Patent Application
20240390853
The present application claims priority from Japanese patent application JP 2023-084149 filed on May 22, 2023, the entire content of which is hereby incorporated by reference into this application.
The present disclosure relates to an exhaust gas purification device.
An exhaust gas emitted from an internal combustion engine used in a vehicle, such as an automobile, contains a harmful substance, such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx). Regulations on emission amounts of these harmful substances have been tightened year by year. To remove these harmful substances, an exhaust gas purification device including a noble metal, such as platinum (Pt), palladium (Pd), and rhodium (Rh), as a catalyst has been used.
JP 2001-205051 A discloses an exhaust gas purification device for satisfying a warm-up performance, an HC conversion performance, and durability.
It is desired to further improve the warm-up performance of the exhaust gas purification device. It is also desired to further reduce performance deterioration of the exhaust gas purification device in use.
In such a circumstance, the present disclosure provides an exhaust gas purification device having a high warm-up performance and a reduced performance deterioration due to use.
The present disclosure includes the following aspects.
1. An exhaust gas purification device comprising:
The exhaust gas purification device of the present disclosure has the high warm-up performance and reduced performance deterioration due to use.
The following will describe embodiments of the present disclosure with reference to the drawings. In the drawings referred in the following description, same reference numerals may be used for the same members or members having similar functions, and their repeated descriptions may be omitted in some cases. For convenience of explanation, a dimensional ratio in the drawings may differ from the actual ratio, and a part of a member may be omitted from the drawing in some cases. A numerical range expressed herein using the term “to” includes values described before and after the term “to” as the lower limit value and the upper limit value, respectively. Upper limit values and lower limit values of numerical ranges described herein can be appropriately combined. The term “on” herein includes both of “directly on” and “indirectly on” insofar as it is not especially specified in the context. The terms “comprise”, “include”, and “contain” herein mean that an additional component may be contained, and encompass the term “consist essentially of” and the term “consist of.” The term “consist essentially of” means that an additional component having substantially no adverse effect may be contained. The term “consist of” means including only described materials, but does not exclude inclusion of inevitable impurities.
An exhaust gas purification device 100 according to the embodiment will be described with reference to
The shape of the substrate 10 is not specifically limited. For example, as illustrated in
For example, the substrate 10 may be formed of a ceramic material having a high heat resistance, such as cordierite (2MgO·2Al2O3·5SiO2), alumina, zirconia, and silicon carbide, or a metal foil, such as a stainless-steel foil.
In
The first catalyst layer 20 is disposed on the substrate 10 in a first region X extending between the downstream end J and a first position P, which is at a first distance La from the downstream end J toward the upstream end I (that is, in an opposite direction of the flow direction of the exhaust gas). The first distance La is from 50% to 70% of the total length Ls of the substrate 10. The first catalyst layer 20 may have a length equal to the first distance La in the extending direction of the cell 14.
The first catalyst layer 20 contains rhodium. Rhodium mainly functions as a catalyst to reduce NOx. Rhodium may be particulate. Rhodium may be supported on carrier particles. The carrier particles may contain a metal oxide.
The first catalyst layer 20 may contain an oxygen storage material that stores oxygen in the atmosphere under oxygen excess atmosphere and releases oxygen under oxygen deficient atmosphere. Examples of the oxygen storage material include ceria (CeO2), composite oxides of ceria and another oxide (for example, a Ce—Zr composite oxide, which is a composite oxide of ceria and zirconia (ZrO2), and an Al—Ce—Zr composite oxide, which is a composite oxide of alumina (Al2O3), ceria, and zirconia), materials obtained by adding an additive to them, and mixtures thereof. The additive may be, for example, at least one of lanthana (La2O3), yttria (Y2O3), neodymia (Nd2O3), or praseodymia (Pr6O11), and these materials allow the heat resistance of the oxygen storage material to be improved. The additive may form a composite oxide together with a main component of the oxygen storage material. In particular, a Ce—Zr composite oxide may be used as the oxygen storage material because it has a high oxygen storage capacity (OSC) and is relatively inexpensive. The Ce—Zr composite oxide may have a structure of a pyrochlore type or a fluorite type. The oxygen storage material in the first catalyst layer 20 may contain a pyrochlore type Ce—Zr composite oxide and a fluorite type Ce—Zr composite oxide.
