Alumina with specific pore profile

Abstract

The present invention relates to an alumina having a specific pore profile 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 of 0.50 to 0.75 mL / g, more specifically 0.50 to 0.70 mL / g, for pores with sizes between 5 nm and 100 nm; and a pore volume of 0.20 mL / g or less, more specifically 0.15 mL / g or less, or even 0.10 mL / g or less, for pores with sizes between 100 nm and 1000 nm.

Description

[Technical Field]

[0001] This patent application claims priority from European Patent Applications Nos. 19315154.5 and 19315155.2, filed November 29, 2019, the contents of which are incorporated by reference in their entirety. In the event of any discrepancy between the text of this patent application and the text of the French patent application that would affect the clarity of the terms or expressions, reference shall be made exclusively to this application.

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

[0003] Technical Field It is a known practice to use alumina for the preparation of automobile pollution control catalysts for converting pollutants emitted from gasoline or diesel thermal engines. Alumina is used as a support for precious metals, in particular platinum, palladium, and / or rhodium. It can also be combined with other catalytic components, which depend on the catalyst and its intended use (diesel or gasoline pollution control). 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, which are used as oxygen-mobile materials for gasoline engine catalysts (three-way catalysts (TWC) or gasoline particulate filters (GPF)). Alumina is used to convert NOx emitted from diesel engines. x For example, they may be combined with zeolites used as hydrocarbon traps for diesel catalysts, or with copper and / or iron exchanged zeolites for catalysts for catalytic reduction (SCR) of nitrogen oxides with ammonia, for example, for the reduction of CO₂.

[0004] technical challenges In all these automotive pollution control applications, alumina needs to have high thermal stability in order to be able to maintain catalytic efficiency for a long period of time, i.e., to maintain good conversion of gaseous pollutants. 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 at high temperature, e.g., 1200°C for 5 hours in air.

[0005] The preparation of automotive anti-pollution catalysts typically 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 low viscosity suspensions, which allows the preparation of suspensions with a high alumina content. Furthermore, the high density of the alumina of the present invention makes the alumina powder easy to handle.

[0006] The thermal stability of alumina is usually related to the pore volume of the alumina. Increasing the pore volume generally increases the thermal stability. However, increasing the pore volume significantly reduces the density of the alumina during the catalyst preparation process and increases the viscosity of the alumina suspension.

[0007] To solve this problem, it has been observed that the particular porosity of the alumina of the present invention makes it possible to obtain both high thermal stability and high bulk density. [Background technology]

[0008] Technical background US Patent No. 4,154,812 describes a method for preparing alumina, which does not include step (e). [Brief explanation of the drawings]

[0009] [Figure 1] The diffraction pattern of the alumina of the present invention is shown (Example 1), and it can be observed that this alumina has the characteristic peaks of crystalline alumina. DETAILED DESCRIPTION OF THE INVENTION

[0010] Brief description of the invention The present invention relates to an alumina according to any one of claims 1 to 42.

[0011] The alumina therefore comprises the elements Al and O and an additional element (E) which is La, Pr or a combination of La+Pr, the proportion of element (E) being possibly between 0.1% and 6.0% by weight, or even between 0.5% and 6.0% by weight, or even between 1.0% and 6.0% by weight, or even between 2.0% and 6.0% by weight, this proportion being expressed as the weight of element (E) expressed in the form of its oxide relative to the total weight of the alumina, This includes the following two void profiles: First profile: - a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.60 to 0.85 mL / g, more particularly 0.60 to 0.80 mL / g; and - a pore volume in the range of pores of a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g, more particularly less than or equal to 0.15 mL / g, or even less than or equal to 0.10 mL / g, or even less than or equal to 0.05 mL / g; and / or Second profile: After sintering in air at 1100°C for 5 hours: a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.50 to 0.75 mL / g, more particularly 0.50 to 0.70 mL / g; and a pore volume in the range of pores of a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g, more particularly less than or equal to 0.15 mL / g, or even less than or equal to 0.10 mL / g, or even less than or equal to 0.05 mL / g; characterized by at least one of the following: These pore volumes are determined by the mercury porosimetry method.

[0012] This alumina may contain sodium and sulfate as well as other impurities.

[0013] The invention also relates to a catalytic composition according to claim 43 and to the use of an alumina according to claim 44.

[0014] The present invention relates to a method for preparing alumina according to any one of claims 45 to 52.

[0015] All these topics are explained in more detail below.

[0016] Details of the invention In this patent application, for the continuation of the present description, it is specified that in the ranges of values ​​given, the limits are inclusive unless otherwise specified. It is also specified that the firing is carried out in air.

[0017] It is further specified that the concentrations of the solutions or the proportions of the elements Al and (E) in the alumina are expressed as weight percent of oxide equivalents. Therefore, for the calculation of these concentrations or proportions, the following oxides are used: Al2O3 for the element Al, La2O3 for the element La, and Pr6O for the element Pr. 11 For example, an aluminum sulfate solution with an aluminum concentration of 2.0 wt% corresponds to a solution containing 2.0 wt% Al2O3 equivalents. Similarly, alumina containing 4.0% lanthanum corresponds to 4.0% La2O3 equivalents.

[0018] The term "particle" refers to aggregates formed from primary particles. The particle size is determined from the particle size volume distribution 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 meaning in the technical field of laser diffraction measurements. Dx therefore represents the value determined for the particle size volume distribution at which x% of the particles have a size equal to or less than this value Dx. D50 therefore 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. Measurements are usually carried out on aqueous dispersions of the particles.

