Aluminum-based and zirconium-based mixed oxides

Abstract

The present invention relates to a mixed oxide of aluminum, zirconium, cerium, lanthanum and optionally at least one rare earth metal other than cerium and lanthanum, which makes it possible to prepare a catalyst which retains good thermal stability and good catalytic activity after severe ageing. The invention also relates to a process for preparing this mixed oxide, and also to a process for treating exhaust gases from internal combustion engines using a catalyst prepared from this mixed oxide.

Description

TECHNICAL FIELD

[0001] The present invention relates to a mixed oxide of aluminum, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and lanthanum, which makes it possible to prepare a catalyst which maintains a specific porosity, good thermal stability and good catalytic activity after severe aging. The invention also relates to a process for preparing 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.

[0002] Technical problem

[0003] In exhaust emission systems which connect a vehicle engine and a muffler to each other, a catalytic converter for purifying exhaust gases is generally provided. The engine emits substances harmful to the environment, such as CO, NO x or unburned hydrocarbons. In order to convert such harmful substances into environmentally acceptable substances, the exhaust gas is caused to flow through the catalytic converter, so that CO is converted into CO2, NO x is converted into N2and O2, and unburned hydrocarbons are combusted. In this catalytic converter, a catalyst layer having a noble metal catalyst (such as Rh, Pd, or Pt) supported on a carrier is formed on the cell wall surface of a substrate. Examples of the carrier for supporting the noble metal catalyst include a mixed oxide based on cerium and zirconium. Such a carrier is also called a promoter, and is a main component of a three-way catalyst which simultaneously removes harmful components in the exhaust gas, such as CO, NO x and unburned hydrocarbons. Cerium is important because the oxidation number of cerium changes depending on the partial pressure of oxygen in the exhaust gas. CeO2has a function of adsorbing and desorbing oxygen as well as a function of storing oxygen (referred to as OSC ability).

[0004] Rh is known to be an effective noble metal for reducing the content of NO x in exhaust gases. Rh III in a high oxidation state is preferred compared to Rh 0 because it provides better NO x removal activity. It is known that in a conventional three-way catalyst in which a cerium-zirconium-based mixed oxide is used as a promoter and a carrier for one or more noble metals, the presence of cerium oxide is detrimental to NO x removal activity, because Rh 0 is oxidized by oxygen desorbed from CeO2to Rh III .

[0005] Zirconium oxide is known to be a good carrier for rhodium because it helps to stabilize and disperse Rh 0 , but better thermal stability of the catalyst, particularly maintaining effective NO x removal activity over time, is required.

[0006] Therefore, there is a need for a rhodium support having a specific porosity for a good mass transfer, which remains thermally stable under the severe conditions (high temperature and presence of corrosive gases (such as CO, O2and NO x ) encountered in catalytic converters and allows an effective de-NO x x over time, in particular an effective catalytic activity of rhodium over time.

[0007] The mixed oxide of the application aims to solve this problem.

[0008] For the continuity of this specification, it is specified that, unless otherwise stated, the limit values are included in the range of values given, including for expressions such as "at most" and "at least". In addition, wt% corresponds to % expressed by weight. It is also specified that, unless otherwise indicated, calcination is carried out in air. BACKGROUND

[0009] EP 3085667 discloses a zirconia matrix which exhibits a P / W ratio of 0.03 or more after heat treatment at 1000°C for 12 hours, where P represents the peak height and W represents the peak width. The P / W ratio of the disclosed product is between 0.01 and 0.11, which corresponds to a high W / P ratio between 9 and 100.

[0010] EP 3345870 discloses a zirconia powder comprising between 2 and 6 mol% of yttria, which can also comprise alumina in an amount lower than 2.0%.

[0011] US 9,902,654 B2 discloses Zr02-A1203 ceramics. A specific composition of the ceramic with 80 wt% (97 mol% Zr02-3 mol% Y203) - 20 wt% A1203 is given, which corresponds to 75.6 wt% Zr02.

[0012] WO 2019 / 122692 discloses an aluminum hydrate H for the preparation of a mixed oxide containing cerium, which is different from the mixed oxide of the application.

[0013] None of the cited documents discloses the mixed oxide as claimed in claim 1.

[0014] Figures

[0015] Figure 1 / 1 The porosity curve (C) of the composition of Example 1 obtained by the nitrogen porosimetry technique after calcination of the mixed oxide in air at 950°C for 3 hours is shown. For this composition, D p950℃ / 3h = 17 nm. SUMMARY

[0016] The mixed oxide of the application is a mixed oxide of Al, Zr, La and optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM.

[0017] The mixed oxide of the application is disclosed in claims 1-41. It is thus a mixed oxide of aluminum, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM, in a weight proportion of the elements as follows:

[0018] ■ aluminum between 20.0 and 45.0 wt%;

[0019] ■ lanthanum between 1.0 and 15.0 wt%;

[0020] ■ rare earth metal other than cerium and other than lanthanum between 0 and 10.0 wt%, provided that if the mixed oxide comprises more than one rare earth metal other than cerium and other than lanthanum, this proportion applies to each of these rare earth metals;

[0021] ■ zirconium between 50.0 and 70.0 wt%;

[0022] These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxide,

[0023] characterized in that the specific surface area (BET) of the mixed oxide is at least 25 m 2 / g after calcination in air at 1100°C for 5 hours;

[0024] and in that the porosity of the mixed oxide, measured by N2 porosimetry after calcination in air at 950°C for 3 hours, is such that:

[0025] ■ in the domain of pores with a size less than 100 nm, the porosimetry profile of the mixed oxide exhibits a peak at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm;

[0026] ■ the ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h is greater than or equal to 0.85;

[0027] ■ V 总,950℃ / 3h is greater than or equal to 0.35 ml / g;

[0028] V <30nm,950℃ / 3h , V 总,950℃ / 3h respectively represent the pore volume of the mixed oxide of pores with a size less than 30 nm and its total pore volume after calcination in air at 950°C for 3 hours.

[0029] The present invention also relates to a process as defined in claims 42-44, to the use of a mixed oxide as defined in one of claims 45-47, to a composition as defined in claims 48-49 and to a catalytic converter as defined in claim 50. The present invention also relates to the use of an aluminum hydrate for the preparation of a mixed oxide as defined hereinafter and in claims 51-56. These objects will now be further defined hereinafter. DETAILED DESCRIPTION

[0030] With regard to the composition of the mixed oxide of the present invention, the mixed oxide is a mixed oxide of aluminum, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM, the proportions by weight of these elements, expressed in oxide equivalent, relative to the total weight of the mixed oxide, are as follows:

[0031] ■ aluminum between 20.0 and 45.0 wt%;

[0032] ■ lanthanum between 1.0 and 15.0 wt%;

[0033] ■ between 0 and 10.0 wt% of a rare earth metal other than cerium and other than lanthanum, with the proviso that if the mixed oxide comprises more than one rare earth metal other than cerium and other than lanthanum, this proportion applies to each of these rare earth metals;

[0034] ■ zirconium between 50.0 and 70.0 wt%.

[0035] The rare earth metal (REM) is understood to mean an element chosen from the group of yttrium and the elements of the periodic table having an atomic number between 57 and 71, inclusive.

[0036] In the mixed oxide, the elements Al, La, REM if present, and Zr described above are generally present in the form of oxides. Thus, the mixed oxide can be defined as a mixture of oxides. However, it is not excluded that these elements can be at least partially present in the form of hydroxides or oxyhydroxides. The proportions of these elements can be determined using the analytical techniques customary in the laboratory, in particular plasma torch and X-ray fluorescence. As is customary in the field of mixed oxides, the proportions of these elements are given by weight in oxide equivalent, relative to the total weight of the mixed oxide.

[0037] The mixed oxide comprises the elements described above in the proportions indicated, but it can also comprise other elements, for example like impurities. In this regard, it must be noted that the mixed oxide does not comprise cerium or cerium oxide, or if cerium is detectable, it is only in the form of an impurity.

[0038] These impurities generally originate from the starting materials or starting 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 wt%, or even less than 1.0 wt%. The proportion of cerium, expressed by weight of oxide Ce02relative to the total weight of the mixed oxide, is generally less than 1.0 wt%, even less than 0.5 wt%, or less than 0.2 wt% or less than 0.05 wt%.

[0039] The mixed oxide can also comprise hafnium, which is generally associated with zirconium in the natural ore. The proportion of hafnium relative to zirconium depends on the ore from which the zirconium is extracted. Thus, the weight proportion of Zr / Hf in some ores can be about 50 / 1. Thus, for example, for 2 wt% of hafnium oxide, the xenotime contains approximately 98 wt% of zirconium oxide. As for zirconium, hafnium is generally present in the form of an oxide. However, it cannot be excluded that it can be at least partially present in the form of a hydroxide or oxyhydroxide. The weight proportion of hafnium in the mixed oxide, expressed in oxide equivalent relative to the total weight of the mixed oxide, is less than or equal to 2.0 wt%. The proportion of hafnium can be between 0 and 2.0 wt%. The proportions of impurities and of hafnium can be determined using inductively coupled plasma mass spectrometry (ICP-MS).

