JP6013243B2 - Honeycomb catalyst body - Google Patents

Description

  The present invention relates to a honeycomb catalyst body. More specifically, the present invention relates to a honeycomb catalyst body that suppresses generation of cracks during use and is excellent in light-off performance at the time of engine cold start.

Currently, in order to purify exhaust gas discharged from various engines and the like, a honeycomb catalyst body formed by supporting a catalyst on a honeycomb structure (honeycomb base material) is used (for example, Patent Documents 1 to 3). reference). In such a honeycomb catalyst body, fluid (exhaust gas) flows into each cell from the end face on the inflow side, and hydrocarbons, nitrogen oxides (NO _x ), etc. contained in the exhaust gas are purified by the catalyst.

JP 2002-59009 A JP 2003-502261 A JP 2004-82091 A

  In the conventional honeycomb catalyst body, there is a problem that cracks are likely to occur due to thermal shock, particularly in a severe use environment where the temperature is suddenly lowered from a temperature exceeding 1000 ° C. to several hundred ° C. One of the causes is that the catalyst with different thermal expansion is supported on the honeycomb base material, and at the interface between the catalyst and the honeycomb base material, the thermal stress at the time of temperature change becomes large, and the honeycomb base material is cracked. It is easy to do. In particular, when the supported catalyst enters deep inside the honeycomb base material, the interface between the catalyst and the honeycomb base material increases, and cracks are more likely to occur in the honeycomb base material. Another reason is that the catalyst and the honeycomb base material are likely to react at temperatures exceeding 1000 ° C., and cracks are likely to occur in the honeycomb base material when the temperature changes due to thermal stress caused by reactants having different thermal expansion. . Further, the conventional honeycomb catalyst body has a problem that it is difficult to purify the exhaust gas because the temperature does not reach the temperature range at which the catalyst is activated when the engine is cold started.

  The present invention has been made in view of such problems of the prior art, and it is possible to suppress the occurrence of cracks during use, and to provide a honeycomb catalyst body excellent in light-off performance at the time of engine cold start. It is to provide.

  The following honeycomb catalyst body is provided by the present invention.

[1] A honeycomb base material having a porous partition wall that partitions and forms a plurality of cells extending from one end face to the other end face, which serves as a fluid flow path, and a catalyst layer disposed on the surface portion of the partition wall. The catalyst layer contains a catalyst component and a high specific surface area material, and the catalyst layer includes a surface portion that is a portion located on the surface of the partition wall and an intrusion portion that is a portion that enters the partition wall. a thickness value of the ratio of the surface portion to the thickness of the entire catalyst layer Ri der .50-.95, of the partition wall, a range from the surface to 10% of the depth of the partition wall thickness the average pore diameter in the partition wall surface layer is found and a 5μm or less, of the partition wall, porosity of the partition wall central layer is in the range excluding the partition wall surface layer is 40% to 70% der Ru honeycomb catalyst body.

[ 2 ] The honeycomb catalyst body according to [1 ], wherein an average pore diameter of the whole partition wall is 5 to 200 μm.

[ 3 ] The honeycomb catalyst body according to [1] or [2] , wherein the partition wall thickness is 0.020 to 0.500 mm.

[4] cell density is 0.7 to 233 cells / cm ² [1] ~ honeycomb catalyst body according to any one of [3].

[ 5 ] The material constituting the partition is selected from the group consisting of silicon carbide, silicon-silicon carbide composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite composite material, lithium aluminum silicate, and aluminum titanate. The honeycomb catalyst body according to any one of [1] to [ 4 ], comprising at least one kind of ceramic.

[ 6 ] The honeycomb catalyst body according to any one of [1] to [ 5 ], which is used for exhaust gas purification of an internal combustion engine.

  In the honeycomb catalyst body of the present invention, the value of the ratio of the “surface portion thickness b” to the “total thickness a of the catalyst layer” is 0.50 to 0.95. The magnitude of the thermal stress received from the catalyst layer becomes smaller. Thereby, it is suppressed that a crack generate | occur | produces in a honeycomb base material. In particular, since the upper limit value of the above “ratio value” is as large as 0.95, the number of intrusion portions that enter the partition walls is reduced, and the magnitude of thermal stress that the honeycomb base material receives from the catalyst layer during use. However, it becomes smaller.

