JP5555524B2 - Exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst.

  Patent Document 1 describes an exhaust gas purifying catalyst including a honeycomb substrate and a catalyst layer. The catalyst layer employs a multilayer structure including a lower layer and an upper layer in order to achieve high exhaust gas purification efficiency.

  In such an exhaust gas purifying catalyst, when the lower layer is thickened, the thickness of the entire catalyst layer increases, and as a result, the pressure loss increases. As pressure loss increases, engine performance may be reduced.

  Further, as described in Patent Document 2, in the exhaust gas purifying catalyst, the composition of the catalyst layer may be different between the upstream portion and the downstream portion. Such a configuration is widely adopted as a technique for improving exhaust gas purification efficiency.

JP 2008-23501 A JP 2009-622 A

  When the composition of the catalyst layer is made different between the upstream part and the downstream part, it is considered that the pressure loss of the exhaust gas can be reduced if the thickness of the catalyst layer is reduced in both the upstream part and the downstream part.

However, the present inventors have found that even such an exhaust gas purification catalyst has room for improvement in terms of pressure loss.
An object of the present invention is to make it possible to reduce pressure loss of exhaust gas in an exhaust gas purification catalyst.

According to an aspect of the present invention, the base material having first and second end surfaces and provided with a through hole extending from the first end surface to the second end surface, and the first of the side walls of the through hole. A first catalyst layer covering a portion from a position of one end face to a first position between the first and second end faces, and having a thickness decreasing from the position of the first end face toward the first position; The portion of the side wall of the through hole from the position of the second end surface to the second position between the first and second end surfaces is in contact with the first catalyst layer at the end on the first end surface side. And a second catalyst layer having a thickness that decreases from the position of the second end surface toward the second position, and the minimum thickness of the first catalyst layer at the position of the first end surface the through hole of the difference d _F1 -d _FM of the first catalytic layer minimum thickness d _FM of the middle position of the the d _F1 first and second position The ratio (d _F1 -d _FM ) / R to the minimum diameter R is in the range of 0.01 to 0.06, and the minimum thickness d _R2 of the second catalyst layer at the position of the second end face and the intermediate The ratio (d _R2 -d _RM ) / R of the difference d _R2 -d _RM from the minimum thickness d _RM of the second catalyst layer at the position to the minimum diameter R of the through hole is in the range of 0.01 to 0.06. An exhaust gas purifying catalyst is provided.

  According to the present invention, it is possible to reduce the pressure loss of exhaust gas in the exhaust gas purification catalyst.

1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing a part of the exhaust gas-purifying catalyst shown in FIG. 1. Sectional drawing which expanded a part of structure shown in FIG. Sectional drawing which expanded another part of the structure shown in FIG. The top view which looked at the structure shown in FIG. 2 from the upstream. The top view which looked at the structure shown in FIG. 2 from the downstream. The figure which drew one cross section perpendicular | vertical to the flow direction of waste gas of the structure shown in FIG. Sectional drawing which shows a part of exhaust gas purification catalyst which concerns on a comparative example. Sectional drawing which shows a part of exhaust gas purification catalyst which concerns on a modification. The graph which shows an example of the influence which the structure of the catalyst for exhaust gas purification has on pressure loss. The graph which shows the other example of the influence which the structure of the catalyst for exhaust gas purification has on pressure loss. The graph which shows an example of the influence which the structure of the exhaust gas purification catalyst has on the hydrocarbon purification ability.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same referential mark is attached | subjected to the component which exhibits the same or similar function through all the drawings, and the overlapping description is abbreviate | omitted. In order to facilitate understanding, the structure is exaggerated or simplified in some drawings.

  FIG. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is a sectional view showing a part of the exhaust gas-purifying catalyst shown in FIG. FIG. 3 is an enlarged cross-sectional view of a part of the structure shown in FIG. FIG. 4 is an enlarged cross-sectional view of another part of the structure shown in FIG. FIG. 5 is a plan view of the structure shown in FIG. 2 as viewed from the upstream side. FIG. 6 is a plan view of the structure shown in FIG. 2 as viewed from the downstream side. FIG. 7 is a diagram illustrating a cross section perpendicular to the flow direction of the exhaust gas having the structure shown in FIG.

  The exhaust gas-purifying catalyst 1 shown in FIGS. 1 to 7 includes a base material 11, a first catalyst layer 12F, and a second catalyst layer 12R. In FIGS. 2 to 4, the flow direction of the exhaust gas is indicated by white arrows. The terms “upstream” and “downstream” are used with reference to this flow direction of the exhaust gas.

  The substrate 11 is, for example, a monolith honeycomb substrate. The base material 11 consists of heat resistant ceramics, such as a cordierite, for example.

  The base material 11 has a cylindrical shape. The base material 11 may have other shapes. For example, the base material 11 may have an elliptic cylinder shape or a prism shape.

