Alumina having a specific pore structure

Abstract

The present invention relates to an alumina having a specific pore structure and good thermal stability. The alumina is also characterized by a high bulk density. After calcination at 1100°C in air for 5 hours, the alumina has a pore volume in the range of pores sized from 5 nm to 100 nm of -0.50 to 0.75 mL / g, more specifically 0.50 to 0.70 mL / g, and a pore volume in the range of pores sized from 100 nm to 1000 nm of -0.20 mL / g or less, more specifically 0.15 mL / g or less, or even 0.10 mL / g or less.

Description

Technical Field

[0001] This patent application claims the priority of European Patent Applications Nos. 19315153.7 and 19315155.2 filed on November 29, 2019, the content of which is incorporated herein by reference in its entirety. In case of any contradiction between the text of this patent application and the text of the French patent application that may affect the clarity of terms and expressions, only this application shall be referred to.

[0002] The present invention relates to alumina having a specific pore structure and good thermal stability. This alumina is also characterized by having a high bulk density.

[0003] It is a known practice to use alumina for the preparation of automotive pollution prevention catalysts for converting pollutants discharged from gasoline or diesel heat engines. Alumina is used as a support for noble metals, especially platinum, palladium, and / or rhodium. It can also be combined with other catalyst components, and said components depend on the catalyst and the intended use (diesel or gasoline pollution prevention). Among other common components present in the catalyst, mention can be made of rare earth metal oxides such as cerium oxide or mixed cerium zirconium oxide used as materials having oxygen mobility for gasoline engine catalysts (three-way catalysts (TWC) or gasoline particulate filters (GPF)). Alumina can also be combined with zeolite used, for example, as a hydrocarbon trap for diesel catalysts for the reduction of NO x emitted from diesel engines, or zeolite exchanged with copper and / or iron for catalysts for the catalytic reduction of nitrogen oxides by ammonia (SCR).

[0004] Technical Problem In order to maintain the efficiency of the catalyst over a long period of time, i.e., to maintain good conversion of gaseous pollutants, it is necessary to enhance the thermal stability of alumina in all these automotive pollution prevention applications. The term "thermal stability" means maintaining a high specific surface area after heat treatment at high temperature. A simple and common way to characterize the thermal stability of alumina is to measure the specific surface area after heat treatment in air at a high temperature, for example 1200 °C, for 5 hours.

[0005] The preparation of automotive pollution prevention catalysts usually involves the deposition or coating of an alumina-based suspension onto a substrate or monolith. The alumina of the present invention is suitable for the preparation of suspensions with low viscosity, so that suspensions with a high proportion of alumina can be prepared. Furthermore, the high density of the alumina of the present invention facilitates the handling of the alumina powder.

[0006] The thermal stability of alumina is usually related to a certain extent to the pore volume of the alumina. By increasing this pore volume, the thermal stability generally increases. However, this increase in pore volume significantly reduces the density of the alumina during the process for preparing the catalyst and increases the viscosity of the alumina suspension.

[0007] To solve this problem, it has been observed that by virtue of the specific porosity of the alumina of the present invention, it is possible to obtain both high thermal stability and high bulk density.

[0008] Technical Background U.S. Patent No. 4,154,812 describes a method for preparing alumina. This method does not include step (e). Brief Description of the Drawings

[0009]

Figure 1

[0010] Brief Description of the Invention The present invention relates to alumina according to any one of claims 1 to 41.

[0011] This has the following two pore structures: · First structure: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, more specifically 0.60 to 0.80 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, more specifically 0.15 mL / g or less, further 0.10 mL / g or less, or even 0.05 mL / g or less, and / or · Second structure: After calcination in air at 1100 °C for 5 hours: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, more specifically 0.50 to 0.70 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, more specifically 0.15 mL / g or less, further 0.10 mL / g or less, or even 0.05 mL / g or less, characterized by at least one of these, and these pore volumes are determined by the mercury porosimetry method.

[0012] This alumina is usually represented by the general formula Al2O3. It may contain sodium, sulfates, and impurities.

[0013] The present invention also relates to the catalyst composition according to claim 42 and the use of the alumina according to claim 43.

[0014] The present invention also relates to a method for preparing alumina according to any one of claims 44 to 51.

[0015] All of these subjects will be described in more detail hereinafter.

Mode for Carrying Out the Invention

[0016] In this patent application, for the sake of continuity of this description, unless otherwise specified, it is specified that the limit values are included within the given range of values. Further, the concentration of the solution or the proportion in alumina is specified to be expressed as weight percent of oxide equivalent. For the calculation of these concentrations or proportions, the formula Al2O3 is used. For example, an aqueous solution of aluminum sulfate with an aluminum concentration of 2.0% by weight corresponds to a solution containing 2.0% by weight of Al2O3 equivalent.

