JP2019150781A - Exhaust gas treatment member - Google Patents

Abstract

To provide an exhaust gas treatment member and the like which can further reduce an ignition temperature of an air-fuel mixture of fuel and air in an engine.SOLUTION: The exhaust gas treatment member comprises at least: a base material 10 arranged in an exhaust gas flow path; a first catalyst layer 11 including platinum and palladium provided on the base material 10 and arranged at an upstream side of the exhaust gas flow path; a second catalyst layer 12 including platinum and palladium provided on the base material 10 and arranged at a downstream side of the exhaust gas flow path; and a third catalyst layer 13 including platinum and palladium arranged on the first and second catalyst layers 11 and 12. For total densities of platinum and palladium in the catalyst layers, the total densities are highest in the first catalyst layer 11 and lowest in the second catalyst layer 12, density ratios (Pt/Pd) of platinum to palladium in the first and second catalyst layers 11 and 12 are equal to 1.0 or more and 3.5 or less, and a density ratio (Pt/Pd) of platinum to palladium in the third catalyst layer 13 is equal to 2.5 or more and 6.0 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to environmental technology, and relates to an exhaust gas treatment member.

  Exhaust gas emitted by lean combustion of fuel in combustion engines such as lean burn gasoline engines and diesel engines contains various harmful substances. Hazardous substances include hydrocarbons (HC), soluble organic components (SOF), carbon monoxide (CO), nitrogen oxides (NOx), and soot that are regulated by the Air Pollution Control Law. Including.

Therefore, a filter is disposed in the exhaust gas flow path in order to reduce harmful particulate components such as soot and SOF in the exhaust gas. However, when harmful particulate components accumulate on the filter, the filter becomes clogged. Therefore, in order to burn and remove harmful particulate components deposited on the filter, it has been studied to use the heat of exhaust gas and nitrogen dioxide (NO ₂ ) (see, for example, Patent Documents 1 to 6).

In order to increase the temperature of the exhaust gas and increase the concentration of nitrogen dioxide (NO ₂ ), a member having an oxidation catalyst is disposed in the exhaust gas flow path between the engine and the filter. The oxidation catalyst oxidizes hydrocarbons (HC) contained in the exhaust gas and raises the temperature of the exhaust gas. Further, the oxidation catalyst of nitrogen monoxide (NO) contained in the exhaust gas is oxidized to nitrogen dioxide (NO _2), increasing the concentration of nitrogen dioxide (NO _2). In addition, in order to increase the temperature of exhaust gas reaching the filter, the amount of harmful particulates deposited on the filter is increased by increasing the amount of fuel supplied to the engine and increasing the amount of hydrocarbon (HC) oxidized by the oxidation catalyst. Ingredients are burned.

A selective catalytic reduction method (SCR) that selectively reduces NOx contained in exhaust gas to nitrogen (N ₂ ) using a reducing agent such as ammonia (NH ₃ ) and a catalyst containing a reducing agent adsorbing component. : Selective Catalytic Reduction) has been proposed. In this method, ammonia (NH ₃ ) is supplied to the reducing agent adsorbing component, and the nitrogen oxides of the exhaust gas come into contact with the ammonia (NH ₃ ) adsorbed on the reducing agent adsorbing component, whereby the following chemical formulas (1) to (3) ), The nitrogen oxides are reduced to nitrogen (N ₂ ).
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)
2NO ₂ + 4NH ₃ + O ₂ → 3N ₂ + 6H ₂ O (2)
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (3)

In the chemical reactions represented by the chemical formulas (1) to (3), the chemical reaction using nitrogen dioxide (NO ₂ ) represented by the chemical formula (3) is supposed to proceed preferentially. Therefore, oxidizing nitric oxide (NO) to nitrogen dioxide (NO ₂ ) is also useful for the purpose of reducing nitrogen oxides.

In addition, a method for reducing NOx by reducing NOx by adsorbing NOx to an LNT (Lean NOx Trap) catalyst containing a component that adsorbs an NOx component and supplying a reducing agent to the LNT catalyst has been studied. Examples of the component that adsorbs the NOx component include alkali metals such as barium carbonate, alkaline earth metal components, and rare earth components such as ceria. As the reducing agent, HC contained in the exhaust gas when burned with a rich air fuel ratio or fuel sprayed in the exhaust pipe is used. In an LNT catalyst, nitrogen dioxide (NO ₂ ) is more efficiently reduced than nitrogen monoxide (NO), and therefore, nitric oxide (NO) is oxidized into nitrogen dioxide (NO ₂ ) upstream of the LNT catalyst. It is preferable.

  On the other hand, in forced regeneration of the exhaust gas filter, the exhaust gas temperature supplied to the exhaust gas filter is increased by light oil post spray or exhaust gas pipe light oil spray. The lower limit temperature at which the exhaust gas temperature supplied to the filter during light oil spraying in the oxidation catalyst does not decrease is called the ignition temperature. Lower fuel temperature improves fuel efficiency.

JP 2017-501032 A JP, 2006-513484, A JP, 2006-503344, A Japanese Patent Laid-Open No. 2006-500331 JP 2008-272659 A International Publication No. 2014/141903

  This invention is made | formed in view of the said subject, and it aims at providing the waste gas processing member etc. which can lower the ignition temperature by a light oil post spray or a waste gas pipe light oil spray. Another object of the present invention is to provide an exhaust gas treatment member that can improve fuel consumption.

