DE19805259A1 - Oxygen=storing cerium complex oxide - Google Patents

Abstract

An oxygen-storing cerium (Ce) complex oxide of formula Ce1-(x+y)ZrxRyO2-z (where R = rare earth metal or rare earth metal except Ce; z = degree of oxygen deficiency determined by valency of the rare earth; x+y = 0.2 - 0.9; x = 0.1-0.8; and y = 0.05-0.3).

Description

Background of the Invention 1. Field of the Invention

The present invention relates to an oxygen-storing cerium complex oxide, which is advantageously used in a catalytic converter of a vehicle for the efficient cleaning of exhaust gases from an internal combustion engine by removing nitrogen oxides (NO _x ), carbon monoxide (CO) and hydrocarbons (HC) can be.

2. Description of the prior art

As is known, the exhaust gases of a motor vehicle internal combustion engine inevitably contain harmful substances, such as NO _x , CO, HC. To protect the environment, restrictions on exhaust gas have recently become stricter.

On the other hand, in view of fuel savings a rising slope, an internal combustion engine in lean State instead of stoichiometric air-fuel mixture operate while a vehicle other than empty  running and acceleration phases runs normally. For this Is basically the development of a catalytic converter, which is able to remove the above harmful sub punch not only in a stoichiometric state but also efficient to remove in a lean condition, highly desirable.

Most commonly, a so-called three-way catalyst is used to remove the above harmful substances. A three-way catalyst uses a noble metal or metals such as Pt, Pd and / or Rh as the active substance in order to reduce NO _x to N ₂ and to oxidize CO and HC to CO ₂ and H ₂ O. In this way, the catalytic converter functions as a catalyst for both oxidation and reduction.

Various research has been done to improve the operation of a three-way catalyst. One of the three-way catalysts that have followed from such research uses ceria (CeO ₂ ) with an ability to store oxygen; ie the ability to store gaseous oxygen in the crystal structure and to release stored oxygen from the crystal structure. Specifically, CeO _{2 is added} to a three-way catalyst in order to adjust the oxygen concentration of the gas phase in such a way that, in the case of an oxygen-rich state, excess oxygen in the gas phase is incorporated in the crystal structure of CeO _{2 in} order to reduce the catalyst to support from NO _x to N ₂ , and that in the CO and / or HC-rich state, stored oxygen is released into the gas phase in order to support the catalyst in the oxidation of CO and HC to CO ₂ and H ₂ O. .

On the other hand, there is an increasing need to move the mounting position of the catalytic converter from below the floor panel to the exhaust manifold which is close to the engine, whereby the catalyst can be warmed up quickly after the engine is started. However, the catalytic converter, if located near the engine, can often be exposed to high temperatures of not less than 900 ° C, which can cause the grain size of CeO ₂ to grow due to sintering processes. As a result, the specific surface area of the CeO ₂ and the oxygen storage capacity of the CeO _{2 are} reduced, so that the desired improvement of the three-way catalyst cannot be achieved.

In view of this, it has been proposed to add grain growth preventing elements such as Zr and La to CeO ₂ (see, for example, JP-A-61-262521 or JP-A-61-262522). However, it was found that the added Zr or La crystallized on the grains of CeO ₂ (locally crystallized), so that the inherent properties of CeO ₂ can be lost. As a result, there are difficulties in using CeO ₂ at high temperatures.

Disclosure of the invention

It is therefore an object of the present invention, an oxygen to provide storage cerium complex oxide which in the Location, even under difficult operating conditions, especially at high temperatures, high oxygen to preserve storage capacity.

According to the present invention, an oxygen-storing cerium complex oxide with the following formula is proposed:

Ce _{1- (x + y)} Zr _x R _y O _2-z ,

where "R" is a rare earth metal or rare earth metals except Zer, where "z" is the valence of contained rare earth metal certain degree of acid  represents lack of material and where 0.2 ≦ x + y ≦ 0.9, 0.1 ≦ x ≦ 0.8 and Is 0.05 ≦ y ≦ 0.3.

