果糖一步转化制备呋喃基燃料:溶剂效应及离子液体修饰活性金属对产物选择性的决定作用（英文）

在众多生物基化合物中,2,5-二甲基呋喃(DMF)是一种有实用前景的可再生液体生物质燃料,也是一种具有重要价值的化学品,可作为生产对苯二甲酸的原料.2,5-二甲基四氢呋喃(DMTF)是DMF进一步加氢产物,该化合物比DMF更稳定,适合长期保存;由于具有更高的氢碳比,用作生物燃料燃烧时能够释放更多能量.研究生物质资源制备DMF和DMTF对可再生资源制备液体燃料和化学品具有重要意义.从生物质多糖出发制备这两类化合物,中间经历了水解、脱水、加氢、加氢脱氧等多个反应步骤,每一步反应都十分复杂,包含许多副反应途径.此外,由于每一步反应条件的不兼容性,大多数研究集中在分步反应阶段,鲜有文献能够实现从碳水化合物原料直接转化为DMF和DMTF.发展由生物质一锅法多步耦合转化技术制备化学品和燃料,不仅具有科学意义,而且可大大简化反应过程,避免中间产物分离和损失,节省资源和时间,历来受到化学家和工业界的关注.本文利用离子液体对Ru/C催化剂电子性质的修饰作用以及溶剂效应的影响,设计了离子液体/THF双相体系中果糖直接催化转化制备2,5-二甲基呋喃(DMF)和2,5-二甲基四氢呋喃(DMTF)的新路线.该转化过程耦合了果糖脱水制HMF、HMF加氢及加氢脱氧生成DMF和DMTF等多步反应.通常在HMF加氢转化过程中,Ru/C催化剂的高活性易导致HMF深度加氢生成大量开环产物及气体,我们借助离子液体与有机溶剂的不同溶解性,筛选出[BMIm]Cl/THF双相溶剂体系,使极性HMF在离子液体层反应,生成弱极性的DMF和DMTF能及时被THF萃取出来,有效稳定了目标产物.其次,果糖转化为HMF会产生少量水,通常水的存在易导致HMF发生水合等副反应,对下一步的加氢转化是不利因素;然而在本催化体系中,由于[BMIm]Cl能与水以较强的氢键结合形成水合物,对水分子起到了束缚作用,减少了HMF发生水解、水合等副反应的机会.另一方面,离子液体粘度较大,微量水的存在能降低离子液体层粘度,改善传质,从而提高反应速率.在HMF加氢处理过程中,离子液体对DMF和DMTF的生成起了决定作用.当反应体系中不添加离子液体,以THF为溶剂,反应结束后未检测到DMF生成,DMTF的收率仅为2%,但HMF已经完全转化.取气体样品进行GC分析,发现有部分气相产物生成,包括CO2、CH4和C2H6等.液体混合物进行GC-MS检测,发现产物主要包括DHMTF、5-甲基四氢糠醇(MTFA)、四氢糠醇(TFA)、1,2-戊二醇、DMTF、2-己醇和少量戊醇,产物中所有呋喃环结构的双键都发生加氢反应.以上结果表明,没有离子液体的THF中,Ru/C催化的HMF涉氢反应平衡已发生改变.当反应体系中添加0.2 g离子液体[BMIm]Cl进行HMF的加氢时,此时开始有DMF生成,随着[BMIm]Cl量依次增加,DMF以及DMTF的收率也呈上升趋势.1.0 g离子液体获得两种产物最高收率为68%.然而,如果进一步增加[BMIm]Cl的量到2.0 g,呋喃基液体燃料DMF和DMTF的收率却开始下降.综合以上实验结果,我们认为适量的[BMIm]Cl存在有可能会对催化剂物理化学性质造成影响,从而对产物的选择性起了决定性作用.通过对催化剂进行元素分析、XPS、H2-TPR表征以及一系列对比实验证明,离子液体不仅促进果糖脱水转化为HMF,同时在HMF选择性加氢反应中可修饰活性金属电子性质,改变催化路径,是多步串联反应能够耦合的关键因素.在[BMIm]Cl/THF双相溶剂体系中,离子液体的"溶剂笼效应"促进DMF和DMTF高效生成,THF的萃取功能对目标产物的稳定起了关键作用.以上对催化剂和溶剂的合理设计共同促进高产率呋喃基燃料的获得.该研究实现由六碳糖直接选择转化获取DMF和DMTF,为生物质高效催化转化制备生物基能源化学品提供了新思路.     

