JP6806588B2 - Auxiliary catalyst for purifying automobile exhaust gas and its manufacturing method - Google Patents

Description

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

So-called three-way catalysts are used to purify hydrocarbons (HC), carbon monoxide (CO), and nitrogen carbides (NO _x ) contained in automobile exhaust gas. Cerium oxide has an oxygen occlusion / release ability (OSC) that takes in oxygen in an oxidizing atmosphere and releases oxygen in a reducing atmosphere, and is therefore used as an auxiliary catalyst for an automobile exhaust gas purification catalyst. And, as described in Patent Document 1 and Patent Document 2, at present, in order to improve durability at high temperature, ceria zirconia composite oxide in which ceria and zirconia are solid-solved is generally used. There is.

Japanese Patent Application Laid-Open No. 2009-537304 Japanese Unexamined Patent Publication No. 2016-008168

It is known that the function of a uniform solid solution of ceria zirconia in which ceria and zirconia are uniformly dissolved is significantly reduced at a low temperature. When the engine of an automobile is started in a cold state, the gas exhausted until the catalyst reaches an operating temperature at which a sufficient purification function is exhibited does not sufficiently react with the catalyst and is released into the atmosphere.

Therefore, in order to prevent the discharge of unreacted release material, tin is added to the co-catalyst in Patent Document 1 for the purpose of lowering the temperature Tcz showing the peak of the oxygen release characteristic. However, if the number of additives is increased in this way, the component system of the co-catalyst becomes complicated, and the solid solution ratio of ceria and zirconia may deteriorate, resulting in a decrease in oxygen occlusion and release capacity. ..

On the other hand, the co-catalyst described in Patent Document 2 has a drawback that the oxygen occlusion and release ability is considerably low, probably because the amount of cerium added is small.

The present invention has been made in the context of the above circumstances, and an object of the present invention is to have a high oxygen occlusion / release capacity (OSC) at a relatively low temperature, and to have oxygen release characteristics, that is, thermal conductivity of a reducing gas. It is an object of the present invention to provide an auxiliary catalyst for purifying automobile exhaust gas, which has a low temperature Tcz which shows a peak in a time course change curve (TPR curve) and a high cerium utilization rate, and a method for producing the same.

As a result of various studies against the background of the above circumstances, the present inventors have made a core containing zirconia as a main component and a shell (outer shell) fixed to the surface of the core and containing ceria zirconia as a main component. In the configured auxiliary catalyst for purifying automobile exhaust gas, the composition ratio of ceria zirconia, which is the main component of the shell, is in the range of ceria: zirconia = 25:75 to 60:40 in terms of oxide weight ratio, and is included in the shell. When the ratio of the ceria that is not solid-dissolved with the zirconia contained in the shell is within the range of 10 to 20% by weight, the temperature Tcz that shows a peak in the oxygen release characteristics becomes low, and the cerium utilization rate becomes high. We have found that a high co-catalyst can be obtained. The present invention has been made based on such findings.

That is, the gist of the first invention is (a) an auxiliary for purifying automobile exhaust gas, which is composed of a core containing zirconia as a main component and a shell fixed to the surface of the core and containing ceria zirconia as a main component. The composition ratio of ceria zirconia, which is a catalyst and is the main component of the shell, is ceria: zirconia = 25: 75 to 60:40 in terms of oxide weight ratio, and (c) ceria contained in the shell. The proportion of the shell contained in the shell that is not solid-dissolved with the zirconia is 10 to 20% by weight, and (d) the core has a tetragonal crystal structure.

The gist of the second invention is that the core has an average primary particle diameter of 5 to 50 nm.

The gist of the third invention is that in the powder X-ray diffraction pattern of ceria zirconia, the vertical axis passing through the point where the X-ray intensity is maximum is the center line, and the two points where the left and right slopes are zero are defined. The vertical axis passing through each is the left end line and the right end line, the straight line passing through the two points where the slope is zero is the baseline, and the length between the center line and the left edge line and the center line on the baseline are When the ratio of the length to the right end line is taken as the left-right width ratio, the left-right width ratio of the ceria zirconia is 55:45 to 70:30.

The gist of the fourth invention is the method for producing an auxiliary catalyst for purifying automobile exhaust gas according to the first invention or the second invention, wherein (a) a water-soluble zirconium salt and at least one of yttrium, lantern, placeodim, and neodym. A dissolution step of dissolving the water-soluble salt of the seed in distilled water, (b) a first precipitate formation step of adding a precipitant to the liquid obtained by the dissolution step to form a first precipitate, and (c) A first hydrothermal reaction step of applying hydrothermal treatment to the first precipitate obtained by the first precipitate formation step, and (d) a dried product of the first hydrothermal reaction product hydrothermally treated by the first hydrothermal treatment step. A first calcining step of obtaining a crystallized core powder, and (e) a mixing step of mixing the core powder, distilled water, a water-soluble zirconium salt, and a water-soluble cerium salt. f) A second precipitate forming step of adding a precipitant to the mixed solution obtained in the mixing step to form a second precipitate, and (g) a second precipitate formed by the second precipitate forming step. The dried product of the second hydrothermal reaction product which was hydrothermally treated by the second hydrothermal treatment step of adding hydrothermal treatment to the above and (h) the second hydrothermal reaction step was calcined to the surface of the core containing zirconia as a main component. The present invention includes a second calcining step of obtaining particles of an auxiliary catalyst for purifying automobile exhaust gas to which a shell containing ceria zirconia as a main component is fixed.

The gist of the fifth invention is that the mixing step further mixes at least one water-soluble salt of yttrium, lantern, praseodymium, and neodymium.

According to the first invention, the composition ratio of ceria zirconia, which is the main component of the shell, is in the range of ceria: zirconia = 25:75 to 60:40 in terms of oxide weight ratio, and the ceria contained in the shell. The proportion of the shell contained in the shell that is not solid-dissolved with the zirconia is in the range of 10 to 20% by weight, and the core has a tetragonal crystal structure, so that the oxygen release characteristic peaks. A co-catalyst having a low temperature Tcz and a high cerium utilization rate can be obtained. In addition, since the core carrying the shell containing cerium zirconia as the main component has a tetragonal crystal structure, high durability can be obtained, and oxygen can easily move, so that high oxygen occlusion and release capacity can be obtained. The cerium utilization rate is high.

