Exhaust gas purifier

Abstract

To provide an exhaust gas purifier having high HC purification performance and NOx purification performance.SOLUTION: The exhaust gas purifier includes a substrate having an upstream end and a downstream end, a first catalyst layer containing rhodium and provided on the substrate in a first region between the downstream end and a first position, a second catalyst layer containing rhodium-supported particles and provided on the substrate in a second region between the upstream end and a second position, and a third catalyst layer containing palladium and barium sulfate and provided on the second catalyst in a third region between the upstream end and a third position. The rhodium-supported particles include a porous carrier, monoclinic zirconium dioxide particles, and rhodium particles supported on the porous carrier. The total mass of barium sulfate based on the volume of the substrate in the third region is 10 to 20 g / L.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an exhaust gas purification device. [Background technology]

[0002] Exhaust gas discharged from internal combustion engines used in automobiles and other vehicles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Regulations on the emission of these harmful components are becoming stricter every year, and exhaust gas purification devices containing precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) as catalysts are used to remove these harmful components.

[0003] Patent Document 1 describes an exhaust gas purification device that includes a substrate and a catalytic layer provided on the substrate, the catalytic layer including a porous support, a catalytic metal belonging to the platinum group supported on the porous support, an alkaline earth metal supported on the porous support, and an alkaline earth metal not supported on the porous support, and at least a part of the alkaline earth metal supported on the porous support is supported inside the porous support, and it describes that the alkaline earth metal suppresses HC poisoning. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-066935 Summary of the Invention [Problem to be solved by the invention]

[0005] As exhaust gas regulations become more stringent, there is a demand for improved purification performance of exhaust gas purification devices. Therefore, the present disclosure provides an exhaust gas purification device having excellent HC purification performance and NOx purification performance. [Means for solving the problem]

[0006] Aspects of the present disclosure include the following. [Aspect 1] An exhaust gas purification device, A substrate having a total length (Ls), the substrate having an upstream end where exhaust gas flows into the substrate and a downstream end where the exhaust gas flows out of the substrate; a first catalyst layer containing rhodium provided on the substrate in a first region between the downstream end and a first position separated by a first distance (La) from the downstream end toward the upstream end, the first distance (La) being 50% to 70% of the total length (Ls) of the substrate; a second catalyst layer including rhodium-supported particles provided on the substrate in a second region between the upstream end and a second position separated by a second distance (Lb) from the upstream end toward the downstream end, the second distance (Lb) being 50% or more of the total length (Ls) of the substrate, the rhodium-supported particles including a porous carrier, and monoclinic zirconium dioxide particles and rhodium particles supported on the porous carrier; a third catalyst layer including palladium and barium sulfate provided on the second catalyst layer in a third region between the upstream end and a third position separated by a third distance (Lc) from the upstream end toward the downstream end, the third distance (Lc) being 40% or less of the total length (Ls) of the substrate, and a total mass of the barium sulfate based on the volume of the substrate in the third region being 10 to 20 g / L; An exhaust gas purification device comprising: Effect of the Invention

[0007] The exhaust gas purification device of the present disclosure has excellent HC purification performance and NOx purification performance. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an enlarged end view of a main part of an exhaust gas purification device according to one embodiment, cut along a plane parallel to the flow direction of exhaust gas, and shows a schematic configuration of partition walls of a substrate and their vicinity. [Diagram 2] FIG. 2 is a perspective view that illustrates an example of the base material. [Diagram 3] FIG. 3 is a graph showing the relationship between the amount of barium sulfate and the HC purification rate and NOx-T50. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In this application, a numerical range expressed using the symbol "~" includes the numerical values ​​before and after the symbol "~" as the lower and upper limits, respectively. In this application, "comprising ~" means that additional components may be included, and includes "consisting essentially of ~" and "consisting of ~". "Consisting essentially of ~" means that additional components that do not have a substantial adverse effect may be included. "Consisting of ~" means that only the materials described are included, but does not exclude the inclusion of unavoidable impurities.

[0010] An exhaust gas purification device 100 according to an embodiment will be described with reference to Figures 1 and 2. The exhaust gas purification device 100 according to the embodiment includes a substrate 10, a first catalyst layer 20, a second catalyst layer 30, and a third catalyst layer 40.

