Exhaust gas purification catalyst system

Abstract

An exhaust gas purification catalyst system comprises an upstream side exhaust gas purification catalyst device and a downstream side exhaust gas purification catalyst device, wherein the upstream side exhaust gas purification catalyst device has an upstream side substrate and an upstream side catalyst coating layer on the upstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and the flat metal foil and / or corrugated metal foil of the upstream side substrate having openings, the downstream side exhaust gas purification catalyst device has a downstream side substrate and a downstream side catalyst coating layer on the downstream side substrate, the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and the flat metal foil and / or corrugated metal foil of the downstream side substrate having openings, and a gap is present between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device.

Description

EXHAUST GAS PURIFICATION CATALYST SYSTEM

[0001] The present invention relates to an exhaust gas purification catalyst system using a metal substrate.

[0002] Exhaust gas emitted from internal combustion engines such as automobile engines is released into the air after having been purified by exhaust gas purification catalyst devices. Exhaust gas purification catalyst devices are constructed, for example, with a honeycomb-shaped substrate and a catalyst coating layer formed on the substrate.

[0003] In an exhaust gas purification catalyst device for an internal combustion engine for a two-wheel vehicle, or for a generator or agricultural machinery, it is very common to employ an exhaust gas purification catalyst device using a metal base material (metal substrate) as the honeycomb substrate.

[0004] PTL 1, for example, discloses a metal carrier having multiple metal honeycomb bodies joined together via brazing materials in a metal casing, and teaches that the metal carrier has excellent long-term durability.

[0005] PTL 2 discloses, for a catalyst substrate having a plurality of exhaust gas flow paths, a first flow channel with the inlet end closed and the outlet end open, and a second flow channel, adjacent to the first flow channel, with both the inlet end and outlet end open, wherein communicating pores are formed in the walls separating the first flow channel and second flow channel. PTL 2 teaches that an exhaust gas purification catalyst using such a substrate has a turbulent exhaust gas flow and increased exhaust gas purification efficiency.

[0006] Japanese Unexamined Patent Publication HEI No. 8-131845Japanese Unexamined Patent Publication No. 2015-120134

[0007] Exhaust gas purification catalyst devices produced using conventionally known metal substrates, including both of the substrates disclosed in PTLs 1 and 2, are inadequate in terms of at least one of the properties of pressure loss, warm-up property and exhaust gas purification efficiency.

[0008] It is an object of the present invention to provide an exhaust gas purification catalyst system that employs a metal substrate and is superior in terms of all of the properties of pressure loss, warm-up property and exhaust gas purification efficiency.

[0009] The present invention is as follows.

[0010] <Aspect 1> An exhaust gas purification catalyst system comprising an upstream side exhaust gas purification catalyst device and a downstream side exhaust gas purification catalyst device, wherein: the upstream side exhaust gas purification catalyst device has an upstream side substrate and an upstream side catalyst coating layer on the upstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the upstream side substrate having openings, the downstream side exhaust gas purification catalyst device has a downstream side substrate and a downstream side catalyst coating layer on the downstream side substrate, the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the downstream side substrate having openings, and a gap is present between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device. <Aspect 2> The exhaust gas purification catalyst system according to aspect 1, wherein a ratio of the opening area of the upstream side substrate to a total area thereof is equal to or greater than a ratio of the opening area of the downstream side substrate to a total area thereof. <Aspect 3> The exhaust gas purification catalyst system according to aspect 1, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 5 mm or greater. <Aspect 4> The exhaust gas purification catalyst system according to aspect 3, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 150 mm or smaller. <Aspect 5> The exhaust gas purification catalyst system according to aspect 2, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 5 mm or greater. <Aspect 6> The exhaust gas purification catalyst system according to aspect 5, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 150 mm or smaller. <Aspect 7> The exhaust gas purification catalyst system according to any one of aspects 1 to 6, wherein the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device are loaded into an outer cylinder. <Aspect 8> A substrate set to be used in an exhaust gas purification catalyst system according to any one of aspects 1 to 6, wherein: the substrate set comprises an upstream side substrate and a downstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings, and the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings. <Aspect 9> An exhaust gas purification method which includes: disposing an exhaust gas purification catalyst system according to any one of aspects 1 to 6 in the exhaust system of an internal combustion engine so that the upstream side exhaust gas purification catalyst device is on the upstream side of the exhaust gas flow, and contacting it with exhaust gas emitted from the internal combustion engine. <Aspect 10> The exhaust gas purification method according to aspect 9, wherein the internal combustion engine is an engine of an automobile or automatic two-wheel vehicle.

