EP3728122A1

EP3728122A1 - Porous aluminum hydrate

Info

Publication number: EP3728122A1
Application number: EP18833975.8A
Authority: EP
Inventors: Julien Hernandez; Olivier Larcher
Original assignee: Rhodia Operations SAS
Current assignee: Rhodia Operations SAS
Priority date: 2017-12-22
Filing date: 2018-12-18
Publication date: 2020-10-28
Also published as: JP2023159170A; FR3075777A1; KR20200101417A; US11897783B2; CN111542495A; WO2019122692A1; US20210070623A1; JP7458979B2; JP2021507867A

Abstract

The present invention relates to a porous aluminum hydrate, to a method for preparing same, and to the use thereof as an intermediate product in the preparation of an alumina or a mixed oxide based on aluminum, cerium and zirconium. The invention also relates to the alumina obtained from the aluminium hydrate.

Description

Porous aluminum hydrate

The present application claims the priority of the French patent application No. 1762940 filed on December 22, 2017, the contents of which are incorporated in full by reference. In case of inconsistency between the text of the present application and the text of the French patent application which affects the clarity of a term or expression, reference will be made to this application only.

Technical area

The present invention relates to a porous aluminum hydrate, its process of preparation and its use as an intermediate in the preparation of an alumina or a mixed oxide based on aluminum, cerium, zirconium, lanthanum and possibly at least one rare earth (TR) other than cerium and lanthanum. The invention also relates to alumina obtained from aluminum hydrate.

Technical problem

Aluminum hydrates are used for the preparation of catalysts or catalyst supports. The preparation usually consists of shaping the aluminum hydrate and then calcining it to transform it into alumina. The properties of aluminum hydrate influence the characteristics of the alumina obtained and, therefore, the application properties of catalysts and catalyst supports. In the case of the preparation of a high surface area alumina, aluminum hydrate is generally boehmite.

Mixed oxides based on aluminum, cerium and / or zirconium can be obtained by processes in which the aluminum is provided in the form of an aluminum hydrate. It is necessary that the aluminum hydrate be well dispersible in the reaction mixture of these processes so as to obtain a mixed oxide having good properties, including a high thermal resistance.

The Applicant has developed a particular aluminum hydrate which aims to solve this technical problem. Brief description of the invention

The invention relates to an aluminum hydrate based on a boemite, which may optionally comprise at least one additional element selected from the group formed by lanthanum, praseodymium or a mixture of the two elements, characterized in that after have been calcined in air at a temperature of 900 ° C for 2 hours, it presents:

^■ a pore volume in the area of pores whose size is less than or equal to 20 nm (noted VP o ₂ nm-N2) as VP o ₂ nm-N _2:

is greater than or equal to 10% x VPT-N ₂ , more particularly greater than or equal to 15% x VPT-N ₂ , or even greater than or equal to 20% x VPT-N ₂ , or even greater than or equal to 30% x VPT-N ₂ ;

- is less than or equal to 60% x VPT-N ₂ ;

^■ a pore volume in the area of pores whose size is between 40 and 100 nm (denoted _40-i VP oo nm-N _2), such as VP _40-i oo nm-N ₂ is greater than or equal to 20% x VPT-N ₂ , more particularly greater than or equal to 25% x VPT-N ₂ , or even greater than or equal to 30% x VPT-N ₂ ;

^■ VPT-N ₂ denoting the total pore volume of aluminum hydrate after calcination in air at 900 ° C for 2 h;

^■ the pore volume being determined by the technique of nitrogen porosimetry.

The invention also relates to the process for obtaining this aluminum hydrate comprising the following steps:

(a) is introduced into a stirred tank containing an aqueous solution of nitric acid:

^■ an aqueous solution (A) comprising aluminum sulphate, optionally the additional components in the form of nitrate (s) and nitric acid;

^■ an aqueous sodium aluminate solution (B);

the aqueous solution (A) being introduced continuously throughout step (a) and the rate of introduction of the solution (B) being regulated so that the average pH of the reaction mixture is equal to a value a target of between 4.0 and 6.0, more particularly between 4.5 and 5.5;

(b) when all the aqueous solution (A) has been introduced, the aqueous solution (B) is continued to reach a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0; (c) the reaction mixture is then filtered and the recovered solid is washed with water;

(d) the solid from step (c) is then dried.

The invention also relates to the use of the hydrate to prepare an alumina and to the use of aluminum hydrate in the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and possibly at least one rare earth (TR) other than cerium and lanthanum.

Technical background

WO 2006/119549 and WO 2013007242 describe processes for the preparation of mixed oxides based on aluminum, cerium and zirconium in which the aluminum source is an aluminum-based solid compound.

EP 1098848 discloses a different boehmite.

figures

Fig. 1 represents the cumulated pore volume obtained by nitrogen porosimetry for the aluminum hydrates of Examples 1 and 3.

Fig. 2 shows the porous nitrogen porosimetry distribution of the aluminum hydrates of Examples 1 and 3. The porogram in this figure represents the derivative (dV / dlogD) as a function of D (V: pore volume; D: pore size ).