Br(o)nsted酸性离子液体催化异丁醛和叔丁醇缩合反应

考察了Br(o)nsted酸性离子液体同时作为溶剂和催化剂催化异丁醛和叔丁醇缩合制备 2,5-二甲基-2,4-己二烯的反应性能.结果表明,Br(o)nsted酸性离子液体具有良好的催化性能,反应后反应产物与离子液体自动分层易分离,离子液体经过真空干燥处理后可以作为溶剂和催化剂循环使用.调变离子液体中的阳离子或阴离子的结构对催化性能有较大的影响.     

载体对其负载的Cu-Co双金属催化剂上5-羟甲基糠醛氢解选择性生成2,5-二甲基呋喃的影响

碳-氧键氢解是生物质呋喃基化合物制备交通燃料常见的模型反应,其中5-羟甲基糠醛(HMF)转化为汽油添加剂2,5-二甲基呋喃(DMF)尤为引人关注.本文采用CeO2,ZrO2和Al2O3负载的Cu-Co双金属催化剂用于HMF选择性氢解制DMF的反应中.采用X射线衍射、N2吸附-脱附、投射电镜、H2-程序升温还原、氨-程序升温脱附和元素分析表征了新鲜的和使用过催化剂的结构,并将其与催化活性相关联.Cu-Co/CeO2催化剂通过在大的Cu颗粒上还原C=O键生成了最多的2,5双(羟甲基呋喃)(BHMF).但Cu-Co/Al2O3催化剂具有高度分散的Cu,Cu-Co复合氧化物和大量的弱酸位,因而生成DMF的选择性最高.Cu-Co/ZrO2催化剂则由于存在强酸位,DMF选择性较低,生成了各种过度氢解产物,如2,5而甲基四氢呋喃和5,5-二(亚甲基)双(2-甲基呋喃).因此,考察了Cu-Co/Al2O3催化剂上的反应路径,以及温度、氢气压力和时间等操作条件的影响,使其具有较优的HMF转化率和DMF选择性.     

助溶剂在离子液体催化制备5-羟甲基糠醛中的应用

本文研究了不同助溶剂对酸性离子液体催化制备5-羟甲基糠醛的(HMF)的影响.以果糖为反应原料,二甲基亚砜(DMSO)、二甲基乙酰胺(DMA)、二甲基甲酰胺(DMF)以及乙二醇(EG)四种不同的有机溶剂作为助溶剂,运用酸性离子液体催化制备5-羟甲基糠醛.结果表明:以DMSO作为反应助溶剂,38.5wt%的果糖反应液在催化...     

硅胶固定功能化离子液体的制备及其在5-羟甲基糠醛合成中的应用

通过γ-氯丙基三甲氧基硅烷将磺基功能化离子液体-N-磺丙基咪唑盐化学键合到微球硅胶上,制得微球硅胶固定化离子液体(IL3). 用FTIR、TG、~(13)C NMR、SEM、BET及酸度测定等测试技术对IL3进行了表征,并考察其在果糖脱水合成5-羟甲基糠醛(HMF)过程中的催化性能. 研究结果表明,氯丙基三甲氧基硅烷可以将磺基功能化咪唑型离子液体化学键合到微球硅胶上. 微球硅胶固定化磺基咪唑离子液体能有效催化果糖脱水生成HMF. 果糖在固载率45.4%的IL3催化下、乙二醇甲醚(EGME)溶剂中、115 ℃反应5 h,HMF收率可达82.1%. 催化剂循环使用4次后,HMF的收率下降为53.0%.     

