THERMALLY STABLE DOPED AND UNDOPED POROUS ALUMINUM OXIDES AND NANOCOMPOSITE CeO2-ZrO2 AND Al2O3 CONTAINING MIXED OXIDES
The present invention relates to doped or undoped aluminas having after calcination at 1200° C. for 5-24 hours a pore volume ≧0.5 ml/g and a BET surface area greater then 35 m 2 /g. The invention also relates to a method for preparing these aluminas comprising the steps of: a. preparing an aqueous solution of an aluminum salt with optional co-dopants, b. treating the aqueous solution with hydrogen peroxide, c. precipitating the alumina using a base, and d. filtering, drying and calcining the alumina.
1 . A doped or undoped alumina having after calcination at 1200° C. for 5-24 hours a pore volume ≧0.5 ml/g and a BET surface area greater than 30 m 2 /g wherein the alumina is an alumina-containing nanocomposite material containing within its matrix agglomerated particles of more than one crystallographic phase.
2 . An alumina as claimed in claim 1 , wherein the BET surface area is greater than 50 m 2 /g.
3 . An alumina as claimed in claim 2 , wherein the BET surface area is greater than 60 m 2 /g.
4 . (canceled)
5 . An alumina as claimed in claim 1 , having an average particle size of between 2 and 400 nm.
6 . An alumina as claimed in claim 1 , having a ratio gs ρ , to gs 30% , <20 for relative densities 80<ρ<98%.
7 . An alumina as claimed in claim 1 , comprising a nanosized doped or undoped CeO 2 —ZrO 2 mixed oxide phase and a nanosized doped or undoped alumina phase, wherein more than 50% of the particles of the ceria-zirconia phase are smaller than 30 nm and more than 50% of the particles of the alumina phase are smaller than 15 nm after calcination at 1100° C. for 5 hours.
8 . An alumina as claimed in claim 1 , having after calcination at 1200° C. for 5 hours a BET surface area greater than 50 m 2 /g.
9 . An alumina as claimed in claim 8 , wherein the BET surface area is greater than 70 m 2 /g.
10 . An alumina as claimed in claim 1 , wherein the alumina is doped with at least one of barium, lanthanum or a rare earth element.
11 . An alumina as claimed in claim 1 , wherein no α-Al 2 O 3 can be detected by XRD technique after calcination of the material at 1200° C. for at least 5 hours.
12 . An alumina as claimed in claim 1 , having after calcination at 1100° C. for 5 hours a BET surface area greater than 75 m 2 /g.
13 . An alumina as claimed in claim 12 , wherein the BET surface area is greater than 100 m 2 /g.
14 . An alumina as claimed in claim 1 , composed of a nanosized doped or undoped CeO 2 —ZrO 2 mixed oxide phase and doped or undoped alumina phase, where OSC performance as measured by CO pulse technique is deactivated by less than 20% after a simulated ageing consisting of a redox cycle consisting of an TPR experiment, followed by an oxidation at 427° C. or 1000° C.
15 . A method of preparing thermally stable transitional alumina comprising the following steps:
a. preparing an aqueous solution of an aluminium salt,
b. treating the aqueous solution with hydrogen peroxide,
c. precipitating the alumina using a base, and
d. filtering, drying and calcining the alumina at a temperature and for a time sufficient to produce a doped or undoped alumina having after calcination at 1200° C. for 5-24 hours a pore volume ≧0.5 ml/g and a BET surface area greater than 30 m 2 /g wherein the alumina is an alumina-containing nanocomposite material containing within its matrix agglomerated particles of more than one crystallographic phase.
16 . A method as claimed in claim 15 , wherein the aluminum salt is aluminium nitrate.
17 . A method as claimed in claim 15 , wherein the base is ammonia, sodium hydroxide or potassium hydroxide.
18 . A method as claimed in claim 15 , wherein the precipitation is an inverse precipitation.
19 . A method as claimed in claim 15 , wherein the method includes the step of washing the alumina with alcohol and filtering it between steps c and d.
20 . A method as claimed in claim 19 , wherein the alcohol is iso-propanol.
21 . A method as claimed in claim 19 , wherein the method includes a hydrothermal treatment step between steps c and d, but after said alcohol washing step.
22 . A method as claimed in claim 21 , wherein the hydrothermal treatment is carried out for between 4 and 24 hours.
23 . A method as claimed in claim 21 , wherein the hydrothermal treatment step is carried out using water, iso-propanol or acetone.
24 . A method as claimed in claim 21 , wherein the alumina is washed with acetone following the hydrothermal treatment step.
25 . A method as claimed in claim 15 , wherein the alumina is dried at between 120° C. and 180° C.
26 . A method as claimed in claim 15 , wherein the alumina is calcined at between 500° C. and 700° C.
27 . A method as claimed in claim 15 , wherein the alumina is doped with CeO 2 .
28 . A method as claimed in claim 15 , wherein the alumina is doped with oxides of one or more of the rare earth metals, alkali metals, alkali earth metals, Zr or Si.
29 . A method as claimed in claim 15 wherein said aqueous solution includes co-dopants.
30 . A doped or undoped alumina prepared by a method as claimed in claim 15 having after said calcination at 1200° C. for 5-24 hours said pore volume ≧0.5 ml/g and said BET surface area greater than 30 m 2 /g wherein the alumina is said alumina-containing nanocomposite material containing within its matrix agglomerated particles of more than one crystallographic phase.