阅读说明：本技术 具有高孔体积的混合氧化物 (Mixed oxides having high pore volume ) 是由 大竹尚孝 T·佐佐木 于 2020-02-28 设计创作，主要内容包括：本发明涉及一种基于锆和铈的混合氧化物组合物、其制备方法以及其在催化领域中的用途。该混合氧化物的特征在于在1100℃下煅烧之后的高比表面积和特定孔隙率。(The invention relates to a mixed oxide composition based on zirconium and cerium, to a method for preparing same and to the use thereof in the field of catalysis. The mixed oxides are characterized by a high specific surface area and a specific porosity after calcination at 1100 ℃.)

1. A mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth element (RE) other than cerium and lanthanum, having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Zr) are given relative to the mixed oxide as a whole by weight of oxide, characterized in that:

■ the mixed oxide exhibits a calcination time of at least 28m at 1100 ℃ in air after 4 hours²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²Specific surface area per gram (BET);

■ the peak having the highest intensity in the range of pores having a size below 500nm corresponds to a pore size D between 70nm, excluding this value, and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}；

■ the mixed oxide exhibits a total pore volume V of pores having a size below 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h}；

The size of the hole D_{p，1100℃/4h}And the total pore volume V_{500nm，1100℃/4h}Is determined by mercury intrusion on the mixed oxide after calcination in air at 1100 ℃ for 4 hours.

2. The mixed oxide of claim 1, further comprising hafnium.

3. The mixed oxide according to claim 2, wherein the proportion of hafnium, given by weight of oxide with respect to the mixed oxide as a whole, is lower than or equal to 2.5%, even lower than or equal to 2.0%.

4. The mixed oxide according to claims 1 to 3, wherein the elements Ce, Zr, La, RE, if present, and Hf, if present, are present as oxides in the mixed oxide.

5. The mixed oxide according to claims 1 to 3, wherein the elements Ce, Zr, La, RE, if present, and Hf, if present, are present as oxides in the mixed oxide and also partly in the form of hydroxides or oxyhydroxides.

6. A mixed oxide consisting of: a combination of oxides of zirconium, cerium, lanthanum, optionally at least one rare earth element other than cerium and lanthanum, and optionally hafnium, the mixed oxide having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ hafnium in a proportion lower than or equal to 2.5%, even lower than or equal to 2.0%;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Hf, Zr) are given relative to the mixed oxide as a whole, by weight of oxide, characterized in that:

■ the mixed oxide showed that after calcination at 1100 c for 4 hours in air,at least 28m²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²Specific surface area per gram (BET);

■ the peak having the highest intensity in the range of pores having a size below 500nm corresponds to a pore size D between 70nm, excluding this value, and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}；

■ the mixed oxide exhibits a total pore volume V of pores having a size below 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h}；

The size of the hole D_{p，1100℃/4h}And the total pore volume V_{500nm，1100℃/4h}Is determined by mercury intrusion on the mixed oxide after calcination in air at 1100 ℃ for 4 hours.

7. The mixed oxide according to any of the preceding claims, wherein the proportion of cerium is:

-between 18.0% and 65.0% (not including this value); or

-between 25.0% and 70.0%; or

-between 25.0% and 65.0% (not including this value).

8. The mixed oxide according to any one of claims 1 to 6, wherein the proportion of cerium is:

-between 18.0% and 25.0%, more particularly between 18.0% and 22.0%; or

-between 35.0% and 45.0%, more particularly between 38.0% and 42.0%; or

-between 45.0% and 55.0%, more particularly between 48.0% and 52.0%; or

-between 60.0% and 70.0%, more particularly between 63.0% and 67.0%.

9. The mixed oxide according to any of the preceding claims, wherein the proportion of lanthanum is between 1.0% and 10.0%, more particularly between 3.0% and 10.0%, even more particularly between 3.0% and 7.0%.

10. The mixed oxide according to any of the preceding claims, wherein the total proportion of the one or more rare earth elements other than cerium and lanthanum is up to 10.0%, more particularly up to 7.0%.

11. The mixed oxide according to claims 1 to 9, wherein the mixed oxide does not contain any rare earth elements other than cerium and lanthanum, and the proportion of lanthanum is at least 5.0%.

12. The mixed oxide according to claims 1 to 10, wherein the mixed oxide comprises at least one rare earth element other than cerium and lanthanum, and the total proportion of lanthanum and the one or more rare earth elements other than cerium and lanthanum is at least 5.0%.

13. The mixed oxide according to claims 1 to 10 and 12, wherein the mixed oxide comprises at least one rare earth element other than cerium and other than lanthanum, and the total proportion of lanthanum and the one or more rare earth elements other than cerium and other than lanthanum is at most 15.0%, more particularly at most 12.0%.

14. Mixed oxide according to any of the preceding claims, wherein the proportion of zirconium is at least 10.0%, more particularly at least 20.0%, more particularly at least 25.0%, excluding this value.

15. The mixed oxide according to any of the preceding claims, wherein the proportion of zirconium is at most 81.0%, more particularly at most 79.0%, more particularly at most 60.0%.

16. The method of any preceding claimA mixed oxide, wherein the mixed oxide exhibits a particle size of at least 50m after calcination in air at 1000 ℃ for 4 hours²A/g, more particularly at least 55m²Specific surface area (BET) in g.

17. The mixed oxide according to any of the preceding claims, wherein the mixed oxide exhibits at least 60m after calcination in air at 900 ℃ for 4 hours²A/g, more particularly at least 65m²Specific surface area (BET) in g.

18. The mixed oxide according to any of the preceding claims, wherein it exhibits, after calcination at 1100 ℃ for 4 hours in air, a total pore volume V of pores having a size lower than 500nm of between 0.30 and 0.70mL/g, more particularly between 0.40 and 0.70mL/g, even more particularly between 0.50 and 0.70mL/g_{500nm，1100℃/4h}。

19. The mixed oxide according to any of the preceding claims, characterized in that it exhibits a total pore volume of at least 0.60mL/g, more particularly at least 0.90mL/g, even more particularly at least 1.00mL/g or at least 1.50mL/g after calcination at 1100 ℃ for 4 hours in air.

20. Mixed oxide according to one of the preceding claims, characterized in that it is calcined in air at 1100 ℃ for 4 hours at 28m²G and 40m²Between/g, more particularly at 28m²G and 35m²Between/g, even more particularly at 30m²G and 35m²Specific surface area (BET) between/g.

21. Mixed oxide according to one of the preceding claims, characterized in that it is calcined in air at 1000 ℃ for 4 hours at 50m²G and 70m²Between/g, more particularly at 55m²G and 60m²Specific surface area (BET) between/g.

22. Mixed oxide according to one of the preceding claims, characterized in that it is calcined in air at 900 ℃ for 4 hours at 60m²G and 90m²Between/g, more particularly 65m²G and 80m²Specific surface area (BET) between/g.

23. Mixed oxide according to one of the preceding claims, characterized in that:

-at least 30m after calcination in air at 1100 ℃ for 4 hours²Specific surface area per gram (BET);

a peak with the highest intensity in the range of pores with a size below 500nm, corresponding to a pore size D between 100 and 400nm or between 100 and 370nm or between 120 and 370nm_{p，1100℃/4h}；

-a total pore volume V of at least 0.50mL/g of pores having a size below 500nm_{500nm，1100℃/4h}；

-a total pore volume of at least 1.00mL/g after calcination in air at 1100 ℃ for 4 hours.

24. Mixed oxide according to any one of the preceding claims, characterized in that the ratio α, of less than 0.35, more particularly of less than 0.30, is defined by the following formula:

α＝V_{70nm，1100℃/4h}/V_{500nm，1100℃/4h}

wherein V_{70nm，1100℃/4h}Is the total pore volume of pores having a size below 70nm after calcination in air at 1100 ℃ for 4 hours.

25. The mixed oxide according to any of the preceding claims, which exhibits a d50 strictly above 2.5 μm, d50 being determined from the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer.

