Mixed oxides based on aluminum and zirconium

Abstract

The present invention relates to a mixed oxide of aluminium, of zirconium, of cerium, of lanthanum and optionally of at least one rare earth metal other than cerium and lanthanum, which makes it possible to restore a catalyst that retains good thermal stability and good catalytic activity after severe ageing. The present invention also relates to a process for the preparation of this mixed oxide and also to a process for treating exhaust gases from an internal combustion engine using a catalyst prepared from this mixed oxide. This mixed oxide has the following three properties (i), (ii) and (iii): (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100); - (ii)Δ * is less than 55.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h × 100); - (iii)S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g) At least one of the following is shown.

Description

[Technical field]

[0001] This application claims priority to European Patent Application No. 21306679.8, filed December 1, 2021, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a mixed oxide of aluminum, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and other than lanthanum, which makes it possible to prepare a catalyst which retains a particular porosity, good thermal stability and good catalytic activity after intensive ageing. The present invention also relates to a process for the preparation of this mixed oxide and also to a process for the treatment of exhaust gases from an internal combustion engine using a catalyst prepared from this mixed oxide. [Background technology]

[0003] technical challenges A catalytic converter is generally provided in an exhaust system for exhaust gas that connects a vehicle engine and a muffler to purify the exhaust gas. The engine is configured to purify the exhaust gas by removing CO, NO, and the like. x In order to convert such harmful substances into environmentally acceptable substances, the exhaust gas is converted from CO to CO2 and from NO to CO3. x The catalyst is passed through a catalytic converter so that the carbon dioxide is converted to N2 and O2 and unburned hydrocarbons are burned. In the catalytic converter, a catalyst layer in which a precious metal catalyst such as Rh, Pd or Pt is supported on a support is formed on the cell wall surface of the substrate. Examples of supports for supporting precious metal catalysts include mixed oxides based on cerium and zirconium. The support is also called a cocatalyst and is used to remove CO, NO, x Cerium is an essential component of three-way catalysts that simultaneously remove harmful components from exhaust gases, such as cerium oxide and unburned hydrocarbons. Cerium is important because its oxidation number changes depending on the partial pressure of oxygen in the exhaust gas. CeO2 has the ability to adsorb and desorb oxygen, as well as store oxygen (the so-called OSC ability).

[0004] Rh is used to remove NO from exhaust gases. x It is known to be an efficient precious metal to reduce its content. 0 It is better to use DeNO x Provides activity, so Rh III In traditional three-way catalysts where cerium-zirconium mixed oxides are used as promoters and supports for precious metals, the desorption of oxygen from CeO2 results in the formation of Rh. 0 Rh III The presence of cerium oxide is x are known to be detrimental to activity.

[0005] Zirconia is Rh 0 It is known to be a good support for rhodium because it helps to stabilize and disperse DeNO x To maintain activity for a long period of time, better thermal stability of the catalyst is required.

[0006] Therefore, the harsh conditions encountered in catalytic converters (high temperatures and CO, O2 and NO x Remain thermally stable in the presence of aggressive gases such as x There is a need for a support for catalytic activity, especially for rhodium, that has a specific porosity for good mass transport, allowing efficient catalytic activity of rhodium for a long period of time. The mixed oxide should withstand temperatures as high as 1100° C. or 1200° C.

[0007] In particular, the structure of the mixed oxide must survive thermal stresses to prevent the catalytically active precious metals (especially Rh) from being encapsulated due to sintering effects, and therefore the changes in the porosity and in the specific surface area of ​​the mixed oxide must be limited or minimized.

[0008] The mixed oxide of the present invention aims to solve these problems.

[0009] For the continuity of the description, it is specified that the ranges of values ​​given, such as with respect to expressions such as "at most" and "at least", include the boundary values, unless otherwise indicated. Furthermore, weight percentages correspond to percentages expressed by weight. It is also specified that, unless otherwise indicated, firing is carried out in air.

[0010] EP 3085667 discloses zirconia-based bodies that exhibit a P / W ratio (where P represents the height of the peak and W represents the width of the peak) of 0.03 or more after heat treatment for 12 hours at 1000° C. The P / W ratio of the disclosed products is between 0.01 and 0.11, which corresponds to a high W / P ratio of 9-100.

[0011] EP 3345870 discloses a zirconia powder containing 2-6 mole % yttria, which may also contain an aluminium oxide content of less than 2.0%.

[0012] US Patent No. 9,902,654 B2 discloses ZrO2-Al2O3 ceramics. A ceramic with the specific composition 80 wt% (97 mol% ZrO2-3 mol% Y2O3)-20 wt% Al2O3 is shown, which corresponds to 75.6 wt% ZrO2.

[0013] WO 2019 / 122692 discloses an aluminum hydrate H which is used for the preparation of cerium-containing mixed oxides which are different from the mixed oxides of the present invention.

[0014] None of the cited documents discloses a mixed oxide as in claim 1. Summary of the Invention [Means for solving the problem]

[0015] The mixed oxides of the present invention are mixed oxides of Al, Zr, La and optionally at least one rare earth metal (denoted REM) other than cerium and other than lanthanum.

[0016] The mixed oxide of the invention is disclosed in claims 1 to 48. It is therefore a mixed oxide of aluminium, of zirconium, of lanthanum and optionally of at least one rare earth metal other than cerium and other than lanthanum (denoted REM), in which the weight proportions of these elements are as follows: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0 to 10.0% by weight of rare earth metals other than cerium and lanthanum (provided that, where the mixed oxide contains two or more rare earth metals other than cerium and lanthanum, this percentage applies to each of these rare earth metals); 50.0% to 70.0% by weight of zirconium and These percentages are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of the mixed oxide is at least 25.0 m after calcination at 1100 °C in air for 5 hours. 2 / g; and the porosity of the mixed oxides measured by N2 porosimetry after calcination at 950 °C for 3 h in air. In the domains of pores having a size of less than 100 nm, the porograms of the mixed oxide have a diameter D p,950℃ / 3h indicates a peak located at; · Ratio V <40nm,950℃ / 3h / V total,950℃ / 3h is 0.80 or more; V total,950℃ / 3h is 0.35ml / g or more It is like; V <40nm,950℃ / 3h , V total,950℃ / 3h represent the pore volume for pores with a size less than 40 nm and the total pore volume of the mixed oxide after calcination at 950° C. in air for 3 hours, respectively. Characterized by; The mixed oxide furthermore has the following three properties (i), (ii) and (iii): (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100); - (ii)Δ * is less than 55.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h × 100); - (iii)S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g) (Here, S 950℃ / 3h , S 1100℃ / 5h and S 1200℃ / 5h represent the BET specific surface area for the mixed oxides after calcination in air at 950°C for 3 hours, 1100°C for 5 hours, and 1200°C for 5 hours, respectively). characterized by one or more of It is a mixed oxide.

[0017] The present invention also relates to a method according to claims 49 to 51, to the use of a mixed oxide according to any one of claims 52 to 53, to a composition according to claims 54 to 55 and to a catalytic converter according to claim 56. It also relates to the use of an aluminium hydrate as defined below and as specified in claims 57 to 61 for the preparation of a mixed oxide. All these subjects will now be more clearly defined below.

