Mixed oxides based on aluminum and zirconium

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 restore a catalyst after severe degradation, retaining excellent thermal stability and excellent catalytic activity. The present invention also relates to a method for preparing this mixed oxide, and to a method for treating exhaust gases from an internal combustion engine 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 other than lanthanum, which makes it possible to prepare a catalyst that retains a particular porosity, good thermal stability, and good catalytic activity after severe aging. The present invention also relates to a method for preparing this mixed oxide, and to a method for treating exhaust gases from an internal combustion engine using a catalyst prepared from this mixed oxide.

[0002] technical challenges The exhaust system that connects the engine and the muffler of a car is generally equipped with a catalytic converter to purify the exhaust gas. x To convert these harmful substances into environmentally acceptable substances, the exhaust gases are passed through a catalytic converter, which converts CO to CO2 and NO x The carbon dioxide is converted to N2 and O2, and unburned hydrocarbons are burned. In a 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. The support for supporting the precious metal catalyst can be a mixed oxide based on cerium and zirconium. This support is also called a co-catalyst, and it is used to remove CO, NO, x Cerium is an essential component of three-way catalysts, which simultaneously remove harmful components from exhaust gases, such as oxidants and unburned hydrocarbons. Cerium is important because its oxidation number changes depending on the oxygen partial pressure in exhaust gases. CeO2 has the ability to adsorb and desorb oxygen, as well as store oxygen (the so-called OSC ability).

[0003] Rh is a compound that reduces NO from exhaust gases. x It is known that Rh is an effective precious metal for reducing its content. 0 is a better DeNO x Rh IIIIn conventional three-way catalysts where cerium-zirconium mixed oxides are used as promoters and supports for precious metals, oxygen released from CeO2 causes Rh to be desorbed. 0 Rh III The presence of cerium oxide is x known to be detrimental to activity.

[0004] Zirconia is Rh 0 It is known as an excellent carrier for rhodium because it helps stabilize and disperse DeNO x To maintain activity for extended periods of time, better thermal stability of the catalyst is required.

[0005] 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 rhodium that has specific porosity for good mass transfer that allows for activity, particularly efficient catalytic activity of rhodium over an extended period of time.

[0006] The mixed oxide of the present invention aims to solve this problem.

[0007] For the purposes of continuing description, unless otherwise indicated, ranges of values ​​indicated with expressions such as "up to" and "at least" are intended to include the bounding values. Furthermore, weight percent corresponds to percent expressed by weight. Also, unless otherwise indicated, firing is performed in air. [Background technology]

[0008] EP 3085667 discloses zirconia-based bodies that exhibit a P / W ratio (P represents the peak height and W represents the peak width) of 0.03 or greater after heat treatment at 1000° C. for 12 hours. The P / W ratios of the disclosed products are between 0.01 and 0.11, which corresponds to a high W / P ratio of 9-100.

[0009] EP 3345870 discloses a zirconia powder containing 2-6 mole % yttria, which may also contain an aluminum oxide content of less than 2.0%.

[0010] U.S. Patent No. 9,902,654 B2 discloses a ZrO2-Al2O3 ceramic. The specific composition of the ceramic is 80 wt% (97 mol% ZrO2 - 3 mol% Y2O3) - 20 wt% Al2O3, which corresponds to 75.6 wt% ZrO2.

[0011] WO 2019 / 122692 discloses an aluminum hydrate H used to prepare a mixed oxide containing cerium, which is different from the mixed oxide of the present invention.

[0012] None of the cited documents discloses the mixed oxide of claim 1. [Brief explanation of the drawings]

[0013] [Figure 1] Figure 1 shows the porosity curve (C) of the composition of Example 1 obtained by nitrogen porosimetry technique after calcining the mixed oxide in air at 950°C for 3 hours. For this composition, Dp950°C / 3h=17 nm.

[0014] Brief description of the invention 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.

[0015] The mixed oxides of the present invention are disclosed in claims 1 to 41. They are therefore mixed oxides of aluminium, zirconium, lanthanum and optionally at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, in which the weight proportions of these elements are: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0-10.0% 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 and; These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of the mixed oxide after calcination in air at 1100°C for 5 hours is at least 25 m 2 / g; The porosity of the mixed oxides determined by N2 porosimetry after calcination at 950 °C for 3 h in air was In the region of pores with a size of less than 100 nm, the porogram of the mixed oxide has a diameter D of 10 to 25 nm, more particularly 10 to 22 nm, even more particularly 13 to 19 nm. p,950℃ / 3h Showing the peak located at; ·Ratio V <30nm,950℃ / 3h / V total,950℃ / 3h is 0.85 or more; ·V total,950℃ / 3h is 0.35 ml / g or more It's like; V <30nm,950℃ / 3h and V total,950℃ / 3h represent the pore volume of pores with a size less than 30 nm and the total pore volume of the mixed oxide after calcination at 950 °C in air for 3 h, respectively. The mixed oxide is characterized by:

[0016] The present invention also relates to a method according to any one of claims 42 to 44, to the use of a mixed oxide according to any one of claims 45 to 47, to a composition according to any one of claims 48 to 49, and to a catalytic converter according to claim 50. It also relates to the use of an aluminum hydrate according to the following and any one of claims 51 to 56 for the preparation of a mixed oxide. These objects are further defined hereinafter.

[0017] Detailed Description of the Invention As regards 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 being as follows: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0-10.0% 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.

[0018] Rare earth metals (REM) are understood to mean elements selected from the elements of the yttrium group and the elements with atomic numbers 57 to 71 of the periodic table.

[0019] In mixed oxides, the above-mentioned elements Al, La, REM (if present), and Zr are usually 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 determined in the laboratory using conventional analytical techniques, in particular plasma torch and X-ray fluorescence. As is common in the field of mixed oxides, the proportions of these elements are expressed in terms of the weight of the equivalent amount of oxide relative to the total weight of the mixed oxide.

[0020] The mixed oxide contains the elements mentioned above in the proportions indicated, but it may also contain other elements, for example impurities. In this regard, it should 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.

[0021] The impurities usually 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 usually 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 usually less than 1.0% by weight, or even less than 0.5% by weight, or less than 0.2% by weight, or even less than 0.05% by weight.

[0022] The mixed oxide may also contain hafnium, which is typically present in association with zirconium in natural ores. The ratio of hafnium to zirconium depends on the ore from which the zirconium is extracted. Thus, the Zr / Hf weight ratio in some ores may be approximately 50 / 1. Thus, for example, baddeleyite contains approximately 98% zirconium oxide to 2% hafnium oxide. Like zirconium, hafnium generally exists in the oxide form. However, it is not excluded that it may exist at least partially in the hydroxide or oxyhydroxide form. The weight percentage of hafnium in the mixed oxide, expressed as the amount of oxide equivalent relative to the total weight of the mixed oxide, is 2.0% or less. The hafnium percentage may be 0-2.0% by weight. Impurities and the percentage of hafnium may be measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0023] The percentages of the constituent elements Al, La, REM, Zr, and sometimes Hf are given as the weight of the oxide. In calculating these percentages, 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 oxides of the rare earth metals, except praseodymium, are in the form of REM2O3, which is Pr6O 11 As an example, a mixed oxide with only one REM, having the proportions of 30 wt. % Al, 60 wt. % Zr, 5 wt. % La, and 5 wt. % Y, calculated as oxides, corresponds to 30 wt. % Al2O3, 60 wt. % ZrO2, 5 wt. % La2O3, and 5 wt. % Y2O3.