26. The mixed oxide according to claim 25, wherein the distribution is obtained from the dispersion of the particles in water, optionally in the presence of a dispersant (sodium hexametaphosphate).

27. The mixed oxide according to claim 25 or 26, wherein d50 is between 2.5 μ ι η (not including this value) and 20.0 μ ι η, more particularly between 2.5 μ ι η (not including this value) and 10.0 μ ι η, even more particularly between 2.5 μ ι η (not including this value) and 7.0 μ ι η.

28. A method of preparing the mixed oxide of any one of claims 1 to 27, comprising the steps of:

(a) heating an aqueous acidic dispersion S at a temperature between 100 ℃ and 180 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, wherein the dispersion S comprises:

(i) having at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio;

(ii) lanthanum nitrate;

(iii) optionally at least one nitrate of a rare earth element (RE) other than cerium and other than lanthanum; and

(iv) particles of zirconium oxyhydroxide, wherein the powder of zirconium oxyhydroxide used to prepare the dispersion exhibits an average size d50 between 5.0 μm and 100.0 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer;

the dispersion S is characterized by a molar ratio H of between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr；

(b) Adding an ammonia solution to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0;

(c) then adding the organic structuring agent to the mixture obtained at the end of step (b), stirring the mixture with a high shear rate mixer;

(d) the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air.

29. A process for preparing a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth element (RE) other than cerium and lanthanum, having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Zr) are given relative to the mixed oxide as a whole by weight of oxide,

the method comprises the following steps:

(a) heating an aqueous acidic dispersion S at a temperature between 100 ℃ and 180 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, wherein the dispersion S comprises:

(i) having at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio;

(ii) lanthanum nitrate;

(iii) optionally at least one nitrate of a rare earth element (RE) other than cerium and other than lanthanum; and

(iv) particles of zirconium oxyhydroxide, wherein the powder of zirconium oxyhydroxide used to prepare the dispersion exhibits an average size d50 between 5.0 μm and 100.0 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer;

the dispersion is characterized by a molar ratio H of between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr；

(b) Adding an ammonia solution to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0;

(c) then adding the organic structuring agent to the mixture obtained at the end of step (b), stirring the mixture with a high shear rate mixer;

(d) the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air.

30. The process according to claim 28 or 29, wherein H in the acidic dispersion S⁺Is between 0.05 and 1.40mol/L, more particularly between 0.30 and 0.80 mol/L.

31. The method of claims 28 to 30, wherein the organic structuring agent is selected from the group consisting of: caproic acid, caprylic acid, capric acid, lauric acid, myristic acid and palmitic acid or salts of these acids.

32. The method according to claims 28 to 31, wherein the organic structuring agent is lauric acid or a salt of lauric acid.

33. The method according to claims 28 to 32, wherein the tip speed T of the high shear rate mixer is between 5.0m/s and 25.0m/s, more particularly between 7.0m/s and 20.0m/s, T being calculated by the following formula: t (m/s) ═ D pi R/60, where D is the diameter of the rotor (m) and R is the rotation rate of the rotor (rpm).

34. A catalytic composition, comprising:

(i) at least one mineral material; and

(ii) at least one dispersed platinum group metal; and

(iii) the mixed oxide of any one of claims 1 to 27.

35. A catalytic converter comprising a porous support and a catalytic composition according to claim 34 on a surface of the support.

36. Use of a mixed oxide according to any one of claims 1 to 27 for the preparation of a catalytic composition, in particular according to claim 35.

37. Use of a mixed oxide according to any of claims 1 to 27 for the production of a catalytic converter, in particular according to claim 35.

38. Use of a zirconium oxyhydroxide characterized by an average size d50 between 5.0 μ ι η and 100.0 μ ι η, more particularly between 5.0 μ ι η and 50.0 μ ι η, even more particularly between 25.0 μ ι η and 40.0 μ ι η, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer, for the preparation of the mixed oxide according to claims 1 to 27.

[ technical field ]

Currently, "multi-function" catalysts are used to treat exhaust gas from internal combustion engines (motor vehicle post-combustion catalysis). The term "multifunctional" is understood to mean a catalyst capable of not only oxidizing, in particular oxidizing, the carbon monoxide and hydrocarbons present in the exhaust gases, but also of reducing, in particular reducing, the nitrogen oxides also present in these gases (a "three-way" catalyst). Compositions based on zirconium and rare earth oxides can now be considered as advantageous elements that can be incorporated into the composition of this type of catalyst.

Products of this type must exhibit a compromise between porosity and temperature resistance suitable for use. In particular, they must exhibit a sufficiently high pore volume and therefore contain pores of sufficiently large size in order to allow good diffusion of the gas from and to the catalytic sites. The proper diffusion of the gases also allows to maintain the air/fuel ratio in an optimum condition of oxygen absorption and desorption capacity, which favours the optimum performance of the mixed oxides.

The porosity should also be such that the mixed oxide is easily mixed with the other components of the washcoat and such that the platinum group metal(s) (PGM) is well impregnated and/or well dispersed in the washcoat. The mixed oxides of the invention disclosed below are intended to solve these technical problems.

[ background art ]

In WO 2017/185224, the mixed oxide shows a total pore volume comprised between 0.2 and 0.5mL/g after calcination in air at 1000 ℃ for 4 hours.

WO 2011/006780 does not disclose at least 28m after calcination in air at 1100 ℃ for 4 hours²Specific surface area (BET) in g.

EP 2566617 discloses a mixed oxide exhibiting a population of pores with diameters centered around a value between 30nm and 70 nm.

US 7,767,617B 2 (equivalent to US 2006/178261) discloses a process in which a dispersion of the precipitate is subjected to a moderate energy milling operation, for example using a colloid mill or a turbine stirrer. However, the precipitate is obtained by contact with an alkaline solution and not by thermal hydrolysis. Furthermore, in US 7,767,617B 2, no mention is made of particles of zirconium oxyhydroxide having a d50 between 5.0 μm and 100 μm.

US 8,158,551 (equivalent to US 2009/220398) discloses a process in which particles of zirconium oxyhydroxide having a d50 between 5.0 μm and 100 μm are not mentioned.

US 2013/288891 and EP 0955267 disclose complex oxides, but do not mention the features of the mixed oxides of the present invention.

[ summary of the invention ]

The invention firstly relates to a mixed oxide as claimed in claims 1 to 27. The invention therefore relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth element (RE) other than cerium and lanthanum, having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Zr) are given relative to the mixed oxide as a whole by weight of oxide, characterized in that:

■ the mixed oxide exhibits a calcination time of at least 28m at 1100 ℃ in air after 4 hours²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²Specific surface area per gram (BET);

■ the peak having the highest intensity in the range of pores having a size below 500nm corresponds to a pore size D between 70nm (excluding this value) and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}；

■ the mixed oxide exhibits a total pore volume V of pores having a size below 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h}；

The size of the hole D_{p，1100℃/4h}And the total pore volume V_{500nm，1100℃/4h}Is determined by mercury intrusion on the mixed oxide after calcination in air at 1100 ℃ for 4 hours.

The invention also relates to a mixed oxide consisting of: a combination of oxides of zirconium, cerium, lanthanum, optionally at least one rare earth element other than cerium and lanthanum, and optionally hafnium, the mixed oxide having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ hafnium in a proportion lower than or equal to 2.5%, even lower than or equal to 2.0%;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Hf, Zr) are given relative to the mixed oxide as a whole, by weight of oxide, characterized in that:

■ the mixed oxide exhibits a calcination time of at least 28m at 1100 ℃ in air after 4 hours²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²Specific surface area per gram (BET);

■ the peak having the highest intensity in the range of pores having a size below 500nm corresponds to a pore size D between 70nm (excluding this value) and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}；

■ the mixed oxide exhibits a total pore volume V of pores having a size below 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h}；

The size of the hole D_{p，1100℃/4h}And the total pore volume V_{500nm，1100℃/4h}Is determined by mercury intrusion on the mixed oxide after calcination in air at 1100 ℃ for 4 hours.