Substrate 11, as shown in FIG. 2, has a first end surface E _F and a second end surface E _R. The substrate 11, each extending from the first end surface E _F to the second end surface E _R, through holes TH are provided partitioned from each other by a partition wall PW. The length L of the base material 11 along the flow direction of the exhaust gas is, for example, in the range of 50 mm to 200 mm, and typically in the range of 95 mm to 155 mm.

  The cross section of the through hole TH perpendicular to the flow direction of the exhaust gas has a square shape as shown in FIG. These cross sections may have other shapes. For example, these cross sections may have a hexagonal shape or a circular shape. Also, typically, the shape and dimensions of the previous cross section are constant over the entire length of the through hole TH.

  As shown in FIGS. 5 to 7, the through holes TH are arranged in a square lattice pattern when observed from a direction parallel to the flow direction of the exhaust gas. Other structures may be employed for the arrangement of the through holes TH. For example, the through holes TH may be arranged in a hexagonal lattice shape.

The minimum diameter R of the through hole TH is, for example, in the range of 0.785 mm to 1.21 mm, and typically in the range of 0.95 mm to 1.15 mm. Minimum thickness d _PW of the partition wall PW, for example located on 0.065mm to within the range of 0.3 mm, typically in the range of 0.09mm to 0.15 mm. The ratio R / d _PW of the minimum diameter R of the through hole TH to the minimum thickness d _PW of the partition wall PW is, for example, in the range of 2.6 to 18.6, and is typically 6.3 to 12.7. Is in range.

  The minimum diameter R of the through hole TH is the length of the shortest line segment that crosses the center line of the through hole TH and whose both ends are located on the partition wall PW. The minimum thickness of the partition wall PW is the shortest distance between adjacent through holes TH.

The first catalyst layer 12F covers an upstream portion of the side wall PW of the through hole TH. Specifically, the first catalyst layer 12F, the through-hole TH of the side wall PW of, from the position of the first end surface E _F to the first position P1 between the first end surface E _F and a second end surface E _R The part is covered.

The ratio L _F / L of the length L _F shown in FIG. 2 to the length L, that is, the ratio of the dimension of the first catalyst layer 12F along the exhaust gas flow direction to the length L of the base material 11 is, for example, 0.2. In the range of 0.8 to 0.8, typically in the range of 0.3 to 0.6.

The thickness of the first catalyst layer 12F is decreased toward the position of the first end surface E _F to the first position P1. The difference d _F1 -d _FM with a minimum thickness d _FM of the first catalyst layer 12F in the minimum thickness d _F1 and the intermediate position PM of the first catalyst layer 12F in the position of the first end surface E _F is, for example 15μm or of 175μm In the range, typically in the range of 50 μm to 150 μm. The difference d _F1 -d ratio to the length L _F of the _{FM (d F1 -d FM) /} L F , for example is in the 0.00016 to within the range of 0.018, typically 0.0005 to 0 Within the range of .002. The ratio (d _F1 -d _FM ) / R of the difference d _F1 -d _FM to the diameter R of the through hole TH is in the range of 0.01 to 0.06, typically 0.02 to 0. Within the range of .05.

The minimum thickness d _F1 of the first catalyst layer 12F in the position of the first end surface E _F do not necessarily means a minimum thickness of the first catalytic layer 12F in the plane containing the first end surface E _F . For example, when observing the cross section of the first catalytic layer 12F along the flow direction of the exhaust gas, when the end portion of the first end surface E _F side of the first catalyst layer 12F is rounded, the end that the rounded The department is not considered. That is, such a case, the thickness d _F1 is equal to the minimum thickness of the first catalytic layer 12F in orthogonal projection to the plane containing the first end surface E _F. The intermediate position PM is here, second interposed between the position P2, it is parallel to the end surface E _F and E _R and the position on the distance equal plane from P1 and P2 to be described later to the first position P1 Is the position.

  The first catalyst layer 12F includes, for example, catalytic metal particles such as noble metal particles or an active component, and a heat-resistant carrier such as alumina particles supporting these. The first catalyst layer 12F may further contain other components. For example, the first catalyst layer 12F may further include an oxygen storage material such as cerium oxide.

The second catalyst layer 12R covers a downstream portion of the side wall PW of the through hole TH. Specifically, the second catalyst layer 12R, the through-hole TH of the side wall PW of, from the position of the second end surface E _R to the second position P2 between the first end surface E _F and a second end surface E _R partial, end of the first end surface E _F side is coated to be in contact with the first catalyst layer 12F. The length L _ovl of the overlapping portion of the first catalyst layer 12F and the second catalyst layer 12R along the exhaust gas flow direction is, for example, in the range of 0 mm to 120 mm, and typically in the range of 10 mm to 40 mm. is there.

