Flame made metal oxides
View Patent ↗Described is a method for the production of metal oxides by flame spray pyrolysis, in particular mixed metal oxides such as ceria/zirconia, and metal oxides obtainable by said method. Due to high enthalpy solvents with a high carboxylic acid content said metal oxides have improved properties. For example ceria/zirconia has excellent oxygen storage capacity at high zirconium levels up to more than 80% of whole metal content.
1. A method for the production of a metal oxide, wherein at least one metal oxide precursor is dissolved in a high enthalpy carboxylic acid solvent comprising at least one carboxylic acid with a mean carbon content at least 2.2 carbon atoms in an amount of at least 60% of the whole solvent to form a solution, and wherein said solution is then formed into droplets and flame oxidized.
2. The method of claim 1 , wherein the carboxylic acid content is at least 75% of the whole solvent.
3. The method of claim 1 , wherein the at least one carboxylic acid has a mean carbon content per acid group of at least 3.
4. The method of claim 1 , wherein the carboxylic acid is selected from C1 to C18 monocarboxylic acids and mixtures thereof.
5. The method of claim 4 , wherein the carboxylic acid is a mixture of formic acid and/or acetic acid and at least one further acid with at least 3 carbon atoms.
6. The method of claim 1 , wherein at least one of the carboxylic acids comprises one or more —OH and/or —NH 2 and/or —CONH 2 groups.
7. The method of anyone of claim 1 , wherein the solvent has an enthalpy of at least 15 kJ/g.
8. The method of claim 1 , wherein the metal oxide precursor is a salt or a salt precursor.
9. The method of claim 8 , wherein the salt or salt precursor comprises a hydrate.
10. The method of anyone of claim 1 , wherein the flame has a temperature of at least 1000° C.
11. The method of claim 10 , wherein the temperature is within the range of 1600 to 2600° C.
12. The method of anyone of claim 1 , wherein the droplets have an average diameter of 0.1 to 100 microns.
13. The method of anyone of claim 1 , wherein the metal is selected from the alkali metal group and/or the alkaline earth metal group and/or the transition metal group.
14. The method of claim 1 , wherein the at least one carboxylic acid has a mean carbon content per acid group within the range of 4 to 8.
15. The method of claim 1 , wherein at least one of the carboxylic acids comprises double bonds and/or substituents.
16. The method of claim 1 , wherein the solvent has an enthalpy of at least 20 kJ/g.
17. The method of claim 1 , wherein the solvent has an enthalpy of at least 23 kJ/g.
18. The method of claim 1 , wherein the metal oxide precursor is an organic group comprising salt.
19. The method of claim 18 , wherein the salt is purely organic.
20. The method of claim 1 , wherein the metal oxide precursor is a salt of at least one carboxylic acid and/or acetylacetonate.
21. The method of claim 1 , wherein the droplets have an average diameter within the range of 1 of 20 microns.
22. A metal oxide that is obtainable by a method of claim 1 .
23. A metal oxide according to claim 22 , that has a surface after heat treatment at 900° C. for 2 hours in air of at least 39 m 2 /g.
24. A metal oxide according to claim 22 , that is ceria/zirconia.
25. The metal oxide of claim 24 , with the zirconium being present in at most 90 atom-% of total metal atoms.
26. The metal oxide of claim 25 wherein the zirconium is present in at most 80 atom-% of total metal atoms.
27. A metal oxide claim 24 , that is phase stable upon heating at 900° C. for 2 hours in air.
28. A metal oxide according to claim 24 , wherein the two or more metals are homogeneously mixed at atomic level.
29. A metal oxide according to claim 22 , that has a dynamic oxygen storage capacity after heat treatment at 700° C. for 16 hours in air of at least 1.5 liters O 2 per kg catalyst.
30. A metal oxide according to claim 22 , to that is zirconium stabilized with cerium and/or yttrium, in an amount of cerium and/or yttrium of at most 10 atom-% of whole metal content.
31. A metal oxide according to claim 22 , that has a surface after heat treatment at 900° C. for two hours in air of above 50 mg 2 /g.
32. A metal oxide according to claim 22 that is a mixed metal oxide.
33. A metal oxide according to claim 22 , that is zirconium stabilized with cerium and/or yttrium.