The invention also relates to a method for producing mixed oxides, in particular the mixed oxides according to the invention as claimed in claims 28 to 33.

The method comprises the following steps:

(a) heating an aqueous acidic dispersion S at a temperature between 100 ℃ and 180 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, wherein the dispersion S comprises:

(i) having at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio;

(ii) lanthanum nitrate;

(iii) optionally at least one nitrate of a rare earth element (RE) other than cerium and other than lanthanum; and

(iv) particles of zirconium oxyhydroxide, wherein the powder of zirconium oxyhydroxide used to prepare the dispersion exhibits an average size d50 between 5.0 μm and 100.0 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer;

the dispersion S is characterized by a molar ratio H of between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr；

(b) Adding an ammonia solution to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0;

(c) then adding the organic structuring agent to the mixture obtained at the end of step (b), stirring the mixture with a high shear rate mixer;

(d) the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air.

The invention also relates to a catalytic composition comprising:

(i) at least one mineral material; and

(ii) at least one dispersed platinum group metal; and

(iii) the mixed oxides of the present invention.

The invention also relates to the use of the mixed oxides according to the invention for producing catalytic compositions or catalytic converters.

More details about these inventions are given below.

[ description of the drawings ]

Fig. 1 shows the dispersion elements S18N-19G (1. shaft tube; 2. grooved piston ring bearing; 3. shaft; 4. stator; 5. rotor; 6. drive collar) used in example 1.

FIG. 2 shows a pore map (porogen) of the mixed oxide of example 7. The peak having the highest intensity in the range of pores having a size below 500nm is at D_{p，1100℃/4h}Visible at 363nm and corresponds to D_{p，1100℃/4h}＝363nm。

Unless otherwise mentioned, the calcination, more particularly the calcination after which the values of specific surface area or porosity are given, is calcination in air. For the sake of continuity of the description, it is also specified that, unless otherwise indicated, a limit value is included within the range of the values given. This also applies to expressions comprising "at least" or "at most".

[ detailed description of the invention ]

The invention relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth element (RE) other than cerium and lanthanum, having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, characterized in that:

■ the mixed oxide exhibits a calcination time of at least 28m at 1100 ℃ in air after 4 hours²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²Specific surface area per gram (BET);

■ the peak having the highest intensity in the range of pores having a size below 500nm corresponds to a pore size D between 70nm (excluding this value) and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}；

■ the mixed oxide exhibits a total pore volume V of pores having a size below 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h}；

The size of the hole D_{p，1100℃/4h}And the total pore volume V_{500nm，1100℃/4h}Is determined by mercury intrusion on the mixed oxide after calcination in air at 1100 ℃ for 4 hours.

The mixed oxides of the invention may also contain the element hafnium. In fact, this element is generally present in combination with zirconium in ores that exist in the natural state. The relative proportion of hafnium relative to zirconium depends on the extraction therefromAn ore of zirconium. In some ores, the relative ratio of Zr/Hf by weight may be about 50/1. Thus, baddeleyite contains approximately 98% ZrO₂And 2% HfO₂. The proportion of hafnium is less than or equal to 2.5%, even less than or equal to 2.0%.

The elements mentioned above are usually present as oxides in mixed oxides. However, they may also be present partly in the form of hydroxides or oxyhydroxides. Like zirconium, hafnium is typically present as an oxide. However, it is not excluded that hafnium is also partly present in the form of hydroxide or oxyhydroxide. Thus, the elements Ce, Zr, La, RE (if present), and Hf (if present) are present as oxides in the mixed oxide, but they may also be present as oxides in the mixed oxide and also partly in the form of hydroxides or oxyhydroxides.

As in the field of mixed oxides, the proportions of the elements are given relative to the mixed oxide as a whole by weight of the oxide. For the calculation of these ratios, the following oxides are considered: CeO (CeO)₂、ZrO₂、HfO₂、La₂O₃、RE₂O₃(except Pr (for which Pr is considered)₆O₁₁) All but RE). Thus, for example, a proportion of 20.0% of cerium means CeO in the mixed oxide₂Is 20.0% by weight. The proportion of elements is determined by common analytical methods such as X-ray fluorescence or by inductively coupled plasma mass spectrometry. It is also noted that, unless otherwise mentioned, a limit value is included within the range of the given value.

The mixed oxide of the present invention contains the above-mentioned elements in the above-mentioned proportions, but it may additionally contain other elements such as impurities. The impurities may originate from the starting materials or starting materials used in the process for preparing the mixed oxides. The total proportion of impurities can generally be less than or equal to 0.25% (. ltoreq.0.25%) by weight, more particularly less than or equal to 0.20% (. ltoreq.0.20%) by weight, relative to the mixed oxides.

First of all, the mixed oxides according to the invention are characterized by the nature and the proportions of their components. The proportion of cerium in the mixed oxide can vary within wide limits. In practice, the proportion of cerium is between 18.0% and 70.0%, more particularly between 18.0% and 65.0% (not including this value) or more particularly between 25.0% and 70.0% or between 25.0% and 65.0% (not including this value). The proportion of cerium may also be more particularly:

-between 18.0% and 25.0%, more particularly between 18.0% and 22.0%; or

-between 35.0% and 45.0%, more particularly between 38.0% and 42.0%; or

-between 45.0% and 55.0%, more particularly between 48.0% and 52.0%; or

-between 60.0% and 70.0%, more particularly between 63.0% and 67.0%.

The proportion of lanthanum in the mixed oxide is between 1.0% and 10.0%, more particularly between 3.0% and 10.0%. This ratio may be between 3.0% and 7.0%.

The mixed oxide may further comprise at least one rare earth element (RE) other than cerium and other than lanthanum. The rare earth element may be selected from the group consisting of yttrium and elements of the periodic table having an atomic number between 57 and 71 (inclusive). More particularly, the one or more rare earth elements may be selected from the group consisting of Nd, Y, and Pr. More particularly, Y and Pr are preferable. The mixed oxide may contain one or two rare earth elements other than cerium and other than lanthanum. The total proportion of the one or more rare earth elements other than cerium and other than lanthanum is up to 10.0%, more particularly up to 7.0%.

According to one embodiment, if the mixed oxide does not contain any rare earth elements other than cerium and lanthanum, the proportion of lanthanum is at least 5.0%. According to another embodiment, if the mixed oxide comprises at least one rare earth element other than cerium and lanthanum, the total proportion of lanthanum and one or more rare earth elements other than cerium and lanthanum in the mixed oxide is at least 5.0%. According to another embodiment, if the mixed oxide comprises at least one rare earth element other than cerium and other than lanthanum, the total proportion of lanthanum and one or more rare earth elements other than cerium and other than lanthanum in the mixed oxide is at most 15.0%, more particularly at most 12.0%.

Zirconia is the remainder of the composition. The proportion by weight of zirconium is the remainder to 100% of the other elements (Ce, La, RE, Hf) as mixed oxides. The proportion of zirconium in the mixed oxide is at least 10.0%, more particularly at least 20.0%, more particularly at least 25.0% (excluding this value). This proportion may be at most 81.0%, more particularly at most 79.0%, more particularly at most 60.0%.

The mixed oxides of the invention are also characterized by a high specific surface area. The specific surface area (BET) of the mixed oxide after calcination in air at 1100 ℃ for 4 hours is at least 28m²A/g, more particularly at least 30m²A/g, even more particularly at least 31m²(ii) in terms of/g. The specific surface area (BET) is generally at most 40m²G, more particularly up to 35m²(ii) in terms of/g. The specific surface area (BET) may be at 28m²G and 40m²Between/g, more particularly at 28m²G and 35m²Between/g, more particularly 30m²G and 35m²Between/g.

The mixed oxides may also exhibit at least 50m after calcination in air at 1000 ℃ for 4 hours²A/g, more particularly at least 55m²Specific surface area (BET) in g. The specific surface area (BET) may be in the range of 50m²G and 70m²Between/g, more particularly at 55m²G and 60m²Between/g.

