JP6826000B2 - Manufacturing method of catalyst for exhaust gas purification - Google Patents

Description

The present invention relates to a catalyst for purifying exhaust gas and a method for producing the same.

Conventionally, as a catalyst for purifying exhaust gas mounted on automobiles, etc., in order to purify harmful gases (hydrogen (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc.) contained in the exhaust gas. , Three-way catalysts, oxidation catalysts, NOx storage reduction catalysts, etc. have been developed.

As such an exhaust gas purification catalyst, for example, in Japanese Patent Application Laid-Open No. 2000-246103 (Patent Document 1), after a noble metal is supported on carbon black (a solid substance gasified by combustion) to form a noble metal carrier. , The carrier source and the noble metal carrier are mixed in a solution, then a carrier precursor containing the noble metal carrier is synthesized from the carrier source, and the obtained carrier precursor is heat-treated to form a porous oxide carrier. A method of obtaining a catalyst for purifying exhaust gas by burning carbon black contained in the noble metal carrier while forming the above, and a catalyst for purifying exhaust gas obtained by the method are specifically disclosed by Examples and the like. However, the conventional exhaust gas purification catalyst as described in Patent Document 1 is not sufficient in terms of catalytic activity.

Japanese Unexamined Patent Publication No. 2000-246103

The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to efficiently manufacture an exhaust gas purification catalyst capable of having a higher catalytic activity and an exhaust gas purification catalyst thereof. It is an object of the present invention to provide a possible method for producing an exhaust gas purification catalyst.

As a result of diligent research to achieve the above object, the present inventors have made the exhaust gas purification catalyst composed of a molded body of metal oxide particles and having macropores having an average pore diameter of 0.5 to 20 μm. When the carrier and the noble metal supported on the carrier are provided and the distribution state of the noble metal supported on the carrier is confirmed using an electronic probe microanalyzer, the amount of the noble metal supported at all measurement points is measured. At the measurement point of the total region of the region of 3 μm from the wall surface of the macro hole toward the carrier side and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole with respect to the average value (A). We have found that it is possible to exert a higher level of catalytic activity by making the average value (B) of the supported amount of the noble metal 1.1 times or more, and have completed the present invention.

The method for producing an exhaust gas purification catalyst of the present invention includes a step of supporting a noble metal on a fibrous pore-forming material having an average diameter of 0.7 to 15 μm to obtain a noble metal-supported pore-forming material.
A step of mixing the noble metal-supported metal oxide particles and the noble metal-supported pore-forming material to obtain a catalyst slurry, and
By firing after molding the catalyst slurry, precious metal Li Kui average pore diameter such from the molded body of the metal oxide particles are supported on a carrier and the carrier that have a macropores of 0.5~20μm When the distribution state of the noble metal supported on the carrier is confirmed by using an electron probe microanalyzer, the macropores are based on the average value (A) of the amount of noble metal supported at all measurement points. The average value (B) of the amount of the noble metal supported at the measurement point of the total region of the region of 3 μm from the wall surface toward the carrier side and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole is 1. .The process of obtaining a catalyst for purifying exhaust gas, which is more than 1 time , and
It is a method characterized by including.

In the method for producing an exhaust gas purification catalyst of the present invention, the content of the noble metal in the noble metal-supported pore-forming material is preferably 10% by mass or more of the total amount of the noble metal in the exhaust gas purification catalyst . Further, in the method for producing an exhaust gas purification catalyst of the present invention, the metal oxide particles are metal oxide particles in which 90% by mass or less of the total amount of noble metals in the exhaust gas purification catalyst is supported. preferable.

The reason why the above object is achieved by the exhaust gas purification catalyst of the present invention is not always clear, but the present inventors presume as follows. That is, first, the present inventors have conducted intensive studies to achieve the above object, and the exhaust gas purification catalyst described in Patent Document 1 utilizes carbon black as a solid substance that is gasified by combustion during production. Therefore, it has been found that the pores have a size of about several tens of nm to several hundreds of nm, and the gas diffusivity is low, so that the catalytic activity is not sufficient. Therefore, in the present invention, the carrier used for the catalyst is a carrier made of a molded body of metal oxide particles and having macropores having an average pore diameter of 0.5 to 20 μm. By using a carrier having such macropores, the diffusibility of the gas into the catalyst is dramatically improved by using the macropores as the main gas flow path, and as a result, a higher level of catalytic activity is exhibited. The inventors infer. Further, in the catalyst for purifying exhaust gas of the present invention, a noble metal is supported on the carrier, but when the distribution state of the noble metal supported on the carrier is confirmed by using an electron probe microanalyzer, the distribution state of the noble metal supported on the carrier is confirmed at all measurement points. With respect to the average value (A) of the amount of the noble metal supported, the total of the region of 3 μm from the wall surface of the macro hole toward the carrier side and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole. The average value (B) of the amount of noble metal supported at the measurement point in the region is 1.1 times or more. As described above, the concentration of the noble metal supported near the wall surface of the macropores of the carrier is higher than the concentration of the noble metal supported on other parts (in other words, the noble metal is the wall surface of the macropores of the carrier. Since it is selectively supported in the vicinity), the chances of contact between the gas diffused through the macropores and the noble metal are further increased, and the catalytic activity is further improved accordingly. Those guess.

According to the present invention, there is provided an exhaust gas purification catalyst capable of having a higher catalytic activity and a method for producing an exhaust gas purification catalyst capable of efficiently producing the exhaust gas purification catalyst thereof. Is possible.

It is a schematic diagram which shows typically the state of the cross section of the carrier around the part where the opening of a macro hole is formed. It is a figure which shows an example (one Embodiment) of the reflected electron image of the surface of a carrier measured by EPMA. It is a part of the EPMA measurement result for the exhaust gas purification catalyst (coat layer) obtained in Reference Example 1, and (a) is a reflected electron image of the catalyst surface measured by EPMA and in the reflected electron image. A graph showing the concentration of Pd at the measurement site of the line analysis shown in is shown in (b), and (b) is a diagram showing an image showing the distribution state of palladium (Pd) at the site of the backscattered electron image. With respect to the graph of the concentration of Pd shown in FIG. 3A, it is an enlarged graph showing the region X shown by the dotted line in FIG. 3A. Is a graph showing a reference example 1-2, until conversion to Example 1 and the exhaust gas purifying catalyst obtained in Comparative Example 1 to 3 CO ₂ reaches approximately 50% of the time _(CO 2 -T50) ..

Hereinafter, the present invention will be described in detail according to its preferred embodiment.

[Catalyst for purifying exhaust gas]
First, the exhaust gas purification catalyst of the present invention will be described. The catalyst for purifying exhaust gas of the present invention comprises a carrier made of a molded body of metal oxide particles and having macropores having an average pore diameter of 0.5 to 20 μm.
The precious metal supported on the carrier and
When the distribution state of the noble metal supported on the carrier is confirmed by using an electron probe microanalyzer, the macropores of the macropores are based on the average value (A) of the amount of noble metal supported at all measurement points. The average value (B) of the amount of noble metal supported at the measurement points in the total region of the region 3 μm from the wall surface toward the carrier side and the region 1 μm from the wall surface of the macro hole toward the void side of the macro hole is 1. It is characterized by being 1 times or more.

The metal oxide particles constituting such a carrier are not particularly limited, and particles made of known metal oxides that can be used as a carrier for an exhaust gas purification catalyst or the like can be appropriately used. Examples of such metal oxide particles include aluminum oxide (Al ₂ O ₃ , alumina), cerium oxide (CeO ₂ , ceria), zirconium oxide (ZrO ₂ , zirconia), silicon oxide (SiO ₂ , silica), and the like. Examples thereof include porous oxide particles composed of oxides such as yttrium oxide (Y ₂ O ₃ , itria) and neodymium oxide (Nd ₂ O ₃ ) or composite oxides thereof. Among such metal oxide particles, aluminum oxide, cerium oxide, and zirconium oxide are preferably used, and aluminum oxide is particularly preferable, from the viewpoint of interaction with a noble metal (maintenance of an active state). Further, as such metal oxide particles, those on which a noble metal is supported may be used.

The average particle size of the metal oxide particles constituting such a carrier is not particularly limited, but is preferably 1 to 10 μm, and more preferably 3 to 8 μm. If the average particle size is less than the lower limit, the molded body tends to be dense and the gas diffusibility tends to decrease, while if it exceeds the upper limit, the molded body tends to be brittle and the strength tends to be insufficient. Such an average particle size can be obtained by measuring the particle size distribution of the slurry. For example, a slurry is prepared using the metal oxide particles to be measured, the particle size distribution of the slurry is obtained using a particle size distribution measuring device using a laser diffraction method, and the arithmetic mean diameter of the particles is averaged from the result. It may be obtained by calculating as a particle size.

The form of the molded body of the metal oxide particles is not particularly limited, and may be, for example, a coat layer supported on a base material, pellets, agglomerates of particles, or the like, depending on the desired design. , The form can be changed as appropriate. When supported on a base material, the base material is not particularly limited, and a known base material that can be used as a base material for an exhaust gas purification catalyst can be used.

