JP2006326532A - Production method for gas reaction catalyst and manufacturing apparatus used for it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method capable of efficiently producing, with less step, a gas reaction catalyst capable of enhancing a utilization efficiency of a precious metal fine particle by sufficiently carrying only selectively an area of a surface layer part circulated with a gas of a wash coat and a surface layer part of the wash coat at an inner depth part of a penetration hole with the precious metal fine particle and effectively treating an exhaust gas component of a low temperature immediately after starting of an engine only by using the carried precious metal fine particle, and a production apparatus. <P>SOLUTION: In the production method, an ion of the precious metal is reduced by an action of a reducing agent while circulating a solution containing the ion of the precious metal and the reducing agent through the inside of respective penetration holes only in one direction while directing it from an opening at one end surface side of the honeycomb structure body to an opening at the other end surface side, thereby, the precious metal fine particle is precipitated. In the production apparatus, the solution L is repeatedly circulated through a circulation passage member 2 connected to a retaining member 1 in the state that the honeycomb structure body H is retained by the retaining member 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention has a large number of through-holes connecting two different end faces for allowing gas to pass, and the wash coat of the honeycomb structure in which the inner wall surface of each through-hole is covered with a wash coat is used for gas treatment. The present invention relates to a method for producing a gas reaction catalyst by supporting noble metal fine particles functioning as a catalyst for the production, and a production apparatus used therefor.

  As a gas reaction catalyst used for exhaust gas purification of automobiles, etc., it has a large number of through-holes connecting two different end faces for passing exhaust gas, and the inner wall surface of each through-hole is made of powder such as alumina. A honeycomb structure made of cordierite or metal, covered with a porous layer called a washcoat, having a structure in which noble metal fine particles functioning as a catalyst for gas treatment are supported on the washcoat. Generally used.

  In the gas reaction catalyst having the above structure, the honeycomb structure is usually immersed in a solution containing noble metal ions so that the solution is mainly impregnated into the porous structure of the washcoat, and then pulled up and fired. Thus, it is manufactured by a so-called impregnation method in which the step of reducing the ions to precipitate the noble metal fine particles is repeated.

  However, in the impregnation method, since the noble metal fine particles are deposited and supported on the outer surface of the honeycomb structure that does not come into contact with the exhaust gas, there is a problem that the use efficiency of the noble metal fine particles as a catalyst is low and wasteful. is there. In addition, since the amount of noble metal fine particles that can be supported by one immersion-firing is small, in order to produce a gas reaction catalyst by supporting a predetermined amount of noble metal fine particles on the washcoat, the immersion-firing process is repeated many times. There is a problem that the productivity of the gas reaction catalyst is low and the manufacturing cost is high because it is necessary to perform the process and requires a lot of energy and time.

  Furthermore, in the supporting method, since the honeycomb structure is immersed in a solution in a static state, the wash in the inner and inner parts of the through-hole farther from the opening becomes larger as the size of the honeycomb structure increases. There is a tendency that the solution does not spread sufficiently to the coat. Therefore, the immersed honeycomb structure is also moved up and down in the liquid. However, in particular, in the case of a large honeycomb structure, the solution is passed through the through-holes to the inner and outer washcoats. As a result, there is a problem that a region in which the noble metal fine particles are not sufficiently supported is formed in the washcoat in the inner and inner portions of the through holes where the solution is not sufficiently distributed.

It has been proposed to form a washcoat on the inner wall surface of the through-holes of the honeycomb structure by using a powder of alumina or the like as a basis for the washcoat, on which the noble metal fine particles are previously supported. (See Patent Document 1). According to this method, the noble metal is almost uniformly formed only in the washcoat, selectively, and even to the washcoat in the inner and rear portions of the through hole far from the opening, without causing a region where the noble metal fine particles are not sufficiently supported. The gas reaction catalyst carrying the fine particles can be produced with fewer steps.
JP-A-6-327978 (Claims, columns 0005 to 0006, column 0039, columns 0042 to 0044, FIGS. 7 and 8)

  However, when the gas reaction catalyst is used, the exhaust gas actually circulates from the surface exposed in the through hole of the washcoat to a depth of about 1/3 in the thickness direction of the washcoat. Even if the noble metal fine particles existing only in the surface layer region and only the noble metal fine particles existing in the surface layer region are in contact with the exhaust gas and function for gas treatment, Can not function as. Therefore, in the case where the entire washcoat is formed using a powder carrying precious metal fine particles in advance, the problem that the utilization efficiency of precious metal fine particles is low and wasteful is not solved.

  In claim 2, column 0043 to column 0044 of FIG. 1, and FIG. 8, the inner wall surface of the through hole of the honeycomb structure has a function of first adsorbing a low-temperature exhaust gas component immediately after starting the engine. It is described that a lower layer made of modified crystalline aluminosilicate particles is formed, and an upper layer made of particles carrying noble metal fine particles is formed thereon. If this laminated structure is used, noble metal fine particles are not sufficiently supported selectively only on the surface layer portion of the washcoat in the through-hole, and further up to the surface layer portion of the washcoat in the inner deep portion far from the opening of the through-hole. It is considered that the use efficiency of the noble metal fine particles can be improved by supporting the noble metal fine particles almost uniformly without generating a region.