The mixed oxides may also exhibit at least 60m after calcination in air at 900 ℃ for 4 hours²A/g, more particularly at least 65m²Specific surface area (BET) in g. The specific surface area (BET) may be in the range of 60m²G and 90m²Between/g, more particularly 65m²G and 80m²Between/g.

The term "specific surface area (BET)" is understood to mean the BET specific surface area determined by nitrogen adsorption. Specific surface areas are well known to the skilled person and are measured according to the Brunauer-Emmett-Teller method. The theory of The process was initially described in The Journal of The American Chemical Society, 60,309 (1938). More detailed information on the theory can also be found in chapter 4 of "Powder surface area and porosity", 2 nd edition, ISBN 978-94-015-. The nitrogen adsorption process is disclosed in standard ASTM D3663-03 (re-approved in 2008).

In practice, the specific surface area (BET) can be determined automatically according to the manufacturer's guidelines (guidelines of the construction) using the device Flowsorb II 2300 of Mimmeritics or the device Tristar 3000. They can also be measured automatically according to the manufacturer's guidelines with a Macsorb Analyzer model I-1220 from Maultech corporation (Mountech). Prior to the measurement, the sample is degassed by heating at a temperature of up to 300 ℃ optionally under vacuum to remove adsorbed volatile species. More specific conditions can be found in the examples.

The mixed oxides are also characterized by a specific porosity in the range of 70-500nm pores after calcination in air at 1100 ℃ for 4 hours. In fact, mixed oxides are characterized by a high pore volume in this range. Thus, it is possible to determine on the porosity curve, for the mixed oxide after calcination at 1100 ℃ for 4 hours in air, the peak with the highest intensity in the range of pores with a size below 500nm, corresponding to a pore size D between 70nm (excluding this value) and 500nm, more particularly between 100nm and 500nm, even more particularly between 100nm and 400nm or between 100nm and 370nm or between 120nm and 370nm_{p，1100℃/4h}。

Furthermore, the mixed oxide exhibits, after calcination at 1100 ℃ for 4 hours in air, a total pore volume (V) of pores having a size lower than 500nm of at least 0.30mL/g, more particularly at least 0.40mL/g, even more particularly at least 0.50mL/g, even more particularly at least 0.60mL/g_{500nm，1100℃/4h})。V_{500nm，1100℃/4h}May be between 0.30mL/g and 0.70mL/g, more particularly between 0.40mL/g and 0.70mL/g, even more particularly between 0.50mL/g and 0.70mL/g or between 0.60mL/g and 0.70 mL/g. Furthermore, the mixed oxides may also be characterized by a value of less than 0.35, more particularly less than 0.30The ratio α, α is defined by the following formula:

α＝V_{70nm，1100℃/4h}/V_{500nm，1100℃/4h}

wherein V_{70nm，1100℃/4h}Is the total pore volume of pores having a size below 70nm after calcination in air at 1100 ℃ for 4 hours.

According to one embodiment, the porosity curve of the mixed oxide does not show any peaks in the range of pores having a size below 70nm after calcination in air at 1100 ℃ for 4 hours.

The mixed oxide may exhibit a total pore volume of at least 0.60mL/g, more particularly at least 0.90mL/g, even more particularly at least 1.00mL/g, or at least 1.50mL/g, after calcination in air at 1100 ℃ for 4 hours. This total pore volume may be between 0.60mL/g and 1.90mL/g, more particularly between 0.90mL/g and 1.90mL/g, even more particularly between 1.00mL/g and 1.90mL/g or between 1.50mL/g and 1.90 mL/g.

Similar parameters can also be determined after calcination at 900 ℃ for 4 hours in air. In fact, after calcination at 900 ℃ for 4 hours in air, the porosity curve of the mixed oxide shows a peak with the highest intensity in the range of pores with a size below 500nm, for which the maximum corresponds to a pore size D between 35nm and 75nm_{p，900℃/4h}. Furthermore, the mixed oxide exhibits a total pore volume (V) of pores having a size below 500nm of at least 0.50mL/g, more particularly at least 0.70mL/g, after calcination in air at 900 ℃ for 4 hours_{500nm，900℃/4h})。V_{500nm，900℃/4h}Can be between 0.50mL/g and 1.00mL/g, more particularly between 0.70mL/g and 1.00 mL/g.

Parameters of porosity (e.g. D)_{p，1100℃/4h}、V_{500nm，1100℃/4h}、V_{70nm，1100℃/4h}、D_{p，900℃/4h}And V_{500nm，900℃/4h}) The determination is carried out by mercury intrusion after calcination of the mixed oxide in air at 1100 ℃ for 4 hours or at 900 ℃ for 4 hours. Mercury porosimetry is a well-known technique used in the field of porous catalysts and involves the use of a strictly controlled pressureMercury is gradually pressed into the pores of the porous structure. Porosity is measured by mercury intrusion according to techniques well known in the art. The porosimeter comprises a powder penetrometer. The method is based on the determination of the pore volume as a function of the pore size (V ═ f (d), V denotes the pore volume and d denotes the pore size). From these data, the pore volume can be calculated and curve (C) obtained, giving the derivative dV/dlogD.

Porosity can be determined according to standard ASTM D4284-83 ("standard method for determining pore volume distribution of catalysts by mercury porosimetry"). Porosity can be determined by the method disclosed in the examples. Porosity can be determined using the apparatus Autopore IV 9500 from the company macmerrilek.

From curve (C), D can be determined_{p，1100℃/4h}And D_{p，900℃/4h}. For the sake of clarity:

·D_{p，1100℃/4h}: after calcination of the mixed oxide in air at 1100 ℃ for 4 hours, the porosity curve of the mixed oxide shows a peak with the highest intensity in the range of pores with a size below 500nm, for which the maximum corresponds to the pore size D_{p，1100℃/4h}；

·D_{p，900℃/4h}: after calcination of the mixed oxide in air at 900 ℃ for 4 hours, the porosity curve of the mixed oxide shows a peak with the highest intensity in the range of pores with a size below 500nm, for which the maximum corresponds to the pore size D_{p，900℃/4h}。

Porosity can be determined using a macrmericek V9620 automated mercury porosimeter according to manufacturer's guidelines.

The mixed oxides of the invention are in the form of particles exhibiting a d50 strictly above 2.5 μm. d50 (median) has the usual meaning used in statistics. d50 represents the particle size such that 50% of the particles are less than or equal to the size. d50 is determined from the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer. Typically, this distribution is obtained by the dispersion of the particles in water, optionally in the presence of a dispersant (sodium hexametaphosphate).

For example, d50 can be determined according to the following method. A laser particle size analyzer model LS13320 from Beckman Coulter, Beckman-Coulter, Inc. was used. Fraunhofer model (Fraunhofer mode) may be used following the manufacturer's guidelines. This distribution is obtained by the dispersion of the particles in water in the presence of a dispersant (sodium hexametaphosphate). A relative refractive index of 1.6 was used.

Typically, d50 is between 2.5 μm (excluding this value) and 20.0 μm, more particularly between 2.5 μm (excluding this value) and 10.0 μm, even more particularly between 2.5 μm (excluding this value) and 7.0 μm.

The specific mixed oxides according to the invention exhibit the following characteristics:

-at least 30m after calcination in air at 1100 ℃ for 4 hours²Specific surface area per gram (BET);

a peak with the highest intensity in the range of pores with a size below 500nm, corresponding to a pore size D between 100 and 400nm or between 100 and 370nm or between 120 and 370nm_{p，1100℃/4h}；

-a total pore volume V of at least 0.50mL/g of pores having a size below 500nm_{500nm，1100℃/4h}；

-a total pore volume of at least 1.00mL/g after calcination in air at 1100 ℃ for 4 hours.

This specific surface area may also exhibit a ratio α lower than 0.35, more particularly lower than 0.30.