[0019] Porosity data are obtained by mercury porosimetry. This technique allows the determination of pore volume (V) as a function of pore diameter (D). A Micromeritics Autopore 9520 instrument equipped with a powder penetrometer can be used according to the manufacturer's recommended instructions. The procedure of ASTM D 4284-07 can be followed. These data allow the determination of pore volume (PV) in the range of pore sizes from 5 nm to 100 nm. 5~100nm ), pore volume (PV) in the range of pore sizes from 100 nm to 1000 nm 100~1000nm ), and total pore volume (TPV) can be determined.

[0020] The term "specific surface area" refers to the BET specific surface area determined by nitrogen adsorption according to the Brunauer-Emmett-Teller method. This method was described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". The recommendations of the standard ASTM D3663-03 can be followed. Unless otherwise indicated, calcination at a given temperature and for a given time corresponds to calcination in air at a constant temperature step for the indicated time.

[0021] The alumina of the present invention is an alumina containing an additional element (E), which is La, Pr, or a combination of La and Pr. Thus, the alumina is composed of the elements Al, O, and E. The element (E) can be particularly advantageously the element La. Alumina of this type containing such an element is generally described as doped alumina. The proportion of the element (E) is 0.1% to 6.0% by weight, or even 0.5% to 6.0% by weight, expressed as the weight of the element (E) expressed in the form of its oxide relative to the total weight of the alumina. This proportion may be 1.0% to 6.0% by weight, or even 2.0% to 6.0% by weight. The element (E) is usually present in the alumina in the form of its oxide.

[0022] The alumina of the present invention is characterized by a particular porosity, and therefore has at least one of the following two porosity profiles: First profile: - a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.60 to 0.85 mL / g, more particularly 0.60 to 0.80 mL / g; and - a pore volume in the range of pores of a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g, more particularly less than or equal to 0.15 mL / g, or even less than or equal to 0.10 mL / g, or even less than or equal to 0.05 mL / g; Second profile: After firing in air at 1100°C for 5 hours: a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.50 to 0.75 mL / g, more particularly 0.50 to 0.70 mL / g; and - a pore volume in the range of pores of a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g, more particularly less than or equal to 0.15 mL / g, or even less than or equal to 0.10 mL / g, or even less than or equal to 0.05 mL / g.

[0023] Alumina may also be defined by at least one of the following two porosity profiles: First profile: - a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.60 to 0.85 mL / g; and - a pore volume in the range of pores sized from 100 nm to 1000 nm that is less than or equal to 0.20 mL / g; and and / or Second profile: After sintering in air at 1100°C for 5 hours: - a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.50 to 0.75 mL / g; and - A pore volume in the range of pores of size 100 nm to 1000 nm that is less than or equal to 0.20 mL / g.

[0024] It is understood that the aluminas described in this patent application may have at least one of the above two profiles, but may also have both profiles simultaneously.

[0025] Furthermore, alumina can have a high specific surface area, which is 100-200 m 2 / g, more specifically 150-200m 2 / g. This specific surface area is 120 m 2 / g or more, preferably 140m 2 / g or more. This specific surface area is 100 to 140 m 2 / g, or even 100-120m 2 / g.

[0026] Alumina also has high thermal stability, which is 45-60 mPa after calcination in air at 1200°C for 5 hours. 2 / g BET specific surface area.

[0027] Alumina generally has a total pore volume usually strictly greater than 1.05 mL / g. This total pore volume may advantageously be at least 1.10 mL / g, or even at least 1.20 mL / g, or even 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 not more than 2.40 mL / g.

[0028] Alumina maintains a high total pore volume even after calcination at 1100°C for 5 hours. Thus, after calcination at 1100°C for 5 hours, alumina typically has a total pore volume that is at least 0.90 mL / g. This total pore volume is preferably at least 1.00 mL / g, or even at least 1.10 mL / g, or even more advantageously at least 1.20 mL / g. This total pore volume is typically 1.80 mL / g or less.

[0029] Alumina is 0.25 g / cm 3 ~0.55g / cm 3 , more specifically 0.40 g / cm 3 ~0.55g / cm 3 This bulk density of the alumina powder corresponds to the weight of a particular amount of powder relative to the volume it occupies: Bulk density (g / mL) = (mass of powder (g)) / (volume of powder (mL)).

[0030] This bulk density can be determined by the method described below. First, the volume of a measuring cylinder of approximately 25 mL without a spout is accurately determined. To do this, the empty measuring cylinder is weighed (tare T). Distilled water is then poured into the measuring cylinder up to the brim, but not over the brim (no meniscus). The measuring cylinder filled with distilled water is weighed (M). The resulting mass of water in the measuring cylinder is: E=MT.

[0031] The calibrated volume of a graduated cylinder is V メスシリンダー = E / (density of water at measurement temperature). The density of water is equal to 0.99983 g / mL at a measurement temperature of, for example, 20°C.

[0032] Carefully pour the alumina powder into an empty, dry graduated cylinder using a funnel until it reaches the rim of the cylinder. Use a spatula to smooth out any excess powder. Do not compress or tamp the powder during filling. Then weigh the graduated cylinder containing the powder. Bulk density (g / mL) = (mass of measuring cylinder containing alumina powder - tare weight T (g)) / (V メスシリンダー (mL).

[0033] The alumina may have a D50 of 2.0 μm to 80.0 μm. It may have a D90 of 150.0 μm or less, more specifically 100.0 μm or less. It may have a D10 of 1.0 μm or more.