  However, in order to manufacture a gas reaction catalyst having the above-described laminated structure, a process for forming a two-layer washcoat of a lower layer and an upper layer is required, so the productivity of the gas reaction catalyst is low and the manufacturing cost is low. The problem of being expensive again occurs. In addition, in order to simplify the structure, when the lower layer is formed of a powder such as alumina not supporting noble metal fine particles, the noble metal powder is a surface layer of the wash coat in the inner and inner part of the through hole far from the opening. Since it is supported almost uniformly up to the upper part (upper layer), there is no problem in terms of utilization efficiency of the noble metal fine particles, but the effect of effectively removing the low-temperature exhaust gas component immediately after the engine is started is not sufficient. Therefore, in Patent Document 1, as described above, the lower layer is formed of modified crystalline aluminosilicate particles, which is another cause of low productivity and high manufacturing cost. .

  The object of the present invention is to produce a region where noble metal fine particles are not sufficiently supported selectively only in the region of the surface layer portion of the washcoat where gas flows, and to the surface layer portion of the washcoat in the inner part of the through hole. Therefore, it is possible to sufficiently support the noble metal fine particles and improve the utilization efficiency of the noble metal fine particles, and to effectively treat the low-temperature exhaust gas components immediately after starting the engine using only the noble metal fine particles supported. An object of the present invention is to provide a production method capable of efficiently producing a gas reaction catalyst that can be produced with fewer steps than before. Another object of the present invention is to provide a production apparatus capable of producing a gas reaction catalyst more efficiently and with high productivity by the above production method.

  The invention according to claim 1 is the above-described washcoat of a honeycomb structure having a plurality of through holes connecting two different end faces for allowing gas to pass through, and covering the inner wall surface of each through hole with a wash coat In addition, a method for producing a gas reaction catalyst by supporting noble metal fine particles functioning as a catalyst for gas treatment, wherein noble metal ions that are the basis of the noble metal fine particles and the ions are reduced to form noble metal fine particles. By causing the solution containing the reducing agent to be precipitated to flow from the opening on the one end surface side of the honeycomb structure toward the opening on the other end surface side, through each through hole only in one direction, by the action of the reducing agent. A method for producing a gas reaction catalyst, wherein noble metal fine particles are precipitated and supported on a washcoat by reducing noble metal ions.

  The invention according to claim 2 is an apparatus for carrying out the method for producing a gas reaction catalyst according to claim 1, wherein the holding member has a holding portion for holding a plurality of honeycomb structures individually, and the holding member The solution containing the noble metal ions and the reducing agent is connected from the openings on one end face side of the honeycomb structure to the openings on the other end face side. A gas reaction catalyst manufacturing apparatus comprising: a circulation path member that constitutes a circulation path for repeatedly circulating inside each through hole while flowing in only one direction.

  According to a third aspect of the present invention, the holding member holds one end surface of one of the plurality of honeycomb structures in which the through hole is opened at a position facing the solution supply port of the circulation path member. A holding portion is provided, and one end face of each of the other honeycomb structures having the through holes opened is opposed to the supply port at an equal distance around the one end face of the one honeycomb structure. It is a manufacturing apparatus of the gas reaction catalyst of Claim 2 provided with the holding part hold | maintained in the made position.

  In the first aspect of the present invention, the noble metal ions are reduced by the action of the reducing agent while the solution containing the noble metal ions and the reducing agent is circulated in the through holes of the honeycomb structure to precipitate the noble metal fine particles. By performing a reduction precipitation reaction, noble metal fine particles are selectively selected only on the surface layer portion of the washcoat in the through hole in the honeycomb structure, and further up to the surface layer portion of the wash coat in the inner depth of the through hole. Noble metal fine particles can be sufficiently supported without generating a region where the is not sufficiently supported.

  In other words, when noble metal ions are reduced by the action of the reducing agent in the solution flowing through the through hole, the surface of the washcoat that comes into contact with the solution (not only the apparent surface of the washcoat but also the deep part from the surface). In addition, the noble metal fine particles are precipitated starting at the same time as the starting point of precipitation (including the inner surface of the porous structure reaching the surface), and the reduction precipitation reaction supported on these surfaces proceeds. At this time, the solution reaches the entire inside of the porous structure of the washcoat at the initial point when the flow into the through-hole is started, but after that, new solutions are supplied one after another to reduce the precipitation reaction. Therefore, the region where the precious metal fine particles are concentrated and deposited is substantially the same as the region of the surface layer portion through which the gas flows when the gas reaction catalyst is used. This is because both the gas and the solution are fluids and behave similarly in the through hole. Moreover, since the solution is forcibly distributed through the through hole from the opening on one end surface side to the opening on the multi-end surface side, the solution does not sufficiently spread on the washcoat, and the noble metal fine particles are not sufficiently supported. There is no area.