With regard to the use of the mixed oxides according to the invention, this is in the field of motor vehicle pollution control catalysis. The mixed oxides according to the invention can be used for the production of catalytic converters, the function of which is to treat motor vehicle exhaust gases. The catalytic converter comprises at least one catalytically active coating prepared from mixed oxides and deposited on a solid support. The coating functions to convert certain pollutants in the exhaust gas, particularly carbon monoxide, unburned hydrocarbons and nitrogen oxides, into environmentally less harmful products by chemical reaction. The chemical reaction involved may be the following:

2CO+O₂→2CO₂

2NO+2CO→N₂+2CO₂

4C_xH_y+(4x+y)O₂→4x CO₂+2y H₂O

the solid support may be a metallic monolith, such as a Fe-Cr alloy, or made of ceramic. The ceramic may be cordierite, silicon carbide, aluminum titanate, or mullite. A commonly used solid support consists of a generally cylindrical monolith comprising a large number of small parallel channels with porous walls. This type of carrier is usually made of cordierite and exhibits a compromise between a high specific surface and a limited pressure drop.

A coating, commonly referred to as a "washcoat", is deposited on the surface of the solid support. The coating is formed from a catalytic composition comprising a mixed oxide mixed with at least one mineral material. The mineral material may be selected from the group consisting of: alumina, titania, ceria, zirconia, silica, spinel, zeolites, silicates, crystalline silicoaluminophosphates and crystalline aluminophosphates. The composition may also contain other additives specific to each formulator: h₂S scavenger, organic or inorganic modifier with coating promoting effect, colloidal alumina, etc. Thus, the coating comprises such a composition. Alumina is a commonly used mineral material, it being possible for this alumina to be optionally doped with, for example, an alkaline earth metal, such as barium. The coating further comprises at least one dispersed Platinum Group Metal (PGM), more particularly selected from the group consisting of Pt, Rh or Pd. The amount of PGM is generally between 1g and 400g, in ft, with respect to the volume of the monolith³And (4) showing. The noble metal has catalytic activity.

The catalytic composition thus comprises:

(i) at least one mineral material; and

(ii) at least one dispersed platinum group metal; and

(iii) the mixed oxides of the present invention.

One method of dispersing PGM and preparing a catalyst comprises mixing an aqueous solution of a salt of PGM with an aqueous dispersion of a mixed oxide or a mineral material or a mixture formed of a mixed oxide and a mineral material; the mixture is dried to remove some or all of the water and the resulting solid is calcined in air. The salt may be, for example, a chloride or nitrate salt of PGM, such as rhodium nitrate. The water is removed from the dispersion in order to deposit the PGM, the solid is dried and calcined in air at a temperature generally between 300 ℃ and 800 ℃. An example of preparing a catalyst can be found in example 1 of US 7,374,729.

The coating is obtained by applying the dispersion to a solid support. Thus, the coating exhibits catalytic activity and can act as a pollution control catalyst. Pollution control catalysts may be used to treat exhaust gases from internal combustion engines. For this reason, the invention also relates to a method for treating exhaust gases from an internal combustion engine, characterized in that a catalytic converter is used which comprises a coating, as described above.

A particular advantage of the mixed oxides of the invention is that the PGM is well and uniformly dispersed on the surface of the catalyst.

Process for preparing the mixed oxides according to the invention

The mixed oxide of the present invention can be prepared by the following method comprising the steps of:

(a) heating an aqueous acidic dispersion S at a temperature between 100 ℃ and 180 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, wherein the dispersion S comprises:

(i) having at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio;

(ii) lanthanum nitrate;

(iii) optionally at least one nitrate of a rare earth element (RE) other than cerium and other than lanthanum; and

(iv) particles of zirconium oxyhydroxide, wherein the powder of zirconium oxyhydroxide used to prepare the dispersion exhibits an average size d50 between 5.0 μm and 100.0 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer;

the dispersion isS is characterized by a molar ratio H between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr；

(b) Adding an ammonia solution to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0;

(c) then adding the organic structuring agent to the mixture obtained at the end of step (b), stirring the mixture with a high shear rate mixer;

(d) the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air.

In step (a), heating an aqueous dispersion S at a temperature of at least 100 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, the aqueous dispersion comprising (i) Ce with at least 90.0 mol-%^IV/Ce^IV+Ce^III(ii) lanthanum nitrate, (iii) optionally at least one salt of a rare earth element (RE) other than cerium and lanthanum, and (iv) particles of zirconium oxyhydroxide in a molar ratio.

The invention also relates to a method for producing a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth element (RE) other than cerium and lanthanum, having the following composition:

■ between 18.0% and 70.0% by weight cerium;

■ between 1.0% and 10.0% by weight lanthanum;

■ up to 10.0% by weight of one or more rare earth elements (RE) other than cerium and other than lanthanum;

■ the remainder being zirconium;

the mixed oxide is in the form of particles exhibiting a d50 strictly higher than 2.5 μm, and the proportions of the elements (Ce, La, RE, Zr) are given relative to the mixed oxide as a whole by weight of oxide,

the method comprises the following steps:

(a) heating an aqueous acidic dispersion S at a temperature between 100 ℃ and 180 ℃ so as to obtain a dispersion comprising a liquid medium and a precipitate, wherein the dispersion S comprises:

(i) having at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio;

(ii) lanthanum nitrate;

(iii) optionally at least one nitrate of a rare earth element (RE) other than cerium and other than lanthanum; and

(iv) particles of zirconium oxyhydroxide, wherein the powder of zirconium oxyhydroxide used to prepare the dispersion exhibits an average size d50 between 5.0 μm and 100.0 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm, d50 corresponding to the median of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer;

the dispersion is characterized by a molar ratio H of between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr；

(b) Adding an ammonia solution to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0;

(c) then adding the organic structuring agent to the mixture obtained at the end of step (b), stirring the mixture with a high shear rate mixer;

(d) the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air.

The term "dispersion" as used in this application denotes a system in which solid particles are dispersed in a continuous liquid medium. The solid particles typically exhibit a size (volume distribution) below 500 μm as determined by a laser diffraction particle size analyzer.

The aqueous dispersion S comprises at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIICerium nitrate in a molar ratio. The molar ratio may be between 90.0% and 99.9%, more particularly between 94.0% and 99.9%.

The cerium nitrate used for preparing the aqueous dispersion S may result from dissolving a cerium compound (such as cerium hydroxide) with nitric acid. It is advantageous to use cerium salts having a purity of at least 99.5%, more particularly at least 99.9%. The cerium salt solution may be an aqueous cerium nitrate solution. The solution being prepared by reacting nitric acid with hydrated cerium oxideObtained by reacting a solution of a cerium salt with an aqueous ammonia solution in the presence of an aqueous hydrogen peroxide solution to react Ce^IIIConversion of cations to Ce^IVCationic and conventionally prepared. It is also particularly advantageous to use a cerium nitrate solution obtained according to the electrolytic oxidation process of a cerium nitrate solution disclosed in FR 2570087. The cerium nitrate solution obtained according to the teaching of FR2570087 may exhibit an acidity of about 0.6N.

