JP4797797B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Exhaust gas purification catalyst and method for producing the same Download PDF

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JP4797797B2
JP4797797B2 JP2006147257A JP2006147257A JP4797797B2 JP 4797797 B2 JP4797797 B2 JP 4797797B2 JP 2006147257 A JP2006147257 A JP 2006147257A JP 2006147257 A JP2006147257 A JP 2006147257A JP 4797797 B2 JP4797797 B2 JP 4797797B2
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雅紀 中村
英昭 森坂
広憲 若松
克雄 菅
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日産自動車株式会社
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The present invention relates to an exhaust gas purification catalyst that efficiently purifies carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO x ) contained in exhaust gas discharged from an automobile engine or the like, and production thereof. Regarding the method.

In a three-way catalyst that can simultaneously purify carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO x ) contained in exhaust gas, Pt (platinum), Rh (rhodium), Pd (palladium), etc. Noble metals are widely used as active components of catalysts. These noble metal particles are supported on an oxide substrate such as alumina, zirconia, or titania.

  The temperature of exhaust gas discharged from automobile engines tends to be higher than before due to the high output of gasoline engines and the increase in high-speed driving. In addition, in order to enable exhaust gas purification immediately after starting the engine, the catalyst has come to be placed directly under the engine in order to quickly raise the catalyst from normal temperature to the exhaust purification temperature when the engine is started. Also in this respect, the catalyst has been used in a higher temperature range.

  However, the conventional catalyst has a problem that the durability in actual exhaust gas is poor, and the noble metal itself undergoes grain growth due to heat, resulting in a decrease in activity. Therefore, in order to improve the heat resistance of the catalyst, the structure around the noble metal particles that are catalytically active species is important. Conventionally, these designs are difficult. For example, when precious metal particles are supported on the surface of an oxide by an impregnation method, the pH and salt of the solution are variously changed and brought into contact with each other under favorable conditions. It wasn't.

In addition, recently, transition metals or transition metal compounds such as cerium (Ce) and manganese (Mn) that function as OSC (Oxygen Storage Component) materials are disposed in the vicinity of noble metal particles by an impregnation method. Attempts have been made to improve the durability of the noble metal particles by suppressing the change in atmosphere by a transition metal or a transition metal compound (see Patent Documents 1 to 4). In addition, according to such a method, in addition to the improvement in durability of the noble metal particles, an improvement in the activity of the noble metal particles can be expected.
JP-A-8-131830 JP-A-2005-000829 Japanese Patent Laid-Open No. 2005-000830 JP 2003-117393 A

  However, even when the atmosphere around the noble metal particles is suppressed by the transition metal compound, even if the conventional catalyst can contact the noble metal particles and the transition metal compound particles, both do not become fine particles, or It was difficult to arrange the transition metal compound particles in the vicinity of the noble metal particles as designed because they could not be brought into contact with each other even when they became fine particles or the amount that could be brought into contact was small.

Exhaust gas purifying catalyst of the present invention to advantageously solve the above problem, a catalytic activity particles formed by the first oxide particles carrying said noble metal particles and noble metal particles on the surface, around the catalytic ability particles comprising a plurality of second oxide particles provided, the composite particles containing the catalytic ability particles are included in the enclosed within the area by the plurality of second oxide particles, the composite particles, fine The gist is that gaps are formed between the plurality of second oxide particles when the maximum peak of the pore distribution is in the range of 1 nm to 200 nm.

  Further, the method for producing an exhaust gas purification catalyst of the present invention comprises mixing a colloidal solution in which catalytic ability particles or a precursor thereof are dispersed and an oxide precursor, and surrounding the catalytic ability particles or the precursor thereof. The gist of the present invention is that after the oxide precursor is disposed, the obtained composite precursor is dried and fired.

  According to the exhaust gas purification catalyst of the present invention, an exhaust gas purification catalyst that is durable at a high temperature can be obtained by designing the catalyst so that the pore distribution is in an appropriate range.

