JP2018134618A - Automobile exhaust gas cleaning cocatalyst and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automobile exhaust gas cleaning cocatalyst having a high oxygen storage/release capacity (OSC) and a high cerium utilization factor at relatively low temperatures, and also to provide a method of manufacturing the same.SOLUTION: A ceria:zirconia ratio as the composition ratio in a ceria-zirconia which is the main component of a shell 14 is within a range of 25:75 to 60:40 in terms of oxide weight ratio and the rate of the ceria contained in the shell 14 not solid-dissolved to the zirconia contained in the shell 14 to the ceria contained in the shell is within the range of 10 to 20 wt.%, so that a cocatalyst 10 is obtained in which a temperature Tcz representing a peak is lower in an oxygen release characteristic, or a temporal change curve (TPR curve) of a heat conductivity of the reduction gas, and the cerium utilization factor is high.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an automobile exhaust gas purification co-catalyst and a method for producing the same.

A so-called three-way catalyst is used to purify hydrocarbon (HC), carbon monoxide (CO), and nitrogen carbide (NO _x ) contained in automobile exhaust gas. Cerium oxide is used as a promoter for an automobile exhaust gas purification catalyst because it has an oxygen storage / release capability (OSC) that takes in oxygen in an oxidizing atmosphere and releases oxygen in a reducing atmosphere. As described in Patent Document 1 and Patent Document 2, at present, a ceria zirconia composite oxide in which ceria and zirconia are dissolved is generally used in order to enhance durability at high temperatures. Yes.

Special table 2009-537304 gazette JP, 2006-008168, A

  It is known that the function of a ceria zirconia homogeneous solid solution in which ceria and zirconia are uniformly dissolved is greatly reduced at low temperatures. When the automobile engine is started in a cold state, the gas exhausted until reaching the operating temperature at which the catalyst exhibits a sufficient purification function does not sufficiently react with the catalyst and is released to the atmosphere.

  Therefore, in order to reduce the temperature Tcz showing the peak of the oxygen release characteristic in order to prevent discharge of unreacted emissions, in Patent Document 1, tin is added to the promoter. However, when the additive is increased in this way, the component system of the promoter becomes complicated, and the inconvenience that the solid solution ratio of ceria and zirconia deteriorates and the oxygen storage / release ability decreases may occur. .

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

  The present invention has been made against the background of the above circumstances, and its object is to have a high oxygen storage / release capacity (OSC) at a relatively low temperature and to provide oxygen release characteristics, that is, heat conduction of a reducing gas. The object is to provide an automobile exhaust gas purifying co-catalyst having a low temperature Tcz and a high cerium utilization rate, and a method for producing the same.

  As a result of various investigations in the background of the above circumstances, the present inventors, as a result, a core mainly composed of zirconia, and a shell (outer shell) mainly adhered to the surface of the core and mainly composed of ceria zirconia. The composition ratio of ceria zirconia, which is the main component of the shell, in the configured automobile exhaust gas purification co-catalyst is within the range of ceria: zirconia = 25: 75-60: 40 in terms of oxide weight ratio, and is included in the shell If the ratio of the ceria not dissolved in the zirconia contained in the shell is within the range of 10 to 20% by weight, the temperature Tcz showing the peak in the oxygen release characteristic is lowered, and the cerium utilization rate is reduced. It was found that a high promoter can be obtained. The present invention has been made based on such knowledge.

  That is, the gist of the first invention is that (a) an automobile exhaust gas purification assistant comprising a core mainly composed of zirconia and a shell fixed to the surface of the core and mainly composed of ceria zirconia. The composition ratio of ceria zirconia, which is a catalyst as a 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. Among them, the proportion of the shell not dissolved in 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 the 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 inclinations are zero 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 inclination is zero is the base line, and on the base line, the length between the center line and the left end line and the center line When the ratio of the length to the right end line is 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 a method for producing an automotive exhaust gas purifying co-catalyst of the first invention or the second invention, wherein (a) at least one of water-soluble zirconium salt and yttrium, lanthanum, praseodymium, neodymium. A dissolution step of dissolving a seed water-soluble salt in distilled water; (b) a first precipitate generation step of generating a first precipitate by adding a precipitant to the liquid obtained by the dissolution step; and (c). A first hydrothermal treatment step in which hydrothermal treatment is performed on the first precipitate obtained in the first precipitate generation step; and (d) a dried product of the first hydrothermal reaction product hydrothermally treated in the first hydrothermal treatment step. A first calcination step of obtaining a crystallized core powder, (e) a mixing step of mixing the core powder, distilled water, a water-soluble zirconium salt, and a water-soluble cerium salt; f) obtained by the mixing step A second precipitate generating step for generating a second precipitate by adding a precipitant to the mixed solution; and (g) a second hydrothermal treatment for applying a hydrothermal treatment to the second precipitate generated by the second precipitate generating step. And (h) calcining a dried product of the second hydrothermal reaction product hydrothermally treated in the second hydrothermal treatment step, and a shell containing ceria zirconia as a main component on a surface of a core mainly containing zirconia. And a second calcination step of obtaining particles of a cocatalyst for purifying automobile exhaust gas that has been fixed.