Fig. 3 represents the X-ray diffractogram of aluminum hydrate of Example 1 and reference (product corresponding to Example B1 of Application US 2013/017947). Also given as an indication in this figure are the peaks of the boehmite of JCPDS sheet 00-021-1307.

detailed description

The invention relates to a boehmite-based aluminum hydrate which has a particular porosity (described later). The term "boehmite" refers in the European nomenclature and in a known manner, gamma oxyhydroxide (g-AIOOH). In the present application, the term "boehmite" refers to a variety of aluminum hydrate having a particular crystalline form which is known to those skilled in the art. Boehmite can be characterized by X-ray diffraction. The term "boehmite" covers also the "pseudo-boehmite" which according to some authors, is only related to a particular variety of boehmite and which simply shows an enlargement of the characteristic peaks of boehmite.

X-ray diffraction revealed boehmite through its characteristic peaks. These are given in JCPDS sheet 00-021-1307 (JCPDS = Joint Committee on Powder Diffraction Standards). It will be noted that the peak apex (020) can be between 13.0 ° and 15.0 ° depending in particular:

- the degree of crystallinity of boehmite;

- the size of the crystallites of boehmite.

Reference may 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 described for a number of boehmites that the position of the peak varies depending on the number of layers in the crystal or the size of the crystallites. This peak may be more particularly between 13.5 ° and 14.5, or even between 13.5 ° and 14.485 °.

The aluminum hydrate may optionally comprise at least one additional element selected from the group formed by lanthanum, praseodymium or a mixture of these two elements. Aluminum hydrate can therefore include La or Pr or La + Pr. The proportion of this element or the total proportion of these elements may be between 0% and 15% by weight, more particularly between 0% and 10% by weight, more particularly between 0% and 8%. This proportion can be between 2% and 8%. This proportion is given by weight of the element or elements expressed as oxide with respect to the total weight of elements Al, La and / or Pr also expressed in the form of oxides. For the calculation of this proportion, it is considered that the lanthanum oxide is in the La 2 O 3 form, the praseodymium oxide is in the Pr ₆ O 2 form and the aluminum oxide is in the Al 2 O 3 form. Thus, an aluminum hydrate comprising lanthanum in a proportion of 7% is such that it contains the equivalent of 7% of La 2 O 3 and the equivalent of 93% of Al 2 O 3. The proportion of additional element (s) can be determined by calcining the hydrate of aluminum in air to transform it into alumina and oxide (s) of the additional element (s), then by attacking the product thus calcined, for example with a concentrated nitric acid solution, so as to dissolve its elements in a solution which can then be analyzed by the techniques known to those skilled in the art, such as for example ICP. The boehmite contained in the aluminum hydrate 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 size of the crystallites is determined by the X-ray diffraction technique and corresponds to the size of the coherent domain calculated from the width at half height of the line (020).

For the calculation of the crystallite size, the Debye-Scherrer model is used which is used in a known manner in X-ray diffraction on powders and which makes it possible to determine the size of the crystallites from the half-height width of the crystallites. diffraction peaks. For more information, we can refer to Appl. Cryst. 1978, 11, 102-113 "Scherrer after sixty years: A survey and some new results in the determination of crystallite size, J. I. Langford and A.

JC Wilson "The formula used is as follows:

t: crystallite size

k: form factor of 0.9

l (lambda): wavelength of the incident beam (l = 1.5406 Angstrom)

H: width at half height of the diffraction line

s: width due to instrumental optics defect which depends on the instrument used and angle 2Q (theta)

Q: Bragg angle

The aluminum hydrate of the invention may be in the form of a mixture of a boehmite, identifiable as previously described by the X-ray diffraction technique, and a non-visible phase diffracted from X-rays, in particular an amorphous phase.

The aluminum hydrate may have a% crystalline phase (boehmite) which is 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 even between 45% and 50%. This% is determined in a manner known to those skilled in the art. The following formula can be used to determine this%:% crystallinity = peak intensity (120) / peak intensity (120) of the reference x 100 in which the peak intensity (120) of the hydrate is compared. aluminum and peak intensity (120) of a reference. The reference used in the present application is the product corresponding to the example B1 of the application US 2013/017947. The intensities measured correspond to the areas of the peaks (120) above the line of based. These intensities are determined on the diffractograms with respect to a baseline taken over the range of angle between 5.0 ° and 90.0 °. The baseline is determined automatically from the diffractogram data analysis software.

Aluminum hydrate has a particular porosity. Thus, after calcination under air at 900 ° C. for 2 hours, the aluminum hydrate has a pore volume in the pore area whose size is less than or equal to 20 nm (denoted VP ₂ o _nm -N 2) such that VP20 _nm -N2 is greater than or equal to 20 / ox VPT-N2, more particularly greater than or equal to 25% x VPT-N ₂ , or even greater than or equal to 30% x VPT-N ₂ . On the other hand, VP ₂ o _nm -N 2 is less than or equal to 60% x VPT-N ₂ .

