JP4971918B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst suitable for a process for purifying exhaust gas discharged from an internal combustion engine, and a method for manufacturing the same.

  Up to now, Pt (platinum) and Rh (rhodium) have been used as catalytically active components of a three-way catalyst capable of simultaneously purifying carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) contained in exhaust gas. And noble metals such as Pd (palladium) are widely known. Further, exhaust gas purifying catalysts in which these noble metals are supported on an oxide carrier such as alumina, zirconia, and titania are widely known. These exhaust gas purification catalysts are applied and formed on the surface of the inner wall of a honeycomb substrate made of cordierite or the like, and purify the exhaust gas introduced from the internal combustion engine to the honeycomb substrate.

  Some exhaust gas purifying catalysts have a promoter component added to improve the catalyst performance. The promoter component is, for example, an oxide of a transition metal, and is added so as to come into contact with or close to particles of the noble metal that is a catalytically active component, thereby exhibiting a function as an active site, thereby improving catalytic activity. Can be improved.

  In recent years, the exhaust gas temperature of automobiles tends to become high against the background of higher output of gasoline engines or increased high-speed driving. In addition, when the engine is started, the honeycomb base material on which the exhaust gas purification catalyst is formed is placed directly under the engine so that the temperature of the honeycomb base material can be raised quickly until the exhaust gas purification catalyst reaches a temperature at which the exhaust gas can be purified. It has come to be. For these reasons, the exhaust gas purification catalyst is used in a higher temperature range than before.

  Conventional catalysts have poor durability in actual exhaust gas, and high heat may cause grain growth in the noble metal itself, resulting in a decrease in activity.

In the exhaust gas purifying catalyst to which the promoter component has been added, the promoter component is disposed in the vicinity of the noble metal particles, whereby the atmospheric fluctuation around the noble metal particles can be suppressed by the transition metal or the transition metal compound. Thus, attempts have been made to improve the durability of noble metal particles in actual exhaust gas (see Patent Documents 1 to 4). In addition, according to such a measure, in addition to improving the durability of the noble metal particles, it can be expected to improve the activity of the noble metal particles.
JP-A-8-131830 JP-A-2005-000829 Japanese Patent Laid-Open No. 2005-000830 JP 2003-117393 A

  However, in the case of an exhaust gas purifying catalyst in which the promoter component is arranged in the vicinity of the noble metal particles and manufactured using a general impregnation method, the noble metal particles and the promoter component are in the liquid during the manufacturing process. As a result, the cocatalyst component particles are likely to be thermally condensed, and it is difficult to expect improvement in durability and activity of the catalyst.

  Further, in the case of an exhaust gas purifying catalyst in which noble metal particles are supported on alumina widely used as a metal oxide carrier, the noble metal particles move in a high temperature atmosphere, and the noble metal particles come into contact with each other, thereby precious metal particles. Will aggregate. Further, since the transition metal compound is easily dissolved in alumina, it is difficult to obtain the effect of improving the activity of the noble metal particles simply by arranging the transition metal compound in the vicinity of the noble metal particles.

Further, in the case of an exhaust gas purifying catalyst in which alumina supporting noble metal particles is coated with ceria (CeO ₂ ), the movement of the noble metal particles is suppressed, but since this ceria has poor heat resistance, catalytic activity at high temperatures is low. Therefore, it was difficult to improve the durability and activity of the catalyst.

  The exhaust gas purifying catalyst according to the present invention includes noble metal particles, a first compound that comes into contact with the noble metal particles and suppresses movement of the noble metal particles, the noble metal particles and the first compound, A second compound that suppresses the movement of the particles and suppresses the aggregation of the first compound accompanying the contact between the first compounds, the first compound carrying the noble metal particles, and Summary of the invention is that a single compound or an aggregate of a first compound supporting noble metal particles is contained in a compartment separated by the second compound, and the first compound is a composite containing a rare earth element. And

The method for producing an exhaust gas purifying catalyst according to the present invention is a method for producing the exhaust gas purifying catalyst according to the present invention, wherein after pre-sintering the first compound, the precious metal particles are added to the precious metal particles. A step of supporting on the first compound, a step of pulverizing the first compound on which the noble metal particles are supported, and a step of forming a second compound around the pulverized noble metal-supporting first compound; It is made to include.

  According to the exhaust gas purifying catalyst of the present invention, the first compound on which the noble metal particles are supported is a composite containing a rare earth element, and the noble metal particles and the first compound are covered with the second compound. Thus, since the aggregation of the first compounds is suppressed simultaneously with the movement of the noble metal particles, it is possible to maintain the effect of improving the activity of the noble metal particles by the first compound without increasing the manufacturing cost and the environmental load. .

  According to the method for producing an exhaust gas purification catalyst according to the present invention, the exhaust gas purification catalyst according to the present invention can be produced without impairing the catalytic activity.

  Hereinafter, embodiments of an exhaust gas purifying catalyst of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of an exhaust gas purifying catalyst according to an embodiment of the present invention. The exhaust gas purifying catalyst of the present embodiment shown in the figure includes a noble metal particle 1 having catalytic activity, a first compound 2 that contacts the noble metal particle 1 and suppresses the movement of the noble metal particle 1, and the noble metal. From the second compound 3 containing the particle 1 and the first compound 2 and suppressing the movement of the noble metal particle 1 and suppressing the aggregation of the first compound 2 due to the contact between the first compounds 2. Become. The first compound 2 carries noble metal particles 1. The second compound is formed around the first compound 2 carrying the noble metal particles 1, whereby the carrier of the first compound 2 carrying the noble metal particles 1 or a plurality of aggregates are formed. In compartments separated by two compounds 3.

  In the exhaust gas purifying catalyst of this embodiment shown in FIG. 1, the first compound 2 is in contact with the noble metal particles 1 and carries the noble metal particles 1 as described above. Since the first compound 2 carries the noble metal particles 1 as described above, the first compound 2 is chemically bonded to the noble metal particles 1. Therefore, the first compound 2 acts as an anchor material for the noble metal particles 1 and suppresses the movement of the noble metal particles 1. Thus, chemically suppressing the movement of the noble metal particles 1 contributes to suppressing aggregation of the noble metal particles 1.

  In addition, the exhaust gas purifying catalyst of the present embodiment is configured such that the first compound 2 carrying the noble metal particles 1 is covered with the second compound 3 and included. Thereby, the second compound 3 physically suppresses the movement of the noble metal particles 1. Thus, physically suppressing the movement of the noble metal particles 1 contributes to suppressing aggregation of the noble metal particles 1.

  Further, by including the precious metal particles 1 and the first compound 2 encapsulated in the section separated by the second compound 3, the first compound beyond the section separated by the second compound 3 is contained. It prevents that compound 2 of these contacts and aggregate. The suppression of aggregation of the first compounds 2 in this way contributes to suppression of aggregation of the noble metal particles supported on the first compound 2.