[0040] The proportions of the constituent elements Al, La, REM, Zr and possibly Hf are given by weight of oxide. To calculate these proportions, the zirconium oxide is considered in the form of Zr02, the hafnium oxide in the form of Hf02, the aluminium in the form of Al203, the rare earth metal oxides in the form of REM203, with the exception of praseodymium which is expressed in the form of Pr606 11 As an example, a mixed oxide with only one REM having the following proportions expressed in oxide equivalent, 30 wt% Al, 60 wt% Zr, 5 wt% La and 5 wt% Y corresponds to: 30 wt% Al203, 60 wt% Zr02, 5 wt% La203and 5 wt% Y203.

[0041] In the mixed oxide according to the application, the above-mentioned elements are intimately mixed, which distinguishes this mixed oxide from a simple mechanical mixture of oxides in solid form. This intimate mixing is achieved by the precipitation step of preparation of the mixed oxide.

[0042] The weight proportion of aluminium is between 20.0 and 45.0 wt%, more particularly between 25.0 and 40.0 wt%, even more particularly between 25.0 and 35.0 wt%.

[0043] The weight proportion of lanthanum is between 1.0 and 15.0 wt%, more particularly between 1.0 and 10.0 wt%, even more particularly between 1.0 and 7.0 wt%, or even between 2.0 and 7.0 wt%.

[0044] The mixed oxide can also contain one or more rare earth metals (REM) other than cerium or other than lanthanum. The rare earth metal can for example be chosen from yttrium, neodymium, praseodymium or a combination of these elements. The mixed oxide can for example contain only a single REM in a proportion of between 0 and 10.0 wt%. The proportion of REM can be between 1.0 and 10.0 wt%, even more particularly between 1.0 and 7.0 wt%, or even between 2.0 and 7.0 wt%.

[0045] The mixed oxide can also contain more than one REM and in this case the disclosed proportions apply to each REM. Also in this case the total proportion of the REMs should remain less than 25.0 wt%, more particularly less than 20.0 wt%.

[0046] More particularly, one of the REMs or the REM is Y.

[0047] The mixed oxide also comprises zirconium. The proportion of zirconium can be between 50.0 and 70.0 wt%, more particularly between 55.0 and 65.0 wt%.

[0048] The specific mixed oxide C has the following composition:

[0049] ■ between 25.0 and 35.0 wt% of aluminium;

[0050] ■ between 1.0 and 7.0 wt% of lanthanum;

[0051] ■ between 1.0 and 7.0 wt% of at least one REM;

[0052] ■ between 55.0 and 65.0 wt% of zirconium.

[0053] The proportion of lanthanum can also be between 2.0 and 7.0 wt%, more particularly between 3.0 and 7.0 wt%. The proportion of REM can also be between 2.0 and 7.0 wt%, more particularly between 3.0 and 7.0 wt%.

[0054] The mixed oxide of the application advantageously comprises a combination of oxides of aluminium and zirconium. For the mixed oxide of the application and more particularly for the mixed oxide C, the total proportion of zirconium and aluminium is preferably greater than or equal to 80.0 wt%, more particularly greater than or equal to 85.0 wt%.

[0055] Characterization of mixed oxides

[0056] Crystallite size

[0057] The mixed oxide is characterised in that it:

[0058] - the average size of the crystallites of the crystalline phase based on zirconia is at most 28 nm, or at most 25 nm, or even at most 22 nm after calcination at 1100°C for 5 hours; and / or

[0059] - the average size of the crystallites of the crystalline phase based on zirconia is at most 44 nm, or at most 35 nm, or even at most 33 nm after calcination at 1200°C for 5 hours.

[0060] The average size of the crystallites of the crystalline phase based on zirconia is at most 28 nm after calcination at 1100°C for 5 hours. It is preferably at most 25 nm, more preferentially at most 22 nm.

[0061] The average size of the crystallites of the crystalline phase based on zirconia is at most 44 nm after calcination at 1200°C for 5 hours. It is preferably at most 35 nm, more preferentially at most 33 nm.

[0062] The crystalline phase based on zirconia is generally characterized by a peak located at an angle 2 theta between 29° and 31° (origin: Cu Kalpha 1, l = 1.5406 Angstroms). This peak is generally located at an angle 2 theta between 29.0° and 31.0° (origin: Cu Kalpha 1, l = 1.5406 Angstroms).

[0063] The crystalline phase comprises zirconia and can also contain lanthanum and optionally one or more rare earth metals other than cerium and other than lanthanum.

[0064] The crystalline phase generally exhibits a tetragonal structure. This tetragonal structure can be characterized by x-ray diffraction techniques or Raman spectroscopy. When using x-ray diffraction techniques, the tetragonal structure is identified after calcination of the mixed oxide in air at a temperature of 950°C for 3 hours.

[0065] The average size of the crystallites is determined by x-ray diffraction techniques. It corresponds to the size of the coherence domain calculated from the width of the diffraction line 2 theta and using the Scherrer equation. According to the Scherrer equation, t is given by formula (I):

[0066] t = k l / (b cos 0) (I)

[0067] t: average crystallite size;

[0068] k: shape factor equal to 0.9;

[0069] l (lambda): wavelength of the incident light beam (l = 1.5406 Angstroms);

[0070] b: line broadening measured at half the maximum intensity;

[0071] 0: Bragg angle

[0072] In order to determine β, the instrumental broadening is generally taken into account.

[0073] In formula (II), the instrumental broadening is s and the following equation can be used:

[0074]

[0075] t: average crystallite size;

[0076] k: shape factor equal to 0.9;

[0077] λ (lambda): wavelength of the incident beam (λ = 1.5406 angstroms);

[0078] H: full width at half maximum of the diffraction line;

[0079] s: instrumental line broadening;

[0080] θ: Bragg angle.

[0081] s depends on the instrument used and the 2θ (theta) angle.

[0082] Specific surface area

[0083] The mixed oxides according to the application also have a large specific surface area. The specific surface area is understood to mean the BET specific surface area obtained by nitrogen adsorption. It is determined using the well-known Brunauer-Emmett-Teller method.

[0084] The BET method is described in particular in the journal "The Journal of the American Chemical Society, 60, 309 (1938)". The recommendations of the standard ASTM D3663-03 can be followed. In what follows, the abbreviation S T(℃) / x(h) is intended to denote the specific surface area of the composition obtained by the BET method after a period of time x of calcination of the composition at a temperature T expressed in °C. For example, S 1100℃ / 5h denotes the BET specific surface area of the composition after calcination of the composition at 1100°C for 5 hours.

[0085] For the determination of the specific surface area by nitrogen adsorption, the following apparatuses can be used according to the manufacturer's guidelines: Flowsorb II 2300 or Tristar 3000 from Micromeritics. They can also be determined automatically with a Macsorb analyzer from Mountech, model I-1220, according to the manufacturer's guidelines. Before the measurement, the samples are preferably degassed under vacuum and by heating at a temperature of at most 300°C in order to remove adsorbed volatile substances.

[0086] The specific surface area S can be at least 25 m2 / g. 1100℃ / 5h / g. This specific surface area can preferably be at least 28 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g.

[0087] The specific surface area S can be at least 25 m2 / g. 950℃ / 3h / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g.

[0088] The specific surface area S can be at least 25 m2 / g. 1200℃ / 5h / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more preferably at least 30 m2 / g, even more preferably at least 31 m2 / g. Thus, this specific surface area can be between 25 and 40 m2 / g, more particularly between 28 and 40 m2 / g, still more particularly between 31 and 40 m2 / g. This specific surface area can be at most 40 m2 / g, more particularly at most 35 m2 / g. This specific surface area can also be at least 35 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g. 2 / g, more particularly at most 95 m2 / g, or at most 90 m2 / g.

[0089] Nitrogen porosimetry

[0090] The mixed oxide is also characterized by a specific porosity which allows good mass transfer and good dispersion of the noble metal. In the context of the present invention, the specific porosity is given after calcination of the mixed oxide in air at 950°C for 3 hours.

[0091] The data on porosity disclosed in the present application are obtained by nitrogen porosimetry technique. This technique makes it possible to define the pore volume (V) as a function of the pore diameter (D). More precisely, from the nitrogen porosimetry data, a curve (C) representing the derivative of the function V as a function of log D (dV / dlogD) can be obtained. The derivative curve (C) can exhibit one or more peaks, each peak being located at a diameter D p representing. From these data, the following characteristics related to the porosity of the mixed oxide can also be obtained:

[0092] ■the total pore volume (in ml / g) obtained from the porosimetry data as read on the cumulative curve (V 总 representing);

[0093] ■the pore volume (in ml / g) formed by the pores having a size less than or equal to 30 nm obtained from the porosimetry data as read on the cumulative curve (V <30nm representing).

[0094] When these parameters are determined after calcination of the mixed oxide in air at 950°C for 3 hours, they are respectively denoted D p,950℃ / 3h , V 总,950℃ / 3h and V <30nm,950℃ / 3h .

[0095] The nitrogen porosimetry technique is a well-known technique, often applied to inorganic materials. The porosimetry can be obtained with a Tristar II 3000 apparatus from Micromeritics. The conditions for determining the porosimetry can be as detailed in the examples. The nitrogen porosimetry technique can be performed according to ASTM D4641-17.

