JP2021192893A - Exhaust gas treatment member - Google Patents

Abstract

To provide an exhaust gas treatment member and the like which are excellent in phosphorous poisoning resistance.SOLUTION: An exhaust gas treatment member includes at least a substrate arranged in an exhaust gas flow passage and a catalyst layer provided on the substrate. A pore volume in the catalyst layer is 0.160 cc/g or more. The catalyst layer does not contain barium oxide. The substrate forms a honeycomb structure. 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. Exhaust gas is the exhaust gas of a diesel engine.SELECTED DRAWING: Figure 5

Description

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

Exhaust gas emitted by lean combustion of fuel in a combustion engine such as a lean burn type gasoline engine and a diesel engine contains various harmful substances. Hazardous substances include hydrocarbons (HC), soluble organic components (SOF: Solid Organic Fraction), carbon monoxide (CO), nitrogen oxides (NOx), soot, and other components regulated by the Air Pollution Control Act. include. Therefore, in order to reduce harmful substances in the exhaust gas, an exhaust gas treatment member that holds a catalyst is arranged in the exhaust gas flow path.

However, the exhaust gas also contains a phosphorus compound derived from a lubricating oil such as zinc dialkyldithiophosphate, and the phosphorus compound is deposited or permeated into the catalyst. This is called phosphorus poisoning. Phosphorus compounds deposited or permeated into the catalyst can inhibit the diffusion of exhaust gas in the catalyst layer. When the catalyst contains cerium, which is an oxygen occlusion / release substance, the cerium reacts with the phosphorus compound to become cerium phosphate having no oxygen occlusion / release effect. Therefore, when the catalyst is poisoned with phosphorus, the function of the catalyst deteriorates (see, for example, Patent Document 1).

Further, it is known that palladium (Pd), which is one of the catalysts, deteriorates the purification performance of hydrocarbons (HC) when the exhaust gas is in a low temperature state. That is, at a low temperature immediately after starting the engine, a part of the hydrocarbon remains without being purified, and the remaining hydrocarbon is adsorbed on the surface of palladium to form a film on the surface of the palladium particles, so that the active point becomes active. Decrease. As a result, the purification performance of the catalyst deteriorates. On the other hand, it has been proposed to suppress hydrocarbon poisoning of palladium by adding barium (Ba) (see, for example, Patent Document 2).

International Publication No. 2014/11974 Japanese Unexamined Patent Publication No. 2013-91041

The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust gas treatment member having excellent phosphorus poisoning resistance.

As a result of diligent studies to solve the above problems, the present inventor has found that the above problems can be solved by adjusting the pore volume in the catalyst layer and not including barium oxide in the catalyst layer. The present invention has been completed. That is, the present invention provides various specific embodiments shown below.

(1) A base material arranged in the exhaust gas flow path and a catalyst layer provided on the base material are provided, the pore volume in the catalyst layer is 0.160 cc / g or more, and the catalyst layer is oxidized. Exhaust gas treatment member that does not contain barium.

(2) The exhaust gas treatment member according to (1), wherein the pore volume in the catalyst layer is 0.170 cc / g or more.

(3) The exhaust gas treatment member according to (1) or (2), wherein the base material constitutes a honeycomb structure.

(4) Of (1) to (3), wherein platinum and palladium are supported on the carrier, and the carrier contains at least one selected from the group consisting of alumina, titania, zirconia, silica, boehmite and silica-alumina. The exhaust gas treatment member described in any one.

(5) The exhaust gas treatment member according to (4), wherein the alumina is at least one selected from the group consisting of γ-alumina, δ-alumina, and θ-alumina.

(6) The exhaust gas treatment member according to any one of (1) to (5), wherein the exhaust gas is the exhaust gas of a diesel engine.

According to the present invention, it is possible to provide an exhaust gas treatment member or the like having excellent phosphorus poisoning resistance.