[0018] To the extent that the disclosures of any patents, patent applications, and publications incorporated herein by reference conflict with the statements of this application to the extent that a term may be unclear, this statement shall control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Regarding the composition of the mixed oxide of the invention, the latter is a mixed oxide of aluminum, of zirconium, of lanthanum and optionally of at least one rare earth metal other than cerium and other than lanthanum (denoted REM), the proportions by weight of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0 to 10.0% by weight of non-cerium and non-lanthanum rare earth metals (provided that, if the mixed oxide contains two or more non-cerium and non-lanthanum rare earth metals, this percentage applies to each of these rare earth metals); 50.0% to 70.0% by weight of zirconium It is.

[0020] REM is understood to mean elements other than Ce and other than La selected from among the elements in the group of elements of the periodic table of yttrium and of the elements with atomic numbers from 57 to 71 (inclusive).

[0021] In mixed oxides, the abovementioned elements Al, La, REM (if any) and Zr are generally present in the form of oxides. A mixed oxide can therefore be defined as a mixture of oxides. However, it is not excluded that these elements can be present at least partially in the form of hydroxides or oxyhydroxides. The proportions of these elements can be measured in the laboratory using conventional analytical techniques, in particular plasma torch and X-ray fluorescence. As is customary in the field of mixed oxides, the proportions of these elements are indicated by the weight of the equivalent amount of oxide relative to the total weight of the mixed oxide.

[0022] The mixed oxide contains the elements mentioned above in the indicated proportions, but it may also contain other elements, for example impurities. In this connection, it must be noted that the mixed oxide does not contain cerium or cerium oxide or, if cerium is detectable, it is only in the form of an impurity.

[0023] The impurities generally originate from the starting materials or reactants used. The total proportion of impurities expressed by weight relative to the total weight of the mixed oxide is generally less than 2.0% by weight, or even less than 1.0% by weight. The proportion of cerium expressed by weight of oxide CeO2 relative to the total weight of the mixed oxide is generally less than 1.0% by weight, or even less than 0.5% by weight, or less than 0.2% by weight, or less than 0.05% by weight.

[0024] The mixed oxide may also contain hafnium, which is generally present in association with zirconium in natural ores. The ratio of hafnium to zirconium depends on the ore from which it is extracted. Thus, the Zr / Hf weight ratio in some ores may be about 50 / 1. Thus, for example, baddeleyite contains approximately 98% zirconium oxide to 2% hafnium oxide. Like zirconium, hafnium is generally present in the form of oxide. However, it is not excluded that it may be present at least partially in hydroxide or oxyhydroxide form. The weight percentage of hafnium in the mixed oxide, expressed as the amount of oxide converted to the total weight of the mixed oxide, is not more than 2.0%. The percentage of hafnium may be between 0 and 2.0% by weight. The percentage of impurities and of hafnium may be measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0025] The proportions of the constituent elements Al, La, REM, Zr and sometimes Hf are given as the weight of the oxide. For the calculation of these proportions, zirconium oxide is in the form of ZrO2, hafnium oxide is in the form of HfO2, aluminum is in the form of Al2O3 and the proportions are given in the form Pr6O 11 With the exception of praseodymium and terbium, the proportions of which are expressed in the form Tb4O7, the oxides of the rare earth metals are considered to be in the form REM2O3. As an example, a mixed oxide with only one REM having the following proportions by weight, expressed as equivalent oxide amounts, 30% Al, 60% Zr, 5% La and 5% Y corresponds to 30% Al2O3, 60% ZrO2, 5% La2O3 and 5% Y2O3.

[0026] In the mixed oxide according to the invention, the abovementioned elements are intimately mixed, which distinguishes the present mixed oxide from a simple mechanical mixture of oxides in solid form, which is obtained by the precipitation step of the mixed oxide preparation process.

[0027] The weight proportion of aluminum is 20.0% to 45.0% by weight, more particularly 25.0% to 40.0% by weight, and even more particularly 25.0% to 35.0% by weight.

[0028] The weight proportion of lanthanum is between 1.0% and 15.0% by weight, more particularly between 1.0% and 10.0% by weight, even more particularly between 1.0% and 7.0% by weight, or even between 2.0% and 7.0% by weight.

[0029] The mixed oxide may also contain one or more REMs. The REMs may be selected, for example, from the group consisting of yttrium, neodymium, praseodymium or combinations thereof. The mixed oxide may, for example, contain only a single REM in a proportion of 0 to 10.0% by weight. The proportion of REMs may be 1.0% to 10.0% by weight, even more particularly 1.0% to 7.0% by weight or even 2.0% to 7.0% by weight.

[0030] The mixed oxide may also contain two or more REMs, in which case the disclosed proportions then apply to each REM, again with the total proportion of these REMs preferably remaining below 25.0% by weight, more particularly below 20.0% by weight.

[0031] More particularly, REM or one of REM is Y.

[0032] The mixed oxide also contains zirconium. The weight proportion of zirconium may be between 50.0% and 70.0% by weight, more particularly between 55.0% and 65.0% by weight.

[0033] The specific mixed oxide C has the following composition: 25.0% to 35.0% by weight of aluminum; 1.0% to 7.0% by weight of lanthanum; 1.0% to 7.0% by weight of at least one REM; 55.0% to 65.0% by weight of zirconium has.

[0034] The proportion of lanthanum may also be 2.0% to 7.0% by weight, more particularly 3.0% to 7.0% by weight. The proportion of REM may also be 2.0% to 7.0% by weight, more particularly 3.0% to 7.0% by weight.

[0035] For the mixed oxides according to the invention, and more particularly for mixed oxide C, the total proportion of zirconium and of aluminium is preferably greater than or equal to 80.0% by weight, more particularly greater than or equal to 85.0% by weight.

[0036] Mixed oxide characterization Surface Area and Properties (i), (ii), (iii) The mixed oxides according to the invention exhibit a high specific surface area, which is understood to mean the Brunauer-Emmett-Teller (BET) specific surface area obtained by nitrogen adsorption using the well-known BET method.

[0037] The BET method is described, inter alia, in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". It is possible to comply with the recommendations of the standard ASTM D3663-03. In the following of this specification, the abbreviation S T(℃) / x(h) is used to represent the specific surface area of ​​a composition, obtained by the BET method, after calcination of the composition at a temperature T, expressed in °C, for a period of x hours. For example, S 1100℃ / 5h represents the BET specific surface area of ​​the composition after calcination at 1100° C. for 5 hours.

[0038] To measure the specific surface area by nitrogen adsorption the following equipment may be used, following the manufacturer's guidelines: Flowsorb II 2300 or Tristar 3000 from Micromeritics. They may also be measured automatically using a Macsorb analyzer model I-1220 from Mountech, following the manufacturer's guidelines. Prior to the measurement, the samples are preferably degassed by heating under vacuum and at a temperature of at most 300° C. to remove adsorbed volatile species.

[0039] Specific surface area S 1100℃ / 5h is at least 25.0m 2 / g. This specific surface area is preferably at least 30.0 m 2 / g, more preferably at least 32.0m 2 / g, more preferably at least 35.0m 2 / g, and even more preferably 40.0m 2 The specific surface area may be 30.0 to 50.0 m / g. 2 / g, more particularly 32.0~50.0m 2 / g, more particularly 35.0 to 50.0 m 2 / g, more particularly 40.0~50.0m 2 / g. The specific surface area can be at most 50.0 m 2 / g, more particularly at most 45.0m 2 / g.