[0011] The present invention provides an exhaust gas purification catalyst system that employs a metal substrate and is superior in terms of all of the properties of pressure loss, warm-up property and exhaust gas purification efficiency.

[0012] <Exhaust gas purification catalyst system> The exhaust gas purification catalyst system of the invention comprises an upstream side exhaust gas purification catalyst device and a downstream side exhaust gas purification catalyst device, wherein: the upstream side exhaust gas purification catalyst device has an upstream side substrate and an upstream side catalyst coating layer on the upstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the upstream side substrate having openings, the downstream side exhaust gas purification catalyst device has a downstream side substrate and a downstream side catalyst coating layer on the downstream side substrate, the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the downstream side substrate having openings, and a gap is present between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device.

[0013] The exhaust gas purification system of the invention has openings in both the upstream side substrate and downstream side substrate, and has a gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device. The exhaust gas purification system of the invention therefore provides at least the following advantages. (1) The presence of openings results in low heat capacity and facilitates warm-up, (2) the gaps between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device allow concentrated warm-up of the upstream side exhaust gas purification catalyst device without loss of heat from the exhaust gas into the downstream side exhaust gas purification catalyst device during cold periods, and (3) the openings create a turbulent exhaust gas flow, improving contact efficiency between the exhaust gas and the purifying active species in the catalyst coating layer, and thus exhibiting excellent exhaust gas purification performance with a smaller catalyst amount.

[0014] <Upstream side exhaust gas purification catalyst device> The upstream side exhaust gas purification catalyst device in the exhaust gas purification catalyst system of the invention: has an upstream side substrate and an upstream side catalyst coating layer on the upstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the upstream side substrate having openings.

[0015] (Upstream side substrate) The upstream side substrate is composed of a wound laminate of a flat metal foil and a corrugated metal foil, with either or both the flat metal foil and the corrugated metal foil having openings. Both the flat metal foil and the corrugated metal foil of the upstream side substrate may have openings.

[0016] - Flat metal foil - When the flat metal foil has openings, the opening shapes may be circular, elliptical, polygonal or amorphous, for example, or any combination of these shapes. The openings in the flat metal foil may all have the same shape, or openings with differing shapes may be present. The openings may be present uniformly through the entire surface of the flat metal foil, or they may be present in an uneven distribution.

[0017] The openings may be either present or absent at the edges of the flat metal foil. For example, the openings do not need to be present in a range of 1 mm or more, 3 mm or more, 5 mm or more or 10 mm or more and 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less or 10 mm or less, from the two end face outer edges when the rectangular metal foil is wound up. The openings may also be present, for example, up to the two edges parallel to the axis when the rectangular metal foil has been wound up.

[0018] The flat metal foil may be an expanded metal.

[0019] The circle-equivalent diameter of the openings may be 5.0 mm or greater, 7.5 mm or greater, 10.0 mm or greater or 12.5 mm or greater, and 20.0 mm or smaller, 17.5 mm or smaller, 15.0 mm or smaller or 12.5 mm or smaller, for example. If the circle-equivalent diameter of the openings of the flat metal foil is within this range it will be possible to create a suitable turbulent flow of exhaust gas passing through the upstream side substrate, helping to increase the probability of contact between the exhaust gas and upstream side catalyst coating layer and avoiding loss of strength of the upstream side substrate. The “circle-equivalent diameter” of a opening as referred to herein means the diameter of a circle with the same area as the area of the opening.

[0020] A ratio of the opening area of the flat metal foil to the total area thereof may be 10.0% or higher, 15.0% or higher, 20.0% or higher or 25.0% or higher, and 50.0% or lower, 45.0% or lower, 40.0% or lower, 35.0% or lower or 30.0% or lower. Hereinafter, the ratio of the opening area of the flat metal foil to the total area thereof is referred to as “the opening area ratio of the flat metal foil”. If the opening area ratio of the flat metal foil is within this range it will be possible to create a suitable turbulent flow of exhaust gas passing through the upstream side substrate, helping to ensure the non-opening area forming the upstream side catalyst coating layer, and to avoid loss of strength of the upstream side substrate. The opening area ratio of the metal foil mentioned herein is the percentage of the total area of the opening with respect to the total area of the metal foil (the area of the metal foil assuming no openings in the metal foil). When the edges of the metal foil have regions without openings, the area of those regions is also included in calculating the opening area ratio.