  As a result of intensive studies in order to solve the above problems, the present inventor determined the blending composition of the oxidation catalyst in the upper catalyst layer and the lower catalyst layer in the exhaust gas treatment member having the catalyst layer of the laminated structure. By adjusting, it discovered that the said subject could be solved and came to complete this invention. That is, the present invention provides various specific modes shown below.

(1) A base material disposed in the exhaust gas flow path, a first catalyst layer provided on the base material and disposed on the upstream side of the exhaust gas flow path, including at least platinum and palladium, and the base material A second catalyst layer containing at least platinum and palladium disposed on the downstream side of the exhaust gas flow path, and a third catalyst containing at least platinum and palladium disposed on the first and second catalyst layers A total concentration of platinum and palladium in each catalyst layer is highest in the first catalyst layer, lowest in the second catalyst layer, and platinum relative to palladium in the first and second catalyst layers. The concentration ratio of platinum (Pt / Pd) is 1.0 or more and 3.5 or less, and the concentration ratio of platinum to palladium (Pt / Pd) in the third catalyst layer is 2.5 or more and 6.0 or less. , Exhaust gas treatment member.

(2) The concentration ratio of platinum in the first catalyst layer to platinum in the second catalyst layer (Pt in the first catalyst layer / Pt in the second catalyst layer) is 2.5 or more and 3.5 or less. The exhaust gas treatment member according to (1).

(3) The concentration ratio of palladium in the first catalyst layer to Pd in the second catalyst layer (Pd in the first catalyst layer / Pd in the second catalyst layer) is 2.5 or more and 3.5 or less. The exhaust gas treatment member according to (1) or (2).

(4) The exhaust gas treatment member according to any one of (1) to (3), wherein the base material constitutes a honeycomb structure.

(5) Platinum and palladium are supported on a carrier, and the carrier contains one or more selected from the group consisting of alumina, titania, zirconia, silica, boehmite, and silica-alumina. The exhaust gas treatment member according to any one of the above.

(6) The exhaust gas treatment member according to (5), wherein the alumina is at least one selected from the group consisting of γ-alumina, δ-alumina, and θ-alumina.

(7) The exhaust gas treatment member according to any one of (1) to (6), wherein the exhaust gas is exhaust gas of a diesel engine.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the exhaust gas processing member which can lower the ignition temperature by light oil post spray or exhaust gas pipe light oil spray, and it contributes to the further improvement of fuel consumption performance.

It is a typical sectional view showing the exhaust gas processing member concerning an embodiment. It is typical sectional drawing which shows the modification of an waste gas processing member. It is typical sectional drawing which shows the modification of an waste gas processing member.

  Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these. In addition, the present invention can be implemented with any modifications without departing from the scope of the invention. In the present specification, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. In addition, in this specification, when a numerical value or a physical property value is put before and after using “to”, the value before and after that is used. For example, the description of a numerical range of “1 to 100” includes both the upper limit value “100” and the lower limit value “1”. This also applies to other numerical range notations.

  As shown in FIG. 1, the exhaust gas treatment member 100 according to the present embodiment is provided with a base material 10 disposed in the exhaust gas flow channel, and provided on the base material 10 and on the upstream side of the exhaust gas flow channel. A first catalyst layer 11 including at least platinum and palladium; a second catalyst layer 12 including at least platinum and palladium provided on the base material 10 and disposed on the downstream side of the exhaust gas flow path; And a third catalyst layer 13 including at least platinum and palladium disposed on the catalyst layers 11 and 12. Therefore, the exhaust gas treatment member 100 according to the present embodiment includes a catalyst layer having a two-layer structure including at least a lower layer and an upper layer in the height direction from the surface of the base material 10, and the first catalyst layer 11 and the second catalyst layer. 12 is a lower catalyst layer, and the third catalyst layer 13 is an upper catalyst layer.

  In the exhaust gas treatment member 100 according to this embodiment, the total concentration of platinum and palladium in each catalyst layer is highest in the first catalyst layer 11 and lowest in the second catalyst layer 12. In the exhaust gas treatment member 100 according to the present embodiment, the concentration ratio of platinum to palladium (Pt / Pd) in the first and second catalyst layers 11 and 12 is 1.0 or more and 3.5 or less, and the third catalyst. The concentration ratio of platinum to palladium in the layer 13 is set to 2.5 or more and 6.0 or less, respectively. The exhaust gas processing member 100 according to the present embodiment is disposed, for example, downstream of a diesel engine and processes exhaust gas.

  The type of the substrate 10 is not particularly limited as long as it is excellent in heat resistance and can support the first and second catalyst layers 11 and 12. Examples thereof include metals, alloys such as stainless steel, ceramics, and laminated structures combining these, but are not particularly limited thereto. In addition, the shape, planar shape, thickness, and the like may be appropriately set according to the application and required performance. These can be used individually by 1 type or in combination of 2 or more types as appropriate.