Further, the carrier made of a molded body of such metal oxide particles has macropores having an average pore diameter of 0.5 to 20 μm. If the average pore diameter is less than the lower limit, the diffusibility of the gas is lowered and a sufficiently high level of catalytic activity cannot be achieved. On the other hand, if the average pore diameter exceeds the upper limit, the strength of the molded product is lowered. In addition, since the bulk of the molded body becomes larger than necessary, there are problems such as a large pressure loss when a catalyst coated on a carrier having a honeycomb structure is prepared. Further, the average pore diameter of the macropores contained in such a carrier is preferably 1 to 10 μm, more preferably 2 to 10 μm, because a higher effect can be obtained in terms of gas diffusion. It is more preferably 3 to 10 μm, and particularly preferably 3 to 10 μm. It should be noted that such macropores can be easily formed in a molded body of metal oxide particles by using, for example, a pore-forming material described later as a template. Moreover, the average pore diameter of the macropores contained in such a carrier can be measured as follows. That is, the average pore diameter of the macropores is, for example, using an electron probe microanalyzer (EPMA: for example, trade name "JXA-8500F" manufactured by Nippon Denshi Co., Ltd.) as a measuring device to first set a region of 50 μm square. As one visual field, 50 μm square reflected electron images are measured (plane analysis) for each of a plurality of arbitrary measurement visual fields (measurement regions), and based on all the obtained reflected electron images (surface analysis results of all measurement visual fields). , For any 20 or more pores (macropores), the length of each pore is the longest in the longitudinal direction of the pore opening (when the length of the pore opening is measured in all directions). The maximum length of the opening of the pore in the direction perpendicular to the lengthening direction (the maximum length of the opening of the pore in the direction perpendicular to the longitudinal direction) is the maximum length of each pore. It can be measured by measuring as the diameter of the above and calculating the average of the diameter (the maximum length). In particular, when the macropores are formed by using the fibrous pore-forming material described later as a template, the pores (macro) confirmed on the surface of the carrier in the reflected electron image by EPMA. Since the opening of the hole) basically has an elongated shape so that the longitudinal direction can be confirmed, the length of the opening of the pore in the direction perpendicular to the longitudinal direction is adopted by adopting the above-mentioned measurement method. The average pore diameter can be obtained by mimicking the maximum length of the template with the diameter of the pores. In addition, such a method of measurement by an electron probe microanalyzer (EPMA) is adopted in, for example, a method of confirming the distribution state of a noble metal supported on a carrier by using an electron probe microanalyzer (EPMA) described later. By adopting the same conditions as the conditions (conditions such as device and acceleration voltage), it is possible to adopt a method of measuring the reflected electron image in any plurality of measurement fields. For such an average pore diameter, for example, using SEM, X-ray CT, or the like as a measuring device, a cross-sectional image or a three-dimensional image of the molded body is measured to calculate the length of a portion corresponding to the diameter. You can also check by doing.

The average aspect ratio of the pores of such a carrier is preferably in the range of 9 to 40, more preferably in the range of 9 to 30, and particularly preferably in the range of 9 to 28. .. If the average aspect ratio is less than the lower limit, the gas diffusivity tends to be insufficient, while if it exceeds the upper limit, the diffusivity becomes too large, so that the gas passes through without contacting the catalytic active site. There is a tendency that sufficient catalytic performance cannot be obtained due to an increase in the proportion of gas. As described above, when the average aspect ratio of the pores is within the above range, the balance between gas diffusivity and catalytic performance tends to be further improved. The average aspect of such pores can be obtained by using an electron probe microanalyzer (EPMA: for example, a trade name "JXA-8500F" manufactured by JEOL Ltd.) with a 50 μm square region as one field of view. Each 50 μm square reflected electron image is measured (surface analysis) for the measurement field (measurement area), and based on all the obtained reflected electron images (surface analysis results of all measurement fields), any 20 or more points are fine. For the pores (macropores), the value (aspect ratio) of "the length of the opening of the pore in the longitudinal direction / the maximum length of the opening of the pore in the direction perpendicular to the longitudinal direction" for each pore. Can be obtained by finding and averaging.

As such a carrier, the specific surface area is preferably 10 m ² / g or more, and more preferably 50 m ² / g or more. If the specific surface area is less than the lower limit, it tends to be difficult to support the noble metal in the macropore portion (the portion near the pore wall of the macropore) in a highly dispersed manner. Such a specific surface area can be calculated as a BET specific surface area from the adsorption isotherm of nitrogen gas using the BET isotherm adsorption formula. For the adsorption isotherm, the carrier is cooled to the liquid nitrogen temperature (-196 ° C.), nitrogen gas is introduced, the adsorption amount is determined by the constant volume method (gas adsorption method) or the gravimetric method, and then the nitrogen to be introduced is introduced. It can be obtained by gradually increasing the gas pressure and plotting the amount of nitrogen gas adsorbed for each equilibrium pressure.

The noble metal supported on the carrier is not particularly limited, but platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au), silver (Ag), iridium (Ir) and ruthenium (Ru). It is preferable to use at least one selected from the group consisting of). Among these, at least one selected from the group consisting of Pt, Rh, Pd, Ir and Ru is more preferable, and at least one selected from the group consisting of Pt, Rh and Pd is particularly preferable from the viewpoint of catalytic performance.

Further, in the present invention, when the distribution state of the noble metal supported on the carrier is confirmed using an electron probe microanalyzer (EPMA), the average value (A) of the amount of the noble metal supported at all measurement points is relative to the average value (A). , The average value of the amount of noble metal supported at the measurement points in the total region of the region 3 μm from the wall surface of the macropore toward the carrier side and the region 1 μm from the wall surface of the macropore toward the void side of the macropore. B) needs to be 1.1 times or more. As described above, the condition that the average value (B) of the carried amount of the noble metal is 1.1 times or more the average value (A) of the carried amount of the noble metal is a region of 3 μm from the wall surface of the macropore toward the carrier side. This means that the amount (concentration) of the noble metal present in the total region of 1 μm from the wall surface of the macropore to the void side of the macropore is higher than that of other portions. In the present invention, since the amount of the noble metal near the wall surface of the macropore, which is the main flow path of the gas, is larger than that of other positions on the carrier, the contact frequency between the gas and the noble metal, which is the catalytically active point, is large. Can be further enhanced, which makes it possible to obtain a higher level of catalytic activity. Hereinafter, such a method for measuring the average value (A) and the average value (B) (a method for confirming the distribution state of the noble metal supported on the carrier using an electron probe microanalyzer (EPMA)) will be described with reference to the drawings. explain.