[0024] In the mixed oxides according to the invention, the above-mentioned elements are thoroughly mixed, which distinguishes them from simple mechanical mixtures of oxides in solid form, which is achieved by the precipitation step in the preparation of the mixed oxides.

[0025] The weight percentage of aluminum is 20.0% to 45.0% by weight, more specifically 25.0% to 40.0% by weight, and even more specifically 25.0% to 35.0% by weight.

[0026] The weight percentage of lanthanum is 1.0 wt % to 15.0 wt %, more specifically 1.0 wt % to 10.0 wt %, even more specifically 1.0 wt % to 7.0 wt %, or even 2.0 wt % to 7.0 wt %.

[0027] The mixed oxide may also contain one or more rare earth metals (REM) other than cerium or lanthanum. The rare earth metals may be selected from, for example, yttrium, neodymium, praseodymium, or a combination of these elements. The mixed oxide may, for example, contain only a single REM in a proportion of 0 to 10.0% by weight. The proportion of REM may be 1.0% to 10.0% by weight, more specifically 1.0% to 7.0% by weight, or even 2.0% to 7.0% by weight.

[0028] The mixed oxide may also contain two or more REMs, in which case the disclosed percentages apply to each REM, provided that the total percentage of these REMs remains below 25.0% by weight, more specifically below 20.0% by weight.

[0029] More specifically, REM or one of REM is Y.

[0030] The mixed oxide also contains zirconium, the weight proportion of which may be 50.0% to 70.0% by weight, more particularly 55.0% to 65.0% by weight.

[0031] 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.

[0032] The lanthanum content may be 2.0% to 7.0% by weight, more specifically 3.0% to 7.0% by weight, and the REM content may be 2.0% to 7.0% by weight, more specifically 3.0% to 7.0% by weight.

[0033] The mixed oxides of the invention advantageously comprise a combination of oxides of aluminum and zirconium. For the mixed oxides of the invention, more particularly for mixed oxide C, the total proportion of zirconium and aluminum is preferably greater than or equal to 80.0% by weight, more particularly greater than or equal to 85.0% by weight.

[0034] Mixed oxide characterization Crystallite size The mixed oxides are characterized by the following facts after calcination in air: - at 1100°C for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is at most 28 nm, or at most 25 nm, or even at most 22 nm; and / or At 1200° C. for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is at most 44 nm, or at most 35 nm, or even at most 33 nm.

[0035] At 1100° C. for 5 hours, the average crystallite size of the zirconium oxide based crystalline phase is at most 28 nm, preferably at most 25 nm, more preferably at most 22 nm.

[0036] At 1200° C. for 5 hours, the average crystallite size of the zirconium oxide based crystalline phase is at most 44 nm, preferably at most 35 nm, more preferably at most 33 nm.

[0037] Crystalline phases based on zirconium oxide are typically characterized by peaks located at 2θ angles between 29° and 31° (source: CuKα1, λ = 1.5406 Å). Peaks typically occur at 2θ angles between 29.0° and 31.0° (source: CuKα1, λ = 1.5406 Å).

[0038] The crystalline phase comprises zirconium oxide and may also comprise lanthanum and optionally a rare earth metal other than cerium and other than lanthanum.

[0039] The crystalline phase usually exhibits a tetragonal structure, which can be characterized by X-ray diffraction techniques or 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.

[0040] The average crystallite size is determined by X-ray diffraction techniques. It corresponds to the size of the coherent region calculated from the diffraction line width 2θ using the Scherrer equation. According to the Scherrer equation, t is given by Equation (I): t=kλ / (βcosθ) (I) t: average crystallite size; k: shape factor equal to 0.9; λ (lambda): wavelength of incident beam (λ = 1.5406 Å); β: line broadening measured at half maximum intensity; θ: Bragg angle

[0041] Typically, instrumental broadening is taken into account to determine β.

[0042] In equation (II), the following equation can be used, where s is the instrumental broadening:

number

[0043] s depends on the instrument used and the 2θ (theta) angle.

[0044] specific surface area The mixed oxides according to the invention also have a large specific surface area, which is understood to mean the BET specific surface area obtained by nitrogen adsorption, which is determined using the well-known Brunauer-Emmett-Teller method.

[0045] The BET method is specifically described in the journal "The Journal of the American Chemical Society, 60, 309 (1938)." The recommendations of the standard ASTM D3663-03 can be followed. Hereinafter, the abbreviation S T(℃) / x(h) is used to mean 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 after the composition is fired at 1100°C for 5 hours.

[0046] To determine specific surface area by nitrogen adsorption, Micromeritics Flowsorb II 2300 or Tristar 3000 instruments can be used, following the manufacturer's guidelines. They can also be measured automatically using Mountech Macsorb Analyzer Model I-1220, following the manufacturer's guidelines. Prior to measurement, samples are preferably degassed by heating under vacuum at temperatures up to 300°C to remove adsorbed volatile species.

[0047] Specific surface area S 1100℃ / 5h is at least 25m 2 / g. This specific surface area is preferably at least 28 m 2 / g, more preferably at least 30m 2 / g, more preferably at least 31m 2 / g. Therefore, the specific surface area is 25 to 40 m 2 / g, more specifically 28-40m 2 / g, more specifically 31-40m 2 / g. This specific surface area can be up to 40 m 2 / g, more specifically up to 35m 2 / g. This specific surface area may be at least 35 m 2 / g.

[0048] Specific surface area S 950℃ / 3h is at least 65m 2 / g, more preferably at least 80m 2 / g, more preferably at least 85m 2 / g. This specific surface area can be up to 110 m 2 / g, more specifically up to 95m 2 / g, or up to 90m 2 / g.

[0049] Specific surface area S 1200℃ / 5h is at least 9m 2 / g, more preferably at least 10m 2 / g, more preferably at least 12m 2 / g. This specific surface area can be up to 15m 2 / g.

[0050] Nitrogen Porosimetry The mixed oxides are also characterized by a particular porosity that allows for good mass transport and good dispersion of the precious metals. In the context of the present invention, the particular porosity is shown for the mixed oxides after calcination in air at 950°C for 3 hours.

[0051] The porosity data disclosed in this application were obtained by nitrogen porosimetry techniques. This technique allows the determination of pore volume (V) as a function of pore diameter (D). More precisely, from nitrogen porosimetry data, it is possible to obtain a curve (C) that represents the derivative of the function V as a function of log D (dV / dlogD). The derivative curve (C) is the function of D. p From these data it is also possible to obtain the following characteristics regarding the porosity of the mixed oxide: Total pore volume (V) in ml / g obtained from the porosimetry data read on the cumulative curve total represented by); Pore ​​volume (V) in ml / g caused by pores of size 30 nm or less, obtained from porosimetry data read on the cumulative curve <30nm (represented by

[0052] When these parameters were measured after calcining the mixed oxides at 950 °C for 3 h in air, they were D p,950℃ / 3h , V total,950℃ / 3h , and V <30nm,950℃ / 3h It is expressed as:

[0053] The nitrogen porosimetry technique is a well-known technique and is very commonly applied to inorganic materials. Porosity can be obtained on a Micromeritics Tristar II 3000 instrument. The conditions for determining porosity can be as detailed in the examples. The nitrogen porosimetry technique can be performed according to ASTM D4641-17.

