RU2755558C2 - Method for the synthesis of a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to methods for producing composite powder materials by hydrometallurgical method, namely, to compositions based on stabilized aluminum oxide and a solid solution of cerium and zirconium oxides, which can be used as carriers of the catalytically active phase in an automotive catalytic unit. A method for synthesizing a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides includes the preparation of an aqueous suspension of cerium, zirconium and possibly yttrium or lanthanum hydroxides with a pH of 7 to 10 with the addition of ammonia at room temperature, the preparation of an aqueous suspension of aluminum hydroxides and possibly zirconium or lanthanum at room temperature. Next, the resulting suspensions are mixed at room temperature to produce a total suspension. The precipitate is separated from the mother liquor and isopropyl alcohol is injected. The mixture is dried and burnt. Before separating the precipitate from the mother liquor, the total suspension is ground so that the D90 value is less than 9.5 mcm, or subjected to hydrothermal treatment at a temperature above 110°C with the duration of 0 hours or more.

EFFECT: increase in the thermal stability of the surface of the particles of the composite powder material is provided.

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Description

The invention relates to methods for producing composite powder materials by a hydrometallurgical method, in particular to compositions based on stabilized alumina and a solid solution of cerium and zirconium oxides, which can be used as carriers of a catalytically active phase in an automotive catalytic unit.

Hereinafter, stabilized aluminum oxide is understood to mean aluminum oxide with additions of rare earth elements (REE), in which the phase transition temperature with the formation of corundum shifts to a temperature range of more than 1100 ° C. Recommendations on the type of stabilizing REE and its amount can be found, for example, in the articles [Patel K. Structural Effects of Lanthanide Dopants on Alumina / Ketan Patel, Victoria Blair, Justin Douglas, Qilin Dai, Yaohua Liu, Shenqiang Ren, Raymond Brennan // Scientific Reports 2017, 1-9] and [Yang J. Rapid preparation process, structure and thermal stability of lanthanum doped alumina aerogels with a high specific surface area / Jingfeng Yang, Qihua Wang, Tingmei Wang, Yongmin Liangc // RSC Advances 6, 2016 , 26271-26279].

A mixture of stabilized alumina and a solid solution of cerium and zirconium oxides is widely used as a carrier of a catalytically active phase, which simultaneously converts CO, HCx, and NOx gases to environmentally friendly compounds. Stabilized alumina in such a system provides high values of the specific surface area of the support, and the solid solution of cerium-zirconium oxides makes it possible to smooth out the deviations of the air / fuel ratio in the catalytic unit from the most favorable value for the simultaneous conversion of CO, HCx, and NOx gases.

Traditionally, such a mixture is prepared by mechanical mixing of powder materials of two substances with water in a common suspension, followed by a stage of grinding the powder particles. However, this approach does not allow to prevent the sintering of particles of one substance in the common system, which leads to degradation of the catalytic activity values after the catalyst is operated at operating temperatures of more than 1000 ° C. In the last decade, a method has been significantly developed aimed at preventing such a negative effect, namely, the use of a composite powder material, where the primary particles or crystallites of two substances are uniformly distributed relative to each other. This approach allows you to create a so-called "diffusion barrier", when the primary particles of one substance surround a particle of another substance and prevent diffusion. Due to the presence of a "diffusion barrier", the surface of the carrier of the catalytically active phase is more thermally stable, therefore, a less significant drop in the catalytic activity of the automotive catalytic unit occurs.

There are several approaches to the synthesis of such a composite powder material based on aluminum oxide and a solid solution of cerium and zirconium oxides. One of them is based on the simultaneous precipitation of hydroxides of all components of the composite; methods that provide for the organization of the synthesis process in such a way that hydroxide particles are formed at a constant pH of the reaction medium are especially effective. For example, the method described in RU 2698674 contains the following steps: a) contacting an acidic solution of precursors (a solution of salts of aluminum, cerium, zirconium and other REE) and a basic solution at a constant pH value equal to 5-6.75, adjusting the flow rate and / or the concentration of an acidic solution, a basic solution or two solutions at the same time, the settling time can be from 5 to 120 minutes; b) stabilization of the sediment by increasing the pH value to a value of 8 -9; c) firing at a temperature of 600 - 1100 ° C for 2 - 4 hours. An additional stage can be heating from 50 to 200 ° C of the precipitated or precipitated sediment from 15 minutes to 6 hours.

