JP2004337840A - Oxygen occluding material, manufacturing method of the oxygen occluding material and catalyst for clarifying exhaust gas of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent oxygen occluding material which can be obtained by forming a co-precipitation material from cerium and at least one second metal M<SP>1</SP>, finally drying and calcining the co-precipitation material to form an oxide particle mixture (a Ce/M<SP>1</SP>oxide particle mixture) from cerium and the second metal M<SP>1</SP>. <P>SOLUTION: The oxygen occluding material is characterized by forming the Ce/M<SP>1</SP>oxide particle mixture from cerium oxide and the second metal oxide and contains cerium oxide and at least one kind of oxide of the second metal M<SP>1</SP>chosen from a group composed of alkaline earth metal, rare-earth metal, zirconium, zinc, cobalt, copper and manganese. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cerium oxide-based oxygen storage material (OSC), a method for producing the oxygen storage material and the application of the oxygen storage material in an exhaust gas aftertreatment catalyst. The oxygen storage material of the present invention contains cerium oxide, at least one second metal oxide, and preferably other metal oxides. These oxides have a very fine particle size, high sintering resistance, and high oxygen storage capacity and high oxygen release capacity.

  The oxygen storage material of the present invention can be used as a catalyst or a catalyst component for purifying exhaust gas of an internal combustion engine, in particular, a stoichiometrically operated Otto engine. The catalysts according to the invention show outstanding activity for the purification of harmful pollutants such as carbon monoxide, nitrogen oxides and hydrocarbons.

Automobile exhaust gas is mainly carbon monoxide as a contaminant (CO), consisting of carbon hydrogen (HC) and various nitrogen oxides (NO _x). To remove these undesirable compounds, catalytic converter more or less having a catalytic activity for the reduction of simultaneous oxidation and NO _x in the CO and HC are used. The conversion of harmful substances is preferably carried out under stoichiometric conditions, i.e., the oxidizing and reducing components of the exhaust gas are just in equilibrium, so that CO and CO to harmless carbon dioxide, water and nitrogen are converted. reduction and oxidation and NO _x in the HC means that can occur at the same time. For conventional fuels, the oxygen content of the exhaust gas under stoichiometric conditions is about 0.7% by volume.

  The λ value is defined as the exhaust gas air / fuel ratio (A / F) normalized to stoichiometric conditions. The air / fuel ratio for stoichiometric combustion of conventional gasoline and diesel fuels is about 14.7, which means that 1 kilogram of fuel requires 14.7 kilograms of air to completely burn. I do. The λ value at this point is λ = 1. Depending on the load and the rotational speed, a typical gasoline engine usually operates at a λ value of about λ = 1 with periodic fluctuations. This can be achieved by so-called lambda sensor control. For this application, so-called three-way catalysts are widely used for exhaust gas aftertreatment.

  The three-way catalyst is composed of a heat-resistant support composed of kyanite or a metal, a high-surface-area catalyst support such as γ-alumina, and at least one noble metal element of a platinum group element supported on the catalyst support. Cerium oxide-based oxygen storage materials are used to increase the conversion level of oxidizable compounds.

Each of the oxygen storage materials is capable of storing oxygen in an oxidizing atmosphere and releasing oxygen under reducing conditions. Oxygen storage and release is associated with a change in oxidation state from Ce ³⁺ to Ce ⁴⁺ and vice versa. Oxygen consumption or release and adsorption / desorption rates under dynamic elimination conditions are highly dependent on the chemical composition, synthesis conditions and structural parameters of a given material.

  In addition, more stringent emission controls will place more demands on oxygen storage materials with improved oxygen storage capacity and higher thermal stability. In particular, so-called close-coupled catalytic converters located close to the engine can reach temperatures up to 1100 ° C. when the engine is operating under full load. Under these harsh conditions, the primary particles of the oxygen storage material usually tend to sinter to form larger aggregates, which not only loses surface area but also oxygen storage capacity. As a result, the catalyst purification activity is reduced.

  It is known to those skilled in the art that by impregnating bulk ceria or a bulk ceria precursor with an aqueous dispersion of an aluminum stabilizer precursor and calcining the impregnated ceria, improved thermal stability can be obtained. It is known (US Pat. No. 4,714,694).

  Furthermore, if the oxygen storage material is highly dispersed on the surface of a thermally stable support oxide having a large surface area, such as alumina, the oxygen storage material will have higher sintering resistance and significantly higher oxygen storage capacity. The indications are known (see, for example, Kaspar et al., J. Chem. Soc. Chem. Commun. 2000, 2167).

  The prior art discloses a composite oxide support based on alumina and at least one member of the group consisting of ceria, zirconia or ceria-zirconia, and a process for producing the composite oxide support (US Pat. No. 6,306,794). ). Further, the composite oxide may contain barium or lanthanum.

  In order to produce the composite oxide support described in US Pat. No. 6,306,794, a solution of a salt of a plurality of elements containing at least one of cerium and zirconium and aluminum defining this composite oxide is mixed using a high-speed mixer. First, the precursor is mixed with an alkaline solution to form an oxide precursor including a plurality of elements. The precipitate is first dried and then calcined at 650 ° C. for 1 hour in air. Use a high-speed rotary stirrer to achieve high mixing speeds. A major disadvantage of this method is that it uses an alkali hydroxide that cannot be completely removed from the product.

