Compositions and methods for improving the hydrothermal stability of mesostructured zeolites by rare earth ion exchange
View Patent ↗Compositions and methods for preparing mesostructured zeolites having improved hydrothermal stability. Such mesostructured zeolites can be prepared by subjecting a zeolite to rare earth ion exchange prior to and/or subsequent to introducing mesoporosity into the zeolite.
1. A method of forming a material comprising at least one mesostructured zeolite one-phase hybrid single crystal having long-range crystallinity and enhanced hydrothermal stability and microporosity retention after regeneration, comprising the steps of:
(a) providing a fully-crystalline non-mesoporous zeolite having long-range crystallinity wherein said non-mesoporous zeolite comprises a faujasite;
(b) adding rare earth elements to said non-mesoporous zeolite;
(c) acid washing said non-mesoporous zeolite to thereby form an acid-washed zeolite, wherein said acid washing modifies the silicon to aluminum ratio in said non-mesoporous zeolite; and
(d) forming a plurality of mesopores within said acid-washed zeolite to thereby form said mesostructured zeolite, wherein said forming occurs in the presence of at least one surfactant.
2. The method of claim 1 , further comprising subjecting at least a portion of said mesostructured zeolite to hydrothermal regeneration, wherein a microporosity of said mesostructured zeolite after said hydrothermal regeneration is at least about 85% of a microporosity of said mesostructured zeolite before said hydrothermal regeneration.
3. The method of claim 1 , further comprising subjecting at least a portion of said mesostructured zeolite to hydrothermal regeneration, wherein said mesostructured zeolite has substantially more microporosity after said hydrothermal regeneration than does a second fully-crystalline mesoporous zeolite of substantially the same structure and initial composition as said mesostructured zeolite, which is formed by steps (a), (c), and (d), without adding rare earth elements to the zeolite.
4. The method of claim 1 , wherein said non-mesoporous zeolite comprises said rare-earth elements following step (b) in a total concentration of 0.01-15 weight percent on the basis of RE 2 O 3 present in said zeolite.
5. The method of claim 1 , wherein said non-mesoporous zeolite consists essentially of a type Y zeolite.
6. The method of claim 1 , further comprising:
(e) stabilizing said non-mesoporous zeolite or said mesostructured zeolite by hydrothermal calcination.
7. The method of claim 6 , wherein step (e) is performed before step (c).
8. The method of claim 6 , wherein step (b) is performed after step (e).
9. The method of claim 6 , wherein step (e) results in said mesostructured zeolite having a unit cell size of about 24.50 to 24.60 Angstroms.
10. The method of claim 1 , further comprising subjecting at least a portion of said mesostructured zeolite to hydrothermal regeneration, wherein the microporosity of said mesostructured zeolite after said hydrothermal regeneration is enhanced compared to a third fully-crystalline mesoporous zeolite of substantially the same structure and initial composition as said mesostructured zeolite that is formed by steps (a) through (d), but wherein step (b) is performed after step (d).
11. The method of claim 1 , further comprising subjecting at least a portion of said mesostructured zeolite to hydrothermal regeneration, wherein the microporosity of said mesostructured zeolite after said hydrothermal regeneration is enhanced compared to a another fully crystalline mesoporous zeolite of substantially the same structure and initial composition as said mesostructured zeolite that is formed by steps (a) through (d), but wherein step (c) is not performed directly after step (b).
12. The method of claim 1 , wherein said rare earth elements are added to said non-mesoporous zeolite by ion exchange.
13. The method of claim 1 , wherein said surfactant comprises cetyltrimethylammonium bromide (“CTAB”).