[0096] In the region of pores having a size less than 100 nm, the porosimetry plot of the mixed oxide after calcination in air at 950°C for 3 hours exhibits a peak located at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm. Said porosimetry plot can exhibit more than one peak in the region of pores having a size less than 100 nm, but the peak located at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm is the highest. However, there is generally only one peak in the region of pores having a size less than 100 nm after calcination in air at 950°C for 3 hours, and said peak is located at a diameter D p,950℃ / 3hThe application also relates to a mixed oxide of aluminum, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM, the proportions by weight of these elements being as follows:

[0097] ■ aluminum between 20.0 and 45.0 wt%;

[0098]

[0099] ■ lanthanum between 1.0 and 15.0 wt%;

[0100] ■ zirconium between 50.0 and 70.0 wt%;

[0101] These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxide,

[0102] characterized in that, 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;

[0103] and in that, after calcination in air at 950°C for 3 hours, the porosity of the mixed oxide, measured by N2 porosimetry, is such that:

[0104] ■ in the region of pores with a size less than 100 nm, the porosimetry profile of the mixed oxide exhibits a single peak and this peak is located at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm;

[0105] ■ the ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h is greater than or equal to 0.85;

[0106] ■ V 总,950℃ / 3h is greater than or equal to 0.35 ml / g;

[0107] V <30nm,950℃ / 3h , V 总,950℃ / 3h respectively represent the pore volume of the mixed oxide, after calcination in air at 950°C for 3 hours, of the pores with a size less than 30 nm and its total pore volume.

[0108] ■ the ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h is greater than or equal to 0.85. This ratio can preferably be greater than or equal to 0.90.

[0109] V 总,950℃ / 3h ​Also greater than or equal to 0.35 ml / g.V 总,950℃ / 3h It can be preferred to be greater than or equal to 0.40 ml / g, even more preferably greater than or equal to 0.45 ml / g.

[0110] Furthermore, the half-width of the peak located at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm, is at most 10 nm, more particularly at most 8 nm. This shows that the process of the application makes it possible to fine-tune the porosity.

[0111] The mixed oxide is generally in the form of a powder.

[0112] All of the above disclosed remains applicable to a mixed oxide consisting essentially of or consisting of a combination of oxides of aluminum, zirconium, lanthanum, optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM, and optionally hafnium, the proportions by weight of these elements being as follows:

[0113] ■ aluminum between 20.0 and 45.0 wt%;

[0114] ■ lanthanum between 1.0 and 15.0 wt%;

[0115] ■ rare earth metal other than cerium and other than lanthanum between 0 and 10.0 wt%, provided that if the mixed oxide contains more than one rare earth metal other than cerium and other than lanthanum, this proportion applies to each of these rare earth metals;

[0116] ■ hafnium in a proportion less than or equal to 2.0 wt%;

[0117] ■ zirconium between 50.0 and 70.0 wt%;

[0118] These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxide,

[0119] characterized in that, 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;

[0120] and in that, after calcination in air at 950°C for 3 hours, the porosity of the mixed oxide, measured by N2 porosimetry, is such that:

[0121] ■ in the region of pores of size less than 100 nm, the porosimetry graph of the mixed oxide exhibits a peak located at a diameter D p,950℃ / 3h between 10 and 25 nm, more particularly between 10 and 22 nm, even more particularly between 13 and 19 nm;

[0122] ■ the ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h greater than or equal to 0.85;

[0123] ■ the ratio V 总,950℃ / 3h greater than or equal to 0.35 ml / g;

[0124] V <30nm,950℃ / 3h , V 总,950℃ / 3h respectively represent the pore volume of the pores of the mixed oxide having a size less than 30 nm and the total pore volume thereof after calcination in air at 950°C for 3 hours.

[0125] Process for preparing mixed oxides

[0126] As regards the preparation of the mixed oxide according to the application, it can be according to the process (A) or (B) disclosed below. Process (A) comprises the following steps:

[0127] (a1 ) introducing into a stirred tank containing an aqueous basic solution, an aqueous acidic dispersion comprising nitric acid and precursors of oxides of zirconium, lanthanum and optionally one or more rare earth metals other than cerium and lanthanum, in which are dispersed aluminium hydrates;

[0128] (a2) heating and stirring the dispersion obtained at the end of step (a1 ) at a temperature of at least 130°C;

[0129] (a3) recovering the solids of the dispersion of step (a2) by solid / liquid separation and washing the filter cake with water;

[0130] (a4) calcining the solids obtained at the end of step (a3) in air at a temperature of at least 800°C.

[0131] Process (A) does not comprise any step of adding a texturing agent such as lauric acid.

[0132] Step (a1)

[0133] In step (a1 ), an aqueous acidic dispersion comprising precursors of oxides of zirconium, lanthanum and optionally one or more rare earth metals other than cerium and other than lanthanum, nitric acid, in which are dispersed aluminium hydrates, such as aluminium monohydrate, is used. This aqueous acidic dispersion does not comprise any cerium oxide precursor.

[0134] The precursor of zirconium oxide can be zirconyl nitrate. For example, the zirconyl nitrate can be crystalline. The precursor of zirconium oxide can also be obtained by dissolving zirconium subcarbonate or zirconium hydroxylate with nitric acid. This acid attack can be preferably between 1.4 and 2.3 NO3 -The zirconium nitrate solution used in Example 1 resulting from the erosion of the carbonate had a concentration of 295 g / l expressed in Zr02. The zirconium nitrate solution used in Example 2 resulting from the erosion of the carbonate had a concentration of 350 g / l expressed in Zr02.

[0135] The precursor of the zirconia can be lanthanum nitrate. The precursor of the oxide of the rare earth metal other than cerium and lanthanum can be a nitrate or a chloride. For example, it can be praseodymium nitrate, neodymium nitrate, yttrium chloride YCI3or yttrium nitrate Y(N03)3.

[0136] According to one embodiment, the precursor of the Zr oxide, the precursor of the La oxide and the precursor of the oxide of the one or more REMs are all in the form of nitrates.

[0137] The aqueous acidic dispersion also contains nitric acid. The concentration of H + in the aqueous acidic dispersion is advantageously between 0.04 and 3.0 mol / l, more particularly between 0.5 and 2.0 mol / l. The amount of H + should be sufficiently high to obtain a dispersion in which the particles of the aluminium hydrate are sufficiently dispersed.

[0138] The aqueous acidic dispersion also contains an aluminium hydrate, more particularly an aluminium hydrate based on boehmite and optionally also containing lanthanum. The aluminium hydrate is more preferably an aluminium hydrate having a specific porosity, which is described in WO 2019 / 122692 and is denoted hereinafter as aluminium hydrate H. This specific aluminium hydrate H is sufficiently dispersible in the aqueous acidic medium.

[0139] Concerning the aluminum hydrate H

[0140] This aluminium hydrate H is based on a boehmite optionally also containing lanthanum, which is characterised in that, after calcination in air at a temperature of 900°C for 2 hours, it exhibits:

[0141] ■a pore volume in the region of pores having a size of less than or equal to 20 nm (denoted by VP20 nm-N2) such that VP20 nm-N2:

[0142] - greater than or equal to 10% x VPT-N2, more particularly greater than or equal to 15% x VPT-N2, or even greater than or equal to 20% x VPT-N2, or even greater than or equal to 30% x VPT-N2;

[0143] - less than or equal to 60% x VPT-N2;

[0144] ■ the pore volume in the region of pores having a size between 40 and 100 nm (denoted VP40-100nm-N2), such that VP40-100 nm-N2 is greater than or equal to 20% x VPT-N2, more particularly greater than or equal to 25% x VPT-N2, or even greater than or equal to 30% x VPT-N2;

[0145] ■ VPT-N2 denotes the total pore volume of the aluminium hydrate after calcination in air at 900°C for 2 hours;

[0146] ■ these pore volumes are determined by nitrogen porosimetry techniques.

[0147] The term "boehmite" denotes in the European nomenclature and as known is a gamma hydroxy oxide (γ-AI OOH). In the present application, the term "boehmite" denotes various aluminium hydrates having a particular crystalline form, as known to the person skilled in the art. Thus, boehmite can be characterised by x-ray diffraction. The term "boehmite" also encompasses "pseudo-boehmite", which according to certain authors is only similar to a particular kind of boehmite and only has a broadening of the boehmite characteristic peaks. Boehmite is identified by x-ray diffraction of its characteristic peaks. These are given in the document JCPDS 00-021-1307 (JCPDS = Joint Committee on Powder Diffraction Standards). It will be noted that the apex of the peak (020) can be between 13.0° and 15.0°, in particular depending on:

[0148] - the crystallinity of the boehmite;

[0149] - the crystallite size of the boehmite.

[0150] Reference can be made to Journal of Colloidal and Interface Science, 2002, 253, 308-314 or J. Mater. Chem., 1999, 9, 549-553, in which it is set out that for a certain number of boehmites, the position of the peak varies according to the number of layers in the crystal or the size of the crystallites. This apex can more particularly be between 13.5° and 14.5°, or between 13.5° and 14.485°.

[0151] When the aluminum hydrate contains lanthanum, the proportion of lanthanum is between 1.0 and 8.0 wt%, more particularly between 3.0 and 8.0 wt% or between 4.0 and 8.0 wt%. This proportion is given by the weight of La203relative to the weight of Al203and La203(in other words, the proportion of La (in wt%) = weight of La203 / weight of La203+ Al203x 100). In other words, this proportion does not take into account the amount of hydrate contained in the aluminum hydrate either. Of course, in order 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 form of lanthanum oxide in the aluminum hydrate.

[0152] The conventional method for determining the proportion of La in the aluminum hydrate comprises calcining the aluminum hydrate in air and eroding the calcined product by, for example, with a concentrated nitric acid solution so as to dissolve the elements thereof in solution, which can then be analyzed by techniques known to the person skilled in the art, such as, for example, ICP, to determine the proportions of Al and La. Calcination also makes it possible to determine the loss on ignition (LOI) of the hydrate. The LOI of the aluminum hydrate can be between 20.0 and 30.0%.