According to the second invention, the core has an average primary particle size of 5 to 50 nm. Therefore, a large specific surface area of 20 to ²⁰⁰ m ² / g can be obtained, and high catalytic performance can be obtained.

According to the third invention, since the lateral width ratio of the ceria zirconia is 55:45 to 70:30, a co-catalyst having a high solid solution ratio of ceria zirconia and a high cerium utilization rate can be obtained.

According to the method for producing an auxiliary catalyst for purifying automobile exhaust gas according to the fourth invention, (a) a dissolution step of dissolving at least one water-soluble zirconium salt and at least one of yttrium, lanthanum, placeodium, and neodym in distilled water. , (B) A first precipitate forming step of adding a precipitant to the liquid obtained by the dissolution step to form a first precipitate, and (c) a first precipitate obtained by the first precipitate forming step. A first hydrothermal treatment step of adding hydrothermal treatment to a product and (d) a first method of calcining a dried product of the first hydrothermal reaction product hydrothermally treated by the first hydrothermal treatment step to obtain a crystallized core powder. A calcining step, (e) a mixing step of mixing the core powder, distilled water, a water-soluble zirconium salt, and a water-soluble cerium salt, and (f) precipitation in the mixed solution obtained by the mixing step P8. A second precipitate forming step of adding an agent to form a second precipitate, and (g) a second hydrothermal treatment step of adding hydrothermal treatment to the second precipitate produced by the second precipitate forming step, ( h) An automobile in which a dried product of the second hydrothermal reaction product hydrothermally heat-treated in the second hydrothermal treatment step is calcined, and a shell containing ceria zirconia as a main component is fixed to the surface of a core containing zirconia as a main component. Since the second calcining step of obtaining the particles of the auxiliary catalyst for exhaust gas purification is included, the auxiliary catalyst for automobile exhaust gas purification of the first invention and the auxiliary catalyst for automobile exhaust gas purification of the second invention are preferably obtained.

According to the fifth invention, since the mixing step further mixes at least one water-soluble salt of yttrium, lanthanum, praseodymium, and neodymium, the auxiliary catalyst for purifying automobile exhaust gas of the first invention and The auxiliary catalyst for purifying automobile exhaust gas of the second invention is preferably obtained.

It is a schematic diagram which shows the particle of the co-catalyst which is one Example of this invention. It is a process diagram explaining the core manufacturing process for manufacturing a core among the manufacturing process of the auxiliary catalyst of FIG. It is a process diagram explaining the shell manufacturing process for manufacturing the shell sticking to the surface of the core manufactured by the manufacturing process of FIG. 2 in the manufacturing process of the auxiliary catalyst of FIG. It is a figure which shows the time-dependent change curve (TPR curve) of the thermal conductivity of the reduction gas obtained by the temperature-heating reduction method, and (a) is an Example product as a representative example of Example products 1 to 3. The TPR curve of Comparative Example Product 1 is shown, and FIG. 1B shows the TPR curve of Comparative Example Product 2 as a representative example of Comparative Example Products 1 to 3. It is a figure which shows the diffraction pattern of the powder X-ray diffraction (XRD) of the co-catalyst sample to be measured, and (a) is an Example shown by a 1-point chain line as a representative example of Example products 1 to 6. The diffraction pattern of product 1 and the diffraction pattern of the core used in Example 1 shown by thin lines and the peak derived from tetragonal zirconia indicated by black circles are shown, and (b) is one point when the diffraction angle 2θ is around 30 °. The diffraction pattern of Example Product 1 shown by the chain line and the diffraction pattern of tetragonal zirconia, which is the core used in Example 1 shown by the thin line, are shown superimposed. It is a figure which shows the left-right width ratio in the diffraction pattern of the comparative example product 3. It is a figure corresponding to FIG. 5A which shows the diffraction pattern of the comparative example product 2. It is a figure corresponding to FIG. 5A which shows the diffraction pattern of the comparative example product 3. Of the diffraction pattern of Example product 1 shown by the alternate long and short dash line, the diffraction pattern of Comparative Example product 2 shown by the broken line, and the diffraction pattern of Comparative Example product 3 shown by the solid line, the pattern in which the diffraction angle 2θ is around 30 °. Are superimposed on each other. A chart showing the characteristics of a plurality of types of test products composed of different material ratios or materials using the steps shown in FIGS. 2 and 3, that is, the characteristics of Example products 1-7 and Comparative example products 1-3, respectively. Is.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows one particle of the co-catalyst 10 to which the present invention has been preferably applied. The co-catalyst 10 is composed of a core 12 and a shell 14 fixed to the surface thereof, and has a so-called core-shell structure in which the shell 14 is supported in an outer shell shape around the core 12. The co-catalyst 10 is, for example, an automobile exhaust gas which is a three-way catalyst converter that purifies carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO _x ) which are harmful components contained in the exhaust gas from an internal combustion engine. A catalyst phase provided on the inner peripheral surfaces of a plurality of insertion holes of a honeycomb-shaped main body member (not shown) made of porous ceramic of a purification catalyst device is supported together with a powder of a main catalyst such as platinum.

Celia zirconia, which is the main component of the shell 14, suppresses the inefficiency of platinum due to fluctuations in the oxygen concentration in the exhaust gas due to operating conditions, etc., so that when the oxygen around the catalytic phase is excessive, It functions as an oxygen storage / release material having an oxygen storage / release capacity (OSC) that stores oxygen and releases oxygen when the oxygen around the catalyst phase is insufficient. The amount of OSC is the amount of oxygen that can be stored and supplied, that is, the amount of oxygen released (L / mol).

The core 12 of the co-catalyst 10 is composed mainly of zirconia (ZrO ₂ ) having a tetragonal crystal structure. Further, the shell 14 fixed to the surface of the core 12 is composed mainly of ceria zirconia in which ceria (CeO ₂ ) reacts with zirconia by firing. The composition ratio of ceria zirconia, which is the main component of the shell 14, is ceria: zirconia = 25: 75 to 60:40 in terms of oxide weight ratio, and among the ceria contained in the shell 14, it is not solidly dissolved with zirconia. The proportions range from 10 to 20% by weight.