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

  FIG. 1 is a schematic view of an embodiment of an exhaust gas purification catalyst according to the present invention. The exhaust gas purification catalyst 1 shown in the figure has noble metal particles 2 as catalytic ability particles and oxide particles 3 provided around the noble metal particles 2, and the noble metal particles 2 and the oxide particles. 3 and composite particles. Since the particles of the composite particles are partially in contact with each other, voids are formed in the composite particles. The voids of the oxide particles 3 are represented by secondary pore diameters. In the exhaust gas purification catalyst of the present embodiment, the maximum pore distribution represented by the pore diameters of the composite particles measured by the gas adsorption method. The peak is in the range of 1 nm to 200 nm. The gas adsorption method is a method of measuring the pore distribution from the theory obtained by correcting the adsorption isotherm to the capillary condensation theory based on multimolecular adsorption, and can measure the pore distribution with high reproducibility and high accuracy. .

  FIG. 2 is a schematic view of another embodiment of the exhaust gas purification catalyst according to the present invention. The exhaust gas purifying catalyst 1 shown in FIG. 2 is composed of a plurality of unit particles 20 whose catalytic ability particles are composed of noble metal particles 2 that are active components of the catalyst and oxide particles 4 that support the noble metal particles. Thus, composite particles of the unit particles 20 and the oxide particles 3 provided around the unit particles 20 are formed. The void A of the unit particle 20 of the composite particle is represented by the secondary pore diameter of the unit particle 20, and the void B of the oxide particle 3 is represented by the secondary pore diameter of the oxide particle 3. . In the exhaust gas purification catalyst of this embodiment, the maximum peak of the pore distribution of the composite particles measured by the gas adsorption method is in the range of 1 nm to 200 nm. When the unit particle 20 is composed of a plurality of fine particles as shown in FIG. 2, the pore distribution measured by the gas adsorption method is such that the volume peak indicating the void A of the unit particle 20 and the oxide particle In some cases, the peak of the pore volume indicating the void B of the oxide particle 3 shows the maximum peak.

  The effects of the exhaust gas purifying catalyst according to the embodiment of the present invention shown in FIGS. 1 and 2 will be described. In the case of an exhaust gas purification catalyst in which noble metal particles 2 as catalytic ability particles or unit particles 20 in which noble metal particles 2 are supported on oxide particles 4 are supported on an oxide by an impregnation method as in the prior art. In the exhaust gas purification temperature range, the catalytic ability particles are aggregated and the active surface area is reduced, so that the purification performance is lowered. In particular, when the exhaust gas temperature is high, the particles tend to aggregate and the tendency of aggregation of the catalytic ability particles increases.

  On the other hand, the exhaust gas purifying catalyst of the present embodiment shown in FIGS. 1 and 2 has a configuration in which oxide particles 3 are positively arranged around catalytic ability particles such as noble metal particles 2 and unit particles 20. Therefore, the oxide particles 3 arranged between the catalytic ability particles serve as a wall between the catalytic ability particles to suppress the aggregation of the catalytic ability particles, thereby maintaining the active surface area even in the exhaust gas purification temperature range. The purification performance can be maintained.

  Furthermore, the maximum peak of the pore distribution of the composite particles comprising the noble metal particles 2 or the unit particles 20 in which the noble metal particles 2 are supported on the oxide particles 4 and the oxide particles 3 is in the range from 1 nm to 200 nm. As a result, an exhaust gas purification catalyst in which a gap between the oxide particles 3 is appropriately secured is obtained. Therefore, the exhaust gas purification catalyst according to the present embodiment can improve the purification performance because the exhaust gas can sufficiently reach the active point of the catalytic ability particles.

Exhaust gas purifying catalyst the maximum peak of the pore distribution is less than 1nm, since the gap of the oxide particles 3 is too narrow, purification performance inferior without exhaust gas catalytic ability particles not sufficiently reach with activity point . Further, in the exhaust gas purification catalyst having a maximum peak of pore distribution exceeding 200 nm, the oxide particles do not serve as a movement barrier for the noble metal particles 2 or the unit particles 20, and the noble metal particles 2 or the unit particles 20 are aggregated with each other. Since the active surface area decreases, the purification performance is poor. Therefore, in the exhaust gas purification catalyst of the present invention, the maximum peak of the pore distribution is in the range of 1 to 200 nm.

