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    • 专利摘要:
    EXHAUST GAS PURIFICATION CATALYST. The present invention relates to an exhaust gas purification catalyst which is provided with a substrate 10 and a catalyst coating layer 30 which is formed on the surface of the substrate 10. The catalyst coating layer 30 is formed in a structure in layers having upper and lower layers, with a lower layer 50 which is closer to the surface of the substrate 10 and an upper layer 40 which is relatively farther from it. The catalyst coating layer 30 is provided with Rh and Pd as precious metal catalysts and is provided with an OSC material that has an oxygen storage capacity as a support. Rh is disposed in the upper layer 40 of the catalyst coating layer 30, and the Pd is disposed in both the upper layer 40 and the lower layer 50 of the catalyst coating layer 30. At least a portion of the Pd in the upper layer 40 and the bottom layer 50 is supported on the OSC material. The mass ratio between the Pd disposed in the upper layer 40 and the Pd disposed in the lower layer 50 is not greater than 0.4.
    公开号:BR112014016151B1
    申请号:R112014016151-8
    申请日:2012-12-26
    公开日:2020-12-22
    发明作者:Yuki Aoki
    申请人:Toyota Jidosha Kabushiki Kaisha；
    IPC主号:
    专利说明:

    [001] The present invention relates to an exhaust gas purification catalyst that purifies the exhaust gas discharged from an internal combustion engine.
    [002] This international application claims priority to Japanese patent application number 2011-288798, filed on December 28, 2011, all contents of which are incorporated in this document for reference.
    [003] Three-way catalysts containing at least one precious metal selected from platinum (Pt), palladium (Pd), and rhodium (Rh) are often used to purify exhaust gas discharged from an engine internal combustion engine, such as a car engine (Patent Literature 1 to 3). In a typical three-way catalyst structure, a catalyst coating layer made of alumina is formed on the surface of a highly heat resistant ceramic substrate and at least one precious metal selected from Pd, Pt, and Rh is supported in that layer of catalyst coating. Of these precious metals, Pd and Pt mainly contribute with a purification capacity (oxidative purification capacity) for carbon monoxide (CO) and hydrocarbon (HC) and Rh contribute mainly with a purification capacity (reducing purification capacity) for NOx. As a result, the harmful components in the exhaust gas can be efficiently purified at once using Rh in combination with Pd or Pt.
    [004] In order to efficiently purify the components mentioned above in the exhaust gas using such a three-way catalyst, that is, in order to convert these components through oxidation or reduction to H2O, CO2, or N2, the ratio between air / fuel, which is the mixing ratio between air and gasoline fed to the engine, should be close to the theoretical air / fuel ratio (stoichiometric). A complex cerium-zirconia oxide was widely used as the support for these precious metals, in order to smooth the changes in the atmosphere from the air / fuel ratio in which the catalyst can operate effectively. This complex cerium-zirconia oxide works to store oxygen in the exhaust gas when the air / fuel to exhaust gas ratio is poor (that is, an excess oxygen atmosphere) and to release stored oxygen when the ratio between air / fuel for the exhaust gas is rich (ie an atmosphere of excess fuel). As a consequence, a stable catalyst performance is achieved even when the oxygen concentration in the exhaust gas varies and the catalyst purification performance is improved.
    [005] In order to increase the purification performance even more, exhaust gas purification catalysts have been proposed in recent years in which the catalyst coating layer has a two-layer structure and the Pd and Rh are supported in a way separate. All precious metal catalyst is not supported on a single support layer and the catalyst coating layer is formed in a layered structure that has at least two layers, that is, an upper layer and a lower layer. A support that has a good affinity for Rh and a support that has a good affinity for Pd can be selected by supporting the Pd with this separate in one layer and supporting Rh with this separate in another layer. For example, ZrO2 is preferred as a support for Rh. Patent Literature 1 describes an exhaust gas purification catalyst that has a two-layer structure formed by an upper layer in which Rh is supported on ZrO2 and a lower layer in which Pd is supported on a complex CeO2-ZrO2 oxide . PTL Citation List 1: Japanese patent application number 2011 -183317 PTL 2: Japanese patent publication number 4751916 PTL 3: Japanese patent application number 2010-005591
    [006] In exhaust gas purification catalysts that have a two-layer top / bottom layer structure, as noted above, ZrO2 is preferred as the support for Rh in the top layer and a complex CeO2-ZrO2 oxide, which has an oxygen storage capacity (OSC), is preferred as the support for Pd in the lower layer, however, Rh in the upper layer is, in some cases, supported in a complex CeO2-ZrO2 oxide when a higher OSC is required. However, the catalytic activity of Rh in CeO2 is not as high as that of Rh in ZrO2, and this raises the concern that Rh supported on a complex CeO2-ZrO2 oxide may not be able to develop the desired NOx purification capacity . In addition, the development of low precious metal exhaust gas purification catalysts, which use a lower amount of precious metal catalyst, is underway in recent years in order to reduce production costs and create a supply situation of stable material. These low precious metal exhaust gas purification catalysts, however, have a low precious metal content, which mediates oxygen absorption and, as a consequence, the oxygen absorption efficiency in the OSC support ends up being substantially reduced. A technology that can efficiently improve the OSC of the catalyst as a whole is also desired in order to compensate for the decline in CSO caused by this reduction in precious metal content. Summary of the Invention
    [007] The present invention was made in view of these circumstances and, with respect to an exhaust gas purification catalyst equipped with a layer of layered catalyst type catalyst, its main objective is the introduction of a catalyst exhaust gas purification for which the OSC of the catalyst as a whole is effectively increased while a high NOx purification capacity is maintained.
    [008] In relation to an exhaust gas purification catalyst that has a layer of layered structure-type catalyst coating in which the Pd supported in an OSC material is disposed in the lower layer and Rh is disposed in the upper layer, the inventor concluded that the OSC of the catalyst as a whole can be improved by transferring a portion of the Pd disposed in the lower layer to the upper layer, and found that the OSC of the catalyst as a whole can be effectively improved, without reducing the capacity of purification of Rh NOx in the upper layer, by carefully defining the mass ratio between the Pd in the upper layer and the Pd in the lower layer. The present invention was made based on this discovery.
