JP2006206390A - Ceramic body, ceramic carrier having catalyst carrying capacity, ceramic catalyst body and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acicular ceramic body and an acicular ceramic catalyst body using a cordierite porous body having high temperature stability and a high specific surface area as a base material, and to provide a method for producing the catalyst body. <P>SOLUTION: The acicular ceramic body using a whisker-grown acicular cordierite crystal phase as a base material is produced by blending raw material particles having an acicular shape or a columnar shape (kaolin) or a pore forming material disappearing when fired (carbon black) into raw materials, and preparing growth spaces of acicular cordierite crystals. The acicular ceramic catalyst body is obtained by using the same. The production method therefor is also provided. According to this invention, a cordierite honeycomb having a large quantity of whisker-grown acicular particles, having a small thermal capacity for the initial activation of a catalyst, further having a low pressure loss, and having excellent thermal shock resistance can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a needle-shaped ceramic body and a needle-shaped ceramic catalyst body, and more specifically, for example, a three-way catalyst for automobiles for removing NOx, a combustion catalyst for a gas turbine, and a catalyst for high-temperature gas purification. In addition, the present invention relates to a needle-shaped ceramic honeycomb catalyst body that can be suitably used in a portion exposed to a high-temperature and high-speed air flow exceeding 700 ° C.

  The present invention, for example, in the field of manufacturing technology of an oxide honeycomb structure for supporting a catalyst for a three-way catalyst of an automobile, has conventionally had a high specific surface area and is sintered even when exposed to a high temperature for a long time. In view of the strong demand for the development of a high specific surface area cordierite porous body that has a low specific surface area reduction due to the above, it has a high specific surface area, and even when exposed to temperatures exceeding 800 ° C for a long time, It is possible to manufacture needle-shaped ceramic bodies based on cordierite porous bodies with a small decrease in specific surface area due to sintering, and honeycomb structures for catalyst support formed directly with such porous cordierites. It is useful as a new cordierite porous material manufacturing technology and its product.

  The present invention is characterized by using a porous cordierite composed of a porous structure in which needle-like crystals are three-dimensionally connected, particularly as a honeycomb structure for supporting a catalyst. In addition, for needle-shaped ceramic bodies based on cordierite porous bodies, it is possible to suppress the decrease in specific surface area due to sintering, to directly produce honeycomb bodies with cordierite sintered bodies themselves, and to coat the honeycomb interior It is possible to simplify the conventional processes to be performed and to provide an inexpensive manufacturing method thereof.

  Conventionally, oxide-based honeycomb structures for supporting a catalyst have already been put to practical use in parts that are exposed to high temperatures for a long time, such as automobile three-way catalysts and combustion catalysts. Therefore, development aimed at further improving the characteristics is being actively promoted. Among them, cordierite, in particular, has a high melting point of about 1400 ° C., an extremely small thermal expansion coefficient, and excellent thermal shock resistance. The honeycomb structure is used as a carrier for a catalyst in a high temperature part exceeding 800 ° C., such as a combustion catalyst for high temperature or a catalyst for purifying high temperature gas.

  Thus, although the usefulness of cordierite as a catalyst carrier has been recognized in the past, the conventional method for producing a cordierite porous material has a high specific surface area and produces a thermally stable material. Therefore, as a catalyst for exhaust gas purification, a carrier surface made of cordierite honeycomb structure with high thermal shock resistance is conventionally coated (coated) with gamma alumina to carry a noble metal catalyst. Things are widely used. The reason why the coat layer is formed is that the specific surface area of cordierite is small, and as it is, the necessary amount of the catalyst component cannot be supported. For this reason, a high specific surface area material such as gamma alumina is used. Thus, the surface area of the carrier is increased.

  However, coating the cell wall surface of the support with gamma alumina leads to an increase in heat capacity due to an increase in weight. In recent years, it has been studied to reduce the heat capacity by thinning the cell wall for the early activation of the catalyst. However, when the coating layer is formed, the effect is halved. It was. In addition, the pressure loss increases because the opening area of each cell decreases, the thermal expansion coefficient as a carrier becomes larger than that of cordierite alone, gamma alumina is transferred to alpha alumina at a high temperature of 1000 ° C. or higher, Moreover, since sintering progressed, there existed a malfunction that it had the problem that it was difficult to maintain a high specific surface area.

  The present inventors have so far succeeded in developing a cordierite porous body composed of cordierite needle-like crystals having a submicron diameter, and a honeycomb structure composed of a cordierite porous body. As the body, as described in the prior art documents, those using the cordierite porous body directly and those coated on the inner wall of the cordierite porous body were proposed (see Patent Documents 1 to 8). ). When cordierite is used in a portion exposed to high temperature, there is no method other than coating the inner wall of the honeycomb structure with gamma alumina or the like.

  For this reason, various studies have been made on ceramic bodies capable of supporting a catalyst component without forming a coating layer. For example, a method for improving the specific surface area of cordierite itself by heat treatment after acid treatment has been proposed (see Patent Document 9). However, this method is not practical because there is a problem that the crystal lattice of cordierite is destroyed by acid treatment or heat treatment and the strength is lowered.

  Accordingly, the present inventors have previously proposed a ceramic carrier capable of supporting a necessary amount of a catalyst component without forming a coat layer for improving the specific surface area (see Patent Document 10). This ceramic carrier is formed by substituting at least one element or more of the elements constituting the base ceramic with an element other than the constituent elements. For example, the ceramic carrier may be hexachloroplatinic acid, secondary chloride. It is possible to directly support the noble metal catalyst on the substituting element by immersing in a solution of a noble metal compound such as platinum or rhodium chloride and then firing. Therefore, this carrier has higher strength and improved durability as compared with conventional carriers in which pores are formed by performing acid treatment or heat treatment. Further, when the main catalyst component and the cocatalyst component are directly supported on the surface of the support on the ceramic support capable of directly supporting the catalyst component, a catalyst body that is less likely to be thermally deteriorated by supporting the main catalyst first and the cocatalyst later. A ceramic catalyst has been proposed (see Patent Document 11).

JP 2003-321280 A JP 2003-212672 A Japanese Patent Laid-Open No. 2003-025316 JP 2002-355511 A Japanese Patent Laid-Open No. 2002-111988 JP 2002-172329 A JP 2001-310128 A Japanese Patent Laid-Open No. 11-171537 Japanese Patent Publication No. 05-050338 Japanese Patent Laid-Open No. 2003-080080 JP 2003-230838 A

  Under such circumstances, in view of the above prior art, the present inventors have developed a new cordierite honeycomb structure for supporting a catalyst that makes it possible to drastically solve the problems in the above prior art. As a result of intensive research aimed at developing, acicular crystals having a controlled aspect ratio and growing in the space formed in the firing process are three-dimensionally connected to form acicular particles. The structure can be produced, thereby making it possible to dramatically increase the specific surface area, and since the entire bulk is composed of the acicular crystal phase, it can be sintered even when subjected to heat treatment at high temperatures. It is difficult to proceed, and it is possible to dramatically suppress the decrease in specific surface area due to sintering, and the process such as coating gamma alumina on the inner wall of the honeycomb structure in the conventional manufacturing method It found such that it is possible to omit, further extensive research, and completed the present invention.

  An object of the present invention is to realize a ceramic catalyst body having more excellent catalytic performance by using a ceramic carrier capable of directly supporting the catalyst component. The present invention also provides a needle-shaped ceramic body based on a novel cordierite porous body having a high specific surface area and capable of suppressing a decrease in the specific surface area even when heat treatment at 1000 ° C. or higher, and a honeycomb thereof It is an object of the present invention to provide a structure, a production method thereof, and an acicular ceramic catalyst body as a product thereof.

  The present invention for solving the above-mentioned problems is a ceramic body in which some or all of the ceramic particles contain at least Si, Al, and Mg, and the shape thereof is needle-like. A ceramic body characterized by having needle-shaped particles generated from raw material particles. In addition, the present invention provides a raw material particle having a needle-like or columnar shape in a ceramic body containing at least Si, Al, Mg as a coating layer on a part or all of the surface of the ceramic body and having a needle-like shape. A ceramic body characterized by having needle-shaped particles produced from In addition, the present invention provides a ceramic body in which some or all of the ceramic particles contain at least Si, Al, and Mg and have a needle shape, and are generated from raw material particles having a needle shape or a columnar shape. The ceramic body is characterized in that it has at least one of pores and elements capable of directly supporting a catalyst component on the surface of the ceramic particles of the ceramic body. In addition, the present invention provides a raw material particle having a needle-like or columnar shape in a ceramic body containing at least Si, Al, Mg as a coating layer on a part or all of the surface of the ceramic body and having a needle-like shape. A ceramic body characterized in that it has needle-shaped particles produced from the above and has at least one of pores and elements capable of directly supporting a catalyst component on the ceramic particle surface of the ceramic body.