  As a result, the exhaust gas purifying catalyst of the present invention suppresses the aggregation of the noble metal particles 1 without increasing the manufacturing cost and the environmental burden, and thus prevents the catalyst activity from being lowered due to the aggregation of the noble metal particles 1. it can. Further, the first compound 2 as the cocatalyst is prevented from aggregating by the second compound 3 and has an appropriate positional relationship between the noble metal particle 1 and the second compound. The activity improving effect of the noble metal particle 1 due to 2 can be maintained.

  In the exhaust gas purifying catalyst of the present invention, the first compound 2 can be a composite containing a rare earth element. By using a composite containing a rare earth element as the first compound 2 capable of suppressing migration aggregation of the noble metal particles 1 as the anchor material, the first compound 2 exhibits high affinity with the noble metal particles 1. As a result, the movement of the noble metal particle 1 from the first compound 2 toward the second compound 3 can be effectively suppressed. Therefore, the noble metal particle 1 is stabilized on the first compound 2 and does not move to the second compound 3 even under high-temperature exhaust gas conditions, and the aggregation of the noble metal particles is further suppressed, and the noble metal particle diameter is about several nm. Can be maintained. The durability of the catalyst can be improved by the effect of maintaining the stable nanoparticles of the noble metal, and good catalyst performance can be maintained after exhaust durability. The ability to maintain good catalytic performance even after exhaust durability means that the catalytic activity required for automobile exhaust gas purification catalysts can be achieved with less noble metal than in the past. The amount of noble metal used in the conventional process can be greatly reduced.

  Details of the reason why the migration aggregation of the noble metal particles 1 from the first compound 2 to the second compound 3 is suppressed by using a composite containing a rare earth element for the first compound 2 are not necessarily clear. However, by applying a compound having a large amount of surface oxygen, such as a rare earth element, to the first compound 2, the first compound 2 is strongly bonded to the noble metal particle 1 through the surface oxygen. This is thought to be due to the formation of

  In the exhaust gas purifying catalyst of the present invention, the first compound 2 is preferably a composite containing a rare earth element and at least one kind of alkali metal and alkaline earth metal. By using, as the anchor material, a composite containing a rare earth element and at least one kind of alkali metal and alkaline earth metal as the first compound 2 that enables the movement aggregation of the noble metal particles 1 to be suppressed. The first compound 2 can exhibit high affinity with the noble metal particle 1, and as a result, the noble metal particle 1 moves from the first compound 2 toward the second compound 3. Can be effectively suppressed. Therefore, the noble metal particles 1 are stabilized on the first compound 2 and do not move to the second compound 3 even under high-temperature exhaust gas conditions, and the aggregation of the noble metal particles 1 is further suppressed, and the noble metal particle diameter of about several nm. Can be maintained. The durability of the catalyst can be improved by the effect of maintaining the stable nanoparticles of the noble metal, and good catalyst performance can be maintained after exhaust durability. The ability to maintain good catalytic performance even after exhaust durability means that the catalytic activity required for automobile exhaust gas purification catalysts can be achieved with less noble metal than in the past. The amount of noble metal used in the conventional process can be greatly reduced.

  By using a composite containing a rare earth element and at least one kind of alkali metal and alkaline earth metal as the first compound 2, the noble metal particles 1 can be secondly added from above the first compound 2. Although the details of the reason why the migration aggregation to the compound 3 is suppressed are not necessarily clear, by applying a compound having a large amount of surface oxygen such as a rare earth element to the first compound 2, This is probably because the first compound 2 forms a strong covalent bond with the noble metal particle 1 through oxygen. Furthermore, by including at least one of alkaline, alkaline earth metal and alkaline earth metal that is easy to emit electrons in the first compound 2, electron donation to the oxygen occurs, and the above-described covalent bond is further strengthened. It is thought that there is.

  In the exhaust gas purifying catalyst of the present invention, the first compound 2 is also preferably a composite containing a rare earth element and zirconium. By using a composite containing a rare earth element and zirconium as the first compound 2 that enables the migration aggregation of the noble metal particles 1 to be suppressed as an anchor material, the first compound 2 is high in comparison with the noble metal particles 1. Affinity can be expressed, and as a result, the movement of the noble metal particle 1 from the first compound 2 toward the second compound 3 can be effectively suppressed. Therefore, the noble metal particle 1 is stabilized on the first compound 2 and does not move to the second compound 3 even under high-temperature exhaust gas conditions, and the aggregation of the noble metal particles is further suppressed, and the noble metal particle diameter is about several nm. Can be maintained. The durability of the catalyst can be improved by the effect of maintaining the stable nanoparticles of the noble metal, and good catalyst performance can be maintained after exhaust durability. The ability to maintain good catalytic performance even after exhaust durability means that the catalytic activity required for automobile exhaust gas purification catalysts can be achieved with less noble metal than in the past. The amount of noble metal used in the conventional process can be greatly reduced.

  Details of the reason why the migration aggregation of the noble metal particles 1 from the first compound 2 to the second compound 3 is suppressed by using a composite containing a rare earth element and zirconium for the first compound 2. Although it is not necessarily clear, by applying a compound having a large amount of surface oxygen, such as a rare earth element, to the first compound 2, the first compound 2 and the noble metal particles 1 are bonded via the surface oxygen. This is probably because a strong covalent bond is formed. Furthermore, by adding Zr to the first compound 2, the stability of the first compound 2 as the anchor material is further improved, and as a result, the effect of stabilizing the noble metal can be exhibited. When the first compound does not contain an alkali element or an alkaline earth element, the composition of the rare earth element and the Zr element in the anchor material is Zr-rich so that the first compound is the same as zirconia. Thus, the first compound can be further stabilized.

  FIG. 2 is an example of a metallographic photograph of the exhaust gas purifying catalyst according to the present invention. FIG. 2A is an example in which the first compound is a composite containing a rare earth and at least one metal of an alkali metal and an alkaline earth metal. Specifically, the first compound Is an example of a CeMgOx-based compound. FIG. 2B is an example in which the first compound is a composite containing a rare earth and zirconium, and specifically, an example in which the first compound is a ZrCeOx-based compound. As shown in these photographs, the Pd particles as the noble metal particles are supported by the first compound that is the anchor material, and the second material that is the inclusion material so as to cover the first compound that supports the Pd particles. Is formed.

  In the exhaust gas purifying catalyst according to the present invention, the rare earth element in the composite that is the first compound 2 preferably contains at least one selected from La, Ce, Pr, and Nd. La, Ce, Pr, and Nd all have high thermal stability and high surface oxygen donating property, so that the effects of the first compound 2 in the present invention described above can be obtained more easily. .

  The rare earth element in the composite that is the first compound 2 can further contain Y. By adding Y, it is possible to further maintain the OSC function of the anchor material after exhaust durability while maintaining the precious metal fine particle maintaining effect. As a result, it is possible to relax the atmosphere when the A / F ratio (Air Fuel Ratio) changes greatly during acceleration / deceleration during vehicle travel. As a result, it is possible to absorb and release oxygen into the nano noble metal particles that can be maintained by the present catalyst structure, and as a result, it is possible to further reduce exhaust gas emissions or reduce the amount of noble metal used.