碱性条件下Ru/C催化5-羟甲基糠醛选择氧化反应

以活性炭负载金属钌(Ru/C)为催化剂,在碱性水溶液中研究了5-羟甲基糠醛(HMF)选择氧化反应.与MgO,Ca(OH)₂和NaOH相比,加入具有合适碱强度的镁铝水滑石有利于生成5-甲酰基-2-呋喃甲酸(FFCA)或2,5-呋喃二甲酸(FDCA).X射线光电子能谱实验表明金属态的钌是活性催化中心.同位素示踪结果则表明水而非氧气提供了5-甲酰基-2-呋喃甲酸及2,5-呋喃二甲酸等羧酸产物的氧源.根据这些结果,并结合HMF和2,5-呋喃二甲醛氧化的动力学研究,我们提出HMF选择性氧化制备FFCA遵循Langmuir-Hinshelwood反应机理.其中,HMF在金属Ru表面饱和解离吸附,在解离吸附的氧原子的协助下发生β-脱氢生成2,5-呋喃二甲醛(DFF)吸附物种.该DFF物种进一步发生水合与氧化形成FFCA产物.     

离子液体中磺化无定形炭催化菊糖制备5-羟甲基糠醛

研究了以1-丁基-3-甲基咪唑氯盐([Bmim]Cl)离子液体作溶剂,磺化无定形炭为催化剂催化菊糖脱水制5-羟甲基糠醛(HMF)的反应.考察了溶剂、水量、反应温度、反应时间和催化剂用量对HMF收率的影响.实验结果表明,反应温度为100°C,反应时间60min,R=5(R为水的物质的量与菊糖中所含果糖单位的物质的量的比值),m(催化剂):m(菊糖)=1:3时,HMF的收率可达50%.     

离子液体中树脂催化转化果糖为5-羟甲基糠醛

开发了以离子液体1-丁基-3-甲基咪唑氯盐([BMIM]Cl)为溶剂, 固体酸离子交换树脂NKC-9为催化剂转化果糖为5-羟甲基糠醛的绿色工艺. 在此催化体系中, 100 ℃下反应10 min时5-HMF的产率达到78.0%, 其反应时间远远小于已有文献报道的长达数小时的反应时间. 在此催化体系中, 果糖起始浓度的增加对5-HMF产率影响不大, 因而此工艺同样适用于处理高浓度的果糖溶液. 离子液体[BMIM]Cl和树脂组成的催化体系可以循环使用, 经过9次重复使用后仍能保持稳定的催化活性.     

Brnsted酸性离子液体催化异丁醛和叔丁醇缩合反应

考察了Brnsted酸性离子液体同时作为溶剂和催化剂催化异丁醛和叔丁醇缩合制备2,5-二甲基-2,4-己二烯的反应性能.结果表明,Brnsted酸性离子液体具有良好的催化性能,反应后反应产物与离子液体自动分层易分离,离子液体经过真空干燥处理后可以作为溶剂和催化剂循环使用.调变离子液体中的阳离子或阴离子的结构对催化性能有较大的影响.     

硅胶固定功能化离子液体的制备及其在HMF合成中的应用

通过氯丙基三甲氧基硅烷将磺基功能化离子液体--N-磺丙基咪唑盐化学键联到微球硅胶上,制得微球硅胶固定化离子液体（IL3）。用FTIR、TG、13C-NMR、SEM、BET及酸度测定等方法对IL3进行了表征,并考察其在果糖脱水合成5-羟甲基糠醛（HMF）过程中的催化性能。研究结果表明：氯丙基三甲氧基硅烷可以将磺基功能化咪唑型离子液体化学键联到微球硅胶上。微球硅胶固定化磺基咪唑离子液体能有效催化果糖脱水生成HMF。在45.4-IL3催化下、乙二醇甲醚(EGME)溶剂中、115℃反应5小时, HMF收率可达82.1％。使用后的催化剂可以方便地循环使用。但随次数增加,HMF收率明显下降。45.4-IL3催化剂循环使用四次后,HMF的收率下降为53.0%。     

