, zirconia contains a monoclinic zirconia (m-ZrO2) phase and / or a tetragonal zirconia (t-ZrO2) phase, and ceria-zirconia composite oxide is tetragonal ceria-zirconia (t-Ce X Zr 1-X The presence of the O2 phase can be confirmed by measuring the X-ray diffraction (XRD) pattern.

[0052] The zirconia content percentages listed below include both zirconia present individually in the particle components and zirconia forming ceria-zirconia composite oxides.

[0053] When the particulate component contains zirconia, the zirconia content in the particulate component is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more.

[0054] (3) Additives The methane oxidation catalyst 10 may contain additives as needed.

[0055] The additives are not particularly limited, as long as they are additives commonly used in methane oxidation catalysts 10, and examples include diluents and binders.

[0056] The diluent is a substance that is inert to the methane oxidation reaction, and by adding the diluent to the methane oxidation catalyst 10, temperature control can be easily achieved.

[0057] Examples of diluents include alumina (e.g., α-alumina, θ-alumina, γ-alumina), silica, and titania (e.g., rutile titania, anatase titania). Diluents may be used individually or in combination of two or more.

[0058] The binder is, for example, a binding component used to bind the methane oxidation catalysts 10 together when a methane oxidation catalyst is used in a fluidized bed reactor.

[0059] Examples of binders include silicates, titanates, and aluminates. Binders can be used alone or in combination of two or more types.

[0060] The proportions of diluent components and binders in the methane oxidation catalyst 10 can be arbitrarily selected depending on the specific application of the methane oxidation catalyst 10.

[0061] (4) Base material Examples of the base material 12 include inorganic fiber sheets. Examples of inorganic fiber sheets include glass paper and ceramic paper. Glass paper is preferred.

[0062] Commercially available glass paper containing an organic binder can also be used. Examples of organic binders used in commercially available glass paper include acrylic resin, polyvinyl alcohol (PVA)-polyvinyl acetate copolymer, unsaturated polyester resin, and epoxy resin.

[0063] The base material 12 has thickness in the height direction and extends in the surface direction (the direction of exhaust gas flow and the width direction). The shape of the base material 12 is, for example, a flat plate and / or corrugated plate that extends in the direction of exhaust gas flow and the width direction. Preferably, the base material 12 is a flat plate of glass paper and / or corrugated glass paper that extends in the direction of exhaust gas flow and the width direction. As shown in Figure 3, the direction perpendicular to the height direction is the surface direction, and in the surface direction, the direction perpendicular to the direction of exhaust gas flow is the width direction (the same applies to Figures 1 and 2 below).

[0064] Since the external shape of the base material 12 is the same as the external shape of each methane oxidation catalyst 10, the shape of the base material 12 and the shape of each methane oxidation catalyst 10 are the same. In other words, the shape of each methane oxidation catalyst 10 is, for example, a flat plate and / or corrugated plate that extends in the direction of exhaust gas flow and width.

[0065] The dimensions of the base material 12 are adjusted as appropriate according to the application. Specifically, the length in the exhaust gas flow direction and the length in the width direction of the base material 12 are not particularly limited. The length of the base material 12 in the exhaust gas flow direction is, for example, 100 mm to 1000 mm. The length of the base material 12 in the width direction is, for example, 100 mm to 500 mm. The length of the base material 12 in the exhaust gas flow direction is preferably longer than the length in the width direction of the base material 12. The thickness (length in the height direction) of the base material 12 is, for example, 0.2 mm to 1.0 mm.

[0066] The amount of active metal 11 supported per unit area of ​​the substrate 12 is, for example, 0.5 g / m². 2 Preferably, 1 g / m 2 In addition, for example, 50g / m 2 Preferably, 25 g / m 2The following applies. In this embodiment, the amount of activated metal 11 supported on the substrate 12 is substantially uniform in the direction of exhaust gas flow. The amount of activated metal 11 supported per unit area of ​​the substrate 12 is the amount of activated metal 11 supported per unit area on the surface of the substrate 12 that extends in the surface direction (direction of exhaust gas flow and width direction). Furthermore, the amount of activated metal 11 supported per unit area of ​​the substrate 12 is the same as the amount of activated metal 11 per unit area of ​​each methane oxidation catalyst 10.