[0021] - Corrugated metal foil - The corrugated metal foil is a metal foil that has been processed to have corrugations. The wave pitch may be 2.0 mm to 5.0 mm, for example, and the wave depth may be 0.5 mm to 3.0 mm, for example. The wave pitch referred to herein means the distance between two adjacent wave crests, and the wave depth means the distance from a wave crest to a wave trough.

[0022] When the corrugated metal foil has openings, the opening shapes and opening distribution may be as described above for the flat sheet with openings. The openings of the corrugated metal foil also do not need to be present at the foil edges, similar to the flat metal foil.

[0023] The corrugated metal foil may be expanded metal processed by corrugation, for example.

[0024] The circle-equivalent diameter of the openings of the corrugated metal foil may be 1.0 mm or greater, 2.0 mm or greater, 3.0 mm or greater or 4.0 mm or greater, and 8.0 mm or smaller 6.0 mm or smaller, 5.5 mm or smaller or 5.0 mm or smaller, for example. If the circle-equivalent diameter of the openings of the corrugated metal foil is within this range it will be possible to create a suitable turbulent flow of exhaust gas passing through the upstream side substrate, helping to increase the probability of contact between the exhaust gas and upstream side catalyst coating layer and avoiding loss of strength of the upstream side substrate.

[0025] The circle-equivalent diameter of the openings of the corrugated metal foil may be smaller than the circle-equivalent diameter of the openings of the flat metal foil. If the circle-equivalent diameter of the openings of the corrugated metal foil is smaller than the circle-equivalent diameter of the openings of the flat metal foil, both low pressure loss and high exhaust gas purification performance will be exhibited. This is thought to be because large openings in the corrugated metal foil can cause reduction in pressure loss as well as reduction in exhaust gas purification performance, while large openings in the flat metal foil reduce the pressure loss without significantly reducing exhaust gas purification performance. Therefore if the circle-equivalent diameters of the openings of both metal foils are adjusted to this size relationship it is possible to obtain an exhaust gas purification catalyst device having excellent balance between pressure loss and exhaust gas purification performance. The circle-equivalent diameter of the openings of the corrugated metal foil may be 80% or smaller, 60% or smaller, 50% or smaller, 45% or smaller, 40% or smaller or 35% or smaller, and 10% or greater, 15% or greater, 20% or greater, 25% or greater or 30% or greater, for example, based on the circle-equivalent diameter of the openings of the flat metal foil.

[0026] A ratio of the opening area of the corrugated metal foil to the total area thereof may be 15.0% or greater, 20.0% or greater, 25.0% or greater or 30.0% or greater, and 60.0% or lower, 50.0% or lower, 40.0% or lower or 35.0% or lower, for example. Hereinafter, the ratio of the opening area of the corrugated metal foil to the total area thereof is referred to as “the opening area ratio of the corrugated metal foil”. If the opening area ratio is within this range it will be possible to create a suitable turbulent flow of exhaust gas passing through the upstream side substrate, helping to ensure the non-opening area that forms the upstream side catalyst coating layer, and to avoid loss of strength of the upstream side substrate.

[0027] The opening area ratio of the corrugated metal foil may be greater than the opening area ratio of the flat metal foil. The opening area ratio of the corrugated metal foil may be 105% or greater, 110% or greater or 115% or greater, and 150% or lower, 140% or lower, 130% or lower or 120% or lower, for example, based on the opening area ratio of the flat metal foil.

[0028] - Materials and thicknesses of metal foils - The exhaust gas purification catalyst system of the invention is expected to be installed in the exhaust system of an internal combustion engine and to directly contact with exhaust gas emitted from the internal combustion engine. Therefore the flat metal foil and corrugated metal foil composing the upstream side substrate of the exhaust gas purification catalyst system should have heat resistance to the temperature of exhaust gas emitted from an internal combustion engine. The flat metal foil and corrugated metal foil should also have workability to allow formation of the desired openings. It should also be stable against the different chemical species in exhaust gas.

[0029] From these viewpoints, the flat metal foil and corrugated metal foil may each be composed of stainless steel, for example. The stainless steel may be ferrite-based stainless steel or austenite-based stainless steel, for example.