[0040] Specific surface area S 950℃ / 3h is at least 40m 2 / g, more preferably at least 50m 2 / g, more preferably at least 60m 2 / g. This specific surface area is at most 90 m 2 / g, more particularly at most 85m 2 / g, or a maximum of 80m 2 / g. The specific surface area may be 40 to 90 m 2 / g or 50~85m 2 / g or 60~80m 2 / g.

[0041] Mixed oxides also have three properties: (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100); - (ii)Δ * is less than 55.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h × 100); - (iii)S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g) It is characterized by exhibiting at least one of the following:

[0042] Property (i): Small change in specific surface area at 950℃~1200℃ Under characteristic (i), the change in specific surface area, Δ, is less than 82.0% (Δ is expressed by the following formula; Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100). Δ is preferably less than 80.0%. Δ is usually 60.0% to 82.0% or 60.0% to 80.0%.

[0043] Property (ii): Small change in specific surface area at 950℃~1100℃ Similarly, under characteristic (i), the change in specific surface area Δ * is less than 50.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h × 100). Δ * is usually 5.0% to 50.0%.

[0044] Property (iii): High specific surface area after sintering at 1200°C for 5 hours Under characteristic (iii), the specific surface area S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g). This specific surface area is 16.0 m 2 / g. It is generally between 15.0 (the excluded value) and 25.0 m 2 / g or 15.0 (rejected value) to 20.0m 2 / g.

[0045] The mixed oxide may exhibit property (i) or (ii) or (iii). It may also exhibit a combination of properties (i) and (ii); or (i) and (iii); or (ii) and (iii). It may also exhibit a combination of properties (i), (ii) and (iii). All three properties demonstrate the very good heat resistance of the mixed oxide.

[0046] Nitrogen Porosimetry The mixed oxide is also characterized by a specific porosity that allows good mass transport and good dispersion of the precious metals. In the context of the present invention, the specific porosity is exhibited for the mixed oxide after calcination at 950° C. in air for 3 hours.

[0047] The porosity data disclosed in this application were obtained by the nitrogen porosimetry technique. With this technique it is possible to clearly define the pore volume (V) as a function of the pore diameter (D). More precisely, from the nitrogen porosity data it is possible to obtain a curve (C) which represents the derivative (dV / dlogD) of the function V as a function of log D. The derivative curve (C) is p From these data, the following characteristics regarding the porosity of the mixed oxides can be observed: Total pore volume (V) in ml / g obtained from the porosimetry data as read on the cumulative curve total represented by); Pore ​​volume (V) in ml / g expressed by pores whose size is less than or equal to 40 nm obtained from the porosimetry data as read on the cumulative curve <40nm(represented by It is also possible to obtain

[0048] When these parameters are measured after calcining the mixed oxide in air at 950 °C for 3 h, they are D p,950℃ / 3h , V total,950℃ / 3h and V <40nm,950℃ / 3h It is expressed as:

[0049] Nitrogen porosimetry technique is a well-known technique and is most often applied to inorganic materials. Porosity can be obtained with a Tristar II 3000 device manufactured by Micromeritics. The conditions for measuring porosity can be as detailed in the examples. Nitrogen porosimetry technique can be carried out according to ASTM D4641-17.

[0050] The porogram of the mixed oxide after calcination at 950 °C for 3 h in air shows that in the domains of pores with sizes less than 100 nm, diameters D of 15 to 35 nm are observed. p,950℃ / 3h The peak located at D p,950℃ / 3h The thickness may be 15 to 30 nm. p,950℃ / 3h Alternatively, it may be 20 to 30 nm.

[0051] The porogram may show two or more peaks within the domain of pores having a size less than 100 nm, but with a diameter D p,950℃ / 3h Moreover, after calcination in air at 950° C. for 3 hours, there is generally only one peak in the domain of pores with a size less than 100 nm, said peak being located at a diameter D p,950℃ / 3h The invention therefore also relates to mixed oxides of aluminium, of zirconium, of lanthanum and optionally of at least one rare earth metal other than cerium and other than lanthanum (designated REM), the weight proportions of these elements being as follows: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0 to 10.0% by weight of rare earth metals other than cerium and lanthanum (provided that, where the mixed oxide contains two or more rare earth metals other than cerium and lanthanum, this percentage applies to each of these rare earth metals); 50.0% to 70.0% by weight of zirconium and These percentages are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of the mixed oxide is at least 25.0 m after calcination at 1100 °C in air for 5 hours. 2 / g; and the porosity of the mixed oxides measured by N2 porosimetry after calcination at 950 °C for 3 h in air. Within the domain of pores having a size of less than 100 nm, the porogram of the mixed oxide shows a single peak, which has a diameter D p,950℃ / 3h Located in; · Ratio V <40nm,950℃ / 3h / V total,950℃ / 3h is 0.80 or more; V total,950℃ / 3h is 0.35ml / g or more It is like; V <40nm,950℃ / 3h , V total,950℃ / 3h represent the pore volume for pores with a size less than 40 nm and the total pore volume of the mixed oxide after calcination at 950 °C in air for 3 h, respectively. Characterized by; Mixed oxides have three additional properties: (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100); - (ii)Δ * is less than 55.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h× 100); - (iii)S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g) (Here, S 950℃ / 3h , S 1100℃ / 5h and S 1200℃ / 5h represent the BET specific surface area for the mixed oxides after calcination in air at 950°C for 3 hours, 1100°C for 5 hours, and 1200°C for 5 hours, respectively). It is characterized by one or more of the following:

[0052] Ratio V <40nm,950℃ / 3h / V total,950℃ / 3h is greater than or equal to 0.80. This ratio may preferably be greater than or equal to 0.85 or even greater than or equal to 0.90.

[0053] V total,950℃ / 3h is also 0.35 ml / g or more. total,950℃ / 3h may be preferably 0.40 ml / g or more, even more preferably 0.45 ml / g or more. total,950℃ / 3h is generally less than 1.00 ml / g, more particularly less than 0.90 ml / g, or less than 0.80 ml / g.

[0054] In addition, the diameter D p,950℃ / 3h The width at half-peak of the peak located at is strictly more than 10 nm and less than 20 nm, showing that the method of the invention allows to fine-tune the porosity.

[0055] The mixed oxide is generally in powder form.

[0056] Crystallite Size The mixed oxide of the present invention comprises a crystalline phase based on zirconium oxide, said crystalline phase comprising zirconium oxide and which may also contain lanthanum and optionally rare earth metals other than cerium and other than lanthanum.

[0057] The average size of the crystallites of the zirconium oxide based crystalline phase is strictly greater than 10 nm, this size being measured after calcination of the mixed oxide in air at 950° C. for 3 hours. This average size is usually less than 25 nm, or even less than 20 nm.