  The maximum peak of the preferable pore distribution in the exhaust gas purification catalyst of the present invention is in the range of 10 nm to 200 nm. Among the gaps between the oxide particles 3, pores having a diameter of 1 nm to less than 10 nm are easily collapsed in the exhaust gas purification temperature range, and the catalytic ability particles such as the noble metal particles 2 and the unit particles 20 are associated with the oxide particles 3. There is a possibility that the gas to be purified is confined in the closed pores, and it becomes difficult to contact the particles having catalytic ability. Therefore, when the catalyst has a maximum peak of 10 nm or more and 200 nm or less, the exhaust gas reliably comes into contact with the catalytic ability particles, so that stable purification performance can be obtained over a long period of time.

  The maximum peak of the more preferable pore distribution is in the range of 50 nm to 200 nm. A pore having a pore diameter of less than 10 to 50 nm is less likely to collapse than a pore having a diameter of less than 1 nm to less than 10 nm, but may still collapse in the exhaust gas purification temperature range. Catalytic particles such as particles 20 are confined in the closed pores of the oxide particles 3, and the gas to be purified may not easily come into contact with the particles having catalytic activity. Therefore, when the catalyst has a maximum peak of 10 nm or more and 200 nm or less, the exhaust gas more reliably touches the catalytic particles, so that stable purification performance can be obtained over a long period of time.

  The catalytic ability particles may be the noble metal particles 2 as shown in FIG. 1 or the particles in which the noble metal particles 2 as shown in FIG. The average particle diameter of such catalytic ability particles is preferably 1 nm to 200 nm. The smaller the particle size, the larger the active surface area and the higher the activity of the catalytic ability particles. Further, when the particle size of the catalytic ability particles is 1 nm to 200 nm, the aggregation is suppressed by the oxide particles 3 arranged around the catalytic ability particles, so that the reduction in purification performance due to the coarsening of the catalytic ability particles is suppressed. If the particle size of the catalytic ability particles is too small to be less than 1 nm, the catalytic ability particles move freely through the gaps between the oxide particles 3 arranged around the catalytic ability particles in the exhaust gas purification temperature region. As a result, the active particles are aggregated to increase the size of the active particles. As a result, the active surface area is decreased, and the catalyst performance may be decreased. In addition, if the particle size of the catalytic activity particles is too large to exceed 200 nm, the exhaust gas purification temperature region does not agglomerate or deteriorate, but the catalytic activity particles have a small active surface area and the exhaust gas purification may not be sufficient. is there. Accordingly, the catalytic capacity particles are preferably in the range of 1 nm to 200 nm. In order to prevent the catalytic ability particles from moving through the gaps between the oxide particles 3, the average particle diameter of the catalytic ability particles is larger than the pore diameter which is the maximum peak of the pore distribution of the catalyst described above. Is also large.

  The average particle diameter of the catalytic ability particles described above is more preferably 2 to 50 nm. When the average particle size is 2 to 50 nm, the active surface area is particularly wide, and excellent catalytic performance is exhibited.

The oxide particles 3 provided around the catalytic ability particles include at least one oxide selected from Al 2 O 3 , La 2 O 3 , Y 2 O 3 , Nd 2 O 3 , CeO 2 and ZrO 2. be able to. It is because the oxide particle 3 can use the oxide generally used as a catalyst base material. From the viewpoint of heat resistance, a solid solution of these oxides can also be used.

  In the exhaust gas purifying catalyst according to the present invention, the catalytic ability particles may be the noble metal particles 2 as shown in FIG. 1, but a more preferable embodiment is that the catalytic ability particles are oxides as shown in FIG. These are unit particles 20 in which the noble metal particles 2 are supported on the surfaces of the particles 4. By supporting the noble metal particles 2 on the oxide particles 4, the noble metal particles 2 and the oxide particles 4 are chemically bonded, and the movement of the noble metal particles 2 is suppressed by this affinity. Therefore, the exhaust gas purification catalyst is excellent in durability at high temperatures.

  The unit particles 20 may be singularly provided in one region surrounded by the plurality of oxide particles 3 arranged around the unit particles 20, or as shown in FIG. You may have.