As a result, the co-catalyst 10 has a specific surface area of 40 (m ² / g) or more even after endurance at 1000 ° C., has a low reduction peak temperature Tcz, and has a high cerium utilization rate.

The co-catalyst 10 adjusts the average primary particle diameter D50 (nm) of the zirconia particles in the core 12 to a predetermined range of a relatively small nanoorder, for example, 5 to 50 nm, thereby adjusting the amount of OSC (L) per 1 mol of Ce of the ceria zirconia. / Mol) is higher than the OSC amount (L / mol) per 1 mol of Ce of the conventional core-shell structure ceria zirconia material or ceria zirconia material of a uniform solid solution in which ceria and zirconia are uniformly dissolved, and Ce is used. The rate (utilization rate of cerium) is preferably high.

Hereinafter, an example of an experiment conducted by the present inventors on a plurality of types of samples in which the components and their ratios are changed will be described. First, the measurement method for evaluating the performance of the co-catalyst used in the experimental example will be described.
(Measurement of average primary particle size of core)
The average primary particle size of the core is measured by the average value of the diameters of 50 core particles imaged during observation with TEM (field emission transmission electron microscope manufactured by Nippon Denshi Co., Ltd .: model JEM-2100F). is there.
(Measurement of reduction characteristics (TCD change curve) of co-catalyst)
In a catalyst analyzer (BELCAT-A) manufactured by Microtrac Bell Co., Ltd., 5% hydrogen gas (5% H ₂ / Ar) diluted with argon using a temperature reduction method (TPR) is used. The oxygen release characteristic was evaluated by measuring the temporal change (TCD) characteristic of the thermal conductivity of the reduction gas, which indicates the amount of oxygen released from the co-catalyst, in the process of rising from room temperature to 800 ° C. as the reducing gas. FIG. 4 is a diagram showing an example of a time-dependent change curve (TCD change curve) of the thermal conductivity of the reduced gas.
(Measurement of the amount of undissolved Ce)
Of the above-mentioned curves over time of thermal conductivity of the reduced gas (TCD curve), a curve showing a peak in the range of 500 ° C. to 600 ° C. and a curve showing a peak in the vicinity of 800 ° C. are separated, and the areas of these two curves are separated. Was calculated, the area ratio was calculated, and the amount of undissolved Ce was calculated.
(Measurement of specific surface area)
A co-catalyst sample to be measured For example, a powder fired at 800 ° C. is further subjected to endurance firing at 1000 ° C. for 12 hours, and the specific surface area of the powder after the endurance firing is measured by a specific surface area measuring device (Macsorb) manufactured by Mountech. It was measured using HM model-120).
(Evaluation of crystallinity)
Powder X-ray diffraction (XRD) of the co-catalyst sample to be measured was performed, and the crystallinity was evaluated based on the peak generated in the diffraction pattern. FIG. 5 shows an example of the diffraction pattern.
(Ce utilization rate)
First, in a catalyst analyzer (BELCAT-A) manufactured by Microtrac Bell Co., Ltd., a sample (auxiliary catalyst) is placed in a quartz glass tube, and 800 at a heating rate of 10 ° C./min under a 5% hydrogen / argon atmosphere. The temperature was raised and reduced to ℃, and the TPR curve showing the oxygen release behavior from the sample was detected by monitoring the gas composition change with a thermal conductivity detector (TCD), and the TPR curve was arbitrarily drawn from the detected TPR curve. The area up to 800 ° C. surrounded by the reference line (baseline BL), that is, the amount of oxygen released from the sample was calculated. That is, the OSC amount (L / mol) per 1 mol of Ce in the co-catalyst is the amount of oxygen released per 1 mol of Ce in the sample of the co-catalyst 10, that is, the amount of oxygen released from the sample of the co-catalyst when the temperature is reduced to 800 ° C. is there. Next, the Ce utilization rate (%) of the sample (co-catalyst) is calculated from the following equation (1) based on the amount of OSC per 1 mol of Ce. Note that 6.2 (L / mol) in Eq. (1) is the amount of OSC (L / mol) per 1 mol of Ce when all Ce are effectively used, and is calculated by Eq. (2) below. To. Further, the amount of OSC per 1 g of the sample (standard state) in the formula (2) is the TPR curve at 600 ° C. after switching from a 5% hydrogen / argon atmosphere to an argon atmosphere after the temperature rise and reduction according to the evaluation of the OSC performance described above. It was obtained experimentally by performing an atmosphere replacement treatment until the value of TCD Signal became constant, and then introducing the sample into a sample until 100% oxygen pulse was saturated. Further, in the formula (2), the sample is Ce _a Zr _(1-a) O ₂ , and a is the ratio of the amount of Ce contained in the sample Ce _a Zr _(1-a) O ₂ .
Ce utilization rate (%) = OSC amount per 1 mol of Ce of each sample (L / mol) ÷ 6.2 (L / mol) × 100% ... (1)
OSC amount per 1 mol of Ce (L / mol) = (140.116 × a + 91.22 × (1-a) +32) × OSC amount per 1 g of sample (L / g) ÷ a ... (2)
(XRD lateral width ratio)
For example, in the powder X-ray diffraction (XRD) pattern as shown in FIG. 6, which is the diffraction pattern of Comparative Example Product 3, the vertical line passing through the point (peak) where the X-ray intensity is maximum is set as the center line L1 on the left and right. For example, the vertical axis passing through the two points where the slopes are zero on the moving average is the left end line L2 and the right end line L3, and the center line is on the baseline L4 (bottom line) which is a straight line passing through the two points where the slopes are zero. The ratio of the length between L1 and the left end line L2 and the length between the center line L1 and the right end line L3 was defined as the left-right width ratio.

(Example product 1)
In the following, production of Example 1 of the co-catalyst 10 (composite oxide in which a ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core (La: Zr: Ce = 10: 70: 20 in terms of oxide weight ratio)). The method will be described with reference to FIGS. 2 and 3. FIG. 2 shows a method of synthesizing the core powder, that is, the core 12, and FIG. 3 shows a method of synthesizing the shell 14 on the surface of the core powder, that is, the core 12 synthesized in FIG. The reagents used are all manufactured by Wako Pure Chemical Industries, but the present invention is not limited to this.