[0030] The thicknesses of the flat metal foil and corrugated metal foil may each be 20 μm or larger, 40 μm or larger, 80 μm or larger or 100 μm or larger, and 500 μm or smaller, 300 μm or smaller, 200 μm or smaller, 100 μm or smaller or 80 μm or smaller, for example.

[0031] - Wound body - The upstream side substrate of the invention is composed of a wound laminate of the flat metal foil and the corrugated metal foil. The axis of the wound body may be parallel to the direction of corrugation of the corrugated sheet (the direction of the ridge lines, in which the corrugated sheet has no curvature). The manner of winding the wound body may be any desired manner such as helical, S-shaped or swirling, as viewed in the axial direction of the wound body.

[0032] In the upstream side substrate, a cell flow channel is formed in the gap between the corrugated form of the corrugated metal foil and the flat metal foil in the wound body, allowing exhaust gas to be distributed in the direction of corrugation of the corrugated foil. The number of cell flow channels in the upstream side substrate may be 50 / in2or greater, 80 / in2or greater, 100 / in2or greater, 150 / in2or greater, 200 / in2or greater or 300 / in2or greater, and 600 / in2or less, 400 / in2or less, 300 / in2or less, 200 / in2or less, or 150 / in2.

[0033] - Upstream side catalyst coating layer - The upstream side catalyst coating layer is present on the upstream side substrate. Specifically, the upstream side catalyst coating layer is formed on the respective surfaces of the flat metal foil and corrugated metal foil composing the upstream side substrate, in a manner protruding to the cell flow channel side. The opening sections of the flat metal foil and corrugated metal foil composing the upstream side substrate do not need to have the upstream side catalyst coating layer.

[0034] The upstream side catalyst coating layer may have a construction known in the field of exhaust gas purification catalyst devices. The upstream side catalyst coating layer may also include inorganic oxide particles and precious metal catalyst particles, as well as other optional components as desired.

[0035] The inorganic oxide particles may be particles of a rare earth oxide other than alumina, zirconia, silica, titania, ceria or ceria, or of a complex oxide comprising more than one of these, selecting one or more types for use. The precious metal catalyst may be a platinum group metal, for example, and specifically platinum, palladium or rhodium, using any one or more selected from among these. The precious metal catalyst may be supported on one or more inorganic oxide particles, as microparticles.

[0036] The coating amount of the upstream side catalyst coating layer and the amount of precious metal catalyst may be set as appropriate by a person skilled in the art in consideration of the purpose of use and the desired purification performance for the exhaust gas purification catalyst system. The coating amount for the upstream side catalyst coating layer may be 50 g / L or greater and 250 g / L or less, for example, as the mass of the upstream side catalyst coating layer per unit capacity of the upstream side substrate. The precious metal catalyst amount may be 0.1 g / L or greater and 5.0 g / L or less, for example, as the total metal equivalent mass of the precious metal catalyst per unit capacity of the upstream side substrate.

[0037] - Length of upstream side exhaust gas purification catalyst device - The length of the upstream side exhaust gas purification catalyst device (the length in the direction of exhaust gas flow) may be appropriately set by a person skilled in the art in consideration of the purpose of use of the exhaust gas purification catalyst system of the invention.

[0038] An embodiment of the exhaust gas purification catalyst system of the invention wherein the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device are loaded together into a single outer cylinder is advantageous as it allows handling in the same manner as a single exhaust gas purification catalyst device. In this case the length of the exhaust gas purification catalyst system may be set to be about the same as any existing exhaust gas purification catalyst device, allowing an existing exhaust gas purification catalyst device to be replaced by the exhaust gas purification catalyst system of the invention.

[0039] Considering such a possible application, the length of the upstream side exhaust gas purification catalyst device may be 30 mm or larger, 40 mm or larger, 50 mm or larger, 60 mm or larger, 80 mm or larger or 100 mm or larger, and 150 mm or smaller, 120 mm or smaller, 100 mm or smaller, 80 mm or smaller, 70 mm or smaller or 60 mm or smaller.

[0040] <Downstream side exhaust gas purification catalyst device> The downstream side exhaust gas purification catalyst device in the exhaust gas purification catalyst system of the invention: has a downstream side substrate and a downstream side catalyst coating layer on the downstream side substrate, the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the downstream side substrate having openings.