Further, by adopting a honeycomb structure as the base material 10, application to an exhaust gas purification application installed in the exhaust gas flow becomes easy. A honeycomb structure generally includes a plurality of cells through which exhaust gas flows are provided in parallel in the long axis direction, and the exhaust gas flows from the inlet to the outlet of each cell. In this case, the base material 10 forms an inner wall of each cell of the honeycomb structure through which exhaust gas flows. As such a honeycomb structure, those known in the art can be appropriately selected. For example, honeycomb structures for automobile exhaust gas applications include ceramic monolith carriers such as cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), silicon carbide (SiC), and silicon nitride (Si ₃ N ₄ ), and metals such as stainless steel. Examples thereof include a honeycomb carrier, a wire mesh carrier made of stainless steel, and a steel wool knit wire carrier. These can be used individually by 1 type or in combination of 2 or more types as appropriate. The outer shape of the honeycomb structure can be selected from any shape such as a columnar shape, a quadrangular columnar shape, a hexagonal columnar shape, a spherical shape, a honeycomb shape, and a sheet shape, and is not particularly limited.

  The size of the honeycomb structure described above can be appropriately set according to the application and required performance, and is not particularly limited. For example, a honeycomb structure having a diameter (length) of several millimeters to several centimeters is preferably used. The number of cells of the honeycomb structure (cell density) may be appropriately set based on the type of exhaust gas to be treated, the flow rate of exhaust gas, the desired pressure loss, the desired removal efficiency of harmful substances contained in the exhaust gas, and the like. . For example, when processing exhaust gas from a diesel engine, the number of cells is preferably 100 cpsi or more and 500 cpsi or less, more preferably 150 cpsi or more and 400 cpsi or less, from the viewpoint of suppressing an increase in pressure loss while maintaining a high surface area for the exhaust gas flow. It is. The cell density means the number of cells per unit area in a cross section when the honeycomb structure is cut at right angles to the gas flow path. The wall thickness of the cell is preferably 4 mil or more and 12 mil or less, more preferably 5 mil or more and 10 mil or less, and further preferably 6 mil or more and 9 mil or less. In addition, as a honeycomb structure for automobile exhaust gas, a flow-through type structure in which a gas flow path is communicated, a part of the end face of the gas flow path is sealed, and gas can flow through the wall surface of the gas flow path. Wall flow type structures are widely known, and both are applicable

  On the surface of the base material 10, the first catalyst layer 11 is disposed on the upstream side of the exhaust gas flow path, and the second catalyst layer 12 is disposed on the downstream side of the exhaust gas flow path. The first catalyst layer 11 and the second catalyst layer 12 cover at least part of the surface of the substrate 10. In the present embodiment, the first catalyst layer 11 and the second catalyst layer 12 are disposed adjacent to each other on the base material 10. The third catalyst layer 13 covers at least part or all of the first catalyst layer 11 and the second catalyst layer 12. The first catalyst layer 11 mainly oxidizes carbon monoxide (CO) and hydrocarbons (HC). The second catalyst layer 12 mainly oxidizes nitric oxide (NO). The third catalyst layer 13, carbon monoxide (CO), hydrocarbon (HC), and nitric oxide (NO) are oxidized.

  The first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13 are washcoat layers. In the first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13, platinum (Pt) and palladium (Pd), which are oxidation catalysts, are supported on a particulate carrier. The carrier is also called matrix particle. The support and platinum and palladium form catalyst particles that are composite particles. The size of platinum and palladium supported on the support is on the order of several nanometers to several hundred nanometers. The presence of platinum and palladium on the support is, for example, observed with a transmission electron microscope (TEM), powder X-ray diffraction (XRD), electron probe microanalyzer (EPMA). ) And X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron Spectroscopy, or ESCA: Electron Spectroscopy for Chemical Analysis).

The carrier can be appropriately selected from known ones as long as it has high heat resistance and can stably disperse platinum and palladium, and the kind thereof is not particularly limited. For example, silica, boehmite, alumina (α-Al ₂ O ₃ , δ-Al ₂ O ₃ , γ-Al ₂ O ₃ , δ-Al ₂ O ₃ , η-Al ₂ O ₃ , θ-Al ₂ O ₃ ) Metal oxides or metal composite oxides such as ceria (CeO ₂ ), zirconia (ZrO ₂ ), ceria-zirconia, lanthanum oxide, neodymium oxide, and praseodymium oxide; zirconia doped with rare earth elements and / or transition elements Composite oxides such as ceria-zirconia; perovskite oxides; composite oxides containing alumina such as silica-alumina, silica-alumina-zirconia, silica-alumina-boria; barium compounds, anatase titania, zeolite, etc. However, it is not particularly limited to these. Among these, as the carrier, porous particles having a large BET specific surface area are preferable. Specific examples include alumina, titania, zirconia, silica, boehmite, and silica-alumina. Examples of alumina include γ-alumina, δ-alumina, and θ-alumina. An example of titania is anatase-type titania. As zirconia, stabilized zirconia or partially stabilized zirconia is preferable. Stabilized zirconia or partially stabilized zirconia is obtained by dissolving a rare earth oxide such as calcium oxide, magnesium oxide, or yttrium oxide in zirconia. Stabilized zirconia or partially stabilized zirconia forms oxygen vacancies in the structure, stabilizes cubic crystals and tetragonal crystals even at room temperature, and suppresses breakage due to elevated temperature. Silica includes amorphous silica, glassy, colloidal silica and the like in addition to crystalline silica having various different phase transformations. Silica generally has a higher BET specific surface area than alumina, and platinum and palladium are highly dispersed. Silica-alumina can be either crystalline or amorphous. In silica-alumina, the Si / Al ratio varies and is appropriately set according to the application. Examples of crystalline zeolite include ZSM type zeolite and β type zeolite. A support | carrier can be used individually by 1 type or in combination of 2 or more types as appropriate.

