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US-20260125272-A1 - ZEOLITIC MATERIALS AND METHODS OF MAKING AND USING THEREOF

US20260125272A1US 20260125272 A1US20260125272 A1US 20260125272A1US-20260125272-A1

Abstract

Described herein are methods for preparing a zeolitic material including a microporous crystalline framework isomorphously substituted with one or more paired Lewis acid sites.

Inventors

  • Leah FORD
  • Alexander Spanos
  • Ambarish KULKARNI
  • Nicholas Brunelli

Assignees

  • OHIO STATE INNOVATION FOUNDATION

Dates

Publication Date
20260507
Application Date
20231009

Claims (20)

  1. 1 . A method for preparing a zeolitic material comprising a microporous crystalline framework isomorphously substituted with one or more paired Lewis acid sites, wherein each of the one or more paired Lewis acid sites comprises a first Lewis acid metal center and a second Lewis acid metal center, and wherein the first Lewis acid metal center and the second Lewis acid metal center are separated by three or fewer atoms within the crystalline framework; the method comprising: (i) combining, in aqueous solution, a silicon source, a Lewis acid metal precursor, and optionally a structure-directing agent to form a precursor gel; (ii) reacting the precursor gel under conditions effective to form a protected zeolitic material; (iii) treating the protected zeolitic material to form the zeolitic material comprising the microporous crystalline framework isomorphously substituted with one or more paired Lewis acid-open defect sites, each comprising a first Lewis acid metal center and an open defect site; and (iv) post-synthetically incorporating a metal at the open defect sites to form one or more paired Lewis acid sites comprises a first Lewis acid metal center and a second Lewis acid metal center.
  2. 2 . The method of claim 1 , wherein step (i) comprises combining, in aqueous solution, the silicon source, the Lewis acid metal precursor, and the structure-directing agent to form a precursor gel.
  3. 3 . The method of claim 1 , wherein step (ii) comprises incubating the precursor gel to hydrolyze the silicon source.
  4. 4 . The method of claim 1 , wherein step (ii) comprises heating the precursor gel in the presence of zeolite seed crystals, a fluoride source, or a combination thereof to form the protected zeolitic material.
  5. 5 . The method of claim 1 , wherein step (iii) comprises calcining the protected zeolitic material to form the zeolitic material comprising the microporous crystalline framework isomorphously substituted with one or more paired Lewis acid-open defect sites.
  6. 6 . The method of claim 5 , wherein calcining is performed immediately after step (ii).
  7. 7 . The method of claim 5 , wherein calcining is performed from 5 minutes after step (ii) to 10 days after step (ii).
  8. 8 . The method of claim 5 , wherein calcining is performed at least 7 days after step (ii).
  9. 9 . The method of claim 1 , wherein step (iii) comprises heating the protected zeolitic material in air at a temperature of from 400° C. to 750° C.
  10. 10 . The method of claim 1 , wherein step (iii) comprises extracting the protected zeolitic material to form the zeolitic material comprising the microporous crystalline framework isomorphously substituted with one or more paired Lewis acid-open defect sites.
  11. 11 . The method of claim 1 , wherein the Lewis acid metal precursor is defined by Formula II: wherein R is alkyl, cycloalkyl, aryl, or any combination thereof, M is a transition metal, post transition metal, or any combination thereof, Z is a halogen, acetate, sulfate, nitrate phosphate, carbonate, or bicarbonate, x is an integer from 1-3, and y is an integer from 1-3, wherein the total charge of the compound of Formula II is a neutral charge.
  12. 12 . The method of claim 11 , wherein M comprises a post-transition metal.
  13. 13 . The method of claim 11 , wherein M is chosen from Sn, Hf, Zn, Zr, Ti, V, Ta, Ga, Ge, Nb, and Cr.
  14. 14 . (canceled)
  15. 15 . The method of claim 11 , wherein R comprises C 1 -C 10 alkyl, C 3 -C 10 cycloalkyl, C 3 -C 10 aryl, or any combination thereof.
  16. 16 . (canceled)
  17. 17 . (canceled)
  18. 18 . The method of claim 11 , wherein Z comprises a halogen.
  19. 19 . (canceled)