[0058] Mixed oxides in air: - after calcination at 1100°C for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is at most 30 nm, preferably at most 28 nm, even more preferably at most 25 nm; and / or after calcination at 1200° C. for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is at most 45 nm, preferably at most 40 nm, even more preferably at most 38 nm; It is characterized by the fact that

[0059] After calcination at 1100°C for 5 hours, the average size is at most 28 nm. After calcination at 1100°C for 5 hours, the average size is at most 25 nm. After sintering at 1200°C for 5 hours, the average size is at most 40 nm. After sintering at 1200°C for 5 hours, the average size is at most 38 nm.

[0060] Zirconium oxide based crystalline phases are generally characterized by peaks located at 2θ angles between 29.0° and 31.0° (radiation source: CuKα1, λ=1.5406 Å).

[0061] The crystalline phase generally exhibits a tetragonal structure, which can be characterized by X-ray diffraction or by Raman spectroscopy. When X-ray diffraction is used, the tetragonal structure is preferably identified after calcining the mixed oxide in air at a temperature of 950° C. for 3 hours.

[0062] The average size of the crystallites is measured by X-ray diffraction. It corresponds to the size of the coherent domains calculated from the width of the diffraction line 2θ from 29.0° to 31.0° taking into account the instrumental line broadening and using the Scherrer equation. According to the Scherrer equation, t is given by formula (I): t=kλ / ((β-s)cosθ) (I) (t: average crystallite size; k: shape factor equal to 0.9; λ (lambda): wavelength of the incident beam (λ=1.5406 angstroms); β: line broadening measured at half maximum intensity; s: instrument line spread; θ: Bragg angle) is given by s depends on the instrument used and on the 2θ (theta) angle. It is measured using LaB6 as a reference material and is recorded according to the same experimental conditions as for the measurement of the diffractograms of the mixed oxides.

[0063] All that has been disclosed above remains applicable to mixed oxides consisting essentially of or consisting of combinations of oxides of aluminum, of zirconium, of lanthanum, optionally of at least one rare earth metal other than cerium and other than lanthanum (denoted REM), and optionally of hafnium, the weight proportions of these elements being as follows: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0 to 10.0% by weight of rare earth metals other than cerium and lanthanum (provided that, where the mixed oxide contains two or more rare earth metals other than cerium and lanthanum, this percentage applies to each of these rare earth metals); Hafnium in a proportion not exceeding 2.0% by weight; 50.0% to 70.0% by weight of zirconium and These percentages are expressed as the amount of oxide equivalent based on the total weight of the mixed oxides, After calcination in air at 1100°C for 5 hours, the specific surface area (BET) of the mixed oxide is at least 25 m 2 / g; and the porosity of the mixed oxides measured by N2 porosimetry after calcination at 950 °C for 3 h in air. In the domains of pores having a size of less than 100 nm, the porograms of the mixed oxide have a diameter D p,950℃ / 3h Showing the peak located at; · Ratio V <40nm,950℃ / 3h / V total,950℃ / 3h is 0.80 or more; V total,950℃ / 3h is 0.35ml / g or more It is like; V <40nm,950℃ / 3h , V total,950℃ / 3h represent the pore volume for pores with a size less than 40 nm and the total pore volume of the mixed oxide after calcination at 950 °C in air for 3 h, respectively. It is characterized by: Mixed oxides furthermore have the following three properties (i), (ii) and (iii): (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S 950℃ / 3h -S 1200℃ / 5h ) / S 950℃ / 3h × 100); - (ii)Δ * is less than 55.0% (Δ * is expressed by the following formula: Δ * =(S 950℃ / 3h -S 1100℃ / 5h ) / S 950℃ / 3h × 100); - (iii)S 1200℃ / 5h is exactly 15.0m 2 / g (>15.0m 2 / g) (Here, S 950℃ / 3h , S 1100℃ / 5h and S 1200℃ / 5hrepresent the BET specific surface area for said mixed oxides after calcination in air at 950°C for 3 hours, 1100°C for 5 hours and 1200°C for 5 hours, respectively. It is characterized by one or more of the following:

[0064] Method for preparing mixed oxides For the preparation of the mixed oxide according to the invention, it comprises the following steps: (a0) preparing an acidic aqueous dispersion comprising nitric acid and precursors of oxides of zirconium, lanthanum and optionally rare earth metals other than cerium and lanthanum, in which aluminum hydrate is dispersed, and stirring the resulting dispersion for a duration strictly greater than 5 hours; (a1) a step in which an acidic aqueous dispersion is introduced into a stirred tank containing a basic aqueous solution; (a2) heating and stirring the dispersion obtained at the end of step (a1) at a temperature of at least 130°C; (a3) recovering the solids of the dispersion of step (a2) by solid / liquid separation and washing the cake with water; (a4) calcining the solid obtained at the end of step (a3) ​​in air at a temperature between 900°C and 1050°C; The method disclosed below may be followed, which includes:

[0065] This method does not include any step where a texturing agent such as lauric acid is added.

[0066] Process (a0) In step (a0), - precursors of oxides of zirconium, of lanthanum and optionally of one or more rare earth metals other than cerium and lanthanum; - Nitric acid; aluminium hydrates, such as aluminium monohydrate An aqueous acidic dispersion is prepared comprising: The aqueous acidic dispersion does not contain any precursors of cerium oxide.

[0067] The precursor of zirconium oxide may be zirconyl nitrate. For example, the zirconyl nitrate may be crystalline. The precursor of zirconium oxide may also be obtained by dissolving basic zirconium carbonate or zirconium oxyhydroxide with nitric acid. The acid attack is preferably performed with 1.4 to 2.3 NO3 - / Zr molar ratio. Thus, usable zirconium nitrate solutions resulting from carbonate attack can have a concentration, expressed as ZrO2, of 250 to 350 g / l. For example, the zirconyl nitrate solution used in Example 1 resulting from carbonate attack has a concentration of 295 g / l.

[0068] The precursor of lanthanum oxide may be lanthanum nitrate. The precursor of the oxide of rare earth metal other than cerium and other than lanthanum may be a nitrate or chloride. For example, it may be praseodymium nitrate, neodymium nitrate, yttrium chloride YCl3 or yttrium nitrate Y(NO3)3.

[0069] According to one embodiment, the precursors of the oxides of Zr, La and REM are all in the form of nitrates.

[0070] The aqueous acid dispersion also contains nitric acid. + The concentration of is advantageously between 0.04 and 3.0 mol / l, more particularly between 0.5 and 2.0 mol / l. + The amount of must be high enough to obtain a dispersion in which the aluminum hydrate particles are well dispersed.

[0071] The aqueous acidic dispersion also contains an aluminum hydrate, more particularly one based on boehmite and optionally also containing lanthanum. The aluminum hydrate, optionally containing La, is more preferably one having a specific porosity as described in WO 2019 / 122692 and hereinafter designated aluminum hydrate H. This specific aluminum hydrate H is well dispersible in an aqueous acidic medium. Of course, if the aluminum hydrate contains lanthanum, the amount of lanthanum present in the aluminum hydrate is taken into account for calculating the amount of precursor of lanthanum.

[0072] The aqueous acidic dispersion can be prepared by mixing the ingredients in any order of introduction. According to a preferred embodiment (as illustrated in Example 1), aluminum hydrate is introduced into an aqueous solution already containing other precursors.