The first catalyst layer 20 may further contain another optional ingredient. Examples of another optional ingredient include, for example, a binder and an additive.
The total mass of the first catalyst layer 20 may be 170 g/L or more based on the capacity (volume) of the substrate 10 in the first region X. This provides the first catalyst layer 20 with a large thermal capacity (heat capacity), which reduces the temperature drop of the first catalyst layer 20 when a low-temperature exhaust gas flows into the exhaust gas purification device 100, allowing the exhaust gas purification device 100 to perform a satisfactory exhaust gas purification performance.
The first catalyst layer 20 can be formed as follows, for example. First, a slurry is prepared by mixing an aqueous solution of rhodium salt, an oxygen storage material, and an optional ingredient. The slurry is applied to the substrate 10 in the first region X, thus forming a slurry layer. The slurry layer is heated to be dried and sintered. Thus, the first catalyst layer 20 is formed on the substrate 10 in the first region X.
The second catalyst layer 30 is disposed on the substrate 10 in a second region Y extending between the upstream end I and a second position Q, which is at a second distance Lb from the upstream end I toward the downstream end J (that is, in the flow direction of the exhaust gas). The second distance Lb is 50% or more of the total length Ls of the substrate 10. The sum of the first distance La and the second distance Lb is equal to or greater than the total length Ls of the substrate 10. This allows the whole region of the substrate 10 to be covered with at least one of the first catalyst layer 20 or the second catalyst layer 30, which provides the exhaust gas purification device 100 with the satisfactory exhaust gas purification performance. The second catalyst layer 30 may have a length equal to the second distance Lb in the extending direction of the cell 14.
The second catalyst layer 30 contains rhodium. Rhodium mainly functions as a catalyst to reduce NOx. Rhodium may be particulate. Rhodium may be supported on carrier particles. The carrier particles may contain a metal oxide.
The second catalyst layer 30 contains an oxygen storage material. Examples of the oxygen storage material are as described above. The oxygen storage material in the second catalyst layer 30 contains a pyrochlore type Ce—Zr composite oxide and a fluorite type Ce—Zr composite oxide at a weight ratio of from 0.2:1 to 0.4:1. This allows the exhaust gas purification device 100 to have a high warm-up performance and a reduced deterioration of performance in use.
The second catalyst layer 30 may further contain another optional ingredient. Examples of another optional ingredient include, for example, a binder and an additive.
The second catalyst layer 30 can be formed as follows, for example. First, a slurry is prepared by mixing an aqueous solution of rhodium salt, an oxygen storage material, and an optional ingredient. The slurry is applied to the substrate 10 in the second region Y, thus forming a slurry layer. The slurry layer is heated to be dried and sintered. Thus, the second catalyst layer 30 is formed on the substrate 10 in the second region Y.
The third catalyst layer 40 is disposed on the second catalyst layer 30 in a third region Z extending between the upstream end I and a third position R, which is at a third distance Lc from the upstream end I toward the downstream end J (that is, in the flow direction of the exhaust gas). The third catalyst layer 40 formed on the second catalyst layer 30 allows the exhaust gas purification device 100 to have a high warm-up performance. The third distance Lc is 40% or less, especially 30% or less of the total length Ls of the substrate 10. This allows the exhaust gas purification device 100 to have a high warm-up performance. The third catalyst layer 40 may have a length equal to the third distance Lc in the extending direction of the cell 14.
The third catalyst layer 40 contains palladium. Palladium mainly functions as a catalyst to oxidize HC. Palladium may be particulate. Palladium may be supported on carrier particles. The carrier particles may contain a metal oxide.
