JP6206115B2 - Method for producing exhaust gas purification catalyst material - Google Patents

Description

The present invention relates to a method for producing an exhaust gas purifying catalyst material .

  As a three-way catalyst known as an automobile exhaust gas purification catalyst, a catalyst material in which Rh is supported on a composite oxide has been conventionally used. However, when the catalyst is exposed to high-temperature exhaust gas for a long period of time, Rh aggregates and sinters, which may reduce the catalytic activity.

  As an exhaust gas purifying catalyst material for dealing with this problem, Patent Document 1 describes a catalyst in which Rh is supported on a carrier made of an Nd / Al / Ce / Zr / La inorganic mixed oxide.

According to Patent Document 1, the manufacturing method is generally as follows. A solution obtained by dissolving aluminum nitrate, cerium nitrate, zirconium oxynitrate, and lanthanum nitrate in pure water is dropped into ammonia water, and the resulting precipitate is dried and fired to form La-added CeO ₂ —ZrO _2. A powder of secondary particles in which the first particles and the _second particles made of La-added Al ₂ O ₃ are mixed and aggregated is obtained. This powder is mixed with water-solubilized neodymium nitrate, stirred, dried, and fired to obtain a powdered inorganic mixed oxide in which Nd is segregated on the surface layers of the first particles and the second particles. The inorganic mixed oxide is immersed in an aqueous rhodium nitrate solution and fired to obtain the catalyst.

  Patent Document 2 discloses a catalyst in which a noble metal is supported on an oxide carrier, the noble metal is present in a highly oxidized state on the surface of the carrier in an oxidizing atmosphere, and the carrier is positively bonded via oxygen on the surface of the carrier. It has a surface oxide layer combined with ions, and in a reducing atmosphere, the precious metal is present on the surface of the support in a metallic state, and the amount of the precious metal exposed on the surface of the support is supported on the support. It is described that the atomic ratio is 10% or more with respect to the total amount of the precious metal formed.

Patent Document 2 discloses, as examples of the oxide support, CeO ₂ —ZrO ₂ —Y ₂ O ₃ , ZrO ₂ —La ₂ O ₃ , CeO ₂ —ZrO ₂ , CeO ₂ —ZrO ₂ —La ₂ O. Each composite oxide of _3- Pr ₂ O ₃ is described, and as a catalyst production method, the composite oxide is stirred in ion-exchanged water, and a mixed solution obtained by adding neodymium nitrate thereto is evaporated to dryness, and further dried. It is described that after calcination, the catalyst is obtained by immersing in an aqueous rhodium nitrate solution, filtering and washing, and then drying and calcination.

JP 2011-136319 A JP 2007-289920 A

  Patent Documents 1 and 2 describe that Nd is supported on the surface of a CeZr-based composite oxide and then further Rh is supported so that the movement of Rh is suppressed by Nd. It describes that Rh is made into a metal state by reduction treatment.

  In the present invention, unlike Patent Documents 1 and 2, Rh is doped in a CeZr-based composite oxide (Rh constitutes a composite oxide together with Ce and Zr, and the composite oxide has crystal lattice points or between lattice points. Rh-doped composite oxide in which Rh is arranged) is an object. In the case of this Rh-doped composite oxide, a part of Rh is exposed on the surface of the composite oxide and works to purify the exhaust gas. However, since the amount of Rh exposed on the surface of the composite oxide is small, when this Rh is exposed to high-temperature exhaust gas and sintered, the catalyst activity decreases greatly.

  Then, this invention makes it a subject to improve the high temperature durability, aiming at the activity improvement of the catalyst material for exhaust gas purification which consists of said Rh dope complex oxide.

  In the present invention, in order to solve the above problems, in the Rh-doped CeZrNd-based composite oxide, Nd is concentrated on the surface portion of the composite oxide.

That is, the method for producing an exhaust gas purifying catalyst material according to the present invention comprises an Rh-doped composite oxide containing a rare earth metal other than Ce, Zr, and Ce and doped with Rh, and at least as the rare earth metal. A method for producing an exhaust gas purifying catalyst material containing Nd, wherein the Nd is present at a higher concentration in the surface portion than in the composite oxide ;
A basic solution is added to an acidic solution containing Ce, Zr, and Rh ions to coprecipitate Ce, Zr, and Rh, thereby producing a RhCeZr-containing coprecipitation gel.
After adding a basic solution to the RhCeZr-containing coprecipitation gel, an acidic solution containing each ion of Rh and Nd is added and mixed, whereby Rh hydroxide and Nd water are added onto the RhCeZr-containing coprecipitation gel. The oxide is precipitated and precipitated, and then fired.

