JP2016175043A - Catalyst for exhaust gas purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for exhaust gas purification capable of suppressing deterioration of the catalyst during high load operation, maintaining a NOx purification rate of the catalyst during low-speed traveling, and improving the NOx purification rate of the catalyst during high-speed traveling.SOLUTION: A catalyst for exhaust gas purification includes a cylindrical substrate to be passed by exhaust gas, having a circular cross section which is vertical to a flow direction of exhaust gas, and a catalyst coat layer formed on the surface of the substrate. In the catalyst for exhaust gas, potassium in the catalyst coat has two different concentration regions.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purifying catalyst.

  Exhaust gas discharged from internal combustion engines such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). These harmful components are used for exhaust gas purification. After being purified by the catalyst, it is released into the atmosphere. In particular, NOx discharged under an oxygen-excess atmosphere is difficult to purify with an oxidation catalyst or a three-way catalyst put to practical use in gasoline automobiles, and selective reduction type NOx as a promising catalyst capable of purifying NOx. Catalysts (hereinafter referred to as SCR catalysts) and NOx occlusion reduction type catalysts (hereinafter referred to as NSR catalysts) are being developed.

  In Patent Document 1, it is an object to maximize the functions of Pt and Rh in the exhaust gas purification catalyst and further improve the NOx purification performance. And at least one NOx occlusion material selected from alkali metals, alkaline earth metals and rare earth elements, and a catalyst coating layer carrying at least one of Pt and Pd and Rh, and the exhaust gas atmosphere has an excess of oxygen. NOx occlusion reduction type exhaust gas purifying catalyst that stores NOx in NOx occlusion material in lean atmosphere, changes exhaust gas atmosphere to stoichiometric to rich atmosphere with excess reducing components, and releases NOx occluded in NOx occlusion material for reduction The catalyst coat layer has a two-layer structure of a lower layer formed on the surface of the support substrate and an upper layer formed on the surface of the lower layer, and has a small amount of Pt and Pd. At least one is supported on at least the upper layer, and Rh is supported on the upper layer in an amount of 40% by mass or less relative to the total supported amount of Rh in the catalyst coat layer, and is supported on the lower layer in an amount of 60% by mass or more. The problem is solved by the exhaust gas purifying catalyst.

  In Patent Document 2, it is an object to provide an NOx occlusion reduction type exhaust gas purification catalyst that is more excellent in NOx purification performance than a catalyst composition in which the supported ratio of palladium is larger than that of platinum. And a ratio of the supported amount of palladium (y) to the supported amount of platinum (x) (y / x; molar ratio) is 0 <y / The problem is solved by a NOx occlusion reduction type exhaust gas purification catalyst having a second catalyst layer satisfying x ≦ 1.0 in order from the support base material side.

  In Patent Document 3, NOx desorption and purification are suppressed in a NOx catalyst using strong alkali at high temperature and S poisoning is suppressed, and S poisoning can be easily released, and the NOx purification function is not further deteriorated. The catalyst component part containing a cerium compound and a cesium compound is coated on a porous carrier, and the cerium compound is contained more in the upper surface side of the catalyst component part. The problem is solved by an exhaust gas purification catalyst characterized in that it is contained in a larger amount on the lower surface side of the catalyst component part.

  In Patent Document 4, in the NOx occlusion reduction type catalyst in use, deterioration of the NOx occlusion material during regeneration processing for eliminating sulfur poisoning is suppressed, and most of the NOx occlusion material carried is reliably An object of the present invention is to make it possible to regenerate, a base material having an exhaust gas passage, a support layer formed on the surface of the exhaust gas passage, a noble metal supported on the support layer, and a sulfur desorption supported on the support layer. An exhaust gas purifying catalyst comprising a first NOx occlusion material having a high separation temperature and a second NOx occlusion material having a low sulfur desorption temperature carried on the carrier layer, wherein the exhaust gas has a flow velocity distribution and has a large flow velocity. The problem is solved by an exhaust gas purifying catalyst characterized in that a larger amount of the first NOx occlusion material is supported on the carrier layer in the exhaust gas passage through which the exhaust gas flows than the second NOx occlusion material.

  As a system using such a catalyst, for example, Patent Document 5 includes an ammonia generation catalyst such as a NOx occlusion reduction (NSR) or lean NOx trap (LNT) catalyst combined with a selective catalytic reduction (SCR) catalyst. An emission treatment system is described.

JP 2009-285604 A JP 2010-201284 A JP 2003-326164 A JP 2004-1114016 A Special table 2012-522636 gazette

  From the viewpoint of improving fuel efficiency, it is desirable that the internal combustion engine be a lean burn system in which the lean burn operation is performed up to high speed running (catalyst bed temperature: about 450 ° C.).

  However, since the lean burn system is operated in a lean state where oxygen is excessive, a catalyst for efficiently purifying generated NOx is required. Furthermore, the lean burn system needs to be operated with stoichiometry in order to ensure a necessary output during high load operation on a slope or the like. The exhaust gas temperature at this time is about 760 ° C. at the center of the catalyst as shown in FIG.

{Evaluation of FIG. 13:
A catalyst (1 L) having a two-layer catalyst coating layer having Pt, Pd and Rh as noble metals and 0.15 mol / L potassium, 0.2 mol / L barium and 0.1 mol / L lithium as NOx storage material × 2) is installed downstream of a 3.5-liter V-6 lean combustion engine}

  Thus, a lean burn system requires a catalyst that efficiently purifies NOx and has heat resistance.

  On the other hand, in an NSR catalyst that is a NOx purification catalyst, the temperature range for efficiently purifying NOx differs depending on the type of NOx storage material used. In order to obtain a sufficient NOx occlusion capacity at the time of high-speed running required by the lean burn system, the NSR catalyst needs to use a strongly basic alkali metal such as potassium as the NOx occlusion material.

  However, when the high load operation is repeated in the lean burn system, potassium as the storage material for the NSR catalyst moves to the downstream portion of the catalyst or the cordierite base material as shown in FIGS.

{Evaluation method of FIG. 14:
A catalyst having a two-layered catalyst coat layer having Pt, Pd and Rh as noble metals and 0.15 mol / L potassium, 0.2 mol / L barium and 0.1 mol / L lithium as NOx storage material (1 .3L) at room temperature for 5 hours. Analysis of potassium in the catalyst coating layer after calcination by ICP}

  This decrease in the amount of potassium in the NSR catalyst reduces the NOx storage amount of the NSR catalyst, and accordingly, reduces the NOx purification rate.

  Further, when the amount of potassium in the catalyst is excessively increased, there arises a problem that potassium decreases the catalytic activity of the noble metal, particularly the noble metal catalytic activity during low speed running (catalyst bed temperature: about 300 ° C.).

  As a result, the lean burn system contains potassium as a NOx occlusion material to the extent that it does not reduce the catalytic activity of the noble metal during low-speed driving, and exhibits high NOx purification performance during high-speed driving. A purification catalyst is required.

  In order to solve such a problem, for example, in the method described in Patent Document 3, the NOx performance during high-speed operation decreases due to a decrease in the amount of the occlusion material at the center of the base material. In Patent Document 4, the central storage material having a high contact frequency with the exhaust gas has a low NOx adsorption capability at high speed operation, and therefore has a low lean NOx purification performance at high speed operation. Therefore, with conventional catalysts, satisfactory NOx purification performance could not be obtained.

  Therefore, the present invention maintains the NOx purification performance of the catalyst during low-speed running at a catalyst bed temperature of about 300 ° C. even after a high load operation at a catalyst bed temperature of about 760 ° C. An object of the present invention is to provide an exhaust gas purifying catalyst in which the NOx purification performance of the catalyst during high-speed traveling is improved.