At least part of the cerium complex oxide can preferably be a solid solution. Specifically, part of the Ce in the crystal of CeO _{2 can be} replaced by Zr and the other rare earth metal in solid solution. The Zr in solid solution in the crystal made of CeO ₂ prevents a mass transport of Ce (as a cation) and thus prevents grain growth (sintering) of the CeO ₂ at high temperatures.

As defined above, the Zr content is in the decomposition Complex oxide, defined as "x", between 0.1 and 0.8. A Zr content below this range is for prevention grain growth of the cerium complex oxide is insufficient. A Salary above this salary range leads to an over moderate reduction of the Ce content and thereby to a unacceptable reduction in oxygen storage capacity Cerium complex oxide. To get a good result len, "x" should preferably be in the range of 0.35 to 0.7 lie. It should be noted that the Zr, which Complex oxide is incorporated, 1% to 2% hafnium (Hf) ent can hold, which is inevitably contained in Zr ores.

The reason for the substitution of Ce in the CeO ₂ by the other rare earth metal in solid solution is that this substitution stabilizes the uniform fluorite structure of the cerium complex oxide at room temperature. The content of the other rare earth metal in the cerium oxide complex, defined as "y", is between 0.05 and 0.3. A content of the other rare earth metal below this range causes the difficulty in maintaining a stable and uniform fluorite structure, since due to the difference in the ionic radii of Ce and Zr, the cerium complex oxide is divided into a CeO ₂ area and a Ce containing ZrO ₂ - Area splits. A content of the other rare earth metal above this range means that the excess rare earth metal can lead to by-products, while the Ce and Zr contained can no longer perform the corresponding functions due to the relative content reduction. To get good results, "y" should preferably be between 0.05 and 0.2.

The other rare earth metal "R" can, for example, Y, Sc, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu include. These rare earth metals can be used individually or in Combination can be added. A preferred example is Y.

The sum of "x" and "y", ie "x + y", is between 0.2 and 0.9 selected. The Ce content in the cerium complex oxide becomes represented by 1- (x + y), which is between 0.1 and 0.8 lies. The oxygen storage capacity of the cerium complex oxide is essentially determined by the fact that the Ce oxidizes or is reduced and its valence changes. Taking into account Given this fact, the cerium complex oxide is not in the Able to have adequate oxygen storage capacity as they is needed to provide when the Ce content increases is low. On the other hand, the Zr content is reduced and / or the other rare earth metal if the content of Ce is too high and these cannot function properly satisfying enough. Hence the value of "x + y" should be between between 0.2 and 0.9, preferably between 0.2 and 0.6 gene.

The cerium complex oxide according to the invention can be obtained by known Process are made. In a first example of a process for producing the cerium complex oxide performed the following steps. First, water added a carbonate powder and a slurry provided. Next, an aqueous solution of a Zirconium salt and a rare earth metal salt in front  certain stoichiometric ratio of the slurry added. Finally, the slurry produced heat treated after sufficient mixing and a ge desired cerium complex oxide generated.

The carbonate powder can be any commercially available one, it should however, preferably a possible large specific upper have area. For this purpose, preferably Zerkar Bonate powder of not less than 0.1 µm can be used. 1 part by weight of water can be 10 to 50 parts by weight of one such carbonate powder to be given above Prepare slurry.

The zirconium salt can be, for example, zirconium oxychloride, Zirconium oxynitrate, zirconium oxysulfate or zirconium oxyaze which zirconium oxynitrate is preferred. The rare earth metals can, for example, sulfates, nitrates, Hydrochlorides, phosphates, acetates and oxalates include although a rare earth metal nitrate is preferred. In the Providing the above aqueous solution becomes 1 part by weight Zirconium salt (selected from the examples above) and des rare earth metal salt (from the examples above selects) in a predetermined stoichiometric ratio in 0.1 dissolved up to 10 parts by weight of water.

