無電解質自發性之化學生質氧化反應研究

Abstract

隨著石化工業的日益進步，全球塑膠製品產量亦持續增長，然而，大量塑膠廢棄物對自然環境造成了嚴重威脅，為應對傳統PET寶特瓶對環境的負面影響，近年來的研究逐漸聚焦於以生物質2,5-呋喃二甲酸(2,5-furandicarboxylic acid; FDCA)為原料製備的生物塑料聚呋喃二甲酸乙二酯(Polyethylene furanoate; PEF)，與石化衍生產物聚對苯二甲酸乙二酯(Polyethylene terephthalate; PET)相比，PEF不僅具有更高的機械強度，還可以從可再生資源中提取，因此被視為PET的永續替代品。 電化學催化羥甲基糠醛(5-hydroxymethylfurfural; HMF)氧化生成FDCA被視為最具未來性的永續生產方法，不僅能夠結合可再生能源驅動反應，實現高附加值化學品的綠色轉化，還能通過產氫反應(hydrogen evolution reaction; HER)生成清潔能源氫氣，然而，為提高反應效率，目前研究多於鹼性溶液中進行，然而在該環境下HMF分子可能引發如歧化反應和自聚合反應等副反應，此外，HER過程中陰極對HMF分子所造成之碳損失在現有研究中常被忽視，為解決上述問題，本次研究引入氧化還原儲庫(redox reservoir; RR)概念，通過氫氧化鎳電極實現了HMF氧化反應與HER的高效解耦，憑藉氫氧化鎳電極稍正的形式電位特性，在開路電位下於純水中(無輔助電解質)自發驅動HMF氧化反應，這不僅消除了對產物的後續純化需求，還避免了副反應所造成的碳損失，在高濃度反應物(300 mM)的條件下，實現超越95%的FDCA產率。 臨場X光吸收光譜(in-situ X-ray absorption spectroscopy)說明RR電極中的Ni3+為反應之活性位點，且反應遵循一級動力學，此外，RR電極的靈活性在糠醛(furfural)氧化生成2-糠酸(2-furoic acid)的成功應用中得到了驗證，表明其對各種含醛基或醇基的生物質分子均具有廣泛適用性。

Plastic production has surged with the growth of the petrochemical industry, causing severe environmental issues. To address the impact of polyethylene terephthalate(PET) bottles, bio-based polyethylene furanoate(PEF), made from biomass-derived 2,5-furandicarboxylic acid (FDCA), has emerged as a sustainable alternative with superior strength and renewable sourcing. Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to FDCA represents a sustainable production route, with the green conversion of biomass into high-value chemicals. Simultaneously, the process generates clean hydrogen energy through the hydrogen evolution reaction (HER). However, to achieve high efficiency, most current studies employ alkaline electrolytes, which induce significant side reactions in HMF molecules, such as disproportionation and self-polymerization. Moreover, carbon loss due to cathodic reduction during HER remains an often-overlooked challenge. Our study introduces redox reservoirs (RRs), using nickel hydroxide electrodes to decouple 5-hydroxymethylfurfural oxidation (HMFOR) and HER. The RR electrode, with its positive formal potential, spontaneously drives HMFOR in pure water under open-circuit conditions, eliminating the need for supporting electrolytes and reducing side reactions. This approach achieves over 95% FDCA yield at high reactant concentrations (300 mM) without requiring product purification. In-situ X-ray absorption spectroscopy identified Ni3+ species as active sites for HMFOR, which follows first-order kinetics. The RR system also demonstrated versatility in oxidizing furfural to 2-furoic acid, highlighting its broad applicability.