[0073] The aqueous acidic dispersion is left under stirring for a duration strictly greater than 5 hours. The temperature at which the aqueous acidic dispersion is left under stirring is usually below 30° C. or even below 25° C.

[0074] On the aluminum hydrate H, which is preferentially used for the preparation of acidic aqueous dispersions This aluminium hydrate H is based on boehmite, optionally also containing lanthanum, and after calcination in air at a temperature of 900° C. for 2 hours, it has the following properties: VP20nm-N2, - 10% x VPT-N2 or more, more particularly 15% x VPT-N2 or more, or even 20% x VPT-N2 or more, or even 30% x VPT-N2 or more; - 60% × VPT-N2 or less pore volume in the domain of pores with a size of 20 nm or less (denoted as VP20nm-N2); the pore volume in the domain of pores having a size between 40 and 100 nm (expressed as VP40-100nm-N2), such that VP40-100nm-N2 is equal to or greater than 20% × VPT-N2, more particularly equal to or greater than 25% × VPT-N2, or even equal to or greater than 30% × VPT-N2; indicates; · VPT-N2 represents the total pore volume of aluminum hydrate after calcination in air at 900 °C for 2 h; Pore ​​volume is measured by nitrogen porosimetry technique It is characterized by:

[0075] In European nomenclature and as known, the term "boehmite" means gamma oxyhydroxide (γ-AlOOH). In the present application, the term "boehmite" means various aluminum hydrates with a specific crystal morphology known to the skilled artisan. Boehmite can therefore be characterized by X-ray diffraction. The term "boehmite" also encompasses "pseudoboehmites", which according to certain authors only resemble one particular variant of boehmite and simply have the broadening of the characteristic peaks of boehmite. Boehmite is identified by X-ray diffraction by its characteristic peaks. These are shown in the file JCPDS00-021-1307 (JCPDS = Joint Committee on Powder Diffraction Standards). The apex of the peak (020) is in particular: - crystallinity of boehmite; - boehmite crystallite size It will be noted that the angle may be between 13.0° and 15.0° depending on the application.

[0076] Reference may be made to Journal of Colloidal and Interface Science 2002, 253, 308-314 or to J. Mater. Chem. 1999, 9, 549-553, in which it is stated that for a certain number of boehmites, the position of the peak varies depending on the number of layers in the crystal or the size of the crystallites. This apex may be more particularly between 13.5° and 14.5°, or between 13.5° and 14.485°.

[0077] When the aluminum hydrate contains lanthanum, the proportion of lanthanum is 1.0% to 8.0% by weight, more particularly 3.0% to 8.0% by weight or 4.0% to 8.0% by weight. This proportion is given by the weight of La2O3 relative to the weight of Al2O3 and La2O3 (in other words, the proportion of La in weight % = weight of La2O3 / weight of La2O3 + Al2O3 x 100). In other words, this proportion also does not take into account the amount of hydrate contained in the aluminum hydrate. Of course, to target a specific amount of La in the final mixed oxide, the amount of La in the aluminum hydrate H is taken into account. Lanthanum is generally present in the aluminum hydrate in the form of lanthanum oxide.

[0078] A convenient way to measure the proportion of La in the aluminum hydrate is to calcinate the aluminum hydrate in air and to attack the calcined product with, for example, a concentrated nitric acid solution in order to dissolve the elements in solution, and to measure the proportions of Al and La by analyzing the solution subsequently by techniques known to those skilled in the art, for example ICP. Calcination also makes it possible to measure the loss on ignition (LOI) of the hydrate. The LOI of the aluminum hydrate may be between 20.0 and 30.0%.

[0079] The boehmite contained in the aluminum hydrate, more particularly in the aluminum hydrate H, may have an average crystallite size of at most 6.0 nm, or even at most 4.0 nm, more particularly still at most 3.0 nm. The average crystallite size corresponds to the size of the coherent domains measured by X-ray diffraction and calculated from the full width at half maximum of the line (020).

[0080] The aluminum hydrate H may be in the form of a mixture of boehmite and X-ray invisible phases, especially amorphous phases, distinguishable as described above by X-ray diffraction methods. The aluminum hydrate H may have a % of crystalline phase (boehmite) of less than 60%, more especially less than 50%. This % may be between 40% and 55%, or between 45% and 55%, or between 45% and 50%. This % is determined by methods known to those skilled in the art. It is possible to determine this % using the following formula: % crystallinity = intensity of peak (120) / intensity of peak (120) of standard x 100, where the intensity of peak (120) of the aluminum hydrate is compared with the intensity of peak (120) of the standard. The standard used in this application is the product corresponding to Example B1 of US Patent Application Publication No. 2013 / 017947. The measured intensity corresponds to the surface area of ​​peak (120) above the baseline. These intensities are determined in the diffractogram relative to a baseline acquired over the 2θ angle range of 5.0° to 90.0°. The baseline is determined automatically using software for analyzing the data of the diffractogram.

[0081] The aluminum hydrate H has a particular porosity such that, after calcination in air at 900° C. for 2 hours, it has a pore volume (expressed as VP20nm-N2) in the domain of pores having a size of 20 nm or less, such that VP20nm-N2 is equal to or greater than 20%×VPT-N2, more particularly equal to or greater than 25%×VPT-N2, or even equal to or greater than 30%×VPT-N2. Moreover, VP20nm-N2 is equal to or less than 60%×VPT-N2.

[0082] Furthermore, after calcination at 900° C. for 2 hours in air, aluminum hydrate H has a pore volume (expressed as VP40-100nm-N2) in the domain of pores having a size between 40 and 100 nm, such that VP40-100nm-N2 is equal to or greater than 15%×VPT-N2, more particularly equal to or greater than 20%×VPT-N2, or even equal to or greater than 25%×VPT-N2, or even equal to or greater than 30%×VPT-N2. Furthermore, VP40-100nm-N2 may be equal to or less than 65%×VPT-N2.

[0083] After calcination in air at 900° C. for 2 hours, the aluminum hydrate H may have a total pore volume (VPT-N2) of 0.65-1.20 ml / g, more particularly 0.70-1.15 ml / g, or 0.70-1.10 ml / g. It will be noted that the pore volume thus measured is mainly represented by pores whose diameter is less than or equal to 100 nm.

[0084] Aluminum hydrate H is at least 200m 2 / g, more particularly at least 250m 2 The specific surface area may be 200 to 400 m 2 Further, after calcination in air at 900° C. for 2 hours, the aluminum hydrate H may have a molecular weight of at least 130 m 2 / g, more particularly at least 150m 2 The specific surface area may be 130 to 220 m / g. 2 After calcination in air at 940° C. for 2 hours, followed by calcination in air at 1100° C. for 3 hours, the aluminum hydrate H may have a molecular weight of at least 80 m 2 / g, more particularly at least 100m 2 The specific surface area may be 80 to 120 m / g. 2 / g.