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

  According to 1st invention, the composition ratio of the ceria zirconia which is the main component of the said shell is set to the range of ceria: zirconia = 25: 75-60: 40 by oxide weight ratio, The said ceria contained in the said shell The proportion not dissolved in the zirconia contained in the shell is within the range of 10 to 20% by weight, and the core has a tetragonal crystal structure. Thus, a promoter having a low temperature Tcz and a high cerium utilization rate can be obtained. Further, since the core supporting the shell mainly composed of ceria zirconia has a tetragonal crystal structure, high durability is obtained, and oxygen is easily transferred, so that a high oxygen storage / release capability is obtained, and Increases cerium utilization.

According to the second invention, the core has an average primary particle diameter of 5 to 50 nm. For this reason, a large specific surface area of 20 to ²⁰⁰ m ² / g is obtained, and high catalyst performance is obtained.

  According to the third invention, since the ceria zirconia has a left-right width ratio of 55:45 to 70:30, a promoter 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 automobile exhaust gas purifying co-catalyst of the fourth invention, (a) a dissolving step of dissolving at least one water-soluble zirconium salt and yttrium, lanthanum, praseodymium, neodymium in distilled water; (B) a first precipitate generating step for generating a first precipitate by adding a precipitant to the liquid obtained by the dissolving step; and (c) a first precipitate obtained by the first precipitate generating step. A first hydrothermal treatment step of subjecting the product to hydrothermal treatment; and (d) a first hydrothermal reaction product hydrothermally treated by the first hydrothermal treatment step, calcined 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 liquid obtained by the mixing step P8. Agent is added to form a second precipitate (G) a second hydrothermal treatment step in which hydrothermal treatment is performed on the second precipitate produced in the second precipitate production step; and (h) water is produced in the second hydrothermal treatment step. The heat-treated dried product of the second hydrothermal reaction product is calcined to obtain particles of an automobile exhaust gas purification co-catalyst in which a shell mainly composed of ceria zirconia is fixed to the surface of the core mainly composed of zirconia. Since the two calcining steps are included, the automobile exhaust gas purification promoter of the first invention and the automobile exhaust gas purification promoter of the second invention are suitably obtained.

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

It is a schematic diagram which shows the particle | grains of the promoter which is one Example of this invention. It is process drawing explaining the core manufacturing process for manufacturing a core among the manufacturing processes of the promoter of FIG. It is process drawing explaining the shell manufacturing process for manufacturing the shell fixed to the surface of the core manufactured by the manufacturing process of FIG. 2 among the manufacturing processes of the promoter of FIG. It is a figure which shows the time-dependent change curve (TPR curve) of the thermal conductivity of the reducing gas obtained by the temperature rising reduction method, (a) is an Example product as a representative example of Example product 1 to Example product 3. 2 shows a TPR curve of Comparative Example Product 2 as a representative example of Comparative Example Product 1 to Comparative Example Product 3. FIG. It is a figure which shows the powder X-ray-diffraction (XRD) diffraction pattern of the co-catalyst sample used as a measuring object, (a) is the Example shown with a dashed-dotted line as a representative example of Example goods 1-Example goods 6 The diffraction pattern of the product 1 and the diffraction pattern of the core used in Example 1 indicated by the thin line and the peak derived from tetragonal zirconia indicated by the black circles are shown, (b) is one point when the diffraction angle 2θ is around 30 °. The diffraction pattern of Example product 1 indicated by a chain line and the diffraction pattern of tetragonal zirconia, which is a core used in Example 1 indicated by a 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 Drawing 5 (a) showing a diffraction pattern of comparative example goods 2. It is a figure corresponding to Drawing 5 (a) showing a diffraction pattern of comparative example goods 3. Of the diffraction pattern of the example product 1 indicated by the one-dot chain line, the diffraction pattern of the comparative example product 2 indicated by the broken line, and the diffraction pattern of the comparative example product 3 indicated by the solid line, a pattern having a diffraction angle 2θ of around 30 ° FIG. FIG. 2 is 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 FIG. 2 and FIG. 3, that is, the characteristics of Example Product 1-7 and Comparative Product 1-3. It 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 a promoter 10 to which the present invention is preferably applied. The co-catalyst 10 is constituted by 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 around the core 12 in an outer shell shape. The co-catalyst 10 is an automobile exhaust gas that is a three-way catalytic converter that purifies, for example, carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO _x ), which are harmful components contained in exhaust gas from an internal combustion engine. A catalyst phase provided on the inner peripheral surfaces of a plurality of insertion holes (not shown) of a honeycomb-shaped main body member (not shown) made of porous ceramic of a purification catalyst device is supported together with a main catalyst powder such as platinum.