    [009] Thus, the exhaust gas purification catalyst provided by the present invention is an exhaust gas purification catalyst that has a substrate and a catalyst coating layer formed on a surface of that substrate. This catalyst coating layer is formed into a layered structure that has upper and lower layers with the lower layer being closer to the substrate surface and the upper layer being relatively farther away from that surface. This catalyst coating layer is equipped with Rh and Pd as precious metal catalysts. The catalyst coating layer is also provided with an OSC material that has an oxygen storage capacity as a support. Rh is disposed in the upper layer of the catalyst coating layer, and Pd is disposed in both the upper and lower layer of the catalyst coating layer. At least a portion of this Pd in the top layer and the bottom layer is supported on the OSC material. The mass ratio between the Pd disposed in the upper layer and the Pd disposed in the lower layer is not greater than 0.4 (and is typically 0.01 to 0.4 and preferably 0.06 to 0.32) .
    [010] The Pd supported on an OSC material is disposed in both the upper and lower layers in the exhaust gas purification catalyst structured in this way. Having this Pd supported in an OSC material not only in the lower layer, but also in the upper layer, where the exhaust gas diffuses easily, a greater opportunity for contact between the OSC material and the exhaust gas is provided in comparison to a conventional catalyst coating layer in which the Pd is disposed only in the lower layer. This makes it possible to bring about a better improvement in the OSC of the catalyst as a whole.
    [011] The mass ratio x of the Pd in the upper layer and the lower layer (upper layer / lower layer) preferentially satisfies [Mat. 1] 0.01 <x in the exhaust gas purification catalyst described in this document and most preferably satisfies [Mat. 2] 0.06 <x, satisfies even more preferably [Mat. 3] 0.15 <x, and satisfies particularly preferentially [Mat. 4] 0.2 <x.
    [012] When, on the other hand, this mass ratio between x and Pd is very large, the Rh and Pd in the upper layer react and bond with each other at elevated temperatures, which increases the concern that the purification capacity of NOx of Rh is reduced and, therefore, is disadvantaged. Generally x <0.4 from the point of view of inhibiting the bond between Rh and Pd, and, for example, Pd is desirably arranged in both the upper and lower layers in a mass ratio between x and Pd that provides [Mat. 6] 0.01 <x <0.4 (preferably, [Mat. 7] 0.06 <x <0.32).
    [013] In doing so, the OSC of the catalyst as a whole can be more effectively increased while a higher NOx purification capacity can be maintained by Rh in the upper layer than for a conventional exhaust gas purification catalyst in that Pd is disposed only in the lower layer or where the mass ratio between x and Pd does not satisfy the range indicated above. In this way, in comparison to conventional catalysts, the present invention can provide an optimum exhaust gas purification catalyst that exhibits excellent purification capacity, and in which the NOx purification capacity and OSC are improved in a well-balanced manner .
    [014] In a preferred aspect of the exhaust gas purification catalyst described in this document, the OSC material that supports at least a portion of the Pd in the upper and lower layers is made of CeO2 or a complex oxide of CeO2- ZrO2. CeO2 and CeO2-ZrO2 complex oxides have a high OSC and are well suited as the OSC material used in the exhaust gas purification catalyst described in this document.
    [015] In a preferred aspect of the exhaust gas purification catalyst described in this document, the support that supports Rh in the upper layer is made of a complex oxide ZrO2 containing Y2O3. A high purification capacity of NOx can be exhibited by supporting Rh in ZrO2. In addition, the heat resistance of ZrO2 can be improved and a durable exhaust gas purification catalyst can be obtained by adding Y2O3 to ZrO2.
    [016] In a preferred aspect of the exhaust gas purification catalyst described in this document, the mass ratio between Rh and Pd arranged in the upper layer is 1.25 to 5. This construction provides a favorable balance for the ratio between Rh and Pd in the upper layer, and because of that, an improved CSO can be reliably displayed while the connection between Rh and Pd is inhibited. Brief Description of Drawings
    [017] Figure 1 is a diagram showing schematically an exhaust gas purification catalyst according to an embodiment of the present invention.
    [018] Figure 2 is a diagram showing schematically the structure of the rib wall region in an exhaust gas purification catalyst, according to an embodiment of the present invention.
    [019] Figure 3 is a diagram showing schematically the structure of the rib wall region in an exhaust gas purification catalyst, according to an embodiment of the present invention.
    [020] Figure 4 is a graph showing the relationship between the Pd mass ratio (upper layer / lower layer) and the average amount of oxygen storage.
    [021] Figure 5 is a graph showing the relationship between the mass ratio of Pd (upper layer / lower layer) and the amount of NOx emission. Description of Modalities
    [022] The preferred embodiments of the present invention are described below based on the Figures. The questions required for the execution of the present invention, however, not included in the questions particularly described in that Description (for example, general items, such as those that refer to the disposition of the exhaust gas purification catalyst in an automobile), can be understood as design issues for the individual versed in the technique based on the conventional technique of the relevant field. The present invention can be implemented on the basis of the contents described in that description and knowledge of the common general technique in the relevant field. In the following description, an exhaust gas for a poor, stoichiometric or rich air / fuel ratio denotes an exhaust gas that has the same air / fuel ratio as the air / fuel ratio of the exhaust gas discharged from an internal combustion engine when a poor, stoichiometric or rich mixed gas, respectively, is burned in the internal combustion engine, or indicates an exhaust gas provided by the post-injection of hydrocarbon into an exhaust gas that has the same air / fuel ratio that the air / fuel ratio of the exhaust gas discharged from an internal combustion engine when a poor, stoichiometric or rich mixed gas, respectively, is burned in the internal combustion engine.
    [023] The exhaust gas purification catalyst described in this document comprises a substrate, a layer of catalyst coating comprising a porous support formed on the surface of the substrate, and a precious metal catalyst supported on the porous support of the catalyst coating, when that catalyst coating layer is formed into a layered structure.