  The above-mentioned effect due to the addition of Y is particularly advantageous when the first compound 2 is a composite containing Zr. The catalyst according to the embodiment of the present invention itself has high heat resistance, but by combining Y, the crystal structure of the zirconia-based anchor material can be stabilized, thereby further improving the heat resistance. It becomes. This is because it is possible to suppress a phase transition in which the zirconia crystal structure is changed from a tetragonal crystal to a monoclinic crystal during exhaust durability, and as a result, it is possible to suppress a decrease in OSC ability.

  In the case where the first compound 2 contains at least one of alkali metal and alkaline earth metal, the alkali metal or alkaline earth metal is Na, K, Rb, Cs, Mg, Ca, It is preferable to include at least one selected from Sr and Ba. In particular, an alkaline earth metal is more preferable. These Na, K, Rb, Cs, Mg, Ca, Sr and Ba all have no sublimation or the like, and have high thermal stability, so that the electron donating property described above is stable. Conceivable. In particular, alkaline earth metals have a slightly lower electron donating property than alkali metals, but easily form composites with rare earth elements, so that the first compound is formed as a composite having high affinity with noble metal particles. can do.

  When the first compound 2 includes the rare earth element described above and at least one metal selected from alkali metals and alkaline earth metals, it can further contain Zr. When the first compound 2 contains Zr in addition to the rare earth element and at least one of the alkali metal and the alkaline earth metal, it can impart a higher oxygen storage capacity (OSC), and is more effective. Can be demonstrated. In addition, by incorporating Zr into the first compound 2 and making it complex, it becomes possible to further bring out the nanoparticle stabilization effect of the noble metal particles. Although the details are unknown, the ability to maintain nanoparticles increases the area that can be contacted with exhaust gas, and as a result, oxygen supply is required. (Anchor effect) and smooth oxygen supply effect to nano-noble metals can both be achieved.

  The noble metal particle 1 supported on the first compound 2 preferably contains at least one selected from Pt, Pd and Rh as its component. Pt, Pd and Rh are all components having catalytic activity capable of purifying exhaust gas. In addition, the first compound is a noble metal that can sufficiently exhibit the above-described effects and is stabilized on the first compound. Since the noble metal particle 1 contains at least one of Pt, Pd and Rh, the noble metal particle 1 has a high affinity with the surface oxygen of the first compound 2, so There is no transfer to the compound.

  The precious metal particles 1 are more preferably Pd among the above-mentioned Pt, Pd and Rh. As the combination of the noble metal particles 1 with the first compound 2 in the exhaust gas purification catalyst of the present invention, it is particularly effective to use Pd. This is because the effect of the first compound 2 described above is particularly effective because Pd has a high affinity with the first compound 2 and the effect of suppressing the burying of the noble metal particles 1 is taken into account. Because.

  The second compound 3 is not particularly limited in the exhaust gas purifying catalyst of the present invention, but is desirably an oxide of at least one element selected from Al and Zr. Among these, it is preferable that the second compound 3 is alumina because the second compound 3 can be made porous. Since the second compound 3 is porous, in the structure of the exhaust gas purifying catalyst of the present invention, the exhaust gas passes through the second compound 3 to the noble metal particles 1 supported on the first compound 2. It is possible to reach it sufficiently.

  It is more preferable that the second compound 3 further contains at least one element selected from Ce, Zr, La and Ba in addition to alumina. In order to stably maintain the particles of the first compound 2 supporting the noble metal particles 1 in the exhaust gas purifying catalyst according to the present invention, at least one element selected from Ce, Zr, La and Ba is used as the second compound. By adding to this compound (inclusion material), it becomes possible to improve the heat resistance of alumina as the inclusion material. Thereby, compared with the case where at least one element selected from, for example, Ce, Zr, La and Ba is not added, it is possible to suppress α-alumination, which is a deteriorated state of alumina, and as a result, the present invention. The durability of the catalyst having the structure according to the above can be further enhanced. Furthermore, when the noble metal particle 1 is Pd, there is an essential problem that it is susceptible to poisoning due to HC at the time of low temperature starting, but this HC poisoning action is mitigated by adding Ba to the second compound. As a result, low-temperature activation can be achieved.

  In the exhaust gas catalyst according to the present invention, the crystallite diameter (D1) of the first compound 2 of the exhaust gas catalyst powder and the secondary particle diameter (D2) of the first compound on which noble metal particles are supported The ratio D2 / D1 of D2 to D1 is preferably 1 ≦ D2 / D1 ≦ 50. Since the first compound 2 made of the composite described above has a high affinity with the noble metal, the state of the nano noble metal particles 1 can be maintained, but the first compound 2 aggregates at a high temperature and is sintered. When the particles become secondary particles, the nano noble metal particles 1 supported on the first compound 2 may be taken into the secondary particles of the first compound 2 in some cases. As a result, since the number of noble metal particles that can come into contact with the exhaust gas is reduced, the effect of maintaining the nanoparticles of the noble metal particles according to the present invention may be relatively diminished.

  Therefore, in order to suppress the burying of the noble metal particles 1 inside the first compound 2 and to sufficiently exhibit the nanoparticle maintaining effect of the noble metal particles 1, the second compound 2 of the first compound 2 supporting the noble metal particles 1 is used. The secondary particle diameter D2 is not excessively large with respect to the crystallite diameter D1 of the first compound 2. That is, even after sintering, the secondary particle diameter D2 of the first compound 2 is set not to be excessively large. Specifically, the ratio D2 / D1 of D2 to D1 is set in a range of 1 ≦ D2 / D1 ≦ 50. By setting it as this range, the noble metal particles 1 can be sufficiently exposed on the surface of the secondary particles of the first compound 2.

  More specifically, in the exhaust gas purifying catalyst of the present invention, the first compound 2 is contained and fixed by the second compound 3, so that the second compound 3 moves so as to jump out. There is no. For this reason, when the first compound 2 is aggregated and sintered, it is sintered only as secondary particles in a compartment included in the second compound 3. Therefore, in order to prevent the noble metal particles 1 supported on the first compound 2 from being buried in the secondary particles of the first compound 2, the first compound in the compartment included in the second compound 3 is used. The secondary particles 2 are in the state of primary particles that are one crystal body, that is, D2 / D1 = 1 is the ideal state, and most preferable (D2 / D1 <1 is not possible). When the value of D2 / D1 exceeds 50, the noble metal particle 1 can maintain the nanoparticle state, but the noble metal particle 1 is often embedded in the secondary particles of the first compound 2, It becomes difficult to exhibit the effect of maintaining the nanoparticle state of the noble metal particles as expected in the invention. Therefore, the ratio D2 / D1 of D2 to D1 is preferably in the range of 1 ≦ D2 / D1 ≦ 50. D1 can be examined by XRD diffraction (XRD) of the exhaust gas purifying catalyst powder, and D2 can be examined by an optical spectroscopy for the average particle size.

  FIG. 3 is a graph showing the relationship between the ratio D2 / D1 of D2 to D1 and the temperature at which the HC conversion rate of the exhaust purification catalyst becomes 50%. As can be seen from FIG. 3, when the ratio D2 / D1 of D2 to D1 is in the range of 1 ≦ D2 / D1 ≦ 50, good exhaust gas purification characteristics are obtained.