[0017] The term "particle" means an aggregate formed from primary particles. The particle size is determined from the volume distribution of particle sizes obtained by a laser particle size analyzer. The particle size distribution is characterized by the parameters D10, D50, and D90. These parameters have their usual meanings in the field of measurement by laser diffraction. Thus, Dx represents a value determined with respect to the particle size volume distribution in which x% of the particles have a size less than this value Dx. Thus, D50 corresponds to the median value of the distribution. D90 corresponds to the size at which 90% of the particles have a size less than D90. D10 corresponds to the size at which 10% of the particles have a size less than D10. The measurement is usually carried out with an aqueous dispersion of the particles.

[0018] The porosity data is obtained by the mercury porosimetry method. By this method, the pore volume (V) can be defined as a function of the pore diameter (D). In accordance with the manufacturer's recommended instructions, a Micromeritics Autopore 9520 equipped with a powder penetrometer can be used. The procedure of ASTM D4284-07 can be followed.

[0019] The term "specific surface area" means the BET specific surface area determined by nitrogen adsorption by the Brunauer-Emmett-Teller method. This method is described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". It can follow the recommendations of standard ASTM D3663-03. Unless otherwise instructed, firing at a given temperature and for a given time corresponds to firing in air at a steady temperature stage over the indicated time.

[0020] The alumina of the present invention can be represented by the general formula Al2O3.

[0021] The alumina may contain residual sodium. The content of residual sodium may be 0.50% by weight or less, further 0.15% by weight or less. The sodium content may be 50 ppm or more. This content may be 50 to 900 ppm, further 100 to 800 ppm. This content is expressed as the weight of Na2O relative to the total weight of the alumina. Therefore, for alumina with a residual sodium content of 0.15%, it is considered to be 0.15 g of Na2O per 100 g of alumina. Methods for determining the sodium content within this concentration range are known to those skilled in the art. For example, inductively coupled plasma spectrometry can be used.

[0022] The alumina may contain residual sulfate. The content of residual sulfate may be 1.00% by weight or less, further 0.20% by weight or less, or further 0.10% by weight or less. The sulfate content may be 50 ppm or more. This content may be 100 to 1500 ppm, further 400 to 1000 ppm. This content is expressed as the weight of sulfate relative to the total weight of the alumina. Therefore, for alumina with a residual sulfate content of 0.50%, it is considered to be 0.50 g of SO4 per 100 g of alumina. Methods for determining the sulfate content within this concentration range are known to those skilled in the art, such as inductively coupled plasma spectrometry. Microanalysis can also be used. The Horiba EMIA320-V2 type microanalyzer may be suitable for use.

[0023] Alumina may also contain impurities other than sodium and sulfates, such as impurities based on silicon, titanium, or iron. The proportion of each impurity is usually less than 0.07% by weight (≤ 0.07%), and more preferably less than 0.05% by weight (≤ 0.05%).

[0024] The alumina of the present invention is characterized by a specific porosity. Thus, this alumina has at least one of the following two pore structures: · First structure: - A pore volume within the range of pores having a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, more specifically 0.60 to 0.80 mL / g, and - A pore volume within the range of pores having a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, more specifically 0.15 mL / g or less, further more specifically 0.10 mL / g or less, or even more specifically 0.05 mL / g or less. · Second structure: After calcination in air at 1100 °C for 5 hours: - A pore volume within the range of pores having a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, more specifically 0.50 to 0.70 mL / g, and - A pore volume within the range of pores having a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, more specifically 0.15 mL / g or less, further more specifically 0.10 mL / g or less, or even more specifically 0.05 mL / g or less.

[0025] Alumina can also be defined by at least one of the following two pore structures: · First structure: - A pore volume within the range of pores having a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, and - A pore volume within the range of pores having a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, and / or · Second structure: After calcination in air at 1100 °C for 5 hours: - A pore volume within the range of pores sized 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, and - A pore volume within the range of pores sized 100 nm to 1000 nm, which is 0.20 mL / g or less.

[0026] It is understood that the alumina described in this patent application may have at least one of the above two structures, and may have both structures simultaneously.

[0027] Furthermore, the alumina may have a high specific surface area. This may have a BET specific surface area of 100 to 200 m 2 / g, more specifically 150 to 200 m 2 / g. This specific surface area may be 120 m 2 / g or more, preferably 140 m 2 / g or more. This specific surface area may be 100 to 140 m 2 / g, further 100 to 120 m 2 / g.

[0028] The alumina has higher thermal stability. This may have a BET specific surface area of 70 to 100 m 2 / g after being calcined in air at 1200 °C for 5 hours.

[0029] The alumina generally has a total pore volume that strictly exceeds 1.05 mL / g. This total pore volume may advantageously be at least 1.10 mL / g, further at least 1.20 mL / g, or further at least 1.30 mL / g, or at least 1.40 mL / g, or at least 1.50 mL / g. This total pore volume is usually 2.40 mL / g or less.