  The noble metal particles 2 supported on the oxide particles 4 in the unit particles 20 or the noble metal particles 2 around which the oxide particles 3 shown in FIG. 1 are arranged are at least one selected from Pt, Rh and Pd. Types of precious metal particles can be included. Since Pt, Rh and Pd are all active components having catalytic activity for purifying exhaust gas discharged from automobiles, at least one of the above-mentioned noble metals can be included in the noble metal particles 2.

The oxide particles 4 supporting the noble metal particles 2 in the unit particles 20 are made of at least one oxide selected from Al 2 O 3 , La 2 O 3 , Y 2 O 3 , Nd 2 O 3 , ZrO 2 and CeO 2. It is preferable to include. Since these oxides all have strong chemical affinity with the noble metal particles 2, the noble metal particles 2 are firmly supported and aggregation of the noble metal particles 2 can be suppressed. Of these oxides, CeO 2 has the ability to absorb and release oxygen, and by carrying the noble metal particles 2 on CeO 2 , it can be purified stably even if the exhaust gas atmosphere changes. Can do.

At least one selected from Al 2 O 3 , La 2 O 3 , Y 2 O 3 , Nd 2 O 3 , ZrO 2 and CeO 2 listed above as the oxide particles 4 supporting the noble metal particles 2 in the unit particles 20. The oxide is preferably an oxide having a higher affinity for the noble metal particles 2 than the oxides of the oxide particles 3 disposed around the unit particles 20. Since the oxide particles 4 have higher affinity with the noble metal particles 2 than the oxide particles 3, the noble metal particles 2 supported on the oxide particles 4 are separated from the oxide particles 4 and around the unit particles 20. Movement and adhesion to the oxide particles 3 are suppressed. As a result, it is possible to prevent the noble metal particles 2 from aggregating and deteriorating the purification performance.

  Next, an example of a method for producing an exhaust gas purification catalyst according to the present invention will be described.

  In advance, a colloidal solution in which catalytically active particles or precursors thereof are dispersed is prepared. When the catalytic ability particles are the noble metal particles 2, they can be dispersed in the liquid by adding a solution containing the noble metal particles 2 to the colloidal solution. When the catalytic ability particles are the unit particles 20, the oxide particles 4 having a predetermined particle size or a precursor thereof are added to the colloidal solution in which the noble metal particles 2 are dispersed, and the unit particles are stirred. 20 or its precursor can be dispersed in the liquid.

  Next, by mixing the colloidal solution in which the catalytic ability particles or the precursor thereof are dispersed and the precursor of the oxide, the precursor of the oxide is mixed around the catalytic ability particles or the precursor. Arrange. Thereafter, the obtained composite precursor is dried and fired to obtain an exhaust gas purification catalyst powder. In the manufacturing process of the exhaust gas purifying catalyst according to the present invention, the adjustment of the maximum peak of the pore distribution in the range from 1 nm to 200 nm is, for example, control of the colloid concentration in the colloidal solution in which the catalytic ability particles are dispersed or oxidation. It can be carried out by controlling the particle size of the product particles 3 or the like.

  In the method for producing an exhaust gas purification catalyst of the present invention, steps other than those described above can be performed according to a conventional method, and the obtained exhaust gas purification catalyst powder is used as a slurry to obtain the surface of the inner wall surface of the honeycomb substrate. Then, it is applied to the actual machine.

[Example 1]
After adding cerium nitrate Ce (NO 3 ) 3 · 6H 2 O in an amount of 122.360 g to 2000 g of water and mixing, 25% aqueous ammonia solution was added dropwise with stirring until pH 11 to obtain a ceria precursor. . Then, the resulting ceria precursor filtration, washed with water, and the ceria precursor in water 2000 g, Poribinirupi b pyrrolidone platinum Pt-PVP (Pt: 4wt% , particle size: 4 nm) and was charged 37.500g The mixture was stirred. Furthermore, it was added and stirred Poribinirupi b pyrrolidone PVP in an amount of 50.000 g.