  In addition, in the conventional dipping method, since noble metal ions cannot be further adhered on the surface of the washcoat after the noble metal ions are adhered to the surface of the washcoat, In addition, the precious metal particles are generated from the noble metal ions that are pulled up from the solution and fired, and after the surface of the washcoat is exposed, the work is again immersed in the solution to attach the noble metal ions. As described above, it must be repeated until a predetermined amount of noble metal fine particles are supported. In contrast, in the reduction precipitation reaction, the solution containing the noble metal ions and the reducing agent is continuously supplied to the through-holes of the honeycomb structure so that the washcoat surface is brought into contact with the solution. One after another, new noble metal fine particles can be deposited and supported.

  In addition, in order to form a wash coat in which noble metal fine particles are supported only on the surface layer by a method of forming a wash coat using a powder in which noble metal fine particles are supported in advance, the noble metal fine particles are supported as described above. Two steps are required, in which a lower layer is formed using a non-powder powder, and an upper layer is formed thereon using a powder carrying precious metal fine particles. On the other hand, in the reduction precipitation report, the wash coat is formed in only one step.

  Therefore, according to the first aspect of the present invention, the noble metal fine particles are selectively applied only to the region of the surface layer portion of the washcoat where gas flows, and to the surface layer portion of the washcoat in the inner part of the through hole. Since the noble metal fine particles are sufficiently supported without generating a region that is not sufficiently supported, a gas reaction catalyst excellent in the use efficiency of the noble metal fine particles can be efficiently produced with fewer production steps.

  Moreover, according to the first aspect of the present invention, the amount of the noble metal fine particles supported in the washcoat is determined by continuously flowing the solution unilaterally from the opening on one end side into the through hole of the honeycomb structure. As much as possible in the area of the entrance side of the. This is because the reduction precipitation reaction proceeds when flowing through the through-hole, thereby causing a concentration gradient of the metal ion in the solution to be high on the inlet side and low on the outlet side.

  For this reason, the produced gas reaction catalyst is incorporated into an exhaust system of an automobile or the like, with the region on the inlet side of the solution carrying more noble metal fine particles supported as an exhaust gas inlet, whereby particles of modified crystalline aluminosilicate are obtained. Without combining with the lower layer made of, etc., it becomes possible to effectively treat the low-temperature exhaust gas immediately after the engine start with only the noble metal fine particles. Further, if the entire washcoat is formed of modified crystalline aluminosilicate particles, the exhaust gas at a low temperature immediately after engine start can be treated more effectively due to the synergistic effect of the above two configurations. .

  According to the second aspect of the present invention, the noble metal fine particles can be carried almost simultaneously on the washcoat in the through holes of the plurality of honeycomb structures held by the holding portion of the holding member. Further, by repeatedly circulating the solution through the circulation path, the noble metal ions in the solution can be reduced and precipitated without waste as much as possible, and can be supported on the washcoat as noble metal fine particles. Therefore, according to the production apparatus of the second aspect of the present invention, there is provided a gas reaction catalyst that has high utilization efficiency of noble metal fine particles and can effectively treat low-temperature exhaust gas immediately after engine startup with only noble metal fine particles. It becomes possible to manufacture more efficiently and with high productivity.

  According to the third aspect of the present invention, the one end surface of one honeycomb structure, in which the through holes are opened, is held at a position facing the solution supply port of the circulation path member by each holding portion of the holding member. In addition, the positions of the other end surfaces of the plurality of honeycomb structures having the through holes opened are respectively opposed to the supply port at an equal distance around the one end surface of the one honeycomb structure. Therefore, the solution supplied from the supply port can be supplied to the through-holes of the honeycomb structure held in each holding portion in almost equal amounts. Therefore, according to the manufacturing apparatus of the third aspect of the present invention, substantially the same amount of the noble metal fine particles are similarly applied to the washcoat in the through holes of the plurality of honeycomb structures held by the holding portion of the holding member. The performance of each produced gas reaction catalyst can be made as uniform as possible.

(Production method of gas reaction catalyst)
In the method for producing a gas reaction catalyst of the present invention, a solution containing a noble metal ion that is a source of noble metal fine particles and a reducing agent for reducing the ions and precipitating them as noble metal fine particles is obtained. While flowing through each through hole in only one direction from the opening on the end face side to the opening on the other end face side, the noble metal ions are reduced by the action of the reducing agent to precipitate the noble metal fine particles and wash coat. It is characterized in that it is supported on the surface.

  The honeycomb structure that is the basis of the gas reaction catalyst is made of a ceramic such as cordierite, which is a composite oxide of magnesium, aluminum, and silicon, or a metal such as titanium or stainless steel, as in the past, and exhaust gas. Any structure having a large number of through-holes connecting two different end surfaces can be used.

Further, as a wash coat for covering the inner wall surface of the through hole of the honeycomb structure, alumina (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), Examples thereof include those having a porous structure formed from particles such as metal oxides such as magnesium oxide (MgO) and cerium oxide (CeO ₂ ), zeolite, and composite oxides of aluminum, zirconium and lanthanum. The washcoat is prepared by preparing a slurry containing the various particles described above, immersing the honeycomb structure in the slurry, etc., and forming a slurry layer on the inner peripheral surface of the through hole, followed by drying. It is formed so as to cover the inner wall surface.