[0030] Alumina maintains a high total pore volume even after firing at 1100 °C for 5 hours. Thus, after firing at 1100 °C for 5 hours, alumina typically has a total pore volume of at least 0.90 mL / g. This total pore volume is preferably at least 1.00 mL / g, more preferably at least 1.10 mL / g, and even more preferably at least 1.20 mL / g. This total pore volume is typically 1.80 mL / g or less.

[0031] It is also noted that the alumina is crystalline. This can be shown by an X-ray diffraction pattern. The alumina can include the delta phase, the theta phase, the gamma phase, or a mixture of at least two of these phases.

[0032] Alumina has a bulk density of 0.25 g / cm 3 ~0.55 g / cm 3 , more specifically 0.40 g / cm 3 ~0.55 g / cm 3 and can have a bulk density of. This bulk density of the alumina powder corresponds to the weight of a specific amount of powder relative to the volume occupied by this powder: Bulk density (g / mL) = (mass of powder (g)) / (volume of powder (mL))

[0033] This bulk density can be determined by the method described below. First, accurately determine the volume of a graduated cylinder of about 25 mL without a spout. To do this, measure the weight of the empty graduated cylinder (tare weight T). Then, pour distilled water into the graduated cylinder up to the rim, but do not exceed the rim (no meniscus). Weigh the graduated cylinder filled with distilled water (M). As a result, the mass of the water in the graduated cylinder is as follows: E = M - T

[0034] The calibrated volume of the graduated cylinder is V メスシリンダー = E / (density of water at the measurement temperature). The density of water is equal to 0.99983 g / mL at a measurement temperature of 20 °C, for example.

[0035] The alumina powder is carefully poured into an empty, dry graduated cylinder using a funnel until it reaches the edge of the cylinder. Use a spatula to level off any excess powder. Do not compress or pack the powder during filling. Then, weigh the graduated cylinder containing the powder. Bulk density (g / mL) = (Mass of graduated cylinder containing alumina powder - tare weight T (g)) / (V メスシリンダー (mL))

[0036] The alumina can have a D50 of 2.0 μm to 80.0 μm. This can have a D90 of 150.0 μm or less, more specifically 100.0 μm or less. This can have a D10 of 1.0 μm or more.

[0037] First Embodiment According to the first embodiment, the alumina has a D50 of 2.0 to 15.0 μm, and further 4.0 to 12.0 μm. The D90 can be 20.0 μm to 60.0 μm, and further 25.0 μm to 50.0 μm.

[0038] According to one embodiment, when the D50 is 2.0 to 15.0 μm, - The bulk density is 0.25 to 0.40 g / cm 3 ; and / or - The total pore volume is 1.40 to 2.40 mL / g.

[0039] This total pore volume can advantageously be 1.50 to 2.40 mL / g.

[0040] Second Embodiment According to the second embodiment, the alumina has a D50 of 15.0 to 80.0 μm, and further 20.0 to 60.0 μm. The D90 can be 40.0 μm to 150.0 μm, and further 50.0 μm to 100.0 μm.

[0041] According to the second embodiment, when the D50 is 15.0 to 80.0 μm, - The bulk density is 0.4 to 0.55 g / cm 3is; and / or - The total pore volume is 1.05 (this value is excluded) to 1.80 mL / g.

[0042] This total pore volume may more preferably be 1.20 to 1.80 mL / g.

[0043] Specific alumina The alumina of the present invention may more specifically have at least one of the following two pore structures: · First structure: - The pore volume within the range of pores having a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, more specifically 0.60 to 0.80 mL / g, and - The pore volume within the range of pores having a size of 100 nm to 1000 nm, which is 0.05 mL / g or less. and / or · Second structure: After calcination in air at 1100 °C for 5 hours: - The pore volume within the range of pores having a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, more specifically 0.50 to 0.70 mL / g, and - The pore volume within the range of pores having a size of 100 nm to 1000 nm, which is 0.05 mL / g or less.

[0044] As described above, it is understood that this specific alumina may have at least one of the above two structures, and may have both structures simultaneously.

[0045] This may also have the following characteristics. - BET specific surface area of 150 to 200 m 2 / g; and BET specific surface area of 70 to 100 m 2 / g after calcination in air at 1100 °C for 5 hours; and - Bulk density of 0.40 g / cm 3 to 0.55 g / cm 3 ; and - D50 of 15.0 μm to 80.0 μm; and - D90 of 40.0 μm to 150.0 μm.

[0046] Furthermore, this specific alumina may also have the characteristics of the total pore volume described above. Therefore, it generally has a total pore volume greater than 1.05 mL / g, usually strictly. This total pore volume may advantageously be at least 1.10 mL / g, further at least 1.20 mL / g, or even 1.30 mL / g, or at least 1.40 mL / g, or at least 1.50 mL / g. This total pore volume is usually 2.40 mL / g or less.