The aqueous dispersion S also contains dispersed particles of zirconium oxyhydroxide. The zirconium oxyhydroxide can generally be represented by the formula ZrO (OH)₂And (4) showing. The powder used for preparing dispersion S is characterized by an average size d50 of between 5.0 μm and 100 μm, more particularly between 5.0 μm and 50.0 μm, even more particularly between 25.0 μm and 40.0 μm or between 28.0 μm and 30.0 μm. d50 corresponds to the median value of the size distribution (by volume) of the particles obtained with a laser diffraction particle size analyzer, such as HORIBA LA-920. The zirconium oxyhydroxide is represented by ZrO₂The oxide content of wt% is typically between 35% and 55%. Preferably, aqueous dispersion S comprises TZH-40 dispersed particles commercialized by yao corporation (teiio corporation). This product had the following characteristics: ZrO (ZrO)₂+HfO₂>40% min, d50 ═ between 27.0 μm and 32.0 μm. More details about this product can be found here:http://www.terio.cn/product/detail/11。

the acidic aqueous dispersion S generally exhibits a total concentration Ce of between 1.0g/L and 60.0g/L^III+Ce^IVExpressed as cerium oxide. For example, a cerium nitrate concentration of 112.50g/L corresponds to a CeO concentration of 50.0g/L₂。

The aqueous dispersion S also comprises lanthanum nitrate and optionally at least one nitrate of a rare earth element (RE) other than cerium and lanthanum. The nitrate of RE may be, for example, praseodymium nitrate, neodymium nitrate or yttrium nitrate (Y (NO)₃)₃)。

The aqueous dispersion S needs to be acidic. Characterized by a molar ratio H between 1.0 and 3.5, more particularly between 1.5 and 3.0⁺/Zr。H⁺Is generally between 0.05 and 1.40mol/L, more particularly between 0.30 and 0.80mBetween ol/L. H in the dispersion⁺The amount of (B) is determined by the H from the solution of the raw material used (like cerium nitrate)⁺And H added by controlled addition of nitric acid⁺The amount of the control. H⁺And hence the molar ratio H⁺the/Zr is determined by mass balance (as for example in example 1). The nitric acid added may be, for example, a 60 wt% nitric acid solution.

The aqueous dispersion S thus contains dispersed particles of Zr oxyhydroxide, Ce^IVOptionally Ce^III、H⁺、NO₃ ^-、La³⁺And optionally RE³⁺. It can be prepared by mixing the appropriate amount of Zr oxyhydroxide with a nitrate solution of the elements of the mixed oxide and by controlled addition of HNO₃Adjusting acidity to obtain. An example of an aqueous dispersion S is disclosed in example 1.

In step (a), the aqueous dispersion S is heated at a temperature between 100 ℃ and 180 ℃, more particularly between 120 ℃ and 150 ℃, to obtain a dispersion comprising a liquid medium and a precipitate. Either a sealed container or an open container may be used. In particular, an autoclave reactor may be preferably used. The duration of the heat treatment is generally between 30 minutes and 10 hours, preferably between 2 hours and 5 hours. The conditions of example 1 (135 ℃ C.; 4h) can be used.

In step (b), an aqueous ammonia solution is added to the mixture obtained at the end of step (a) until the pH of the mixture is at least 8.0. The pH of the mixture may be between 8.0 and 10.0, more particularly between 8.0 and 9.0. Aqueous ammonia solutions with concentrations between 10 and 14mol/L can be conveniently used.

Step (c) is carried out by means of a high shear rate mixer. In practice, in step (c), the organic structuring agent (or "templating agent") is added to the mixture obtained at the end of step (b), and the mixture is mixed with a high shear rate mixer.

The skilled artisan can select a high shear rate mixer from the mixers disclosed in chapter 8 of Handbook of Industrial Mixing, 2004, Science and Practice, John Wiley & Sons, Inc., ISBN 0-471 & 26919-0.

The high shear mixer may be a rotor-stator high shear mixer. This type of mixer comprises a rotor (or impeller) and a fixed part called stator. The distance between the rotor and the stator is typically small and the speed of the rotor is high, so that when the rotor rotates, high shear and turbulent energy is generated in the gap between the rotor and the stator. The fluid within the short distance of the mixer is thus subjected to high shear rates and turbulent energy. An example of such a high shear mixer may be, for example, the ultra-turrax stirrer T18, commercially available from IKA, equipped with dispersing elements S18N-19G (diameter of rotor: 12.7 mm; diameter of rotor: 19 mm; gap between rotor and stator: 0.4 mm). An example of such a dispersive element is shown in figure 1.

The high shear rate mixer may also be a mixer that also includes a rotor and a stator and that operates in a slightly different manner than previous mixers. Rotation of the rotor creates suction, causing fluid to be drawn up the center of the working head. The centrifugal force then drives the fluid towards the periphery of the working head, where it undergoes an abrasive action in the gap between the rotor and the stator. It is also subjected to high shear as the fluid is forced out through the perforations present in the stator. The fluid is thus expelled from the head and ejected radially at high velocity. At the same time, some new fluid is continuously sucked into the working head. Examples of such high shear rate mixers may be, for example, L5M-A or EX-60, both commercially available from Silverson and both equipped with square hole high shear screens^TM(stator). This stator is known to provide a particularly high shear rate, which is desirable for rapid size reduction of soluble and insoluble particulate solids. It is also suitable for the preparation of emulsions and fine colloidal suspensions.

The tip speed T of the mixer should preferably be between 5.0m/s and 25.0m/s, more particularly between 7.0m/s and 20.0 m/s. T can be calculated by: t (m/s) ═ D pi R/60, where

-D is the diameter of the rotor (m); and is

-R is the rotation rate (rpm) of the rotor.

The tip speed is thus the peripheral speed of the rotor.

The duration of step (c) may be between 5min and 120min, more particularly between 10min and 60min, even more particularly between 30min and 40 min.

Step (b) may be carried out with a high shear rate mixer at high shear rate. The same high shear rate mixer may be used for optional step (b) and step (c). The same conditions may apply to optional step (b): the same high shear rate and/or the same speed T and/or the same duration. Step (b) can also be carried out using a classical mixer at low shear rates (see example 6).

Organic structurant means an organic compound (such as a surfactant) capable of altering the porous structure of the mixed oxide, especially for pores below 500nm in size. The texturizing agent may be added in the form of a solution or dispersion. The amount of organic structuring agent, expressed as a percentage by weight of additive with respect to the weight of mixed oxide obtained after the calcination step, is generally between 5% and 100% and more particularly between 15% and 60%.

The organic structuring agent (or "templating agent") is preferably selected from the group consisting of: (i) anionic surfactants, (ii) nonionic surfactants, (iii) polyethylene glycols, (iv) monobasic acids and their salts with hydrocarbon chains (hydro carbon tails) containing between 7 and 25, more particularly between 7 and 17 carbon atoms, and (v) surfactants of the carboxymethylated fatty alcohol ethoxylate type.

As anionic type surfactants, mention may be made of ethoxy carboxylates, ethoxylated fatty acids, sarcosinates, phosphate esters, sulfates such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, and sulfonates such as sulfosuccinates, and alkyl benzene or alkyl naphthalene sulfonates. As nonionic surfactants, mention may be made of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide/propylene oxide copolymers, sorbitan derivativesEthylene glycol, propylene glycol, glycerol, polyglycerol esters and ethoxylated derivatives thereof, alkylamines, alkylimidazolines, ethoxylated oils and alkylphenol ethoxylates. Mention may in particular be made of the trade marksAndthe product for sale.

The organic structuring acid may also be a monocarboxylic acid having a hydrocarbon chain comprising between 7 and 25, more particularly between 7 and 17 carbon atoms. More particularly mention may be made of compounds of formula C_nH_2n+1Saturated acids of COOH, wherein n is an integer between 7 and 25, more particularly between 7 and 17. More particularly the following acids may be used: caproic acid, caprylic acid, capric acid, lauric acid, myristic acid and palmitic acid. More particularly, lauric acid and ammonium laurate may also be mentioned.

Finally, it is also possible to use surfactants selected from those of the carboxymethylated fatty alcohol ethoxylate type. The expression "carboxymethylated fatty alcohol ethoxylate type product" is intended to mean a product consisting of a polymer comprising-CH at the end of the chain₂-fatty alcohols ethoxylated or propoxylated of COOH groups. These products may correspond to the following formula:

R₁-O-(CR₂R₃-CR₄R₅-O)_n-CH₂-COOH

wherein R is₁Represents a saturated or unsaturated carbon-based chain, generally of length up to 22 carbon atoms, preferably at least 12 carbon atoms; r₂、R₃、R₄And R₅May be the same and may represent hydrogen, or R₂May represent an alkyl group such as CH₃Radical and R₃、R₄And R₅Represents hydrogen; n is a non-zero integer that may be up to 50 and more particularly between 5 and 15, inclusive. It will be noted that the surfactant may be derived from a product having the above formula (wherein R is₁May be saturated or unsaturated, respectively) or alternatively comprises-CH₂-CH₂-O-and-C (CH)₃)＝CH₂A mixture of products of both-O-groups.