Here, in explaining the method of measuring the average values (A) and (B), first, using FIG. 1, a region of 3 μm from the wall surface of the macro hole toward the carrier side and the macro hole. The total area including the area of 1 μm from the wall surface toward the void side of the macro hole will be briefly described. FIG. 1 schematically shows the state of the carrier S and the noble metal N existing in the peripheral portion of the portion where the opening O of the macro hole is formed, and shows the portion in the vicinity of the opening O of the macro hole of the carrier S. It is a schematic diagram of a cross section. In the figure, P indicates the wall surface (pore wall) of the macro hole, which is the boundary portion between the carrier S and the opening O (void portion) of the macro hole, and the arrow D1 indicates the wall surface of the carrier S on the left side of the figure. The direction on the carrier side with respect to P is indicated, and the arrow D2 indicates the direction on the void side of the macropore with respect to the wall surface P of the carrier S on the left side of the drawing. In the present invention, referring to the support S on the left side in FIG. 1, the total area includes an area A ₁ of 3μm towards the carrier side (D1 direction) from the wall surface P of the macropores, the wall surface P of macropores It becomes a region (A ₁ + A ₂ ) combined with the region A _{2 of} 1 μm toward the void side (D2 direction) of the macro hole. Then, in measuring the average values (A) and (B), first, regarding the carrier S carrying the noble metal N, an electron probe microanalyzer (EPMA: for example, a trade name "JXA-8500F" manufactured by JEOL Ltd. ”), Acceleration voltage: 10 KV, sample current: 100 nA, beam diameter: 1 μm or less, one field of view is 50 μm square, and each surface in any plurality of measurement fields (measurement areas). The analysis is performed, and a 50 μm square backscattered electron image is measured for each measurement field. In such surface analysis, the sizes of all measurement points (pixels: pixels) are analyzed as 200 nm in length × 200 nm in width (200 nm square). By such measurement, the number (total number) of the number of measurement points (pixels: pixels) in the obtained reflected electron image is 62500 (250 pixels x 250 pixels), and each of the measurement points (pixels) in the reflected electron image is obtained. At the position, data on the concentration of the noble metal can be obtained. The concentration of the noble metal for each measurement point (pixel: pixel) mentioned here is the ratio of the noble metal to all the elements (all elements including the noble metal) existing at each measurement point, and when confirming the distribution state of the noble metal, , The concentration can be directly replaced with the amount of precious metal for each measurement point. Then, for each measurement field (each reflected electron image), the total number of measurement points (62,500 points) and the total amount of precious metals at all the measurement points are obtained, and the total is calculated as the total number of the measurement points (62500 points). By dividing, the "average value (a) of the amount of precious metal carried" at all the measurement points (62,500 points) can be obtained for each measurement field (reflected electron image). Then, by using the "average value (a) of the amount of precious metal carried" obtained for each measurement field (all measurement areas), the average of the average value (a) is calculated to "support the precious metal". The average value (A) of the quantity can be obtained. As described above, in the present invention, the average value of the average value (a) is adopted as the "average value (A) of the amount of the noble metal supported". From such a measurement method, it can be said that the "mean value (A) of the supported amount of precious metal" is a value obtained as a result of surface analysis. Next, for all the measurement visual fields (measurement regions) for which the above-mentioned "mean value (a) of the amount of precious metal carried" was obtained, the reflected electron image (EPMA analysis result) obtained as the measurement result for each measurement visual field. ) Is used for line analysis. Such line analysis is performed by measuring an arbitrary three or more line-shaped regions for each measurement field of view (measurement region: the reflected electron image). In such line analysis, it is necessary to select a part (measurement line) to be measured so that a part of the line to be analyzed always passes over the opening O of the pores, and the opening O is Sites that do not exist (sites that can measure only the surface of the carrier) are not selected as sites for line analysis. In such line analysis, acceleration voltage: 10 KV, sample current: 100 nA, beam diameter: 1 μm or less, using an electron probe microanalyzer (EPMA) for each measurement field (measurement area: the reflected electron image). The line analysis is performed on any three or more line-shaped regions under the condition that the length of the line to be analyzed is 50 μm. Further, in such line analysis, data on the concentration of precious metal is obtained for each measurement point (size: 200 nm square, total number: 250 pixels) on the line. Then, the macro from the results of such line analysis, a measurement point on the measurement line of the line analysis and toward the wall surface P of the macropores in the support side region A ₁ of 3μm from the wall surface P of the macropores The number of measurement points in the total region (A ₁ + A ₂ ) with the region A _{2 of} 1 μm toward the void side of the hole and the amount of precious metal for each measurement point in the total region (A ₁ + A ₂ ), respectively. Ask. Then, from the results of line analysis of all measurement visual fields (all reflected electron images), the total number of measurement points existing in the total region (A ₁ + A ₂ ) in all measurement visual fields (total number A: total). and a measuring point on the entire measurement line and the total area in the measurement field (a 1 _{+ a 2)} the total number of the number of measurement points present in), the total area of all the measurement field of view (a 1 ₊ a ₂ ) All measurement points (measurement points on all measurement lines in all measurement fields and measurement points existing in the total region (A ₁ + A ₂ )) are calculated as the sum of the amounts of precious metals. By dividing the total by the total number A, the total of the region of 3 μm from the wall surface of the macro hole toward the carrier side and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole. The "average value (B) of the amount of noble metal carried" at the measurement point in the region can be obtained. In this way, from the results of line analysis of all measurement fields (all reflected electron images), all the total regions (A ₁ + A ₂ ) existing on all measurement lines in all measurement fields are present. The number of measurement points (total number A) and the total amount of precious metals at all measurement points existing in all the total regions (A ₁ + A ₂ ) on all measurement lines in all measurement fields are calculated. By calculating the average amount of noble metals ([total amount of the noble metals] / [total number A]), the "average value (B) of the amount of noble metals carried" can be obtained. In this way, the "mean value (B) of the amount of noble metal carried" is the average value of the amount of noble metal at all measurement points in the total area (A ₁ + A ₂ ) on all measurement lines in all measurement fields. From the results of all line analysis of all measurement fields, the amount of precious metal at all measurement points in the total area (A ₁ + A ₂ ) of all measurement fields is calculated, and the average value of the amount of precious metal is calculated. Is the value to be. In this way, using the measurement results (results of surface analysis, results of line analysis) of the entire measurement field of view (total reflected electron image), the "mean value (A)" and "mean value" are as described above. (B) ”can be obtained respectively.

The measurement of the average value (A) and the average value (B) will be further described with reference to FIG. FIG. 2 shows a reflected electron image (250 pixels) measured when surface analysis is performed using EPMA on an arbitrary region (one of the measurement fields of view) having a length of 50 μm and a width of 50 μm on the surface of the carrier. It is a drawing showing one form (× 250 pixels) (note that the black-filled area in the drawing is the opening O of the macro hole). As described above, FIG. 2 is a form of a reflected electron image (250 pixels × 250 pixels) obtained when one field is surface-analyzed with a size of 50 μm square, and in the measurement of the reflected electron image by EPMA, , Data on the concentration of noble metal can be obtained at each position of each pixel (each pixel) forming the image. Then, from the result of such surface analysis (reflected electron image), the total number of measurement points (62,500 points) in the reflected electron image and the total amount of precious metal at the measurement points are obtained, and the measurement region (reflected electrons) is obtained. The "mean value (a) of the amount of noble metal carried" at all the measurement points in the image) can be obtained. Then, in the present invention, the "average value (a) of the amount of the noble metal carried" is obtained for each of a plurality of arbitrary measurement fields (measurement regions), and the average value (a) of all the measurement regions (all measurement fields) is obtained. ), The “average value (A) of the amount of precious metal carried” can be obtained. Further, in the present invention, in order to obtain the "mean value (B) of the amount of the noble metal supported", as described above, line analysis is performed in each measurement field of view for which the mean value (a) is obtained. In such a line analysis, in the backscattered electron image (one field of view), regions on any three or more lines as measurement lines (in the form shown in FIG. 2, line L1 _and line L). _2. Arbitrary ₃ lines of line L3, length of each line: 50 μm) is selected. Thus, based on the measurement result of the reflected electron image, the line L ₁ as any measurement region of line analysis (line _measuring), the line L _2, if you select the line L _3, FIG. 2 (250 × 250 In the reflected electron image shown in (pixels), the number of measurement points (pixels: pixels) for each line (for each measurement site) is 250 (the size of each pixel is 200 nm square), and these measurements are taken. Since the noble metal concentration data can be obtained for each point, based on the data, the total region (A ₁ + A _{2) of the} region A ₁ and the region A ₂ on the line is obtained for each line L _{1 to} L _3. The number of measurement points (measurement points on the line) in) and the amount of precious metal for each measurement point (measurement point on the line) in the total area (A ₁ + A ₂ ) can be obtained. Then, such line analysis is performed in each measurement field, and from the results of measurement (line analysis) in all measurement fields, the total area (A ₁₎ existing on all measurement lines in all measurement fields is obtained. The total number of measurement points in + A ₂ ) (total number A) and the precious metal of all measurement points in the total area (A ₁ + A ₂ ) existing on all measurement lines in all measurement fields. By obtaining the total amount of the above and dividing the total by the total number A, the "average value (B) of the amount of precious metal carried" can be obtained. In this way, the "average value of the amount of the noble metal supported (A)" and the "average value of the amount of the noble metal supported (B)" can be obtained.

In the present invention, as described above, the average value (B) of the amount of noble metal supported needs to be 1.1 times or more the average value (A) of the amount of noble metal supported. Further, in the present invention, the average value (B) of the supported amount of the noble metal is more preferably 1.1 to 5.5 times the average value (A) of the supported amount of the noble metal, and 1.15 to 1.15. It is more preferably 5.5 times, and particularly preferably 1.2 to 4.0 times. If the ratio of the average value of the amount of the noble metal supported (B) to the average value (A) of the amount of the noble metal supported is less than the lower limit, the effect of selectively supporting the noble metal in the gas flow path tends to be small. On the other hand, if the upper limit is exceeded, the loading density of the noble metal becomes excessive, the particle size of the noble metal tends to increase, and the activity tends to decrease.

In the present invention, the amount of the noble metal supported is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, and 0.03 to 2 parts by mass with respect to 100 parts by mass of the carrier. It is particularly preferable that it is by mass. If the amount of the noble metal supported (total amount) is less than the lower limit, the active sites tend to be insufficient and the activity tends not to be exhibited. On the other hand, if the amount exceeds the upper limit, the grain growth of the noble metal is promoted and the cost is increased. There is a tendency.

Such an exhaust gas purification catalyst of the present invention can be in various forms depending on the form of the molded body of the carrier. For example, it may be in the form of a base material and a catalyst component (catalyst for purifying exhaust gas) supported as a coat layer formed on the surface of the base material. The base material is not particularly limited, and a known base material that can be used as a base material for an exhaust gas purification catalyst can be used, and a honeycomb-shaped base material can be preferably used. The honeycomb-shaped base material is not particularly limited, and a known honeycomb-shaped base material that can be used as a base material for an exhaust gas purification catalyst can be used. Specifically, a honeycomb-shaped monolith group can be used. Materials (honeycomb filter, high-density honeycomb, etc.) are preferably used. Further, the material of such a base material is not particularly limited, and a base material made of ceramics such as cordierite, silicon carbide, silica, alumina, and mullite, and a base material made of a metal such as stainless steel containing chromium and aluminum are preferable. Will be adopted by. Among these, cordierite is preferable from the viewpoint of cost.