[0047] This specific alumina maintains a high total pore volume even after being calcined at 1100 °C for 5 hours. Therefore, after being calcined at 1100 °C for 5 hours, the alumina usually has a total pore volume of at least 0.90 mL / g. This total pore volume is preferably at least 1.00 mL / g, further at least 1.10 mL / g, or even more preferably at least 1.20 mL / g. This total pore volume is usually 1.80 mL / g or less.

[0048] The contents of sodium and sulfate for this specific alumina are as described above.

[0049] Use of Alumina The alumina of the present invention can be used in the field of anti-pollution catalytic action of the exhaust gas of gasoline or diesel heat engines. A catalyst composition containing the alumina of the present invention and at least one oxide based on cerium and at least one rare earth metal other than cerium, optionally, is used in this field. This oxide may be, for example, cerium oxide (usually represented by the general formula CeO2), or a mixed oxide based on cerium, zirconium, and at least one rare earth metal other than cerium, optionally. The rare earth metal other than cerium can be selected from the group formed by yttrium, praseodymium, and neodymium.

[0050] Preparation Method The present invention also relates to a method for preparing alumina, in particular the aforementioned alumina, or the alumina according to any one of claims 1 to 39, which comprises the following steps: (a) into a tank initially containing an acidic aqueous solution having a pH of 0.5 to 4.0, more preferably 0.5 to 3.5: (a1) - an aqueous solution of sodium aluminate until the pH of the reaction mixture reaches 8.0 to 10.0, more preferably 8.5 to 9.5; (a2) - or, simultaneously, an aqueous solution of (i) aluminum sulfate and (ii) an aqueous solution of sodium aluminate until the pH of the reaction mixture reaches 6.5 to 10, more preferably 7.0 to 8.0, or 8.5 to 9.5; while stirring, and at the end of step (a), adjusting the aluminum concentration of the reaction mixture to 0.50 wt% to 3.0 wt%; (b) Subsequently, a step of simultaneously introducing an aqueous solution of aluminum sulfate and an aqueous solution of sodium aluminate at a rate such that the average pH of the reaction mixture is maintained within the pH range targeted in step (a); (The temperature of the reaction mixture in steps (a) and (b) is at least 60 °C) (c) At the end of step (b), optionally adjusting the pH of the reaction mixture to a value of 7.5 to 10.5, or 8.0 to 9.0, or 9.0 to 10.0; (d) Then filtering the reaction mixture and washing the recovered solid; (e) Performing mechanical treatment or ultrasonic treatment on the aqueous dispersion of the solid recovered at the end of step (d) to reduce the particle size of the dispersion; (f) Drying the dispersion obtained at the end of step (e); (g) Subsequently, firing the solid obtained from step (f) in air.

[0051] Step (a) In step (a), into a tank initially containing an acidic aqueous solution having a pH of 0.5 to 4.0: (a1) - an aqueous solution of sodium aluminate until the pH of the reaction mixture reaches 8.0 to 10.0, or 8.5 to 9.5; (a2) - Or, simultaneously, until the pH of the reaction mixture reaches 6.5 to 10.0, further 7.0 to 8.0, or 8.5 to 9.5, (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate; are introduced while being stirred, As a result, at the end of step (a), the aluminum concentration of the reaction mixture is adjusted to 0.50 wt% to 3.0 wt%.

[0052] The pH of the acidic aqueous solution initially contained in the tank is 0.5 to 4.0, further 0.5 to 3.5. This solution can be composed of a dilute aqueous solution of a mineral acid, such as sulfuric acid, hydrochloric acid, or nitric acid.

[0053] The acidic aqueous solution may be composed of an aqueous solution of an acidic aluminum salt, such as aluminum nitrate, chloride, or sulfate. Preferably, the aluminum concentration of this solution is 0.01 wt% to 2.0 wt%, further 0.01 wt% to 1.0 wt%, or further 0.10 wt% to 1.0 wt%. Preferably, the acidic aqueous solution is an aqueous solution of aluminum sulfate. This solution is prepared by dissolving aluminum sulfate in water or diluting a pre-formed aqueous solution with water. The pH of the aqueous solution obtained by the presence of aluminum sulfate is usually 0.5 to 4.0, further 0.5 to 3.5.

[0054] Step (a) is carried out according to two embodiments (a1) or (a2). According to embodiment (a1), an aqueous solution of sodium aluminate is introduced while being stirred. According to embodiment (a2), (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate are introduced simultaneously with stirring.

[0055] Preferably, the aqueous solution of sodium aluminate does not contain precipitated alumina. Sodium aluminate preferably has an Na2O / Al2O3 ratio of 1.20 or more, for example 1.20 to 1.40.

[0056] The aqueous solution of sodium aluminate may have an aluminum concentration of 15.0% by weight to 35.0% by weight, more specifically 15.0% by weight to 30.0% by weight, and still more specifically 20.0% by weight to 30.0% by weight. The aqueous solution of aluminum sulfate may have an aluminum concentration of 1.0% by weight to 15.0% by weight, more specifically 5.0% by weight to 10.0% by weight.