[0153] The boehmite contained in the aluminum hydrate, more particularly in the aluminum hydrate H, can have an average size of the crystallites of at most 6.0 nm, or even at most 4.0 nm, still more particularly at most 3.0 nm. The average size of these crystallites is determined by x-ray diffraction techniques and corresponds to the size of the coherence domain calculated from the half-peak full width of the line (020).

[0154] The aluminum hydrate H can be in the form of a mixture of boehmite (as identifiable above by x-ray diffraction techniques) and of phases that are not visible in x-ray diffraction, in particular amorphous phases. The aluminum hydrate H can have a % of crystalline phases (boehmite) of less than or equal to 60%, more particularly less than or equal to 50%. This % can be between 40 and 55%, or between 45 and 55%, or between 45 and 50%. This % is determined in a manner known to the person skilled in the art. This % can be determined using the following formula: % crystallinity = intensity of the peak (120) of the aluminum hydrate / intensity of the peak (120) of the reference x 100, in which the intensity of the peak (120) of the aluminum hydrate and the intensity of the peak (120) of the reference are compared. The reference used in the present application is the product corresponding to Example B1 of application US 2013 / 017947. The intensity measured corresponds to the surface area of the peak (120) above the baseline. These intensities are determined on a diffractogram chosen with respect to a baseline in the range of 2 theta angles between 5.0 and 90.0°. The baseline is determined automatically using software for analyzing diffractogram data.

[0155] The aluminum hydrate H has a specific porosity. Thus, after calcination in air at 900°C for 2 hours, it has a pore volume in the domain of pores having a size less than or equal to 20 nm (denoted by VP20 nm-N2) such that VP20 nm-N2 is greater than or equal to 20% x VPT-N2, more particularly greater than or equal to 25% x VPT-N2, or even greater than or equal to 30% x VPT-N2. Moreover, VP20 nm-N2 can be less than or equal to 60% x VPT-N2.

[0156] Moreover, after calcination in air at 900°C for 2 hours, the aluminum hydrate H has a pore volume in the domain of pores having a size between 40 and 100 nm (denoted by VP40-100 nm-N2) such that VP40-100 nm-N2 is greater than or equal to 15% x VPT-N2, more particularly greater than or equal to 20% x VPT-N2, or even greater than or equal to 25% x VPT-N2, or even greater than or equal to 30% x VPT-N2. Moreover, VP40-100 nm-N2 can be less than or equal to 65% x VPT-N2.

[0157] After calcination in air at 900°C for 2 hours, the aluminum hydrate H can have a total pore volume (VPT-N2) between 0.65 and 1.20 ml / g, more particularly between 0.70 and 1.15 ml / g, or between 0.70 and 1.10 ml / g. It will be noted that the pore volume thus measured is formed mainly by pores having a diameter less than or equal to 100 nm.

[0158] The aluminum hydrate H can have a specific surface area by the BET method of at least 200 m 2 / g, more particularly at least 250 m 2 / g. This specific surface area can be between 200 and 400 m 2 / g. Moreover, after calcination in air at 900°C for 2 hours, the aluminum hydrate H can have a specific surface area by the BET method of at least 130 m 2 / g, more particularly at least 150 m 2 / g. This specific surface area can be between 130 and 220 m 2 / g. After calcination in air at 940°C for 2 hours then at 1100°C for 3 hours in air, the aluminum hydrate H can have a specific surface area by the BET method of at least 80 m 2 / g, more particularly at least 100 m 2 / g. This specific surface area can be between 80 and 120 m 2 / g.

[0159] The aluminum hydrate H can be obtained by a process comprising the following steps:

[0160] (a) introducing into a stirred tank containing an aqueous nitric acid solution:

[0161] ■an aqueous solution (A) comprising aluminium sulfate, lanthanum nitrate and nitric acid;

[0162] ■an aqueous sodium aluminate solution (B);

[0163] continuously introducing the aqueous solution (A) throughout step (a) and adjusting the introduction rate of the solution (B) so that the average pH of the reaction mixture is equal to a target value comprised between 4.0 and 6.0, more particularly between 4.5 and 5.5;

[0164] (b) when the entire aqueous solution (A) has been introduced, continuing the introduction of the aqueous solution (B) until reaching a target pH comprised between 8.0 and 10.5, preferably between 9.0 and 10.0;

[0165] (c) then filtering the reaction mixture and washing the recovered solid with water;

[0166] (d) then drying the solid resulting from step (c) to give an aluminium hydrate H.

[0167] Further details on the process for obtaining the aluminium hydrate H are also provided in the examples of WO 2019 / 122692. The aluminium hydrate H disclosed in the examples of the present patent application can be used.

[0168] The present application thus also relates to the use of the aluminium hydrate H for the preparation of a mixed oxide of aluminium, zirconium, lanthanum and optionally at least one rare earth metal other than cerium and other than lanthanum, denoted REM, in particular of a mixed oxide of these elements in a weight ratio such as follows:

[0169] ■aluminium between 20.0 and 45.0 wt%;

[0170] ■lanthanum between 1.0 and 15.0 wt%;

[0171] ■a rare earth metal other than cerium and other than lanthanum between 0 and 10.0 wt%, provided that if the mixed oxide comprises more than one rare earth metal other than cerium and other than lanthanum, this proportion applies to each of these rare earth metals;

[0172] ■zirconium between 50.0 and 70.0 wt%;

[0173] These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxide.

[0174] The present application thus also relates to the use of the aluminium hydrate H for the preparation of a mixed oxide of the application, in particular as disclosed in any one of claims 1-40.

[0175] For the preparation of the aqueous acidic dispersion used in process (A), it is advantageous to keep the mixture under stirring for a sufficient period of time to obtain a high specific surface area (see comparative example 1). The mixture should be stirred preferably for a duration comprised between 1 hour and 5 hours.

[0176] The aqueous acidic dispersion used in step (al) is introduced into a stirred tank containing an aqueous basic solution so as to obtain a precipitate (so-called "reverse" precipitation). The basic compound dissolved in the aqueous basic solution can be a hydroxide, for example an alkali or alkaline earth metal hydroxide. Secondary, tertiary or quaternary amines, as well as ammonia, can also be used. As in the examples described below, an aqueous ammonia solution can be used. As in the examples, an aqueous ammonia solution having a concentration comprised between 3 and 5 mol / l can be used for example.

[0177] The amount of base should be in excess relative to the cations present in the aqueous acidic dispersion. This excess ensures the complete precipitation of the cations. A molar ratio of base / Σ valence of cations from precursors + H from nitric acid higher than 1.2, more particularly higher than 1.4 can be used. This ratio takes into account the valence of the cations from the precursors (for example 2 for Zr and 3 for La). +

[0178] Step (a2)

[0179] The dispersion obtained at the end of step (al) is heated and stirred at a temperature of at least 130°C. This temperature can be comprised between 130°C and 200°C, more particularly between 130°C and 170°C. The duration of step (a2) is generally comprised between 10 minutes and 5 hours, more particularly between 1 hour and 3 hours. For example, the dispersion can be heated at 150°C and maintained at this temperature for 2 hours.

[0180] Step (a2) can be conveniently carried out in a closed vessel under the temperature conditions given above. Thus, it can be specified by way of illustration that the pressure in the closed vessel can vary between a value greater than 1 bar (10 5 Pa) and 165 bar (1.65 x 10 7 Pa), preferably between 5 bar (5 x 10 5 Pa) and 165 bar (1.65 x 10 7 Pa).

[0181] Step (a3)

[0182] ​The solids of the dispersion of step (a2) are recovered by solid / liquid separation and the filter cake is washed with water. It is convenient to wash the filter cake using a dilute aqueous ammonia solution. For example, a vacuum filter (e.g. Nutsche type), centrifugation or a filter press can be used.

[0183] Of course, the filter cake recovered at the end of step (a3) can still contain some residual water, but this has no real impact on the quality of the mixed oxide. However, the filter cake can optionally be dried to remove some residual water.

[0184] Step (a4)

[0185] The solids obtained at the end of step (a3) are calcined in air at a temperature of at least 800°C. The calcination temperature should be high enough to convert the solids into mixed oxides and to increase their crystallinity. The temperature should not be too high to maintain a high specific surface area. The calcination temperature can be between 800°C and 1200°C, more particularly between 900°C and 1100°C or between 900°C and 1000°C. The duration of the calcination can be between 30 minutes and 5 hours, more particularly between 1 hour and 4 hours. The conditions of example 1 (950°C; 3 hours) can be used.

[0186] The preparation of the mixed oxide according to the application can be based on the conditions of example 1 given below.

[0187] The mixed oxide can also be prepared by process (B) comprising the following steps:

[0188] (b1) heating and stirring an acidic aqueous dispersion comprising nitric acid, a precursor of zirconyl hydroxide, and oxides of lanthanum and optionally of a rare earth metal other than cerium and other than lanthanum, in which an aluminium hydrate is dispersed, at a temperature of at least 80°C;

[0189] (b2) adding an ammonia solution to the mixture obtained at the end of step (b1) until the pH of the mixture is at least 8.0;

[0190] (b3) then adding an organic structuring agent to the mixture obtained at the end of step (b2) and stirring the mixture;

[0191] (b4) recovering the solids of the dispersion of step (b3) by solid / liquid separation and washing the filter cake with water;

[0192] (b5) calcining the solids obtained at the end of step (b4) in air at a temperature of at least 800°C.