It is a table which shows the manufacturing condition and the evaluation result of the exhaust gas treatment member which concerns on Examples 1 to 3 and Comparative Examples 1 and 2. It is a graph which shows the relationship between _{the particle size (d 90} ) of the composite particle which concerns on Example and the comparative example, and the pore volume of a catalyst layer. It is a table which shows the manufacturing condition and the evaluation result of the exhaust gas treatment member which concerns on Example 4 and Comparative Examples 3 to 5. It is a graph which shows the relationship between the pore volume of a catalyst layer, and the temperature which the purification rate of HC reaches 50%. It is a graph which shows the relationship between the content of barium oxide of a catalyst layer, and the temperature which the purification rate of HC reaches 50%.

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of embodiments of the present invention, and the present invention is not limited thereto. Further, the present invention can be arbitrarily modified and implemented without departing from the gist thereof. Further, in the present specification, when a numerical value or a physical property value is inserted before and after using "~", it is used as including the values before and after that. For example, the notation of the numerical range of "1 to 100" includes both the upper limit value "100" and the lower limit value "1". The same applies to the notation of other numerical ranges.

The exhaust gas treatment member according to the present embodiment includes at least a base material arranged in the exhaust gas flow path and a catalyst layer provided on the base material. In the exhaust gas treatment member according to the present embodiment, the pore volume in the catalyst layer is 0.160 cc / g or more. In the exhaust gas treatment member according to the present embodiment, the catalyst layer does not contain barium oxide. The exhaust gas treatment member according to the present embodiment is arranged downstream of a diesel engine, for example, and treats exhaust gas.

The type of the base material is not particularly limited as long as it has excellent heat resistance and can support the catalyst layer. Examples thereof include metals, alloys such as stainless steel, ceramics, and laminated structures combining these, but the present invention is not particularly limited thereto. Further, the shape, the planar shape, the thickness and the like may be appropriately set according to the application, the required performance and the like. 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 a base material, it becomes easy to apply it to an exhaust gas purification application installed in an exhaust gas flow. In the honeycomb structure, a plurality of cells through which exhaust gas flows are generally provided in parallel in the long axis direction, and the exhaust gas flows from the introduction port to the exhaust port of each cell. In this case, the base material forms the inner wall of each cell of the honeycomb structure through which the exhaust gas flows. As such a honeycomb structure, one known in the art can be appropriately selected. For example, as a honeycomb structure in automotive exhaust applications, cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2), of silicon carbide (SiC), and a ceramic monolithic carrier, such as a silicon nitride (Si ₃ N _4), metal stainless steel or the like Examples thereof include a honeycomb carrier, a wire mesh carrier made of stainless steel, and a steel wool-like 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 square 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, but for example, a honeycomb structure having a diameter (length) of several millimeters to several centimeters is preferably used. The number of cells (cell density) of the honeycomb structure may be appropriately set based on the type of exhaust gas to be treated, the flow rate of the exhaust gas, the desired pressure loss, the desired removal efficiency of harmful substances contained in the exhaust gas, and the like. .. For example, when treating the exhaust gas of 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. Is. The cell density means the number of cells per unit area in the cross section when the honeycomb structure is cut at a right angle 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 and a partial end face of the gas flow path are sealed so that gas can flow through the wall surface of the gas flow path. The wall flow type structure is widely known, and both are applicable.

On the surface of the base material, the catalyst layer is arranged so as to be in contact with the exhaust gas flow path. The catalyst layer covers at least a part of the surface of the base material. The catalyst layer oxidizes, for example, carbon monoxide (CO), hydrocarbons (HC), and nitric oxide (NO).

The catalyst layer is, for example, a wash coat layer. In the catalyst layer, platinum (Pt) and palladium (Pd), which are oxidation catalysts, are supported on a particulate carrier. The carrier is also called a base particle. The carrier and platinum and palladium form catalyst particles which are composite particles. The size of platinum and palladium supported on the carrier is on the order of several nanometers to several hundred nanometers. The presence of platinum and palladium on the carrier is, for example, observed by a transmission electron microscope (TEM), powder X-ray Diffraction (XRD), and Electron Probe Micro Analyzer (EPMA). ), X-ray Photoelectron Spectroscopy (XPS: X-ray Photoelectron Spectroscopy, or ESCA: Electron Spectroscopy for Chemical Analysis) and the like.