[0057] At the end of step (a), the aluminum concentration of the reaction mixture is 0.50% by weight to 3.0% by weight.

[0058] In this step (a), the introduction time of the solution is usually 2 minutes to 30 minutes.

[0059] In step (a), the introduction of the aqueous solution of sodium aluminate has the effect of increasing the pH of the reaction mixture.

[0060] In particular, in embodiment (a1), the aqueous solution of sodium aluminate can be introduced directly into the reaction medium, for example, from at least one introduction cannula. In particular, in embodiment (a2), the two solutions can be introduced directly into the reaction medium, for example, from at least two introduction cannulas. In these two embodiments (a1) and (a2), in order to efficiently mix the introduced solutions in the reaction mixture, the solutions are preferably introduced into a sufficiently stirred zone of the reactor, for example, a zone close to the stirring rotor. In embodiment (a2), when the solution is introduced from at least two introduction cannulas, the injection locations where the two solutions are introduced into the reaction mixture are distributed such that the solutions are efficiently diluted in the mixture. Thus, for example, two cannulas can be arranged in the tank such that the injection locations of the solutions into the reaction mixture are exactly opposite.

[0061] Step (b) In step (b), the aqueous solution of aluminum sulfate and the aqueous solution of sodium aluminate are introduced simultaneously, and the introduction rate of this solution is adjusted to maintain the average pH of the reaction mixture within the pH range targeted in step (a). Thus, the target value of the average pH is - When carried out according to Embodiment (a1) in step (a), it is 8.0 to 10.0, more preferably 8.5 to 9.5; or - When carried out according to Embodiment (a2) in step (a), it is 6.5 to 10.0, more preferably 7.0 to 8.0 or 8.5 to 9.5; It is as follows.

[0062] The term "average pH" means the arithmetic mean of the pH values of the reaction mixture continuously recorded during step (b).

[0063] Preferably, an aqueous solution of sodium aluminate is introduced simultaneously with an aqueous solution of aluminum sulfate at a flow rate adjusted so that the average pH of the reaction mixture equals the target value. The flow rate of the aqueous solution of sodium aluminate useful for adjusting the pH may vary during step (b).

[0064] The introduction time of the two solutions may be 10 minutes to 2 hours, more preferably 30 minutes to 90 minutes. The flow rate of the introduction of the solution or the two solutions may be constant.

[0065] The temperature of the reaction mixture in steps (a) and (b) needs to be at least 60°C. This temperature may be 60°C to 95°C. To achieve this, the solution initially contained in the tank in step (a) can be preheated before starting the introduction of the solution. The solutions introduced into the tank in steps (a) and (b) can also be preheated in advance.

[0066] Step (c) In step (c), the pH of the reaction mixture is optionally adjusted to a value of 7.5 to 10.5, more preferably 8.0 to 9.0 or 9.0 to 10.0 by adding a basic or acidic aqueous solution.

[0067] The acidic aqueous solution that can be used to adjust the pH can be composed of a mineral acid, such as an aqueous solution of sulfuric acid, hydrochloric acid, or nitric acid. The acidic aqueous solution may be composed of an aqueous solution of an acidic aluminum salt, such as aluminum nitrate, chloride, or sulfate.

[0068] The basic aqueous solution that can be used to adjust the pH can be composed of inorganic bases such as sodium hydroxide, potassium hydroxide, or aqueous ammonia. The basic aqueous solution may be composed of an aqueous solution of a basic aluminum salt such as sodium aluminate. An aqueous solution of sodium aluminate is preferably used.

[0069] Preferably, the pH is adjusted by stopping the following: (c1) - Continuing the introduction of the sulfate aqueous solution and the introduction of the sodium aluminate aqueous solution until the target pH is reached; or (c2) - Continuing the introduction of the sodium aluminate aqueous solution and the introduction of the aluminum sulfate aqueous solution until the target pH is reached.

[0070] According to one embodiment, the introduction of the aluminum sulfate aqueous solution is stopped, and the introduction of the sodium aluminate aqueous solution is continued until a target pH of 8.0 to 10.5, preferably 9.0 to 10.0, is reached. The duration of step (c) may be variable. This duration may be from 5 minutes to 30 hours.

[0071] Step (d) In step (d), the reaction mixture is filtered. The reaction mixture is usually in the form of a slurry. The solid recovered on the filter may be washed with water. To do this, warm water having a temperature of at least 50 °C can be used.

[0072] Step (e) In step (e), the dispersion of the solid recovered at the end of step (d) in water is subjected to mechanical treatment or ultrasonic treatment to reduce the particle size of the dispersion. The pH of this dispersion before grinding can optionally be adjusted to 5.0 to 8.0. To do this, for example, a nitric acid solution can be used.