1 is a perspective view schematically showing one embodiment of a honeycomb catalyst body of the present invention. It is a schematic diagram which shows a cross section parallel to the central axis of one embodiment of the honeycomb catalyst body of the present invention. FIG. 3 is a schematic view showing a part of a cross section of a partition wall constituting one embodiment of the honeycomb catalyst body of the present invention perpendicular to the central axis of the honeycomb catalyst body. FIG. 3 is a schematic view showing a part of a cross section of a partition wall constituting one embodiment of the honeycomb catalyst body of the present invention perpendicular to the central axis of the honeycomb catalyst body. FIG. 3 is a schematic diagram showing a state where a honeycomb catalyst body is inserted into a can body in a “thermal cycle test” of an example. It is a schematic diagram which shows the apparatus used in the "HC (hydrocarbon) purification test" of an Example.

  Hereinafter, the form for implementing this invention is demonstrated concretely. The present invention is not limited to the following embodiments. It should be understood that design changes, improvements, and the like can be made as appropriate based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

(1) Honeycomb catalyst body:
As shown in FIG. 1 to FIG. 3, one embodiment of the honeycomb catalyst body of the present invention is a porous material that partitions and forms a plurality of cells 2 extending from one end face 11 to the other end face 12 to be a fluid flow path. A honeycomb substrate 3 having partition walls 1 is provided. The honeycomb catalyst body 100 of the present embodiment includes the catalyst layer 4 disposed on the surface portion of the partition wall 1. The catalyst layer 4 contains a catalyst component and a high specific surface area material. Further, the catalyst layer 4 has a surface portion 14 that is a portion located on the surface of the partition wall 1 (partition wall surface 21) and an intrusion portion 15 that is a portion that enters the partition wall 1. Furthermore, the value (b / a) of the ratio of the thickness b of the surface portion to the thickness a of the entire catalyst layer is 0.50 to 0.95. FIG. 1 is a perspective view schematically showing one embodiment of a honeycomb catalyst body of the present invention. FIG. 2 is a schematic view showing a cross section parallel to the central axis of one embodiment of the honeycomb catalyst body of the present invention. FIG. 3 is a schematic view showing a part of a cross section perpendicular to the central axis of the honeycomb catalyst body of the partition walls constituting one embodiment of the honeycomb catalyst body of the present invention.

  Thus, in the honeycomb catalyst body 100 of the present embodiment, the value (b / a) of the ratio of the thickness b of the surface portion to the thickness a of the entire catalyst layer is 0.50 to 0.95. Therefore, when the honeycomb catalyst body 100 is mounted on an exhaust gas pipe and used, even if a rapid “repetition of heating and cooling” occurs, generation of cracks can be suppressed. This is because when “b / a” is 0.50 to 0.95, the thickness of the surface portion b is relatively thin, so that stress is applied to the catalyst layer 4 and the honeycomb substrate 3. This is because cracks occur in the thin surface portion 14 without cracks occurring in the honeycomb base material.

  In the honeycomb catalyst body 100 of the present embodiment, the catalyst layer 4 includes a surface portion 14 that is a portion located on the surface of the partition wall 1 (partition wall surface 21) and a portion that enters the inside of the partition wall 1 (inside the pores). It has a certain intrusion 15.

  The ratio (b / a) of the “surface portion thickness b” to the “total thickness a of the catalyst layer” is 0.50 to 0.95, preferably 0.70 to 0.90. . Since the honeycomb catalyst body 100 of the present embodiment is configured as described above, it is possible to suppress the occurrence of cracks during use. If b / a is less than 0.50, cracks are likely to occur during use, and if it is greater than 0.95, the catalyst is liable to peel off from the partition wall due to vibration and wind pressure of exhaust gas during use, and the catalyst efficiency decreases, which is not preferable. . The “surface portion thickness b” means the thickness of the catalyst on the surface portion 14.

  1-50 micrometers is preferable and, as for the thickness of the surface part 14 which comprises the catalyst layer 4, 10-30 micrometers is still more preferable. If it is thinner than 1 μm, the catalyst efficiency may be lowered. If it is thicker than 50 μm, cracks may easily occur in the honeycomb catalyst body 100. However, it is appropriately selected depending on the thickness of the surface portion 14 constituting the catalyst layer 4, the type of catalyst, and the purpose of use.