  20. 20 . The method of claim 11 , wherein x is 1.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Application 63/414,445, filed on Oct. 7, 2022, the contents of which is hereby incorporated in its entirety. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government Support under Grant No. 1653587 awarded by the National Science Foundation. The Government has certain rights in the invention. BACKGROUND Zeolites are widely used as solid acid catalysts for conversion of biomass and petroleum-based feedstocks to chemicals and fuels. While the predominant use of zeolites remains for Brønsted acid catalyzed reactions, the catalytic capabilities of zeolites have greatly expanded with the introduction of Lewis acidic zeolites, such as TS-1, CIT-6, Sn-BEA, and other Lewis acidic zeolites. These powerful Lewis acidic zeolites can catalyze a whole new landscape of intriguing chemical reactions such as Meerwein-Poondorf-Verley reductions (MPV), aldol condensations, and the isomerization of glucose to fructose. Existing Lewis acidic zeolites include isolated metal centers, such as Ti, Zn, Hf, Zr, and Sn. Intriguingly, enzymes that catalyze similar reactions often include pairs of metal centers as opposed to isolated metal centers. In these enzymes, the catalytic pairs of metal centers are thought to increase both selectivity and activity. However, paired metal centers are challenging to achieve in heterogeneous catalytic materials. Translating these beneficial features of enzymes to heterogeneous catalytic materials has been a longstanding challenge for the field of catalysis. Creating catalysts that include paired sites has been a challenge because heterogeneous catalytic materials typically possess catalytic sites that are non-uniform and/or randomly distributed. Yet, enzymes and homogeneous catalysis clearly demonstrate a benefit to creating catalytic material with paired sites. Numerous examples from homogeneous catalyst demonstrate that catalytic pairs can influence activity and selectivity. The key challenge remains how to achieve these catalytic pairs in heterogeneous catalytic materials such as zeolites. Zeolites are attractive targets since they are crystalline, can be shape selective, and can be made hydrophobic to enable Lewis acid chemistry in water. However, zeolites are highly challenging because these materials are synthesized using crystallization procedures that are only beginning to be understood beyond a phenomenological level. There is a need for controlling the nature of the catalytic site and the environment around the catalytic active site to create highly active and selective catalytic materials. The compositions and methods disclosed herein address these and other needs. SUMMARY This application generally related to methods for creating catalytic materials (e.g., zeolitic materials) containing one or more paired Lewis acid sites. These methods can be used to create well-defined Lewis Acid site pairs in a zeolite framework. The overall strategy can involve using an organometallic agent (e.g., an alkyl tin compound, an aryl tin compound, an alkylaryl tin compound, an alkyl Ge compound, an aryl Ce compound, an alkylaryl Ge compound, etc.) to create an open-defect Lewis acid (ODLA) site. The defect is a location that is the target for post-synthetic insertion of a second heteroatom. In some examples, the first Lewis acid could be either alkyl-Sn or alkyl-Ge. In some embodiments, the second Lewis acid could either be: Sn, Zr, Hf, Ti, Nb. Many different pairs could be of interest, but some specific examples of interest would be: (1) Ti—Ge; (2) Sn—Sn; (3) Zr—Sn; (4) Ti—Sn. Titanium paired with different Lewis acids have been demonstrated to have increased catalytic activity for the epoxidation of olefins. Sn—Sn and Sn—Zr pairs have the potential for cooperative activation of substrates for the aldol reaction. Each of the one or more paired Lewis acid sites within the zeolitic material can comprise a first Lewis acid metal center and a second Lewis acid metal center. The first Lewis acid metal center and the second Lewis acid metal center can be separated by three or fewer atoms within the crystalline framework. For example, the first Lewis acid metal center and the second Lewis acid metal center can be separated by three atoms within the crystalline framework, or separated by one atom within the crystalline framework. The first Lewis acid metal center and the second Lewis acid metal center can be separated by less than 10 Angstroms (e.g., less than 5 Angstroms, or less than 4 Angstroms), measured metal center to metal center. In certain embodiments, the first Lewis acid metal center and the second Lewis acid metal center are separated by from 2 to 4 Angstroms. In one embodiment, the first Lewis acid metal center and the second Lewis acid metal center are separated by from 2.5 to 3 Angstroms. In some embodiments, each of the one or more paired Lewis acid sites i