Furthermore, after calcination under air at 900 ° C. for 2 hours, the aluminum hydrate has a pore volume in the pore area whose size is between 40 and 100 nm (denoted VP _40-i oo _nm -N 2 ), such that VP _40-i oo _nm -N2 is greater than or equal to 15% x VPT-N ₂ , more particularly greater than or equal to 20% x VPT-N ₂ , or even greater than or equal to 25% x VPT- N ₂ , or even greater than or equal to 30% x VPT-N ₂ . On the other hand, VP ₄₀ _nm may be less than or equal to 65% x VPT-N ₂ .

After calcination in air at 900 ° C. for 2 hours, the aluminum hydrate of the invention may have a total pore volume (VPT-N ₂ ) of between 0.65 and 1, 20 ml / g, more particularly included. between 0.70 and 1.15 ml / g, or even between 0.70 and 1.10 ml / g. It will be noted that the pore volume thus measured is mainly developed by pores whose diameter is less than or equal to 100 nm.

The aluminum hydrate may have a surface area of at least 200 m ² / g, more particularly at least 250 m ² / g. This specific surface may be between 200 and 400 m ² / g. By specific surface is meant the BET specific surface area obtained by nitrogen adsorption. This is the specific surface as conventionally understood by those skilled in the art. This surface is determined by nitrogen adsorption on a powder according to the known Brunauer-Emmett-Teller method (BET method). This method is described in ASTM D 3663-03 (re-approved 2015). This method is also described in "The Journal of the American Chemical Society, 60, 309 (1938)". The pore volumes given in the present application are determined by the nitrogen porosimetry technique. For the measurements of porosity or specific surface, the samples are pretreated before heat and / or under vacuum to eliminate volatile surface species (such as for example H ₂ 0, ...). For example, the sample may be heated to 200 ° C for 2 hours.

On the other hand, after calcination in air at 900 ° C. for 2 hours, the aluminum hydrate may have a specific surface area (BET) of at least 130 m ² / g, more particularly at least 150 m ² / g. This specific surface may be between 130 and 220 m ² / g.

After calcination in air at 940 ° C. for 2 hours, followed by calcination under air at 1100 ° C. for 3 hours, the aluminum hydrate can have a specific surface area (BET) of at least 80 m ² / g. more particularly at least 100 m ² / g. This specific surface may be between 80 and 120 m ² / g.

When the aluminum hydrate comprises at least additional element as described above, the aluminum hydrate may have a high thermal resistance. Thus, after calcination in air at 940 ° C. for 2 hours, followed by calcination in air at 1200 ° C. for 5 hours, the aluminum hydrate can have a specific surface area (BET) of at least 45 m ^2. g, more particularly at least 50 m ² / g. This specific surface may be between 45 and 75 m ² / g.

In the present application, the term "after calcination in air at the temperature x ° C for y hours, aluminum hydrate present" is used to characterize the aluminum hydrate even if the measured property (specific surface or porous volume) is that of the product resulting from the calcination of aluminum hydrate.

Aluminum hydrate may include residual sulfate. The residual sulphate level may be less than or equal to 0.50% by weight, or even less than or equal to 0.20% by weight. The sulfate level may be greater than or equal to 50 ppm. This content is expressed as the weight of sulphate relative to the weight of the oxides of the elements Al and possibly the additional element (s). Thus, a residual sulphate level of 0.5% corresponds to 0.5 g of SO ₄ per 100 g of oxides (Al 2 O 3, Pr ₆ On, I_a203). The method for determining the sulfate level in this concentration range is known to those skilled in the art. For example, the microanalysis technique can be used. A Horiba EMIA 320-V2 microanalysis apparatus can thus be used.

Aluminum hydrate may include residual sodium. The residual sodium content may be less than or equal to 0.15% by weight, or even less than or equal to 0.10% by weight. The sodium level may be greater than or equal to 50 ppm. This level is expressed by weight of Na 2 O with respect to the weight of the oxides of the elements Al and possibly the additional element (s). Thus, a residual sodium content of 0.15% corresponds to 0.15 g of Na 2 O per 100 g of oxides (Al ₂ O _3, Pr ₆ is, La ₂ 0 _3). The method of determining the sodium level in this concentration range is known to those skilled in the art. For example, the plasma emission spectroscopy technique can be used.

The aluminum hydrate of the invention is obtained by the process comprising the following steps:

^■ an aqueous sodium aluminate solution (B);

(b) when all the aqueous solution (A) has been introduced, the aqueous solution (B) is continued to reach a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0;

(c) the reaction mixture is then filtered and the recovered solid is washed with water;

(d) the solid resulting from step (c) is then dried to give the hydrate of the invention.

The aqueous solution (A) is obtained from aluminum sulphate and nitric acid. The aqueous solution (A) may also include the additional element (s) in the form of nitrate (s). The aqueous solution (A) may have an alumina equivalent concentration of between 1% and 5% by weight.

The aqueous solution (B) is obtained from sodium aluminate. Preferably, it does not present precipitated alumina. The sodium aluminate preferably has an Na ₂ O / Al ₂ O 3 ratio greater than or equal to 1.2, for example between 1.20 and 1.40.