  In addition, the washcoat may be formed of modified crystalline aluminosilicate particles described in Patent Document 1. In this case, since the entire washcoat can be formed in one step with the modified crystalline aluminosilicate particles, the productivity of the gas reaction catalyst is not lowered. In addition, as described above, coupled with supporting as much precious metal fine particles as possible in the region on the inlet side of the solution in the surface layer portion of the washcoat in the through hole, the low-temperature exhaust gas immediately after the engine is started, Even more effective processing is possible.

  As the noble metal fine particles deposited and supported on the surface of the washcoat including the porous inner surface by the reduction precipitation reaction, at least one selected from platinum, palladium, rhodium, ruthenium, iridium, gold, silver, and osmium. Fine particles made of a kind of noble metal can be mentioned. As the noble metal forming the noble metal fine particles, one or more kinds of noble metals may be selected from the above according to the components in the exhaust gas to be treated by the gas reaction catalyst.

  In order to deposit and carry noble metal fine particles on the surface of the washcoat, the solution that circulates in the through-holes of the honeycomb structure has a metal compound that serves as a noble metal ion source and a reducing agent that are common to both components. It is prepared by dissolving in a solvent, particularly water. Among these, as the metal compound serving as a noble metal ion source, any of various metal compounds that are soluble in a solvent such as water can be used.

  However, if possible, the metal compound should not contain halogen elements such as chlorine and impurity elements such as sulfur, phosphorus and boron, which may cause abnormal nucleus growth as a starting point of nucleus growth. preferable. As a result, as many precious metal fine particles as small as possible can be carried on the surface of the washcoat, thereby improving the efficiency of gas treatment. However, even when using a metal compound containing an impurity element, by adjusting the reaction conditions, etc., abnormal nucleus growth is suppressed, and as many noble metal fine particles as small as possible are supported on the surface of the washcoat. It is possible to make it.

The metal compound suitable as the ion source for the noble metal is not limited to this. For example, in the case of platinum, dinitrodiammine platinum (II) [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ], hexachloroplatinum (IV ) Acid hexahydrate [H ₂ [PtCl ₆ ] · 6H ₂ O] and the like, and dinitrodiammine platinum (II) is particularly preferable. In the case of silver, silver nitrate (I) [AgNO ₃ ], silver methanesulfonate [CH ₃ SO ₃ Ag] and the like can be mentioned, and silver nitrate (I) is particularly preferable. In the case of gold, tetrachloroauric (III) acid tetrahydrate [HAuCl ₄ · 4H ₂ O] and the like can be mentioned. In the case of palladium, palladium chloride (II) solution [PdCl ₂ ], palladium nitrate (II) solution [Pd (NO ₃ ) ₂ ], and in the case of iridium, hexachloroiridium (III) hexahydrate [2 (IrCl ₆ ) · 6H ₂ O], rhodium, rhodium (III) chloride solution [RhCl ₃ · 3H ₂ O], ruthenium, ruthenium nitrate (III) solution [Ru (NO ₃ ) ₃ ] It is done.

  As the reducing agent, any of various reducing agents capable of depositing and supporting noble metal fine particles on the surface of the washcoat by reducing noble metal ions in the metal compound can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, and transition metal element ions (trivalent titanium ions, divalent cobalt ions, and the like).

  However, in consideration of improving the efficiency of gas treatment, as described above, it is preferable to carry as many precious metal fine particles as small as possible with the individual particle diameters on the surface of the washcoat. It is effective to slow down the reduction and precipitation rate of the ions, and in order to slow down the reduction and precipitation rate, it is preferable to select and use a reducing agent having a reducing power as weak as possible.

  Examples of the reducing agent having a weak reducing power include alcohols such as methanol, ethanol and isopropyl alcohol, ascorbic acid, and the like, as well as ethylene glycol, glutathione, and organic acids (citric acid, malic acid, tartaric acid, etc.). , Reducing sugars (glucose, galactose, mannose, fructose, sucrose, maltose, raffinose, stachyose, etc.) and sugar alcohols (sorbitol, etc.). Among them, reducing sugars and sugars as derivatives thereof Alcohols are preferred. Further, when alcohol and another reducing agent are used in combination as the reducing agent, the loading ratio of the noble metal fine particles supported on the surface of the washcoat can be increased. That is, a larger number of noble metal fine particles can be carried on the surface of the washcoat to improve the efficiency of gas treatment.

  Further, in the solution, for example, various pH adjusters for adjusting the pH of the solution to a range suitable for reduction and precipitation of noble metal ions, and a viscosity adjuster for adjusting the viscosity of the solution. Additives may be added. Among these, as the pH adjuster, any of various acids and alkalis can be used. In particular, as described above, an impurity element that may cause abnormal nuclear growth as a starting point of nuclear growth is used. It is preferable to use an acid or alkali not contained. Nitric acid etc. can be mentioned as this acid which does not contain an impurity element, Ammonia water etc. can be mentioned as an alkali.

  The preferred range of the pH of the solution varies depending on the kind of precious metal fine particles to be deposited, the kind of metal compound as the ion source of the precious metal that forms the base, and the smaller the pH within the preferred range, the more There is a tendency that the particle diameter of the precious metal fine particles to be reduced becomes small. Therefore, select whether or not to add a pH adjuster, taking into account the type and particle size of the precious metal particles to be formed, the type of reducing agent to be used, and other conditions. It is preferable to do this.

