Abstract
A series of Lewis acidic metal salts were used for glucose dehydration to 5-hydroymethylfurfural (HMF) in water. Effect of valence state, ionic radii of Lewis acidic cation, and the type of anions on the catalytic performance have been studied systematically. The experimental results showed that the valence state played an important role in determining catalytic activity and selectivity. It was found that a higher glucose conversion rate and HMF selectivity could be obtained over high valent Lewis acid salts, where the ionic radii of these Lewis acidic metal salts are usually relatively small. Analysis on the effect of the anions of Lewis acid salts on the catalytic activity and the selectivity suggested that a higher glucose conversion and HMF selectivity could be readily obtained with Cl−. Furthermore, the recyclability of high valence state Lewis acid salt was also studied, however, inferior catalytic performance was observed. The deactivation mechanism was speculated to be the fact that high valence state Lewis acid salt was comparatively easier to undergo hydrolysis to yield complicated metal aqua ions with less catalytic activity. The Lewis acidic activity could be recovered by introducing a stoichiometric amount of hydrochloric acid (HCl) to the catalytic before the reaction.
Highlights
Growing concerns about global warming and depletion of fossil-derived carbon resources has prompted the exploration of developing sustainable alternative energy sources to lessen human dependence on the finite fossil reserves
Based on our previous work regarding the effect of reaction conditions, such as Lewis acidic metal type, pH values of the reaction media, temperature, etc., on the glucose dehydration [29], in the present work we seek to further explore the effect of the valence state, ionic radii of Lewis acid salts, and metal and anion type of the investigated Lewis acid salts
All these results collectively suggest that the ionic radii of Lewis acid salts had an important role in controlling catalytic activity of glucose dehydration, with the yield of HMF decreasing upon increasing the ionic radii of Lewis acidic metal salts
Summary
Growing concerns about global warming and depletion of fossil-derived carbon resources has prompted the exploration of developing sustainable alternative energy sources to lessen human dependence on the finite fossil reserves. In our previous work [29], the effect of the reaction conditions, such as Lewis acidic metal type, pH values of the reaction media, temperature, etc., were systematically studied; the glucose conversion kinetic profiles and HMF product selectivity were used to examine the importance of the. In order to further understand the characteristics of the Lewis acid salts, such as the valence state, ionic radii of Lewis acid salts, the metal and anion type of the Lewis acid salts, the recyclability of these catalysts under reaction conditions, in this work the glucose dehydration reaction was carried out with various Lewis acid salts in an aqueous/sec-butyl phenol biphasic reaction system to explore these parameters. Valence state Lewis acid salt was carried out and the deactivation mechanisms were explored with possible catalytic activity recovery strategies being developed
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