Further, as the exhaust gas purification catalyst of the present invention, the porosity of the macropores is preferably 2 to 30% by volume, more preferably 5 to 20% by volume. If such a porosity is out of the above range, the catalytic activity tends to decrease. The porosity (volume%) of the macropores of such a catalyst can be determined, for example, when a catalyst for purifying exhaust gas is formed using a pore-forming material (fibrous pore-forming material) described later. Based on the amount of particles used and the amount of fibrous porosity used, based on the specific gravity of each component when the specific gravity of the fibrous porosity is 1, the fibrous porosity incorporated into the particles during production. It can be estimated by obtaining the total volume of the portion occupied by the macropores and regarding the value as the volume of the void portion of the macropore (the volume of the pores). Further, the porosity (volume%) of the macropores of such a catalyst can be measured by obtaining the volume of the corresponding pores by a mercury porosimeter or a gas adsorption measurement method. The void ratio (volume%) of the macropores should be confirmed by analyzing the cross-sectional image from the three-dimensional information of the macropores obtained by FIB-SEM (Focused Ion Beam-Scanning Electron Microscope) or X-ray CT. You can also.

Further, in the form of a coat layer in which the catalyst for purifying exhaust gas of the present invention is supported on a base material, the average thickness of the coat layer is preferably 20 to 300 μm, more preferably 50 to 200 μm. If the average thickness is less than the lower limit, the amount of catalyst is insufficient and the activity tends not to be obtained. On the other hand, if the average thickness exceeds the upper limit, the gas flow path is narrowed and the pressure loss is increased, or the lower part of the coat layer is formed. The gas tends not to diffuse. The term "thickness" as used herein refers to the length in the direction perpendicular to the center of the flat portion of the base material of the coat layer. Such a thickness is determined by determining the catalyst coat layer by scanning electron micrograph (SEM) observation, optical microscope observation, or the like, and measuring the thickness of any 10 or more portions to obtain "average thickness". Can be measured by calculating the average value of its thickness.

Further, in the form of a coat layer in which the exhaust gas purification catalyst of the present invention is supported on a base material, the coating amount of the catalyst on the base material (amount of the coat layer) is 20 to 300 g / L (amount of the coat layer) per unit volume of the base material. More preferably, it is in the range of 50 to 250 g / L). If the coating amount is less than the lower limit, the catalytic activity performance tends not to be sufficiently obtained, while if it exceeds the upper limit, the pressure loss tends to increase and the fuel consumption tends to decrease.

Further, the exhaust gas purification catalyst of the present invention may contain other components as long as the effects of the present invention are not impaired. As such other components, other metal oxides, additives and the like used in the exhaust gas purification catalyst can be used. Specific examples of such other components include alkali metals such as potassium (K), sodium (Na), lithium (Li), and cesium (Cs), barium (Ba), calcium (Ca), and strontium ( Examples thereof include alkaline earth metals such as Sr), rare earth elements such as lanthanum (La), ittrium (Y) and cesium (Ce), and transition metals such as iron (Fe).

Further, the exhaust gas purification catalyst of the present invention may be used in combination with other catalysts. Such other catalysts are not particularly limited, and are known catalysts (for example, in the case of an automobile exhaust gas purification catalyst, an oxidation catalyst, a NOx reduction catalyst, a NOx storage reduction catalyst (NSR catalyst), and a dilute NOx trap. A catalyst (LNT catalyst), NOx selective reduction catalyst (SCR catalyst), etc.) may be used as appropriate.

Regarding the effect when the catalyst for purifying exhaust gas of the present invention is used for purifying exhaust gas, pores (macropores) having an average pore diameter of 0.5 to 20 um serve as a main gas flow part. The gas is more diffusible into the macropores than the other parts, and the gas is more diffusible into the catalyst, and the catalyst selectively acts on the wall surface of the macropores than the other parts. Since the noble metal is supported at a high concentration, the chance of contact between the gas and the noble metal can be further increased, as compared with the catalyst in which the noble metal is uniformly dispersed and supported (distributed) throughout the carrier. The present inventors speculate that it is possible to make the catalytic activity more advanced. Further, in the exhaust gas purification catalyst of the present invention, as described above, the diffusibility of the gas into the catalyst is high and the chance of contact between the gas and the noble metal is further increased. Therefore, the sensitivity to changes in the gas atmosphere is particularly high. The present inventors speculate that it is possible to achieve a higher level. Further, as described above, in the exhaust gas purification catalyst of the present invention, since the noble metal is selectively supported in the macropores so as to further improve the contact opportunity between the gas and the noble metal, the utilization efficiency of the noble metal is improved. The present inventors speculate that it is possible to further reduce the amount of precious metal used and the catalyst physique.

[Manufacturing method of catalyst for exhaust gas purification]
Next, a method for producing the exhaust gas purification catalyst of the present invention will be described. The method for producing an exhaust gas purification catalyst of the present invention includes a step (I) of supporting a noble metal on a fibrous pore-forming material having an average diameter of 0.7 to 15 μm to obtain a noble metal-supported pore-forming material.
The step (II) of mixing the metal oxide particles and the noble metal-supported pore-forming material to obtain a catalyst slurry, and
The step (III) of obtaining the catalyst for exhaust gas purification of the present invention comprising a carrier made of a molded body of metal oxide particles and a noble metal supported on the carrier by molding the catalyst slurry and then firing the catalyst slurry.
It is a method characterized by including. Hereinafter, each step will be described separately.

<Step (I) of obtaining a noble metal-supported pore-forming material>
Such a step (I) is a step of supporting a noble metal on a fibrous pore-forming material having an average diameter of 0.7 to 15 μm to obtain a noble metal-supported pore-forming material.

As described above, in the present invention, the fibrous pore-forming material is used. Then, after supporting the noble metal on such a fibrous pore-forming material, the noble metal is contained in the catalyst slurry, and at least a part of the fibrous pore-forming material is removed by firing in a subsequent step to form a fibrous material. It is possible to form voids having the same shape as the pore material inside the molded body of the metal oxide particles, and further, the noble metal supported on the fibrous pore-forming material is formed in the molded body of the metal oxide particles. It is possible to carry (transfer) the pore-forming material in the vicinity of the site where the pore-forming material was present. In the present invention, the noble metal is selectively supported in the vicinity of the portion where the noble metal-supporting pore-forming material was present in this way. As described above, the fibrous pore-forming material is used as a template for forming macropores and as a material for selectively supporting a noble metal in the vicinity of the pore wall of the macropores. To. Therefore, such a fibrous pore-forming material can be used as a template for forming pores in a molded body such as an aggregate of metal oxide particles, and supports a noble metal. A fibrous organic substance that can be produced is preferable, and the type thereof is not particularly limited.

Examples of such fibrous pore-forming materials include polyethylene terephthalate (PET) fibers, acrylic fibers, nylon fibers, rayon fibers, and cellulose fibers. Among such fibrous pore-forming materials, it is preferable to use at least one selected from the group consisting of PET fibers and nylon fibers from the viewpoint of the balance between processability and firing temperature.

Further, the fibrous pore-forming material according to the present invention needs to have an average diameter (average fiber diameter) of 0.7 to 15 μm. If the average diameter of the fibrous pore-forming material is less than the lower limit, macropores cannot be formed, and the catalytic performance of the obtained exhaust gas purification catalyst deteriorates. On the other hand, if the average diameter exceeds the upper limit, the obtained catalyst If the bulk of the pores becomes larger than necessary, or if the amount of the fibrous pore-forming material added is reduced in order to prevent the bulk from becoming larger, the function of the formed pores as a gas flow path deteriorates. It ends up. The average diameter of the fibrous pore-forming material (average fiber diameter) is preferably in the range of 1 to 12 μm, preferably in the range of 2 to 10 μm, from the viewpoint of the size of the range suitable for gas diffusivity. It is particularly preferable to be inside. Such an average diameter (average fiber diameter) can be obtained by randomly extracting 50 or more fibrous pore-forming materials, measuring the fiber diameters of these fibrous pore-forming materials, and averaging them.

Further, as the fibrous pore-forming material used in such a catalyst slurry preparation step, the average aspect ratio is preferably in the range of 9 to 40, more preferably in the range of 9 to 30, and 9 to 30. It is particularly preferably in the range of 28. If the average aspect ratio is less than the lower limit, the permeability of the pores becomes insufficient, so that the gas diffusivity tends to be insufficient. On the other hand, if the average aspect ratio exceeds the upper limit, the diffusivity becomes too large. , The proportion of gas that passes through without contacting the catalytic active site increases, and there is a tendency that sufficient catalytic performance cannot be obtained. When the average aspect ratio is within the above range, the balance between gas diffusivity and catalytic performance tends to be further improved. The average aspect of such a fibrous pore-forming material is defined as "average fiber length / average diameter (average fiber diameter)". Here, the fiber length is a straight line distance connecting the start point and the end point of the fiber. The average fiber length can be obtained by randomly extracting 50 or more fibrous pore-forming materials, measuring the fiber lengths of these fibrous pore-forming materials, and averaging them. The average diameter is as described above.