[0011] (1) Base material 10 The shape of the substrate 10 is not particularly limited, but for example, as shown in Fig. 2, the substrate 10 may be composed of a frame portion 12 and partition walls 16 that divide the space inside the frame portion 12 to define a plurality of cells 14. The partition walls 16 extend between a first end (first end face) I and a second end (second end face) J of the substrate 10, and define a plurality of cells 14 extending between the first end I and the second end J.

[0012] The substrate 10 is, for example, cordierite (2MgO·2Al 2 O 3 5SiO 2 ), a ceramic material having high heat resistance such as alumina, zirconia, silicon carbide, or a metal foil such as stainless steel foil.

[0013] 1 and 2, dashed arrows indicate the flow direction of exhaust gas in the exhaust gas purification device 100 and the substrate 10. Exhaust gas flows into the cells 14 of the substrate 10 through the first end I and flows out of the cells 14 of the substrate 10 through the second end J. Therefore, hereinafter, the first end I will also be referred to as the upstream end I and the second end J as the downstream end J, as appropriate. In this specification, the length between the upstream end I and the downstream end J, i.e., the total length of the substrate 10, will be represented as Ls.

[0014] (2) First catalyst layer 20 The first catalyst layer 20 is formed on the substrate 10 in a first region X between the downstream end J and a first position P separated by a first distance La from the downstream end J toward the upstream end I (i.e., in the opposite direction to the flow direction of the exhaust gas). The first distance La is 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 extension direction of the cells 14.

[0015] The first catalyst layer 20 includes rhodium (Rh). Rh mainly functions as a catalyst for reducing NOx. Rh may be in particulate form. Rh may be supported on support particles. The support particles may be porous particles including a metal oxide. The metal oxide may be, for example, an oxide of at least one metal selected from the group consisting of metals of groups 3, 4, and 13 of the periodic table and metals of the lanthanoid series, and may optionally include yttria (Y 2 O 3 ), Lantana (La 2 O 3 ), neodymia (Nd 2 O 3 ), or praseodymia (Pr 6 O 11 ) may further be included as an additive. Yttria, lanthana, neodymia, and praseodymia can improve the heat resistance of the metal oxide.

[0016] The first catalyst layer 20 may include an oxygen storage material that stores oxygen in an oxygen-rich atmosphere and releases oxygen in an oxygen-deficient atmosphere. Examples of oxygen storage materials include ceria (CeO 2), composite oxides of ceria and other oxides (e.g., ceria and zirconia (ZrO 2 ) composite oxide (Ce-Zr composite oxide), alumina (Al 2 O 3 ), composite oxides of ceria and zirconia (Al-Ce-Zr composite oxide), materials to which additives have been added, and mixtures thereof. The additive may be, for example, at least one of lanthana, yttria, neodymia, and praseodymia. The first catalyst layer 20 may further contain other optional components. Examples of the other optional components include binders and additives.

[0017] (3) Second catalyst layer 30 The second catalyst layer 30 is formed on the substrate 10 in a second region Y between the upstream end I and a second position Q separated by a second distance Lb from the upstream end I toward the downstream end J (i.e., 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 second catalyst layer 30 may have a length equal to the second distance Lb in the extension direction of the cells 14.

[0018] The second catalyst layer 30 includes Rh-supporting particles. The Rh-supporting particles are formed of a porous support and monoclinic zirconium dioxide (ZrO 2 ) particles and Rh particles. The Rh particles mainly function as a catalyst for reducing NOx. The porous support may be in particulate form and may include the metal oxides mentioned above. Rh particles and ZrO 2 The particles may be supported within the pores of a porous support, and the Rh particles and ZrO 2 The particles may be in contact.

[0019] By using such Rh-supported particles, as shown in the examples described later, the barium sulfate (BaSO 4 ) can suppress the decrease in NOx purification performance associated with an increase in the NOx purification efficiency.

[0020] The second catalyst layer 30 may include an oxygen storage material. Examples of the oxygen storage material are as described above. The oxygen storage material in the second catalyst layer 30 may include a pyrochlore-type Ce—Zr composite oxide and a fluorite-type Ce—Zr composite oxide. The second catalyst layer 30 may further include other optional components. Examples of the other optional components include a binder and an additive.