The present invention also provides a ceramic catalyst body characterized in that a catalyst component is supported on the ceramic body. Moreover, this invention is a ceramic catalyst body characterized by containing a promoter component in said ceramic body and / or ceramic catalyst body. Further, the present invention uses a raw material composed of a compound of SiO ₂ and Al ₂ O ₃ as a Si source, and among the ceramic particles, some or all of the particles contain at least Si, Al, Mg, and the shape thereof A method for producing a ceramic body, characterized in that a ceramic body is produced using raw material particles having a needle shape or a columnar shape for acicularization in a ceramic body having a needle shape. In the present invention, the surface of the sintered body is coated with a slurry containing kaolin, dried, fired, and by growing a needle-shaped ceramic body using the kaolin as a part of the raw material, In a ceramic body in which some or all of the particles contain at least Si, Al, and Mg, and the shape of the ceramic body is needle-like, the raw material particles having a needle-like or columnar shape are used for acicularization. A manufacturing method of a ceramic body, characterized by manufacturing.

  The present invention also provides a ceramic body having needle-shaped particles, wherein the ceramic body produced by the above-described method is subjected to acid treatment, alkali treatment, or dry etching to develop needle-shaped particles. Manufacturing method. The present invention also provides a method for producing a ceramic catalyst body, wherein a catalyst component is supported on the ceramic body. Furthermore, the present invention is a method for producing a ceramic catalyst body, wherein a promoter component is supported on the ceramic body and / or the ceramic catalyst body.

Next, the present invention will be described in more detail.
The present invention makes it possible to support the required amount of catalyst component on the ceramic support itself consisting of needle-like crystal layers, thereby eliminating the need for coating with gamma alumina to increase the specific surface area and reducing heat capacity and pressure loss. The present invention provides a ceramic carrier and a ceramic catalyst body capable of lowering the thermal expansion coefficient and a method for producing the same. The ceramic body of the present invention basically has a controlled aspect ratio, and has a structure in which acicular crystal phases grown in the space formed in the firing process are three-dimensionally intertwined. The body is based on the bulk of the body, and the needle-shaped crystal is three-dimensionally connected to improve the specific surface area. The cord has a high specific surface area and is a porous structure having a predetermined porosity. It is formed from an elite porous body.

  Further, the present invention uses a raw material particle having a needle shape or a columnar shape for acicularization, thereby generating elongated needle-shaped particles from the raw material particles having a needle shape or a columnar shape, In order to delay the completion of sintering and provide a space for growing the acicular ceramic body, a material (pore forming material) that disappears in the firing process is blended as part of the raw material, and the material is burned off in the firing process. And a step of immersing in a slurry containing acicular and columnar kaolin on the surface of the sintered body, and after drying, firing, and growing the acicular ceramic body using the kaolin as a part of the raw material. Is.

First, the acicular ceramic body of the present invention will be described. In the present invention, a starting powder blended so as to have a cordierite composition is used as a starting material. For example, kaolin, talc, alumina, or silica powder having needle-like or columnar crystals is used as a starting material, and these are weighed and blended so as to have a cordierite composition. At this time, in order to lower the cordierite formation temperature, a crystallization temperature lowering agent such as boron oxide (B ₂ O ₃ ) or the like can be added to the starting powder in an amount of 3 wt% or less. In order to grow whiskers, a needle-like additive, for example, an alkaline earth metal oxide such as strontium oxide (SrO) is added to the starting powder in an amount of 2 wt% or less, or a rare earth oxide is added in an amount of 5 wt% or less. Can do. Furthermore, in order to increase the porosity of the sintered body after sintering, a substance that disappears during the firing process, for example, 10 to 30 wt% of carbon black can be added. Thereby, a space for growing acicular crystals is formed, the amount of acicular crystals generated is increased, and for example, a sintered body having a porosity of 38 to 55% can be obtained.

  In the present invention, the mixed powder of the above starting powder and additive is, for example, ball mill mixed, the resulting mixed slurry is dried in an evaporator, an oven, etc., and the resulting dried product is pulverized, classified, and then This powder is pressure-molded and sintered at 1200 to 1400 ° C. Thereby, the cordierite bulk which has a submicron cordierite needle crystal can be produced.

The cordierite ceramic body of the present invention has a large amount of acicular shaped particles, and the aspect ratio of the particles is preferably 5 or more. These needle-shaped particles can be connected in a three-dimensional manner to have a high specific surface area that is improved in specific surface area. In producing the cordierite ceramic body of the present invention, it is preferable to use raw material particles having a needle shape or columnar shape as the raw material particles, and depending on the aspect ratio of the raw material particles, the cordierite needle crystal to be generated It is possible to control the aspect ratio. As the material, for example, kaolin having a needle shape or a columnar shape is preferably used. By using the raw material particles having a needle shape or a columnar shape, the generation of needle-like particles having a very long shape is promoted in the firing process. Kaolin is a mineral having a composition of Al ₂ O ₃ · 2SiO ₂ and is a general raw material component for cordierite production. In the present invention, kaolin having a needle-like or columnar shape is particularly used. For example, kaolin as a raw material particle having a needle shape or a columnar shape preferably has an aspect ratio of 5 to 20. The raw material particles having such needle-like or columnar shapes are preferably contained in the raw material for producing the ceramic body in an amount of 30 to 60% by weight, particularly 35 to 50% by weight.

  In producing the cordierite ceramic of the present invention, it is preferable that the needle-shaped particles are developed before firing is completed in the firing process. In order to develop the needle-shaped particles before the firing is completed, for example, a substance that disappears in the firing process (pore forming material) is blended as a part of the raw material, and the pore forming material is burned off in the firing process. Is implemented. In the process of burning out the pore former, the completion of sintering is delayed, during which acicular shaped particles grow. Since a space is formed in the trace of the pore former being burned, acicular shaped particles can grow in the space before the completion of sintering. Therefore, it becomes possible to increase the acicular shaped particles contained in the produced ceramic body.

  In addition, this space provides a margin for the growth of the needle-shaped particles, and thus contributes to an increase in the aspect ratio. Examples of the pore former include carbon black, starch, and phenol resin. It is preferable to blend these pore formers in the raw material in an amount of 2 to 15% by weight, particularly 5 to 10% by weight. The size of the space for the growth of the needle-shaped particles formed in the firing process is related to the particle size of the pore former, and in order to form the optimum growth space, the average particle size of the pore former is 0.02 to 5 μm, particularly 0.02 to 1 μm is preferable. Further, the porosity of the sintered body itself can be controlled by blending the pore former.

  As described above, in the present invention, the needle-like or columnar-shaped raw material is used, and / or the substance (pore forming material) that disappears in the firing process is added to the raw material, whereby the needle-like shape of the ceramic body produced It is possible to obtain a ceramic body having excellent characteristics by controlling the particle shape such as the aspect ratio of the shaped particles and the amount of the particles formed. The ceramic body of the present invention includes, as a starting material, a ceramic raw material blended to have a cordierite composition, for example, high-purity kaolin, talc, alumina, silica powder, a crystallization temperature lowering agent, and an acicularizing additive. A compound such as a substance (pore forming material) that disappears in the firing process can be formed into a honeycomb or the like and fired at 1200 to 1400 ° C.

  As another production method, a needle-shaped ceramic body is fired using kaolin as a part of its raw material by immersing a slurry containing kaolin on the surface of the sintered body, coating, drying and firing. The ceramic body which has the acicular shaped particle | grains of this invention can be produced by making it grow on a bonded surface. As the slurry containing kaolin, for example, a slurry containing kaolin, aluminum hydroxide, or silica is suitable. For example, the surface of the cordierite sintered body is coated with this slurry and fired to obtain a cordier. Light needle-shaped particles are formed on the coating layer by a dissolution-precipitation mechanism. Further, as kaolin, needle-shaped particles can be easily developed by using needle-shaped or columnar-shaped particles.

  In producing the ceramic body of the present invention, it is preferable to blend a crystallization temperature lowering agent such as boron oxide in order to promote the development of the needle-shaped particles at the lowest possible temperature. Moreover, it is suitable to mix | blend the additive (acicularization additive) for making a crystal particle develop in needle shape. As the acicular additive, at least one selected from a lanthanoid element, a transition metal element, an alkali metal element, and an alkaline earth metal element is used, and more specifically, strontium oxide and the like are preferable.

  A technique for making a cordierite sintered body porous by treating with an acid is already known, and the specific surface area can be dramatically improved by treating the cordierite sintered body with a strong acid. However, since a cordierite porous body having a high specific surface area that has been generally reported is to make the silica phase of the crystal grain surface porous, for example, sintering proceeds at a high temperature of 1000 ° C. There was a problem that the surface area was extremely reduced. In the cordierite porous material developed previously by the present inventors, by using kaolin as a raw material, a needle crystal phase of cordierite can be precipitated, and this is treated with a weak acid. Thus, it has become possible to produce a high-strength cordierite porous body composed of acicular crystal phases having a diameter of submicron order.