[0054] In the pore region with a size of less than 100 nm, the porogram of the mixed oxide after calcination at 950 °C for 3 hours in air shows diameters D of 10 to 25 nm, more specifically 10 to 22 nm, and even more specifically 13 to 19 nm. p,950℃ / 3h The porogram may show two or more peaks in the pore region with sizes less than 100 nm, but shows peaks with diameters D between 10 and 25 nm, more specifically between 10 and 22 nm, and even more specifically between 13 and 19 nm.p,950℃ / 3h However, after calcination at 950°C for 3 hours in air, there is usually only one peak in the region of pores with sizes less than 100 nm, said peak being at a diameter D of 10 to 25 nm, more specifically 10 to 22 nm, and even more specifically 13 to 19 nm. p,950℃ / 3h The present invention therefore relates to a mixed oxide of aluminium, zirconium, lanthanum and optionally at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, in which the weight proportions of these elements are: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0-10.0% 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 and; These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of the mixed oxide after calcination in air at 1100°C for 5 hours is at least 25 m 2 / g; The porosity of the mixed oxides determined by N2 porosimetry after calcination at 950 °C for 3 h in air was In the region of pores with a size of less than 100 nm, the porogram of the mixed oxide has a diameter D of 10 to 25 nm, more particularly 10 to 22 nm, even more particularly 13 to 19 nm. p,950℃ / 3h shows a single peak located at ; ·Ratio V <30nm,950℃ / 3h / V total,950℃ / 3h is 0.85 or more; ·V total,950℃ / 3h is 0.35 ml / g or more It's like; V <30nm,950℃ / 3h and V total,950℃ / 3hrepresent the pore volume of pores with a size less than 30 nm and the total pore volume of the mixed oxide after calcination at 950 °C in air for 3 h, respectively; The present invention also relates to a mixed oxide, characterized in that

[0055] Ratio V <30nm,950℃ / 3h / V total,950℃ / 3h is 0.85 or more. This ratio may preferably be 0.90 or more.

[0056] V total,950℃ / 3h The V is also 0.35 ml / g or more. total,950℃ / 3h may be preferably 0.40 ml / g or more, more preferably 0.45 ml / g or more.

[0057] Additionally, a diameter D of 10 to 25 nm, more specifically 10 to 22 nm, and even more specifically 13 to 19 nm p,950℃ / 3h The half-width of said peak located at is up to 10 nm, more particularly up to 8 nm, demonstrating that the method of the invention allows fine tuning of the porosity.

[0058] The mixed oxide is usually in powder form.

[0059] All that has been disclosed above is still applicable to mixed oxides 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 weight percentages of these elements being: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0-10.0% 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); Hafnium in a proportion of not more than 2.0% by weight; 50.0% to 70.0% by weight of zirconium and these proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of the mixed oxide after calcination in air at 1100°C for 5 hours is at least 25 m 2 / g; The porosity of the mixed oxides determined by N2 porosimetry after calcination at 950 °C for 3 h in air was In the region of pores with a size of less than 100 nm, the porogram of the mixed oxide has a diameter D of 10 to 25 nm, more particularly 10 to 22 nm, even more particularly 13 to 19 nm. p,950℃ / 3h Showing the peak located at; ·Ratio V <30nm,950℃ / 3h / V total,950℃ / 3h is 0.85 or more; ·V total,950℃ / 3h is 0.35 ml / g or more It's like; V <30nm,950℃ / 3h and V total,950℃ / 3h represent the pore volume of pores with a size less than 30 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:

[0060] Method for preparing mixed oxides For the preparation of the mixed oxide according to the invention, the following disclosed methods (A) or (B) can be followed: Method (A) comprises the following steps: (a1) introducing an acidic aqueous dispersion containing nitric acid and precursors of oxides of zirconium, lanthanum, and optionally rare earth metals other than cerium and other than lanthanum, in which aluminum hydrate is dispersed, 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 solid content of the dispersion from 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 of at least 800°C.

[0061] Method (A) does not include the step of adding a texturing agent such as lauric acid.

[0062] Process (a1) In step (a1), an aqueous acidic dispersion is used that contains precursors of oxides of zirconium, lanthanum, and optionally one or more rare earth metals other than cerium and lanthanum, and nitric acid, in which an aluminum hydrate, for example, aluminum monohydrate, is dispersed. The aqueous acidic dispersion does not contain a precursor of cerium oxide.

[0063] 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 carried out 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 250-350 g / l. For example, the zirconyl nitrate solution used in Example 1 obtained by carbonate attack has a concentration of 295 g / l.

[0064] The precursor of lanthanum oxide may be lanthanum nitrate. The precursor of the rare earth metal oxide other than cerium and lanthanum may be a nitrate or chloride, such as praseodymium nitrate, neodymium nitrate, yttrium chloride YCl3, or yttrium nitrate Y(NO3)3.

[0065] According to one embodiment, the precursors of the oxides of Zr, La, and REM are all in the form of nitrates.

[0066] The aqueous acid dispersion also contains nitric acid. + The concentration of H 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.

[0067] The aqueous acidic dispersion comprises an aluminum hydrate, more particularly one based on boehmite, optionally also containing lanthanum. The aluminum hydrate is more preferably one described in WO 2019 / 122692 and having a particular porosity, hereinafter designated Aluminum Hydrate H. This particular Aluminum Hydrate H is well dispersible in aqueous acidic media.

[0068] About Aluminum Hydrate H This aluminum hydrate H is based on boehmite, optionally also containing lanthanum, characterized in that after calcination in air at a temperature of 900° C. for 2 hours it exhibits the following: ·VP20nm-N2, - ≥ 10% × VPT-N2, more particularly ≥ 15% × VPT-N2, or even ≥ 20% × VPT-N2, or even ≥ 30% × VPT-N2; - 60% × VPT-N2 or less pore volume in the pore region with a size of 20 nm or less (represented by VP20nm-N2); the pore volume in the region of pores having a size between 40 and 100 nm (expressed as VP40-100nm-N2), such that VP40-100nm-N2 is 20% × VPT-N2 or more, more particularly 25% × VPT-N2 or even 30% × VPT-N2; ·VPT-N2 represents the total pore volume of aluminum hydrate after calcination in air at 900 °C for 2 h; Pore ​​volume is determined by nitrogen porosimetry technique.