The carrier may consist of a plurality of materials. Further, for example, in order to improve the heat resistance of the support, a rare earth oxide such as lanthanum, silica, zirconia, or the like may be added to the support. The specific surface area of the carrier is appropriately set based on the heat resistance and the dispersibility and stability of Pt and Pd supported on the carrier. For example, the specific surface area is preferably 50 m ² / g or more and 300 m ² / g or less. The specific surface area is measured by, for example, the BET method.

  In addition, the support | carrier used here is not specifically limited by a manufacturing method. This type of carrier can be obtained by each known production method, for example, after dissolving a starting material in the form of a nitrate, sulfate, carbonate, acetate, chloride or the like containing the above elements in an aqueous solution. Then, a carrier having an arbitrary composition and crystallinity can be obtained by baking the solid obtained by mixing, precipitating as a precipitate by adjusting pH, or evaporating to dryness. In addition, when mixing or complexing the carrier raw material, these treatments may be performed by solubilizing a plurality of these metal salts at once, or by performing the above treatment on a single or a plurality of metal salts. After the oxide is formed, the remaining metal salt may be added all at once or sequentially.

  The first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13 may further include a co-catalyst that assists the oxidation catalytic ability of platinum and palladium. Examples of the promoter component include cerium oxide (ceria), ceria-zirconia, various zeolites, neodymium, rare earth oxides such as lanthanum oxide, zirconia, and the like. Cerium oxide can store oxygen in an oxygen-rich atmosphere and release oxygen in an oxygen-deficient atmosphere due to a change in the oxidation number of cerium (Ce). Therefore, cerium oxide is effective in oxidizing and burning soot and soluble organic components (SOF) in an oxygen-deficient atmosphere. Further, cerium oxide promotes an oxidation reaction of platinum, palladium, and the like at low temperatures such as CO, HC, and NO. Various zeolites store HC at a low temperature, release HC at a high temperature, and promote an oxidation reaction of HC at a low temperature by platinum or palladium. Rare earth oxides such as neodymium and lanthanum oxide, and zirconia are believed to inhibit platinum and palladium from moving and aggregating on the support by heat.

  In the exhaust gas treatment member 100 in each catalyst layer of the present embodiment, the total concentration of platinum and palladium is highest in the first catalyst layer 11 among the first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13. The second catalyst layer 13 is the second highest and the second catalyst layer 12 is the lowest. In this way, by setting the total concentration of the catalytically active species to a relatively low concentration in the third catalyst layer 13, the influence of deterioration of the catalyst performance due to poisoning of phosphorus (P) and the like contained in the exhaust gas is reduced, and By making the total concentration of the catalytically active species relatively high in the first catalyst layer 11, the catalyst performance can be maintained high, and as a result, the ignition temperature can be further lowered.

  Specifically, the platinum concentration ratio (Pt / Pd) to palladium in the first catalyst layer 11 and the second catalyst layer 12 is preferably 1.0 or more and 3.5 or less, more preferably 1.0 or more and 3. It is 0 or less, more preferably 1.5 or more and 2.5 or less. In other words, in the first catalyst layer 11 and the second catalyst layer 12, the concentration of platinum is preferably 1 to 3.5 times the concentration of palladium. The concentration ratio of platinum to palladium (Pt / Pd) in the third catalyst layer 13 is preferably 2.5 or more and 6.0 or less, more preferably 3.5 or more and 5.0 or less, and still more preferably 4.0. It is 5.0 or less. In other words, in the third catalyst layer 13, the platinum concentration is preferably 2.5 times or more and 6.0 times or less the palladium concentration. By setting the preferable range, the ignition temperature of the oxidation catalyst can be lowered.

On the other hand, the concentration ratio of platinum in the first catalyst layer 11 to platinum in the second catalyst layer 12 (Pt in the first catalyst layer 11 / Pt in the second catalyst layer 12) is, for example, 2.5 or more and 3. 5 or less is preferable. In other words, the platinum concentration in the first catalyst layer 11 is preferably 2.5 times to 3.5 times the platinum concentration in the second catalyst layer 12. The concentration ratio of palladium in the first catalyst layer to palladium in the second catalyst layer (Pd in the first catalyst layer 11 / Pd in the second catalyst layer 12) is preferably 2.5 or more and 3.5 or less. . In other words, the palladium concentration in the first catalyst layer 11 is not less than 2.5 times and not more than 3.5 times the palladium concentration in the second catalyst layer 12. By setting the preferable range, the ignition temperature of the oxidation catalyst can be lowered.

  When the substrate 10 has a honeycomb structure, the amount of platinum and palladium supported on the honeycomb structure (supported amount) can be appropriately set according to the desired performance, and is not particularly limited. From the viewpoints of the above, it is preferably 0.2 g or more and 5.0 g or less, more preferably 0.3 g or more and 3.0 g in terms of metal per 1 L of the coating part volume of the honeycomb structure. The coated portion volume of the honeycomb structure is the volume of the coated portion of the honeycomb structure excluding the outer wall, and includes the volume of the space portion in the honeycomb structured body as long as it is on the coated portion. Refers to volume.

