Qiu Guo, Wang Xincheng, Huang Chongpin, Li Yingxia, Chen Biaohua
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology Beijing 100029 China
Beijing Key Laboratory of Fuels Cleaning and Advanced Catalytic Emission Reduction Technology, Beijing Institute of Petrochemical Technology Beijing 102617 China.
RSC Adv. 2018 Sep 18;8(57):32423-32433. doi: 10.1039/c8ra05940c.
The efficient conversion of carbohydrates to 5-hydroxymethylfurfural (5-HMF) under mild conditions represents a very attractive and promising method of producing important building blocks. In this work, niobium phosphotungstates, with Nb/P molar ratios of 0.6, 1.0, 2.0 and 4.0 (NbPW-06, NbPW-1, NbPW-2, and NbPW-4, respectively) have been prepared by a facile, one-pot, alcohol-mediated thermal process and used for the direct conversion of fructose to 5-HMF. By adding a certain amount of Nb, the surface of the catalyst became enriched in P, and this enrichment was associated with the presence of surface P-OH groups that offered Brønsted acid sites that can activate superficial hydrogen species to facilitate 5-HMF generation. Pyridine-FTIR confirmed the presence of Brønsted and Lewis acid sites, which might play important roles in the dehydration of fructose to 5-HMF. Furthermore, polar aprotic solvents were well-suited for the conversion, and higher yields of 5-HMF were obtained in polar aprotic solvents than in nonpolar solvents. A 5-HMF yield of 96.7% with complete fructose consumption was obtained over NbPW-06 in DMSO at 80 °C after 90 min. In addition, NbPW-06 could be recycled several times without a significant decrease in the catalytic activity. A catalytic mechanism for this reaction was proposed. Moreover, this catalytic system can also be utilized for the dehydration of sucrose and inulin to 5-HMF in satisfactory yields. This study establishes an important platform for the further design of Nb-containing catalysts for the production of 5-HMF from carbohydrates under mild conditions.
在温和条件下将碳水化合物高效转化为5-羟甲基糠醛（5-HMF）是一种非常有吸引力且前景广阔的制备重要结构单元的方法。在本工作中，通过简便的一锅法醇介导热过程制备了铌磷钨酸盐，其铌/磷摩尔比分别为0.6、1.0、2.0和4.0（分别为NbPW-06、NbPW-1、NbPW-2和NbPW-4），并用于将果糖直接转化为5-HMF。通过添加一定量的铌，催化剂表面富含磷，这种富集与表面P-OH基团的存在有关，这些基团提供了布朗斯台德酸位点，可活化表面氢物种以促进5-HMF的生成。吡啶-傅里叶变换红外光谱证实了布朗斯台德和路易斯酸位点的存在，它们可能在果糖脱水生成5-HMF中起重要作用。此外，极性非质子溶剂非常适合该转化过程，在极性非质子溶剂中获得的5-HMF产率高于非极性溶剂。在80℃下于二甲基亚砜（DMSO）中反应90分钟后，NbPW-06上获得了96.7%的5-HMF产率且果糖完全消耗。此外，NbPW-06可以循环使用多次，催化活性没有显著降低。提出了该反应的催化机理。此外，该催化体系还可用于将蔗糖和菊粉脱水生成5-HMF，产率令人满意。本研究为进一步设计用于在温和条件下由碳水化合物生产5-HMF的含铌催化剂建立了一个重要平台。