[0069] In European nomenclature and as known, the term "boehmite" refers to gamma oxyhydroxide (γ-AlOOH). In this application, the term "boehmite" refers to various aluminum hydrates with specific crystalline forms known to those skilled in the art. Therefore, boehmite can be characterized by X-ray diffraction. The term "boehmite" also includes "pseudoboehmites," which, according to certain authors, resemble only one specific variety of boehmite and simply possess the characteristic peak broadening of boehmite. Boehmite is identified by X-ray diffraction by its characteristic peaks, which are listed in file JCPDS00-021-1307 (JCPDS = Joint Committee on Powder Diffraction Standards). It should be noted that the apex of the peak (020) can be between 13.0° and 15.0°, depending, among other things: - crystallinity of boehmite; - boehmite crystallite size.

[0070] Reference may be made to Journal of Colloidal and Interface Science 2002, 253, 308-314 or J. Mater. Chem. 1999, 9, 549-553, which states that for a certain number of boehmite, the position of the peak varies depending on the number of layers in the crystal or the size of the crystallite. This peak may be more specifically between 13.5° and 14.5°, or between 13.5° and 14.485°.

[0071] When the aluminum hydrate contains lanthanum, the proportion of lanthanum is 1.0 wt% to 8.0 wt%, more specifically 3.0 wt% to 8.0 wt%, or 4.0 wt% to 8.0 wt%. This proportion is given by the weight of La2O3 relative to the weight of Al2O3 and La2O3 (in other words, the ratio of La in weight % = weight of La2O3 / weight of La2O3 + weight of Al2O3 × 100). In other words, this proportion 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 usually present in the aluminum hydrate in the form of lanthanum oxide.

[0072] A convenient method for determining the percentage of La in aluminum hydrate is to calcinate the aluminum hydrate in air, attack the calcined product with, for example, concentrated nitric acid solution to dissolve the elements in solution, and then analyze it by techniques known to those skilled in the art, such as ICP, to determine the percentage of Al and La. Calcination can also determine the loss on ignition (LOI) of the hydrate. The LOI of aluminum hydrate may be 20.0-30.0%.

[0073] The boehmite contained in the aluminum hydrate, more particularly aluminum hydrate H, may have an average crystallite size of at most 6.0 nm, or even at most 4.0 nm, more particularly at most 3.0 nm. The average crystallite size is determined by X-ray diffraction techniques and corresponds to the size of the coherent region calculated from the full width at half maximum of the (020) line.

[0074] Aluminum hydrate H may be in the form of a mixture of boehmite, distinguishable by X-ray diffraction techniques as described above, and phases not visible by X-ray diffraction, particularly amorphous phases. Aluminum hydrate H may have a crystalline phase (boehmite) percentage of 60% or less, more specifically 50% or less. This percentage may be 40% to 55%, or 45% to 55%, or 45% to 50%. This percentage is determined by methods known to those skilled in the art. This percentage can be determined using the following formula, which compares the intensity of the (120) peak of the aluminum hydrate with the intensity of the (120) peak of the standard: % crystallinity = (120) peak intensity / (120) peak intensity of the standard × 100. The standard used in this application is a product corresponding to Example B1 of U.S. Patent Application Publication No. 2013 / 017947. The measured intensity corresponds to the surface area of ​​the (120) peak above the baseline. These intensities are determined in a diffractogram based on a baseline acquired in the 2θ angle range of 5.0° to 90.0°. The baseline is determined automatically using software for analyzing the diffractogram data.

[0075] 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 region of pores having a size of 20 nm or less (denoted as VP20nm-N2) such that VP20nm-N2 is 20% × VPT-N2 or more, more particularly 25% × VPT-N2 or more, or even 30% × VPT-N2 or more. Furthermore, VP20nm-N2 is 60% × VPT-N2 or less.

[0076] Furthermore, after calcination at 900°C for 2 hours in air, aluminum hydrate H has a pore volume in the region of pores having a size of 40 to 100 nm (denoted as VP40-100nm-N2) such that VP40-100nm-N2 is 15% x VPT-N2 or more, more particularly 20% x VPT-N2 or more, or even 25% x VPT-N2 or more, or even 30% x VPT-N2 or more. Furthermore, VP40-100nm-N2 may be 65% x VPT-N2 or less.

[0077] After calcination in air at 900°C for 2 hours, aluminum hydrate H may have a total pore volume (VPT-N2) of 0.65 to 1.20 ml / g, more specifically 0.70 to 1.15 ml / g, or 0.70 to 1.10 ml / g. It is noted that the pore volume measured in this manner is primarily represented by pores with diameters of 100 nm or less.

[0078] Aluminum hydrate H is at least 200m 2 / g, more specifically at least 250m 2 / g. This specific surface area is 200 to 400 m 2 Furthermore, 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 specifically at least 150m 2 / g. This specific surface area is 130 to 220 m 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 viscosity of at least 80 m 2 / g, more specifically at least 100m 2 / g. This specific surface area is 80 to 120 m 2 / g.

[0079] The aluminum hydrate H can be obtained by a process comprising the following steps: (a) In a stirring vessel containing an aqueous solution of nitric acid, an aqueous solution containing aluminum sulfate, lanthanum nitrate and nitric acid (A); Sodium aluminate aqueous solution (B) introducing aqueous solution (A) continuously throughout step (a) and adjusting the rate of introduction of solution (B) so that the average pH of the reaction mixture is equal to a target value of 4.0 to 6.0, more specifically 4.5 to 5.5; (b) continuing the introduction of aqueous solution (B) until the target pH reaches 8.0 to 10.5, preferably 9.0 to 10.0, when the entire aqueous solution (A) is introduced; (c) then filtering the reaction mixture and washing the recovered solid with water; (d) thereafter drying the solid obtained from step (c) to obtain aluminum hydrate H.

[0080] Details of the method for obtaining aluminum hydrate H are also described in the examples of WO 2019 / 122692. The aluminum hydrate H disclosed in the examples of this patent application can be used.

[0081] The invention therefore relates to mixed oxides of aluminium, zirconium, lanthanum and, optionally, at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, in particular in which the weight proportions of these elements are: 20.0% to 45.0% by weight of aluminum; 1.0% to 15.0% by weight of lanthanum; 0-10.0% 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 and; It also relates to the use of aluminum hydrate H for the preparation of mixed oxides, wherein these proportions are expressed as equivalent amounts of oxide relative to the total weight of the mixed oxide.

[0082] The present invention therefore also relates to the use of aluminium hydrate H for the preparation of the mixed oxides according to the invention, in particular the mixed oxides disclosed in any one of claims 1 to 40.

[0083] For the preparation of the aqueous acidic dispersion used in method (A), it is advantageous to keep the mixture under stirring for a time sufficient to obtain a high specific surface area (see Comparative Example 1). The mixture should preferably be stirred for 1 to 5 hours.

[0084] The aqueous acidic dispersion used in step (a1) 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 also be used. As described in the examples below, an aqueous ammonia solution may be used. As in the examples, an aqueous ammonia solution with a concentration of, for example, 3 to 5 mol / l may be used.

[0085] The amount of base should be in excess of the amount of cations present in the aqueous acidic dispersion. This excess ensures complete precipitation of the cations. The ratio of base / Σ cations from precursor × valence + H from nitric acid should be greater than 1.2, more specifically greater than 1.4. + can be used, where the molar ratio takes into account the valence of the cations from the precursor (e.g., 2 for Zr and 3 for La).