Separately, 2,000 g of water was mixed with 210.390 g of zirconyl nitrate ZrO (NO 3 ) 2 · 2H 2 O and 1.994 g of lanthanum nitrate La (NO 3 ) 3 · 6H 2 O, and then mixed. Then, a 25% aqueous ammonia solution was added dropwise until pH 11 was obtained to obtain a lanthanum-zirconia precursor. Next, the lanthanum-zirconia precursor precipitate was filtered and washed with water to obtain a lanthanum-zirconia precursor cake. This cake was added to the previously prepared platinum-ceria precursor mixture and further stirred. After filtering and discarding the supernatant liquid, it was left to stand overnight in a thermostatic bath at 150 ° C. to evaporate water. The dried powder was calcined at 400 ° C. for 1 hour to obtain a catalyst powder. The obtained catalyst powder is a powder in which lanthanum-zirconia composite oxide particles are arranged around unit particles made of platinum-ceria.

[Example 2]
After adding cerium nitrate Ce (NO 3 ) 3 · 6H 2 O in an amount of 122.360 g to 2000 g of water and mixing, 25% aqueous ammonia solution was added dropwise to pH 11 with stirring to obtain a ceria precursor. . Then filtered and the resulting ceria precursor, washed with water, and the ceria precursor in water 2000 g, Poribinirupi b pyrrolidone platinum P t -PVP (Pt: 4wt% , particle size: 4 nm) charged with 37.500g The mixture was stirred. Furthermore, it was added and stirred Poribinirupi b pyrrolidone PVP in an amount of 100.000 g.

Separately, 2,000 g of water was mixed with 210.390 g of zirconyl nitrate ZrO (NO 3 ) 2 · 2H 2 O and 1.994 g of lanthanum nitrate La (NO 3 ) 3 · 6H 2 O, and then mixed. Then, a 25% aqueous ammonia solution was added dropwise until pH 11 was obtained to obtain a lanthanum-zirconia precursor. Next, the lanthanum-zirconia precursor precipitate was filtered and washed with water to obtain a lanthanum-zirconia precursor cake. This cake was added to the previously prepared platinum-ceria precursor mixture and further stirred. After filtering and discarding the supernatant liquid, it was left to stand overnight in a thermostatic bath at 150 ° C. to evaporate water. The dried powder was calcined at 400 ° C. for 1 hour to obtain a catalyst powder. The obtained catalyst powder is a powder in which lanthanum-zirconia composite oxide particles are arranged around unit particles made of platinum-ceria.

[Example 3]
After adding cerium nitrate Ce (NO 3 ) 3 · 6H 2 O in an amount of 122.360 g to 2000 g of water and mixing, 25% aqueous ammonia solution was added dropwise to pH 11 with stirring to obtain a ceria precursor. . Then, the resulting ceria precursor filtration, washed with water, and the ceria precursor in water 2000 g, Poribinirupi b pyrrolidone platinum Pt-PVP (Pt: 4wt% , particle size: 4 nm) and was charged 37.500g The mixture was stirred. Furthermore, it was added and stirred Poribinirupi b pyrrolidone PVP in an amount of 200.000G.

Separately, 210.390 g of zirconyl nitrate ZrO (NO 3 ) 2 · 2H 2 O and 1.994 g of lanthanum nitrate La (NO 3 ) 3 · 6H 2 O were added to and mixed with 2000 g of water, followed by stirring. A 25% aqueous ammonia solution was added dropwise until the pH was 11 to obtain a lanthanum-zirconia precursor. Next, the lanthanum-zirconia precursor precipitate was filtered and washed with water to obtain a lanthanum-zirconia precursor cake. This cake was added to the previously prepared platinum-ceria precursor mixture and further stirred. After filtering and discarding the supernatant liquid, it was left to stand overnight in a thermostatic bath at 150 ° C. to evaporate water. The dried powder was calcined at 400 ° C. for 1 hour to obtain a catalyst powder. The obtained catalyst powder is a powder in which lanthanum-zirconia composite oxide particles are arranged around unit particles made of platinum-ceria.

[Example 4]
50 g of ceria powder (average particle size: 1 μm) was added to 1950 g of water and mixed, and then a ceria suspension (average particle size: 200 nm, solid content 2.5%) was obtained using a bead mill. The bead mill is one of wet pulverizers, and is an apparatus that can pulverize a material to be pulverized to a submicron level particle size with fine beads. The suspension 2000g and Poribinirupi b pyrrolidone platinum Pt-PVP (Pt: 4wt% , particle size: 4 nm) was 37.500g was charged mixture stirred. Furthermore, it was added and stirred Poribinirupi b pyrrolidone PVP in an amount of 50.000 g.

