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    • 专利摘要:
    CATALYTIC CONVERTER. The present invention relates to a catalytic converter, capable of obtaining superior NOx purification performance while reducing the amount of a noble metal catalyst. A catalytic converter (10) includes: a substrate (1) having a cellular structure in which exhaust gas flows; and catalytic layers (3), which are formed on cell wall surfaces (2) of the substrate (1). The catalytic layers (3) include a first catalytic layer (4), disposed on an upstream side of the substrate (1), in a discharge gas flow direction, and a second catalytic layer (5), disposed on one side. downstream of the substrate, in the direction of discharge gas flow. The first catalytic layer (4) is formed of a support and rhodium, which is a noble metal catalyst supported on the support. The second catalytic layer (5) is formed of a support, and palladium or platinum, which is a noble metal catalyst supported on the support. The first catalytic layer (4) is formed in a range of 80 to 100% of the total length of the substrate (1), starting from one end of the substrate on the upstream side, and the second catalytic layer (5) is formed in a range from 20% to 50% of the total length of the substrate (1), starting from one end of the substrate (...).
    公开号:BR112015019210B1
    申请号:R112015019210-6
    申请日:2013-12-19
    公开日:2021-05-11
    发明作者:Yuki Aoki
    申请人:Toyota Jidosha Kabushiki Kaisha；
    IPC主号:
    专利说明:

    TECHNICAL FIELD
    [0001] The present invention relates to a catalytic converter, which is accommodated and fixed in a tube, which constitutes a discharge system for discharge gas. BACKGROUND
    [0002] In various industries, various attempts to reduce environmental impacts have been made on a global scale. In particular, in the automobile industry, the development of techniques has progressed towards the spread of having not only a gasoline engine vehicle having superior fuel efficiency, but also a so-called eco-friendly vehicle, such as a hybrid vehicle or an electric vehicle, and towards a further improvement in vehicle performance. Along with the development of this eco-friendly vehicle, studies on an exhaust gas purification catalyst, which purifies the exhaust gas originating from an engine, were intensively carried out. This flue gas purification catalyst includes an oxidation catalyst, a three-way catalyst and a NOx storage reduction catalyst. In the flue gas purification catalyst, the catalytic activity is exhibited by a noble metal catalyst, such as platinum (Pt), palladium (Pd) or rhodium (Rh). In general, this noble metal catalyst is used in a state of being supported on a support, formed from a porous oxide, such as alumina.
    [0003] In a discharge system for exhaust gas, which connects a vehicle engine and a muffler together, a catalytic converter for purifying exhaust gas is usually provided. The engine can emit environmentally harmful materials such as CO, NOx, or unburned HC or VOC. To convert these harmful materials into environmentally acceptable materials, the exhaust gas is forced to flow through a catalytic converter so that CO is converted to CO2, NOx is converted to N2 and O2, and VOC is combusted to produce CO2 and H2O. In the catalytic converter, catalytic layers having a noble metal catalyst, such as Rh, Pd, or Pt, supported on a support, are formed on cell wall surfaces of a substrate.
    [0004] Examples of the support, to support the noble metal catalyst, include a solid solution of CeO2 - ZrO2 (also referred to as a CZ material, an oxide composed of cerium oxide - ceria - and zirconia, and the like). This support is also called a cocatalyst, and is an essential component of the three-way catalyst, which simultaneously remove harmful components such as CO, NOx and HC. Examples of an essential component of the cocatalyst include CeO2. The oxidation number of CeO2 varies, for example, from Ce3+ or Ce+4, depending on the partial pressure of oxygen in the discharge gas to which the CeO2 is exposed. To compensate for the deficiency of charges, CeO2 has an oxygen absorbing and desorbing function and an oxygen storing function (OSC: Oxygen Storage Capacity). To maintain a three-way catalyst purification window, a variation in the off-gas atmosphere is absorbed and relieved so that the purification window can be maintained substantially in the theoretical air-fuel ratio.
    [0005] Eventually, from the viewpoints of risk reduction, rare earth metals material and the like and the achievement of cost competitiveness, such as decreasing the noble metal catalyst content, used in the three-way catalyst, is a important factor. However, when the content of the noble metal catalyst is significantly decreased, the catalytic activity is also significantly decreased. Consequently, OSC, low temperature activity, NOx purification performance in a high temperature environment and the like are significantly decreased. The reason is presented below. Along with a significant decrease in the amount of noble metal catalyst, the number of active sites is also significantly decreased, and the number of catalytic reaction sites is significantly decreased. Therefore, a decrease in purification performance is significant.