[0067] The amount of particulate components supported per unit area of ​​the substrate 12 is, for example, 10 g / m². 2 Preferably, 20 g / m 2 In addition, for example, 500g / m 2 Preferably, 450 g / m 2 The following applies. In this embodiment, the amount of particulate matter on the substrate 12 is substantially uniform in the direction of exhaust gas flow. The amount of particulate matter per unit area of ​​the substrate 12 is the amount of particulate matter per unit area on the surface of the substrate 12 that extends in the surface direction (direction of exhaust gas flow and width direction).

[0068] 1.2. Methane Oxidation Catalyst Unit The methane oxidation catalyst unit 2 has a methane oxidation catalyst 10. More specifically, as shown in Figure 2, the methane oxidation catalyst unit 2 has a casing 21 and a methane oxidation catalyst 10 filled inside the casing 21.

[0069] The shape of the casing 21 is not particularly limited, but examples include a rectangular tube shape and a cylindrical shape extending in the direction of exhaust gas flow. Preferably, a rectangular tube shape extending in the direction of exhaust gas flow is used. Specifically, the casing 21 may consist of a casing body with a roughly U-shaped cross-section and a flat plate-shaped cover that covers its opening, a casing body with a roughly square-shaped cross-section only, and a casing body with a roughly L-shaped cross-section and a roughly inverted L-shaped cover that fits thereto.

[0070] The dimensions of the casing 21 are adjusted as appropriate depending on the application. Specifically, the width and height of the casing 21 are not particularly limited, as long as they can accommodate the methane oxidation catalyst 10.

[0071] An inorganic fiber blanket 22 may be laid over the entire inner surface of the casing 21. By laying an inorganic fiber blanket 22 on the inner surface of the casing 21, vibrations can be suppressed. Examples of inorganic fibers in the inorganic fiber blanket 22 include ceramic fibers, glass fibers, silica sol fibers, alumina fibers, and rock wool. Ceramic fibers are preferred.

[0072] In the methane oxidation catalyst unit 2, the methane oxidation catalyst 10 is packed within the casing 21 in a height direction perpendicular to the exhaust gas flow direction. Specifically, in the methane oxidation catalyst unit 2, flat methane oxidation catalysts 10 and corrugated methane oxidation catalysts 10 are stacked alternately within the casing 21 without being bonded together. This stacking arrangement causes the methane oxidation catalysts 10 to form a cross-sectional network structure (honeycomb structure). In other words, the methane oxidation catalyst unit 2 comprises multiple stacked methane oxidation catalysts 10. The number of stacked flat methane oxidation catalysts 10 and corrugated methane oxidation catalysts 10 is not particularly limited.

[0073] In this embodiment, the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 is substantially uniform in the direction of exhaust gas flow.

[0074] Furthermore, when we say that the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 is substantially uniform in the direction of exhaust gas flow, we mean that the content of the active metal 11 per unit area of ​​each individual methane oxidation catalyst 10 is substantially uniform, and that the methane oxidation catalyst unit 2 is formed using only such methane oxidation catalysts 10.

[0075] 1.3. Methane oxidation catalyst apparatus As described above, the methane oxidation catalyst device 1 of this embodiment comprises a plurality of methane oxidation catalyst units 2, each having a methane oxidation catalyst 10, arranged along the direction of exhaust gas flow. Each of the plurality of methane oxidation catalyst units 2 has a methane oxidation catalyst 10. In other words, the methane oxidation catalyst device 1 is equipped with a methane oxidation catalyst 10 for oxidizing methane contained in the exhaust gas. Therefore, when exhaust gas containing methane is supplied to the methane oxidation catalyst device 1, the methane in the exhaust gas is oxidized to CO2 and H2O.