  Here, the acidic solution for generating the coprecipitated gel may contain Nd ions.

  By the above production method, an Rh-doped composite oxide containing Ce, Zr, Nd, and Rh and having Nd in a high concentration on the surface of the composite oxide together with Rh is obtained, and the activity of the catalyst is improved and the high temperature durability is obtained. It becomes advantageous for improvement.

  Here, Nd is present at a higher concentration in the surface portion than in the complex oxide. Nd is present in the surface portion of the complex oxide, and Nd is not substantially present in the complex oxide. including. The complex oxide may further contain La and Y as the rare earth metal.

  In such a catalyst, Rh doped in the composite oxide is strongly fixed and dispersed by Nd present at a high concentration in the surface portion of the composite oxide. And the high-temperature durability of the catalyst is increased, and it is avoided that the activity of the catalyst is greatly reduced when the catalyst is used in a state where it is exposed to high-temperature exhaust gas.

In the step of generating the RhCeZr-containing coprecipitation gel, a basic solution is added to an acidic solution containing Ce, Zr, Nd, La, Y, and Rh ions, and Ce, Zr, Nd, La, Y, and Rh are added. You may make it co-precipitate.

  Preference is given to heating in a reducing atmosphere after the calcination, whereby the Rh metallization (into a metallic state) proceeds and the activity of the catalyst increases. Further, by the heat reduction treatment, precipitation of Rh embedded in the composite oxide on the surface of the composite oxide proceeds, and Rh is strongly dispersed on the surface of the composite oxide with Nd. This is considered to be possible, and is advantageous for improving the activity of the catalyst and improving the high-temperature durability.

According to the method for producing an exhaust gas purifying catalyst material according to the present invention, a basic solution is added to an acidic solution containing Ce, Zr and Rh to co-precipitate Ce, Zr and Rh, thereby co-precipitation containing RhCeZr. A gel is formed, and after adding a basic solution to the co-precipitated gel, an acidic solution containing Rh and Nd is added and mixed to form a Rh hydroxide and Nd hydroxide on the co-precipitated gel. Rd-doped composite oxide containing Ce, Zr, Nd and Rh, and Nd together with Rh at a high concentration on the surface of the composite oxide is obtained. It is advantageous for improving activity and durability at high temperature.

It is a figure which shows typically the Rh dope complex oxide which concerns on embodiment of this invention. It is a figure which shows typically the state which Rh couple | bonded with Nd of complex oxide through oxygen. 6 is a block diagram illustrating a manufacturing process of an Rh-doped composite oxide according to Example 1. FIG. It is a graph which shows the specific surface area and Rh surface dispersion degree of Rh dope complex oxide of Example 1, 2 and each comparative example. It is a graph which shows the light-off temperature of Examples 1, 2 and a comparative example. It is a graph which shows the high temperature purification rate of Examples 1, 2 and a comparative example. It is a graph which shows the relationship between the catalyst inlet gas temperature of Examples 1, 2, and a comparative example, and HC purification | cleaning rate. It is a graph which shows the light-off temperature of Example 1, 3 and a comparative example. It is a graph which shows the light-off temperature of Example 1, 2, 4, 5 and a comparative example.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

<Configuration of exhaust gas purification catalyst material>
The exhaust gas purifying catalyst material according to the present invention is a catalyst material suitable for purifying automobile exhaust gas, and is composed of Rh-doped composite oxide particles 1 schematically shown in FIG. The Rh-doped composite oxide particle 1 is formed by doping Rh with a composite oxide containing at least Nd as a rare earth metal other than Ce, Zr, and Ce. Nd exists as Nd ₂ O ₃ constituting the complex oxide, and the Nd concentration in the surface portion of the particle 1 is higher than that in the particle. Rh is arranged between crystal lattice points or between lattice points of the complex oxide, a part of Rh is exposed on the surface of the particle 1, and the Rh concentration in the surface portion of the particle 1 is higher than that in the particle. . As shown in FIG. 2, Rh exposed on the surface of the particles 1 is strongly bonded to Nd of Nd ₂ O _{3 on} the surface portion constituting the composite oxide via oxygen 2.