The ratio of the dimension of the second catalyst layer 12R along the exhaust gas flow direction to the length L of the base material 11, that is, the ratio L _R / L of the length L _R shown in FIG. In the range of 0.8 to 0.8, typically in the range of 50 to 70.

The thickness of the second catalyst layer 12R is decreased toward the position of the second end surface E _R to the second position P2. The difference d _R2 −d _RM between the thickness d _R2 of the second catalyst layer 12R at the position of the second end face E _R and the thickness d _RM of the second catalyst layer 12R at the intermediate position PM is, for example, in the range of 15 μm to 175 μm. Typically in the range of 50 μm to 150 μm. Further, the length L ratio _{R (d R2 -d RM) /} L R of the difference d _R2 -d _RM, for example, is in the 0.00016 to within the range of 0.018, typically 0.0005 to the 0 Within the range of .002. The ratio (d _R2 -d _RM ) / R of the difference d _R2 -d _RM to the diameter R of the through hole TH is in the range of 0.01 to 0.06, typically 0.02 to 0 Within the range of .05.

The minimum thickness d _R2 of the second catalyst layer 12R in the position of the second end surface E _R do not necessarily means a minimum thickness of the second catalyst layer 12R in a plane including the second end surface E _R . For example, when observing the cross section of the second catalyst layer 12R along the flow direction of the exhaust gas, when the end portion of the second end surface E _R side of the second catalyst layer 12R is rounded, the end that the rounded The department is not considered. That is, in such a case, the minimum thickness d _R2 is equal to the minimum thickness of the second catalyst layer 12R in the orthogonal projection onto the plane including the second end surface E _R.

  The second catalyst layer 12R may have the same composition as the first catalyst layer 12F, but typically has a different composition from the first catalyst layer 12F. The second catalyst layer 12R includes, for example, catalyst metal particles such as noble metal particles and a heat-resistant carrier such as alumina particles supporting these. The second catalyst layer 12R may further contain other components. For example, the second catalyst layer 12R may further include an oxygen storage material such as cerium oxide.

The exhaust gas-purifying catalyst 1 shown in FIGS. 1 to 7 can be manufactured, for example, by the following method.
First, a first slurry for forming the first catalyst layer 12F is prepared. The first slurry contains the component of the first catalyst layer 12F or its raw material. The first slurry has a much higher viscosity than the slurry used in the production of a general exhaust gas purification catalyst. The first slurry has, for example, a shear viscosity in the range of 100 mPa · S to 160 Pa · S when measured using a cone-and-plate viscometer with a shear rate of 100 s ^−1. And having a shear viscosity in the range of 2500 mPa · S to 4000 Pa · S when measured at a shear rate of 1 s ⁻¹ . A thickener may be used for adjusting the viscosity of the first slurry.

Next, fitting one end of the substrate 11, i.e. the end portion of the first end surface E _F side to one opening of the cylindrical guide member, placing them, so that the guide member is positioned above the substrate 11 . The guide member typically has a diameter that increases from the end where the base material 11 is fitted to the other end. The guide member forms a liquid reservoir above the base material 11.

Next, a predetermined amount of the first slurry is supplied to the liquid reservoir, and if necessary, the base material 11 to which the guide member is attached is precessed to flatten the liquid surface of the first slurry. Subsequently, to suck the gas in the through-hole TH from the end portion of the second end surface E _R side of the substrate 11. Thus, to facilitate the movement of the first slurry to the end surface E _R side from the end face E _F side. Here, optimizing the suction force and the viscosity of the first slurry and the suction time, thickness decreases towards the position of the first end surface E _F like the first catalyst layer 12F mentioned above to the first position P1 The first coating film is obtained.

  Then, a guide member is removed from the base material 11, and a 1st coating film is dried as needed. Furthermore, this coating film is optionally calcined or baked. Thereby, the 1st catalyst layer 12F or its precursor is obtained.

Next, a second slurry for forming the second catalyst layer 12R is prepared. The second slurry contains the component of the second catalyst layer 12R or its raw material. Similarly to the first slurry, the second slurry has a much higher viscosity than the slurry used in the production of a general exhaust gas purification catalyst. The second slurry has, for example, a shear viscosity in the range of 100 mPa · S to 160 Pa · S when measured using a cone-and-plate viscometer with a shear rate of 100 s ^−1. And having a shear viscosity in the range of 2500 mPa · S to 4000 Pa · S when measured at a shear rate of 1 s ⁻¹ . A thickener may be used for adjusting the viscosity of the second slurry.