[0076] In the methane oxidation catalyst apparatus 1 of this embodiment, a plurality of methane oxidation catalyst units 2 are arranged in alignment along the direction of exhaust gas flow. In the methane oxidation catalyst apparatus 1 shown in Figure 1, three methane oxidation catalyst units 2a, 2b, and 2c are arranged in alignment along the direction of exhaust gas flow.

[0077] Furthermore, in the methane oxidation catalyst apparatus 1, multiple methane oxidation catalyst units 2 may be arranged in a planar direction perpendicular to the exhaust gas flow direction (both width and height directions). In the methane oxidation catalyst apparatus 1 shown in Figure 1, multiple (nine in Figure 1) methane oxidation catalyst units 2 are arranged in alignment in the width and height directions.

[0078] In other words, in the methane oxidation catalyst apparatus 1 shown in Figure 1, multiple (27 in Figure 1) methane oxidation catalyst units 2 are arranged in alignment in the direction of exhaust gas flow, width, and height.

[0079] The number and arrangement of methane oxidation catalyst units 2 in the methane oxidation catalyst device 1 are not particularly limited and can be adjusted as appropriate depending on the installation space and other factors.

[0080] In the methane oxidation catalyst device 1 of this embodiment, in methane oxidation catalyst units 2 adjacent to each other in the exhaust gas flow direction, the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction is greater than the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction.

[0081] In other words, in Figure 1, in the methane oxidation catalyst units 2a, 2b, and 2c which are arranged linearly in the direction of exhaust gas flow, the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2a is greater than the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b. Furthermore, the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b is greater than the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2c.

[0082] As described above, in this embodiment, the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 is substantially uniform in the direction of exhaust gas flow. Therefore, in such a methane oxidation catalyst device 1, as shown in Figure 4, the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 decreases in stages from the upstream side to the downstream side in the direction of exhaust gas flow.

[0083] In other words, in the methane oxidation catalyst device 1, the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0084] Figure 4 is an example of a schematic graph showing the relationship between the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 and the distance from the upstream side in the exhaust gas flow direction in the methane oxidation catalyst device 1 of this embodiment. In the graph of Figure 4, the upstream side in the exhaust gas flow direction indicates the first position in the methane oxidation catalyst device 1 where the exhaust gas comes into contact with the methane oxidation catalyst 10.

[0085] In methane oxidation catalyst units 2 adjacent to each other in the exhaust gas flow direction, the ratio of the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction to the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction (content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction / content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction) is, for example, 0.1 to 1.0, preferably 0.2 to 0.9, more preferably 0.3 to 0.8, and even more preferably 0.4 to 0.7. Furthermore, the above ratios are, for example, less than 1.0, preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less, and also, for example, 0.1 or more, preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more.

[0086] The above ratio may be the same or different for all methane oxidation catalyst units 2 adjacent to each other in the exhaust gas flow direction. Note that the above ratio being the same for all methane oxidation catalyst units 2 adjacent to each other in the exhaust gas flow direction means that the ratio of the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b to the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2a is the same as the ratio of the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2c to the amount of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b. The above ratio differs for methane oxidation catalyst units 2 that are adjacent to each other in the exhaust gas flow direction, which means that the ratio of the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b to the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2a is different from the ratio of the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2c to the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in methane oxidation catalyst unit 2b.

[0087] From the viewpoint of ease of manufacture, the above ratio is preferably the same for all methane oxidation catalyst units 2 that are adjacent to each other in the exhaust gas flow direction. Figure 4 shows a case where the above ratio is the same for all methane oxidation catalyst units 2 that are adjacent to each other in the exhaust gas flow direction.

[0088] In the methane oxidation catalyst apparatus 1, the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst units 2 adjacent to each other in the planar direction is not particularly limited and may be the same or different.

[0089] When the methane oxidation catalyst device 1 is used for exhaust gas containing methane discharged from an LNG-fueled ship, the total amount of methane oxidation catalyst 10 packed into the methane oxidation catalyst device 1 is, for example, 0.5 kg or more, preferably 5 kg or more, more preferably 10 kg or more, even more preferably 50 kg or more, particularly preferably 100 kg or more, and most preferably 150 kg or more.