[0041] As regards the conditions for: the flat metal foil and corrugated metal foil composing the downstream side substrate of the downstream side exhaust gas purification catalyst device, the openings of the metal foils, the wound laminate of the flat metal foil and the corrugated metal foil composing the downstream side substrate, and the downstream side catalyst coating layer, as well as the length of the downstream side exhaust gas purification catalyst device, the same conditions may be applied as described above for the upstream side exhaust gas purification catalyst device.

[0042] The flat metal foil and corrugated metal foil of the downstream side exhaust gas purification catalyst device, their openings, the construction of the laminate wound body and the downstream side catalyst coating layer may each be the same as or different from the corresponding parts of the upstream side exhaust gas purification catalyst device.

[0043] <Open area ratio of upstream side substrate and downstream side substrate> A ratio of the opening area of the upstream side substrate to the total area thereof in the exhaust gas purification catalyst system of the invention may be equal to or greater than a ratio of the opening area of the downstream side substrate to the total area thereof. Hereinafter, the ratio of the opening area of the upstream side substrate to the total area thereof is referred to as “the opening area ratio of the upstream side substrate” and the ratio of the opening area of the downstream side substrate to the total area thereof is referred to as “the opening area ratio of the downstream side substrate”. The opening area ratio of the upstream side substrate may be the same as, or a larger value than, the opening area ratio of the downstream side substrate.

[0044] With this aspect it is possible to effectively reduce the heat capacity of the upstream side substrate while maintaining the effect of creating a turbulent flow of exhaust gas flow provided by the openings, thereby allowing an exhaust gas purification catalyst system with an excellent warm-up property to be obtained.

[0045] For the present purpose, the opening area ratios of the upstream side substrate and the downstream side substrate are the respective percentages of the total area of openings of the flat metal foil and corrugated metal foil with respect to the total area of the flat metal foil and corrugated metal foil (the total area of each metal foil assuming no openings in the metal foil). When the edges of each metal foil have regions without openings, the areas of those regions are also included in calculating the opening area ratio.

[0046] The opening area ratio of the downstream side substrate may be 100% or lower, lower than 100%, 95% or lower, 90% or lower, 85% or lower, 80% or lower or 75% or lower, and 40% or higher, 50% or higher, 60% or higher, 70% or higher or 80% or higher, for example, with respect to the opening area ratio of the upstream side substrate. By setting the ratio of the opening area ratios of the substrates within this range it is possible to ensure the formation area of the downstream side catalyst coating layer while maintaining balance between creation of a turbulent exhaust gas flow and the warm-up property of the exhaust gas purification catalyst system, thereby allowing a high degree of exhaust gas purification performance to be exhibited.

[0047] <Gap between upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device> The exhaust gas purification catalyst system of the invention has a gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device. With the presence of a gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device, concentrated warm-up of the upstream side exhaust gas purification catalyst device is possible without loss of heat from the exhaust gas to the downstream side exhaust gas purification catalyst device, during cold periods such as engine start-up. The exhaust gas purification catalyst system of the invention therefore has an extremely high warm-up property during cold periods.

[0048] The gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is preferably large from the viewpoint of preventing dissipation of heat during cold periods, while it is preferably smaller from the viewpoint of warm-up of the downstream side exhaust gas purification catalyst device. From this viewpoint, the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device may be 5 mm or larger, 7 mm or larger, 10 mm or larger, 15 mm or larger, 20 mm or larger, 30 mm or larger, 40 mm or larger or 50 mm or larger, and 150 mm or smaller, 120 mm or smaller, 100 mm or smaller, 80 mm or smaller, 60 mm or smaller, 40 mm or smaller, 30 mm or smaller, 25 mm or smaller, 20 mm or smaller or 15 mm or smaller, for example.

[0049] <Outer cylinder> The upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device in the exhaust gas purification catalyst system of the invention may be loaded into an outer cylinder. The upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device loaded into the outer cylinder may each be anchored to the outer cylinder by appropriate means such as fusion welding (including arc welding and laser beam welding), pressure welding (including resistance welding and diffusion bonding), brazing and soldering (including induction heating brazing and laser brazing).

[0050] The upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device may each be loaded into separate outer cylinders, or they may be loaded together into a single outer cylinder. Loading the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device together into a single outer cylinder provides the advantage of allowing the entirety to be handled in the same manner as a single exhaust gas purification catalyst device.