[0193] Step (b1)

[0194] An aqueous acidic dispersion is used, which aqueous acidic dispersion comprises nitric acid, a precursor of zirconium oxyhydroxide, and an oxide of lanthanum and optionally a precursor of an oxide of a rare earth metal other than cerium and other than lanthanum, wherein aluminium hydrate is dispersed. What is disclosed for the precursor of lanthanum oxide and the precursor of REM oxide used in method (A) applies also here.

[0195] The aqueous acidic dispersion also contains nitric acid. The concentration of H + in the aqueous acidic dispersion is advantageously between 0.04 and 3.0 mol / l, more particularly between 0.5 and 2.0 mol / l. The amount of H + should be sufficiently high to obtain a dispersion in which the particles of aluminium hydrate are sufficiently dispersed.

[0196] The precursor of zirconium oxide is zirconium oxyhydroxide. Zirconium oxyhydroxide can generally be represented by the formula ZrO(OH)2. The powder used to prepare the aqueous acidic dispersion is advantageously characterized by an average size d50 between 5.0 and 100 pm, more particularly between 5.0 and 50.0 pm, even more particularly between 25.0 and 40.0 pm or between 28.0 and 30.0 pm. d50 corresponds to the median value of the particle size distribution (by volume) obtained with a laser diffraction particle size analyser, such as a HORIBA LA-920. d50 is generally determined with a dispersion of the hydroxide in water. The oxide content of the zirconium oxyhydroxide, expressed as %wt of ZrO2, is generally between 35.0 and 55.0 %. An example of zirconium oxyhydroxide that can be conveniently used as a raw material as a precursor of zirconium oxide is the TZH-40 grade commercialized by Terio corporation (Shandong Province, Qingdao City, Shandong Road 2A, Huaren International Building 18 / A, China). This grade has the following characteristics: content expressed in oxide equivalent: ZrO2+HfO2>40 wt% min, %ZrO2= 43.0 wt%; d50 = between 27 and 32 pm. More details on this product can be found here: http: / / www.terio.cn / product / detail / 11.

[0197] The aqueous acidic dispersion is heated at a temperature of at least 80°C, more particularly at least 90°C or even at least 100°C. This temperature can be as high as 200°C. The temperature should be sufficiently high to form a precipitate comprising Zr, La and one or more REM, if present.

[0198] The aluminium hydrate is preferably the aluminium hydrate H disclosed above.

[0199] Step (b2)

[0200] An ammonia solution is added to the mixture obtained at the end of step (bl) until the pH of the mixture is at least 8.0.

[0201] Step (b3)

[0202] An organic texturizing agent is then added to the mixture obtained at the end of step (b2) and the mixture is stirred.

[0203] An organic texturizing agent (or "templating agent") means an organic compound (such as a surfactant) capable of modifying the porous structure of the mixed oxide, especially for pores having a size below 500 nm. The organic texturizing agent can be added in the form of a solution or a dispersion. The amount of organic texturizing agent, expressed as a percentage by weight of additive with respect to the weight of the mixed oxide obtained after the calcination step, is generally between 5 and 100 wt% and more particularly between 15 and 60 wt%.

[0204] The organic texturizing agent is preferably chosen from the group consisting of (i) anionic surfactants, (ii) non-ionic surfactants, (iii) polyethylene glycols, (iv) monoacids having a hydrocarbon tail comprising between 7 and 25, more particularly between 7 and 17, carbon atoms, and salts thereof, and (v) surfactants of the carboxymethylated fatty alcohol ethoxylate type.

[0205] As anionic type surfactants, mention can be made of ethoxycarboxylates, ethoxylated fatty acids, sarcosinates, phosphate esters, sulfates such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, and sulfonates such as sulfosuccinates, and alkylbenzene or alkylnaphthalene sulfonates. As non-ionic surfactants, mention can be made of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide / propylene oxide copolymers, sorbitan derivatives, ethylene glycol, propylene glycol, glycerol, polyglycerol esters and ethoxylated derivatives thereof, alkyl amines, alkyl imidazolines, ethoxylated oils and alkylphenol ethoxylates. Mention can in particular be made of the products sold under the trademarks and .

[0206] The organic texturizing acid can also be a monocarboxylic acid having a hydrocarbon tail comprising between 7 and 25, more particularly between 7 and 17, carbon atoms. More particularly mention can be made of saturated acids of formula C n H 2n+1 COOH, in which n is an integer between 7 and 25, more particularly between 7 and 17. More particularly the following acids can be used: hexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid and palmitic acid. More particularly mention can also be made of lauric acid and ammonium laurate.

[0207] Finally, it is also possible to use surfactants chosen from those of the carboxymethylated fatty alcohol ethoxylate type. The expression "products of the carboxymethylated fatty alcohol ethoxylate type" is intended to mean products consisting of ethoxylated or propoxylated fatty alcohols comprising a -CH2-COOH group at the end of the chain. These products can correspond to the following formula:

[0208] R1-O-(CR2R3-CR4R5-O) m -CH2-COOH

[0209] in which R1 represents a saturated or unsaturated carbon-based chain, generally of length up to 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4 and R5 can be identical and can represent hydrogen, or R2 can represent an alkyl group such as a CH3 group and R3, R4 and R5 represent hydrogen; m is a non-zero integer which can be up to 50 and more particularly between 5 and 15, these values being included. It should be noted that the surfactant can consist of a mixture of products having the above formula in which R1 can be saturated or unsaturated respectively, or alternatively a mixture of products comprising both -CH2-CH2-O- and -C(CH3)=CH2-O- groups.

[0210] The proportion of texturizing agent used is generally between 20 and 40% by weight, more particularly between 25 and 35%, this proportion being expressed as the weight percentage of texturizing agent relative to the mixed oxide.

[0211] Step (b4)

[0212] The solids of the dispersion of step (b3) are recovered by solid / liquid separation and the filter cake is washed with water. It is convenient to wash the filter cake using a dilute aqueous ammonia solution. What is described for step (a3) also applies here.

[0213] Step (b5)

[0214] The solids obtained at the end of step (b4) are calcined in air at a temperature of at least 800°C. What is described for step (a4) also applies here.

[0215] The preparation of the mixed oxide according to the application can be based on the conditions of Example 2 given below.

[0216] Step (a5) or (b6)

[0217] During step (a5) or (b6), the mixed oxide obtained in step (a4) or step (b5), respectively, can optionally be milled in order to obtain a powder having the desired particle size. For example, a hammer mill or a mortar mill can be used. The powder can also be sieved in order to control its particle size.

[0218] The present application also relates to a mixed oxide obtainable by the just described methods (A) and (B).

[0219] Use of the mixed oxides

[0220] As regards the use of the mixed oxide according to the present application, this belongs to the field of motor vehicle pollution control catalysis. The mixed oxide according to the present application can be used for the manufacture of catalytic converters, the role of which is to treat motor vehicle exhaust gases.

[0221] The catalytic converter comprises a catalytically active washcoat prepared from the mixed oxide and deposited on a solid support. The role of this washcoat is to transform certain pollutants in the exhaust gases, in particular carbon monoxide, unburned hydrocarbons and nitrogen oxides, into products that are less harmful to the environment, by chemical reactions. The chemical reactions involved can be the following chemical reactions:

[0222] 2CO + O2→ 2CO2

[0223] 2NO + 2CO → N2+ 2CO2

[0224] 4C x H y + (4x + y)O2→ 4x CO2+ 2y H2O

[0225] The solid support can be a metallic monolith, for example FeCr alloy, or made of ceramic. The ceramic can be cordierite, silicon carbide, aluminium titanate or mullite. The solid support commonly used consists of a monolith, usually cylindrical, comprising a large number of small parallel channels with porous walls. This type of support is usually made of cordierite and exhibits a compromise between high specific surface and limited pressure drop.

[0226] 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 present application and optionally at least one mineral material. The mineral material can be chosen from alumina, boehmite or pseudoboehmite, titania, zirconia, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminophosphate. Alumina is a mineral material commonly used, it is possible to optionally dope this alumina, for example with an alkaline earth metal such as barium. According to one embodiment, the washcoat does not contain any ceria (“ceria-free washcoat”). According to another embodiment, the washcoat does not contain any mineral material other than the mixed oxide of the application.

[0227] The composition can also comprise other additives specific to each formulator: H2S scavengers, organic or inorganic modifiers with a promoting coating effect, colloidal alumina, etc. The washcoat thus comprises such a composition. The washcoat also comprises at least one dispersed noble metal. The noble metal can be chosen from the group consisting of Pt, Rh or Pd. Rh can be used in particular in a washcoat intended to treat NO x x. The amount of noble metal is generally between 1 g and 400 g relative to the volume of the monolith expressed in ft 3 x. The noble metal is catalytically active.

[0228] To disperse the noble metal, a salt of the noble metal can be added to a suspension made from the mixed oxide or the mixture of mineral material, if present, or mixed oxide and mineral material. For example, the salt can be a chloride or nitrate of the noble metal (for example, Rh III nitrate). The water is removed from the suspension in order to fix the noble metal, the solid is dried and calcined in air at a temperature generally between 300°C and 800°C. An example of a dispersion of noble metal can be found in Example 1 of US 7,374,729.