    [0006] Among the noble metal catalysts including Pt, Pd and Rh, which are particularly used in the three-way catalyst, Rh has the highest NOx purification performance, but the highest market price per unit weight. Furthermore, it is known that Rh has a high OSC because it is supported in a cocatalyst containing cerium oxide (ceria). However, it is also known that a compromise relationship is established, by the fact that as the amount of cerium oxide in the cocatalyst to support Rh increases, and, conversely, the NOx purification performance, as a function of of the Rh characteristic, decreases. Therefore, when Rh is used as the noble metal catalyst, the design criteria during the preparation of the three-way catalyst need to be adjusted so that both the NOx purification performance and the OSC are optimized simultaneously.
    [0007] Regarding the preparation of the optimized three-way catalyst, considering the fact that the performances of various catalytic noble metals and supports vary, depending on their respective components, a zone-coated catalyst, in which different components are arranged on an upstream and a downstream side of a substrate, in order to efficiently present characteristics of the respective components, has been intensively studied.
    [0008] With respect to such zone coated catalyst, PTL 1 describes a flue gas purification catalyst including: a substrate for forming a gas passage, through which the flue gas flows; and catalytic layers, which are formed on the substrate. More specifically, the catalytic layers applied in this case include: a lower catalytic layer, which is formed on a surface of the substrate; a front upper catalytic layer, with which a surface of the lower catalytic layer, on an upstream side in a gas flow direction, is coated; and an upper back catalytic layer, with which a surface of the lower catalytic layer, on a downstream side of the front upper catalytic layer, in the gas flow direction, is coated. In addition, at least one of Pd and Pt is supported in the lower catalytic layer, Rh is supported in the upper back catalytic layer, Pd is supported in the upper front catalytic layer, and a support to support Pd in the upper front catalytic layer is an oxide composite of ZrO2 containing Y2O3. According to this configuration, the purification characteristics of the catalytic noble metal can be sufficiently presented, and the purification performance at a low temperature of the catalyst can be improved. In addition, by using ZrO2 composite material, to which Y2O3 is added, which has a low specific heat resistance and a superior heat resistance, as the support material of the upper front catalytic layer, the heat resistance can be guaranteed while optimizing catalyst temperature rise performance, and catalyst heating performance, including durability, can be obtained.
    [0009] On the other hand, PTL 2 describes a flue gas purification catalyst, including: a substrate; a lower catalytic layer, which is formed on the substrate and contains at least one of Pd and Pt; and an upper catalytic layer, which is formed in the lower catalytic layer and contains Rh, wherein a region not including the upper catalytic layer is disposed on an off-gas upstream side of the off-gas purification catalyst, the The lower catalytic layer includes a front lower catalytic layer, disposed on the upstream side of exhaust gas, and a lower back welding consumable material, disposed on a downstream side of exhaust gas, and the lower front catalytic layer contains an exhaust material. oxygen storage. According to this configuration, the grain growth of the respective catalytic metals supported in the respective catalytic layers, in particular in the lower back catalytic layer and in the upper catalytic layer, on the downstream side of off-gas, can be significantly eliminated. Further, by making the region not include an upper catalytic layer on the upstream side of off-gas, the diffusibility of HC in the inner part of the lower front catalytic layer can be improved, and the purification of HC, in the catalytic layer lower front, is accelerated so that sufficient catalyst heating performance can be obtained.
    [0010] Further, PTL 3 describes a flue gas purification catalyst, in which the catalytic layers include: a lower catalytic layer, which is formed on a surface of a substrate; a front upper catalytic layer, with which a surface of the lower catalytic layer, on an upstream side in a gas flow direction, is coated; and a rear upper catalytic layer, with which a surface of the lower catalytic layer, on a downstream side of the front upper catalytic layer in the gas flow direction, is coated. In the off-gas purification catalyst, at least one of Pd and Pt is supported in the rear upper catalytic layer, and a concentration of Pd, supported in the front upper catalytic layer, is 4.5% by mass to 12% by mass. According to this configuration, the purification characteristics of the catalytic noble metal can be sufficiently presented, and the purification performance at a low temperature of the catalyst can be improved.
    [0011] Thus, several techniques relating to the zone-coated catalyst are present. In accordance with the circumstances presented above, the present inventors have reviewed the configuration of the zone-coated catalyst and devised a catalytic converter, capable of obtaining superior NOx purification performance while reducing the amount of a noble metal catalyst. LIST OF QUOTES PATENTS LITERATURE
    [0012] PTL 1: Japanese Patent Application Publication No. 2012-040547
    [0013] PTL 1: Japanese Patent Application Publication No. 2012-152702
    [0014] PTL 1: Japanese Patent Application Publication No. 2012-020276 SUMMARY OF THE INVENTION
    [0015] The present invention was made considering the problems described above, and an objective of it is to provide a catalytic converter, capable of obtaining superior NOx purification performance, while reducing the amount of a noble metal catalyst.