  The depth of the intrusion portion 15 constituting the catalyst layer 4 is a value measured by cross-sectional observation using an SEM (scanning electron microscope). The “total thickness a of the catalyst layer” is a total value of “surface thickness b” and “depth of intrusion 15”.

  The catalyst layer 4 contains a catalyst component and a high specific surface area material, and preferably contains the catalyst component and the high specific surface area material as main components. Here, the “main component” means a component contained 90% or more of the whole. The catalyst component is preferably supported on the partition wall 1 while being supported on the surface and inside of the high specific surface area material. In addition, a state in which the catalyst component is directly supported on the partition wall 1 is also a preferable embodiment. Further, it is preferable that the catalyst component is supported on the partition wall in a state of being supported on the high specific surface area material and is directly supported on the partition wall.

  Examples of the catalyst component include “a three-way catalyst based on a noble metal such as Pt, Pd, and Rh”, an oxidation catalyst, a deodorizing catalyst, and “a base metal catalyst such as Mn, Fe, and Cu”.

Examples of the high specific surface area material include γ-alumina. The high specific surface area material is a powder material having a specific surface area of 100 m ² / g or more.

  In the honeycomb catalyst body 100 of the present embodiment, the amount of catalyst supported is preferably 10 to 400 (g / liter), and more preferably 50 to 200 (g / liter). If the amount of the catalyst supported is less than 10 (g / liter), the exhaust gas purification performance may be lowered. When the amount of the catalyst supported is larger than 400 (g / liter), the pressure loss may increase. Here, the catalyst loading (g / liter) is a value obtained by dividing the total mass of the catalyst on the partition wall surface and the catalyst in the partition wall by the volume of the honeycomb substrate (total volume of the partition walls and the “cell space”).

  In the honeycomb catalyst body 100 of the present embodiment, the honeycomb base material 3 has a porous partition wall that partitions and forms a plurality of cells 2 extending from one end surface 11 serving as a fluid flow path to the other end surface 12 as described above. 1 is included.

As shown in FIG. 4, a range from the partition wall surface 21 to “a depth of 10% of the partition wall thickness” of the partition wall 1 is defined as a “partition wall surface layer 22”. Further, a range of the partition wall 1 excluding the partition wall surface layer 22 is defined as a “partition wall central layer 23”. Partition wall 1 has an average pore diameter in the partition wall surface layer 22 is in the range of from the partition wall surface 21 to "10% of the depth of the partition wall thickness" is, 5 [mu] m Ri der less, good preferable is 3μm or less. Since the average pore diameter of the partition wall surface layer 22 is in such a range, the honeycomb base material is not easily subjected to stress due to a difference in thermal expansion from the catalyst layer even if there is rapid heating or cooling during use, and the honeycomb base material is cracked. Can be prevented from occurring. The reason why the honeycomb base material is less susceptible to the stress due to the difference in thermal expansion from the catalyst layer is that the average pore diameter of the partition wall surface layer 22 is small, so that the size of the “part entering the partition wall (intrusion part)” of the catalyst layer is small. This is because the force that the honeycomb substrate receives from the catalyst layer is reduced. When the average pore diameter in the partition wall surface layer 22 is larger than 5 μm, cracks may be generated in the honeycomb base material due to a rapid heat and cooling stress during use. In particular, since the pore diameter on the partition wall surface is large, the size of the “part entering the partition wall (intrusion part)” of the catalyst layer increases, so that the force that the honeycomb substrate receives from the catalyst layer when thermal stress is generated. It becomes large and cracks are likely to occur in the honeycomb substrate. The average pore diameter is a value measured using an SEM (scanning electron microscope). FIG. 4 is a schematic view showing a part of a cross section perpendicular to the central axis of the honeycomb catalyst body of the partition walls constituting one embodiment of the honeycomb catalyst body of the present invention.

The partition wall 1, the porosity in a range excluding the partition wall surface layer 22 "partition wall central layer 23" is Ru 40% to 70% der. If it is less than 40%, the ignition performance (light-off performance) of the catalyst (catalyst component) may deteriorate. If it is larger than 70%, the strength of the partition wall 1 may decrease. The porosity of the “partition wall surface layer 22” is preferably 20 to 50%, and more preferably 30 to 40%. If it is less than 20%, it may be difficult to support the catalyst on the partition wall surface layer. If it is larger than 50%, the catalyst may easily enter the partition wall middle layer 23, which may cause a problem that the effects of the present invention are hardly exhibited. The porosity is a value obtained by imaging a cross section of the partition wall (partition wall surface layer 22 and partition wall central layer 23) using an SEM (scanning electron microscope) and analyzing the observed image.