    [024] Figure 1 is a schematic diagram of a typical example of an exhaust gas purification catalyst. The exhaust gas purification catalyst 100, according to this embodiment, has a honeycomb-shaped substrate 10 that has a plurality of regularly arranged cells 12 and that has rib walls 14 that form these cells 12. In this Description, "per liter of substrate volume" indicates per liter of the mass volume of the entire article including the volume of cell passages in the volume of the substrate itself. The use of (g / L) in the description below indicates the amount present in 1 liter of the volume of the substrate.
    [025] The various materials and formats used so far in this type of service can be used for the substrate that constitutes the exhaust gas purification catalyst described in this document. For example, a honeycomb substrate with a honeycomb structure formed from a ceramic, for example, cordierite, silicon carbide (SiC), and so on, or an alloy (for example, stainless steel, and so on) can be used properly. An example here is a honeycomb-shaped substrate that has an external cylindrical shape; that it is provided, along the direction of the geometric axis of that cylinder, with through holes (cells) that function as exhaust gas passages; and that make it possible to contact via the exhaust gas with the partitions (rib walls) that delineate the individual cells. In addition to a honeycomb configuration, the substrate may have, for example, a foam configuration or a pellet configuration. In addition to a cylindrical shape, an elliptical tube shape or a polyhedral tube shape can be used for the external shape of the substrate as a whole. <The catalyst coating layer>
    [026] Figure 2 is a diagram showing schematically the structure of the surface region of the rib wall 14 in the honeycomb substrate 10 of Figure 1. The rib wall 14 is provided with a substrate 10 and, formed and its surface, a layer of catalyst coating 30 having a two-layer structure. This two-layer catalyst coating layer 30 is formed into a layered structure having upper and lower layers where the lower layer 50 is closer to the surface of the substrate 10 and the upper layer 40 is relatively farther away from it. In the technique described in this document, the catalyst coating layer 30 is provided with Rh and Pd as precious metal catalysts. The catalyst coating layer 30 is also provided with an OSC material that has an oxygen storage capacity as a support. Rh is disposed in the upper layer 40 of the catalyst coating layer 30 and the Pd is disposed in both the upper layer 40 and the lower layer 50 of the catalyst coating layer 30. At least a portion of the Pd in the upper layer 40 and in the lower layer 50 is supported on the OSC material.
    [027] In the catalyst coating layer 30 provided by the present invention, the Pd supported on an OSC material is disposed not only in the lower layer 50, but also in the upper layer 40, where the exhaust gas easily diffuses. In doing so, a greater opportunity for contact between the OSC material and the exhaust gas is provided compared to a conventional catalyst coating layer in which the Pd is disposed only in the lower layer 50. This makes better improvement possible in the OSC of the catalyst as a whole. The mass x ratio between the Pd disposed in the upper layer 40 and the Pd disposed in the lower layer 50 (upper layer / lower layer) preferably satisfies [Mat. 8] 0.01 <x, most preferably satisfies [Mat. 9] 0.06 <x, satisfies even more preferably [Mat. 10] 0.15 <x, and satisfies particularly preferably 0.2 <x
    [028] The increase described above in the OSC is inadequate when the mass ratio of Pd (upper layer / lower layer) is very small.
    [029] When, on the other hand, this mass ratio of Pd (upper layer / lower layer) x is very large, the Rh and Pd in the upper layer 40 may undergo a partial reaction and bond with each other at elevated temperatures, resulting in a decline in Rh's NOx purification capacity and is therefore disadvantaged. Observed from the perspective of preventing the connection between Rh and Pd, preferably [Mat. 12] x <0.4 is satisfied (for example, [Mat. 13] x <0.32 and particularly [Mat. 14] x <0.25.
    [030] For example, a catalyst coating layer 30 that has a value of at least 0.06, but no more than 0.32 (particularly at least 0.15 but no more than 0.3) for that mass ratio Pd (top layer / bottom layer) is well suited in terms of obtaining both an increase in OSC and an inhibition of the bond between Rh and Pd. <The bottom layer>
    [031] The bottom layer 50 that constitutes the catalyst coating layer described in this document 30 is provided with a support and a precious metal catalyst that contains at least Pd and is supported on the support. Pd mainly purifies HC and CO in the exhaust gas. <The support in the bottom layer>
    [032] The support that supports the Pd in the lower layer 50 contains an OSC material that has an oxygen storage capacity. This OSC material works to capture and store oxygen in the exhaust gas when the air / fuel-to-exhaust gas ratio is poor (that is, an excess oxygen atmosphere) and to release stored oxygen when the ratio between air / fuel and the exhaust gas is rich (that is, an excess fuel atmosphere). This OSC material can be exemplified by cerium oxide (cerium: CeO2) and complex cerium-containing oxides (for example, cerium-zirconia complex oxide (CeO2-ZrO2 complex oxide)). Variations in oxygen concentration in the lower layer are attenuated and a stable catalyst function is achieved using CeO2 or CeO2-ZrO2 complex oxide as the support for Pd in the lower layer. A better catalyst function can be reliably performed as a result.
    [033] The use of CeO2-ZrO2 complex oxide is preferred among the OSC materials mentioned above. By producing the solid solution of ZrO2 in CeO2, grain growth by CeO2 can be inhibited and the decline in post-aging of OSC can be inhibited. The mixing ratio between CeO2 and ZrO2 in the complex oxide of CeO2ZrO2 can be CeO2 / ZrO2 = 0.25 to 0.75 (preferably 0.3 to 0.6 and more preferably about 0.5). High catalytic activity and oxygen storage capacity (OSC) can be performed in the lower layer containing Pd 50 by bringing CeO2 / ZrO2 to the indicated range.