In FIG. 2, first, in the dissolution step P1 and the first stirring step P2, 83.79 g of zirconium oxychloride octahydrate was dissolved in 234 ml of distilled water, and 157.94 g of 30% hydrogen peroxide solution was added to the solution. After that, 17.1 g of lanthanum nitrate hexahydrate is added and stirred. The zirconium oxychloride octahydrate, hydrogen peroxide, and lanthanum nitrate hexahydrate may be added to any step before the addition of aqueous ammonia. Next, in the first precipitate forming step P3, 25 to 28% aqueous ammonia is added to the liquid being stirred to form the first precipitate, and the mixture is put into a slurry state. The pH of the solution at the time of forming this precipitate is about 10 to 14. In the first hydrothermal treatment step P4, after stopping the above stirring, the slurry is transferred to a Teflon (registered trademark) container, and hydrothermal treatment is performed at 180 ° C. for 5 hours using an autoclave. In the subsequent first filtration / washing step P5, the slurry after the hydrothermal treatment is filtered and washed to collect the precipitate, and in the first drying step P6, it is dried at 80 ° C. for 24 hours. Then, in the first calcining step P7, the dried powder of the slurry is crushed (unraveled) in a mortar to obtain a uniform powder without aggregates, and then the first calcining at 750 ° C. for 3 hours is performed. The reaction is carried out to obtain a calcined powder, that is, a core powder. The hydrogen peroxide solution does not necessarily have to be added in the first stirring step P2. Further, the first hydrothermal treatment step P4 and the first calcining step P7 do not necessarily have to be provided.

In FIG. 3, in the mixing step P8, 30 g of the calcined powder, 90 g of distilled water, 26.16 g of zirconium oxychloride octahydrate, and 31.85 g of diammonium nitrate are placed in a 1 L ball mill container containing 300 g of zirconia balls. Put in and grind with a ball mill for 18 hours. Next, in the second stirring step P9, 13.8 g of 30% hydrogen peroxide solution is added to the slurry after the ball mill, and this slurry is added to 300 g of 28% ammonia water and stirred for 18 hours. Next, in the second precipitate forming step P10, 28% aqueous ammonia is added to the stirring liquid to form a second precipitate, and the mixture is put into a slurry state. In the subsequent second hydrothermal treatment step P11, the above slurry is transferred to a Teflon container and hydrothermally treated at 180 ° C. for 5 hours using an autoclave. In the second filtration / washing step P12, the slurry after the hydrothermal treatment is filtered and washed to collect the precipitate, and in the second drying step P13, it is dried at 80 ° C. for 24 hours. Then, in the second calcining step P14, the dried powder of the slurry is crushed (unraveled) in a mortar to obtain a uniform powder without aggregates, and then the second calcining at 800 ° C. for 3 hours is performed. The reaction is carried out to obtain a powder of Example Product 1 having a so-called core-shell structure in which the shell 14 is supported in an outer shell shape around the core 12. This powder is, for example, particles having an average primary particle diameter of 7 nm. In Example Product 1 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 50:50 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 15% by weight, the specific surface area after endurance firing at 1000 ° C. was 45 m ² / g, and the Ce utilization rate was 97%. The left-right width ratio of XRD was 57:43. The hydrogen peroxide solution does not necessarily have to be added in the second stirring step P9. Further, the second hydroheat treatment step P11 does not necessarily have to be provided.

(Example product 2)
A method for producing Example 2 of the co-catalyst 10 (composite oxide (La: Zr: Ce = 10: 80: 10 in oxide weight ratio) in which a ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core) will be described. To do. Example product 2 is produced through substantially the same steps as those shown in FIGS. 2 and 3, but in order to change the ratio of zirconia to ceria with respect to Example product 1, FIG. In the above, the amount of zirconium oxychloride octahydrate added in the mixing step P8 is 39.24 g, the amount of diammonium cerium nitrate is 15.94 g, and the 30% hydrogen peroxide solution added to the slurry in the second stirring step P9. It differs from Example Product 1 in that it weighs 20.78 g. In Example Product 2 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 25: 75 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 11% by weight, the specific surface area after endurance firing at 1000 ° C. was 41 m ² / g, and the Ce utilization rate was 99%. The left-right width ratio of XRD was 68:32.

(Example product 3)
A method for producing Example 3 of the co-catalyst 10 (composite oxide in which a ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core (La: Zr: Ce = 10: 67: 23 in terms of oxide weight ratio)) will be described. To do. Example product 3 is produced through substantially the same steps as those shown in FIGS. 2 and 3, but the point that the first calcining in FIG. 2 is 650 ° C. and the ratio of zirconia to ceria In FIG. 3, the amount of zirconium oxychloride octahydrate added in the mixing step P8 is 22.23 g and the amount of diammonium cerium nitrate is 36.62 g in order to change with respect to the product 1 of the second embodiment. It differs from Example Product 1 in that the amount of 30% hydrogen peroxide solution added to the slurry in P9 is 11.73 g. In Example Product 3 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 58:42 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 18% by weight, the specific surface area after endurance firing at 1000 ° C. was 41 m ² / g, and the Ce utilization rate was 96%. The left-right width ratio of the XRD was 59:41.

(Example product 4)
A method for producing Example 4 of the co-catalyst 10 (composite oxide (La: Zr: Ce = 14: 70: 16 in oxide weight ratio) in which a ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core) will be described. To do. Example product 4 is produced through substantially the same steps as those shown in FIGS. 2 and 3, but the point that the first calcining in FIG. 2 is 800 ° C. and the ratio of zirconia to ceria In FIG. 3, the point that the amount of diammonium cerium nitrate added in the mixing step P8 is 25.48 g, the point that 5.32 g of lanthanum nitrate hexahydrate is further added, and the point that the mixture is changed with respect to the product 1 of Example. 2 It differs from Example Product 1 in that the amount of 30% hydrogen peroxide solution added to the slurry in the stirring step P9 is 13.8 g. In Example Product 4 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 44:56 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 14% by weight, the specific surface area after endurance firing at 1000 ° C. was 41 m ² / g, and the Ce utilization rate was 97%. The left-right width ratio of XRD was 63:37.