Further, in such a step (I), the noble metal is supported on the fibrous pore-forming material. As described above, the method of supporting the noble metal on the fibrous pore-forming material is not particularly limited, and a known method can be appropriately adopted. As a method for supporting the noble metal on such a fibrous pore-forming material, for example, a salt (for example, acetate, carbonate, nitrate) of the noble metal (for example, Pt, Rh, Pd, Ru, etc., or a compound thereof) is used. , Ammonium salt, citrate, dinitrodiammine salt, etc.) or a solution thereof (for example, tetraammine complex) dissolved in a solvent such as water or alcohol is impregnated and supported in a fibrous pore-forming material, and then the solvent is removed. Then, a method of supporting the noble metal on the fibrous pore-forming material can be mentioned.

When platinum is used as the noble metal, the platinum salt is not particularly limited, and for example, acetate, carbonate, nitrate, ammonium salt, citrate, dinitrodiammine salt, etc. of platinum (Pt) or a complex thereof can be used. Among them, the dinitrodiammine salt is preferable from the viewpoint of ease of carrying and high dispersibility. When palladium is used as the noble metal, the palladium salt is not particularly limited, but for example, acetic acid salt, carbonate, nitrate, ammonium salt, citrate, dinitrodiammine salt, etc. of palladium (Pd) or a complex thereof. Examples thereof include solutions, and among them, nitrates and dinitrodiammine salts are preferable from the viewpoint of ease of carrying and high dispersibility. Further, the solvent is not particularly limited, and examples thereof include a solvent that can be dissolved in an ionic state such as water (preferably pure water such as ion-exchanged water and distilled water).

By supporting the noble metal on the fibrous pore-forming material in this way, the noble metal-supported pore-forming material can be obtained. The amount of the noble metal supported on such a fibrous pore-forming material is not particularly limited, and a required amount may be appropriately supported according to a target design or the like. The amount of such a noble metal supported is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, and 0, with respect to 100 parts by mass of the fibrous pore-forming material. .5 to 3 parts by mass is particularly preferable. If the amount of such noble metal supported is less than the lower limit, the effect of selectively arranging the noble metal in the gas flow path tends to be small, while if it exceeds the upper limit, the carrying density of the noble metal becomes excessive and the particle size becomes large. It tends to be.

<Step of obtaining catalyst slurry (II))
Such a step (II) is a step of mixing the metal oxide particles and the noble metal-supported pore-forming material to obtain a catalyst slurry.

Such metal oxide particles are the same as those described in the above-mentioned exhaust gas purification catalyst of the present invention (metal oxide particles constituting a carrier) (the same applies to suitable ones). Further, as such metal oxide particles, metal oxide particles (precious metal-supported particles) in which a noble metal is previously supported may be used as the metal oxide particles.

Further, the amount of the noble metal-supporting pore-forming material used in such step (II) is preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the metal oxide particles, and is preferably 1 to 8 parts. It is more preferably parts by mass, and particularly preferably 3 to 5 parts by mass. If the amount of the noble metal-supported pore-forming material used (mixed amount) is less than the lower limit, the amount of the pore-forming material is insufficient, and the pores have sufficient pore communication properties with the macropores formed in the molded body. On the other hand, if the above upper limit is exceeded, the effect is saturated, the bulk becomes larger than necessary, and the strength is lowered, because the diffusibility of the gas is lowered and the catalytic activity is lowered. There is a tendency for inconveniences such as.

Further, in the present invention, the content of the noble metal in the noble metal-supported pore-forming material used for producing the catalyst is preferably 10% by mass or more of the total amount of the noble metal in the exhaust gas purification catalyst to be produced, and is 12 to 100. It is more preferably mass%, and particularly preferably 15 to 100 mass%. If the content of such noble metal is less than the above lower limit, the amount of noble metal existing in a portion other than the vicinity of the pore wall (wall surface) of the macropores becomes large, and the obtained catalyst is obtained with respect to the total amount of noble metals in the catalyst. The activity tends to be inadequate. Further, if the content of such a noble metal is less than the lower limit, it tends to be difficult to produce the exhaust gas purification catalyst of the present invention. When a noble metal other than the noble metal in the noble metal-supported pore-forming material is supported on the carrier in the obtained exhaust gas purification catalyst, the method of supporting such the noble metal is not particularly limited, and for example, each step is carried out. After forming the catalyst, a method may be adopted in which a salt or the like of a noble metal is separately supported on the carrier and a noble metal other than the noble metal in the noble metal-supporting pore-forming material is supported on the carrier by firing. As the metal oxide particles used for producing the purification catalyst, a method may be adopted in which metal oxide particles (noble metal-supported particles) on which a noble metal is supported in advance are prepared and the catalyst is produced using the metal oxide particles.

Further, from the viewpoint of efficiently producing the catalyst for purifying exhaust gas of the present invention, when metal oxide particles (precious metal-supported particles) on which a noble metal is previously supported are used as the metal oxide particles, the noble metal-supported particles are used. It is preferable that the amount of the noble metal supported on the surface is 90% by mass or less of the total amount of the noble metal in the obtained exhaust gas purification catalyst. If such a supported amount exceeds the upper limit, it becomes difficult to make the concentration of the noble metal supported in the vicinity of the wall surface of the pores sufficiently high, and it becomes difficult to manufacture the exhaust gas purification catalyst of the present invention. There is a tendency. As described above, from the viewpoint of efficiently producing the exhaust gas purification catalyst of the present invention, the content of the precious metal in the noble metal-supporting pore-forming material used for producing the catalyst is the same as that of the noble metal in the exhaust gas purification catalyst to be produced. Satisfying the condition that the total amount is 10% by mass or more (the amount of the noble metal contained in the noble metal-supported pore-forming material and the noble metal contained in the metal oxide particles (precious metal-supported particles) previously supported). The noble metal-bearing particles as the metal oxide particles (so that the condition that the amount of the noble metal contained in the noble metal-bearing pore-forming material is 10% by mass or more with respect to the total amount of the precious metal) is satisfied. It is preferable to use.

Further, in such a step (II), the method for preparing the catalyst slurry by mixing the metal oxide particles and the noble metal-supported pore-forming material is not particularly limited, and the metal oxide particles and the noble metal are not particularly limited. Any method may be used as long as it is possible to obtain a slurry by mixing it with a supported pore-forming material, and a method similar to a known method for preparing a slurry can be appropriately adopted. The method for preparing such a catalyst slurry is not particularly limited, but for example, the metal oxide particles are dispersed in a dispersion medium to obtain a dispersion liquid containing the metal oxide particles, and then the noble metal is supported on the dispersion liquid. Method of mixing pore-forming materials, a dispersion liquid containing a noble metal-supported pore-forming material is obtained by dispersing the noble metal-supported pore-forming material in a dispersion medium, and then metal oxide particles and fibrous organic substances are mixed with the dispersion liquid. A method, a method of simultaneously adding a noble metal-supporting pore-forming material and metal oxide particles to a dispersion medium and mixing them can be adopted. The conditions for such mixing may be appropriately set so that the noble metal-supported pore-forming material can be uniformly dispersed and mixed in the catalyst slurry, and are not particularly limited. For example, the stirring speed is set to 100 to 100 using an attritamill. It is preferable that the speed is 400 rpm and the processing time is 30 minutes or more. Further, the dispersion medium (solvent) used for preparing such a slurry is not particularly limited, and a known solvent that can be used for producing the slurry at the time of producing the catalyst can be appropriately used, for example, water. (Preferably pure water such as ion-exchanged water and distilled water) and the like.

In addition to the metal oxide particles and the noble metal-supported pore-forming material, such a catalyst slurry can be used for producing an exhaust gas purification catalyst as long as the effects of the present invention are not impaired. Other components may be appropriately contained. As such other components, known components that can be used in the production of the exhaust gas purification catalyst can be appropriately selected according to the design of the target exhaust gas purification catalyst. For example, a binder component ( Alumina sol, etc.), alkali metal salts or complexes, alkaline earth metal salts or complexes, rare earth element salts or complexes, transition metal salts or complexes, and the like.

<Step of obtaining catalyst for exhaust gas purification (III)>
In such a step (III), the catalyst for exhaust gas purification of the present invention comprises a carrier made of a molded body of metal oxide particles and a noble metal supported on the carrier by firing after molding the catalyst slurry. Is the process of obtaining.