In the prior art, Ce, Zr, the group of the amount of at least 50% by weight based on the total weight of the oxide composite oxide of a metal M ₁ of the group of alkaline earth metals or rare earth metals, Al, Ti or Si the composite oxide consisting of an oxide of a metal M _2, and the precipitation method have also been disclosed, in which the metal oxide M ₂ are insoluble in the oxide of the metal M _1, both of these metals nano It is dispersed at the metric level (EP1206965A1). The oxide of the metal M ₁ or M ₂ may further contain an oxide of another metal M ₃ which is a group of Zr, an alkaline earth metal or a rare earth metal. The material is prepared by mixing the desired precursors of the metal oxides in the desired amounts, precipitated by adding aqueous ammonia, dried and finally calcined.

Based on the prior art, there is a need for a ceria-containing oxygen storage material that has a high specific surface area after thermal aging and has improved oxygen storage and release capabilities under dynamic evacuation conditions.
US4714694 US6306794 EP1206965A1 Kaspar et al., J. Chem. Soc. Chem. Commun. 2000, 2167.

The present invention, cerium and at least form a coprecipitate from the other one metal M ¹ Tokyo, finally drying and calcining the coprecipitate, cerium and another metal M ¹ Tokyo a mixed oxide particles ( An excellent oxygen storage material obtained by forming Ce / M ¹ mixed oxide particles) is provided. During co-precipitation, the combined solution of the precursor from cerium and another metal is mixed vigorously to avoid agglomeration of the precipitated particles formed. Upon calcination in air, the precipitated compounds are decomposed and converted to the desired oxide.

Therefore, in the first aspect of the present invention, cerium oxide, an alkaline earth metal, and a rare earth metal, wherein the cerium oxide and the second metal oxide form Ce / M ¹ mixed oxide particles. , zirconium, zinc, cobalt, oxygen storage material containing an oxide of at least one second metal M ¹ selected from the group consisting of copper and manganese is provided. This material has an unprecedented high oxygen storage capacity and exhibits excellent dynamic properties with respect to oxygen storage and release compared to conventional materials.

The oxygen storage material of the first aspect of the present invention, the oxide of the additional metal M ^2, for example, alumina, or by doping or coated with any other thermally stable metal oxide, the oxygen storage material It can be further stabilized against heat sintering.

Accordingly, in a second aspect of the present invention, the oxygen storage material is provided containing Ce / M 1 ^/ M ² mixed oxide particles, in a third aspect of the present invention, additional oxide of a metal M ² An oxygen storage material comprising the Ce / M ¹ mixed oxide particles of the first aspect of the present invention coated with a. In either case of these additional metal M ² is selected from aluminum, magnesium, zirconium, silicon, titanium, gallium, indium, from the group consisting of lanthanum, and mixtures thereof.

Hereinafter, the oxygen storage capacity of the storage material according to the present invention is evaluated using so-called temperature-reduction (H ₂ -TPR) using hydrogen. According to this evaluation method, a pre-oxidized sample is heated from room temperature to 1000 ° C. in a hydrogen-containing atmosphere (5% by volume of H ₂ , 95% by volume of argon or nitrogen) with a temperature gradient of 10 ° C./min. The representation of the hydrogen consumed by the reaction with the stored oxygen as a function of temperature is used as a detection of the total oxygen storage capacity (OSC). For the evaluation of the oxygen storage material, it is also possible to use the ignition temperature _{Tign at the} start of hydrogen consumption and the temperature window calculated from the half width of the TPR curve.

  For a better understanding of the invention with further and further advantages and embodiments, reference is made to the following description, which, in the context of the appended claims, is associated with examples.

  The preferred embodiments of the present invention have been selected for illustrative and descriptive purposes, and are not intended to limit the scope of the present invention. A particular range of advantageous embodiments of the invention will be described with reference to the figures.

  The invention is described in connection with an advantageous embodiment. These embodiments are helpful in understanding the present invention and should not be construed as limiting the invention. All alternatives, modifications and equivalents that are obvious to a person skilled in the art from the description of the invention are included in the spirit and scope of the invention.

  Since the present invention is not a primer on oxygen storage materials, it does not elaborate on basic concepts known to those skilled in the art.

Oxygen storage material of the present invention, at least one second mixed oxide particles of the metal M ¹ and cerium oxide (hereinafter, Ce / M ¹ particles) and a base. In a preferred embodiment of the invention, these mixed oxide particles form a single-phase solid solution. Solid solution is a term known to those skilled in the art and includes a homogeneous solid that can exist beyond the range of component chemicals that are heterogeneously mixed at the atomic level. If the solid exhibits only one crystal structure, a single phase is present.

In a preferred embodiment of the present invention, the material is additionally contain oxides of other metals M ^2, which forms an additional oxide component mixed oxide particles of the first aspect of the present invention . In a most advantageous aspect of the present invention, the particles of Ce / M ¹ mixed oxide is coated with an oxide of another metal M ^2. This most advantageous embodiment has proven to be particularly advantageous, since the particles are prevented from sintering under high temperature loads.