[0090] The oxidation temperature of methane in the methane oxidation catalyst apparatus 1 (the contact temperature between the methane oxidation catalyst 10 and methane in the methane oxidation catalyst apparatus 1) is, for example, 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, and also, for example, 700°C or lower.

[0091] In the methane oxidation catalyst apparatus 1, the oxidation rate (%) of methane according to the following formula is, for example, 60% or more, preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.

[0092] Methane oxidation rate (%) = (Methane concentration of exhaust gas supplied to methane oxidation catalyst 1 - Methane concentration of exhaust gas that has passed through methane oxidation catalyst 1) / (Methane concentration of exhaust gas supplied to methane oxidation catalyst 1) × 100

[0093] The methane concentration of the exhaust gas supplied to the methane oxidation catalyst device 1 described above is the methane concentration before contact with the methane oxidation catalyst 10, and the methane concentration of the exhaust gas that has passed through the methane oxidation catalyst device 1 is the methane concentration after contact with the methane oxidation catalyst 10.

[0094] 1.4. Effects (1) The methane oxidation catalyst apparatus 1 of the present disclosure comprises a methane oxidation catalyst 10 having an active metal 11, and the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 decreases from the upstream side to the downstream side in the direction of exhaust gas flow. In such a methane oxidation catalyst apparatus 1, since the temperature of the exhaust gas increases from the upstream side to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained even if the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the direction of exhaust gas flow. In other words, the content of the active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0095] (2) In the methane oxidation catalyst apparatus 1 of this disclosure, all methane oxidation catalysts 10 have an active metal 11. Therefore, the methane oxidation efficiency can be further improved.

[0096] (3) In the methane oxidation catalyst apparatus 1 of this disclosure, the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 decreases in stages from the upstream side to the downstream side in the direction of exhaust gas flow. Therefore, a methane oxidation catalyst apparatus 1 that can maintain the desired methane oxidation efficiency and reduce the content of the active metal 11 can be easily manufactured.

[0097] (4) The methane oxidation catalyst apparatus 1 of the present disclosure comprises a plurality of methane oxidation catalyst units 2 having a methane oxidation catalyst 10 along the exhaust gas flow direction, and the content of the active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 is substantially uniform in the exhaust gas flow direction. Therefore, each of the plurality of methane oxidation catalyst units can be easily manufactured, and as a result, the methane oxidation catalyst apparatus can be easily manufactured.

[0098] (5) In the methane oxidation catalyst apparatus 1 of the present disclosure, in methane oxidation catalyst units 2 adjacent to each other in the direction of exhaust gas flow, the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 of the methane oxidation catalyst unit 2 located upstream in the direction of exhaust gas flow is greater than the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 of the methane oxidation catalyst unit 2 located downstream in the direction of exhaust gas flow. Therefore, the amount of active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0099] (6) In the methane oxidation catalyst apparatus 1 of this disclosure, the methane oxidation catalyst 10 has a base material 12, the active metal 11 is supported on the base material 12, and the methane oxidation catalyst unit 2 comprises multiple stacked methane oxidation catalysts 10. Therefore, the methane oxidation catalyst apparatus can be easily manufactured.

[0100] 2. Method for manufacturing a methane oxidation catalyst apparatus One embodiment of a method for manufacturing a methane oxidation catalyst will be described.

[0101] A method for manufacturing a methane oxidation catalyst device includes, for example, a catalyst preparation step for preparing a methane oxidation catalyst 10, a filling step for filling a casing 21 with the methane oxidation catalyst 10 to produce a methane oxidation catalyst unit 2, and a placement step for arranging the methane oxidation catalyst unit 2 to manufacture a methane oxidation catalyst device 1.

[0102] 2.1.Catalyst preparation process The catalyst preparation step includes, for example, a step of preparing a slurry containing the active metal 11 (preparation step), a step of applying or immersing the slurry on a substrate 12 (application step), and a step of firing the substrate 12 to which the slurry has been applied or immersed (firing step).