  The present inventors have conducted various studies on the cordierite porous body for the purpose of developing a method capable of further improving the specific surface area while maintaining the strength. It has been found that a cordierite needle crystal phase is formed by treating the body with a weak acid having a low degree of dissociation, such as an acid having a carboxyl group (—COOH), phosphoric acid, hydrogen sulfide and the like. Furthermore, it has been found that when the treatment is performed with a weak acid, the size and number of nano-order acicular crystal phases deposited, that is, the specific surface area can be controlled by changing the time required for the treatment and the concentration of the weak acid. Examples of the weak acid used in the present invention include carboxylic acids such as oxalic acid, acetic acid, formic acid, and acrylic acid, but are not limited to these, and any equivalent or similar carboxylic acid may be used. It can be used as well.

  That is, the needle-shaped ceramic body based on the high-temperature stable high specific surface area cordierite porous body of the present invention, the entire porous body is composed of a needle-like crystal phase. Treatment with a weak acid is required, and the structure, porosity, and specific surface area of the cordierite porous material can be changed arbitrarily by adjusting the acid type, acid concentration, and / or treatment time. It is possible to make it. In the present invention, in relation to the type of acid, the concentration of acid, and / or the processing time, in consideration of the time that can be practically applied in practical use, all weak acids listed above are considered. Thus, it is possible to set suitable treatment conditions that maximize the specific surface area within the acid concentration range of 0.001 N to 2 N.

  The mechanism of the porous formation of cordierite by acid treatment is not yet clear, but it has been found that the components of cordierite phase are eluted from the surface by the acid treatment. When treated with an acid with a high degree of dissociation, i.e., a strong acid, a large amount of components are eluted and porous, but the elution rate is high, so the elution rate cannot be adjusted and the surface of the crystalline phase is immediately adjusted. It was found that the specific surface area was not improved.

  When treated with an acid with a low degree of dissociation, that is, a weak acid, the elution mechanism is thought to be the same as in the case of a strong acid. The treatment can be stopped at the stage where the acicular crystal phase is precipitated. That is, it becomes easy to stop the treatment when the specific surface area is suitable, and a cordierite porous body having a high specific surface area can be produced.

  Even when a weak acid is used, the treatment can be more easily adjusted at a stage where the specific surface area is suitable by treating with a solution having a low concentration. When the acid treatment is stopped at a stage where the specific surface area is suitable, if the acid concentration is low, the processing time required is long, and if the concentration is high, the processing time required is short. That is, the processing conditions that make the specific surface area suitable can be adjusted by the concentration of the weak acid and the processing time.

Since the degree of acid dissociation varies depending on the type of acid, in the method for producing a high specific surface area cordierite porous body of the present invention, the processing conditions having a suitable high specific surface area are the type of acid, the concentration of acid, and / or Or it can adjust suitably with processing time. In the present invention, the treatment with a weak acid can stop the treatment at the stage where a fine acicular crystal phase formed in the initial stage of elution is precipitated, and thereby connects the acicular crystals three-dimensionally. The present invention includes all acid treatments that enable these treatments. The high temperature stable high specific surface area cordierite porous body of the present invention has a high specific surface area of 1 m ² / g or more, and a decrease in specific surface area due to sintering at a high temperature of 1000 ° C. or higher is suppressed.

  Regarding the production of a cordierite porous body having a high specific surface area, a method of forming a silica layer on a cordierite polycrystal and making the silica layer porous is known. However, the cordierite porous material having a high specific surface area that has been reported so far is a polycrystalline body through a grain boundary layer. For example, the sintering proceeds by heat treatment at 1050 ° C., and the specific surface area becomes extremely large. It is known to decline.

In the present invention, the acicular ceramic body preferably has at least one of pores and elements capable of directly supporting a catalyst component on the surface of the ceramic particles. That is, in the present invention, the ceramic body surface has pores having a diameter of 1000 times or less, preferably 1 to 1000 times the diameter of the catalyst component ions to be supported, or a width of 1 to 10 × 10. ^A ceramic carrier of ¹¹ pieces / L or more, preferably 1 × 10 ¹⁶ pieces / L or more, more preferably 1 × 10 ¹⁷ pieces / L or more is preferably used. Specifically, the pores are formed by defects such as oxygen defects and lattice defects in the ceramic crystal, fine cracks formed on the ceramic surface, and defects of elements constituting the ceramic. These pores only have to be formed on at least one type of ceramic support, but can also be formed by combining a plurality of types.

In the present invention, as the ceramic carrier, for example, a cordierite honeycomb structure including a cordierite having a theoretical composition represented by 2MgO · 2Al ₂ O ₃ · 5SiO ₂ as a main component and having a honeycomb-shaped carrier shape Are preferably used. Since the diameter of the catalyst component ions is usually about 0.1 nm, the diameter or width of the pores formed on the surface of the cordierite honeycomb structure is 0.1 to 100 nm, which is 1 to 1000 times larger, The depth of the pores is preferably at least 1/2 times the diameter of the catalyst component ions, that is, at least 0.05 nm. The ceramic support has such a predetermined number or more of pores, thereby enabling direct support of the catalyst component while ensuring the necessary strength.

When the ceramic carrier has pores composed of oxygen defects and lattice defects, the number of pores is greatly related to the amount of oxygen in the cordierite honeycomb structure, and in order to make the pores more than the predetermined number, The amount of oxygen in the cordierite honeycomb structure is set to be less than 47% by weight or greater than 48% by weight. Further, among the crystal axes of the cordierite crystals, _{b 0} may lattice constant of the axis is set to be smaller than 16.99 larger or 16.99. Specifically, the cordierite honeycomb structure has 4 × 10 ⁻⁶ % or more, preferably 4 ×, of cordierite crystal having at least one kind of oxygen defect or lattice defect in the unit crystal lattice. ^10-5 % or more, or at least one kind of oxygen defect or lattice defect is 4 × 10 ⁻⁸ or more, preferably 4 × 10 ⁻⁷ or more per unit crystal lattice of cordierite. The number of pores of the carrier is 1 × 10 ¹⁶ / L or more, preferably 1 × 10 ¹⁷ / L or more.

  In general, when a catalyst component is supported, the catalyst component is supported by dissolving catalyst component ions in a solvent and immersing a ceramic carrier in this solution. In the case of a cordierite honeycomb structure coated with a conventional gamma alumina, the pore diameter of the gamma alumina supporting the catalyst component is usually about 2 nm, but the catalyst metal particles are usually about 5 nm, Larger than the pore size. From this, it is considered that the pores of gamma alumina are necessary for holding the catalyst component ions when the catalyst is supported, rather than holding the catalyst metal particles. The catalyst component ions can be retained as long as the diameter, width, or width of the catalyst component ions is equal to or greater than that of the catalyst component ions, that is, a pore having a diameter or width of 0.1 nm or more. However, in order to ensure the strength of the honeycomb structure, it is necessary that the diameter or width of the pores is about 1000 times or less the diameter of the catalyst component ions. 100 nm or less. Further, if the depth of the pore is at least ½ times the diameter of the supported catalyst component ions, the catalyst component ions can be retained.

  Since the pores composed of defects and cracks are extremely fine and the specific surface area cannot be measured by a normal method, the present invention defines the number of pores necessary to carry a predetermined amount of the catalyst component. The catalytic metal supported on the currently used three-way catalyst is approximately 1.5 g per liter of the honeycomb structure volume. In order for the catalyst metal to exhibit exhaust gas purification performance, the diameter of the catalyst metal particles needs to be about 1000 nm, preferably less than about 20 nm.

Assuming that 1.5 g / L of platinum, which is the same as the currently used three-way catalyst, is supported and all the platinum particles have a diameter of 1000 nm, the number of supported platinum particles is 1.34 × 10 ^11. / L, 20 nm, 1.67 × 10 ¹⁶ / L. In order to support the catalyst metal, approximately one pore is required for one catalyst metal particle. Therefore, the number of pores required to directly support the catalyst metal particle is at least 1 ×. 10 ¹¹ pieces / L or more, preferably 1 × 10 ¹⁶ pieces / L or more. Further, when the average diameter of the catalytic metal particles is all about 10 nm, the purification performance is equivalent to that of the three-way catalyst. The number of catalyst metal particles at this time is 1.34 × 10 ¹⁷ particles / L, and the number of required pores is more preferably 1 × 10 ¹⁷ particles / L or more.

On the other hand, the weight of the cordierite honeycomb structure having a cell wall thickness of 100 μm and a cell density of 400 cpsi (number of cells per square inch) is about 230 g per liter of volume. Assuming that this is all made of cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ), the number of cordierite crystals is 1 × 10 ¹⁶ / L in the cordierite honeycomb structure. If only one defect is formed in one crystal, the ratio of the crystal having a defect to the entire cordierite crystal is 4 × 10 ⁻⁵ % when the number of defects is 1 × 10 ^17. Become. The number of defects contained per cordierite crystal is 4 × 10 ⁻⁸ and 1 × 10 ⁸ defects per unit crystal lattice when the number of defects is 1 × 10 ¹⁶ / L. ^In the case of ¹⁷ / L, the number of defects per unit crystal lattice is 4 × 10 ⁻⁷ .