Metal M ¹ is an alkaline earth metal, rare earth metals, zirconium, zinc, cobalt, is selected from the group consisting of copper and manganese. Alkaline earth metals are metals of Group 2 of the Periodic Table of the Elements. Rare earth metals are the 58th to 71st elements of the periodic table. Preferred metals M ¹ for forming a ce / M ¹ mixed oxide particles, calcium, zirconium, magnesium, lanthanum, praseodymium, neodymium, yttrium, cobalt, zinc, copper, manganese or mixtures thereof. The most advantageous M ¹ are calcium and zirconium. Or metal M ² which are present as an additional component of the Ce / M ¹ mixed oxides for oxides to form a Ce / M 1 ^/ M ² mixed oxide particles are preferably aluminum, silicon, titanium, gallium , Indium and mixtures thereof.

When particles of ce / M ¹ mixed oxide is coated with an oxide of a metal M ^2, the metal M ² is aluminum, magnesium, zirconium, silicon, titanium, gallium, indium, from the group consisting of lanthanum, and mixtures thereof May be selected. Therefore, the oxygen storage material of the present invention may be composed of, for example, Ce / Zr mixed oxide particles coated with zirconium oxide in order to improve the stability against sintering. Most advantageous M ² metal is aluminum. In another preferred embodiment of this embodiment, the oxide of the metal M ² is an oxide of a rare earth metal, are admixed with preferably lanthanum oxide.

The method for producing the new oxygen storage material will be described in detail below. This method ensures that the Ce / M ¹ or Ce / M ¹ / M ² mixed oxide particles form a solid solution having a crystallite size of less than 10 nm.

To ensure sufficient oxygen storage capacity of this material, about 99 mole percent greater than about 50 mole% of Ce / M ¹ mixed oxide particles of cerium with respect to the composition of Ce / M ¹ mixed oxide particles in amounts below with oxides M ² is, it is advantageous present in an amount of about 1 mole% to about 80 mol% relative to the total composition of the oxygen storage material. Such materials exhibit a very high oxygen storage capacity, measured with a hydrogen consumption of at least about 0.9 mmol of hydrogen per gram of oxygen storage material. _Furthermore, the temperature window of H 2-TPR curve is wider than 120 ° C..

In one of the embodiments, the method for producing an oxygen storage material of the present invention comprises the following steps:
step of mixing the aqueous solution of the precursor of the oxide of the aqueous solution and the metal M ¹ of a precursor of a) cerium,
b) adding a first precipitant to the mixture, whereby an aqueous suspension containing the precipitate is formed; and c) separating the precipitate from the suspension, drying and drying the precipitate. Including the step of baking.

  Drying is carried out in air at an elevated temperature between 50 and 180 ° C. for a period of 1 to 20 hours. After drying, the precipitated compound is calcined in air at 350-500 ° C. for 1-10 hours, preferably at 400 ° C. for 4 hours. Upon calcination in air, the precipitated compounds are decomposed and converted to the desired oxide. The obtained oxygen storage material is hereinafter referred to as a new material.

The above method may be improved by adding a precursor of other oxides of metals M ² in step a), whereby the oxygen storage material according to the second aspect of the present invention is obtained.

In another embodiment this method, the precipitate in step c) is added before the separation from the aqueous suspension, the suspension precursor of other oxides of metals M ^2, a second precipitation By depositing on the precipitate by adding an agent, an oxygen storage material according to the third aspect of the present invention is obtained.

Ammonium oxalate is preferably used as the first precipitant. Barium hydroxide is used as a second precipitant for depositing M ² on the surface of the Ce / M ¹ particles.

Preparation of Oxygen Storage Material The method for preparing the oxygen storage material and its characteristics will be described in detail below.

  As shown in FIG. 1, an oxygen storage material is prepared by a coprecipitation method in a specially designed synthesis reactor. The synthesis reactor includes a precipitation reactor (1) and a hydrolysis reactor (2). The precipitation reactor mixes the precipitant with the cerium and additional metal precursor solution and precipitates the metal in the form of fine primary particles suspended in the liquid phase of the solution and the precipitant. It is a tubular flow reactor. The precursor solution is passed (3) and the precipitation solution is passed (4) to a tubular flow reactor.

  The two combined solutions form a precipitation mixture. After the two solutions come into contact, precipitation starts immediately. After about one second, the precipitation is complete. Therefore, the residence time in the tubular flow reactor should not be less than 0.1 seconds, but may be extended, however, beyond 5 to 10 seconds to prevent the formed primary particles from agglomerating. Should not be.

  The quality and speed of mixing of the two components is important for obtaining small precipitated particles. Thus, additional measures are provided to improve the mixing of the components. It has been found that bubbling nitrogen gas into the tubular flow reactor just below the level of the precipitation mixture gives good results in terms of particle size. In FIG. 1, nitrogen gas is passed through a gas supply unit (9) to a tubular flow reactor. Instead of bubbling nitrogen into the precipitation mixture, it is also possible to insert an ultrasonic transducer into the tubular flow reactor and to use ultrasonic waves to facilitate the mixing of the two solutions. Generally, it is advantageous to create turbulence in the tubular flow reactor to enhance the quality of the mixing.