    [034] This CeO2-ZrO2 complex oxide may be a CeO2ZrO2 complex oxide in which another compound (typically, an inorganic oxide) is mixed as an auxiliary component. For example, a rare earth element, such as lanthanum, an alkaline earth element such as calcium, or a transition metal element can be used for that compound. Among these, a rare earth element such as lanthanum is preferably used as a stabilizer from the point of view of causing an increase in the specific surface area at elevated temperatures without poisoning the catalytic function. For example, a rare earth oxide such as La2O3, Y2O3, or Pr6O11 can be mixed for the purpose of, for example, preventing sintering. This rare earth oxide can be physically mixed as an independent oxide in the support powder or it can be made into a complex oxide component. The content (mass ratio) of the auxiliary component is preferably 2% to 30% (for example, 3% to 6%) of the support as a whole. The effect, for example, of a sintering inhibition, and so on, is reduced when the content of the auxiliary component is very low. When the content of the auxiliary component is very high, the amounts of ZrO2 and CeO2 in the support undergo a relative decline and the resistance to heat and OSC can be reduced.
    [035] The support that supports the Pd in the lower layer described in this document 50 can contain a support material different from an OSC material, that is, a non-OSC material. A highly heat-resistant porous metal oxide is preferably used for this non-OSC material. Examples here are aluminum oxide (alumina: Al2O3), zirconium oxide (zirconia: ZrO2), and so on, where the use of Al2O3 is preferred. Al2O3 has a smaller specific surface area and higher durability (particularly heat resistance) than the complex CeO2-ZrO2 oxide. As a consequence, the Pd support in Al2O3 can improve the thermal stability of the support as a whole and can result in the optimal amount of Pd being supported in the support as a whole. Al2O3 and CeO2-ZrO2 complex oxide are preferably mixed in a mass mixing ratio (Al2O3: CeO2-ZrO2) in the range of 80:20 to 20:80. Using this composition, the ratio between Al2O3 and CeO2-ZrO2 complex oxide occurs in an appropriate balance and the effect due to the mixture of Al2O3 and CeO2-ZrO2 complex oxide (this effect is, for example, the ability to combine the the oxygen absorption, storage and release capacity possessed by the complex oxide CeO2-ZrO2 with the large specific surface area and high durability possessed by Al2O3) can then be even more favorably exhibited.
    [036] Barium (Ba) can be added to a support that supports Pd in the lower layer described in this document 50. Ba is added to the support in the lower layer in order to inhibit HC poisoning of Pd and increase catalytic activity (particularly, low temperature activity). In addition, the dispersion capacity of the Pd in the support is improved and high temperature sintering, which is accompanied by the growth of the Pd particle, is more completely inhibited. The amount of Ba addition to the support described in this document is preferably an amount that satisfies 5% by mass to 10% by weight, based on the total mass of the support and which satisfies, in a particularly preferential way, 5% by mass to 8% by mass in relation to the total mass of the support. Bringing the Ba content into this range provides a better inhibition of Pd HC poisoning and makes it possible to develop a high catalytic activity even immediately after the engine starts. This also achieves better inhibition of Pd sintering and improved durability for Pd. When the Ba content is much greater than 10% by mass or much less than 5% by mass, the improvement in catalytic performance due to the addition of Ba, as described above, is inadequate and a high purification capacity may not be achieved. <The precious metal catalyst in the bottom layer>
    [037] The palladium (Pd) present in the lower layer described in this document 50 is supported on a support that contains the CSO material previously described. There is no particular limitation on the amount of Pd supported, however, this amount is suitably in the range of 0.01 wt% to 1 wt% (eg 0.05 wt% to 0.5 wt%) with reference to the total mass of the support in the lower layer 50. An adequate catalytic activity is not obtained for less, while the saturation of the effect occurs and the cost becomes unfavorable when more than this is supported. There is no particular limitation in the method for supporting the Pd in the support in the lower layer 50. For example, production can be carried out by impregnating a powder of the support containing the OSC material with an aqueous solution containing a palladium salt (for example, example, nitrate) and / or a palladium complex (for example, a tetraamine complex) followed by drying and calcination.
    [038] The lower layer described in this document 50 may contain another precious metal catalyst to the extent that Pd performance is not impaired. The non-Pd precious metal catalyst can be exemplified by platinum (Pt), ruthenium (Ru), iridium (Ir), and osmium (Os).
    [039] The amount of formation of the bottom layer 50 (the amount of coating) is not particularly limited, however, for example, it is preferably about 40 g to 200 g per liter of volume of the honeycomb-shaped substrate 10. When the amount of formation of the lower layer 50 is very small, this can result in a weak function as a catalyst coating layer and can cause the growth of particles of the supported Pd. In addition, when the amount of formation of the lower layer 50 is very large, this can cause an increase in pressure loss when exhaust gas passes through the cells of the honeycombed substrate 10. <The top layer>
    [040] The top layer 40 that constitutes the catalyst coating layer described in this document 30 is provided with a support and a precious metal catalyst that contains at least Rh and Pd supported on that support. Rh mainly purifies NOx in the exhaust gas. <Support for the upper layer>
    [041] The support that supports Rh in the upper layer 40 may contain a substance used until now as a support of this type, for example, zirconia (ZrO2), alumina (Al2O3), and their solid solutions and complex oxides. For example, a support containing ZrO2 is preferred. The Rh supported on ZrO2 generates hydrogen through a hydrogen reform reaction from the HC in the exhaust gas. The NOx in the exhaust gas is more completely purified through the hydrogen's reducing power. The support that supports Rh in the upper layer 40 preferably does not contain cerium oxide (CeO2).
    [042] The support that supports Rh in the upper layer 40 is preferably a complex oxide of ZrO2 containing Y2O3. The heat resistance of ZrO2 can be improved and the decline in the purification capacity after aging at high temperature can be inhibited by having ZrO2 containing Y2O3. The Y2O3 content, expressed with reference to the total mass of the complex ZrO2 oxide containing Y2O3, is, in general, suitably from 5 wt% to 20 wt%, and preferably from 6 wt% to 10 wt%. High catalytic activity and durability at high temperature can be exhibited by the top layer containing Rh 40 when the Y2O3 content is placed in the indicated range.
