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Reaction of Glucose Catalyzed by Framework and Extraframework Tin Sites in Zeolite Beta


Bermejo-Deval, Ricardo (2014) Reaction of Glucose Catalyzed by Framework and Extraframework Tin Sites in Zeolite Beta. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6AYX-9086.


The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup, and is now being considered as an intermediate step in the possible route of biomass conversion into fuels and chemicals. Recently, it has been shown that a hydrophobic, large pore, silica molecular sieve having the zeolite beta structure and containing framework Sn4+ (Sn-Beta) is able to isomerize glucose into fructose in aqueous media. Here, I have investigated how this catalyst converts glucose to fructose and show that it is analogous to that achieved with metalloenzymes. Specifically, glucose partitions into the molecular sieve in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center (framework Sn4+), isomerizes into the acyclic form of fructose and finally ring closes to yield the furanose product. Akin to the metalloenzyme, the isomerization step proceeds by intramolecular hydride transfer from C2 to C1. Extraframework tin oxides located within hydrophobic channels of the molecular sieve that exclude liquid water can also isomerize glucose to fructose in aqueous media, but do so through a base-catalyzed proton abstraction mechanism. Extraframework tin oxide particles located at the external surface of the molecular sieve crystals or on amorphous silica supports are not active in aqueous media but are able to perform the isomerization in methanol by a base-catalyzed proton abstraction mechanism. Post-synthetic exchange of Na+ with Sn-Beta alters the glucose reaction pathway from the 1,2 intramolecular hydrogen shift (isomerization) to produce fructose towards the 1,2 intramolecular carbon shift (epimerization) that forms mannose. Na+ remains exchanged onto silanol groups during reaction in methanol solvent, leading to a near complete shift in selectivity towards glucose epimerization to mannose. In contrast, decationation occurs during reaction in aqueous solutions and gradually increases the reaction selectivity to isomerization at the expense of epimerization. Decationation and concomitant changes in selectivity can be eliminated by addition of NaCl to the aqueous reaction solution. Thus, framework tin sites with a proximal silanol group are the active sites for the 1, 2 intramolecular hydride shift in the isomerization of glucose to fructose, while these sites with Na-exchanged silanol group are the active sites for the 1, 2 intramolecular carbon shift in epimerization of glucose to mannose.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Sn-Beta zeolite, glucose isomerization fructose, bilik reaction, tin oxide, lactic-acid
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Minor Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Davis, Mark E.
Thesis Committee:
  • Davis, Mark E. (chair)
  • Flagan, Richard C.
  • Agapie, Theodor
  • Labinger, Jay A.
Defense Date:12 May 2014
Funding AgencyGrant Number
U.S. Department of EnergyMED.EFRC01-1-UDELAW.DOE2009
Record Number:CaltechTHESIS:05192014-100254158
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8241
Deposited By: Ricardo Bermejo De Val
Deposited On:27 May 2015 23:41
Last Modified:04 Oct 2019 00:04

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