  Further, when the substrate 10 has a honeycomb structure, the amounts (coating amounts) of the first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13 can be appropriately set according to the desired performance. Although not particularly limited, from the viewpoint of catalyst performance, pressure loss, cost, etc., the amount is preferably 10 g or more and 300 g or less, more preferably 15 g or more and 250 g or less, per 1 L of the coating portion volume of the honeycomb structure.

Next, an example of the manufacturing method of the exhaust gas processing member according to the present embodiment will be described.
First, in order to support platinum and palladium on a carrier, as an initial salt of platinum, an ethanolamine solution of platinum hydroxide (IV) acid, tetraammineplatinum (II) acetate, tetraammineplatinum (II) carbonate, tetraammineplatinum ( II) Prepare nitrate, nitric acid solution of platinum hydroxide (IV) acid, platinum nitrate, dinitrodiamine platinum nitric acid, platinum chloride (IV) acid and the like. Further, tetraamminepalladium (II) acetate, tetraamminepalladium (II) carbonate, tetraamminepalladium (II) nitrate, dinitrodiamminepalladium, palladium nitrate, palladium chloride and the like are prepared as palladium starting salts.

  Here, when the acidity of the platinum starting salt aqueous solution is close to the acidity of the palladium starting salt aqueous solution, precipitation hardly occurs when both aqueous solutions are mixed, and the dispersibility of the solution is easily maintained. Examples of combinations having close acidity include tetraammineplatinum (II) acetate-tetraamminepalladium (II) acetate (alkaline), ethanolamine solution of platinum hydroxide (IV) acid-tetraamminepalladium (II) acetate ( Alkaline), platinum nitrate-palladium nitrate (acidic), dinitrodiamine platinum nitrate-palladium nitrate (acidic), platinum chloride (IV) acid-palladium chloride (acidic), and the like. These are examples and are not limited.

  Then, using any method such as an impregnation method, an ion exchange method, and a kneading method, platinum and palladium contained in the prepared metal salt aqueous solution are supported on a carrier to form catalyst particles that are composite particles. . Thereafter, for example, the catalyst particles are dried at 50 ° C. or more and 200 ° C. or less, and further, for example, the catalyst particles are calcined at 350 ° C. or more and 1200 ° C. or less. Next, the catalyst particles and water or a water-soluble organic solvent obtained by adding a water-soluble organic solvent to water are mixed to obtain a slurry. In mixing, a known pulverization method or mixing method such as pulverization and mixing using a ball mill or the like can be applied. The slurry can be mixed with a binder, other catalyst, promoter particles, OSC material, base material particles, additives, and the like known in the art at a desired blending ratio, if necessary. Examples of additives include pH adjusters such as acids and bases for pH adjustment, nonionic surfactants and dispersion stabilizers such as anionic surfactants for improving dispersibility, and viscosity. Although the viscosity modifier for adjustment etc. are mentioned, it does not specifically limit to these.

  Here, among the slurry for forming each of the first catalyst layer 11, the second catalyst layer 12, and the third catalyst layer 13, the total concentration of platinum and palladium is the slurry for forming the first catalyst layer 11. And the second highest in the slurry for forming the third catalyst layer 13 and the lowest in the slurry for forming the second catalyst layer 12. Alternatively, as described above, the slurry coating amount is set so that the total concentration of platinum and palladium is highest in the first catalyst layer 11, second highest in the third catalyst layer 13, and lowest in the second catalyst layer 12. In this case, the total concentration of platinum and palladium in each slurry can be arbitrarily set.

  The concentration ratio of platinum to palladium (Pt / Pd) in the slurry for forming the first catalyst layer 11 and the second catalyst layer 12 is not particularly limited, but is preferably 1: 1 to 3.5: 1, more preferably. Is 1.0 or more and less than 3.0, more preferably 1.5 or more and 2.5 or less. The concentration ratio of platinum to palladium (Pt / Pd) in the slurry for forming the third catalyst layer 13 is not particularly limited, but is preferably 2.5 or more and 6.0 or less, more preferably 3. It is 5 or more and 5.0 or less, More preferably, it is 4.0 or more and 5.0 or less.

  The concentration ratio of platinum in the slurry for forming the first catalyst layer 11 to platinum in the slurry for forming the second catalyst layer 12 (Pt in the slurry of the first catalyst layer / Pt in the slurry of the second catalyst layer) ) Is not particularly limited, but is preferably 2.5: 1 to 3.5: 1. Further, the concentration ratio of palladium in the slurry for forming the first catalyst layer to palladium in the slurry for forming the second catalyst layer (Pd in the slurry of the first catalyst layer / Pd in the slurry of the second catalyst layer) ) Is not particularly limited, but is preferably 2.5: 1 to 3.5: 1.

  Next, slurry is applied on the substrate 10. The application | coating method of a slurry should just be performed in accordance with a conventional method, and the kind is not specifically limited. Various known coating methods such as a wash coat method can be applied. Moreover, in order to form a different catalyst layer for every part of the base material 10, what is called a zone coat method of giving a different slurry for every said part can also be applied.

