Oxidation of 5-hydroxymethylfurfural (HMF) with molecular oxygen to maleic acid (MAc) was performed on graphene oxide (V-GO) supported vanadium composite. The solvent effects (γ-valerolatctone (GVL), acetic acid and H₂O) on the reaction were investigated by combing the characterizations of X-ray Photoelectron Spectroscopy (XPS), ¹³C and ¹H Nuclear Magnetic Resonance (¹³C-NMR and ¹H-NMR), Inductive Coupled Plasma Emission Spectrometer (ICP), and Elemental Analysis (EA), and kinetic studies. GVL was the most efficient solvent with the highest yield of MAc, while acetic acid and H₂O benefited the C-C cleavage, giving more formic acid (FAc) than GVL. These variation in the solvent effects originated from the different ability of solvents to convert HMF molecules and 5-hydroxyl-2(5H)-furanone (HF) intermediate. Besides, the protons (H⁺) in graphene oxide were identified to promote HMF oxidation to MAc, whereas the added NaHCO₃ caused the catalyst deactivation. By combing the fabrication of model catalyst and XPS analysis, this negative effect of NaHCO₃ resulted from both the inhibition in the reduction of V⁵⁺→V⁴⁺ and/or V⁴⁺→V³⁺ and the loss in the H⁺ sites on the GO support caused by neutralization reaction. Furthermore, the reaction intermediates were identified by NMR. Oxidation of HMF to MAc was a two-step process, i.e., HMF oxidization to HF intermediate and its following oxidation to MAc. Both oxidation steps required the presence of vanadium and O₂. A feasible path for HMF oxidation to MAc was proposed based on the NMR observations.

在氧化石墨烯（V-GO）负载的钒复合材料上，用分子氧将5-羟甲基糠醛（HMF）氧化为马来酸（MAc）。通过结合X射线光电子能谱（XPS），¹³ C和¹ H核磁共振（¹³ C-NMR ）的表征，研究了溶剂对反应的影响（γ-戊内酯（GVL），乙酸和H ₂ O）。和¹ H-NMR），电感耦合等离子体发射光谱仪（ICP），元素分析（EA）和动力学研究。GVL是MAc收率最高的最有效溶剂，而乙酸和H ₂O有利于CC裂解，比GVL产生更多的甲酸（FAc）。溶剂作用的这些变化源于溶剂转化HMF分子和5-羟基-2（5H）-呋喃酮（HF）中间体的不同能力。此外，还发现氧化石墨烯中的质子（H ⁺）可以促进HMF氧化成MAc，而添加的NaHCO _3则使催化剂失活。通过组合模型催化剂的制备和XPS分析，NaHCO _3的这种负面影响既是由于抑制了V ⁵⁺ →V ⁴⁺和/或V ⁴⁺ →V ³⁺的还原以及H ⁺的损失中和反应引起GO载体上的位点。此外，反应中间体通过NMR鉴定。HMF氧化为MAc的过程分为两步，即HMF氧化为HF中间体及其随后的氧化为MAc。这两个氧化步骤都需要存在钒和O ₂。基于NMR观察结果，提出了HMF氧化为MAc的可行途径。