Then, fitting the opposite end of the base member 11, i.e. the end of the second end surface E _R side guide member, installed them, so that the guide member is positioned above the substrate 11. A predetermined amount of the second slurry is supplied to the liquid reservoir formed above the base material 11 by the guide member, and if necessary, the guide member is attached to flatten the liquid surface of the first slurry. The substrate 11 is precessed. Subsequently, to suck the gas in the through-hole TH from the end portion of the first end surface E _F side of the substrate 11. Thus, to facilitate the movement of the second slurry into the end face E _F side from the end surface E _R side. Here, optimizing the suction force and the viscosity of the second slurry and the suction time, thickness decreases towards the position of the second end surface E _R similarly to the second catalyst layer 12R described above to the second position P2 A second coating film is obtained.

Then, a guide member is removed from the base material 11, and a coating film is dried. Furthermore, this coating film is calcined or baked. As a result, the second catalyst layer 12R or the first catalyst layer 12F and the second catalyst layer 12R are obtained.
As described above, the exhaust gas-purifying catalyst 1 shown in FIGS. 1 to 7 is completed.

  This exhaust gas-purifying catalyst 1 has a relatively small pressure loss of exhaust gas. This will be described by comparing FIG. 2 and FIG.

FIG. 8 is a cross-sectional view showing a part of the exhaust gas purifying catalyst according to the comparative example.
FIG. 8 shows a general structure of a conventional exhaust gas purifying catalyst in which the composition of the catalyst layer is different between the upstream portion and the downstream portion. The exhaust gas-purifying catalyst 1 ′ shown in FIG. 8 is obtained, for example, by the following method.

  First, a third slurry for forming the catalyst layer 12F is prepared. The third slurry contains the component of the catalyst layer 12F or its raw material. The third slurry has a much lower viscosity than the first slurry described above for the exhaust gas-purifying catalyst 1.

Then, one end of the substrate 11 to the third slurry, i.e. by immersing the end portion of the end surface E _F side, to suck the gas in the through-hole TH and the other end of the substrate 11, i.e. from the end portion of the end surface E _R side . Thus, sucking from the end face E _F side to the end surface E _R side of the third slurry. Suction is continued until the third slurry reaches a predetermined position, and then suction is stopped. If you stop the suction, third slurry in the through-hole TH, leaving a part on the partition wall PW, it is discharged from the opening end face E _F side. Thus, a 3rd coating film is formed in the upstream part of the partition PW.

  Thereafter, the third coating film is dried as necessary, and this coating film is optionally calcined or baked. Thereby, the catalyst layer 12F or its precursor is obtained.

  Next, a fourth slurry for forming the catalyst layer 12R is prepared. The fourth slurry includes a component of the catalyst layer 12R or a raw material thereof. The fourth slurry has a much lower viscosity than the second slurry described above for the exhaust gas-purifying catalyst 1.

Then, the opposite end of the substrate 11 in a fourth slurry, that is, the end portion of the second end surface E _R side is immersed, the other end of the base member 11, i.e. the end surface E _F side from the end portion of the through hole TH Aspirate the gas. Thus, sucking from the end face E _R side to the end surface E _F side fourth slurry. Suction is continued until the fourth slurry reaches a predetermined position, and then suction is stopped. If you stop the suction, fourth slurry in the through-hole TH, leaving a part on the partition wall PW, it is discharged from the opening end face E _R side. Thus, a 4th coating film is formed in the downstream part of the partition PW.

Thereafter, the coating film is dried, and the coating film is further calcined or baked. Thereby, the catalyst layer 12R or the catalyst layer 12F and the catalyst layer 12R are obtained.
As described above, the exhaust gas-purifying catalyst 1 shown in FIG. 8 is completed.

In the conventional exhaust gas purification catalyst in which the composition of the catalyst layer is different between the upstream portion and the downstream portion, generally, as in the exhaust gas purification catalyst 1 ′ shown in FIG. It has increased toward downstream from the position of the upstream end surface E _F of the substrate 11. On the other hand, the thickness of the downstream catalyst layer 12 </ b> _R increases from the position of the downstream end surface ER of the base material 11 toward the upstream side. Moreover, in order to prevent the crack resulting from inadequate heat conduction, the catalyst layers 12F and 12R are provided so that it may mutually contact. In general, a design is adopted in which the catalyst layers 12F and 12R partially overlap in view of the positional error of the catalyst layers 12F and 12R.

For this reason, in a general structure of an exhaust gas purifying catalyst in which the composition of the catalyst layer is different between the upstream portion and the downstream portion, the exhaust gas at the position where the upstream catalyst layer 12F and the downstream catalyst layer 12R overlap each other. and the diameter of the flow channel, a large difference between the diameter of the flow path of the exhaust gas in the vicinity of the near or downstream end face E _R of the upstream-side end surface E _F. For this reason, it is considered that the exhaust gas pressure loss was relatively large in the conventional exhaust gas purifying catalyst in which the composition of the catalyst layer was different between the upstream portion and the downstream portion.