In step (d), the solid material obtained at the end of step (c) is separated from the liquid medium and calcined in air. The isolation can be carried out by conventional means known to the skilled worker. A Nutsche (Nutsche) filter may be conveniently used.

Prior to calcination, the solid material may optionally be washed with an aqueous solution, preferably with water at basic pH (e.g. aqueous ammonia solution) (see comparative example 3). Further, the solid material may optionally be dried to a suitable degree prior to calcination.

The temperature of the calcination may be between 500 ℃ and 1000 ℃. The temperature can be chosen as desired, depending on the desired values of specific surface area and bulk density. The duration of the calcination may be appropriately determined according to the temperature, and may preferably be between 1 hour and 20 hours. The calcination may preferably be carried out at a temperature comprised between 600 ℃ and 950 ℃. The calcination conditions of example 1(700 ℃ C.; 4 hours) or example 3(740 ℃ C.; 3 hours) can be used.

Step (d) may be followed by step (e) wherein the calcined product is milled. This enables powders with a defined particle size to be obtained. This step (e) can be carried out, for example, with a hammer mill. Despite step (d), d50 is strictly higher than 2.5 μm.

The invention also relates to a mixed oxide obtainable by the process disclosed above.

[ examples ]

The following examples illustrate the invention.

Particle size

D50 was determined using a laser particle size analyzer model LS13320 from Beckmann Coulter. The fraunhofer model was used following the manufacturer's guidelines. This distribution is obtained by the dispersion of the particles in water in the presence of a dispersant (sodium hexametaphosphate). A relative refractive index of 1.6 was used.

Specific surface area (BET)

The specific surface area was automatically determined on Macsorb Analyzer model I-1220 from Geniteng. Prior to any measurement, the sample was carefully degassed to desorb the volatile adsorbed species. For this purpose, the sample can be heated in an oven at 200 ℃ for 2 hours and then in the chamber of the apparatus at 300 ℃ for 15 minutes.

Hg porosimetry

Parameters of porosity were determined by mercury porosimetry. Following the manufacturer's recommendations, an Autopore IV 9500 from the company macmerrilek was used. The BJH method using Harkins and Jura isotherms was used.

In examples 1-9 and in comparative examples 4-6, the sources of zirconium were TZH-40, a Zr-based material commercialized by yao corporation:

-average particle size d50 ═ 28.9 μm or 29.8 μm;

-％ZrO₂43.2 wt% or 43.7 wt%.

For the mixed oxides described below, the proportions of the constituent elements are given by weight of the oxide relative to the mixed oxide as a whole.

Example 1: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

An aqueous acidic dispersion S was prepared by mixing:

cerium nitrate solution ([ CeO ]₂]258 g/L; the density is 1.442 kg/L; at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIIMolar ratio) corresponding to 20g of CeO₂；

-TZH-40 powder (average particle size 28.9 μm;% ZrO;)₂43.2% (in ZrO)₂Expressed)), corresponding to 25g of ZrO₂；

Lanthanum nitrate solution ([ La)₂O₃]388.6 g/L; density 1.612kg/L), corresponding to 2.5g of La₂O₃；

Yttrium nitrate solution ([ Y ]₂O₃]197.1 g/L; density 1.376kg/L), corresponding to 2.5g of Y₂O₃；

55.9g of a 60 wt% nitric acid solution (13.14 mol/L; density 1.38).

Molar ratio H of the dispersion⁺the/Zr is therefore equal to 2.9. This ratio is calculated based on:

h from cerium nitrate⁺: 0.05mol (determined by acid-base titration);

h from 60 wt% nitric acid solution⁺：0.53mol；

Zr from zirconium oxyhydroxide: 0.20 mol.

The dispersion was prepared in a reactor equipped with an inclined blade stirring rotor and adjusted to a total amount of 1L by adding deionized water. Dispersion S was heated at 135 ℃, maintained at this temperature for 4 hours, and allowed to cool to obtain a yellow slurry.

Stirring of the slurry was started using a homogenizer (ULTRA-TURRAX S18N-19G, IKA) at a tip speed T of 13.3m/S (D: 12.7 mm; R: 20,000 rpm). During mixing, an aqueous ammonia solution (13.5mol/L) was introduced into the slurry until a pH of 8.3 was obtained, then after 10 minutes 12.5g of lauric acid was added and the high shear rate mixing was maintained for 30 minutes.

The thus obtained alkaline slurry was subjected to solid-liquid separation by a nuta filter, and washed with an aqueous ammonia solution to obtain a cake. The cake was calcined in air at 700 ℃ for 4 hours to obtain a mixed oxide.

Example 2: preparation of a blend based on cerium oxide (50%), zirconium oxide (40%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 1 except that;

-CeO₂the amount of (A) is 25g instead of 20 g;

-ZrO₂the amount of (A) is 20g instead of 25 g;

h from cerium nitrate⁺：0.06mol；

The amount of 60 wt% nitric acid is 37.9g instead of 55.9g,so that dispersion S exhibits a molar ratio H⁺/Zr＝2.6。

Example 3: preparation of a blend based on cerium oxide (20%), zirconium oxide (70%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 1 except that;

-CeO₂the amount of (A) is 10g instead of 20 g;

-ZrO₂the amount of (a) is 35g instead of 25 g;

h from cerium nitrate⁺：0.02mol；

The amount of 60% nitric acid was 78.2g instead of 55.9g (so that the molar ratio H was⁺The Zr content was 2.7).

Example 4: preparation of a blend based on cerium oxide (65%), zirconium oxide (25%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 1 except that;

-CeO₂the amount of (a) is 32.5g instead of 20 g;

-ZrO₂the amount of (A) is 12.5g instead of 25 g;

h from cerium nitrate⁺：0.08mol；

The amount of 60% nitric acid is 23.9g instead of 55.9g, so that dispersion S exhibits a molar ratio H⁺/Zr＝3.0。

Example 5: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 1, except that stirring of the slurry after heating at 135 ℃ was performed at a tip speed T of 16.2m/s using a high shear mixer (L5M-a, Silverson corporation).

Example 6: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide powder was prepared in the same manner as in example 1, except that for step (b), aqueous ammonia (13.5mol/L) was introduced into the slurry with stirring using an inclined blade stirring rotor at a stirring speed of 500rpm (tip speed T ═ 0.6 m/s). Step (c) was then carried out with homogenizer ULTRA-TURRAX at a tip speed T of 13.3 m/s.

Example 7: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

An aqueous acidic dispersion S was prepared by mixing:

cerium nitrate solution ([ CeO ]₂]261 g/L; the density is 1.445 kg/L; at least 90.0 mol% Ce^IV/Ce^IV+Ce^IIIMolar ratio) corresponding to 4kg of CeO₂；

-TZH-40 powder (average particle size 29.8 μm;% ZrO;)₂43.7% (in ZrO)₂Expressed)), corresponding to 5.0kg of ZrO₂；

Lanthanum nitrate solution ([ La)₂O₃]470.0 g/L; density 1.715kg/L), corresponding to 0.5kg of La₂O₃；

Yttrium nitrate solution ([ Y ]₂O₃]218.2 g/L; density 1.416kg/L), corresponding to Y of 0.5kg₂O₃；

6.1kg of a 60 wt% nitric acid solution (13.14 mol/L; density 1.38).

Molar ratio H of the dispersion⁺The value of/Zr is 1.7. The dispersion was prepared by mixing in a reactor equipped with an inclined blade stirring rotor and adjusted to a total amount of 200L with deionized water.

Dispersion S was heated to 120 ℃, maintained at this temperature for 2 hours, and allowed to cool to obtain a yellow slurry. Stirring of the slurry was started using a high shear mixer (EX60, Silverson) at a tip speed T of 18.5 m/s. During stirring, aqueous ammonia (13.5mol/L) was introduced into the slurry to reach pH 8.9, then after 5 minutes, 2.5kg of lauric acid was added, and stirring was maintained for 17 minutes.

