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Active Sites in Sn-Beta for Glucose Isomerization to Fructose and Epimerization to Mannose

Bermejo-Deval, Ricardo and Orazov, Marat and Gounder, Rajamani and Hwang, Son-Jong and Davis, Mark E. (2014) Active Sites in Sn-Beta for Glucose Isomerization to Fructose and Epimerization to Mannose. ACS Catalysis, 4 (7). pp. 2288-2297. ISSN 2155-5435. doi:10.1021/cs500466j.

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Framework Lewis acidic tin sites in hydrophobic, pure-silica molecular sieves with the zeolite beta topology (Sn-Beta) have been reported previously to predominantly catalyze glucose−fructose isomerization via 1,2 intramolecular hydride shift in water and glucose–mannose epimerization via 1,2 intramolecular carbon shift in methanol. Here, we show that alkali-free Sn-Beta predominantly isomerizes glucose to fructose via 1,2 intramolecular hydride shift in both water and methanol. Increasing extents of postsynthetic Na+ exchange onto Sn-Beta, however, progressively shifts the reaction pathway toward glucose–mannose epimerization via 1,2 intramolecular carbon shift. Na^+ remains exchanged onto silanol groups proximal to Sn centers during reaction in methanol solvent, leading to nearly exclusive selectivity toward epimerization. In contrast, decationation occurs with increasing reaction time in aqueous solvent and gradually shifts the reaction selectivity to isomerization at the expense of epimerization. Decationation and the concomitant selectivity changes are mitigated by the addition of NaCl to the aqueous reaction solution. Preadsorption of ammonia onto Sn-Beta leads to near complete suppression of infrared and ^(119)Sn nuclear magnetic resonance spectroscopic signatures attributed to open Sn sites and of glucose−fructose isomerization pathways in water and methanol. These data provide evidence that Lewis acidic open Sn sites with either proximal silanol groups or Na-exchanged silanol groups are respectively the active sites for glucose–fructose isomerization and glucose–mannose epimerization.

Item Type:Article
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URLURL TypeDescription Information
Gounder, Rajamani0000-0003-1347-534X
Hwang, Son-Jong0000-0002-3210-466X
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2014 American Chemical Society. Received: April 8, 2014; Revised: May 29, 2014. Publication Date (Web): June 2, 2014. This work was financially supported as part of the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001004. M.O. wishes to acknowledge funding from the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1144469. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0001004
NSF Graduate Research FellowshipDGE-1144469
Subject Keywords:tin-beta, open site, closed site, silanol, Bilik reaction, epimerization, isomerization, fructose, glucose, mannose, sodium exchange
Issue or Number:7
Record Number:CaltechAUTHORS:20140623-111830392
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Official Citation:Active Sites in Sn-Beta for Glucose Isomerization to Fructose and Epimerization to Mannose Ricardo Bermejo-Deval, Marat Orazov, Rajamani Gounder, Son-Jong Hwang, and Mark E. Davis ACS Catalysis 2014, 4, pp 2288–2297
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46435
Deposited By: Tony Diaz
Deposited On:23 Jun 2014 19:53
Last Modified:10 Nov 2021 17:25

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