[0021] (4) Third catalyst layer 40 The third catalyst layer 40 is formed on the second catalyst layer 30 in a third region Z between the upstream end I and a third position R separated by a third distance Lc from the upstream end I toward the downstream end J (i.e., in the flow direction of exhaust gas). By forming the third catalyst layer 40 on the second catalyst layer 30, the exhaust gas purification device 100 can have high warm-up properties. The third distance Lc is 40% or less, particularly 30% or less, of the total length Ls of the substrate 10. This allows the exhaust gas purification device 100 to have high warm-up properties. The third catalyst layer 40 may have a length equal to the third distance Lc in the extension direction of the cells 14.

[0022] The third catalyst layer 40 contains palladium (Pd). Pd mainly functions as a catalyst for oxidizing HC. The palladium may be in particulate form. The Pd may be supported on support particles. The support particles may be porous particles containing the above-mentioned metal oxides.

[0023] The third catalyst layer 40 is made of BaSO 4 The volume of the substrate in the third region is based on BaSO. 4 The total mass of BaSO is 10 to 20 g / L. As a result, as shown in the examples described later, the exhaust gas purification device 100 according to the embodiment can have high HC purification performance. 4 and the second catalyst layer 30 contains the above-mentioned Rh-supported particles, the exhaust gas purification device 100 according to the embodiment can have high NOx purification performance in addition to high HC purification performance, as shown in the examples described later.

[0024] The third catalytic layer 40 may include an oxygen storage material. Examples of the oxygen storage material are as described above. The oxygen storage material in the third catalytic layer 40 may include a fluorite-type Ce-Zr composite oxide. The third catalytic layer 40 may further include other optional components. Examples of the other optional components include a binder and an additive.

[0025] The exhaust gas purification device 100 according to the embodiment can be applied to various vehicles equipped with an internal combustion engine.

[0026] The present invention is not limited to the above-described embodiment. Various modifications, additions, and deletions can be made without departing from the technical idea or scope of the present invention described in the claims. EXAMPLES

[0027] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0028] (1) Materials used in the Examples and Comparative Examples a) Substrate (honeycomb substrate) Material: Cordierite, Capacity: 875cc, Partition thickness: 2mil (50.8μm), Cell density: 600 cells per square inch, Cell cross-sectional shape: hexagonal

[0029] b) Material 1: Al 2 O 3 To La 2 O 3 The material obtained by adding La 2 O 3 :1wt%~10wt%).

[0030] c) Material 2 (fluorite type Ce-Zr composite oxide): Al 2 O 3 -CeO 2 -ZrO 2 A trace amount of Nd in the composite oxide 2 O 3 , La 2 O 3 , and Y 2 O3 The material with a fluorite structure (CeO 2 :15wt%~30wt%).

[0031] d) Material 3 (Pyrochlore-type Ce-Zr composite oxide): CeO 2 and ZrO 2 A complex oxide containing approximately equal amounts of rare earth metals, such as Pr, 6 O 11 , La 2 O 3 , Y 2 O 3 , and Nd 2 O 3 The pyrochlore structure material (CeO 2 : 45mol%~65mol%, ZrO 2 :45mol%~65mol%).

[0032] e) Material 4: Palladium nitrate aqueous solution

[0033] f) Material 5: Rhodium nitrate aqueous solution

[0034] g) Material 6: Barium sulfate

[0035] h) Material 7: Monoclinic ZrO 2 Particle dispersion liquid (ZSL00013 manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.)

[0036] (2) Construction of exhaust gas purification device Comparative Example 1 Materials 1, 2, 3, and 5 were added to the stirred distilled water and mixed to prepare a suspended slurry 1. Slurry 1 was poured into the cell from the downstream end of the substrate, and excess slurry was blown off with a blower. As a result, the partition walls of the substrate were coated with slurry 1 in a first region between the downstream end of the substrate and a first position separated by a distance of 50% of the total length of the substrate from the downstream end of the substrate toward the upstream end of the substrate. The substrate was placed in a dryer with an internal temperature maintained at 120° C. for 2 hours to evaporate the water in slurry 1. Then, the substrate was baked in an electric furnace at 500° C. for 2 hours. As a result, a first catalyst layer was formed.

[0037] The amount of material 1 contained in the first catalyst layer based on the volume of the substrate in the first region was 80 g / L, the amount of material 2 was 60 g / L, the amount of material 3 was 30 g / L, and the amount of Rh particles derived from material 5 was 0.3 g / L.