[0034] First embodiment According to a first embodiment, the alumina has a D50 of 2.0 to 15.0 μm, or even 4.0 to 12.0 μm. The D90 may be 20.0 to 60.0 μm, or even 25.0 to 50.0 μm.

[0035] According to the first embodiment, when D50 is 2.0 to 15.0 μm, - Bulk density is 0.25~0.40g / cm 3 is; and / or - The total pore volume is 1.40~2.40mL / g.

[0036] This total pore volume may advantageously be between 1.50 and 2.40 mL / g.

[0037] Second embodiment According to a second embodiment, the alumina has a D50 of 15.0 to 80.0 μm, or even 20.0 to 60.0 μm. The D90 may be 40.0 μm to 150.0 μm, or even 50.0 μm to 100.0 μm.

[0038] According to the second embodiment, when D50 is 15.0 to 80.0 μm, - Bulk density is 0.40~0.55g / cm 3 may be; and / or - The total pore volume is 1.05 (this value is excluded) to 1.80 mL / g.

[0039] More advantageously, the total pore volume may be 1.20 to 1.80 mL / g.

[0040] The alumina may contain residual sodium. The residual sodium content may be 0.50% by weight or less, or even 0.15% by weight or less. The sodium content may be 50 ppm or more. This content may be 50 to 900 ppm, or even 100 to 800 ppm. This content is expressed as the weight of Na2O relative to the total weight of alumina. Thus, for alumina with a residual sodium content of 0.15%, there would be 0.15 g of Na2O per 100 g of alumina. Methods for determining sodium content within this concentration range are known to those skilled in the art. For example, inductively coupled plasma spectroscopy can be used.

[0041] The alumina may contain residual sulfate. The residual sulfate content may be 1.00% by weight or less, or even 0.20% by weight or less, or even 0.10% by weight or less. The sulfate content may be 50 ppm or more. This content may be 100 to 1500 ppm, or even 400 to 1000 ppm. This content is expressed as the weight of sulfate relative to the total weight of the alumina. Thus, for an alumina with a residual sulfate content of 0.50%, 0.50 g of SO4 is considered to be present per 100 g of alumina. Methods for determining sulfate content within this concentration range are known to those skilled in the art, such as inductively coupled plasma spectroscopy. Microanalysis methods can also be used. A Horiba EMIA 320-V2 type microanalyzer may be suitable.

[0042] The alumina may also contain impurities other than sodium and sulfate, such as silicon-, titanium- or iron-based impurities, the proportion of each impurity usually being less than 0.10% by weight, or even less than 0.05% by weight.

[0043] It is also noted that alumina is crystalline, which can be shown by an X-ray diffractogram. The alumina may comprise a delta phase, a theta phase, a gamma phase, or a mixture of at least two of these phases.

[0044] Certain aluminas The alumina of the present invention may more specifically have at least one of the following two porosity profiles: First profile: - a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.60 to 0.85 mL / g, more particularly 0.60 to 0.80 mL / g; and - a pore volume in the range of pores with a size of 100 nm to 1000 nm that is less than or equal to 0.05 mL / g; and / or Second profile: After firing in air at 1100°C for 5 hours: a pore volume in the range of pores with a size of 5 nm to 100 nm of 0.50 to 0.75 mL / g, more particularly 0.50 to 0.70 mL / g; and - A pore volume in the range of pores of size 100 nm to 1000 nm that is less than or equal to 0.05 mL / g.

[0045] As previously mentioned, this particular alumina may have at least one of the above two profiles, but it is understood that it may have both profiles simultaneously.

[0046] This particular alumina may also have the following characteristics: - 150~200m 2 / g BET specific surface area; and - 70-100mm after sintering in air at 1100°C for 5 hours 2 / g BET specific surface area; and - 0.40g / cm 3 ~0.55g / cm 3 Bulk density of; and - D50 between 15.0 μm and 80.0 μm; and - D90 from 40.0μm to 150.0μm.

[0047] The sodium and sulfate content of this particular alumina is as previously described.

[0048] Furthermore, this particular alumina may also have the total pore volume characteristics described above. Thus, it generally has a total pore volume that is usually strictly greater than 1.05 mL / g. This total pore volume may advantageously be at least 1.10 mL / g, or even 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.

[0049] This particular alumina maintains a high total pore volume even after calcination at 1100°C for 5 hours. Thus, after calcination at 1100°C for 5 hours, the 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, or even at least 1.10 mL / g, or even more advantageously at least 1.20 mL / g. This total pore volume is typically 1.80 mL / g or less.

[0050] Uses of Alumina The alumina of the present invention can be used in the technical field of anti-pollution catalysis of exhaust gases from gasoline or diesel heat engines. A catalytic composition comprising the alumina of the present invention and at least one oxide based on cerium and, optionally, at least one rare earth metal other than cerium is used in this technical field. This oxide can be, for example, cerium oxide (usually represented by the formula CeO2) or a mixed oxide based on cerium, zirconium, and, optionally, at least one rare earth metal other than cerium. The rare earth metal other than cerium can be selected from the group formed by yttrium, praseodymium, and neodymium.