  Ceria zirconia, which is the main component of the shell 14, suppresses the deterioration of platinum efficiency due to fluctuations in the oxygen concentration in the exhaust gas depending on operating conditions and the like. When the oxygen around the catalyst phase is excessive, It functions as an oxygen storage / release material having an oxygen storage / release capability (OSC) that stores oxygen and releases oxygen when the oxygen around the catalyst phase is insufficient. The OSC amount 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 promoter 10 is composed mainly of zirconia (ZrO ₂ ) having a tetragonal crystal structure. The shell 14 fixed to the surface of the core 12 is mainly composed 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 of the ceria contained in the shell 14, it is not dissolved in zirconia. The proportion ranges 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 durability at 1000 ° C., and the reduction peak temperature Tcz is low and the cerium utilization rate is high.

  The cocatalyst 10 adjusts the average primary particle diameter D50 (nm) of the zirconia particles of the core 12 to a relatively small nano-order within a predetermined range, for example, 5 to 50 nm, whereby the amount of OSC per mol of ceria zirconia (L / Mol) is higher than the amount of OSC per 1 mol (L / mol) of the ceria zirconia material having a conventional core-shell structure or the uniform solid solution ceria zirconia material in which ceria and zirconia are uniformly dissolved, and Ce utilization The rate (utilization rate of cerium) is suitably increased.

Below, the experiment example which this inventor etc. performed about the multiple types of sample which changed the component and its ratio is demonstrated. First, a measurement method for evaluating the performance of the promoter used in the experimental example will be described.
(Measurement of average primary particle size of core)
The measurement of the average primary particle diameter of the core is an average value of the measured values of the diameters of the 50 core particles imaged at the time of observation with a TEM (JEOL Co., Ltd. field emission transmission electron microscope: model JEM-2100F). is there.
(Measurement of cocatalyst reduction characteristics (TCD change curve))
In a catalyst analyzer (BELCAT-A) manufactured by Microtrac Bell, 5% hydrogen gas (5% H ₂ / Ar) diluted with argon using a temperature-reduction method (TPR: Temperature-programmed reduction) The oxygen release characteristic was evaluated by measuring the time-dependent change (TCD) characteristic of the thermal conductivity of the reducing gas, which indicates the amount of oxygen released from the cocatalyst in the process of rising from room temperature to 800 ° C. as a reducing gas. FIG. 4 is a diagram showing an example of a temporal change curve (TCD change curve) of the thermal conductivity of the reducing gas.
(Measurement of the amount of Ce not dissolved)
Of the time-dependent change curves (TCD curves) of the thermal conductivity of the reducing gas, 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 Was calculated, the area ratio was calculated, and the amount of Ce not dissolved was calculated.
(Measurement of specific surface area)
A cocatalyst sample to be measured, for example, a powder fired at 800 ° C., is further subjected to durable firing at 1000 ° C. for 12 hours, and the specific surface area of the powder after the durable firing is determined by a specific surface area measuring device (Macsorb) manufactured by Mountec Co., Ltd. HM model-120).
(Evaluation of crystallinity)
Powder X-ray diffraction (XRD) of the promoter 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 (promoter) is placed in a quartz glass tube and heated at a rate of temperature increase of 10 ° C./min in a 5% hydrogen / argon atmosphere at 800 ° C./min. The TPR curve indicating the oxygen release behavior from the sample was detected by monitoring the gas composition change with a thermal conductivity detector (TCD), and was arbitrarily drawn with 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 amount of OSC per mol of Ce in the promoter (L / mol) is the amount of oxygen released per mole of Ce in the sample of the promoter 10, that is, the amount of oxygen released from the sample of the promoter when the temperature is reduced to 800 ° C. is there. Next, the Ce utilization rate (%) of the sample (promoter) is calculated based on the amount of OSC per 1 mol of Ce from the following equation (1). In addition, 6.2 (L / mol) in the formula (1) is the amount of OSC per 1 mol of Ce (L / mol) when all Ce is effectively used, and is calculated by the following formula (2). The The amount of OSC per gram of sample (standard state) in the formula (2) is the TPR curve at 600 ° C. after switching from 5% hydrogen / argon atmosphere to argon atmosphere after temperature reduction based on the above-mentioned evaluation of OSC performance. This was experimentally obtained by performing an atmosphere substitution process until the value of TCD Signal became constant and then introducing a 100% oxygen pulse into the sample until it was saturated. In the formula (2), the sample is Ce _a Zr _(1-a) O ₂ , and a is a ratio of the amount of Ce contained in the sample Ce _a Zr _(1-a) O ₂ .
Ce utilization rate (%) = OSC amount per mol of Ce of each sample (L / mol) ÷ 6.2 (L / mol) × 100% (1)
OSC amount per mol of Ce (L / mol) = (140.116 × a + 91.22 × (1-a) +32) × OSC amount per 1 g of sample (L / g) ÷ a (2)
(Right / left width ratio of XRD)
For example, in the powder X-ray diffraction (XRD) pattern as shown in FIG. 6 which is the diffraction pattern of the comparative product 3, the vertical line passing the point (peak) where the X-ray intensity is maximum is the center line L1, and the left and right For example, the vertical axis passing through two points where the respective 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 base line L4 (bottom line) which is a straight line passing through the two points where the slope is zero. The ratio between 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 product 1 of cocatalyst 10 (composite oxide in which ceria zirconia shell is fixed on the surface of 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. FIG. 2 shows a method for synthesizing the core powder or core 12, and FIG. 3 shows a method for synthesizing the shell 14 on the surface of the core powder or core 12 synthesized in FIG. Although all reagents are manufactured by Wako Pure Chemicals, it is not limited to this.