The aqueous solution (A) is introduced continuously throughout step (a) into the stirred tank. The duration of introduction of the aqueous solution (A) can be between 10 minutes and 2 hours. The aqueous solution (B) is introduced at the same time as the aqueous solution (A) at a rate which is regulated so that the average pH of the reaction mixture is equal to a target value. The target value is between 4.0 and 6.0, more preferably between 4.5 and 5.5. The term "average pH" means the arithmetic mean of the pH values recorded continuously during step (a). Since the flow rate of the aqueous solution (B) is regulated, it is possible that it is at certain times zero, that is to say that only the aqueous solution (A) is introduced into the stirred tank.

During step (b), when all the aqueous solution (A) has been introduced into the reactor at the end of step (a), the aqueous solution (B) is continued until achieve a target pH of between 8.0 and 10.5, preferably between 9.0 and 10.0. The duration of step (b) can be variable. This duration can be between 5 minutes and 2 hours.

The temperature of the aqueous solution of nitric acid present initially in the tank may be between 50 ° C and 80 ° C. During step (a), the temperature of the reaction mixture may also be between 50 ° C and 80 ° C. During step (b), the temperature of the reaction mixture may also be between 50 ° C and 80 ° C.

During step (c), the reaction mixture (in the form of a slurry) is filtered. The solid recovered on the filter can be washed with water. Hot water with a temperature of at least 50 ° C can be used. During step (d), the solid resulting from step (c) is dried using any drying technique known to those skilled in the art. Spray drying can be usefully employed. Aluminum hydrate is in the form of a dry powder.

The powder may be optionally milled and / or sieved so as to obtain a powder of fixed particle size. The aluminum hydrate, ground or not, may be in the form of a powder having an average diameter d50 (median) of between 1.0 and 40.0 miti, more particularly between 3.0 and 30.0 miti , d50 being determined by laser diffraction on a volume distribution.

The aluminum hydrate of the invention can be used to prepare an alumina. Alumina is obtained by calcination of aluminum hydrate in air. The invention also relates to the process for obtaining an alumina by calcination of the aluminum hydrate of the invention. The calcination temperature is at least 500 ° C. It can be between 500 ° C and 1100 ° C. The duration of the calcination can be between 30 minutes and 10 hours.

The alumina of the invention has the same porosity characteristics as aluminum hydrate. After calcination in air at 1100 ° C. for 3 hours, the alumina may have a specific surface area of at least 80 m ² / g, more particularly at least 100 m ² / g. This specific surface may be between 80 and 120 m ² / g. When the alumina comprises at least additional element as described above, the alumina may have a high thermal resistance. Thus, after calcination in air at 1200 ° C. for 5 hours, the alumina may have a specific surface area of at least 45 m ² / g, more particularly at least 50 m ² / g. This specific surface may be between 45 and 75 m ² / g.

The alumina of the invention can be used advantageously as a catalyst support. This alumina can be used in particular as a support for at least one precious metal for the automotive depollution catalysis. In the case of catalysis called "traies ways" for gasoline vehicle, it may advantageously use an alumina containing at least one additional element because of its high temperature thermal stability, typically above 1100 ° C. The porous alumina obtained according to the invention will advantageously be used under the conditions in which a high flow of gas passes over the catalyst. Alumina can also be used in engine depollution applications operating under oxidizing conditions (diesel or gasoline). In the case of diesel vehicles which are usually subjected to lower thermal stresses, pure alumina with or without additional element can be used.

The aluminum hydrate of the invention may also be used in the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and possibly at least one rare earth (TR) other than cerium and lanthanum. TR may for example be chosen from yttrium, neodymium or praseodymium.

In the mixed oxide, the aforementioned elements Al, Ce, La, TR and Zr are generally present in the form of oxides. The mixed oxide can therefore be defined as a mixture of oxides. However, it is not excluded that these elements may be present at least partly in the form of hydroxides or oxyhydroxides. The proportions of these elements can be determined using standard laboratory analysis techniques, including the plasma torch and X-ray fluorescence.

An example of such a mixed oxide may for example comprise the abovementioned elements in the following proportions, expressed by weight of oxide:

^■ between 20 and 60% aluminum;

^■ between 15 and 35% of cerium;

^■ between 1 and 10% of lanthanum;

^■ between 0 and 10% for the rare earth other than cerium and lanthanum, provided that if the mixed oxide comprises more than one rare earth other than cerium and lanthanum, this proportion applies to each of these rare earths and that the sum of the proportions of these rare earth remains less than 15%;

^■ between 15% and 50% zirconium.

The mixed oxide may also comprise hafnium whose proportion may be less than or equal to 2.0%, expressed as oxide equivalent relative to the total weight of the mixed oxide. These proportions are given by weight in oxide equivalent relative to the total weight of the mixed oxide. They are given in oxide mass unless otherwise indicated. For these calculations, it is considered that the cerium oxide is in the form of ceric oxide, that the oxides of Other rare earths are in TR2O3 form, where TR denotes the rare earth except for praseodymium which is expressed as Pr ₆ On. The zirconium and hafnium oxide are in the form of ZrO ₂ and HfO ₂ . Aluminum is present in AI2O3 form.