  As the viscosity modifier, conventionally known various compounds can be used, and it is particularly preferable to use a polymer-based viscosity modifier. Examples of such a polymer-based viscosity modifier include, for example, amine-based polymer compounds such as polyethyleneimine and polyvinylpyrrolidone, and hydrocarbon-based polymers having a carboxylic acid group in the molecule, such as polyacrylic acid and carboxymethylcellulose. Examples thereof include molecular compounds, polyalkylene oxide polymer compounds such as polyethylene glycol, and copolymers having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule.

  The addition amount of the viscosity modifier is not particularly limited, but as the addition amount is increased, the viscosity of the solution increases and the particle size of the formed noble metal fine particles tends to be small. It is preferable to set a suitable range of the addition amount in consideration of the particle size, the type of reducing agent used and other conditions. Further, as described above, water is preferably used as a solvent for preparing the solution.

  The solution containing each of the above components is reduced while flowing through each through hole only in one direction from the opening on one end surface side to the opening on the other end surface side of the honeycomb structure under a predetermined temperature condition. When the noble metal ions are reduced by the action of the agent, the reaction mechanism described above selectively and only in the surface layer portion of the washcoat in each through hole through which the exhaust gas flows. The noble metal fine particles can be sufficiently supported up to the surface layer portion of the innermost washcoat without causing a region where the noble metal fine particles are not sufficiently supported, and the supported amount can be set on the inlet side of the through hole. Can be as much as possible in the area. Therefore, it is possible to efficiently produce a gas reaction catalyst that is excellent in the utilization efficiency of the noble metal fine particles and that can effectively treat a low-temperature exhaust gas component immediately after the engine is started, with fewer production steps.

  At this time, by adjusting the temperature and viscosity of the solution, the flow rate in the through-hole, etc., the particle size, loading amount and loading amount distribution of the noble metal fine particles carried on the surface of the washcoat are adjusted. be able to. That is, the lower the temperature of the liquid, the higher the viscosity, and the higher the flow rate, the smaller the particle size of the noble metal fine particles formed. Further, the slower the solution flow rate, the smaller the difference in the amount of noble metal fine particles supported in each through hole. Therefore, it is preferable to set the temperature, viscosity, flow rate, etc. of the liquid while taking into consideration the type and particle size of the noble metal fine particles to be formed, the distribution of the supported amount, the type of reducing agent used and other conditions.

(Production equipment for gas reaction catalyst)
FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a gas reaction catalyst production apparatus of the present invention for producing a gas reaction catalyst by the production method described above. FIG. 2 (a) is a perspective view showing an appearance of the holding member 1 for holding a plurality (seven in the figure) of the honeycomb structures H in the manufacturing apparatus, and FIG. 2 is a perspective view showing an appearance of one honeycomb structure H held by the holding member 1. FIG.

  Referring to FIG. 2 (b), the manufacturing apparatus of this example is formed in a cylindrical shape as a whole, and has a large number of through holes H1 parallel to the axial direction of the column, and each through hole. Although only one of H1 is shown in the figure, a washcoat formed in advance in the through-hole H1 of the honeycomb structure H using the honeycomb structure H opened at the end faces H2 on both sides of the cylinder. It is used for producing a gas reaction catalyst by supporting noble metal fine particles on the surface.

  Referring to FIG. 1, the manufacturing apparatus is connected to a holding portion 1 that holds a plurality of honeycomb structures H, and through holes H1 of the plurality of honeycomb structures H that are held in the holding portions 1. Circulation that constitutes a circulation path for circulating the solution L containing the noble metal ions and the reducing agent as shown by the one-dot chain line arrow in the figure, and repeatedly circulating through the through holes H1 of the honeycomb structures H. A road member 2 is provided.

  Referring to FIG. 2 (a), the holding member 1 is provided with a through hole 10 having a circular cross section as a holding part for holding one honeycomb structure H at the center. A through-hole 11 having a circular cross section, which is the same as a holding portion for holding the remaining six honeycomb structures H, is separated from the central through-hole 10 by an equal distance, and adjacent through-holes 11 are also equal to each other. The whole is formed in a columnar shape provided at a distance.

  With reference to FIG. 1, the central through hole 10 is disposed at a position of the circulation path member 2 facing the supply port 2a of the solution L, whereby the end face H2 of one honeycomb structure H is formed. It functions as a holding part for holding the circulating path member 2 at a position facing the supply port 2a of the solution L. In addition, since the other through holes 11 are arranged at an equal distance from the central through hole 10 as described above, the end face H2 of the other honeycomb structure H is arranged at an equal distance from the supply port 2a. It functions as a holding part that holds the parts at a distance. And by these functions, since the solution L supplied from the supply port 2a can be supplied almost evenly to the through holes H1 of the honeycomb structure H held in each holding portion, each of the gas reaction catalysts to be manufactured is supplied. The performance can be made uniform.

