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Formation of 5-(Hydroxymethyl)furfural by Stepwise Dehydration over TiO with Water-Tolerant Lewis Acid Sites 2
Ryouhei Noma, Kiyotaka Nakajima, Keigo Kamata, Masaaki Kitano, Shigenobu Hayashi, and Michikazu Hara J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 22 Jun 2015 Downloaded from http://pubs.acs.org on June 23, 2015
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The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
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Formation
of
5-(Hydroxymethyl)furfural
by
Stepwise Dehydration over TiO2 with WaterTolerant Lewis Acid Sites Ryouhei Noma†,‡, Kiyotaka Nakajima†,∴,§, Keigo Kamata†, Masaaki Kitano#, Shigenobu Hayashi⊥, Michikazu Hara*,†,∃,∇ †
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259-R3-33 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan.
‡
Research Fellowship of the Japan Society for the
Promotion of Science (JSPS), 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan.
∴
Present
address: Catalysis Research Center, Hokkaido University, Kita 21 Nishi 10, Sapporo 001-0021, Japan.
§
Japan Science and Technology Agency (JST), Precursory Research for Embryonic
Science and Technology (PRESTO), 4-1-8 Honcho, Kawaguchi 332-0012, Japan.
#
Materials
Research Center for Element Strategy, Tokyo Institute of Technology, 4259-S2-16 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. ⊥ National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8561, Japan ∃ Frontier Research Center, Tokyo Institute of Technology, 4259-S2-2 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. ∇ JST, Advanced Low Carbon Technology Research and Development Program (ALCA), 4-1-8 Honcho, Kawaguchi 332-0012, Japan.
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ABSTRACT
The reaction mechanism for the formation of 5-(hydroxymethyl)furfural (HMF) from glucose in water over TiO2 and phosphate-immobilized TiO2 (phosphate/TiO2) with water-tolerant Lewis acid sites was studied using isotopically-labeled molecules and
13
C nuclear magnetic resonance
(NMR) measurements for glucose adsorbed on TiO2. Scandium trifluoromethanesulfonate (Sc(OTf)3), a highly active homogeneous Lewis acid catalyst workable in water, converts glucose into HMF through aldose-ketose isomerization between glucose and fructose involving a hydrogen transfer step and subsequent dehydration of fructose. In contrast to Sc(OTf)3, Lewis acid sites on bare TiO2 and phosphate/TiO2 do not form HMF through the isomerizationdehydration route but through the stepwise dehydration of glucose via 3-deoxyglucosone as an intermediate. Continuous extraction of the evolved HMF with 2-sec-butylphenol results in the increase in the HMF selectivity for phosphate/TiO2 even in high concentrated glucose solution. These results suggest that limiting the reactions between HMF and the surface intermediates improves the efficiency of HMF production.
KEYWORDS: Sugar conversion, 5-(hydroxymethyl)furfural, Water-tolerant solid Lewis Acid Catalyst, TiO2, Reaction mechanism
1. Introduction Diminishing our dependence on petroleum resources have generated a strong demand for the development of new technologies that will enable sustainable and environmentally benign
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production of fuels and industrially important chemicals from a renewable feedstock, represented by lignocellulose-based carbohydrates.1 Glucose and xylose, the main components of cellulose and hemicellulose, respectively, are the most attractive biomass-derived carbohydrates and have been widely studied as starting materials for the production of a variety of platform chemicals.2,3 Among the various furans and organic acids obtained from biomass-derived carbohydrates, HMF, which can be produced from glucose with an acid catalyst, has been recognized as a highly valuable platform chemical and was listed in the top ten bio-based chemicals by the US Department of Energy.4 HMF can be converted into promising building blocks for the production of next generation polyesters, such as 2,5-furandicarboxylic acid,5 2,5-bis(hydroxymethyl)furan,6 and 2,5-bis(hydroxymethyl)tetrahydrofuran,7 and potential biofuel candidates, such as 2,5dimethylfuran,8,9 ethyl levulinate,10 and γ-valerolactone11. HMF is easily decomposed into organic acids (levulinic and formic acids) in the presence of a homogeneous Brønsted acid (HCl and H2SO4) through a hydration reaction;12 therefore, the Brønsted acid catalyst alone does not provide an efficient HMF production system. However, the successive use of homogeneous and heterogeneous Lewis acid catalysts has been effective for HMF production from glucose in water or an organic solvent.13–24 Zhang and co-workers reported that CrCl2 acts as an efficient catalyst for glucose conversion into HMF in an ionic liquid, where the HMF yield reached ca. 70% at 373 K.13 In this catalytic system, the Lewis acid center of CrCl2 plays a crucial role, especially in the rate-determining proton transfer of glucose into fructose.25 Tin-containing beta (Sn-β) zeolite in combination with a Brønsted acid catalyst is also an effective catalytic system for the reaction.14 This catalyst has water-tolerant Sn Lewis acid sites and exhibits high catalytic performance for various reactions such as Baeyer-Villiger oxidation26 and Meerwein-Ponndorf-Verley (MPV) reduction.27 Tetrahedrally coordinated Sn
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species within the zeolite network can activate the carbonyl groups of various reactants, including the ring-opening of glucose, even in water. This facilitates the isomerization of glucose into fructose through intramolecular MPV reduction.28 Sn-β can selectively produce HMF from glucose in the presence of a Brønsted acid and an appropriate organic solvent, which suppresses the hydration of HMF into levulinic and formic acids by the fast extraction of HMF into the organic solvent phase. These studies have revealed that isomerization of glucose into fructose, followed by an intramolecular dehydration process, provides efficient HMF production from glucose according to Scheme 1. This mechanism has been widely accepted for various HMF production systems. In the case of the Sn-β zeolite/HCl system, for example, the Lewis acid sites of Sn-β zeolite simultaneously activate the carbonyl group at the C1 position and the hydroxyl group at the C2 position on glucose, which promotes the intramolecular hydride transfer of a cyclic intermediate via the MPV reduction mechanism.28 Subsequent dehydration of fructose occurs with a conventional Brønsted acid, which results in HMF formation in a one-pot reaction system.29 Ståhlberg and co-workers also reported that HMF formation proceeds in a boric acid/ionic liquid mixture through the isomerization-dehydration mechanism.30 We recently reported that early transition metal oxides, such as Nb2O515 and TiO2,16,17 have water-compatible Lewis acid sites due to unsaturated coordination metal species such as NbO4 and TiO4 tetrahedra formed on the oxide surface. Such species function as highly active Lewis acid sites that promote various reactions, including MPV reduction16 and Mukaiyama-aldol reactions.31,32 Although Nb2O5 and TiO2 catalyze the direct formation of HMF from glucose, the HMF yield and selectivity with these oxides are considerably low (HMF yield