As a result of examining various means for solving the above-mentioned object, the present inventors have found that a cylindrical base material through which the exhaust gas having a circular cross section perpendicular to the flow direction of the exhaust gas passes, An exhaust gas purifying catalyst having a catalyst coat layer formed on a surface thereof, wherein the catalyst coat layer includes two layers having a lower layer formed on the surface of the substrate and an upper layer formed on the upper surface of the lower layer A catalyst metal containing rhodium (Rh), platinum (Pt) and palladium (Pd), a NOx occlusion material containing potassium (K), barium (Ba) and lithium (Li) in the lower layer; A composite oxide containing at least one selected from alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and ceria (CeO ₂ ) supporting a metal and NOx storage material and / or Containing an oxide, and in the upper layer, a catalyst metal containing Pt and Pd, a NOx occlusion material containing K, Ba and Li, and Al ₂ O ₃ , TiO ₂ supporting the catalyst metal and the NOx occlusion material, A composite oxide and / or oxide containing at least one selected from ZrO ₂ and CeO ₂ is contained, and in the region supporting K, K is the same center as the central axis of the cylindrical substrate A column-shaped first support concentration region (first support concentration region) having an axis and a region (second support concentration K) that is a circular columnar second support concentration existing on the outer periphery of the first support concentration region. The first support concentration region is adjusted to a support concentration of 0.11 to 0.15 mol / L, and the second support concentration region is set to 0.04 to 0.13 mol / L. L carrying concentration, and the first The ratio of the support concentration of the support concentration region to the support concentration of the second support concentration region (the support concentration of the first support concentration region / the support concentration of the second support concentration region) is in the range of 1.1 to 3.3; Further, the ratio of the diameter of the circle of the first support concentration region of the cylindrical type to the diameter of the outermost circle of the second support concentration region of the annular column type (the diameter of the circle of the first support concentration region / the second support concentration region) The diameter of the outermost circle of the catalyst is 0.20 to 0.90, so that even after a high load operation at a catalyst bed temperature of about 760 ° C., the catalyst is not The present inventors have found that the NOx purification performance is maintained and that the NOx purification performance of the catalyst is improved during high-speed running at a catalyst bed temperature of about 450 ° C., and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) a cylindrical base material through which the exhaust gas, whose cross section perpendicular to the flow direction of the exhaust gas is a circle,
A catalyst coat layer formed on the surface of the substrate;
The catalyst coat layer has a two-layer structure having a lower layer formed on the surface of the substrate and an upper layer formed on the upper surface of the lower layer,
The lower layer comprises a catalyst metal containing rhodium (Rh), platinum (Pt) and palladium (Pd), a NOx storage material containing potassium (K), barium (Ba) and lithium (Li), the catalyst metal and NOx. Containing a composite oxide and / or oxide containing at least one selected from alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and ceria (CeO ₂ ) supporting the storage material. ,
The upper layer is selected from a catalyst metal containing Pt and Pd, a NOx storage material containing K, Ba and Li, and Al ₂ O ₃ , TiO ₂ , ZrO ₂ and CeO ₂ supporting the catalyst metal and the NOx storage material. A composite oxide and / or an oxide containing at least one selected from
A catalyst for exhaust gas purification,
The K-supported region includes a column type first support concentration (first support concentration region) in which K has the same central axis as the center axis of the cylindrical base material, and K is the first support concentration region. There is a region (second supported concentration region) that is an annular column type second supported concentration that exists on the outer periphery of the supported concentration region,
The first supported concentration region is a supported concentration of 0.11 to 0.15 mol / L, and
The second supported concentration region is a supported concentration of 0.04 to 0.13 mol / L, and
The ratio of the carrier concentration in the first carrier concentration region to the carrier concentration in the second carrier concentration region (the carrier concentration in the first carrier concentration region / the carrier concentration in the second carrier concentration region) is 1.1 to 3.3. Yes, and
The ratio of the diameter of the circle of the first support concentration region of the cylindrical type to the diameter of the outermost circle of the second support concentration region of the annular column type (the diameter of the circle of the first support concentration region / the second support concentration region) A catalyst for exhaust gas purification, wherein the diameter of the outermost circle is 0.20 to 0.90.

  According to the present invention, the NOx purification rate of the catalyst during low-speed running at a catalyst bed temperature of about 300 ° C. is maintained even after a high load operation at a catalyst bed temperature of about 760 ° C., and a high speed at a catalyst bed temperature of about 450 ° C. is maintained. It is possible to provide an exhaust gas purification catalyst with an improved NOx purification rate of the catalyst during traveling.

It is a schematic diagram which shows the structure of the exhaust gas purification catalyst of this invention. It is a schematic diagram which shows the relationship of the relative magnitude | size of the 1st carrying | support density | concentration area | region of an exhaust gas purification catalyst of this invention, and an exhaust pipe. It is a schematic diagram which shows the catalyst for exhaust gas purification of Comparative Examples 1-11 and Examples 1-6. It is a schematic diagram which shows the relative positional relationship of the engine of the displacement of 3.5L and the exhaust gas purification catalyst in the measurement of the NOx purification rate. It is a figure which shows the relationship between the potassium carrying | concentration density | concentration by the difference in catalyst bed temperature, and a NOx purification rate in the exhaust gas purification catalyst of Comparative Examples 1-7. It is a schematic diagram which shows the catalyst for exhaust gas purification of the comparative example 12 and Examples 7-9. FIG. 3 is a schematic diagram showing a relative positional relationship between an engine with a displacement of 2.0 L and an exhaust gas purification catalyst in measurement of a NOx purification rate. Ratio of the diameter of the circle in the first support concentration region of the column type to the diameter of the outermost circle of the second support concentration region of the annular column in the exhaust gas purification catalyst (the diameter of the circle in the first support concentration region / the second support) It is a figure which shows the relationship between the NOx purification rate in the engine of displacement 3.5L and the diameter of the outermost circle of a density | concentration area | region. It is a figure which shows the relationship of the NOx purification rate in the engine of 2.0L of exhaust gas (diameter of the 1st carrying | concentration density | concentration area | region / diameter of the outermost circle of a 2nd carrying | support density | concentration area | region) in the exhaust gas purification catalyst. Relative sizes of the cylindrical cordierite honeycomb substrate used in Comparative Example 1 and Examples 2, 7 and 8 and the cylindrical cordierite honeycomb substrate used in Comparative Example 13 and Examples 10-12 It is a schematic diagram which shows the relationship. It is a figure which shows each NOx purification performance of the exhaust gas purification catalyst of Example 2, 7 or 8 when the NOx purification rate of Comparative Example 1 is 1. It is a figure which shows each NOx purification performance of the exhaust gas purification catalyst of Example 10, 11 or 12 when the NOx purification rate of the comparative example 13 is set to 1. It is a figure which shows the relationship between the base-material radius of a catalyst and catalyst temperature in the exhaust gas purification catalyst at the time of high load driving | running | working. It is a figure which shows the relationship between a calcination temperature and the reduction | decrease amount of potassium in the catalyst coat layer of the exhaust gas purification catalyst. It is a figure which shows the relationship between a calcination temperature and the potassium amount in the base material in a catalyst for exhaust gas purification, a catalyst coat layer, or the whole catalyst.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present specification, features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the size and shape of each part are exaggerated for clarity, and the actual size and shape are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the size and shape of each part shown in these drawings. The exhaust gas purifying catalyst of the present invention is not limited to the following embodiments, and can be implemented in various forms that have been modified or improved by those skilled in the art without departing from the scope of the present invention. can do.