    [043] Another compound (typically an inorganic oxide) can be mixed into this complex ZrO2 oxide as an auxiliary component. For example, a rare earth element, such as lanthanum, an alkaline earth element such as calcium, or a transition metal element can be used for that compound. Among these, a rare earth element such as lanthanum is preferably used as a stabilizer from the point of view of causing an increase in the specific surface area at elevated temperatures without poisoning the catalytic function. For example, a rare earth oxide such as La 2O3 or Nd2O3 can be mixed for the purpose, for example, of preventing sintering. This rare earth oxide can be physically mixed as an independent oxide in the support powder or a complex oxide component can be produced. The content (mass ratio) of the auxiliary component is preferably from 2 mass% to 30 mass% (for example, 5 mass% to 15 mass%) of the support as a whole. There is little effect, for example, a sintering inhibition, and so on, when the content of the auxiliary component is well below 2% by mass, while the amount of ZrO2 in the support suffers a relative decline well above 30% by mass and catalytic activity can be reduced as a result.
    [044] The support that supports Rh in the upper layer described in this document 40 may contain a support material other than the complex ZrO2 oxide. A highly heat-resistant porous metal oxide is preferably used for this support material. For example, the use of Al2O3 is preferred. Al2O3 has a smaller specific surface area and higher durability (particularly heat resistance) than the complex ZrO2 oxide. As a consequence, the Rh support in Al2O3 can improve the thermal stability of the support as a whole and can cause an optimal amount of Rh supported in the support as a whole. Al2O3 and the ZrO2 complex oxide are preferably mixed in a mass mixing ratio (Al2O3: ZrO2 complex oxide) in the range 80:20 to 20:80. <The precious metal catalyst in the top layer>
    [045] The Rh present in the upper layer described in this document 40 is supported on a support containing the previously described ZrO2 complex oxide. Although the amount of Rh supported is not particularly limited, it is preferably brought up to the range of 0.01 wt% to 1 wt% (eg 0.05 wt% to 0.5 wt%) with reference to total mass of the support that supports Rh in the upper layer. A satisfactory catalytic activity is not achieved for less than that, while saturation of the effect occurs and the cost becomes unfavorable when more than this is borne. There is no particular limitation on the Rh support method on the support in the top layer 40. For example, production can be carried out by impregnating the powder of a support made of a complex ZrO2 oxide with an aqueous solution containing a rhodium salt. (for example, a nitrate) or a rhodium complex (for example, a tetra-amine complex) and then drying and calcination.
    [046] As indicated above, the top layer 40 of the catalyst coating layer described in this document 30 contains Pd in addition to Rh. The support that supports the Pd in the upper layer 40 can be the same as the support that supports the Pd in the lower layer 50 and be a support that contains an OSC material, for example, a complex oxide of CeO2-ZrO2. Among the above, a support that is equal to the support for Pd in the previously described lower layer 50 is particularly suitable and a detailed description of it is therefore omitted.
    [047] The mass ratio (Rh / Pd) between Rh and Pd in the upper layer 40 is adequately within the range, in general, from 1.25 to 5, preferably 1.25 to 4, more preferably 1, 25 to 3 and, particularly preferably, 1.25 to 2. According to this construction, due to the fact that the ratio between Rh and Pd in the upper layer 40 is in a favorable balance, an increase in CSO can be reliably displayed while the connection between Rh and Pd is inhibited. When the proportion of Pd is very large, a satisfactory NOx purification effect through Rh may not be obtained due to the connection between Rh and Pd; when, on the other hand, the proportion of Pd is very small, the enhancement effect of the OSC becomes inadequate.
    [048] The upper layer described in this document 40 may contain another precious metal catalyst to the extent that the functionalities of Rh and Pd are not impaired. The precious metal catalyst other than Rh and Pd can be exemplified by platinum (Pt), ruthenium (Ru), iridium (Ir), and osmium (Os).
    [049] The amount of formation of the top layer 40 (the amount of coating) is not particularly limited, however, for example, it is preferably about 20 g to 200 g per liter of volume of the honeycomb-shaped substrate 10. When the amount of the lower layer formation 40 is much less than 20 g, this can result in a weak function as a catalyst coating layer and can cause the growth of supported Rh and Pd particles. In addition, when the amount of lower layer formation 40 exceeds 200 g, this can cause an increase in pressure loss when the exhaust gas passes through the honeycomb-shaped substrate cells 10. <The catalyst coating layer formation method>
    [050] Regarding the formation of the bottom layer 50 of the catalyst coating layer 30, a slurry containing a powder from the support can be coated by washing (washcoated) on the substrate surface (for example, a honeycomb-shaped substrate) 10 and the Pd can be supported therein, or a catalyst powder can be prepared in advance by supporting the Pd in a support powder and a slurry containing this catalyst powder can be coated by washing the surface of the substrate 10. Regarding the layer higher than 40 of the catalyst coating layer 30, a slurry can be prepared by mixing a support powder in which Rh has been previously supported and a support powder in which Pd has been previously supported and washed that slurry in the bottom layer surface 50.
    [051] In the process of forming the catalyst coating layer 30 by washing coating (washcoating), a binder is preferably present in the slip in order to cause a favorable adhesion of the slip to the surface of the substrate 10 or to the surface of the layer lower 50. For example, a sun. of alumina or sun. silica is preferably used for this binder. The viscosity of the slurry can be adjusted as appropriate so that the slurry can easily flow into the cells of the substrate (for example, a honeycomb-shaped substrate). The drying conditions for the wash coated slurry on the surface of the substrate 10 will vary with the shapes and dimensions of the substrate or support, however, they are typically from approximately 1 hour to approximately 10 hours. [Mat. 15] 80 ° C to 120 ° C (for example, [Mat. 16] 100 ° C to 110 ° C).
    [052] The calcination conditions are approximately 2 hours to 4 hours at approximately [Mat. 17] 400 ° C to 1,000 ° C (for example, [Mat. 18] 500 ° C to 700 ° C).