[0038] Material 1 was added to distilled water under stirring, and nitric acid was added to adjust the pH to 3. Material 7 was added to the water and stirred. The mixture was dried and calcined. 2 O 3 Added Al 2 O 3 Particles and monoclinic ZrO supported on them 2 Monoclinic ZrO composed of particles 2 Supported Al 2 O 3 particles were obtained.

[0039] Monoclinic ZrO 2 Supported Al 2 O 3The particles, material 2, material 3, and material 5 were added and mixed to prepare a suspended slurry 2. The slurry 2 was poured into the cell from the upstream end of the substrate, and excess slurry was blown off with a blower. As a result, the partition walls of the substrate were coated with the slurry 2 in the second region between the upstream end of the substrate and a second position separated by a distance of 50% of the total length of the substrate from the upstream end of the substrate toward the downstream end of the substrate. The substrate was placed in a dryer with an internal temperature maintained at 120°C for 2 hours to evaporate water in the slurry 2, and then calcined in an electric furnace at 500°C for 2 hours. As a result, a second catalyst layer was formed.

[0040] The amount of monoclinic ZrO contained in the second catalyst layer based on the volume of the substrate in the second region. 2 Supported Al 2 O 3 The particle amount is 66g / L (including monoclinic ZrO 2 The amount of Rh particles from material 1 was 0.4 g / L, the amount from material 2 was 45 g / L, the amount from material 3 was 9 g / L, and the amount of Rh particles from material 5 was 0.3 g / L.

[0041] Materials 1, 2, 4, and 6 were added to the stirred distilled water and mixed to prepare a suspended slurry 3. The slurry 3 was poured into the cell from the upstream end of the substrate, and excess slurry was blown off with a blower. As a result, a layer of the slurry 3 was formed in a third region between the upstream end of the substrate and a third position separated by a distance of 30% of the total length of the substrate from the upstream end of the substrate toward the downstream end of the substrate. The substrate was placed in a dryer with an internal temperature maintained at 120° C. for 2 hours to evaporate the water in the slurry 3, and then calcined in an electric furnace at 500° C. for 2 hours. As a result, a third catalyst layer was formed on the second catalyst layer.

[0042] The amount of material 1 contained in the third catalyst layer based on the volume of the substrate in the third region was 30 g / L, the amount of material 2 was 50 g / L, the amount of Pd particles derived from material 4 was 5.0 g / L, and the amount of material 6 (barium sulfate) was 5 g / L. In this manner, the exhaust gas purification device of Comparative Example 1 was obtained.

[0043] Examples 1 and 2 An exhaust gas purification device was prepared in the same manner as in Comparative Example 1, except that the amount of material 6 (barium sulfate) contained in the third catalyst layer based on the volume of the substrate in the third region was as shown in Table 1.

[0044] Comparative Example 2 Monoclinic ZrO 2 Supported Al 2 O 3 Without particle preparation, monoclinic ZrO 2 Supported Al 2 O 3 An exhaust gas purifying device was produced in the same manner as in Comparative Example 1, except that Material 1 was used instead of the particles.

[0045] Comparative Examples 3 and 4 An exhaust gas purification device was prepared in the same manner as in Comparative Example 2, except that the amount of material 6 (barium sulfate) contained in the third catalyst layer based on the volume of the substrate in the third region was as shown in Table 1.

[0046] Comparative Example 5 An exhaust gas purifying device was produced in the same manner as in Comparative Example 2, except that the slurry 3 was prepared without adding the material 6.

[0047] (3) Aging treatment The exhaust gas purification devices of the Example and Comparative Example were each connected to the exhaust system of a 4.6L V8 engine. While maintaining the bed temperature of the exhaust gas purification device at 950°C for 50 hours, a stoichiometric mixture (air-fuel ratio A / F=14.6) and a lean mixture containing excess oxygen (A / F>14.6) were alternately introduced into the engine at a time ratio of 3:1 at a fixed interval. This aging treatment was performed on the exhaust gas purification device.