[0229] The washcoat is obtained by applying the suspension to a solid support. The washcoat thus exhibits catalytic activity and can act as a pollution control catalyst. The pollution control catalyst can be used to treat exhaust gases from internal combustion engines. Finally, the catalytic system of the invention, as well as the mixed oxide, can be used as a NO x x. capture agent or even to promote the reduction of NO x x. in an oxidizing environment.

[0230] For this reason, the invention also relates to a method for treating exhaust gases from internal combustion engines, characterized in that a catalytic converter comprising a washcoat as described is used.

[0231] Examples

[0232] BET specific surface area:

[0233] The BET specific surface area is determined automatically on a Macsorb analyser of the trade name I-1220 from Shimadzu. Before any measurement, the sample is carefully degassed to desorb volatile adsorbed species. To do this, the sample can be heated in a cell of the device under vacuum at 200°C for 30 min.

[0234] Nitrogen porosimetry:

[0235] A Tristar II 3000 apparatus from Micromeritics was used. This apparatus uses the principles of physical adsorption and capillary condensation to obtain information about the surface area and porosity of solid materials. Nitrogen pore distribution measurements were performed using a pressure gauge at 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 was 5 s for relative pressures between 0.01 and 0.995 (except). The equilibration time was 600 s for relative pressures greater than or equal to 0.995. The tolerance on pressure was 5 mm Hg for absolute pressure and 5% for relative pressure. During the analysis, the p0 value was measured every certain time (2 h). The Barett, Joyner and Halenda method (BJH) with Harkins-Jura law was used to determine the mesoporosity. The analysis of the results was performed on the desorption curve.

[0236] X-ray diffraction:

[0237] X-ray diffraction was performed with a copper source (Cu K al, l = 1.5406 Angstrom). The output power of the x-rays was 40 kV / 40 mA. A RINT 2000 from Rigaku, Japan was used. A 2 theta angular increment = 0.010° and a recording time of 2 seconds per step were used and the instrument width s equal to 2 theta = 0.11° was determined in the 2 theta angular range from 28° to 32°.

[0238] The intensities were determined on diffractograms selected with respect to a baseline between 2 theta angular range of 26.0° and 32.0°. The baseline was determined automatically using software for analyzing diffractogram data.

[0239] Aluminum hydrate H (93.6% AI2O3 - 6.4% La2O3)

[0240] Aluminum nitrate H was prepared according to the teachings of Example 1 of WO 2019 / 122692. Characterization of aluminum hydrate H

[0241] - Composition: 67.3% AI2O3- 4.6% La2O3- LOI 28.1% (loss on ignition), which corresponds to 93.6% AI2O3- 6.4% La2O3;

[0242] - This powder has a BET surface area of 344 m 2 / g.

[0243] - Other characteristics:

[0244]

[0245]

[0246] Example 1 : Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (A) Example 2: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (B)

[0247] A solution containing oxide precursors of Zr, La and Y was prepared by introducing into a stirred tank 37.1 kg of zirconyl nitrate solution ([Zr02]= 295 g / 1; density = 1.461), 1.79 kg of lanthanum nitrate solution ([La203]= 321.1 g / 1; density = 1.511), 4.02 kg of yttrium nitrate solution ([Y203]= 219.7 g / 1; density = 1.414) and 16.9 kg of 60 wt% nitric acid solution. The volume was adjusted to a total of 85 L with deionized water. Next, 5.49 kg of the aluminum hydrate H containing 68.3% by weight equivalent of alumina (3.75 kg of AI2O3) and 4.6% by weight equivalent of La203(0.25 kg) disclosed above were introduced under stirring to the solution obtained and the total amount of the mixture thus obtained was adjusted to 125 L with deionized water. The concentration of H in the aqueous acidic dispersion thus prepared was 1.3 mol / 1. The aqueous acidic dispersion was maintained under stirring for 3 hours. +

[0248] The aqueous acidic dispersion was then introduced into a reactor containing 125 L of a 4.5 mol / 1 ammonia solution stirred by a rotor with three blades (225 rpm) over 60 min at ambient temperature. 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 lower than 50°C.

[0249] The medium was filtered on a filter press under a pressure of about 4 bars and the filter cake was then washed with 20 L of deionized water. The filter cake was then compacted under a pressure of 19.5 bars for 10 min. The wet filter cake obtained was then introduced into an electric furnace. The product was calcined at 950°C for 3 hours. The mixed oxide recovered was then ground in a "Forplex" type blade mill.

[0250] Example 3: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (A) Example 4: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (A)

[0251] ​A solution containing oxide precursors of La and Y was prepared by introducing into a reactor stirred by means of a rotor with three blades 1.12 kg of lanthanum nitrate solution ([La2O3] = 343.1 g / 1; density = 1.541), 2.75 kg of yttrium nitrate solution ([Y2O3] = 219.1 g / 1; density = 1.417) and 24.5 kg of 60% by weight nitric acid solution. The volume was adjusted to a total of 150 L with deionized water. Next, 11.9 kg of hydroxyl oxide TZH-40 commercialized by the company Tayca (d50 = between 27 and 32 μm; containing 43.0% by weight of equivalent zirconium oxide; it therefore corresponds to 5.1 kg of ZrO2) and 3.79 kg of the above-mentioned aluminum hydrate H containing 67.3% by weight of equivalent aluminum oxide (2.55 kg of Al2O3) and 4.6% by weight of equivalent La2O3(0.18 kg) were introduced into the solution obtained, with stirring, and the total amount of the mixture thus obtained was adjusted to 170 L with deionized water.

[0252] The aqueous acidic dispersion thus prepared was heated to a temperature of 100°C and maintained at this temperature for 4 hours. After cooling the mixture to 50°C, a 25% ammonia solution was introduced with stirring until a pH = 8.4 was obtained, then, after 10 min, 2.55 kg of lauric acid was introduced (corresponding to a ratio lauric acid / mixed oxide of 30% by weight).

[0253] The medium was filtered on a filter press at a pressure of about 4 bar, then the filter cake was washed with 85 L of deionized water. The filter cake was then compacted at a pressure of 19.5 bar for 10 min. The wet filter cake obtained was then introduced into an electric furnace. The product was calcined at 950°C for 3 hours. The mixed oxide recovered was then ground in a "Forplex" type blade mill.

[0254] Example 5: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (A) Example 5: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) using process (A)

[0255] The mixed oxide was prepared in the same way as in Example 1, except that the stirring time of the precursor mixture was reduced from 3 hours to 1 hour.

[0256] Comparative Example 1 : Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight) Comparative Example 2: Preparation of the mixed oxide AI2O3 (30%) - ZrO2 (60%) - La2O3 (5%) - Y2O3 (5%) (in % by weight)

[0257] The mixed oxide was prepared in the same way as in Example 1, except that the concentration of the ammonia solution was reduced from 4.5 mol / 1 to 3.5 mol / 1.

[0258] Table I ​

[0259] The mixed oxide was prepared in the same way as in Example 1, except that:

[0260] - the amount of 60% nitric acid solution was reduced from 16.9 kg to 0.44 kg.

[0261] - the concentration of the ammonia solution was reduced from 4.5 mol / 1 to 2.2 mol / 1.

[0262] Other mixed oxides having a composition according to claim 1 can be obtained under the conditions of examples 1-5.

[0263] ​ ​

[0264] The mixed oxide was prepared in the same way as in example 1, except that:

[0265] - the stirring time of the precursor mixture was reduced from 3 hours to 1 hour.

[0266] - the mixture obtained after reaction with the ammonia solution was heated to a temperature of 100°C and kept at this temperature for 2 hours.

[0267] ​ ​

[0268] The mixed oxide was prepared in the same way as in example 1, except that:

[0269] - the stirring time of the precursor mixture was reduced from 3 hours to 10 minutes;

[0270] - a 25% ammonia solution was introduced into the precursor mixture under stirring until a pH = 8.5 was obtained;

[0271] - no thermal ageing of the mixture was performed.

[0272] ​

[0273]

[0274]

[0275] All calcined in air

[0276] * Single peak in the region of pores having a size less than 100 nm

[0277] It can be noted that low crystallite sizes can be obtained using method (B). It can also be noted that the porosity of the mixed oxide can be fine-tuned in order to obtain D p,950℃ / 3h and the ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h > 0.85. A narrow peak below 25 nm can also be obtained.

Claims

1. A mixed oxide of aluminum, zirconium, lanthanum, and optionally at least one rare earth metal REM other than cerium and lanthanum, wherein the weight proportions of these elements are as follows: ■ Aluminum between 20.0 and 45.0 wt%; ■ Lanthanum content between 1.0 and 15.0 wt%; ■ The rare earth metal other than cerium and lanthanum is between 0 and 10.0 wt%, provided that if the mixed oxide contains more than one rare earth metal other than cerium and lanthanum, this proportion applies to each of these rare earth metals. ■ Zirconium content between 50.0 and 70.0 wt%; These ratios are expressed as oxide equivalents relative to the total weight of the mixed oxides. Its features After calcining in air at 1100°C for 5 hours, the specific surface area (BET) of the mixed oxide is at least 25 m². 2 / g; Furthermore, after calcining in air at 950°C for 3 hours, the porosity of the mixed oxide, as determined by the N2 porosity assay, was as follows: ■ In the region of pores smaller than 100 nm, the porosity map of this mixed oxide shows a diameter D between 10 and 25 nm. p,950℃ / 3h The peak at the location; ■Ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h Greater than or equal to 0.85; ■V 总,950℃ / 3h Greater than or equal to 0.35 ml / g; V <30nm,950℃ / 3h V 总,950℃ / 3h These represent the pore volume of the mixed oxide with a size less than 30 nm and its total pore volume, respectively, after calcination in air at 950°C for 3 hours.