[0051] Preparation method The present invention also relates to a method for preparing an alumina, optionally comprising an additional element (E) chosen from lanthanum, praseodymium or a combination of these two elements, in particular an alumina as defined above or according to any one of claims 1 to 41, which method comprises the steps of: (a) into a tank initially containing an acidic aqueous solution having a pH of 0.5 to 4.0, or even 0.5 to 3.5: (a1) - an aqueous solution of sodium aluminate until the pH of the reaction mixture is 8.0-10.0, or even 8.5-9.5; (a2) - or simultaneously, (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate, until the pH of the reaction mixture is between 6.5 and 10.0, or even between 7.0 and 8.0, or between 8.5 and 9.5, introducing, with stirring, either at the end of step (a), providing an aluminum concentration in the reaction mixture of 0.50 wt% to 3.0 wt%; (b) subsequently introducing simultaneously 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); (wherein 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 from 7.5 to 10.5, or even from 8.0 to 9.0, or from 9.0 to 10.0; (d) thereafter filtering the reaction mixture and washing the recovered solids; (e) subjecting the dispersion of solids in water recovered at the end of step (d) to mechanical or ultrasonic treatment to reduce the particle size of the dispersion; (f) adding at least one salt of element (E) to the dispersion obtained at the end of step (e); (g) drying the dispersion obtained at the end of step (f); (h) then calcining the solid obtained from step (g) in air. Includes.

[0052] Process (a) In step (a), in a tank initially containing an acidic aqueous solution having a pH of 0.5 to 4.0, or even 0.5 to 3.5: (a1) - an aqueous solution of sodium aluminate until the pH of the reaction mixture is 8.0-10.0, or even 8.5-9.5; (a2) - or simultaneously, (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate, until the pH of the reaction mixture is between 6.5 and 10.0, or even between 7.0 and 8.0, or between 8.5 and 9.5, is introduced with stirring; As a result, at the end of step (a), the aluminum concentration in the reaction mixture is between 0.50% and 3.0% by weight.

[0053] The pH of the aqueous acid solution initially contained in the tank is between 0.5 and 4.0, or even between 0.5 and 3.5. This solution can consist of a dilute aqueous solution of a mineral acid, such as sulfuric acid, hydrochloric acid, or nitric acid.

[0054] 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% to 2.0% by weight, or even 0.01% to 1.0% by weight, or even 0.10% to 1.0% by weight. Preferably, the acidic aqueous solution is an aqueous solution of aluminum sulfate. This solution is prepared by dissolving aluminum sulfate in water or by diluting a preformed aqueous solution with water. The pH of the resulting aqueous solution, due to the presence of aluminum sulfate, is typically 0.5 to 4.0, or even 0.5 to 3.5.

[0055] Step (a) is carried out according to two embodiments (a1) or (a2): according to embodiment (a1), an aqueous solution of sodium aluminate is introduced with stirring; according to embodiment (a2), (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate are introduced simultaneously with stirring.

[0056] Preferably, the aqueous solution of sodium aluminate does not contain precipitated alumina. The sodium aluminate preferably has a Na2O / Al2O3 ratio of 1.20 or more, for example 1.20 to 1.40.

[0057] The aqueous solution of sodium aluminate may have an aluminum concentration of 15.0% to 35.0% by weight, more specifically 15.0% to 30.0% by weight, or even 20.0% to 30.0% by weight. The aqueous solution of aluminum sulfate may have an aluminum concentration of 1.0% to 15.0% by weight, more specifically 5.0% to 10.0% by weight.

[0058] At the end of step (a), the aluminum concentration in the reaction mixture is 0.50% to 3.0% by weight.

[0059] In this step (a), the solution is usually introduced for 2 to 30 minutes.

[0060] In step (a), the introduction of the aqueous solution of sodium aluminate has the effect of raising the pH of the reaction mixture.

[0061] In particular, in embodiment (a1), the aqueous solution of sodium aluminate can be introduced directly into the reaction medium, for example, through at least one introduction cannula. In particular, in embodiment (a2), the two solutions can be introduced directly into the reaction medium, for example, through at least two introduction cannulae. In these two embodiments (a1) and (a2), in order to efficiently mix the introduced solutions into the reaction mixture, the solutions are preferably introduced into a well-stirred zone of the reactor, for example, a zone close to the stirring rotor. In embodiment (a2), when the solutions are introduced through at least two introduction cannulae, the injection points at which the two solutions are introduced into the reaction mixture are distributed so that the solutions are efficiently diluted in said mixture. Thus, for example, two cannulae can be arranged in a tank so that the injection points of the solutions into the reaction mixture are diametrically opposed.

[0062] Process (b) In step (b), an aqueous solution of aluminum sulfate and an aqueous solution of sodium aluminate are introduced simultaneously, and the introduction rates of these solutions are 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: - from 8.0 to 10.0, or even from 8.5 to 9.5, if embodiment (a1) is followed in step (a); or - if embodiment (a2) is followed in step (a), between 6.5 and 10.0, or even between 7.0 and 8.0 or between 8.5 and 9.5 is.

[0063] The term "average pH" means the arithmetic mean of the pH values ​​of the reaction mixture recorded continuously during step (b).

[0064] Preferably, the aqueous solution of sodium aluminate is introduced simultaneously with the aqueous solution of aluminum sulfate at a flow rate adjusted to equalize the average pH of the reaction mixture to the target value. The flow rate of the aqueous solution of sodium aluminate, which serves to adjust the pH, can be varied during step (b).

[0065] The introduction time of the two solutions may be between 10 minutes and 2 hours, or even between 30 minutes and 90 minutes. The flow rate of the introduction of the solutions or of the two solutions may be constant.

[0066] The temperature of the reaction mixture in steps (a) and (b) must be at least 60°C. This temperature may be between 60°C and 95°C. To achieve this, the solution initially contained in the tank in step (a) can be preheated before the introduction of the solution begins. The solutions introduced into the tank in steps (a) and (b) can also be preheated in advance.