The process for obtaining the mixed oxide consists in calcining in air a solid precipitate obtained from a dispersion of aluminum hydrate and a solution comprising the salts of the elements Ce, Zr, where appropriate. and where appropriate TR.

A particular method (P1) for preparing a mixed oxide of the elements Al, Ce, Zr, La and optionally TR can for example comprise the following steps

(i) adding a basic aqueous solution to a dispersion formed of aluminum hydrate and an aqueous solution S comprising the salts of cerium, zirconium, optionally lanthanum and, if appropriate, rare earth other than cerium and lanthanum, so as to precipitate the salts of the constituent elements of solution S;

(ii) optionally washing the solid obtained at the end of step (i);

(iii) calcining under air the solid obtained at the end of step (i) or (ii) at a temperature of between 700 ° C. and 1200 ° C.

A particular process (P2) for preparing a mixed oxide of the elements Al, Ce, Zr, La and optionally TR can comprise the following steps:

(i) adding an aqueous solution S comprising the salts of cerium, zirconium, optionally lanthanum and, where appropriate, rare earth other than cerium and lanthanum, to a dispersion formed of aluminum hydrate and a basic aqueous solution, so as to precipitate the salts of the elements of the solution S;

(ii) optionally washing the solid obtained at the end of step (ii);

A particular method (P3) for preparing a mixed oxide of the elements Al, Ce, Zr, La and optionally TR can comprise the following steps:

(i) adding to a basic aqueous solution a dispersion formed of aluminum hydrate and an aqueous solution S comprising the salts of cerium, zirconium, optionally lanthanum and, if appropriate, rare earth other than cerium and lanthanum so as to precipitate the salts of solution S;

(ii) optionally washing the solid obtained at the end of step (ii);

The step (i) by which the aqueous solution is brought into contact with the dispersion is carried out with stirring. Moreover, at this stage, the term "add" may more particularly denote the operation by which the aqueous solution or the dispersion is introduced into the dispersion or the aqueous solution, in particular at the bottom of the tank.

Between steps (ii) and (iii) or (iii) and (iv), an intermediate step may be provided during which the solid is subjected to heating at a temperature of between 70 ° C and 150 ° C. This heating is preferably carried out on the solid dispersed in water.

The salts of the elements Ce, Zr, La and TR can be chosen from the group formed by nitrates, chlorides or acetates. It will be noted that in the case where TR represents lanthanum and / or praseodymium, these elements may be provided in whole or in part by aluminum hydrate. The basic aqueous solution may be, for example, an ammonia solution. An example of such a method for preparing a mixed oxide is given in US 9,289,751 as well as in the applications WO 13007272 and WO 14201094.

Aluminum hydrate makes it possible to obtain a homogeneous dispersion. This makes it possible to obtain a mixed oxide having good properties, in particular thermal resistance. The mixed oxide may thus have a BET specific surface area greater than 30 m ² / g after calcination in air at 1100 ° C. for 5 h.

The invention also relates to a dispersion of aluminum hydrate in an aqueous solution, in particular an acidic solution, comprising cerium, zirconium, lanthanum and optionally rare earth salts other than cerium and lanthanum. The invention also relates to a dispersion of aluminum hydrate in a basic aqueous solution, in particular an ammonia solution. Examples

For measurements of porosity or specific surface area, the samples are pretreated at 200 ° C. for 2 h to eliminate volatile surface species (such as, for example, H ₂ O, etc.).

The specific surface area is automatically determined using a Micromeritics Tristar II 3020 unit, following the manufacturer's instructions. The porosity measurements from which the porous volumes are deduced are determined automatically using a Tristar II 3020 Micromeritics device. The method of Barett, Joyner and Halenda (BJH) with the law of Harkins & Jura is used. The analysis of the results is done on the desorption curve. X-ray diffraction analyzes are obtained with a copper source (CuKal, l = 1.5406 Angstrom). A Panalytical X Per Pro goniometer with a copper source, a spinner sample holder and a X Celerator 1D detector with an angular width of 2.122 ° was used. The unit is equipped with a nickel filter at the front and programmable slots to illuminate a constant square surface of 10 mm side.

Example 1 Preparation of an Aluminum Hydrate According to the Invention with 6.2% Lanthanum (93.8% Al ₂ O 3 - 6.2% La ₂ O 3)

In a stirred tank, a solution (A) is prepared by introducing 34.7 kg of deionized water, 10.95 kg of a solution of aluminum sulphate with a concentration of 8.31% by weight of alumina (Al 2 O 3). , 1, 43 kg of a concentration of lanthanum nitrate solution 26.9% by weight of La ₂ 03 and 4.97 kg of a nitric acid solution at 68% by weight. Solution (B) is a solution of sodium aluminate with a concentration of 24.9% by weight of alumina (Al ₂ Os).