[0086] Process (a2) The dispersion obtained at the end of step (a1) is heated and stirred at a temperature of at least 130°C. The temperature may be between 130°C and 200°C, more specifically between 130°C and 170°C. The duration of step (a2) is typically between 10 minutes and 5 hours, more specifically between 1 hour and 3 hours. For example, the dispersion can be heated to 150°C and maintained at this temperature for 2 hours.

[0087] 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 can be 1 bar (10 5 Pa) to 165 bar (1.65 × 10 7 Pa), preferably 5 bar (5 × 10 5 Pa) ~ 165 bar (1.65 × 10 7 It can be defined that the temperature can vary in increments of 100 Pa.

[0088] Process (a3) The solids of the dispersion of step (a2) are recovered by solid / liquid separation and the cake is washed with water. For washing the cake, it is convenient to use a diluted ammonia solution. For example, a vacuum filter, e.g., of the Nutsche type, a centrifuge or a filter press can be used.

[0089] Of course, the cake recovered at the end of step (a3) ​​may still contain small amounts of residual water, but this does not substantially affect the quality of the mixed oxide, although the cake may optionally be dried to remove small amounts of residual water.

[0090] Process (a4) The solid obtained at the end of step (a3) ​​is calcined in air at a temperature of at least 800°C. The calcination temperature must be high enough to convert the solid into a mixed oxide and develop its crystallinity. To maintain a high specific surface area, the temperature must not be too high. The calcination temperature can be 800°C to 1200°C, more specifically 900°C to 1100°C, or 900°C to 1000°C. The calcination duration can be 30 minutes to 5 hours, more specifically 1 hour to 4 hours. The conditions of Example 1 (950°C; 3 hours) can be applied.

[0091] The preparation of the mixed oxide according to the invention can be based on the conditions of Example 1 given below.

[0092] The mixed oxide can also be prepared by a method (B) comprising the steps of: (b1) heating and stirring an acidic aqueous dispersion comprising nitric acid, zirconium oxyhydroxide, a precursor of lanthanum oxide, and optionally a precursor of an oxide of a rare earth metal other than cerium and other than lanthanum, and having aluminum hydrate dispersed therein, at a temperature of at least 80°C; (b2) adding ammonia solution to the mixture obtained at the end of step (b1) until the pH of the mixture is at least 8.0; (b3) thereafter adding an organic texturing agent to the mixture obtained at the end of step (b2) and stirring the mixture; (b4) recovering the solids of the dispersion of step (b3) by solid / liquid separation and washing the cake with water; (b5) calcining the solid obtained at the end of step (b4) in air at a temperature of at least 800°C.

[0093] Process (b1) An acidic aqueous dispersion is used that contains nitric acid, zirconium oxyhydroxide, a precursor of lanthanum oxide, and optionally a precursor of an oxide of a rare earth metal other than cerium and other than lanthanum, with aluminum hydrate dispersed therein. What has been disclosed about the precursors of lanthanum oxide and REM oxides used in method (A) is also applicable here.

[0094] The aqueous acid dispersion also contains nitric acid. + The concentration of H 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.

[0095] The precursor of zirconium oxide is zirconium oxyhydroxide, which can generally be represented by ZrO(OH)2. The powder used to prepare the aqueous acidic dispersion is advantageously characterized by an average size d50 of 5.0 to 100 μm, more specifically 5.0 μm to 50.0 μm, and even more specifically 25.0 μm to 40.0 μm, or 28.0 to 30.0 μm. d50 corresponds to the median value of the particle size (volume) distribution obtained with a laser diffraction particle size analyzer such as the HORIBA LA-920. d50 is typically determined on a dispersion of the oxyhydroxide in water. The oxide content, expressed as a weight percent of ZrO2, of the zirconium oxyhydroxide is typically 35.0% to 55.0%. An example of a zirconium oxyhydroxide that can be conveniently used as a raw material and precursor to zirconium oxide is grade TZH-40, available from Terio (18 / A, Huaren International Building, 2A Shandong Road, Qingdao, Qingdao, Shandong, China). This grade has the following properties: oxide content: ZrO2 + HfO2 > 40 wt.%, %ZrO2 = 43.0 wt.%, d50 = 27 μm - 32 μm. Further product details can be found at http: / / www.terio.cn / product / detail / 11.

[0096] The aqueous acidic dispersion is heated to a temperature of at least 80° C., more specifically at least 90° C., or even at least 100° C. The temperature may reach 200° C. The temperature must be high enough to form a precipitate containing Zr, La, and, if present, REM.

[0097] The aluminum hydrate is preferably aluminum hydrate H as disclosed above.

[0098] Process (b2) Ammonia solution is added to the mixture obtained at the end of step (b1) until the pH of the mixture is at least 8.0.

[0099] Process (b3) An organic texturing agent is then added to the mixture obtained at the end of step (b2) and the mixture is stirred.

[0100] Organic texturing agents (or "template agents") refer to organic compounds, such as surfactants, that can modify the porous structure of the mixed oxide, especially pores less than 500 nm in size. The organic texturing agent can be added in the form of a solution or dispersion. The amount of organic texturing agent, expressed as the weight percentage of the additive relative to the weight of the mixed oxide obtained after the calcination step, is typically 5-100 wt. %, more specifically 15-60 wt. %.

[0101] The organic texturing agent is preferably selected from the group consisting of: (i) anionic surfactants, (ii) nonionic surfactants, (iii) polyethylene glycols, (iv) monoacids with a hydrocarbon tail containing from 7 to 25, more particularly from 7 to 17, carbon atoms and salts thereof, and (v) carboxymethylated fatty alcohol ethoxylate type surfactants.

[0102] Anionic surfactants include ethoxy carboxylates, ethoxylated fatty acids, sarcosinates, phosphate esters, sulfates such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, as well as sulfosuccinates and sulfonates such as alkylbenzene or alkylnaphthalene sulfonates. Nonionic surfactants include 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, polyglyceryl esters and their ethoxylated derivatives, alkylamines, alkylimidazolines, ethoxylated oils, and alkylphenol ethoxylates. Products sold under the brands Igepal®, Dowanol®, Rhodamox®, and Alkamide® are particularly well-known.

[0103] The organic texturing acid may be a monocarboxylic acid having a hydrocarbon tail containing from 7 to 25, more specifically from 7 to 17, carbon atoms. More specifically, the organic texturing acid may be a monocarboxylic acid having a hydrocarbon tail containing from 7 to 25, more specifically from 7 to 17, carbon atoms. n H 2n+1 Mention may be made of saturated COOH acids (n is an integer from 7 to 25, more particularly from 7 to 17). The following acids may in particular be used: caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, and palmitic acid. More particularly, mention may also be made of lauric acid and ammonium laurate.