[0067] Process (c) In step (c), the pH of the reaction mixture is optionally adjusted to a value between 7.5 and 10.5, or even between 8.0 and 9.0 or between 9.0 and 10.0, by adding a basic or acidic aqueous solution.

[0068] The aqueous acid solution that can be used to adjust the pH can consist of an aqueous solution of a mineral acid, such as sulfuric acid, hydrochloric acid, or nitric acid. The aqueous acid solution can also consist of an aqueous solution of an acidic aluminum salt, such as aluminum nitrate, chloride, or sulfate.

[0069] The basic aqueous solution that can be used to adjust the pH can be composed of an inorganic base, such as sodium hydroxide, potassium hydroxide, or aqueous ammonia. The basic aqueous solution can also be composed of an aqueous solution of a basic aluminum salt, such as sodium aluminate. An aqueous solution of sodium aluminate is preferably used.

[0070] Preferably, the pH is adjusted by terminating: (c1) - continuing the introduction of the aqueous sulfate solution and the aqueous sodium aluminate solution until the target pH is reached; or (c2) - Continuing the introduction of the aqueous sodium aluminate solution and the aqueous aluminum sulfate solution until the target pH is reached.

[0071] According to one embodiment, the introduction of the aqueous solution of aluminum sulfate is stopped and the introduction of the aqueous solution of sodium aluminate 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 between 5 and 30 minutes.

[0072] Process (d) In step (d), the reaction mixture is filtered. The reaction mixture is usually in the form of a slurry. The solid collected on the filter may be washed with water. To do this, warm water having a temperature of at least 50°C may be used.

[0073] Process (e) In step (e), the aqueous dispersion of solids recovered at the end of step (d) is subjected to mechanical or ultrasonic treatment to reduce the particle size of the dispersion. The pH of this dispersion before milling can optionally be adjusted to 5.0-8.0. To do this, for example, a nitric acid solution can be used.

[0074] The D50 of the particles in the dispersion before mechanical or ultrasonic treatment is usually 10.0 μm to 40.0 μm, or even 10.0 μm to 30.0 μm. The D50 of the solid particles after mechanical or ultrasonic treatment is preferably 1.0 μm to 15.0 μm, or even 2.0 μm to 10.0 μm.

[0075] Mechanical treatment involves applying mechanical stress or shear to the dispersion to break down 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 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, yttrium-stabilized zirconium oxide beads can be used. For example, ZetaBeads Plus 0.2 mm balls can be used.

[0076] Sonication consists, in part, of irradiating a dispersion with sound waves. Sound waves propagating through the liquid medium induce cavitation, which can break up particles. 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 power delivered are adjusted to achieve the target D50.

[0077] The mechanical or ultrasonic treatment can be carried out in batch mode or continuously.

[0078] Process (f) In step (f), at least one salt of element (E) is added. In this step, it is also possible to envisage adding an aqueous ammonia solution to raise the pH, preferably to a value between 5.0 and 8.0.

[0079] Process (g) In step (g), the dispersion from step (f) is dried, preferably by spraying.

[0080] Spray drying has the advantage of producing 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 in a hot gas stream (e.g., a hot air stream) circulating in a chamber. The quality of the spray controls the size distribution of the droplets and, consequently, the size distribution of the dried particles. Atomization can be carried out using any atomization device known per se. There are two main types of atomization devices: turbines and nozzles. Regarding the various atomization 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 atomization 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.

[0081] The D50 of the powder recovered at the end of step (g) is typically between 2.0 μm and 80.0 μm. This size is related to the size distribution of droplets exiting the atomizer. The evaporation capacity of the atomizer is usually related to the chamber size. Thus, at a laboratory scale (Büchi B 290), the D50 may be between 2.0 and 15.0 μm. At larger scales, the D50 may be between 15.0 and 80.0 μm.

[0082] Process (h) In step (h), the solid obtained in step (g) is calcined in air. The calcination temperature is usually 500°C to 1000°C, more specifically 800°C to 1000°C. The calcination time is usually 1 to 10 hours. The calcination conditions shown in the examples can be used.

[0083] It can be envisaged that the two steps (g) and (h) are carried out in the same equipment in which the dispersion obtained from step (f) undergoes a heat treatment to both dry and calcinate it.

[0084] Preferably, the alumina recovered at the end of step (h) (i.e., at the end of the calcination) typically has a D50 of 2.0 μm to 80.0 μm. It typically has a D90 of 150.0 μm or less, more specifically 100.0 μm or less.

[0085] According to a first embodiment, at the end of step (h), D50 may be 2.0 to 15.0 μm, or even 4.0 to 12.0 μm. D90 may be 20.0 μm to 60.0 μm, or even 25.0 μm to 50.0 μm. This embodiment is more feasible when step (f) is carried out on a laboratory scale, for example using a Büchi B 290 atomizer.

[0086] According to a second embodiment, at the end of step (h), D50 may be 15.0 to 80.0 μm, or even 20.0 to 60.0 μm. D90 may be 40.0 μm to 150.0 μm, or even 50.0 μm to 100.0 μm. This embodiment can be carried out if step (f) is carried out on a larger scale.

[0087] The method may also include a final step of milling the solid obtained in the previous step to adjust the particle size of the solid. A knife mill, an air jet mill, a hammer mill, or a ball mill may be used. Preferably, the milled product typically has a D50 of 2.0 μm to 15.0 μm. The D90 may be 20.0 μm to 60.0 μm, or even 25.0 μm to 50.0 μm.

[0088] The alumina of the present invention is in the form of a powder.