  For example, when a honeycomb structure is used as the substrate 10, a predetermined length of the honeycomb structure is immersed in the slurry for forming the first catalyst layer 11 from the inlet side of the honeycomb structure to form the honeycomb structure. A predetermined length from the body inlet side is coated with a slurry for forming the first catalyst layer 11. Thereafter, the honeycomb structure is pulled up from the slurry, and excess slurry is blown out by air. Furthermore, the first catalyst layer 11 is formed on the substrate 10 that is the inner wall of the honeycomb structure by appropriately drying and firing the honeycomb structure as necessary.

  Although the drying temperature at this time is not specifically limited, For example, 70 to 200 degreeC is preferable, More preferably, it is 80 to 150 degreeC. The drying time is, for example, 0.5 hours or more and 2 hours or less. Moreover, although baking temperature is not specifically limited, either, 350 degreeC or more and 1200 degrees C or less are preferable, for example, More preferably, they are 400 degreeC or more and 600 degrees C or less. The firing time is, for example, about 0.5 to 48 hours, and preferably 1 hour or more and 3 hours or less. Note that the firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. Here, as the heating means, for example, a known heating means such as an electric furnace or a gas furnace can be used.

  Next, a predetermined length of the honeycomb structure is immersed in the slurry for forming the second catalyst layer 12 from the discharge port side of the honeycomb structure, and the predetermined length is increased from the discharge port side of the honeycomb structure. Coating with the slurry for forming the second catalyst layer 12. Thereafter, the slurry for forming the second catalyst layer 12 is dried and fired to form the second catalyst layer 12 on the base material 10 which is the inner wall of the honeycomb structure. The conditions for drying and firing are the same as for the slurry for forming the first catalyst layer 11. Note that after the honeycomb structure is coated with the slurry for forming the second catalyst layer 12, the honeycomb structure may be coated with the slurry for forming the first catalyst layer 11.

  Next, the entire length of the honeycomb structure is immersed in the slurry for forming the third catalyst layer 13, and the slurry for forming the third catalyst layer 13 on the surfaces of the first catalyst layer 11 and the second catalyst layer 12. Coat with. Thereafter, the slurry for forming the third catalyst layer 13 is dried and fired to form the third catalyst layer 13 on the surfaces of the first catalyst layer 11 and the second catalyst layer 12. The conditions for drying and firing are the same as for the slurry for forming the first catalyst layer 11. Thereby, the exhaust gas treatment member 100 according to the present embodiment can be obtained.

  In the above embodiment, as shown in FIG. 1, the first catalyst layer 11 and the second catalyst layer 12 are disposed adjacent to each other. For example, as shown in FIG. The catalyst layer 12 can be spaced apart. In addition, a layer 14 other than these may be provided between the first catalyst layer 11 and the second catalyst layer 12, for example, as shown in FIG. Examples of the catalyst layer 14 include a catalyst layer other than the third catalyst layer and the first to third catalyst layers described above.

  Hereinafter, the features of the present invention will be described more specifically with reference to test examples, examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. In addition, various production conditions and evaluation result values in the following examples have a meaning as a preferable upper limit value or a preferable lower limit value in the embodiment of the present invention, and a preferable range is the above-described upper limit or lower limit value. And a range defined by a combination of values of the following examples or values of the examples.

Example 1
A platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 2: 1 to obtain a mixed solution of platinum and palladium. Next, an alumina powder having a particle size (d ₅₀ ) of 30 μm and a BET specific surface area of 140 m ² / g is impregnated with platinum and palladium in the mixed solution, and then the composite particles are fired at 500 ° C. for 1 hour. Thus, composite particles for forming the first catalyst layer were obtained. In order to form the first catalyst layer by putting the obtained composite particles, water, thickener, surfactant and pH adjuster into a ball mill and milling until the composite particles have a predetermined particle size. A slurry of was obtained.

  Moreover, platinum nitrate aqueous solution and palladium nitrate aqueous solution were mixed so that the mass ratio of platinum and palladium might be 1.99: 1, and the liquid mixture of platinum and palladium was obtained. A slurry for forming the second catalyst layer was obtained by the same method as the method for forming the slurry for forming the first catalyst layer except that the mixed solution was used. Further, an aqueous platinum nitrate solution and an aqueous palladium nitrate solution were mixed so that the mass ratio of platinum to palladium was 4.7: 1, thereby obtaining a mixed solution of platinum and palladium. A slurry for forming the third catalyst layer was obtained by the same method as the method for forming the slurry for forming the first catalyst layer except that the mixed solution was used.

  Next, a flow-through type honeycomb structure made of cordierite was prepared. The honeycomb structure had a cell density of 300 cpsi / 8 mil, a diameter of 143.8 mm, a length of 76.2 mm, and a volume of 1.238 L. About half of the honeycomb structure is immersed in the slurry for forming the first catalyst layer from the inlet side of the honeycomb structure, and the first catalyst layer is formed on the upstream side inside each cell of the honeycomb structure. Coated with slurry. Thereafter, the slurry is dried at 150 ° C. for 1 hour, calcined at 450 ° C. in an air atmosphere, and the first catalyst layer containing 0.94 g / L of platinum and 0.47 g / L of palladium per volume of the coating part is formed. Formed.