2. The mixed oxide according to claim 1, wherein the porosity map of the mixed oxide shows a diameter D between 10 and 22 nm. p,950 ℃ / 3h The peak at that location.

3. The mixed oxide according to claim 1, wherein the porosity map of the mixed oxide shows a diameter D between 13 and 19 nm. p,950 ℃ / 3h The peak at that location.

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

5. The mixed oxide according to claim 4, wherein, The proportion of hafnium is less than or equal to 2.0 wt%, which is expressed as HfO2 relative to the total weight of the mixed oxides.

6. The mixed oxide according to any one of claims 1 to 5, wherein, These elements Zr, La, REM—if present, and Hf—if present, exist as oxides in the mixed oxide.

7. The mixed oxide according to any one of claims 1 to 5, wherein, These elements Ce, Zr, La, REM—if present, and Hf—if present, exist as oxides in the mixed oxide and also partly as hydroxides or hydroxy oxides.

8. A mixed oxide comprising an oxide of aluminum, zirconium, lanthanum, optionally at least one rare earth metal REM other than cerium and lanthanum, and optionally hafnium, wherein the weight proportions of these elements are as follows: ■ Aluminum between 20.0 and 45.0 wt%; ■ Lanthanum content between 1.0 and 15.0 wt%; ■ The rare earth metals other than cerium and lanthanum are between 0 and 10.0 wt%, provided that if the mixed oxide contains more than one rare earth metal other than cerium and lanthanum, this proportion applies to each of these rare earth metals. ■ The proportion of hafnium is less than or equal to 2.0 wt%; ■ Zirconium content between 50.0 and 70.0 wt%; These ratios are expressed as oxide equivalents relative to the total weight of the mixed oxides. Its features After calcining in air at 1100°C for 5 hours, the specific surface area (BET) of the mixed oxide is at least 25 m². 2 / g; Furthermore, the porosity of the mixed oxide, determined by the N2 porosity assay after calcination in air at 950°C for 3 hours, is as follows: ■ In the region of pores smaller than 100 nm, the porosity map of this mixed oxide shows a diameter D between 10 and 25 nm. p,950℃ / 3h The peak at the location; ■Ratio V <30nm,950℃ / 3h / V 总,950℃ / 3h Greater than or equal to 0.85; ■V 总,950℃ / 3h Greater than or equal to 0.35 ml / g; V <30nm,950℃ / 3h V 总,950℃ / 3h These represent the pore volume of the mixed oxide with a size less than 30 nm and its total pore volume, respectively, after calcination in air at 950°C for 3 hours.

9. The mixed oxide according to claim 8, wherein the porosity map of the mixed oxide shows a diameter D between 10 and 22 nm. p,950℃ / 3h The peak at that location.

10. The mixed oxide according to claim 8, wherein the porosity map of the mixed oxide shows a diameter D between 13 and 19 nm. p,950℃ / 3h The peak at that location.

11. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, In the air: - After calcination at 1100℃ for 5 hours, the average crystallite size of the zirconium oxide-based crystalline phase was at most 28 nm; and / or - After calcination at 1200℃ for 5 hours, the average size of the microcrystals based on the zirconium oxide phase is at most 44 nm.

12. The mixed oxide according to claim 11, wherein, After calcination at 1100℃ for 5 hours, the average size of the microcrystals based on the zirconium oxide phase was at most 25 nm.

13. The mixed oxide according to claim 11, wherein, After calcination at 1100℃ for 5 hours, the average size of the microcrystals based on the zirconium oxide phase was at most 22 nm.

14. The mixed oxide according to claim 11, wherein, After calcination at 1200℃ for 5 hours, the average size of the microcrystals based on the zirconium oxide phase is at most 35 nm.

15. The mixed oxide according to claim 11, wherein, After calcination at 1200℃ for 5 hours, the average size of the microcrystals based on the zirconium oxide phase was at most 33 nm.

16. The mixed oxide according to claim 11, wherein, The average crystallite size is given by formula (I): t=kλ / (βcosθ)(I) t: Average crystallite size; k: a form factor equal to 0.9; λ, lambda: the wavelength of the incident beam, λ = 1.5406 angstroms; β: Spectral line broadening measured at half the maximum intensity; θ: Bragg angle.

17. The mixed oxide according to claim 11, wherein, The average crystallite size is given by formula (II): t: Average crystallite size; k: a form factor equal to 0.9; λ, lambda: the wavelength of the incident beam, λ = 1.5406 angstroms; H: Full width at half maximum (FWHM) of the diffraction line; s: Increased spectral line width; θ: Bragg angle.

18. The mixed oxide according to claim 11, wherein, This crystalline phase is characterized by a peak at a 2θ angle between 29° and 31°, originating from CuKα1, with λ = 1.5406 Å.

19. The mixed oxide according to claim 11, wherein, This crystalline phase is characterized by a peak at a 2θ angle between 29.0° and 31.0°, originating from CuKα1, λ = 1.5406 Å.

20. The mixed oxide according to claim 11, wherein, This crystalline phase contains zirconium oxide.

21. The mixed oxide according to claim 20, wherein, The crystal phase also contains lanthanum and, optionally, one or more rare earth metals other than cerium and lanthanum.

22. The mixed oxide according to claim 11, wherein, This crystal phase exhibits a tetragonal structure.

23. The mixed oxide according to any one of claims 1-5 or 8-10, wherein the proportion of aluminum is between 25.0 and 40.0 wt%.

24. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The proportion of aluminum is between 25.0 and 35.0 wt%.

25. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The proportion of lanthanum is between 1.0 and 10.0 wt%.

26. The mixed oxide according to claim 25, wherein, The proportion of lanthanum is between 1.0 and 7.0 wt%.

27. The mixed oxide according to claim 25, wherein, The proportion of lanthanum is between 2.0 and 7.0 wt%.

28. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, REM, or when the mixed oxide contains more than one REM, the proportion of each REM is between 1.0 and 10.0 wt%.

29. The mixed oxide according to claim 28, wherein, REM, or when the mixed oxide contains more than one REM, the proportion of each REM is between 1.0 and 7.0 wt%.

30. The mixed oxide according to claim 28, wherein, REM, or when the mixed oxide contains more than one REM, the proportion of each REM is between 2.0 and 7.0 wt%.

31. The mixed oxide according to claim 28, wherein, REM, or when the mixed oxide contains more than one REM, the proportion of each REM is between 2.0 and 7.0 wt%.

32. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The zirconium content is between 55.0 and 65.0 wt%.

33. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The total proportion of zirconium and aluminum is greater than or equal to 80.0 wt%.

34. The mixed oxide according to claim 33, wherein, The total proportion of zirconium and aluminum is greater than or equal to 85.0 wt%.

35. The mixed oxide according to any one of claims 1-5 or 8-10, characterized in that, If the mixed oxide contains more than one REM, the total proportion of these REMs is less than 25.0 wt%.

36. The mixed oxide according to any one of claims 1-5 or 8-10, characterized in that, If the mixed oxide contains more than one REM, the total proportion of these REMs is less than 20.0 wt%.

37. The mixed oxide according to any one of claims 1-5 or 8-10, having the following composition: ■ Aluminum between 25.0 and 35.0 wt%; ■ Lanthanum content between 1.0 and 7.0 wt%; ■ At least one REM between 1.0 and 7.0 wt%; ■ Zirconium content between 55.0 and 65.0 wt%.

38. The mixed oxide according to claim 37, wherein: - The proportion of lanthanum is between 2.0 and 7.0 wt%; and / or - The proportion of REM is between 2.0 and 7.0 wt%.

39. The mixed oxide according to claim 38, wherein, The proportion of lanthanum is between 3.0 and 7.0 wt%.

40. The mixed oxide according to claim 37, wherein, - The proportion of REM is between 3.0 and 7.0 wt%.

41. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The REM is selected from yttrium, neodymium, praseodymium, or a combination of these elements.

42. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The REM, or one of these REMs, is Y.

43. The mixed oxide according to any one of claims 1-5 or 8-10, characterized in that, It does not contain cerium or cerium oxide.

44. The mixed oxide according to any one of claims 1-5 or 8-10, characterized in that, The proportion of cerium, expressed as a percentage of the total weight of the mixed oxides (based on the weight of CeO2 oxide), is less than 1.0 wt%.

45. The mixed oxide according to claim 44, characterized in that, The proportion of cerium is less than 0.5 wt%.

46. ​​The mixed oxide according to claim 44, characterized in that the proportion of cerium is less than 0.2 wt%.

47. The mixed oxide according to claim 44, characterized in that the proportion of cerium is less than 0.05 wt%.

48. The mixed oxide according to claim 44, characterized in that, The proportion of cerium, expressed as a percentage of the total weight of the mixed oxides (based on the weight of CeO2 oxide), is less than 0.05 wt%.

49. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The specific surface area (BET) after calcination in air at 1100°C for 5 hours is at least 28 m². 2 / g.

50. The mixed oxide according to claim 49, wherein, The specific surface area BET is at least 30m². 2 / g.

51. The mixed oxide according to claim 49, wherein, The specific surface area BET is at least 31m². 2 / g.

52. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The specific surface area (BET) after calcination in air at 1100℃ for 5 hours is at most 40 m². 2 / g.