As described above, it becomes ready in this way posed solution of the slurry added and the resul heat slurry after sufficient mixing treated. The heat treatment includes a previous one Vacuum drying step in which the slurry dried using a vacuum dryer to to get a pre-dried mixture, one step a heat drying, in which the pre-dried Mix at 50 to 200 ° C for about 1 to 48 hours additional Lich dried, and a baking step, in which the additionally dried mixture at about 350 to 1000 ° C,  preferably at about 400 to 700 ° C, for about 1 to 12 Hours, preferably baked for about 2 to 4 hours becomes. During the baking step, the baking bedin conditions (baking temperature and baking time) depending who is chosen from the composition of the cerium complex oxide the so that at least part of the cerium complex oxide in Form of a solid solution is present to the thermal resistance of the cerium complex oxide to enlarge.

In a second example of a manufacturing process of the cerium complex oxide are carried out through the following steps guided. First, a mixed salt solution is prepared which represents the corresponding salts of cerium, zirconium and a rare earth metal (except Zer) in selected interference contains chiometry. Then an alkaline aqueous solution or added an organic acid to the mixed solution, so that the corresponding salts of cerium, zirconium and of the rare earth metal. After filtering the precipitate obtained is heat-treated to a desired one to produce cerium complex oxide.

In the second method, the salts can be used, for example Sulphates, nitrates, hydrochlorides, phosphates, acetates and Include oxalates. The zirconium salts can, for example Zirconium oxychloride, zirconium oxynitrate, zirconium oxysulfate or zirconium oxyacetate. According to the above examples the rare earth metal salts sulfates, Nitrates, hydrochlorides, phosphates, acetates and oxalates grasp. The alkaline aqueous solution can, for example Ammonia or aqueous ammonium carbonate. Furthermore Ren the organic acid, for example oxalic acid or Include citric acid.

The heat treatment in the second example can be the same same way as in the first example.  

In a third example of a method of manufacture of the cerium complex oxide are carried out through the following steps guided. First an alkoxide solution is prepared which Cerium, zirconium and a rare earth metal (except cerium) in selected stoichiometry. Then it becomes deionized Water was added to the alkoxide solution to make the cerium, the zirco nium and the rare earth metal co-precipitate or hydroly sieren. After filtering, the precipitate or the hydrol sat heat treated and the desired cerium complex oxide testifies.

The alkoxides for the preparation of the alkoxide solution can the third example methoxides, ethoxides, propoxides or Butoxides from cerium, zirconium and the rare earth metal grasp. Instead, there are also ethylene oxide addition salts of Cerium, zirconium and rare earth metals can be used.

The heat treatment in the third example can also be done in be carried out in the same way as in the first Example.

The oxygen-storing cerium complex oxide is present Invention can preferably be a noble metal or noble metals carry or hold. A precious metal is an excellent one Catalytic converter for cleaning vehicle exhaust gases via redox actions and can therefore advantageously feed with oxygen cerium complex oxide of the present invention combined to clean the vehicle exhaust gases even more efficiently. Furthermore, the precious metal worn can also be the one conclusion and the release of oxygen in and out of the Support complex oxide. As a precious metal such. B. Ru, Rh, Pd, Ag, Os, Ir, Pt and / or Au are used, although Pd and Rh are preferred.

Alternatively, and for a similar reason, oxygen can cerium complex oxide storing one or more transition metals  le wear. These can e.g. B. Fe, Co, Ni and Cu include from which Fe is preferred.

The precious or transition metals described above can be known on the cerium complex oxide by using Techniques are kept. E.g. can first find a solution prepared which is a salt (e.g. 1 to 20 wt .-%) of a noble or Contains transition metal, and then the cerium complex oxide be impregnated with this saline solution. The for salts used for this purpose can, for example, nitrates (e.g. palladium nitrate, rhodium nitrate, iron nitrate, cobalt ni stepped, nickel nitrate, copper nitrate), dinitrodiammine nitrates (e.g. dinitrodiammine palladium nitrate), amine nitrates (e.g. Ammin palladium (IV) nitrate) and chlorides (e.g. rhodium chloride) include. After impregnation and filtering, it becomes Cerium complex oxide preferably with heating to 50 to 200 ° C. dried for about 1 to 48 hours and then at about 350 to 1000 ° C for about 1 to 12 hours baked.