    [0016] To achieve the objective described above, according to an aspect of the invention, there is provided a catalytic converter including: a substrate having a cellular structure in which exhaust gas flows; and catalytic layers, which are formed on cell wall surfaces of the substrate, wherein the catalytic layers include a first catalytic layer disposed on an upstream side of the substrate in a discharge gas flow direction, and a second catalytic layer, disposed on a downstream side of the substrate in the direction of discharge gas flow, the first catalytic layer is formed of a support and rhodium, which is a noble metal catalyst supported on the support, the second catalytic layer is formed of a support and palladium or platinum, which is a noble metal catalyst supported on the support, the first catalytic layer is formed over a range of 80% to 100% of the total length of the substrate, starting from one end of the substrate on the upstream side, and the second catalytic layer is formed over a range of 20% to 50% of the total length of the substrate, starting from one end of the substrate on the downstream side.
    [0017] In the catalytic converter according to the present invention: the zone coated catalyst is used as the catalytic layers, which are formed in the cell walls of the substrate having a cell structure; the first catalytic layer is arranged on the upstream side (Fr side) of the substrate, in the discharge gas flow direction; the second catalytic layer is arranged on the downstream side (Rr side) of the substrate, in the direction of discharge gas flow; rhodium is used as the noble metal catalyst of the first catalytic layer; palladium or platinum is used as the noble metal catalyst of the second catalytic layer; the length of the first catalytic layer is in a range of 80% to 100% with respect to the length of the substrate; and the length of the second catalytic layer is in a range of 20% to 50% with respect to the length of the substrate. Therefore, in the catalytic converter, a superior NOx purification performance can be obtained, while reducing as much as possible the amount of a noble metal catalyst used, in particular, rhodium.
    [0018] In this case, as the substrate having a cellular structure, not only a ceramic material, such as cordierite or silicon carbide, which is formed from an oxide composed of magnesium oxide, aluminum oxide and silicon dioxide, but also a material other than a ceramic material, such as a metallic material, can be used. Furthermore, in this configuration, a so-called alveolar structure, including cells having various network contours, which have, for example, rectangular, hexagonal and octagonal shapes, can be adopted.
    [0019] Furthermore, examples of a support constituting the catalytic layers, which are formed on the substrate cell wall surfaces, include: oxides containing at least one porous oxide of CeO2, ZrO2 and Al2O3 as a main component; an oxide between ceria (CeO2), zirconia (ZrO2) and alumina (Al2O3); and a composite oxide formed from two or more oxides between ceria (CeO2), zirconia (ZrO2) and alumina (Al2O3) (for example, a CeO2 - ZrO2 composite, which is a CZ material, or a ternary composite oxide Al2O3 - CeO2 - ZrO2 - ACZ material, in which Al2O3 is introduced as a diffusion barrier).
    [0020] According to the verification of the present inventors, it was found that the NOx purification performance is extremely superior under the following conditions: the length of the first catalytic layer is in a range of 80% to 100% with respect to substrate length; and the length of the second catalytic layer is in a range of 20% to 50% with respect to the length of the substrate.
    [0021] For example, when the length of the first catalytic layer is 90% of the length of the substrate, and when the length of the second catalytic layer is 50% of the length of the substrate, both catalytic layers are superimposed in a band 40% in relation to the length of the substrate. In this case, for example, all the catalytic layers are formed so that the first catalytic layer is directly superimposed on the second catalytic layer.
    [0022] Palladium is prone to form an alloy with rhodium. Therefore, rhodium, in which sintering is less likely to occur, due to its relatively high melting point, is applied to the first catalytic layer, which is formed on the upstream side of substrate discharge gas flow, in which gas discharge, having a relatively high temperature, drains. On the other hand, palladium, in which sintering is likely to occur, due to its relatively low melting point, is applied to the second catalytic layer, which is formed on the downstream side of the substrate discharge gas flow, in the which exhaust gas, having a relatively low temperature, flows out. Therefore, NOx purification performance can be improved while eliminating alloying between noble metal catalysts.
    [0023] By using platinum having an air-fuel ratio range greater than that of palladium, as the noble metal catalyst of the second catalytic layer, a catalytic converter, having a higher purification performance, can be obtained.
    [0024] In the catalytic converter, according to a preferable embodiment of the invention, the support of the first catalytic layer does not contain cerium.
    [0025] According to the verification of the present inventors, it was specified that the purification performance of NOx can be further improved by not using cerium as the support, which constitutes the first catalytic layer, in which rhodium is used as the catalyst of noble metal.