[0085] Aluminum hydrate H can be prepared by the following steps: (a) Into a stirred tank containing an aqueous solution of nitric acid An aqueous solution containing aluminum sulfate, lanthanum nitrate and nitric acid (A); Sodium aluminate solution (B) during step (a) the aqueous solution (A) is continuously introduced and the rate of introduction of solution (B) is adjusted so that the average pH of the reaction mixture is equal to a target value between 4.0 and 6.0, more particularly between 4.5 and 5.5; (b) when the entire aqueous solution (A) has been introduced, aqueous solution (B) continues to be introduced until a target pH of 8.0 to 10.5, preferably 9.0 to 10.0, is reached; (c) then filtering the reaction mixture and washing the recovered solid with water; (d) the solid obtained from step (c) is then dried to obtain aluminum hydrate H. The method may be obtained by a method comprising:

[0086] More details on how to obtain aluminum hydrate H are also provided in the examples of WO 2019 / 122692. Aluminum hydrate H disclosed in Example 1 of this patent application can be used.

[0087] Process (a1) The aqueous acidic dispersion is introduced into a stirred tank containing an aqueous basic solution to obtain a precipitate (so-called "reverse" precipitation). The basic compound dissolved in the aqueous basic solution may be a hydroxide, for example an alkali metal or alkaline earth metal hydroxide. Secondary, tertiary or quaternary amines as well as ammonia may be used. As in the examples described below, an aqueous ammonia solution may be used. As in the examples, an aqueous ammonia solution may be used, for example with a concentration of 3 to 5 mol / l.

[0088] The amount of base must be in excess of the amount of cations present in the aqueous acidic dispersion. This excess ensures complete precipitation of the cations. A molar ratio of base / Σ cations x valences from precursors + H from nitric acid of greater than 1.2, more particularly greater than 1.4. + may be used, where the ratio takes into account the valence of the cations from the precursor (e.g., 2 for Zr, 3 for La).

[0089] Process (a2) The dispersion obtained at the end of step (a1) is heated and stirred at a temperature that is at least 130° C. The temperature may be between 130° C. and 200° C., more particularly between 130° C. and 170° C. The duration of step (a2) is generally between 10 minutes and 5 hours, more particularly between 1 hour and 3 hours. For example, the dispersion may be heated to 150° C. and maintained at this temperature for 2 hours.

[0090] Under the above temperature conditions, step (a2) can be conveniently carried out in a closed vessel. Thus, by way of example, the pressure in the closed vessel is 1 bar (10 5 Pa) Super~165bar(1.65×10 7 Pa), preferably 5 bar (5 × 10 5 Pa) ~ 165 bar (1.65 × 10 7 It can be defined as being variable in increments of 10 Pa.

[0091] Process (a3) The solids of the dispersion of step (a2) are recovered by solid / liquid separation and the cake is washed with water. It is convenient to use a dilute ammonia solution to wash the cake. A vacuum filter, a centrifuge or a filter press, for example of the Nutsche type, can for example be used.

[0092] Of course, the cake recovered at the end of step (a3) ​​may still contain some residual water, but this does not actually affect the quality of the mixed oxide. Nevertheless, the cake may be optionally dried to remove any residual water.

[0093] Process (a4) The solid obtained at the end of step (a3) ​​is calcined in air at a temperature between 900° C. and 1050° C. The temperature of calcination must be high enough to convert the solid into mixed oxides and to develop its crystallinity. The temperature must not be too high in order to maintain a high specific surface area. The duration of calcination may be between 30 min and 5 h, more particularly between 1 h and 4 h. The conditions of example 1 (950° C.; 3 h) may be applied.

[0094] The preparation of the mixed oxide according to the invention can be based on the conditions of Example 1 given below. The present invention also relates to the mixed oxide obtainable by the process just described above.

[0095] Use of mixed oxides As regards the use of the mixed oxides according to the invention, this falls within the field of automobile pollution control catalysis: the mixed oxides according to the invention can be used in the manufacture of catalytic converters, the role of which is to treat automobile exhaust gases.

[0096] Catalytic converters contain a catalytically active washcoat prepared from mixed oxides and deposited on a solid support. The role of the washcoat is to convert, by chemical reactions, certain pollutants in the exhaust gases, particularly carbon monoxide, unburned hydrocarbons and nitrogen oxides, into products that are less harmful to the environment. The chemical reactions involved are: 2CO+O2→2CO2 2NO+2CO→N2+2CO2 4C x H y +(4x+y)O2 → 4×CO2+2yH2O It is possible that.

[0097] The solid support may be a metal monolith, for example an FeCr alloy, or may be made of ceramic. The ceramic may be cordierite, silicon carbide, alumina titanate or mullite. A commonly used solid support consists of a monolith, generally cylindrical, containing a large number of small parallel channels with porous walls. This type of support is often made of cordierite and represents a compromise between a high specific surface area and a limited pressure drop.

[0098] The washcoat is deposited on the surface of the solid support. The washcoat is formed from a composition comprising the mixed oxide according to the invention and optionally at least one inorganic material. The inorganic material may be selected from alumina, boehmite or pseudoboehmite, titanium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline aluminum silicon phosphate or crystalline aluminum phosphate. Alumina is a commonly used inorganic material, which can be optionally doped with an alkaline earth metal, for example barium. According to one embodiment, the washcoat does not contain any cerium oxide ("cerium-free washcoat"). According to another embodiment, the washcoat does not contain any inorganic material other than the mixed oxide according to the invention.

[0099] The composition may also contain other additives specific to each author: H2S scavengers, organic or inorganic modifiers that serve to facilitate coating, colloidal alumina, etc. Thus, a washcoat includes such a composition. The washcoat also contains at least one dispersed precious metal. The precious metal may be selected from the group consisting of Pt, Rh, or Pd. Rh is a metal that is highly effective in reducing NO x The amount of precious metal is generally in the range of ft 3 Expressed in units, it ranges from 1 to 400 g relative to the volume of the monolith. Noble metals are catalytically active.

[0100] To disperse the precious metals, it is possible to add salts of the precious metals to the suspension made of the mixed oxide or of the inorganic material (if any) or of the mixture formed from the mixed oxide and from the inorganic material. The salts are, for example, chlorides or nitrates of the precious metals (e.g. Rh III The suspension may be a nitrate salt. To fix the precious metal, water is removed from the suspension, the solid is dried, and it is calcined in air at a temperature generally between 300 and 800°C. An example of a precious metal dispersion can be found in Example 1 of U.S. Pat. No. 7,374,729.

[0101] The washcoat is obtained by applying the suspension to a solid support. The washcoat thus exhibits catalytic activity and can function as an anti-pollution catalyst. The anti-pollution catalyst can be used to treat exhaust gases from internal combustion engines. The catalytic system and mixed oxide of the present invention finally suppresses NO 2 even in an oxidizing environment. x As a trap or NO x It can be used to promote the reduction of

[0102] For this reason, the present invention also relates to a method for the treatment of exhaust gases from an internal combustion engine, characterized in that a catalytic converter containing a washcoat is used, the washcoat being as described. EXAMPLES

[0103] BET specific surface area: The BET surface area is measured automatically on a Mountech Macsorb analyzer model I-1220. Prior to any measurement, the samples are carefully degassed to desorb volatile adsorbed species. To do so, the samples may be heated in the instrument cell under vacuum at 200° C. for 30 minutes.

[0104] The specific surface area after firing at 950°C, 1100°C or 1200°C was measured after placing the crucible containing the mixed oxide sample in an oven at the temperature of the test for the targeted period of time.