In the present invention, in order to give the cordierite honeycomb structure a catalyst supporting ability, (1) oxygen defects and lattice defects (metal vacancies, lattice strain) are formed in the cordierite crystal lattice. (2) A large number of fine cracks are formed in at least one of an amorphous phase and a crystalline phase, (3) a cordierite constituent element and impurities are eluted by a liquid phase method, and a defect is formed. Alternatively, pores are formed by a method of physically forming defects or (5) containing a substance having an oxygen storage capacity. In the present invention, the catalyst component can be directly supported without coating with gamma alumina by forming the above-mentioned predetermined number or more of these pores. In addition, the pores formed by these methods do not destroy the ceramic crystal lattice as in the prior art. Therefore, even if the cell wall thickness is reduced, the crushing strength in the flow path direction is 10 MPa or more, and the thermal expansion coefficient. Of 1 × 10 ⁻⁶ / ° C. or less.

  Next, a cordierite honeycomb structure having a catalyst supporting ability by these methods will be described. First, a cordierite honeycomb structure having oxygen defects / lattice defects (metal vacancies and lattice strain) in the cordierite crystal lattice of (1) will be described. Defects that can support the catalyst component include oxygen defects and lattice defects. Among these, the oxygen defect is a defect caused by the lack of oxygen for constituting the cordierite crystal lattice, and the catalyst component can be supported in the pores formed by the loss of oxygen. In order to support the required amount of the catalyst component, it is preferable that the amount of oxygen in the crystal phase contained in the honeycomb structure is less than 47% by weight. Lattice defects are lattice defects caused by taking in more oxygen than necessary to form a cordierite crystal lattice, and a catalyst component is supported in pores formed by crystal lattice distortion and metal vacancies. It becomes possible to do. Specifically, it is preferable that the amount of oxygen contained in the honeycomb structure is greater than 48% by weight.

  A cordierite honeycomb structure having defects in the crystal lattice can be manufactured by adjusting the firing atmosphere of the honeycomb structure or by using a specific starting material. Among these, for oxygen defects, 1) the firing atmosphere is reduced or reduced, and 2) firing is performed in a low oxygen concentration atmosphere using a compound that does not contain oxygen in at least a part of the cordierite forming raw material. 3) It can be formed by replacing at least one of the constituent elements of cordierite other than oxygen with an element having a lower valence than the element. The lattice defects can be formed by 4) substituting some of the constituent elements of cordierite other than oxygen with elements having a higher valence than the elements.

Next, these forming methods will be described. First, when a cordierite honeycomb structure having oxygen defects is manufactured by the method 1) above, as a starting material, a material generally used as a cordierite forming material, for example, talc (Mg ₃ Si ₄ O _{10) is used.} (OH) ₂ ), kaolin (Al ₂ Si ₂ O ₅ (OH) ₄ ), calcined kaolin (calcined kaolin), alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ), etc. Can be used. In addition to these compounds, oxides, hydroxides and the like containing at least one of Si, Al, and Mg, which are constituent elements of cordierite, can be used as the Si source, Al source, and Mg source.

  These cordierite-forming raw materials are blended so as to have the above theoretical composition, and molding aids such as a binder, a lubricant, a moisturizing agent, and the like are added, kneaded and extruded to form a honeycomb shape. To do. This formed body is heated to about 500 ° C. or higher in the air, degreased, and then fired in a reduced pressure atmosphere or a reducing atmosphere to obtain a honeycomb structure. When firing in a reduced-pressure atmosphere, the degree of vacuum is preferably about 4000 Pa (30 Torr) or less, and firing is usually performed by holding at about 1350 ° C. or higher for 2 hours or longer.

  By firing in a reduced-pressure atmosphere, oxygen contained in the raw material is released as a gas in the reaction process during firing, so there is not enough oxygen to form cordierite crystals, and cordierite crystal lattice Oxygen vacancies are formed. The same applies when firing in a reducing atmosphere. When firing in a reducing gas atmosphere such as hydrogen under the same conditions as described above, oxygen contained in the raw material reacts with the reducing gas during the reaction process during firing. Get out. For this reason, oxygen for constituting the cordierite crystal is insufficient, and oxygen defects are formed in the cordierite crystal lattice. When only the oxide is used as the cordierite forming raw material, it is possible to cover the oxygen for constituting the cordierite crystal only with the oxygen contained in the raw material. It is necessary to remove oxygen.

  In the case of producing a cordierite honeycomb structure having oxygen defects by the method 2), Si, Al, Mg is added to at least part of the Si source, Al source, and Mg source that are cordierite forming raw materials. A compound containing at least one of the above and not containing oxygen is used. Examples of these compounds include nitrides containing at least one of Si, Al, and Mg, which are constituent elements of cordierite, halides such as fluorides and chlorides, and the like. Si source, Al source, Mg source Of these, at least one of them may be partially or entirely made of the above-mentioned compound containing no oxygen. As other cordierite forming raw materials, those similar to the above method 1) can be used.

  This cordierite-forming raw material is prepared so as to have the above theoretical composition, formed into a honeycomb shape and degreased in the same manner as in 1) above, and then fired in a low oxygen concentration atmosphere. The oxygen concentration in the atmosphere is 0% or more and less than 3%, preferably 0% or more and 1% or less, whereby oxygen defects are formed in the cordierite crystal lattice. When a compound containing no oxygen is used as a cordierite forming raw material, oxygen for constituting the cordierite crystal is insufficient only with oxygen contained in the raw material. Therefore, an attempt is made to replenish the insufficient oxygen from the firing atmosphere, but because the oxygen concentration in the firing atmosphere is low, the oxygen necessary for constituting the cordierite crystal in the reaction process is not sufficiently supplied, Oxygen defects are formed in the cordierite crystal lattice.

  As described above, when a compound not containing oxygen is used as a cordierite forming raw material, instead of firing in a low oxygen concentration atmosphere, firing can be performed in a reduced pressure atmosphere or a reducing atmosphere as in the method 1). . In this case as well, oxygen necessary for constituting the cordierite crystal is not sufficiently supplied in the reaction process, so that oxygen defects are formed in the cordierite crystal lattice. In the above method 3), oxygen defects are formed by substituting at least part of Si, Al, and Mg, which are constituent elements of cordierite, with an element having a valence lower than that element. When a cordierite honeycomb structure is manufactured by this method, some of the Si source, Al source, and Mg source are replaced by these elements in place of Si, Al, and Mg, which are constituent elements of cordierite. A cordierite-forming raw material substituted with a compound containing a small number of elements is used.

  Since the valence of the constituent element of cordierite is Si (4+), Al (3+), and Mg (2+), respectively, at least one of the elements has a smaller valence than the element. A compound containing may be used. These compounds may use any of oxides, hydroxides, nitrides, halides, and other Si sources, Al sources, and Mg sources, using ordinary raw materials, cordierite forming raw materials To prepare. This is formed into a honeycomb shape by the same method, degreased, and then fired. The firing atmosphere may be an oxygen-containing atmosphere such as a reduced pressure atmosphere, a reducing atmosphere, an air atmosphere, or an oxygen-free atmosphere. Oxygen necessary for the configuration of cordierite is contained in the raw material, and oxygen defects are caused by element substitution, so that oxygen defects are formed in an oxygen concentration range of 0 to 100% without being affected by the oxygen concentration.

  The constituent elements of cordierite have positive charges such as Si (4+), Al (3+), and Mg (2+). If these elements are replaced with elements having a small valence, the difference in valence with the substituted element and the positive charge corresponding to the amount of substitution will be insufficient, and in order to maintain the electrical neutrality as a crystal lattice, O (2-) having is released. In this way, oxygen defects are also formed in the cordierite crystal lattice by replacing the constituent elements of cordierite with elements having a small valence.

  In the method 4), lattice defects are formed by substituting at least a part of Si, Al, and Mg, which are constituent elements of cordierite, with an element having a higher valence than that element. When a cordierite honeycomb structure is manufactured by this method, a part of the Si source, Al source, and Mg source is replaced by a valence of these elements instead of Si, Al, and Mg, which are constituent elements of cordierite. A cordierite-forming raw material substituted with a compound containing a large number of elements is used. Also in this case, at least one of Si, Al, and Mg is a compound that includes an element having a higher valence than the element, and other Si sources, Al sources, and Mg sources are made of ordinary raw materials. To prepare a cordierite forming raw material. This is formed into a honeycomb shape by the same method, degreased, and then fired.