<Examples and comparative examples of exhaust gas purifying catalysts>
Example 1
As shown in FIG. 3, an aqueous solution in which cerium sulfate, neodymium sulfate, lanthanum sulfate, and yttrium sulfate were mixed and an aqueous zirconyl oxynitrate solution were mixed, and an aqueous rhodium nitrate solution was further added thereto. Here, the charged amount of the aqueous neodymium sulfate solution is 50% of the target addition amount (the total amount planned for the configuration of the Rh-doped composite oxide) (“%” means “mass%”. The same applies hereinafter). It was made to become. Further, the amount of the rhodium nitrate aqueous solution charged here was 65% of the target addition amount.

  Ce, Zr, Nd, La, Y, and Rh were coprecipitated by adding a basic solution (aqueous ammonia) to the obtained mixed solution (acidic) of Ce, Zr, Nd, La, Y, and Rh. . After adding a basic solution to the obtained RhCeZrNdLaY-containing coprecipitation gel to adjust the pH to about 11, add the remaining amount of neodymium sulfate aqueous solution (50%) and the remaining amount of rhodium nitrate aqueous solution (35%) and mix did. Thereby, Rh hydroxide and Nd hydroxide were deposited on the particles of the coprecipitated gel. The entire precipitate obtained was washed with water, dried overnight at 150 ° C. in the atmosphere, and the dried product was pulverized and then baked at 520 ° C. for 2 hours in the atmosphere to obtain the target Rh-doped composite oxidation. (Rh-doped CeZrNdLaY composite oxide) was obtained.

The composition excluding Rh of the Rh-doped composite oxide is CeO ₂ : ZrO ₂ : Nd ₂ O ₃ : La ₂ O ₃ : Y ₂ O ₃ = 10: 75: 5: 5: 5 (mass ratio). The total amount of Rh doping is 1% by mass of the CeZrNdLaY composite oxide.

  The feature of the method for preparing the Rh-doped composite oxide is that the amounts of neodymium sulfate and rhodium nitrate at the time of coprecipitation are 50% and 65%, and the respective remaining amounts are added to the coprecipitation gel. .

  Since a part (50%) of neodymium sulfate is added to the coprecipitation gel, the resulting Rh-doped composite oxide has a higher concentration of Nd in the surface than in the composite oxide. . Since a part (35%) of rhodium nitrate was added to the coprecipitation gel, the resulting Rh-doped composite oxide had a higher concentration of Rh in the surface portion than in the composite oxide. .

Then, the Rh-doped composite oxide was mixed with a binder and water to form a slurry, and this slurry was coated on the honeycomb carrier. And the catalyst which concerns on Example 1 was obtained by baking for 2 hours at 500 degreeC in air | atmosphere. As the carrier, a cordierite honeycomb carrier (capacity: 100 mL) having a cell wall thickness of 3.5 mil (8.89 × 10 ⁻² mm) and 600 cells per square inch (645.16 mm ² ) was used. The amount of Rh-doped composite oxide supported per liter of support is 100 g.

-Example 2-
Regarding the preparation of neodymium sulfate, unlike in Example 1, after obtaining a RhCeZrLaY-containing coprecipitation gel with the amount of preparation at the time of coprecipitation being 0%, the total target addition amount of neodymium sulfate (100 %) Was added. On the other hand, regarding the preparation of rhodium nitrate, as in Example 1, the preparation amount during coprecipitation was set to 65% of the target addition amount, and the remaining amount of 35% was added to the coprecipitation gel. The others were the same as in Example 1 to obtain the target Rh-doped composite oxide. The composition of the obtained Rh-doped composite oxide excluding Rh and the amount of Rh doping are the same as in Example 1. This Rh-doped composite oxide was coated on the same honeycomb carrier as in Example 1 in the same manner to obtain a catalyst according to Example 2. The amount of Rh-doped composite oxide supported on the honeycomb carrier is 100 g / L as in Example 1.

  Also in Example 2, since the entire amount of neodymium sulfate was added to the coprecipitation gel, the resulting Rh-doped composite oxide has Nd in a higher concentration in the surface portion than in the composite oxide. Rh is present in a higher concentration in the surface portion than in the complex oxide as in Example 1.