(Example product 5)
Example product 5 of the co-catalyst 10 (composite oxide in which a neodymium-doped ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core (Nd: La: Zr: Ce = 5: 5: 70: 20 in oxide weight ratio) ) Will be described. Example product 5 is produced through substantially the same steps as those shown in FIGS. 2 and 3, but in order to change the ratio of zirconia to ceria with respect to Example product 1, FIG. In the first stirring step P2 of the above, 8.56 g of lanthanum nitrate hexahydrate was added. In FIG. 3, 28.53 g of zirconium oxychloride octahydrate added in the mixing step P8 and 34. Example product 1 in that it is 75, that 5.65 g of neodymium nitrate hexahydrate is further added, and that the amount of 30% hydrogen peroxide solution added to the slurry in the second stirring step P9 is 15.06 g. Different for. In Example Product 5 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 50:50 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 16% by weight, the specific surface area after endurance firing at 1000 ° C. was 43 m ² / g, and the Ce utilization rate was 97%. The left-right width ratio of XRD was 58:42.

(Example product 6)
Example product 6 of the co-catalyst 10 (composite oxide in which an yttrium-doped ceria zirconia shell is fixed on the surface of a lanthanum-doped zirconia core (Y: La: Zr: Ce = 7: 3: 60: 30 in terms of oxide weight ratio) ) Will be described. Example product 6 is produced through substantially the same steps as those shown in FIGS. 2 and 3, but in order to change the ratio of zirconia to ceria with respect to Example product 1, FIG. In the first stirring step P2 of the above, 8.56 g of lanthanum nitrate hexahydrate was added, the first calcining in FIG. 2 was at room temperature (without firing), the distilled water was 180 g, and in FIG. The point that the amount of zirconium oxychloride octahydrate added in the mixing step P8 is 71.32 g, the point that the amount of diammonium cerium nitrate is 86.87, the point that 12.02 g of yttrium hexahydrate added is further added, the second point. It differs from Example Product 1 in that the amount of 30% hydrogen peroxide solution added to the slurry in the stirring step P9 is 37.64 g. In Example Product 5 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 60:40 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 19% by weight, the specific surface area after endurance firing at 1000 ° C. was 41 m ² / g, and the Ce utilization rate was 95%. The left-right width ratio of XRD was 56:44.

(Example product 7)
The method for producing Example 7 of the co-catalyst 10 (composite oxide in which a ceria zirconia shell is fixed on the surface of an yttrium-doped zirconia core (Y: Zr: Ce = 2: 68:30 in terms of oxide weight ratio)) will be described. To do. First, in order to prepare a core powder, yttrium oxide is dissolved in hydrochloric acid to prepare a 0.1 mol / l yttrium oxide solution. Then, 83.79 g of zirconium oxychloride octahydrate is dissolved in 234 ml of distilled water. After adding 157.94 g of 30% hydrogen peroxide solution to the solution, 149 ml of 0.1 mol / l yttrium oxide solution is added and stirred, and 28% aqueous ammonia is added to form a precipitate. The slurry containing this precipitate is transferred to a Teflon container, subjected to hydrothermal treatment at 180 ° C. for 5 hours using an autoclave, and then the precipitate is collected and washed by filtration, dried at 80 ° C. for 24 hours, and placed in a mortar. After pulverization, the first calcining is performed at 750 ° C. for 3 hours.
Next, a shell is prepared using the core powder obtained as described above. First, 20 g of the above core powder, 90 g of distilled water, 39.23 g of zirconium oxychloride octahydrate, 47.78 g of diammonium cerium nitrate, and 300 g of zirconia balls are placed in a 1 L container and ball milled for 18 hours. 20.4 g of 30% hydrogen peroxide solution is added to the slurry after the ball mill, and this slurry is added to 28% aqueous ammonia to form a precipitate. The slurry containing this precipitate is placed in a 1 L container together with 300 g of zirconia balls and ball milled for 18 hours. After the ball mill, the slurry is transferred to a Teflon container and hydrothermally treated at 180 ° C. for 5 hours using an autoclave. The precipitate is collected and washed by filtration, dried at 80 ° C. for 24 hours, crushed in a mortar, and then subjected to a second calcining at 800 ° C. for 3 hours. Then, a durability test at 1000 ° C. for 12 hours is performed.
In Example Product 7 produced in this way, the composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 50:50 in terms of oxide weight ratio, and among the ceria contained in the shell, zirconia and The ratio of non-solid solution was 15% by weight, the specific surface area after endurance firing at 1000 ° C. was 41 m ² / g, and the Ce utilization rate was 98%. The left-right width ratio of XRD was 57:43.

(Comparative example product 1)
Comparative Example Product 1 of the co-catalyst is manufactured as follows. That is, zirconia sol and ceria sol are mixed so that the oxide weight ratio is Zr: Ce = 65: 35, an aqueous nitric acid solution is added to lower the pH to 3, and then 28% aqueous ammonia is added to raise the pH to 11. Then, the precipitate was recovered from the slurry and dried, and then calcined at 800 ° C. for 3 hours to obtain Comparative Example Product 1. Comparative Example Product 1 produced in this way is a composite oxide in which zirconia sol is used and ceria is fixed on the surface of the zirconia core, and the composition ratio of ceria zirconia, which is the main component of the shell. Is ceria: zirconia = 100: 0 in terms of oxide weight ratio, and the ratio of ceria contained in the shell that is not solid-dissolved with zirconia is 28% by weight, and the specific surface area after endurance firing at 1000 ° C. is It was 20 m ² / g, and the Ce utilization rate was 72%.