[0103] (preparation process) In the preparation step, a slurry containing the activated metal 11 is prepared. Specifically, the particulate components are suspended in a solution containing the activated metal (activated metal-containing solution), additives are added as needed, and the suspension is stirred to obtain the slurry.

[0104] An activated metal-containing solution is, for example, a solution containing an activated metal salt and a solvent. Examples of activated metal salts include activated metal nitrates, activated metal chlorides, and activated metal acetates, with activated metal nitrates being preferred.

[0105] Examples of active metal salts include platinum group metal salts. Examples of platinum group metal salts include palladium salts, platinum salts, and ruthenium salts. Examples of palladium salts include palladium nitrate, palladium chloride, and palladium acetate. Palladium nitrate is preferred. Examples of platinum salts include platinum nitrate and platinum chloride. Platinum nitrate is preferred. Examples of ruthenium salts include ruthenium chloride and ruthenium nitrate.

[0106] The solvent is not particularly limited, as long as it is one that is commonly used as an activated metal-containing solution. Examples of solvents include deionized water, ultrapure water, carboxylic acids, and alcohols. Deionized water is preferred.

[0107] When an activated metal-containing solution contains multiple activated metals, it may be prepared, for example, by mixing solutions containing each activated metal, or by adding salts of each activated metal to a single solvent. From the viewpoint of manufacturability, it is preferable to prepare the solution by mixing solutions containing each activated metal. Specifically, an activated metal-containing solution can be prepared by mixing a palladium(II) nitrate solution, a tetraammineplatinum(II) nitrate solution, and deionized water.

[0108] A slurry can be formed by adding the above-mentioned particulate components and, if necessary, additives to the above-mentioned activated metal-containing solution and stirring.

[0109] The stirring temperature is, for example, 5°C or higher, and for example, 35°C or lower. The stirring time can be set appropriately according to the amount to be prepared, for example, 15 hours or more, and for example, 21 hours or less.

[0110] (Coating process) In the coating process, the slurry obtained in the preparation process described above is applied to or impregnated onto the substrate 12.

[0111] In the coating process, the shape of the substrate 12 is preferably flat. The substrate 12 is, for example, flat glass paper.

[0112] Methods for application or impregnation include, for example, the so-called dipping method, brush application method, spray application method, and drop application method. Preferably, the dipping method and brush application method are mentioned.

[0113] Specifically, when impregnating the substrate 12 with slurry using a dipping method, the substrate 12 is impregnated with the slurry obtained in the preparation step.

[0114] Furthermore, when applying the slurry to the substrate 12 using a brush application method, the slurry obtained in the preparation step is dropped onto the substrate 12 and spread over the substrate 12 using a brush.

[0115] Furthermore, when a methane oxidation catalyst 10 is formed on a substrate 12 using a slurry containing a certain concentration of activated metal 11 (for example, a slurry containing a certain concentration of activated metal 11 is applied to or immersed in the substrate 12 to form the methane oxidation catalyst 10), it is determined that the content of activated metal 11 per unit area of ​​the methane oxidation catalyst 10 is substantially uniform.

[0116] In this way, the slurry can be applied to or impregnated onto the substrate 12.

[0117] (Firing process) In the firing process, the substrate 12 coated or impregnated with slurry (slurry-coated substrate 12) is fired. More specifically, the slurry-coated substrate 12 is dried and then fired.

[0118] One method for drying the slurry-coated substrate 12 is to place the slurry-coated substrate 12 in a heated mold and dry the slurry.

[0119] The drying temperature of the slurry-coated substrate 12 (mold heating temperature) is, for example, 50°C or higher, and for example, 200°C or lower. The drying time of the slurry-coated substrate 12 is, for example, 0.5 hours or more, and for example, 50 hours or less.