    [053] The layered structure of the catalyst coating layer 30 should have a catalyst layer containing Rh and Pd, as described above for the upper layer 40 and a catalyst layer containing Pd, as described above for the lower layer 50, however, it can have three or more layers containing another layer or layers (for example, a separate layer adjacent to the substrate) in addition to these two layers. In addition, the catalyst coating layer 30 need not be a two-layer upper / lower layer structure in which the upper layer 40 and the lower layer 50 extend over the entire substrate area (e.g., a substrate honeycomb shape) 10, and can have a structure in which partial stacking takes place between a portion of the upper layer 40 and a portion of the lower layer 50. For example, as shown in Figure 3, the upper layer 40 and the lower layer 50 can be stacked, so that one end of one layer extends beyond one end of the other layer. In the example shown in Figure 3, and considered with reference to the direction of continuous flow of the exhaust gas, the stacking is performed so that the downstream end 40A of the upper layer 40 extends beyond the downstream end 50A of the lower layer 50. Stacking is also carried out with the upstream end 50B of the lower layer 50 which extends beyond the upstream end 40B of the lower layer 40. The upper layer 40 and the lower layer 50 preferably form a two-layer structure of the layer upper / lower layer over a region (band) that is greater than 50% (for example, 70% to 80% or more) of the entire substrate area 10.
    [054] In the example shown in Figure 3, an upper layer of anterior stage 60 is formed on the upstream side of upper layer 40, which is the surface of the extension region 52 of the lower layer 50. In this embodiment, the upper layer of stage previous 60 is provided with a support and, supported on that support, a precious metal catalyst containing at least Pd. The poisons (particularly HC) in the exhaust gas can be very efficiently purified by having such an upper layer of Pd 60 front stage on the upstream side of the upper layer 40. Thus, due to the fact that the upper layer of anterior stage 60 is on the upper side (surface side), where the HC diffuses readily, and is arranged on the upstream side of the substrate 10, where high temperatures are readily reached, a greater opportunity for contact between the Pd and the Exhaust gas is created and the exhaust gas can be very efficiently purified at high temperatures.
    [055] The support that supports the Pd in the upper layer of the previous stage 60 preferably contains an OSC material. In this embodiment, the support that supports the Pd in the upper layer of the previous stage 60 contains a complex oxide of CeO2-ZrO2. The complex oxide of CeO2-ZrO2 can be a complex oxide of CeO2ZrO2 in which another compound (typically an inorganic oxide) is mixed as an auxiliary component. For example, a rare earth element, such as lanthanum, an alkaline earth element such as calcium, or a transition metal element can be used for that compound. For example, a rare earth oxide such as La2O3, Y2O3, or Pr6O11 can be mixed, for example, for the purpose of preventing sintering. The support that supports Pd in the upper layer of previous stage 60 can also contain Al2O3. In addition, barium (Ba) can be added to the support that supports Pd in the upper layer of the previous stage 60.
    [056] The upper layer of anterior stage 60 is preferably formed over a region that corresponds to 10% to 40% (for example, 15% to 25%) of the total length of the substrate 10 until the downstream side of the end to upstream 10B of substrate 10. The bottom layer 50 is preferably formed over a region that corresponds to 70% to 100% (for example, 85% to 95%) of the total length of substrate 10 to the downstream side of the end to upstream 10B of substrate 10. The top layer 40 is preferably formed over a region that corresponds to 70% to 100% (for example, 75% to 85%) of the total length of substrate 10 to the upstream side of the end to downstream 10A from substrate 10.
    [057] Several examples referring to the present invention are described below, however, the present invention is not intended to be limited by the description of those specific examples.
    [058] The exhaust gas purification catalyst of these examples, as shown in Figure 1, is provided with a honeycomb-shaped substrate 10 that has a plurality of regularly arranged cells 12 and rib walls 14 that form cells 12. The honeycomb-shaped substrate 10 is a cylinder with a length of 105 mm and a volume of 0.875 L and is made of cordierite; a catalyst coating layer 30, as shown in Figure 3, is formed on the surfaces of the rib walls 14 that form the cells 12; and gas passages are formed in the spaces on those surfaces. The catalyst coating layer 30 is comprised of a lower layer 50, an upper layer 40, and a previous stage upper layer 60.
    [059] The bottom layer 50 contains Pd, Al2O3, CeO2-ZrO2 complex oxide, and barium. The top layer 40 contains Rh, Pd, Al2O3, ZrO2 complex oxide. The upper layer of previous stage 60 contains Pd, Al2O3, complex oxide of CeO2ZrO2, and barium.
    [060] The upper layer of anterior stage 60 is formed, as shown in Figure 1 and Figure 3, along a region that corresponds to 20% of the total length of the honeycomb substrate to the downstream side from the end upstream of the hive-shaped substrate. The lower layer 50 is formed over a region that corresponds to 90% of the total length of the honeycomb substrate to the downstream side from the upstream end of the honeycomb substrate. The upper layer 40 is formed over a region corresponding to 80% of the total length of the honeycomb substrate to the upstream side from the downstream end of the honeycomb substrate.
    [061] The method of forming the exhaust gas purification catalyst of these examples is described below. Example 1
    [062] An exhaust gas purification catalyst was manufactured in Example 1 in which Rh was disposed in the upper layer and Pd was disposed only in the lower layer. (1) Formation of the lower layer
    [063] A dispersion was prepared by suspending 75 g / L alumina powder (Al2O3) in a nitric acid reagent solution that contained 0.82 g / L Pd. The following was mixed into this dispersion to obtain a slurry: a powder of an OSC material of CeO2-ZrO2 complex oxide (CeO2: 30% by weight, ZrO2: 60% by weight, Y2O3: 5% by weight, La2O3: 5% by weight), 5% by weight of barium acetate, 5% by weight of Al2O3 binder, and distilled water. This slurry was dried for 30 minutes at [Mat. 19] 120 ° C and was calcined for 2 hours at [Mat. 20] 500 ° C
    [064] to obtain a catalyst material for the lower layer.