The third catalyst layer 40 may contain an oxygen storage material. Examples of the oxygen storage material are as described above. The oxygen storage material in the third catalyst layer 40 may contain a fluorite type Ce—Zr composite oxide.
The third catalyst layer 40 may further contain another optional ingredient. Examples of another optional ingredient include, for example, a binder and an additive.
The total mass of the third catalyst layer 40 may be more than 0 g/L and 105 g/L or less based on the capacity of the substrate 10 in the third region Z. This provides the third catalyst layer 40 with a small thermal capacity, which allows the temperature of the third catalyst layer 40 to rise in a short period of time during warm-up, resulting in a satisfactory exhaust gas purification performance. That is, the exhaust gas purification device 100 can have the high warm-up performance.
The third catalyst layer 40 can be formed as follows, for example. First, a slurry is prepared by mixing an aqueous solution of palladium salt, an oxygen storage material, and an optional ingredient. The slurry is applied on the second catalyst layer 30 in the third region Z, thus forming a slurry layer. The slurry layer is heated to be dried and sintered. Thus, the third catalyst layer 40 is formed on the second catalyst layer 30 in the third region Z.
The exhaust gas purification device 100 according to the embodiment is applicable to various vehicles that include internal combustion engines.
The present disclosure is not limited to the above-described embodiments. The present disclosure can be subjected to various kinds of changes, additions, and deletions without departing from the technical spirit or scope of the present disclosure described in the claims.
The following will specifically describe the present disclosure with the examples, but the present disclosure is not limited to these examples.
A material obtained by adding La2O3 to Al2O3(La2O3: 1 wt % to 10 wt %).
c) Material 2 (fluorite type Ce—Zr composite oxide)
A material having a fluorite type structure obtained by adding trace amounts of
Nd2O3, La2O3, and Y2O3 to an Al2O3—CeO2—ZrO2 composite oxide (CeO2: 15 wt % to 30 wt %).
A material having a pyrochlore type structure obtained by adding trace amounts of rare-earth metal oxides, such as Pr6O11, La2O3, Y2O3, and Nd2O3, to a composite oxide containing CeO2 and ZrO2 by approximately equal molecular weights and subjecting it to a reduction treatment at a high temperature (CeO2: 45 mol % to 65 mol %, ZrO2: 45 mol % to 65 mol %).
Aqueous solution of palladium nitrate
Aqueous solution of rhodium nitrate
Barium sulfate
The material 1, the material 2, the material 3, and the material 5 were added to stirred distilled water and mixed to prepare a suspended slurry 1. The prepared slurry 1 was poured through the downstream end of the substrate into the cells, and excess slurry was blown off with a blower. Consequently, the partition wall of the substrate was coated with the slurry 1 in the first region between the downstream end of the substrate and the first position, which was at a distance of 50% of the total substrate length from the downstream end of the substrate toward the upstream end of the substrate. The substrate was placed in a drying machine whose inside was held at 120° C. for two hours to vaporize water contained in the slurry 1. Next, the substrate was heated in an electric furnace at 500° C. for two hours. Thus, a first catalyst layer was formed.
The first catalyst layer contained the material 1 in an amount of 80 g/L, the material 2 in an amount of 60 g/L, the material 3 in an amount of 30 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the first region.
Next, the material 1, the material 2, the material 3, and the material 5 were added to stirred distilled water and mixed to prepare a suspended slurry 2. The prepared slurry 2 was poured through the upstream end of the substrate into the cells, and excess slurry was blown off with a blower. Consequently, the partition wall of the substrate was coated with the slurry 2 in the second region between the upstream end of the substrate and the second position, which was at a distance of 50% of the total substrate length from the upstream end of the substrate toward the downstream end of the substrate. The substrate was placed in a drying machine whose inside was held at 120° C. for two hours to vaporize water contained in the slurry 2. Next, the substrate was heated in an electric furnace at 500° C. for two hours. Thus, a second catalyst layer was formed.