In Figure 1 through the exhaust gas purifying catalyst 1 described with reference to FIG. 7, the thickness of the first catalyst layer 12F is decreasing toward the position of the first end surface E _F to the first position P1, the second catalyst the thickness of the layer 12R is reduced towards the position of the second end surface E _R to the second position P2. Therefore, the exhaust gas flow path is not significantly narrowed at the position where the first catalyst layer 12F and the second catalyst layer 12R overlap each other. Therefore, in the exhaust gas-purifying catalyst 1, the pressure loss of the exhaust gas is relatively small. That is, when the structure described with reference to FIGS. 1 to 7 is employed, the pressure loss of the exhaust gas in the exhaust gas purification catalyst can be reduced.

When the ratio (d _F1 -d _FM ) / R or the ratio (d _R2 -d _RM ) / R is small, the exhaust gas flow path is wide at the position where the first catalyst layer 12F and the second catalyst layer 12R overlap. That may be insufficient. That is, in this case, there is a possibility that the pressure loss of the exhaust gas in the exhaust gas purification catalyst cannot be sufficiently reduced.

Further, the ratio of (d _F1 -d _FM) / R or the ratio (d _R2 -d _RM) / R is increased, the flow path of the exhaust gas is narrowed at the location of the end face E _F or E _R. Even if the flow path of the exhaust gas at the position of the end face E _F or E _R is narrow, not sufficiently reduce the pressure loss of the exhaust gas in the exhaust gas purifying catalyst.

  When the shape of the exhaust gas flow path is changed, the frequency of contact between the component to be purified in the exhaust gas and the catalyst metal or the like changes. That is, changing the shape of the exhaust gas flow path affects the exhaust gas purification performance of the exhaust gas purification catalyst.

When the ratio (d _F1 -d _FM ) / R and the ratio (d _R2 -d _RM ) / R are within the above ranges, the pressure loss of the exhaust gas in the exhaust gas purification catalyst can be sufficiently reduced. In addition, in this case, excellent exhaust gas purification ability can be achieved.

Various modifications can be made to the exhaust gas-purifying catalyst 1.
For example, instead of interposing the downstream end of the first catalyst layer 12F between the upstream end of the second catalyst layer 12R and the substrate 11, the upstream end of the second catalyst layer 12R is used as the first catalyst. You may interpose between the downstream edge part of the layer 12F, and the base material 11. FIG. Alternatively, the exhaust gas-purifying catalyst 1 may employ the structure shown in FIG.

FIG. 9 is a cross-sectional view showing a part of the exhaust gas purifying catalyst according to one modification.
Exhaust gas purification catalyst 1 shown in FIG. 9 has been described with reference to FIGS. 1 to 7 except that catalyst layers 12F and 12R do not overlap and are provided so that their end faces are in contact with each other. This is the same as the exhaust gas-purifying catalyst 1. When this structure is adopted, the intermediate position PM means a position in the interface between the catalyst layers 12F and 12R.

  When the design shown in FIG. 9 is adopted, higher positional accuracy is required for the catalyst layers 12F and 12R. However, even if a positional error occurs such that the catalyst layers 12F and 12R partially overlap, the exhaust gas flow path does not become excessively narrow in the overlapping portion. Therefore, in this case, substantially the same effect as that obtained when the structure described with reference to FIGS. 1 to 7 is employed can be obtained.

Examples of the present invention will be described below.
<Manufacture of catalyst C1>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  First, a palladium nitrate aqueous solution containing 1.5 g of palladium and 100 g of alumina powder were mixed. The mixture was dried at 250 ° C. for 8 hours, and the powder thus obtained was calcined at 500 ° C. for 2 hours. Hereinafter, the powder thus obtained is referred to as “powder P1”.

  Next, 100 g of powder P1 and 50 g of ceria powder were dispersed in 400 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S1”.

Then, fitting the end portion of the first end surface E _F side of the substrate 11 to the one opening of the above-mentioned guide member, these guide members are installed so as to be located above the substrate 11. Here, a cordierite monolith honeycomb substrate having a cylindrical shape was used as the substrate 11. The diameter of the base material 11 used here was 103 mm, and the length was 105 mm. In addition, the base material 11 is provided with 600 through holes TH having a square cross section perpendicular to the exhaust gas flow direction of the through holes TH at a density of 600 per square inch. Had a volume. The minimum diameter R of the through hole TH was 0.95 mm, and the minimum thickness of the partition wall PW was 0.09 mm.

Next, 300 g of slurry S1 was supplied to the liquid reservoir formed by the guide member above the base material 11. After guide member precession exercised substrate 11 with attached to flatten the liquid surface of the slurry S1, and suction gas in the through-hole TH from the end portion of the second end surface E _R side of the substrate 11. This suction was performed for 5 seconds at a wind speed of 40 m / sec.

  Next, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 50 g of alumina powder, and 50 g of zirconia powder were dispersed in 250 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S2”.

