Introduction of mesoporosity in low Si/Al zeolites
View Patent ↗Compositions and methods for preparing mesoporous materials from low Si/Al ratio zeolites. Such compositions can be prepared by acid wash and/or isomorphic substitution pretreatment of low Si/Al ratio zeolites prior to introduction of mesoporosity.
1. A method of forming a material comprising at least one mesoporous zeolite, said method comprising the steps of:
(a) acid washing a non-mesoporous initial zeolite with an acidic medium thereby forming an acid-washed zeolite, wherein said initial zeolite has a total silicon-to-aluminum (Si/Al) ratio of less than 30, wherein said acid washing of step (a) removes aluminum atoms from said initial zeolite such that said acid-washed zeolite has a higher Si/Al ratio than said initial zeolite;
(b) recovering said acid-washed zeolite from said acidic medium thereby forming a recovered zeolite; and
(c) contacting said recovered zeolite with a mesopore-forming medium thereby forming at least one mesopore within said recovered zeolite and providing said mesoporous zeolite.
2. The method of claim 1 , wherein said recovering of step (b) involves washing, filtering, drying, or a combination thereof.
3. The method of claim 1 , wherein said initial zeolite has a Si/Al of less than 10.
4. The method of claim 1 , wherein said acidic medium does not comprise hydrofluoric acid.
5. The method of claim 1 , wherein said acidic medium comprises at least one acid selected from the group consisting of chlorhidric acid, sulphuric acid, nitric acid, acetic acid, sulfonic acid, oxalic acid, ethylenediaminetetraacetic acid (EDTA), citric acid, and combinations thereof.
6. The method of claim 1 , wherein said initial zeolite has a total 20 to 80 Å diameter mesopore volume of less than 0.05 cc/g, wherein said mesoporous zeolite has a total 20 to 80 Å diameter mesopore volume of at least 0.1 cc/g.
7. The method of claim 1 , wherein said initial zeolite has an average unit cell size of at least 24.40 Å and said acid-washed zeolite has an average unit cell size of at least 24.35 Å.
8. The method of claim 1 , wherein said mesoporous zeolite is a mesostructured zeolite, a one-phase hybrid single crystal having long-range crystallinity.
9. The method of claim 1 , wherein said acid washing is performed at a temperature of not more than 100° C., wherein said acid washing is performed for a time period of not more than 12 hours.
10. The method of claim 1 , wherein said acidic medium comprises an acid that is present in an amount in the range of from about 1 to about 10 milliequivalents per gram of initial zeolite.
11. The method of claim 1 , wherein said acidic medium comprises a chelating agent selected from the group consisting of oxalic acid, citric acid, and ethylenediaminetetraacetic acid (EDTA).
12. The method of claim 1 , wherein said acidic medium is in liquid form during said acid-washing.
13. The method of claim 1 , wherein said mesopore-forming medium comprises a base.
14. The method of claim 13 , wherein said mesopore-forming medium comprises at least one surfactant.
15. The method of claim 13 , wherein said base comprises ammonium hydroxide.
16. The method of claim 14 , wherein said surfactant comprises cetyltrimethyl ammonium halide.
17. The method of claim 1 , wherein said initial zeolite has an extra-framework aluminum content of 25% to 100%.
18. The method of claim 1 , further comprising recovering said mesoporous zeolite from said mesopore-forming medium, wherein said recovering involves washing, filtering, drying, or a combination thereof.
19. The method of claim 1 , wherein said initial zeolite comprises a faujasite.
20. The method of claim 1 , further comprising blending said mesoporous zeolite with a binder, a matrix, and/or an additive to thereby form a blended material, further comprising shaping said blended material into a catalyst composition.