    [0026] The catalytic converter according to the present invention has a cordierite alveolar support, having a superior thermal shock resistance, but it can be an electrically heated catalytic converter (EHC: Electrically Heated Converter). In the electrically heated catalytic converter, for example, a pair of electrodes is trapped in an alveolar catalyst, the alveolar catalyst is heated by causing a current to flow through the electrodes, and the activity of the alveolar catalyst is improved to detoxify the gas discharge passing through it. By applying this electrically heated catalytic converter to a discharge system for the exhaust gas, which connects a vehicle engine and a muffler to each other, the exhaust gas can be purified not only at room temperature, but also at a cold temperature by catalyst activation due to electrical heating.
    [0027] As can be seen from the description presented above, in the catalytic converter according to the present invention, the first catalytic layer is arranged on the upstream side of the substrate, in the direction of discharge gas flow; the second catalytic layer is arranged on the downstream side of the substrate, in the direction of discharge gas flow; rhodium is used as the noble metal catalyst of the first catalytic layer; palladium or platinum is used as the noble metal catalyst of the second catalytic layer; the length of the first catalytic layer is in a range of 80 to 100% with respect to the length of the substrate; and the length of the second catalytic layer is in a range of 20% to 50% with respect to the length of the substrate. Therefore, in the catalytic converter, a superior NOx purification performance can be obtained, while reducing as much as possible the amount of a noble metal catalyst used, in particular, rhodium. BRIEF DESCRIPTION OF THE DRAWINGS
    [0028] Figure 1(a) is schematic diagram showing a catalytic converter in accordance with the present invention, and Figure 1(b) is an enlarged view showing a portion of cells.
    [0029] Figure 2(a) is a vertical sectional view showing embodiment 1 of catalytic layers, and Figure 2(b) is a vertical sectional view showing embodiment 2 of catalytic layers.
    [0030] Figure 3(a) is a vertical sectional view showing embodiment 3 of catalytic layers, and Figure 3(b) is a vertical sectional view showing embodiment 4 of catalytic layers.
    [0031] Figure 4(a) is a vertical sectional view showing embodiment 5 of catalytic layers, and Figure 4(b) is a vertical sectional view showing embodiment 6 of catalytic layers.
    [0032] Figure 5 is a graph showing the experimental measurement results of the degree of NOx emission, when the length of the first catalytic layer is fixed at 80%, with respect to the length of the substrate, and when the length of the second catalytic layer is changed.
    [0033] Figure 6 is a graph showing the experimental measurement results of the degree of NOx emission, relative to the comparative examples and the examples. WAYS TO CONDUCT THE INVENTION
    [0034] In the following, an embodiment of a catalytic converter, according to the present invention, will be described with reference to the drawings. Discharge system for discharge gas
    [0035] First, a discharge system for discharge gas, in which the catalytic converter according to the present invention is provided, will be briefly described. In the discharge system for discharge gas, in which the catalytic converter, according to the present invention, is applied, a motor, a catalytic converter, a three-way catalytic converter, an auxiliary muffler and a main muffler are arranged and connected each other through a piping system, and the exhaust gas, produced from the engine, flows to each unit through the piping system and is discharged. Next, then, the embodiment of the catalytic converter will be described. Realization of catalytic converter
    [0036] Figure 1(a) is a schematic diagram showing a catalytic converter in accordance with the present invention, and Figure 1(b) is an enlarged view showing a portion of cells. Furthermore, Figures 2(a), 2(b), 3(a), 3(b), 4(a) and 4(b) are vertical sectional views showing embodiments 1 to 6 of catalytic layers.
    [0037] Briefly, a catalytic converter 10, shown in Figure 1, includes: a cylindrical substrate 1 having several cells; and catalytic layers 3, which are formed on cell wall surfaces 2 constituting the cells.
    [0038] In that case, examples of a material of substrate 1 include: a ceramic material, such as cordierite or silicon carbide, which is formed from an oxide composed of magnesium oxide, aluminum oxide and silicon dioxide; and a material other than a ceramic material, such as a metallic material. Furthermore, examples of a support constituting the catalytic layers, which are formed on the substrate cell wall surfaces, include oxides containing at least one porous oxide of CeO2, ZrO2 and Al2O3 as a major component; an oxide between ceria (CeO2), zirconia (ZrO2) and alumina (Al2O3); and a composite oxide formed from two or more oxides between ceria (CeO2), zirconia (ZrO2) and alumina (Al2O3) (for example, a CeO2 - ZrO2 composite, which is a CZ material, or a ternary composite oxide Al2O3 - CeO2 - ZrO2 - ACZ material, in which Al2O3 is introduced as a diffusion barrier.
    [0039] The substrate 1 has an alveolar structure, including cells having various network contours, which have, for example, rectangular, hexagonal and octagonal shapes. Discharge gas, which flows into cells at one end of substrate 1, on an upstream side (Fr side) in a discharge gas flow direction, flows into substrate 1. During the process of flow, the exhaust gas is purified, and the purified exhaust gas flows from one end of the substrate, on a downstream side (Rr side) in the exhaust gas flow direction (X direction).