[0073] The D50 of the particles in the dispersion before mechanical treatment or ultrasonic treatment is usually 10.0 μm to 40.0 μm, and more preferably 10.0 μm to 30.0 μm. The D50 of the solid particles after mechanical treatment or ultrasonic treatment is preferably 1.0 μm to 15.0 μm, and more preferably 2.0 μm to 10.0 μm.

[0074] Mechanical treatment consists of applying mechanical stress or shear force to the dispersion to divide the particles. Mechanical treatment can be carried out, for example, by a ball mill, a high-pressure homogenizer, or a grinding system including a rotor and a stator. On a laboratory scale, a Microcer or a Labstar Zeta ball mill can be used, both of which are sold by Netzsch (for details, see https: / / www.netzsch-grinding.com / fr / produits-solutions / broyage-humide / broyeurs-de-laboratoire-serie-mini / ). The grinding system described in the examples can be used. For the ball mill, for example, zirconium oxide beads stabilized with yttrium can be used. For example, ZetaBeads Plus 0.2 mm balls can be used.

[0075] Ultrasonic treatment consists, at least in part, of irradiating the dispersion with sound waves. The sound waves propagating through the liquid medium can induce cavitation, by which the particles can be divided. On a laboratory scale, an ultrasonic system equipped with a Sonics Vibracell VC750 generator with a 13 mm probe can be used. The duration and the power supplied are adjusted to achieve the target D50.

[0076] Mechanical treatment or ultrasonic treatment can be carried out in batch mode or continuously.

[0077] Step (f): In step (f), the dispersion from step (e) is preferably dried by spraying.

[0078] Spray drying has the advantage of providing particles with a controlled particle size distribution. This drying method also offers excellent production efficiency. It consists of spraying the dispersion as a mist of droplets into a stream of hot gas (e.g., a stream of hot air) circulating within the chamber. The quality of the spraying controls the size distribution of the droplets and, as a result, the size distribution of the dried particles. Spraying can be carried out using any spraying device known per se. There are two main types of spraying devices: turbines and nozzles. For the various spraying techniques that can be implemented in this method, reference can be made in particular to the standard manual by Masters entitled "Spray-Drying" (second edition, 1976, published by George Godwin, London). The operating parameters that can be varied by a person skilled in the art are, in particular, the flow rate and temperature of the dispersion entering the spraying device; the flow rate, pressure, humidity, and temperature of the hot gas. The inlet temperature of the gas is usually between 100°C and 800°C. The outlet temperature of the gas is usually between 80°C and 150°C.

[0079] The D50 of the powder recovered at the end of step (g) is usually between 2.0 μm and 80.0 μm. This size is related to the size distribution of the droplets leaving the spraying device. The evaporation capacity of the sprayer is usually related to the size of the chamber. Thus, on a laboratory scale (Buechi B290), the D50 may be between 2.0 and 15.0 μm. On a larger scale, the D50 may be between 15.0 and 80.0 μm.

[0080] Step (g) In step (g), the solid obtained from step (f) is calcined in air. The calcination temperature is usually between 500°C and 1000°C, more specifically between 800°C and 1000°C. The calcination time is usually between 1 hour and 10 hours. The calcination conditions shown in the examples can be used.

[0081] It can be envisaged that steps (f) and (g) are carried out in the same apparatus in which the dispersion obtained from step (e) undergoes a heat treatment for both drying and calcination.

[0082] Preferably, the alumina recovered at the end of step (g) (i.e., at the end of firing) usually has a D50 of 2.0 μm to 80.0 μm. This usually has a D90 of 150.0 μm or less, more specifically 100.0 μm or less.

[0083] According to the first embodiment, at the end of step (g), the D50 may be 2.0 to 15.0 μm, and further 4.0 to 12.0 μm. The D90 may be 20.0 μm to 60.0 μm, and further 25.0 μm to 50.0 μm. This embodiment can be carried out when step (f) is carried out, for example, on a laboratory scale using a Buechi B290 spraying device.

[0084] According to the second embodiment, at the end of step (g), the D50 may be 15.0 to 80.0 μm, and further 20.0 to 60.0 μm. The D90 may be 40.0 μm to 150.0 μm, and further 50.0 μm to 100.0 μm. This embodiment can be carried out when step (f) is carried out on a larger scale.

[0085] The method may also include a final step of grinding the solid obtained in the previous step in order to adjust the particle size of the solid. A knife mill, an air jet mill, a hammer mill, or a ball mill can be used. Preferably, the ground product usually has a D50 of 2.0 μm to 15.0 μm. The D90 may be 20.0 μm to 60.0 μm, and further 25.0 μm to 50.0 μm.

[0086] The alumina of the present invention is in the form of a powder.

[0087] More detailed matters regarding the preparation of the alumina of the present invention will be found in the following exemplary examples.