  The precipitate mixture is slowly led from the tubular flow reactor to the hydrolysis reactor (2), where it may be equilibrated for about 1 hour while mixing the precipitate vigorously with the mixer (7). Since the equilibrium of the precipitation reaction depends on the pH, it is important to take care that the pH value of the solution in the hydrolysis reactor (2) is kept constant. To achieve this, the pH value is monitored online with a pH meter (8) and corrected by adding a basic or acidic solution via feed (5). The resulting product is collected by filtration, washed with deionized water, and finally calcined in air at 400 ° C. for 4 hours to obtain a freshly prepared oxygen storage material.

Supply unit (6), at least one other oxide of a metal M ^2, and the advantage that is provided for the addition of a precursor solution of the alumina, thereby, M on the already precipitated particles ^{The two} precursors can be precipitated. Accordingly, the primary particles are coated with a metal precipitate M ^2.

  The method for producing an oxygen storage material according to the present invention is described in further detail in connection with FIG.

  In general, FIG. 2 shows two methods for producing an oxygen storage material according to the present invention. Method (A) is a co-precipitation method for the production of an oxygen storage material according to the second aspect of the invention, while method (B) is a method of production of the oxygen storage material according to the third aspect of the invention. Is a sequential precipitation method.

To prepare the oxygen storage material by the co-precipitation method, an aqueous solution A containing a suitable cerium oxide precursor (eg, nitrate) and an aqueous solution D of a suitable precipitant (eg, ammonium oxalate) are mixed with a desired molar amount. Mix in a suitable mixing reactor in a ratio (eg, the tubular flow reactor (5) of the precipitation reactor (1) of FIG. 1). _{^{CexMe 1 y Me n 1-x}} -y O when _2-[delta] type of the blended metal oxide of the two-component or multi-component, the precursor solution separate mixer prior to contacting the precursor solution and the precipitation solution D Premix in the flask.

Precipitation forms fine primary particles of Ce / M ¹ or Ce / M ¹ / M ^{2 which} still contain the anion of the precipitant. The precipitated particles are separated from the liquid phase by filtration, then dried and calcined to obtain the desired oxygen storage material as a homogeneous composite oxide. Upon calcination, the primary particles form larger aggregates.

Method (B) in FIG. 2 describes a sequential precipitation method for obtaining an oxygen storage material according to the third aspect of the present invention. The first precipitation step is the same as the simultaneous precipitation method. Unlike co-precipitation, without separating the primary particles precipitated from the precipitation mixture, adding a third precursor solution C containing a precursor of an oxide of a metal M ^2. The precursor is then precipitated on the primary particles already formed in the first step by appropriately adjusting the pH value of the combined solution.

  Suitable precipitants D for the process according to the invention are any inorganic or organic chemicals which react with the precursor solution A and give a precipitate which is almost insoluble. For example, hydroxides, carbonates, oxalates, tartrate salts, citrate salts of the elements of Groups 1 to 3 of the Periodic Table of the Elements or their corresponding free acids can be used. An ammonium salt was used. Advantageously, polydentate organic ligands, such as oxalic acid or citric acid or their salts, can be applied, which act as molecular spacers for metal ions in mixed metal oxides and have a high elemental homogeneity (elemental homogeneity).

Best results were obtained with ammonium oxalate. In general, cerium oxide precipitates doped with ammonium oxalate show significant advantages over other precipitants:
a) According to equation (1), when a metal oxalate is exposed to an elevated temperature, the metal oxalate will simply form a gas such as carbon dioxide without forming a residue such as elemental carbon. Decomposes only to the state component.
b) The oxalate ligand acts as an electron donor when it is broken down into carbon dioxide (Eq. 2a). This results in partial reduction of Ce ⁴⁺ to Ce ³⁺ and oxygen deficiency (2b).
c) Finally, the resulting mixed oxide shows a more structured surface with a larger pore size than the commercial reference material.

  Achieving a high degree of homogeneity of the material requires vigorous mixing of the combined solutions.

The degree of homogeneity of the synthesized material, using electron dispersive spectroscopy (EDS), element distribution of the calcined product can be determined by measuring the average value (a verage v alue (av)) is defined as the percentage of the standard deviation (sd) for each dopant. For example, the homogeneity of Zr and Ce is (sd / av) of the ratios Zr / (Ce + Zr) and Ce / (Ce + Zr), respectively.

  The best results with regard to homogeneity were obtained when small bubbles of an inert gas (9) such as nitrogen or argon were passed through a tubular precipitation reactor (1) which provided turbulence of the mixture. Separately, sonication was successfully applied during precipitation. To obtain fine primary particles, the residence time in the turbulence reactor (1) before the mixture leaves the hydrolysis reactor (2) is about 0.1 to 10 seconds, preferably about 0 to 10 seconds. It is important to hold from about 1 to about 5 seconds, most preferably from about 1 to 5 seconds.

In a preferred embodiment, the resulting material contains ceria in an amount greater than about 50 mol% and less than about 99 mol%. Equilibrium is formed by an oxide of the metal M ^1. Advantageously, M ¹ is zirconium, calcium or a mixture thereof.