In a stirred reactor (250 rpm, mobile four pale inclined at 45 °), 71 kg of deionized water is introduced. The reactor is then heated to a temperature of 65 ° C. This temperature is maintained throughout the reaction. A solution of 69% nitric acid is introduced into the stirred reactor until a pH of 3 is reached. In a step (a), the solution (A) and the solution (B) are simultaneously introduced into the reactor stirred by introduction rods close to the stirring device. Solution (A) is introduced at a rate of 1.05 kg / min. Solution (B) is introduced at a rate to reach a pH of 5 in 3 minutes.

The flow rate of the solution (A) remains constant at 1.05 kg / min and the flow rate of the solution (B) is regulated so as to maintain the pH at a value of 5.1 for 46 minutes.

In a step (b), the introduction of the solution A is stopped and the solution (B) is added until a pH of 10 is reached in 15 minutes.

In step (c), the reaction slurry is then poured onto a vacuum filter. At the end of the filtration, the cake is washed with deionized water at 60 ° C. The cake has a solids content of 11% by weight of oxide (Al 2 O 3 - La 2 O 3). The cake is then redispersed in deionized water to obtain a suspension of concentration close to 8% by weight of oxide (Al ₂ O 3 - La ₂ Os).

In step (d), the suspension is atomized to obtain a dry powder of lanthanum-doped aluminum hydrate. The loss on ignition of the powder is obtained by the loss of mass after calcination at 950 ° C-2 hours. It is 31.2% by mass. The aluminum hydrate powder contains an equivalent of 64.5% by weight of Al ₂ O ₃ and 4.2% by weight of La ₂ O ₃ . This powder has a BET surface area of 344 m ² / g.

Example 2 Preparation of an Alumina of Composition 93.8% Al ₂ O ₃ 6.2% La ₂ O ₃

The powder of Example 1 is calcined in air at 940 ° C. for 2 hours to obtain a lanthanum doped alumina powder. The rise in temperature occurs at a rate of 2.5 ° C / min.

Example 3 Preparation of Aluminum Hydrate at 6.2% La (93.8% Al ₂ O ₃ - 6.2% La ₂ Ü ₃ )

In a stirred tank, a solution (A) is prepared by introducing 34.7 kg of deionized water, 10.95 kg of an aluminum sulphate solution with a concentration of 8.31% by weight of alumina (Al ₂ O ₃ ), 1.43 kg of a solution of lanthanum nitrate concentration of 26.9% by weight of La 2 O 3 and 4.96 kg of a solution of 68% nitric acid. Solution (B) is a solution of sodium aluminate with a concentration of 24.9% by weight of alumina.

In a stirred reactor (250 rpm, mobile four pale inclined at 45 °), 71 kg of deionized water is introduced. The reactor is then heated to a temperature of 65 ° C. This temperature is maintained throughout the reaction. A solution of 69% nitric acid is introduced into the stirred reactor until a pH of 3 is reached.

In a step (a), the solution (A) and the solution (B) are simultaneously introduced into the reactor stirred by introduction rods close to the stirring device. Solution (A) is introduced at a rate of 1.05 kg / min. Solution (B) is introduced at a rate to reach a pH of 4.4 in 3 minutes. The flow rate of the solution (A) remains constant at 1.05 kg / min and the flow rate of the solution (B) is regulated so as to maintain the pH at a value of 4.4 for 46 minutes.

In a step (b), the introduction of the solution (A) is stopped and solution B is added until a pH of 10 is reached in 15 minutes.

In a step (c), the reaction slurry is then poured onto a vacuum filter. At the end of the filtration, the cake is washed with deionized water at 60 ° C. The cake has a solids content of 13% by weight of oxide (Al 2 O 3 - La 2 O 3). The cake is then redispersed in deionized water to obtain a suspension of concentration close to 8% by weight of oxide (Al ₂ O 3 - La ₂ Os).

In a step (d), the suspension is atomized to obtain a lanthanum doped aluminum hydrate powder. The loss on ignition of the powder is obtained by the loss of mass after calcination at 950 ° C-2 hours. It is 38.5% by weight. The aluminum hydrate powder contains an equivalent of 57.8% by weight of Al 2 O 3 and 3.8% by weight of La 2 O 3. This powder has a BET surface area of 259 m ² / g. EXAMPLE 4 Preparation of an Alumina of Composition 93.8% Al 2 O 3 6.2% La 2 O 3

The powder of Example 3 is then calcined at 940 ° C. under air for 2 hours to obtain a lanthanum doped alumina powder. The rise in temperature occurs at a rate of 2.5 ° C / min.

Characterizations of atomized powders and calcined powders are reported in Tables I and II.

Example 5: Use of the aluminum hydrate of Example 1 in the preparation of a mixed oxide composition of Al2O3 (30%) - Z1Ό2 (35%) - Ce0 ₂ (27%) - La ₂ 0 ₃ ( 4%) - Y ₂ 0 ₃ (4%) (% by weight)

A solution based on the nitrates of the precursors is prepared by introducing into a stirred tank with a 45 ° -standarded four-blade mobile, 357 g of water, 114 g of a solution of zirconyl nitrate ([ ZrO2] = 260 g / L; density

1, 406), 56 g of a solution of nitrate of Ce "to ([Ce 2 O 2] = 496 g / L;

1, 714), 4.4 g of a solution of lanthanum nitrate ([La 2 O 3] = 472 g / L;

1, 711) and 16 g of a solution of yttrium nitrate ([Y ₂ O ₃ ] = 208.5 g / L;

1, 392).