    [0040] Next, the catalytic layers, formed on the surfaces of cell walls 2, will be described with reference to Figures 2 to 4. In each drawing, the lower and upper cell walls, which form a cell, are shown.
    [0041] Figure 2(a) shows zone-coated catalytic layers 3 according to embodiment 1.
    [0042] Catalytic layers 3, shown in the same drawing, include a first catalytic layer 4 and a second catalytic layer 5, in which the first catalytic layer 4 has a length of 80% with respect to the length (100%) of substrate 1 , starting from the end of the substrate on the upstream side (Fr side) in the direction of exhaust gas flow, the second catalytic layer 5 has a length of 20% with respect to the length (100%) of the substrate 1, starting from the end of substrate 1 on the downstream side (Rr side) in the discharge gas flow direction, and both catalytic layers are not superimposed.
    [0043] In the first catalytic layer 4, rhodium is used as a noble metal catalyst supported on a support. In the second catalytic layer 5, palladium or platinum is used as a supported noble metal catalyst.
    [0044] As the support for supporting rhodium in the first catalytic layer 4, a material not containing cerium is preferably used. Examples of the support include an oxide formed from one of zirconia (ZrO2) and alumina (Al2O3); and a binary composite oxide of Al2O3 - ZrO2 (material AZ).
    [0045] According to catalytic layers 3, shown in the drawing, rhodium is not used along their entire length. Therefore, the amount of rhodium used, which is the most expensive among noble metal catalysts, can be reduced. Furthermore, the first catalytic layer has a length of 80% on the upstream side with respect to the length of the substrate 1. The second catalytic layer 5, in which palladium or the like is used as the noble metal catalyst, has a length of 20 % on the downstream side with respect to the length of substrate 1. Therefore, catalytic layer 3, having a superior NOx purification performance, is formed.
    [0046] On the other hand, Figure 2(b) shows the zone-coated catalytic layers 3A, according to embodiment 2. In the configuration of the catalytic layers 3A shown in the same drawing, a second catalytic layer 5A has a length of 50 % with respect to the length of substrate 1, a first catalytic layer 4A has a length of 80% with respect to the length of substrate 1, and both catalytic layers are overlapped in a 30% range. Due to the 3A catalytic layers shown in the drawing, the amount of rhodium used is reduced, and superior NOx purification performance can be expected.
    [0047] On the other hand, Figure 3(a) shows the zone-coated catalytic layers 3B, according to embodiment 3. In the configuration of the catalytic layers 3B shown in the same drawing, the second catalytic layer 5 has a length of 20 % with respect to the length of substrate 1, a first catalytic layer 4B has a length of 90% with respect to the length of substrate 1, and both catalytic layers are overlapped in a 10% range. Due to the 3B muffler shown in the drawing, the amount of rhodium used is reduced, and superior NOx purification performance can be expected.
    [0048] On the other hand, Figure 3(b) shows the zone coated catalytic layers 3C, according to embodiment 4. In the configuration of the catalytic layers 3C shown in the same drawing, the second catalytic layer 5A has a length of 50 % with respect to the length of substrate 1, the first catalytic layer 4B has a length of 90% with respect to the length of substrate 1, and both catalytic layers are overlapped in a 40% range. Due to the 3C catalytic layers shown in the drawing, the amount of rhodium used is reduced, and superior NOx purification performance can be expected.
    [0049] On the other hand, Figure 4(a) shows the 3D zone coated catalytic layers, according to embodiment 5. In the configuration of the 3D catalytic layers shown in the same drawing, the second catalytic layer 5 has a length of 20 % with respect to the length of substrate 1, a first catalytic layer 4C has a length of 100% with respect to the length of substrate 1, and both catalytic layers are overlapped in a range of 20%. Due to the 3C catalytic layers shown in the drawing, the amount of rhodium used is reduced, and superior NOx purification performance can be expected.
    [0050] In addition, Figure 4(b) shows the zone-coated catalytic layers 3E according to embodiment 6. In the configuration of the catalytic layers 3E shown in the same drawing, the second catalytic layer 5A has a length of 50% with respect to the length of substrate 1, the first catalytic layer 4C has a length of 100% with respect to the length of substrate 1, and both catalytic layers are overlapped in a 50% range. Due to the 3C catalytic layers shown in the drawing, the amount of rhodium used is reduced, and superior NOx purification performance can be expected.
    [0051] In addition to the examples shown in the drawings, there are several combinations of embodiments, which satisfy the following configurations: the first catalytic layer is formed in a range of 80% to 100% of the total length of substrate 1, starting from the end of substrate 1 on the upstream side; and the second catalytic layer is formed over a range of 20% to 50% of the total length of substrate 1, starting from the end of substrate 1 on the downstream side.