[0089] Further details regarding the preparation of the aluminas of the present invention will be found in the illustrative examples below. [Example]

[0090] Specific surface area measurement: For the continuation of this description, the term "specific surface area" refers to the BET specific surface area measured by nitrogen adsorption according to 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 determined automatically, for example, using a Micromeritics Tristar II 3020 instrument, following the manufacturer's recommended instructions. The sample is pretreated at 250 °C for 90 minutes under vacuum (for example, until a pressure of 50 mmHg is reached). This treatment allows the removal of volatile species (e.g., HO) physically adsorbed on the surface.

[0091] Mercury porosity measurement Measurements were performed using a mercury porosimetry instrument. In this case, a Micromeritics Autopore IV 9520 instrument equipped with a powder penetrometer was used, following the manufacturer's recommended operating instructions. The following parameters were used: penetrometer volume: 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 dynes / cm; density of mercury: 13.5335 g / ml. At the start of the measurement, a vacuum of 50 mmHg was applied to the sample for 5 minutes. The equilibration times were as follows: low pressure range (1.3-30 psi): 20 seconds; high pressure range (30-60,000 psi): 20 seconds. Prior to the measurement, the sample was treated at 200 °C for 120 minutes to remove volatile species (e.g., HO) physisorbed on the surface.

[0092] From this measurement, the pore volume can be estimated.

[0093] Particle size measurement (D10, D50, D90) To perform particle size measurements, a Malvern Mastersizer 2000 or 3000 laser diffraction particle size analyzer is used (details about this instrument are described at https: / / www.malvernpanalytical.com / fr / products / product-range / mastersizer-range / mastersizer-3000). The laser diffraction technique used consists of measuring the intensity of light scattered during the passage of a laser beam through a sample of dispersed particles. A laser beam passes through the sample and the intensity of the scattered light is measured as a function of angle. The diffracted intensity is then analyzed to calculate particle size using Mie scattering theory. The measurement allows for a volume-based size distribution to be obtained, from which the parameters D10, D50, and D90 can be deduced.

[0094] Example 1: Preparation of aluminum oxide according to the invention (96% Al2O3 - 4% La2O3) containing 4% lanthanum according to embodiment (a1) 3200 g of deionized water is placed in a tank stirred with a pitched blade agitator. A pH probe is placed above the liquid, and the water is heated to 75°C. This temperature is maintained throughout steps (a) through (c). 285 g of aluminum sulfate solution with a concentration of 8.3 wt% alumina (Al2O3) is introduced at a flow rate of 19 g / min through an inlet cannula close to the agitator rotor. After introduction is complete, the pH of the feed is near 1.5, and the aluminum concentration is 0.7 wt%. The introduction of the aluminum sulfate solution is then stopped.

[0095] Step (a): A sodium aluminate solution with an alumina (Al2O3) concentration of 24.9% by weight and a Na2O / Al2O3 molar ratio of 1.27 is introduced at a flow rate of 14 g of solution / min through a second inlet cannula near the stirring rotor until a pH of 9.0 is reached. Then, the introduction is stopped. At this point, the aluminum concentration of the reaction mixture is 2.10%.

[0096] In step (b), the introduction of the aluminum sulfate solution is resumed at a flow rate of 12 g of solution / min, and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a flow rate adjusted to maintain the pH at a value of 9.0. This step is continued for 45 minutes.

[0097] 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 5 g of solution / min until a pH of 9.5 is reached, after which the addition of the sodium aluminate solution is stopped.

[0098] In step (d), the reaction slurry is poured into a vacuum filter. After filtration is complete, the cake is washed with deionized water at 60°C.

[0099] In step (e), the cake is redispersed in deionized water to obtain a dispersion with an oxide (Al2O3) concentration in the region of 11% by weight. A nitric acid solution with a concentration of 69% by weight is added to the suspension to obtain a pH of around 6.2. The suspension is passed through a ball mill of the Labstar Zeta brand from the manufacturer Netzsch. The operating conditions of the mill are adjusted to obtain a D50 of 4.2 microns.

[0100] In step (f), an aqueous solution of lanthanum acetate is prepared with a concentration of the oxide (La2O3) in the region of 8% by weight, and this solution is added, under stirring, to the suspension obtained from step (e) so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 4.0%.

[0101] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0102] In step (h), the atomized powder is calcined at 900°C for 2 hours (temperature increase rate of 4°C / min), during which the mass loss observed is 26.1%.

[0103] Example 2: Preparation of aluminum oxide according to the invention (98% Al2O3 - 2% La2O3) containing 2% lanthanum according to embodiment (a1) In the same stirred reactor, 157 kg of deionized water is placed and heated to 85°C. This temperature is maintained throughout steps (a) to (c). 13.8 kg of aluminum sulfate solution having an alumina (Al2O3) concentration of 8.3 wt% is introduced through an introduction cannula close to the stirring rotor at a flow rate of 920 g of solution / min. After introduction is complete, the pH of the feed is near 2.6 and the aluminum concentration is 0.7 wt%. The introduction of the aluminum sulfate solution is then stopped.

[0104] Step (a): A sodium aluminate solution with an alumina (Al2O3) concentration of 24.9% by weight and a Na2O / Al2O3 molar ratio of 1.27 is introduced at a flow rate of 690 g of solution / min through a second inlet cannula near the stirring rotor until a pH of 9.0 is reached. Then, the introduction is stopped. At this point, the aluminum concentration of the reaction mixture is 2.10%.

[0105] In step (b), the introduction of the aluminum sulfate solution is resumed at a flow rate of 570 g of solution / min, and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a flow rate adjusted to maintain the pH at a value of 9.0. This step is continued for 45 minutes.