  The average pore diameter of the entire partition wall 1 is preferably 5 to 200 μm, and more preferably 10 to 100 μm. If it is smaller than 5 μm, the ignition performance (light-off performance) of the catalyst (catalyst component) may be lowered. If it is larger than 200 μm, the strength of the partition wall 1 may decrease.

  Furthermore, it is most preferable that the average pore diameter of the whole partition wall 1 is 5 to 200 μm and the average pore diameter in the partition wall surface layer 22 is 5 μm or less.

  The partition wall thickness (partition wall thickness) is preferably 0.020 to 0.500 mm. Even if the honeycomb catalyst body 100 of the present embodiment has such a structure that the partition wall thickness is thin and the partition wall is easily cracked, the generation of cracks in the partition wall can be suppressed. If the partition wall thickness is less than 0.020 mm, the strength of the honeycomb catalyst body is lowered, and cracks may easily occur in the partition wall during use. When the partition wall thickness is larger than 0.500 mm, the pressure loss may be deteriorated (increased). The thickness of the partition wall is a value measured by a cross-sectional observation method using an SEM (scanning electron microscope).

The cell density is preferably 0.7 to 233 cells / cm ² . If it is less than 0.7 cells / cm ² , the honeycomb catalyst body may have insufficient strength. If it is greater than 233 cells / cm ² , the pressure loss of the honeycomb catalyst body increases, and clogging of the cells by the catalyst may occur.

  The partition wall 1 is preferably made of a material containing ceramic. Furthermore, it is preferable that the material constituting the partition wall 1 includes at least one kind of ceramic selected from the following “material group”. The “material group” is “a group consisting of silicon carbide, silicon-silicon carbide composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite composite material, lithium aluminum silicate, and aluminum titanate”.

  In the honeycomb catalyst body 100 of the present embodiment, the shape of the cell 2 in the cross section orthogonal to the extending direction of the cell 2 is not particularly limited. For example, “a polygon such as a triangle, a quadrangle, a pentagon, a hexagon, a heptagon, an octagon”, a circle, an ellipse, and the like can be given. Moreover, the aspect which combined several of these shapes is also a preferable aspect. Moreover, in a square, a square or a rectangle is preferable.

  The external shape of the honeycomb catalyst body 100 (the overall shape of the honeycomb catalyst body 100) is not particularly limited, but may be a cylindrical shape, an elliptical cylinder shape, a “bottom polygonal cylinder shape such as a square cylinder shape”, a “bottom surface indefinite shape”. A cylindrical shape "etc. can be mentioned. The size of the honeycomb catalyst body 100 is not particularly limited, but the length in the central axis direction is preferably 25 to 350 mm. For example, when the honeycomb catalyst body 100 has a cylindrical outer shape, the bottom surface has a diameter of preferably 30 to 500 mm.

  The honeycomb catalyst body 100 of the present embodiment may have an outer peripheral wall 5 located at the outermost periphery as shown in FIGS. In addition, the outer peripheral wall 5 located at the outermost periphery of the honeycomb catalyst body 100 is an integrally formed wall (the partition wall and the outer peripheral wall are sintered so that the boundary between the partition wall and the outer peripheral wall is sintered). It is preferable that the state is not clearly left). Moreover, it is also a preferable aspect that the outer peripheral wall 5 is a cement coat wall in which the outer periphery of the honeycomb formed body is ground to a predetermined shape after forming and the outer peripheral wall is formed with cement or the like. The thickness of the outer peripheral wall is preferably 0.1 to 1.0 mm. The thickness of the outer peripheral wall is a value measured by cross-sectional observation using an SEM (scanning electron microscope). Further, when the outer peripheral wall is a cement coated wall, the material of the cement coated wall is not particularly limited, but the same material as that of the honeycomb substrate is preferable.

  The honeycomb catalyst body 100 of the present embodiment is preferably used for exhaust gas purification (filter) of an internal combustion engine. Thereby, it becomes a filter which a crack does not generate | occur | produce easily at the time of use.

(2) Manufacturing method of honeycomb catalyst body:
Next, a manufacturing method of an embodiment of the honeycomb catalyst body of the present invention will be described.

