期刊
JOURNAL OF CATALYSIS
卷 341, 期 -, 页码 62-71出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2016.06.013
关键词
Tin silsesquioxanes; Glucose conversion; Epimerization; Isomerization; Lewis acid
资金
- Catalysis Center for Energy Innovation, an Energy Frontier Research Center - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [DE-SC0001004]
- National Science Foundation [DGE-1144469, 0750966]
- George W. Laird Merit Fellowship
- Direct For Education and Human Resources
- Division Of Graduate Education [0750966] Funding Source: National Science Foundation
Tin-containing zeolite Beta (Sn-Beta) has been investigated as a catalyst for isomerizing aldohexoses into ketohexoses through a Lewis acid mediated hydride shift. Recent studies on the reactivities of Lewis base doped and alkali-exchanged Sn-Beta samples have conclusively demonstrated that the open tin site performs the glucose isomerization reaction. With Lewis base doped Sn-Beta, glucose conversion is almost completely eliminated and product selectivity is shifted predominantly to mannose. These data suggest that glucose reactions may occur through pathways that do not involve the open site in Sn-Beta; albeit at significantly lower rates. To examine this possibility, reactions of glucose catalyzed by a homogeneous model of Sn-Beta that does not contain open sites, methyl-ligated tin silsesquioxane la, is experimentally and theoretically examined. la is an active glucose conversion catalyst selectively producing mannose, although the rates of reaction are far below those obtained from Sn-Beta. A hybrid quantum mechanical/molecular mechanics model is constructed, and the complete catalytic cycle is computationally examined, considering ring-opening, three distinct pathways for each hydride- and carbon-shift reaction, and ring-closing. The combined experimental and computational results suggest that there could be reaction pathways that involve Si-O-Sn cleavage that give much slower reaction rates than the open tin site in Sn-Beta. (C) 2016 Elsevier Inc. All rights reserved.
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