[0106] 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.

[0107] 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.

[0108] In step (e), the cake is redispersed in deionized water to obtain a suspension with an oxide (Al2O3) concentration in the region 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 from the manufacturer Netzsch. The operating conditions of the mill are adjusted to obtain a D50 of 3.5 microns.

[0109] In step (f), a solution of lanthanum acetate is prepared with a concentration of the oxide (La2O3) in the region of 6.9% by weight. This solution is added, under stirring, to the suspension obtained from step (e) so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 2%.

[0110] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0111] In step (h), the atomized powder is calcined at 940°C for 2 hours (temperature increase rate of 3°C / min), during which the mass loss observed is 25.8%.

[0112] Example 3: Preparation of aluminum oxide according to the present invention containing 4% lanthanum (96% Al2O3 - 4% La2O3) Steps (a) to (e) of Example 2 are repeated. In step (f), a lanthanum acetate solution is prepared with a concentration of 6.9% by weight of lanthanum oxide (La2O3). This solution is added to the suspension obtained from step (e) with stirring so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 4%. Then, a 10.0% by weight aqueous ammonia solution is added to bring the pH to 8.7.

[0113] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0114] In step (h), the atomized powder is calcined at 940°C for 2 hours (temperature increase rate of 3°C / min), during which the mass loss observed is 26.9%.

[0115] Example 4: Preparation of aluminum oxide according to the invention (96% Al2O3 - 4% La2O3) containing 4% lanthanum according to embodiment (a2) In the same stirred reactor, 120 kg of deionized water is placed and heated to 67°C. This temperature is maintained throughout steps (a) to (c). 1.85 kg of aluminum sulfate solution with a concentration of 8.3% by weight of alumina (Al2O3) is introduced through an inlet cannula close to the stirring rotor at a flow rate of 370 g of solution / min. After the introduction is complete, the pH of the feed is near 3.0 and the concentration, expressed as oxide equivalents, is 0.13% by weight.

[0116] Step (a): The flow rate of the aluminum sulfate solution is increased to 1020 g of solution / min, and a sodium aluminate solution with an alumina (Al2O3) concentration of 24.9 wt% and a Na2O / Al2O3 molar ratio of 1.27 is simultaneously introduced at a flow rate of 1020 g of solution / min through a second cannula near the stirring rotor until a pH of 7.3 is reached, at which point the aluminum concentration of the reaction mixture is 1.40%.

[0117] In step (b), the introduction of the aluminum sulfate solution is maintained at a flow rate of 1020 g of solution / min, and the sodium aluminate solution is simultaneously introduced into the stirred reactor at a flow rate adjusted to maintain the pH at a value of 7.3. This step lasts for 45 minutes.

[0118] 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 1020 g of solution / min until a pH of 10.3 is reached. The addition of the sodium aluminate solution is stopped.

[0119] 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.

[0120] In step (e), the cake is redispersed in deionized water to obtain a suspension with an oxide (Al2O3) concentration in the region of 13% by weight. A nitric acid solution with a concentration of 69% by weight is added to the suspension to obtain a pH of around 6.2. The suspension is passed through a ball mill of the LME20 brand from the manufacturer Netzsch. The operating conditions of the mill are adjusted to obtain a D50 of 13.4 microns.

[0121] In step (f), a solution of lanthanum acetate is prepared with a concentration of the oxide (La2O3) in the region of 6.9% by weight, and this solution is added, under stirring, to the suspension obtained from step (e) so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 4.0%.

[0122] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0123] In step (h), the atomized powder is calcined at 1035°C for 2 hours (temperature increase rate of 3°C / min), during which the mass loss observed is 33%.

[0124] Example 5: Preparation of aluminum oxide according to the present invention containing 4% lanthanum (96% Al2O3 - 4% La2O3) Steps (a) to (d) of Example 1 are repeated.

[0125] In step (e), the cake from step (d) is redispersed in deionized water to obtain a dispersion with an oxide (Al2O3) concentration in the region of 11% by weight. A nitric acid solution with a concentration of 69% by weight is added to the suspension to obtain a pH of around 6.2. 250 g of this suspension is taken and treated with an ultrasonic probe. The following equipment is used: an ultrasonic system with a 750 W Sonics Vibracell VC750 generator equipped with a 13 mm probe (replaceable tip) (converter: CV334 + 13 mm probe tip (part number: 630-0220)). The ultrasonic treatment lasts for 320 seconds. The delivered energy, as measured by the generator, is 33,000 joules. The final temperature of the suspension is 56 °C. The suspension is allowed to cool. At the end of this treatment, the D50 of the suspension is 6.2 microns.

[0126] In step (f), a solution of lanthanum acetate is prepared with a concentration of the oxide (La2O3) in the region of 8% by weight, and this solution is added, under stirring, to the suspension obtained from step (e) so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 4.0%.

[0127] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0128] In step (h), the atomized powder is calcined at 900°C for 2 hours (temperature increase rate of 4°C / min), during which the mass loss observed is 26.3%.

[0129] Example 6: Preparation of aluminum oxide according to the present invention containing 4% lanthanum (96% Al2O3 - 4% La2O3) Steps (a) to (d) of Example 1 are repeated.

[0130] In step (e), the cake is redispersed in deionized water to obtain a dispersion with an oxide (Al2O3) concentration in the region of 11% by weight. A nitric acid solution with a concentration of 69% by weight is added to the suspension to obtain a pH of around 6.2. 250 g of this suspension is taken and placed in a ball mill of the Microcer brand from the manufacturer Netzsch. The operating conditions of the mill are adjusted to obtain a D50 of 3.3 microns.