    [0052] Experiment (Part 1) to determine the optimal range of the second catalytic layer, and its results.
    [0053] The present inventors defined the length of the first catalytic layer to be 80% with respect to the length of the substrate, and changed the length of the second catalytic layer to be 0, 10, 30, 50, 80 and 100% with in relation to the length of the substrate. A catalytic converter, including catalytic layers from all cases, was prepared, a durability test was carried out, and an experiment measuring the amount of NOx, in a normal rich state, was conducted.
    [0054] Regarding the process of preparing catalyst slurry.
    [0055] In connection with the preparation of a slurry to form the second catalytic layer (Pd was used as the noble metal catalyst), an oxide composed of Al2O3 at 65 g/L, as a support, was impregnated with a solution of palladium nitrate. Therefore, 1.0% by mass of powdered support was prepared. Then, an oxide composed of CeO2 - ZrO2 (CeO2/ZrO2/La2O3/Y2O3 = 30/60/5/5 - % by mass) at 65 g/L, barium acetate at 10 g/L, water, a binder of Al2O3, acetic acid, a thickener and the like were mixed together in predetermined amounts. Therefore, a Pd catalyst slurry was obtained.
    [0056] On the other hand, regarding the preparation of a slurry to form the first catalytic layer (Rh was used as the noble metal catalyst), an oxide composed of CeO2 - ZrO2 (Al2O3/CeO2/ZrO2/La2O3/Y2O3/Nd2O3 = 30/20/ 44/2/2/2 - % by mass) at 65 g/L was prepared, and Rh at 0.3% by mass was supported on each support. In addition, Al2O3 impregnated with La at 25 g/L, barium acetate at 10 g/L, water, an Al2O3 binder, acetic acid, a thickener, and the like were mixed together in predetermined amounts. Therefore, an Rh catalyst slurry was obtained.
    [0057] 875 cm3 of a monolithic substrate were prepared and were coated with the pastes described above using a suction process.
    [0058] The secondary catalytic layers (Pd-supported catalytic layers), which had lengths of 0%, 10%, 30%, 50%, 80% and 100% with respect to the length of the substrate, starting from the end of the substrate on the side Rr, were formed by coating using the same amount of paste.
    [0059] On the other hand, the first catalytic layer (Rh-supported catalytic layer), which had a length of 80% with respect to the length of the substrate, starting from the end of the substrate on the Fr side, was formed by coating using the paste . Regarding the durability test
    [0060] The prepared catalytic converter was placed immediately below a real engine, and a durability test was conducted on it, at a bed temperature of 1000°C for 5 hours, under a composite model in which an A/F ratio (air/fuel) varied cyclically. Regarding the engine bench evaluation
    [0061] After the durability test, the catalytic converter was placed in another real engine, and the purification performance was calculated as the average amount of NOx emission, when an A/F ratio was changed into a rectangular shape, from from a rich state to a poor state, and was held in the rich state for 120 seconds. The test results are shown in Figure 5.
    [0062] In the same drawing, the amount of NOx emission showed an inflection point, when the length of the second catalytic layer was 50% with respect to the length of the substrate. When the length of the second catalytic layer was greater than 50%, the amount of NOx emission was increased to be in an unfavorable range, such as purification performance, and approached 500 ppm. On the other hand, when the length of the second catalytic layer was equal to or less than 50%, the amount of NOx emission was significantly decreased and saturated at 200 ppm or less.
    [0063] Based on the experimental results, the upper limit of the second catalytic layer length for the substrate length can be set to 50%.
    [0064] Next, then, in another experiment, the lower limit of the length ratio of the second catalytic layer will be defined. Experiment (Part 2) to determine the optimal second catalytic layer range, and its results
    [0065] The present inventors prepared a catalytic converter including the catalytic layers according to all examples and comparative examples, a durability test was conducted, and an experiment measuring the amount of NOx, in a normal rich state, was done. Regarding the catalyst slurry preparation process
    [0066] In connection with the preparation of a slurry to form the second catalytic layer (Pd was used as the noble metal catalyst), an oxide composed of Al2O3 at 65 g/L, as a support, was impregnated with a solution of palladium nitrate. Therefore, a support powder at 1.0% by mass was prepared. Next, an oxide composed of CeO2 - ZrO2 (CeO2/ZrO2/La2O3/Y2O3 = 30/60/5/5 - % by mass) at 85 g/L, barium acetate at 10 g/L, water, a binder of Al2O3, acetic acid, a thickener and the like were mixed together in predetermined amounts. Therefore, a Pd catalyst slurry was obtained.
