Aqueous-phase selective aerobic oxidation of 5-hydroxymethylfurfural on Ru/C in the presence of base

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。The aerobic oxidation of 5-hydroxymethylfurfural (HMF) was performed on an activated car-bon-supported ruthenium (Ru/C) catalyst in water. The presence of Mg-Al hydrotalcite (HT, Mg/Al molar ratio=3/1) as a base afforded higher selective oxidation of HMF to 5-formyl-2-furancarbox-ylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) than with the bases MgO, Ca(OH)2 and NaOH owing to its appropriate strength of basicity. X-ray photoelectron spectroscopy characterization confirmed that metallic Ru0 species were the active sites for HMF oxidation. Isotopic tracer experi-ments conducted with 18O2 and 16O2 indicated that H2O rather than O2 provided the oxygen atom for the oxidation of HMF to FFCA and FDCA via hydration of the formyl group. These results and kinetic studies of the oxidation of HMF and 2,5-diformylfuran (DFF) led to the proposition that the aerobic oxidation of HMF to FFCA follows a Langmuir-Hinshelwood mechanism. The oxidation involved dissociative adsorption of HMF and O2 to form adsorbed alcoholate and atomic oxygen species fol-lowed by kinetically relevant abstraction ofβ-H from the alcoholate species via the atomic oxygen species to adsorbed DFF species on the Ru surface, which then underwent hydration and oxidation to FFCA under basic conditions.the National Basic Research Program of China; the National Natural Science Foundation of China (21373019,21173008).@@@@国家自然科学基金; 国家重点基础研究发展计划http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000337120600021&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)EI中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)6hcliu@pku.edu.cn6937-9443