  First, a forming raw material containing a ceramic raw material is formed, partition walls (partitions before firing) for partitioning a plurality of cells serving as fluid flow paths, and outer peripheral walls (outer peripheral walls before firing) positioned at the outermost periphery A cylindrical honeycomb formed body is provided.

As the ceramic raw material contained in the forming raw material, for example, at least one kind of ceramic selected from the following “raw material group” is preferable. “Raw material group” means “a group consisting of silicon carbide, silicon-silicon carbide composite material, cordierite forming raw material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite composite material, lithium aluminum silicate, and aluminum titanate. Is. By using these raw materials, a honeycomb catalyst body excellent in strength and heat resistance can be obtained. The cordierite forming raw material is a ceramic raw material blended so as to have a chemical composition that falls within the range of 42 to 56% by mass of silica, 30 to 45% by mass of alumina, and 12 to 16% by mass of magnesia. It is fired to become cordierite. Examples of the raw material component (silica source component) serving as the silica source include quartz and fused silica. As a raw material component (alumina source component) serving as an alumina source, since there are few impurities, it is preferable to use at least one (or both) of aluminum oxide and aluminum hydroxide. Examples of raw material components (magnesia source components) that serve as a magnesia source include talc and magnesite. Talc as the magnesia source component preferably has an average particle size of 10 to 30 μm. Further, the magnesia source component may contain Fe ₂ O ₃ , CaO, Na ₂ O, K ₂ O and the like as impurities.

  The forming raw material is preferably prepared by mixing the ceramic raw material with a pore former, a binder, a dispersant, a surfactant, a dispersion medium, and the like.

  Examples of the pore former include graphite, wheat flour, starch, foamed resin, water-absorbing polymer, “hollow or solid,“ synthetic resin of phenol resin, polymethyl methacrylate, polyethylene, polyethylene terephthalate, etc. ””, etc. Can do. The content of the pore former is preferably 1 to 10% by mass when the ceramic raw material is 100% by mass.

  Examples of the binder include hydroxypropyl methylcellulose, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. The content of the binder is preferably 1 to 10% by mass when the ceramic raw material is 100% by mass.

  Examples of the dispersant include dextrin and polyalcohol.

  Examples of the surfactant include ethylene glycol and fatty acid soap. The content of the surfactant is preferably 0.1 to 5% by mass when the ceramic raw material is 100% by mass.

  As the dispersion medium, water is preferable. The content of the dispersion medium is preferably 30 to 150% by mass when the ceramic raw material is 100% by mass.

  When forming a honeycomb formed body using a forming raw material, it is preferable to first knead the forming raw material into a kneaded material and shape the obtained kneaded material into a honeycomb shape.

  There is no restriction | limiting in particular as a method of kneading | mixing a shaping | molding raw material and forming a clay, For example, the method of using a kneader, a vacuum clay kneader, etc. can be mentioned.

  The method for forming a kneaded clay to form a honeycomb formed body is not particularly limited, and a molding method such as an extrusion molding method, an injection molding method, or a press molding method can be used. Since continuous molding is easy and, for example, cordierite crystals can be oriented, it is preferable to employ an extrusion molding method. The extrusion molding method can be performed using an apparatus such as a vacuum kneader, a ram type extruder, or a twin screw type continuous extruder. Moreover, it is preferable to perform extrusion molding by attaching a die that becomes a honeycomb molded body having a desired partition wall thickness, cell pitch, cell shape and the like to an apparatus used for extrusion molding. As the material of the die, stainless steel, cemented carbide, etc., which are difficult to wear, are preferable.

  It is preferable to dry the obtained honeycomb formed body after forming the honeycomb formed body. The drying method is not particularly limited, and examples thereof include hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying. Among these, since the entire honeycomb formed body can be dried quickly and uniformly, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination. Further, the drying conditions can be appropriately determined depending on the drying method.

  Next, it is preferable to obtain the honeycomb substrate by firing (main firing) the obtained honeycomb formed body. “Main firing” means an operation for sintering and densifying the forming raw material constituting the honeycomb formed body to ensure a predetermined strength.