To the solution obtained, we then add 2.3 g of nitric acid at 69% by weight to obtain the precursor solution. To this solution, 28 g of aluminum hydrate of Example 1 containing an equivalent of 64.5% by weight of alumina (18 g Al ₂ O ₃ ) and 4, are added by spatulas, while still stirring. 2% by weight of La2O3 (1.17 g). The mixture is left stirring until the precursor mixture is in the form of a homogeneous dispersion. 5.3 g of an aqueous solution of hydrogen peroxide at 9.8 mol / l are then added. The precursor mixer is kept stirring.

The precursor mixture is introduced over 60 min into a stirred reactor with a 45 ° (575 rpm) 45 ° slant mobile, containing 500 mL of a 2 mol / L ammonia solution at room temperature.

At the end of the addition of the precursor mixture, the mixture is heated to a temperature of 95 ° C. and maintained at this temperature for 30 min. The mixture is then cooled to a temperature below 40 ° C. To this mixture cooled, 12 g of lauric acid are added with stirring at 650 rpm. This stirring is maintained for 30 minutes.

The mixture is vacuum-filtered and the cake is washed with 720 g of ammonia water of pH = 9. The wet cake obtained is then introduced into a muffle furnace. The temperature of the oven is raised with a speed of 4 ° C / min until reaching 950 ° C, this temperature is then maintained for 4 hours. At the end of this calcination under air, the mixed oxide is obtained. The recovered mixed oxide is then ground with a mortar.

Specific surfaces of the mixed oxide after calcination under air 4 h:

950 ° C .: 82 m ² / g

1000 ° C: 68 m ² / g

1100 ° C: 40 m ² / g

A solution based on the nitrates of the precursors is prepared by introducing into a stirred tank with a 45 ° -standarded four-blade mobile, 357 g of water, 114 g of a solution of zirconyl nitrate ([ ZrO 2] = 260 g / L, density 1, 406), 56 g of a solution of nitrate of Ce "to ([CeO ₂ ] = 496 g / L;

1, 714), 4.4 g of a solution of lanthanum nitrate ([La ₂ O ₃ ] = 472 g / L;

1, 392). To the solution obtained, we then add 2.3 g of nitric acid at 69% by weight to obtain the precursor solution. To this solution, 31.1 g of aluminum hydrate from Example 3 containing an equivalent of 57.8% by weight of alumina (18 g Al ₂ O ₃ ) and 31.1 g of aluminum hydrate are added by spatulas, while still stirring. 3.8% by weight of La ₂ 0 ₃ (1, 18 g). The mixture is left stirring until the precursor mixture is in the form of a homogeneous dispersion. 5.3 g of an aqueous solution of hydrogen peroxide at 9.8 mol / l are then added. The precursor mixer is kept stirring. In a stirred reactor (600 rpm, mobile at four pale angles inclined at 45 °), 500 ml of a 2 mol / l ammonia solution are introduced. The precursor mixture is introduced in 60 min into the stirred reactor. It operates at room temperature. At the end of the addition of the precursor mixture, the reaction medium is heated to a temperature of 95 ° C. and maintained at this temperature for 30 min. The reaction medium is then cooled to a temperature below 40 ° C. To this cooled mixture was added 12 g of lauric acid with stirring at 500 rpm. This stirring is maintained for 30 minutes. The reaction medium is vacuum filtered and the cake is washed with 1 L of ammonia water (pH = 9). The wet cake obtained is then introduced into a muffle furnace. The temperature of the oven is raised with a speed of 4 ° C / min to 950 ° C, this temperature is maintained for 4 hours. At the end of this calcination under air, the mixed oxide is obtained. The recovered mixed oxide is then ground with a mortar.

Specific surfaces of the mixed oxide after calcination under air 4 h:

950 ° C: 79 m ² / g

1000 ° C: 66 m ² / g

1100 ° C: 41 m ² / g

O

Table I: Characterizations of aluminum hydrates (atomized powders)

Bone

* product corresponding to the example B1 of the application US 2013/017947

not

H

S

o *

TABLE II Characterizations of Alumina (aluminum hydrate powders calcined under air at 940 ° C.-2 h)

Claims

1. Aluminum hydrate based on a boemite, which may optionally comprise at least one additional element selected from the group formed by lanthanum, praseodymium or a mixture of the two elements, characterized in that after having been calcined under air at a temperature of 900 ° C for 2 hours, it has:

- is less than or equal to 60% x VPT-N ₂ ;

^■ the pore volume being determined by the technique of nitrogen porosimetry.

2. aluminum hydrate according to claim 1 characterized in that VPT-N ₂ is 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.

3. Aluminum hydrate according to one of claims 1 or 2 characterized in that it is in the form of a mixture of a boehmite and a non-visible phase in X-ray diffraction, including an amorphous phase .