-Example 3-
Regarding the preparation of neodymium sulfate, the amount of preparation at the time of coprecipitation was set to 50% and the remaining amount of 50% was added to the coprecipitation gel as in Example 1, but the preparation of rhodium nitrate was the same as in Example 1. In contrast, the amount charged during coprecipitation was 20%, and the remaining amount of 80% was added to the coprecipitation gel. Other than that, the target Rh-doped CeZrNdLaY composite oxide was obtained in the same manner as in Example 1. The composition of the Rh-doped composite oxide excluding Rh and the amount of Rh doping are the same as in Example 1. The catalyst according to Example 3 was obtained by coating this Rh-doped composite oxide on the same honeycomb carrier as in Example 1 by the same method. The amount of Rh-doped composite oxide supported on the honeycomb carrier is 100 g / L as in Example 1.

  Also in Example 3, since a part (50%) of neodymium sulfate was added to the coprecipitation gel, the resulting Rh-doped composite oxide has a higher concentration of Nd in the surface portion than in the composite oxide. It will be. Rh is present in a higher concentration in the surface portion than in the complex oxide as in Example 1.

-Comparative example-
Regarding the preparation of neodymium sulfate, the total amount of target addition was charged at the time of coprecipitation, and the amount of neodymium sulfate added to the coprecipitation gel was set to zero. Regarding the preparation of rhodium nitrate, as in Example 1, the amount of charge during coprecipitation was set to 65% of the target addition amount, and the remaining amount of 35% was added to the coprecipitation gel. Other than that, the target Rh-doped CeZrNdLaY composite oxide was obtained in the same manner as in Example 1. The composition of the obtained Rh-doped composite oxide excluding Rh and the amount of Rh doping are the same as in Example 1. This Rh-doped composite oxide was coated on the same honeycomb carrier as in Example 1 by the same method to obtain a catalyst according to a comparative example. The amount of Rh-doped composite oxide supported on the honeycomb carrier is 100 g / L as in Example 1.

  In the case of the comparative example, since the entire amount of neodymium sulfate is charged at the time of coprecipitation, it is recognized that in the obtained Rh-doped composite oxide, the Nd concentration is substantially uniform throughout the composite oxide. Rh is present in a higher concentration in the surface portion than in the complex oxide as in Example 1.

<Specific surface area and surface dispersion degree of Rh>
The specific surface area of each Rh-doped composite oxide in Examples 1 and 2 and Comparative Example Fresh sample was measured by an automatic specific surface area / pore distribution measuring device (TiStar 3000, manufactured by Miracometics), and each Rh in the Fresh sample was also measured. The degree of dispersion on the surface of the composite oxide was measured by the CO pulse method using an oxygen storage / release measurement device (All Vacuum Create). The measurement results are shown in FIG. The surface dispersion degree of Rh was obtained as the degree of dispersion of the ratio of metal Rh amount on the surface of the composite oxide derived from the CO adsorption amount to the supported Rh amount calculated as a theoretical value from the sample charge amount. . This time, assuming that one CO atom is adsorbed to one Rh atom, CO gas with a fixed number of moles is introduced into the sample at regular intervals as a pulse gas, and the amount of CO not adsorbed by the sample is measured. The amount of adsorbed CO obtained by doing so was determined.

  According to the figure, the difference between Examples 1 and 2 and the comparative example is small with respect to the specific surface area. On the other hand, looking at the surface dispersion degree of Rh, Examples 1 and 2 are higher than the comparative example, and in particular, Example 2 has a very high surface dispersion degree of Rh. In Example 1, 50% of the target addition amount of neodymium sulfate was added to the coprecipitation gel, whereas in Example 2, the total amount of neodymium sulfate was added to the coprecipitation gel. It is considered that the degree of surface dispersion is further increased.

<High temperature durability>
Bench aging was performed on each catalyst of Examples 1-3 and Comparative Examples. In this bench aging, the catalyst is attached to the exhaust pipe of the engine, the engine speed / load is set so that the catalyst bed temperature is 900 ° C., and the catalyst is exposed to the exhaust gas of the engine for 50 hours.

  After the bench aging, a core sample having a carrier volume of about 25 mL was cut out from each catalyst and attached to a model gas flow reactor. Then, the temperature of the model gas flowing into the catalyst was gradually increased from room temperature, and changes in the concentrations of HC and CO in the gas flowing out of the catalyst were detected. Based on this detection result, the purification rate and light-off temperature for each catalyst for HC, CO, and NOx were determined. The light-off temperature is the catalyst inlet gas temperature when the purification rate of each component of HC, CO, and NOx reaches 50%, and serves as an evaluation index for the low-temperature activity of the catalyst.