Typical BET specific surface areas for the oxygen storage materials of the present invention vary from about 50 to about 200 m ² / g for new materials, with average particle sizes d ₅₀ = 0.5 to about 1 μm (for comparison, (Commercial cerium / zirconium mixed oxide: d ₅₀ = 5 to about 30 μm).

  XRD measurements indicate the formation of a single phase solid solution having a crystallite size of less than about 17 nm.

According to TPR measurement (FIG. 3), this material has a higher OSC compared to a commercial reference material having the same composition. Hydrogen consumption was typically found to exceed the H ₂ 0.9 mmoles per gram. In addition, a lower ignition temperature ( _Tign ) was observed. The degree of material heterogeneity is generally less than about 5%.

To also improve the temperature stability of the desired material not the oxygen storage capacity only, at least one oxide of another metal M ^2, preferably the precursor solution of alumina, prior to precipitation treatment (formula 3a and 3b) or later (Formula 4b) may be added in an amount of about 1 to about 80 mol%. When performing this added before the precipitation treatment, oxide of a metal M ² whereas distributed in homogeneously Ce / M ¹ mixed oxide particles, when performing the addition after the precipitation treatment, metal oxide of M ² is heterogeneously deposited on the outer surface of the Ce / M ¹ mixed oxide particles.

  FIG. 2 shows a schematic of these two methods.

  Equations (3a) and (3b) show the simultaneous precipitation method (sim), and equations (4a) to (4c) show the sequential precipitation method (seq). In these formulas, L represents the ligand of the precursor, PA represents the precipitant, and A represents the anion of the precipitant. ΔT represents treatment at an elevated temperature during calcination.

For thermal stability for further improvement, by adding a precursor of the precursor, for example, lanthanum oxide of an oxide of a metal M ^2, 1 or more rare earth elements oxides of about 1 to about 60 mole% of the amount things, advantageously lanthanum oxide can be admixed with the oxide of metal M ^2.

If the precipitation method is performed sequentially, the metal oxide M ² O _x is deposited in the form of a (mixed) hydroxide on the surface of the oxygen storage material by adding a suitable basic solution. Suitable basic compounds may be any base such as ammonia, alkali or alkaline earth hydroxide or tetraalkylammonium hydroxide. It is advantageous to use an alkali metal-free precipitant. Alkali metals cannot be removed from the oxygen storage material during the calcination process. The alkali metal can later damage the honeycomb carrier coated with the catalyst coating containing the oxygen storage material. Therefore, it is most advantageous to use ammonia, tetraalkylammonium hydroxide or barium hydroxide as the precipitant.

  Although the present invention has been described in general, the present invention can be more readily understood by reference to the following examples, wherein the following examples are provided with the aid of the figures, They are not intended to limit the invention unless stated.

_Freshly prepared oxygen storage materials were used to measure the specific surface area (S _BET ), crystallite size and heterogeneity. Thereafter, the oxygen storage material was _subjected to TPR measurement, and the oxygen storage capacity, ignition temperature _Tign and width of the TPR curve were measured. Table 1 shows the obtained data.

  Further, this material was aged at 650 ° C. for 4 hours in air. After aging, a second specific surface area measurement was performed. Table 1 also shows the surface area of both the new material and the aged material.

Control Example R1:
The oxygen storage material used as Control Example R1 was a commercially available Ce _0.63 / Zr _0.37 mixed oxide calcined at 400 ° C. for 4 hours.

Control Example R2: (CeO ₂ )
In this example, pure cerium oxide was produced by the method according to the invention for comparison.

  A 1.0 mol / l aqueous solution of cerium (III) nitrate hexahydrate and a 0.3 mol / l aqueous solution of ammonium oxalate in the desired molar ratio were pumped into the tubular flow reactor at a constant flow rate. Turbulence was achieved by blowing nitrogen gas into the reactor in the flow direction. The combined solution was added slowly to the hydrolysis reactor under constant pH conditions (pH = 4-5). The pH value was kept constant by adding the required amounts of nitric acid or ammonia respectively. The precipitate obtained was allowed to reach equilibrium with the hydrolysis solution during one hour of stirring, after which the precipitate was filtered off and washed twice with 0.01 mol / l aqueous oxalic acid, Dried in air at 120 ° C. overnight and finally calcined in air at 400 ° C. for 4 hours.

  Table 1 shows the composition and physicochemical properties of this pure cerium oxide. Tables 3 and 4 show the results of the catalyst test.

Example E1: (Ce _0.9 Ca _0.1 O ₂ )
Instead of using cerium (III) nitrate alone as described in Control Example R2, a 1.0 mol / l cerium (III) nitrate hexahydrate solution and 1.0 mol / l tetranitric acid An aqueous solution of a calcium solution was used. The procedure of Example R2 was followed.

  The final product contained 90% cerium and 10% calcium. The properties of this powder are shown in Table 1.

Example E2: (Ce _0.63 Zr _0.37 O ₂ )
Instead of using cerium (III) nitrate alone as described in Control Example R2, a 1.0 mol / l cerium (III) nitrate hexahydrate solution and 1.0 mol / l zirconium nitrate An aqueous solution of the solution was used. Other methods followed the method described in Example R2.

