Production of hydrothermally stable CHA zeolites
A method of producing hydrothermally stable chabazite (CHA) zeolites is disclosed. The disclosed method is based on the use of reaction mixtures that (1) are essentially void of alkali metal cations and (2) contain the N,N,N-trimethyl-1-adamantyl ammonium (TMAda+) organic as the sole OSDA. The disclosed method results in a higher crystalline CHA zeolite that exhibits hydrothermal stability. There is also disclosed a zeolite material having a CHA-type framework structure made by the disclosed method. A method of selective catalytic reduction of NOx in exhaust gas using the material described herein is also disclosed.
1. A method of making a microporous crystalline material, the method comprising:
mixing reaction mixtures comprising sources of alumina, silica, water, TMAdaOH and optionally a chabazite seed material to form a gel, wherein the reaction mixtures are essentially void of alkali metal cations, wherein the source of TMAdaOH comprises N,N,N-trimethyl-1-adamantyl ammonium (TMAda+) organic as the sole OSDA;
heating the gel in a vessel at a temperature ranging from 80° C. to 200° C. to form a crystalline chabazite product; and
calcining the product to produce an aluminosilicate zeolite having a CHA structure, and a silica-to-alumina ratio (SAR) ranging from 20 to 100.
2. The method of claim 1 , wherein the reaction mixtures with (A) molar composition 1 SiO 2 :w Al 2 O 3 :x TMAdaOH:y H 2 O, where w=0.010-0.050, x=0.04-0.20, y=1-25 and (B) trace concentrations of alkali cations.
3. The method of claim 2 , wherein w ranges from 0.014-0.050.
4. The method of claim 2 , wherein x ranges from 0.05-0.15.
5. The method of claim 2 , wherein y ranges from 5-20.
6. The method of claim 1 , wherein the aluminosilicate zeolite has a silica-to-alumina ratio (SAR) ranging from 20-70.
7. The method of claim 1 , further comprising adding to the microporous crystalline material at least one metal chosen from copper, iron or combinations thereof to form a metal containing chabazite.
8. The method of claim 7 , wherein the metal containing chabazite retains at least 70% of its initial surface area and micropore volume after exposure to temperatures of up to 900° C. in the presence of up to 10 volume percent water vapor for up to 1 hour.
9. The method of claim 7 , wherein copper and/or iron are introduced by liquid-phase or solid ion-exchange or impregnation or incorporated by direct-synthesis.
10. The method of claim 9 , wherein copper comprises at least 1.0 weight percent of the total weight of the material.
11. The method of claim 10 , wherein copper comprises an amount ranging from 1.0 to 6.0 weight percent of the total weight of the material.
12. The method of claim 7 , wherein iron comprises at least 0.5 weight percent of the total weight of said material.
13. The method of claim 12 , wherein iron comprises an amount ranging from 0.5 to 6.0 weight percent of the total weight of said material.
14. The method of claim 1 , wherein the source of alumina is aluminum trihydroxide.
15. The method of claim 14 , wherein the aluminum trihydroxide is dissolved into a TMAdaOH solution.
16. The method of claim 1 , wherein the source of silica is a silica sol.
17. The method of claim 1 , wherein during heating, the gel is stirred while a seed material with a CHA topology is added before loading into an autoclave.
18. The method of claim 1 , wherein after calcining the calcined zeolite was ion-exchanged with copper in a copper (II) acetate solution.
19. The method of claim 18 , wherein the initial surface area of the copper containing chabazite is at least 650 m 2 /g.
20. The method of claim 18 , wherein the initial micropore volume of the copper containing chabazite is at least 0.25 cc/g.