In such a step (III), first, the catalyst slurry is molded. The method for forming such a catalyst slurry is not particularly limited, and a known method for forming a slurry can be appropriately adopted according to a desired design. For example, the slurry is charged into a specific molding die and dispersed. In the case of a method of molding by evaporating a medium (solvent) or a coating layer in which the obtained exhaust gas purification catalyst is supported on a base material, the catalyst slurry is applied to the surface of the base material to form a catalyst slurry. A method of molding into the form of a coat layer by forming a layer, or the like can be appropriately adopted. The method for forming such a slurry is not limited to the above method, and for example, a known molding method such as extrusion molding, injection molding, or uniaxial press molding may be appropriately adopted.

Here, a preferred embodiment of the method of molding the catalyst slurry is "a method of molding the catalyst slurry into the form of a coat layer by applying the catalyst slurry to the surface of the base material to form the catalyst slurry layer. Will be briefly explained. In the case of such molding, the method that can be adopted as the method of applying the catalyst slurry to the surface of the base material is not particularly limited, and a known method can be appropriately adopted. Specific examples thereof include a method of immersing the base material in the catalyst slurry and applying it (immersion method), a wash coat method, a method of press-fitting the catalyst slurry by a press-fitting means, and the like. As such coating conditions, the catalyst slurry is placed on the surface of the base material so that the average thickness of the catalyst coat layer after firing is in the range of 20 to 300 μm (more preferably 50 to 200 μm). , It is preferable to apply the catalyst slurry. Further, when the catalyst slurry is applied, the coating amount of the coat layer after firing is set to be within the range of 20 to 300 g / L (more preferably 50 to 250 g / L) per unit volume of the base material. It is preferable to apply the catalyst slurry. The base material used in the method of molding such a catalyst slurry into the form of a coat layer is not particularly limited, but for example, the same base material as that described in the exhaust gas purification catalyst of the present invention may be used. Can be done. In this way, by applying the catalyst slurry to the surface of the base material to form the catalyst slurry layer, the catalyst slurry can be molded in the form of a coat layer. The suitable conditions and the like that can be adopted when molding the catalyst slurry into the form of the coat layer have been described above, but the methods and conditions that can be adopted when molding the catalyst slurry are the above-mentioned methods and the like. It is not limited to.

After molding the catalyst slurry in this way, in the present invention, the formed molded product is fired. By firing the molded product in such a firing step, at least a part of the fibrous pore-forming material in the noble metal-supported pore-forming material incorporated in the molded product is removed (burned). This makes it possible to form voids in the portion where the pore-forming material was present. Such voids are derived from the shape of the fibrous pore-forming material in the noble metal-supported pore-forming material, and in the present invention, a fibrous pore-forming material having an average diameter of 0.7 to 15 μm is used. Therefore, due to the size of the fibrous pore-forming material, it is possible to form macropores having an average pore diameter of 0.5 to 20 μm on the carrier made of the molded body of the metal oxide particles. .. Since the macropores (voids) prepared in this way serve as a diffusion flow path for exhaust gas in the finally obtained catalyst, the obtained exhaust gas purification catalyst is an excellent catalyst even in a high load region with a high gas flow rate. It can demonstrate its performance. Further, in the present invention, the above-mentioned macropores are formed by such a firing step, and the metal oxide particles (macropores) existing in the vicinity of the portion where the noble metal-supported pore-forming material was present are formed. It is possible to transfer and support the noble metal supported on the pore-forming material on the particles forming the wall surface of the metal or the particles existing in the vicinity of the particles), and as a result, the molded body of the metal oxide particles. It is possible to selectively support a noble metal in the vicinity of the wall surface of the pores (macropores) of the carrier made of the above. As described above, in the present invention, in the firing step, at least a part of the fibrous pore-forming material in the noble metal-supported pore-forming material is removed from the molded product obtained after molding the catalyst slurry, and the noble metal is metal-oxidized. It can be said that it is a process of supporting on a physical particle. When the fibrous pore-forming material in the noble metal-supported pore-forming material is removed by firing, the noble metal is transferred to the vicinity of the wall surface of the pores (macropores) of the carrier as described above and becomes the portion near the wall surface. At this time, the noble metal is supported on the surface of the wall surface of the macropores, and when the fibrous pore-forming material is burnt down, a part of the metal is melted and flows between the metal oxide particles. Therefore, the noble metal tends to invade and be supported in the region of 3 μm from the wall surface of the macro hole toward the carrier side with the inflow, and therefore, the region of 3 μm from the wall surface of the macro hole toward the carrier side. It is possible to increase the concentration of the noble metal in the total region of 1 μm from the wall surface of the macropore to the void side of the macropore.

In such a firing step, after molding the catalyst slurry, it is preferable to fire it at a temperature in the range of 300 to 800 ° C., and more preferably to fire it at a temperature in the range of 400 to 700 ° C. If the firing temperature is less than the lower limit, the fibrous pore-forming material tends to remain and it tends to be difficult to sufficiently form pores, while if it exceeds the upper limit, precious metal particles grow. There is a tendency. Further, the firing (heating) time varies depending on the firing temperature, and therefore cannot be unconditionally stated, but is preferably 20 minutes or more, and more preferably 30 minutes to 2 hours. Further, the atmosphere in such a firing step is not particularly limited, but is preferably in the atmosphere or in an inert gas such as nitrogen (N ₂ ).

By firing the catalyst slurry after molding in this way, it is possible to obtain the catalyst for exhaust gas purification of the present invention, which comprises a carrier made of a molded body of metal oxide particles and a noble metal supported on the carrier. The form of the molded body of the metal oxide particles thus obtained is derived from the form of the molded product of the catalyst slurry. Therefore, the form of the obtained exhaust gas purification catalyst is also derived from the form of the molded product of the catalyst slurry.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

( Reference example 1 )
First, a fibrous pore-forming material made of polyethylene terephthalate fibers having an average diameter of 4 μm (average aspect ratio: 14) is impregnated with a palladium nitrate solution and supported and dried at 110 ° C. for 12 hours. Palladium (Pd) was supported on the shaped pore-forming material to obtain a Pd-supported pore-forming material. In the impregnation supporting step, a palladium nitrate solution was used so that the amount of Pd supported with respect to 100 parts by mass of the fibrous pore-forming material was 1 part by mass.

Next, 4 g of the Pd-supported pore-forming material, 100 g of alumina particles (particles prepared by crushing the trade name "C20" manufactured by Nippon Light Metal Co., Ltd.) having an average particle diameter of 6 μm by crushing in advance, and alumina sol ( By adding 53 g of the trade name "A520" manufactured by Nissan Chemical Industries, Ltd. and the solid content of alumina is 20.9% by mass) to 125 mL of ion-exchanged water and mixing with an attritamill at a stirring speed of 300 rpm for 30 minutes. , A catalyst slurry was prepared. As described above, the amount of the Pd-supported pore-forming material used was 4 parts by mass with respect to 100 parts by mass of the alumina particles.

Next, the catalyst slurry was applied to a honeycomb base material (diameter 30 mm, length 25 mm, volume: 17.5 ml, cell density: 400 cell / inch ² ) made of Cordellite, and the coated layer (layer of the catalyst for exhaust gas purification) after firing was applied. A catalyst slurry layer (coat layer) was formed on the surface of the honeycomb base material by wash-coating so that the supported amount (coating amount) was 200 g / L per 1 L of the capacity of the honeycomb base material. Next, the honeycomb base material on which the catalyst slurry layer was formed was fired in the air at a temperature of 500 ° C. for 1 hour to produce an exhaust gas purification catalyst as a coat layer on the honeycomb base material. The thickness of the coat layer (layer of the catalyst for purifying exhaust gas) after such firing was 100 μm.

By such firing at 500 ° C., the fibrous pore-forming material in the Pd-supported pore-forming material was burnt and removed from the coat layer of the catalyst slurry before firing, and further, the Pd-supported pore-forming material was formed. The supported Pd was supported (transferred) on the metal oxide particles (alumina particles). Therefore, in the obtained catalyst for purifying exhaust gas, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) was 0.04 parts by mass. The average pore diameter of the pores of the molded body (carrier) of the metal oxide particles constituting the coat layer thus obtained is measured as an electron probe microanalyzer (trade name "JXA-" manufactured by JEOL Ltd.) as a measuring device. Using 8500F ”), the surface of the carrier was analyzed under the conditions of acceleration voltage: 10 KV, sample current: 100 nA, beam diameter: 1 μm (minimum size), and for any plurality of 50 μm square measurement fields (measurement regions). , The reflected electron image on the surface of the carrier (the image for a square region of 50 μm square) is measured, and based on all the obtained reflected electron images (results of surface analysis of the entire measurement field), the pores are arbitrary. The maximum length of the opening in the direction perpendicular to the longitudinal direction of the opening of the pore was obtained for each of the 20 points, and all the obtained values of the maximum length were averaged. However, it was confirmed that the average pore diameter was 4 μm, and that the molded product (carrier) of the metal oxide particles (alumina particles) had macropores. The average aspect ratio of the pores was 15.