[0120] When the slurry-coated substrate 12 is to be formed into a flat plate shape after drying, it is dried using a flat plate-shaped mold. When the slurry-coated substrate 12 is to be formed into a corrugated plate shape after drying, it is molded into a corrugated plate shape at the same time as drying. Specifically, the slurry-coated substrate 12 is placed in a heated corrugated plate-shaped mold and molded using a jig.

[0121] Next, the substrate 12 with the dried slurry is fired.

[0122] The method for firing the slurry-coated substrate 12 after drying is not particularly limited, and known methods can be used. The slurry-coated substrate 12 after drying can be fired in a stacked state. Specifically, flat-plate-shaped slurry-coated substrate 12 and corrugated-plate-shaped slurry-coated substrate 12 can be stacked alternately and fired.

[0123] The firing temperature of the substrate 12 with slurry after drying is, for example, 300°C or higher, and for example, 800°C or lower. The firing time of the substrate 12 with slurry after drying is, for example, 0.5 hours or higher, and for example, 10 hours or lower.

[0124] In this way, the methane oxidation catalyst 10 can be obtained.

[0125] 2.2. Filling process In the filling process, the methane oxidation catalyst 10 is filled into the casing 21 to produce the methane oxidation catalyst unit 2.

[0126] Specifically, a casing 21 is prepared with an inorganic fiber blanket 22 laid on its inner surface, and flat methane oxidation catalysts 10 and corrugated methane oxidation catalysts 10 are alternately layered inside the casing 21 without being bonded together. This layering causes the methane oxidation catalysts 10 to form a cross-sectional network structure (honeycomb structure).

[0127] In this way, a methane oxidation catalyst unit 2 is manufactured in which a laminate of methane oxidation catalysts 10 is filled into a casing 21.

[0128] The manufactured methane oxidation catalyst units 2 have a substantially uniform content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in each methane oxidation catalyst unit 2. However, the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in each manufactured methane oxidation catalyst unit 2 differs.

[0129] 2.3. Placement process In the placement process, the methane oxidation catalyst units 2 are placed to manufacture the methane oxidation catalyst apparatus 1. Specifically, the methane oxidation catalyst units 2 obtained in the filling process are aligned in the direction of exhaust gas flow, the width direction, and the height direction, as shown in Figure 1.

[0130] The methane oxidation catalyst units 2 obtained in the filling process are arranged in descending order of the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2, from the upstream side to the downstream side in the direction of exhaust gas flow.

[0131] In other words, in the methane oxidation catalyst device 1, the methane oxidation catalyst units 2 are arranged such that the amount of active metal per unit area of ​​the methane oxidation catalyst 10 decreases in stages from the upstream side to the downstream side in the direction of exhaust gas flow.

[0132] In this way, the methane oxidation catalyst apparatus 1 is manufactured.

[0133] 3. First modified example of a methane oxidation catalyst apparatus In the modified examples, components and processes similar to those in the above-described embodiment of the methane oxidation catalyst apparatus are given the same reference numerals, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and functions as the above-described embodiment of the methane oxidation catalyst apparatus, unless otherwise specified. Moreover, the above-described embodiment and modified examples of the methane oxidation catalyst apparatus can be combined as appropriate.

[0134] In the methane oxidation catalyst device 1 described above, the content of active metal 11 per unit area of ​​each methane oxidation catalyst 10 is substantially uniform, and the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 is also substantially uniform. However, in the methane oxidation catalyst device 1, if the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 decreases from the upstream side to the downstream side in the exhaust gas flow direction, the content of active metal 11 per unit area of ​​each methane oxidation catalyst 10 does not have to be substantially uniform, and the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 does not have to be substantially uniform.

[0135] In the first modified example of the methane oxidation catalyst device 1, the content of the active metal 11 per unit area of ​​each methane oxidation catalyst 10 is not substantially uniform. Specifically, the content of the active metal 11 per unit area of ​​each methane oxidation catalyst 10 decreases from the upstream side to the downstream side in the exhaust gas flow direction. More specifically, as shown in Figure 5, the content of the active metal 11 per unit area of ​​each methane oxidation catalyst 10 decreases linearly from the upstream side to the downstream side in the exhaust gas flow direction. Although not shown, the content of the active metal 11 per unit area of ​​each methane oxidation catalyst 10 may decrease in steps or nonlinearly from the upstream side to the downstream side in the exhaust gas flow direction.