  In FIG. 2, first, in dissolution step P1 and first stirring step P2, 83.79 g of zirconium oxychloride octahydrate is dissolved in 234 ml of distilled water, and 157.94 g of 30% hydrogen peroxide is added to the solution. After that, 17.1 g of lanthanum nitrate hexahydrate is added and stirred. These zirconium oxychloride octahydrate, hydrogen peroxide, and lanthanum nitrate hexahydrate may be added to any step before adding ammonia water. Next, in the 1st deposit production | generation process P3, 25-28% ammonia water is added to the liquid under stirring, a 1st deposit is produced | generated, and it is set as a slurry state. The pH of the solution at the time of precipitation is about 10-14. In the 1st hydrothermal treatment process P4, after stopping said stirring, a slurry is moved to a Teflon (trademark) container, and hydrothermal treatment is performed for 180 degreeC-5 hours using an autoclave. In the subsequent first filtration / washing step P5, the hydrothermally treated slurry is filtered and washed to collect the precipitate, and dried in the first drying step P6 at 80 ° C. for 24 hours. In the first calcination step P7, the dried powder of the slurry is crushed in a mortar to form a uniform powder without aggregates, and then the first calcination is performed at 750 ° C. for 3 hours. Reaction is performed to obtain calcined powder, that is, core powder. In the first stirring step P2, the hydrogen peroxide solution does not necessarily have to be added. The first hydrothermal treatment step P4 and the first calcination step P7 are not necessarily 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 cerium nitrate are placed in a 1 L ball mill container containing 300 g of zirconia balls. And pulverization with a ball mill for 18 hours. Next, in the second stirring step P9, 13.8 g of 30% hydrogen peroxide water 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 generation step P10, 28% ammonia water is added to the stirring liquid to generate a second precipitate, which is in a slurry state. In the subsequent second hydrothermal treatment step P11, the 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 hydrothermally treated slurry is filtered and washed to collect a precipitate, and dried in the second drying step P13 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 form a uniform powder without aggregates, and then subjected to a second calcining at 800 ° C. for 3 hours. By reacting, the powder of Example Product 1 having a so-called core-shell structure in which the shell 14 is supported in the outer shell shape around the core 12 is obtained. This powder is, for example, particles having an average primary particle diameter of 7 nm. In Example Product 1 manufactured in this manner, 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 not solid solution was 15% by weight, the specific surface area after 1000 ° C. endurance firing was 45 m ² / g, and the Ce utilization rate was 97%. The left-right width ratio of XRD was 57:43. In the second stirring step P9, the hydrogen peroxide solution does not necessarily have to be added. Further, the second hydrothermal treatment step P11 is not necessarily provided.

(Example product 2)
Explaining the production method of Example Product 2 of the co-catalyst 10 (composite oxide in which ceria zirconia shell is fixed on the surface of the lanthanum-doped zirconia core (La: Zr: Ce = 10: 80: 10 in terms of oxide weight ratio)) To do. Example product 2 is manufactured through substantially the same steps as those described in FIGS. 2 and 3, but in order to change the ratio of zirconia and ceria with respect to example product 1, FIG. In the mixing step P8, the zirconium oxychloride octahydrate added in the mixing step P8 is 39.24 g, the diammonium cerium nitrate is 15.94 g, and the 30% hydrogen peroxide solution added to the slurry in the second stirring step P9 is It is different from Example Product 1 in that it is 20.78 g. In Example Product 2 manufactured in this manner, 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 not solid solution was 11% by weight, the specific surface area after 1000 ° C. endurance firing 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)
Explaining the production method of Example Product 3 of the co-catalyst 10 (complex oxide in which ceria zirconia shell is fixed on the surface of lanthanum-doped zirconia core (La: Zr: Ce = 10: 67: 23 in terms of oxide weight ratio)) To do. Example product 3 is manufactured through substantially the same steps as those described in FIGS. 2 and 3 except that the first calcining in FIG. 2 is at 650 ° C., and the ratio of zirconia to ceria. In FIG. 3, the second stirring step in FIG. 3 shows that 22.23 g of zirconium oxychloride octahydrate and 36.62 g of diammonium cerium nitrate are added in FIG. The difference from Example Product 1 is that 30% hydrogen peroxide solution added to the slurry in P9 is 11.73 g. In Example Product 3 manufactured in this manner, 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 not solid-solving was 18% by weight, the specific surface area after 1000 ° C. durable firing was 41 m ² / g, and the Ce utilization rate was 96%. The left-right width ratio of XRD was 59:41.