    [065] This lower layer catalyst material was then dispersed in an aqueous acid solution to prepare a lower layer forming slurry (A). Using this lower layer forming fluid (A), a wash coating was carried out in the region corresponding to 90% of the total length from the end on the upstream side of the honeycomb substrate, followed by drying and calcination to form a bottom layer 50 on the substrate surface. (2) Formation of the upper layer
    [066] A dispersion was prepared by suspending 65 g / L of a powder of a complex ZrO2 oxide (ZrO2: 80% by weight, Y2O3: 8% by weight, Nd2O3: 12% by weight) in a reagent solution of Rh type nitric acid that contained 0.2 g / L of Rh. The following was mixed in this dispersion to obtain a top layer (B) slurry: 25 g / L Al2O3 powder, 5 wt.% Al2O3 binder, and distilled water. Using this top layer forming fluid (B), wash coating was performed a wash coating was performed in the region that corresponds to 80% of the total length of the other downstream end (the opposite end of the end for forming the bottom layer ) of the honeycomb-shaped substrate 10, followed by drying and calcination to form an upper layer 40 on the substrate surface. (3) Formation of the upper layer of the previous stage
    [067] A dispersion was prepared by suspending 50 g / L alumina powder (Al2O3) in a nitric acid Pd reagent solution containing 1.0 g / L Pd. The following was mixed in this dispersion to obtain a slurry: a powder of a CeO2-ZrO2 complex oxide OSC material (CeO2: 60% by weight, ZrO2: 30% by weight, La2O3: 3% by weight, Pr6O11: 7% by weight), 5% by weight barium acetate, 5% by weight of Al2O3 binder, and distilled water. This slurry was dried for 30 minutes at [Mat. 21] 120 ° C and was calcined for 2 hours at [Mat. 22] 500 ° C to obtain a catalyst material for the previous stage top layer.
    [068] This catalyst material for the upper layer of the previous stage was then dispersed in an acidic aqueous solution to prepare a slurry (C) to form the upper layer of the previous stage. Using this slurry (C) to form the upper layer of the previous stage, a wash coating was carried out in the region corresponding to 20% of the total length from the end on the upstream side of the honeycomb substrate, followed by drying and calcination to form the anterior stage upper layer 60 on the substrate surface. Examples 2 to 5
    [069] Exhaust gas purification catalysts were prepared in Examples 2 to 5 where Rh was disposed in the upper layer and Pd was disposed in both the upper and the lower layer. Specifically, a quantity of the lower layer catalyst material was subtracted from the lower layer forming slurry (A) described above and that same amount of lower layer catalyst material was mixed into the upper layer slurry (B) . The slurry (C) to form the upper layer of the previous stage was prepared as in Example 1. Proceeding as in Example 1, these three slurries (A), (B), and (C) were washed by washing on the substrate and dried and calcined to produce the exhaust gas purification catalyst. This production was carried out in order to provide 0.04 g, 0.08 g, 0.16 g and 0.24 g for the amount of Pd in the upper layer as a whole for the sequence of Examples 2 to 5, respectively. The amount of Pd in the catalyst as a whole was kept constant at 0.65 g. Example 6
    [070] An exhaust gas purification catalyst was manufactured in Example 6 where Rh was disposed in the upper layer and Pd was disposed in both the upper and the lower layer. However, in this example, the Pd on the top layer was placed on it without being supported on a support. Specifically, a specific amount of Pd (without support) was subtracted from the lower layer forming slurry (A) indicated above and that same amount of Pd (without support) was mixed in the upper layer forming slurry (B) ). The slurry (C) to form the upper layer of the previous stage was prepared as in Example 1. Proceeding as in Example 1, these three slurries (A), (B), and (C) were washed by washing on the substrate and dried and calcined to produce the exhaust gas purification catalyst. This production was carried out in order to provide 0.16 g for the amount of Pd in the upper layer as a whole.
    [071] The following are provided in Table 1 for exhaust gas purification catalysts, according to Examples 1 to 6: the amount of Pd in the top layer, the amount of Al2O3 in the top layer, the amount of Pd in the bottom layer, the amount of Al2O3 in the bottom layer, and the mass ratio between the amount of Pd in the top layer and the amount of Pd in the bottom layer.
    (4) Durability test
    [072] The durability test was carried out on the exhaust gas purification catalysts of Examples 1 to 6 obtained as described above. In this durability test, the exhaust gas purification catalyst from the particular example was installed in the exhaust system of a V8 engine and the V8 engine was put into operation and maintained in operation for 50 hours at a catalyst bed temperature of [Mat. 23] 1,000 ° C (5) CSO assessment test
    [073] The oxygen storage capacity (OSC) of each of the exhaust gas purification catalysts of Examples 1 to 6 was assessed after the durability test described above. Specifically, the exhaust gas purification catalyst was removed from the V8 engine after the durability test and was installed in the exhaust gas system of an in-line 4-cylinder engine. An O2 sensor was placed downstream from the particular sample. Although the air / fuel A / F ratio of the mixed gas fed to the 4-cylinder engine periodically changes between rich and poor in accordance with a prescribed schedule, the average amount of oxygen storage of the particular exhaust gas purification catalyst was calculated from the O2 sensor behavior delay. The results are provided in Figure 4. Figure 4 is a graph of the relationship between the mass ratio Pd (upper layer / lower layer) and the amount of oxygen storage.