  The firing atmosphere in the method 4) needs to be an atmosphere in which oxygen is sufficiently supplied, such as an air atmosphere. If the firing atmosphere is an air atmosphere, degreasing can be performed during firing, so the degreasing step can be omitted. Conversely, when the constituent element of cordierite is replaced with an element having a large valence, the difference in valence with the substituted element and the positive charge corresponding to the amount of substitution become excessive, and the electrical neutrality as a crystal lattice is increased. In order to maintain it, a necessary amount of O (2-) having a negative charge is taken in. The incorporated oxygen becomes an obstacle, and the cordierite crystal lattice cannot be arranged in an orderly manner, and lattice defects are formed.

When oxygen defects are formed in the cordierite crystal lattice, the amount of oxygen contained in the cordierite unit crystal lattice is smaller than that in the unit crystal lattice having no oxygen defects. Further, since the crystal lattice as missing portion of the oxygen collapse is deformed, the lattice constant of the b ₀ axis of the crystal axis of cordierite becomes smaller. On the other hand, when lattice defects are formed in the cordierite crystal lattice, the amount of oxygen contained in the cordierite unit crystal lattice is larger than that in the unit crystal lattice having no lattice defect, and the lattice constant of the b ₀ axis is Changes. Specifically, when the oxygen content of the honeycomb structure is less than 47% by weight due to the formation of oxygen defects, the number of oxygen contained in the cordierite unit crystal lattice becomes less than 17.2, lattice constant of the _{b 0} axis of the crystal axes of Eraito is smaller than 16.99.

In addition, when the amount of oxygen in the honeycomb structure exceeds 48% by weight due to the formation of lattice defects, the number of oxygen contained in the cordierite unit crystal lattice becomes more than 17.6, and the crystal axis b _{The zero-} axis lattice constant is larger or smaller than 16.99. As described above, in the present invention, the cordierite honeycomb structure can be loaded with a necessary amount of the catalyst component by oxygen defects or lattice defects formed in the cordierite crystal lattice. In addition, since it is thought that the magnitude | size of these defects is several angstroms or less, it cannot measure as a specific surface area with the normal measuring method of a specific surface area like the BET method using a nitrogen molecule.

  Next, the cordierite honeycomb structure having a large number of fine cracks in at least one of the amorphous phase and the crystalline phase of (2) will be described. These fine cracks are formed in the amorphous phase or the crystalline phase by 1) giving a thermal shock or 2) giving a shock wave to the cordierite honeycomb structure, and a large number of fine cracks formed thereby. A catalyst component can be supported in the pores. In order to carry the catalyst component, the crack width is about the same as or larger than the diameter of the catalyst component ion, usually 0.1 nm or more, and the depth is 1/2 or more of the diameter of the catalyst component ion, usually 0.05 nm or more. Is required. In order to ensure the strength of the honeycomb structure, it is preferable that the cracks are small, and the width is usually about 100 nm or less, preferably about 10 nm or less.

  As a method of applying the thermal shock of 1), a method of rapidly cooling the cordierite honeycomb structure after heating is used. The thermal shock may be applied after the cordierite crystal phase and the amorphous phase are formed in the cordierite honeycomb structure, and the cordierite containing Si source, Al source, and Mg source is formed by a normal method. A cordierite honeycomb structure obtained by shaping, degreasing and firing the lightening raw material is reheated to a predetermined temperature, and then rapidly cooled, or in the course of firing and cooling, from the predetermined temperature. Any method of rapid cooling can be employed. In order to generate cracks due to thermal shock, the difference between the heating temperature and the temperature after rapid cooling (thermal shock temperature difference) should be about 80 ° C. or more, and the size of the crack increases the thermal shock temperature difference. It grows with. However, if the crack becomes too large, it becomes difficult to maintain the shape of the honeycomb structure, and therefore, the thermal shock temperature difference is usually preferably about 900 ° C. or less.

  In the cordierite honeycomb structure, the amorphous phase is present in layers around the crystal phase. When a cordierite honeycomb structure is heated and then subjected to a thermal shock by quenching, there is a difference in the thermal expansion coefficient between the amorphous phase and the crystalline phase, so there is a difference between this thermal expansion coefficient difference and the thermal shock temperature difference. Corresponding thermal stress acts near the interface between the amorphous phase and the crystalline phase. If the amorphous phase or crystalline phase cannot withstand this thermal stress, fine cracks are generated. The amount of fine cracks generated can be controlled by the amount of amorphous phase present in the cordierite honeycomb structure. Since the fine cracks are formed near the boundary between the amorphous phase and the crystal phase, the more amorphous phases, the more fine cracks that are formed.

  The amorphous phase present in the cordierite honeycomb structure is considered to be that an alkali metal element or alkaline earth metal element contained in a trace amount in the cordierite raw material acts as a flux during honeycomb firing to form an amorphous phase. It is done. Therefore, by adding an alkali metal element or an alkaline earth metal element, the amount of fine cracks can be increased when the amount of the amorphous phase is increased and a thermal shock is applied. In addition, the amount of fine cracks can be controlled by the amount of alkali metal element or alkaline earth metal element added. In order to obtain the effect of the addition, the alkali metal element or alkaline earth metal element is contained in an amount more than that contained as an impurity in the raw material, usually the alkali metal element and the alkaline earth metal element are contained in the cordierite honeycomb structure. In total, it may be contained at 0.05% by weight or more. These alkali metal elements and alkaline earth metal elements are added as compounds containing alkali metal elements and alkaline earth metal elements, for example, oxides, hydroxides, and carbonates, when preparing the cordierite forming raw material. can do.

  A fine crack can be formed in the amorphous phase or the crystalline phase by the method of applying the shock wave of 2) instead of the thermal shock. In this case, fine cracks occur when the low-strength portion in the honeycomb structure cannot withstand the energy of the shock wave. As a method of applying a shock wave, there are ultrasonic waves, vibrations, and the like, and the amount of generation of fine cracks can be controlled by the energy of the shock wave.

In the honeycomb structure in which oxygen defects or lattice defects are formed in the cordierite crystal lattice as in (1) above, and in addition, a number of fine cracks are formed in at least one of the amorphous phase and the crystal phase as in (2). Can also be formed. In this case, an oxygen defects or lattice defects by the method described in the above (1), the amount of oxygen exceeds or 48 wt% less than 47 wt%, the lattice constant of the b ₀ axis of the crystal axis is greater than 16.99 Or after firing a small honeycomb structure, a cordierite honeycomb structure having at least one kind of oxygen defect and lattice defect and a large number of fine cracks by applying a thermal shock or a shock wave by the method shown in (2) You can get a body. In order to carry the required amount of catalyst component, the total number of oxygen defects, lattice defects and fine cracks is 1 × 10 ⁷ / L or more, preferably 1 × 10 ⁸ / L or more. Fine cracks can also be formed in the amorphous phase or the crystalline phase by the method 2) of applying a shock wave.

  Next, a cordierite honeycomb structure in which defects are formed by eluting cordierite constituent elements and impurities by the liquid phase method (3) above will be described. This deficiency is caused by the fact that metal elements such as Mg and Al in cordierite crystals, alkali metal elements and alkaline earth metal elements contained in the amorphous phase, or the amorphous phase itself is high-temperature / high-pressure water, supercritical fluid, or alkaline solution, etc. The catalyst component can be supported on the pores formed by the deficiency of these elements and the like.

The cordierite honeycomb structure is obtained by forming a cordierite-forming raw material containing a Si source, an Al source, and an Mg source by a conventional method, degreasing, and firing in the air. The structure is immersed in high-temperature high-pressure water, a supercritical fluid, or an alkaline solution. As a result, metal elements such as Mg and Al in the cordierite crystal, alkali metal elements and alkaline earth metal elements contained in the amorphous phase, or the amorphous phase itself elute into these solutions to form pores. The size of the pores can be controlled by the temperature, pressure, solvent, etc. of the solution, specifically, 10 MPa, 300 ° C. high-temperature high-pressure water, supercritical fluid such as CO ₂ , alkali such as sodium hydroxide solution, etc. A solution such as a solution is used. In addition, as described above, by adding an alkali metal element or an alkaline earth metal element to the cordierite forming raw material, the formed amorphous phase can be adjusted, so by adjusting these addition amounts However, it is possible to control the pores.

Next, a cordierite honeycomb structure in which defects are formed chemically or physically by the vapor phase method (4) will be described. Fine pores are formed by dry etching or sputter etching the cordierite honeycomb structure. In the case of dry etching, the reaction gas is discharged by high frequency or the like to bring the reaction gas into an excited state. When this reaction gas reacts with cordierite constituent elements Si, Al, and Mg, a volatile substance is formed, and this substance is volatilized and exhausted, whereby cordierite is etched. As described above, the defect portions where the cordierite is chemically etched become pores, and the catalyst can be supported. CF ₄ or the like is used as the reactive gas, and this reacts with cordierite constituent elements to form volatile substances such as SiF ₄ . The degree of dry etching can be controlled by etching time, reaction gas type, supply energy, and the like.