Example

[0088] Measurement of specific surface area: For the purposes of the present description, the term "specific surface area" means the BET specific surface area measured by nitrogen adsorption in accordance with standard ASTM D 3663-03 established from the Brunauer-Emmett-Teller method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". The specific surface area is automatically determined, for example, using a Micromeritics Tristar II 3020 apparatus in accordance with the manufacturer's recommended instructions. The sample is pretreated at 250 °C for 90 minutes under vacuum (e.g., until a pressure of 50 mmHg is reached). This treatment can remove volatile chemical species (e.g., H2O, etc.) physically adsorbed on the surface.

[0089] Measurement of Porosity with Mercury The measurement is carried out using a mercury porosimetry apparatus. In this case, a Micromeritics Autopore IV 9520 apparatus equipped with a powder penetrometer was used in accordance with the manufacturer's recommended instructions. The following parameters were used: penetrometer used: 3.2 ml (Micromeritics reference: penetrometer type No. 8); capillary volume: 0.412 ml; maximum pressure ("head pressure"): 4.68 psi; contact angle: 130°; surface tension of mercury: 485 dyn / cm; density of mercury: 13.5335 g / ml. At the start of the measurement, a reduced pressure of 50 mmHg is applied to the sample for 5 minutes. The equilibrium times are as follows: low pressure range (1.3 - 30 psi): 20 seconds - high pressure range; (30 - 60000 psi): 20 seconds. Before the measurement, the sample is treated at 200 °C for 120 minutes to remove volatile chemical species (e.g., H2O, etc.) physically adsorbed on the surface.

[0090] Measurement of Particle Size (D10, D50, D90) To perform particle size measurement, a Malvern Mastersizer 2000 or 3000 laser diffraction particle size analyzer is used (detailed information about this device is described at https: / / www.malvernpanalytical.com / en / products / product-range / mastersizer-range / mastersizer-3000). The laser diffraction technique used consists of measuring the intensity of light scattered as a laser beam passes through a sample of dispersed particles. The laser beam passes through the sample, and the intensity of the scattered light is measured as a function of the angle. Subsequently, the diffraction intensity is analyzed to calculate the particle size using Mie scattering theory. From the measurement, a volume-based size distribution can be obtained, from which the parameters D10, D50, and D90 are estimated.

[0091] Example: Preparation of Aluminum Oxide According to the Present Invention Place 157 kg of deionized water in a tank stirred by an inclined blade agitator rotor, install a pH probe at the upper part of the liquid, and heat the water to 85 °C. This temperature is maintained throughout steps (a) to (c). Introduce 13.8 kg of an aluminum sulfate solution having a concentration of 8.3 wt% alumina (Al2O3) from an introduction cannula near the agitator rotor at a flow rate of 920 g of solution / min. After the introduction is complete, the pH of the raw material is around 2.6 and the aluminum concentration is 0.7 wt%. Then, stop the introduction of the aluminum sulfate solution.

[0092] Step (a): Introduce a sodium aluminate solution having a concentration of 24.9 wt% alumina (Al2O3) and a Na2O / Al2O3 molar ratio of 1.27 from a second introduction cannula near the agitator rotor at a flow rate of 690 g of solution / min until a pH of 9.0 is reached. Then, stop the introduction. At this time, the aluminum concentration of the reaction mixture is 2.10%.

[0093] In step (b), the introduction of the aluminum sulfate solution is restarted at a flow rate of 570 g of solution / min, and the sodium aluminate solution is simultaneously introduced into a stirred reactor at a flow rate adjusted to maintain a pH value of 9.0. This step is continued for 45 minutes.

[0094] In step (c), the introduction of the aluminum sulfate solution is stopped, and the addition of the sodium aluminate solution is continued at a flow rate of 320 g of solution / min until a pH of 9.5 is reached. The addition of the sodium aluminate solution is stopped.

[0095] In step (d), the reaction slurry is poured into a vacuum filter. After filtration is complete, the cake is washed with deionized water at 65°C.

[0096] In step (e), the cake is redispersed in deionized water to obtain a dispersion having an oxide (Al2O3) concentration in the range of 10% by weight. A nitric acid solution with a concentration of 69% by weight is added to the suspension to obtain a pH of around 6. The suspension is passed through a ball mill of the LME20 brand by Netzsch. The operating conditions of the mill are adjusted so that a D50 of 3.5 microns is obtained.

[0097] In step (f), the suspension obtained from step (e) is sprayed to obtain a dried lanthanum-doped aluminum hydroxide powder.

[0098] In step (g), the sprayed powder is calcined at 940°C for 2 hours (with a temperature increase rate of 3°C / min). The mass loss observed during this calcination is 26.9%.

[0099] As a result, alumina having the following characteristics is obtained. - Specific surface area: 174 m 2 / g; - Specific surface area after calcination in air at 1100°C / 5 h; 81 m 2 / g; - Pore volume in the pore size range of 5 nm to 100 nm: 0.69 mL / g; - Pore volume in the pore size range of 100 nm to 1000 nm: 0.02 mL / g; - Total pore volume: 1.51 mL / g; - Pore volume in the pore size range of 5 nm to 100 nm after firing in air at 1100 °C for 5 h: 0.55 mL / g; - Pore volume in the pore size range of 100 nm to 1000 nm after firing in air at 1100 °C for 5 h: 0.01 mL / g; - Total pore volume after firing in air at 1100 °C for 5 h: 1.15 mL / g.