    [074] As shown in Figure 4, the exhaust gas purification catalysts of Examples 2 to 5, in which Pd was disposed in both the upper and lower layers, had a significantly greater amount of oxygen storage than the carbon catalyst. exhaust gas purification of Example 1, in which Pd was disposed only in the lower layer. In addition, a comparison of Examples 2 to 5 demonstrates a trend towards an increasing amount of oxygen storage that accompanies an increase in the mass ratio of Pd between the upper layer and the lower layer (upper layer / lower layer). In the case of the exhaust gas purification catalysts tested here, a large amount of oxygen storage, that is, of at least 0.5 g, can be displayed by driving the mass ratio Pd (upper layer / lower layer) up to at least 0.06. In particular, a very large amount of oxygen storage, i.e., at least 0.53 g, can be carried out by conducting the mass ratio of Pd (upper layer / lower layer) to at least 0.3. Viewed from the perspective of elevating the catalyst's OSC, a mass ratio of Pd (top layer / bottom layer) is generally at least 0.06, although at least 0.15 is preferred and at least 0.2 is particularly preferred. As compared to Examples 2 to 5, a satisfactory improvement in OSC was not achieved with the exhaust gas purification catalyst of Example 6, and that the Pd was disposed in the top layer without being supported on a support. The Pd, therefore, is preferably arranged in the upper layer supported on a support. (6) NOx purification test
    [075] The exhaust gas purification catalysts of Examples 1 to 6 were subjected, after the durability test described above, to an assessment of the purification capacity of NOx. Specifically, after the durability test, the exhaust catalyst exhaust gas purification was installed in the exhaust system of an inline 4-cylinder engine; the exhaust gas at a gas inlet temperature of [Mat. 24] 550 ° C (the catalyst bed temperature from [Mat. 25] 600 ° C to 630 ° C
    [076] was passed through the catalyst; and the poor control in A / F = 15.1 was performed followed by the change to the control rich in A / F 14,1. The amount of NOx emission was measured in 2 minutes after switching to control rich in A / F = 14.1. The results are shown in Figure 5. Figure 5 is a graph showing the relationship between the mass ratio of Pd (upper layer / lower layer) and an amount of NOx emission.
    [077] As shown in Figure 5, the amount of NOx emission for the exhaust gas purification catalyst of Example 5, in which the Pd mass ratio (upper layer / lower layer) was brought to 0.58, increased over those of the other samples. It is assumed here that Rh's NOx purification capacity has decreased due to the bond between Pd and Rh in the upper layer. Observed from the perspective and maintenance of a high NOx purification capacity for Rh, the mass ratio of Pd (upper layer / lower layer) is, in general, suitably no more than 0.4 and, preferably, not more than 0.32 and, particularly preferably, no more than 0.25. Observed from the perspective of satisfying both the purification capacity of NOx and OSC, the mass ratio of Pd (upper layer / lower layer) is, in general, adequately at least 0.01 and no more than 0.4, preferably at least 0.06 and no more than 0.32, more preferably at least 0.15 and no more than 0.35 and, particularly preferably, at least 0.2 and no more than 0.3 .
    [078] The specific examples of the present invention have been described in detail above, however, these are nothing more than examples and do not limit the claims. The technique described in the claims encompasses various adjustments and modifications to the specific examples provided such as the examples above.
    [079] The exhaust gas purification catalyst described herein can provide an exhaust gas purification catalyst in which the OSC of the catalyst as a whole is effectively increased while a high NOx purification capacity is maintained.
    权利要求:
    Claims (5)
    [0001]
    (1). Exhaust gas purification catalyst CHARACTERIZED by the fact that it comprises a substrate (10) and a catalyst coating layer (30) formed on a substrate surface, where the catalyst coating layer comprises a structure in layers that have upper and lower layers with the lower layer (50) being closer to the substrate surface and the upper layer (40) being relatively farther from it, the catalyst coating layer is equipped with Rh and Pd as the catalysts of precious metals, the catalyst coating layer is provided with an OSC material that has an oxygen storage capacity as a support, Rh is disposed on the top layer of the catalyst coating layer, Pd is disposed on both the the upper layer and the lower layer of the catalyst coating layer, the support that supports Rh in the upper layer is made of a complex ZrO2 oxide containing Y2O3, at least one portion of the Pd in the upper layer and the lower layer is supported on the OSC material, a mass ratio between the Pd placed in the upper layer and the Pd placed in the lower layer is at least 0.01 and not greater than 0.4, each one between the top layer and the bottom layer has an upstream end with respect to a continuous flow direction of the exhaust gas, the upstream end of the bottom layer includes an extension region that expands beyond the upstream end of the top layer , an upper layer of previous stage is arranged on a portion of the surface of the extension region of the lower layer, the portion corresponding to 10% to 40% of the total length of the substrate from the amount downstream in it, and the upper layer of previous stage is provided with a support and contains OSC material, and Pd is supported on the support.
    [0002]
    (2) Exhaust gas purification catalyst according to claim 1, CHARACTERIZED by the fact that the OSC material that supports at least a portion of the Pd in the upper layer and in the lower layer is made of CeO2 or a complex oxide of CeO2-ZrO2.
    [0003]
    (3) Exhaust gas purification catalyst, according to claim 1, CHARACTERIZED by the fact that the mass ratio between Rh and Pd arranged in the upper layer is 1.25 to 5.
    [0004]
    (4) Exhaust gas purification catalyst, according to claim 1, CHARACTERIZED by the fact that the mass ratio between the Pd disposed in the upper layer and the Pd disposed in the lower layer is 0.06 to 0.32.
    [0005]
    (5) Exhaust gas purification catalyst according to claim 1, CHARACTERIZED by the fact that the support that supports Rh contains a complex oxide ZrO2 that contains Y2O3 and Nd2O3, and the OSC material that supports at least one portion of the Pd contains a complex CeO2-ZrO2 oxide that contains La2O3 and Pr6O11.
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    同族专利:
    公开号 | 公开日
    RU2572810C1|2016-01-20|
    BR112014016151A2|2017-06-13|
    US20140357480A1|2014-12-04|
    BR112014016151A8|2017-07-04|
    ZA201405124B|2015-12-23|
    CN104039426A|2014-09-10|
    JP2013136032A|2013-07-11|
    EP2797678B1|2017-11-15|
    JP5807782B2|2015-11-10|
    CN104039426B|2016-08-24|
    EP2797678A1|2014-11-05|
    US9440223B2|2016-09-13|
    WO2013099251A1|2013-07-04|
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    法律状态:
    2018-03-27| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2019-08-20| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|
    2020-09-01| B09A| Decision: intention to grant|
    2020-12-22| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 26/12/2012, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2011-288798|2011-12-28|
    JP2011288798A|JP5807782B2|2011-12-28|2011-12-28|Exhaust gas purification catalyst|
    PCT/JP2012/008343|WO2013099251A1|2011-12-28|2012-12-26|Exhaust gas purification catalyst|
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