[0104] Finally, it is also possible to use surfactants selected from those of the carboxymethylated fatty alcohol ethoxylate type. The expression "carboxymethylated fatty alcohol ethoxylate type products" is intended to mean products consisting of ethoxylated or propoxylated fatty alcohols containing a -CH2-COOH group at the end of the chain. These products have the following formula: R1-O-(CR2R3-CR4R5-O) m -CH2-COOH wherein R1 denotes a saturated or unsaturated carbon-based chain whose length is usually at most 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4 and R5 may be identical or represent hydrogen, or R2 may represent an alkyl group, e.g., a CH3 group, and R3, R4 and R5 represent hydrogen; and m is a non-zero integer which may be at most 50, more particularly 5 to 15, inclusive. It is noted that the surfactant may consist of a mixture of products of the above formula in which R1 may each be saturated or unsaturated, or alternatively a mixture of products containing both -CH2-CH2-O- and -C(CH3)=CH2-O- groups.

[0105] The proportion of texturing agent used is typically between 20% and 40% by weight, more particularly between 25% and 35% by weight, this proportion being expressed as a weight percentage of texturing agent relative to the mixed oxide.

[0106] Process (b4) The solids of the dispersion of step (b3) are recovered by solid / liquid separation and the cake is washed with water. For washing the cake, it is convenient to use a diluted ammonia solution. What has been said about step (a3) ​​also applies here.

[0107] Process (b5) At the end of step (b4) the solid obtained is calcined in air at a temperature of at least 800° C. What was stated for step (a4) also applies here.

[0108] The preparation of the mixed oxide according to the invention can be based on the conditions of Example 2 given below.

[0109] Step (a5) or (b6) During step (a5) or (b6), the mixed oxide obtained in step (a4) or step (b5), respectively, may optionally be milled to obtain a powder of the desired particle size. For example, a hammer mill or a mortar mill may be used. The powder may also be sieved to control its particle size.

[0110] The present invention also relates to mixed oxides obtainable by the processes (A) and (B) described above.

[0111] 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.

[0112] Catalytic converters contain a catalytically active washcoat made 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 may be: 2CO+O2→2CO2 2NO+2CO→N2+2CO2 4C x H y +(4x+y)O2 → 4×CO2 + 2yH2O

[0113] The solid support may be a metal monolith, e.g., an FeCr alloy, or may be made of ceramic. The ceramic may be cordierite, silicon carbide, alumina titanate, or mullite. Commonly used solid supports consist of monoliths, generally cylindrical, containing many small parallel channels with porous walls. This type of support is often made of cordierite, which offers a compromise between a high specific surface area and a limited pressure drop.

[0114] The washcoat is deposited on the surface of a solid support. The washcoat is formed from a composition comprising the mixed oxide of the present invention and, optionally, at least one inorganic material. The inorganic material can 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, and this alumina can be optionally doped with, for example, an alkaline earth metal such as barium. According to one embodiment, the washcoat does not contain cerium oxide (a "cerium-free washcoat"). According to another embodiment, the washcoat does not contain any inorganic material other than the mixed oxide of the present invention.

[0115] The compositions may also contain other additives specific to each formulation: H2S scavengers, organic or inorganic modifiers that facilitate coating, colloidal alumina, etc. Thus, washcoats include such compositions. The washcoats also contain at least one dispersed noble metal. The noble metal may be selected from the group consisting of Pt, Rh, or Pd. Rh, in particular, may be added to the noble metals, such as NO x The amount of precious metal is generally in the range of ft 3 The unit is 1 to 400 g relative to the volume of the monolith. Noble metals have catalytic activity.

[0116] To disperse the precious metals, it is possible to add salts of the precious metals to the suspension made from the mixed oxides or inorganic substances (if present) or to the suspension of the mixture formed from the mixed oxides and inorganic substances. These salts are, for example, chlorides or nitrates of the precious metals (e.g., Rh III To immobilize the precious metal, water is removed from the suspension, the solid is dried, and it is calcined in air, typically at temperatures 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.

[0117] The washcoat is obtained by applying the suspension to a solid support. As a result, the washcoat 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 ultimately suppresses NOx, even in an oxidizing environment. x As a trap or NO x can be used to promote the reduction of

[0118] For this reason, the present invention also relates to a method for treating exhaust gases from an internal combustion engine, characterized in that it uses a catalytic converter comprising a washcoat, the washcoat being as described above. [Example]

[0119] BET specific surface area: BET specific surface area is determined automatically on a Mountech Macsorb analytical analyzer, model I-1220. Prior to any measurement, the sample is carefully degassed to desorb volatile adsorbed species. To do this, the sample can be heated in the instrument's cell under vacuum at 200 °C for 30 min.

[0120] Nitrogen Porosity: A Micromeritics Tristar II 3000 instrument 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. Nitrogen pore size distribution measurements were performed at 85 points using a pressure table (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 (excluding boundary values) was 5 seconds. The equilibration time for relative pressures above 0.995 was 600 seconds. The pressure tolerances were 5 mmHg for absolute pressures and 5% for relative pressures. The p0 values ​​were measured at regular intervals during the analysis (2 hours). The Barrett, Joyner, and Halenda (BJH) method based on the Harkins-Jura law was used to determine mesoporosity. The results were analyzed using desorption curves.

[0121] 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. A Rigaku RINT2000 was used. A 2θ angle step of 0.010°, a recording time of 2 seconds per step, and an instrument width s equal to 2θ = 0.11° were used to determine the 2θ angle range from 28° to 32°.

[0122] Intensities were determined from diffractograms based on a baseline acquired over the 2θ angle range of 26.0° to 32.0°. The baseline was determined automatically using software for analyzing the diffractogram data.

[0123] Aluminum nitrate H (93.6% Al2O3 - 6.4% La2O3) Aluminum nitrate H was prepared according to the teachings of Example 1 of WO 2019 / 122692. Characteristics 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; - The BET surface area of ​​this powder is 344m 2 / g. - Other features:

[0124] [Table 1]

[0125] Example 1: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) by method (A) A solution containing precursors of the oxides of Zr, La, and Y was prepared by introducing 37.1 kg of zirconyl nitrate solution ([ZrO] = 295 g / L; density = 1.461), 1.79 kg of lanthanum nitrate solution ([LaO] = 321.1 g / L; density = 1.511), 4.02 kg of yttrium nitrate solution ([YO] = 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. Next, 5.49 kg of aluminum hydrate H, as disclosed above, containing an amount equivalent to 68.3 wt% alumina (3.75 kg AlO) and 4.6 wt% LaO (0.25 kg), was introduced into the resulting solution with stirring, and the total volume of the resulting mixture was adjusted to 125 L with deionized water. The H in the aqueous acidic dispersion thus prepared + The concentration of was 1.3 mol / l. Stirring of the aqueous acidic dispersion was continued for 3 hours.

[0126] The aqueous acidic dispersion was then introduced into a reactor containing 125 L of 4.5 mol / L ammonia solution and stirred by a three-blade spindle (225 rpm) at ambient temperature for 60 minutes. 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.

[0127] The medium is filtered through a press filter at approximately 4 bar pressure, and the cake is then washed with 20 L of deionized water. The cake is then compressed at 19.5 bar pressure for 10 minutes. The resulting wet cake is then placed in an electric furnace. The product is calcined at 950°C for 3 hours. The recovered mixed oxide is then crushed in a "Forplex" blade mill.