  As shown in FIG. 1, the present invention includes a cylindrical base material through which the exhaust gas having a circular cross section perpendicular to the flow direction of the exhaust gas passes, and a catalyst coating layer formed on the surface of the base material. And the catalyst coat layer contains a catalyst metal, a NOx occlusion material containing potassium (K), and a composite oxide and / or an oxide carrying the catalyst metal and the NOx occlusion material. In the region supporting potassium, a region where the potassium has a first supporting concentration of a cylindrical type having the same central axis as the central axis of the cylindrical substrate (first supporting concentration region), potassium Is an annular column-shaped second support concentration region (second support concentration region) existing on the outer periphery of the first support concentration region, and the potassium support concentration in the first support concentration region and the second support concentration region The potassium loading concentration in the loading concentration range has a specific value. And relates to a catalyst for exhaust gas purification, characterized in that has a particular relationship further the size of the size and the second support concentration region of said first carrier concentration region.

  In the present invention, exhaust gas refers to gas discharged from the engine exhaust system to the outside. The exhaust gas is, for example, exhaust gas discharged from an internal combustion engine such as an automobile, and mainly includes harmful components such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx).

  The engine in which the exhaust gas purifying catalyst of the present invention is used is not particularly limited, but the displacement is preferably 1 L to 5 L, more preferably 1.5 L to 3.5 L, and particularly preferably 2.0 L to 3.5 L. Various types of engines such as an in-line 4-cylinder and a V-type 6-cylinder can be used.

  In the present invention, as the cylindrical base material through which the exhaust gas passes, cylindrical base materials having various shapes used for this kind of conventional applications such as a honeycomb shape can be used. As another preferred example, an exhaust gas purification filter such as a cordierite filter can also be used. The material of the substrate can be selected from various materials used for this type of conventional application, such as cordierite, heat-resistant ceramics such as silicon carbide (SiC), alloys such as stainless steel, or metals. In the present invention, as the columnar substrate through which the exhaust gas passes, it is preferable to use a honeycomb-shaped columnar substrate made of cordierite.

  By using a honeycomb-shaped cordierite columnar base material, it is possible to ensure physical characteristics suitable for use as an exhaust gas purification catalyst for automobiles, such as vibration resistance and heat resistance.

  In the present invention, the size and capacity of the cylindrical substrate through which the exhaust gas passes are not particularly limited, but the size is 129 mm in diameter and 100 mm in length of the cylinder used in this type of conventional application. The diameter of the circle 103 mm × the length of the cylinder 155 mm, the diameter of the circle 129 mm × the length of the cylinder 150 mm, the diameter of the circle 117 mm × the length of the cylinder 122 mm, the diameter of the circle 103 mm × the length of the cylinder 130 mm, Various sizes such as diameter 93 mm × cylinder length 155 mm, circle diameter 103 mm × cylinder length 105 mm, and the like can be used, for example, 1L or 1.3L. Various capacities such as 0L, 0.9L, etc. can be used.

  By setting the size and capacity of the cylindrical base material through which the exhaust gas passes, the exhaust gas can be treated efficiently.

  In the present invention, the catalyst coat layer formed on the surface of the substrate preferably has a two-layer structure having a lower layer formed on the surface of the substrate and an upper layer formed on the upper surface of the lower layer. The catalyst coat layer of the present invention may have a single-layer structure or a structure having more than two layers, instead of a two-layer structure.

  When the catalyst coat layer has a two-layer structure, for example, a decrease in catalyst activity due to alloying of catalyst metals can be suppressed.

  In the present invention, the catalyst coat layer preferably contains a catalyst metal, a NOx occlusion material, a composite oxide and / or an oxide that supports the catalyst metal and the NOx occlusion material. Various other additives used, for example, binders such as alumina sol and silica sol can be included.

  In the present invention, the addition amount of the additive is not particularly limited, but is preferably 20 g or less, and more preferably 10 g or less, per liter of the base material.

  In the present invention, the catalyst metal preferably contains platinum (Pt), rhodium (Rh) and palladium (Pd). In the two-layer catalyst coat layer, the lower layer formed on the surface of the substrate is used. It is preferable that Pt, Rh and Pd are included, and that the upper layer formed on the upper surface of the lower layer includes Pt and Pd. In the present invention, the catalyst metal is not limited to Pt, Rh, and Pd, but may be any catalyst that oxidizes HC and CO and a catalyst that can reduce NOx. Pt, Rh, Pd, iridium (Ir), It may contain at least one selected from noble metals such as ruthenium (Ru), transition metals such as iron (Fe) and cobalt (Co), and other conventional catalytic metals used for this type of application. In particular, Pt has an effect of increasing the NOx occlusion speed.

  In the present invention, the amount of the catalyst metal supported is not particularly limited, but Rh is preferably 0.01 g to 5.0 g, more preferably 0.05 g to 2.5 g, and further preferably 0.1 g to 1.g. 0 g is more preferable. Further, Pt is preferably 0.05 g to 10.0 g, more preferably 0.1 g to 5.0 g, and further preferably 0.5 g to 3.0 g per liter of the base material. Further, Pd is preferably 0.05 g to 10.0 g, more preferably 0.1 g to 5.0 g, and further preferably 0.2 g to 3.0 g per liter of the base material. If it is less than this, sufficient catalytic activity cannot be obtained, and even if it is supported more than this, the effect is saturated and the cost is disadvantageous.

  In the present invention, the NOx storage material contains potassium (K). In the present invention, the NOx storage material preferably further contains lithium (Li) and / or barium (Ba). In the present invention, the NOx occlusion material is replaced with Li and / or Ba, or in addition to Li and / or Ba, an alkali metal such as sodium (Na), cesium (Cs), rubidium (Rb), This kind of conventional, such as alkaline earth metals such as calcium (Ca), magnesium (Mg), strontium (Sr), rare earth elements such as lanthanum (La), yttrium (Y), neodymium (Nd), praseodymium (Pr) It can contain various elements used in the above applications.

  In the present invention, the amount of the NOx occlusion material supported excluding K is not particularly limited, but in the NOx occlusion material, Ba is preferably 0.01 mol to 2.0 mol, and 0.05 mol to 0.00 mol per liter of the base material. 3 moles is more preferred. Further, Li is preferably 0 to 0.5 mol, more preferably 0.05 mol to 0.2 mol, per liter of the base material.

In the present invention, the composite oxide and / or oxide supporting the catalyst metal and the NOx storage material may be alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and ceria (CeO ₂ ). A composite oxide and / or oxide containing at least one selected from the above is preferable. In the present invention, various composite oxides and / or oxides used for this kind of conventional applications can be used as the composite oxide and / or oxide supporting the catalyst metal.

  In the present invention, the addition amount of the composite oxide and / or oxide is not particularly limited. However, if the addition amount is too large, the catalyst coat layer becomes thick, the airflow resistance increases, the fuel consumption deteriorates, and the amount is too small. Then, the catalyst coat layer becomes thin, the supporting density of the noble metal becomes too high, the activity decreases due to grain growth, and the heat resistance cannot be obtained. In the present invention, the amount of the composite oxide and / or oxide is generally preferably about 100 to 500 g, more preferably 150 to 350 g as a whole per liter of the base material.

  In the present invention, the region in the substrate supporting potassium contained as the NOx storage material is a region in which potassium is the first supporting concentration of the cylindrical type having the same central axis as the central axis of the cylindrical substrate (first 1 support concentration region) and a region (second support concentration region) that is a second support concentration of an annular column type that exists in the outer periphery of the first support concentration region unlike potassium support concentration. To do.

