Organic-free synthesis of small pore zeolite catalysts

1. A method for improving the catalytic activity of a precursor 8-MR zeolite, the method comprising:

(a) treating the precursor 8-MR zeolite, prepared in the absence of any organic structure directing agent and having an Si/Al atom ratio of less than 5, with high temperature steam for a period of time sufficient to extract at least a portion of the aluminum oxide from the precursor zeolite framework to form a steam-treated zeolite of the same topology as the precursor zeolite, and

(b) optionally washing the steam-treated zeolite with acid to remove the extracted aluminum oxide;

wherein:

the steam has a temperature in a range of from 350° C. to 650° C.;

the precursor 8-MR zeolite contains aluminum that is practically all tetrahedral, as measured by 27 Al NMR;

the precursor 8-MR zeolite has a framework comprising 8-MR as the largest ring for entrance of molecules into the intracrystalline void space, and

the ratio of the silicon to tetrahedral aluminum atoms in the steam-treated zeolite is in a range of from 5 to 120.

2. The method of claim 1 , wherein the ratio of the silicon to tetrahedral aluminum atoms in the steam-treated zeolite is in a range of from 10 to 20.

3. The method of claim 1 , wherein the precursor 8-MR ring zeolite has a CHA, RHO, or KFI framework.

4. The method of claim 1 , wherein the high temperature of the steam is in a range of from 500° C. to 600° C.

5. The method of claim 1 , wherein Si/Al atom ratio of the precursor zeolite is in a range of from 2.5 to less than 5.

6. The method of claim 1 , further comprising exchanging any alkali or alkaline earth metals in the precursor 8-MR zeolite with an acidifying agent prior to exposing the precursor 8-MR zeolite to the high temperature steam.

7. The method of claim 1 , wherein at least a portion of the aluminum sites in the precursor 8-MR zeolite are acid in character.

8. The method of claim 1 , wherein the steam-treated zeolite contains tetrahedral, pentacoordinate and hexacoordinate aluminum, as characterized by 27 Al NMR.

9. The method of claim 1 , wherein the atomic ratio of tetrahedral aluminum to total aluminum content in the steam-treated zeolite is in a range of from about 0.12 to about 0.6.

10. The method of claim 1 , wherein the steam-treated zeolite has a micropore volume in a range of from 0.03 to 0.8 cc/gram of the steamed zeolite.

11. The method of claim 1 , wherein the steam-treated zeolite has Brønsted acid site density in a range of from 0.6 to 1.2 mmol/gram of the steamed zeolite, as determined by ammonia temperature-programmed desorption.

12. The method of claim 8 , further comprising washing the steam-treated zeolite with acid.

13. The method of claim 12 , wherein the acid wash removes at least a portion of pentacoordinate, hexacoordinate aluminum, or both pentacoordinate and hexacoordinate aluminum formed in the steam-treated zeolite.

14. The method of claim 1 , wherein the precursor 8-MR zeolite and the steam treated 8-MR zeolite have ABW, ANA, BIK, BRE, CAS, CHA, EAB, EDI, EPI, ERI, ESV, GIS, GOO, JBW, KFI, LEV, LTA, MER, MON, PAU, PHI, RHO, THO, TSC, UFI, or YUG topologies.

15. The method of claim 1 , wherein the high temperature steam contains water in a range of from about 20 vol % to about 70 vol % water.

16. The method of claim 1 , wherein the steam-treated 8-MR zeolite exhibits a 29 Si-MAS NMR spectrum containing no measurable Si(3A1) environment.

17. The method of claim 3 , wherein the high temperature of the steam is in a range of from 500° C. to 600° C.

18. The method of claim 3 , wherein the high temperature steam contains water in a range of from about 20 vol % to about 70 vol % water.

19. The method of claim 3 , further comprising exchanging any alkali or alkaline earth metals in the precursor 8-MR zeolite with an acidifying agent prior to exposing the precursor 8-MR zeolite to the high temperature steam.

20. The method of claim 3 , wherein the steam-treated zeolite contains tetrahedral, pentacoordinate, and hexacoordinate aluminum, as characterized by 27 Al NMR.

21. The method of claim 3 , wherein the atomic ratio of tetrahedral aluminum to total aluminum content in the steam-treated zeolite is in a range of from about 0.12 to about 0.6.

22. The method of claim 3 , wherein the ratio of the silicon to tetrahedral aluminum atoms in the steam-treated zeolite is in a range of from 10 to 20.

23. The method of claim 3 , wherein the steam-treated zeolite has a micropore volume in a range of from 0.03 to 0.8 cc/gram of the steamed zeolite.

24. The method of claim 3 , wherein the steam-treated zeolite has Brønsted acid site density in a range of from 0.6 to 1.2 mmol/gram of the steamed zeolite, as determined by ammonia temperature-programmed desorption.

25. The method of claim 1 , wherein the steam-treated 8-MR zeolite exhibits a 29 Si-MAS NMR spectrum containing no measurable signals attributable to Si(3Al) sites.

26. The method of claim 3 , further comprising washing the steam-treated zeolite with acid.

27. The method of claim 12 , wherein the acid comprises HCl, H 2 SO 4 , H 3 PO 4 , or oxalic acid.

28. The method of claim 25 , wherein the acid comprises HCl, H 2 SO 4 , H 3 PO 4 , or oxalic acid.

29. The method of claim 1 , wherein:

the precursor 8-MR zeolite and the steam-treated zeolite both have a CHA topology;

the precursor 8-MR zeolite is prepared by a gel process in the absence of an organic structure directing agent to form an alkali metal-containing product that is subsequently ion-exchanged with an ammonium salt to form the precursor 8-MR zeolite;

the steam temperature is in a range of from 500° C. to 600° C., the steam containing 46 vol % to 70 vol % water; and wherein

the ratio of the silicon to tetrahedral aluminum atoms in the steam-treated zeolite is in a range of from 10 to 20.