[0128] Example 2: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) by method (B) A solution containing precursors of the oxides of La and Y was prepared by introducing 1.12 kg of lanthanum nitrate solution ([La2O3] = 343.1 g / L; density = 1.541), 2.75 kg of yttrium nitrate solution ([Y2O3] = 219.1 g / L, density = 1.417), and 24.5 kg of 60 wt% nitric acid solution into a reactor stirred with a three-blade spindle. The volume was adjusted to a total of 150 L with deionized water. Next, 11.9 kg of oxyhydroxide TZH-40 (d50 = 27 μm - 32 μm; contains 43.0% by weight of zirconium oxide; this corresponds to 5.1 kg of ZrO2) commercially available from Terio, 3.79 kg of aluminum hydrate H as disclosed above containing 67.3% by weight of alumina (2.55 kg of Al2O3), and 4.6% by weight of La2O3 (0.18 kg) were introduced into the resulting solution with stirring, and the total volume of the resulting mixture was adjusted to 170 L with deionized water.

[0129] The aqueous acidic dispersion thus prepared is heated to a temperature of 100° C. and maintained at this temperature for 4 hours. After the mixture has cooled to 50° C., a 25% ammonia solution is introduced with stirring until a pH of 8.4 is reached, and then, after 10 minutes, 2.55 kg of lauric acid (corresponding to a lauric acid / mixed oxide ratio of 30% by weight) is introduced.

[0130] The medium is filtered through a press filter at approximately 4 bar pressure, and the cake is then washed with 85 L of deionized water. The cake is then compressed at 19.5 bar pressure for 10 minutes. The resulting wet cake is then placed in an electric furnace. The product is calcined at 950°C for 3 hours. The recovered mixed oxide is then crushed in a "Forplex" blade mill.

[0131] Example 3: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) by method (A) The mixed oxide was prepared in the same manner as in Example 1, except that the stirring time of the precursor mixture was reduced from 3 hours to 1 hour.

[0132] Example 4: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) by method (A) The mixed oxide was prepared in the same manner as in Example 1, except that the concentration of the ammonia solution was reduced from 4.5 mol / l to 3.5 mol / l.

[0133] Example 5: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) by method (A) The mixed oxide is prepared in the same manner as in Example 1, with the following exceptions: - Reduce the amount of 60% nitric acid solution from 16.9 kg to 0.44 kg. - Reduce the concentration of the ammonia solution from 4.5 mol / l to 2.2 mol / l.

[0134] Using the conditions of Examples 1 to 5, it is possible to obtain other mixed oxides having the composition according to claim 1.

[0135] Comparative Example 1: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) The mixed oxide is prepared in the same manner as in Example 1, with the following exceptions: - Reduce the stirring time of the precursor mixture from 3 hours to 1 hour. - The mixture obtained after reaction with the ammonia solution is heated to a temperature of 100 ° C and maintained at this temperature for 2 hours.

[0136] Comparative Example 2: Preparation of the mixed oxide Al2O3 (30%)-ZrO2 (60%)-La2O3 (5%)-Y2O3 (5%) (wt%) The mixed oxide is prepared in the same manner as in Example 1, with the following exceptions: - Reducing the stirring time of the precursor mixture from 3 hours to 10 minutes; - introducing a 25% ammonia solution into the precursor mixture while stirring until pH=8.5; - No heat aging of the mixture is performed.

[0137] [Table 2]

[0138] It can be seen that it is possible to obtain small crystallite sizes with method (B). p,950℃ / 3h and a ratio V greater than 0.85 <30nm,950℃ / 3h / V total,950℃ / 3h It can also be seen that the porosity of the mixed oxide can be fine-tuned to obtain narrow peaks below 25 nm.

Claims

1. A mixed oxide of aluminum, zirconium, lanthanum and, optionally, at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, in which the weight proportions of these elements are: 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; and These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of said mixed oxide after calcination in air at 1100°C for 5 hours is at least 25 m ２ / g; After firing in air at 950°C for 3 hours, ２ The porosity of said mixed oxide as determined by porosimetry is In the region of the pores having a size of less than 100 nm, the porogram of the mixed oxide has a diameter D between 10 and 25 nm. ｐ，９５０℃／３ｈ indicates the peak located at ・Ratio V ＜３０ｎｍ，９５０℃／３ｈ / V ｔｏｔａｌ，９５０℃／３ｈ is 0.85 or more; ・V ｔｏｔａｌ，９５０℃／３ｈ is 0.35 ml / g or more; It's like, V ＜３０ｎｍ，９５０℃／３ｈ and V ｔｏｔａｌ，９５０℃／３ｈ represent the pore volume of pores with a size less than 30 nm and the total pore volume of the mixed oxide, respectively, after calcination at 950° C. for 3 hours in air; A mixed oxide characterized in that

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

3. The proportion of hafnium is not more than 2.0% by weight, and this proportion is HfO ２ 3. The mixed oxide of claim 2, wherein:

4. 4. Mixed oxide according to any one of claims 1 to 3, wherein the elements Zr, La, if present REM, and if present Hf are present as oxides in said mixed oxide.

5. A mixed oxide consisting of a combination of oxides of aluminum, zirconium, lanthanum, optionally at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, and optionally hafnium, in which the weight proportions of these elements are: 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); hafnium in a proportion of less than or equal to 2.0% by weight; 50.0% to 70.0% by weight of zirconium; and These proportions are expressed as oxide equivalents relative to the total weight of the mixed oxides, The specific surface area (BET) of said mixed oxide after calcination in air at 1100°C for 5 hours is at least 25 m ２ / g; After firing in air at 950°C for 3 hours, ２ The porosity of said mixed oxide as determined by porosimetry is In the region of the pores having a size of less than 100 nm, the porogram of the mixed oxide has a diameter D between 10 and 25 nm. ｐ，９５０℃／３ｈ indicates the peak located at ・Ratio V ＜３０ｎｍ，９５０℃／３ｈ / V ｔｏｔａｌ，９５０℃／３ｈ is 0.85 or more; ・V ｔｏｔａｌ，９５０℃／３ｈ is 0.35 ml / g or more; It's like, V ＜３０ｎｍ，９５０℃／３ｈ and V ｔｏｔａｌ，９５０℃／３ｈ represent the pore volume of pores with a size less than 30 nm and the total pore volume of the mixed oxide, respectively, after calcination at 950° C. for 3 hours in air; A mixed oxide characterized in that

6. After firing in air, - at 1100°C for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is at most 28 nm; and / or - at 1200°C for 5 hours, the average crystallite size of the crystalline phase based on zirconium oxide is up to 44 nm; The mixed oxide according to any one of claims 1 to 5.

7. The average size of the crystallites is represented by formula (I): t=kλ / (βcosθ)(I) (t: average crystallite size; k: shape factor equal to 0.9; λ (lambda): wavelength of incident beam (λ = 1.5406 Å); β: line broadening measured at half maximum intensity; θ: Bragg angle) 7. The mixed oxide of claim 6, wherein

8. The average crystallite size has formula (II): [Equation 1] (t: average crystallite size; k: shape factor equal to 0.9; λ (lambda): wavelength of incident beam (λ = 1.5406 Å); H: full width at half maximum of the diffraction line; s: instrument line spread; θ: Bragg angle) 7. The mixed oxide of claim 6, wherein

9. 9. The mixed oxide according to claim 6, wherein the crystalline phase is characterized by peaks located at 2θ angles between 29° and 31° (source: CuKα1, λ=1.5406 Å).