Alternatively, the process for applying the precious or Transition metal on the cerium complex oxide during manufacture position of the Zer complex oxide take place. In detail a solution that contains a precious or transition metal salt (which is identical to one of those described above is) to the mixed salt solution or the alkoxide solution given when the latter solution is precipitated, so that the precious or transition metal salt together with the others existing salts fail. After filtration, the Precipitation in the same manner as above for the manufacturers described the Zer complex oxide, a heat treatment subjected.

Other features and advantages of the present invention will become apparent in the following detailed description of preferred embodiment men clearly.  

Detailed description of preferred embodiments

The preferred embodiments of the present invention are shown below along with a comparative example described.

[1. Embodiment]

In this embodiment, a cerium complex oxide with the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 / 0.5% by weight Fe was produced. The resistance of the cerium complex oxide under difficult operating conditions was then determined by comparing the initial oxygen storage capacity of the cerium complex oxide with the oxygen storage capacity after aging after carrying out a redox aging test at high temperatures. The results of the resistance determination are listed in Table 1 below.

It should be noted that the designation "/ 0.5% by weight Fe" indicates that the cerium complex oxide carries 0.5% by weight of Fe, where the percentage based on zero Fe-bearing Zer-Kom plexoxide is determined. Furthermore correspond in the Table 1 the abbreviations "beginn." "n.a." and "Ex." the Terms "initial", "after aging" and "comparative" example ". The numbering corresponds to the numbering of the Embodiments.

(Production of the cerium complex oxide)

The cerium complex oxide with the above composition was produced by the so-called alkoxide process. First, 38.4 g (0.102 mol) of cerium isopropoxide, 16.7 g (0.051 mol) of zirconium isopropoxide and 4.5 g (0.017 mol) of yttrium isopropoxide were dissolved in 200 ml of toluene to provide an alkoxide solution. Then, 600 ml of deionized water was gradually added to the alkoxide solution by dropping over about 10 minutes to cause hydrolysis of the alkoxides. Then the resulting hydrolyzate (intermediate) was separated from the solution mixture by evaporation of the solvent and water. Thereafter, the intermediate was dried at 60 ° C for 24 hours with ventilation and then baked at 450 ° C for 3 hours in an electric oven to a Zer-complex oxide powder with the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 .

To apply the transition metal (Fe), 20 ml of deionized water was added to 20 g of the cerium oxide powder and a slurry was generated. Furthermore, 0.73 g of an iron (III) nitrate reagent (which contains 13.8% by weight of iron) was dissolved in 20 ml of deionized water and an egg nitrate solution with 1% by weight of iron (III) was prepared. The slurry was then uniformly mixed with the iron nitrate solution and then dried by evaporating the H ₂ O. The powder thus obtained was further dried at 60 ° C for 24 hours with ventilation and then baked at 450 ° C for 3 hours in an electric oven to give a Fe-bearing cerium complex oxide having the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 / 0.5 wt .-% Fe.

(Determination of the initial oxygen storage capacity, beginning OSC)

A sample of 18 mg of the as described above was obtained made Fe-carrying Zer complex oxide taken. The sample was first placed in a 50% oxygen gas stream (the rest was Nitrogen) at 500 ° C for 15 minutes. Subsequently the sample was subjected to a redox cycle, which a alternating gas flow of 20% hydrogen (the rest was nitrogen) and 50% oxygen (the rest was stick material) at 500 ° C. This redox cycle was repeated three times repeated while constantly weighting the sample  a thermal balance was measured. The weight of the sample was plotted to show the most stable Re Find the dox cycle, which is the basis for the calculation a difference between immediately after oxidation measured and measured immediately after the reduction Sample weight served. The calculated weight difference, which for the stored and released by the sample Oxygen weight is representative, was further considered Basis for calculating the number of moles of oxygen per mole used the sample.