[0136] In the first modified methane oxidation catalyst apparatus 1, in methane oxidation catalyst units 2 adjacent to each other in the exhaust gas flow direction, the minimum content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction is greater than the maximum content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction.

[0137] The minimum content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction refers to the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 at the downstream end in the exhaust gas flow direction of the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction. Conversely, the maximum content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 in the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction refers to the content of active metal 11 per unit area of ​​the methane oxidation catalyst 10 at the upstream end in the exhaust gas flow direction of the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction.

[0138] A methane oxidation catalyst 10 in which the content of activated metal 11 per unit area decreases linearly from the upstream to the downstream side in the direction of exhaust gas flow is manufactured by applying a slurry containing multiple different concentrations of activated metal to a substrate. Specifically, by preparing slurries containing multiple different concentrations of activated metal and applying them to the substrate in order from the slurry with the highest concentration of activated metal to the slurry from the upstream to the downstream side in the direction of exhaust gas flow, a methane oxidation catalyst 10 can be formed in which the content of activated metal 11 per unit area decreases from the upstream to the downstream side in the direction of exhaust gas flow.

[0139] In addition, in the first modified example of the methane oxidation catalyst device 1, it is not necessary to have multiple methane oxidation catalyst units 2, and it is sufficient to have at least one methane oxidation catalyst unit 2.

[0140] 4. Second modified example of the methane oxidation catalyst apparatus In the methane oxidation catalyst apparatus 1 described above, all of the methane oxidation catalysts 10 have an active metal 11, but the apparatus is not limited to this.

[0141] The second modified methane oxidation catalyst apparatus 1 comprises a plurality of methane oxidation catalysts 10. More specifically, at least a portion of the methane oxidation catalysts 10 is a methane oxidation catalyst 10 (first methane oxidation catalyst) having an active metal 11 containing platinum group metals and oxides of platinum group metals, and at least a portion of the methane oxidation catalysts 10 is a methane oxidation catalyst 10 (second methane oxidation catalyst) that does not have an active metal 11 containing platinum group metals and oxides of platinum group metals. The first methane oxidation catalyst is the methane oxidation catalyst 10 of the above-described embodiment.

[0142] Specifically, in the second modified methane oxidation catalyst 10, the methane oxidation catalyst 10 (first methane oxidation catalyst) positioned upstream in the exhaust gas flow direction has an active metal 11, while the methane oxidation catalyst 10 (second methane oxidation catalyst) positioned downstream in the exhaust gas flow direction does not have an active metal 11 containing platinum group metals and oxides of platinum group metals.

[0143] In the second modified methane oxidation catalyst device 1, the methane oxidation catalyst unit 2 located upstream in the exhaust gas flow direction has a methane oxidation catalyst 10 (first methane oxidation catalyst) having an active metal 11, and the methane oxidation catalyst unit 2 located downstream in the exhaust gas flow direction has a methane oxidation catalyst 10 (second methane oxidation catalyst) that does not have an active metal 11 containing platinum group metals and oxides of platinum group metals.

[0144] Referring to Figure 1, in the second modified methane oxidation catalyst device 1, of the three methane oxidation catalyst units 2 arranged along the direction of exhaust gas flow, two methane oxidation catalyst units 2a and 2b, located upstream in the direction of exhaust gas flow, have a methane oxidation catalyst 10 (first methane oxidation catalyst) containing an active metal 11, while one methane oxidation catalyst unit 2c, located downstream in the direction of exhaust gas flow, has a methane oxidation catalyst 10 (second methane oxidation catalyst) that does not contain an active metal 11 containing platinum group metals and oxides of platinum group metals.

[0145] The schematic graph shown in Figure 6 illustrates the relationship between the amount of active metal 11 per unit area of ​​the methane oxidation catalyst 10 and the distance from the upstream side in the direction of exhaust gas flow in the second modified methane oxidation catalyst device 1.