Separately, after adding 367.919 g of aluminum nitrate Al (NO 3 ) 3 · 9H 2 O to 2000 g of water and mixing, 25% aqueous ammonia solution was added dropwise to pH 11 with stirring to obtain an alumina precursor. It was. Next, the precipitate of the alumina precursor was filtered and washed with water to obtain an alumina precursor cake. This cake was added to the previously prepared platinum-ceria precursor mixture and further stirred. After stirring for a whole day and night, the mixture was filtered and the supernatant was discarded, and then left in a constant temperature bath at 150 ° C. for a whole day and night to evaporate water. The dried powder was calcined at 400 ° C. for 1 hour to obtain a catalyst powder. The obtained catalyst powder is a powder in which alumina particles are arranged around unit particles made of platinum-ceria.

[Comparative Example 1]
In water 1950 g, ceria powder 50 g (average particle: 1 [mu] m) and Poribinirupi b pyrrolidone platinum Pt-PVP (Pt: 4wt% , particle size: 4 nm) was a 37.500g was charged mixture stirred. Furthermore, it was added and stirred Poribinirupi b pyrrolidone PVP in an amount of 50.000 g.

Separately, after adding 367.919 g of aluminum nitrate Al (NO 3 ) 3 · 9H 2 O to 2000 g of water and mixing, 25% aqueous ammonia solution was added dropwise to pH 11 with stirring to obtain an alumina precursor. It was. Next, the precipitate of the alumina precursor was filtered and washed with water to obtain an alumina precursor cake. This cake was added to the previously prepared platinum-ceria precursor mixture and further stirred. After stirring for a whole day and night, the mixture was filtered and the supernatant was discarded, and then left in a constant temperature bath at 150 ° C. for a whole day and night to evaporate water. The dried powder was calcined at 400 ° C. for 1 hour to obtain a catalyst powder. The obtained catalyst powder is a powder in which alumina particles are arranged around unit particles made of platinum-ceria.

  The catalysts of Examples 1 to 4 and Comparative Example 1 obtained by the sample preparation process were evaluated by the following methods.

<Measurement of pore distribution>
The pore distribution was measured by a gas adsorption method using a specific surface area / pore distribution measuring device manufactured by Micromeritics.

  FIG. 3 shows the pore distribution of the catalysts of Examples 1 to 4 and Comparative Example 1.

  Moreover, the average particle diameter of unit particle | grains and the average particle diameter of oxide particle | grains were investigated about the catalyst of Examples 1-4 and the comparative example 1. As a result, in the catalyst of Example 1, the average particle size of the unit particles was 22 nm, and the average particle size of the lanthanum-zirconia composite oxide particles was 29 nm. In the catalyst of Example 2, the average particle size of the unit particles was 31 nm, and the average particle size of the lanthanum-zirconia composite oxide particles was 60 nm. In the catalyst of Example 3, the average particle size of the unit particles was 23 nm, and the average particle size of the lanthanum-zirconia composite oxide particles was 135 nm. In the catalyst of Example 4, the average particle size of the unit particles was 195 nm, and the average particle size of the alumina particles was 140 nm.

In the catalyst of Comparative Example 1, the average particle size of the unit particles is 1253 nm, and the average particle size of the alumina particles is
It was 255 nm.

<Catalyst durability test>
After slurrying each catalyst powder, it was put into a 0.0595L cordierite honeycomb substrate (400 cells / 4 mil) to remove excess slurry in an air stream, dried at 120 ° C, and then air stream The honeycomb substrate was fired at 400 ° C. to coat the honeycomb substrate with the catalyst powder. The amount of catalyst coated on the catalyst-supporting honeycomb obtained at this time is 220 g per liter of catalyst. The amount of Pt contained per liter of catalyst was 3 g.

  In a Nissan V-type 6-cylinder engine, the catalyst inlet temperature was set to 1000 ° C., and a durability test was performed for 30 hours. In addition, unleaded gasoline was used as fuel.