Method US 2011/0183840 consists of the following steps: preparation of an aqueous solution of metal salts; bringing the specified solution and base into contact in such a way that the pH in the reaction volume remains constant (changes by less than 0.5 units) and is set above 8.5 and below 10.5 (preferably 10); an additional stage of heating the precipitate (in mother liquor or pre-washed), where the pH is adjusted to a value from 8 to 10.5 at a temperature equal to or higher than 60 ° C; separation from the mother liquor; drying and roasting.

The method described in RU 2590162 includes the following stages: a) preparation of a suspension of boehmite (modified with organic compounds) with a pH of 8 to 11.5; b) preparation of an aqueous solution of the remaining metals; c) combining the suspension and the total solution at temperatures from 5 to 95 ° C, preferably from 80 to 95 ° C, or by adding the basic suspension to the acidic solution to bring the pH to 8.5-10, or by adding an acidic solution to the basic suspension to adjust the pH to 8, 5-10, or simultaneous dosing of the acidic solution and ammonia into the suspension so that the pH remains constant at 8.5-10; d) flushing; e) possible hydrothermal treatment at a temperature of more than 90 ° C and a time of more than 1 hour; f) separation of the sediment from the mother liquor, washing; g) drying and firing.

Another group of methods provides for the combination of separately obtained suspensions of hydroxides of the composite components, joint filtration and heat treatment. As a prototype, the method described in RU 2608741 was chosen, which contains the following stages: a) preparation of an aqueous suspension of cerium, zirconium hydroxides, possibly other metals from REE with a pH of 7 to 10 by adding ammonia at room temperature in the presence of H ₂ O ₂ , b) preparing an aqueous suspension of aluminum hydroxide at room temperature, c) mixing the resulting suspensions at room temperature; d) separation from the mother liquor and introduction of a surfactant; e) drying and firing.

The technical problem to be solved by the invention is the need to increase the catalytic activity of systems for neutralizing exhaust gases from motor vehicles operating at high temperatures.

The technical result of the proposed invention is a more thermally stable surface of the particles of a composite powder material based on aluminum oxide and a solid solution of cerium and zirconium oxides, that is, higher values of the specific surface area after processing at a temperature of 1100 ^o C.

The technical result is achieved due to a combination of phenomena: precise control of the amount of stabilizer additive in stabilized aluminum oxide at the stage of synthesis of its hydroxide, which makes it possible to achieve its high thermal stability, and the creation of a "diffusion barrier" during the joint processing of suspensions of aluminum and cerium hydroxides, zirconium, possibly other metals from REE. As such a joint treatment of hydroxide suspensions, it is possible to use both the grinding of the suspension, and its hydrothermal treatment, and the combination of hydrothermal treatment and grinding.

One of the methods for synthesizing a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides contains the steps of preparing an aqueous suspension of aluminum hydroxide with a pH of 7 to 10 by adding ammonia at room temperature, preparing an aqueous suspension of cerium, zirconium hydroxides, and possibly other metals from REE with pH from 7 to 10 by adding ammonia at room temperature, mixing a suspension of aluminum hydroxide and a suspension of hydroxides of cerium, zirconium, possibly other metals from REE to obtain a total suspension, grinding the total suspension so that the D90 value belongs to the range from 6 to 10 μm, separation sediment from the mother liquor from the total suspension, the introduction of isopropyl alcohol, drying and roasting.

Another method for synthesizing a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides contains the steps of preparing an aqueous suspension of aluminum hydroxide with a pH of 7 to 10 by adding ammonia at room temperature, preparing an aqueous suspension of cerium, zirconium hydroxides, and possibly other metals from rare earth elements with a pH from 7 to 10 with ammonia at room temperature, mixing the aluminum hydroxide slurry and the slurry hydroxides of cerium, zirconium, possibly other metals from the rare earth elements to obtain a total slurry, hydrothermal treatment, total slurry at a temperature above 110 ^{° C} from 0 hours or more, sludge separation from the mother liquor from the total suspension, the introduction of isopropyl alcohol, drying and roasting.