The second catalyst layer contained the material 1 in an amount of 66 g/L, the material 2 in an amount of 45 g/L, the material 3 in an amount of 9 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the second region.
Next, the material 1, the material 2, the material 4, and the material 6 were added to stirred distilled water and mixed to prepare a suspended slurry 3. The prepared slurry 3 was poured through the upstream end of the substrate into the cells, and excess slurry was blown off with a blower. Consequently, a layer of the slurry 3 was formed in the third region between the upstream end of the substrate and the third position, which was at a distance of 30% of the total substrate length from the upstream end of the substrate toward the downstream end of the substrate. The substrate was placed in a drying machine whose inside was held at 120° C. for two hours to vaporize water contained in the slurry 3. Next, the substrate was heated in an electric furnace at 500° C. for two hours. Thus, a third catalyst layer was formed on the second catalyst layer.
The third catalyst layer contained the material 1 in an amount of 30 g/L, the material 2 in an amount of 50 g/L, Pd particles derived from the material 4 in an amount of 5.0 g/L, and the material 6 in an amount of 20 g/L, based on the capacity of the substrate in the third region.
Thus, an exhaust gas purification device of Example 1 was obtained.
An exhaust gas purification device was produced similarly to Example 1 except that the second catalyst layer contained the material 1 in an amount of 58 g/L, the material 2 in an amount of 45 g/L, the material 3 in an amount of 17 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the second region.
An exhaust gas purification device was produced similarly to Example 1 except that the second catalyst layer contained the material 1 in an amount of 70 g/L, the material 2 in an amount of 45 g/L, the material 3 in an amount of 4.5 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the second region.
An exhaust gas purification device was produced similarly to Example 1 except that the second catalyst layer contained the material 1 in an amount of 41 g/L, the material 2 in an amount of 45 g/L, the material 3 in an amount of 34 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the second region.
An exhaust gas purification device was produced similarly to Comparative Example 1 except that the first catalyst layer contained the material 1 in an amount of 60 g/L, the material 2 in an amount of 60 g/L, the material 3 in an amount of 30 g/L, and Rh particles derived from the material 5 in an amount of 0.3 g/L, based on the capacity of the substrate in the first region, and that the second catalyst layer was formed after the third catalyst layer was formed (that is, the third catalyst layer was formed between the substrate and the second catalyst layer).
An exhaust gas purification device was produced similarly to Comparative Example 1 except that the third catalyst layer contained of the material 1 in an amount of 50 g/L, the material 2 in an amount of 50 g/L, Pd particles derived from the material 4 in an amount of 5.0 g/L, and the material 6 in an amount of 20 g/L, based on the capacity of the substrate in the third region, and that the second catalyst layer was formed after the third catalyst layer was formed (that is, the third catalyst layer was formed between the substrate and the second catalyst layer).
Table 1 summarizes the weight ratio (P:F) of the material 3 (pyrochlore type Ce—Zr composite oxide) to the material 2 (fluorite type Ce—Zr composite oxide) in the second catalyst layer, the vertical relation between the second catalyst layer and the third catalyst layer, the total amount of the first catalyst layer based on the capacity of the substrate in the first region, the total amount of the second catalyst layer based on the capacity of the substrate in the second region, and the total amount of the third catalyst layer based on the capacity of the substrate in the third region in each of the examples and the comparative examples.
Each of the exhaust gas purification devices of the examples and the comparative examples was connected to an exhaust system of a V8 engine with a displacement of 4.6 L. A stoichiometric air-fuel mixture (air-fuel ratio A/F=14.6) and a lean air-fuel mixture containing excess oxygen (A/F>14.6) were alternately introduced to the engine at a time ratio of 3:1 on a fixed time cycle for 50 hours while a bed temperature of the exhaust gas purification device was maintained at 950° C. This was how the aging treatment of the exhaust gas purification devices was carried out.
