Process for the preparation of nanocrystalline metal oxides

Abstract

The present invention relates to a process for the preparation of nanocrystalline metal oxide particles comprising the steps of a) the introduction of a starting compound into a reaction chamber by means of a carrier fluid, b) the subjecting of the starting compound in a treatment zone to a pulsating thermal treatment, c) the forming of nanocrystalline metal oxide particles, d) the removal of the nanocrystalline metal oxide particles obtained in steps b) and c) from the reactor, wherein the starting compound is introduced into the reaction chamber in the form of a solution, slurry, suspension or in solid aggregate state. Further, the present compound relates to a catalyst material, obtainable by the process according to the invention, in particular a catalyst material for use in the preparation of methanol from carbon monoxide and hydrogen.

Claims

1. Process for the preparation of nanocrystalline metal oxide particles comprising the steps of a) the introduction of a starting compound into a combustion chamber of a reactor by means of a carrier fluid, the reactor comprising the combustion chamber and a resonance tube, wherein the resonance tube is attached to an exhaust side of the combustion chamber, b) the subjecting of the starting compound in a treatment zone of the combustion chamber to a thermal treatment of a pulsating flow at a temperature of 240 to 600 C., wherein the starting compound has a residence time in the treatment zone of 200 milliseconds to 2 seconds, c) the forming of nanocrystalline metal oxide particles, d) the removal of the nanocrystalline metal oxide particles obtained in steps b) and c) from the reactor, characterized in that the starting compound is introduced into the combustion chamber in the form of a solution, slurry, suspension or in solid aggregate state.

2. Process according to claim 1, characterized in that the carrier fluid is a gas.

3. Process according to claim 1, characterized in that the starting compound is introduced into the combustion chamber in atomized form.

4. Process according to claim 1, characterized in that one or more starting compounds are used which are identical to or different from one another.

5. Process according to claim 4, characterized in that the pulsation of the pulsating flow is regular or irregular.

6. Process according to claim 1, characterized in that after the thermal treatment in the treatment zone, the nanocrystalline metal particles that have formed are transferred into a colder zone of the reactor.

7. Process according to claim 6, characterized in that a metal oxide is used as starting material.

8. Process according to claim 6, characterized in that a soluble metal compound is used as starting compound.

9. Process according to claim 1, characterized in that the process is carried out at a pressure between 15-40 bar.

Description

EXAMPLES

(1) General

(2) Variant 1

(3) Direct Feed of Spray-Dried Powder into the Reaction Chamber

(4) The optionally spray-dried powder comprising metal oxides was fed by means of a Schenk dispenser. The residence time of the powder in the reactor was between 510 and 700 ms. A feed quantity of approximately 10 kilogrammes per hour was chosen. The temperatures were between 245 C. and 265 C.

(5) Variant 2

(6) Feed of Suspensions

(7) Aqueous suspensions (30% solids content) were prepared from two filter cakes of a precipitated starting product and the suspensions were sprayed into the combustion chamber of the reactor by means of a two-component nozzle. The process was carried out at temperatures of 460 C. to 680 C.

(8) Before being introduced into the reactor space, the suspensions were separated from non-dissolved residues by means of a screen.

(9) Variant 3

(10) Injection of a Solution

(11) An aqueous solution (approx. 40%) of CuZnAl formate (alternatively CuMnAl formate) was sprayed into the combustion chamber by means of a Schlick nozzle. A temperature range of 350 C. to 460 C. was chosen for carrying out the process according to the invention. It was further found that even lower concentrations (10 to 30%) of the corresponding solution could be used. The BET surface area of the material was between 60 (Cu/Mn/Al mixed oxide) and 70 m.sup.2/g (Cu/Zn/Al mixed oxide). In the case of Cu/Zn/Al mixed oxides prepared conventionally by the wet-chemical process the BET surface area was between 15 and 35 m.sup.2/g. The pore-volume distribution of the material according to the invention is shown in Table 1.

(12) An amorphous nanocrystalline monomodal material was always obtained in all variants.

(13) TABLE-US-00001 TABLE 1 Pore-size distribution of Cu/Zn/Al mixed oxide according to the invention (BET: 70 m.sup.2/g) Pore-volume distribution Pore radius (nm) in % 7500-875 0.83 875-40 9.42 40-7 67.27 7-3.7 22.48

(14) As can be seen from Table 1, the product that has formed has an almost monomodal distribution of pore radii, wherein the majority of the pore radii are in a range of 40 to 7 nm.

Example 1

(15) By using different starting materials, it is also possible to obtain different powder properties, for example in respect of the BET surface area and the particle size, in the nanocrystalline powders obtainable by means of the process according to the invention.

(16) Table 2 shows powder properties of aluminium oxide which was obtained starting from different starting materials.

(17) TABLE-US-00002 TABLE 2 Powder properties of Al.sub.2O.sub.3 when using different starting materials Specific XRD surface corundum Particle Starting Empirical area D = 2.088 size material formula m.sup.2/g cps nm Al alkoxide Al(C.sub.4H.sub.9O).sub.3 53 33 0.5-50 Al chloride AlCl.sub.3 81 3 5-100 Al nitrate Al(NO.sub.3).sub.3 * 17 56 5-75 9H.sub.2O Pseudo AlO(OH) * 11 286 300-500 boehmite H.sub.2O Gibbsite Al(OH).sub.3 26 419 60-100 Al oxide Al.sub.2O.sub.3 55 12 30-50

(18) Properties of nanocrystalline powders obtained by means of the process according to the invention are shown in Table 3 for different metal oxides.

(19) TABLE-US-00003 TABLE 3 Properties of different nanocrystalline powders Product TiO.sub.2 Al.sub.2O.sub.3 ZnO ZrO.sub.2 ZrO.sub.2Y.sub.2O.sub.3 Particle 5 . . . 50 5 . . . 75 50 . . . 100 10 . . . 50 10 . . . 50 size (nm) Morphology spherical spherical spherical spherical hollow spheres Crystal rutile 80% --Al.sub.2O.sub.3 zincite mixed phase tetragonal phase anatase 20% tetragonal/ monoclinic Specific 25 50 . . . 150 19 14 10 surface area (BET) (m.sup.2/g)

(20) BET values for the products in Table 2 which were prepared by conventional processes (wet-chemical precipitation and calcining) were measured as follows:

(21) TiO.sub.2: 15-17 m.sup.2/g

(22) Al.sub.2O.sub.3: 30-40 m.sup.2/g

(23) ZnO: 1.0-1.5 m.sup.2/g

(24) ZnO.sub.2: 1-1.8 m.sup.2/g

(25) ZnO.sub.2/Y.sub.2O.sub.3: 0.5-1.5 m.sup.2/g

(26) This clearly shows that oxides with a particularly large BET surface area can be prepared by means of the process according to the invention.