果糖催化合成5-羟甲基糠醛研究的新进展

5-羟甲基糠醛(HMF)是一种具有重要应用价值的原材料和中间体,以果糖脱水合成HMF具有实现生物质转化利用的重大意义。本文综述了近三年来果糖制备HMF过程的两大关键因素:催化剂和反应介质的重要进展。固体酸(特别是杂多酸及其盐)、离子液体(ILs)中添加卤化物或ILs作为催化剂是近几年来研究的热点,固体酸的优点是可多次重复使用且易于分离,而ILs中果糖的降解条件较温和,副反应较少。目前,用于果糖转化HMF的反应溶剂优、缺点并存。最后对该反应存在的问题和今后的研究进行了总结和展望。     

One-pot,two-step,practical catalytic synthesis of 2,5-diformylfuran from fructose

[reaction: see text] A practical, one-pot, two-step catalytic method is described for the synthesis of 2,5-diformylfuran (DFF) from fructose via dehydration to 5-(hydroxymethyl)furfural (HMF), followed by in situ catalytic air-oxidation.     

离子液体催化制备5-羟甲基糠醛的研究进展

本文综述了离子液体催化制备5-羟甲基糠醛的研究进展。运用离子液体作为反应溶剂和催化剂,与常规合成HMF的方法相比,其反应在常压、低温下进行,更易于操作控制;副反应数量明显减少,HMF的产率稳定,可达90%;离子液体催化活性稳定,可重复利用,减少了有机溶剂的使用量;利用离子液体作为媒介,能将反应原料从单一的果糖扩展到葡萄糖和纤维素等廉价原料,降低了生产成本。由此可见,运用离子液体催化制备HMF将是今后研究的重点和发展的必然趋势。     

Molecular aspects of glucose dehydration by chromium chlorides in ionic liquids

A combined experimental and computational study of the ionic‐liquid‐mediated dehydration of glucose and fructose by Cr^II and Cr^III chlorides has been performed. The ability of chromium to selectively dehydrate glucose to 5‐hydroxymethylfurfural (HMF) in the ionic liquid 1‐ethyl‐3‐methyl imidazolium chloride does not depend on the oxidation state of chromium. Nevertheless, Cr^III exhibits higher activity and selectivity to HMF than Cr^II. Anhydrous CrCl₂ and CrCl₃?6 H₂O readily catalyze glucose dehydration with HMF yields of 60 and 72 %, respectively, after 3 h. Anhydrous CrCl₃ has a lower activity, because it only slowly dissolves in the reaction mixture. The transformation of glucose to HMF involves the formation of fructose as an intermediate. The exceptional catalytic performance of the chromium catalysts is explained by their unique ability to catalyze glucose to fructose isomerization and fructose to HMF dehydration with high selectivity. Side reactions leading to humins by means of condensation reactions take predominantly place during fructose dehydration. The higher HMF selectivity for Cr^III is tentatively explained by the higher activity in fructose dehydration compared to Cr^II. This limits the concentration of intermediates that are involved in bimolecular condensation reactions. Model DFT calculations indicate a substantially lower activation barrier for glucose isomerization by Cr^III compared to Cr^II. Qualitatively, glucose isomerization follows a similar mechanism for Cr^II and Cr^III. The mechanism involves ring opening of D ‐glucopyranose coordinated to a single Cr ion, followed by a transient self‐organization of catalytic chromium complexes that promotes the rate‐determining hydrogen‐shift step.     

Understanding solvent effects in the selective conversion of fructose to 5-hydroxymethyl-furfural: a molecular dynamics investigation