  In the present invention, the first support concentration region preferably has a support concentration of 0.11 to 0.15 mol / L, and more preferably a support concentration of 0.12 to 0.14 mol / L.

  In the present invention, the second loading concentration region preferably has a loading concentration of 0.04 to 0.13 mol / L, more preferably 0.04 to 0.12 mol / L, and 0.06 to 0.10 mol / L. L loading density is particularly preferred.

  In the present invention, the carrier concentration in the first carrier concentration region is greater than the carrier concentration in the second carrier concentration region, and the ratio of the carrier concentration in the first carrier concentration region to the carrier concentration in the second carrier concentration region (the first carrier concentration). The carrier concentration in the region / the carrier concentration in the second carrier concentration region) is preferably 1.1 to 3.3, more preferably 1.2 to 3.3, and particularly preferably 1.3 to 2.0.

  In the present invention, the ratio of the diameter of the circle of the first support concentration region of the cylindrical type to the diameter of the outermost circle of the second support concentration region of the annular column type (the diameter of the circle of the first support concentration region / the second support concentration) The diameter of the outermost circle in the region is preferably 0.20 to 0.90, more preferably 0.20 to 0.80, and particularly preferably 0.25 to 0.70.

Increasing the amount of potassium in the first supported concentration region (that is, the central portion of the exhaust gas purifying catalyst) and decreasing the amount of potassium in the second supported concentration region (that is, the outer peripheral portion of the exhaust gas purifying catalyst) increases the gas flow rate of the exhaust gas. When traveling at high speed (catalyst bed temperature: about 450 ° C), the frequency of contact between the exhaust gas and the central portion where the potassium loading concentration is high can be increased, while the gas flow rate of exhaust gas is small (slow) at low speed traveling ( At the catalyst bed temperature: about 300 ° C., the exhaust gas can be brought into contact with the entire exhaust gas purifying catalyst. In other words, NOx can be efficiently purified mainly using the active point of the exhaust gas purifying catalyst center during high speed running with a high catalyst bed temperature, while exhaust gas purifying catalyst during low speed running with a low catalyst bed temperature. Decreasing the activity of noble metal catalyst by adjusting the total amount of potassium (does not increase the amount of potassium too much) and using the entire catalyst including the outer periphery of the exhaust gas purifying catalyst (especially oxidation activity of Pt from NO to NO ₂₎ ) Can be suppressed.

  In the present invention, the diameter of the circular columnar first support concentration region is, for example, 0.5 to 1.5 times the inner diameter of the exhaust pipe carrying the exhaust gas flowing into the exhaust gas purification catalyst, preferably 0.9 to It can be 1.1 times. In the present invention, it is preferable that the diameter of the circle of the cylindrical first support concentration region is larger than the inner diameter of the exhaust pipe as shown in FIG. Increasing the contact frequency between the exhaust gas and the central portion where the potassium concentration is high at high speed when the gas flow rate of the exhaust gas is high by making the diameter of the circle of the first support concentration region of the cylindrical type larger than the inside diameter of the exhaust pipe Can do.

  In the present invention, the catalyst coat layer can be formed on the substrate surface by a conventional coating technique. In the present invention, for example, the catalyst coat layer is a mixture of a solvent such as water and the above-described catalyst metal, NOx occlusion material, composite oxide and / or oxide supporting the catalyst metal and NOx occlusion material. The slurry prepared in this manner is wash-coated on the surface of the substrate, and the excess slurry is blown off, followed by drying and firing. When the catalyst coat layer has a two-layer structure, it can be formed by forming a lower layer on the substrate surface by the above method and then forming an upper layer on the upper surface of the lower layer by the above method. In the present invention, when the potassium concentration is changed in the first supported concentration region and the second supported concentration region, for example, masking is first performed by masking portions other than the portion where the catalyst coat layer of the first supported concentration region is formed. A catalyst coat layer is formed by wash coating in the first supported concentration region, and then the portion where the first supported concentration catalyst coat layer is formed is masked, and the catalyst coat layer is washed by coating in the second supported concentration region. It can be prepared by forming.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Preferable range of potassium loading concentration in the first loading concentration region and the second loading concentration region>
1. Preparation of exhaust gas purifying catalyst having the same potassium loading concentration in the first loading concentration region and the second loading concentration region

Comparative Example 1 1. Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.13 mol / L 1-1. Preparation of lower layer slurry (1) Composite oxide composed of alumina (Al ₂ O ₃ ), titania (TiO ₂ ) and zirconia (ZrO ₂ ) (alumina: 50 mass%, titania: 15 mass%, zirconia: 35 mass) %) Was supported on rhodium (Rh) using an aqueous rhodium nitrate solution and calcined in the atmosphere at 500 ° C. for 2 hours to obtain a rhodium-supported composite oxide powder. When the obtained rhodium-supported composite oxide powder was 100% by mass, the supported rhodium was 1% by mass.
(2) Platinum (Pt) using a platinum nitrate aqueous solution and a palladium nitrate aqueous solution with respect to a composite oxide composed of alumina, titania and zirconia (alumina: 50% by mass, titania: 15% by mass, zirconia: 35% by mass). And palladium (Pd) were supported and fired at 500 ° C. for 2 hours in the atmosphere to obtain a composite oxide powder supporting platinum and palladium. When the obtained composite oxide powder carrying platinum and palladium was 100% by mass, the platinum and palladium carried were 0.25% by mass of platinum and 0.05% by mass of palladium.
(3) Alumina powder (6 g) was supported with palladium using an aqueous palladium nitrate solution and calcined at 500 ° C. for 2 hours in the atmosphere to obtain a palladium-supported composite oxide powder. When the obtained palladium-supported composite oxide powder was 100% by mass, the supported palladium was 4% by mass.
(4) Noble metal-supported powder obtained in (1) to (3) ((1) 25 g, (2) 100 g, (3) 5 g), complex oxide (ceria) composed of ceria (CeO ₂ ) and zirconia : 80% by mass, zirconia: 20% by mass, 15g), (19.5g) as barium, (0.5g) as lithium, (3.6g) as potassium, alumina binder (8g), pure Water (340 g) was mixed to prepare a lower layer slurry.
1-2. Preparation of slurry for upper layer (1) A platinum nitrate aqueous solution and a palladium nitrate aqueous solution were used for a composite oxide composed of alumina, titania and zirconia (alumina: 50 mass%, titania: 15 mass%, zirconia: 35 mass%). Then, platinum and palladium were supported and calcined at 500 ° C. for 2 hours in the atmosphere to obtain a composite oxide powder supporting platinum and palladium. When the obtained composite oxide powder carrying platinum and palladium was 100% by mass, the platinum and palladium carried were 1.8% by mass of platinum and 0.4% by mass of palladium.
(2) The noble metal-supported composite oxide powder (50 g) obtained in (1), a composite oxide composed of ceria and zirconia (ceria: 80 mass%, zirconia: 20 mass%, 5 g), and barium ( 8.1 g), lithium (0.2 g), potassium (1.5 g), alumina binder (3 g), and pure water (140 g) were mixed to prepare an upper layer slurry.
1-3. Formation of Coat Layer (1) The lower layer slurry was washed on the surface of a cylindrical cordierite honeycomb substrate (Denso, diameter 129 mm × base length 100 mm, 1.3 L) to form a lower layer coat layer. 150 g of the lower coat layer was formed on 1 L of the honeycomb substrate.
(2) The upper layer slurry was wash-coated on the honeycomb base material on which the lower layer coat layer obtained in (1) was formed to form an upper layer coat layer. 70 g of the upper coat layer was formed on 1 L of the honeycomb substrate.
The concentration of each component in the exhaust gas purification catalyst is as follows: platinum: 1.3 g / L, palladium: 0.5 g / L, rhodium: 0.3 g / L, barium: 0.2 mol / L, lithium: 0.1 mol / L L, potassium: 0.13 mol / L.