The model gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h ⁻¹ , and the heating rate is 30 ° C./min. Table 1 shows the gas composition when A / F = 14.7, A / F = 13.8, and A / F = 15.6.

  The results of the light-off temperatures of Examples 1 and 2 and the comparative example are shown in FIG. 5, and the purification rates of the HC, CO, and NOx components when the catalyst inlet gas temperature reaches 400 ° C. are shown in FIG.

  According to FIGS. 5 and 6, in any of HC, CO, and NOx, Examples 1 and 2 have lower light-off temperatures and higher 400 ° C. purification rates than Comparative Examples. FIG. 7 shows the relationship between the catalyst inlet gas temperature and the HC purification rate in Examples 1 and 2 and Comparative Example. According to the figure, Examples 1 and 2 have higher HC purification rates than the comparative example over the catalyst inlet gas temperature from 300 ° C to 500 ° C.

  From the above results, when a part or all of neodymium sulfate is added to the coprecipitation gel as in Examples 1 and 2 to increase the Nd concentration in the surface portion of the composite oxide, the high temperature durability of the catalyst is increased. I understand. Moreover, it can be seen from the comparison between Example 1 and Example 2 that the higher the Nd concentration in the surface portion of the composite oxide, the higher the high temperature durability of the catalyst.

  Next, the light-off temperature of Example 3 is shown in FIG. 8 together with the light-off temperatures of Example 1 and Comparative Example. As described above, Example 3 is a case where the amount of rhodium nitrate added to the coprecipitation gel is 80% and the Rh concentration on the surface of the composite oxide is higher than that in Example 1. According to the figure, it can be seen that the higher the Rh concentration on the surface of the complex oxide, the better the low-temperature activity of the catalyst.

<Influence of heat reduction treatment>
Example 4
The Rh-doped composite oxide of Example 1 was subjected to a heat reduction treatment with CO, and then this was coated on the same honeycomb carrier as in Example 1 by the same method to obtain a catalyst according to Example 4. The amount of Rh-doped composite oxide supported on the honeycomb carrier is 100 g / L as in Example 1. In the heat reduction treatment, the Rh-doped composite oxide is placed in a reducing atmosphere having a CO concentration of 1% (remaining N ₂ ) and a temperature of 600 ° C. for 60 minutes. Note that a reducing atmosphere using H ₂ instead of CO may be employed.

-Example 5
The Rh-doped composite oxide of Example 2 was subjected to the same heat reduction treatment as in Example 4, and then coated on the same honeycomb carrier as in Example 1 by the same method to obtain the catalyst according to Example 5. It was. The amount of Rh-doped composite oxide supported on the honeycomb carrier is 100 g / L as in Example 1.

[Light-off temperature]
Each catalyst of Examples 4 and 5 was bench-aged by the method described in the section <High Temperature Durability>, and then measured for the light-off temperature related to the purification of HC, CO and NOx by the same method. The results are shown in FIG. 9 together with the previous Examples 1 and 2 and the comparative example. In Examples 4 and 5, the light-off temperature is lower than the corresponding Examples 1 and 2, and it can be seen that the low-temperature activity of the catalyst is improved by the heat reduction treatment.

1 Rh-doped composite oxide particles 2 Oxygen

Claims (3)

Rh-doped composite oxide containing rare earth metal other than Ce, Zr, and Ce and doped with Rh, and containing at least Nd as the rare earth metal, the Nd being a surface portion than the inside of the composite oxide A method for producing a catalyst material for exhaust gas purification present in a high concentration,
A basic solution is added to an acidic solution containing Ce, Zr, and Rh ions to coprecipitate Ce, Zr, and Rh, thereby producing a RhCeZr-containing coprecipitation gel.
After adding a basic solution to the RhCeZr-containing coprecipitation gel, an acidic solution containing each ion of Rh and Nd is added and mixed, whereby Rh hydroxide and Nd water are added onto the RhCeZr-containing coprecipitation gel. A method for producing an exhaust gas purifying catalyst material, characterized by depositing and precipitating an oxide, followed by firing. In claim 1 ,
In the step of generating the RhCeZr-containing coprecipitation gel, a basic solution is added to an acidic solution containing Ce, Zr, Nd, La, Y, and Rh ions, and Ce, Zr, Nd, La, Y, and Rh are added. A method for producing a catalyst material for exhaust gas purification, characterized by co-precipitation. In claim 1 or claim 2,
A method for producing an exhaust gas purifying catalyst, comprising heating in a reducing atmosphere after the firing.

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