  In the case of sputter etching, when a cordierite honeycomb structure is placed in a plasma of Ar or the like excited by high frequency or the like, Ar ions and the like collide with the cordierite surface, and a single atom or a plurality of cordierite constituent elements As a result, the cordierite is etched. In this way, the defect portions where cordierite is physically etched become pores, and the catalyst can be supported. The degree of sputter etching can be controlled by etching time, excitation gas type, supply energy, and the like.

Next, the cordierite honeycomb structure containing the substance (5) having an oxygen storage capacity will be described. A substance having an oxygen storage capacity, such as CeO _2, takes in and out oxygen as the oxygen concentration in the atmosphere changes. That is, when the oxygen concentration in the atmosphere is high, the valence of Ce is 4+, but when the oxygen concentration is lowered, the valence becomes 3+, and the change in valence destroys the electrical neutrality, so that oxygen is released or absorbed. To maintain electrical neutrality. Such a substance having an oxygen storage capacity has been conventionally used as a co-catalyst in a three-way catalyst, and has the effect of adjusting the air-fuel ratio to near the stoichiometric air-fuel ratio by taking in and out oxygen according to fluctuations in oxygen concentration in the exhaust gas. Have.

As described above, when Ce that can take a plurality of valences is included in the cordierite honeycomb structure in a form that replaces the constituent elements of cordierite, the change in valence is caused as in the case of (1) above. In order to compensate for this, oxygen deficiency occurs, and oxygen defects or lattice defects are formed in the crystal lattice of cordierite. The oxygen defects or lattice defects become pores, and the catalyst can be supported, and at the same time, the cordierite honeycomb structure can be provided with an oxygen storage capacity. That is, the catalyst can be directly supported without coating with gamma alumina, and the oxygen storage ability can be exhibited without separately supporting a promoter having oxygen storage ability. In order to provide oxygen storage capacity, it is desirable that the CeO ₂ content in the cordierite honeycomb structure is 0.01% by weight or more.

In order to obtain a cordierite honeycomb structure containing CeO ₂ , Ce is replaced with at least one part of Si, Al, and Mg that are constituent elements of cordierite. The replacement method is the same as in the case of (1) above, and a cordierite forming raw material in which a part of Si source, Al source, and Mg source is replaced with a compound containing Ce instead of Si, Al, and Mg is used. That's fine. In the air atmosphere, the valence of Ce is normally 4+. Therefore, when substituting Mg (2+) and Al (3+) with smaller valences, lattice defects are obtained in the same manner as in (1) 4). Of course, even if it is replaced with Si (4+), since a part of Ce usually has a valence of 3+, pores due to oxygen defects are formed.

Thus, by using Ce as the substitution element, a cordierite honeycomb structure having a catalyst supporting ability and an oxygen storage ability can be obtained. When CeO ₂ as a co-catalyst is supported on the support, CeO ₂ may grow due to thermal degradation and reduce the oxygen storage capacity, but when CeO ₂ is contained in the cordierite structure Since no grain growth occurs, oxygen storage capacity does not decrease. Further, after firing the cordierite honeycomb structure, fine cracks may be generated by applying a thermal shock or a shock wave as shown in (2) above. As a result, the number of pores formed is increased, and the catalyst supporting ability can be improved. Alternatively, in combination with the method shown in (1) above, the number of oxygen defects or lattice defects formed can be adjusted by using a substitution element other than Ce or adjusting the firing atmosphere.

The cordierite honeycomb structure provided with the catalyst supporting ability by the methods (1) to (4) above is supported with an oxygen storage ability promoter such as CeO ₂ to provide the oxygen storage ability. You can also. In this case, since the co-catalyst can be supported by utilizing the pores of the cordierite honeycomb structure without coating with gamma alumina, a cordierite honeycomb structure having an oxygen storage capacity in addition to the catalyst supporting capacity can be obtained. Can be easily obtained. When a promoter having oxygen storage capacity is supported, it may be supported by supporting a pre-catalyst material such as an ion or a complex and heat-treating it.

Furthermore, in the ceramic body of the present invention, by replacing at least one element or more of the elements constituting the base ceramic with an element other than the constituent elements, the catalyst component is directly applied to the substituted element. It can be supported. The ceramic catalyst body obtained by directly supporting the catalyst component is suitably used as, for example, an automobile exhaust gas purification catalyst. The substrate ceramic, theoretical composition is a ceramic containing cordierite represented by _{2MgO · 2A1 2 O 3 · 5SiO} 2 as the component is preferably used. Specifically, a ceramic body containing cordierite at 1% by volume or more, preferably 5% by volume or more is suitably used. The shape of the ceramic body is not particularly limited, and may be various shapes such as a honeycomb shape, a foam shape, a hollow fiber shape, a fiber shape, a powder shape, or a pellet shape.

  Elements that replace the constituent elements (Si, A1, Mg) of the base ceramic have a stronger binding force with the supported catalyst component than these constituent elements, and elements that can support the catalyst component by chemical bonding are Used. Specific examples of such a substitution element include at least one element having d or f orbital in the electron orbital thereof, and preferably d or f. An element having an empty orbit in the f orbit or an element having two or more oxidation states is used. An element having a vacant orbit in the d or f orbital is close to the energy level of the noble metal catalyst and the like to be supported, and is easy to give an electron, so that it easily binds to a catalyst component. An element having two or more oxidation states also has a similar effect because it is easy to donate electrons.

  Specific examples of the substitution element having an empty orbit in the d or f orbit include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Tc, Ru, Rh, La, and Ce. , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Ta, W, Re, ○ s, Ir, Pt, etc., preferably Ti, V At least one element selected from Cr, Mn, Fe, Co, Ni, Zr, Mo, Ru, Rh, Pd, Ce, W, Os, Ir, and Pt is used. Of the above elements, Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Tc, Ru, Rh, Ce, Pr, Eu, Tb, Ta, W, Re, Os, Ir, Pt Is also an element having two or more oxidation states.

  Further, specific examples of elements having two or more oxidation states other than these include Cu, Ga, Ge, As, Se, Br, Pd, Ag, In, Sn, Sb, Te, I, Yb, Au, and the like. Preferably, at least one element selected from Cu, Ga, Ge, Se, Pd, Ag, and Au is used. The high specific surface area cordierite porous body, which is the base material of the ceramic body of the present invention, is composed only of acicular crystal phases and has a structure in which sintering does not proceed easily. The decrease in the specific surface area due to can be suppressed. From this, it becomes possible to manufacture a honeycomb structure as a catalyst carrier directly from the high-temperature stable and high specific surface area cordierite porous body that is the base material of the ceramic body of the present invention.

  That is, by manufacturing a honeycomb structure as a catalyst carrier directly from a high-temperature stable and high specific surface area cordierite porous body, which is the base material of the ceramic body of the present invention, a conventionally manufactured honeycomb structure is manufactured. In the process, it is possible to omit a process such as coating with gamma alumina, and the manufacturing cost of the honeycomb structure for supporting a catalyst can be greatly reduced. In the present invention, the above-mentioned high-temperature stable / high specific surface area cordierite porous body is used as a catalyst-supporting honeycomb structure, resulting from peeling of the gamma alumina coating layer due to long-term use, which has been a problem in the past. It is possible to eliminate the deterioration of the catalyst quality.

  Further, in the present invention, the honeycomb catalyst manufacturing process can be simplified by using the above high-temperature stable and high specific surface area cordierite porous body as a honeycomb structure for supporting a catalyst. Since the high-temperature stable and high specific surface area cordierite porous body of the ceramic body substrate of the present invention is composed of fine acicular crystal phases of 1 nanometer or more and 0.1 micron or less, Pt, Ph, and It becomes possible to easily carry an active catalyst such as Pd.

  That is, in the present invention, by using the above high-temperature stable and high specific surface area cordierite porous body as a honeycomb structure for supporting a catalyst, it is possible to manufacture and provide a honeycomb catalyst supporting a noble metal catalyst at a low cost. Is done. Since the cordierite porous body of the present invention is entirely composed of a needle-like crystal phase, it is possible to suppress a decrease in specific surface area due to sintering even in heat treatment at a high temperature, and a honeycomb structure having a large specific surface area. For example, it can be suitably used as a cordierite porous material for supporting a high-temperature stable and high specific surface area catalyst.

  The cordierite honeycomb structure having a catalyst supporting capacity manufactured by the above-described method is suitably used as a ceramic carrier used for an exhaust gas purification catalyst of an internal combustion engine. For example, this ceramic carrier can carry a catalyst component of 0.1 g / L or more in the pores of the cordierite honeycomb structure without coating with gamma alumina, thereby providing a low heat capacity and high heat resistance. A ceramic catalyst body with impact and low pressure loss can be obtained. As the catalyst component, at least one of a metal having catalytic ability and an oxide of a metal having catalytic ability is used. Examples of the metal having catalytic ability include noble metals such as Pt, Pd, and Rh. Examples of the metal oxide having catalytic ability include V, Nb, Ta, Cr, Mo, W, Mn, Fe, and Co. An acid containing at least one metal among metals such as Ni, Cu, Zn, Ga, Sn, and Pb is used. Further, as a co-catalyst, one or more of a lanthanoid element, a transition metal element, an alkali metal element, an alkaline earth metal element, or an oxide complex oxide thereof can be used at the same time.

