Lactic acid is an important platform molecule in the synthesis of a wide range of chemicals. However, in aqueous solutions without alkali, its efficient preparation via the direct catalysis of sugars is hindered by a side dehydration reaction to 5-hydroxymethylfurfural due to Brønsted acid, which originates from organic acids. Herein, we report that a previously unappreciated combination of common two metal mixed catalyst (Zn-Sn-Beta) prepared via solid-state ion exchange synergistically promoted this reaction. In water without a base, a conversion exceeding 99% for sucrose with a lactic acid yield of 54% was achieved within 2 hours at 190 °C under ambient air pressure. Studies of the acid and base properties of the Zn-Sn-Beta zeolite suggest that the introduction of Zn into the Sn-Beta zeolite sequentially enhanced both the Lewis acid and base sites, and the base sites inhibited a series of side reactions related to fructose dehydration to 5-hydroxymethylfurfural and its subsequent decomposition.
Recently, it was discovered that single-crystalline VO 2 nanostructures exhibit unique, single-domain metal-insulator phase transition. They enable a wide range of device applications as well as discoveries of oxide physics beyond those can be achieved with VO 2 bulk or thin films. Previous syntheses of these nanostructures are limited in density, aspect ratio, single-crystallinity, or by substrate clamping. Here we break these limitations and synthesize ultra-long, ultra-dense, and free-standing VO 2 micro/nanowires using a simple vapor transport method. These are achieved by enhancing the VO 2 nucleation and growth rates using rough-surface quartz as the substrate and V 2 O 5 powder as the evaporation source. V
As a typical transition-metal dichalcogenides, vanadium diselenide (VSe 2 ) is a promising electrode material for aqueous zinc-ion batteries due to its metallic characteristics and excellent electronic conductivity. In this work, we propose a strategy of hydrothermal reduction synthesis of stainless-steel (SS)supported VSe 2 nanosheets with defect (VSe 2−x -SS), thereby further improving the conductivity and activity of VSe 2−x -SS. Density functional theory calculations confirmed that Se defect can adjust the adsorption energy of Zn 2+ ions. This means that the adsorption/desorption process of Zn 2+ ions on VSe 2−x -SS is more reversible than that on pure SS-supported VSe 2 (VSe 2 -SS). As a result, the Zn// VSe 2−x -SS battery showed more excellent electrochemical performance than Zn// VSe 2 -SS. The VSe 2−x -SS electrode shows a good specific capacity of 265.2 mA h g −1 (0.2 A g −1 after 150 cycles), satisfactory rate performance, and impressive cyclic stability. In addition, we also have explored the energy-storage mechanism of Zn 2+ ions in this VSe 2−x -SS electrode material. This study provides an effective strategy for the rational design of electrode materials for electrochemical energy-storage devices.
A highly enantioselective Friedel-Crafts alkylation reaction of indoles with β-CF(3)-β-disubstituted nitroalkenes was achieved using a Ni(ClO(4))(2)-bisoxazoline complex as a catalyst, which afforded indole-bearing chiral compounds with trifluoromethylated all-carbon quaternary stereocenters in good yields with excellent enantioselectivities (up to 97% ee). The transformation of one of the products into first a trifluoromethylated tryptamine and then a trifluoromethylated tetrahydro-β-carboline by sequential nitro reduction and Pictet-Spengler cyclization were realized with complete preservation of enantiopurity.
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