  Referring to FIG. 2 (a), the holding member 1 is provided with seven cylinders 1a having through holes 10 and 11 in a cylinder 1b having a larger diameter, and each cylinder 1a, 1b. It is formed, for example, by filling the gap 1 between them with the filler 1c. The cylinders 1a and 1b and the filler 1c can be formed of various materials. However, in order to prevent the precious metal fine particles from precipitating from the surface of these members as the starting point of precipitation, to reduce the wasteful consumption of precious metal ions in the solution L as much as possible, and to allow the reduction precipitation reaction to proceed smoothly. Considering that the entire apparatus is heated to about 60 to 100 ° C., etc., the cylinders 1a and 1b are made of resin or glass having a certain degree of heat resistance, or metal or glass coated with the resin. It is preferable to form by.

  Examples of the resin include polypropylene, polyethylene, polyethylene terephthalate, polyvinyl chloride, polyvinylidene fluoride, and polytetrafluoroethylene. In addition, as the filler 1c filled between the cylinders 1a and 1b, in consideration of ease of filling, heat resistance after filling, etc., it exhibits a liquid state before curing and has high heat resistance after curing. It is preferable to use a thermosetting resin such as a silicone resin.

  In the example shown in the figure, the cylindrical body 1a is formed such that the inner diameters of the through holes 10 and 11 are slightly larger than the outer diameter of the honeycomb structure H to be held. When the honeycomb structure H is held in the through holes 10 and 11, a pair of O-rings R are fitted and fixed between them, and the solution L does not circulate on the outer peripheral surface of the honeycomb structure H. , Only in the through hole H1.

  Specifically, two O-rings R whose inner diameter is equal to or slightly smaller than the outer diameter of the honeycomb structure H and whose outer diameter is equal to or slightly larger than the inner diameter of the through holes 10 and 11 are provided. The honeycomb structure H is used as a holding portion by preparing and inserting it into the through holes 10 and 11 in a state where the outer peripheral surface of the honeycomb structure H is fitted to the positions near the both end faces H2. Are held in the through holes 10 and 11. At the same time, the outer peripheral surface of the honeycomb structure H is blocked from the circulation path by a pair of O-rings, so that the solution L does not circulate around the outer peripheral surface and only flows through the through hole H1.

  With reference to FIG. 1, the holding member 1 has the honeycomb structure H held in the through holes 10 and 11, and the axis of the honeycomb structure H is directed in the vertical direction, and the circulation path member is disposed above and below the axis. In the state where the connection members 22 and 23 for connecting 2 are connected, they are arranged in the heating tank 3.

  The circulation path member 2 connected to the holding member 1 comes out of the storage tank 20 for storing the solution L, the pump P for circulating the solution L in the circulation path member 2, and the storage tank 20. The first pipe member 21 that reaches the connection member 22 via the pump P, the tip of which is the supply port 2a, and the second pipe member that reaches the storage tank 20 through the connection member 23 24. Among these, the storage tank 20 is connected with the reflux pipe 4 for preventing the pressure increase by connecting the inside of the storage tank 20 to the outside air while preventing the solution L from being diffused. The storage tank 20 is arranged in the heating tank 3 together with the holding member 1 and the throwing heater 5. Then, in the state where the heating tank 3 is filled with the water W, the throwing heater 5 is energized to heat the water W, so that the entire apparatus has a predetermined temperature (about 60 to 100 ° C. as described above). Is warmed.

  Among the above parts, the storage tank 20, the pipe members 21 and 24, the connection members 22 and 23, and the reflux pipe 4 that are in direct contact with the solution L deposit noble metal fine particles with the surface of these members as the starting point of precipitation. In order to prevent wasteful consumption of precious metal ions in the solution L as much as possible and to allow the reduction precipitation reaction to proceed smoothly, the entire apparatus is heated to about 60 to 100 ° C. as described above. In consideration of heating, etc., it is preferable to form with a resin having a certain degree of heat resistance, glass, or a metal or glass coated with the resin as in the case of the cylinders 1a and 1b. Also, as the pump P, it is preferable to use a pump in which a portion that is in direct contact with the solution L is coated with the resin or the like.

  In order to manufacture the gas reaction catalyst by the manufacturing method of the present invention using the above manufacturing apparatus, first, as shown in FIG. 2 (a), the O-ring R is formed in the through holes 10, 11 of the holding member 1. A plurality of honeycomb structures H (7 in the example shown in the figure as described above) are inserted and held. As the honeycomb structure H, a structure in which a wash coat is formed in advance on the inner wall surface of the through hole H1 is used. Next, as shown in FIG. 1, the connecting members 22 and 23 are connected to the upper and lower sides of the holding member 1 and installed in the heating tank 3 before filling the water W, and the connecting members 22 and 23 are connected to the connecting members 22 and 23. The road members 21 and 24 are connected.

  Further, a predetermined amount of the solution L is put in the storage tank 20, the water tank W is filled with water W, and the throwing heater 5 is energized. Then, when the entire apparatus reaches a predetermined temperature, the pump P is operated, and the solution L is circulated in order along a path indicated by a one-dot chain line arrow in the figure, thereby each honeycomb structure. The operation of circulating in the H through hole H1 only in one direction is continued for a certain time.

