Molecular sieve precursors and synthesis of molecular sieves
Molecular sieves, improved methods for their synthesis, and catalysts, systems and methods of using these molecular sieves as catalysts in a variety of processes such as abating pollutants in exhaust gases and conversion processes are described. The molecular sieves are made using a tailored colloid including an alumina source, a silica source and a structure directing agent.
1. A zeolite precursor comprising a solution comprising colloidal particles, wherein:
each particle comprises alumina, silica, and a first structure directing agent; and
the amounts of the alumina, silica, and the first structure directing agent are present in amount sufficient to form a zeolite having 8-ring pore openings and double-six ring secondary building units.
2. The zeolite precursor of claim 1 , wherein a ratio of the structure directing agent to the silica is less than about 0.07.
3. The zeolite precursor of claim 1 , wherein the first structure directing agent comprises an adamantyl-substituted compound.
4. The zeolite precursor of claim 1 , wherein the first structure directing agent comprises an adamantylammonium compound.
5. The zeolite precursor of claim 4 , wherein the first structure directing agent comprises trimethyl adamantylammonium cation.
6. The zeolite precursor of claim 1 , wherein the colloidal solution is stable at room temperature for at least 30 days.
7. The zeolite precursor of claim 1 , wherein the colloidal solution has a pH of less than 12.
8. The zeolite precursor of claim 7 , wherein the colloidal solution has a pH of less than 11.
9. The zeolite precursor of claim 1 , wherein the colloidal particles have a SiO 2 to Al 2 O 3 molar ratio from 10 to 1000.
10. The zeolite precursor of claim 1 , wherein the colloidal particles have a SiO 2 to Al 2 O 3 molar ratio from 20 to 40.
11. The zeolite precursor of claim 1 , wherein the solution contains an additional metal selected from iron, copper, cerium, cobalt, platinum and combinations thereof.
12. The zeolite precursor of claim 3 further comprising a second structure directing agent.
13. The zeolite precursor of claim 12 , wherein the second structure directing agent comprises a benzyl-substituted compound.
14. The zeolite precursor of claim 1 , wherein the zeolite has a structure type that is AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, or SAV.
15. The zeolite precursor of claim 13 , wherein the zeolite has the CHA structure type.
16. The zeolite precursor of claim 1 , wherein the colloidal particles have an average particle size of less than about 100 nm.
17. The zeolite precursor of claim 16 , wherein the colloidal particles have an average particle size from about 10 nm to about 50 nm.
18. The zeolite precursor of claim 1 having an aluminum-27 nuclear magnetic resonance (NMR) peak in the frequency shift range of 77-50 ppm with full width at half maximum of 100 to 2000 Hz.
19. A zeolite made from the precursor of claim 1 .
20. The zeolite of claim 19 , having primary crystals less than 100 nm in diameter.
21. The zeolite precursor of claim 1 , wherein the alumina is derived from aluminum chlorohydrate, to form the colloid particle.
22. A method of making a zeolite having 8-ring pore openings and double-six ring secondary building units, the method comprising
providing a solution of colloidal particles comprising alumina, silica, and a first structure directing agent, wherein the solution has a first pH; and
performing a crystallization process comprising adjusting the pH of the solution and hydrothermally treating the solution to form a zeolite.
23. The method of claim 22 , wherein the solution is formed in a first reaction vessel, and the crystallization process is performed up to 6 months after forming the solution.
24. The method of claim 23 , wherein the crystallization process is performed in a second reaction vessel.
25. The method of claim 22 , wherein prior to the crystallization process, the solution has a pH of less than about 12, and hydrothermally treating the solution comprises heating the solution to a temperature exceeding 100° C.
26. The method of claim 25 , wherein the solution has a pH of less than 11.
27. The method of claim 22 , wherein the zeolite has a structure type that is AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, or SAV.
28. The method of claim 27 , wherein the zeolite has the CHA structure type.
29. The method of claim 22 , wherein the structure directing agent and the silica are present in a ratio of less than about 0.07 structure directing agent to silica.