The most preferred method for synthesizing a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides contains the steps of preparing an aqueous suspension of aluminum hydroxide with a pH of 7 to 10 by adding ammonia at room temperature, preparing an aqueous suspension of cerium, zirconium hydroxides, and possibly other metals from REE with pH of from 7 to 10 with ammonia at room temperature, mixing the aluminum hydroxide slurry and the slurry hydroxides of cerium, zirconium, possibly other metals from the rare earth elements to obtain a total slurry, hydrothermal treatment, total slurry at a temperature above 110 ^{° C} from 0 hours or more, grinding total suspension so that the D90 value belongs to the interval less than 9.5 μm, separating the precipitate from the mother liquor from the total suspension, introducing isopropyl alcohol, drying and calcining.

The essence of the invention is illustrated by the figures, which show

- in Fig. 1 - Table of values of the specific surface area of the carrier powder samples.

The step of preparing an aqueous suspension of aluminum hydroxide is carried out by any method known in the art, involving contacting a compound of aluminum and ammonia to form a suspension of aluminum hydroxide. The most preferred embodiment of the invention is to contact the aluminum compound and ammonia to form a suspension of aluminum hydroxide so that the pH of the suspension is in the range from 8 to 9 throughout the entire process. To obtain stabilized aluminum oxide, not only aluminum compounds are brought into contact with ammonia, but also a compound of a rare earth element. It is most preferable to introduce the compound of the rare earth element in a molar ratio of Al: REE = from 997: 3 to 967: 33. As REE can be used, for example, Zr or La.

The stage of preparing an aqueous suspension of cerium, zirconium hydroxides, possibly other metals from REE is carried out by any method known in the art, involving the contact of cerium, zirconium compounds, possibly other metals from REE and ammonia to form a suspension of cerium, zirconium hydroxides, possibly others metals from REE. The most preferred embodiment of the invention is the contacting of compounds of cerium, zirconium, possibly other metals from REE and ammonia with the formation of a suspension of hydroxides of cerium, zirconium, possibly other metals from REE so that the pH of the suspension belongs to the range from 8 to 9 during the whole process.

The stage of mixing a suspension of aluminum hydroxide and a suspension of hydroxides of cerium, zirconium, possibly other metals from REE to obtain a total suspension is carried out by any method known in the art, providing for a homogeneous distribution of particles of hydroxide precipitates of different composition in the volume of the total suspension.

A step of hydrothermal treatment total slurry at a temperature above 110 ^{° C} lasting between 0 hours and more carried out by any method known in the art, e.g., subjecting the slurry heated in a closed vessel type autoclave. The heating rate is not critical. The duration of 0 hours corresponds to such an organization of the process that the heating of the suspension stops at the moment as soon as the temperature of the suspension becomes equal to that selected for the hydrothermal treatment.

The stage of grinding the total slurry so that the D90 value is less than 9.5 μm. Milling can be organized by any method known in the art, in particular, it is possible to use rotary dispersers, colloid mills, bead mills.

The steps of separating the precipitate from the mother liquor from the total suspension and introducing isopropyl alcohol are carried out by any method known in the art, ensuring that isopropyl alcohol molecules hit the surface of the particles of the total suspension. It is preferable to organize the process of separating the precipitate from the mother liquor from the total suspension and introducing isopropyl alcohol such that the liquid phase in contact with the surface of the particles of the total suspension is a mixture of isopropyl alcohol and water with an alcohol content greater than that in the azeotropic mixture of isopropyl alcohol and water.

As an example of such a method for organizing the process of separating the precipitate from the mother liquor from the general suspension and introducing isopropyl alcohol, the authors of the invention proposed the following sequence of operations: separating the precipitate from the mother liquor from the general suspension using vacuum filtration to obtain a wet precipitate, suspending the wet precipitate in an azeotropic mixture of isopropyl alcohol and water, separating the precipitate from the liquid phase using vacuum filtration to obtain a wet precipitate, suspending the wet precipitate in absolute isopropyl alcohol, separating the precipitate from the liquid phase using vacuum filtration, the density of the liquid phase being higher than the density of the azeotropic mixture of isopropyl alcohol and water.

The drying and calcining steps are carried out to convert the metal hydroxides to the oxide form in order to obtain the final powder product. The drying and firing parameters are not essential features of the invention and can be borrowed from the description of the prototype of the invention.

