Rapid synthesis of beta zeolites
The invention provides methods for rapidly synthesizing heteroatom containing zeolites including Sn-Beta, Si-Beta, Ti-Beta, Zr-Beta and Fe-Beta. The methods for synthesizing heteroatom zeolites include using well-crystalline zeolite crystals as seeds and using a fluoride-free, caustic medium in a seeded dry-gel conversion method. The Beta zeolite catalysts made by the methods of the invention catalyze both isomerization and dehydration reactions.
1. A method of synthesizing molecular sieves, said method comprising the steps of:
a) preparing a seed solution comprising aluminosilicate zeolite beta nanocrystals,
b1) dealuminating said nanocrystals,
b2) preparing a suspension of the dealuminated nanocrystals without drying,
c) preparing a solution comprising a structure directing agent and a heteroatom source,
d) adding the suspension of dealuminated nanocrystals to the solution of step c),
e) allowing a gel to form,
f) heating said gel at a temperature and a time sufficient to form a solid,
g) filtering, washing and drying said solid, and
h) calcining said solid.
2. The method of claim 1 , wherein said gel is heated to at least 175° C. for 12 hours or less.
3. The method of claim 1 , wherein said gel is heated to 200° C. for 6 hours.
4. The method of claim 1 , wherein said aluminosilicate zeolite beta nanocrystals are well-crystalline 200 nm crystals comprising a crystallinity equal to or greater than 80% crystalline.
5. The method of claim 1 , wherein said seed solution is a stable suspension comprising well dispersed beta zeolite seeds.
6. The method of claim 1 , wherein said dealuminating step comprises directly treating said seed solution with a concentrated nitric acid solution.
7. The method of claim 1 , further comprising collecting, washing and dispersing said dealuminated nanocrystals in liquid prior to step d).
8. The method of claim 1 , wherein said structure directing agent comprises a compound selected from the group consisting of tetraethylammonium hydroxide solution (TEAOH), tetrabutylammonium hydroxide, tetramethylammonium hydroxide, 4,4′trimethylene bis(N-methyl N-benzyl-piperidinium) hydroxide, 1,2-diazabicyclo 2,2,2, octane, and dialkylbenzyl ammonium hydroxide.
9. The method of claim 1 , wherein said heteroatom source comprises a compound selected from the group consisting of tin butoxide, SnCl 4 , SnCl 2 , SnO 2 , tin(II)acetate, tin ethoxide, tin propoxide, metallic tin, amorphous silica, tetraalkylorthosilicate, colloidal silica, fumed silica, silica gels, titanium tetrachloride, titanium ethoxide, titanium isopropoxide, titanium butoxide, zirconium oxychloride, zirconium propoxide, zirconium butoxide, zirconium ethoxide, iron chloride and iron nitrate.
10. The method of claim 1 , wherein said solution of step c) further comprises tetraethylorthosilicate (TEOS) and hydrofluoric acid (HF).
11. The method of claim 1 , wherein said formed gel has a composition comprising SiO 2 :0.5TEAOH:0.5HF:7H 2 O.
12. The method of claim 1 , wherein said formed gel has a composition comprising SiO 2 :0.54TEAOH:0.54HF:0.008SnO 2 :7.5H 2 O.
13. The method of claim 1 , wherein said solid obtained in step h) is a zeolite selected from the group consisting of Sn-Beta, Si-Beta, Ti-Beta, Zr-Beta and Fe-Beta.
14. The method of claim 1 , wherein said solution of step c) further comprises tetraethylorthosilicate (TEOS) and ammonium fluoride (NH 4 F).
15. The method of claim 1 , wherein said formed gel has a composition comprising SiO 2 :0.54TEAOH:0.54NH 4 F:0.008SnO 2 :7.5H 2 O.
16. The method of claim 1 , wherein said solution of step c) further comprises a caustic medium having a pH in the range of about 9 to about 13.
17. The method of claim 16 , wherein said caustic medium is selected from the group consisting of sodium hydroxide (NaOH) and potassium hydroxide (KOH).
18. The method of claim 1 , wherein said formed gel has a composition comprising SiO 2 :0.008SnO 2 :0.22TEA 2 O:0.034 Na 2 O.