选择性氧化HMF

近年来,利用储量丰富且可再生的生物质资源制备高附加值化学品和液体燃料是目前化学研究领域的热点之一,同时契合可持续发展的国家战略.5-羟甲基糠醛(HMF)是关键的生物质平台化合物之一,广泛应用于制备精细平台化合物、药物的中间体、聚合物的合成、液体燃料的前驱体等.因此,HMF的选择性氧化逐渐成为生物质领域的研究热点.本文主...     

Furfural and 5-Hydroxymethylfurfural Production from Sugar Mixture Using Deep Eutectic Solvent/MIBK System

Choline chloride (ChCl) / glycolic acid (GA) deep eutectic solvent (DES) media with high water content but without any additional catalyst are introduced in furfural and 5-hydroxymethylfurfural (HMF) production. The effects of water content, reaction time, and reaction temperature are investigated with two feedstocks: a glucose/xylose mixture and birch sawdust. Based on the results, 10 equivalent quantities of water (32.9 wt.%) were revealed to be beneficial for conversions without rupturing the DES structure. The optimal reaction conditions were 160 °C and 10 minutes for the sugar mixture and 170 °C and 10 minutes for birch sawdust in a microwave reactor. High furfural yields were achieved, namely 62 % from the sugar mixture and 37.5 % from birch sawdust. HMF yields were low, but since the characterization of the solid residue of sawdust, after DES treatment, was revealed to contain only cellulose (49 %) and lignin (52 %), the treatment could be potentially utilized in a biorefinery concept where the main products are obtained from the cellulose fraction. Extraction of products into the organic phase (methyl isobutyl ketone, MIBK) during the reaction enabled the recycling of the DES phase, and yields remained high for three runs of recycling.     

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5‐Hydroxymethylfurfural over Mesoporous Nb and Nb‐W Oxides

A series of mesoporous Nb and Nb‐W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5‐hydroxymethylfurfural (HMF ). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb‐W oxides varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Brønsted to Lewis acid sites. All Nb‐W oxides show a relatively high selectivity of HMF , whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2‐butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2‐butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.     

Fructose dehydration to 5HMF in a green self-catalysed DES composed of N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA)

Due to the increasing concerns about the availability and accessibility of fossil fuel reserves, and the subsequent effect of using them on climate change, production of green energy has recently become a hot area of interest in the research field. As a renewable energy source, biomass conversion to biofuels has shown a great potential towards green fuel production; particularly fructose conversion to 5-hydroxymethylfurfural (5HMF) as a building block material and source of green fuels and other high value chemicals.Herein, we investigate fructose dehydration to 5-hydroxymethylfurfural (5HMF) as a green fuel precursor, using a green self-catalysed environmentally friendly Deep Eutectic Solvent (DES), composed of inexpensive N,N-diethylethanolammonium chloride as organic salt and p-toluenesulfonic acid monohydrate (p-TSA) as a hydrogen bond donor (HBD) and novel medium for the fructose dehydration reaction.The advantage of using this DES is its ability to act as a solvent and catalyst simultaneously. It has shown to actively catalyse the dehydration reaction of fructose under moderate reaction conditions with a high 5HMF yield of 84.8% at a reaction temperature of 80 °C, reaction time of 1 h, DES mixing ratio of 1:0.5 salt to p-TSA (w/w), and initial fructose ratio of 5.     

Faceted Branched Nickel Nanoparticles with Tunable Branch Length for High‐Activity Electrocatalytic Oxidation of Biomass

Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic‐core hexagonal‐branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5‐hydroxymethylfurfural (HMF), as an example for biomass conversion.