The authors found that the synthesis of aluminum hydroxide at a separate stage makes it possible to introduce a sufficient amount of REE for stabilization, while in the joint synthesis of aluminum hydroxides of cerium, zirconium and other metals from REE, stabilization of aluminum oxide after synthesis does not occur, since REE is isomorphically included in the crystal lattice of a solid solution of cerium-zirconium, and not the crystal lattice of aluminum oxide. The stage of hydrothermal treatment makes it possible, due to the formation of bridging ol and oxo groups, to more firmly bind aluminum hydroxide and REE hydroxide, which increases the thermal stability of stabilized aluminum oxide. Also, during hydrothermal treatment, diffusion of the components of the total suspension occurs, which provides a stronger manifestation of the "diffusion barrier" effect in the composition based on stabilized alumina and a solid solution of cerium and zirconium oxides. Milling allows the particles of the two substances to be more uniformly distributed relative to each other, which also provides a stronger manifestation of the "diffusion barrier" effect.

The essence and advantages of the invention can be illustrated by the following examples.

The specific surface area was measured by the method of low-temperature adsorption / desorption of nitrogen according to the BET theory using a Quantochrom Nova 1200e instrument. To assess the thermal stability of the specific surface area, additional firing was carried out at 1100 ° C for 4 hours.

Example 1 (Comparative).

Preparation of an aqueous suspension of aluminum hydroxide and REE hydroxide. Into the first beaker was introduced 1 dm3 of an aqueous solution of aluminum nitrate with a concentration of 50 g / dm3 in terms of aluminum oxide and 0.02 dm3 of lanthanum nitrate with a concentration of 150 g / dm3 in terms of lanthanum oxide. Into the second beaker was introduced 1 dm3 of an aqueous solution of ammonia with a concentration of 10 wt.%. 0.25 dm3 of water was introduced into a reactor with a volume of 3 dm3. With active stirring using peristaltic pumps, a solution of aluminum nitrate was fed at a constant rate of 10 cm3 / min and an aqueous solution of ammonia discretely when the pH dropped below 8.0 so that during the precipitation the pH was 8.5 ± 0.5 units. The deposition was carried out until the solution of aluminum nitrate and lanthanum nitrate ran out in the first glass.

Preparation of an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides. Into the first beaker was added 1 dm3 of an aqueous solution of cerium, zirconium, yttrium and lanthanum nitrates in a molar ratio of 0.4: 0.5: 0.05: 0.05, respectively, with a total metal concentration of 50 g / l in terms of total oxide. Into the second glass, 1 dm3 of an aqueous solution of ammonia with a concentration of 10 wt.% Is introduced. Peroxide was added in a fivefold excess in relation to the content of cerium in moles. 0.25 dm3 of water was introduced into a reactor with a volume of 3 dm3. With active stirring using peristaltic pumps, a solution of metal nitrates was fed at a constant rate of 10 cm3 / min and an aqueous solution of ammonia discretely when the pH dropped below 8.0 so that during the precipitation the pH was 8.5 ± 0.5 units. Precipitation was carried out until the solution of metal nitrates ran out in the first glass.

A suspension of aluminum hydroxide and a suspension of cerium, zirconium, yttrium, and lanthanum hydroxides were placed in a beaker with a volume of 5 dm3 and then stirred with an overhead stirrer at a speed of 500 rpm. This is how a general suspension of aluminum hydroxide and hydroxides of cerium, zirconium, yttrium and lanthanum was obtained.

The separation of the precipitate from the mother liquor from the total suspension was carried out using vacuum filtration to obtain a wet cake. Then the precipitate was suspended in an azeotropic mixture of isopropyl alcohol and water. After that, the precipitate was again separated from the liquid phase using vacuum filtration. The resulting precipitate was suspended in absolute isopropyl alcohol and the next separation of the precipitate from the liquid phase was carried out using vacuum filtration. The operations of filtration and suspension in absolute alcohol were carried out until the density of the liquid phase became higher than the density of the azeotropic mixture of isopropyl alcohol and water.

After the precipitate was dried at 130 ℃ 2 hours, then fired either at 700 ℃ 2 hours.

Example 2.