(Redox aging test)

After determining the initial oxygen storage capacity, the sample was then subjected to a redox aging test in which the sample was exposed to gas conditions which, in a simplified form, simulate the variation of current exhaust gases from a vehicle. Specifically, the sample was sequentially exposed to a purifying inert gas stream for 5 minutes, then to an oxidizing gas stream for 10 minutes, then to the purifying inert gas stream again for 5 minutes, and then to a reducing gas stream for 10 minutes, this cycle for a total of 2 hours was repeated four times. The cleaning inert gas stream contained 8% by volume of CO ₂ and 10% by volume of water vapor, the remainder being N ₂ . The oxidizing gas stream contained 1 vol.% O ₂ , 8 vol.% CO ₂ and 10 vol.% Water vapor, the rest being N ₂ . The reducing gas stream contained 1.5 vol.% CO, 0.5 vol.% H ₂ and 10 vol.% Water vapor, the rest being N ₂ . Furthermore, the temperature of each gas stream was adjusted to 1000 ° C.

(Determination of the oxygen storage capacity after aging, OSC n.d. A.)

After performing the redox aging test, the Oxygen storage capacity of the sample in the same way determined as in determining the initial acid fabric storage capacity.

(Determination of the change in the oxygen storage capacity)

Table 1 shows the change in oxygen storage capacity of the sample is calculated according to the following equation. Change (%) = 1- (OSC after the beginning / beginning of the OSC) × 100.

As can be seen from the above equation, the value of the Change represents how much the initial oxygen changes capacity of the sample deteriorates after the redox aging test has.

[2nd Embodiment]

In this embodiment, a _{cerium complex oxide of} the composition Ce _0.5 Zr _0.375 Y _0.125 O _1.9375 / 0.5% by weight Fe was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, and then the oxygen storage capacity of the cerium complex oxide after the aging was determined and the change in the oxygen storage capacity was last calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the second embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment and that the slurry of Ce _0.5 Zr _0.375 Y _0.125 O _1.9375 powder add level amount of iron (III) nitrate solution (containing 1 wt .-% iron) was appropriately adjusted to the desired weight percent of Fe to get on the cerium complex oxide.

[3rd Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.4 Zr _0.45 Y _0.15 O _1.925 / 0.4% by weight Co was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the third embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a cobalt (II) nitrate solution (containing 1% by weight cobalt) was used in place of the iron (III) nitrate solution and that the slurry of Ce _0.4 Zr _0.45 Y _0.15 O _1.925 powder the amount of cobalt (II) nitrate solution was suitably adjusted to obtain the desired weight percent of Co on the cerium complex oxide.

[4th Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.2 Zr _0.6 Y _0.2 O _1.9 / 0.7% by weight Ni was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the fourth embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a nickel nitrate solution (containing 1% by weight of nickel) was used instead of the iron (III) nitrate solution and that the slurry of Ce _0.2 Zr _0.6 Y _0.2 O _1.9 powder was added added amount of nickel nitrate solution was suitably adjusted to obtain the desired weight percent of Ni on the cerium complex oxide.

[5th Embodiment]

In this embodiment, a _{cerium complex oxide of} the composition Ce _0.5 Zr _0.375 Y _0.125 O _1.9375 / 1.0% by weight Cu was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, and then the oxygen storage capacity of the cerium complex oxide after the aging was determined and the change in the oxygen storage capacity was last calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the fifth embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a copper (II) nitrate solution (containing 1% by weight copper) was used instead of the iron (III) nitrate solution and that the amount to be added to the slurry of Ce _0.5 Zr _0.375 Y _0.125 O _1.9375 powder was suitably adapted to copper (II) nitrate solution in order to obtain the desired weight percent of Cu on the cerium complex oxide.

[6. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 / 0.1% by weight Rh was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium oxide complex used in the sixth embodiment was prepared in the same manner as that used in the first embodiment, except that a rhodium nitrate solution (containing 0.98 wt% rhodium) was used instead of the iron (III) nitrate solution and that the amount of rhodium nitrate solution added to the slurry of the Ce _0.6 Zr _0.3 Y _0.1 O _1.95 powder was suitably adjusted in order to obtain the desired weight percentage of Rh on the cerium complex oxide.