  As a method for supporting the catalyst component, for example, by dissolving the catalyst component in a solvent and impregnating the cordierite honeycomb structure, in addition to the liquid phase method in which the catalyst component is supported in pores such as defects and cracks, A vapor phase method such as a CVD method or a PVD method, a method using a supercritical fluid, or the like is used. In the present invention, since the pores such as defects and cracks formed in the cordierite honeycomb structure, a medium that easily enters the fine pores as in the gas phase method or the method using a supercritical fluid is used. The method used is more desirable. In the liquid phase method, water can be used as a solvent, but a solvent having a surface tension smaller than that of water, for example, an alcohol solvent such as methanol is preferably used.

  By using a solvent having a smaller surface tension than water, it is possible to sufficiently penetrate into the pores. At this time, if the immersion is performed while applying vibration or vacuum degassing, the solvent easily enters the pores. Moreover, it is good to carry | support to a required quantity by dividing a catalyst component into multiple times by the same composition or a different composition. By these methods, it is possible to carry a catalyst component of 0.5 g / L or more by utilizing the pores more effectively. The ceramic catalyst body of the present invention thus produced has a purification performance in which a required amount of catalyst components are supported directly and at a narrow interval without forming a coating layer of gamma alumina on the surface of the ceramic support. It becomes an excellent ceramic catalyst body.

  According to the present invention, 1) an acicular ceramic body and acicular ceramic catalyst body composed of cordierite acicular particles having a high specific surface area can be provided, and 2) at least a part of the cordierite porous body is acicular. Since it is composed of a crystalline phase, for example, even if it is exposed to a high temperature exceeding 1000 ° C. for a long time, the decrease in specific surface area due to sintering is suppressed. 3) The aspect ratio of needle-shaped particles can be controlled. A) a large amount of acicular cordierite crystal phase is generated; 5) a honeycomb body can be directly produced by a cordierite sintered body itself; and 6) this porous body has a high specific surface area that is stable at high temperatures. It is useful as a cordierite honeycomb structure for catalyst support, 7) The conventional process of coating the inside of the honeycomb can be omitted, and 8) A high-quality honeycomb body is manufactured at low cost. 9) According to the conventional method, for example, in a product in which gamma alumina or the like is coated on the inner wall of a cordierite honeycomb body, gamma alumina becomes alpha alumina at a high temperature of 1000 ° C. or higher. There was a problem that it was difficult to maintain a high specific surface area due to the transition and sintering, but the product of the present invention has a special effect that there is no such problem. The

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.

In this example, a cordierite ceramic body was produced from a raw material blended with acicular kaolin. Based on the ternary phase diagram of MgO—Al ₂ O ₃ —SiO ₂ , the cordierite composition with a constant mixing ratio of starting materials, ie, Al ₂ O ₃ : MgO: SiO ₂ = 2: 2: 5 Thus, kaolin, talc, Al (OH) ₃ , SiO ₂ , B ₂ O ₃ , and SrO were weighed in predetermined amounts. Here, the kaolin had a needle-like (needle-like) shape. Further, SrO and B ₂ O ₃ were added for the purpose of promoting whisker growth and lowering the crystallization temperature. Table 1 shows the blending ratio. The mixed powder is mixed with ethanol as a medium in a ball mill for 24 hours, dried and granulated using a spray dryer, placed in a mold, and uniaxially pressed into a pellet-shaped test piece having a diameter of 20 mm and a thickness of 5 mm. Was made. The maximum firing temperature was changed in 5 ways between 1100 ° C. and 1400 ° C., the holding time at the maximum temperature was 4 hours, and the heating rate was constant at 3 ° C./min. As a result, it has been found that it is preferable to set the maximum temperature between 1300 ° C. and 1400 ° C. in order to generate acicular cordierite. FIG. 1 shows an example in which the structure of a sample obtained at a firing temperature of 1350 ° C. is observed by SEM. Moreover, Si, Mg, and Al were detected from the analysis result of EDS, and as a result of examination together with the analysis result of XRD, it was confirmed that acicular cordierite was generated.

  In this example, carbon was blended as a substance (pore forming material) that disappeared during the firing process to produce a cordierite ceramic body. 10% by weight of carbon having an average particle size of 0.02 μm was added to the mixed powder shown in Table 1. Carbon is a pore former. This mixed powder is mixed with ethanol as a medium for 24 hours in a ball mill, dried and granulated using a spray dryer, then placed in a mold and uniaxially pressed into a pellet with a diameter of 20 mm and a thickness of 5 mm. A test piece was prepared. The maximum firing temperature was 1350 ° C., the retention time at the maximum temperature was 4 hours, and the rate of temperature increase was 5 ° C./min. It was confirmed that a larger amount of needle-shaped body than the amount of needle-shaped body obtained in Example 1 was produced. Si, Mg, and Al were detected from the analysis result of EDS. As a result of examination together with the analysis result of XRD, it was found that the amount of needle-like bodies increased due to the addition of carbon compared to the additive-free material. The reason for this is considered that a growth space was formed by the addition of carbon in the previous stage of sintering and densification, and anisotropic growth due to the crystal structure became easy.

  Using the same components as in Example 2, a honeycomb was manufactured by extrusion. The result of having cut out the test piece from the obtained cordierite honeycomb and observing with SEM. As in the case of using pellets, acicular bodies are generated on the surface, and as a result of analysis by EDS, Si, Mg, Al are detected, and acicular cordierite is generated. Was confirmed.

In this example, the surface of the honeycomb was coated with a slurry containing kaolin, and acicular cordierite was formed on the surface of the honeycomb. Kaolin (Kyoritsu Materials, Japan), aluminum hydroxide (Al (OH) ₃ , (Koujyundo Chemicals, Japan), silica (silica quartz, d50 to 0.8 μm, Koujyundo Chemicals, Japan) were used as starting materials for the coating slurry. First, an aqueous slurry of a starting material was prepared, and polyelectrolyte (ammonium polyacrylate, Toa Gohsei, ALON A-6114) was added as a dispersing agent in an amount of 1 to 2% by weight, and the chemical composition of the slurry is shown in Table 2. The slurry is a beaker. The solid component contained in the degassed slurry was kept at 20 to 30%, and the cordier had a height of 1.5 cm and a diameter of 5.0 cm. The light honeycomb carrier was coated with the slurry, and the honeycomb carrier was dipped in the slurry at least twice to coat the slurry. The rally was completely removed, and an excess slurry in the pores was blown off with an air gun for the purpose of obtaining a uniform coating layer.The slurry-coated honeycomb carrier was dried at room temperature for 24 hours, and then a vacuum dryer was used. And dried at 70 ° C. for 24 hours.

  Sintering was performed in an air stream at 1300 ° C. for 4 hours using a tubular furnace. The conditions shown below were used for the firing pattern. Temperature rise to 600 ° C at 1 ° C / min, hold at 600 ° C for 1 hour, temperature rise to 1300 ° C at 3 ° C / min, hold at 1300 ° C for 4 hours, temperature drop to 1000 ° C at 2 ° C / min, rapid temperature drop to room temperature did. The microstructure of the sample was evaluated using FE-SEM. The results are shown in FIG. From observation of the microstructure of the honeycomb carrier sintered at 1350 ° C. for 4 hours or more, it was found that cordierite whiskers grow on the coating layer. When the fine structure of the coat layer was observed (FIG. 2), whisker growth by the VLS mechanism was not recognized, and only needle-like whiskers were confirmed. In this case, needle-like whiskers were produced by a dissolution-precipitation mechanism.

  In this example, the honeycomb obtained by the process shown in Example 3 was etched. Etching was performed with HF for the purpose of removing excess silica produced on the surface. The FE-SEM was used to evaluate the microstructure of the sample that was etched with HF and the sample that was not etched. FIG. 3 shows the microstructure of the sample etched with HF. As can be seen from FIG. 3, excess silica is removed by etching with HF, and whiskers embedded in excess silica are observed.

  According to the present invention, for example, needle-shaped particles having a controlled high aspect ratio can be obtained by blending raw material particles having a needle-like or columnar shape, or a substance (pore forming material) that disappears in the firing process into the raw material. A high specific surface area cordierite having a structure in which a nano-sized acicular crystal phase is precipitated by producing a ceramic body containing a large amount and growing a acicular ceramic body on the surface of the sintered body. A porous body can be manufactured and provided. In this case, it is possible to control the shape and characteristics of the needle-shaped particles to be generated according to the type, shape, slurry concentration, processing conditions, and the like of the raw material. In the present invention, since the entire cordierite porous body of the ceramic body is composed of a needle-like crystal phase, it is possible to dramatically suppress a decrease in specific surface area due to sintering even at high temperature heat treatment. It becomes. From this, in the production of a cordierite honeycomb structure for supporting a catalyst, steps such as coating gamma alumina on the honeycomb inner wall can be omitted. A technique for producing a cordierite honeycomb having a high specific surface area that is stable at high temperatures can be provided. The present invention also provides an acicular ceramic body comprising a high specific surface area cordierite porous body, a method for producing the acicular ceramic body, and an acicular ceramic catalyst body as a product thereof. Useful for providing.