Preparation of an aqueous suspension of aluminum hydroxide and lanthanum hydroxide. Into the first glass, 2 dm3 of a solution of aluminum nitrate with a concentration of 50 g / dm3 in terms of aluminum oxide and 0.01 dm3 of a solution of lanthanum nitrate with a concentration of 151 g / dm3 in terms of lanthanum oxide are introduced. Into the second beaker, 1.5 dm3 of an aqueous ammonia solution with a concentration of 10 wt.% Is introduced. 0.5 dm3 of water is introduced into a 5 dm3 reactor. The acid solution feed rate into the reactor is 3 cm3 / min.

The preparation of an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides and their general suspension was carried out as in Example 1.

Further, the total suspension was subjected to hydrothermal treatment at a temperature of 130 ° C for 10 hours in a glass sealed container placed in a steel autoclave.

The separation of the precipitate from the mother liquor from the total suspension and the introduction of isopropyl alcohol, drying and firing were carried out as in Example 1.

Example 3.

The preparation of an aqueous suspension of aluminum hydroxide and lanthanum hydroxide, an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides and their general suspension was carried out as in Example 1.

Next, the total suspension was milled in a bead mill using corundum grinding bodies with a diameter of 1 mm at a shaft rotation speed of 5000 rpm. The process was stopped every 15 minutes and the D90 value was measured using the laser diffraction method. The process was considered complete as soon as the measured D90 value became less than 9.5 μm based on the results of three parallel measurements.

The separation of the precipitate from the mother liquor from the total suspension and the introduction of isopropyl alcohol, drying and firing were carried out as in Example 1.

Example 4.

Preparation of an aqueous suspension of aluminum hydroxide and zirconium hydroxide. Into the first beaker is introduced 2 dm3 of an aqueous solution of aluminum nitrate with a concentration of 50 g / l in terms of aluminum oxide. An additional 0.16 dm3 of a solution of zirconium nitrate with a concentration of 320 g / l in terms of zirconium oxide is added to the first beaker. Into the second beaker, 1.5 dm3 of an aqueous ammonia solution with a concentration of 10 wt.% Is introduced. 0.5 dm3 of water is introduced into a 5 dm3 reactor. With active stirring using peristaltic pumps, a solution of aluminum nitrate is fed at a constant rate of 10 cm3 / min and an aqueous ammonia solution at a variable rate so that during the precipitation process the pH belongs to the range from 7 to 10 units. Precipitation is carried out until the aluminum nitrate solution runs out in the first glass.

Preparation of an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides. Into the first glass, 1 dm3 of an aqueous solution of cerium, zirconium, yttrium and lanthanum nitrates is introduced in a molar ratio of 0.4: 0.5: 0.05: 0.05, respectively, with a total metal concentration of 50 g / l in terms of oxides. Into the second glass, 1 dm3 of an aqueous solution of ammonia with a concentration of 10 wt.% Is introduced. Peroxide is added in a fivefold excess in relation to the content of cerium in moles. 0.25 dm3 of water is introduced into a 3 dm3 reactor. With active stirring using peristaltic pumps, a solution of aluminum nitrate is fed at a constant rate of 10 cm3 / min and an aqueous ammonia solution at a variable rate so that during the precipitation process the pH belongs to the range from 7 to 10 units. Precipitation is carried out until the solution of metal nitrates ends in the first glass.

The preparation of a total suspension of aluminum hydroxide and zirconium hydroxide and hydroxides of cerium, zirconium, yttrium and lanthanum was carried out as in Example 1.

Then the total suspension was heated to a temperature of 110 ° C, heating was stopped and cooled to room temperature. Thus, the total suspension was subjected to a hydrothermal treatment at 110 ° C for 0 hours in a glass sealed container placed in a steel autoclave.

Next, the total suspension was milled in a bead mill using corundum grinding bodies with a diameter of 1 mm at a shaft rotation speed of 5000 rpm. The process was stopped every 15 minutes and the D90 value was measured using the laser diffraction method. The process was considered complete as soon as the measured D90 value became less than 9.5 μm based on the results of three parallel measurements.

The separation of the precipitate from the mother liquor from the total suspension and the introduction of isopropyl alcohol, drying and firing were carried out as in Example 1.

Example 5 (comparative).

The preparation of an aqueous suspension of aluminum hydroxide and lanthanum hydroxide, an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides and their general suspension was carried out as in Example 1.