  FIG. 4 is a micrograph of the exhaust gas after the exhaust gas durability test at 900 ° C. of the exhaust gas purifying catalyst in which D2 / D1 is in the range of 1 ≦ D2 / D1 ≦ 50. As can be seen from FIG. 4, when D2 / D1 is 1 ≦ D2 / D1 ≦ 50, the noble metal particles of the nanoparticles are supported on the surface of the first compound and buried in the first compound. It was not.

  A more preferable range of the ratio D2 / D1 of D2 to D1 is 1 ≦ D2 / D1 ≦ 20. When D2 / D1 is 1 ≦ D2 / D1 ≦ 20, the above effect can be more exhibited. The reason is not necessarily clear, but in the range of 1 ≦ D2 / D1 ≦ 20, noble metal particles by being involved in the secondary particles of the first compound 2 in the unit partitioned by the second compound 3 This is probably because the exposed area reduction of No. 1 is less likely to occur, and a performance improvement allowance by maintaining the fine particle state of the noble metal particles 1 can be obtained more. Also in the graph shown in FIG. 3, the exhaust gas purification characteristics are particularly excellent in the range of 1 ≦ D2 / D1 ≦ 20.

In the exhaust gas catalyst according to the present invention, the powder pore volume determined by N ₂ adsorption analysis of the exhaust gas catalyst powder is 0.3 [ml / g] to 0.5 [ml / g] per 1 g of powder, and The average pore diameter is preferably 30 [nm] or less. Since the exhaust gas catalyst powder according to the present invention has a pore structure that satisfies such conditions, it is harmful to the catalyst active points (noble metal particles) maintained as fine particles in the first compound particles. The exhaust gas can be reached, and as a result, the catalyst performance can be sufficiently extracted. If the pore volume of the powder is less than 0.3 [ml / g] per gram of powder, gas diffusibility will be reduced, making it difficult to effectively use nano-active sites, and as a result, exhaust gas purification performance will be reduced. Become. On the other hand, if it exceeds 0.5 [ml / g], the gas diffusibility is sufficient, but the catalyst coat layer tends to be brittle and causes problems such as peeling off of the coat layer. In addition, when the average pore diameter exceeds 30 [nm], movement and aggregation of the noble metal-supported first compound particles are likely to occur, resulting in embedding of the noble metal particles in the first compound particles, resulting in a decrease in catalyst performance. Produce.

The exhaust gas purifying catalyst of the present invention preferably contains noble metal particles in a total amount of 8 × 10 ⁻²⁰ mol or less in the compartments separated by the second compound 3. As shown in FIG. 1, the noble metal particle 1 is included in the second compound 3 together with the first compound. The plurality of noble metal particles 1 contained in the compartment separated by the second compound 3 may move at a high temperature, but the second compound 3 is converted into the second compound 3 by the effect of the first compound 2 as an anchor material. Does not move, moves only within the compartment (within the unit) separated by the second compound 3, and aggregates into one or more noble metal particles.

  Here, when noble metal particles are aggregated in one unit, if the aggregated noble metal particles have a particle size of 10 nm or less, sufficient catalytic activity is exhibited and deterioration of catalytic activity due to aggregation is suppressed. Can do. FIG. 5 is a graph showing the relationship between the noble metal particle diameter and the noble metal surface area for platinum or palladium as a noble metal having catalytic activity. In the figure, since the curves are almost the same when the noble metal is platinum and palladium, they are shown as one curve. As is clear from the figure, when the particle diameter of the noble metal is 10 [nm] or less, the particle surface area is large and sufficient activity can be obtained, so that deterioration of the catalyst activity due to aggregation can be suppressed.

FIG. 6 is a graph showing the relationship between the noble metal particle diameter and the number of noble metal atoms for platinum or palladium as a noble metal having catalytic activity. In the figure, since the curves are almost the same when the noble metal is platinum and palladium, they are shown as one curve. As is clear from the figure, the number of atoms when the particle diameter of the noble metal is 10 [nm] is about 48000, and when this value is converted into the number of moles, the amount is about 8 × 10 ⁻²⁰ moles or less. .

From these viewpoints, by limiting the amount of noble metal in the unit and setting it to an amount of 8 × 10 ⁻²⁰ mol or less, deterioration of the catalyst activity can be suppressed even if it aggregates into one in the unit.

As a means for reducing the amount of the noble metal contained in the unit to 8 × 10 ⁻²⁰ mol or less, the concentration of the noble metal particles 1 of the first compound 2 is lowered or the first compound 2 carrying the noble metal particles 1 is used. There are two means of reducing the particle size of the. In the present invention, although not limited to these means, when actual catalyst production is considered, the former method of lowering the supported concentration can be used for exhaust gas purification in order to maintain the performance of a predetermined exhaust gas purification catalyst. Since the volume of the honeycomb carrier coated with the catalyst has to be increased, and therefore, it is necessary to coat the honeycomb carrier with a coating amount that is usually an order of magnitude larger than that of the catalyst, it is not practical.

Next, regarding the composite particles composed of the noble metal particles 1 and the first compound 2 supporting the noble metal particles 1, the size of the composite particles (average particle diameter of the composite particles) D2 and the first particles enclosing the composite particles The average pore diameter D3 of the pores formed in the compound 3 of No. 2 is preferably such that the ratio D2 / D3 of D2 to D3 is 1 or more. The fact that D2 / D3 is 1 or more means that the average particle diameter D2 of the composite particle unit composed of the noble metal particles 1 and the first compound 2 is the average diameter D3 of the voids formed in the second compound 3. Means greater than. When D2 / D3 is 1 or more, the movement of the composite particles of the noble metal particles 1 and the first compound 2 through the pores formed in the second compound 3 is suppressed. Therefore, a decrease in the inclusion effect due to the second compound 3 is suppressed. This effect has been confirmed by experiments by the inventors. FIG. 7 shows the crystal growth ratio of CeO ₂ as the first compound and the surface area of Pt as the noble metal particles after the exhaust durability test, with the ratio D2 / D3 of the composite particle size D2 and the average pore diameter D3 as the horizontal axis. It is a graph which shows these relationships by making ordinate the vertical axis. From FIG. 7, when D2 / D3 is 1 or more, the crystal growth ratio of CeO ₂ is remarkably reduced, that is, the inclusion effect is large because there is little sintering of CeO ₂ , and Pt after the durability test It can be seen that the surface area of the catalyst is large, that is, the Pt agglomeration is small, so that the catalytic activity is hardly lowered.

  Next, when manufacturing the exhaust gas purifying catalyst of the present invention, the first compound is pre-sintered and then the noble metal particles are supported on the first compound, and the noble metal particles are supported. In addition, a method including a step of pulverizing the first compound and a step of forming a second compound around the pulverized noble metal-supported first compound can be used.