10. A mixed oxide according to any one of claims 6 to 9, wherein the crystalline phase exhibits a tetragonal structure.

11. 11. The mixed oxide according to claim 1, wherein the proportion of aluminum is between 25.0% and 40.0% by weight.

12. 12. The mixed oxide according to claim 1, wherein the proportion of lanthanum is between 1.0% and 10.0% by weight.

13. 13. The mixed oxide according to claim 1, wherein the proportion of the REM or the proportion of each REM when the mixed oxide contains two or more REMs is 1.0% by weight to 10.0% by weight.

14. 14. The mixed oxide according to claim 1, wherein the proportion of zirconium is between 55.0% and 65.0% by weight.

15. 15. The mixed oxide according to claim 1, wherein the total proportion of zirconium and aluminum is at least 80.0% by weight.

16. 16. 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.

17. 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; 17. The mixed oxide according to claim 1, wherein

18. the proportion of lanthanum is between 2.0% and 7.0% by weight; and / or the proportion of said REM is between 2.0% and 7.0% by weight; 18. The mixed oxide of claim 17.

19. 19. The mixed oxide according to claim 17 or 18, wherein the proportion of REM is between 3.0% and 7.0% by weight.

20. 20. The 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.

21. A mixed oxide according to any one of the preceding claims, wherein the or one of the REMs is Y.

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

23. oxide CeO relative to the total weight of the mixed oxides ２ 22. The mixed oxide according to claim 1, wherein the proportion of cerium, expressed by weight, is less than 1.0% by weight.

24. A specific surface area (BET) of at least 28 m after calcination at 1100°C for 5 hours in air ２ / g of the mixed oxide according to any one of claims 1 to 23.

25. A specific surface area (BET) of at least 65 m after calcination at 950°C for 3 hours in air ２ / g of the mixed oxide according to any one of claims 1 to 24.

26. The specific surface area (BET) after calcination in air at 1200°C for 5 hours is at least 9m ２ / g of the mixed oxide according to any one of claims 1 to 25.

27. After calcination at 950° C. for 3 hours in air, the porogram of the mixed oxide shows that in the pore region having a size of less than 100 nm, the diameter D ｐ，９５０℃／３ｈ 27. The mixed oxide according to claim 1, characterized in that it exhibits a single peak located at

28. ratio V ＜３０ｎｍ，９５０℃／３ｈ / V ｔｏｔａｌ，９５０℃／３ｈ 28. The mixed oxide according to claim 1, wherein is greater than or equal to 0.

90.

29. V ｔｏｔａｌ，９５０℃／３ｈ A mixed oxide according to any one of claims 1 to 28, wherein the solubility is at least 0.40 ml / g.

30. Diameter D of 10 to 25 nm ｐ，９５０℃／３ｈ 30. The mixed oxide according to claim 1, wherein the peak located at

31. A process for preparing a mixed oxide according to any one of claims 1 to 30, comprising the steps of: (a1) introducing an acidic aqueous dispersion comprising nitric acid and precursors of oxides of zirconium, lanthanum, and optionally rare earth metals other than cerium and other than lanthanum, in which aluminum hydrate is dispersed, 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 solid content 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 of at least 800°C; A method comprising:

32. A process for the preparation of a mixed oxide according to any one of claims 1 to 30, comprising the steps of: (b1) heating and stirring an acidic aqueous dispersion comprising nitric acid, zirconium oxyhydroxide, a precursor of an oxide of lanthanum, and optionally a precursor of an oxide of a rare earth metal other than cerium and other than lanthanum, and having aluminum hydrate dispersed therein, at a temperature of at least 80°C to obtain a first mixture; (b2) adding an ammonia solution to the first mixture obtained at the end of step (b1) until the pH of the mixture is at least 8.0 to obtain a second mixture; (b3) thereafter, adding an organic texturing agent to said second mixture obtained at the end of step (b2) to obtain a third mixture, and agitating said third mixture to obtain a dispersion; (b4) recovering the solids of the dispersion of step (b3) by solid / liquid separation and washing the cake with water; (b5) calcining the solid obtained at the end of step (b4) in air at a temperature of at least 800°C; A method comprising:

33. The aluminum hydrate used in step (a1) or step (b1) is aluminum hydrate H based on boehmite, optionally also containing lanthanum, and has the following porosity after calcination in air at a temperature of 900° C. for 2 hours: ・VP20nm-N2 is - 10% x VPT-N2 or more; - 60% x VPT-N2 or less; the pore volume in the region of pores having a size of 20 nm or less (represented by VP20nm-N2); the pore volume in the region 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; VPT-N2 represents the total pore volume of aluminum hydrate after calcination in air at 900°C for 2 hours; Pore ​​volume is determined by nitrogen porosimetry technique 33. The method of claim 31 or 32, wherein:

34. Use of the mixed oxide according to any one of claims 1 to 30 for the production of catalytic converters.

35. Use of the mixed oxide according to any one of claims 1 to 30 as a support for at least one noble metal selected from the group consisting of Pt, Rh or Pd.

36. Use of the mixed oxide according to any one of claims 1 to 30 as a support for Rh.

37. A composition comprising a mixed oxide according to any one of claims 1 to 30 and optionally at least one inorganic substance.

38. 38. The composition of claim 37, also comprising at least one precious metal selected from the group consisting of Pt, Rh, or Pd.

39. A catalytic converter comprising a catalytically active washcoat made from the mixed oxide of any one of claims 1 to 30, the catalytically active washcoat being deposited on a solid support.

40. Mixed oxides of aluminum, zirconium, lanthanum and, optionally, at least one rare earth metal (denoted REM) other than cerium and other than lanthanum, in particular in which the weight proportions of these elements are: 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; and 1. Use of aluminum hydrate for the preparation of a mixed oxide, wherein these proportions are expressed as the amount of oxide equivalent relative to the total weight of the mixed oxide, The aluminum hydrate is based on boehmite and optionally also contains lanthanum and has the following properties: After calcination in air at a temperature of 900°C for 2 hours, ・VP20nm-N2 is - 10% x VPT-N2 or more; - 60% x VPT-N2 or less; the pore volume in the region of pores having a size of 20 nm or less (represented by VP20nm-N2); the pore volume in the region 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; characterized in that it has VPT-N2 represents the total pore volume of aluminum hydrate after calcination in air at 900°C for 2 hours; The pore volume is determined by nitrogen porosimetry; use.

41. Use according to claim 40, wherein the mixed oxide is according to any one of claims 1 to 30.

42. 42. Use according to claim 40 or 41, wherein the aluminium hydrate has a percentage of crystalline phase (boehmite) of not more than 60%.

43. 43. The use according to claim 40 or 42, wherein the aluminium hydrate has a total pore volume (VPT-N2) of 0.65 to 1.20 ml / g.

44. The aluminum hydrate has a thickness of at least 200 m ２ 44. The use according to any one of claims 40 to 43, wherein the surface area exhibits a BET specific surface area of ​​1 / 2 g.

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