4. Aluminum hydrate according to one of the preceding claims characterized by a% of crystalline phase less than or equal to 60%, more particularly less than or equal to 50%.

5. Aluminum hydrate according to one of the preceding claims characterized in that the boehmite has an average crystallite size of at most 6.0 nm, or even at most 4.0 nm, more particularly of not more than 3.0 nm.

6. aluminum hydrate according to one of the preceding claims characterized in that after being calcined in air at 900 ° C for 2 h, it has a specific surface area (BET) of at least 130 m ² / g, more particularly at least 150 m ² / g.

7. aluminum hydrate according to one of the preceding claims characterized in that after having first calcined in air at 940 ° C for 2 h and then calcined in air at 1100 ° C for 3 h, it has a specific surface area (BET) of at least 80 m ² / g, more particularly at least 100 m ² / g.

8. aluminum hydrate according to one of the preceding claims characterized in that it comprises an additional element selected from the group formed by lanthanum, praseodymium or a mixture of the two elements and that after being d ' first calcined in air at 940 ° C. for 2 hours, then calcined under air at 1200 ° C. for 5 hours, it has a specific surface area (BET) of at least 45 m ² / g, more particularly at least 50 m ² / g.

9. Aluminum hydrate comprising residual sulphate, the residual sulphate level may be less than or equal to 0.50% by weight, or even less than or equal to 0.20% by weight.

10. Aluminum hydrate comprising residual sodium, the residual sodium content may be less than or equal to 0.15% by weight, or even less than or equal to 0.10% by weight.

11. Aluminum hydrate according to one of the preceding claims, characterized in that the proportion of the additional element or the total proportion of additional elements is between 0% and 15% by weight, more particularly between 0% and 10%. more particularly between 0% and 8%, or between 2% and 8%.

12. Process for the preparation of aluminum hydrate according to one of claims 1 to 11 comprising the following steps:

(a) is introduced into a stirred tank containing an aqueous solution of nitric acid: ^■ an aqueous solution (A) comprising aluminum sulphate, optionally the additional components in the form of nitrate (s) and nitric acid;

^■ an aqueous sodium aluminate solution (B);

(d) the solid from step (c) is then dried.

13. The method of claim 12 wherein the powder obtained at the end of step (d) is ground and / or sieved.

14. Use of an aluminum hydrate according to one of claims 1 to 11 for preparing an alumina.

15. A process for the preparation of an alumina of calcining in air aluminum hydrate according to one of claims 1 to 11.

16. Use of an aluminum hydrate according to one of claims 1 to 11 in the preparation of a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth. (TR) other than cerium and lanthanum.

17. A process for preparing a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth (TR) other than cerium and lanthanum consisting of calcining under air a precipitate solid obtained from a dispersion of aluminum hydrate according to one of claims 1 to 11 and an aqueous solution comprising the salts of the elements Ce, Zr, where appropriate La and where appropriate TR.

18. A process for preparing a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth (TR) other than cerium and lanthanum comprising the following steps:

(I) adding a basic aqueous solution to a dispersion formed of aluminum hydrate according to one of claims 1 to 11 and an aqueous solution S comprising cerium, zirconium, optionally lanthanum and where appropriate, rare earth other than cerium and lanthanum, so as to precipitate the salts of the constituent elements of solution S;

(ii) optionally washing the solid obtained at the end of step (i);

19. A process for preparing a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth (TR) other than cerium and lanthanum comprising the following steps:

(i) adding an aqueous solution S comprising the salts of cerium, zirconium, optionally lanthanum and, if appropriate, rare earth other than cerium and lanthanum to a dispersion formed of aluminum hydrate according to one of claims 1 to 11 and a basic aqueous solution, so as to precipitate the salts of the elements of the solution S;

(ii) optionally washing the solid obtained at the end of step (ii);

20. A process for preparing a mixed oxide based on aluminum, cerium, zirconium, lanthanum and optionally at least one rare earth (TR) other than cerium and lanthanum comprising the following steps:

(i) adding to a basic aqueous solution, a dispersion formed of aluminum hydrate according to one of claims 1 to 11 and an aqueous solution S comprising the cerium salts, zirconium, optionally lanthanum and if necessary rare earth other than cerium and lanthanum so as to precipitate the salts of solution S;

(ii) optionally washing the solid obtained at the end of step (ii);

21. Method according to one of claims 18 to 20 comprising between steps (ii) and (iii) or (iii) and (iv), a step during which the solid is subjected to heating at a temperature between 70 ° C and 150 ° C.

22. Method according to one of claims 17 to 21 wherein the mixed oxide comprises hafnium.

23. The method of claim 22 wherein the hafnium proportion is less than or equal to 2.0%, expressed in oxide equivalent relative to the total weight of the mixed oxide.

24. Dispersion of aluminum hydrate according to one of claims 1 to 11 in an aqueous solution, including acid, including cerium, zirconium, lanthanum and optionally rare earth salts other than cerium and lanthanum.

25. Dispersion of aluminum hydrate according to one of claims 1 to 11 in a basic aqueous solution, in particular an ammonia solution.