[0146] The second methane oxidation catalyst can oxidize methane without containing the active metal 11 which includes platinum group metals and oxides of platinum group metals. In other words, the second methane oxidation catalyst can oxidize methane without containing platinum group metals and oxides of platinum group metals. More specifically, among the methane oxidation catalysts 10, the first methane oxidation catalyst has high methane oxidation capacity even when the exhaust gas is at a relatively low temperature, whereas the second methane oxidation catalyst has low methane oxidation capacity when the exhaust gas is at a relatively low temperature, and has methane oxidation capacity when the exhaust gas is at a relatively high temperature.

[0147] The second methane oxidation catalyst is not particularly limited as long as it does not contain an active metal 11 (platinum group metals and oxides of platinum group metals). For example, the second methane oxidation catalyst may include an active component that does not contain platinum group metals and oxides of platinum group metals, a particulate component, and a substrate 12.

[0148] The active ingredients and particulate components, which do not contain platinum group metals or oxides of platinum group metals, are supported on the substrate 12, for example.

[0149] Examples of active ingredients include metals and metal oxides other than platinum group metals and oxides of platinum group metals. Examples of active ingredients include composite oxides of metals containing cobalt, composite oxides of metals containing lanthanum, composite oxides of metals containing samarium, and composite oxides containing manganese. Note that these composite oxides of metals do not contain platinum group metals or oxides of platinum group metals.

[0150] The metal composite oxide used as the active ingredient is not particularly limited as long as it is a composite oxide of two or more metals, and may be a composite oxide of two metals, three metals, or four or more metals.

[0151] The second methane oxidation catalyst is prepared using the same procedure as the methane oxidation catalyst 10 (first methane oxidation catalyst) described above, but instead of a slurry containing the active metal 11, a slurry containing active components (for example, metals and metal oxides other than platinum group metals and oxides of platinum group metals) is used. Specifically, the second methane oxidation catalyst is prepared using the procedure shown in the catalyst preparation step described above. [Explanation of Symbols]

[0152] 1. Methane oxidation catalyst device 2. Methane oxidation catalyst unit 10 Methane oxidation catalyst 11 Active metals 12 Base material

Claims

1. A methane oxidation catalyst apparatus equipped with a methane oxidation catalyst for oxidizing methane contained in exhaust gas, At least a portion of the methane oxidation catalyst has an active metal that oxidizes the oxidizable components, including methane, in the exhaust gas. A methane oxidation catalyst apparatus in which the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

2. The methane oxidation catalyst apparatus according to claim 1, wherein all of the methane oxidation catalysts have the active metal.

3. The methane oxidation catalyst apparatus comprises a plurality of the methane oxidation catalysts, The methane oxidation catalyst, which is positioned upstream in the flow direction of the exhaust gas, has the active metal, The methane oxidation catalyst apparatus according to claim 1, wherein the methane oxidation catalyst disposed downstream in the flow direction of the exhaust gas does not have the active metal.

4. The methane oxidation catalyst apparatus according to claim 1, wherein the content of the active metal per unit area of ​​the methane oxidation catalyst decreases in stages from the upstream side to the downstream side in the flow direction of the exhaust gas.

5. The exhaust gas flow direction is provided with a plurality of methane oxidation catalyst units, Each of the plurality of methane oxidation catalyst units has the methane oxidation catalyst, The methane oxidation catalyst apparatus according to any one of claims 1 to 4, wherein the content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit is substantially uniform in the direction of the exhaust gas flow.

6. The methane oxidation catalyst apparatus according to claim 5, wherein, in the methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the amount of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the upstream side in the direction of exhaust gas flow is greater than the amount of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the downstream side in the direction of exhaust gas flow.

7. The methane oxidation catalyst has a substrate, The activated metal is supported on the substrate, The methane oxidation catalyst apparatus according to claim 5, wherein the methane oxidation catalyst unit comprises a plurality of stacked methane oxidation catalysts.

Images