Yunlei Zhang,Bing Li,Yanan Wei,Changhao Yan,Minjia Meng,Yongsheng Yan
Developing a green and economically viable approach for the direct synthesis of metal-organic frameworks (MOFs) catalysts with multifunctional active sites remains the key step for their applications in heterogeneous catalysis field. Herein, we report a green (aqueous solutions), mild (90 °C, atmospheric pressure), and modulated hydrothermal (MHT) approach to synthesize UiO-66-type MOFs catalysts with acid–base bi-functional sites, which were obtained via the coordination of monosodium 2-sulfoterephthalate and 2-aminoterephthalic with zirconium (Zr) ions. More importantly, a series of acid, base and acid–base catalysts with varied acid–base strengths can be readily prepared, by simply varying the ratio of organic ligands for preparing MOFs. The synthesized catalysts were characterized and their performances in glucose dehydration to produce 5-hydroxymethylfurfural (5-HMF) have been evaluated. The developed approach in this work has clearly depicted a roadmap for the facile synthesis of MOFs catalysts to facilitate their potential use in acid–base catalysis.
Jing Guo,Shanhui Zhu,Youliang Cen,Zhangfeng Qin,Jianguo Wang,Weibin Fan
A series of ordered mesoporous Nb x W (8 − x) oxides with tunable Nb/W ratio were successfully synthesized by evaporation-induced self-assembly method. The mesoporous structure, morphologies, surface chemical state, and acidic properties of these catalysts were fully characterized by low-temperature sorption of N 2 , small-angle and wide-angle XRD, TEM, Raman, XPS, and Py-IR. It was shown that the Nb x W (8 − x) oxides created large amounts of Lewis as well as Brønsted acid sites, which promoted the isomerization of glucose to fructose followed its dehydration to 5-hydroxymethylfurfural (HMF). Mannose was also formed via the epimerization of glucose. Of them, the mesoporous Nb 4 W 4 exhibited the best catalytic activity with a comparatively low E a about 90.2 kJ/mol and good stability in aqueous medium. The kinetic behavior revealed that Lewis acid sites facilitated to glucose-to-fructose isomerization while Brønsted acid sites promoted the dehydration of fructose to form HMF.
The catalytic transformation of furfuryl alcohol and hexose into value-added chemicals have been investigated with a series of polymer-based catalysts including poly(styrenesulfonic acid) (PSS), graphite oxide-doped poly(styrenesulfonic acid) (PSS-GO), and graphite-doped poly(styrenesulfonic acid) (PSS-C). It is found that the selective conversion of furfuryl alcohol to methyl levulinate (MLE) was successfully performed with PSS as the catalyst, in which a 96.4% yield is attained in methanol solvent. Moreover, the efficient dehydration of d -fructose to produce 5-hydroxymethylfurfural (HMF) has also been achieved using PSS-GO as the catalyst, where a 76.5% yield of HMF was obtained in N -methylpyrrodinone solvent. The effects of reaction temperature, time and solvent were investigated. Furthermore, the used catalysts have been respectively characterized by XRD, TG, FTIR, SEM and TEM techniques to reveal the physical properties and structures of these polymeric catalytic materials.
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