(Example product 4)
Explaining the production method of Example Product 4 of the co-catalyst 10 (complex oxide in which ceria zirconia shell is fixed on the surface of the lanthanum-doped zirconia core (La: Zr: Ce = 14: 70: 16 in terms of oxide weight ratio)) To do. Example product 4 is manufactured through substantially the same steps as those described in FIGS. 2 and 3 except that the first calcining in FIG. 2 is 800 ° C., and the ratio between zirconia and ceria. In order to change the example product 1, in FIG. 3, the diammonium cerium nitrate added in the mixing step P8 is 25.48 g, the lanthanum nitrate hexahydrate is further added by 5.32 g, The difference from Example Product 1 is that 30% hydrogen peroxide solution added to the slurry in 2 stirring step P9 is 13.8 g. In Example Product 4 thus manufactured, 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. Among ceria contained in the shell, zirconia and The ratio of not solid solution was 14% by weight, the specific surface area after 1000 ° C. durable firing 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 co-catalyst 10 (complex 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 terms of oxide weight ratio)) ) Will be described. The example product 5 is manufactured through substantially the same process as described in FIGS. 2 and 3, but in order to change the ratio of zirconia and ceria with respect to the example product 1, FIG. In the first stirring step P2, 8.56 g of lanthanum nitrate hexahydrate is added. In FIG. 3, 28.53 g of zirconium oxychloride octahydrate added in the mixing step P8 and 34.3% of diammonium cerium nitrate are added. Example product 1 in that 5.65 g of neodymium nitrate hexahydrate is further added to 75, 30% hydrogen peroxide solution added to the slurry in the second stirring step P9 is 15.06 g. Is different. In Example Product 5 manufactured in this manner, 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 not solid solution was 16% by weight, the specific surface area after 1000 ° C. endurance firing 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 co-catalyst 10 (complex oxide in which 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. The example product 6 is manufactured through substantially the same steps as those described in FIGS. 2 and 3, but in order to change the ratio of zirconia and ceria with respect to the example product 1, FIG. In the first stirring step P2, the point of adding 8.56 g of lanthanum nitrate hexahydrate, the point that the first calcination of FIG. 2 is at room temperature (no firing), the point that distilled water is 180 g, in FIG. The point that zirconium oxychloride octahydrate added in the mixing step P8 is 71.32 g, the point that diammonium cerium nitrate is 86.87, the point that 12.02 g of yttrium chloride hexahydrate is further added, The difference from Example Product 1 is that 30% hydrogen peroxide solution added to the slurry in the stirring step P9 is 37.64 g. In Example Product 5 thus manufactured, 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 not solid solution was 19% by weight, the specific surface area after 1000 ° C. endurance firing 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)
Explains the production method of Example Product 7 of the co-catalyst 10 (composite oxide in which ceria zirconia shell is fixed on the surface of yttrium-doped zirconia core (Y: Zr: Ce = 2: 68: 30 in terms of oxide weight ratio)). To do. First, in order to prepare the core powder, yttrium oxide is dissolved in hydrochloric acid to prepare a 0.1 mol / l yttrium oxide solution. Next, 83.79 g of zirconium oxychloride octahydrate is dissolved in 234 ml of distilled water. After adding 157.94 g of 30% aqueous hydrogen peroxide 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 collected and washed by filtration, dried at 80 ° C. for 24 hours, and placed in a mortar. After pulverization, first calcination 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% aqueous hydrogen peroxide 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 the precipitate is accommodated 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, pulverized in a mortar, and then subjected to second calcination at 800 ° C. for 3 hours. Thereafter, a durability test at 1000 ° C. for 12 hours is performed.
In Example Product 7 thus manufactured, 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 not solid-solved was 15% by weight, the specific surface area after 1000 ° C. endurance firing was 41 m ² / g, and the Ce utilization rate was 98%. The left-right width ratio of XRD was 57:43.

(Comparative product 1)
The comparative example product 1 of the cocatalyst is produced as follows. That is, zirconia sol and ceria sol are mixed so that the oxide weight ratio is Zr: Ce = 65: 35, and after adding an aqueous nitric acid solution to pH 3, 28% ammonia water is added to raise it to pH 11. Then, a precipitate was produced, and then the precipitate was recovered from the slurry and dried, followed by baking at 800 ° C. for 3 hours to obtain Comparative Example Product 1. The comparative example product 1 manufactured in this way is a composite oxide in which ceria is fixed to the surface of the zirconia core, using a zirconia sol, 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, of the ceria contained in the shell, the proportion not dissolved in zirconia is 28% by weight, and the specific surface area after 1000 ° C. durable firing is was 20m ² / g, Ce utilization rate was 72%.

(Comparative product 2)
Comparative product 2 of the cocatalyst is produced as follows. First, a core powder is obtained by the same method as in FIG. Next, 30 g of the core powder, 30 g of the 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 generation step P10, the slurry after the stirring is pulverized by a ball mill for 12 hours. In the subsequent second filtration / washing step P12, the slurry is filtered and washed to collect the precipitate, and dried in the second drying step P13 at 80 ° C. for 24 hours. Then, in the second calcining step P14, the dried powder of the slurry is pulverized in a mortar to obtain a uniform powder without aggregates, and then calcined at 800 ° C. for 3 hours to be reacted. A powder of Comparative Example 2 having a shell supported around is obtained. In the production of this comparative example product 2, with respect to FIG. 3, 26.16 g of zirconium oxychloride octahydrate was not used in the mixing step P8, and the slurry was added with 30% hydrogen peroxide water in the second stirring step P9. It is not added to 13.8 g, and the second hydrothermal treatment step P11 is not used. The comparative product 2 obtained in this way is a composite oxide in which ceria is fixed to the surface of the zirconia core, using zirconia powder, 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 of the ceria contained in the shell, the proportion not dissolved in zirconia is 48% by weight, and the specific surface area after 1000 ° C. durable firing Was 34 m ² / g, and the Ce utilization rate was 66%. The left-right width ratio of XRD was 53:47.

(Comparative product 3)
Comparative product 3 of the cocatalyst is produced as follows. First, 83.79 of zirconium oxychloride octahydrate is dissolved in 234 ml of distilled water, 157.94 g of 30% hydrogen peroxide 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. Thereafter, 600 ml of ammonia water is added to form a precipitate. Stirring is stopped, the slurry is transferred to a Teflon container, and hydrothermal treatment is performed at 180 ° C. for 5 hours using an autoclave. The slurry after hydrothermal treatment is filtered and washed, and the collected precipitate is dried at 80 ° C. for 24 hours. The dried powder is pulverized (unraveled) in a mortar and calcined at 800 ° C. for 3 hours. The comparative product 3 thus obtained was not a core-shell structure but uniform solid solution particles, the specific surface area after 1000 ° C. endurance firing was 40 m ² / g, and the Ce utilization rate was 80%.

  As shown in the co-catalyst 10, the example product 1 to the example product 7 have a core-shell structure in which a ceria zirconia shell 14 is fixed to the surface of a core 12 mainly composed of zirconia, and the core 12 is tetragonal. The shell 14 has a composition ratio of ceria: zirconia in the range of 25:75 to 60:40 in terms of oxide weight ratio of the ceria: the ceria of the ceria that is not solid-dissolved with zirconia in the shell 14 ceria. 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 which shows the time-dependent change curve (TPR curve) of the thermal conductivity of the reducing gas obtained by the temperature reduction method, (a) is an example product as a representative example of the example product 1 to the example product 7. 2 shows a TPR curve of Comparative Example Product 2 as a representative example of Comparative Example Product 1 to Comparative Example Product 3. FIG. Example product 1 and comparative product 2 show TPR curve peaks in the range of 500 ° to 600 °, respectively. Example product 1 has a higher thermal conductivity of reducing gas than comparative product 2 and high oxygen. It has occlusion and release ability (OSC).

  The present inventors have used the above-mentioned promoter sample to be measured using Cu-Kα rays under the conditions of 50 kV, 50 mA, 2θ = 2 ° using an X-ray analyzer RINT-TTRIII manufactured by Rigaku Corporation. Example product and Comparative product) were subjected to powder X-ray diffraction (XRD). 5, 6, 7, 8, and 9 show the diffraction patterns of the X-ray diffraction.

  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 peaks derived from tetragonal zirconia indicated by black circles. FIG. 5B is a diagram in which the diffraction pattern (one-dot chain line) of the example product 1 and the core diffraction pattern (solid line) used in the example product 1 are overlapped in the vicinity of 2θ = 30 °. is there. In FIG. 5 (b), the ceria-derived peak and the zirconia-derived peak adjacent to each other are linked to each other, for example, the ceria-derived peak at 2θ = 30 ° is linked to the zirconia-derived peak and is almost not seen. One peak is formed, indicating that ceria and zirconia are in solid solution with each other. Example product 1 has a feature in which the base on the side where the diffraction angle of the peak is small is wider than that of zirconia. Such characteristics are the same in other peaks of the diffraction pattern.

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

  FIG. 8 shows the diffraction pattern of Comparative Example Product 3. Black inverted triangles in FIG. 8 indicate ceria zirconia solid solution peaks. Thereby, it is shown that the comparative example product 3 is composed of a uniform solid solution of ceria zirconia.

  9 shows the diffraction pattern (dotted line) of the example product 1 shown in FIG. 5 (a), the diffraction pattern (broken line) of the comparative example product 2 shown in FIG. 7, and the comparative example shown in FIG. FIG. 3 is a diagram showing the diffraction pattern (solid line) of the product 3 superimposed on a common horizontal axis (diffraction angle axis), with the diffraction angle 2θ = 30 ° being taken out. In FIG. 9, the diffraction pattern of Example Product 1 indicated by a solid line is similar to that of tetragonal zirconia as shown in FIG. 5B, but the peak base spreads toward the low diffraction angle side. ing. In the diffraction pattern of Comparative Example 2 indicated by the one-dot chain line, the peak derived from tetragonal zirconia and the peak derived from cerium oxide (ceria) appear apart, and it is estimated that there is a large amount of ceria that is not dissolved. Is done. In the diffraction pattern of Comparative Example 3 indicated by a two-dot chain 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 in solid solution. Is estimated.

FIG. 10 shows the core average primary particle diameter (nm), the weight ratio of CeO ₂ and ZrO ₂ in the shell of each of the above-mentioned Example product 1 to Example product 7 and Comparative example product 1 to Comparative example product 3. Total composition (oxide weight ratio), temperature Tcz (° C.) showing the peak of oxygen release characteristics, ratio of shell ceria not dissolved in zirconia (wt%), specific surface area after 1000 ° C. endurance firing (weight%) It is a graph which shows m < ² > / g) and a cerium utilization factor (%). In FIG. 10, Example Product 1 to Example Product 7 have a core average primary particle size of 5 to 50 nm. In addition, Example Product 1 to Example Product 7 have a ratio of 10-20% that is not solid-solved with respect to Comparative Product 1 to Comparative Product 3, and a specific surface area after 1000 ° C. endurance firing is 41%. (M ² / g) or more and relatively large, and Ce utilization 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 expressed by the following equation (3). In the formula (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 diameter of zirconia is d = 1 μm from the formula (3), the specific surface area Rs is 1 m ² / g, so the particle diameter of zirconia is When d = 5 nm, the specific surface area Rs is estimated to be 200 m ² / g. That is, when the core average primary particle diameter is 5 to 50 nm, the specific surface area of the core is estimated to be 20 to ²⁰⁰ m ² / g.

  Moreover, in FIG. 10, in the XRD of Example product 1 to Example product 7, the peak near 30 ° is not cracked and shows a single peak, but has a left-right asymmetric shape, and the left-right width ratio is 55:45 to 70:30. In the XRDs of Comparative Examples 1 and 2, the peak near 30 ° is broken. Although the comparative example product 3 is not cracked, the left-right width ratio is 51:49. In XRD, there is a zirconia-derived peak at around 30 °, a ceria-derived peak at around 28.5 °, and when ceria and zirconia are dissolved, they are around 28.5 ° and around 30 °. A peak is detected between In Comparative Example Product 2, since a zirconia-derived peak and a ceria-derived peak are present, it is presumed that solid solution of ceria and zirconia has not progressed so much. On the other hand, in Comparative Example Product 3, since ceria and zirconia are almost completely dissolved, the left-right width ratio is 51:49. In Example Product 1, since a small amount of ceria that is not dissolved is present, the peak spreads to the low angle side, so the left-right width ratio of the peak changes according to the amount of ceria that is not dissolved. When the ratio of the ceria not dissolved in zirconia is high, the ceria particles are combined to form large particles, the specific surface area is reduced, and the Ce utilization rate is reduced.

  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 the ceria contained in the shell 14 not dissolved in zirconia is in the range of 10 to 20% by weight, so that the oxygen release characteristic, that is, the time-dependent change curve of the thermal conductivity of the reducing gas ( A temperature Tcz showing a peak in the TPR curve) is lowered, and a promoter having a high Ce utilization rate is obtained.

  Moreover, according to the promoter 10 of the present embodiment, the core 12 has a tetragonal crystal structure in which oxygen can be easily transferred. Since the core 12 supporting the shell 14 mainly composed of ceria zirconia has a tetragonal crystal structure, high durability can be obtained. Further, since the core 12 has a tetragonal crystal structure in which oxygen easily moves, a high oxygen storage / release capability is obtained and the Ce utilization rate is increased.

  In addition, the production method of the automobile exhaust gas purification co-catalyst of this example is as follows. (A) Zirconium oxychloride octahydrate (water-soluble zirconium salt) and lanthanum nitrate hexahydrate (water-soluble lanthanum salt) in distilled water. A dissolving step P1 for dissolving, and (b) a first precipitate generating step P3 for adding ammonia water, potassium hydroxide or the like (precipitating agent) to the liquid obtained by the dissolving step P1 to generate a first precipitate; c) a first hydrothermal treatment step P4 in which hydrothermal treatment is performed on the first precipitate obtained in the first precipitate generation step P3; and (d) a first hydrothermal reactant hydrothermally treated in the first hydrothermal treatment step P4. A first calcining step P7 for calcining the dried product to obtain a core powder, (e) the core powder, distilled water, zirconium oxychloride octahydrate (water-soluble zirconium salt) and diammonium cerium nitrate ( Water-soluble cerium salt A mixing step P8 for mixing with (f) a second precipitate generation step P10 for adding ammonia water, potassium hydroxide or the like (precipitating agent) to the mixed solution obtained by the mixing step P8 to generate a second precipitate; (G) a second hydrothermal treatment step P11 in which a hydrothermal treatment is applied to the second precipitate produced in the second precipitate production step P10, and (h) a second hydrothermal treatment hydrothermally treated in the second hydrothermal treatment step P11. A second calcining step P14 for calcining a dried product of the reaction product to obtain particles in which a shell mainly composed of ceria zirconia is fixed to a surface of a core mainly composed of zirconia. From this, the co-catalyst 10 for purifying automobile exhaust gas is suitably obtained.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.

  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 “lanthanum nitrate hexahydrate” is used as the water-soluble lanthanum salt. “Hydrates” have been used, but they are exemplary, and others may be used as in Example 7. In short, in the dissolving step P1, at least one water-soluble salt of yttrium, lanthanum, praseodymium, and neodymium can be dissolved together with the water-soluble zirconium salt. Moreover, in 1st precipitate production | generation process P3 and 2nd precipitate production | generation process P10, although ammonia water, potassium hydroxide, etc. were used as a precipitating agent, they are illustrations, and other things are 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. May be.

  In the first calcination step P7 of FIG. 2 described above, firing conditions of 750 ° C.-3 hours were used, and in the second calcination step P14 of FIG. 3, firing conditions of 800 ° C.-3 hours were used. However, they are exemplifications, and temperatures lower than those temperatures, for example, temperatures of 300 ° C. and 400 ° C., may be used for a firing time of 1 hour or 2 hours.

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

  Further, in the first hydrothermal treatment step P4 in FIG. 2 and the second hydrothermal treatment step P11 in FIG. 3, the treatment conditions were 180 ° C. for 5 hours, respectively. There may be.

  In addition, in the core manufacturing process of FIG. 2 and the shell manufacturing process of FIG. 3 described above, other elements such as rare earth elements may be contained in the core or shell by adding rare earth elements or the like.

  In Example 1 described above, “zirconium oxychloride octahydrate” that is a water-soluble zirconium salt and “diammonium cerium nitrate” that is a water-soluble cerium salt were used in the mixing step P8. Further, as in Examples 4 to 6, “lanthanum nitrate hexahydrate”, “neodymium nitrate hexahydrate”, “yttrium chloride hexahydrate” are further used, or the water-soluble salt of “praseodymium” is used. Similar results are obtained when used. In short, in the mixing step P8, at least one water-soluble salt of yttrium, lanthanum, praseodymium, and neodymium can be further mixed together with the water-soluble zirconium salt and the water-soluble cerium salt.

  The above description is only an embodiment, and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

10: Cocatalyst 12: Core 14: Shell L1: Center line L2: Left end line L3: Right end line L4: Base line P1: Dissolution process P3: First precipitate generation process P4: First hydrothermal treatment process P7: First calcination Step P8: Mixing step P10: Second precipitate generation step P11: Second hydrothermal treatment step P14: Second calcination step

Claims (5)

A co-catalyst for purification of automobile exhaust gas composed of a core mainly composed of zirconia and a shell adhered to the surface of the core and mainly composed of ceria zirconia,
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,
Of the ceria contained in the shell, the proportion not dissolved in the zirconia contained in the shell is 10 to 20% by weight,
The core has a tetragonal crystal structure. An automobile exhaust gas purifying promoter. The said core has an average primary particle diameter of 5-50 nm. The automobile exhaust gas purification promoter of Claim 1 characterized by the above-mentioned. In the X-ray powder 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 inclinations are zero is the left end line and the right end line. And a straight line passing through two points where the inclination becomes zero is a base line, and on the base line, a length between the center line and the left end line and a length between the center line and the right end line The vehicle exhaust gas purifying co-catalyst according to claim 1 or 2, wherein the left-right width ratio of the ceria zirconia is 55:45 to 70:30 when the ratio is the left-right width ratio. A method for producing a promoter for purifying automobile exhaust gas according to any one of claims 1 to 3,
A dissolving step of dissolving a water-soluble zirconium salt and at least one water-soluble salt among yttrium, lanthanum, praseodymium and neodymium in distilled water;
A first precipitate generating step of adding a precipitant to the liquid obtained by the dissolving step to generate a first precipitate;
A first hydrothermal treatment step of applying hydrothermal treatment to the first precipitate obtained by the first precipitate generation step;
A first calcining step 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 mixing step of mixing the core powder, distilled water, a water-soluble zirconium salt, and a water-soluble cerium salt;
A second precipitate generating step of adding a precipitant to the mixed solution obtained by the mixing step to generate a second precipitate;
A second hydrothermal treatment step of applying a hydrothermal treatment to the second precipitate produced by the second precipitate production step;
Car exhaust gas purification in which the dried product of the second hydrothermal reaction product hydrothermally treated in the second hydrothermal treatment step is calcined, and the shell mainly composed of ceria zirconia is fixed to the surface of the core mainly composed of zirconia. A second calcination step for obtaining particles of the promoter for use.
A method for producing a co-catalyst for purifying automobile exhaust gas. The method for producing a promoter for purifying automobile exhaust gas according to claim 4, wherein the mixing step further comprises mixing at least one water-soluble salt among yttrium, lanthanum, praseodymium, and neodymium.

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