<Catalyst evaluation test>
The catalyst was evaluated by setting a part of the catalyst carrier having the above durability to 40 mL. The reaction gas flow rate was 40 L / min, the reaction gas temperature was 350 ° C., and the reaction gas composition was as shown in Table 1. The reaction gas flow rate was 40 L / min.

<Catalyst purification performance>
Table 2 shows the unit particle diameters having catalytic ability of Examples 1 to 4 and Comparative Example 1, the pore peak diameter of the catalyst, and the 50% purification temperature (HC-T50) of HC.

  The unit particle sizes of Examples 1 to 3 were almost the same at 20 to 30 nm. As the pore peak position increased, HC-T50 decreased and the catalytic activity improved.

  When the unit particle sizes of Example 3 and Example 4 were compared, Example 4 was larger. The pore peak positions were almost the same. HC-T50 of Example 3 was lower than that of Example 4, and the catalytic activity improved when the unit particles were made smaller.

  The unit particle diameter of Comparative Example 1 was much larger than that of Examples 1 to 4, and the pore peak position was 225 nm. HC-T50 was 486 ° C.

  From the above, it is clear that the difference between the unit particle diameter and the pore distribution peak position affects the catalyst performance.

1 is a schematic diagram of an exhaust gas purification catalyst according to an embodiment of the present invention. 1 is a schematic diagram of an exhaust gas purification catalyst according to an embodiment of the present invention. 1 is a schematic diagram of an exhaust gas purification catalyst according to an embodiment of the present invention.

Explanation of symbols

1 Exhaust gas purification catalyst 2 Noble metal particles 3 Oxide particles 4 Oxide particles 20 Unit particles

Claims (11)

  1. Catalytic particles formed by noble metal particles and first oxide particles supporting the noble metal particles on the surface ;
    A plurality of second oxide particles provided around the catalytic ability particles,
    Comprising composite particles comprising
    The catalytic ability particles are included in a region surrounded by the plurality of second oxide particles,
    An exhaust gas purification catalyst, wherein the composite particles have a maximum peak of pore distribution in a range from 1 nm to 200 nm , whereby gaps are formed between the plurality of second oxide particles .
  2.   The exhaust gas purification catalyst according to claim 1, wherein the maximum peak of the pore distribution is in the range of 10 nm to 200 nm.
  3. The exhaust gas purification catalyst according to claim 2 , wherein the maximum peak of the pore distribution is in the range of 50 nm to 200 nm.
  4. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the catalytic capacity particles have an average particle diameter of 1 nm to 200 nm.
  5. The exhaust gas purifying catalyst according to claim 4 , wherein the catalytic capacity particles have an average particle diameter of 2 nm to 50 nm.
  6. The second oxide particles provided around the catalytic ability particles are at least one oxide selected from Al 2 O 3 , La 2 O 3 , Y 2 O 3 , Nd 2 O 3 , CeO 2 and ZrO 2 . The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the exhaust gas purification catalyst is contained.
  7. The noble metal particles, Pt, an exhaust gas purifying catalyst according to any one of claims 1 to 6, characterized in that it comprises at least one kind selected from Rh and Pd.
  8. The first oxide particles carrying said noble metal particles include the A l 2 O 3, La 2 O 3, Y 2 O 3, Nd 2 O 3, at least one oxide selected from ZrO 2 and CeO 2 The exhaust gas purification catalyst according to any one of claims 1 to 7 ,
  9.   The exhaust gas purification catalyst according to any one of claims 1 to 8, wherein an average particle diameter of the catalytic ability particles is larger than a pore diameter at a maximum peak of a pore distribution of the composite particles.
  10. The exhaust gas purification catalyst according to any one of claims 1 to 9, wherein an average particle size of the second oxide particles is 29 nm to 140 nm.
  11. A method for producing the exhaust gas purification catalyst according to claim 1, comprising:
    A colloidal solution prepared by dispersing the catalytic ability particles or a precursor thereof, by mixing a precursor of the second oxide particles, the precursor of the catalytic ability particles or the second oxide particles around the precursor A method for producing an exhaust gas purifying catalyst, comprising: drying and calcining the obtained composite precursor after arranging the body.
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