Selective conversion of fructose to 5-hydroxymethyl-furfural (HMF) involves the participation of high-boiling solvents like dimethyl sulfoxide (DMSO). In order to replace DMSO with low-boiling solvents, it is imperative that we understand the effect of DMSO solvation in protecting (i) HMF from rehydration and humins formation reactions and (ii) fructose from side reactions, other than its dehydration to HMF. In the present work, molecular dynamics simulations of HMF and fructose in water and in water-DMSO mixtures are carried out using the OPLS-AA force field. Radial pair distribution functions, coordination numbers and the hydrogen-bond network between the HMF/fructose molecule and the solvent molecules are analysed. The local 3-dimensional picture of the arrangement of solvent molecules around the solute, which cannot be accessed from pair distribution functions, is also computed. We show preferential coordination of DMSO around HMF and explain how this could provide a shielding effect to the HMF molecule, thus protecting it from further rehydration to levulinic acid and formic acid and from humins formation. In the case of fructose, the presence of DMSO also reduces the number of water molecules in the immediate vicinity of fructose. Though fewer water molecules coordinate around fructose, they are bound strongly to it. Analysis of the local 3-dimensional arrangement of DMSO molecules suggests that it protects the fructose molecule from side reactions that would lead to condensation or reversion products. However, the presence of DMSO molecules does not hamper the water molecules coming into contact with the oxygen atom of the hydroxyl groups of fructose, which is required for a proton transfer from water to fructose, to initiate the dehydration reaction to HMF.     

Cellulose sulfuric acid as a bio-supported and recyclable solid acid catalyst for the synthesis of 5-hydroxymethylfurfural and 5-ethoxymethylfurfural from fructose

In this study, we have developed a new and green method for the synthesis of 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) from fructose using cellulose sulfuric acid as catalyst. Firstly, HMF was synthesized from fructose, and a high yield of 93.6 % was obtained in DMSO for 45 min in the presence of cellulose sulfuric acid. Cellulose sulfuric acid also showed high catalytic activity for the synthesis of EMF. EMF was obtained in a high yield of 84.4 % by the etherification of HMF under the optimal reaction conditions. More importantly, a high EMF yield of 72.5 % was also obtained from fructose through one-pot reaction strategy, which integrated the dehydration of fructose into HMF and the followed etherification of HMF into EMF. The reaction work-up was very simple and the catalyst could be reused several times without the loss of its catalytic activity.     

Highly efficient preparation of 5-hydroxymethylfurfural from sucrose using ionic liquids and heteropolyacid catalysts in dimethyl sulfoxide–water mixed solvent

Several types of ILs and solid acids were used as catalysts in one-pot conversion of sucrose to 5-hydroxymethylfurfural (abbreviated as 5-HMF) in a dimethyl sulfoxide (DMSO)/water mixed solvent under hydrothermal conditions. A remarkable 5-HMF yield of 91.8% was achieved catalyzed by the cesium salt of dodecatungstophosphoric acid (Cs_2.3H_0.7PW₁₂O₄₀) within 3 h at 180 ℃. The ionic liquid N-methylimidazolium hydrogen sulfate ([Hmim][HSO₄]) gave the 5-HMF in 82.0% yield from sucrose. To the best of our knowledge, it was almost the highest yield of HMF from sucrose by now. Various reaction parameters including reaction temperature and time and catalyst dosage were optimized. A possible mechanism for this catalytic process was proposed. Furthermore, fructose and glucose were also investigated, good yields of 5-HMF was obtained respectively. This increases the possibility of large-scale production of 5-HMF from carbohydrates.     

Electrochemical Oxidation of 5‐Hydroxymethylfurfural on Nickel Nitride/Carbon Nanosheets: Reaction Pathway Determined by In Situ Sum Frequency Generation Vibrational Spectroscopy

2,5‐Furandicarboxylic acid was obtained from the electrooxidation of 5‐hydroxymethylfurfural (HMF) with non‐noble metal‐based catalysts. Moreover, combining the biomass oxidation with the hydrogen evolution reaction (HER) increased the energy conversion efficiency of an electrolyzer and also generated value‐added products at both electrodes. Here, the reaction pathway on the surface of a carbon‐coupled nickel nitride nanosheet (Ni₃N@C) electrode was evaluated by surface‐selective vibrational spectroscopy using sum frequency generation (SFG) during the electrochemical oxidation. The Ni₃N@C electrode shows catalytic activities for HMF oxidation and the HER. As the first in situ SFG study on transition‐metal nitride for the electrooxidation upgrade of HMF, this work not only demonstrates that the reaction pathway of electrochemical oxidation but also provides an opportunity for nonprecious metal nitrides to simultaneously upgrade biomass and produce H₂ under ambient conditions.