  As described above, the first compound is composed of a composite containing a rare earth element and at least one metal selected from an alkali metal and an alkaline earth metal. By sintering, the complexing of the rare earth element with an alkali metal or alkaline earth metal can be promoted and sintering can be suppressed. By supporting the noble metal particles after sintering the first compound, the noble metal particles can maintain the nanoparticle state without causing the noble metal particles to be buried. By pulverizing the first compound on which the noble metal particles are supported, it becomes possible to adjust the amount of the noble metal in the compartment (unit) encapsulated by the second compound in a later step to a predetermined range. By forming the second compound in the pulverized noble metal particle-supporting first compound, the noble metal particle-supporting first compound is included in the second compound and included in the compartment separated by the second compound To be. The conditions for performing these steps can be set to appropriate conditions. Moreover, about processes other than these processes, the exhaust gas purification catalyst of this invention can be manufactured in accordance with a conventional method.

  The exhaust gas purification catalyst powder obtained in this way is made into a slurry, and this slurry is coated on the inner wall surface of the catalyst honeycomb substrate, which is a refractory inorganic carrier, and used for exhaust gas purification. .

  Hereinafter, the present invention will be specifically described based on examples.

[Manufacture of catalyst]
Exhaust gas purifying catalysts of Examples 1 to 27 and Comparative Examples 1 to 5 shown in Tables 1 and 2 were produced as follows. Table 1 shows the precious metal particles and the first compound in the exhaust gas purifying catalysts of Examples 1 to 27 and Comparative Examples 1 to 5, and Table 2 shows Examples 1 to 27 and Comparative Examples 1 to 5. The 2nd compound in an exhaust gas purification catalyst, the catalyst powder characteristic, and the catalyst performance are shown.

[Example 1]
<Powder preparation process>
The nano-oxidized Ce fine particle powder was impregnated and supported with Rb acetate so as to be 5 mol% with respect to the oxidized Ce, and then dried and further baked in an air atmosphere at 600 ° C. for 3 hours. A first compound was obtained. This powder was measured by XRD, and the crystallite diameter when calculated by Scherrer's formula was as shown in Table 1.

  The powder obtained in the above step was loaded with an aqueous tetraammine Pd solution so that the noble metal loading concentration was 0.5 wt%, dried, and calcined in air at 400 ° C. for 1 hour.

This Pd (0.5 wt%) / CeRbO _x powder was pulverized in an aqueous solution to obtain a dispersed slurry having an average particle diameter of 310 nm.

  On the other hand, the precious metal-supported first compound-dispersed slurry obtained above was added to the dispersed slurry in which boehmite powder was dispersed, dried, and then fired in air at 550 ° C. for 3 hours. A catalyst powder was obtained.

The boehmite (precursor of the second compound) used at this time had an average pore diameter calculated by the N ₂ adsorption method of 22 nm when only boehmite was dried and calcined under the same conditions. Therefore, it can be considered that the void diameter of the second compound of the noble metal-containing powder is similar to this.

<Coating process on honeycomb substrate>
A predetermined amount of the above powder and a predetermined amount of boehmite are put into a magnetic pot, and after pulverizing the average particle size to 3 μm, it is applied to a 0.119 L (400 cpsi, 6 mil) cordierite honeycomb substrate, and an excess slurry is applied. After removing it with an air stream, it was dried at 130 ° C. and fired at 400 ° C. for 1 hour in an air atmosphere to obtain a catalyst honeycomb substrate of Example 1. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[Example 2]
A catalyst honeycomb of Example 2 was obtained in the same manner except that Rb acetate in the powder preparation step in Example 1 was changed to Ba acetate.

Example 3
A catalyst honeycomb of Example 3 was obtained in the same manner except that Rb acetate in the powder preparation step in Example 1 was changed to Cs acetate.

Example 4
A catalyst honeycomb of Example 4 was obtained in the same manner except that Rb acetate in the powder preparation step in Example 1 was changed to Mg acetate and the average particle size of the Pd-supported CeMgO _x powder dispersion slurry was changed to 330 nm.

Example 5
In the same manner as in Example 1, except that the nano-oxidized Ce powder in the above powder preparation step was Nd ₂ O ₃ , Rb acetate was Mg acetate, and the average particle size of the Pd-supported NdMgO _x powder dispersion slurry was 290 nm. The catalyst honeycomb of Example 5 was obtained.

Example 6
In the same manner as in Example 1, except that the nano-oxidized Ce powder in the powder preparation step was Pr ₂ O ₃ , acetate Rb was Ca acetate, and the average particle size of the Pd-supported PrCaO _x powder dispersion slurry was 310 nm. The catalyst honeycomb of Example 6 was obtained.

Example 7
The nano-oxidized Ce powder in the above powder preparation step in Example 1 was impregnated with La nitrate so as to become LaO 5 mol% -supported CeO ₂ , dried, and calcined at 400 ° C. for 1 hour in an air stream. A fixed amount of Mg acetate was impregnated, dried, and fired, a precious metal was supported, and the same firing treatment was performed. Next, a catalyst honeycomb of Example 7 was obtained in the same manner except that the average particle diameter was 310 nm in the step of finely pulverizing the powder thus obtained.

Example 8
A catalyst honeycomb of Example 8 was obtained in the same manner except that the step of firing the first compound raw material in the powder preparation step of Example 4 at 600 ° C. for 3 hours was performed at 800 ° C. for 3 hours.

Example 9
The step of calcining the first compound raw material in the powder preparation step in Example 4 at 600 ° C. for 3 hours was performed at 1000 ° C. for 3 hours, and the slurry was pulverized in the same manner except that the average particle size was 340 nm. Thus, a catalyst honeycomb of Example 9 was obtained.

Example 10
The same procedure as in Example 4 except that the first compound raw material in the powder preparation step was calcined at 600 ° C. for 3 hours at 1100 ° C. for 3 hours, and the average particle size was 350 nm in the slurry grinding step. Thus, a catalyst honeycomb of Example 10 was obtained.

Example 11
A catalyst honeycomb of Example 11 was obtained in the same manner except that the nano-oxidized Ce in the powder production process in Example 9 was changed to CeO ₂ containing 10 mol% of Zr and the average particle diameter was changed to 330 nm in the slurry grinding process.

Example 12
A catalyst honeycomb of Example 12 was obtained in the same manner except that tetraammine Pd in Example 11 was changed to tetraammine Pt.

Example 13
A catalyst honeycomb of Example 13 was obtained in the same manner except that tetraammine Pd in the powder preparation step of Example 9 was Rh nitrate and the average particle size was 180 nm.

Example 14
In Example 11, the supported concentration of Pd with respect to CeZrMgO _x was 1.0%, the average particle diameter of the slurry was 155 nm, and when applied to the catalyst honeycomb, γ alumina was mixed so that the amount of noble metal per 1 L of honeycomb was equal, A catalyst honeycomb of Example 14 was obtained in the same manner except that the coating was applied.

Example 15
A catalyst honeycomb of Example 15 was obtained in the same manner except that CeMgO _x was changed to CeNaO _x in Example 4.

Example 16
Except that the CeMgO _x in Example 4 was CeKO _x in the same manner to obtain a catalyst honeycomb of Example 16.