53. The mixed oxide according to claim 52, wherein, The specific surface area BET is at most 35m². 2 / g.

54. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The specific surface area (BET) after calcination in air at 950°C for 3 hours is at least 65 m². 2 / g.

55. The mixed oxide according to claim 54, wherein, The specific surface area BET is at least 80m². 2 / g.

56. The mixed oxide according to claim 54, wherein, The specific surface area BET is at least 85m². 2 / g.

57. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The specific surface area (BET) after calcination in air at 950°C for 3 hours is at most 110 m². 2 / g.

58. The mixed oxide according to claim 57, wherein, The specific surface area BET is at most 95m². 2 / g.

59. The mixed oxide according to claim 57, wherein, The specific surface area BET is at most 90m². 2 / g.

60. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The specific surface area (BET) after calcination in air at 1200°C for 5 hours is at least 9 m². 2 / g.

61. The mixed oxide according to claim 60, wherein, The specific surface area BET is at least 10m². 2 / g.

62. The mixed oxide according to claim 60, wherein, The specific surface area BET is at least 12m². 2 / g.

63. The mixed oxide according to any one of claims 1-5 or 8-10, characterized in that, After calcination in air at 950°C for 3 hours, the porosity diagram of the mixed oxide exhibits a single peak in the region of pores smaller than 100 nm, and this peak is located at a diameter D between 10 and 25 nm. p,950 ℃ / 3h Place.

64. The mixed oxide according to claim 63, wherein the single peak is located at a diameter D between 10 and 22 nm. p,950 ℃ / 3h Place.

65. The mixed oxide according to claim 63, wherein the single peak is located at a diameter D between 13 and 19 nm. p,950 ℃ / 3h Place.

66. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, Ratio V <30nm,950 ℃ / 3h / V 总 ,950℃ / 3h is greater than or equal to 0.

90.

67. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, V 总 The concentration at 950℃ for 3 hours is greater than or equal to 0.40 ml / g.

68. The mixed oxide according to claim 67, wherein the V 总 The concentration at 950℃ for 3 hours is greater than or equal to 0.45 ml / g.

69. The mixed oxide according to any one of claims 1-5 or 8-10, wherein, The diameter D is located between 10 and 25 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 10 nm.

70. The mixed oxide according to claim 69, wherein, The diameter D is located between 10 and 22 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 10 nm.

71. The mixed oxide according to claim 69, wherein, The diameter D is located between 13 and 19 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 10 nm.

72. The mixed oxide according to claim 69, wherein, The diameter D is located between 10 and 25 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 8 nm.

73. The mixed oxide according to claim 72, wherein, The diameter D is located between 10 and 22 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 8 nm.

74. The mixed oxide according to claim 72, wherein, The diameter D is located between 13 and 19 nm. p,950 ℃ / 3h The peak at that location is characterized by a width of at most 8 nm.

75. A method for preparing a mixed oxide according to any one of claims 1 to 74, the method comprising the following steps: (a1) An acidic aqueous dispersion is introduced into a stirred tank containing an alkaline aqueous solution, the acidic aqueous dispersion comprising nitric acid and precursors of oxides of zirconium, lanthanum and, optionally, rare earth metals other than cerium and lanthanum, wherein aluminum hydrate is dispersed. (a2) The dispersion obtained at the end of step (a1) is heated and stirred at a temperature of at least 130°C; (a3) The solids of the dispersion from step (a2) are recovered by solid / liquid separation and the filter cake is washed with water; (a4) The solid obtained at the end of step (a3) ​​is calcined in air at a temperature of at least 800°C.

76. A method for preparing a mixed oxide according to any one of claims 1 to 74, the method comprising the following steps: (b1) Heating and stirring an acidic aqueous dispersion at a temperature of at least 80°C, the acidic aqueous dispersion comprising precursors of nitric acid, zirconium oxyhydroxide, and lanthanum, and optionally oxides of rare earth metals other than cerium and lanthanum, wherein aluminum hydrate is dispersed. (b2) Add the ammonia solution to the mixture obtained at the end of step (b1) until the pH of the mixture is at least 8.0; (b3) Then add the organic texturer to the mixture obtained at the end of step (b2) and stir the mixture; (b4) The solids of the dispersion from step (b3) are recovered by solid / liquid separation and the filter cake is washed with water; (b5) The solid obtained at the end of step (b4) is calcined in air at a temperature of at least 800°C.

77. The method according to claim 75 or 76, wherein, The aluminum hydrate used in step (a1) or step (b1) is based on boehmite aluminum hydrate H, which optionally also contains lanthanum, and exhibits the following porosity after being calcined in air at 900°C for 2 hours: ■ The pore volume in the region of pores with a size less than or equal to 20 nm, denoted by VP20 nm-N2, such that VP20 nm-N2: - Greater than or equal to 10% x VPT-N2; - Less than or equal to 60% x VPT-N2; ■ The pore volume in the region of pores with sizes between 40 and 100 nm is represented by VP40-100nm-N2, such that VP40-100 nm-N2 is greater than or equal to 20% x VPT-N2; ■VPT-N2 represents the total pore volume of the aluminum hydrate after calcination in air at 900°C for 2 hours; ■ These pore volumes were determined using nitrogen porosity measurement techniques.

78. The method of claim 77, wherein the VP20 nm-N2 is greater than or equal to 15% x VPT-N2.

79. The method of claim 77, wherein the VP20 nm-N2 is greater than or equal to 20% x VPT-N2.

80. The method of claim 77, wherein the VP20 nm-N2 is greater than or equal to 30% x VPT-N2.

81. The method of claim 77, wherein the VP40-100 nm-N2 is greater than or equal to 25% xVPT-N2.

82. The method of claim 77, wherein the VP40-100 nm-N2 is greater than or equal to 30% xVPT-N2.

83. Use of the mixed oxide as defined in any one of claims 1 to 74 for the preparation of a catalytic converter.

84. Use of the mixed oxide as defined in any one of claims 1 to 74 as a carrier for at least one noble metal selected from the group consisting of Pt, Rh or Pd.

85. Use of the mixed oxide as defined in any one of claims 1 to 74 as a support for Rh.

86. A composition comprising a mixed oxide according to any one of claims 1 to 74 and optionally at least one mineral material.

87. The composition according to claim 86, further comprising at least one noble metal selected from the group consisting of Pt, Rh or Pd.

88. A catalytic converter comprising a catalytically active support coating prepared from a mixed oxide according to any one of claims 1 to 74 and deposited on a solid support.

89. Use of aluminum hydrates in the preparation of mixed oxides of aluminum, zirconium, lanthanum, and optionally at least one rare earth metal REM other than cerium and lanthanum, particularly mixed oxides of these elements in the following weight proportions: ■ Aluminum between 20.0 and 45.0 wt%; ■ Lanthanum content between 1.0 and 15.0 wt%; ■ The rare earth metals other than cerium and lanthanum are between 0 and 10.0 wt%, provided that if the mixed oxide contains more than one rare earth metal other than cerium and lanthanum, this proportion applies to each of these rare earth metals. ■ Zirconium content between 50.0 and 70.0 wt%; These ratios are expressed as oxide equivalents relative to the total weight of the mixed oxides. The aluminum hydrate is based on boehmite and optionally also contains lanthanum, and is characterized by The following characteristics: - After being calcined in air at 900°C for 2 hours, it exhibits the following characteristics: ■ The pore volume in the region of pores with a size less than or equal to 20 nm is represented by VP20nm-N2, such that VP20 nm-N2: - Greater than or equal to 10% x VPT-N2; - Less than or equal to 60% x VPT-N2; ■ The pore volume in the region of pores with sizes between 40 and 100 nm is represented by VP40-100nm-N2, such that VP40-100 nm-N2 is greater than or equal to 20% x VPT-N2; ■VPT-N2 represents the total pore volume of the aluminum hydrate after calcination in air at 900°C for 2 hours; These pore volumes were determined using nitrogen porosity measurement techniques.

90. The use according to claim 89, wherein the VP20 nm-N2 is greater than or equal to 15% x VPT-N2.

91. The use according to claim 89, wherein the VP20 nm-N2 is greater than or equal to 20% x VPT-N2.

92. The use according to claim 89, wherein the VP20 nm-N2 is greater than or equal to 30% x VPT-N2.

93. The use according to claim 89, wherein the VP40-100 nm-N2 is greater than or equal to 25% xVPT-N2.

94. The use according to claim 89, wherein the VP40-100 nm-N2 is greater than or equal to 30% xVPT-N2.

95. The use according to claim 89, wherein, The mixed oxide is any one of claims 1 to 74.

96. The use according to claim 89, wherein, The aluminum hydrate has a crystalline phase of less than or equal to 60% boehmite.

97. The use according to claim 96, wherein, The aluminum hydrate has a crystalline phase of less than or equal to 50% boehmite.

98. The use according to claim 89, wherein, The aluminum hydrate has a total pore volume VPT-N2 between 0.65 and 1.20 ml / g.

99. The use according to claim 98, wherein, The aluminum hydrate has a total pore volume VPT-N2 between 0.70 and 1.15 ml / g.

100. The use according to claim 98, wherein, The aluminum hydrate has a total pore volume VPT-N2 between 0.70 and 1.10 ml / g.

101. The use according to any one of claims 89-100, wherein, This aluminum hydrate exhibits at least 200m 2 / g BET specific surface area.

102. The use according to claim 101, wherein, This aluminum hydrate exhibits at least 250m 2 / g BET specific surface area.

Images