By adjusting the particle size of the composite particles, it is possible to adjust the pore volume in the catalyst layer. The particle size (d ₉₀ ) of the composite particle is, for example, 15.0 μm or more, 15.5 μm or more, or 16.0 μm or more.

The carrier can be appropriately selected from known ones as long as it has high heat resistance and can stably and highly disperse platinum and palladium, and the type 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, placeodium oxide; zirconia doped with rare earth elements and / or transition elements. Composite oxides such as ceria-zirconia; perovskite-type oxides; composite oxides containing alumina such as silica-alumina, silica-alumina-zirconia, and silica-alumina-boria; anatase-type titania, zeolite, etc. It is not particularly limited to. Among these, as the carrier, porous particles having a large BET specific surface area are preferable. Specific examples thereof include alumina, titania, zirconia, silica, boehmite and silica-alumina. Examples of alumina include γ-alumina, δ-alumina, and θ-alumina. Examples of titania include anatase-type titania. As the 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 yttria oxide in zirconia. In stabilized zirconia or partially stabilized zirconia, oxygen vacancies are formed in the structure, cubic crystals and tetragonal crystals are stabilized even at room temperature, and destruction due to elevating temperature is suppressed. Silica includes crystalline silica having various different phase transformations, amorphous silica, glass-like silica, colloidal silica and the like. Silica generally has a higher BET specific surface area than alumina, and platinum and palladium are highly dispersed. Silica-alumina includes crystalline and amorphous ones. In silica-alumina, the Si / Al ratio varies and is appropriately set according to the application. Examples of crystalline zeolites include ZSM-type zeolites and β-type zeolites. As the carrier, one type may be used alone, or two or more types may be used in combination as appropriate.

The carrier may consist of a plurality of materials. Further, for example, in order to improve the heat resistance of the carrier, rare earth oxides such as lanthanum, silica, zirconia and the like may be added to the carrier. Further, 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, for example, by the BET method.

The carrier used here is not particularly limited depending on the production method. This type of carrier can be obtained by each known production method, for example, after dissolving a starting material having a form such as nitrate, sulfate, carbonate, acetate, chloride containing the above elements in an aqueous solution. A carrier having an arbitrary composition and crystallinity can be obtained by calcining the solid product obtained by mixing and precipitating as a precipitate by adjusting the pH or by evaporating to dryness. When the carrier raw materials are mixed or complexed, these plurality of metal salts may be solubilized at once to perform the above treatment, or a single or a plurality of metal salts may be subjected to the above treatment. After forming the oxide, the remaining metal salts may be added all at once or sequentially.

The catalyst layer may further include an auxiliary catalyst that assists in the oxidation catalytic ability of platinum and palladium. Examples of co-catalyst components include cerium oxide (ceria), ceria-zirconia, various zeolites, neodymium, rare earth oxides such as lanthanum oxide, and zirconia. Cerium oxide can store oxygen in an oxygen-rich atmosphere and release oxygen in an oxygen-deficient atmosphere by changing the oxidation number of cerium (Ce). Therefore, cerium oxide is effective for oxidation and combustion of soot and soluble organic component (SOF) in an oxygen-deficient atmosphere. In addition, cerium oxide promotes the oxidation reaction of platinum and palladium at low temperatures such as CO, HC and NO. Various zeolites store HC at a low temperature and release HC at a high temperature to promote the oxidation reaction of HC by platinum and palladium at a low temperature. Rare earth oxides such as neodymium and lanthanum oxide, as well as zirconia, are thought to prevent platinum and palladium from moving on the carrier by heat and aggregating.

The pore volume in the catalyst layer is 0.160 cc / g or more, for example, 0.165 cc / g or more, 0.170 cc / g or more, or 0.172 cc / g or more. By setting the pore volume in the catalyst layer to the above size, 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 the catalyst performance is maintained high, as a result. , The ignition temperature can be lowered.

When the base material forms a honeycomb structure, the amount (supported amount) of platinum and palladium supported on the honeycomb structure can be appropriately set according to the desired performance, and is not particularly limited, but the catalyst performance, cost, etc. From the viewpoint of the above, 0.2 g or more and 5.0 g or less in terms of metal is preferable, and more preferably 0.3 g or more and 3.0 g per 1 L of the coated portion volume of the honeycomb structure. The volume of the coated portion of the honeycomb structure is the volume of the coated portion of the honeycomb structure excluding the outer wall, and if it is on the coated portion, the volume of the space portion in the honeycomb structure is also included. Refers to volume.

Further, when the base material forms a honeycomb structure, the amount (coating amount) of the catalyst layer can be appropriately set according to the desired performance and is not particularly limited, but from the viewpoint of catalyst performance, pressure loss, cost, etc. The volume of the coated portion of the honeycomb structure 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 coated portion.

According to the findings of the present inventor, by reducing the basic substances in the catalyst layer, 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 the catalyst performance is improved. It can be kept high and, as a result, the ignition temperature can be lower. Therefore, in the exhaust gas treatment member according to the present embodiment, the catalyst layer does not contain barium oxide.

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

Here, when the acidity of the starting salt aqueous solution of platinum and the acidity of the starting salt aqueous solution of palladium are close to each other, precipitation is unlikely to occur when both aqueous solutions are mixed, and the dispersibility of the solution can be easily maintained. Examples of combinations with similar acidity are tetraammine platinum (II) acetate-tetraammine palladium (II) acetate (alkaline to each other), ethanolamine solution of platinum hydroxide (IV) acid-tetraammine palladium (II) acetate ( Platinum nitrate-palladium nitrate (acidic each other), dinitrodiamine platinum nitrate-palladium nitrate (acidic each other), platinum chloride (IV) acid-palladium chloride (acidic each other) and the like. These are examples and are not limited.

Then, platinum and palladium contained in the prepared aqueous solution of the metal salt are supported on a carrier to form catalyst particles as composite particles by using an arbitrary method such as an impregnation method, an ion exchange method, and a kneading method. .. Then, the catalyst particles are dried at, for example, 50 ° C. or higher and 200 ° C. or lower, and the catalyst particles are further fired at, for example, 350 ° C. or higher and 1200 ° C. or lower. 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. At the time of mixing, a known pulverizing method or mixing method such as pulverizing and mixing with a ball mill or the like can be applied.

The pore volume of the catalyst layer of the produced exhaust gas treatment member can be adjusted by setting the particle size of the composite particles to a predetermined particle size when obtaining the slurry. The particle size (d ₉₀ ) of the composite particle is, for example, 15.0 μm or more, 15.5 μm or more, or 16.0 μm or more. Barium hydroxide is not added when the slurry is obtained.

Binders known in the art, other catalysts, co-catalyst particles, OSC materials, base material particles, additives and the like can be mixed in the slurry in a desired blending ratio, if necessary. Examples of the additive include a pH adjuster such as an acid or a base for adjusting the pH, a surfactant such as a nonionic surfactant or an anionic surfactant for improving dispersibility, a dispersion stabilizer, and a viscosity. Examples thereof include a viscosity regulator for adjustment, but the present invention is not particularly limited thereto.

Next, the slurry is applied onto the substrate. The method of applying the slurry may be carried out according to a conventional method, and the type thereof is not particularly limited. Various known coating methods, for example, a wash coat method and the like can be applied. Further, in order to form a different catalyst layer for each portion of the base material, a so-called zone coating method in which a different slurry is applied to each portion can also be applied.

For example, when a honeycomb structure is used as a base material, the honeycomb structure is immersed in a slurry, and the honeycomb structure is coated with a slurry for forming a catalyst layer. After that, the honeycomb structure is pulled up from the slurry, and the excess slurry is blown out by air. Further, if necessary, the honeycomb structure is appropriately dried and fired to form a catalyst layer on the base material which is the inner wall of the honeycomb structure. As a result, the exhaust gas treatment member according to the present embodiment can be obtained.

The temperature at the time of drying is not particularly limited, but is preferably 70 ° C. or higher and 200 ° C. or lower, and more preferably 80 ° C. or higher and 150 ° C. or lower. The drying time is, for example, 0.5 hours or more and 2 hours or less. The firing temperature is also not particularly limited, but is preferably 350 ° C. or higher and 1200 ° C. or lower, and more preferably 400 ° C. or higher and 600 ° C. or lower. The firing time is, for example, about 0.5 to 48 hours as a guide, preferably 1 hour or more and 3 hours or less. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. Here, as the heating means, a known heating means such as an electric furnace or a gas furnace can be used.

Hereinafter, the features of the present invention will be described in more detail with reference to Test Examples, Examples and Comparative Examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Further, the values of various production conditions and evaluation results in the following examples have meanings as a preferable upper limit value or a preferable lower limit value in the embodiment of the present invention, and the preferable range is the above-mentioned upper limit value or the lower limit value. And may be in the range specified by the combination of the values of the following examples or the values of the examples.

(Examples 1 to 3 and Comparative Examples 1 and 2)
The exhaust gas treatment members according to Examples 1 to 3 and Comparative Examples 1 and 2 which had different particle sizes of the particles to be supported and did not contain barium oxide in the catalyst layer were produced by the methods shown below.

An aqueous solution of platinum nitrate and an aqueous solution of palladium nitrate were mixed so that the mass ratio of platinum and palladium was 3: 1 to obtain a mixed solution of platinum and palladium. Next, alumina powder having a particle size (d ₅₀ ) of 30 μm and a BET specific surface area of 140 m ² / g was impregnated with platinum and palladium in the mixed solution, and then the composite particles were calcined at 500 ° C. for 1 hour. , Composite particles for forming a catalyst layer were obtained. The obtained composite particles, water, thickener, surfactant, and pH adjuster are put into a ball mill and milled until the particle size of the composite particles reaches a predetermined particle size to form a slurry for forming a catalyst layer. Got

The particle size (d ₉₀ ) of the composite particles was measured by a laser diffraction type particle size distribution measuring device (SALD-3100, Shimadzu Corporation). _{The particle size (d 90} ) of the composite particles used in Examples 1 to 3 and Comparative Examples 1 and 2 is shown in FIG. _{The particle size (d 90} ) of the composite particles used in Example 1 was 16.4 μm. _{The particle size (d 90} ) of the composite particles used in Example 2 was 20.4 μm. _{The particle size (d 90} ) of the composite particles used in Example 3 was 24.9 μm. _{The particle size (d 90} ) of the composite particles used in Comparative Example 1 was 6.6 μm. _{The particle size (d 90} ) of the composite particles used in Comparative Example 2 was 8.4 μm.

Next, a flow-through type honeycomb structure made of Kojulite was prepared. The cell density of this honeycomb structure was 300 cpsi / 8 mil, the diameter was 25.4 mm, the length was 76.2 mm, and the volume was 0.039 L. From the introduction port side of the honeycomb structure, the honeycomb structure was immersed in a slurry for forming the catalyst layer, and the inside of each cell of the honeycomb structure was coated with the slurry for forming the catalyst layer. Then, the slurry was dried at 150 ° C. for 1 hour and calcined at 450 ° C. in an air atmosphere to form a catalyst layer containing 1.5 g / L of platinum and 0.5 g / L of palladium per the volume of the coated portion. ..

By the method shown above, the exhaust gas treatment members according to Examples 1 to 3 and Comparative Examples 1 and 2 having different particle sizes of the particles to be supported were manufactured.

