摘要
5-羥甲基糠醛(5-hydroxymethylfurfural，HMF)來自纖維素生物質，本身的應用有限，甚至被認為對人類有毒或致癌。然而，HMF能夠反應成實用且高經濟附加價值產物，尤其是2,5-二甲酰呋喃(2,5-diformylfuran，DFF)。本篇為首次使用非晶相Co10-aCeaOx (“a”為鈰的原子比例)於DFF高選擇性的研究。此外，本研究深入探討了觸媒特性及反應參數與反應路徑之間的關係，並提出HMF的可能氧化反應路徑。本篇研究透過光化學金屬有機沉積製備出的非晶相Co10-aCeaOx在HMF催化反應上展現優異的性能，其電流表現是CoOx的1.35倍。本研究由Operando Raman光譜實驗中證實鈰的電子結構能使Co10-aCeaOx的鈷被提升到更高的氧化態，而高氧化態的鈷通常被認為是HMF氧化的活性位點。值得一提的是，本篇研究發現氧化產物的選擇性極大程度上取決於電解液的酸鹼值和施加的電位，在強鹼性環境(pH13)中發現5-甲酰基-2-呋喃甲酸 (5-formyl-2-furancarboxylic acid，FFCA) 為主要產物，選擇性在所有產物中約佔60%。然而，當pH從13降到 7.0 時， DFF變成了主要產品，選擇性為79%。此外，透過調整施加電位， DFF的選擇性從60%到達92%。
中文關鍵詞: 5-羥甲基糠醛、2,5-二甲酰呋喃、非晶相金屬氧化物、選擇性電催化、酸鹼值影響

Abstract
5-hydroxymethylfurfural (HMF), derived from cellulosic biomass, has limiting applications and is even considered toxic or carcinogenic to humans. However, HMF has emerged as a precursor chemical that can be converted into high-value and useful compounds, especially 2,5-diformylfuran (DFF). Herein, this study reports for the first time using amorphous Co10-aCeaOx (“a” is the nominal atomic ratio of Ce) for high selectivity of DFF. Besides, the oxidation reaction pathway of HMF is also systematically studied. Amorphous Co10-aCeaOx obtained by photochemical metal-organic deposition exhibits an outstanding catalytic HMF oxidation performance, with the recorded current is 1.35 times over the value of CoOx. Operando Raman spectroscopy confirms the influence in the electronic structure of Ce on Co10-aCeaOx by promoting Co to the higher oxidation states, which are usually considered as the active sites for HMF oxidation. Interestingly, it is found that the selectivity of oxidative products strongly depends on the pH of the electrolyte and the applied potential. In strong alkaline media (pH 13.0), 5-formyl-2-furancarboxylic acid (FFCA) is found to be the main product that contributes the selectivity of 60% among all oxidative products. However, as pH decreases from 13.0 to 7.0, DFF turns to be the dominant product with a selectivity of 79%. Additionally, DFF could be produced with the selectivity of 60% ̴ 92% by adjusting applied potential. This study provides a deep understanding of the catalyst property, the relationship between reaction parameters and the reaction pathway. We, the early comers, report HMF electrooxidation in the neutral media, open the new route for electrocatalytic DFF production.
Keyword: 5-hydroxymethylfurfural, 2,5-diformylfuran, amorphous metal oxides, selective electrooxidation, pH effect

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