The center of the exhaust gas purification device after the aging treatment was cooled to 50° C., and then the exhaust gas purification device was connected to an exhaust system of an L4 engine with a displacement of 2.5 L. An air-fuel mixture having A/F of 14.4 was introduced to the engine, and the exhaust gas at about 500° C. from the engine was introduced to the exhaust gas purification device. The THC contents of the exhaust gases at the upstream and downstream ends of the exhaust gas purification device were measured to determine the THC conversion rate. The time from the start of the introduction of the exhaust gas at 500° C. to the exhaust gas purification device until the THC conversion rate reached 50% is shown in Table 2 and
As illustrated in
The exhaust gas purification device of Comparative Example 4 in which the total amount of the third catalyst layer was 125 g/L exhibited the lower warm-up performance than the exhaust gas purification device of Comparative Example 3 in which the total amount of the third catalyst layer was 105 g/L. This would be because the total amount of the third catalyst layer was larger, i.e., the thermal capacity was larger, in Comparative Example 4, so the time required to raise the temperature of the exhaust gas purification device was longer. Although the total amount of the first catalyst layer was also different between Comparative Example 3 and Comparative Example 4, the difference in the total amount of the first catalyst layer would have had little effect on the warm-up performance because the first catalyst layer was kept at a relatively low temperature during the warm-up performance evaluation test, which would have led to only a small amount of THC conversion by the first catalyst layer.
The exhaust gas purification device of Comparative Example 1 in which the second catalyst layer was the lower layer and the third catalyst layer was the upper layer exhibited the higher warm-up performance than the exhaust gas purification device of Comparative Example 3 in which the second catalyst layer was the upper layer and the third catalyst layer was the lower layer. Although the total amount of the first catalyst layer was also different between Comparative Example 1 and Comparative Example 3, the difference in the total amount of the first catalyst layer would have had little effect on the warm-up performance as described above.
The exhaust gas purification device after the aging treatment was connected to an exhaust system of an L4 engine with a displacement of 2.5 L. An air-fuel mixture having A/F of 14.4 was introduced to the engine, and the exhaust gas at 600° C. from the engine was cooled to 200° C. by a heat exchanger and introduced to the exhaust gas purification device. While the heat exchanger was controlled to raise the temperature of the exhaust gas introduced to the exhaust gas purification device from 200° C. at a constant rate, the NOx contents of the exhaust gases at the upstream and downstream ends of the exhaust gas purification device were measured to determine the NOx conversion rate. The flow rate of the exhaust gas was sufficiently large, and the rate of increase of the exhaust gas temperature was sufficiently small so that the exhaust gas purification device always had a uniform temperature in the gas flow direction. The exhaust gas temperature when the NOx conversion rate reached 50% (NOx-T50) is shown in Table 2 and
As illustrated in
The exhaust gas purification device of Comparative Example 1 exhibited the lower catalytic activity than the exhaust gas purification devices of Comparative Examples 3 and 4 in which the second catalyst layer was the upper layer and the third catalyst layer was the lower layer. However, the exhaust gas purification devices of Examples 1 and 2 and Comparative Example 2 exhibited the catalytic activity equal to or greater than the catalytic activity of the exhaust gas purification devices of Comparative Examples 3 and 4.
The exhaust gas purification device after the aging treatment was connected to an exhaust system of an LA engine with a displacement of 2.5 L. An air-fuel mixture having A/F of 14.4 was introduced to the engine, and the exhaust gas from the engine was introduced to the exhaust gas purification device. The temperature of the exhaust gas at the upstream end of the exhaust gas purification device was first set at 600° C., and then lowered to 500° C. or less, during which the NOx contents of the exhaust gases at the upstream and downstream ends of the exhaust gas purification device were measured to determine the NOx conversion rate. The NOx conversion rate when the temperature of the exhaust gas at the upstream end of the exhaust gas purification device became 500° C. is shown in Table 2 and
As illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-084149 | May 2023 | JP | national |