Comparative Example 2 Preparation of exhaust gas purifying catalyst with potassium loading concentration of 0.00 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, an exhaust gas purifying catalyst was prepared in the same manner as Comparative Example 1 except that potassium was not added. .

Comparative Example 3 Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.04 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, 1-1. The amount of potassium in step (4) is 3.6 g to 1.1 g, 1-2. Exhaust gas purification catalyst was prepared in the same manner as Comparative Example 1 except that the amount of potassium in the step (2) was changed from 1.5 g to 0.4 g.

Comparative Example 4 Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.08 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, 1-1. The amount of potassium in step (4) is 3.6 g to 2.2 g, 1-2. Exhaust gas purifying catalyst was prepared in the same manner as Comparative Example 1 except that the amount of potassium in the step (2) was changed from 1.5 g to 0.9 g.

Comparative Example 5 Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.11 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, 1-1. The amount of potassium in the step (4) is 3.6 g to 3.1 g, 1-2. Exhaust gas purifying catalyst was prepared in the same manner as Comparative Example 1 except that the amount of potassium in the step (2) was changed from 1.5 g to 1.2 g.

Comparative Example 6 Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.15 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, 1-1. The amount of potassium in the step (4) is 3.6 g to 4.1 g, 1-2. Exhaust gas purifying catalyst was prepared in the same manner as Comparative Example 1 except that the amount of potassium in the step (2) was changed from 1.5 g to 1.7 g.

Comparative Example 7 Preparation of exhaust gas purifying catalyst having a potassium loading concentration of 0.18 mol / L In the preparation of exhaust gas purifying catalyst of Comparative Example 1, 1-1. The amount of potassium in the step (4) is 3.6 to 5.0 g, and 1-2. Exhaust gas purifying catalyst was prepared in the same manner as Comparative Example 1 except that the amount of potassium in the step (2) was changed from 1.5 g to 2.1 g.

  A schematic diagram of the exhaust gas purifying catalysts of Comparative Examples 1 to 7 is shown in FIG.

2. Preparation of exhaust gas purifying catalyst having different potassium loading concentration in the first loading concentration region and the second loading concentration region

Comparative Example 8. 2. Preparation of exhaust gas purification catalyst having a potassium loading concentration of 0.13 mol / L in the first loading concentration region and a potassium loading concentration of 0.02 mol / L in the second loading concentration region 2-1. Preparation of lower layer slurry for first carrier concentration region 1-1 of Comparative Example 1-1. A slurry was prepared in the same manner as in the step (4), and the slurry was used as a lower slurry for a first supported concentration region.
2-2. Preparation of lower layer slurry for second supported concentration region 1-1 of Comparative Example 1-1. A slurry was prepared in the same manner as in the step 1-1 of Comparative Example 1 except that the amount of potassium in the step (4) was changed from 3.6 g to 0.6 g, and the slurry was second loaded. A lower layer slurry for the concentration region was obtained.
2-3. Preparation of slurry for upper layer for first carrying concentration region 1-2 of Comparative Example 1 A slurry was prepared in the same manner as in the step (2), and the slurry was used as an upper layer slurry for the first supported concentration region.
2-4. Preparation of upper layer slurry for second carrier concentration region 1-2 of Comparative Example 1-2. Except that the amount of potassium in the step (2) was changed from 1.5 g to 0.2 g, a slurry was prepared in the same manner as in the step 1-2 of Comparative Example 1, and the slurry was second supported. A slurry for the upper layer for the concentration region was obtained.
2-5. Formation of Coat Layer (1) On the end surface of a cylindrical cordierite honeycomb substrate (DENSO, diameter 129 mm × substrate length 100 mm, 1.3 L), the first supported concentration region (center is the same as the center of the honeycomb substrate) The second supported concentration region (circular region having a diameter of 66 mm) (annular region around the outer periphery of the first supported concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm with the center being the same as the center of the honeycomb substrate) And the lower slurry for the first supported concentration region prepared in 2-1 was wash coated to form a lower coat layer in the first supported concentration region. 150 g of the lower coat layer in the first supported concentration region was formed on the honeycomb substrate 1L.
(2) The first support concentration region upper layer slurry prepared in 2-3 is wash-coated on the honeycomb base material in which the lower support layer is formed in the first support concentration region obtained in (1). An upper coat layer was formed in the supported concentration region. 70 g of the upper coat layer in the first supported concentration region was formed on 1 L of the honeycomb substrate.
(3) On the end face of the honeycomb substrate on which the coating layer was formed in the first supporting concentration region obtained in (2), the first supporting concentration region on which the coating layer was formed was masked and prepared in 2-2. The lower layer slurry for the second supported concentration region was washcoated to form a lower layer coat layer in the second supported concentration region. 150 g of the lower coat layer in the second supported concentration region was formed on the honeycomb substrate 1L.
(4) The second support concentration region upper layer slurry prepared in 2-4 is washed on the honeycomb substrate having the lower support concentration region formed in the second support concentration region obtained in (3) and second An upper coat layer was formed in the supported concentration region. 70 g of the upper coating layer in the second supported concentration region was formed on the honeycomb substrate 1L.
The concentration of each component in the exhaust gas purification catalyst is as follows: platinum: 1.3 g / L, palladium: 0.5 g / L, rhodium: 0.3 g / L, barium: 0.2 mol / L, lithium: 0.1 mol / L L, potassium (first supported concentration region): 0.13 mol / L, potassium (second supported concentration region): 0.02 mol / L.

Comparative Example 9 Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.13 mol / L in the first support concentration region and a potassium support concentration of 0.15 mol / L in the second support concentration region. In the same manner as in Comparative Example 8, except that the amount of potassium in step 2 was changed from 0.6 g to 4.1 g, and the amount of potassium in step 2-4 was changed from 0.2 g to 1.7 g. An exhaust gas purification catalyst was prepared.

Comparative Example 10 Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.18 mol / L in the first support concentration region and a potassium support concentration of 0.08 mol / L in the second support concentration region. The amount of potassium in step 1 is 3.6 g to 5.0 g. The amount of potassium in step 2-2 is 0.6 g to 2.2 g. The amount of potassium in step 2-3 is 1.5 g. To 2.1 g, a catalyst for exhaust gas purification was prepared in the same manner as in Comparative Example 8 except that the amount of potassium in the steps 2-4 was changed from 0.2 g to 0.9 g.

Comparative Example 11 Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.15 mol / L in the first support concentration region and a potassium support concentration of 0.04 mol / L in the second support concentration region. The amount of potassium in step 1 is 3.6 g to 4.1 g. The amount of potassium in step 2-2 is 0.6 g to 1.1 g. The amount of potassium in step 2-3 is 1.5 g. To 1.7 g, a catalyst for exhaust gas purification was prepared in the same manner as Comparative Example 8 except that the amount of potassium in the steps 2-4 was changed from 0.2 g to 0.4 g.

Example 1. Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.13 mol / L in the first support concentration region and a potassium support concentration of 0.04 mol / L in the second support concentration region. Except that the amount of potassium in step 2 was changed from 0.6 g to 1.1 g, and the amount of potassium in step 2-4 was changed from 0.2 g to 0.4 g, as in Comparative Example 8. An exhaust gas purification catalyst was prepared.

