Supermicroporous metal oxides
A new class of supermicroporous mixed oxides, with pore sizes in the 10-20 Å range has been prepared utilizing basic metal acetates. The reactions are carried out in non-aqueous solvent media to which an excess of amine is added. Hydrolysis of the reagents is effected by addition of a water-propanol mixture and refluxing. The amine and solvent are removed by thorough washing and/or calcining at temperatures as low as 200° C. Mixtures of transition metal oxides with either ZrO 2 , TiO 2 , La 2 O 3 , SiO 2 , Al 2 O 3 or mixtures thereof were prepared. The surface area curves of the pure oxides are Type I with surface areas of 400-600 m 2 /g and up to 1100 m 2 /g for the mixed oxides.
1. A method for preparing supermicroporous metal oxides comprising:
combining at least one metal salt in the presence of a carboxyl anion to form a mixture;
adding to the mixture an amine to form either a homogeneous solution or a thixotropic gel;
hydrolyzing the mixture by utilizing water present in the reagents and/or adding water/water diluted with solvent to the mixture;
stirring and/or refluxing the mixture; and
collecting and drying the solid from the mixture to form a supermicroporous metal oxide.
2. The method of claim 1 where the resulting supermicroporous metal oxide has pores within the range of about 8 to about 25 Å.
3. The method of claim 1 where the resulting supermicroporous metal oxide has pores within the range of about 10 to about 20 Å.
4. The method of claim 1 where the metal salt is selected from the group consisting of titanium acetate, vanadium acetate, vanadium phosphate, vanadium sulfate, chromium acetate, chromium nitrate, nickel acetate, nickel nitrate, manganese acetate, iron acetate, copper acetate, cobalt acetate, cobalt nitrate, cobalt chloride, zinc acetate, zirconium acetate, niobium acetate, molybdenum acetate, lanthanum acetate, aluminum acetate, tetraethyl orthosilicate, zirconium propoxide, zirconium isopropoxide, zirconium oxochloride, titanium isopropoxide, aluminum nitrate, aluminum tri-sec-butoxide, aluminum chloride, and mixtures thereof.
5. The method of claim 1 where the solvent is selected from the group consisting of acetone, methanol, ethanol, propanol, isopropanol, butanol, hexanol, pentanol, heptanol and mixtures thereof.
6. The method of claim 1 where the amine is selected from the group consisting of amines having from 1 to 18 carbon atoms.
7. The method of claim 1 where the amine is selected from the group consisting of methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, trimethylammonium compounds, tetrabutylammonium compounds, dipropylamine, diethylamine, tripropylamine, and mixtures thereof.
8. The method of claim 1 where the drying is conducted in the range of about 45 to about 200° C.
9. The method of claim 1 further comprising treating the mixture hydrothermally in addition to stirring or refluxing.
10. The method of claim 1 further comprising aging the thixotropic gel for periods of time between about 10 min and about 96 hours prior to reflux.
11. The method of claim 1 where the ratio of solvent to amine ranges from about 0.1:8.0 to about 200:1.
12. The method of claim 1 further comprising adding a phosphate or sulfate to the mixture to improve the stability of the supermicroporous metal oxide and/or to alter its ion-exchange and/or catalytic properties.
13. The method of claim 1 further comprising calcining the metal oxide at a temperature in the range of from about 190 to about 950° C.
14. A method for tailoring the pore size distribution of supermicroporous metal oxides prepared by the method comprising:
combining at least one metal salt in the presence of an acetate to form a mixture;
adding to the mixture an amine to form either a homogeneous solution or a thixotropic gel;
hydrolyzing the mixture by utilizing water present in a reagent and/or adding water diluted with solvent to the mixture;
stirring and/or refluxing the mixture;
treating the mixture hydrothermally; and
collecting and drying the solid from the mixture to form a supermicroporous metal oxide;
where tailoring the pore size distribution is accomplished by a method selected from the group consisting of:
the choice of the solvent;
the amount of solvent;
the choice of the amine;
the amount of amine;
the amount of water;
a time of reaction;
the time of refluxing;
the time of hydrothermal treatment;
the calcination temperature; and
the time of calcinations.
15. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via choice of the solvent.
16. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via choice of the amount of solvent used.
17. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via choice of the amine.
18. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected by the change of the concentration of amine.
19. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via altering the amount of water added.
20. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via time of reaction.
21. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via time of refluxing.
22. The method of claim 14 where tailoring the pore size distribution in the supermicroporous metal oxides is effected via time of hydrothermal treatment.
23. The method of claim 14 where the solid is washed prior to collecting and drying it to form the supermicroporous metal oxide, and tailoring the pore size distribution is effected via choice of the washing agent or absence thereof.
24. The method of claim 14 further comprising providing for presence of mesopores in the supermicroporous material to enhance its catalytic properties due to improved diffusion as compared with an otherwise identical catalyst absent mesopores.