(Comparative example product 2)
Comparative Example Product 2 of the co-catalyst is manufactured as follows. First, the core powder is obtained by the same method as in FIG. Next, 30 g of the above calcined powder, 90 g of distilled water, and 15.94 g of diammonium cerium nitrate are placed in a 1 L ball mill container containing 300 g of zirconia balls, and pulverized by a ball mill for 12 hours. Next, in the second stirring step P9, the slurry after the ball mill is added to 300 g of 28% ammonia water, and in the second precipitate formation step P10, the slurry after the stirring is pulverized by the ball mill for 12 hours. In the subsequent second filtration / washing step P12, the slurry is filtered and washed to collect the precipitate, and in the second drying step P13, it is dried at 80 ° C. for 24 hours. Then, in the second calcining step P14, the dried powder of the slurry is crushed in a mortar to obtain a uniform powder without aggregates, and then calcined at 800 ° C. for 3 hours to react the core. A powder of Comparative Example Product 2 having a shell supported around it is obtained. In the production of this Comparative Example Product 2, 26.16 g of zirconium oxychloride octahydrate was not used in the mixing step P8, and 30% hydrogen peroxide solution was added to the slurry in the second stirring step P9 with respect to FIG. It is not added to 13.8 g, and the second hydrothermal treatment step P11 is not used. Comparative Example Product 2 thus obtained is a composite oxide in which zirconia powder is used, in which ceria is fixed to the surface of the zirconia core, and the composition of ceria zirconia, which is the main component of the shell. The ratio is ceria: zirconia = 100: 0 in terms of oxide weight ratio, and the ratio of ceria contained in the shell that is not solid-dissolved with zirconia is 48% by weight, and the specific surface area after endurance firing at 1000 ° C. Was 34 m ² / g, and the Ce utilization rate was 66%. The left-right width ratio of XRD was 53:47.

(Comparative example product 3)
Comparative Example Product 3 of the co-catalyst is manufactured as follows. First, 83.79 of zirconium oxychloride octahydrate is dissolved in 234 ml of distilled water, 157.94 g of 30% hydrogen peroxide solution is added thereto, and then 17.11 g of lanthanum nitrate hexahydrate is added. Further, 81.68 g of diammonium cerium nitrate is added and stirred. Then, 600 ml of aqueous ammonia is added to form a precipitate. Stop stirring, transfer the slurry to a Teflon container, and perform hydrothermal treatment at 180 ° C. for 5 hours using an autoclave. The slurry after hydrothermal treatment is filtered and washed, and the recovered precipitate is dried at 80 ° C. for 24 hours. The dried powder is crushed (unraveled) in a mortar and baked at 800 ° C. for 3 hours. The Comparative Example product 3 thus obtained was not a core-shell structure but uniform solid solution particles, had a specific surface area of 40 m ² / g after endurance firing at 1000 ° C., and had a Ce utilization rate of 80%.

As shown in the co-catalyst 10, the Examples 1 to 7 have a core-shell structure in which a ceria zirconia shell 14 is fixed to the surface of a core 12 containing zirconia as a main component, and the core 12 is a tetragonal crystal. Shell 14 has a composition ratio of ceria: zirconia in the range of 25:75 to 60:40 in oxide weight ratio, and the ceria of shell 14 that is not solid-dissolved with zirconia. The ratio is in the range of 10 to 20% by weight, the temperature Tcz showing a peak in the TPR curve is low, and the cerium utilization rate is high.

In FIG. 4 showing a time-dependent change curve (TPR curve) of the thermal conductivity of the reduced gas obtained by the temperature-increasing reduction method, (a) is an example product as a representative example of the example products 1 to 7. The TPR curve of Comparative Example Product 1 is shown, and FIG. 1B shows the TPR curve of Comparative Example Product 2 as a representative example of Comparative Example Products 1 to 3. Example product 1 and Comparative Example product 2 each show a peak of the TPR curve in the range of 500 ° C to 600 ° C. However, Example product 1 has a higher thermal conductivity of the reducing gas than Comparative Example product 2 and has high oxygen. It has the ability to store and release (OSC).

The present inventors used the X-ray analyzer RINT-TTRIII manufactured by Rigaku Denki Co., Ltd., and used Cu-Kα rays under the conditions of 50 kV, 50 mA, and 2θ = 2 ° to measure the above-mentioned co-catalyst sample ( Powder X-ray diffraction (XRD) of the example product and the comparative example product was performed. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9 show the diffraction pattern of the X-ray diffraction.

FIG. 5A shows the diffraction pattern of Example product 1 as a representative example of Example product 1 to Example product 3, and in FIG. 5A, 29 ° in the diffraction pattern of Example product 1 The peaks at 34 °, 49 °, 59 °, and 62 ° can be attributed to the peaks derived from tetragonal zirconia indicated by black circles. FIG. 5B is a diagram showing the diffraction pattern (dashed line) of Example Product 1 and the diffraction pattern (solid line) of the core used in Example Product 1 in the vicinity of 2θ = 30 ° in an overlapping manner. is there. In FIG. 5 (b), peaks derived from ceria and peaks derived from zirconia, which are adjacent to each other, are linked to each other. For example, a peak derived from ceria at 2θ = 30 ° is linked to a peak derived from zirconia and is almost invisible. It forms two peaks, indicating that ceria and zirconia are in solid solution with each other. Example product 1 is characterized in that the base on the side where the peak diffraction angle is small is wider than that of zirconia. Such characteristics are the same for other peaks of the diffraction pattern.

FIG. 7 shows the diffraction pattern of Comparative Example Product 2. The peak of the black rhombus in FIG. 7 is attributed to the diffraction pattern of cerium oxide (ceria). The peaks marked with black rhombus and the peaks derived from tetragonal zirconia indicated by black circles are not linked to each other, indicating that the solid solution between ceria and zirconia has not progressed.

FIG. 8 shows the diffraction pattern of Comparative Example Product 3. The black inverted triangle mark in FIG. 8 indicates the peak of the ceria zirconia solid solution. This indicates that Comparative Example Product 3 is composed of a uniform solid solution of ceria zirconia.