[0051] The size of the outer cylinder may be set as appropriate by a person skilled in the art in a range allowing loading of the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device, without any substantial gap between each exhaust gas purification catalyst device and the inner surface of the outer cylinder.

[0052] When the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device are each loaded into separate outer cylinders, the length of the outer cylinder for the upstream side exhaust gas purification catalyst device and the length of the outer cylinder for the downstream side exhaust gas purification catalyst device may be substantially equal to the length of the exhaust gas purification catalyst device. The length of the outer cylinder in this case may be 30 mm or larger, 40 mm or larger, 50 mm or larger, 60 mm or larger, 80 mm or larger or 100 mm or larger, and 150 mm or smaller, 120 mm or smaller, 100 mm or smaller, 80 mm or smaller, 70 mm or smaller or 60 mm or smaller, for example, on both the upstream side and the downstream side.

[0053] When the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device are loaded together into a single outer cylinder, the length of the outer cylinder may be substantially equal to the length of the gap between the exhaust gas purification catalyst devices added to the total length of the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device. The length of the outer cylinder in this case may be appropriately set in a range of 65 mm or greater and 450 mm or smaller, for example.

[0054] If the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device are loaded together into a single outer cylinder and the length of the exhaust gas purification catalyst system (i.e. the length of the outer cylinder) is set to be about the same as any existing exhaust gas purification catalyst device, this will allow an existing exhaust gas purification catalyst device to be replaced by the exhaust gas purification catalyst system of the invention.

[0055] Considering such application, the length of the outer cylinder may be appropriately set within a range of 65 mm or greater and 200 mm or smaller, for example.

[0056] The outer cylinder should have heat resistance to withstand exhaust gas temperatures, suitable workability, and stability against chemical species in exhaust gas, similar to the upstream side and downstream side exhaust gas purification catalyst devices.

[0057] From these viewpoints, the outer cylinder may be composed of stainless steel, for example. The stainless steel may be ferrite-based stainless steel or austenite-based stainless steel, for example. The outer cylinder may be composed of the same material as the metal foil composing the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device, or it may be composed of a different material.

[0058] The thickness of the outer cylinder may be 0.5 mm or greater, 1.0 mm or greater or 1.2 mm or greater, and 5.0 mm or smaller, 3.0 mm or smaller, 2.0 mm or smaller or 1.5 mm or smaller, for example.

[0059] <Substrate set> A different aspect of the invention provides a substrate set to be used in the exhaust gas purification catalyst system of the invention described above.

[0060] The substrate set of the invention comprises an upstream side substrate and a downstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings, and the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings.

[0061] The substrate set of the invention may also be loaded into an outer cylinder.

[0062] The explanations for the respective parts for the exhaust gas purification catalyst system of the invention may be applied as appropriate for the upstream side substrate, downstream side substrate and outer cylinder of the substrate set of the invention as well.

[0063] <Exhaust gas purification method> Yet a different aspect of the invention provides an exhaust gas purification method using the exhaust gas purification catalyst system of the invention described above.

[0064] The exhaust gas purification method of the invention is an exhaust gas purification method that includes: disposing the exhaust gas purification catalyst system of the invention in the exhaust system of an internal combustion engine so that the upstream side exhaust gas purification catalyst device is on the upstream side of the exhaust gas flow, and contacting it with exhaust gas emitted from the internal combustion engine.

[0065] The internal combustion engine may be an automobile engine, automatic two-wheel vehicle engine or general purpose engine, for example, and especially an automobile or automatic two-wheel vehicle engine.

[0066] <Example 1> (1) Production of upstream side exhaust gas purification catalyst device A flat sheet with openings and a corrugated sheet with openings were stacked and wound to a size with a diameter of 73.3 mm (cross-sectional area: 4,220 mm2), a length of 60 mm and an apparent volume of 253 mL, and inserted into a stainless steel outer cylinder having an outer diameter of 76.3 mm and a wall thickness of 1.5 mm, anchoring them by brazing, to fabricate an upstream side substrate having 400 cell / inch2. The flat and corrugated sheets used were both 50 μm-thick SUS sheets. The opening diameters of the flat sheet were 13.0 mm, and the diameters of the corrugated sheet were 4.5 mm. The opening area ratio of the flat sheet was 26.0%, the opening area ratio of the corrugated sheet was 34.2%, and the average opening area ratio for the flat sheet and corrugated sheet was 30.9%.