  In addition, before firing (main firing) the honeycomb formed body, it is preferable to calcine the honeycomb formed body. The calcination is performed for degreasing, and the method thereof is not particularly limited as long as the organic matter (binder, dispersant, pore former, etc.) therein can be removed. Generally, the combustion temperature of a binder (organic binder) is about 100 to 300 ° C. The combustion temperature of the pore former varies depending on the type, but is about 200 to 1000 ° C. Therefore, it is preferable to heat at about 200 to 1000 ° C. for about 3 to 100 hours in an oxidizing atmosphere as a condition for calcination.

  Since the firing conditions (temperature and time) in the main firing vary depending on the type of the forming raw material, appropriate conditions may be selected according to the type. For example, when a cordierite forming raw material is used, the firing maximum temperature is preferably 1410 to 1440 ° C. The firing maximum temperature keeping (holding) time is preferably 3 to 15 hours.

  Next, it is preferable to obtain a honeycomb catalyst body by supporting a catalyst component on the obtained honeycomb base material.

There is no particular limitation on the method for supporting the catalyst component, and the catalyst can be supported in accordance with a method used in a conventionally known method for manufacturing a honeycomb catalyst body. For example, when a noble metal such as Pt, Pd, or Rh is supported as an automobile exhaust gas catalyst, it can be supported as follows. First, the honeycomb substrate that has been subjected to the acid treatment and heat treatment is immersed in a slurry of γ-alumina containing “a noble metal catalyst component such as an aqueous chloroplatinic acid solution” and “rare earth oxide such as CeO ₂ ”. The excess slurry of the honeycomb substrate coated with the slurry is preferably removed with air or the like and dried to form a honeycomb catalyst body. The honeycomb substrate may be coated with the slurry, and excess slurry may be removed with air or the like, and then baked (fired) at a temperature of 500 to 600 ° C. to form a honeycomb catalyst body.

  Examples of the catalyst component include “a three-way catalyst based on a noble metal such as Pt, Pd, and Rh”, an oxidation catalyst, a deodorizing catalyst, and “a base metal catalyst such as Mn, Fe, and Cu”. It is also a preferred embodiment that a catalyst component is supported on the surface of a honeycomb substrate made of cordierite having a high specific surface area after acid treatment, and then heat-treated at 600 to 1000 ° C.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1
Talc, kaolin and alumina, silica, a combination of aluminum hydroxide, its chemical _composition, SiO 2 42 to 56 _{wt%, Al} 2 O 3 30-45% by weight, and predetermined such that the MgO12~16 mass% A cordierite-forming raw material was obtained by blending at a ratio. 10% by mass of a pore former, 100% by mass of methylcellulose as a binder, 50% by mass of water as a dispersion medium, and 50% by mass of water as a dispersion medium are added to 100% by mass of the cordierite forming raw material. Obtained. Then, a kneaded material was kneaded to obtain a clay. As the pore former, a mixture of two types of graphite having different average particle diameters at a predetermined ratio was used. As the graphite, those having an average particle diameter of 10 μm and those having an average particle diameter of 50 μm were used.

  Next, the kneaded material was extruded using a predetermined die, and a honeycomb formed body including partition walls for forming a plurality of cells and an outer peripheral wall was obtained. The honeycomb formed body had a square cell shape (a cell shape in a cross section perpendicular to the cell extending direction) and a cylindrical shape as a whole.

Next, the obtained honeycomb formed body was dried with hot air at 120 ° C., and then fired at 1400 to 1430 ° C. for 10 hours to prepare a honeycomb substrate. The obtained honeycomb substrate had a cylindrical shape with a diameter of the bottom surface (cross section perpendicular to the central axis) of 100 mm and a length in the central axis direction of 100 mm. The honeycomb substrate had a cell density of 62 cells / cm ² and a partition wall thickness of 0.11 mm. The partition wall thickness is a value measured by a method of cross-sectional observation using an SEM (scanning electron microscope).

  Next, a catalyst component and a high specific surface area material were supported on the obtained honeycomb substrate to produce a honeycomb catalyst body. As the catalyst component, palladium, platinum and rhodium were used. As the high specific surface area material, γ-alumina was used.

  Specifically, first, palladium, platinum, rhodium, γ-alumina and water were mixed to obtain a catalyst slurry. The mass ratio of palladium, platinum and rhodium was 15: 1: 1 (palladium: platinum: rhodium = 15: 1: 1). The amount of γ-alumina in the catalyst slurry was 20 times the amount (mass) of the “total mass of palladium, platinum and rhodium”.