    [0067] On the other hand, regarding the preparation of a slurry to form the first catalytic layer (Rh was used as the noble metal catalyst), an oxide composed of CeO2 - ZrO2 (Al2O3/CeO2/ ZrO2/La2O3/Y2O3 /Nd2O3 = 30/20/ 44/2/2/2 - % by mass) at 65 g/L was prepared. In this case, with respect to Example 2, the same content of an oxide composed of ZrO2 (Al2O3/ZrO2/La2O3/Nd2O3 = 50/46/2/2 - % by mass) was used. Rh at 0.3% by mass was supported on each support. Furthermore, Al2O3 impregnated with La at 25 g/L, barium acetate at 10 g/L, water, an Al2O3 binder, acetic acid, a thickener and the like were mixed together in predetermined amounts. Therefore, an Rh catalyst slurry was obtained.
    [0068] 875 cm3 of a monolithic substrate were prepared and were coated with the pastes described above using a suction process.
    [0069] In Comparative Example 1, catalytic layers having a two-layer structure, in which a Pd-supported catalytic layer and a Rh-supported catalytic layer were laminated, using the pastes described above, were formed over the entire length of the substrate.
    [0070] In Comparative Example 2, catalytic layers having a three-layer structure, in which a Pd-supported catalytic layer and a Rh-supported catalytic layer were laminated, using the pastes described above, were formed over the entire length of the substrate.
    [0071] On the other hand, in Example 1, as shown in Figure 2(a), the first catalytic layer having a length of 80% was formed on the upstream side, and the second catalytic layer having a length of 20% was formed on the downstream side (both layers were not overlapped).
    [0072] Furthermore, the configuration of the catalytic layers of Example 2 was the same as that of Example 1, although in the paste for forming the first catalytic layer, an oxide composed of ZrO2 not containing cerium was used. Regarding the durability test
    [0073] The prepared catalytic converter was placed immediately below a real engine, and a durability test was conducted on it, at a bed temperature of 1000°C for 5 hours, under a composite model in which an A/F ratio (air/fuel) varied cyclically. Regarding the engine bench evaluation
    [0074] After the durability test, the catalytic converter was placed in another real engine, and the purification performance was calculated as the average amount of NOx emission, when an A/F ratio was changed into a rectangular shape, from from a rich state to a poor state, and was held in the rich state for 120 seconds. The test results are shown in Figure 6.
    [0075] It has been found from the same drawing that the amount of NOx emission of Example 1 can be reduced by about 60% - 70%, compared to that of Comparative Examples 1 and 2.
    [0076] Furthermore, when Example 1 was compared with Example 2, it was found that the amount of NOx emission of Example 2 can be reduced to about 20% of that of Example 1.
    [0077] It was found from the experimental results that the ratio of the length of the second catalytic layer to the length of the substrate is preferably guaranteed to be equal to or greater than 20%. This 20% value can be defined as the lower limit of the second catalytic layer length ratio. Considering the results presented above and the results of experimental part 1, the ratio of the length of the second catalytic layer to the length of the substrate can be defined as being in a range of 20% to 50%.
    [0078] In the experiments described above, the ratio of the length of the first catalytic layer to the length of the substrate was set at 80%. It goes without saying that as the length of the first rhodium-containing catalytic layer increases, a catalytic converter, having superior NOx purification performance, can be obtained. Consequently, the value described above 80% can be defined as the lower limit of the ratio of the length of the first catalytic layer, and the value of 100%, in which the length of the first catalytic layer is equal to the length of the substrate, can be defined as the upper limit of the first catalytic layer length ratio. From the standpoint of reducing the amount of rhodium used, it is preferable that the length of the first catalytic layer be set to be about 80%. Therefore, the length of the first catalytic layer can be suitably adjusted over a range of length ratios from 80% to 100%.
    [0079] Furthermore, it was found that when the support constituting the first catalytic layer does not contain cerium, the NOx purification performance can be further improved.