Example 2 Preparation of exhaust gas purification catalyst having potassium support concentration of 0.13 mol / L in the first support concentration region and potassium support concentration of 0.08 mol / L in the second support concentration region Except that the amount of potassium in step 2 was changed from 0.6 g to 2.2 g, and the amount of potassium in step 2-4 was changed from 0.2 g to 0.9 g, as in Comparative Example 8. An exhaust gas purification catalyst was prepared.

Example 3 Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.13 mol / L in the first support concentration region and a potassium support concentration of 0.11 mol / L in the second support concentration region. Except that the amount of potassium in step 2 was changed from 0.6 g to 3.0 g, and the amount of potassium in step 2-4 was changed from 0.2 g to 1.2 g, as in Comparative Example 8. An exhaust gas purification catalyst was prepared.

Example 4 Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.11 mol / L in the first support concentration region and a potassium support concentration of 0.08 mol / L in the second support concentration region. The amount of potassium in step 1 is 3.6 g to 3.1 g, the amount of potassium in step 2-2 is 0.6 g to 2.2 g, and the amount of potassium in step 2-3 is 1.5 g. To 1.2 g, except that the amount of potassium in the step 2-4 was changed from 0.2 g to 0.9 g, an exhaust gas purification catalyst was prepared in the same manner as in Comparative Example 8.

Embodiment 5 FIG. Preparation of an exhaust gas purification catalyst having a potassium support concentration of 0.15 mol / L in the first support concentration region and a potassium support concentration of 0.08 mol / L in the second support concentration region. The amount of potassium in step 1 is 3.6 g to 4.1 g. The amount of potassium in step 2-2 is 0.6 to 2.2 g. The amount of potassium in step 2-3 is 1.5 g. To 1.7 g, a catalyst for exhaust gas purification was prepared in the same manner as in Comparative Example 8, except that the amount of potassium in the steps 2-4 was changed from 0.2 g to 0.9 g.

Example 6 Preparation of exhaust gas purifying catalyst of Comparative Example 8 in preparation of exhaust gas purifying catalyst having potassium supporting concentration of 0.15 mol / L in the first supporting concentration region and potassium supporting concentration of 0.13 mol / L in the second supporting concentration region. The amount of potassium in step 1 is 3.6 g to 4.1 g. The amount of potassium in step 2-2 is 0.6 g to 3.6 g. The amount of potassium in step 2-3 is 1.5 g. To 1.7 g, a catalyst for exhaust gas purification was prepared in the same manner as in Comparative Example 8 except that the amount of potassium in the steps 2-4 was changed from 0.2 g to 1.5 g.

  A schematic diagram of the exhaust gas purifying catalysts of Comparative Examples 8 to 11 and Examples 1 to 6 is shown in FIG.

3. Test / Evaluation The NOx purification rate was measured for the exhaust gas purification catalysts of Comparative Examples 1 to 11 and Examples 1 to 6.

3-1. Measurement Method (1) An exhaust gas purifying catalyst was installed on the downstream side of an engine with a displacement of 3.5 L.
(2) The rotational speed and accelerator opening were adjusted so that the catalyst bed temperature was 760 ° C., and heat treatment was performed for 50 hours.
(3) As shown in FIG. 4, an exhaust gas purification catalyst is installed on the downstream side of a 3.5-liter V-type 6-cylinder lean combustion engine using an exhaust pipe having an exhaust pipe diameter of 60 mm, and the amount of intake air (Ga) was set to 52 g / s, and the rotation speed and accelerator opening were adjusted so that the catalyst bed temperature was 450 ° C.
(4) Rich (A / F = 12.5) 3 seconds, Lean (A / F = 24) 60 seconds as one set, and 4 sets reciprocating between rich and lean, NOx concentration is MEXA-7500D ( And the NOx purification rate was calculated.
(5) In a lean combustion engine with a displacement of 3.5 L, the intake air amount (Ga) was 14 g / s, and the rotational speed and accelerator opening were adjusted so that the catalyst bed temperature was 300 ° C.
(6) Rich (A / F = 12.5) 5 seconds, Lean (A / F = 24) 90 seconds as one set, and 4 sets reciprocating between rich and lean, NOx concentration is MEXA-7500D ( And the NOx purification rate was calculated.

In this evaluation, a sufficient amount of rich gas was supplied to reduce the stored NOx. Thus, by repeatedly evaluating rich and lean, the NOx occlusion performance and the reduction performance of the catalyst can be comprehensively evaluated, and the performance in an actual use environment can be evaluated.
The measurement conditions for the NOx purification rate are summarized in Table 1.

3-2. Evaluation result The NOx purification rate was calculated by the following formula.
NOx purification rate (%) = {(NOx concentration in exhaust gas) − (NOx concentration in gas flowing out from exhaust gas purification catalyst)} / (NOx concentration in exhaust gas) × 100
The NOx purification rate is summarized in Table 2.

  In addition, in the exhaust gas purification catalyst of Comparative Examples 1-7, the relationship between the potassium carrying | concentration density | concentration in the difference in catalyst bed temperature and a NOx purification rate is shown in FIG. As shown in FIG. 5, when the catalyst bed temperature is 300 ° C. and 450 ° C., the optimum potassium loading concentration in the NOx purification rate seems to be different.

  When the exhaust gas purifying catalysts of Comparative Examples 1-7 and Examples 1-6 are compared, the NOx purification performance during low speed running (catalyst bed temperature: 300 ° C.) is about 60% to about 70% in Comparative Examples 1-7. However, Examples 1-6 are about 70%, and the NOx purification rate of Examples 1-6 is substantially the same as the high NOx purification rate in the comparative examples. Further, regarding the NOx purification performance during high speed running (catalyst bed temperature: 450 ° C.), the NOx purification rates of Comparative Examples 1 to 7 do not exceed 80% at the highest, but the NOx purification rates of the examples are all 80%. As described above, the NOx purification rate of the example is a better result than the NOx purification rate of the comparative example.

  Further, by comparing the exhaust gas purifying catalysts of Comparative Examples 8 to 11 and Examples 1 to 6, the exhaust gas purifying catalyst has a potassium support concentration in the exhaust gas purifying catalyst of 0. 0 in the first support concentration region. 11 to 0.15 mol / L, 0.04 to 0.13 mol / L in the second supported concentration region, and the ratio of the supported concentration in the first supported concentration region to the supported concentration in the second supported concentration region It was found that when the (supported concentration in the first supported concentration region / supported concentration in the second supported concentration region) was 1.1 to 3.3, it had excellent NOx purification performance.

<Preferable range of the ratio of the diameter of the circle of the first supported concentration region to the diameter of the outermost circle of the second supported concentration region>
4). Exhaust gas purification in which the ratio of the diameter of the circle of the first supported concentration region to the diameter of the outermost circle of the second supported concentration region (the diameter of the circle of the first supported concentration region / the diameter of the outermost circle of the second supported concentration region) differs Catalyst preparation

Comparative Example 12 The ratio of the diameter of the circle in the first supported concentration region (potassium supported concentration: 0.13 mol / L) to the diameter of the outermost circle in the second supported concentration region (potassium supported concentration: 0.08 mol / L) is 0.12. Preparation of certain exhaust gas purifying catalyst In the preparation of the exhaust gas purifying catalyst of Example 2, 2-5 in Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first support concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, respectively, and a first support concentration region (a circular region having a diameter of 15 mm with the center being the same as the center of the honeycomb substrate) and the first support concentration region. 2 The same as in Example 2 except that it was changed to the support concentration region (the center was the same as the center of the honeycomb substrate, and the outer periphery was an annular region around the first support concentration region having an inner diameter of 15 mm to an outer diameter of 129 mm). Thus, an exhaust gas purification catalyst was prepared.