[0048] (4) Measurement of HC purification rate under continuous rich conditions The aged exhaust gas purification device was connected to the exhaust system of a 2.5L L-type 4-cylinder engine. A fuel-rich air-fuel mixture (A / F=14.4) was introduced into the engine, and exhaust gas from the engine at approximately 550°C was introduced into the exhaust gas purification device. The HC content of the exhaust gas at the upstream and downstream ends of the exhaust gas purification device was measured approximately 3 minutes after the start of the introduction of the air-fuel mixture, and the HC purification rate was calculated. The results are shown in Table 1 and Figure 3.

[0049] Al in the second catalyst layer 2 O 3 Monoclinic ZrO to particles 2 Regardless of whether or not Pd was supported, the more barium sulfate in the third catalyst layer, the higher the HC purification rate under fuel-rich conditions. This is presumably because barium sulfate suppresses the HC poisoning of Pd.

[0050] (5) NOx purification performance evaluation The aged exhaust gas purification device was connected to the exhaust system of a 2.5L L-type 4-cylinder engine. A fuel-rich mixture (A / F=14.4) was introduced into the engine, and the exhaust gas from the engine at about 600°C was cooled to 200°C by a heat exchanger and introduced into the exhaust gas purification device. The heat exchanger was controlled to raise the temperature of the exhaust gas introduced into the exhaust gas purification device from 200°C at a constant rate, and during this time, the NOx content of the exhaust gas at the upstream and downstream ends of the exhaust gas purification device was measured to determine the NOx purification rate. Note that the exhaust flow rate was made sufficiently large and the exhaust temperature rise rate was made sufficiently small so that the exhaust gas purification device always had a uniform temperature in the gas flow direction. The exhaust temperature when the NOx purification rate reached 50% (NOx-T50) is shown in Table 1 and Figure 3. The lower the NOx-T50, the higher the NOx purification performance.

[0051] Al in the second catalyst layer 2 O 3 Monoclinic ZrO to particles 2When no Rh was supported, the NOx purification performance was greatly improved by the inclusion of barium sulfate in the third catalyst layer. However, as the amount of barium sulfate in the third catalyst layer increased, the NOx purification performance decreased. The inventors speculate that this is because Rh was deactivated by coming into contact with barium sulfate and being stabilized as an oxide.

[0052] On the other hand, Al in the second catalyst layer 2 O 3 Particles are monoclinic ZrO 2 When Rh was supported on the catalyst, the decrease in NOx purification performance due to the increase in barium sulfate in the third catalyst layer was small. This is because Rh was supported on the catalyst in monoclinic ZrO 2 The inventors speculate that this is because Rh is stabilized by being supported on the carrier together with Rh, and the interaction between Rh and barium sulfate in the third catalyst layer is reduced. In particular, when the amount of barium sulfate was within the range of 10 to 20 g / L, there was almost no decrease in NOx purification performance due to an increase in barium sulfate.

[0053] [Table 1] [Explanation of symbols]

[0054] 10: substrate, 12: frame, 14: cell, 16: partition wall, 20: first catalyst layer, 30: second catalyst layer, 40: third catalyst layer, 100: exhaust gas purification device, I: upstream end (first end), J: downstream end (second end), P: first position, Q: second position, R: third position, X: first region, Y: second region, Z: third region

Claims

[Claim 1] An exhaust gas purification device, A substrate having a total length (Ls), the substrate having an upstream end where exhaust gas flows into the substrate and a downstream end where the exhaust gas flows out of the substrate; a first catalyst layer including rhodium provided on the substrate in a first region between the downstream end and a first position separated by a first distance (La) from the downstream end toward the upstream end, the first distance (La) being 50% to 70% of the total length (Ls) of the substrate; a second catalyst layer including rhodium-supported particles provided on the substrate in a second region between the upstream end and a second position separated by a second distance (Lb) from the upstream end toward the downstream end, the second distance (Lb) being 50% or more of the entire length (Ls) of the substrate, the rhodium-supported particles including a porous carrier, and monoclinic zirconium dioxide particles and rhodium particles supported on the porous carrier; and a third catalyst layer including palladium and barium sulfate provided on the second catalyst layer in a third region between the upstream end and a third position separated by a third distance (Lc) from the upstream end toward the downstream end, the third distance (Lc) being 40% or less of the total length (Ls) of the substrate, and a total mass of the barium sulfate based on the volume of the substrate in the third region being 10 to 20 g / L; An exhaust gas purification device comprising:

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