    [0080] Above, embodiments of the present invention have been described with reference to the drawings. However, a specific configuration is not limited to the embodiments, and design changes and the like, which are made within a range, which do not depart from the scope of the present invention, are included in the invention. LIST OF REFERENCE SIGNALS 1 - SUBSTRATE, 2 - CELL WALL, 3, 3A, 3B, 3C, 3D, 3E - CATALYTIC LAYER, 4, 4A, 4B, 4C - FIRST CATALYTIC LAYER, 5, 5A - SECOND CATALYTIC LAYER, 10 - CATALYTIC CONVERTER, Fr - SIDE-UPSIDE IN THE DIRECTION OF DISCHARGE GAS FLOW, Rr - DOWNSTREAM SIDE IN THE DIRECTION OF DISCHARGE GAS FLOW
    权利要求:
    Claims (9)
    [0001]
    1. Catalytic converter (10), comprising: a substrate (1) having a cellular structure in which exhaust gas flows; and catalytic layers (3, 3A, 3B, 3C, 3D, 3E), which are formed on cell wall surfaces (2) of the substrate (1), characterized in that the catalytic layers (3, 3A, 3B, 3C , 3D, 3E) include a first catalytic layer (4, 4A, 4B, 4C) disposed on an upstream side (Fr) of the substrate (1) in a discharge gas flow direction and a second catalytic layer (5 , 5A), arranged on a downstream side (Rr) of the substrate (1) in the discharge gas flow direction, the first catalytic layer (4, 4A, 4B, 4C) is formed of a support and rhodium, which is a support-supported noble metal catalyst, the second catalytic layer (5, 5A) is formed of a support and a noble metal catalyst selected from a group consisting of palladium and platinum, the noble metal catalyst being supported on the support, the first catalytic layer (4, 4A, 4B, 4C) is formed in a first band from 80% to 100% of the total length of the substrate (1), the first band starting from a the end of the substrate (1) on the upstream side (Fr), and the second catalytic layer (5, 5A) is formed in a second strip of 20% to 50% of the total length of the substrate (1), the second strip leaving from one end of the substrate (1) on the downstream side (Rr), wherein the support of the first catalytic layer (4, 4A, 4B, 4C) does not contain cerium, and the first catalytic layer (4, 4A, 4B, 4C) ) is formed in the second catalytic layer (5, 5A), in a portion where the first catalytic layer (4, 4A, 4B, 4C) and the second catalytic layer (5, 5A) are superimposed on each other, the support of the the first catalytic layer (4, 4A, 4B, 4C) comprises a first oxide compound, the second catalytic layer support (5, 5A) comprises a second oxide compound, the first oxide compound is different from the second oxide compound, and the first layer catalytic (4, 4A, 4B, 4C) and the second catalytic layer (5, 5A) are arranged to form a layer structure as follows: (i) a single structure a layer of the first catalytic layer (4, 4A, 4B, 4C), (ii) a two-layer structure wherein the first catalytic layer (4, 4A, 4B, 4C) is stacked on top of the second catalytic layer (5 , 5A), and (iii) a single layer structure of the second catalytic layer (5, 5A) are arranged in this order from the upstream side (Fr) of the substrate (1) in the exhaust gas flow direction to the downstream side (Rr) of the substrate (1) in the direction of exhaust gas flow.
    [0002]
    2. Catalytic converter (10) according to claim 1, characterized in that the first catalytic layer (4, 4A, 4B, 4C) directly contacts the substrate (1) on the upstream side (Fr) of the substrate (1), and the second catalytic layer (5, 5A) directly contacts the substrate (1) on the downstream side (Rr) of the substrate (1).
    [0003]
    3. Catalytic converter (10) according to claim 1, characterized in that the second catalytic layer (5, 5A) directly contacts the substrate (1) along the entire length of the second catalytic layer ( 5, 5A).
    [0004]
    4. Catalytic converter (10) according to claim 1, characterized in that the first catalytic layer (4, 4A, 4B, 4C) comes directly in contact with the substrate (1) over 50% to 80 % of the total length of the substrate (1).
    [0005]
    5. Catalytic converter (10) according to claim 2, characterized in that the first catalytic layer (4, 4A, 4B, 4C) comes directly in contact with the substrate (1) over 50% to 80 % of the total length of the substrate (1).
    [0006]
    6. Catalytic converter (10) according to claim 3, characterized in that the first catalytic layer (4, 4A, 4B, 4C) directly contacts the substrate (1) over 50% to 80 % of the total length of the substrate (1).
    [0007]
    7. Catalytic converter (10) according to claim 1, characterized in that the second catalytic layer (5, 5A) is formed in a second range from 20% to less than 50% of the total length of the substrate (1).
    [0008]
    8. Catalytic converter (10) according to claim 1, characterized in that the second catalytic layer (5, 5A) is formed in a second range from 20% to 30% of the total length of the substrate (1).
    [0009]
    9. Catalytic converter (10), according to claim 1, characterized in that the second catalytic layer (5, 5A) is formed in a second range from 30% to 50% of the total length of the substrate (1).
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    同族专利:
    公开号 | 公开日
    BR112015019210A2|2017-07-18|
    WO2014125734A1|2014-08-21|
    US20150375206A1|2015-12-31|
    JP2014151306A|2014-08-25|
    US10010873B2|2018-07-03|
    CN104981288B|2017-07-21|
    CN104981288A|2015-10-14|
    JP5846137B2|2016-01-20|
    DE112013006665T5|2015-11-26|
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    法律状态:
    2018-11-21| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-08-13| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2021-03-30| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-05-11| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 19/12/2013, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2013025698A|JP5846137B2|2013-02-13|2013-02-13|Catalytic converter|
    JP2013-025698|2013-02-13|
    PCT/JP2013/084081|WO2014125734A1|2013-02-13|2013-12-19|Catalytic converter|
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