Example 7 The ratio of the diameter of the circle in the first supported concentration region (potassium supported concentration: 0.13 mol / L) to the diameter of the outermost circle in the second supported concentration region (potassium supported concentration: 0.08 mol / L) is 0.23. Preparation of certain exhaust gas purifying catalyst In the preparation of the exhaust gas purifying catalyst of Example 2, 2-5 in Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first supported concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, and a first supported concentration region (a circular region having a diameter of 30 mm with the center being the same as the center of the honeycomb substrate) and 2 The same as in Example 2 except that it was changed to the support concentration region (the center was the same as the center of the honeycomb substrate, and the outer periphery was an annular region on the outer periphery of the first support concentration region having an inner diameter of 30 mm to an outer diameter of 129 mm). Thus, an exhaust gas purification catalyst was prepared.

Example 8 FIG. The ratio of the diameter of the circle in the first supported concentration region (potassium supported concentration: 0.13 mol / L) to the diameter of the outermost circle in the second supported concentration region (potassium supported concentration: 0.08 mol / L) is 0.67. Preparation of certain exhaust gas purifying catalyst In the preparation of the exhaust gas purifying catalyst of Example 2, 2-5 in Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first support concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, respectively, and a first support concentration region (a circular region having a diameter of 86 mm with the center being the same as the center of the honeycomb substrate) and the first support concentration region. 2 The same as in Example 2 except that it was changed to the support concentration region (the center was the same as the center of the honeycomb substrate, and the outer periphery was an annular region on the outer periphery of the first support concentration region having an inner diameter of 86 mm to an outer diameter of 129 mm). Thus, an exhaust gas purification catalyst was prepared.

Example 9 The ratio of the diameter of the circle in the first supported concentration region (potassium supported concentration: 0.13 mol / L) to the diameter of the outermost circle in the second supported concentration region (potassium supported concentration: 0.08 mol / L) is 0.76. Preparation of certain exhaust gas purifying catalyst In the preparation of the exhaust gas purifying catalyst of Example 2, 2-5 in Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first support concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, respectively, and a first support concentration region (a circular region with a diameter of 98 mm with the center being the same as the center of the honeycomb substrate) and the first support concentration region. 2 The same as in Example 2 except that it was changed to the support concentration region (the center was the same as the center of the honeycomb substrate, and the outer peripheral annular region of the first support concentration region having an inner diameter of 98 mm to an outer diameter of 129 mm). Thus, an exhaust gas purification catalyst was prepared.

  A schematic diagram of the exhaust gas purifying catalyst of Comparative Example 12 and Examples 7 to 9 is shown in FIG.

5. Test / Evaluation Comparative Examples 1, 4 and 12 and Examples 2 and 7 to 9 were measured for NOx purification rates for the exhaust gas purification catalysts.

5-1. Measuring method (1) An exhaust gas purifying catalyst was installed on the downstream side of a 3 L engine.
(2) The rotational speed and accelerator opening were adjusted so that the catalyst bed temperature was 760 ° C., and heat treatment was performed for 50 hours.
(3) As shown in FIG. 4, an exhaust gas purification catalyst is installed on the downstream side of a 3.5-liter V-type 6-cylinder lean combustion engine using an exhaust pipe having an exhaust pipe diameter of 60 mm, and the amount of intake air (Ga) was set to 52 g / s, and the rotation speed and accelerator opening were adjusted so that the catalyst bed temperature was 450 ° C.
(4) Rich (A / F = 12.5) 3 seconds, Lean (A / F = 24) 60 seconds as one set, and 4 sets reciprocating between rich and lean, NOx concentration is MEXA-7500D ( And the NOx purification rate was calculated.
Table 3 summarizes the conditions for measuring the NOx purification rate in a lean combustion engine with a displacement of 3.5 L.

(5) As shown in FIG. 7, an exhaust gas purifying catalyst is installed on the downstream side of an inline 4-cylinder lean combustion engine with a displacement of 2.0 L using an exhaust pipe having an exhaust pipe diameter of 60 mm, and an intake air amount ( Ga) was 29 g / s, and the rotation speed and accelerator opening were adjusted so that the catalyst bed temperature was 450 ° C.
(6) Rich (A / F = 12.5) 3 seconds, Lean (A / F = 24) 120 seconds as one set, and after 4 round trips between rich and lean, NOx concentration is MEXA-7500D ( HORIBA, Ltd.), and the NOx purification rate was calculated.
Table 4 summarizes the conditions for measuring the NOx purification rate in a lean combustion engine with a displacement of 2.0 L.

5-2. Evaluation Result The NOx purification rate was calculated by the formula described in 3-2.
The NOx purification rate is summarized in Table 5.

  Further, when the NOx purification rate is measured using a lean combustion engine having a displacement of 3.5 L or 2.0 L, the ratio of the diameter of the circle in the first supported concentration region to the diameter of the outermost circle in the second supported concentration region FIGS. 8 and 9 show the NOx purification rates with respect to (the diameter of the circle in the first supported concentration region / the diameter of the outermost circle in the second supported concentration region), respectively.

  As shown in Table 5 and FIGS. 8 and 9, it can be seen that there is a suitable range for NOx purification performance in (the diameter of the circle of the first supported concentration region / the diameter of the outermost circle of the second supported concentration region) It was found that it was more preferable that (the diameter of the circle in the first supported concentration region / the diameter of the outermost circle in the second supported concentration region) was 0.20 to 0.80.

  It was also found that the preferred range of the lean combustion engine displacement 2.0L to 3.5L does not change even if the displacement is different.

<Influence of size of cylindrical cordierite honeycomb substrate>
6). Preparation of exhaust gas purification catalyst with deformed cylindrical cordierite honeycomb substrate

Comparative Example 13 Preparation of Exhaust Gas Purification Catalyst Using a Cylindrical Cordierite Honeycomb Base Material (Diameter 103 mm × Base Material Length 155 mm, 1.3 L) Preparation of Exhaust Gas Purification Catalyst of Comparative Example 1 Preparation of Exhaust Gas Purification Catalyst of Comparative Example 1 1-3. The columnar cordierite honeycomb substrate (Denso, diameter 129 mm x substrate length 100 mm, 1.3 L) in the step (1) was used as the columnar cordierite honeycomb substrate (Denso, diameter 103 mm x substrate length). Except for changing to 155 mm, 1.3 L), an exhaust gas purifying catalyst was prepared in the same manner as in Comparative Example 1.

Example 10 Using a cylindrical cordierite honeycomb substrate (diameter 103 mm × substrate length 155 mm, 1.3 L), the second support concentration of the diameter of the circle in the first support concentration region (potassium support concentration: 0.13 mol / L) Exhaust gas in which the ratio of the region (potassium loading concentration: 0.08 mol / L) to the diameter of the outermost circle (diameter of the first loading concentration region / diameter of the outermost circle of the second loading concentration region) is 0.29. Preparation of purification catalyst In preparation of the exhaust gas purification catalyst of Example 2, 2-5 of Comparative Example 8 cited in the preparation of the exhaust gas purification catalyst of Example 2. The columnar cordierite honeycomb substrate (Denso, diameter 129 mm x substrate length 100 mm, 1.3 L) in the step (1) was used as the columnar cordierite honeycomb substrate (Denso, diameter 103 mm x substrate length). 155 mm, 1.3 L) and 2-5. Of Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first supported concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, and a first supported concentration region (a circular region having a diameter of 30 mm with the center being the same as the center of the honeycomb substrate) and 2 The same as in Example 2, except that it was changed to the support concentration region (the center is the same as the center of the honeycomb substrate, and the outer peripheral annular region of the first support concentration region having an inner diameter of 30 mm to an outer diameter of 103 mm). Thus, an exhaust gas purification catalyst was prepared.