Next, fit the end of the second end surface E _R side of the one opening above the base material 11 of the above-mentioned guide member, these guide members are installed so as to be located above the substrate 11. Next, 300 g of slurry S2 was supplied to the liquid reservoir formed by the guide member above the base material 11. After guide member precession exercised substrate 11 with attached to flatten the liquid surface of the slurry S2, and suction gas in the through-hole TH from the end portion of the first end surface E _F side of the substrate 11. This suction was performed for 5 seconds at a wind speed of 40 m / sec.

  Then, the guide member was removed from the base material 11, and the coating film was dried at 150 ° C. for 1 hour. Furthermore, this was baked at 500 ° C. for 1 hour.

  As described above, the exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was obtained. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C1”.

Next, various dimensions of the catalyst C1 were measured. For the catalyst layer 12F, the length L _F was 65 mm, the minimum thickness d _F1 was 0.07 mm, and the minimum thickness d _FM was 0.04 mm. The catalyst layer 12R had a length L _R of 65 mm, a minimum thickness d _R2 of 0.05 mm, and a minimum thickness d _RM of 0.03 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C2>
The exhaust gas-purifying catalyst 1 ′ described with reference to FIG. 8 was produced by the following method.

  First, 1.5 g of powder P1 and 100 g of ceria powder were dispersed in 400 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S3”.

Then, the slurry S3 was immersed end portion of the end surface E _F side of the substrate 11, and the suction gas in the through-hole TH from the end of the end face E _R side of the substrate 11. Thus, it sucked up the slurry S3 and the end surface E _R side from the end face E _F side. Suction was continued until the slurry S3 reached a predetermined position, and then suction was stopped. In this way, a coating film was formed on the upstream portion of the partition wall PW so as to obtain a catalyst layer 12F having the same length L _F as the catalyst C1.

  Next, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 50 g of alumina powder, and 50 g of zirconia powder were dispersed in 250 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S4”.

Subsequently, the slurry S4 was immersed end portion of the end surface E _R side of the substrate 11, and the suction gas in the through-hole TH from the end of the end face E _F side of the substrate 11. Thus, it sucked up the slurry S4 and the end surface E _F side from the end surface E _R side. Suction was continued until the slurry S4 reached a predetermined position, and then suction was stopped. In this way, a coating film was formed on the downstream side of the partition wall PW so as to obtain a catalyst layer 12R having the same length L _R as the catalyst C1.

  Thereafter, the coating film was dried at 150 ° C. for 1 hour. Furthermore, this was baked at 500 ° C. for 1 hour.

  As described above, the exhaust gas-purifying catalyst 1 described with reference to FIG. 8 was obtained. Hereinafter, the exhaust gas-purifying catalyst 1 'is referred to as "catalyst C2".

Next, various dimensions of the catalyst C2 were measured. For the catalyst layer 12F, the minimum thickness d _F1 was 0.07 mm, and the minimum thickness d _FM was 0.1 mm. For the catalyst layer 12R, the minimum thickness d _R2 was 0.05 mm, and the minimum thickness d _RM was 0.08 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C3>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  20 g of powder P1 and 10 g of ceria powder were dispersed in 75 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S5”.

  Further, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 20 g of alumina powder, and 20 g of zirconia powder were dispersed in 100 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S6”.

  The same as described above for the catalyst C1, except that the slurries S5 and S6 are used instead of the slurries S1 and S2, respectively, and the suction conditions of the slurry for forming the catalyst layers 12F and 12R are changed as follows. The exhaust gas-purifying catalyst 1 was produced by the method. That is, here, the suction of the slurry S5 was performed for 3 seconds at a wind speed of 40 m / sec, and the suction of the slurry S6 was performed for 3 seconds at a wind speed of 40 m / sec. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C3”.

Next, various dimensions of the catalyst C3 were measured. For the catalyst layer 12F, the length L _F was 60 mm, the minimum thickness d _F1 was 0.015 mm, and the minimum thickness d _FM was 0.008 mm. The catalyst layer 12R had a length L _R of 60 mm, a minimum thickness d _R2 of 0.015 mm, and a minimum thickness d _RM of 0.008 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C4>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  100 g of powder P1 and 80 g of ceria powder were dispersed in 450 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S7”.

  Further, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 100 g of alumina powder, and 100 g of zirconia powder were dispersed in 500 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S8”.

  The same as described above for the catalyst C1 except that the slurries S7 and S8 are used instead of the slurries S1 and S2, respectively, and the slurry suction conditions for forming the catalyst layers 12F and 12R are changed as follows. The exhaust gas-purifying catalyst 1 was produced by the method. That is, here, the suction of the slurry S7 was performed for 6 seconds at a wind speed of 40 m / sec, and the suction of the slurry S8 was performed for 6 seconds at a wind speed of 40 m / sec. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C4”.