[7th Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.4 Zr _0.45 Y _0.15 O _1.925 / 0.1% by weight Rh was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the seventh embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a rhodium nitrate solution (containing 0.98 wt% rhodium) was used in place of the ferric nitrate solution and that the amount to be added to the slurry of Ce _0.4 Zr _0.45 Y _0.15 O _1.925 powder was suitably adapted to rhodium nitrate solution in order to obtain the desired weight percent Rh on the cerium complex oxide.

[8th. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.2 Zr _0.6 Y _0.2 O _1.9 / 0.05% by weight Rh was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the eighth embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a rhodium nitrate solution (containing 0.98 wt% rhodium) was used instead of the ferric nitrate solution and that the slurry of Ce _0.2 Zr _0.6 Y _0.2 O _1.9 powder appropriate amount of rhodium nitrate solution was adjusted to obtain the desired weight percent Rh on the cerium complex oxide.

[9. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 / 0.1% by weight Pd was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium oxide complex used in the ninth embodiment was prepared in the same manner as that used in the first embodiment, except that a palladium nitrate solution (containing 4.399% by weight palladium) was used instead of the ferric nitrate solution and that the amount of palladium nitrate solution added to the slurry of the Ce _0.6 Zr _0.3 Y _0.1 O _1.95 powder was suitably adjusted in order to obtain the desired weight percent of Pd on the cerium complex oxide.

[10. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.4 Zr _0.45 Y _0.15 O _1.925 / 0.05% by weight Pd was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the tenth embodiment was prepared in the same manner as that used in the first embodiment except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a palladium nitrate solution (containing 8.337% by weight palladium) was used in place of the iron (III) nitrate solution and that the amount to be added to the slurry of Ce _0.4 Zr _0.45 Y _0.15 O _1.925 powder Palladium nitrate solution was suitably adjusted to obtain the desired weight percent of Pd on the cerium complex oxide.

[11. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.2 Zr _0.6 Y _0.2 O _1.9 / 0.2% by weight Pd was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the eleventh embodiment was prepared in the same manner as that used in the first embodiment, except that cerium isopropoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a palladium nitrate solution (containing 8.337% by weight palladium) was used instead of the iron (III) nitrate solution and that the slurry of Ce _0.2 Zr _0.6 Y _0.2 O _1.9 powder vers was suitably adjusted with the amount of palladium nitrate solution in order to obtain the desired weight percentage of Pd on the cerium complex oxide.

[12. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.6 Zr _0.3 Y _0.1 O _{1.95 was} produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide. Complex oxide was determined after aging and the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The Zer complex used in the twelfth embodiment oxide was produced in the same way as that of the used the first embodiment except that the Fe was applied not procedural step of the first embodiment was carried out.

[13. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.6 Zr _0.3 Y _0.1 O _1.95 / 0.1% by weight Pt was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the thirteenth embodiment was prepared in the same manner as that used in the first embodiment, except that a dinodiammine platinum nitrate solution (containing 4.569% by weight of platinum) was used in place of the ferric nitrate solution and that the slurry of Ce _0.6 Zr _0.3 Y _0.1 O _1.95 powder was suitably adjusted with the amount of dinitrodiammine platinum nitrate solution added to obtain the desired weight percentage of Pt on the cerium complex oxide.

[14. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.4 Zr _0.45 Y _0.15 O _1.925 / 0.1 wt.% Pt was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the fourteenth embodiment was prepared in the same manner as that used in the first embodiment, except that cerium propoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a dinitrodiammine platinum nitrate solution (containing 4.569 wt% platinum) was used in place of the ferric nitrate solution and that the amount of dinitrodiammine added to the Ce _0.4 Zr _0.45 Y _0.15 O _1.925 powder slurry Platinum nitrate solution was adapted appropriately in order to obtain the desired weight percentage of Pt on the cerium complex oxide.

[15. Embodiment]

In this embodiment, a cerium complex oxide of the composition Ce _0.2 Zr _0.6 Y _0.2 O _1.9 / 0.1 wt.% Pt was produced. Then, in the same manner as in the first embodiment, the durability of the cerium complex oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium complex oxide, then performing the redox aging test, then the oxygen storage capacity of the cerium oxide plexoxides determined after aging and finally the change in oxygen storage capacity was calculated. The results of the resistance determination are shown in Table 1.