  The final product contained 63% cerium and 37% zirconium. The properties of this powder are shown in Table 1.

Example E3: (Ce _0.8 Zr _0.2 O ₂ )
Example R2 was repeated, except that the molar ratio of cerium to zirconium was changed.

  The final product contained 80% cerium and 20% zirconium. The properties of this powder are shown in Table 1.

Example E4: (Ce _0.9 Ca _0.1 O ₂ × 0.5 Al ₂ O ₃ , sim)
In this example, an oxygen storage material containing cerium, calcium and aluminum was prepared according to the co-precipitation method described above.

  0.3 mol / l in an aqueous solution of 1.0 mol / l cerium (III) nitrate hexahydrate, 1.0 mol / l calcium nitrate and 1.0 mol / l aluminum nitrate hexahydrate An aqueous solution of ammonium oxalate was added. The combined solution was added slowly to the hydrolysis reactor under constant pH conditions (pH = 4-5). The pH value was kept constant by adding the required amounts of nitric acid or ammonia respectively. The precipitate obtained was allowed to reach equilibrium with the hydrolysis solution during one hour of stirring, after which the precipitate was filtered off, washed twice with a 0.01 mol / l aqueous solution of oxalic acid, Dried at 120 ° C. overnight in air and finally calcined in air at 400 ° C. for 4 hours.

  The final product contained 90% cerium and 10% calcium. The amount of alumina was 50 mol%, calculated on the basis of the molecular weight of the Ce / Ca mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E5: (Ce 0.9 Ca 0.1 O} 2 × 0.5Al 2 O 3, seq)
In this example, an oxygen storage material containing cerium, calcium and aluminum was prepared according to the sequential precipitation method described above.

  An aqueous solution of 0.3 mol / l ammonium oxalate was added to an aqueous solution of 1.0 mol / l cerium (III) nitrate hexahydrate and 1.0 mol / l calcium nitrate. The resulting precipitation mixture was slowly added to the hydrolysis reactor and mixed in the reactor at a pH value of 4-5 for 60 minutes. Thereafter, an aqueous solution of 1.0 mol / l aluminum nitrate hexahydrate was added, and the pH value was raised to pH = 8 to 9 by adding a 25% aqueous ammonia solution. The precipitate was filtered off, washed twice with 0.01 mol / l aqueous oxalic acid solution, dried in air at 120 ° C. overnight and finally calcined in air at 400 ° C. for 4 hours.

  The final product contained 90% cerium and 10% calcium, and 50 mol% alumina based on the mass of the Ce / Ca mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E6: (Ce 0.8 Zr 0.2 O} 2 × 0.2Al 2 O 3, seq)
Sequential by precipitating 1.0 mol / l cerium (III) nitrate hexahydrate solution, 1.0 mol / l zirconium nitrate aqueous solution using 0.3 mol / l ammonium oxalate aqueous solution Another oxygen storage material was prepared by the precipitation method. The suspension was further processed according to Example 5.

  The final product contained 80% cerium and 20% zirconium, and 20 mol% alumina, calculated based on the mass of the Ce / Zr mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E7: (Ce 0.8 Zr 0.2 O} 2 × 0.4Al 2 O 3, seq)
Another sample was prepared according to Example E6.

  The final product contained 80% cerium and 20% zirconium, and 40 mol% alumina, calculated based on the mass of the Ce / Zr mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E8: (Ce 0.8 Zr 0.2 O} 2 × 0.4Al 2 O 3 × 0.03La 2 O 3, seq)
Instead of pure aluminum nitrate, a mixture of aluminum nitrate and lanthanum nitrate having a ratio of 97/3, calculated as the corresponding oxide, was used in the method described in Example E7.

  The final product contained 80% cerium, 20% zirconium, and 40 mole% alumina and 3 mole% lanthanum, calculated based on the mass of the Ce / Zr mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E9: (Ce 0.8 Zr 0.2 O} 2 × 0.4Al 2 O 3 × 0.03La 2 O 3 seq, Ba)
Sample according to Example E8.

  The alumina-lanthanum mixed oxide was precipitated by adding an aqueous solution of barium hydroxide. The final product contained 80% cerium, 20% zirconium, 40 mole% alumina and 3% lanthanum, calculated based on the mass of the Ce / Zr mixed oxide, with respect to the Ce / Zr mixed oxide. Table 1 shows the characteristics of the powder.

Example _{E10: (Ce 0.7 Zr 0.2 Ca} 0.1 O 2 × 0.2Al 2 O 3, seq)
Sample according to Example E5.

  An aqueous solution of 1.0 mol / l cerium (III) nitrate hexahydrate solution, 1.0 mol / l zirconium nitrate, 1.0 mol / l calcium nitrate was treated with 0.3 mol / l oxalic acid Precipitated using an aqueous solution of ammonium. The resulting suspension was further processed according to Example E5.

  The final product contained 70% cerium, 20% zirconium, 10% calcium, and 20 mol% alumina, calculated based on the mass of the Ce / Zr mixed oxide. Table 1 shows the characteristics of the powder.

  Tables 1 and 2 show the materials synthesized according to the present invention. The data clearly show the advantageous effects of the above preparation method on the specific surface area of the material and on the total OSC compared to a commercial reference material.