9 shows the diffraction pattern of Example product 1 (dashed line) shown in FIG. 5A, the diffraction pattern of Comparative Example product 2 shown in FIG. 7 (broken line), and the comparative example shown in FIG. It is a figure which superimposes the diffraction pattern (solid line) of the product 3 on a common horizontal axis (diffraction angle axis), and takes out the diffraction angle around 2θ = 30 °. In FIG. 9, the diffraction pattern of Example Product 1 shown by the solid line is similar to the diffraction pattern of tetragonal zirconia as shown in FIG. 5 (b), but the base of the peak spreads toward the low diffraction angle side. ing. In the diffraction pattern of Comparative Example Product 2 shown by the alternate long and short dash line, the peak derived from tetragonal zirconia and the peak derived from cerium oxide (ceria) appear apart, and it is estimated that there are many undissolved ceria. Will be done. In the diffraction pattern of Comparative Example Product 3 shown by the alternate long and short dash line, a peak appears between the peak derived from tetragonal zirconia and the peak derived from cerium oxide (ceria), and most of the ceria is dissolved. Is estimated.

FIG. 10 shows the core average primary particle diameter (nm) of each of the above-mentioned Example products 1 to 7 and Comparative Example products 1 to 3 and the weight ratio of CeO ₂ and ZrO ₂ in the shell. Overall composition (oxide weight ratio), temperature Tcz (° C) showing peak oxygen release characteristics, ratio of shell cerium that is not solid-dissolved with zirconia (% by weight), specific surface area after endurance firing at 1000 ° C (%) It is a chart which shows m ² / g) and cerium utilization rate (%). In FIG. 10, the core average primary particle diameter of Examples 1 to 7 is 5 to 50 nm. Further, in Examples 1 to 7, the ratio of non-solid solution to Comparative Examples 1 to 3 is 10 to 20%, and the specific surface area after endurance firing at 1000 ° C. is 41. It is (m ² / g) or more and relatively large, and the Ce utilization rate is 95% or more and relatively large.

The relationship between the diameter d of the core average primary particles (zirconia) and the specific surface area Rs of the core is shown by the following equation (3). In equation (3), the surface area of the primary particles is S, the mass is M, and the density of zirconia is ρ.
Rs = S / M = 6 / ρ × d ・ ・ ・ (3)
When the density ρ of zirconia is 6 (g / cm ³ ), when the particle size of zirconia is d = 1 μm from Eq. (3), the specific surface area Rs is 1 m ² / g, so the particle size of zirconia is When d = 5 nm, the specific surface area Rs is estimated to be 200 m ² / g. That is, when the average primary particle size of the core is 5 to 50 nm, the specific surface area of the core is estimated to be 20 to ²⁰⁰ m ² / g.

Further, in FIG. 10, in the XRD of Example products 1 to 7, the peak near 30 ° is not broken and shows a single peak, but it has a left-right asymmetric shape and the left-right width ratio is It is from 55:45 to 70:30. In the XRDs of Comparative Examples Products 1 and 2, the peak near 30 ° is broken. Comparative Example product 3 is not cracked, but has a left-right width ratio of 51:49. In XRD, there is a peak derived from zirconia near 30 °, a peak derived from ceria near 28.5 °, and when ceria and zirconia are solid-solved, they are around 28.5 ° and around 30 °. A peak is detected between and. In Comparative Example Product 2, since the peak derived from zirconia and the peak derived from ceria are present, it is presumed that the solid solution between ceria and zirconia is not so advanced. On the other hand, in Comparative Example Product 3, since ceria and zirconia are almost all dissolved in solid solution, the lateral width ratio is 51:49. In Example product 1, since a small amount of undissolved ceria is present, the peak spreads to the low angle side, so that the lateral width ratio of the peak changes according to the abundance of undissolved ceria. When the proportion of ceria that is not solid-solved with zirconia is high, the ceria particles are bonded to each other to form large particles, the specific surface area is reduced, and the Ce utilization rate is lowered.

As described above, according to the co-catalyst 10 of this example, the composition ratio of ceria zirconia, which is the main component of the shell 14, is in the range of ceria: zirconia = 25:75 to 60:40 in terms of oxide weight ratio. The ratio of ceria contained in the shell 14 that is not solid-dissolved with zirconia is in the range of 10 to 20% by weight, so that the oxygen release characteristic, that is, the thermal conductivity of the reducing gas is changed over time. A co-catalyst having a low temperature Tcz showing a peak in the TPR curve) and a high Ce utilization rate can be obtained.

Further, according to the co-catalyst 10 of this example, the core 12 has a tetragonal crystal structure in which oxygen can be easily transferred. High durability can be obtained because the core 12 supporting the shell 14 containing ceria zirconia as a main component has a tetragonal crystal structure. Further, since the core 12 has a tetragonal crystal structure in which oxygen can easily move, a high oxygen occlusion / release ability can be obtained and the Ce utilization rate becomes high.

Further, in the method for producing the auxiliary catalyst for purifying automobile exhaust gas in this example, (a) zirconium oxychloride octahydrate (water-soluble zirconium salt) and lanthanum nitrate hexahydrate (water-soluble lanthanum salt) are used as distilled water. Dissolving step P1 to dissolve, and (b) first precipitate forming step P3 to form a first precipitate by adding aqueous ammonia, potassium hydroxide, etc. (precipitant) to the liquid obtained in the dissolving step P1. c) A first hydrothermal reaction P4 in which a hydrothermal treatment is applied to the first precipitate obtained in the first precipitate formation step P3, and (d) a first hydrothermal reaction product hydrothermally treated in the first hydrothermal treatment step P4. The first calcining step P7 to obtain a core powder by calcining the dried product of the above, and (e) the core powder, distilled water, zirconium oxychloride octahydrate (water-soluble zirconium salt), and diammonium cerium nitrate (cerium nitrate). A second precipitate that produces a second precipitate by adding aqueous ammonia, potassium hydroxide, etc. (precipitant) to the mixed solution obtained in the mixing step P8 to mix with the water-soluble cerium salt) and (f) mixing step P8. The product formation step P10, the second hydrothermal treatment step P11 for adding hydrothermal treatment to the second precipitate produced by (g) the second precipitate formation step P10, and (h) the second hydrothermal treatment step P11 for hydrothermal treatment. Including the second calcining step P14, in which the dried product of the second hydrothermal reaction product is calcined to obtain particles in which a shell containing ceria zirconia is fixed to the surface of a core containing zirconia as a main component. .. From this, the auxiliary catalyst 10 for purifying automobile exhaust gas can be preferably obtained.

Although the examples of the present invention have been described in detail with reference to the drawings, the present invention also applies to other aspects.

