多级孔锰/铌复合催化剂的合成及纯水中催化氧化5-羟甲基糠醛研究

Synthesis of Hierarchical Porous Manganese/Niobium Composite Catalysts and Catalytic Oxidation of 5-Hydroxymethylfurfural in Pure Water

摘要: 采用模板法，在相对温和的条件下成功合成了一系列Nb/Mn-x多级孔铌/锰复合催化剂。使用XRD、FTIR、SEM、XPS和接触角测量等技术对样品进行表征，以确定其形态和亲水/疏水特性，同时也确认了Mn元素的负载并分析了其存在的价态。结果表明，大孔被成功引入了介孔磷硅酸铌中，制备出了多级孔磷硅酸铌载体，并在其上成功地均匀负载了Mn元素。Mn元素以γ-MnO₂晶相和Mn² 、Mn³ 以及Mn⁴ 等价态形式存在。催化剂的表面疏水性随Mn负载量的升高呈现先升高后降低的趋势。这些催化剂在使用纯水作为溶剂将5-羟甲基糠醛转化为2,5-呋喃二甲醛和5-甲酰基呋喃-2-羧酸方面表现出良好的催化效率。其中，Nb/Mn-0.045取得了最佳的催化性能。在最佳反应条件下(140˚C, 3.5 h)，2,5-呋喃二甲醛收率和选择性分别达到最大值7%和28.5%，对于5-甲酰基呋喃-2-羧酸而言，收率在160℃，3.5 h的条件下达到最大5.79%，5-羟甲基糠醛转化率为33.15%。研究结果表明适宜的Mn元素负载量、反应温度与反应时间对催化效率至关重要。此外，Nb/Mn-0.045表现出一定的可回收性。

Abstract: A series of Nb/Mn-x multistage porous niobium/manganese composite catalysts were successfully synthesised under relatively mild conditions using a template method. The samples were characterised using XRD, FTIR, SEM, XPS and contact angle measurements to determine their morphology and hydrophilic/hydrophobic properties, as well as confirming the loading of the Mn element and analysing the valence states present. The results showed that macropores were successfully introduced into mesoporous niobium phosphosilicate to prepare a multistage porous niobium phosphosilicate carrier, which was successfully and homogeneously loaded with elemental Mn. The elemental Mn was present in the form of γ-MnO₂ crystalline phases and valence states such as Mn² , Mn³ , and Mn⁴ . The surface hydrophobicity of the catalysts showed a tendency to increase and then decrease with the increase of Mn loading. These catalysts showed good catalytic efficiency in the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxaldehyde and 5-formylfuran-2-carboxylic acid using pure water as solvent. Among them, Nb/Mn-0.045 achieved the best catalytic performance. The yield and selectivity of 2,5-furandicarboxaldehyde reached a maximum of 7% and 28.5%, respectively, under the optimum reaction conditions (140˚C, 3.5 h), and for 5-formylfuran- 2-carboxylic acid, the yield reached a maximum of 5.79% at 160°C, 3.5 h, and the conversion of 5-hydroxymethylfurfural was 33.15%. The results indicate that the appropriate Mn elemental loading, reaction temperature and reaction time are crucial for the catalytic efficiency. In addition, Nb/Mn-0.045 showed some recoverability.