[0067] An upstream side catalyst coating layer forming coating solution containing alumina particles, ceria-zirconia complex oxide particles (40 mass% ceria content), and a Pt precursor compound and Rh precursor compound was coated onto the obtained upstream side substrate and fired to form an upstream side catalyst coating layer, thus obtaining an upstream side exhaust gas purification catalyst device.

[0068] The coating amount of the upstream side catalyst coating layer on the upstream side exhaust gas purification catalyst device was 110 g / L, the Pt content was 0.5 g / L and the Rh content was 0.3 g / L.

[0069] (2) Production of downstream side exhaust gas purification catalyst device For the downstream side exhaust gas purification catalyst device, the upstream side catalyst coating layer forming coating solution was directly used as a downstream side catalyst coating layer forming coating solution for production in the same manner as for the upstream side exhaust gas purification catalyst device.

[0070] (3) Production of exhaust gas purification catalyst system The obtained upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device were loaded into a SUS outer cylinder to produce an exhaust gas purification catalyst system. A gap of 10 mm was formed between the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device.

[0071] (4) Evaluation of exhaust gas purification catalyst system i) Pressure loss evaluation Pressure gauges were attached to both the upstream side (gas entrance side) and downstream side (gas exit side) of the exhaust gas purification system, and the difference in upstream side pressure and downstream side pressure was measured while flowing air from the upstream side at a space velocity SV of 100,000 (1 / h), using the obtained value as the pressure loss.

[0072] ii) Warm-up property test (bench evaluation) A switchable branch was provided in an exhaust system with a gasoline engine having a cylinder capacity of 2.4 L. The exhaust gas purification catalyst system was installed in one branch, while the other branch was left open. The exhaust gas purification catalyst system was heated with a heater to a temperature of 50℃.

[0073] The engine was started with branch switching to the open side, and operated under stoichiometric conditions with an engine rotational speed of 2,500 rpm and an air intake of 22.5 g / sec. When the exhaust gas temperature reached 530℃, branching was switched to the engine side. Operation of the engine was continued under stoichiometric conditions, and the time required to reach a 50% purification rate for CO, total hydrocarbons (THC) and NOx in the exhaust gas after branch switching was measured.

[0074] iii) Vehicle evaluation for THC emission The obtained exhaust gas purification catalyst system was mounted in the exhaust system of an automatic two-wheel vehicle with an 845 cc cylinder gasoline engine, and the vehicle was driven on a chassis dynamometer in WMTC mode, class 3-2 to examine the total hydrocarbon (THC) emission.

[0075] <Comparative Example 1> (1) Production of upstream side exhaust gas purification catalyst device An upstream side exhaust gas purification catalyst device was produced in the same manner as Example 1.

[0076] (2) Production of downstream side exhaust gas purification catalyst device A downstream side substrate was produced in the same manner as the upstream side exhaust gas purification catalyst device, except that 50 μm-thick SUS flat and corrugated sheets without openings were used.

[0077] A downstream side catalyst coating layer forming coating solution having the same composition as the upstream side catalyst coating layer forming coating solution, except for changing the amounts of the Pt precursor compound and Rh precursor compound, was coated onto the obtained downstream side substrate and fired to form a downstream side catalyst coating layer, thus obtaining a downstream side exhaust gas purification catalyst device.

[0078] The coating amount of the downstream side catalyst coating layer on the downstream side exhaust gas purification catalyst device was 160 g / L, the Pt content was 0.5 g / L and the Rh content was 0.3 g / L. The Pt and Rh contents are each shown in terms of metal equivalent mass.

[0079] <Comparative Example 2> An exhaust gas purification catalyst system was produced and evaluated in the same manner as Example 1, except that for the upstream side substrate there was used a stacked wound body comprising a flat sheet without openings and a corrugated sheet with openings, similar to the downstream side substrate, and the coating amount of the upstream side catalyst coating layer, the Pt content and the Rh content of the upstream side exhaust gas purification catalyst device were each changed in the same manner as for the downstream side exhaust gas purification catalyst device.

[0080] The results are summarized in Table 1 and Table 2.