Furthermore, the positive effect of the coating of cerium oxide doped with another metal oxide, M ² O _x , especially when the coating process is performed sequentially (samples E5 to E10), is shown in FIGS. Can also be seen from The coating provides a stabilization of the BET specific surface area, thereby avoiding sintering of the primary particles at elevated temperatures. This can also be indicated by a smaller crystallite size. In addition, a broader temperature window of the TPR profile is observed, which can be attributed to the highly porous surface of the coating, which allows the gaseous components to better reach the active sites of the oxygen storage material.

Catalyst preparation:
The catalyst was prepared below and tested for its light-off temperature and CO / NO _x cross-over conversion.

The light-off temperature T ₅₀ for a given contaminant, a gas temperature at which the individual pollutant is converted 50%. Light-off temperatures may be different for different contaminants.

By changing the lambda value of the exhaust gas from a value below 1 to a value above 1 or vice versa, the so-called CO / NO _x cross-conversion is measured. If the lambda value is less than 1, while NO _x conversion (reduction to nitrogen) is high, CO conversion (oxidation to carbon dioxide) is low. Conversion of the NO _x as lambda value is increased is reduced, and the conversion of CO increases. The conversion at the crossing point is the CO / NO _x cross conversion. CO / NO _x cross conversion is the highest conversion that can be achieved simultaneously for CO and NO _x . The higher the cross conversion, the better the dynamic behavior of the catalyst.

The honeycomb carrier ^62cm -2 ^{/0.17mm(400cpsi/6.5} mils) of cordierite-made conventional catalytically active coating containing several ceria / zirconia-based mixed oxide of Table 1, wherein Was prepared and tested for catalytic activity. The catalyst according to the invention was prepared using the following raw materials:
La / Al ₂ O ₃ : γ-alumina stabilized with 3% by weight of lanthanum, calculated as lanthanum oxide, resulting specific surface area: 140 m ² / g; average particle size: d ₅₀ -15 μm;
Oxygen storage material: see Table 1 BaO: barium oxide, industrial purity Pd (NO ₃ ) ₂ : palladium nitrate Rh (NO ₃ ) ₃ : rhodium nitrate Catalyst carrier: Kinsokuishi; 62 cm ⁻² /0.17 mm ( 400 cpsi / 6.5 mil); volume: 0.6181
Catalyst Control Example RC1:
La-stabilized γ-Al ₂ O _{3 at} a molar ratio of 6: 6: 1, oxygen storage material R1 and BaO were mixed in deionized water to obtain a dispersion containing 45% by mass of solids. The suspension was pulverized to an average particle size of 2-3 μm.

  A ceramic honeycomb carrier is dipped in this suspension to obtain a homogeneous coating with the desired washcoat load, dried in air at 120 ° C for 1 hour and finally calcined in air at 500 ° C for 2 hours. did. Subsequently, the catalyst coating was impregnated with a solution of palladium nitrate, dried again and calcined. The finished layer contained the following amounts of washcoat ingredients:

  This catalyst is referred to below as RC1. All other catalysts shown in Tables 3 and 4 are designated RC2 and C1 to C10. Instead of oxygen storage material R1, these catalysts contain storage materials R2 and E1 to E10 having the same mass fraction as in catalyst RC1.

Catalyst test:
Prior to the catalyst test, the catalyst was aged under hydrothermal conditions at 985 ° C. for 16 hours in an atmosphere containing 10% by volume of water, 10% by volume of oxygen and 80% by volume of nitrogen. The catalyst test was performed in a model gas test bench using a cylindrical core (diameter: 25.4 mm; length: 76.2 mm). As a detection of the catalyst activity, a light-off test (see Table 2) was performed under a synthetic model gas condition. The catalyst was heated from room temperature to 500 ° C. with a temperature gradient of 15 ° C./min and a space velocity of 225000 h ⁻¹ . The modulation frequency was 1 Hz, the amplitude was ± 0.8 A / F, and the lambda value of the exhaust gas was λ = 0.99. The results of this measurement can be seen in Table 3.

  Table 2 shows the composition of the model exhaust gas, and Table 3 shows the results of the catalyst test.

After measuring the light-off temperature of the catalyst, the CO / NO _x cross-conversion was measured. For this purpose, the lambda value was increased continuously from 0.99 to 1.01 at two different temperatures (400 ° C. and 450 ° C.) at a space velocity of 225000 h ⁻¹ . During this lambda value change, the NO _x conversion falls from a high conversion to a low conversion, but the behavior of the CO conversion is the opposite. The value of the conversion at the crossing point is the CO / NO _x cross conversion.

Table 4 shows the CO / NO _x cross-conversion and the corresponding hydrocarbon conversion at the given temperatures.

Table 3 shows the light-off temperature of the catalyst expressed as _T50 value. The T ₅₀ value corresponds to the temperature at which 50% of the contaminants are converted. The light-off temperature of the catalyst containing the oxygen storage material of the present invention is significantly lower than that of the reference catalyst RC1, especially when an alumina-coated material is selected. In the case of catalyst C9, the best results were obtained. This clearly demonstrates a further dynamic mechanism of the catalyst according to the invention. This is supported by the CO / NO _x crossover values shown in Table 4.