The thus obtained alkaline slurry was subjected to solid-liquid separation by pressure filtration and washed with an aqueous ammonia solution to obtain a cake. The cake was calcined at 740 ℃ for 3 hours and lightly ground to obtain a mixed oxide in powder form.

Example 8: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 7, except that:

the amount of-60% nitric acid is 10.3kg instead of 6.1kg, so that the dispersion S is characterized by a molar ratio H⁺/Zr＝2.7；

The heating temperature is 133 ℃ instead of 120 ℃.

Example 9: preparation of a blend based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) (see above) Oxide complex

A mixed oxide was prepared in the same manner as in example 8, except that the stirring times after addition of ammonia water and after addition of lauric acid were 10 minutes and 30 minutes, respectively, instead of 5 minutes and 17 minutes.

Comparative example 1: following WO 07131901 preparation of a cerium oxide (40%), zirconium oxide based coating Mixed oxide of (50%), lanthanum oxide (5%) and yttrium oxide (5%) (iii)

Adding cerium nitrate solution ([ CeO ]₂]259 g/L; 1.439kg/L of density, at least 90.0% of Ce^IV/Ce^IV+Ce^IIIMolar ratio) corresponding to 6.0kg of CeO₂(ii) a Zirconyl nitrate solution ([ ZrO ] O)₂]266 g/L; density 1.408kg/L), corresponding to 7.5kg of ZrO₂(ii) a Lanthanum nitrate solution ([ La)₂O₃]472.5 g/L; density 1.711kg/L), corresponding to 0.75kg of La₂O₃(ii) a And yttrium nitrate solution ([ Y ]₂O₃]208.5 g/L; density 1.391kg/L), corresponding to Y of 0.75kg₂O₃Mixing in a tank equipped with an inclined blade stirring rotor, andand adjusted to a total amount of 125L with deionized water, followed by stirring to prepare a homogeneous cotitrate (co-nitrate) solution.

An aqueous ammonia solution (40L, 12mol/L) was introduced into a reactor equipped with an inclined blade stirring rotor and the volume was then made up with distilled water, so as to obtain a total volume of 125L and a stoichiometric excess of 40% aqueous ammonia with respect to the cations to be precipitated.

The previously prepared co-nitrate solution was introduced into the reactor within 1 hour with stirring at a speed of 90rpm (tip speed T ═ 1.8 m/s).

The slurry obtained was heated to 135 ℃, maintained at this temperature for 4 hours, and allowed to cool. 5.0kg of lauric acid was added to the dispersion thus obtained, and the dispersion was kept stirring for 1 hour. The dispersion was subjected to solid-liquid separation by pressure filtration, and washed with an aqueous ammonia solution to obtain a cake. The cake was calcined at 750 ℃ for 3 hours to obtain a composite oxide powder.

Comparative example 2: following WO 2011/138255 preparation of a cerium oxide (40%), zirconium oxide based coating Mixed oxide of (50%), lanthanum oxide (5%) and yttrium oxide (5%) (iii)

Two nitrate solutions were prepared in advance, one consisting of cerium nitrate and zirconium nitrate, and the other consisting of lanthanum nitrate and yttrium nitrate. Adding cerium nitrate solution ([ CeO ]₂]259 g/L; 1.439kg/L of density, at least 90.0% of Ce^IV/Ce^IV+Ce^IIIMolar ratio) corresponding to 6.0kg of CeO₂(ii) a And zirconyl nitrate solution ([ ZrO ] O)₂]266 g/L; density 1.408kg/L), corresponding to 7.5kg of ZrO₂Mixed in a first tank equipped with an inclined blade stirring rotor and adjusted to a total amount of 106L with deionized water, followed by stirring to prepare a homogeneous CeZr co-nitrate solution.

Lanthanum nitrate solution ([ La ] is added₂O₃]472.5 g/L; density 1.711kg/L), corresponding to 0.75kg of La₂O₃(ii) a And yttrium nitrate solution ([ Y ]₂O₃]208.5 g/L; density 1.391kg/L), corresponding toAt 0.75kg of Y₂O₃Mixed in a second tank equipped with an inclined blade stirring rotor and adjusted to a total amount of 19L with deionized water, followed by stirring to prepare a homogeneous LaY co-nitrate solution.

An aqueous ammonia solution (40L, 12mol/L) was introduced into a reactor equipped with an inclined blade stirring rotor and the volume was then made up with distilled water, so as to obtain a total volume of 125L and a stoichiometric excess of 40% aqueous ammonia with respect to the cations to be precipitated.

The first CeZr co-nitrate solution was introduced into the reactor within 50 minutes with stirring at a speed of 115 rpm. After 10 minutes, the second LaY co-nitrate solution was introduced into the reactor with stirring at a speed of 85rpm for 10 minutes. Heating, introduction of lauric acid, solid-liquid separation, washing and calcination were carried out following the same procedure as in comparative example 1, except that the calcination temperature was 840 ℃.

Comparative example 3: following WO 2017/187085 preparation of a cerium oxide (30%), zirconium oxide based coating Mixed oxide of (60%), lanthanum oxide (5%) and yttrium oxide (5%) (iii)

8.5L of zirconyl nitrate solution ([ ZrO ] O) was introduced into a tank containing 95.4L of deionized water₂]266 g/L; density 1.408kg/L and 7.0L of cerium nitrate solution ([ CeO)₂]259 g/L; density 1.439kg/L) to prepare a precursor solution. 10.8L of water, 0.53L of lanthanum nitrate solution ([ La ] were also used₂O₃]472.5 g/L; density 1.711kg/L and 1.2L yttrium nitrate solution ([ Y)₂O₃]208.5 g/L; density 1.391kg/L) to prepare an aqueous solution of lanthanum nitrate and yttrium nitrate.

In a 250L large reactor equipped with a mixing device, ammonia solution (12L, 12mol/L) and deionized water were introduced in order to obtain a total volume of 125L of alkaline solution.

The cerium nitrate and zirconium nitrate solutions were then introduced into a stirred reactor containing an ammonia solution at a mixing speed of 200rpm over a period of 45 min. The lanthanum nitrate and yttrium nitrate solutions were then introduced into the stirred reactor at a mixing speed of 25rpm over a period of 15 min.

The obtained dispersion was poured into a stirred autoclave and the dispersion was heated to 150 ℃ for 2 h. After cooling to a temperature below 60 ℃, 1.65kg of lauric acid was added. The dispersion was maintained under stirring for 1h and then filtered and washed with aqueous ammonia (pH 9.5; 250L). The cake obtained was then calcined in air at 825 ℃ for 3 h.

Comparative example 4: preparation based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) Mixed oxide of

A mixed oxide was prepared in the same manner as in example 1, except that 60% nitric acid was not added, so that the aqueous acidic dispersion S exhibited a molar ratio H⁺0.23% Zr (H from cerium nitrate)⁺: 0.047 mol; zr from zirconium oxyhydroxide: 0.203 mol). As can be seen, D_{p，1100℃/4h}Only 56 nm.

Comparative example 5: preparation based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) Mixed oxide of

A mixed oxide was prepared in the same manner as in example 1, except that 83.0g of 60% nitric acid was added so that the aqueous acidic dispersion S exhibited a molar ratio H⁺and/Zr is 4.1. As can be seen, D_{p，1100℃/4h}Only 20 nm.

Comparative example 6: preparation based on cerium oxide (40%), zirconium oxide (50%), lanthanum oxide (5%) and yttrium oxide (5%) Mixed oxide of

This mixed oxide was prepared in the same manner as in example 7, except that stirring of the slurry was performed using an inclined blade stirring rotor at a stirring speed of 92rpm (tip speed T ═ 2.4m/s) instead of the high shear rate mixer. As can be seen, D_{p，1100℃/4h}Only 28 nm.