The pore volume of the catalyst layer of the exhaust gas treatment member according to Examples 1 to 3 and Comparative Examples 1 and 2 produced was measured with a mercury porosimeter (Pascal 140 and Pascal 440, Thermo Scientific). The temperature at the time of measurement was 25 ° C., and the density of mercury was 13.534 g / cm ³ . The contact angle of mercury was 130 °, and the surface tension of mercury was 484 Dyne / cm. The measured pressures were 400 kPa (Pascal 140) and 350 kPa (Pascal 440). The results are shown in FIG. The pore volume of the catalyst layer of the exhaust gas treatment member according to Example 1 was 0.172 cc / g. The pore volume of the catalyst layer of the exhaust gas treatment member according to Example 2 was 0.175 cc / g. The pore volume of the catalyst layer of the exhaust gas treatment member according to Example 3 was 0.186 cc / g. The pore volume of the catalyst layer of the exhaust gas treatment member according to Comparative Example 1 was 0.157 cc / g. The pore volume of the catalyst layer of the exhaust gas treatment member according to Comparative Example 2 was 0.158 cc / g. FIG. 2 shows the relationship between the particle size (d ₉₀ ) of the composite particles and the pore volume of the catalyst layer.

(Example 4, Comparative Examples 3, 4, 5)
The exhaust gas treatment member according to Example 4 was produced by supporting the grain-shaped particles shown in FIG. 3 and having a pore volume by the same method as in Examples 1 to 3. Further, the exhaust gas treatment member according to Comparative Examples 3, 4 and 5 containing barium oxide in the catalyst layer was manufactured by the method shown below.

An aqueous solution of platinum nitrate and an aqueous solution of palladium nitrate were mixed so that the mass ratio of platinum and palladium was 3: 1 to obtain a mixed solution of platinum and palladium. Next, alumina powder having a particle size (d ₅₀ ) of 30 μm and a BET specific surface area of 140 m ² / g was impregnated with platinum and palladium in the mixed solution, and then the composite particles were calcined at 500 ° C. for 1 hour. , Composite particles for forming a catalyst layer were obtained. The obtained composite particles, barium hydroxide, water, thickener, surfactant, and pH adjuster are put into a ball mill and milled until the particle size of the composite particles reaches a predetermined particle size to form a catalyst layer. Obtained a slurry to be used. _{The particle size (d 90} ) of the composite particles used in Comparative Examples 3, 4 and 5 is shown in FIG. _{The particle size (d 90} ) of the composite particles used in Comparative Example 3 was 20.4 μm. _{The particle size (d 90} ) of the composite particles used in Comparative Example 4 was 19.9 μm. _{The particle size (d 90} ) of the composite particles used in Comparative Example 5 was 19.0 μm.

Next, a flow-through type honeycomb structure made of Kojulite was prepared. The cell density of this honeycomb structure was 300 cpsi / 8 mil, the diameter was 25.4 mm, the length was 76.2 mm, and the volume was 0.039 L. From the introduction port side of the honeycomb structure, the honeycomb structure was immersed in a slurry for forming the catalyst layer, and the inside of each cell of the honeycomb structure was coated with the slurry for forming the catalyst layer. Then, the slurry was dried at 150 ° C. for 1 hour and fired at 450 ° C. in an air atmosphere to form a catalyst layer to obtain an exhaust gas treatment member according to Comparative Examples 3, 4 and 5. As shown in FIG. 3, in the exhaust gas treatment member according to Comparative Example 3, the catalyst layer contains 1.5 g / L of platinum, 0.5 g / L of palladium, and 1.0 g / L of barium oxide per coat volume. It contained L. In the exhaust gas treatment member according to Comparative Example 4, the catalyst layer contained 1.5 g / L of platinum, 0.5 g / L of palladium, and 8.0 g / L of barium oxide per coat volume. In the exhaust gas treatment member according to Comparative Example 5, the catalyst layer contained 1.5 g / L of platinum, 0.5 g / L of palladium, and 16.0 g / L of barium oxide per coat volume. The pore volumes of the exhaust gas treatment members according to Example 4 and Comparative Examples 3 to 5 were almost the same.