Next, the total suspension was milled in a bead mill using corundum grinding bodies with a diameter of 1 mm at a shaft rotation speed of 5000 rpm. The process was stopped every 15 minutes and the D90 value was measured using the laser diffraction method. The process was considered complete as soon as the measured D90 value became less than 11 μm based on the results of three parallel measurements.

The separation of the precipitate from the mother liquor from the total suspension and the introduction of isopropyl alcohol, drying and firing were carried out as in Example 1.

Example 6 (comparative).

The preparation of an aqueous suspension of aluminum hydroxide and lanthanum hydroxide, an aqueous suspension of cerium, zirconium, yttrium and lanthanum hydroxides and their general suspension was carried out as in Example 1.

Then the total suspension was subjected to hydrothermal treatment at a temperature of 90 ° C for 1 hour in a glass sealed container heated in an oil bath.

The separation of the precipitate from the mother liquor from the total suspension and the introduction of isopropyl alcohol, drying and firing were carried out as in Example 1.

Claims (8)

1. A method of synthesizing a composition based on aluminum oxide and a solid solution of cerium, zirconium and possibly yttrium or lanthanum oxides, containing the steps of preparing an aqueous suspension of cerium, zirconium and possibly yttrium or lanthanum hydroxides with a pH of 7 to 10 by adding ammonia at room temperature temperature, preparation of an aqueous suspension of aluminum hydroxides and, possibly, zirconium or lanthanum by adding ammonia at room temperature, mixing a suspension of cerium, zirconium and possibly yttrium or lanthanum hydroxides, as well as a suspension of aluminum hydroxides and, possibly, zirconium or lanthanum at room temperature with obtaining a total suspension, separating the precipitate from the mother liquor from the total suspension, introducing isopropyl alcohol, drying and firing, characterized in that before separating the precipitate from the mother liquor, the total suspension is milled so that the D90 value is less than 9.5 μm. 2. The method according to claim 1, characterized in that the preparation of an aqueous suspension of hydroxides of cerium, zirconium and, possibly, yttrium or lanthanum is carried out by adding ammonia at a pH of the suspension from 8 to 9. 3. The method according to PP. 1, 2, characterized in that the preparation of an aqueous suspension of aluminum hydroxide and, possibly, zirconium or lanthanum is carried out by adding ammonia at room temperature at a pH value of 8 to 9. 4. The method according to PP. 1-3, characterized in that the aqueous suspension of aluminum hydroxide and, possibly, zirconium or lanthanum is an aqueous suspension of aluminum hydroxide with the addition of zirconium or lanthanum hydroxide at a molar ratio of Al: Zr or Al: La equal to from 997: 3 to 967: 33. 5. A method of synthesizing a composition based on aluminum oxide and a solid solution of cerium and zirconium oxides, containing the stages of preparing an aqueous suspension of cerium, zirconium and, possibly, yttrium or lanthanum hydroxides with a pH of 7 to 10 by adding ammonia at room temperature, preparing an aqueous suspension of aluminum hydroxides and, possibly, zirconium or lanthanum by adding ammonia at room temperature, mixing a suspension of cerium, zirconium and possibly yttrium or lanthanum hydroxides, as well as a suspension of aluminum hydroxides and, possibly, zirconium or lanthanum at room temperature to obtain a general suspension, separating the precipitate from mother liquor from the total suspension, the introduction of isopropyl alcohol, drying and roasting, characterized in that the total suspension is subjected to hydrothermal treatment before filtration at a temperature above 110 ° C for a duration of 0 hours or more. 6. The method according to claim 5, characterized in that the preparation of an aqueous suspension of hydroxides of cerium, zirconium and, possibly, yttrium or lanthanum is carried out by adding ammonia at a pH of the suspension from 8 to 9. 7. The method according to PP. 5, 6, characterized in that the preparation of an aqueous suspension of aluminum hydroxide and, possibly, zirconium or lanthanum is carried out by adding ammonia at room temperature at a pH value of 8 to 9. 8. The method according to claim 5-7, characterized in that the aqueous suspension of aluminum hydroxide and possibly zirconium or lanthanum is an aqueous suspension of aluminum hydroxide with the addition of yttrium or lanthanum hydroxide at a molar ratio of Al: Zr or Al: La equal to 997: 3 to 967: 33.

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