Stabilities, Regeneration Pathways, and Electrocatalytic Properties of Nitroxyl Radicals for the Electrochemical Oxidation of 5-Hydroxymethylfurfural
Stabilities, Regeneration Pathways, and Electrocatalytic Properties of Nitroxyl Radicals for the Electrochemical Oxidation of 5-Hydroxymethylfurfural
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DOI：
10.1021/acssuschemeng.9b00203
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发表时间：
2019-07-01
影响因子：
8.4
通讯作者：
Choi, Kyoung-Shin
中科院分区：
文献类型：
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作者：
Cardiel, Allison C.;Taitt, Brandon J.;Choi, Kyoung-Shin
2，5_呋喃二甲酸（FDCA）是一种接近市场的单体，其已被确定为在聚对苯二甲酸乙二醇酯（PET）的合成中替代石油衍生的对苯二甲酸的可行的生物质衍生的替代物。FDCA可以由5-羟甲基糠醛（HMF）的氧化产生，所述5-羟甲基糠醛是由从纤维素生物质获得的C-6单糖的脱水产生的通用生物质中间体。在本研究中，我们比较研究了2，2，6，6_四甲基哌啶-1-氧基（克里思）和4-乙酰胺基-TEMPO（ACT）用于电化学氧化HMF为FDCA的用途。克里思-和ACT-介导的HMF电化学氧化的明显优点是它们可以在温和碱性条件（pH 9-10）下有效地实现HMF氧化，而其他非均相催化剂通常需要使用更碱性的介质。由于HMF在强碱性条件下的氧化增加了形成胡敏素的机会，胡敏素难以与FDCA分离并降低FDCA和FDCA衍生产物的商业可行性，因此克里思和ACT介导的HMF氧化可为生产商业级FDCA提供关键优势。在这项研究中，克里思和ACT，这已被确定为一个较便宜的替代克里思的稳定性，电化学性能和电催化性能进行了比较研究电化学HMF氧化。通过考察溶液pH、外加电位、硝酰基自由基与HMF的比例对HMF氧化的影响，确定了克里思和ACT在催化循环中的两种不同再生途径以及影响其再生途径的因素。还研究了克里思和ACT在高温下电化学氧化HMF的稳定性和催化活性。在此研究的基础上，确定了有效氧化浓缩HMF溶液（100 mM）的最佳电化学条件，这与大规模电化学FDCA生产有关。
2,5-Furandicarboxylic acid (FDCA) is a near market monomer that has been identified as a viable biomass derived replacement for petroleum-derived terephthalic acid in the synthesis of polyethylene terephthalate (PET). FDCA can be produced from the oxidation of 5-hydroxymethylfurfural (HMF), which is a versatile biomass intermediate produced from the dehydration of C-6 monosaccharides obtained from cellulosic biomass. In this study, we comparatively investigated the use of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-acetamido-TEMPO (ACT) for electrochemical HMF oxidation to FDCA. The distinct advantage of TEMPO- and ACT-mediated electrochemical oxidation of HMF is that they can efficiently achieve HMF oxidation in mildly basic conditions (pH 9-10), while other heterogeneous catalysts typically require the use of more basic media. Since HMF oxidation in a strongly basic condition increases the chance to form humins, which are difficult to separate from FDCA and decrease the commercial viability of FDCA and FDCA-derived products, TEMPO- and ACT-mediated HMF oxidation may offer a critical advantage for producing commercial-grade FDCA. In this study, the stabilities, electrochemical properties, and electrocatalytic performances of TEMPO and ACT, which has been identified as a less expensive alternative to TEMPO, were comparatively examined for electrochemical HMF oxidation. Through investigating the effect of pH, applied potential, and ratio of nitroxyl radical to HMF in solution on HMF oxidation, two different regeneration pathways of TEMPO and ACT in the catalytic cycle and the factors that affect their regeneration pathways were identified. The stability and catalytic activity of TEMPO and ACT for electrochemical HMF oxidation at an elevated temperature were also studied. On the basis of this investigation, optimal electrochemical conditions to efficiently oxidize a concentrated HMF solution (100 mM), which is relevant to large-scale electrochemical FDCA production, were identified.