(Heat endurance)
The exhaust gas treatment members according to all the examples and comparative examples were subjected to thermal durability at 650 ° C. for 20 hours in an air atmosphere using an electric furnace.

(Phosphorus poisoning)
The exhaust gas treatment member according to all Examples and Comparative Examples was sprayed with a phosphorus-containing solution to poison the exhaust gas treatment member with phosphorus. The temperature at which the phosphorus-containing solution was sprayed was 350 ° C., the gas flow rate was 88 L / min, and the oxygen concentration was 10.5%. As a result, 5 g / L of phosphorus was attached to each of the catalyst layers of the exhaust gas treatment members according to Examples 1 to 3 and Comparative Examples 1 and 2 in _{terms of diphosphorus pentoxide (P 2} O _5). Further, 10 g / L of phosphorus was attached to each of the catalyst layers of the exhaust gas treatment members according to Examples 4 and Comparative Examples 3 to 5 in _{terms of diphosphorus pentoxide (P 2} O _5).

(Evaluation of HC purification performance)
Next, the purification performance of hydrocarbons (HC) of the exhaust gas treatment members according to all the examples and comparative examples poisoned with phosphorus was evaluated. Here, the model gas having the composition shown in Table 1 is treated with exhaust gas according to each of Examples and Comparative Examples at a flow rate of 20.0 L / min, a space velocity (SV) of 31000 / hour, and a temperature rise rate of 30 ° C./min. It was poured into a member, and the temperature (T50) at which the purification rate of HC reached 50% was measured. The measurement results are shown in FIGS. 1 and 3. The lower the temperature at which the purification rate of HC reaches 50%, the higher the purification performance of the exhaust gas treatment member at a low temperature.

FIG. 4 shows the relationship between the pore volume of the catalyst layer and the temperature at which the purification rate of HC reaches 50%. As shown in FIG. 4, the larger the pore volume of the catalyst layer, the lower the temperature at which the purification rate of HC reaches 50%. Further, FIG. 5 shows the relationship between the content of barium oxide in the catalyst layer and the temperature at which the purification rate of HC reaches 50%, based on the results of Examples 4 and Comparative Examples 3 to 5. Conventionally, it has been considered that when barium hydroxide is added when forming a catalyst layer, barium hydroxide interacts with palladium, syntering is suppressed, and the function of the catalyst is not deteriorated. However, as shown in FIG. 5, the smaller the amount of barium hydroxide added when forming the catalyst layer and the smaller the content of barium oxide in the catalyst layer, the lower the temperature at which the purification rate of HC reaches 50%. There was a tendency to become. Therefore, it was clarified that the phosphorus poisoning deterioration of the catalyst layer due to the inclusion of barium oxide has a greater effect on the HC purification rate than the effect of suppressing the sintering of palladium by barium hydroxide.

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

Claims (6)

The base material placed in the exhaust gas flow path and
The catalyst layer provided on the substrate and
At least prepare
The pore volume in the catalyst layer is 0.160 cc / g or more, and the catalyst layer has a pore volume of 0.160 cc / g or more.
The catalyst layer does not contain barium oxide.
Exhaust gas treatment member. The exhaust gas treatment member according to claim 1, wherein the pore volume in the catalyst layer is 0.170 cc / g or more. The exhaust gas treatment member according to claim 1 or 2, wherein the base material constitutes a honeycomb structure. The carrier according to any one of claims 1 to 3, wherein platinum and palladium are supported on a carrier, and the carrier contains at least one selected from the group consisting of alumina, titania, zirconia, silica, boehmite and silica-alumina. The described exhaust gas treatment member. The exhaust gas treatment member according to claim 4, 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 5, wherein the exhaust gas is the exhaust gas of a diesel engine.

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