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Molybdenum-Based Polyoxometalates as Highly Active and Selective Catalysts for the Epimerization of Aldoses

Ju, Feifei and VanderVelde, David and Nikolla, Eranda (2014) Molybdenum-Based Polyoxometalates as Highly Active and Selective Catalysts for the Epimerization of Aldoses. ACS Catalysis, 4 (5). pp. 1358-1364. ISSN 2155-5435. https://resolver.caltech.edu/CaltechAUTHORS:20140606-131532200

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Abstract

In this contribution, we report on the high activity and selectivity of Keggin structure molybdenum-based polyoxometalates (POMs) in catalyzing the epimerization of aldoses. Near-equilibrium conversions and selectivities were obtained within the first hour of operation under aqueous conditions at relatively low temperatures and a wide range of pHs. Characterization of the molybdenum-based POM catalysts using X-ray diffraction and FTIR studies before and after the reaction showed no evidence of their decomposition. Our studies suggest that the active sites for the reaction are the molybdenum oxide octahedra on the surface of the Keggin structure of the molybdenum-based POMs (H_3PMo_(12)O_(40), Ag_3PMo_(12)O_(40), Sn_(0.75)PMo_(12)O_(40)). Further characterization of the system using ^(31)P NMR and X-ray photoelectron spectroscopy experiments showed that the interaction between the aldose (e.g., glucose) and the molybdenum oxide octahedra in the POM results in electron transfer from the aldose to molybdenum, leading to the formation of the reduced form of the POM (also known as heteropoly blue). Isotope labeling experiments demonstrated that the epimerization of glucose using molybdenum-based POMs proceeds via an intramolecular C1–C2 shift mechanism with an activation barrier of as low as 96 kJ/mol, obtained using controlled kinetic experiments. These findings open up avenues for the implementation of molybdenum-based POMs as single, selective, and stable catalytic systems for the efficient epimerization of aldoses under aqueous conditions at relatively low temperatures and a wide range of pHs.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/cs401253z DOIArticle
http://pubs.acs.org/doi/abs/10.1021/cs401253zPublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/cs401253zPublisherSupporting Information
ORCID:
AuthorORCID
VanderVelde, David0000-0002-2907-0366
Nikolla, Eranda0000-0002-8172-884X
Additional Information:© 2014 American Chemical Society. Received: December 29, 2013; Revised: March 3, 2014; Published: March 25, 2014. We gratefully acknowledge the support of the National Science Foundation (CBET-1226569) and Wayne State University. We thank Dr. Kai Sun for his help with XPS and Prof. Mark Barteau for helpful discussions.
Funders:
Funding AgencyGrant Number
NSFCBET-1226569
Wayne State UniversityUNSPECIFIED
Subject Keywords:polyoxometalates; aldose epimerization; kinetic isotope effect; Keggin structure; intramolecular carbon shift; heteropoly blue
Issue or Number:5
Record Number:CaltechAUTHORS:20140606-131532200
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140606-131532200
Official Citation:Molybdenum-Based Polyoxometalates as Highly Active and Selective Catalysts for the Epimerization of Aldoses Feifei Ju, David VanderVelde, and Eranda Nikolla ACS Catalysis 2014 4 (5), 1358-1364
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46130
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Jun 2014 21:00
Last Modified:09 Mar 2020 13:19

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