  Then, according to the mechanism described above, the washcoat formed in the through hole H1 of the honeycomb structure H held in the holding portion 11 of the holding member 1 is selectively selected only in the region of the surface layer portion where the exhaust gas flows. In addition, the noble metal fine particles can be sufficiently supported up to the surface layer portion of the wash coat at the inner back portion of the through hole H1 without generating a region where the noble metal fine particles are not sufficiently supported, and the amount of the noble metal fine particles can be passed through. In the region of the hole H1 on the inlet side (lower side in the figure) of the solution L, it can be increased as much as possible.

  Moreover, in the apparatus shown in the figure, the above processing can be performed simultaneously on a plurality (seven in the figure) of the honeycomb structures H held in the holding portion 11 of the holding member 1, and the holding described above. Based on the arrangement of the portions 11, the solution L supplied from the supply port 2a is supplied to the through holes H1 of the honeycomb structures H held in the holding portions 11 in substantially equal amounts, and the honeycomb structures H are supplied. Almost the same amount of noble metal fine particles can be supported in the same distribution on the washcoat in the through hole H1.

  Therefore, according to the manufacturing apparatus described above, the gas reaction catalyst capable of effectively processing the low-temperature exhaust gas component immediately after the engine is started can be more efficiently used with fewer manufacturing processes. In addition, mass production can be performed with high productivity, and the performance of each produced gas reaction catalyst can be made as uniform as possible.

  In addition, the structure of this invention is not limited to the thing of the example demonstrated above. For example, as the honeycomb structure H, in addition to the columnar shape shown in FIG. 2 (b), a prismatic shape is generally used, and the configuration of the present invention has such a prismatic honeycomb structure. Of course, it can be applied to the body and the like. In that case, what is necessary is just to change the shape of the holding | maintenance part 11 of the holding member 1, a structure, etc. according to the shape of the honeycomb structure to process. In addition, various modifications can be made without departing from the scope of the present invention.

Example 1:
As the honeycomb structure H, an alumina ceramic honeycomb (manufactured by Nagamine Manufacturing Co., Ltd.) having a columnar shape shown in FIG. 2 (b), a diameter of 3 cm, a height of 5 cm, and a diameter of the through hole H1 of 1 mm square is 7 As shown in FIG. 2 (a), each piece is prepared and fixed in the through hole 10 of the holding member 1 with a pair of O-rings R fitted together. It connected with the circulation path member 2 of the manufacturing apparatus shown in FIG.

  Next, a palladium (II) nitrate solution as a palladium compound is mixed with pure water, a polyalkylene oxide polymer compound as a viscosity modifier is added and completely dissolved, and then ethanol and fructose as a reducing agent are added. A reaction solution was prepared by adding a solution of and dissolved in pure water. The concentration of each component was palladium: 5 g / liter, polymer compound: 3062 g / liter, ethanol 300 ml / liter, fructose 5 g / liter.

  Next, 3 liters of the reaction solution is supplied to the storage tank 20 of the manufacturing apparatus shown in FIG. 1, and the pump P is operated to continuously circulate in the circulation path member 2 in one direction, and the reflux pipe. While the cooling water is continuously supplied to 4, the entire apparatus is heated to 80 ° C. by energizing the throwing heater 5 and heating the water W while the heating tank 3 is filled with the water W. The reaction was started. The flow rate for circulating the reaction solution in the circulation path member 2 was 3 liters / minute.

  Then, when 3 hours have elapsed from the start of the reaction, the circulation of the reaction solution is stopped, the honeycomb structure H is taken out from the holding member 1, and dried in the atmosphere at 50 ° C. for 12 hours to obtain the gas reaction catalyst. Manufactured.

Comparative Example 1:
Heating to 200 ° C. in a nitrogen flow with 7 of the same honeycomb structure used in Example 1 immersed in 3 liters of a solution of palladium (II) nitrate as a palladium compound in pure water Then, the gas reaction catalyst was produced by evaporating the water. The concentration of palladium in the solution was 5 g / liter.

Measurement of supported amount of palladium fine particles (Part 1):
X-ray photoelectron spectroscopy was performed on the surface layer portion of the washcoat on the inner wall of the through-hole exposed by cutting the gas reaction catalyst produced in Example 1 and Comparative Example 1 in the axial direction of the cylinder to a depth of 100 μm. The amount distribution of palladium fine particles was measured while sequentially etching from the surface by an analysis method. FIG. 3 shows the measurement results of the distribution of the loading amount in the depth direction when the loading amount of the palladium fine particles on the outermost surface of the washcoat is 1.

  From FIG. 3, it was found that in the gas reaction catalyst of Comparative Example 1, palladium fine particles could be supported only on the surface of the washcoat surface layer. Further, in the gas reaction catalyst of Comparative Example 1, palladium fine particles are deposited on the outer surface of the honeycomb structure that is not in contact with the exhaust gas, and the utilization efficiency of the palladium fine particles as the catalyst is low and wasteful. understood.