Further, the surface of the exhaust gas purification catalyst (coat layer) thus obtained was analyzed by EPMA as follows. That is, in such an analysis, an electron probe microanalyzer (trade name "JXA-8500F" manufactured by JEOL Ltd.) is used as a measuring device, acceleration voltage: 10 KV, sample current: 100 nA, beam diameter: 1 μm (minimum size). ), A surface analysis was performed in each of a plurality of arbitrary 50 μm square measurement visual fields (measurement regions). By such surface analysis, a 50 μm square reflected electron image in which the total number of measurement points (pixels: pixels) is 62500 (250 × 250) points is obtained for each measurement field, and the measurement points (pixels: pixels) are obtained. ), The concentration data of the precious metal (Pd) was obtained. Then, based on the concentration data of the precious metal for each measurement point, the amount of the precious metal for each measurement point (pixel: pixel) was calculated (note that the size of each pixel was 200 nm square). Then, for each obtained reflected electron image (measurement field), the total amount of precious metals (Pd) at all measurement points is obtained, and the total is divided by the number of all measurement points (62500 points) to obtain "precious metal". The average value (a) of the carrying amount of the above was obtained. In this way, after obtaining the "average value (a) of the amount of precious metal carried" for each of the reflected electron images (measurement visual fields), the average value (a) of all the measurement visual fields is obtained. The "mean value (A) of the amount of noble metal carried" at the measurement point was obtained. Next, line analysis was performed for each measurement field of view (total reflected electron image) for which the surface analysis was performed. In such line analysis, line analysis was performed on arbitrary five linear regions (arbitrary five measurement lines) for each measurement field of view (each reflected electron image). In addition, all the lines (measurement points) to be measured in such line analysis are arbitrary points on the surface except that a part of the lines always passes over the openings of the pores. Further, such line analysis is based on the measurement result of the reflected electron image, and the length of the line to be measured is set to 50 μm in the same manner as that in which the measuring device and the measuring conditions are adopted in the surface analysis. , The number of measurement points (pixels) for each line was set to 250 (note that the size of each pixel was 200 nm square). By such a line analysis, the concentration data of the precious metal (Pd) for each measurement point (250 pixels) on the line (line) where the line analysis was performed is obtained, and the amount of the precious metal for each measurement point is calculated based on the result. I asked for each. Then, from the results of line analysis of all measurement fields (all reflected electron images), the measurement points (pixels) on all measurement lines in all measurement fields and from the wall surface of the macropore toward the carrier side. The total number of measurement points existing at the position of the total region of the region of 3 μm and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole (total number A: on all lines in the entire measurement field of view). (Total number of measurement points in all the total regions) and measurement points (pixels) on all measurement lines in the entire measurement field, and a region of 3 μm from the wall surface of the macro hole toward the carrier side. And the sum of the amounts of precious metals at all the measurement points existing at the position of the total region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole, and dividing the sum by the total number A. As a result, the average value of the amount of the noble metal (Pd) carried at all the measurement points in all the total regions on all the measurement lines in all the measurement fields (reflected electron images) is set from the wall surface of the macropore to the carrier side. The "average value (B) of the amount of noble metal carried" at the measurement point of the total region of the region of 3 μm and the region of 1 μm from the wall surface of the macro hole toward the void side of the macro hole was determined. A part of the measurement result of such EPMA is shown in FIG. In FIG. 3, (a) shows a reflected electron image on the surface of the exhaust gas purification catalyst obtained by EPMA, a line-analyzed part and a graph of the Pd concentration of the part, and (b) shows palladium ( An image showing the distribution state of Pd) is shown. Further, FIG. 4 shows an enlarged portion of the graph of the Pd concentration shown in FIG. 3 (a) corresponding to the region X indicated by the dotted line in FIG. 3 (a).

As a result of such analysis by EPMA, the average value (A) of the amount of noble metal supported at all the measurement points is 0.75, and the average value (B) of the amount of noble metal supported at the measurement points in the total region is 2. It was 28. Therefore, in the obtained catalyst for purifying exhaust gas, the average value (B) of the amount of noble metal supported at the measurement points in the total region is 3.04 times the average value (A) of the amount of noble metal supported at all measurement points. It was found that the precious metal (Pd) was selectively supported near the wall surface of the macropores. Table 1 shows the characteristics of the exhaust gas purification catalyst thus obtained.

Further, the void ratio (volume%) of the macropores of the exhaust gas purification catalyst thus obtained is determined by setting the specific gravity of alumina to 4 based on the amount of alumina particles and the amount of fibrous pore-forming material used in the production. It was calculated as 0.0 and the specific gravity of the fibrous pore-forming material was 1. The results obtained are shown in Table 1.

( Reference example 2)
Instead of using a palladium nitrate solution so that the amount of Pd supported on 100 parts by mass of the fibrous pore-forming material is 1 part by mass, the amount of Pd supported on 100 parts by mass of the fibrous pore-forming material is 2 parts by mass. Except that the palladium nitrate solution was used and the amount of Pd-supporting pore-forming material used was changed to 2 parts by mass with respect to 100 parts by mass of alumina particles instead of 4 parts by mass with respect to 100 parts by mass of alumina particles. , A catalyst for purifying exhaust gas was obtained in the same manner as in Reference Example 1. In the catalyst for purifying exhaust gas thus obtained, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) was 0.04 parts by mass. In the same manner as in Reference Example 1, the average pore diameter of the pores of the molded body (carrier) of the metal oxide particles in the obtained exhaust gas purification catalyst and the porosity of the exhaust gas purification catalyst were confirmed (measurement). At the same time, the surface of the exhaust gas purification catalyst (coat layer) is analyzed by EPMA, and the average value of the amount of noble metal supported at all measurement points (A) and the average value of the amount of noble metal supported at the measurement points in the total region (B). ) And the multiplication factor of the average value (B) with respect to the average value (A). Table 1 shows the characteristics of the obtained exhaust gas purification catalyst.

(Example 1 )
Instead of using a palladium nitrate solution so that the amount of Pd supported on 100 parts by mass of the fibrous pore-forming material is 1 part by mass, the amount of Pd supported on 100 parts by mass of the fibrous pore-forming material is 0.5 parts by mass. Using a palladium nitrate solution, the amount of the Pd-supported pore-forming material used was changed to 2 parts by mass with respect to 100 parts by mass of the alumina particles instead of 4 parts by mass with respect to 100 parts by mass of the alumina particles. , the amount of supported Pd advance Pd to the alumina particles instead of using alumina particles as against 100 parts by weight of alumina particles was carried out as 0.03 parts by weight, except for using the Pd-carried alumina particles, reference A catalyst for purifying exhaust gas was obtained in the same manner as in Example 1. In the catalyst for purifying exhaust gas thus obtained, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) was 0.04 parts by mass. The Pd-supported alumina particles are such that the amount of Pd supported is 0 in the alumina particles (particles prepared by crushing the trade name "C20" manufactured by Nippon Light Metal Co., Ltd.) having an average particle diameter of 6 μm. It was produced by impregnating and supporting a palladium nitrate solution so as to have a concentration of .03 wt%, drying at 110 ° C. for 12 hours, and then firing at 500 ° C. for 3 hours. Further, in the same manner as in Reference Example 1, the average pore diameter of the pores of the molded body (carrier) of the metal oxide particles in the obtained exhaust gas purification catalyst and the porosity of the exhaust gas purification catalyst were confirmed (measurement). At the same time, the surface of the exhaust gas purification catalyst (coat layer) is analyzed by EPMA, and the average value of the amount of noble metal supported at all measurement points (A) and the average value of the amount of noble metal supported at the measurement points in the total region (B). ) And the multiplication factor of the average value (B) with respect to the average value (A). Table 1 shows the characteristics of the obtained exhaust gas purification catalyst.

(Comparative Example 1)
First, the amount of Pd supported on 100 parts by mass of alumina particles on alumina particles (particles prepared by crushing the trade name "C20" manufactured by Nippon Light Metal Co., Ltd.) having an average particle diameter of 6 μm by crushing in advance is 0. Pd-supported alumina particles were obtained by impregnating and supporting a palladium nitrate solution so as to have a volume of 04 parts by mass, drying at 110 ° C. for 12 hours, and then firing at 500 ° C. for 3 hours.

Next, the Pd-supported alumina particles and a fibrous pore-forming material made of polyethylene terephthalate fibers having an average diameter of 4 μm (average aspect ratio: 14) were added to 125 mL of ion-exchanged water, and the atomizer mill was used. A catalytic slurry was prepared by mixing at a stirring speed of 300 rpm for 30 minutes. As described above, the amount of the fibrous pore-forming material used was 4 parts by mass with respect to 100 parts by mass of the alumina particles.

Next, the catalyst slurry was applied to a honeycomb base material (diameter 30 mm, length 25 mm, volume: 17.5 ml, cell density: 400 cell / inch ² ) made of Cordellite, and the coated layer (layer of the catalyst for exhaust gas purification) after firing was applied. A catalyst slurry layer (coat layer) was formed on the surface of the honeycomb base material by wash-coating so that the supported amount (coating amount) was 200 g / L per 1 L of the capacity of the honeycomb base material. Next, the honeycomb base material on which the catalyst slurry layer was formed was fired in the air at a temperature of 500 ° C. for 1 hour to produce an exhaust gas purification catalyst as a coat layer on the honeycomb base material.