[0105] Nitrogen Porosity: A Tristar II 3000 instrument from Micromeritics was used. This instrument uses the principles of physical adsorption and capillary condensation to obtain information about the surface area and porosity of solid materials. The measurement of the nitrogen pore distribution is carried out using a pressure table with 85 points (42 points between 0.01 and 0.995 for adsorption and 43 points between 0.995 and 0.05 for desorption). The equilibration time for relative pressures between 0.01 and 0.995 (exclusive) is 5 seconds. The equilibration time for relative pressures above 0.995 is 600 seconds. The tolerances on the pressures are 5 mmHg for absolute pressures and 5% for relative pressures. The p0 values ​​are measured at regular intervals during the analysis (2 hours). The Barrett, Joyner and Halenda (BJH) method of the Harkins-Jura law is used to measure the mesoporosity. The analysis of the results is carried out on the desorption curves.

[0106] X-ray diffraction: X-ray diffraction was performed using a copper source (CuKα1, λ=1.5406 Å). The X-ray power was 40 kV / 40 mA. An Ultima IV from Rigaku Corporation was used. A 2θ angle step=0.010° ​​and a recording time of 2 seconds per step were used.

[0107] Aluminum Hydrate H(93.6% Al2O3-6.4% La2O3) The aluminum hydrate H used was prepared according to the teachings of WO 2019 / 122692. Characterization of aluminum hydrate H: - composition: 67.3% Al2O3-4.6% La2O3-LOI 28.1% (loss on ignition), which corresponds to 93.6% Al2O3-6.4% La2O3; - This powder is 344m 2 / g BET surface area. - Other characteristics:

[0108] [Table 1]

[0109] Example 1: Preparation of the mixed oxide Al2O3 (30 wt%)-ZrO2 (60 wt%)-La2O3 (5 wt%)-Y2O3 (5 wt%) A solution containing precursors of the oxides of Zr, La and Y was prepared by introducing 37.1 kg of zirconyl nitrate solution ([ZrO2] = 295 g / l; density = 1.461), 1.74 kg of lanthanum nitrate solution ([La2O3] = 321.1 g / l; density = 1.511), 4.02 kg of yttrium nitrate solution ([Y2O3] = 219.7 g / l; density = 1.414) and 16.9 kg of 60 wt.% nitric acid solution into a stirred tank. The volume was adjusted to a total of 85 L with deionized water. Then, 5.56 kg of aluminum hydrate H disclosed above, containing the equivalent amounts of 67.3 wt.% alumina (3.74 kg Al2O3) and 4.6 wt.% La2O3 (0.26 kg), were introduced into the solution obtained under stirring and the total volume of the mixture thus obtained was adjusted to 125 L with deionized water. The H in the aqueous acid dispersion thus prepared + The concentration of was 1.3 mol / l. The aqueous acidic dispersion was kept under stirring for 6 hours.

[0110] The aqueous acidic dispersion was then introduced in 60 minutes into a reactor containing 125 L of 4.5 mol / l ammonia solution at ambient temperature and stirred by a three-bladed spindle (225 rpm). At the end of the addition of the dispersion, the mixture was heated to a temperature of 150° C. and maintained at this temperature for 2 hours. The mixture was then cooled to a temperature below 50° C.

[0111] The medium is filtered through a press filter at a pressure of about 4 bar, and the cake is then washed with 20 L of deionized water. The cake is then compressed at a pressure of 19.5 bar for 10 minutes. The wet cake obtained is then introduced into an electric furnace. The product is calcined at 950°C for 3 hours. The recovered mixed oxide is then ground in a "Forplex" type blade mill.

[0112] Characteristics of the mixed oxide of Example 1 specific surface area S 950℃ / 3h =72m 2 / g; S 1100℃ / 5h =41.1m 2 / g; S 1200℃ / 5h =16.1m 2 / g; =>Δ=77.6%; =>Δ * =42.9%. XRD Crystallite size after calcination at 950℃ / 3h = 11nm; Crystallite size after calcination at 1100℃ / 5h = 25nm; Crystallite size after calcination at 1200℃ / 5h = 38nm. Porosity of mixed oxides after calcination at 950°C for 3 hours D p,950℃ / 3h = 26 nm; D p950℃ / 3h Width at half peak of peak at (nm) = 15 nm; V <40nm,950℃ / 3h / V total,950℃ / 3h = 0.90; V total,950℃ / 3h =0.59ml / g.

Claims

1. Mixed oxides of aluminum, of zirconium, of lanthanum and optionally of at least one rare earth metal (denoted REM) other than cerium and lanthanum, in which the weight proportions of these elements are as follows: 20.0% to 45.0% by weight, preferably 25.0% to 40.0% by weight, more preferably 25.0% to 35.0% by weight of aluminum; 1.0% to 15.0% by weight, preferably 1.0% to 10.0% by weight, more preferably 1.0% to 7.0% by weight, and most preferably 2.0% to 7.0% by weight of lanthanum; - 0-10.0% by weight, preferably 1.0-10.0% by weight, more preferably 1.0-7.0% by weight, most preferably 2.0-7.0% by weight of non-cerium and non-lanthanum rare earth metals (provided that in cases where the mixed oxide comprises two or more non-cerium and non-lanthanum rare earth metals, this percentage applies to each of these rare earth metals), preferably the total percentage of non-cerium and non-lanthanum rare earth metals is less than 25.0% by weight, more preferably less than 20.0% by weight; 50.0% to 70.0% by weight, preferably 55.0% to 65.0% by weight, of zirconium and These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, After calcination in air at 1100°C for 5 hours, the mixed oxide has a specific surface area (BET) of at least 25.0 m ２ / g; After calcination in air at 950°C for 3 hours, ２ The porosity of the mixed oxide as measured by porosimetry is the porogram of said mixed oxide is formed in the domains of pores having a size of less than 100 nm, with a diameter D between 15 and 30 nm; ｐ，９５０℃／３ｈ indicates a peak located at ・ Ratio V ＜４０ｎｍ，９５０℃／３ｈ / V ｔｏｔａｌ，９５０℃／３ｈ is 0.80 or more, preferably 0.85 or more, more preferably 0.90 or more; ・V ｔｏｔａｌ，９５０℃／３ｈ is 0.35 ml / g or more, preferably 0.40 ml / g or more, more preferably 0.45 ml / g or more It is like; V ＜４０ｎｍ，９５０℃／３ｈ , V ｔｏｔａｌ，９５０℃／３ｈ represent the pore volume for pores having a size of less than 40 nm and the total pore volume of the mixed oxide after calcination in air at 950° C. for 3 hours, respectively. characterized by: The mixed oxide further has the following three properties (i), (ii), and (iii): (i) Δ is less than 82.0% (Δ is determined by the following formula: Δ=(S ９５０℃／３ｈ -S １２００℃／５ｈ ) / S ９５０℃／３ｈ × 100); - (ii) Δ ＊ is less than 55.0% (Δ ＊ is expressed by the following formula: Δ ＊ = (S ９５０℃／３ｈ -S １１００℃／５ｈ ) / S ９５０℃／３ｈ × 100); - (iii) S １２００℃／５ｈ is exactly 15.0 m ２ / g or more (Here, S ９５０℃／３ｈ , S １１００℃／５ｈ and S １２００℃／５ｈ represent the BET specific surface area for said mixed oxide after calcination in air at 950°C for 3 hours, at 1100°C for 5 hours and at 1200°C for 5 hours, respectively. characterized by one or more of: mixed oxide.