Example 17
A catalyst honeycomb of Example 17 was obtained in the same manner except that CeMgO _x was changed to CeSrO _x in Example 4.

Example 18
<Powder preparation process>
The nano-oxidized Ce fine particle powder was impregnated and supported with Mg acetate so as to be 5 mol% with respect to the oxidized Ce, and then dried and further baked in an air atmosphere at 400 ° C. for 3 hours. 1 compound was obtained. This powder was measured by XRD, and the crystallite diameter when calculated by Scherrer's formula was as shown in Table 1.

  The powder obtained in the above step was loaded with an aqueous tetraammine Pd solution so that the noble metal loading concentration was 0.5 wt%, dried, and calcined in air at 400 ° C. for 1 hour.

This Pd (0.5 wt%) / CeMgO _x powder was pulverized in an aqueous solution to obtain a dispersed slurry having an average particle size of 330 nm.

  On the other hand, the noble metal-supported first compound-dispersed slurry obtained above was added to the dispersed slurry in which boehmite powder was dispersed, dried, and then calcined in air at 550 ° C. for 3 hours. A catalyst powder was obtained.

The boehmite (precursor of the second compound) used at this time had an average pore diameter calculated by the N ₂ adsorption method of 22 nm when only boehmite was dried and calcined under the same conditions. Therefore, it can be considered that the void diameter of the second compound of the noble metal-containing powder is similar to this.

<Coating process on honeycomb substrate>
A predetermined amount of the above powder and a predetermined amount of boehmite are put into a magnetic pot, and after pulverizing the average particle size to 3 μm, it is applied to a 0.119 L (400 cpsi, 6 mil) cordierite honeycomb substrate, and an excess slurry is applied. After removing it with an air stream, it was dried at 130 ° C. and fired at 400 ° C. for 1 hour in an air atmosphere to obtain a catalyst honeycomb substrate of Example 18. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

Example 19
<Powder preparation process>
The nano-oxidized Zr powder was impregnated and supported with Ce acetate at 15 mol%, dried, and then calcined at 900 ° C. for 3 hours in an air atmosphere to obtain the first compound of Example 19. This powder was measured by XRD, and the crystallite diameter when calculated by Scherrer's formula was as shown in Table 1.

  The powder obtained in the above step was loaded with an aqueous dinitrodiamine Pd solution so that the noble metal loading concentration was 0.5 wt%, dried, and calcined in air at 400 ° C. for 1 hour.

  This Pd (0.5 wt%) / ZrCeOx powder was pulverized in an aqueous solution to obtain a dispersed slurry having an average particle diameter of 310 nm.

  On the other hand, the precious metal-supported first compound-dispersed slurry obtained above was added to the dispersed slurry in which boehmite powder was dispersed, dried, and then calcined in air at 550 ° C. for 3 hours. A catalyst powder was obtained.

The boehmite (precursor of the second compound) used at this time had an average pore diameter calculated by the N ₂ adsorption method of 31 nm when only boehmite was dried and fired under the same conditions. Therefore, it can be considered that the void diameter of the second compound of the noble metal-containing powder is similar to this.

  Further, the pore volume of the powder of Example 19 obtained at this time was a value shown in Table 2.

<Coating process on honeycomb substrate>
A predetermined amount of the above powder and a predetermined amount of boehmite are put into a magnetic pot, and after pulverizing to an average particle diameter of 3 μm, it is applied to a 0.119 L (400 cpsi, 6 mil) cordierite honeycomb substrate, and an excess slurry is applied. After removal with an air stream, drying at 130 ° C. and firing at 400 ° C. for 1 hour in an air atmosphere gave a catalyst honeycomb of Example 19. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

Example 20
Instead of adding Ce to Zr oxide in Example 19, a predetermined amount of Ce nitrate and La nitrate was added so as to have the molar composition shown in Table 1, and Ce nitrate was added to the slurry in which boehmite powder was dispersed. A catalyst honeycomb of Example 20 was obtained in the same manner except that boehmite having a pore diameter of 28 nm was used.

Example 21
Instead of Ce added to the Zr oxide in Example 19, was added a predetermined amount of Ce nitrate and nitric acid Nd to be a molar composition shown in Table 1, and nitric C e Zr nitrate in a slurry prepared by dispersing boehmite powder A catalyst honeycomb of Example 21 was obtained in the same manner except that La nitrate was added and boehmite having an average pore diameter of 25 nm was used.

[Example 22]
Instead of Ce addition to Zr oxide of Example 19, a predetermined amount of Ce nitrate and La nitrate was added so as to have the molar composition shown in Table 1, and Ce nitrate, Zr nitrate, and nitrate were added to the slurry in which boehmite powder was dispersed. A catalyst honeycomb of Example 22 was obtained in the same manner except that La and Ba nitrate were used and boehmite having an average pore diameter of 25 nm was used.

Example 23
Instead of adding Ce to the oxidized Zr of Example 19, a predetermined amount of Ce nitrate and Pr nitrate were added so as to have the molar composition shown in Table 1, and Ce nitrate, Zr nitrate, and nitrate were added to the slurry in which boehmite powder was dispersed. A catalyst honeycomb of Example 23 was obtained in the same manner except that La and Ba nitrate were used and boehmite having an average pore diameter of 25 nm was used.

Example 24
Instead of adding Ce to the oxidized Zr of Example 19, a predetermined amount of Ce nitrate and Pr nitrate were added so as to have the molar composition shown in Table 1, and Ce nitrate and Zr nitrate were added to the slurry in which boehmite powder was dispersed. A catalyst honeycomb of Example 24 was obtained in the same manner except that boehmite having an average pore diameter of 25 nm was used and dinitrodiamine Pd was changed to Rh nitrate.

Example 25
A slurry in which the boehmite powder of Example 4 was dispersed was charged with a predetermined amount of Ce nitrate, Zr nitrate and La nitrate so as to have the composition shown in Table 1, except that boehmite having an average pore diameter of 24 nm was used. Similarly, a catalyst honeycomb of Example 25 was obtained.

Example 26
Instead of Ce addition to Zr oxide Zr in Example 19, the catalyst honeycomb of Example 26 was made in the same manner as Example 19 except that predetermined amounts of Ce nitrate and Y nitrate were added so as to have the molar composition shown in Table 1. Got.

Example 27
Instead of adding Ce and Pr to the Zr oxide Zr in Example 24, the same procedure as in Example 24 was performed except that a predetermined amount of Ce nitrate and Y nitrate was added so as to have the molar composition shown in Table 1. A catalyst honeycomb was obtained.

[Comparative Example 1]
Comparative Example 1 is an example in which the first compound in the catalyst powder is different from Examples 1 to 25 and is only a rare earth element (Ce).

<Powder preparation process>
The nano-oxidized Ce fine particle powder was loaded with an aqueous dinitrodiamine Pd solution so that the noble metal loading concentration was 0.5 wt%, dried, and calcined in air at 400 ° C. for 1 hour.

This Pd (0.5 wt%) / CeO ₂ powder was pulverized in an aqueous solution to obtain a dispersed slurry having an average particle diameter of 310 nm.

  On the other hand, the powder-dispersed slurry obtained above was put into a dispersed slurry in which boehmite powder was dispersed, dried, and then fired in air at 550 ° C. × 3 Hr to obtain a catalyst powder of Comparative Example 1.

The boehmite (precursor of the second compound) used at this time had an average pore diameter calculated by the N ₂ adsorption method of 22 nm when only boehmite was dried and fired under the same conditions. Therefore, it can be considered that the void diameter of the second compound of the noble metal-containing powder is similar to this.

<Coating process on honeycomb substrate>
A predetermined amount of the above powder and a predetermined amount of boehmite are put into a magnetic pot, and after pulverizing the average particle size to 3 μm, it is applied to a 0.119 L (400 cpsi, 6 mil) cordierite honeycomb substrate, and an excess slurry is applied. After removal with an air stream, drying at 130 ° C. and firing at 400 ° C. for 1 hour in an air atmosphere gave a catalyst honeycomb substrate of Comparative Example 1. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[Comparative Example 2]
Comparative Example 2 is an example in which the first compound in the catalyst powder is only a rare earth element (Ce—Zr (Ce-rich)) unlike Examples 1 to 25.

<Powder preparation process>
A dinitrodiamine Pd aqueous solution was supported on nano-oxidized Ce fine particle powder containing 10 mol% of Zr so that the noble metal support concentration was 1.0 wt%, dried, and calcined in air at 400 ° C. for 3 hours. This Pd (1.0 wt%) / CeZrO _x powder was pulverized in an aqueous solution to obtain a dispersed slurry having an average particle diameter of 155 nm.

  On the other hand, the powder dispersion slurry obtained above was put into a dispersion slurry in which boehmite powder was dispersed, dried, and then fired in air at 550 ° C. for 3 hours to obtain a catalyst powder of Comparative Example 2. .

The boehmite (precursor of the second compound) used at this time had an average pore diameter calculated by the N ₂ adsorption method of 22 nm when only boehmite was dried and calcined under the same conditions. Therefore, it can be considered that the void diameter of the second compound of the noble metal-containing powder is similar to this.

<Coating process on honeycomb substrate>
A predetermined amount of the above powder, γ-alumina and a predetermined amount of boehmite are put into a magnetic pot, and after pulverizing the average particle size to 3 μm, it is applied to a 0.119 L (400 cpsi, 6 mil) cordierite honeycomb substrate, Excess slurry was removed with an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour in an air atmosphere to obtain a catalyst honeycomb substrate of Comparative Example 2. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[Comparative Example 3]
Comparative Example 3 is an example in which the first compound in the catalyst powder is only a rare earth element (Ce—Zr / alumina), unlike Examples 1 to 25, and does not include the second compound. .

  The γ-alumina was impregnated with Ce nitrate and zirconyl nitrate so as to be 10 mol% as Ce and 3 mol% as Zr, dried at 130 ° C., and calcined at 400 ° C. for 3 hours in air.

Next, dinitrodiamine Pd was supported on this powder so that the concentration of Pd supported was 0.5 wt%, dried, and calcined at 400 ° C. for 1 hour.

  This noble metal-supported powder, γ-alumina, a predetermined amount of boehmite, and nitric acid are put into a magnetic pot, and the average particle size is pulverized to 3 μm. The excess slurry was removed with an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour in an air atmosphere to obtain a catalyst honeycomb substrate of Comparative Example 3. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[Comparative Example 4]
A catalyst honeycomb substrate of Comparative Example 4 was obtained in the same manner except that the supported noble metal salt of Comparative Example 3 was dinitrodiamine Pt. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[Comparative Example 5]
Comparative Example 5 is an example in which the first compound in the catalyst powder is different from Examples 1 to 25 and is only Zr / alumina.

Zirconyl nitrate was impregnated in γ-alumina so as to be 3 mol% as Zr, dried at 130 ° C., and calcined at 400 ° C. Then, the Rh-supporting concentration Rh nitrate aqueous solution to the powder, carried as a 0.5 wt%, after drying, was calcined 1 hour at 400 ° C..

  This noble metal-supported powder, γ-alumina, a predetermined amount of boehmite, and nitric acid are put into a magnetic pot, and the average particle size is pulverized to 3 μm. The excess slurry was removed with an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour in an air atmosphere to obtain a catalyst honeycomb substrate of Comparative Example 5. At this time, the amount of precious metal per 1 L of the catalyst honeycomb was 0.5 g / L-honeycomb.

[An endurance test]
The catalyst honeycomb substrates of Examples 1 to 25 and Comparative Examples 1 to 5 manufactured as described above are mounted on the exhaust system of a Nissan V-type 6-cylinder engine (displacement 3.5 L (MPi)). Then, an endurance test was performed in which the engine was operated for 30 hours at an inlet temperature of 900 [° C.].

[Early activation test]
Each catalyst honeycomb substrate after the endurance test was conducted was incorporated into a simulated exhaust gas circulation device, and simulated exhaust gas having the composition shown in Table 3 below was circulated to raise the temperature from 110 [° C.] to 500 [° C.]. The temperature was raised at a rate of 10 ° C./min, and the temperature at which the conversion rate of HC was 50% was determined from the HC concentrations on the inlet side and outlet side, and used as an index for low-temperature activation.

<Confirmation of noble metal particle aggregation state>
In order to examine the aggregation state of the noble metal particles after the durability test, a catalyst powder was collected from the catalyst honeycomb substrate and observed by TEM. The TEM used is a field emission transmission electron microscope (Hitachi HF-2000), and an EDX analyzer (SIGMA manufactured by Kevex) is attached as an attached device.

〔Test results〕
These test results are also shown in Table 2.

  As is clear from Table 2, the catalyst powders of Examples 1 to 27 were maintained with a small average particle diameter of the noble metal even after the endurance test, and thus were excellent in low-temperature activated catalyst performance. In particular, Examples 1 to 17 and 19 to 25 in which the ratio D2 / D1 of D2 to D1 was in the range of 1 ≦ D2 / D1 ≦ 50 were superior to Example 18 in low-temperature activation catalyst performance. Moreover, it has confirmed that it was not aggregated also by observation of the noble metal particle by TEM. As an example, the micrograph of Example 9 is as shown in FIG.

  On the other hand, Comparative Examples 1 to 5 do not contain alkali metal or alkaline earth metal or zirconia in the first compound in the catalyst powder, or do not include the second compound. Compared with 1-25, the fine particle maintenance effect of precious metal particles and the low temperature activation catalyst performance were inferior.

  Next, actual-size exhaust gas purifying catalysts of Examples 28, 29 and Comparative Example 6 were manufactured as described below.

Example 28
The Pd catalyst powder of Example 19, the Rh catalyst powder of Example 24, boehmite, and a 10% aqueous nitric acid solution were mixed and charged into a magnetic pot, and the average particle size was pulverized to 3 [μm]. The obtained slurry was applied to a cordierite honeycomb substrate (0.92L), the excess slurry was removed with an air stream, dried at 130 ° C, and fired at 400 ° C for 1 hour in an air atmosphere. The actual size catalyst honeycomb of Example 28 was obtained. The amounts of Pd and Rh per 1 L of the catalyst honeycomb at this time were 0.8 g / L and 0.4 g / L.

Example 29
Example 29 is the same as Example 28 except that the Pd powder used in Example 26 is used instead of the Pd powder of Example 28, and the Rh powder used in Example 27 is used as the Rh powder. The actual size catalyst honeycomb was obtained.

  The amount of noble metal in the catalyst honeycomb at this time was the same as in Example 28.

[Comparative Example 6]
In the same manner as in Example 28 except that the Pd powder used in Comparative Example 3 was used instead of the Pd powder in Example 28, and the Rh powder used in Comparative Example 5 was used as the Rh powder, the actual size catalyst honeycomb of Comparative Example 6 was used. Obtained.

  The amount of noble metal in the catalyst honeycomb at this time was the same as in Example 28.

[Vehicle evaluation test]
Each of the actual honeycomb honeycomb substrates of Example 28, Example 29, and Comparative Example 6 was mounted on an exhaust system of a vehicle engine, and exhaust gas emission analysis was performed. The vehicle used in this vehicle evaluation test was manufactured by Nissan Motor Co., Ltd., and the installed engine was QE25DE with a displacement of 2.5 [L]. The capacity of the honeycomb substrate was 0.92 [L]. The evaluation mode was LA4-cold start mode.

[Measurement of OSC amount before and after endurance test]
Durability tests were performed on the actual catalyst honeycomb bases of Example 28, Example 29, and Comparative Example 6 used in the vehicle evaluation test. The amount of OSC before and after the endurance test was measured, and the OSC durability of the catalyst was evaluated based on the ratio of the amount of oxygen stored after the endurance test when the initial amount of oxygen stored in the catalyst was 1.0. For the measurement of the OSC amount, first, a part of the catalyst honeycomb substrate before and after the durability test was taken out, and the catalyst was ground together with the cordierite substrate to prepare a powder before the durability test and a powder after the durability test, respectively. . Each powder was once baked in an air stream at 600 [° C.] for 3 hours to remove organic substances attached to the catalyst. Thereafter, in H ₂ stream, 600 ° C. or in heated and subjected to oxygen desorption process in the catalyst. Then, after stabilizing at 500 [° C.], a fixed amount of oxygen was pulsed, and the amount of adsorbed oxygen was measured with a thermal conductivity detector (TCD). The durability was confirmed by taking the ratio of the initial oxygen adsorption amount Qf by the powder before the durability test and the oxygen adsorption amount Qa after the durability by the powder before the durability test.

Table 4 shows the results of the above-described vehicle evaluation test and OSC amount measurement before and after the durability test.

  As can be seen from Table 4, it was confirmed that Examples 28 and 29 had an exhaust gas remaining rate lower than that of Comparative Example 6 when mounted on an actual vehicle, and had excellent exhaust gas purification performance. . In addition, from the measurement results of the OSC amount measurement before and after the durability test, it was revealed that Examples 28 and 29 were less deteriorated in OSC and superior in durability than Comparative Example 6. In particular, Example 29 containing Y was superior in exhaust gas purification performance and OSC durability in an actual vehicle as compared with Example 28.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

It is a schematic diagram which shows the structure of the exhaust gas purification catalyst used as embodiment of this invention. 1 is a metallographic photograph showing an example of an exhaust gas purifying catalyst according to the present invention. It is a graph which shows the relationship between D2 / D1 and the temperature from which the conversion rate of HC becomes 50%. It is a microscope picture which shows the catalyst powder of the Example of this invention. It is a graph which shows the relationship between a noble metal particle diameter and a noble metal surface area. It is a graph which shows the relationship between a noble metal particle diameter and the number of atoms of a noble metal. It is a graph which shows the relationship between D2 / D3 and the surface area of a noble metal particle.

Explanation of symbols

1 Precious metal particles (PM)
2 First compound (anchor agent)
3 Second compound

Claims (15)

Precious metal particles,
A first compound that contacts the noble metal particles and inhibits movement of the noble metal particles;
Including the noble metal particles and the first compound, and comprising a second compound that suppresses the movement of the noble metal particles and suppresses the aggregation of the first compound accompanying the contact between the first compounds,
The first compound supports the noble metal particles, and includes a single substance or an aggregate of the first compounds supporting the noble metal particles in a compartment separated by the second compound, and
The exhaust gas purifying catalyst, wherein the first compound is a composite containing a rare earth element and at least one metal selected from alkali metals and alkaline earth metals. The exhaust gas purifying catalyst according to claim 1, wherein the rare earth element contained in the first compound contains at least one selected from La, Ce, Pr and Nd. The exhaust gas purifying catalyst according to claim 1 or 2 , wherein the rare earth element contained in the first compound further contains Y. At least one of the alkali metal and alkaline earth metal contained in the first compound includes at least one selected from Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The exhaust gas purifying catalyst according to any one of claims 1 to 3 . The exhaust gas purifying catalyst according to any one of claims 1 to 4 , wherein the noble metal particles supported on the first compound include at least one selected from Pt, Pd, and Rh. The ratio D2 / D1 of the secondary particle diameter (D2) of the first compound carrying the noble metal particles to the crystallite diameter (D1) of the first compound is 1 ≦ D2 / D1 ≦ 50. The exhaust gas purifying catalyst according to any one of claims 1 to 5 . The exhaust gas purifying catalyst according to claim 6 , wherein a ratio D2 / D1 of D2 to D1 is 1≤D2 / D1≤20. The exhaust gas purifying catalyst according to claim 5 , wherein the noble metal particles are made of Pd. The exhaust gas purification catalyst according to any one of claims 1 to 8 , wherein the second compound further contains at least one element selected from Ce, Zr, La, and Ba. The powder pore volume determined by N ₂ adsorption analysis is 0.3 [ml / g] to 0.5 [ml / g] per gram of powder, and the average pore diameter is 30 [nm] or less. Item 10. The exhaust gas purifying catalyst according to any one of Items 1 to 9 . Wherein the second compartment separated by a compound, the exhaust gas according to any one of claims 1 to 10, characterized in that it contains an amount of the noble metal particles total 8 × 10 ^-20 mol or less Purification catalyst. The ratio D2 / D3 of the secondary particle diameter (D2) of the first compound carrying the noble metal particles to the average pore diameter (D3) of the pores of the second compound is 1 or more. The exhaust gas purifying catalyst according to any one of claims 1 to 11 , wherein the exhaust gas purifying catalyst is any one of the above. The exhaust gas purification catalyst according to any one of claims 1 to 12, wherein the first compound further contains Zr. A method for producing the exhaust gas purifying catalyst according to any one of claims 1 to 13 ,
A step of pre-sintering the first compound and then supporting the precious metal particles on the first compound;
Crushing the first compound on which the noble metal particles are supported;
And a step of forming a second compound around the pulverized noble metal-supported first compound. A method for producing an exhaust gas purifying catalyst. A catalyst honeycomb substrate, wherein the exhaust gas purifying catalyst according to any one of claims 1 to 13 is coated and formed on an inner wall surface.