Example 11 Using a cylindrical cordierite honeycomb substrate (diameter 103 mm × substrate length 155 mm, 1.3 L), the second support concentration of the diameter of the circle in the first support concentration region (potassium support concentration: 0.13 mol / L) Exhaust gas in which the ratio of the region (potassium loading concentration: 0.08 mol / L) to the diameter of the outermost circle (diameter of the first loading concentration region / diameter of the outermost circle of the second loading concentration region) is 0.58 Preparation of purification catalyst In preparation of the exhaust gas purification catalyst of Example 2, 2-5 of Comparative Example 8 cited in the preparation of the exhaust gas purification catalyst of Example 2. The columnar cordierite honeycomb substrate (Denso, diameter 129 mm x substrate length 100 mm, 1.3 L) in the step (1) was used as the columnar cordierite honeycomb substrate (Denso, diameter 103 mm x substrate length). 155 mm, 1.3 L) and 2-5. Of Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first supported concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, the first supported concentration region (a circular region having a diameter of 60 mm with the center being the same as the center of the honeycomb substrate) and the first 2 The same as in Example 2 except that the concentration was changed to the support concentration region (the center is the same as the center of the honeycomb substrate, and the outer periphery of the first support concentration region having an inner diameter of 60 mm to an outer diameter of 103 mm). Thus, an exhaust gas purification catalyst was prepared.

Example 12 FIG. Using a cylindrical cordierite honeycomb substrate (diameter 103 mm × substrate length 155 mm, 1.3 L), the second support concentration of the diameter of the circle in the first support concentration region (potassium support concentration: 0.13 mol / L) Exhaust gas in which the ratio of the region (potassium loading concentration: 0.08 mol / L) to the diameter of the outermost circle (diameter of the first loading concentration region / diameter of the outermost circle of the second loading concentration region) is 0.87 Preparation of purification catalyst In preparation of the exhaust gas purification catalyst of Example 2, 2-5 of Comparative Example 8 cited in the preparation of the exhaust gas purification catalyst of Example 2. The columnar cordierite honeycomb substrate (Denso, diameter 129 mm x substrate length 100 mm, 1.3 L) in the step (1) was used as the columnar cordierite honeycomb substrate (Denso, diameter 103 mm x substrate length). 155 mm, 1.3 L) and 2-5. Of Comparative Example 8 cited in the preparation of the exhaust gas purifying catalyst of Example 2. The first supported concentration region (circular region with a diameter of 66 mm with the center being the same as the center of the honeycomb substrate) and the second supported concentration region (the center being the same as the center of the honeycomb substrate) in the steps of (1) and (3) As an annular region on the outer periphery of the first support concentration region having an inner diameter of 66 mm to an outer diameter of 129 mm, respectively, and a first support concentration region (a circular region having a diameter of 90 mm with the center being the same as the center of the honeycomb substrate) and 2 The same as in Example 2 except that it was changed to the supported concentration region (the annular region on the outer periphery of the first supported concentration region having the same center as that of the honeycomb substrate and the inner diameter of 90 mm to the outer diameter of 103 mm). Thus, an exhaust gas purification catalyst was prepared.

  FIG. 10 shows the relative relationship between the cylindrical cordierite honeycomb substrate used in Comparative Example 1 and Examples 2, 7 and 8, and the cylindrical cordierite honeycomb substrate used in Comparative Example 13 and Examples 10-12. The relationship of the size is shown.

7). The NOx purification rate was measured for the exhaust gas purification catalysts of Test / Evaluation Comparative Example 13 and Examples 10-12.
7-1. Measurement method 5-1. (1) It performed by the method as described in (4).
7-2. Evaluation Result The NOx purification rate was calculated by the formula described in 3-2.

  Regarding the NOx purification rate of Comparative Example 1 and Examples 2, 7 and 8, the NOx purification rate of Comparative Example 1 is 1 from the evaluation result of the catalyst bed temperature of 450 ° C. in the lean combustion engine of 5-2 with a displacement of 3.5 L. In this case, the NOx purification performance of the exhaust gas purification catalyst of Example 2, 7 or 8 (NOx purification rate of the exhaust gas purification catalyst of Example 2, 7 or 8 / NOx purification rate of Comparative Example 13) was calculated. The results are shown in FIG.

  Similarly, for the NOx purification rates of Comparative Example 13 and Examples 10 to 12, the NOx purification performance of the exhaust gas purification catalyst of Example 10, 11 or 12 when the NOx purification rate of Comparative Example 13 is 1 (Example) The NOx purification rate of the exhaust gas purification catalyst of 10, 11 or 12 / the NOx purification rate of Comparative Example 13) was calculated. The results are shown in FIG.

  As can be seen from Example 12 in FIG. 12, it can be seen that the effect of the present invention is also exhibited when (the diameter of the circle of the first carrier concentration region / the diameter of the outermost circle of the second carrier concentration region) is 0.87. It was.

  As shown in FIGS. 11 and 12, even if the size of the base material of the exhaust gas purifying catalyst is changed, the effect of the present invention can be achieved if the potassium loading concentration in the exhaust gas purifying catalyst is within the range of the present invention. It was found that

Claims (1)

A cylindrical base material through which the exhaust gas passes, the cross section being perpendicular to the flow direction of the exhaust gas is a circle;
A catalyst coat layer formed on the surface of the substrate;
The catalyst coat layer has a two-layer structure having a lower layer formed on the surface of the substrate and an upper layer formed on the upper surface of the lower layer,
The lower layer comprises a catalyst metal containing rhodium (Rh), platinum (Pt) and palladium (Pd), a NOx storage material containing potassium (K), barium (Ba) and lithium (Li), the catalyst metal and NOx. Containing a composite oxide and / or oxide containing at least one selected from alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ) and ceria (CeO ₂ ) supporting the storage material. ,
The upper layer is selected from a catalyst metal containing Pt and Pd, a NOx storage material containing K, Ba and Li, and Al ₂ O ₃ , TiO ₂ , ZrO ₂ and CeO ₂ supporting the catalyst metal and the NOx storage material. A composite oxide and / or an oxide containing at least one selected from
A catalyst for exhaust gas purification,
The K-supported region includes a column type first support concentration (first support concentration region) in which K has the same central axis as the center axis of the cylindrical base material, and K is the first support concentration region. There is a region (second supported concentration region) that is an annular column type second supported concentration that exists on the outer periphery of the supported concentration region,
The first supported concentration region is a supported concentration of 0.11 to 0.15 mol / L, and
The second supported concentration region is a supported concentration of 0.04 to 0.13 mol / L, and
The ratio of the carrier concentration in the first carrier concentration region to the carrier concentration in the second carrier concentration region (the carrier concentration in the first carrier concentration region / the carrier concentration in the second carrier concentration region) is 1.1 to 3.3. Yes, and
The ratio of the diameter of the circle of the first support concentration region of the cylindrical type to the diameter of the outermost circle of the second support concentration region of the annular column type (the diameter of the circle of the first support concentration region / the second support concentration region) A catalyst for exhaust gas purification, wherein the diameter of the outermost circle is 0.20 to 0.90.

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