[0131] In step (f), a solution of lanthanum acetate is prepared with a concentration of the oxide (La2O3) in the region of 8% by weight, and this solution is added, under stirring, to the suspension obtained from step (e) so that the mass ratio of La2O3 / (La2O3 + Al2O3) is 4.0%.

[0132] In step (g), the suspension obtained from step (f) is atomized to obtain a dry lanthanum-doped aluminum hydroxide powder.

[0133] In step (h), the atomized powder is calcined at 900°C for 2 hours (temperature increase rate of 4°C / min), during which the mass loss observed is 27.4%.

[0134] [Table 1]

[0135] [Table 2]

Claims

1. Alumina containing an additional element (E) which is La, Pr, or a combination of La and Pr, and having a concentration of 0.26 g / cm ３ ~0.55g / cm ３ and doped with an additional element (E), the proportion of said element (E) possibly being between 0.1% and 6.0% by weight, or even between 0.5% and 6.0% by weight, or even between 1.0% and 6.0% by weight, or even between 2.0% and 6.0% by weight, this proportion being expressed as the weight of said element (E) expressed in the form of its oxide relative to the total weight of alumina, and having the following two porosity profiles: First profile: - a pore volume in the range of pores with a size of 5 nm to 100 nm, which is between 0.60 and 0.85 mL / g; and - a pore volume in the range of pores with a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g; and / or Second profile: After firing in air at 1100°C for 5 hours: - a pore volume in the range of pores with a size of 5 nm to 100 nm, which is between 0.50 and 0.75 mL / g; and - a pore volume in the range of pores with a size between 100 nm and 1000 nm that is less than or equal to 0.20 mL / g; and the pore volume of the alumina is determined by mercury porosimetry.

2. 100 to 200 m ２ / g, more specifically 150 to 200 m ２ 2. The alumina of claim 1, having a BET specific surface area of ​​0.1g / g.

3. After firing in air at 1200°C for 5 hours, ２ 3. The alumina according to claim 1, having a BET specific surface area of ​​0.1g / g.

4. 0.40 g / cm ３ ~0.55g / cm ３ 4. The alumina according to claim 1, having a bulk density of

5. 5. An alumina according to any one of claims 1 to 4, having a total pore volume determined using mercury porosimetry methods strictly greater than 1.05 mL / g.

6. 6. The alumina of any one of claims 1 to 5, having a total pore volume of at least 0.90 mL / g, determined using mercury porosimetry, after calcination at 1100°C for 5 hours.

7. 7. Alumina according to any one of claims 1 to 6, characterized in that the first profile has a pore volume in the range of pores with sizes between 100 nm and 1000 nm of 0.05 mL / g or less.

8. 8. Alumina according to any one of claims 1 to 7, characterized in that the second profile has a pore volume in the range of pores between 100 nm and 1000 nm in size, determined after calcination in air at 1100°C for 5 hours, of less than or equal to 0.05 mL / g.

9. 9. Alumina according to any one of claims 1 to 8, characterized by a D50 of 15.0 to 80.0 μm, or even 20.0 to 60.0 μm.

10. 10. The alumina of claim 9, characterized by a D90 of 40.0 μm to 150.0 μm, or even 50.0 μm to 100.0 μm, D90 representing the size at which 90% of the particles have a size less than D90 of the volume distribution of particle sizes obtained by a laser particle size analyzer.

11. The sodium content is 0.50 wt. % or less, or even 0.15 wt. % or less, and the sodium content is 0.50 wt. % or less, or even 0.15 wt. % or less, based on the total weight of the alumina. ２ 11. An alumina according to any one of claims 1 to 10, expressed as weight of O.

12. a sulfate content of 1.00 wt. % or less, or even 0.20 wt. % or less, or even 0.10 wt. % or less, the sulfate content being 0.00 wt. % or less of SO 3 based on the total weight of the alumina; ４ 12. The alumina of any one of claims 1 to 11, expressed as a weight of

13. 13. An alumina according to any one of claims 1 to 12, having said first and second porosity profiles.

14. A catalytic composition comprising an alumina according to any one of claims 1 to 13 and at least one oxide based on cerium and optionally at least one rare earth metal other than cerium.

15. A method for preparing alumina according to any one of claims 1 to 13, comprising the steps of: (a) into a tank initially containing an acidic aqueous solution having a pH of 0.5 to 4.0, or even 0.5 to 3.5: (a1) - an aqueous solution of sodium aluminate until the pH of the reaction mixture is between 8.0 and 10.0, or even between 8.5 and 9.5; (a2)—or simultaneously (i) an aqueous solution of aluminum sulfate and (ii) an aqueous solution of sodium aluminate until the pH of the reaction mixture is between 6.5 and 10.0, or even between 7.0 and 8.0, or between 8.5 and 9.5; with stirring to give an aluminum concentration of 0.50% to 3.0% by weight in the reaction mixture at the end of step (a); (b) subsequently introducing simultaneously 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); wherein 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 from 7.5 to 10.5, or even from 8.0 to 9.0, or from 9.0 to 10.0; (d) thereafter filtering the reaction mixture and washing the recovered solids; (e) subjecting the dispersion of solids in water recovered at the end of step (d) to mechanical or ultrasonic treatment to reduce the particle size of the dispersion; (f) adding at least one salt of element (E) to the dispersion obtained at the end of step (e); (g) drying the dispersion obtained at the end of step (f); (h) thereafter calcining the solid obtained from step (g) in air; A method comprising:

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