  The obtained catalyst slurry was put in a container, and the honeycomb substrate was further immersed in the catalyst slurry. Thereafter, the honeycomb substrate was taken out of the catalyst slurry, excess catalyst slurry was removed with air, and the honeycomb substrate was dried at 120 ° C. Immersion and drying are repeated until a predetermined amount of catalyst (catalyst components (palladium, platinum and rhodium) and γ-alumina) is supported on the honeycomb substrate, and then fired at 550 ° C. in a nitrogen atmosphere. A medium was obtained. The amount of catalyst supported was 30 g / liter.

  For the obtained honeycomb catalyst body, the values of “average partition wall pore diameter”, “partition wall porosity”, and ratio of surface portion thickness b to overall catalyst layer thickness a ( b / a) ". In addition, the obtained honeycomb catalyst body was subjected to a “thermal cycle test” and an “HC (hydrocarbon) purification test”. The results are shown in Table 1.

(Average pore diameter of partition wall)
A partition wall of the honeycomb catalyst body is cut out to a size of 10 mm × 10 mm × 10 mm, a resin is embedded in the pores, and the surface is polished to obtain a measurement sample. A measurement sample is imaged with an SEM (scanning electron microscope), and an average pore diameter is calculated from the obtained image. The SEM image has a magnification of 300 times. By this method, “the average pore diameter of the whole partition wall” and “the average pore diameter of the partition wall surface layer (range from the partition wall surface to a depth of 10 % of the partition wall thickness)” are obtained.

(Porosity of partition wall)
A partition wall of the honeycomb catalyst body is cut out to a size of 10 mm × 10 mm × 10 mm, a resin is embedded in the pores, and the surface is polished to obtain a measurement sample. A measurement sample is imaged with an SEM (scanning electron microscope), and the porosity is calculated from the obtained image. The SEM image has a magnification of 300 times. By this method, “the porosity of the entire partition wall” and “the porosity of the partition wall central layer (the portion of the entire partition wall excluding the partition wall surface layer)” are obtained. The “porosity of the partition walls” can be measured simultaneously with the measurement of the “average pore diameter of the partition walls”.

(Value of the ratio of the thickness b of the surface portion to the thickness a of the entire catalyst layer (b / a)
A partition wall of the honeycomb catalyst body is cut out to a size of 10 mm × 10 mm × 10 mm, a resin is embedded in the pores, and the surface is polished to obtain a measurement sample. The measurement sample is imaged with an SEM (scanning electron microscope), and “the thickness a of the entire catalyst layer” and “the thickness b of the surface portion” are calculated from the obtained image. From the obtained values of “total thickness a of catalyst layer” and “surface thickness b”, “b / a” is obtained.

(Thermal cycle test)
As shown in FIG. 5, the honeycomb catalyst body 100 is mounted (canned) in a test can 31 made of stainless steel. Then, using a gas burner tester (not shown), the combustion gas is caused to flow through the honeycomb catalyst body 100 at a flow rate of 1.0 Nm ³ / min. At this time, propane was used as the fuel. The honeycomb catalyst body 100 is heated to 1100 ° C. in 240 seconds and held at 1100 ° C. for 240 seconds, and then a gas at 25 ° C. is flowed at 0.9 Nm ³ / min for 5 minutes. Then, assuming that “from the start of flowing the combustion gas to the end of flowing the gas at 25 ° C.” is one cycle, the cycle is repeated five times. Thereafter, the honeycomb catalyst body 100 is taken out from the test can body 31, and the end face of the honeycomb catalyst body 100 is observed using a microscope to check for cracks. FIG. 5 is a schematic diagram showing a state in which the honeycomb catalyst body is inserted into the can body in the “thermal cycle test” of the example.

