Method for Producing Composites of Aluminum Oxide and Cerium/Zirconium Mixed Oxides

1 . A method for producing composite aluminum oxide and cerium/zirconium mixed oxides comprising the following steps:

(a) providing a suspension comprising boehmite as the alumina precursor and adjusting the pH to 8 to 11.5;

(b) providing an aqueous metal salt solution comprising metal salts of cerium and of zirconium;

(c) bringing the suspension of step (a) in contact with the metal salt solution of step (b) at a temperature of from 5 to 95° C., or forming a slurry of the suspension of step (a) and the metal salt solution from step (b) and subjecting the slurry to a temperature of 5 to 95° C.;

(d) isolating solids from (c); and

(e) calcining the solids from (d),

wherein

i) the boehmites provided in suspension according to step (a) are in an aqueous suspension and are provided with organic compounds, having at least one carboxyl group and one or more further groups selected from the group consisting of hydroxy, oxo, carboxy and amine groups; or

ii) the suspension of step (c) is hydrothermally aged in an aqueous environment, at a temperature of at least 90° C. for at least one hour, or

iii) the measures according to i) and ii) both are applied.

2 . The method according to claim 1 , wherein isolating the solids comprises separation of the aqueous solution, washing of the solids from (c) with water and drying the solids.

3 . The method according to claim 1 , wherein isolating the solids comprises the drying and dispersing of the solids from (c) and the subsequent spray drying.

4 . The method according to claim 1 , wherein the composite also comprises one or more alkaline earth elements/compounds, rare earth elements/compounds, zirconium or silicon, wherein these are added after step (c) in the form of one or more soluble additional compounds.

5 . The method according to claim 1 , wherein bringing the suspension of (a) in contact with the metal salt solution of (b) comprises:

(c1) starting with the metal salt solution and adding the alumina precursor suspension dropwise and then adjusting the pH to 6.5 to 11;

(c2) starting with the metal salt solution and adding it dropwise to the alumina precursor suspension and at the same time adjusting the pH to 6.5 to 11; or

(c3) starting with the alumina precursor suspension and adding dropwise the metal salt solution and ammonia to maintain a pH of 6.5 to 11.

6 . The method according to claim 1 , wherein the suspension of (c) is hydrothermally aged in an aqueous environment at a temperature of at least 120° C. for at least four hours.

7 . The method according to claim 1 , wherein water-soluble salts of metals are used to prepare the metal salt solution.

8 . The method according to claim 1 , wherein Ce/Zr oxide is present in the form of a solid solution in the composite, and Al 2 O 3 and the Ce/Zr mixed oxides are homogeneously distributed side by side.

9 . The method according to claim 4 , wherein the alkaline earth salts are barium salts.

10 . The method according to claim 1 , wherein the organic compounds of step i) have 2 to 12 carbon atoms, and are provided in an amount by weight of 0.1% to 50% based on the dry weight of the boehmite.

11 . The method according to claim 1 , wherein the pH of the suspension comprising boehmite is adjusted by a nitrogen base.

12 . The method according to claim 1 , wherein the mixed oxide/composite composition comprises 20% to 80% by weight aluminum, 5% to 80% by weight zirconium, 5% to 80% by weight cerium and 0% to 12% by weight rare earth metal(s), calculated as Al 2 O 3 , ZrO 2 , CeO 2 , RE 2 O 3 .

13 . The method according to claim 1 , wherein the boehmite or the boehmite suspension are prepared by hydrolysis of an aluminum alkoxide.

14 . An Al/Ce/Zr oxide composite comprising aluminum oxide and cerium/zirconium mixed oxides in the form of a solid solution, wherein Al 2 O 3 and the Ce/Zr mixed oxides are homogeneously distributed side by side, obtainable according to claim 1 .

15 . The Al/Ce/Zr oxide composite according to claim 14 comprising

20% to 80% by weight aluminum, calculated as Al 2 O 3 ;

5% to 80% by weight zirconium, calculated as ZrO 2 ;

5% to 80% by weight cerium, calculated as CeO 2 ; and

0% to 12% by weight rare earth metal(s) calculated as REO 3 .

16 . The Al/Ce/Zr oxide composite according to claim 14 having, after 4 h at 1200° C., a surface area of at least 20 m 2 /g.

17 . The Al/Ce/Zr oxide composite according to claim 14 , wherein the Al/Ce/Zr oxide composite is an Al/Ce/Zr rare earth oxide composite comprising as rare earth oxides the oxides of neodymium, praseodymium, yttrium or lanthanum.

18 . The Al/Ce/Zr oxide composite according to claim 14 , further comprising at least one of platinum, rhodium or palladium.

19 . The method according to claim 4 , wherein the one or more alkaline earth elements/compounds, rare earth elements/compounds, zirconium or silicon are added after step (d) in the form of one or more soluble additional compounds.

20 . The method according to claim 5 , wherein the pH of (c1), (c2), or (c3) is adjusted to 8.5 to 10.

21 . The method according to claim 7 , wherein acetates, nitrates, or chlorides are used to prepare the metal salt solution.

22 . The method according to claim 10 , wherein the organic compounds have 4 to 8 carbon atoms and are in an amount of 5% to 15% by weight based on the dry weight of the boehmite.

23 . The method according to claim 11 , wherein the suspension comprising boehmite is adjusted to the pH by ammonia, urea, or urotropin.

24 . The Al/Ce/Zr oxide composite according to claim 15 , comprising:

40% to 70% by weight aluminum;

5% to 40% by weight zirconium;

5% to 40% by weight cerium; and

0.1% to 9% by weight rare earth metals.

25 . The Al/Ce/Zr oxide composite according to claim 16 , wherein the surface area after 4 h at 1200° C. is at least 40 m 2 /g.