  Although the present invention has been described in connection with specific embodiments thereof, further modifications are possible and the present invention is generally in accordance with the principles of the invention and known or customary practice within the field to which the invention pertains. And covers all variations, uses, or adaptations of the invention, including any deviations from the disclosure, including those applicable to the essential features described above and in the claims. Is understood.

Schematic showing the arrangement of the precipitation reactor. The figure which shows the simultaneous coating method (A) and the sequential coating method (B). The figure which shows the result of TPR measurement of the materials E1-E3 compared with the commercially available reference material (R1). E3 uncoated diagram coating amount in comparison with reference material R1 impact on the total OSC of coated E6 _{(Al 2 O} 3 20 mol%) and E7 _{(Al 2 O} 3 40 mol%). The figure which shows the influence which the precipitation method (simultaneous or sequential) of the material E4 and E5 has on the total OSC measured by TPR.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Precipitation reactor 2 Hydrolysis reactor 3 Precursor solution supply part 4 Precipitation solution supply part 5 Tubular flow reactor 6 Supply part 7 Mixer 8 pH meter 9 Gas supply part

Claims (24)

Cerium oxide, alkaline earth metals, rare earth metals, zirconium, zinc, cobalt, in the oxygen storage material containing an oxide of at least one second metal M ¹ selected from the group consisting of copper and manganese oxide, An oxygen storage material, wherein cerium and a second metal oxide form Ce / M ¹ mixed oxide particles. Oxygen storage material further, aluminum, manganese, zirconium, silicon, titanium, gallium, indium, lanthanum-containing and oxide of a metal M ² selected from the group consisting of a mixture thereof, the oxygen storage of claim 1, wherein material. Oxides of the metal M ² to form a mixed oxide of an oxide of the oxide and the metal M ¹ of cerium, oxygen storage material of claim 2 wherein. Metal M ¹ is calcium or zirconium, a metal M ² is aluminum, oxygen storage material according to claim 3, wherein. Crystallite size of Ce ^{/ M} 1 ^/ M ² mixed oxide is less than about 10 nm, the oxygen storage material of claim 4 wherein. Oxides of the metal M ² is deposited on the surface of the Ce / M ¹ mixed oxide particles, the oxygen storage material of claim 2 wherein. Metal M ¹ is calcium or zirconium, a metal M ² is aluminum, the oxygen storage material of claim 6 wherein. Oxides of the metal M ² are admixed with oxides of rare earth metals, the oxygen storage material of claim 7, wherein. Rare earth metal is admixed with the metal M ² is lanthanum, oxygen storage material of claim 8. Cerium, in an amount below about 99 mole percent greater than about 50 mole% relative to the composition of Ce / M ¹ mixed oxide particles, in which, the oxide of a metal M ^2, the total of the oxygen storage material The oxygen storage material of any one of claims 3 to 6, wherein the oxygen storage material is present in an amount from about 1 mol% to about 80 mol% based on the composition.   The oxygen storage material of claim 10, wherein the oxygen storage capacity as measured by hydrogen consumption is at least about 0.9 millimoles of hydrogen per gram. H _2-TPR temperature window of the curve is wider than 120 ° C., the oxygen storage material of claim 11, wherein. Oxides of cerium oxide and a metal M ¹ to form a single phase mixed oxide solid solution, the oxygen storage material of claim 1, wherein. Cerium oxide, oxides of metals M ¹ and oxides of a metal M ² forms a single phase mixed oxide solid solution, the oxygen storage material according to claim 3, wherein. The method for producing an oxygen storage material according to claim 1, wherein:
step a) mixing an aqueous solution of a precursor of an oxide of an aqueous solution of cerium oxide precursor and the metal M ^1, to form a mixture;
b) adding a first precipitant to the mixture to form an aqueous suspension containing the precipitate; and c) separating the precipitate from the suspension, drying and calcining the precipitate. The method for producing an oxygen storage material according to claim 1, wherein the oxygen storage material is contained. Adding a precursor of another oxide of the metal M ^2, The method of claim 15, wherein forming the precursor solution in the mixture of step a). Before separating the precipitate from the aqueous suspension in step c), it was added a precursor of another oxide of the metal M ² to the suspension from step b), adding a second precipitant The method according to claim 15, wherein the method deposits on the sediment.   The method according to claim 15, wherein ammonium oxalate is used as the first precipitant. Using barium hydroxide as a second precipitant for depositing M ² on the surface of the ce / M ¹ solid solution particles The method of claim 17.   16. The method of claim 15, wherein the mixing in step a) is performed in a tubular flow reactor by bubbling gaseous nitrogen into the reactor. To achieve cerium metal, the mixing of the precursor solution containing M ¹ and M ² by the microwave treatment method of claim 16, wherein. Cerium metal, achieved by sonication mixing of precursor solution containing M ¹ and M ^2, The method of claim 16, wherein.   An exhaust gas purifying catalyst for an internal combustion engine, comprising the oxygen storage material according to claim 1.   An exhaust gas purifying catalyst for an internal combustion engine, comprising the oxygen storage material according to claim 3.

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