[0100]

Table 1

Claims

1. The following two void structures: ・The first structure: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, and / or ・The second structure: After calcination in air at 1100 °C for 5 hours: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, characterized by at least one of them, having a bulk density of 0.25 g / cm 3 to 0.55 g / cm 3, and these pore volumes being determined by the mercury porosimetry method, alumina.

2. For the first structure, the pore volume in the range of pores with a size of 5 nm to 100 nm is 0.60 to 0.80 mL / g, the alumina according to claim 1.

3. 100 to 200 m ２ The alumina according to claim 1 or 2, having a BET specific surface area of / g.

4. After firing at 1100 °C for 5 hours in air, 70 to 100 m ２ / g of the BET specific surface area, the alumina according to any one of claims 1 to 3.

5. The alumina according to any one of claims 1 to 4, wherein the total pore volume determined using the mercury porosimetry method is strictly greater than 1.05 mL / g.

6. The following two void structures: ・The first structure: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, and / or ・The second structure: After calcination in air at 1100 °C for 5 hours: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, characterized by at least one of them, after calcination at 1100 °C for 5 hours, the total pore volume determined using the mercury porosimetry method is at least 0.90 mL / g, and these pore volumes being determined by the mercury porosimetry method, alumina.

7. For the first structure, the pore volume in the range of pores with a size of 100 nm to 1000 nm is 0.05 mL / g or less, the alumina according to any one of claims 1 to 6.

8. The alumina according to any one of claims 1 to 7, characterized in that for the second structure, the pore volume in the range of pores with a size of 100 nm to 1000 nm determined after firing in air at 1100 °C for 5 hours is 0.05 mL / g or less.

9. The following two void structures: ・ The first structure: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.60 to 0.85 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, and / or ・ The second structure: After firing in air at 1100 °C for 5 hours: - The pore volume within the range of pores with a size of 5 nm to 100 nm, which is 0.50 to 0.75 mL / g, and - The pore volume within the range of pores with a size of 100 nm to 1000 nm, which is 0.20 mL / g or less, characterized by at least one of them, characterized by a D50 of 15.0 to 80.0 μm, The alumina, wherein these pore volumes are determined by the mercury porosimetry method.

10. Characterized by a D90 of 40.0 μm to 150.0 μm, where D90 represents the size at which 90% of the particles have a size less than D90, and D90 is determined from the volume distribution of particle sizes obtained by a laser particle size analyzer, the alumina according to claim 9.

11. 0.40 to 0.55 g / cm ３ The alumina according to claim 9 or 10, characterized by a bulk density of

12. The sodium content is 0.50% by weight or less, and this sodium content is expressed as the weight of Na ２ 2O with respect to the total weight of the alumina. The alumina according to any one of claims 1 to 11.

13. The sulfate content is 1.00% by weight or less, and this sulfate content is SO ４ expressed as the weight of with respect to the total weight of the alumina, the alumina according to any one of claims 1 to 12.

14. The alumina according to any one of claims 1 to 13, having the first and second void structures.

15. A catalyst composition comprising the alumina according to any one of claims 1 to 14 and at least one oxide based on cerium and at least one rare earth metal other than cerium, optionally.

16. A method for preparing alumina, comprising the following steps: (a) In a tank initially containing an acidic aqueous solution with a pH of 0.5 to 4.0: (a1) - An aqueous solution of sodium aluminate until the pH of the reaction mixture reaches 8.0 to 10.0; (a2) - Or, simultaneously, until the pH of the reaction mixture reaches 6.5 to 10, (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate, either of which is introduced while being stirred; At the end of step (a), a step of adjusting the aluminum concentration of the reaction mixture to 0.50 wt% to 3.0 wt%. (b) Subsequently, a step of simultaneously introducing an aqueous solution of aluminum sulfate and an aqueous solution of sodium aluminate, wherein the introduction rate is such that the average pH of the reaction mixture is maintained within the pH range targeted in step (a); The temperature of the reaction mixture in steps (a) and (b) is at least 60 °C; (c) At the end of step (b), a step of optionally adjusting the pH of the reaction mixture to a value of 7.5 to 10.5; (d) Thereafter, a step of filtering the reaction mixture and washing the recovered solid; (e) A step of performing mechanical treatment or ultrasonic treatment on the aqueous dispersion of the solid recovered at the end of step (d) to reduce the particle size of the dispersion; (f) A step of drying the dispersion obtained at the end of step (e); (g) Thereafter, a step of firing the solid obtained from step (f) in air; A method comprising the steps.

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