The co-catalyst 10 of this embodiment is supported on a honeycomb-shaped catalyst device main body together with platinum 14 which is a catalytically active substance, but a catalyst such as palladium or rhodium may be used instead of platinum 14.

Further, in the co-catalyst 10 of this example, in the dissolution step P1 of the above-mentioned Example product 1, "zirconium oxychloride octahydrate" is used as the water-soluble zirconium salt, and "lantern six nitrate" is used as the water-soluble lanthanum salt. "Hydrates" have been used, but they are examples, and others may be used, as in Example 7. In short, in the dissolution step P1, at least one of yttrium, lanthanum, praseodymium, and neodymium can be dissolved together with the water-soluble zirconium salt. Further, in the first precipitate forming step P3 and the second precipitate forming step P10, aqueous ammonia, potassium hydroxide and the like were used as the precipitating agent, but these are examples, and other ones may be used. Good. Further, in the mixing step P8, zirconium oxychloride octahydrate was used as the water-soluble zirconium salt, and diammonium cerium nitrate was used as the water-soluble cerium salt, but these are examples, and others are used. May be done.

Further, in the first calcining step P7 of FIG. 2 described above, the firing conditions of 750 ° C. for 3 hours were used, and in the second calcining step P14 of FIG. 3, the firing conditions of 800 ° C. for 3 hours were used. However, they are exemplary, and temperatures lower than those temperatures, such as 300 ° C. and 400 ° C., may be used for firing times of 1 hour or 2 hours.

Further, in the mixing step P8 of FIG. 3 described above, the mixing time of the ball mill was 18 hours, but it may be shorter than this, for example, 1 hour or 2 hours.

Further, in the first hydrothermal treatment step P4 of FIG. 2 and the second hydrothermal treatment step P11 of FIG. 3, the treatment conditions were 180 ° C. to 5 hours, respectively, but the temperature was lower than this and the time was shorter. There may be.

Further, in the core manufacturing step of FIG. 2 and the shell manufacturing step of FIG. 3 described above, other elements such as rare earth elements may be contained in the core or shell by adding a rare earth element or the like.

Further, in the above-mentioned Example Product 1, in the mixing step P8, "zirconium oxychloride octahydrate" which is a water-soluble zirconium salt and "diamium cerium nitrate" which is a water-soluble cerium salt were used. , "Lanthanum nitrate hexahydrate", "Neodymium nitrate hexahydrate", "Ithrium chloride hexahydrate" are further used as in Examples 4 to 6, and water-soluble salts of "praseodymium" are used. Similar results can be obtained when used. In short, in the mixing step P8, at least one of yttrium, lanthanum, praseodymium, and neodymium can be further mixed with the water-soluble zirconium salt and the water-soluble cerium salt.

It should be noted that the above is only one embodiment, and the present invention can be carried out in a mode in which various changes and improvements are made based on the knowledge of those skilled in the art.

10: Auxiliary catalyst 12: Core 14: Shell L1: Center line L2: Left end line L3: Right end line L4: Base line P1: Melting step P3: First precipitate formation step P4: First hydrothermal treatment step P7: First calcining Step P8: Mixing step P10: Second sediment formation step P11: Second hydrothermal treatment step P14: Second calcining step

Claims (5)

An auxiliary catalyst for purifying automobile exhaust gas, which is composed of a core containing zirconia as a main component and a shell fixed to the surface of the core and containing ceria zirconia as a main component.
The composition ratio of ceria zirconia, which is the main component of the shell, is ceria: zirconia = 25:75 to 60:40 in terms of oxide weight ratio.
The proportion of the ceria contained in the shell that is not solid-solved with the zirconia contained in the shell is 10 to 20% by weight.
The core is an auxiliary catalyst for purifying automobile exhaust gas, which is characterized by having a tetragonal crystal structure. The auxiliary catalyst for purifying automobile exhaust gas according to claim 1, wherein the core has an average primary particle diameter of 5 to 50 nm. In the powder X-ray diffraction pattern of ceria zirconia, the vertical axis passing through the point where the X-ray intensity is maximum is the center line, and the vertical axis passing through the two points where the left and right slopes are zero is the left end line and the right end line, respectively. With the straight line passing through the two points where the slope becomes zero as the baseline, the length between the center line and the left end line and the length between the center line and the right end line on the baseline. The auxiliary catalyst for purifying automobile exhaust gas according to claim 1 or 2, wherein the lateral width ratio of the ceria zirconia is 55:45 to 70:30, where the ratio is the lateral width ratio. The method for producing an auxiliary catalyst for purifying automobile exhaust gas according to any one of claims 1 to 3.
A dissolution step of dissolving the water-soluble zirconium salt and at least one of yttrium, lanthanum, praseodymium, and neodymium in distilled water.
A first precipitate forming step of adding a precipitating agent to the liquid obtained by the dissolution step to form a first precipitate, and
A first hydrothermal treatment step of adding a hydrothermal treatment to the first precipitate obtained by the first precipitate formation step,
The first calcining step of calcining the dried product of the first hydrothermal reaction product hydrothermally heat-treated by the first hydrothermal treatment step to obtain a crystallized core powder.
A mixing step of mixing the core powder, distilled water, a water-soluble zirconium salt, and a water-soluble cerium salt.
A second precipitate forming step of adding a precipitating agent to the mixed solution obtained by the mixing step to form a second precipitate, and a second precipitate forming step.
A second hydrothermal treatment step of adding a hydrothermal treatment to the second precipitate produced by the second precipitate forming step, and a second hydrothermal treatment step.
The dried product of the second hydrothermal reaction product hydrothermally heat-treated in the second hydrothermal treatment step is calcined, and a shell containing ceria zirconia as a main component is fixed on the surface of a core containing zirconia as a main component to purify automobile exhaust gas. Including a second calcining step of obtaining particles of the auxiliary catalyst,
A method for manufacturing an auxiliary catalyst for purifying automobile exhaust gas, which is characterized in that. The method for producing an auxiliary catalyst for purifying automobile exhaust gas according to claim 4, wherein the mixing step further mixes at least one water-soluble salt of yttrium, lanthanum, praseodymium, and neodymium.

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