Mixed template synthesis of low silica CHA zeolite
A transition-metal-CHA molecular sieve catalyst and mixed-template synthesis procedure are disclosed.
1. A composition comprising a synthetic zeolite having a CHA framework structure, a molar silica-to-alumina ratio (SAR) of about 10 to about 30, a unit cell volume of about 2355 to about 2375 Å3, and an in-situ transition metal, wherein the zeolite substance is essentially alkali-metal-free, and wherein the zeolite has a phase purity of at least 95% by weight.
2. The composition of claim 1 , wherein transition metal is selected from copper and iron.
3. The composition of claim 1 , wherein zeolite contains about 0.1 to about 5 weight percent copper.
4. The composition of claim 1 , wherein zeolite contains uniformly distributed ionic copper.
5. The composition of claim 1 , wherein the zeolite contains less than 5 weight percent CuO based on the total weight of the zeolite.
6. A composition of claim 1 , wherein the zeolite contains about 0.1 to about 5 weight percent of non-framework copper based on the total weight of the zeolite, and contains less than 5 weight percent CuO based on the total weight of the zeolite.
7. The catalyst composition of claim 6 , wherein the zeolite is free of post-synthesis exchanged copper.
8. A method for synthesizing a zeolite comprising: preparing a reaction mixture comprising (a) at least one source of alumina, (b) at least one source of silica, (c) a transition-metal-amine organic templating agent, and (d) distinct second organic templating agent, wherein each of the first and second templating agents is suitable for forming a CHA framework structure and wherein the reaction mixture is essentially free of alkali metal; heating the reaction mixture at crystallization conditions for a sufficient time to form zeolite crystals having a CHA framework and containing the transition metal, wherein the CHA framework structure has a composition comprising a molar silica-to-alumina ratio (SAR) of about 10 to about 30, a unit cell volume of about 2355 to about 2375 Å3, and an in-situ transition metal, wherein the zeolite substance is essentially alkali-metal-free, and wherein the zeolite has a phase purity of at least 95% by weight.
9. The method of claim 8 , wherein a majority of the transition metal is ionic metal dispersed in the crystallized zeolite.
10. The method of claim 8 , wherein the transition-metal-amine organic templating agent is formed in-situ in the reaction mixture from individual metal and amine components.
11. The method of claim 8 , wherein the transition-metal-amine organic templating agent is Cu-TEPA.
12. The method of claim 8 , wherein the second organic templating agent is TMAda.
13. The method of claim 8 , wherein the zeolite has an SAR of about 15 to about 24.
14. The method of claim 8 , wherein the zeolite contains about 0.1 to about 5 weight percent ionic copper.
15. The method of claim 8 , wherein the zeolite is washed, dried, and calcined to form a Cu-CHA catalyst.
16. The method of claim 15 , wherein the Cu-CHA catalyst has a phase purity of at least about 95% by weight.