The scanning micrograph of the structure | tissue of the ceramic sample obtained at the firing temperature of 1350 degreeC using the acicular kaolin is shown. The scanning micrograph of the microstructure of the sample produced by coat | covering a slurry on a cordierite honeycomb carrier is shown. A scanning photomicrograph of the microstructure of a sample prepared by coating a cordierite honeycomb carrier with slurry and further etched with HF is shown.

Claims (53)

  Among the ceramic particles, some or all of the particles contain at least Si, Al, Mg, and the needle-shaped particles generated from the raw material particles having a needle-like or columnar shape in a ceramic body having a needle-like shape. A ceramic body comprising:   A part of or all of the surface of the ceramic body contains at least Si, Al, Mg as a coating layer, and in the ceramic body having a needle shape, the needle shape formed from raw material particles having a needle shape or a columnar shape A ceramic body comprising particles.   Among the ceramic particles, some or all of the particles contain at least Si, Al, Mg, and the needle-shaped particles generated from the raw material particles having a needle-like or columnar shape in a ceramic body having a needle-like shape. And a ceramic body having at least one of pores and elements capable of directly supporting a catalyst component on the surface of ceramic particles of the ceramic body.   A part of or all of the surface of the ceramic body contains at least Si, Al, Mg as a coating layer, and in the ceramic body having a needle shape, the needle shape formed from raw material particles having a needle shape or a columnar shape A ceramic body comprising particles and having at least one of a pore and an element capable of directly supporting a catalyst component on a ceramic particle surface of the ceramic body.   The ceramic body according to any one of claims 1 to 4, wherein the ceramic particles contain Sr and / or B.   5. The ceramic body according to claim 3, wherein the pore comprises at least one of defects in a ceramic particle crystal lattice, fine cracks on the surface of the ceramic particle, and defects of elements constituting the ceramic particle.   The ceramic body according to claim 6, wherein a width of the fine crack is 100 nm or less. The ceramic body according to claim 6, wherein the pores have a diameter or width that is 1000 times or less the diameter of the catalyst ions to be supported, and the number of pores is 1 × 10 ¹¹ pieces / L or more.   The ceramic body according to claim 6, wherein the pores are defects formed by substituting a part of constituent elements of the ceramic particles with metal elements having different valences. The said defect consists of at least 1 type of an oxygen defect and a lattice defect, The ceramic crystal which has one or more defects in the unit crystal lattice of the said acicular shaped particle | grain is contained ^4x10 < ^-6 >% or more. Ceramic body.   The ceramic body according to claim 3 or 4, wherein the catalyst component is supported on the substitution element by chemical bonding.   The ceramic body according to claim 11, wherein the substitution element is at least one element having d or f orbits in an electron orbit thereof.   The ceramic body according to any one of claims 1 to 4, wherein the needle-shaped particles include Si, Al, Mg, and at least one of Sr and Ce.   The ceramic body according to any one of claims 1 to 4, wherein the needle-shaped particles are cordierite.   The ceramic body according to claim 14, wherein at least five unit crystal lattices from the surface of the needle-shaped particles are cordierite.   The ceramic body according to any one of claims 1 to 4, wherein an aspect ratio of the needle-shaped particles is 5 or more.   The ceramic body according to any one of claims 1 to 4, wherein a shape of the ceramic body is a powder, a pellet, a nonwoven fabric, or a honeycomb shape. 5. The ceramic body according to claim 1, wherein the ceramic body has a specific surface area of 1 m ² / g or more.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a porosity of 10% or more.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a porosity of 30% or more. The ceramic body according to claim 17, comprising a ceramic honeycomb body having a thermal expansion coefficient in a flow path direction of 2 × 10 ⁻⁶ / ° C. or less. The ceramic body according to claim 17, comprising a ceramic honeycomb body having a thermal expansion coefficient in a flow path direction of 1 × 10 ⁻⁶ / ° C. or less.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a crushing strength in a flow path direction of 5 MPa or more.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a crushing strength in a flow path direction of 10 MPa or more.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a cell wall thickness of 400 µm or less.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a cell wall thickness of 100 µm or less.   The ceramic body according to claim 17, comprising a ceramic honeycomb body having a narrow pore distribution distribution width.   28. The ceramic body according to claim 27, wherein a pore volume included in the distribution width within ± 1/2 of a value of an average pore diameter is 50% or more.   A ceramic catalyst body comprising a catalyst body supported on the ceramic body according to any one of claims 1 to 28.   30. The ceramic catalyst body according to claim 29, wherein the catalyst component is a noble metal.   The ceramic catalyst body according to claim 30, wherein the supported amount of the catalyst component is 0.1 g / L or more.   A ceramic catalyst body containing a promoter component in the ceramic body according to any one of claims 1 to 28 and / or the ceramic catalyst body according to any one of claims 29 to 31.   The ceramic catalyst body according to claim 32, wherein the promoter component is one or more of a lanthanoid element, a transition metal element, an alkali metal element, an alkaline earth metal element or oxide thereof, and a composite oxide.   The ceramic catalyst body according to claim 33, wherein the content of the promoter component is 6 g / L or more. Ceramics using raw materials composed of a compound of SiO ₂ and Al ₂ O ₃ as the Si source, wherein some or all of the ceramic particles contain at least Si, Al, Mg, and the shape is needle-shaped A method for producing a ceramic body, comprising producing a ceramic body using raw material particles having a needle shape or a columnar shape for acicularization.   The method for producing a ceramic body according to claim 35, wherein an additive for acicularization is added.   The method for producing a ceramic body according to claim 36, wherein the additive for acicularization is at least one selected from a lanthanoid element, a transition metal element, an alkali metal element, and an alkaline earth metal element.   36. The method for producing a ceramic body according to claim 35, wherein the raw material particles having a needle shape or a columnar shape are kaolin.   The surface of the sintered body is coated with a slurry containing kaolin, dried, fired, and a needle-shaped ceramic body is grown using the kaolin as a part of the raw material, so that some or all of the ceramic particles A method for producing a ceramic body, comprising producing a ceramic body having an acicular crystal phase formed of needle-shaped particles containing at least Si, Al, and Mg and having a needle shape.   The method for producing a ceramic body according to claim 39, wherein the starting material of the slurry is kaolin, aluminum hydroxide, or silica.   The method for producing a ceramic body according to claim 39, wherein the kaolin is needle-shaped or columnar.   A needle-shaped particle, wherein the needle-shaped particle is expressed by subjecting the ceramic body produced by the method according to any one of claims 35 to 41 to acid treatment, alkali treatment, or dry etching. A method for producing a ceramic body.   43. The method for producing a ceramic body according to claim 42, wherein as the acid treatment, a needle-shaped particle is expressed by a treatment with a weak acid.   44. The method for producing a ceramic body according to claim 43, wherein the weak acid is a 0.001N to 2N weak acid.   45. The method for producing a ceramic body according to claim 43 or 44, wherein the weak acid uses at least one acid among an acid having a carboxyl group (—COOH), phosphoric acid, and hydrogen sulfide.   40. The method for producing a ceramic body according to claim 35 or 39, wherein the needle-shaped particles are grown by forming the needle-shaped particles into a desired shape and firing.   40. The method for producing a ceramic body according to claim 35 or 39, wherein the needle-shaped particles are grown by forming a raw material for forming the needle-shaped particles into a desired shape and firing the raw material.   40. The method of manufacturing a ceramic body according to claim 35 or 39, wherein in the firing process, acicular crystal particles are grown before the sintering is completed.   Claims: In order to delay the completion of sintering and provide a space for growing a needle-shaped ceramic body, a substance that disappears in the firing process is blended as part of the raw material, and the disappeared substance is burned off in the firing process. 40. A method for producing a ceramic body according to 35 or 39.   The method for producing a ceramic body according to claim 49, wherein the substance that disappears in the firing process is carbon.   A method for producing a ceramic catalyst body, comprising supporting a catalyst component on the ceramic body according to any one of claims 1 to 28.   A ceramic catalyst body according to any one of claims 1 to 28 and / or a ceramic catalyst body according to any one of claims 29 to 34, wherein a promoter component is supported. .   53. The promoter component according to claim 52, wherein a promoter component is mixed with the ceramic body according to any one of claims 1 to 28 and / or the ceramic raw material of the ceramic catalyst body according to any one of claims 29 to 34. A method for producing a ceramic catalyst body.