  On the other hand, it was found that in the gas reaction catalyst of Example 1, palladium fine particles can be intensively supported on the surface layer portion of the washcoat from the surface to a depth of 100 μm. Further, in the gas reaction catalyst of Example 1, the palladium fine particles are not deposited on the outer surface of the honeycomb structure that does not come into contact with the exhaust gas, and the utilization efficiency of the palladium fine particles as the catalyst is high and the waste is low. I understood.

Measurement of supported amount of palladium fine particles (part 2):
The gas reaction catalyst produced in Example 1 and Comparative Example 1 was cut in the axial direction of the cylinder, and the washcoat on the inner wall of the through hole was exposed along the length direction of the through hole, which is the axial direction of the cylinder. The amount of palladium fine particles supported at each location was measured by inductively coupled plasma (ICP) emission spectrometry to determine its distribution. FIG. 4 shows the measurement result of the supported amount distribution of palladium fine particles in the length direction of the through-hole when the supported amount of the portion with the largest supported amount in Example 1 is 1.

  From FIG. 4, in Example 1 in which the reaction solution was reduced and precipitated while flowing in only one direction within the through holes of the honeycomb structure, the amount of palladium fine particles supported could be increased on the reaction solution inlet side. understood.

Exhaust gas purification test:
The gas reaction catalyst produced in Example 1 and Comparative Example 1 is treated by flowing hydrocarbon gas (HC), carbon monoxide gas (CO), or nitrogen oxide gas (NOx) as a model gas of exhaust gas. Plotting the gas temperature and the purification rate (volume%) of the gas at that temperature when the model gas was repeatedly performed while increasing the temperature of each model gas stepwise in steps. did. In addition, the gas reaction catalyst of Example 1 was measured by setting the side with a large amount of supported palladium fine particles as the gas inlet side. Then, the lower limit value of the temperature at which 20% by volume of the gas was purified was obtained and set as the 20% purification temperature. The lower the 20% purification temperature, the more effectively the catalyst can treat the lower temperature exhaust gas components. The results are shown in FIG.

  From FIG. 5, it was found that the 20% purification temperature of each model gas in the gas reaction catalyst of Example 1 was significantly lower than that in Comparative Example 1. From this, it was confirmed that, according to the gas reaction catalyst of Example 1, it is possible to effectively treat the low-temperature exhaust gas component immediately after the engine start, as compared with Comparative Example 1.

It is a schematic sectional drawing which shows an example of embodiment of the manufacturing apparatus of the gas reaction catalyst of this invention for manufacturing a gas reaction catalyst with the manufacturing method of this invention. FIG. 4A is a perspective view showing an appearance of a holding member for holding a plurality of honeycomb structures in the manufacturing apparatus, and FIG. 4B is a diagram showing one piece held by the holding member. It is a perspective view which shows the external appearance of a honeycomb structure. The graph which shows the result of having measured the amount distribution of the palladium fine particle in the surface layer part of the washcoat of the inner wall of a through-hole from the surface to the depth of 100 micrometers among the gas reaction catalysts manufactured by the Example of this invention and the comparative example. It is. It is a graph which shows the result of having measured the carrying amount distribution of the palladium fine particle in the length direction of a through-hole of the washcoat of the inner wall of a through-hole among the gas reaction catalysts manufactured by the Example and comparative example of this invention. It is a graph which shows the 20% purification temperature of various gas in the gas reaction catalyst manufactured by the Example of this invention and the comparative example.

Explanation of symbols

H1 through-hole H honeycomb structure 1 holding member 10, 11 through-hole (holding portion)
2 Circuit member L solution

Claims (3)

  A catalyst for gas treatment of a honeycomb structure having a plurality of through-holes connecting two different end faces for allowing gas to pass through, and covering the inner wall surface of each through-hole with a wash coat on the wash coat. A method for producing a gas reaction catalyst by supporting noble metal fine particles that function as a noble metal ion that is a source of noble metal fine particles, and a reducing agent for reducing the ions and precipitating them as noble metal fine particles. By reducing the noble metal ions by the action of the reducing agent while flowing the solution containing the honeycomb structure in one direction from the opening on one end surface side of the honeycomb structure to the opening on the other end surface. A method for producing a gas reaction catalyst, comprising precipitating fine metal particles and supporting them on a washcoat.   It is an apparatus for implementing the manufacturing method of the gas reaction catalyst of Claim 1, Comprising: The holding member which has a holding part which hold | maintains several honeycomb structure separately, and the plurality hold | maintained at the holding part of this holding member A solution containing noble metal ions and a reducing agent is connected to a large number of through holes in the honeycomb structure of the honeycomb structure from one end side opening to the other end side opening of the honeycomb structure in only one direction. An apparatus for producing a gas reaction catalyst, comprising: a circulation path member that constitutes a circulation path for repeatedly circulating the inside of each through hole. The holding member includes a holding portion that holds one end surface of one of the plurality of honeycomb structures, in which the through-holes are opened, at a position facing the solution supply port of the circulation path member. A holding unit that holds one end face of each of the plurality of honeycomb structures, each having a through hole, at a position around the one end face of the one honeycomb structure and facing the supply port at an equal distance. An apparatus for producing a gas reaction catalyst according to claim 2.

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