(HC (hydrocarbon) purification test)
As shown in FIG. 6, an exhaust system (Manifold System) 35 was produced. The exhaust system 35 includes a gasoline engine 33 and a catalytic converter 34 equipped with a honeycomb catalyst body as an evaluation sample from the upstream. A gasoline engine with a displacement of 2000 cc was used as a gasoline engine, and power was absorbed by a dynamometer. A hydrocarbon (HC) purification test was conducted using the exhaust system 35. Specifically, first, the gasoline engine is started and operated at a speed of 3000 rpm for 10 minutes, and then the gasoline engine is stopped. After that, the whole test apparatus is left at 20 ° C. for 10 hours, and after being brought into a so-called cold state (a state where the gasoline engine main body, cooling water, exhaust pipe, etc. are at the same level as room temperature (20 ° C.)) Start the gasoline engine. After starting, the engine is operated at idling for 10 seconds, and then the gasoline engine is operated at 2000 rpm for 130 seconds or more. At this time, the amount of HC in the gas discharged from the catalytic converter 34 is measured until 140 seconds after the gasoline engine is started. The “HC ratio” is shown in the “HC purification test” column of Table 1. The “HC ratio” shown in Table 1 is the ratio (ratio) of the HC amount after mounting the honeycomb catalyst body to the HC amount before mounting the honeycomb catalyst body. The smaller the HC ratio obtained at this time, the more excellent the catalyst ignition performance (light-off performance) of the honeycomb catalyst body tested. FIG. 6 is a schematic diagram showing an apparatus used in the “HC purification test” of the example.

(Examples 2-6, Comparative Examples 1-7)
A honeycomb catalyst body was produced in the same manner as in Example 1 except that the conditions were changed as shown in Table 1. In the same manner as in Example 1, the values of “average partition wall pore diameter”, “partition porosity”, and ratio of the surface portion thickness b to the total catalyst layer thickness a (b / a) "was measured. In addition, the obtained honeycomb catalyst body was subjected to a “thermal cycle test” and an “HC (hydrocarbon) purification test”. The results are shown in Table 1.

  Table 1 shows that when Examples 1 to 4 and Comparative Examples 1 and 2 are compared, cracks are likely to occur when the value of b / a is less than 0.50. In addition, when Examples 1 and 5 are compared with Comparative Examples 3 and 4, it can be seen that cracks tend to occur when the average pore diameter of the partition wall surface layer exceeds 5 μm. Further, when Examples 1 and 6 were compared with Comparative Examples 5 to 7, when the “porosity of the partition wall central layer (the portion excluding the partition wall surface layer from the entire partition wall)” was less than 40%, HC (hydro As a result of the carbon) purification test, it can be seen that the exhaust gas purification becomes worse and the light-off performance is inferior.

  The honeycomb catalyst body of the present invention can be suitably used for the treatment of exhaust gas of automobiles and the like.

1: partition wall, 2: cell, 3: honeycomb substrate, 4: catalyst layer, 5: outer peripheral wall, 11: one end surface, 12: the other end surface, 14: surface portion, 15: intrusion portion, 21: partition wall surface 22: partition wall surface layer, 23: partition wall center layer, 31: test can body, 32: gas, 33: gasoline engine, 34: catalytic converter, 35: exhaust system, 100: honeycomb catalyst body, a: entire catalyst layer , B: thickness of the surface portion.

Claims (6)

A honeycomb substrate having a porous partition wall for partitioning a plurality of cells extending from one end face to the other end face, which serves as a fluid flow path, and a catalyst layer disposed on a surface portion of the partition wall;
The catalyst layer contains a catalyst component and a high specific surface area material,
The catalyst layer has a surface portion that is a portion located on the surface of the partition wall and an intrusion portion that is a portion that enters the interior of the partition wall;
The value of the ratio of the thickness of the surface portion to the thickness of the entire catalyst layer Ri der 0.50 to 0.95,
The average pore diameter in the partition wall surface layer that is in the range from the surface to the depth of 10% of the partition wall thickness of the partition wall is 5 μm or less,
Of the partition wall, porosity of the partition wall central layer is in the range excluding the partition wall surface layer is 40% to 70% der Ru honeycomb catalyst body. The honeycomb catalyst body according to claim 1, wherein an average pore diameter of the whole partition wall is 5 to 200 µm. The honeycomb catalyst body according to claim 1 or 2 , wherein the partition wall thickness is 0.020 to 0.500 mm. Cell density honeycomb catalyst body according to any one of claims 1 to 3, which is 0.7 to 233 cells / cm ^2. The material constituting the partition is at least selected from the group consisting of silicon carbide, silicon-silicon carbide composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite composite material, lithium aluminum silicate, and aluminum titanate. The honeycomb catalyst body according to any one of claims 1 to 4 , comprising a kind of ceramic. The honeycomb catalyst body according to any one of claims 1 to 5 , which is used for exhaust gas purification of an internal combustion engine.

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