The cerium complex oxide used in the fifteenth embodiment was produced in the same manner as that used in the first embodiment, except that cerium propoxide, zirconium isopropoxide and yttrium isopropoxide were mixed in the above stoichiometric ratio, which is different from the ratio in the first embodiment that a dinitrodiammine platinum nitrate solution (containing 4.569% by weight of platinum) was used instead of the ferric nitrate solution and that the amount to be added to the slurry of Ce _0.2 Zr _0.6 Y _0.2 O _1.9 powder was suitably adapted to dinitrodiammine platinum nitrate solution in order to obtain the desired weight percentage of Pt on the cerium complex oxide.

Comparative Example

In this comparative example, a cerium oxide (CeO ₂ ) was produced instead of a cerium complex oxide. Subsequently, in the same manner as in the first embodiment, the durability of the cerium oxide under difficult operating conditions was determined by first determining the initial oxygen storage capacity of the cerium oxide, then performing the redox aging test, then determining the oxygen storage capacity of the cerium oxide after aging and the change in oxygen storage capacity was last calculated. The results of the resistance determination are shown in Table 1.

The cerium oxide used in the comparative example was in manufactured in the same way as that of the first embodiment Form of zer used complex oxide, except that only a cerium isopropoxide solution is used instead of an alkoxide solution (since zirconium and yttrium were not included) and that the Fe-applying process step does not go through was led.

[Result]

As can be seen from Table 1, the cerium complex oxide is detected the embodiments a higher initial oxygen storage capacity (initial OSC) as the comparative example, while there is less waste or less Change between initial oxygen storage capacities activity (initial OSC) and oxygen storage capacity after Aging (OSC not specified) is subject to. This means that cerium complex oxide according to the invention a higher oxygen  storage capacity even when used repeatedly can maintain high temperatures.

They also show the first and second Embodiments obtained results that the Fe-bearing Zer complex oxide a particularly high oxygen storage capa before and after the redox aging test exhibits while there is little waste in its sow storage capacity after the redox aging test lies.

In addition, a comparison of the twelfth execution shows form with the other embodiments that the Zer complex oxide preferably wear a precious or transition metal should.

As a result, it can be said that the Zer complex oxide according to the present invention advantageously with a three Way catalyst can be used that is nearby a vehicle engine is mounted where very high operating temperatures are expected.  

Table 1

Claims (9)

1. An oxygen-storing cerium complex oxide with the following formula:
Ce _{1- (x + y)} Zr _x R _y O _2-z ,
where "R" represents a rare earth metal or rare earth metals except Zer, where "z" represents the degree of oxygen deficiency determined by the valence of the rare earth metal contained therein, and wherein 0.2 ≦ x + y ≦ 0.9, 0.1 ≦ x ≦ 0.8 and 0.05 ≦ y ≦ 0.3. 2. Oxygen-storing cerium complex oxide according to claim 1, in which in the formula the relationships 0.4 ≦ x + y ≦ 0.8, 0.35 ≦ x ≦ 0.7 and 0.05 ≦ y ≦ 0.2 observed will. 3. Oxygen-storing cerium complex oxide according to claim 1 or 2, where the rare earth metal is Y. 4. Oxygen-storing cerium complex oxide according to one of the Claims 1 to 3, in which at least part of the Cerium complex oxide is a solid solution. 5. Oxygen-storing cerium complex oxide according to one of the Claims 1 to 4, wherein the cerium complex oxide Precious metal or precious metals carries. 6. Oxygen-storing cerium complex oxide according to claim 5, in which the noble metal comprises Pd and / or Rh.   7. Oxygen-storing cerium complex oxide according to one of the Claims 1 to 4, wherein the cerium complex oxide Transition metal or metals carries. 8. Oxygen-storing cerium complex oxide according to claim 7, in which the transition metal is selected from a group Fe, Co, Ni and Cu is selected. 9. oxygen-storing cerium complex oxide according to claim 8, in which the transition metal is Fe.