  Next, about half of the honeycomb structure is immersed in the slurry for forming the second catalyst layer from the outlet side of the honeycomb structure, and the second catalyst layer is formed on the downstream side inside each cell of the honeycomb structure. Coated with a slurry to prepare. Thereafter, the slurry was dried and calcined under the same conditions as in the first catalyst layer to form a second catalyst layer containing 0.31 g / L platinum and 0.16 g / L palladium per volume of the coat part.

  Further, the entire honeycomb structure was immersed in a slurry for forming the third catalyst layer, and the surfaces of the first catalyst layer and the second catalyst layer were coated with the slurry for forming the third catalyst layer. Thereafter, the slurry was dried and fired under the same conditions as in the first catalyst layer to form a third catalyst layer containing 0.88 g / L of platinum and 0.19 g / L of palladium per volume of the coat part. The exhaust gas treatment member according to Example 1 was manufactured by the method described above.

(Example 2)
A slurry for forming the first catalyst layer was obtained in the same manner as in Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 3: 1. Moreover, the slurry for forming the 2nd catalyst layer was obtained like Example 1 except having mixed platinum nitrate aqueous solution and palladium nitrate aqueous solution so that mass ratio of platinum and palladium might be set to 3: 1. . Further, a slurry for forming the third catalyst layer was obtained in the same manner as in Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 3: 1. .

  Using each of the obtained slurries, first to third catalyst layers were formed on the honeycomb structure by the same method as in Example 1 to obtain an exhaust gas treatment member according to Example 2. The first catalyst layer contained 1.41 g / L of platinum and 0.47 g / L of palladium per coat part volume. The second catalyst layer contained 0.47 g / L of platinum and 0.16 g / L of palladium per coat part volume. The third catalyst layer contained 0.56 g / L of platinum and 0.19 g / L of palladium per coat part volume.

(Example 3)
A slurry for forming the first catalyst layer was obtained in the same manner as in Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 2.4: 1. . Further, a slurry for forming the second catalyst layer was prepared in the same manner as in Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 2.4: 1. Obtained. Furthermore, a slurry for forming the third catalyst layer was prepared in the same manner as in Example 1 except that an aqueous platinum nitrate solution and an aqueous palladium nitrate solution were mixed so that the mass ratio of platinum to palladium was 3.6: 1. Obtained.

  Using the obtained slurry, first to third catalyst layers were formed on the honeycomb structure in the same manner as in Example 1, and an exhaust gas treatment member according to Example 3 was obtained. The first catalyst layer contained 0.90 g / L of platinum and 0.37 g / L of palladium per coat part volume. The second catalyst layer contained 0.30 g / L of platinum and 0.12 g / L of palladium per coat part volume. The third catalyst layer contained 0.90 g / L of platinum and 0.25 g / L of palladium per coat part volume.

(Comparative Example 1)
As described above, the exhaust gas treatment member according to the example includes a catalyst layer having a two-layer structure including at least a lower layer and an upper layer in the height direction from the surface of the base material, and the lower layer is a first catalyst layer on the upstream side. It was divided into a second catalyst layer on the downstream side. In contrast, an exhaust gas treatment member according to Comparative Example 1 in which the composition of the lower layer was not divided between the upstream side and the downstream side was manufactured.

  Specifically, a slurry for forming a lower catalyst layer in the same manner as in Example 1 except that an aqueous platinum nitrate solution and an aqueous palladium nitrate solution were mixed so that the mass ratio of platinum to palladium was 3: 1. Got. Also, a slurry for forming an upper catalyst layer was obtained in the same manner as in Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 3: 1. .

  The same honeycomb structure as in Example 1 was immersed in a slurry for forming a lower catalyst layer, and a lower catalyst layer was formed under the same coating conditions as in Example 1. Further, the entire honeycomb structure was immersed in a slurry for forming the upper catalyst layer, and the upper catalyst layer was formed on the lower catalyst layer under the same coating conditions as in Example 1. An exhaust gas treatment member according to Example 1 was obtained. The lower catalyst layer contained 0.56 g / L of platinum and 0.19 g / L of palladium per coat part volume. The upper catalyst layer contained 0.94 g / L of platinum and 0.31 g / L of palladium per coat part volume.

(Comparative Example 2)
A slurry for forming a lower catalyst layer was obtained in the same manner as in Comparative Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 2.3: 1. . Further, a slurry for forming an upper catalyst layer was prepared in the same manner as in Comparative Example 1 except that a platinum nitrate aqueous solution and a palladium nitrate aqueous solution were mixed so that the mass ratio of platinum to palladium was 3.7: 1. Obtained.

  Using the obtained slurry, a lower catalyst layer and an upper catalyst layer were formed on the honeycomb structure in the same manner as in Comparative Example 1, and an exhaust gas treatment member according to Comparative Example 2 was obtained. The lower catalyst layer contained 0.59 g / L of platinum and 0.25 g / L of palladium per coat part volume. The upper catalyst layer contained 0.91 g / L platinum and 0.25 g / L palladium per coat part volume.