In the catalyst for purifying exhaust gas thus obtained, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) was 0.04 parts by mass. .. Further, the thickness of the coat layer (layer of the catalyst for purifying exhaust gas) after such firing was 100 μm. Further, in the same manner as in Reference Example 1, the average pore diameter of the pores of the molded body (carrier) of the metal oxide particles in the obtained exhaust gas purification catalyst and the porosity of the exhaust gas purification catalyst were confirmed (measurement). At the same time, the surface of the exhaust gas purification catalyst (coat layer) is analyzed by EPMA, and the average value of the amount of noble metal supported at all measurement points (A) and the average value of the amount of noble metal supported at the measurement points in the total region (B). ) And the multiplication factor of the average value (B) with respect to the average value (A). Table 1 shows the characteristics of the obtained exhaust gas purification catalyst.

(Comparative Example 2)
Exhaust gas purification catalyst in the same manner as in Comparative Example 1 except that the amount of the fibrous pore-forming material used was changed from 4 parts by mass with respect to 100 parts by mass of alumina particles to 2 parts by mass with respect to 100 parts by mass of alumina particles. Got In the catalyst for purifying exhaust gas thus obtained, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) was 0.04 parts by mass. In the same manner as in Reference Example 1, the average pore diameter of the pores of the molded body (carrier) of the metal oxide particles in the obtained exhaust gas purification catalyst and the porosity of the exhaust gas purification catalyst were confirmed (measurement). At the same time, the surface of the exhaust gas purification catalyst (coat layer) is analyzed by EPMA, and the average value of the amount of noble metal supported at all measurement points (A) and the average value of the amount of noble metal supported at the measurement points in the total region (B). ) And the multiplication factor of the average value (B) with respect to the average value (A). Table 1 shows the characteristics of the obtained exhaust gas purification catalyst.

(Comparative Example 3)
An exhaust gas purification catalyst was obtained in the same manner as in Comparative Example 1 except that the fibrous pore-forming material was not used. In the catalyst for purifying exhaust gas thus obtained, as is clear from the production method, the amount of the noble metal (Pd) supported on 100 parts by mass of the molded body (carrier) of the metal oxide particles (alumina particles) is It was 0.04 parts by mass. In the same manner as in Reference Example 1, when the average pore diameter of the pores of the molded body (carrier) of the metal oxide particles in the obtained exhaust gas purification catalyst was confirmed (measured), the average pore diameter was found. No macropores with a diameter of 0.5 to 20 μm were confirmed. Further, in the same manner as in Reference Example 1, the porosity of the exhaust gas purification catalyst is obtained, and the surface of the exhaust gas purification catalyst (coat layer) is analyzed by EPMA, and the average value of the amount of noble metal supported at all measurement points (A). ) Was calculated (Note that the mean value (B) could not be measured because no macropores were confirmed). Table 1 shows the characteristics of the obtained exhaust gas purification catalyst.

[Evaluation of catalytic activity of exhaust gas purification catalyst]
Using the exhaust gas purification catalysts obtained in Reference Examples 1 and 2, Examples 1 and Comparative Examples 1 and 3, the catalytic activity of each catalyst was measured as follows. That is, in such a catalyst activity measurement test, first, a fixed-bed flow reactor is used, and the gas flow after the incoming gas introduced into the gas flow path comes into contact with the exhaust gas purification catalyst (after passing through the catalyst). An exhaust gas purification catalyst was installed in the gas flow path toward the exit of the road. Next, the gas (A) composed of O ₂ (0.28% by volume) and N ₂ (remaining portion) is used as the gas entering the gas flow path at a flow rate of 50,000 ml / min with the temperature (entering gas temperature) of 500 ° C. It was supplied to the gas flow path for 15 minutes. After that, the type of entering gas is changed from the gas (A) to O ₂ (0.28% by volume), C ₃ H ₆ (0.15 by volume C [carbon equivalent volume%]) and N ₂ (remaining). The gas (B) is supplied to the gas flow path at a flow rate of 50,000 ml / min at a temperature (entering gas temperature) of 500 ° C., and the introduction of the gas (B) is started ( From the time when the introduction of C ₃ H ₆ gas was started), the measurement of the concentration of CO _{2 in} the gas emitted after contacting with the exhaust gas purification catalyst (after passing through the catalyst) was started, and the concentration of CO ₂ was 0. The time required to reach 08 volume% C (about half the amount when all C ₃ H ₆ is converted to CO ₂ and H ₂ O) (the time required is hereinafter referred to as “CO ₂ −” in some cases. T50 ”) was measured. Such time _(CO 2 -T50) is the time to conversion to CO ₂ reaches about 50% (unit: seconds) (however, _CO 2 -T50 in the measurement response of the device It is possible to compare the CO ₂ generation rate according to the time taken (the time including the delay time). The composition of the gas (A) and (B) shown in Table 2 shows the results of measurement of _CO 2 -T50 each exhaust gas purifying catalyst in FIG.

As is clear from the results shown in FIG. 5, the exhaust gas purification catalysts obtained in Reference Examples 1 and 2 and Example 1 were all obtained in Comparative Examples 1 and 3 under the temperature condition of 500 ° C. The CO ₂ production rate (conversion rate) is faster than that of the exhaust gas purification catalyst, and the exhaust gas purification catalyst of the present invention (Example 1) and the exhaust gas purification catalysts obtained in Reference Examples 1 and 2 are used. For example, it was confirmed that the catalytic activity becomes higher.

From these results and the results shown in Table 1 for the exhaust gas purification catalyst of the present invention (Example 1) and the exhaust gas purification touch obtained in Reference Examples 1 and 2, the distribution of the noble metal (Pd) in the vicinity of the macropores. Considering the fact that the catalyst for purifying the exhaust gas obtained in Comparative Example 3 does not have macropores, etc., the catalyst for purifying the exhaust gas of the present invention (Example 1) and In the catalyst for purifying exhaust gas obtained in Reference Examples 1 and 2 , the carrier (molded body of metal oxide particles) has macropores, and the amount of noble metal (Pd) supported in the vicinity of the macropores is other. It is clear that the catalytic activity became more advanced based on the fact that it was higher than the amount of the noble metal supported at the site.

As described above, according to the present invention, an exhaust gas purification catalyst capable of having a higher catalytic activity and an exhaust gas purification catalyst capable of efficiently producing the exhaust gas purification catalyst thereof. It becomes possible to provide a manufacturing method. Therefore, the exhaust gas purification catalyst of the present invention and its manufacturing method are particularly useful as an exhaust gas purifying catalyst for purifying harmful components contained in exhaust gas emitted from an internal combustion engine such as an automobile engine and a manufacturing method thereof. is there.

S ... Carrier, N ... Precious metal, P ... Macro hole wall surface, O ... Macro hole opening, D1 ... Carrier side direction with respect to wall surface P of carrier S on the left side of FIG. 1, D2 ... Left side of FIG. The direction of the gap side of the macro hole with respect to the wall surface P of the carrier S, A ₁ ... a region of 3 μm from the wall surface of the macro hole toward the carrier side, A ₂ ... from the wall surface of the macro hole toward the void side of the macro hole. 1 μm region, L _{1 to} L ₃ ... Lines schematically showing the measurement sites of EPMA line analysis.

Claims (3)

A step of supporting a noble metal on a fibrous pore-forming material having an average diameter of 0.7 to 15 μm to obtain a noble metal-supported pore-forming material.
A step of mixing the noble metal-supported metal oxide particles and the noble metal-supported pore-forming material to obtain a catalyst slurry, and
By molding the catalyst slurry and then firing it, a carrier made of a molded body of the metal oxide particles and having macropores having an average pore diameter of 0.5 to 20 μm and a noble metal supported on the carrier are provided. In addition, when the distribution state of the noble metal supported on the carrier was confirmed using an electron probe microanalyzer, the average value (A) of the amount of noble metal supported at all measurement points was seen from the wall surface of the macropore. The average value (B) of the amount of noble metal supported at the measurement points in the total region of the region 3 μm toward the carrier side and the region 1 μm from the wall surface of the macropore toward the void side of the macropore is 1.1 times. The process of obtaining the catalyst for purifying exhaust gas as described above and
A method for producing a catalyst for purifying exhaust gas, which comprises. The content of noble metal of the noble metal loaded pore former in the method for producing a catalyst for purification of exhaust gas according to claim 1, wherein at least 10 wt% of the total amount of noble metal of the exhaust gas purifying catalyst. The exhaust gas purification catalyst according to claim 1 or 2 , wherein the metal oxide particles are metal oxide particles in which 90% by mass or less of the total amount of the noble metal in the exhaust gas purification catalyst is supported. Production method.