Next, various dimensions of the catalyst C4 were measured. For the catalyst layer 12F, the length L _F was 60 mm, the minimum thickness d _F1 was 0.1 mm, and the minimum thickness d _FM was 0.06 mm. The catalyst layer 12R had a length L _R of 60 mm, a minimum thickness d _R2 of 0.1 mm, and a minimum thickness d _RM of 0.06 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C5>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  200 g of powder P1 and 150 g of ceria powder were dispersed in 900 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S9”.

  Further, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 200 g of alumina powder, and 170 g of zirconia powder were dispersed in 900 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S10”.

  The same as described above for the catalyst C1 except that the slurries S9 and S10 were used instead of the slurries S1 and S2, respectively, and the suction conditions of the slurry for forming the catalyst layers 12F and 12R were changed as follows. The exhaust gas-purifying catalyst 1 was produced by the method. That is, here, the suction of the slurry S9 was performed for 10 seconds at a wind speed of 40 m / sec, and the suction of the slurry S10 was performed for 10 seconds at a wind speed of 40 m / sec. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C5”.

Next, various dimensions of the catalyst C5 were measured. For the catalyst layer 12F, the length L _F was 60 mm, the minimum thickness d _F1 was 0.175 mm, and the minimum thickness d _FM was 0.1 mm. The catalyst layer 12R had a length L _R of 60 mm, a minimum thickness d _R2 of 0.175 mm, and a minimum thickness d _RM of 0.1 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C6>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  20 g of powder P1 and 10 g of ceria powder were dispersed in 75 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S11”.

  Further, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 100 g of alumina powder, and 100 g of zirconia powder were dispersed in 500 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S12”.

  The same as described above for the catalyst C1 except that the slurries S11 and S12 are used instead of the slurries S1 and S2, respectively, and the slurry suction conditions for forming the catalyst layers 12F and 12R are changed as follows. The exhaust gas-purifying catalyst 1 was produced by the method. That is, here, the suction of the slurry S11 was performed for 3 seconds at a wind speed of 40 m / sec, and the suction of the slurry S12 was performed for 6 seconds at a wind speed of 40 m / sec. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C6”.

Next, various dimensions of the catalyst C6 were measured. For the catalyst layer 12F, the length L _F was 60 mm, the minimum thickness d _F1 was 0.015 mm, and the minimum thickness d _FM was 0.008 mm. The catalyst layer 12R had a length L _R of 60 mm, a minimum thickness d _R2 of 0.1 mm, and a minimum thickness d _RM of 0.06 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

<Manufacture of catalyst C7>
The exhaust gas-purifying catalyst 1 described with reference to FIGS. 1 to 7 was manufactured by the following method.

  100 g of powder P1 and 80 g of ceria powder were dispersed in 450 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S13”.

  Further, an aqueous rhodium nitrate solution containing 0.15 g of rhodium, 20 g of alumina powder, and 20 g of zirconia powder were dispersed in 100 mL of deionized water. Hereinafter, the slurry thus obtained is referred to as “slurry S14”.

  The same as described above for the catalyst C1 except that the slurries S13 and S14 were used instead of the slurries S1 and S2, respectively, and the suction conditions of the slurry for forming the catalyst layers 12F and 12R were changed as follows. The exhaust gas-purifying catalyst 1 was produced by the method. That is, here, the suction of the slurry S13 was performed for 6 seconds at a wind speed of 40 m / second, and the suction of the slurry S14 was performed for 3 seconds at a wind speed of 40 m / second. Hereinafter, the exhaust gas-purifying catalyst 1 is referred to as “catalyst C7”.

Next, various dimensions of the catalyst C7 were measured. For the catalyst layer 12F, the length L _F was 60 mm, the minimum thickness d _F1 was 0.1 mm, and the minimum thickness d _FM was 0.06 mm. The catalyst layer 12R had a length L _R of 60 mm, a minimum thickness d _R2 of 0.015 mm, and a minimum thickness d _RM of 0.008 mm. The various dimensions of the substrate 11 did not change before and after the formation of the catalyst layers 12a and 12b.

  Various dimensions of the catalysts C1 to C7 are summarized in Table 1 below.

<Performance evaluation 1>
In each of the catalyst C1 and C2, the air 1hPa from the end face E _F side are supplied with 5 m ³ / min flow rate, to measure the pressure of air in the pressure and the end surface E _R side of the air at the end face E _F side The difference between these pressures was determined as pressure loss. Here, the temperature and relative humidity of the air were set to 20 ° C. and 65%, respectively. FIG. 10 shows the result.

  FIG. 10 is a graph showing an example of the influence of the structure of the exhaust gas purifying catalyst on the pressure loss. As shown in FIG. 10, the catalyst C1 had a smaller exhaust gas pressure loss than the catalyst C2.