[0081]

[0082]

[0083] From Table 1 and Table 2 it was confirmed that the exhaust gas purification catalyst system of Example 1, which used a wound stack comprising a flat sheet with openings and a corrugated sheet with openings as the upstream side substrate and downstream side substrate, exhibited overall more excellent properties such as pressure loss, warm-up property and THC emission (actual vehicle evaluation), compared to the exhaust gas purification catalyst system of Comparative Example 1 where the downstream side substrate did not have openings and the exhaust gas purification catalyst system of Comparative Example 2 where both the upstream side substrate and downstream side substrate did not have openings. The exhaust gas purification catalyst system of Example 1 was especially superior in terms of THC emission (actual vehicle evaluation), indicating its suitability for practical use.

[0084] <Reference Examples 1 to 6> In Reference Examples 1 to 6, the effect of the gap size between the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device on exhaust gas purification performance was examined.

[0085] (1) Production of upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device The upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device both used a wound stack of a flat sheet and corrugated sheet without openings as the substrate. An upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device were produced, providing a catalyst coating layer having the same construction as the downstream side catalyst coating layer of the downstream side exhaust gas purification catalyst device of Example 1, except that the coating amount, Pt content and Rh content on the substrates were changed as shown below. Coating amount: 110 g / L Pt content: 1.0 g / L Rh content: 0.3 g / L

[0086] (2) Production of exhaust gas purification catalyst system The obtained upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device were loaded into a SUS outer cylinder to produce an exhaust gas purification catalyst system. The gap as shown in Table 3 was formed between each upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device. For Reference Example 1, no gap was formed between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device, so that they were loaded into the outer cylinder in mutual contact.

[0087] (3) Evaluation of exhaust gas purification catalyst system The obtained exhaust gas purification catalyst system was mounted in the exhaust system of an automatic two-wheel vehicle (scooter) with a 125 cc cylinder 4-stroke gasoline engine, and the vehicle was driven on a chassis dynamometer in ECE-40 mode to examine the CO, HC and NOx purification rate.

[0088] The results are shown in Table 3.

[0089]

[0090] As seen in Table 3, it was confirmed that the exhaust gas purification catalyst systems of Reference Examples 2 to 6 having gaps between the devices exhibited comprehensively superior exhaust gas purification performance compared to the exhaust gas purification catalyst system of Reference Example 1 which did not have a gap between the upstream side exhaust gas purification catalyst device and downstream side exhaust gas purification catalyst device.

Claims

1. An exhaust gas purification catalyst system comprising an upstream side exhaust gas purification catalyst device and a downstream side exhaust gas purification catalyst device, wherein: the upstream side exhaust gas purification catalyst device has an upstream side substrate and an upstream side catalyst coating layer on the upstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the upstream side substrate having openings, the downstream side exhaust gas purification catalyst device has a downstream side substrate and a downstream side catalyst coating layer on the downstream side substrate, the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, and either or both the flat metal foil and corrugated metal foil composing the downstream side substrate having openings, and a gap is present between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device.

2. The exhaust gas purification catalyst system according to claim 1, wherein a ratio of the opening area of the upstream side substrate to a total area thereof is equal to or greater than a ratio of the opening area of the downstream side substrate to a total area thereof.

3. The exhaust gas purification catalyst system according to claim 1, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 5 mm or greater.

4. The exhaust gas purification catalyst system according to claim 3, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 150 mm or smaller.

5. The exhaust gas purification catalyst system according to claim 2, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 5 mm or greater.

6. The exhaust gas purification catalyst system according to claim 5, wherein the gap between the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device is 150 mm or smaller.

7. The exhaust gas purification catalyst system according to any one of claims 1 to 6, wherein the upstream side exhaust gas purification catalyst device and the downstream side exhaust gas purification catalyst device are loaded into an outer cylinder.

8. A substrate set to be used in an exhaust gas purification catalyst system according to any one of claims 1 to 6, wherein: the substrate set comprises an upstream side substrate and a downstream side substrate, the upstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings, and the downstream side substrate being composed of a wound laminate of a flat metal foil and a corrugated metal foil, either or both the flat metal foil and corrugated metal foil having openings.

9. An exhaust gas purification method which includes: disposing an exhaust gas purification catalyst system according to any one of claims 1 to 6 in the exhaust system of an internal combustion engine so that the upstream side exhaust gas purification catalyst device is on the upstream side of the exhaust gas flow, and contacting it with exhaust gas emitted from the internal combustion engine.

10. The exhaust gas purification method according to claim 9, wherein the internal combustion engine is an engine of an automobile or automatic two-wheel vehicle.