(Evaluation of ignition temperature of oxidation catalyst)
The exhaust gas treatment members according to Examples 1 to 3 and Comparative Examples 1 and 2 are connected to a diesel engine, and the lower limit (ignition temperature) at which the mixture of fuel and air does not decrease for more than 1 minute in the engine is set before and after phosphorus poisoning. It was evaluated with. The gross output at an engine volume of 2.4 L and 3 × 10 ³ rpm was 5 × 10 ⁴ W. The rotation speed was maintained at 3 × 10 ³ rpm, the temperature was adjusted by torque fluctuation, and light oil was injected in the exhaust pipe at a frequency of 20 cc / min using light oil of JIS2. The measurement results are shown in Table 1.

(Phosphorus poisoning)
As described above, the exhaust gas treatment member according to Example 1 is connected to a diesel engine, the engine speed is maintained at 3 × 10 ³ rpm, the exhaust gas temperature is maintained at 500 ° C. or more by torque fluctuation, and the phosphorus-containing solution is placed in the exhaust pipe. And the amount of phosphorus adhering to the exhaust gas treatment member according to Example 1 was measured. As a result, 17 g of P ₂ O ₅ adheres in the length direction of 38.1 mm on the upstream side of the honeycomb structure, and 9 g of P ₂ O ₅ adheres in the length direction of 38.1 mm on the downstream side. It was.

(Evaluation of oxidation performance)
As described above, the exhaust gas treatment member according to Example 1 is connected to a diesel engine, the engine speed is maintained at 3 × 10 ³ rpm, the temperature is changed by torque fluctuation, and nitrogen dioxide (NO ₂₎ contained in the exhaust gas is changed. ) Was divided by the concentration of nitric oxide (NOx) to evaluate the ability to oxidize nitric oxide to nitrogen dioxide. The measurement results are shown in Table 2.

  As shown in Tables 1 and 2, the exhaust gas treatment members of Examples 1 to 3 are significantly higher in ignition temperature than the exhaust gas treatment members of Comparative Examples 1 and 2, although the oxidation performance is equivalent or higher. It was confirmed to be low. In particular, the exhaust gas treatment member of Example 1 has greatly improved oxidation performance despite the extremely low ignition temperature of 190 ° C., and in particular, the oxidation performance in a low temperature region of 300 ° C. or less is from Comparative Example 1. It can be seen that the exhaust gas treatment member of 2 is far surpassed.

(Evaluation of CO and HC purification performance)
Next, the purification performance of CO and HC of the exhaust gas treatment members of Examples 1 and 2 and Comparative Example 1 was evaluated. Here, a model gas having the composition shown in Table 3 is allowed to flow through the exhaust gas treatment members of Examples 1 and 2 and Comparative Example 1 at a flow rate of 30.2 L / min and a space velocity (SV) of 47000 / hour, and CO and HC. The temperature (T50) at which the purification rate of the water reached 50% was measured. The measurement results are shown in Table 4.

  As shown in Table 4, it was confirmed that the exhaust gas treatment members of Examples 1 and 2 were significantly improved in CO and HC purification performance as compared with the exhaust gas treatment member of Comparative Example 1. This confirms that the exhaust gas treatment members of Examples 1 and 2 have improved purification performance at low temperatures as compared to the exhaust gas treatment member of Comparative Example 1.

  Although the use of the exhaust gas treatment member according to the embodiment is not particularly limited, the exhaust gas treatment member according to the embodiment can be used as, for example, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) member.

DESCRIPTION OF SYMBOLS 10 ... Base material, 11 ... 1st catalyst layer, 12 ... 2nd catalyst layer 12, 13 ... 3rd catalyst layer, 100, 101, 102 ... Exhaust gas processing member

Claims (7)

A substrate disposed in the exhaust gas flow path;
A first catalyst layer comprising at least platinum and palladium provided on the base material and disposed upstream of the exhaust gas flow path;
A second catalyst layer containing at least platinum and palladium provided on the base material and disposed on the downstream side of the exhaust gas flow path;
A third catalyst layer comprising at least platinum and palladium disposed on the first and second catalyst layers;
Comprising at least
The total concentration of platinum and palladium in each catalyst layer is highest in the first catalyst layer and lowest in the second catalyst layer;
The platinum to platinum concentration ratio (Pt / Pd) in the first and second catalyst layers is 1.0 or more and 3.5 or less,
The concentration ratio of platinum to palladium (Pt / Pd) in the third catalyst layer is 2.5 or more and 6.0 or less.
Exhaust gas treatment member. 2. The concentration ratio of platinum in the first catalyst layer to platinum in the second catalyst layer (Pt in the first catalyst layer / Pt in the second catalyst layer) is 2.5 or more and 3.5 or less. The exhaust gas treatment member according to 1. 2. The concentration ratio of palladium in the first catalyst layer to Pd in the second catalyst layer (Pd in the first catalyst layer / Pd in the second catalyst layer) is 2.5 or more and 3.5 or less. Or the waste gas processing member of 2. The exhaust gas treatment member according to any one of claims 1 to 3, wherein the base material constitutes a honeycomb structure. 5. The method according to claim 1, wherein platinum and palladium are supported on a carrier, and the carrier includes one or more selected from the group consisting of alumina, titania, zirconia, silica, boehmite, and silica-alumina. The exhaust gas treatment member as described. The exhaust gas treatment member according to claim 5, wherein the alumina is at least one selected from the group consisting of γ-alumina, δ-alumina, and θ-alumina. The exhaust gas treatment member according to any one of claims 1 to 6, wherein the exhaust gas is exhaust gas of a diesel engine.