<Performance evaluation 2>
In each of the catalyst C3 and C7, the air 1hPa from the end face E _F side are supplied with 5 m ³ / min flow rate, to measure the pressure of air in the pressure and the end surface E _R side of the air at the end face E _F side The difference between these pressures was determined as pressure loss. Here, the temperature and relative humidity of the air were set to 20 ° C. and 65%, respectively. FIG. 11 shows the result.

FIG. 11 is a graph showing another example of the influence of the structure of the exhaust gas purifying catalyst on the pressure loss. As is clear from the data obtained for the catalysts C3 to C5, increasing each of the ratios (d _F1 -d _FM ) / R and (d _R2 -d _RM ) / R increases the pressure loss, Smaller the pressure loss was smaller. As is clear from the data obtained for the catalysts C3, C4, C6 and C7, if only one of the ratios (d _F1 -d _FM ) / R and (d _R2 -d _RM ) / R is increased, the pressure loss is increased. The pressure loss was reduced when only one of them was increased.

<Performance evaluation 3>
Each of the catalysts C3 to C7 was placed in a flow-type durability test apparatus, and a gas mainly containing nitrogen was passed through the catalyst bed at a flow rate of 500 mL / min for 5 hours. During this time, the temperature of the catalyst was maintained at 1000 ° C. Further, lean gas and rich gas were used as the gas to be circulated through the catalyst, and these gases were switched every 5 minutes. The lean gas is a gas obtained by further adding 10% water vapor to a mixed gas obtained by adding 5% oxygen to nitrogen, and the rich gas is obtained by adding 10% to a mixed gas obtained by adding 10% carbon monoxide to nitrogen. A gas to which water vapor is further added.

  Thereafter, these exhaust gas-purifying catalysts were placed in an atmospheric pressure fixed bed flow reactor. Next, while flowing the model gas through the catalyst bed, the catalyst bed temperature was raised from 100 ° C. to 500 ° C. at a rate of 12 ° C./min, and the exhaust gas purification rate during that time was continuously measured. In addition, as model gas, the gas which made the stoichiometric equivalent the oxidizing component (oxygen and nitrogen oxide) and the reducing component (carbon monoxide, hydrocarbon, hydrogen) was used. The result is shown in FIG.

  FIG. 12 is a graph showing an example of the influence of the structure of the exhaust gas purification catalyst on the hydrocarbon purification ability. In FIG. 12, “HC-T 50%” means the lowest temperature of the catalyst that could purify 50% or more of the hydrocarbons contained in the model gas, that is, the 50% purification temperature of the hydrocarbons.

As is clear from the data obtained for the catalysts C3 to C5, increasing each of the ratios (d _F1 -d _FM ) / R and (d _R2 -d _RM ) / R lowers the 50% hydrocarbon purification temperature. When each of them was made smaller, the 50% purification temperature of hydrocarbons became higher. As is clear from the data obtained for the catalysts C3, C4, C6 and C7, increasing only one of the ratios (d _F1 -d _FM ) / R and (d _R2 -d _RM ) / R The 50% purification temperature was lowered, and when only one of them was reduced, the 50% purification temperature of hydrocarbons was increased.

1 ... exhaust gas purifying catalyst, 11 ... substrate, 12F ... first catalyst layer, 12R ... second catalyst layer, E _F ... first end surface, E _R ... second end surface, P1 ... position, P2 ... position, PM ... Position, PW ... partition wall, TH ... through hole.

Claims (3)

A base material having first and second end surfaces and provided with a through hole extending from the first end surface to the second end surface;
The portion of the side wall of the through-hole is covered from the position of the first end surface to the first position between the first and second end surfaces, and the thickness is increased from the position of the first end surface toward the first position. A decreasing first catalyst layer;
A portion from the position of the second end surface to the second position between the first and second end surfaces of the side wall of the through hole is such that the end portion on the first end surface side is in contact with the first catalyst layer. And a second catalyst layer having a thickness that decreases from the position of the second end surface toward the second position,
The difference d _F1 -d _FM between the minimum thickness d _F1 of the first catalyst layer at the position of the first end face and the minimum thickness d _FM of the first catalyst layer at the intermediate position between the first and second positions. The ratio (d _F1 -d _FM ) / R to the minimum diameter R of the through hole is in the range of 0.01 to 0.06, and the minimum thickness d _R2 of the second catalyst layer at the position of the second end face. ratio and for minimum diameter R of the through hole of the difference d _R2 -d _RM and the minimum thickness d _RM of the second catalytic layer in the intermediate position (d _R2 -d _RM) / R is 0.01 to 0. Exhaust gas purification catalyst in the range of 06.   The exhaust gas purifying catalyst according to claim 1, wherein the first and second catalyst layers have different compositions.   The exhaust gas purifying catalyst according to claim 1 or 2, wherein the first and second catalyst layers partially overlap each other.

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