2. After calcination in air at 950° C. for 3 hours, the porogram of the mixed oxide shows that the domains of pores with a size of less than 100 nm contain pores of diameter D ｐ，９５０℃／３ｈ 2. The mixed oxide according to claim 1, characterized in that it exhibits a single peak located at

3. 3. The mixed oxide according to claim 1, further comprising hafnium.

4. 4. The mixed oxide according to claim 1, wherein the average size of the crystallites of the crystalline phase based on zirconium oxide is strictly more than 10 nm and / or less than 25 nm or less than 20 nm, this size being measured after calcination of the mixed oxide in air at 950° C. for 3 hours.

5. In air: after calcination at 1100°C for 5 hours, the average size of the crystallites of the crystalline phase based on zirconium oxide is at most 30 nm, preferably at most 28 nm, even more preferably at most 25 nm; and / or after calcination at 1200°C for 5 hours, the average size of the crystallites of the crystalline phase based on zirconium oxide is at most 45 nm, preferably at most 40 nm, even more preferably at most 38 nm; The mixed oxide according to any one of claims 1 to 4.

6. The total proportion of aluminum and zirconium is 80.0 wt% to 45.0 wt%, preferably 85.0 wt% or more. The mixed oxide according to any one of claims 1 to 5.

7. 7. The mixed oxide according to claim 1, wherein when the mixed oxide contains two or more REMs, the total proportion of the REMs is less than 25.0% by weight.

8. 8. The mixed oxide according to claim 1, wherein when the mixed oxide contains two or more REMs, the total proportion of the REMs is less than 20.0% by weight.

9. Composition of: 25.0% to 35.0% by weight of aluminum; 1.0% to 7.0% by weight of lanthanum; 1.0% to 7.0% by weight of at least one REM; 55.0% to 65.0% by weight of zirconium 9. The mixed oxide according to claim 1, wherein

10. A mixed oxide according to any one of the preceding claims, wherein the REM is selected from yttrium, neodymium, praseodymium or a combination of these elements, preferably yttrium.

11. 11. The mixed oxide according to claim 1, wherein the mixed oxide is free of cerium or cerium oxide.

12. oxide CeO relative to the total weight of the mixed oxides ２ 12. The mixed oxide according to claim 1, wherein the proportion of cerium, expressed by weight, is less than 1.0% by weight, or even less than 0.5% by weight, or even less than 0.2% by weight, or even less than 0.05% by weight.

13. A specific surface area (BET) after calcination in air at 1100°C for 5 hours is at least 30.0 m ２ / g, more preferably at least 32.0 m ２ / g, more preferably at least 35.0 m ２ / g, and even more preferably at least 40.0 m ２ / g and / or at most 50.0 m ２ / g, more particularly at most 45.0 m ２ / g, or The specific surface area (BET) after calcination in air at 950°C for 3 hours is at least 40 m ２ / g, more preferably at least 50m ２ / g, and even more preferably at least 60 m ２ / g and / or at most 90m ２ / g, more particularly at most 85 m ２ / g, or at most 80m ２ / g, or After firing in air at 1200°C for 5 hours, the specific surface area (BET) was 16.0 m ２ / g or The specific surface area (BET) after firing in air at 1200°C for 5 hours is 15.0 (exclusion value) to 25.0 m ２ / g or 15.0 (exclusion value) to 20.0 m ２ / g of the mixed oxide according to any one of claims 1 to 12.

14. V ｔｏｔａｌ，９５０℃／３ｈ A mixed oxide according to any one of the preceding claims, wherein the viscosity is less than 1.00 ml / g, preferably less than 0.90 ml / g, more preferably less than 0.80 ml / g.

15. A mixed oxide according to any one of claims 1 to 14, exhibiting properties (i) and (ii); or (i) and (iii); or (ii) and (iii); or (i), (ii) and (iii).

16. A method for preparing a mixed oxide according to any one of claims 1 to 15, comprising the following steps: (a0) preparing an acidic aqueous dispersion comprising nitric acid and precursors of oxides of zirconium, lanthanum and optionally rare earth metals other than cerium and lanthanum, in which aluminum hydrate is dispersed, and stirring the resulting dispersion for a duration strictly greater than 5 hours; (a1) introducing the acidic aqueous dispersion into a stirred tank containing a basic aqueous solution; (a2) the dispersion obtained at the end of step (a1) is heated and stirred at a temperature of at least 130°C; (a3) recovering the solids of the dispersion of step (a2) by solid / liquid separation and washing the cake with water; (a4) calcining the solid obtained at the end of step (a3) ​​in air at a temperature between 900°C and 1050°C A method comprising:

17. The aluminum hydrate is based on boehmite, optionally also containing lanthanum, and after calcination in air at a temperature of 900° C. for 2 hours has the following porosity: ・VP20nm-N2 is - 10% x VPT-N2 or more, more particularly 15% x VPT-N2 or more, or even 20% x VPT-N2 or more, or even 30% x VPT-N2 or more; - 60% x VPT-N2 or less the pore volume in the domain of pores with a size of 20 nm or less (denoted VP20nm-N2), such as the pore volume in the domain of pores having a size between 40 and 100 nm (expressed as VP40-100nm-N2) such that VP40-100nm-N2 is equal to or greater than 20% x VPT-N2, more particularly equal to or greater than 25% x VPT-N2, or even equal to or greater than 30% x VPT-N2; indicates, VPT-N2 represents the total pore volume of said aluminum hydrate after calcination in air at 900°C for 2 hours; the pore volume is measured by nitrogen porosimetry techniques; 17. The method of claim 16.

18. Use of the mixed oxide according to any one of claims 1 to 15 for the production of catalytic converters.

19. A catalytic converter comprising a catalytically active washcoat prepared from the mixed oxide of any one of claims 1 to 15 and deposited on a solid support.

20. Use of an aluminium hydrate for the preparation of a mixed oxide according to any one of claims 1 to 15, said aluminium hydrate being based on boehmite and optionally also containing lanthanum, and having the following properties: After being calcined in air at a temperature of 900°C for 2 hours, it ・VP20nm-N2 is - 10% x VPT-N2 or more, more particularly 15% x VPT-N2 or more, or even 20% x VPT-N2 or more, or even 30% x VPT-N2 or more; - 60% x VPT-N2 or less the pore volume in the domain of pores with a size of 20 nm or less (denoted VP20nm-N2), such as the pore volume in the domain of pores having a size between 40 and 100 nm (expressed as VP40-100nm-N2), such that VP40-100nm-N2 is equal to or greater than 20% x VPT-N2, more particularly equal to or greater than 25% x VPT-N2, or even equal to or greater than 30% x VPT-N2; indicates; VPT-N2 denotes the total pore volume of said aluminum hydrate after calcination in air at 900°C for 2 hours; The pore volume is measured by nitrogen porosimetry technique; 10. The use characterized by: