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  • C01F17/00—Compounds of rare earth metals
  • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
  • C01F17/32—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6 oxide or hydroxide being the only anion, e.g. NaCeO2 or MgxCayEuO
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  • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
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Definitions

• the invention relates to a process for the preparation of aluminates containing at least one element A from the group consisting of Sr, Ba and La and at least one element B from the group consisting of Mn, Fe, Co, Ni, Rh, Cu and Zn, the hexaaluminates itself as well as their use.
• composition BaMno.sMgo.sAlnO-ig-a, BaMgAlnO-ig-a, BaMnAlnO-ig-a and SrMnAlnOi9-6- In one example, a solution of aluminum nitrate, lanthanum nitrate, manganese nitrate and magnesium nitrate in water with Ammonia added, the precipitate separated, washed and calcined at 600 ° C to 1200 ° C in air. A composition of the formula Lao, 78Mgo, 9Mno, 9AlnOi9-a is obtained.
• the disadvantage here are also the long Calcinier regulations. These are in the examples 16 h at a temperature of 1200 ° C after Vorkalzination of 4 h at a temperature of 600 ° C.
• the hexaaluminates obtained have specific surface areas of less than 20 m 2 / g.
• M1 is selected from La, Ce, Nd, Sm, Eu, Gd, Er, Yb and Y,
• M2 is selected from Mg, Ca, Sr and Ba, and
• M3 is selected from Mn, Fe, Co, Ni, Cu, Ag, Au, Rh, Ru, Pd, Ir and Pt,
• hexaaluminate catalyst As an application of the hexaaluminate catalyst is called the catalytic combustion of hydrocarbons to reduce NOx emissions.
• This process involves two high temperature calcination steps.
• the preparation of the modified alumoxane takes place at temperatures around 800 ° C and a holding time of 1 h.
• the hexaaluminate is produced at temperatures around 1300 ° C and a holding time of 3 h.
• the hexaaluminates obtained in the examples have specific surface areas between 5 and 10 m 2 / g.
• EP 2 1 19 671 A1 discloses a process for the preparation of hexaaluminates comprising the steps of a) providing a porous template material,
• lanthanum hexaaluminates of the formulas LaAlnOis, LaMnAlnO-ig and LaMgAlnOi9 are obtained by impregnating a carbon xerogel with an aqueous solution of lanthanum nitrate, aluminum nitrate, magnesium nitrate and manganese nitrate, drying and calcining at 1300 ° C in an inert gas atmosphere and removing the template material by calcination at 1000 ° C made in air. Also disclosed is the use of hexaaluminates in the catalytic combustion of lean fuel mixtures to minimize NO x and CO emissions.
• A is at least one element of Ca, Sr, Ba and La,
• B is K and / or Rb
• C represents at least one element from the group Mn, Co, Fe and Cr,
• an aqueous solution of an alkaline earth metal nitrate is prepared, the aqueous solution is acidified to a pH of less than 2, to the acidified aqueous solution, an aluminum salt is added, the resulting clear aluminum-containing solution is added to an aqueous solution of (NH4) 2C03, the Precipitated hexaaluminate is separated and calcined at a temperature of more than 1050 ° C and then ground to a particle size of less than 3 ⁇ .
• the steam reforming of methane with steam to produce hydrogen for fuel cells is given.
• the hexaaluminates prepared by this process reach specific surface areas of less than 20 m 2 / g.
• Another disadvantage is the long calcination time of 16 hours at temperatures above 150 ° C.
• WO 2013/135710 discloses mixed oxides of different structure as catalysts for the "reverse water gas shift reaction” (RWGS reaction), including hexaaluminates, and no statements are made regarding the preparation and properties of the catalysts.
• RWGS reaction reverse water gas shift reaction
• WO 2013/1 18078 and US20131 161 16 disclose the use of various mixed metal oxides as catalysts for the reforming of hydrocarbons, preferably methane, and CO2.
• hydrocarbons preferably methane, and CO2.
• non-phase pure hexaluminates are described with specific surface areas of less than 20 m 2 / g, which are obtained by several hours Caicintechnik at 1100 ° C.
• the object of the invention is to provide a simple and inexpensive process for the preparation of aluminates, preferably hexaaluminates with high specific surface area.
• the aluminates are said to be thermally and chemically stable with respect to their sintering properties and their coking behavior in a gas atmosphere containing hydrocarbons such as methane and at higher temperatures (500-1000 ° C).
• the object of the invention is in particular to provide a simple process for the preparation of aluminates, preferably hexaaluminates, which are suitable as reforming catalysts for the production of synthesis gas from methane and carbon dioxide and as catalysts for the RWGS reaction.
• the object is achieved by a process for the preparation of aluminates of the general formula (I)
• y is a value determined by the oxidation states of the other elements, comprising the steps of (i) providing one or more solutions or suspensions containing precursor compounds of elements A and B and a precursor compound of aluminum in a solvent,
• Aluminates according to the invention may be complex aluminates of the hexaaluminate type (hexaaluminates) or of a structure type related to the gamma A c.
• the aluminate, preferably hexaaluminate, of the general formula (I) forming precursor compounds of elements A and B and the aluminum are fed to the pyrolysis zone as an aerosol. It is expedient to supply to the pyrolysis zone an aerosol which is obtained by nebulization of only one solution which contains all precursor compounds. In this way, it is ensured in each case that the composition of the particles produced is homogeneous and constant.
• the individual components are therefore preferably selected so that the precursor compounds present in the solution are present in homogeneously dissolved state until they have been aerosolized (aerosol formation).
• the solution or solutions may contain both polar and non-polar solvents or solvent mixtures.
• the solution or solutions preferably contain the precursor compounds of elements A, B and of aluminum in the stoichiometric ratio corresponding to formula (I).
• the precursor compounds decompose to form the aluminate of elements A and B.
• approximately spherical particles of varying surface area are obtained.
• the temperature in the pyrolysis zone is above the decomposition temperature of the precursor compounds at a temperature sufficient for oxide formation, usually in the range between 500 and 2000 ° C.
• the adiabatic flame temperature in the pyrolysis zone can be up to 2500 or even 3000 ° C.
• the pyrolysis is carried out at a temperature of 900 to 1500 ° C, in particular at 1000 to 1300 ° C.
• the pyrolysis reactor can be indirectly heated from the outside, for example by means of an electric furnace. Because of the temperature gradient from outside to inside required for indirect heating, the furnace must be much hotter than the temperature required for pyrolysis. Indirect heating requires a temperature-stable furnace material and a complex reactor design, the required total amount of gas is, on the other hand, lower than in the case of a flame reactor.
• the pyrolysis zone is heated by a flame (flame spray pyrolysis).
• the pyrolysis zone then comprises an ignition device.
• conventional fuel gases can be used, but preferably hydrogen, methane or ethylene are used.
• the temperature can be adjusted in the pyrolysis zone targeted.
• the pyrolysis zone instead of air as the 02 source for the combustion of the fuel gas and pure oxygen can be supplied.
• the total amount of gas also includes the carrier gas for the aerosol and the vaporized solvent of the aerosol.
• the one or more of the pyrolysis zone supplied aerosols are conveniently passed directly into the flame. While air is usually preferred as the carrier gas for the aerosol, it is also possible to use nitrogen, CO 2, O 2 or a fuel gas, for example hydrogen, methane, ethylene, propane or butane.
• a flame spray pyrolysis device generally comprises a reservoir for the liquid to be atomized, feed lines for carrier gas, fuel gas and oxygen-containing gas, a central aerosol nozzle and an annular burner arranged around it, a device for gas-solid separation comprising a filter element and a removal device for the solid and an outlet for the exhaust gas.
• the cooling of the particles is carried out by means of a quenching gas, e.g. Nitrogen, air or water vapor.
• the pyrolysis zone comprises a so-called pre-dryer, which pre-dries the aerosol by evaporation of the solvent before it enters the pyrolysis reactor, for example in a flow tube with a heating unit arranged around it. If pre-drying is dispensed with, there is a risk that a product with a broader grain spectrum and, in particular, too much fines will be obtained.
• the temperature The temperature of the pre-dryer depends on the nature of the dissolved precursors and their concentration.
• the temperature in the pre-dryer is above the boiling point of the solvent to 250 ° C; in the case of water as solvent, the temperature in the pre-dryer is preferably between 120 and 250 ° C., in particular between 150 and 200 ° C.
• the pre-dried aerosol fed via a line to the pyrolysis reactor then enters the reactor via an outlet nozzle.
• the combustion chamber which is preferably tubular, can be thermally insulated.
• the combustion chamber may also be a simple combustion chamber.
• a pyrolysis gas containing nano-particles of varying specific surface area is obtained.
• the size distribution of the particles obtained can essentially be obtained directly from the droplet spectrum of the aerosol supplied to the pyrolysis zone, the concentration and the volume flow of the solution or solutions used.
• the pyrolysis gas is cooled sufficiently before deposition of the particles formed from the pyrolysis gas so that co-sintering of the particles is excluded.
• the pyrolysis zone preferably comprises a cooling zone which adjoins the combustion chamber of the pyrolysis reactor.
• cooling of the pyrolysis gas and the aluminate particles contained therein to a temperature of about 100-500 ° C is required, depending on the filter element used.
• a cooling to about 150 - 200 ° C instead.
• the pyrolysis gas containing the aluminate particles and partially cooled, after leaving the pyrolysis zone enters an apparatus for separating the particles from the pyrolysis gas comprising a filter element.
• a quenching gas for example nitrogen, air or air humidified with air, is introduced.
• the element A is lanthanum and the element B is cobalt or nickel.
• element A is lanthanum and element B is cobalt, particularly preferred
• LaCoAlnOi9- y is particularly preferred.
• the element A is strontium or barium and the element B is nickel.
• the element B is nickel.
• iron and nickel are present side by side, for example in
• element A is lanthanum, strontium or barium and element B is iron, manganese, zinc or copper.
• x 0.1 to 1, 0, preferably 1.
• copper and zinc are present side by side, for example in
• Suitable precursor compounds of elements A and B are the acetylacetonates (acac), alkoxides or carboxylates and mixed acetylacetonate alcoholates of elements A and B and their hydrates. Suitable precursor compounds may contain elements A and B side by side, for example AB (acac) x or ABAI (acac) x . In a preferred embodiment of the invention, the precursor compound of element A and / or B is the ace- tylacetonate of element A and / or B used. Examples are lanthanum acetylacetonate, cobalt acetylacetonate and nickel acetylacetonate.
• the precursor compound of element A and / or B used are carboxylates of element A and / or B.
• Suitable carboxylates are, for example, the acetates, propionates, oxalates, octanoates, neodecanoates, stearates and 2-ethylhexanoates of elements A or B.
• a preferred carboxylate of elements A or B is 2-ethylhexanoate, for example lanthanum 2-ethylhexanoate or cobalt-2 ethylhexanoate.
• Preferred precursor compounds of elements A and B are also their nitrates.
• Preferred precursor compounds of elements A and B are furthermore their oxides and hydroxides. These may also be suspended in a suitable solvent.
• Suitable precursor compounds of aluminum are alcoholates of aluminum. Examples are the ethanolate, n-propoxide, isopropanolate, n-butoxide and tert-butoxide of aluminum. Preferred precursor compounds of aluminum are the aluminum sec-butoxide and the aluminum isopropoxide.
• Suitable precursor compounds of aluminum are furthermore its acetylacetonate, carboxylates, nitrate, oxide and hydroxide. These may be dissolved or suspended in a suitable solvent.
• Preferred polar solvents are water, methanol, ethanol, n-propanol, isopropanol, n-butanol, tert. Butanol, n-propanone, n-butanone, diethyl ether, tert-butyl methyl ether, tetrahydrofuran, glycols, polyols, d-Cs carboxylic acids, such as acetic acid, ethyl acetate and mixtures thereof and nitrogen-containing polar solvents such as pyrrolidones, purines, Pyridines, nitriles or amines, eg. For example acetonitrile.
• Suitable apolar solvents are aliphatic or aromatic hydrocarbons having 5 to 15 carbon atoms, for example 6 to 9 carbon atoms, or mixtures thereof, for example benzines.
• Preferred apolar solvents are toluene, xylene, n-pentane, n-heptane, n-octane, iso-octanes, cyclohexane, methyl, ethyl or butyl acetate or mixtures thereof.
• Particularly preferred solvents are xylene or benzene (hydrocarbon mixtures).
• lanthanum acetylacetonate, cobalt acetylacetonate, lanthanum 2-ethylhexanoate and aluminum sec-butoxide are dissolved in xylene.
• the aluminates according to the invention generally have at least 80% by weight, preferably at least 90% by weight, of the hexaaluminate phase.
• the present invention also aluminates of the elements A and B of the general formula (I) having a BET surface area of 60 to 120, preferably 60 to 100 m 2 / g, particularly preferably 60 to 85 m 2 / g. These are in particular obtainable by the process according to the invention.
• the crystallite sizes of the hexaaluminates according to the invention are generally in the range from 5 to 50 nm, preferably from 15 to 25 nm. These can be determined from the XRD using the Scherer equation or from TEM images.
• the hexaaluminates according to the invention are phase-pure (according to the diffractogram), have no undesired LaAlOß- and alpha-A C phases, but instead consist of hexaaluminate and optionally a phase comparable to the gamma-A C.
• the bulk density of the powder deposited from the pyrolysis gas is generally 50 to 200 kg / m 3 .
• the pore volume after BJH of the powder is generally 0.1 to 0.5 cm 3 / g, the pore size after BJH (desorption) of the powder is generally 3 to 10 nm.
• the present invention also provides the use of the hexaaluminates according to the invention as a reforming catalyst for the production of synthesis gas from methane and carbon dioxide.
• the present invention also provides the use of the hexaaluminates according to the invention as a catalyst for the RWGS reaction for the production of CO-containing synthesis gas from a gas mixture containing carbon dioxide and hydrogen and optionally methane.
• hexaalimethylenes which were prepared by means of flame synthesis, compared to conventionally prepared Hexaaluminaten for the "reversed water gas shift reaction" (RWGS reaction), especially in the presence of methane, from a
• RWGS reaction reversed water gas shift reaction
• the hexaalimates of the invention produced by flame spray pyrolysis have a higher hydrogen conversion in the RWGS reaction than hexaaluminates prepared by wet-chemical processes
• the hexaaluminates according to the invention have a significantly lower tendency toward coking than wet-ash aluminas prepared by wet-chemical means.
• LAA Lanthanum acetylacetonate
• CoAA Cobalt acetylacetonate
• AlsB Aluminum sec-butoxide
• the flame synthesis reactor comprises three sections: a dosing unit, a high-temperature zone and a quench. Via the metering unit to the reactor, a refractory-lined or water-cooled combustion chamber, the gaseous fuel ethylene, an N 2/0 2 mixture and dissolved in a suitable solvent organometallic precursor compounds on a standard two-fluid nozzle (for example, the company Schlick) fed.
• the reaction mixture is burned in the high temperature zone to give an oxide product having nanoparticulate properties.
• the particle growth is stopped by a subsequent quench, usually with nitrogen.
• the particles are separated from the reaction offgas by means of a baghouse filter.
• the experiments were aimed at the synthesis of cobalt-based hexaaluminates or mixtures containing high levels of the hexaaluminate phase. Numerous synthesis parameters were varied, in detail i) the temperature of the high-temperature zone (1000 to 1200 ° C);
• Type of lanthanum precursor (LAA or LEH).
• LAA or LEH Type of lanthanum precursor
• the results show that a higher temperature in the reaction zone and the correct molar ratio of precursors in the precursor solution favor formation of the hexaaluminate phase.
• the mass flow, the molality, the atomization pressure of the nozzle (which influences the droplet size) and the type of lanthanum precursor have only a small influence on the formation of the hexaaluminates.
• other product properties such as the crystallite size and the degree of agglomeration, are influenced.
• the crystallite size of the primary particles of the hexaaluminate phase is mainly influenced by the atomization pressure of the two-phase nozzle, the mass flow of the quench and the concentration of the precursor solution used.
• the crystallite size can be estimated from the XRD diffractogram and is a few 10 nm (10 to 20 nm).
• the BET surface area is 60 to 80 m 2 / g and is consistent with the particle size determined by XRD.
• a representative X-ray diffractogram is shown in FIG. 2.
• the material was pressed into tablets with a punch press, and then the tablets were crushed and forced through a 1 mm mesh screen.
• the tablets have a diameter of 5 mm and a height of 5 mm.
• the target fraction has a particle size of 500 to 1000 ⁇ .
• the comparative catalyst was prepared as described in WO2013 / 1 18078.
• Cobalt (83.1 g Co (NO 3 ) 3 ⁇ 6H 2 O) and lanthanum nitrate (284.9 g La (NO 3 ) 3 ⁇ 6H 2 O) are completely dissolved in 250 ml distilled water.
• boehmite Disperal is used by SASOL.
• the suspension is stirred for 15 minutes with a mechanically driven stirrer at a stirring speed of 2000 rpm.
• the dissolved nitrates are completely precipitated by adjusting the pH and separated from the solvent by filtration.
• the material is subsequently precalcined in an oven at 520 ° C. Thereafter, the calcined material is pressed into tablets with a stamping press, and then the tablets are crushed and printed through a 1 mm mesh screen.
• the tablets have a diameter of 13 mm and a thickness of 3 mm.
• the target fraction has a particle size of 500 to 1000 ⁇ .
• the specific surface area determinable by the BET method was 8 m 2 / g.
• composition of the product fluids obtained in the reactions was determined by GC analysis using Agilent GC.
• the evaluation of the results of phase 1, 2 and 6 allow the determination of the activity of the catalyst for the desired
• Phases 3, 4 and 5 of the test protocol allow conclusions to be drawn regarding the influence of hydrocarbons on the RWGS reaction by methane activation as well as the coking behavior and deactivation tendency of the catalyst. By comparing the results of phases 1 and 6, the long-term and coking behavior can be concluded.
• Table 3 compares the catalytic properties of the inventive catalyst (Sample 1) and the comparative catalyst (Sample 2). Table 3
• Sample 1 hexaaluminate prepared according to the invention (flame CoLaAlnOig) according to Example 6
• Sample 2 Comparative Catalyst (wet-chemically produced CoLaAlnOig) The results of the catalysis experiments show the following:
• Sample 1 exhibits, in particular in the presence of methane, higher or equal high hb conversions for the reversed water gas shift reaction as sample 2 (comparison).
• sample 2 catalyzes the methane formation to a much greater extent, which must be taken into account when comparing the hb conversions according to columns 1, 2 and 6. Due to methane formation, overall higher hb conversions result for sample 2 (comparison).
• theroetic hb conversions with and without methane formation were calculated in thermodynamic equilibrium (lines 1 and 2, Table 3). As can be clearly seen, sample 1 of the invention shows no methanation activity.
• Sample 1 does not convert methane present in the gas phase in the presence of CO2 and Hb.
• the reference catalyst activates methane and converts it, especially at higher concentrations (see columns 11 and 12), which is detrimental to the desired reaction. This is also evident in the lower hb conversions for sample 2 (comparison) according to columns 4 and 5. Negative conversion values (methane formation) result from a slight methanation activity of the samples.

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